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(a) FTIR interferogram of DEPSi before adhesion of E. Coli (black), after adhesion of E. Coli (red), and after further removal of E. Coli (blue). (b) FFT image of FTIR spectra from (a), same color encoding. (c) Schematic view of sensor element based on DEPSi. Detection without bacteria (on the left) and with bacteria (green ellipse) on the surface (on the right) is shown. Light sources are shown as violet sectors.
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Combination of conventional electrochemical etching and subsequent metal-assisted chemical etching (MACE) was used to obtain double etched porous silicon (DEPSi) structures with good optical properties and high affinity to bacteria. Second etching step increased the roughness of the surface and created more cavities for entrapping of bacteria, whil...
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... DEPSi samples were used to create a prototype of sen- sor element, which schematic view is shown on Fig. 5c. The element contains silicon wafer (gray colored) with MPSi layer (orange col- ored) and a layer of DEPSi on MPSi layer (orange colored rods). A broadband infrared ray has normally fallen on the surface of the sensor (slightly inclined on the figure for illustrative purpose) and then reflected from all the surface interfaces between ...
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... reflected light was detected by FTIR spectrometer. The scheme shows two cases, i.e. one without bacteria (on the left of the figure) and another one with bacteria (on the right of the figure) specified by different distance between maxima of interference due to additional optical path caused by bacteria (see waveform sketch right from detector on Fig. ...
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... data from detector of DEPSi-based sensor element are shown on Figure 5a. There are interference spectra for the sample before adhesion of bacteria (black curve), after adhesion of the bacteria (red curve) and after further removal of the bacteria by an ethanol solu- tion (blue curve). ...
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... better quantitative characterization of interferen- tial parameters fast Fourier transform (FFT) of the spectra has been performed. The result is shown on Figure 5b with the same color en- coding. Here one can see not only shift of the position of maximum (about 2%), which corresponds to increase of period of interference, but also significant broadening of the band up to 30%. ...
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... While the theoretical LOD of 10³ CFU/mL of our sensing platform is not comparable to the sensitivity of current methods such as PCR or bacterial culture, which can both detect as little as one bacterial cell per mL, it is already sufficient for many food safety and even medical applications. This LOD is also within the LOD range of other reflectance-based PSi sensors studied in the literature [40][41][42][43]. A lower LOD can be obtained by switching to other detection methods such as Surface Enhanced Raman Spectroscopy (SERS) or Electrochemical Impedance Spectroscopy (EIS) [6], which have both been combined with PSi transducers [44,45]. ...
The design of a porous silicon (PSi) biosensor is not often documented, but is of the upmost importance to optimize its performance. In this work, the motivation behind the design choices of a PSi-based optical biosensor for the indirect detection of bacteria via their lysis is detailed. The transducer, based on a PSi membrane, was characterized and models were built to simulate the analyte diffusion, depending on the porous nanostructures, and to optimize the optical properties. Once all performances and properties were analyzed and optimized, a theoretical response was calculated. The theoretical limit of detection was computed as 104 CFU/mL, based on the noise levels of the optical setup. The experimental response was measured using 106 CFU/mL of Bacillus cereus as model strain, lysed by bacteriophage-coded endolysins PlyB221. The obtained signal matched the expected response, demonstrating the validity of our design and models.
... Microbes and other biomolecules must be detected quickly in the medical and food industries in order to monitor air and water quality or perform urgent clinical tests. Traditional testing, on the other hand, is based on time-consuming laboratory analysis, which occasionally necessitates the use of highly qualified experts (Gongalsky, Koval, Schevchenko, Tamarov, & Osminkina, 2017). Thus, porous silicon guarantees the desired sensor due to the features mentioned above. ...
... However, this makes the sensor more expensive and less stable. Another solution is to make changes on the porous surface itself, whereas; this may oblige us to compromise the optical performance of the sensor (Gongalsky et al., 2017). The modifications on the porous surface by using two etching methods allow us to improve the sensitivity of the sensor. ...
... EDX spectroscopy was used to investigate the chemical composition of the sample surface and to see whether the Cu particles exist or not. After that, the double poroused silicon was washed with HNO3 in order to remove Cu metal remnants in the pores as they may play an antibacterial role (Fellahi et al., 2013;Gongalsky et al., 2017). Then the double etched porous silicon is heated at 250 o C for 5 minutes in order to increase its hydrophilicity (Gongalsky et al., 2017) and make it more sensitive. ...
Double-layered porous silicon was prepared by Stain etching and Metal assisted chemical etching (MACE) methods and examined in the detection of Klebsiella. A P-type silicon wafer is firstly poroused by stain etching method using hydrofluoric acid (HF) and nitric acid (HNO3). The poroused silicon is deposited by copper via the classical electrochemical deposition process then the copper-coated silicon is etched again in HF and hydrogen peroxide (H2O2). The stain etching process obtains micro-sized pores on the surface of the silicon; on the other hand, the copper assisted chemical etching step forms more nanopores that help to capture bacteria. The chemical constituent of the double etched porous silicon was measured by Energy Dispersive X-ray Spectroscopy (EDX). The Scanning Electron Microscopy (SEM) method is used to observe the morphology and pore dispersion of the sample. The SEM images show that the nano-sized and micro-sized pores are formed. The prepared porous silicon is applied for Klebsiella detection. The Fourier transform infrared radiation (FTIR) test of the sample illustrates the adhesion of the bacteria to the porous silicon. This can be observed through the formation of the new peaks in the FTIR graphs when the graphs are compared before and after Klebsiella introduction. The carbon-carbon double and triple bonds and phosphorous-oxygen double bond formation proofs the adhesion of the bacteria to the porous silicon. This method of acquiring nanoporous silicon as well as the FTIR results can be used to detect bacteria generally by differentiating the types of bond vibrations of the bacteria. This is a fast, easy and affordable method to manufacture biosensor with an improved affinity.
... These nanostructures increase the sensitivity of the sensors to a high level due to their large surface area. Porous silicon is one of the most useful nanomaterials in sensor manufacturing (Janshoff et al., 1998), due to its easy fabrication procedure, pore morphology (Canham, 1990) astonishingly extraordinary porosity property which makes it have a great surface area to be very sensitive to its environment (Sailor and Link, 2005 (Gongalsky et al., 2017). Thus, porous silicon guarantees the desired sensor due to the features mentioned above. ...
... However, this makes the sensor more expensive and less stable. Another solution is to make changes on the porous surface itself, whereas; this may oblige us to compromise the optical performance of the sensor (Gongalsky et al., 2017). (Ristuccia and Cunha, 1984). ...
... After that, the double etched porous silicon was washed with HNO 3 in order to remove Cu metal remnants in the pores as they may play an antibacterial role (Gongalsky et al., 2017, Fellahi et al., 2013. Then the double etched porous silicon is heated at 250 o C for 5 minutes in order to increase its hydrophilicity (Gongalsky et al., 2017) and make it more sensitive. ...
... Another method of PSi NWs manufacturing is a combination of electrochemical etching to form a layer of porous silicon (PSi) and subsequent MACE of this layer to form a nanowires [26,27]. In this method, one can easily control the ratio of the thickness of the silicon nanowire layer to the PSi layer, which can be important in the development of sensors [28][29][30]. ...
... It is shown that the size and oxidation of the surface of silicon nanocrystals in PSi NWs can be studied by their Raman spectra [33,34]. The possibility of creating an optical interferometric biosensor based on PSi NW arrays for the detection of bacteria [28] and viruses [29], as well as the electrical impedance sensor for virus detection [30] has been demonstrated. Due to the developed surface and intense photoluminescent (PL) properties, PSi NWs are shown can be used as an PL sensor for molecular oxygen detection [35]. ...
Porous silicon nanowires (PSi NWs) are a promising material for applications in sensorics, photovoltaics, and biomedicine. However, the structural and optical properties of PSi NWs are extremely sensitive to the concentrations of chemical solutions used in their manufacture. In this study, PSi NWs were fabricated by a two step metal-assisted chemical etching method from highly doped crystalline silicon wafers with a resistivity of <0.005 Ω cm. It was shown that the structural and optical properties of the obtained samples depend on the concentration of hydrogen peroxide (H2O2), which in our experiments varied from 5 to 30%. As a result of etching, a layer of NWs with a diameter of 50–200 nm is obtained from above, and a thin layer of porous silicon is obtained from below. The ratio of the thicknesses of these two layers can be tuned by choosing the required concentration of H2O2. The porosity of the samples, calculated in the approximation of the effective Bruggeman medium from the IR reflection spectra, was 40–50%. Electron microscopy demonstrated the presence of a large amount of silicon nanocrystals in the volume of PSi NWs, which exhibited efficient visible photoluminescence due to quantum confinement effect. It was shown that the size of the nanocrystals can be also tunable on the used concentration of H2O2.
... Recent works using the RIFTS as transducing mechanism of PSi-based transducers target the detection of, for instance, bacterial surface proteins [8], heat shock protein 70 [9] or bovine mastitis biomarkers [10,11], but this method has also been applied for the detection of bacteria [12][13][14]. These bacteria detectors however lacked sensitivity, with detection limits unable to go below 10 3 colony forming units per mL (CFU/mL). ...
Porous silicon (PSi) has been widely used as a biosensor over the last years due to its large surface area and its optical properties. Most PSi biosensors consist in close-ended porous layers, and, because of the diffusion-limited infiltration of the analyte, they lack sensitivity and speed of response. In order to overcome these shortcomings, PSi membranes (PSiMs) have been fabricated using electrochemical etching and standard microfabrication techniques. In this work, PSiMs have been used for the optical detection of Bacillus cereus lysate. Before detection, the bacteria are selectively lysed by PlyB221, an endolysin encoded by the bacteriophage Deep-Blue targeting B. cereus. The detection relies on the infiltration of bacterial lysate inside the membrane, which induces a shift of the effective optical thickness. The biosensor was able to detect a B. cereus bacterial lysate, with an initial bacteria concentration of 106 colony forming units per mL (CFU/mL), in less than 10 min. This work also demonstrates the selectivity of the lysis before detection. Not only does this detection platform enable the fast detection of bacteria, but the same technique can be extended to other bacteria using selective lysis.
... Recently a photonic crystal of porous silicon has been employed for bacterial detection based antibody-antigen interaction. In addition to one-dimension photonic crystal configurations of PSi, other sophisticated structures such as Bragg mirrors and microcavities have been employed for biological application 14,[17][18][19] . ...
Accuracy and speed of detection, along with technical and instrumental simplicity, are indispensable for the bacterial detection methods. Porous silicon (PSi) has unique optical and chemical properties which makes it a good candidate for biosensing applications. On the other hand, lectins have specific carbohydrate-binding properties and are inexpensive compared to popular antibodies. We propose a lectin-conjugated PSi-based biosensor for label-free and real-time detection of Escherichia coli (E. coli) and Staphylococcus aureus ( S. aureus ) by reflectometric interference Fourier transform spectroscopy (RIFTS). We modified meso-PSiO 2 (10–40 nm pore diameter) with three lectins of ConA (Concanavalin A), WGA (Wheat Germ Agglutinin), and UEA (Ulex europaeus agglutinin) with various carbohydrate specificities, as bioreceptor. The results showed that ConA and WGA have the highest binding affinity for E. coli and S. aureus respectively and hence can effectively detect them. This was confirmed by 6.8% and 7.8% decrease in peak amplitude of fast Fourier transform (FFT) spectra (at 10 ⁵ cells mL ⁻¹ concentration). A limit of detection (LOD) of about 10 ³ cells mL ⁻¹ and a linear response range of 10 ³ to 10 ⁵ cells mL ⁻¹ were observed for both ConA- E. coli and WGA- S. aureus interaction platforms that are comparable to the other reports in the literature. Dissimilar response patterns among lectins can be attributed to the different bacterial cell wall structures. Further assessments were carried out by applying the biosensor for the detection of Klebsiella aerogenes and Bacillus subtilis bacteria. The overall obtained results reinforced the conjecture that the WGA and ConA have a stronger interaction with Gram-positive and Gram-negative bacteria, respectively. Therefore, it seems that specific lectins can be suggested for bacterial Gram-typing or even serotyping. These observations were confirmed by the principal component analysis (PCA) model.
... It also allows Si integrated design for both impedance and optical sensors due to formation of PSi layer inside Si monocrystal by etching techniques [11]. It was applied for sensing of various gases [12], but biosensors based on PSi are still under development [13][14][15]. PSi was previously used for detection of viruses [16][17][18]. However, in present article its structure has been optimized for more efficient entrapping of virions by using double-etched porous silicon (DEPSi), which has pore sizes similar to virions and enhanced surface roughness desirable for binding with glycoprotein receptors [19]. ...
... However, in present article its structure has been optimized for more efficient entrapping of virions by using double-etched porous silicon (DEPSi), which has pore sizes similar to virions and enhanced surface roughness desirable for binding with glycoprotein receptors [19]. Previously DEPSi was successfully applied for optical detection of bacteria [13]. ...
We report new sensing element based on double-etched porous silicon (DEPSi) for sensitive detection of influenza viruses (H1N1). The proposed structure provided efficient penetration of virions into sensitive layer and trapping of them. Adsorption of the viruses led to significant shift of resonant frequency of DEPSi coupled with a coil, measured by impedance spectrometer. The detection limit of virions was lower than 100 TCID50. The results can be used for invention of H1N1 sensor, which provide rapid, label-free and low-cost detection of influenza.
In this work, we developed a biosensor for the indirect detection of bacteria via their lysate. The developed sensor is based on porous silicon membranes, which are known for their many attractive optical and physical properties. Unlike traditional porous silicon biosensors, the selectivity of the bioassay presented in this work does not rely on bio-probes attached to the sensor surface; the selectivity is added to the analyte itself, by the addition of lytic enzymes that target only the desired bacteria. The resulting bacterial lysate is then able to penetrate into the porous silicon membrane and affects its optical properties, while intact bacteria accumulate on top of the sensor. The porous silicon sensors, fabricated using standard microfabrication techniques, are coated with TiO2 layers using atomic layer deposition. These layers serve as passivation but also enhance the optical properties. The performance of the TiO2-coated biosensor is tested for the detection of Bacillus cereus, using the bacteriophage-encoded PlyB221 endolysin as the lytic agent. The sensitivity of the biosensor is much improved compared to previous works, reaching 103 CFU/mL, with a total assay time of 1 h 30 min. The selectivity and versatility of the detection platform are also demonstrated, as is the detection of B. cereus in a complex analyte.
Over the past decade, a variety of porous silicon (PSi)-based sensors and biosensors for targeting various microorganisms have been developed. In the previous edition of this book, we have focused on different approaches for the rapid detection of bacteria using PSi-based biosensors. Herein, we provide an up-to-date review, from 2015 onward, of various integrated approaches for detection and treatment of microorganisms, mostly bacteria, which employ PSi–based systems. We focus on recent advancements of PSi-based biosensors for bacteria monitoring and PSi-based antibacterial platforms, as alternative therapeutic routes.
Porous silicon (PSi) has been widely used as a biosensor in recent years due to its large surface area and its optical properties. Most PSi biosensors consist in close-ended porous layers, and, because of the diffusion-limited infiltration of the analyte, they lack sensitivity and speed of response. In order to overcome these shortcomings, PSi membranes (PSiMs) have been fabricated using electrochemical etching and standard microfabrication techniques. In this work, PSiMs have been used for the optical detection of Bacillus cereus lysate. Before detection, the bacteria are selectively lysed by PlyB221, an endolysin encoded by the bacteriophage Deep-Blue targeting B. cereus. The detection relies on the infiltration of bacterial lysate inside the membrane, which induces a shift of the effective optical thickness. The biosensor was able to detect a B. cereus bacterial lysate, with an initial bacteria concentration of 105 colony forming units per mL (CFU/mL), in only 1 h. This proof-of-concept also illustrates the specificity of the lysis before detection. Not only does this detection platform enable the fast detection of bacteria, but the same technique can be extended to other bacteria using selective lysis, as demonstrated by the detection of Staphylococcus epidermidis, selectively lysed by lysostaphin.
