A novel fluorescent nanosensor based on graphene quantum dots embedded within molecularly imprinted polymer (GQDs@MIP) was developed for detection and determination of methamphetamine (METH). The ...resulting GQDs@MIP nanocomposite exhibited higher methamphetamine selectivity in comparison with corresponding non-imprinted polymer (GQDs@NIP). Characterization of the GQDs@MIP nanocomposite was done by nitrogen adsorption and desorption analysis (BET method), transmission electron microscopy (TEM), photoluminescence (PL), ultraviolet-visible (UV–Vis), and Fourier transform infrared (FT-IR) spectroscopies. The fluorescence intensity of GQDs@MIP was efficiently quenched in the presence of methamphetamine template molecules while no quenching was observed in the presence of other analytes such as amphetamine, ibuprofen, codeine, and morphine. Using this method, the detection limit of 1.7 μg/L was obtained for methamphetamine determination.
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•A novel fluorescent nanosensor based on graphene quantum dots embedded within molecularly imprinted polymer was prepared.•Fluorescence intensity of the prepared nanosensor was quenched in the presence of methamphetamine.•The prepared nanosensor is selective for detection of methamphetamine.
Conventional fluorescence microscopy is limited by the optical diffraction of light, which results in a spatial resolution of about half of the light's wavelength, approximately to 250-300 nm. The ...spatial resolution restricts the utilization of microscopes for studying subcellular structures. In order to improve the resolution and to shatter the diffraction limit, two general approaches were developed: a spatially patterned excitation method and a single-molecule localization strategy. The success of super-resolution imaging relies on bright and easily accessible fluorescent probes with special properties. Carbon dots, due to their unique properties, have been used for super-resolution imaging. Considering the importance and fast development of this field, this work focuses on the recent progress and applications of fluorescent carbon dots as probes for super-resolution imaging. The properties of carbon dots for super-resolution microscopy (SRM) are analyzed and discussed. The conclusions and outlook on this topic are also presented.
Capping agent-free CdS quantum dots (CdS-QDs) were synthesized within the mesopores of MCM-41 and interlayers of montmorillonite (MMT), using a safe manner by a facile ion exchange-precipitation ...protocol. The mesopores of MCM-41 and interlayers of MMT controlled the growth of CdS-QDs. The obtained CdS-QDs@MCM-41 and CdS-QDs/MMT were characterized by X-ray diffraction (XRD) analysis, energy-dispersive X-ray (EDX), diffuse reflectance UV-Vis, and photoluminescence spectroscopies. Photodegradation of rhodamine-B (RhB) over these embedded CdS-QDs was investigated under UV-Vis light irradiation. The influences of some parameters on the photodegradation of RhB such as pH, temperature, and UV-Vis irradiation time were investigated. The results showed that the CdS-QDs/MMT and CdS-QDs@MCM-41 have high efficiencies for RhB photodegradation under UV-Vis illumination.
•One-pot simple synthesis of bright green fluorescent carbon dots.•Sensitive and selective detection of ferrous ions.•Quenching mechanism of carbon dots toward ferrous ions.
Iron is critical to ...living organisms; excess or lack of iron could lead to a series of diseases. In this work, fluorescent carbon dots were developed as an efficient probe for sensitive and selective detection of ferrous ions (Fe2+). We reported on simple and one-pot synthesis of uniform, bright, and green fluorescent carbon dots with aqueous stability in a wide pH range. The formation of green fluorescence is attributed to the doping of nitrogen into carbon materials. The as-synthesized carbon dots demonstrated wavelength-independent emission properties. Fluorescence of carbon dots was quenched efficiently, sensitively and selectively by ferrous ions over a series of other common metal ions and anions, with a detection limit of 16 µM, and a wide detection range of 0.033 -1.044 mM. Efficient quenching of carbon dots could be explained by the efficient binding of ferrous ions on carbon dots surface. Aggregation caused quenching was later proposed and verified as the quenching mechanism of carbon dots toward ferrous ions. The developed carbon dots show great promise in the development of efficient sensors and adsorbents for ferrous ions.
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•Graphene quantum dots (GQDs) were prepared and functionalized with antimorphine antibody.•Fluorescence intensity of the functionalized GQDs enhanced in the presence of morphine.•The ...functionalized GQDs is selective nanosensor for detection of morphine.
Surface functionalization of graphene quantum dots (GQDs) with antimorphine produced a new turn-on fluorescent nanosensor for morphine detection. The antimorphine-GQDs were prepared through the covalent conjugation of GQDs with antimorphine. FT-IR and X-ray photoelectron spectroscopies (XPS) confirmed the conjugation of antimorphine to GQDs. Fluorescence intensity of the antimorphine-GQDs enhanced after addition of morphine allowing its sensitive determination with detection limit of 0.06 μM. Further experiments revealed that this nanosensor has no interaction with other narcotics such as methamphetamine and codeine. Thus, it can act as inexpensive and selective nanosensor for specification of low concentrations of morphine.
A new fluorescent nanosensor based on S and N co-doped graphene quantum dots (S,N-GQDs) modified by boric acid was designed for glucose detection. First, the S,N-GQDs was prepared via one pot ...hydrothermal process utilizing citric acid and thiourea as precursors. Then, S,N-GQDs was modified by boric acid to fabricate (B)/S,N-GQDs. The excitation dependent photoluminescence spectra of (B)/S,N-GQDs confirmed the heteroatom (S,N) dopant effect on GQDs emission. FT-IR and energy dispersive X-ray (EDX) spectroscopies confirmed the modification of S,N-GQDs with boric acid. The optical and electrochemical band gaps of the obtained (B)/S,N-GQDs were found to be 2.7 and 2.5 eV, respectively. The boric acid functionalized S,N-GQDs exhibited fluorescent enhancement at 455 nm upon addition of glucose. Such fluorescence response was used for glucose quantification with a detection limit of 5.5 μM which is comparable with previous boronic acid based fluorescent sensing systems. However, compared with earlier reported expensive boronic acid based glucose sensors, this modified system is simpler, more economical, and efficient. A mechanism was proposed for fluorescence enhancement based on the reaction of cis-diol units of glucose with the boric acid groups of (B)/S,N-GQDs which creates rigid (B)/S,N-GQDs-glucose structures, restricting the non-radiative intramolecular motions and results in the fluorescent enhancement.
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•A new fluorescent nanosensor based on S and N co-doped graphene quantum dots modified by boric acid was designed.•Fluorescence intensity of the prepared nanosensor was enhanced in the presence of glucose.•Compared with other expensive sensors, this modified system is simpler, more economical, and efficient.
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•A new turn-on fluorescent nanosensor based on graphene quantum dots was prepared by thiol-ene reaction.•The prepared nanosensor exhibited fluorescence enhancement in the presence of ...L-morphine.•The present nanosensor is simple, more economical, and efficient in comparison with other expensive sensors.
Here, L- and D-cysteine-functionalized graphene quantum dots (L-/D-cys-GQDs) were designed with the aim of obtaining a selective fluorescent nanosensor to detect L-morphine. Citric acid was pyrolyzed to synthesize the GQDs, which were then functionalized with chiral L- and D-cys species using a thiol-ene click reaction between sulfur group of cysteine species and CC double bonds of GQDs. Energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopies (XPS) provides elemental analysis data which approved the presence of sulfur and nitrogen elements of L- and D-cysteine species on the surface of GQDs. Transmission electron microscopy (TEM) showed that the particle size of the modified GQDs ranges from 2 to 4.2 nm. The results of fluorescence spectroscopy showed that upon functionalization of GQDs with L-/D-cys the fluorescence intensity decreases as a result of Forster resonance energy transfer (FRET) mechanism. Interestingly, in the presence of L-morphine, the fluorescence intensity of D-cys-GQDs was selectively turned on as the FRET mechanism is ceased between the cysteine species and GQDs. Additional tests demonstrated that this nanosensor cannot interact with other drugs like methamphetamine or ibuprofen. As a result, it can serve as a cheap and precise nanosensor for identifying low quantities of L-morphine.
Highly efficient visible-light photoelectrocatalysts were developed for mild oxidation of benzyl alcohol and its derivatives to related aldehydes with air as a safe and environmental friendly ...oxidant. The photoelectrocatalysts were designed by electrostatic association of the amino acids and PMo12O403- for achieving (amino acid)3PMA followed by covalent attachment to Co3O4-QDs. The prepared Co/(ABA)3PMA and Co/(gly)3PMA nanocomposites were immobilized on charcoal using an alternate electrophoretic approach. Interestingly, the formation of nanocomposite structures remarkably enhanced the photo-generated charge separation and photoelectrocatalytic performance. Comparison of the results of photoelectrocatalytic oxidation of benzyl alcohol with that of photocatalytic and catalytic ones revealed that no reaction occurred during the catalytic tests, while the photocatalytic performance was positively affected by the utilization of a small bias (0.9 V vs. saturated calomel electrode). The Co3O4-QDs increases the visible light absorption and H3PMo12O40 with appropriate energy levels increases the charge mobility in nanocomposites structures. A plausible mechanism for the photoelectrocatalytic oxidation was suggested and illustrated using the results of scavenger tests and energy level determination.
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•Functionalization of Co3O4 quantum dots with polyoxometalates produced new nanocomposites.•The nanocomposites exhibited efficient charge separation during light absorption in visible region.•The nanocomposites showed high photoelectrocatalytic activity in the oxidation of benzyl alcohol.
A new core–shell nanocomposite was designed by functionalization of a Co3O4 quantum dots (Co3O4-QDs) core with terephthalic acid (TPA) and growth of an Fe-infinite coordination polymer (Fe-ICP) shell ...on the core surface. High-resolution transmission electron microscopy (HR-TEM) confirmed the core–shell structure of the prepared Co3O4-QDs@Fe-ICP nanocomposite. Co3O4-QDs@Fe-ICP exhibited high catalytic, visible light photocatalytic, and photoelectrocatalytic activity in degradation of rhodamine B (RhB), reactive orange 29 (RAO29), and crystal violet (CV) as compared to the individual Co3O4-QDs and Fe-ICP. The high photocatalytic, photoelectrocatalytic, and catalytic activities of Co3O4-QDs@Fe-ICP in comparison with Co3O4-QDs and Fe-ICP were attributed to the interconnection of Co3O4-QDs and Fe-ICP within the core–shell structure. Impressively, the existence of the Fe-ICP shell is critical for not only efficient charge separation and enhancing the catalytic performance but also preventing Co3O4-QDs from aggregation during the degradation process.
Surface modification of cadmium sulfide quantum dots (CdS-QDs) with anti-methamphetamine (anti-METH) antibody produced a new turn-on fluorescent nanosensor, anti-METH-CdS-QDs, for detection of ...methamphetamine. The anti-METH-CdS-QDs nanosensor was obtained readily via the covalent conjugation of mercaptoacetic acid capped CdS-QDs with anti-METH in the presence of
N
-ethyl-
N
′-(3-dimethylaminopropyl carbodiimide) (EDC) and Sulfo-
N
-hydroxysuccinimide (Sulfo-NHS) as coupling agents. The results of FT-IR and energy dispersive X-ray (EDX) spectroscopies confirmed the functionalization of CdS-QDs with anti-METH species. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses revealed the crystal phase and microstructure of CdS-QDs in the anti-METH-CdS-QDs. The obtained anti-METH-CdS-QDs exhibited fluorescence enhancement upon addition of methamphetamine molecules which allowed the highly sensitive and selective determination of methamphetamine with detection limit of 0.006 mg/L. Further studies disclosed that this nanosensor has little interaction with other drugs such as codeine and ibuprofen. Hence, it can be utilized as simple, inexpensive, and selective nanosensor for determination of methamphetamine in low concentrations.
