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TEM and AFM imaging analysis of GQDs. TEM, HRTEM and AFM images of GQD1 (a-c), GQD2 (d-f), GQD3 (g-i), respectively. Histograms in (a, d, g) signify the size distribution of GQD1, GQD2, and GQD3, respectively. Average diameter hDi is mentioned in each case. The HRTEM lattice image of each GQD sample is indicated by dotted circles in the middle column. The measured lattice spacing is indicated in each case. Inset in (b, e, h) represents the SAED pattern for the GQDs and it signifies the hexagonal structure of few-layered graphene. A line segment in AFM image and its corresponding height profile are shown at the bottom of the (c, f, i). The GQDs consist of a few (1-4) layers of graphene.
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... morphological and structural characteristics of the samples were analyzed by TEM including HRTEM, AFM and XRD analyses. In Fig. 1, the first row (a-c) corresponds to the TEM, HRTEM and AFM images of GQD1, respectively; similarly, the second row (d- f) corresponds to GQD2 and the last row (g-i) refers to that of GQD3. The size distribution of GQD1, GQD2, and GQD3 are shown in the insets of Fig. 1(a, d, g), respectively. The mean size of the GQDs grown by using ...
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... of the samples were analyzed by TEM including HRTEM, AFM and XRD analyses. In Fig. 1, the first row (a-c) corresponds to the TEM, HRTEM and AFM images of GQD1, respectively; similarly, the second row (d- f) corresponds to GQD2 and the last row (g-i) refers to that of GQD3. The size distribution of GQD1, GQD2, and GQD3 are shown in the insets of Fig. 1(a, d, g), respectively. The mean size of the GQDs grown by using DMF, DMSO and water solvents are 5.3 ± 0.1, 8.3 ± 0.1 and 5.7 ± 0.1 nm, respectively. These results sug- gest that the sizes of the GQDs are dependent to some extent on the solvents used during the GQD synthesis. Note that in case of DMF and water solvents the GQDs were ...
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... GQDs were syn- thesized without the autoclave i.e. in an open container. This is due to the higher vapor pressure of DMSO, which did not allow to per- form the reaction inside an autoclave. The higher average size of GQDs in case of DMSO may be due to the lower/atmospheric pres- sure during the reaction. The dotted circles in the middle column in Fig. 1 represents the HRTEM lattice images of the GQDs. The calcu- lated lattice spacing values are 0.29, 0.27 and 0.33 nm for GQD1, GQD2, and GQD3, respectively. The first two values corresponding to the (1120) plane and 0.33 nm confirms the (0 0 2) planes of sp 2 carbon [4]. Further, the SAED patterns for GQD1, GQD2, and GQD3 shown in the ...
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... 1 represents the HRTEM lattice images of the GQDs. The calcu- lated lattice spacing values are 0.29, 0.27 and 0.33 nm for GQD1, GQD2, and GQD3, respectively. The first two values corresponding to the (1120) plane and 0.33 nm confirms the (0 0 2) planes of sp 2 carbon [4]. Further, the SAED patterns for GQD1, GQD2, and GQD3 shown in the inset of Fig. 1(b, e, h), respectively, suggest the sp 2 arrangement of carbon atoms in GQDs. Fig. 1(c, f, i) shows the AFM images of the GQD1, GQD2, and GQD3, respectively. Each line segment in AFM images and its corresponding height profiles are shown at bottom of the AFM image. AFM height profile analysis suggests that GQD1, GQD2, and GQD3 consists ...
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... values are 0.29, 0.27 and 0.33 nm for GQD1, GQD2, and GQD3, respectively. The first two values corresponding to the (1120) plane and 0.33 nm confirms the (0 0 2) planes of sp 2 carbon [4]. Further, the SAED patterns for GQD1, GQD2, and GQD3 shown in the inset of Fig. 1(b, e, h), respectively, suggest the sp 2 arrangement of carbon atoms in GQDs. Fig. 1(c, f, i) shows the AFM images of the GQD1, GQD2, and GQD3, respectively. Each line segment in AFM images and its corresponding height profiles are shown at bottom of the AFM image. AFM height profile analysis suggests that GQD1, GQD2, and GQD3 consists of 1-3, 1-4 and 1-4 layers of graphene, respectively. These results suggest that synthesized ...
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... consists of 1-3, 1-4 and 1-4 layers of graphene, respectively. These results suggest that synthesized GQDs consist of few (1-4) layers of graphene and are good candidates for emerging applications, in particular, the bio-imaging. In addition, to support the sp 2 graphitic frame of the GQDs, we recorded the XRD pattern and the results are shown in Fig. S1 (Supporting Information). Fig. S1(a) shows the XRD pat- tern of GQD2 and GQD3 in the range 2h = 23-34°. It is evident from the figure that both the samples exhibited the (0 0 2) reflection peak, which is a signature of the hexagonal lattice structure of the graphitic material. The (0 0 2) XRD peak is a piece of strong evi- dence for ...
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... of graphene, respectively. These results suggest that synthesized GQDs consist of few (1-4) layers of graphene and are good candidates for emerging applications, in particular, the bio-imaging. In addition, to support the sp 2 graphitic frame of the GQDs, we recorded the XRD pattern and the results are shown in Fig. S1 (Supporting Information). Fig. S1(a) shows the XRD pat- tern of GQD2 and GQD3 in the range 2h = 23-34°. It is evident from the figure that both the samples exhibited the (0 0 2) reflection peak, which is a signature of the hexagonal lattice structure of the graphitic material. The (0 0 2) XRD peak is a piece of strong evi- dence for the graphitic structure. The (0 0 2) ...
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... GQD2 and GQD3 are at 2h = 26.34, 26.08° and their corresponding inter- layer distance (d) are calculated as 3.38 and 3.41 Å, respectively. The interlayer distance in the present case is slightly different from the graphite value 3.40 Å [1], which is possibly due to the strain. In addition, the weak reflection peaks at 2h $ 43° and $45° shown in Fig. S1(b) correspond to the (1 0 0) and (1 1 0) planes, which con- firms the in-plane disorder structure in GQDs [33]. The in-plane disorder includes the crystalline defects and oxygen functional groups in the basal plane and these are created/attached during the growth of the GQDs. These results are further confirmed from the micro-Raman ...
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... morphological and structural characteristics of the samples were analyzed by TEM including HRTEM, AFM and XRD analyses. In Fig. 1, the first row (a-c) corresponds to the TEM, HRTEM and AFM images of GQD1, respectively; similarly, the second row (d-f) corresponds to GQD2 and the last row (g-i) refers to that of GQD3. The size distribution of GQD1, GQD2, and GQD3 are shown in the insets of Fig. 1(a, d, g), respectively. The mean size of the GQDs grown by using DMF, ...
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... of the samples were analyzed by TEM including HRTEM, AFM and XRD analyses. In Fig. 1, the first row (a-c) corresponds to the TEM, HRTEM and AFM images of GQD1, respectively; similarly, the second row (d-f) corresponds to GQD2 and the last row (g-i) refers to that of GQD3. The size distribution of GQD1, GQD2, and GQD3 are shown in the insets of Fig. 1(a, d, g), respectively. The mean size of the GQDs grown by using DMF, DMSO and water solvents are 5.3 ± 0.1, 8.3 ± 0.1 and 5.7 ± 0.1 nm, respectively. These results suggest that the sizes of the GQDs are dependent to some extent on the solvents used ...
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... the GQDs were synthesized without the autoclave i.e. in an open container. This is due to the higher vapor pressure of DMSO, which did not allow to perform the reaction inside an autoclave. The higher average size of GQDs in case of DMSO may be due to the lower/atmospheric pressure during the reaction. The dotted circles in the middle column in Fig. 1 represents the HRTEM lattice images of the GQDs. The calculated lattice spacing values are 0.29, 0.27 and 0.33 nm for GQD1, GQD2, and GQD3, respectively. The first two values corresponding to the (1120) plane and 0.33 nm confirms the (0 0 2) planes of sp 2 carbon [4]. Further, the SAED patterns for GQD1, GQD2, and GQD3 shown in the ...
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... 1 represents the HRTEM lattice images of the GQDs. The calculated lattice spacing values are 0.29, 0.27 and 0.33 nm for GQD1, GQD2, and GQD3, respectively. The first two values corresponding to the (1120) plane and 0.33 nm confirms the (0 0 2) planes of sp 2 carbon [4]. Further, the SAED patterns for GQD1, GQD2, and GQD3 shown in the inset of Fig. 1(b, e, h), respectively, suggest the sp 2 arrangement of carbon atoms in GQDs. Fig. 1(c, f, i) shows the AFM images of the GQD1, GQD2, and GQD3, respectively. Each line segment in AFM images and its corresponding height profiles are shown at bottom of the AFM image. AFM height profile analysis suggests that GQD1, GQD2, and GQD3 consists ...
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... values are 0.29, 0.27 and 0.33 nm for GQD1, GQD2, and GQD3, respectively. The first two values corresponding to the (1120) plane and 0.33 nm confirms the (0 0 2) planes of sp 2 carbon [4]. Further, the SAED patterns for GQD1, GQD2, and GQD3 shown in the inset of Fig. 1(b, e, h), respectively, suggest the sp 2 arrangement of carbon atoms in GQDs. Fig. 1(c, f, i) shows the AFM images of the GQD1, GQD2, and GQD3, respectively. Each line segment in AFM images and its corresponding height profiles are shown at bottom of the AFM image. AFM height profile analysis suggests that GQD1, GQD2, and GQD3 consists of 1-3, 1-5 and 1-4 layers of graphene, respectively. These results suggest that synthesized ...
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... consists of 1-3, 1-5 and 1-4 layers of graphene, respectively. These results suggest that synthesized GQDs consist of few (1-4) layers of graphene and are good candidates for emerging applications, in particular, the bio-imaging. In addition, to support the sp 2 graphitic frame of the GQDs, we recorded the XRD pattern and the results are shown in Fig. S1 (Supporting Information). Fig. S1(a) shows the XRD pattern of GQD2 and GQD3 in the range 2θ = 23-34°. It is evident from the figure that both the samples exhibited the (0 0 2) reflection peak, which is a signature of the hexagonal lattice structure of the graphitic material. The (0 0 2) XRD peak is a piece of strong evidence for the ...
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... of graphene, respectively. These results suggest that synthesized GQDs consist of few (1-4) layers of graphene and are good candidates for emerging applications, in particular, the bio-imaging. In addition, to support the sp 2 graphitic frame of the GQDs, we recorded the XRD pattern and the results are shown in Fig. S1 (Supporting Information). Fig. S1(a) shows the XRD pattern of GQD2 and GQD3 in the range 2θ = 23-34°. It is evident from the figure that both the samples exhibited the (0 0 2) reflection peak, which is a signature of the hexagonal lattice structure of the graphitic material. The (0 0 2) XRD peak is a piece of strong evidence for the graphitic structure. The (0 0 2) ...
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... for GQD2 and GQD3 are at 2θ = 26.34, 26.08° and their corresponding interlayer distance (d) are calculated as 3.38 and 3.41 Å, respectively. The interlayer distance in the present case is slightly different from the graphite value 3.40 Å [1], which is possibly due to the strain. In addition, the weak reflection peaks at 2θ ∼ 43° and ∼45° shown in Fig. S1(b) correspond to the (1 0 0) and (1 1 0) planes, which confirms the in-plane disorder structure in GQDs [33]. The in-plane disorder includes the crystalline defects and oxygen functional groups in the basal plane and these are created/attached during the growth of the GQDs. These results are further confirmed from the micro-Raman ...
Citations
... In recent years, GQDs applications have attained major success in drug delivery [61][62][63], bio-imaging [64,65], magnetic hyperthermia [66][67][68], photothermal therapy [69,70], antibacterial activity [71][72][73], and environmental protection [74]. Several studies employed the density functional theory (DFT) calculations, molecular dynamics (MD) simulations, or other methods to theoretically explore the properties of GQDs in order to optimize their application in drug administration. ...
Graphene quantum dots (GQDs) possess properties like a large surface area, photostability, and biocompatibility, and they can be tailored simply over in-situ synthesis and post-synthesis. GQDs can be altered with biomolecules such as polysaccharides, proteins, DNA, and polymers to generate a hybrid QD system. GQDs and other molecules in hybrid systems serve as carriers for drug delivery of several anticancer treatments. The use of these substances to modify GQDs reduces their cytotoxicity and increases effectiveness as carriers. Because they are less toxic and more biocompatible, the GQDs are potential candidates for biological purposes such as bioimaging, delivering therapeutic agents, and theranostics. This chapter discusses recent breakthroughs in the synthesis of GQDs and their drug delivery applications. Physicochemical, optical, and biological characteristics such as size, chemical composition-dependent fluorescence, therapies, biocompatibility, and cellular toxicity are extensively investigated and summarized. It also provides vital insight into the fact that the performance of QDs as a drug delivery carrier is dependent on a combination of particle formulation factors and the level of cellular absorption.
... The possibility of using GQDs as fluorophores has been demonstrated by labeling a variety of cell types such as neuroendocrine PC12 cells, murine alveolar macrophage cells (MH-S), human cervical carcinoma HeLa cells, human hepatic cancer cells (Huh7), MCF-7 stem cells including neural stem cells, pancreas progenitor cells, and neurosphere cells, some of which have been discussed below. 7,8,15,18 Rajender et al. 115 synthesized edge-controlled and highly fluorescent few-layer GQDs-1 and GQDs-2 using solvents of DMSO and DMF, respectively, using the GO precursor. These GQDs containing a high density of armchair edges, oxygenrich functional groups, or surface edge defects and exhibited high PL and QY up to ∼32% and are highly promising for bioimaging applications. ...
Graphene quantum dots (GQDs) are carbon-based, zero-dimensional nanomaterials and unique due to their astonishing optical, electronic, chemical, and biological properties. Chemical, photochemical, and biochemical properties of GQDs are intensely being explored for bioimaging, biosensing, and drug delivery. The synthesis of GQDs by top-down and bottom-up approaches, their chemical functionalization, bandgap engineering, and biomedical applications are reviewed here. Current challenges and future perspectives of GQDs are also presented.
... They showed well-designed PL emission of the GQDs in distinct liquid solutions, i.e., solvents, stating the strong PL emission of the GQDs due to various edge locations and functional groups linked to the GQDs. 128 GQDs have a single-layer carbon core with chemical groups on the surface or edge. It has oxygen-based functional groups on the basal plane or at the edges. ...
Graphene quantum dots (GQDs) are carbonaceous nanodots that are natural crystalline semiconductors and range from 1 to 20 nm. The broad range of applications for GQDs is based on their unique physical and chemical properties. Compared to inorganic quantum dots, GQDs possess numerous advantages, including formidable biocompatibility, low intrinsic toxicity, excellent dispensability, hydrophilicity, and surface grating, thus making them promising materials for nanophotonic applications. Owing to their unique photonic compliant
properties, such as superb solubility, robust chemical inertness, large specific surface area, superabundant surface conjugation sites, superior photostability, resistance to photobleaching,
and nonblinking, GQDs have emerged as a novel class of probes for the detection of biomolecules and study of their molecular interactions. Here, we present a brief overview of GQDs, their advantages over quantum dots (QDs), various synthesis procedures, and different surface conjugation chemistries for detecting cell-free circulating nucleic acids (CNAs). With the prominent rise of liquid biopsy-based approaches for real-time detection of CNAs, GQDs-based strategies might be a step toward early diagnosis, prognosis, treatment monitoring, and outcome prediction of various non-communicable diseases, including cancers.
... QD are nanomaterials characterized by a set of unique optical properties including superior signal brightness, high sensitivity, resistance to photobleaching, and tunable wavelength [31][32][33]. Surface functionalization of QD via covalent or noncovalent coupling using specific ligands and biomolecules for molecular imaging, diagnostic immunoassays, and targeted drug delivery applications has been the focus of many studies [34][35][36][37][38][39]. The use of QD in QD-based immunohistochemistry (QD-IHC) for the determination of expression levels of biomarkers in tumor tissues has shown their significant efficacy as imaging probes where they gave rise to levels of detection that are more sensitive and precise than conventional IHC with an increased positive detection rate [36,[40][41][42]. ...
Colorectal cancer (CRC) accounts for approximately 10% of all new cancer cases worldwide with significant morbidity and mortality. The current imaging techniques are lacking diagnostic precision while traditional chemotherapeutic strategies are limited by their adverse side effects and poor response in advanced stages. Targeted nanoparticles (NPs) can specifically bind to surface antigens on cancer cells and provide effective delivery of diagnostic and chemotherapeutic agent. Placenta-specific protein 1 (PLAC-1) is overexpressed in CRC and can be used as a target for detection and treatment of the disease. The aim of this work was to develop a targeted nanotheranostic agent for early diagnosis and inhibition of the malignant progression and metastasis of CRC. Graphene oxide quantum dots (QD) were covalently labeled with a peptide (GILGFVFTL) having high affinity to PLAC-1. The covalent coupling between the QD and the peptide was confirmed using a series of physicochemical and morphological characterization techniques. Confocal microscopy was used to evaluate the uptake of QD and QD-P in HCT-29, HT-116 and LS-180 CRC cell lines. Selective targeting of antigen PLAC-1 overexpressed on HT-29 and HCT-116 cells was measured by immunofluorescence. Cell proliferation, cell invasion and extent of PLAC-1 expression in CRC cells after treatment with QD and QD-P were determined. The prepared QD-P showed a significant increase in targeting and specific uptake in cells expressing the antigen PLAC-1 compared to non-functionalized QD. Treatment with QD-P also increased the cell cytotoxicity, reduced the invasiveness of HT-29 and HCT-116 cells by 38% and 62%, respectively, and downregulated the expression of PLAC-1 by 53% and 33%, respectively. These results highlight the potential use of QD-P as a theranostic agent for the detection and treatment of CRC cells expressing the antigen PLAC-1.
... GQDs photoluminescence can also be used for cancer cell confocal imaging. In a study by Rajender et al., 69 edge-controlled, highly fluorescent, thin layer GQDs were synthetized through a solvent dependent procedure. As mentioned before, the synthesis procedure and the solvents ingredients directly influence GQDs emissions strength by affecting its size, edge sites, and the formation of different functional groups on the surface of GQD. ...
Today, nanobiotechnology is a pioneering technology in biomedicine. Every day, new nanomaterials are synthesized with elevated physiochemical properties for better diagnosis and treatment of diseases. One advancing class of materials is the Graphene family. Among different kinds of graphene derivatives, graphene quantum dots (GQDs) show fantastic optical, electrical, and electrochemical features originating from their unique quantum confinement effect. Due to the distinct properties of GQD, including large surface-to-volume ratio, low cytotoxicity, and easy functionalization, this nanomaterial has gone popular in biomedical field. Herein, a short overview of different strategies developed for GQD synthesis and functionalization is discussed. In the following, the most recent progress of GQD based nanomaterials in different biomedical fields, including bio-imaging, drug/gene delivery, antimicrobial, tissue engineering, and biosensors, are reviewed.
... The growing interest in the development of novel materials with better mechanical, electrical, and optical properties has given rise to a rich research field of materials with low dimensionality. In this aspect, research involving zero-dimensional materials, such as carbon quantum dots (CQDs), graphene oxide quantum dots (GOQDs), and graphene quantum dots (GQDs), has brought very interesting results for applications in photonics [1,2], biophotonics [3][4][5], energy generation [6][7][8], photocatalysis [9,10], sensors [11,12], and optoelectronic devices [7,13,14], among others. ...
... The UV-VIS absorption spectra of the GQDs produced in this work are shown in Figure 7. The absorption spectrum of the undoped GQDs showed an absorption peak centered at 275 nm, which refers to the π → π* transition related to the presence of sp 2 hybridized carbons [4,55]. An absorption peak around 330 nm was also observed, which is associated with the n → π* transition, which occurs due to the presence of oxygen heteroatoms in the structure of the quantum dots [4,55]. ...
... The absorption spectrum of the undoped GQDs showed an absorption peak centered at 275 nm, which refers to the π → π* transition related to the presence of sp 2 hybridized carbons [4,55]. An absorption peak around 330 nm was also observed, which is associated with the n → π* transition, which occurs due to the presence of oxygen heteroatoms in the structure of the quantum dots [4,55]. The absorption spectrum of N-GQDs was wider and redshifted in relation to the absorption spectrum of undoped GQDs. ...
The synthesis of carbon-based quantum dots has been widely explored in the literature in recent years. However, despite the fact that synthesis processes to obtain highly efficient carbon quantum dots (CQDs) and graphene quantum dots (GQDs) with redshifted photoluminescence (PL) have been improved, few works have exploited sucrose in the synthesis of GQDs with high PL efficiency. In this work, sucrose, which is a widely available non-toxic saccharide, was used as a precursor of GQDs. Initially, sucrose was carbonized in sulfuric acid, and thereafter, the material obtained was treated in dimethyl sulfoxide (DMSO). Nitrogen doping was also performed in this work through an additional step involving the treatment of carbonized sucrose in nitric acid reflux. Nitrogen-doped GQDs (N-GQDs) showed tunable PL dependent on the excitation wavelength. It was also verified that the intensity of the emission in the red region was much higher in the N-GQDs in comparison with that in undoped GQDs. X-Ray Diffraction, Raman, FTIR, TEM, and AFM analyzes were also performed to obtain greater structural details of the obtained GQDs.
... The photoluminescent graphene quantum dots (GQD) and carbon nanodots (CND) are considered as the next-generation nanomaterials (Zhu et al. 2015;Khoshnevisan et al. 2019;Bak et al. 2016;Shen et al. 2011;Gao et al. 2017;Qu et al. 2014;Deng et al. 2015;Li et al. 2015;Banbela et al. 2022) owing to their photo tuning ability (Gao et al. 2017;Qu et al. 2014Qu et al. , 2015Deng et al. 2015;Li et al. 2015Li et al. , 2012Banbela et al. 2022;Wang et al. 2020;Fu et al. 2019) dominant photobleaching resistivity (Bacon et al. 2014;Lin et al. 2014), excellent biocompatibility (Lin et al. 2014;Song et al. 2017), low cost (Shen et al. 2011;Saisree et al. 2021), and the abundance of raw materials in nature. Hence, they are anticipated as potential candidates for biosensors (Karimzadeh et al. 2018;Si and Song 2018), bio-imaging devices (Song et al. 2017;Shah and Weissleder 2005) theranostic agent (Rajender et al. 2020), photocatalysts (Qu et al. 2013), photovoltaic devices (Qu et al. 2013), fuel cells (Guo et al. 2010), and light-emitting diodes (Luo et al. 2016;Wang et al. 2017). The deep exploration into the mechanism of the photoluminescent characteristics and the electronic properties is still a challenging area of research. ...
... This can result in lower effective conjugation and more surface carboxylate functionalities in N-GQD/ H 2 O compared to N-GQD/DMF. In N-GQD/DMF, DMF, a polar aprotic solvent with an amide functionality, facilitates elimination reactions and enhances the effective conjugation than the other two (Rajender et al. 2020). The enhanced conjugation and the effective N doping from PANI and DMF result in a higher red-shifted emission in N-GQD/DMF than N-GQD/NMP and N-GQD/H 2 O. ...
In the present work, nitrogen-doped graphene quantum dots (N-GQD) with tailored colour emissions were synthesized through a solvothermal route using different solvents: N-Methyl-2-pyrrolidone (NMP), water (H2O) and dimethylformamide (DMF), and polyaniline (PANI) as the precursor material. The N-GQD exhibited a noticeable red-shifted emission from blue to yellow with varying solvents from NMP, H2O, and DMF. The N-GQD/NMP is blue emissive, whereas N-GQD/H2O and N-GQD/DMF are green and yellow emissive. The N-GQD/DMF and N-GQD/NMP exhibited a naked eye detectable reversible colour tweaking property with varying pH. The N-GQD/NMP changed from light green to violet; the N-GQD/DMF changed from pink to light brown when the pH was adjusted from 1 to 11.
... The amplitude of the PVA peak at the (1 0 1) plane decreases after adding ZnO. It is related to a decrease in diffraction on the (1 0 1) plane [26]. ...
A poly (vinyl alcohol) matrix incorporating ZnO-GQD composite structures was used in a photodiode configuration as a novel kind of nanocomposite. The crystal structure and morphology of the composites were studied in depth. The electro-optical properties of the photodiodes fabricated using the composites were interpreted based on the intrinsic characteristics of the composites. The ZnO/PVA-based photodiode offers self-power with approximately high specific detectivity of 4.6×10¹⁰ Jones at zero bias. However, graphene quantum dots provided numerous advantages, particularly improving the response speed of the photodiode ZnO-GQDs/PVA dispossessed the ability due to introducing GQDs. A high-speed response (0.06 s, at least three times faster than ZnO/PVA photodiode) was recorded for ZnO-GQDs/PVA.
... Surface chemistry of GQDs-the presence of oxygenated functional groups and heteroatom doping also act as a key factor to obtain desired optical properties. Attachment of oxygenated functional groups showed the expanded absorption spectra (nearly above 300 nm, higher than generally observed with non-functionalized GQDs) [58]. As per Feng and co-worker's experiment, the absorption spectra of GQDs functionalized with oxygenated groups showed a red shift of absorption maxima (λ max ) from pristine GQDs owing to irregularly distributed hybridized frontier orbitals in functionalized GQDs [59]. ...
The rising demand for early-stage diagnosis of diseases such as cancer, diabetes, neurodegenerative can be met with the development of materials offering high sensitivity and specificity. Graphene quantum dots (GQDs) have been investigated extensively for theranostic applications owing to their superior photostability and high aqueous dispersibility. These are attractive for a range of biomedical applications as their physicochemical and optoelectronic properties can be tuned precisely. However, many aspects of these properties remain to be explored. In the present review, we have discussed the effect of synthetic parameters upon their physicochemical characteristics relevant to bioimaging. We have highlighted the effect of particle properties upon sensing of biological molecules through ‘turn-on’ and ‘turn-off’ fluorescence, and generation of electrochemical signals. After describing the effect of surface chemistry and solution pH on optical properties, an inclusive view on application of GQDs in drug delivery and radiation therapy has been given. Finally, a brief overview on their application in gene therapy has also been included.
... It thus follows that PL can be controlled intrinsically by changing the lateral size of GQDs and inducing edge effects [52,[54][55][56]. For example, GQDs containing high density of armchair edges and oxygen defects (epoxy and carboxylic acid groups) exhibit high PL quantum yield in comparison to those carrying zig-zag edges [57]. Surface functional groups and abundant edge sites allow the attachment of multiple copies of targeting moieties [16] useful for focussed bioimaging of a selective target. ...
... Some studies suggest that edge sites and functional groups in GQDs can be tuned by changing the reaction medium [57,81]. For instance, quantum dots synthesized in dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and water, displayed solvent-dependent PL spectra. ...
... Green emission bands at 490 nm (P3) and 530 nm (P4) originated from oxygen defects. In comparison to DMF, high concentration of zigzag edge sites were recorded in water [57]. ...
Graphene quantum dots (GQDs), zero-dimensional carbon-based nanomaterials, have attracted immense interest for theranostic applications. These applications of GQDs stem from chemical inertness, ultra-small size, and high aqueous dispersibility which probably enable their effective clearance without inflicting toxicity to the host. Relative to heavy metal-based quantum dots and organic fluorophores, GQDs display tunable bandgap and optoelectronic properties. Considerable efforts have been made to modulate their photoluminescence through doping of heteroatoms and controlling the size and edge profile. Subsequent changes in π-conjugation improve the luminescence stability, signal-to-noise ratio, and imaging depth unachievable with organic dyes. This review covers the synthesis and structural aspects of GQDs in context to their application in cancer diagnosis. After discussing the effect of chemistry (surface functionalization and doping) on optical properties, we present an inclusive view on the sensing of cancer-related biomarkers with GQDs.
