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Superparamagnetic Nanostructures for Split-Type and Competitive-Mode Photoelectrochemical Aptasensing
Abstract
Photoelectrochemical sensing has developed rapidly in the past decade because of its inherent advantages of economic devices and low background noise. However, traditional assembly of photoelectric beacons, probes, and targets on the ITO electrode solid-liquid interface inevitably leads to time-consuming, limited selectivity, poor stability, and nonreproducibility. To overcome these drawbacks, in this work, a unique split-type PEC aptasensor for carcinoembryonic antigen (CEA) was developed in virtue of the sandwich-like structure comprised of magnetic-optical [email protected]@CdS-DNA1, CEA aptamer, and signal element SiO2-Au-DNA2. The sandwich-like structure is easily formed in the liquid phase and can be triggered by competition from low-abundance CEA, resulting in dissociation. By further photocurrent measurement in pure phosphate buffer saline, co-existing species can be effectively removed from the modified electrode, improving selectivity, stability, and repeatability. These advantages benefit from the preparation of uniform and monodispersed [email protected]@CdS and SiO2-Au particles, DNAs assembly, and an elegant design. Additionally, the as-designed signal-on PEC aptasensor is highly sensitive, short time-consuming, and economical, enabling the detection of CEA in serum specimens. It not only provides an alternative to CEA immunosensors, but also paves the way for high-performance PEC aptasensors.
... [2] Among them, the PEC sensor has characteristics of low background, fast detection speed, photocurrent detection signal, and high sensitivity due to the complete separation of the excitation source from the detection signal, [3] which is an emerging measurement technique for RNA, [4] proteins, [5] ions, [6] micro-molecules, [7] and other trace biological samples in recent decades. [8] The core components of PEC sensors include welldesigned photosensitive electrodes based on various semiconductor materials to achieve high photoelectric conversion efficiency. Various photoelectric semiconductor materials, including metal oxides, metal chalcogenides, and carbon-based materials, have been investigated in recent years, partially promoting the development of PEC sensors. ...
In the past several decades, Photoelectrochemical (PEC) sensing still remains a great challenge to design highly‐efficient semiconductor photocatalysts via a facile method. It is of much importance to design and synthesize various novel nanostructured sensing materials for further improving the response performance. Herein, we present an In2O3/In2S3 heterostructure obtained by combining microwave assisted hydrothermal method with S‐induced phase change, whose energy band and electronic structure could be adjusted by changing the S content. Combining theoretical calculation and spectroscopic techniques, the introduction of sulfur was proved to produce multifunctional interfaces, inducing the change of phase, oxygen vacancies and band gap, which accelerates the separation of photoexcited carriers and reduces their recombination, improving the electronic injection efficiency around the interface of In2O3/In2S3. As anticipated, an enhanced glucose response performance with a photocurrent of 0.6 mA cm⁻², a linear range of 0.1–1 mM and a detection limit as low as 14.5 μM has been achieved based on the In2O3/In2S3 heterostructure, which is significant superior over its pure In2O3 and S‐doped In2O3 counterparts. This efficient interfacial strategy may open a new route to manipulate the electrical structure, and energy band structure regulation of sensing material to improve the performance of photoelectrodes for PEC.
... To pursue a highly effective approach that can achieve the above goal appears to be a major concern. Up to date, strategies such as establishing a built-in electric field and forming heterojunctions have been explored [9][10][11][12]. For example, hollow CdIn 2 S 4 /In 2 S 3 heterostructured microspheres are prepared, and a PEC sytosensor for HepG2 cells for ultrasensitive sensing via a specific recognition of the CD133 protein on the cell surface with the respective aptamer is constructed based on that heterostructure [13]. ...
The empty-space-induced depletion region in photoelectrodes severely exacerbates the recombination of electron–hole pairs, thereby reducing the photoelectrochemical (PEC) analytical performance. Herein, the chemical bond that can suppress the potential barrier and overcome the high energy barrier of out-of-plane Ohmic or Schottky contact is introduced into the PEC sensor to eliminate the depletion region and dramatically promote the separation of electron–hole pairs. Specifically, three-dimensional (3D) hierarchically wheatear-like TiO2 (HWT) nanostructures featuring a large surface area to absorb incident light are crafted as the substrate. The facile carbonized strategy is further employed to engineer the Ti-C chemical bond, serving as the touchstone. The average PL lifetime of HWT-C (4.14 ns) is much shorter than that of the 3D HWT (8.57 ns) due to the promoting effect of the chemically bonded structure on carrier separation. Consequently, the 3D HWT-C covalent photoelectrode (600 μA/cm2) exhibits a 3.6-fold increase in photocurrent density compared with the 3D HWT (167 μA/cm2). Ultimately, the model analyte of the tumor marker is detected, and the linear range is 0.02 ng/mL–100 ng/mL with a detection limitation of 0.007 ng/mL. This work provides a basic understanding of chemical bonds in tuning charge separation and insights on strategies for designing high-performance PEC sensors.
... At present, various analytical methods have been reported for detecting SAs, including high-performance liquid chromatography (HPLC) [4], ultra-high-performance liquid chromatography-mass spectrometry (UPLC-MS) [5], liquid chromatography-mass spectrometry (LC-MS) [6], capillary electrophoresis [7], immunoassays [8], surface-enhanced Raman spectroscopy (SERS) [9], and using electrochemical sensors [10,11]. Among them, electrochemical methods offer the benefits of elevated sensitivity, accuracy, convenient operation, cheap instrumentation, facile integration, and portability [12]. ...
Efficient methods for monitoring sulfonamides (SAs) in water and animal-source foods are of great importance to achieve environmental safety and protect human health. Here, we demonstrate a reusable and label-free electrochemical sensor for the rapid and sensitive detection of sulfamethizole based on an electropolymerized molecularly imprinted polymer (MIP) film as the recognition layer. To achieve effective recognition, monomer screening among four kinds of 3-substituted thiophenes was performed by computational simulation and subsequent experimental evaluation, and 3-thiopheneethanol was finally selected. MIP synthesis is very fast and green, and can be in situ fabricated on the transducer surface within 30 min in an aqueous solution. The preparation process of the MIP was characterized by electrochemical techniques. Various parameters affecting MIP fabrication and its recognition response were investigated in detail. Under optimized experimental conditions, good linearity in the range of 0.001−10 μM and a low determination limit of 0.18 nM were achieved for sulfamethizole. The sensor showed excellent selectivity, which can distinguish between structurally similar SAs. In addition, the sensor displayed good reusability and stability. Even after 7 days of storage, or being reused 7 times, higher than 90% of the initial determination signals were retained. The practical applicability of the sensor was also demonstrated in spiked water and milk samples at the nM determination level with satisfactory recoveries. Compared to relevant methods for SAs, this sensor is more convenient, rapid, economical, and eco-friendly, and had comparable or even higher sensitivity, which offered a simple and efficient method for SA detection.
... Therefore, PCPEC has more advantages for target detection in complicated samples. Moreover, "signal-on" format is preferred owing to its low background signal and less false-positive results [17]. Therefore, it is interesting to develop "signal-on" PCPEC aptasensor for Kana assay. ...
A “signal-on” dual-mode aptasensor based on photoelectrochemical (PEC) and electrochemical (EC) signals was established for kanamycin (Kana) assay by using a novel Z-scheme AgBr/AgI-Ag-CNTs composite as sensing platform, an aptamer structure switch, and K3[Fe(CN)6] as photoelectron acceptor and electrochemical signal indicator. The aptamer structure switch was designed to obtain a “signal-off” state, which included an extended Kana aptamer (APT), one immobilized probe (P1), and one blocking probe (P2) covalently linked with graphdiyne oxide (GDYO) nanosheets. P1, P2, and aptamer formed the double helix structure, which resulted in the inhibited photocurrent intensity because of the weak conductivity of double helix layer and serious electrostatic repulsion of GDYO towards K3[Fe(CN)6]. In the presence of Kana, APT specifically bound to the target and dissociated from P1 and P2, and thus, a “signal-on” state was initiated by releasing P2-GDYO from the platform. Based on the sensing platform and the aptamer structure switch, the dual-mode aptasensor realized the linear determination ranges of 1.0 pM–2.0 μM with a detection limit (LOD) of 0.4 pM (for PEC method) and 10 pM–5.0 μM with a LOD of 5 pM (for EC method). The aptasensor displayed good application potential for Kana test in real samples.
Graphical abstract
... To date, several detection methods, including electrochemistry (EC)-, photoelectrochemistry (PEC)-, electrochemiluminescence-, surface-enhanced Raman scattering-, fluorescence-, and chemiluminescence-based immunoassays have been utilized to trace CEA detection in the early diagnosis of various cancers [8][9][10][11][12][13]. Among them, electrochemical and photoelectrochemical biosensors, practical and potential analytical techniques, can convert specific analyte information into readable electrical signals, which achieve high sensitivity, low cost, and a small background in comparison with common optical methods [14][15][16][17]. In particular, the proper bio-chemical probes (e.g., antibodies and aptamers) are composed of powerful affinity interactions and satisfactory binding sites and have been regard as indispensable recognition elements in sensing devices [18,19]. ...
Recently, electrochemistry- and photoelectrochemistry-based biosensors have been regarded as powerful tools for trace monitoring of carcinoembryonic antigen (CEA) due to the fact of their intrinsic advantages (e.g., high sensitivity, excellent selectivity, small background, and low cost), which play an important role in early cancer screening and diagnosis and benefit people’s increasing demands for medical and health services. Thus, this mini-review will introduce the current trends in electrochemical and photoelectrochemical biosensors for CEA assay and classify them into two main categories according to the interactions between target and biorecognition elements: immunosensors and aptasensors. Some recent illustrative examples are summarized for interested readers, accompanied by simple descriptions of the related signaling strategies, advanced materials, and detection modes. Finally, the development prospects and challenges of future electrochemical and photoelectrochemical biosensors are considered.
A new photoelectrochemical immunoassay based on self-assembled p-n Ag2O@Bi2O2S nanoflower heterojunction was designed and developed for quantitative monitoring of prostate-specific antigen (PSA) in biological fluids. Primarily, self-assembled p-n Ag2O@Bi2O2S nanoflower heterojunctions were served as the photoactive materials and coated onto the surface of electrodes. Subsequently, the glucose oxidase (GOx) was bound to the detection antibody (mAb2) labeled gold nanoparticles (Au NPs) and then were employed to accomplish a sandwich-like immunoreaction to generate H2O2 on a microplate incubated with monoclonal anti-PSA antibodies. In the presence of PSA, the product (H2O2) was catalyzed by the substrate, which was used as an electron sacrificial agent to improve signal conversion and capture of photogenerated electrons. Under optimum conditions, a wide linear range of 0.01-50 ng mL-1 and a low detection limit of 5.3 pg mL-1 were accomplished with the sensor, exhibiting an excellent photocurrent response. Moreover, the proposed sensor revealed satisfactory reproducibility, high selectivity, and acceptable accuracy for the real sample testing. Importantly, our work provides a novel strategy for high sensitivity detection of disease-associated biomarkers for the early diagnosis of cancers.
False positives and negatives in bioanalytical assays remain a persistent problem. Herein, a multifunctional photoelectrochemical (PEC) biosensor based on ZnIn2S4 (ZIS)/ZnS quantum dots (QDs)@Au-Ag-reversed photocurrent of Cu-metal-organic framework (MOF) coupled with CRISPR/Cas-12a-shearing was innovatively developed for assay of dual targets. First, Cu-MOF as a good PEC material shows cathodic photocurrent. Then, numerous ZIS/ZnS QDs were assembled to the Au-Ag nanoparticles (NPs) to prepare a stable and highly amplified signal probe, which can just match the energy level of Cu-MOFs and realized the polarity-reversed photocurrent of Cu-MOF for the first time. As the empty-core nanostructure of Au-Ag NPs has a high specific surface area and low material density, the bimetallic nanocrystal can much increase the reaction rate and improve the redox efficiency. When target CEA-produced cDNA opened the hairpin DNA (HP1 DNA) on the electrode, the ZIS/ZnS QDs@Au-Ag signal probe was conjugated to the electrode via DNA hybridization, achieving a significantly reversed PEC current for CEA detection. Moreover, the specific binding of kanamycin/aptamer generated the acDNA (activator), which can activate the trans-cleavage activity of the CRISPR-CAS12a system on ssDNA, so the signal probe was sheared and caused the obvious decrease of PEC signal for kanamycin detection. The newly developed ZIS/ZnS QDs@Au-Ag NPs displayed excellent PEC properties and reversed photocurrent to MOF and were combined with the unique CRISPR-Cas12a system to achieve sensitive detection of dual targets, which can open a new polarity-reversed PEC sensing platform for rapid and accurate analysis of multiple targets and can effectively avoid false positives results in clinical testing.
To date, it is still a challenge for high-performance photoelectrochemical (PEC) assay of low-abundance adenosine deaminase (ADA) in fundamental research and clinical diagnosis. Herein, phosphate-functionalized Pt/TiO2 (termed PO43-/Pt/TiO2) was prepared as ideal photoactive material to develop a split-typed PEC aptasensor for detection of ADA activity, coupled by a Ru(bpy)32+ sensitization strategy. We critically studied the effects of the PO43- and Ru(bpy)32+ on the detection signals, and discussed the signal-amplified mechanism. Specifically, hairpin-structured adenosine (AD) aptamer was splited into single chain via ADA-induced catalytic reaction, and subsequently hybridized with complementary DNA (cDNA, initially coating on magnetic beads). The in-situ formed double-stranded DNA (dsDNA) was further intercalated by more Ru(bpy)32+ to amplify the photocurrents. The resultant PEC biosensor showed a broader linear range of 0.05-100 U L-1 and a lower limit of detection (0.019 U L-1), which can fill the blank for analysis of ADA activity. This research would provide some valuable insights for building advanced PEC aptasensors in ADA-related research and clinical diagnosis.
Human epidermal growth factor receptor 2 (HER2) has been regarded as the considerable biomarker of breast and gastric cancer. Thus, precise detection of HER2 is of significance for the early diagnosis and treatment. Here, a photofuel cell-based self-powered biosensor (PFC-SPB) was constructed for the ultrasensitive HER2 detection, which was composed of a plasmonic gold nanoparticles (Au NPs)/organic semiconductor hybrid photoanode and a cathode with biosensing strategy of electrochemical sandwich structure. The localized surface plasmon resonance effect of Au NPs can obviously enhance the separation efficiency of photo-generated electron/hole pair, which was beneficial to the sensitivity and stability of PFC-SPB. Meanwhile, the cathodic sandwich structure not only was used for the target recognition, but also can guarantee the enrichment of electroactive molecules (molybdophosphate). Consequently, with the open circuit voltage (EOCV) as the output signal, the PFC-SPB can achieve the HER2 detection in the range of 0.1–500 pg mL⁻¹ with a low detection limit of 0.02 pg mL⁻¹. Moreover, the as-proposed bioassay can be applied in cell lysate sample without any pretreatment, providing a promising and powerful tool early clinical diagnosis of cancer.
A portable three-dimensional (3D) printed bionic sensing device with enhanced photoelectric response was fabricated for sensitive detection of Bisphenol A (BPA). The proposed sensor is operated upon by using a highly reactive dual-electrode system to generate electrical output and provide the sensing signal under photoirradiation, without an external power source. The fern-shaped nitrogen doped BiVO4 photoanode with enriched oxygen vacancies (Ov) bismuth vanadate (N/Ov/BiVO4) photoanode was first synthesized and applied to construct a bionic sensing device. Density functional theoretical (DFT) calculation shows that the synergistic of nitrogen doping and Ov on the surface of photoanode leads to the emergence of impurity levels in BiVO4’s electronic structure, promoting the effective separation of photogenerated electron-hole pairs. Impressively, the unique fern-shaped bionic structure enhances the mass transfer efficiency of the sensing system and provides abundant binding sites of aptamer, realizing signal amplification. Moreover, a portable sensing device for automatic sample injection and detection is developed by integrating the detection system into a micromodel based on micro-nano 3D printing technology. Benefit from this ingenious design, the proposed bionic aptasensor displayed excellent electricity output and achieved high sensitivity and selectivity of BPA detection with a low limit of detection (0.025 nM) and broad linear range from 0.1 nM to 100 μM, paving a new way for the development of portable and on-site sensing devices.
Mercury ion (Hg2+) is one of the most harmful heavy metal ions with the greatest impact on public health. Herein, based on the excellent catalytic activity toward 3,3',5,5'-tetramethylbenzidine (TMB) and the strong photocurrent-polarity-switching ability to SnS2 photoanode of the split G-quadruplex-hemin complex, the magnetic NiCo2O4@SiO2-NH2 sphere-assisted colorimetric and photoelectrochemical (PEC) dual-mode sensing platform was developed for the Hg2+ assay. First, the amino-labelled single-stranded DNA1 (S1) was immobilized on NiCo2O4@SiO2-NH2 and then partly hybridized with another single-stranded DNA2 (S2). When Hg2+ was present, the thymine-Hg2+-thymine base pairs between S1 and S2 were formed, causing the formation of the split G-quadruplex in the presence of K+. After addition of hemin, the split G-quadruplex-hemin complex was obtained and effectually catalyzed the H2O2-mediated oxidation of TMB. Thus, the color and absorbance intensity of the TMB solution were changed, resulting in the visual and colorimetric detection of Hg2+. The linear response range is 10 pM to 10 nM, and the detection limit is 3.8 pM. Meanwhile, the above G-quadruplex-hemin complex effectively switched the photocurrent polarity of SnS2-modified indium tin oxide electrode, leading to the sensitive and selective PEC assay of Hg2+ with a linear response range of 5 pM to 500 nM and a detection limit of 2.3 pM. Moreover, the developed dual-mode sensing platform provided mutual authentication of detection results in different modes, effectively improving the assay accuracy and confidence, and may have a good potential application in highly sensitive, selective, and accurate determination of Hg2+ in environmental fields.
A signaling strategy can directly determine the analytical performance and application scope of photoelectrochemical (PEC) immunoassays, so it is of great significance to develop an effective signaling strategy. The electro-Fenton reaction has been extensively used to degrade organic pollutants, but it has not been applied to PEC immunoassays. Herein, we report a novel signaling strategy for a PEC immunoassay based on electro-Fenton degradation of liposomes (Lip) on a photoelectrode. Lip vesicles are coated on Au@TiO2 core-shell photoactive material, which can prevent ascorbic acid (AA) from scavenging photogenerated holes. In the presence of a target, the immunomagnetic bead labels are converted to Fe3+ for electro-Fenton reaction, and hydroxyl radicals generated by the electro-Fenton reaction can degrade the Lip vesicles on the photoelectrode. Because of the degradation of Lip vesicles, photogenerated holes can be scavenged more effectively by AA, leading to an increase in photocurrent. Based on the electro-Fenton-regulated interface electron transfer, the sensitive "signal on" PEC immunoassay of a carcinoembryonic antigen is achieved, which features a dynamic range from 0.05 to 5 × 104 pg mL-1 and a detection limit of 0.01 pg mL-1. Our work provides a novel and efficient PEC immunoassay platform by introducing the electro-Fenton reaction into PEC analysis.
This work reported a split-type photoelectrochemical (PEC) immunoassay for the detection of carcinoembryonic antigen (CEA) based on target-induced biocatalytic precipitation (BCP) by using In2O3/CdIn2S4 heterojunctions as the photosensitizers. The synthesized In2O3/CdIn2S4 heterojunctions improved the efficiency of charge separation and shortened the electron convey path to enhance the photocurrent, thus exhibiting high conductivity and low complexation rates of photogenerated electrons and holes. In the presence of CEA, horseradish peroxidase (HRP) catalyzed 4-chloro-1-naphthol (4-CN) to produce benzo-4-chloro-hexadienone (4-CD) through H2O2. Then, 4-CD was deposited onto the surface of In2O3/CdIn2S4 to reduce the photocurrent and realized the signal amplification. The PEC immunoassay revealed an excellent photocurrent toward target CEA within a wide range of 0.01–50 ng mL⁻¹ at a low limit of detection of 2.8 pg mL⁻¹ under the optimum conditions. Multiple switching light excitation tests demonstrated the good reliability and stability of the fabricated PEC biosensor. The accuracy was acceptable in comparison with human CEA enzyme-linked immunosorbent assay (ELISA) kit.
As an important heptapeptide toxin, microcystine-LR (MC-LR) has attracted extensive attention because of its great harm to animals, plants and plankton in water. Therefore, an ultrasensitive photoelectrochemical aptasensor based on ZnIn2S4/CdSe heterojunction was disigned to monitor MC-LR. In this strategy, the ZnIn2S4/CdSe heterojunction with matching energy levels was used as the substrate of the aptasensor. By reason of the effective separation of electrons and holes, the heterojunction exhibited wide light absorption region and increased light utilization rate, resulting in a higher electrical signal. The specific recognition of MC-LR depend on the precise binding with aptamer, which modified on the electrode through base complementary pairing. In the presence of MC-LR, MC-LR was specific recognized by MC-LR aptamer, the photocurrent signal amplifier Bi2S3 was released from the aptasensor electrode, leading to a decreased photocurrent. The designed photoelectrochemical aptasensor showed an ultrasensitive detection for MC-LR with a wide response range from 10⁻¹ to 10⁻⁸ µM, and lower detection limit of 0.55×10⁻⁸ µM (3σ/S).
Herein, a dual signal-quenched electrochemical (EC) biosensing strategy utilizing surface-engineered trisodium citrate (TSC)-glutathione (GSH)/oxidized glutathione (GSSG)-capped triangular silver nanoplates (Tri-Ag NPsTSC-GSH/GSSG) as a novel nanoparticle-based redox mediator was explored for biomarker determination. In contrast with conventional redox mediators, Tri-Ag NPsTSC-GSH/GSSG provided more admirable EC performance along with a lower oxidation potential (∼0.14 V). Taking advantage of the split-type mode, the immune response in a 96-well microplate was independent from EC detection, which could effectively eliminate the biological interference and thereby greatly enhance the sensitivity. As for the surface engineering process of Tri-Ag NPs, it was composed of partial GSH replacement and the formation of the GSH/GSSG surface mixed state. Primarily, the signal response of Ag NPsTSC-GSH decreased due to the hindrance of GSH on electron transfer. Moreover, varying proportions of GSH/GSSG could further impede the oxidation process of Tri-Ag NPsTSC-GSH/GSSG and eventually realize efficient dual signal quenching of this system. Notably, the ZIF-67@MIL-88B-GOx nanocomposite as the label was applied for a cascade reaction system with GSH peroxidase-like activities to form the optimal GSH/GSSG proportion, causing sensitive changes in signal response with a range of different antigen concentrations. On this basis, the fabricated biosensor provided measurable outputs of aflatoxin B1 concentrations in a linear range of 0.0005-50 ng/mL with a low detection limit of 0.61 pg/mL (S/N = 3). All of the results indicated that the novel biosensor could be a promising analytical tool for future biomarker detection.
An ultrasensitive photoelectrochemical (PEC) analysis method based on terminal deoxynucleotidyl transferase (TdT) amplification effect and G-quadruplex/hemin (G4/hemin) catalytic reaction assisted signal amplification was prepared for the determination of ampicillin. A novel Au [email protected]4S8-graphene sensitized structure was used as photoactive material to attain an intense basic photocurrent. In the presence of the target, P1 obtained by strand displacement reaction was introduced into the electrode surface, and abundant G4/hemin was formed in the presence of TdT and hemin. Subsequently, G4/hemin with horseradish peroxidase-mimicking activity catalyzed the oxidation of 4-chloro-1-naphthol by H2O2 to form benzo-4-chlorohexadienone precipitation on the modified electrode surface, which severely hindered the electron transfer and effectively inhibited the photocurrent output. The detection range of the PEC aptasensor for ampicillin was 10 fM-30 nM, and the limit of detection was 4.97 fM. The aptasensor had good stability and high sensitivity, and possessed a promising application in biological analysis and environmental monitoring.
An early diagnosis has the potential to greatly decrease cancer mortality. For that purpose, specific cancer biomarkers have been molecularly targeted by aptamer sequences to enable an accurate and rapid detection. Aptamer-based biosensors for cancer diagnostics are a promising alternative to those using antibodies, due to their high affinity and specificity to the target molecules and advantageous production. Synthetic nucleic acid aptamers are generated by in vitro Systematic Evolution of Ligands by Exponential enrichment (SELEX) methodologies that have been improved over the years to enhance the efficacy and to shorten the selection process. Aptamers have been successfully applied in electrochemical, optical, photoelectrochemical and piezoelectrical-based detection strategies. These aptasensors comprise a sensitive, accurate and inexpensive option for cancer detection being used as point-of-care devices. This review highlights the recent advances in cancer biomarkers, achievements and optimizations made in aptamer selection, as well as the different aptasensors developed for the detection of several cancer biomarkers.
Ofloxacin (OFL), as a typical third-generation fluoroquinolone antibiotic, has been widespread employed in applications of preventing and treating skin tissue and bacterial infections. Detection of the residual OFL in water environment is extremely urgent on account of its toxicity to human body. Herein, a photoelectrochemical (PEC) aptasensor has been developed and fabricated for OFL determination based on CoAl layered double hydroxide/graphitic carbon nitride (CoAl LDH/g-C3N4) with two-dimensional/two-dimensional (2D/2D) structure. Strongly coupled 2D/2D structure with closed-connected contact can be beneficial to the formation of large numbers of high-speed transfer channels at the interfacial heterojunction, thereby shortening the transmission distance of carriers. Photocurrent signal of 2D/2D CoAl LDH/g-C3N4 heterojunction has realized the remarkable amplification, endowing it excellent PEC performance. Based on the oxidation of OFL by photoinduced holes, this developed aptasensing platform exhibited a wide linearity range of 1×10–2~1×10⁵ pmol L–1 with a low limit detection of 3.4 fmol L–1, along with anti-inference and feasibility for OFL assay in actual water samples. This design can be proposed by the layered structure materials coupled with g-C3N4 to significantly amplify the photocurrent signal, which opens the way for the field of PEC analysis and environmental pollutants detection.
Herein, we report CdSe quantum dots (QDs)-decorated ZnIn2S4 nanosheets for “signal-on” photoelectrochemical (PEC) aptasensing of adenosine triphosphate (ATP) by integrating exciton energy transfer with exciton-plasmon coupling. Under visible light irradiation, the CdSe/ZnIn2S4 shows higher PEC activity than ZnIn2S4 nanosheets and CdSe QDs resulting from the formation of n-n type heterojunction. To construct a PEC aptasensor, Au nanoparticle (AuNP)-labeled short DNA strand (denoted as c-DNA) is immobilized on the CdSe/ZnIn2S4 modified indium tin oxide (ITO) electrode and then hybridized with an aptamer to yield a double-stranded DNA. Before ATP incubation, AuNPs are kept away from the CdSe/ZnIn2S4/ITO, so the exciton energy transfer between CdSe QDs and AuNPs greatly quenches the photocurrent (“signal-off” state). After ATP incubation, AuNPs labeled on the c-DNA are in close contact with the CdSe/ZnIn2S4/ITO, and an increased photocurrent can be obtained due to the great exciton-plasmon coupling effect (“signal-on” state). This distance-triggered signaling “off–on” strategy enables sensitive aptasensing of ATP, with a broad linear range from 0.2 pM to 1 μM and a detection limit of 0.1 pM.
Nowadays, brain natriuretic peptide (BNP-32) is fundamental to early cardiovascular clinical diagnosis, whose accurate assay is of significance by photoelectrochemistry (PEC) for the lower background and high precision. Herein, a novel enhanced PEC platform was built by successive deposition of N-doped ZnO nanopolyhedra (N-ZnO NP) and protoporphyrin IX (PPIX). Specifically, the N-ZnO NP with a narrow bandgap of 2.60 eV was synthesized by direct calcination of zeolitic imidazole framework-8 (ZIF-8), and performed as the substrate to enhance the photocurrents of PPIX (as photosensitizer) whose photoelectron transfer pathway and enhanced PEC mechanism were studied in detail. Under such foundation, a label-free PEC aptasensor was developed by deposition of DNA aptamer onto the PEC platform and then ultrasensitive assay of BNP-32 based on a “signal off” model. The biosensor showed a wide linear range (1 pg mL⁻¹- 0.1 μg mL⁻¹) with a limit of detection (LOD) as low as 0.14 pg mL⁻¹. This doping technique of ZnO nanomaterials provides some valuable guidelines for synthesis of advanced PEC probes in bioanalysis.
Electrochemical biosensors based on enzymes modified electrode are attracting special attention due to their broad applications. However, the immobilization of enzymes on electrode is always an important challenge because it's not conducive to conformational expansion of enzymes and affects the bioactivity of enzymes accordingly. Although the imobilization of enzymes in micropores of crystalline covalent-organic framework (COF) and metal-organic framework (MOF) to construct electrochemical biosensors based on pore embedding can achive good reuslts, their micropores can still not guarantee that the enzyme's conformation is well extended. Herein, a multienzyme microcapsules ([email protected]) containing glucose oxidase, horseradish peroxidase and acetylcholinesterase with a 600 nm-sized cavity and a shell of COF was used to construct electrochemical biosensors. The 600 nm-sized cavity ensures free conformation expansion of encapsulated enzymes and the shell of COF with good chemical stablity protects encapsulated enzymes against external harsh environments. And the specific catalytic substrates of the enzymes can infiltrated into the microcapsule through the pores of COF shell. So, the biosensor based on [email protected] microcapsules demonstrated preeminent performances as compared with those of enzymes assembled on electrode. The detection limits were 0.85 μM, 2.81 nM, 3.0×10⁻¹³ g/L, and the detection range were 2.83 μM–8.0 mM, 9.53 nM-7.0 μM, 10⁻¹² g/L-10⁻⁸ g/L for glucose, H2O2 and malathion detection. This work shows that it is feasible to fabricate electrochemical sensors using [email protected] microcapsules.
A signal enhancement photoelectrochemical (PEC) immunoassay system induced by the composite ([email protected]) of electron donor-acceptor with Schottky heterojunction was designed. Carcinoembryonic antigen (CEA) was selected as a model target. Initially, the capture anibody (Ab1) was linked to gold nanoparticles electrodeposited on glassy carbon electrode and sealed by bovine serum albumin. Meanwhile, the organic semiconductor (PTCs) with the structure of electron donor-acceptor was synthetized from perylene tetracarboxylic dianhydride (acceptor) and dopamine (donor) via amidation reaction. Then [email protected] composite with Schottky heterojunction was formed through gold nanoparticles in situ reduction and functionalization with PTCs. Next, the detection antibody was labeled by [email protected] composite ([email protected]) as an immuno-probe. The [email protected] was introduced via sandwich immune reaction leading to enhancement PEC signal without additional electron donor nor acceptor for achieving quantitative detection of CEA under external light. The proposed immunoelectrode showed dynamic ranges of 0.5 fg mL⁻¹ to 10 pg mL⁻¹ and 10 pg mL⁻¹ to 1 μg mL⁻¹ with the detection limit of 0.17 fg mL⁻¹. In addition, this PEC strategy with acceptable selectivity and stability can be potentially applied to detect other targets by choosing appropriate target recognition unit.
Herein, a novel and robust two-electrode photoelectrochemical (PEC) biosensing platform amplified by bilirubin oxidase (BOD) labelling was reported. This two-electrode operating system was composed of photoanode and sensing biocathode. Carcinoembryonic antigen (CEA) was utilized as a model for probing. Specifically, Fe³⁺-doped TiO2 (Fe:TiO2) nanotubes were first prepared and then deposited with ZnIn2S4 (ZIS) nanocrystals to develop the ZIS/Fe:TiO2 photoanode. Toward sensing biocathode, after carbon nanotubes (CNTs) and Au nanoparticles (NPs) were modified on conductive glass, an Au/CNT cathodic substrate was fabricated to anchor the CEA aptamer. Complementary DNA (cDNA) of the CEA aptamer was labelled with BOD to form the cDNA-BOD conjugate that amplified the signal through DNA hybridization. Target detection hinged on an evident decline in the current signal generated by terminated amplification of the BOD labels and evident steric hindrance of the captured CEA molecules. Profiting from excellent PEC property of the ZIS/Fe:TiO2 photoanode and good oxygen-reduction capability of the BOD labels, the two-electrode PEC biosensing platform exhibited high sensitivity. Because of the division of biorecognition with photoanode, the platform also showed satisfactory selectivity in biological matrix. This elegant two-electrode strategy offers a promising path for seeking other robust PEC biosensors applying in complex biological samples.
A novel photoelectrochemical immunosensor was constructed to monitor carcinoembryonic antigen (CEA) based on hybridization chain reaction (HCR)-mediated in situ generation of copper nanoparticles (Cu NPs) and subsequent Cu²⁺-dependent quenching reaction, in which titanium dioxide nanoparticles-sensitized double-shell zinc cadmium sulfide hollow nanospheres (TiO2/DS-ZnCdS)-modified ITO electrode and anti-CEA antibody-modified 96-well plate served as biological recognition and signal detection platforms, respectively. The synergistic effect of TiO2 NPs and DS-ZnCdS hollow nanospheres contributed to the improvement of photoelectric conversion efficiency, and HCR-mediated signal cascade benefited the enhancement of detection sensitivity. In the presence of CEA, biotin-labelled anti-CEA antibodies were immobilized onto anti-CEA antibody-modified 96-well plate, and triggered HCR process to form long double stranded DNA, which could adsorb a large number of Cu²⁺ ions and then in situ form Cu NPs on double stranded DNA template by a facile reduction reaction. After acid treatment, the dissolved Cu²⁺ ions could significantly reduce the photocurrent response due to the generation of CuxS. Under optimal conditions, the immunosensor exhibited a desirable liner range of 1 pg mL–1 – 50 ng mL–1 and a low detection limit of 0.1 pg mL–1, as well as excellent selectivity and stability. Meanwhile, the recoveries of human serum sample analysis ranged from 96.8% to 103.6%, and the relative standard deviation was less than 7.40%, showing a good feasibility in early clinical diagnosis.
In virtue of the inherent molecular recognition and programmability, DNA has recently become the most promising for high-performance biosensors. The rationally engineered nucleic acid architecture will be very advantageous to hybridization efficiency, specificity, and sensitivity. Herein, a robust and split-mode photoelectrochemical (PEC) biosensor for miRNA-196a was developed based on an entropy-driven tetrahedral DNA (EDTD) amplifier coupled with superparamagnetic nanostructures. The DNA tetrahedron structure features in rigidity and structural stability that contribute to obtain precise identification units and specific orientations, improving the hybridization efficiency, sensitivity, and selectivity of the as-designed PEC biosensor. Further, superparamagnetic Fe3O4@SiO2@CdS particles integrated with DNA nanostructures are beneficial for the construction of a split-mode, highly selective, and reliable PEC biosensor. Particularly, the enzyme- and hairpin-free EDTD amplifier eliminates unnecessary interference from the complex secondary structure of pseudoknots or kissing loops in typical hairpin DNAs, significantly lowers the background noise, and improves the detection sensitivity. This PEC biosensor is capable of monitoring miRNA-196a in practical settings with additional advantages of efficient electrode fabrication, stability, and reproducibility. This strategy can be extended to various miRNA assays in complex biological systems with excellent performance.
Organic dyes are typically applied as photosensitizers in photoelectrochemical (PEC) cells but have not been reported in polarity-reversal-mode PEC sensors with excellent sensitivity and accuracy. Herein, an elegant and robust PEC biosensor for carcinoembryonic antigen (CEA) has been designed by photocurrent polarity switching of CdTe quantum dots (QDs), which is obtained by embedding methylene blue (MB) into amplified double-stranded DNA (dsDNA) anchored to the superparamagnetic Fe3O4@SiO2. The target-triggered Exo III-assisted cyclic amplification strategy and in situ magnetic enrichment enable the remarkable sensitivity. The extraction of target-analogue single-stranded DNA (output DNA) contributes to high selectivity resulting from the elimination of possible interferences in real samples or matrixes. Particularly, this exclusive polarity-reversal-mode PEC aptasensing can efficiently eliminate the false-positive or false-negative signals, leading to accurate measurements. Moreover, different from the probes and layer-by-layer assembled photoelectric beacons on electrodes in advance, this rational split-type approach is doomed to help the PEC biosensor with additional merits of convenient fabrication, short time consumption, wider linearity, as well as outstanding reproducibility and stability in practical applications. In light of the ability of MB acting as a kind of signal probe in typical electrochemical sensors, certainly, this ingenious design can not only be extended to a wide variety of target monitoring but also provide new ideas for the construction of high-performance electrochemical and PEC biosensors.
Integrating the advantages of excellent anti-interference and high stability superior to photoanode, cathodic photoelectrochemical (PEC) bioanalysis is promising and competitive in precise monitoring targets in complex matrices. However, serious consideration of the photocathode is far behind the anodic one. Herein, we report a high quality MoS2 QDs-BiOI p-n heterojunctioned material and exemplify the feasibility of constructing cathodic PEC aptasensing platform. Intense visible light-harvesting, high photoelectric conversion efficiency and magnified photocurrent is observed, which origin is detailed explored by various spectroscopic and electrochemical study. Taking the tumor necrosis factor-alpha (TNF-α) as a model analyte and by coupling the simplest target-induced conformational change mechanism, high selectivity and ultrasensitive self-power cathodic PEC detection is exemplified. Stable and reproducible PEC responses are achieved in a wide linear range of 10 fg/mL to 0.1 ug/mL with an ultralow detection limit (5.2 fg/mL) surpassing most sensors reported so far. Monitoring TNF-α in biological system is realized with desired accuracy and satisfactory recovery.
A dual aptamer-conjugates biorecognition chemiluminescence aptasensor was established for detecting carcinoembryonic antigen (CEA). Method for replacing part of the iron source of MIL-88B (Fe) by hemin, a metalloporphyrinic iron-based metal-organic framework, called as [email protected] (Fe), was prepared. Then, [email protected] (Fe)/CEA aptamer1 ([email protected] (Fe)-apt1) as the large signaling strategy and Luminol-CEA aptamer2 (L-apt2) which can generate the chemiluminescent signal were prepared. The ssDNA was immobilized on the surface of Fe3O4@SiO2 magnetic material, and [email protected] (Fe)-apt1 was adsorbed on the Fe3O4@SiO2 by the complementary pairing of the partial bases between ssDNA and CEA apt1. L-apt2 was adsorbed on the matrix material magnetic carbon nanotubes (MCNTs) by the electrostatic adsorption. With CEA as target, [email protected] (Fe)-apt1, L-apt2 and CEA formed by sandwiched-like ternary complexes. Introduction of dual aptamer conjugates could effectively solved the CEA detection problem of false positives. The positively charged [email protected] (Fe) easily accumulates near the hydroperoxide anion (HO2⁻) through electrostatic adsorption, thereby catalyzing the luminol transient chemiluminescence system. Under the optimal conditions, a detection range of this strategy was 0.01–100 ng/mL and a detection limit was 1.5 × 10⁻³ ng/mL. This chemiluminescent aptasensor is expected to detect other proteins with ultra-sensitivity in clinical diagnosis.
MicroRNA (miRNA) has become a key indicator of cancer diagnosis based on its abnormal expression levels. However, high-performance monitoring of miRNA is still a difficult task because of its low concentration, small size, and similarity of sequences. Herein, an elegant and robust photoelectrochemical (PEC) biosensor for miRNA-122 has been flexibly designed based on the split mode between entropy-driven DNA signal amplification and photocurrent expression. The entropy-driven DNA circuit uses a multichain composite structure instead of a DNA hairpin structure, leading to decrease the reversibility of each step of the signal amplification system. Also, the unique increasing entropy mechanism, rather than the free energy release from the new base pairs forming, improves the reaction efficiency and enhances more thermal stability and strong specific identification ability. Particularly, the biologically functionalized superparamagnetic Fe3O4@SiO2 complex endows this split mode PEC biosensor with excellent specificity and enhanced efficiency of electrode fabrication. Additionally, this strategy of only the CdTe-signal DNA modified on the ITO electrode for photocurrent readout overcomes the shortcomings of tediously long layer-by-layer assembly process and multiple rinsing steps, leading to efficient improvement of the stability and reproducibility for the as-designed PEC biosensor. This elegant strategy opens a new path for miRNA measurements with superior performance.
The detection of clinically relevant disease-specific biomolecules, including nucleic acids, circulating tumor cells, proteins, antibodies, and extracellular vesicles, has been indispensable to understand their functions in disease diagnosis and prognosis. Therefore, a biosensor for the robust, ultrasensitive, and selective detection of these low-abundant biomolecules in body fluids (blood, urine, and saliva) is emerging in current clinical research. In recent years, nanomaterials, especially superparamagnetic nanomaterials, have played essential roles in biosensing due to their intrinsic magnetic, electrochemical, and optical properties. However, engineered multicomponent magnetic nanoparticle-based current biosensors that offer the advantages of excellent stability in a complex biomatrix; easy and alterable biorecognition of ligands, antibodies, and receptor molecules; and unified point-of-care integration have yet to be achieved. This review introduces the recent advances in superparamagnetic nanostructures for electrochemical and optical biosensing for disease-specific biomarkers. This review emphasizes the synthesis, biofunctionalization, and intrinsic properties of nanomaterials essential for robust, ultrasensitive biosensing. With a particular emphasis on nanostructure-based electrochemical and optical detection of disease-specific biomarkers such as nucleic acids (DNA and RNA), proteins, autoantibodies, and cells, this review also chronicles the needs and challenges of nanoarchitecture-based detection. These summaries provide further insights for researchers to inspire their future work on the development of nanostructures for integrating into biosensing and devices for a broad field of applications in analytical sensing and in clinic.
High-efficient exciton energy transfer between CdSeTe alloyed quantum dots and SiO2@Au nanocomposites was applied to develop an enhanced photoelectrochemical aptasensing platform with ultrahigh sensitivity, good selectivity, reproducibility and stability.
In this work, an ultra-sensitive electrogenerated chemiluminescence (ECL) biosensor for exosomes and their surface proteins was developed by the in-situ formation of gold nanoparticles (AuNPs) decorated Ti3C2 MXenes hybrid with aptamer modification (AuNPs-MXenes-Apt). In this strategy, the exosomes were efficiently captured on an exosome recognized CD63 aptamer modified electrode interface. Meanwhile, in situ formation of gold nanoparticles on single layer Ti3C2 MXenes with aptamer (MXenes-Apt) modification was obtained, in which MXenes acted as both reductants and stabilizer, and no additional reductant and stabilizer involved. The in situ formed AuNPs-MXenes-Apt hybrid not only presented highly efficient recognition of exosomes specifically, but also provide naked catalytic surface with high electrocatalytic activity of gold nanoparticles with predominated (111) facets that significantly improved the ECL signal of luminol. In this way, a highly sensitive ECL biosensor for exosomes detection was constructed ascribing to the synergistic effects of large surface area, excellent conductivity and catalytic effects of the AuNPs-MXenes-Apt. The detection limit is 30 particles μL-1 for exosomes derived from Hela cell line, which was over 1000 times lower than that of conventional ELISA method and the linear range was from 102 particles μL-1 to 105 particles μL-1. This ECL sensing platform possessed high selectivity towards exosomes and their surface proteins derived different kinds of tumor cell lines (HeLa cells, OVCAR cells and HepG2 cells), and enabled sensitive and accurate detection of exosomes from human serum, which implied that the ECL biosensor provided a feasible, sensitive and reliable tool for exosomes detection in exosomes-related clinical diagnostic.
Magnetic nanoparticles (MNPs) are one of the most promising candidates for their use as theranostic agents in the biomedical field due to their potential as contrast agents in magnetic resonance imaging (MRI) and also as heat generators in magnetic hyperthermia treatments. However, despite the large number of publications about this topic, just some few systematic studies about the influence of MNPs composition on their theranostic capabilities have been carried out. In this work, we show a detailed methodology for the preparation of highly-monodisperse iron oxide-based MNPs with different cobalt, zinc and manganese doping extents in the superparamagnetic regime. We aim to provide the tools to control the composition of the particles, as well as for their functionalization to make them highly stable in biological-mimicking media. Procedures to measure the capability of the particles as magneto-thermal and MRI negative contrast agents as well as to analyze the influence of doping on such properties are also reported. In all of experiments, the applied alternating magnetic fields were within the maximum allowed amplitude, frequency, and amplitude·frequency product range for potential validation of the experimental data towards the potential translation of the present MNPs to the clinical practice.
Selectivity is a crucial parameter for photoelectrochemical (PEC) sensing in a practical setting. Despite the use of specific probes such as aptamers, antibodies, and enzymes, coexisting interferences can still result in inaccuracies in PEC sensing, especially for complex biosample matrices. Here we report the design of a [email protected]@TiO2 magnetic-optical bifunctional beacon applied in a novel PEC sensor that can selectively capture progesterone in complex bio-samples, be magnetically separated and cleaned, and be detected in pure phosphate buffer solution (PBS). The magnetic separation strategy efficiently removes the complex coexisting species from the modified electrode surface and drastically enhances the selectivity of the as-designed PEC sensor. The as-designed PEC sensor is cost-effective, easy to fabricate, highly selective and sensitive, and highly reliable, making it a promising platform for efficient aptasensing.
Photoelectrochemical sensing is an attractive tool for rapid and accurate monitor of chemical and biochemical mole-cules. Compared with conventional analysis techniques, photoelectrochemical sensing exhibits unique technique superiority and has become a hot topic in material chemis-try and analytical chemistry. This review provides an over-view of the important advances in the construction and application of photoelectrochemical sensing in recent year. In the first segment, we briefly introduce the general princi-ple and technical characteristic of photoelectrochemical sensing. In the subsequent sections, we primarily devote to elaborating the typical strategies of design and engineering photoactive materials for improve the light excitation as well as charge separation/transfer to modulate the perfor-mance of photoelectrochemical sensing system. Addition-ally, the current research status of photoelectrochemical sensing with a particular emphasis on the innovative sens-ing devices and detection modes for achieving specific sensing functions is describes in detail with the illustrative examples. Finally, the critical challenges on the journey to achieve real-life applications of photoelectrochemical sens-ing and the viable solutions for solving these problems as well as the future research perspectives are discussed.
Herein, a new "on-off-on" signal switch system combined triple helix molecular switch with efficient charge separation and transfer between different sensitization units was designed for the ultrasensitive photoelectrochemical (PEC) determination of prostate-specific antigen (PSA). Concretely, the initial "signal-on" state was obtained via the cascaded sensitization structure consisting of type-II CdTe@CdSe core-shell quantum dots (QDs), CdS QDs, and ZnO nanotubes, which were assembled on Au nanoparticles modified paper fibers with the aid of signal transduction probe (STP). Thereinto, the type-II CdTe@CdSe QDs with hole-localizing core and electron-localizing shell could enable the ultrafast charge transfer and retard the charge recombination, magnifying the initial photocurrent response and preserving the high efficiency of signal-switchable PEC aptasensing system. Subsequently, the PSA aptamer (PSA-Apt) modified with gold nanoparticles (GNPs) was introduced by the hybridization of PSA-Apt with STP and the hairpin configuration of STP changed from closed to open state, forming a triple-helix structure. Hence, the CdTe@CdSe QDs labeled on the terminal of STP moved away from the electrode surface while the GNPs kept attached close to it. The proposed aptasensor turned to "signal-off" state because of the dual inhibition of vanished cosensitization effect and signal quenching effect of GNPs. Upon the target recognition, the triple-helix structure was perturbed with the formation of DNA-protein complex and the recovery of STP hairpin structure, resulting in the second "switch-on" state. Based on the target-induced photocurrent enhancement, the proposed PEC aptasensor was utilized for the determination of PSA with high sensitivity, persuasive selectivity, and excellent stability.
Development of biosensing platforms plays a key role in research settings for identification of biomarkers and in clinical applications for diagnostics. Biosensors based on nucleic acids have taken many forms, from simple duplex-based constructs to stimuli-responsive nucleic acid nanostructures. In this review, we look at various nucleic acid-based biosensors, the different read-out strategies employed, and their use in chemical and biological sensing. We also look at current developments in DNA nanotechnology-based biosensors and how rational design of such constructs leads to more efficient biosensing platforms.
Trace concentration of formaldehyde can damage human health and environment. Consequently, it is of great significance to develop an ultrasensitive sensor for its determination. Herein, an ingenious and efficient photoelectrochemical sensor for formaldehyde was constructed by amorphous TiO2 hollow spheres incorporated with Ag+ ions, which were brought about by silica templates etching and then the exchange of Ag+/Na+ ions. The amorphous TiO2 acted as the dual role of Ag+ ion probe carriers and photoelectric materials. Upon exposure to the increased concentration of formaldehyde, the Ag nanoparticles were produced in situ and photocurrent amplification was then achieved in a proportional manner. It is attributed to the injection of hot electrons from plasmonic Ag nanoparticles into the conduction band of amorphous titanium dioxide and enhanced the photocurrent therefore. The linear relationship between 1 and 400 pmol L-1 was resulted from the enhanced photocurrent and the increased concentration of formaldehyde, and the detection limit was 0.4 pmol L-1. Benefited from an in situ and unique sensitization strategy, this PEC sensor exhibited many advantages such as sensitivity, selectivity, cost-effectiveness, convenience of fabrication, low power consumption, and stability.
DNA aptamers are single-strand DNA (ssDNA) capable of selectively and tightly binding a target molecule. Capillary electrophoresis-based selection of aptamers for protein targets requires the knowledge of electrophoretic mobilities of protein–aptamer complexes while measuring these mobilities requires having the aptamers. Here we report on breaking this vicious circle. We introduce a mathematical model that allows prediction of protein–aptamer complex mobility while requiring only three easy-to-determine input parameters: the number N of nucleotides in the aptamer, electrophoretic mobility of N-nucleotide-long ssDNA, and a sum molecular weight of the protein–aptamer complex. The model was derived upon a simplifying assumptions of a spherical shape of the protein–aptamer complex. According to this model, the protein–aptamer complex mobility is a linear function of a combination of the three input parameters with empirically determined line’s intercept and slope. The intercept and slope were determined using experimental data for seven complexes. The model was then cross-validated with the leave-one-out approach revealing only 2% residual standard deviations for both the slope and the intercept. Such a precise determination of these constants allowed accurate mobility prediction for the excluded complexes with only a 3% maximum deviation from the experimentally determined mobilities. The model was tested by applying it to three protein–aptamer complexes that were not a part of the training/ cross-validation set; deviations of the predicted mobilities from the experimentally determined ones were within 5% of the latter. To complete this study, the model was fine-tuned using the ten complexes. Our results strongly suggest the validity of the spherical-shape assumption for the protein-aptamer complexes when considering complex mobility. The developed model will make it possible to rationally design capillary electrophoresis-based selection of DNA aptamers for protein targets.
DNA nanotechnology engineered at the solid-liquid interface has advanced our fundamental understanding of DNA hybridization kinetics and facilitated the design of improved biosensing, bioimaging and therapeutic platforms. Three research branches of DNA nanotechnology exist: (i) structural DNA nanotechnology for the construction of various nanoscale patterns; (ii) dynamic DNA nanotechnology for the operation of nanodevices; and (iii) functional DNA nanotechnology for the exploration of new DNA functions. Although the initial stages of DNA nanotechnology research began in aqueous solution, current research efforts have shifted to solid-liquid interfaces. Based on shape and component features, these interfaces can be classified as flat interfaces, nanoparticle interfaces, and soft interfaces of DNA origami and cell membranes. This review briefly discusses the development of DNA nanotechnology. We then highlight the important roles of structural DNA nanotechnology in tailoring the properties of flat interfaces and modifications of nanoparticle interfaces, and extensively review their successful bioapplications. In addition, engineering advances in DNA nanodevices at interfaces for improved biosensing both in vitro and in vivo are presented. The use of DNA nanotechnology as a tool to engineer cell membranes to reveal protein levels and cell behavior is also discussed. Finally, we present challenges and an outlook for this emerging field.
Here, we fabricated a novel photoelectrochemical (PEC) aptasensor based on Br, N-codoped TiO2/CdS quantum dots (QDs) sensitization structure with excellent energy level arrangement for supersensitive detection of carcinoembryonic antigen (CEA). The prepared Br, N-codoped TiO2 could reduce the energy band width of TiO2 from 3.2 eV to 2.88 eV, which could dramatically reduce the basic signal and obviously broaden the absorption of light (400-700 nm). In addition, the energy band width of Br, N-codoped TiO2 (2.88 eV) matched well with that of CdS QDs (2.4 eV), making CdS QDs an ideal signal enhancer for amplifying the photocurrent signal of Br, N-codoped TiO2. More importantly, the constructed Br, N-codoped TiO2/CdS QDs sensitization structure with narrow energy level gradient enabled the effective promotion of electron transfer capability and dramatical improvement of photoelectric conversion efficiency. Simultaneously, a small amount of the CEA was transformed into substantial single chain DNA (T-DNA) via exonuclease III (Exo-III)-assisted cycle strategy. Under optimum conditions, the designed PEC aptasensor demonstrated a wide detection range from 1 fg/mL to 1 ng/mL and a low detection limit as 0.46 fg/mL for CEA assay. This strategy prepared a new photoactive material to markedly improve photoelectric conversion efficiency and initiated a new way to realize the highly sensitive PEC biomolecules detection.
Photoelectrochemical (PEC)sensing and biosensing have received much attention owing to their great potential for future biomolecular detection. The use of an appropriate photoelectrode is essential for PEC sensing and biosensing. Among the numerous semiconductors, many Bi-based ones are of great interest due to their high visible-light-responsivity, easy fabrication and good biocompatibility. Currently, the impetus for advanced Bi-based PEC sensing and biosensing has grown rapidly, as demonstrated by increased scholarly reports. This review introduces the state-of-the-art type and properties of Bi-based photoelectrodes, as well as their analytical applications toward various biomolecules, gas biomolecules and metal ions etc. The future prospects in this area will also be discussed based on our own opinions.
A novel efficient photoelectrochemical (PEC)sensor was assembled for curcumin (Cur)detection using 2-mercaptoacetic acid (TGA)-capped CdTe nanoparticles and nickel tetra-amined phthalocyanine-linked graphene oxide ([email protected]). The TGA-CdTe nanoparticles could be firmly immobilized on the thin film structure of NiTAPc-Gr in a hydrogen-bonded manner, thus producing the proposed PEC sensor with a high photoelectrochemical activity of TGA-CdTe nanoparticles and excellent stability of NiTAPc-Gr. The [email protected] thin film showed a stronger blue light absorption property than the individual precursors, and this resulted in the sensitive detection of Cur ranging from 0.25–100 μM with a detection limit of 12.50 nM. In addition, the PEC sensor exhibited a high sensitivity and selectivity and quite good reproducibility. Thus, it shows potential for Cur detection in real samples.
Establishing an accurate, simple and rapid serodiagnosis method aiming for specific cancer antigens is critically important for the clinical diagnosis, therapy and prognostication of cancer. Currently, surface-enhanced Raman scattering (SERS) readout techniques challenge fluorescent-based detection methods in terms of both optical stability and more importantly multiple detection capability, which become more desirable for clinical diagnostics. We thus started using an interference-free mixing SERS emission (m-SERS) readout to for the first time simultaneously indicate three specific liver cancer antigens, including α-fetoprotein (AFP), carcinoembryonic antigen (CEA), and ferritin (FER), even in one clinical serum sample. And here, three triple bonds (C≡N and C≡C) coded SERS tags contribute separate SERS emissions located at 2105, 2159 and 2227 cm-1, respectively; must have one-to-one correspondence from AFP, FER to CEA, In the process of detection, the mature double antibody sandwich allows the formation of microscale core-satellite assembly structure between a magnetic bead (MB) and single SERS tags, and therefore a pure and single SERS emission can be observed under the routine excitation laser spot. Due to the action of magnetic force, the uniform 3D packing of SERS tags absorbed MBs will in contrast generate a so-called m-SERS signals. With the help of enrichment and separation by MBs, the proposed m-SERS immunoassay provides an extremely rapid, sensitive and accurate solution for multiplex detection of antigens or other biomarkers. Herein, the limit of detection (LOD) for simultaneous m-SERS detection of AFP, CEA and FER was 0.15, 20 and 4 pg/mL, respectively. As expected for 39 clinical serum samples, simultaneous detection of ternary specific antigens can significantly improve the accuracy of liver cancer diagnosis.
A simple magnetic electrochemical aptasensor was established for the detection of prostatic specific antigen (PSA). Ag/CdO nanoparticles (NPs) were fabricated and exhibited strong electroreduction peaks at -1.07 V, attributing to the electron transfer from Cd2+ to Cd0 and the superior electron transportation of Ag. Aptamers modified Ag/CdO NPs were assembled on the surface of superparamagnetic Fe3O4/graphene oxide nanosheets (GO/Fe3O4 NSs) through the hydrophobic and π-π stacking interaction of aptamers and GO NSs. These assemblies possessed superior electroactive properties, efficient electron transfer and superparamagnetic response, and could serve as sensing units for PSA detection with the aid of magnetic electrode. With the increasing concentration of PSA, the high affinity of aptamers to PSA enabled the dissociation of Ag/CdO NPs from GO/Fe3O4 NSs, decreasing the intensity of electroreduction peaks. Ag/CdO NPs engineered magnetic electrochemical aptasensor achieved sensitive and accurate detection of PSA in the range of 50 pg/mL to 50 ng/mL. The limit of detection (LOD) was as low as 28 pg/mL. This developed protocol can be extended to a large set of strong electroactive labels for the reliable tumor biomarkers detection with high sensitivity and specificity.
A near-infrared light (NIRL)-activated ratiometric photoelectrochemical (PEC) aptasensor was fabricated for detection of carcinoembryonic antigen (CEA) coupling with upconversion nanoparticles (UCNPs)-semiconductor nanocrystals-based spatial-resolved technique on a homemade 3D printing device in which a self-regulating integrated electrode was designed for dual signal readout. The as-prepared NaYF4:Yb, Er UCNPs@CdTe nanocrystals were initially assembled on two adja-cent photoelectrodes, then CEA aptamer 1 (A1) and capture DNA (CA) were modified onto two working photoelectrodes (WP1 and WP2) through covalent binding, respectively, and then gold nanoparticle-labeled CEA aptamer 2 (Au NP-A2) were immobilized on the surface of functional WP2 for the formation of double-stranded DNA. Upon target CEA introduction, the various concentrations of CEA were captured on the WP1, whereas the binding of the CEA with Au NP-A2 could be re-leased from the WP2 thanks to the highly affinity of CEA toward A2. The dual signal readout with the 'signal-off' of WP1 and 'signal-on' of WP2 were employed for the spatial-resolved PEC (SR-PEC) strategy to detect CEA as an analytical model. Combining NaYF4:Yb, Er UCNPs@CdTe nanocrystals with spatial-resolved model on 3D printing device, the PEC rati-ometric aptasensor based on steric hindrance effect and exciton-plasmon interactions (EPI) exhibited a linear range from 10.0 pg mL-1 to 5.0 ng mL-1 with a limit of detection of 4.8 pg mL-1 under 980 nm illumination. The SR-PEC ratiometric strategy showed acceptable stability and reproducibility with a superior anti-interference ability. This approach can provide the guidance for the design of ratiometric, multiplexed and point-of-care biosensors.
A ternary WO3/Au/CdS photocatalyst was prepared by reversible redox and ionic adsorption for the first time. The photocatalyst exhibited high photocatalytic activity and good photoelectrochemical (PEC) property in comparison with WO3, CdS, WO3/Au and WO3/CdS, because the localized surface plasmon resonance (LSPR) effect of Au nanoparticles (Au NPs) and the sensitization of CdS benefited the spatial separation of photogenerated electron-hole pairs and the absorption of visible light. Thus, its photocurrent response intensity was quite high, up to about 218-fold of WO3 and 87-fold of CdS under 430 nm LED light irradiation. Based on the large anodic photocurrent and the specific recognition between carcinoembryonic antigen (CEA) and anti-CEA, a novel PEC immunosensor was constructed for the sensitive and selective detection of CEA. Under the selected conditions, the change of photocurrent intensity was linear to the logarithm of CEA concentration over the range from 0.01 to 10 ng/mL, and the detection limit was down to 1 pg/mL. The immunosensor also showed good stability, reproducibility and repeatability. It was successfully applied to the detection of CEA in serum samples.
This work has looked to explore an innovative and powerful visible fluorescence immunoassay method through wet NH3-triggered structural change of NH2-MIL-125(Ti) impregnated on paper for the detection of carcinoembryonic antigen (CEA). Gold nanoparticles heavily functionalized with glutamate dehydrogenase (GDH) and secondary antibody were used for generation of wet NH3 with a sandwiched immunoassay format. Paper-based analytical device (PAD) coated with NH2-MIL-125(Ti) exhibited good visible fluorescence intensity through wet NH3-triggeried structural change with high accuracy and reproducibility. Moreover, NH2-MIL-125(Ti)-based PAD displayed two visual modes of fluorescence color and physical color with naked eyes, and allowed the detection of CEA at a concentration as low as 0.041 ng mL-1. Importantly, the PAD-based assay provides promise for use in the mass production of miniaturized devices and opens new opportunities for pro-tein diagnostics and biosecurity.
Excitonic response between nanomaterials is distance-dependent, thus interparticle distance is a key factor in fabricating diverse photoelectrochemical (PEC) systems. Current studies focus on DNA-mediated regulation of interparticle distance. However, limited by high demands of base-pairing and flexibility of DNA, it is hard for DNA to achieve precise regulation, especially in a short distance. To pursue better PEC performances in bioanalyses, alternative biological materials should be explored to replace DNA as new “distance controllers”. In this work, a peptide with three functional sequences is designed to control interparticle distance between positive-charged Au nanoparticles ((+) AuNPs) and negative-charged CdTe quantum dots ((-) CdTe QDs). Relying on the function of binding sequence, (+) AuNPs and (-) CdTe QDs may be separated to a certain distance by the multi-functional peptide. In this case, the excitonic response is relatively weak, and an evident PEC response can be observed. Since containing the substrate sequence of caspase-3, the peptide is cleaved in the presence of caspase-3. As a result, without the support of intact peptide, electrostatic attraction plays a dominant role, leading to the aggregation of oppositely charged AuNPs and CdTe QDs, which strengthens the excitonic response and attenuates the PEC response. On a basis of these principles, a novel PEC approach was fabricated to sensitively quantify caspase-3. Meanwhile, caspase-3 in staurosporine-treated A549 cells are also determined by the approach, and the obtained results agree well with the fluorescent intensity of confocal images, manifesting that the proposed PEC method can monitor apoptosis in a label-free strategy. Overall, the study reveals the capability of peptides in controlling interparticle distance of nanomaterials, which may accelerate the development of peptide-based PEC analytical methods.
As a new analysis tool, photoelectrochemical (PEC) biosensors have been widely studied in recent years. However, common PEC biosensors usually require a high stable light source to excite the electrical signal and an electrochemical workstation to collect and process the signal data, which limited the development of portable PEC devices. Herein, we propose the design of a sunlight powered portable PEC biosensor that use sunlight as the light source. The sunlight intensity changes over time and weather and bring varied background PEC currents. To eliminate the interference caused by unstable excitation light, the potentiometric resolve ratiometric principle was introduced. Coupled with a miniature electrochemical workstation and a laptop, a sensitive and portable PEC sensing platform was successfully developed. The detection may be achieved under the irradiation of sunlight and no longer need an extra light source. In a proof of concept experiment, this platform was successfully applied in AFB1 analysis, which was promising in the development of portable biosensors.
An innovative near-infrared (NIR) light-driven photoelectrochemical (PEC) aptasensor was constructed for sensitive screening of carcinoembryonic antigen (CEA) on the basis of in-situ formation of Ag2S nanoparticles on the NaYF4:Yb,Er upconversion nanoparticles (UCN), coupling with hybridization chain reaction (HCR) for the signal am-plification. Utilization of UCN as the light nanotransducer could convert the NIR light into an applicable wavelength harvested by semiconductors. The multiemissions of NaYF4:Yb,Er UCN could match well with the absorption charac-teristics of Ag2S. In the presence of target CEA, a sandwich-type reaction was carried out between capture CEA ap-tamer/NaYF4:Yb,Er-modified electrode and trigger CEA aptamer, which underwent an unbiased strand-displacement reaction to open C-rich hairpin probes in sequence between two alternating hairpins with the assistance of C-Ag+-C chelation reaction. Upon addition of sulfidion, the chelated Ag+ ions in the long-nicked DNA poly strands by hybridi-zation chain reaction reacted with S2- to generate Ag2S nanoparticles. The formed Ag2S could utilize effectively the upconversion emissions to amplify the photocurrent. Under optimal conditions, NaYF4:Yb,Er-based NIR light-responsive PEC aptasensing platform exhibited high sensitivity for the determination of CEA within a dynamic linear range of 0.005 – 5.0 ng mL-1. The limit of detection was 1.9 pg mL-1. Good precision and high specificity could be ac-quired in this system for the analysis of target CEA. Human serum samples containing target CEA were measured by using our strategy, and received well-matched results relative to human CEA enzyme-linked immunosorbent assay kits. Importantly, NaYF4:Yb,Er-based NIR light-responsive PEC aptasensing system provides a new ideal on the detection of disease-related biomarkers by using nucleic acid-based amplification strategy.
Proteins are involved in many biological processes. Misfolded, truncated, or mutated proteins as well as over- or underexpressed proteins have been implicated in many diseases. Therefore, detection and quantification of proteins is extremely important. Conventional techniques such as the enzyme-linked immunosorbent assay, Western Blot, and mass spectrometry have enabled discovery and study of proteins in biological samples. However, many important proteins are present at low concentrations, rendering them undetectable using conventional techniques. Furthermore, limited ability to simultaneously measure multiple proteins in a sample has constrained our ability to fully study the proteome. In this review, we comprehensively discuss approaches for protein detection. We first discuss the fundamentals of proteins and protein assays, including affinity reagents, surface functionalization, assay formats, signal detection, and multiplexing. We then discuss the challenges with these methods and review existing methods for highly sensitive and multiplexed protein detection. Finally, we review recent advances in protein detection from the literature and discuss challenges and future directions.
This work described the construction of a novel photoelectrochemical platform with Sn3O4 which was in-situ decorated on a carbon fiber paper (Sn3O4@CFP) as the visible light-active species, and molecularly imprinted polymers (MIPs) as the recognition element. This is the first attempt to apply Sn3O4 in the field of photoelectrochemical sensors. Sn3O4 nanoplates were directly grown on CFPs by a simple hydrothermal process. The MIP layer with special selectivity for 2,4-dichlorophenoxyacetic acid (2,4-D), a kind of carcinogen, was prepared on the Sn3O4@CFP by electropolymerizing pyrrole in the presence of 2,4-D. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques were used to characterize the as-prepared Sn3O4@CFP. Benefiting from the structural advantages of Sn3O4@CFP and selectivity of MIP, the binder-free PEC sensor affords a linearity from 5.0 × 10⁻¹¹ to 1.0 × 10⁻⁷ M for 2,4-D and the detection limit was down to 1.08 × 10⁻¹¹ M. This PEC platform demonstrates excellent stability, reproducibility, remarkably convenience, and cost-effective advantages, as well as low detection limit. The successful detection of 2,4-D in bean sprout samples has been acquired. Furthermore, the flexibility of the Sn3O4@CFP offers an easy integration of PEC sensor onto different non-planar shape and size surfaces which extends its applications for sensors construction.
A new double photosystems-based 'Z-scheme' photoelectrochemical (PEC) sensing platform is designed for ultrasensitive detection of prostate-specific antigen (PSA) by coupling with three-dimensional (3D) DNA walker. Two photosystems consist of CdS quantum dots (photosystem I; PS I) and BiVO4 photoactive materials (photosystem II; PS II), whereas gold nanoparticles (AuNPs) photodeposited on high-active {010} facets of BiVO4 are used as the electron mediators to promote electron transfer from conduction band (CB) of PS II to valence band (VB) of PS I. 3D DNA walker-based amplification strategy is carried out between hairpin DNA1 conjugated onto the AuNP, hairpin DNA2 labeled with CdS quantum dot (QD-H2) and DNA walker complementary with the PSA aptamer modified to magnetic bead (Apt-MB). Upon addition of target, DNA walker strand is displaced from DNA walker/Apt-MB to open hairpin DNA1 on AuNP@BiVO4. In the presence of QD-H2, DNA walker induces the hybridization of DNA1 with DNA2 on the gold nanoparticles step by step, thereby resulting in the assembly of CdS QDs on the AuNP@BiVO4 to form 'Z-scheme' double photosystems with strong photocurrent. Under optimum conditions, the 'Z-scheme' PEC sensing system exhibits good photocurrent responses toward target PSA within the working range of 0.01 – 50 ng mL-1 at a low detection limit of 1.5 pg mL-1. Good reproducibility and accuracy are acquired for analysis of target PSA and human serum specimens relative to commercial PSA ELISA kit. Importantly, our strategy provides a new horizon for photoelectrochemical in vitro diagnostics.
Photoelectrochemical (PEC) analysis is a new detection technique developed in recent years, which has the advantages of high sensitivity, low background signal and desirable selectivity, obtaining the great progress in sensing applications. Semiconductor nanomaterials with excellent photoelectric activity have played a vital role in the construction of PEC sensing platform. Thus, this review introduces the recent advances of semiconductor nanomaterials‐based PEC analysis, and describes the typical PEC sensing strategies. Some representative nanomaterials, including metallic oxides, metallic sulfides, graphitic carbon nitride, transition metal dichalcogenides and quantum dots, are summarized for advanced PEC devices, as well as their applications in nucleic acid analysis, immunoassays, cell detection, protein and enzyme sensing, and small biomolecule monitoring. Finally, some future opportunities and challenges of PEC biosensing are also discussed.
Developing a new ultra-sensitive interface to detect As(III) is highly desirable because of its seriously toxic and low concentration in drinking water. Recently, Fe3O4 nanoparticles of high adsorption toward As(III) become very promising to be such an interface, which is still limited by the poor understanding of their surface physicochemical properties. Herein, we report that dumbbell-like Au/Fe3O4 nanoparticles, when being modified the screen-printed carbon electrode, can serve as an efficient sensing interface for As(III) detection with an excellent sensitivity of 9.43 μA ppb-1 and a low detection limit of 0.0215 ppb. These outstanding records were attributed to the participation of Fe(II)/Fe(III) cycle on Fe3O4 surface in the electrochemical reaction of As(III) redox, as revealed by X-ray photoelectron spectroscopy, X-ray absorption near edge structure, and extended X-ray absorption fine structure. This work provides new insight into the mechanism of electroanalysis from the viewpoint of surface active atoms, and also helps to predict the construction of ultra-highly sensitive electrochemical sensors for other heavy metal ions with nonprecious redox active materials.
A competitive-displacement reaction strategy based on target-induced dissociation of gold nanoparticles-coated graphene nanosheet (AuNPs/GN) from CdS quantum dots-functionalized mesoporous titanium dioxide (CdS QDs/TiO2) was designed for the sensitive photoelectrochemical (PEC) aptasensing of prostate-specific antigen (PSA) through the exciton-plasmon interaction (EPI) between CdS QDs and AuNPs. To construct such an aptasensing system, capture DNA was initially conjugated covalently onto CdS QDs/TiO2-modified electrode, and then AuNPs/GN-labeled PSA aptamer was bound onto biofunctionalized CdS QDs/TiO2 via hybridization chain reaction of partial bases with capture DNA. Introduction of AuNPs/GN efficiently quenched the photocurrent of CdS QDs/TiO2 thanks to energy transfer. Upon addition of target PSA, the sandwiched aptamer between CdS QDs/TiO2 and AuNPs/GN reacted with the analyte analyte, thus resulting in the dissociation of AuNPs/GN from the CdS QDs/TiO2 to increase the photocurrent. Under optimum conditions, the aptasensing platform exhibited a high sensitivity for PSA detection within a dynamic linear range of 1.0 pg/mL – 8.0 ng/mL at a low limitation of detection of 0.52 pg/mL. The interparticle distance of exciton-plasmon interaction and contents of AuNPs corresponding to EPI effect in this system were also studied. Good selectivity and high reproducibility were obtained for the analysis of target PSA. Importantly, the accuracy and matrix effect of PEC aptasensor was evaluated for the determination of human serum specimens and new-born calf serum-diluted PSA standards, giving a well-matched result with the referenced PSA ELISA kit.
In this study, we developed a novel photoelectrochemical (PEC) sensor for the highly sensitive detection of erythromycin by functionalising graphene oxide (GO) with nickel tetra-amined phthalocyanine (NiTAPc) through covalent bonding, which resulted in the formation of NiTAPc-Gr. The fabricated sensor showed a higher PEC efficiency under blue light, exhibiting a peak wavelength of 456 nm, as compared to that of the monomer. Further, the NiTAPc-Gr/indium tin oxide (ITO) sensor exhibited a photocurrent that was 50-fold higher than that for a GO/ITO sensor under the same conditions. Under optimal conditions, the NiTAPc-Gr PEC sensor showed a linear response for erythromycin concentrations ranging from 0.40 to 120.00 μmol L-1, with the minimum limit for detection being 0.08 μmol L-1. Thus, the NiTAPc-Gr sensor exhibited superior performance and excellent PEC characteristics, high stability, and good reproducibility with respect to the sensing of erythromycin. Moreover, it is convenient to use, fast, small, and cheap to produce. Hence, it should find wide use in the analysis of erythromycin in real-world applications.
This work demonstrates that the photoelectric response of defect-engineered TiO2-x modified with Au nanoparticles can be modulated by oxygen vacancy concentration and excitation wavelength. Anchoring strongly plasmonic Au nanoparticles to defect-engineered TiO2-x by DNA hybridization, several times plasmonic enhancement of photocurrent occurs under 585 nm excitation, and it is employed as a novel signaling mode for developing an improved photoelectrochemical sensing platform. This signaling mode combining with exonuclease III-assisted target recycling amplification exhibits excellent analytical per-formance, which provides a novel photoelectrochemical detection protocol.
Carcinoembryonic antigen (CEA), a glycoprotein, is a wide-spectrum tumor marker for cancer diagnosis. Developing simple, stable, and low-cost methods for CEA detection is of great importance. In this work, a novel, label-free, and antibody-free electrochemical sandwich CEA biosensor was developed based on concanavalin A (ConA) and a DNA aptamer against CEA. Horse radish peroxidase (HRP) was labeled on the sandwich structure for signal production and amplification. Both the CEA and the HRP bind to ConA through sugar-lectin interactions. Under optimum conditions, the detection linear range was from 5 to 40 ng mL⁻¹ CEA, with a detection limit of 3.4 ng mL⁻¹, lower than the threshold level in human serum for cancer patients (∼10 ng mL⁻¹). The biosensor is reproducible, accurate, specific, and stable, with RSD value of 3% for inter-biosensors, and relative error of <13% compared with those obtained by a commercial diagnostic kit. No obvious responses were observed toward interfering proteins. Storage did not cause obvious signal diminishment for the biosensor. The simple and low-cost aptasensor is promisingly applicable for CEA detection in cancer diagnosis, and could be able to serve as a general platform for detection of other interested glycoproteins.
Titanium dioxide (TiO2; as a potential photosensitizer) has good photocurrent performance and chemical stability, but often exhibits low utilization efficiency under ultraviolet (UV) region excitation. Herein, we devised a near-infrared (NIR) light-to-UV light-mediated photoelectrochemical (PEC) aptasensing platform for the sensitive detection of carcinoembryonic antigen (CEA) based on core-shell NaYF4:Yb,Tm@TiO2 upconversion microrods by coupling with target-triggered rolling circle amplification (RCA). The upconversion microrods synthesized through the hydrothermal reaction could act as a photosensing platform to convert the NIR excitation into UV emission for generation of photo-induced electrons. Target analyte was determined on functional magnetic bead by using the corresponding aptamers with a sandwich-type assay format. Upon target CEA introduction, a complex was first formed between capture aptamer-1-conjugated magnetic bead (Apt1-MB) and aptamer-2-primer DNA (Apt2-pDNA). Thereafter, the carried primer DNA by the aptamer-2 paired with linear padlock DNA to trigger the RCA reaction. The guanine (G)-rich product by RCA reaction was cleaved by exonuclease I and exonuclease III (Exos I/III), thereby resulting in the formation of numerous individual guanine bases to enhance the photocurrent of core-shell NaYF4:Yb,Tm@TiO2 upconversion microrods under NIR illumination (980 nm). Under optimal conditions, NIR light-mediated PEC aptasensing system could exhibit good photoelectrochemical response toward target CEA, and allowed for the detection of target CEA as low as 3.6 pg mL-1. High reproducibility and good accuracy were achieved for analysis of human serum specimens. Importantly, the NIR-activated PEC aptasensing scheme provides a promising platform for ultrasensitive detection of other biomolecules.
Synthetic DNA machine performs quasi-mechanical movements in response to external intervention, suggesting the promise of constructing sensitive and specific biosensors. Herein, a smart DNA walker biosensor for label-free detection of carcinoembryonic antigen (CEA) is developed for the first time by a novel cascade amplification strategy of exonuclease (Exo) III-assisted target recycling (ERA) and DNA walker. ERA as the first stage of amplification generates the walker-DNA, while the autonomous traveling of the walker-DNA on the substrate-modified silica microspheres as the second stage of amplification produces an ultrasensitive fluorescent signal with the help of N-methylmesoporphyrin IX (NMM). The DNA machine as a biosensor could be applied for transducing and quantifying signals from isothermal molecular amplifications, avoiding the complicated reporter elements and thermal cycling. The present biosensor achieves a detection limit of 1.2 pg·mL−1 within a linear range of 10 pg·mL−1 to 100 ng·mL⁻¹ for CEA, along with a favorable specificity. The practical applicability of the biosensor is demonstrated by the detection of CEA in human serum with satisfactory results, thus it shows great potential in clinical diagnosis.
To the photocatalytic H2 evolution, the exposure of a reduction surface over a catalyst plays an important role for the reduction of hydrogen protons. Here, this study demonstrates the design of a noble-metal-free spatially separated photocatalytic system exposed with reduction surfaces (MnOx@CdS/CoP) for highly solar-light-driven H2 evolution activity. CoP and MnOx nanoparticles are employed as the electron and hole collectors, which are selectively anchored on the outer and inner surface of CdS shells, respectively. Under solar light irradiation, the photogenerated holes and electrons can directionally move to the MnOx and CoP, respectively, leading to the exposure of a reduction surface. As a result, the H2 evolution increases from 32.0 to 238.4 µmol h−1, which is even higher than the activity of platinum-loaded photocatalyst (MnOx@CdS/Pt). Compared to the pure CdS with serious photocorrosion, the MnOx@CdS/CoP maintains a changeless activity for the H2 evolution and rhodamine B degradation, even after four cycles. The research provides a new strategy for the preparation of spatially separated photocatalysts with a selective reduction surface.
Colorimetric assay is a powerful tool for detection of tumor markers with the outstanding advantages of visualization and simple analytical instruments. Herein, a simple and fast chromogenic reaction was developed based on Ag3PO4/Ag nanocomposite synthesized by one-step chemical bath method. And the Ag3PO4/Ag nanocomposite owned the ability of oxidizing of TMB under the acidic condition due to the hydrolytic action. The nanocomposite was characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Then, the colorimetric immunoassay was constructed by utilizing Ag3PO4/Ag nanocomposite as molecular labels for carcino embryonie antigen (CEA, UniProt accession number: P06731) detection. The blue color with gradient change was observed with the increasing of CEA concentrations. Under optimal conditions, the variation between absorbance values and CEA levels was linear in the range of 0.2 ng mL⁻¹ ~ 2.5 ng mL⁻¹ with the detection limit of 0.03 ng mL⁻¹. More importantly, the developed colorimetric immunoassay exhibited good selectivity, repeatability, stability and potential application in the real serum sample detection.
Owing to their excellent multiplexing ability, high sensitivity, and large dynamic range, immunoassays using surface-enhanced Raman scattering (SERS) as the readout signal have found prosperous applications in fields such as disease diagnosis, environmental surveillance, and food safety supervision. Various ever-increasing demands have promoted SERS-based immunoassays from the classical sandwich-type ones to those integrated with fascinating automatic platforms (e.g., test strips and microfluidic chips). As recent years have witnessed impressive progress in SERS immunoassays, we try to comprehensively cover SERS-based immunoassays from their basic working principles to specific applications. Focusing on several basic elements in SERS immunoassays, typical structures of SERS nanoprobes, productive optical spectral encoding strategies, and popular immunoassay platforms are highlighted, followed by their representative biological applications in the last 5 years. Moreover, despite the vast advances achieved to date, SERS immunoassays still suffer from some annoying shortcomings. Thus, proposals on how to improve the SERS immunoassay performance are also discussed, as well as future challenges and perspectives, aiming to give brief and valid guidelines for choosing suitable platforms according to particular applications.
A simple and rapid photoelectrochemical (PEC) sensor is developed for the label-free detection of a phosphoprotein (α-casein) based on a zirconium based porphyrinic metal−organic framework (MOF), PCN-222, which exhibits an enhanced photocurrent response towards dopamine under the O2-saturated aqueous media. In this work, in terms of PEC measurements and cyclic voltammetry, the PEC behaviors of PCN-222 in aqueous media were thoroughly investigated for the first time. Additionally, in the virtue of the steric hindrance effect from the coordination of the phosphate groups and inorganic Zr–O clusters as binding sites in PCN-222, this biosensor shows high sensitivity for detecting α-casein and the limit of detection (LOD) is estimated to be 0.13 g mL-1. Moreover, the proposed method provides a promising platform for clinic diagnostic and therapeutics.
Photoelectrochemical (PEC) bioanalysis represents a unique and dynamically developing methodology that offers an elegant route for sensitive biomolecular detection. Aptamers are synthetic nucleic acid molecules whose binding characteristics can rival those of protein antibodies. Originated from the fusion of PEC bioanalysis and aptamers, PEC aptasensing has rapidly becoming a subject of new research interests in recent years. Using illustrative examples, this review provides the introductory concept, bioanalysis development, signaling strategies, and the state of the art in this field. The future prospects are also discussed.
On the basis of the absorption and emission spectra overlap, an enhanced resonance energy transfer caused by excition-plasmon resonance between carbon nanotubes-gold nanoparticles (CNTs-Au) and pinnate titanium dioxide nanorods array (P-TiO2 NA) was obtained. Three-dimensional single crystalline P-TiO2 were prepared successfully on fluorine-doped tin oxide conducting glass (FTO glass), and its optical absorption properties and photoelectrochemical (PEC) properties were investigated. With the synergy of CNTs-Au as energy acceptor, it resulted in the enhancement of energy transfer between excited P-TiO2 NA and CNTs-Au. Upon the novel sandwichlike structure formed via DNA hybridization, the exciton produced in P-TiO2 NA was annihilated and a damped photocurrent was obtained. With the use of carcinoembryonic antigen (CEA) as a model which bonded to its specific aptamer and destroyed the sandwichlike structure, the energy transfer efficiency was lowered, leading to PEC response augment. Thus a signal-on PEC aptasensor was constructed. Under the optimal conditions, the PEC aptasensor for CEA determination exhibited a linear range from 0.001 to 2.5 ng·mL−1 with a detection limit of 0.39 pg·mL−1 and was satisfactory for clinical sample detection. Furthermore, the proposed aptasensor shows satisfying performance, such as easy preparation, rapid detection and so on. Moreover, since different aptamer can specifically bind to different target molecules, the designed strategy has an expansive application for the construction of versatile PEC platforms.
Acute renal failure (ARF) represents a very important and potentially devastating disorder in clinical nephrology. Neutrophil gelatinase-associated lipocalin (NGAL) is an early biomarker for ARF in a wide range of different disease processes, which is frequently detected in clinical diagnosis. Herein, we present a label-free and sensitive photoelectrochemical (PEC) immunosensor for NGAL by utilizing a biotinylated anti-NGAL Nanobody (Nb) orientedly immobilized to streptavidin-coated 2,9,16,23-tetraaminophthalocyanine (CoPc)-sensitized TiO2 electrode. The Nb was biotinylated at the C-terminus, which is situated at the opposite site of the antigen binding region. Using highly oriented Nb as receptor molecules, a label-free PEC immunosensor for NGAL was developed by monitoring the changes in the photocurrent signals of the electrode resulting from immunoreaction. Immobilization of Nb to streptavidin-coated CoPc-sensitized TiO2 electrode surface provides high binding capacity to NGAL; thus, it can lead to a high sensitivity. The limit of detection (LOD) of the proposed immunosensor has been significantly lowered to 0.6 pg mL-1. This proposed immunosensor reveals high specificity to detect NGAL, with acceptable intra-assay precision and excellent stability. In addition, the present work provides a new approach to design Nb-based PEC immunosensor and increases versatility of Nbs.
Affibodies are a new class of engineered affinity proteins widely used in imaging, diagnostics and therapeutics, due to their improved properties, such as small size, robustness, high stability, and high imaging contrast compared to the best known affinity molecules (i.e., antibodies). Affibodies can also be used as biological receptors in bioassays and their incorporation in biosensors constitutes a research field of high potential at its very beginning. This review provides an up-to-date overview of the analytical applications of affibodies, and their isolation and characteristics. We also address trends in the future outlook on using affibodies in research.
Biosensing and diagnostic platforms with high sensitivity, specificity, and fast response time are based on immobilized biomolecules such as antibodies (Abs), aptamers, enzymes, nucleic acids, receptors, and whole cells for the detection of target analytes. Such sensing biomolecules should be bound to the surface of a signal transducer with a required specific chemical, electrical, or optical property. The biological recognition event generates a quantifiable signal, which is equated to the amount or concentration of the analyte. APTES can be deposited on solid materials, electrode materials, nanomaterials, and nanocomposites under variable conditions of concentration, solvent, temperature, and time. In addition, curing conditions such as air/heat drying might be necessary depending upon the intended application. Pertinent information on the thickness, morphology, and conformation of the APTES layer reported in the literature is often different and conflicting.
An innovative photoelectrochemical (PEC) biosensor platform was designed based on the in situ generation of CdS quantum dots (QDs) on graphene oxide (GO) using an enzymatic reaction. Horseradish peroxidase catalyzed the reduction of sodium thiosulfate with hydrogen peroxide to generate H2S, which reacted with Cd2+ to form CdS QDs. CdS QDs could be photo-excited to generate an elevated photocurrent as a readout signal. This strategy offered a "green" alternative to inconvenient pre-synthesis procedures for the fabrication of semiconducting nanoparticles. The nanomaterials and assembly procedures were characterized by microscopy and spectroscopy techniques. Combined with immune recognition and based on the PEC activity of CdS QDs on GO, the strategy was successfully applied to a PEC assay to detect carcinoembryonic antigen and displayed a wide linear range from 2.5 ng mL-1 to 50 μg mL-1 and a detection limit of 0.72 ng mL-1 at a signal-to-noise ratio of 3. The PEC biosensor showed satisfactory performance for clinical sample detection and was convenient for determining high concentrations of solute without dilution. This effort offers a new opportunity for the development of numerous rapid and convenient analytical techniques using the PEC method that may be applied in the design and preparation of various solar energy-driven applications.
Since the serendipitous discovery 20 years ago of bona fide camelid heavy-chain antibodies, their single-domain antigen-binding fragments, known as VHHs or nanobodies, have received a progressively growing interest. As a result of the beneficial properties of these stable recombinant entities, they are currently highly valued proteins for multiple applications, including fundamental research, diagnostics, and therapeutics. Today, with the original patents expiring, even more academic and industrial groups are expected to explore innovative VHH applications. Here, we provide a thorough overview of novel implementations of VHHs as research and diagnostic tools, and of the recently evaluated production platforms for several VHHs and VHH-derived antibody formats.
On the basis of the absorption and emission spectra overlap, an enhanced resonance energy transfer caused by excition-plasmon resonance between reduced graphene oxide (RGO)-Au nanoparticles (AuNPs) and CdTe QDs was obtained. With the synergy of AuNPs and RGO as a plane-like energy acceptor, it resulted in the enhancement of energy transfer between excited CdTe QDs and RGO-AuNPs nanocomposites. Upon the novel sandwich-like structure was formed between RGO-AuNPs nanocomposites and CdTe QDs via DNA hybridization, the exciton produced in CdTe QDs was annihilated. A damped photocurrent was used for background signal and a universal photoelectrochemical (PEC) platform was developed. Using carcinoembryonic antigen (CEA) as a model which bonded to its specific aptamer and destroyed the sandwich-like structure, it lowed the energy transfer efficiency, leading to PEC response augment. Thus a signal-on PEC aptasensor was constructed. Under 470 nm irradiation at -0.05 V, the PEC aptasensor for CEA determination exhibited a linear range from 0.001 to 2.0 ng•mL-1 with a detection limit of 0.47 pg•mL-1 at a signal-to-noise ratio of 3, and was satisfactory for clinical sample detection. The proposed sandwich-like PEC aptasensor prepared by RGO-AuNPs nanocomposites and CdTe QDs, exhibited good analytical performance. Since different aptamers can specifically bind to different target molecules, the designed strategy has an expansive and promising perspective of application in other plasmonic nanomaterials for the construction of versatile PEC platforms.
Uniform TiO2/SiO2 composite films were prepared on ITO substrates by electrodeposition, and highly photoelectrocatalytic (PEC) activity of
the composite films was observed toward the degradation of methyl orange (MO) in aqueous solutions. It was further found that
their PEC activity was dependent on the electrodeposition parameters including deposition time, solution pH and SiO2 content. Under the optimized condition, the PEC degradation of MO on TiO2/SiO2 composite film electrode could be enhanced about 14 times relative to that on neat TiO2 film electrode. The high PEC activity of the TiO2/SiO2 composite film electrode was mainly attributed to the enhancement of the charge separation of photo-generated electron-hole
pairs by the dispersion of SiO2 nanoparticles in the TiO2 matrix with the aid of the applied electric field.