Multi-Enzyme Activity of MIL-101 (Fe)-Derived Cascade Nano-Enzymes for Antitumor and Antimicrobial Therapy.

The clinical application of oncology therapy is hampered by high glutathione concentrations, hypoxia, and inefficient activation of cell death mechanisms in cancer cells. In this study, Fe and Mo bimetallic sulfide nanomaterial (FeS2@MoS2) based on metal-organic framework structure is rationally prepared with peroxidase (POD)-, catalase (CAT)-, superoxide dismutase (SOD)-like activities and glutathione depletion ability, which can confer versatility for treating tumors and mending wounds. In the lesion area, FeS2@MoS2 with SOD-like activity can facilitate the transformation of superoxide anions (O2 -) to hydrogen peroxide (H2O2), and then the resulting H2O2 serves as a substrate for the Fenton reaction with FMS to produce highly toxic hydroxyl radicals (∙OH). Simultaneously, FeS2@MoS2 has an ability to deplete glutathione (GSH) and catalyze the decomposition of nicotinamide adenine dinucleotide phosphate (NADPH) to curb the regeneration of GSH from the source. Thus it can realize effective tumor elimination through synergistic apoptosis-ferroptosis strategy. Based on the alteration of the H2O2 system, free radical production, glutathione depletion and the alleviation of hypoxia in the tumor microenvironment, FeS2@MoS2 NPS can not only significantly inhibit tumors in vivo and in vitro, but also inhibit multidrug-resistant bacteria and hasten wound healing. It may open the door to the development of cascade nanoplatforms for effective tumor treatment and overcoming wound infection.

Hollow CoZnSe@CN nanocage with enzymatic activity for determination of tetracycline using smartphone platforms and virtual reality revealing.

Antibiotic residues in the environment pose a serious threat to ecosystems and human health. Therefore, it is important to develop sensitive and rapid in situ detection methods. In this work, the designed nanozymes, with excellent four enzyme activities, were proved to be constituted of unique hollow nanocage structures (CoZnSe@CN HCs). Based on the peroxidase-like enzymes, a portable colorimetric sensor was constructed for the on-site determination of tetracycline (TC) in real samples. The linear range of TC detection was 0.1-100 µM, and the detection limit was 0.02 µM. At the same time, colorimetric detection and smartphones have also been combined for on-site colorimetric detection of TC. In-depth exploration of the detection mechanism showed that TC could be bound with the material, inhibiting the production of oxidized 3,3',5,5'-tetramethylbenzidine. The sensor was also used for the detection of TC in environmental soil and water samples. This study can provide an intelligent detection method for environmental monitoring.

Electrocatalytic, Kinetic, and Mechanism Insights into the Oxygen-Reduction Catalyzed Based on the Biomass-Derived FeOx @N-Doped Porous Carbon Composites.

A valid strategy for amplifying the oxygen reduction reaction (ORR) efficiency of non-noble electrocatalyst in both alkaline and acid electrolytes by decorated with a layer of biomass derivative nitrogen-doped carbon (NPC) is proposed. Herein, a top-down strategy for the generally fabricating NPC matrix decorated with trace of metal oxides nanoparticles (FeOx NPs) by a dual-template assisted high-temperature pyrolysis process is reported. A high-activity FeOx /FeNC (namely Hemin/NPC-900) ORR electrocatalyst is prepared via simply carbonizing the admixture of Mg5 (OH)2 (CO3 )4 and NaCl as dual-templates, melamine and acorn shells as nitrogen and carbon source, hemin as a natural iron and nitrogen source, respectively. Owing to its unique 3D porous construction, large BET areas (819.1 m2 ∙g-1 ), and evenly dispersed active sites (FeNx , CN, and FeO parts), the optimized Hemin/NPC-900 catalyst displays comparable ORR catalytic activities, remarkable survivability to methanol, and preferable long-term stability in both alkali and acid electrolyte compared with benchmark Pt/C. More importantly, density function theory computations certify that the interaction between Fe3 O4 nanoparticles and arm-GN (graphitic N at armchair edge) active sites can effectually promote ORR electrocatalytic performance by a lower overpotential of 0.81 eV. Accordingly, the research provides some insight into design of low-cost non-precious metal ORR catalysts in theory and practice.

Portable smartphone device-based multi-signal sensing system for on-site and visual determination of alkaline phosphatase in human serum.

To provide the basis for clinical diagnosis in an emergency case, a portable smartphone device-based multi-signal sensing system for on-site determination of alkaline phosphatase (ALP) is introduced. In this system, cobalt hydroxide (CoOOH) nanoflakes can oxidize O-phenylenediamine (OPD) to produce 2,3-diaminophenazine (OxOPD), resulting in a strong fluorescence at 565 nm and an absorbance at 420 nm, respectively. The ascorbic acid 2-phosphate (AAP) can be hydrolyzed by alkaline phosphatase (ALP) to yield ascorbic acid (AA). Then, AA reduces the CoOOH nanoflakes to produce Co2+, and AA is oxidized to form dehydroascorbic acid (DHAA), thereby inhibiting the formation of OxOPD. The reaction product DHAA further combines with OPD to yield 3-(1,2-dihydroxyethyl)furo[3,4-b]quinoxalin-1(3H)-one (DFQ) accompanied by a strong fluorescence at 430 nm. Based on this, the fluorometric assay for ALP has a wide linear range from 0.8 to 190 U/L with a low detection limit of 0.16 U/L, and the colorimetric assay from 3 to 130 U/L with a detection limit of 1.94 U/L. Moreover, a portable smartphone sensing platform integrated with fluorescent and colorimetric signals was established for rapid determination of ALP without spectrometers. Recoveries of 97-104% for spiked samples and relative standard deviations (RSD) of less than 2% (n = 3) confirmed the feasibility of the developed platform in complicated samples, opening up new horizons for on-site evaluation in the biomedical field.

Ratiometric fluorescence assay for L-Cysteine based on Fe-doped carbon dot nanozymes.

In this work, a ratiometric fluorescence method based on nanozyme was fabricated to determine L-Cysteine. Taking silkworm feces as a carbon source, together with Fe3+, Fe-doped carbon dots (Fe-CDs) were synthesized through a hydrothermal method. Fe-CDs were able to oxidize the enzyme substrate o-phenylenediamine (OPD) to produce oxidized OPD (Ox-OPD) when H2O2 coexisted with them. Based on the fluorescence property of Fe-CDs and Ox-OPD, a dual-emission system was built. Since L-Cysteine contains reductive thiols that can inhibit the production of Ox-OPD, the addition of L-Cysteine caused a decrease in the fluorescence intensity of Ox-OPD. The results showed that the ratio of fluorescence intensities at 450 and 560 nm (I450/I560) varied linearly with the concentration of L-Cysteine in the range of 0.25-90 µM and the limit of detection is as low as 0.047 µM. Furthermore, using this ratiometric fluorescence system to determine L-Cysteine in serum and tap-water samples, average recoveries were evaluated to reach 98.75%-103.27% with the relative standard deviation of no more than 4.5%. Based on the fluorescence property and nanozyme-like activity, this work provides an inspiration to open a new horizon in using natural carbon source to synthesize CDs and for the application of CDs as a nanozyme.

Nitrogen-doped carbon dots from rhizobium as fluorescence probes for chlortetracycline hydrochloride.

Fluorescent nitrogen-doped carbon dots (CDs) were prepared via hydrothermal method at 190 °C for 10 h using rhizobium from soy as the carbon and nitrogen source. Their optical properties, structure, morphology, and functional groups were characterized in detail and the results showed that they possess unique excitation-dependent fluorescence behavior, with average diameter 4.5 ± 2.0 nm and good water dispersibility. Due to the overlap of the UV-vis absorbance of chlortetracycline hydrochloride (CCH) and the fluorescence excitation band of CDs, the fluorescence of the prepared CDs can be quenched by CCH selectively and sensitively. The changes of the fluorescence intensity of CDs have a good linear relationship with the concentration of CCH in a wide concentration range of 5-100 µM, with a detection limit of 0.254 µM. This present method has been successfully applied to determine the CCH in water with recovery ranging from 96.0% to 100.7%.

A dual-readout nanosensor based on biomass-based C-dots and chitosan@AuNPs with hyaluronic acid for determination of hyaluronidase.

A dual-signal strategy is proposed based on fluorescent biomass-based carbon dots (BC-dots) and chitosan stabilized AuNPs (CS@AuNPs) to determine hyaluronidase (HAase). BC-dots can induce aggregation of CS@AuNPs nanoparticles with a colour change from red to blue. Positively charged CS@AuNPs interacted with the negatively charged hyaluronic acid (HA) through electrostatic adsorption, and CS@AuNPs maintained stability due to the semirigid coil conformation of HA. However, in the presence of HAase, due to enzymatic hydrolysis of HA by HAase, the CS@AuNPs agglomerated. Based on the change of fluorescence and colour, quantitative analysis of HAase was achieved. Linear ranges for the fluorometric and colorimetric determinations were 2.0-70 U mL-1 and 8-60 U mL-1 , respectively, with a detection limit of 0.27 U mL-1 . This dual-signal sensing system possesses high potential for determination of HAase in biological matrices.

Colorimetric detection of gallic acid based on the enhanced oxidase-like activity of floral-like magnetic Fe3 O4 @MnO2.

In this study, a colorimetric method was developed for rapid and sensitive determination of gallic acid (GA) by using floral-like magnetic Fe3 O4 @MnO2 composite material with enhanced oxidase-like activity. Fe3 O4 @MnO2 composite material is able to oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to a blue product (oxTMB) with apparent color change and absorbance at 652 nm. GA can reduce the oxTMB yielding a fading blue color. Based on these results, a technique is proposed to detect GA quantitatively and qualitatively with UV-vis spectroscopy and bare eyes. A low detection limit of 0.105 µM and a detection range of 0.01 to 15 µM were obtained with UV-vis spectroscopy. This methodology possesses high potential for application in determination of GA.

A ratiometric fluorometric ciprofloxacin assay based on the use of riboflavin and carbon dots.

Carbon dots (CDs) were hydrothermally synthesized from selenious yeast. They were further coupled with riboflavin to form a dually emitting probe for ciprofloxacin (CIP). Under 370 nm excitation, the probe displays dual (blue and green) emissions with peaks at 443 and 510 nm. When CIP is added, the blue fluorescence of the CDs is enhanced while the green fluorescence remains unaffected. The ratio of the relative fluorescence intensities at 443 and 510 nm increases linearly in the 0.5-200 µM CIP concentration range. The fluorescent probe is selective and has a 0.13 µM detection limit. Satisfactory recoveries (97.9-101.1%) were received when the probe was used to quantify CIP in spiked water and human serum samples. Graphical abstractBlue-emissive carbon dots were prepared from selenious yeast via a hydrothermal method, and then coupled with riboflavin as a ratiometric fluorometric probe for ciprofloxacin determination.

A carbon dot-based ratiometric fluorometric and colorimetric method for determination of ascorbic acid and of the activity of ascorbic acid oxidase.

A dual-mode method was developed for the determination of ascorbic acid (AA) and of ascorbic acid oxidase (AA-Ox) activity. It combines the advantages of ratiometric fluorometry and colorimetry. The assay is based on the oxidation of o-phenylenediamine (OPDA) by permanganate (KMnO4). A yellow substance (referred to as oxOPDA) with an absorption peak at 425 nm is rapidly produced in the presence of the oxidant. oxOPDA reduces the blue fluorescence of carbon dots (C-dots) peaking at 450 nm (upon 380-nm excitation), and a new emission peak is found at 565 nm. If AA is pesent, it consumes a certain fraction of KMnO4, so that less OPDA will be oxidized. This is accompanied by a decrease in the intensity of the fluorescence at 565 nm and an increase in the intensity at 450 nm. In parallel, the color of the solution changes from yellow to colorless. The determination of the activity of ascorbic acid oxidase (AA-Ox) is performed as follows: AA is oxidized by AA-Ox. This causes the fluorescence and colors to change in the opposite directions compared with AA detection. The ratio of fluorescences (I565/I450) becomes larger if the color the solution turns from colorless to yellow. Thus, the fluorescence intensity ratio (I565/I450) and colorimetric "bare-eye" readout can be used for determination of both the concentration of AA and the activity of AA-Ox. The fluorometric assay for AA has a linear range that extends from 0.6 to 40 µM, and the colorimetric assay from 0.2 to 70 µM. The respective data for AA-Ox activity are 0.04 ~ 5 mU·mL-1 and 0.04 ~ 8 mU·mL-1, respectively. The limits of detection for AA are 9 and 40 nM, and the LODs for AA-Ox activity are 0.017 and 0.012 mU·mL-1. Graphical abstract Schematic presentation of the assay. Permanganate (KMnO4) rapidly oxidizes ortho-phenylenediamine oxide to form a product (oxOPDA) having a yellow fluorescence peaking at 565 nm. The yellow color of oxOPDA can be detected visually. It also reduces the intensity of the blue fluorescence of carbon dots (C-dots) peaking at 450 nm. Ascorbic acid (AA) can consume permanganate, and this results less oxidation of OPDA. Ascorbic acid oxidase (AA-Ox) catalyzes the oxidization of AA by oxygen, and this - in turn - causes the changes in absorbance and fluorescence to change in the opposite directions.

Ultrathin films of a metal-organic framework prepared from 2-methylimidazole, manganese(II) and cobalt(II) with strong oxidase-mimicking activity for colorimetric determination of glutathione and glutathione reductase activity.

Nanosheets (NSs; type ZIF-67) of a metal organic framework (MOF) that was prepared from 2-methylimidazole, manganese(II) and cobalt(II) were obtained by an ultrasonic hydrothermal method. Their Mn(II) doping reached as much as 11.3%. The NSs inherit high porosity, a large specific surface, and a large number of active sites. They display superior oxidase-mimicking activity and can catalyze the oxidation of tetramethylbenzidine (TMB) by molecular oxygen to form blue oxTMB. Glutathione (GSH) can reduce oxTMB, so that less blue oxTMB will be present. A simple and rapid method was established for the colorimetric determination of GSH and of the activity of GSH reductase (GR), best at a wavelength of 652 nm. The response to GSH drops linearly in the 0.1-25 µM concentration range. The activity of GR can be quantified in the 0.1 - 3 mU⋅mL-1 activity range. The respective detection limits are 0.07 µM and 0.18 mU⋅mL-1. Graphical abstract Schematic presentation of colorimetric detection of glutathione and glutathione reductase activity by the oxidase-mimicking activity of Mn-Co nanosheets in a metal organic framework.

Molecularly imprinted polydopamine modified with nickel nanoparticles wrapped with carbon: fabrication, characterization and electrochemical detection of uric acid.

An electrochemical sensor is described for determination of uric acid (UA). Carbon-enwrapped nickel nanoparticles (Ni@BC) were coated with polydopamine (PDA) that was molecularly imprinted with UA. The biomass carbon (BC) was synthesized by one-step solid-state pyrolysis from leaves of Firmiana platanifolia. The imprinted polymer was obtained by electrodeposition of DA as the monomer. The amount of monomer, the scan cycles, pH value and adsorption time were optimized. Furthermore, the selectivity of the MIP for UA on a glassy carbon electrode (GCE) was evaluated by selectivity tests. The differential pulse voltammetric responses to UA with and without interferents were consistent. The modified GCE has a linear response in the 0.01-30 µM UA concentration range, and the limit of detection is 8 nM. The MIP electrode was applied to the analysis of UA in urine for which the initial concentrations were determined by the phosphotungstic acid kit. Recoveries ranged from 91.3 to 113.4%, with relative standard deviations between 1.3 and 9.7% (n = 3). Graphical abstract Schematic presentation of electrochemical detection of uric acid by molecularly imprinted polydopamine modified with nickel nanoparticles wrapped with carbon (Ni@BC-MIP).

A fluorometric and colorimetric method for determination of trypsin by exploiting the gold nanocluster-induced aggregation of hemoglobin-coated gold nanoparticles.

A dual-signal assay is described for the determination of trypsin based on the use of gold nanoparticles (AuNPs) that aggregate in the presence of gold nanoclusters (AuNCs) due to electrostatic interaction. This is accompanied by a color change from red to blue. However, if hemoglobin (Hb) is present in the solution, it will attach to the surface of AuNPs, thus preventing aggregation. The Hb-coated AuNPs quench the fluorescence of AuNCs. Trypsin can hydrolyze Hb and destroy the protective coating of Hb on the AuNPs. As a result, AuNP aggregation will occur after the addition of AuNCs, and the blue fluorescence of the AuNCs with 365 nm excitation and 455 nm maximum emission peak is recovered. Thus, trypsin can be determined by measurement of fluorescence emission intensity. Additionally, trypsin can be determined by the maximum absorption peak wavelength between 530 nm and 610 nm. Fluorescence increases linearly in the 10-2500 ng⋅mL-1 concentration range, and absorbance in the 20-2000 ng·mL-1 concentration range. The limits of detection are 4.6 ng·mL-1 (fluorometry) and 8.4 ng·mL-1 (colorimetry), respectively. The assay is sensitive and selective, and can be applied to the determination of trypsin in serum. Graphical abstract Schematic presentation of a fluorometric and colorimetric method for determination of trypsin. The presence of hemoglobin (Hb) protects AuNPs from agglomeration after adding AuNCs and the fluorescence of AuNCs is quenched. With trypsin present, trypsin destroys the coating of AuNPs by Hb. AuNPs aggregate again and the fluorescence recovers after the addition of AuNCs.

Nitrogen-doped carbon frameworks decorated with palladium nanoparticles for simultaneous electrochemical voltammetric determination of uric acid and dopamine in the presence of ascorbic acid.

A glassy carbon electrode (GCE) was modified with nitrogen-enriched carbon frameworks decorated with palladium nanoparticles (Pd@NCF/GCEs). The modified GCE is shown to be a viable tool for determination of uric acid (UA) and dopamine (DA) in the presence of ascorbic acid (AA). The Pd@NCF was fabricated though one-step pyrolysis and characterized by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy and nitrogen-adsorption/desorption analysis. The Pd@NCF/GCE was characterized by differential pulse voltammetry (DPV). Both UA and DA have pronounced oxidation peaks (at 360 mV for UA and 180 mV for DA, all vs. Ag/AgCl) in the presence of AA. Response is linear in the 0.5-100 µM UA concentration range and in the 0.5-230 µM DA concentration range. The detection limits are 76 and 107 nM, respectively (at S/N = 3). This electrode is stable, reproducible and highly selective. It was used for UA and DA determination in spiked serum samples. Graphical abstractSchematic representation of nitrogen-enriched carbon frameworks decorated with palladium nanoparticles co-modified glassy carbon electrode for simultaneous determination of dopamine and uric acid in the presence of ascorbic acid.

Preparation of porous uranium oxide hollow nanospheres with peroxidase mimicking activity: application to the colorimetric determination of tin(II).

Porous uranium oxide hollow sphere nanoparticles were synthesized in ionic liquids under hydrothermal conditions. Various precipitating agents and ionic liquids were investigated to determine their respective impact on the resultant uranium oxide morphologies. Using hydrazine hydrate as precipitating agent and N-butyl pyridinium bromide as templating agent, a porous-hollow structure was created with a surface area of 1958 m2.g-1 and an average pore diameter of 30 nm. The nanoparticles revealed high peroxidase-mimicking activity. This was evaluated by using the peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) that is catalytically oxidized by H2O2 to give oxidized TMB (oxTMB) which is blue (with an absorption peak at 652 nm). The material was used as a nanozyme for colorimetric detection of Sn2+. Meanwhile, it is found that BSA strongly improves the catalytic activity of the nanozyme, while Sn(II) inhibits its activity. Thus, a colorimetric method for Sn2+ detection was designed. The method works in the 0.5-100 µM Sn(II) concentration range and has a lower detection limit of 0.36 µM (at S/N = 3). Graphical abstract The catalytic activity of porous-hollow nano-UO2 toward the oxidation of 3,3',5,5'-tetramethylbenzidine by H2O2 is remarkably improved in the presence of bovine serum albumin, while tin(II) inhibits its activity. This finding has been applied to design a method for colorimetric quantification of tin(II) in water samples.

Preparation of SiO2-MnFe2O4 Composites via One-Pot Hydrothermal Synthesis Method and Microwave Absorption Investigation in S-Band.

MnFe2O4 NPs are successfully decorated on the surface of SiO2 sheets to form the SiO2-MnFe2O4 composite via one-pot hydrothermal synthesis method. The phase identification, morphology, crystal structure, distribution of elements, and microwave absorbing properties in S-band (1.55~3.4 GHz) of the as-prepared composite were investigated by XRD, SEM, TEM, and Vector Network Analyzer (VNA) respectively. Compared with the pure MnFe2O4 NPs, the as-prepared SiO2-MnFe2O4 composite exhibits enhanced microwave absorption performance in this frequency band due to the strong eddy current loss, better impedance matching, excellent attenuation characteristic, and multiple Debye relaxation processes. The maximum reflection loss of -14.87 dB at 2.25 GHz with a broader -10 dB bandwidth over the frequency range of 1.67~2.9 GHz (1.23 GHz) can be obtained at the thickness of 4 mm. Most importantly, the preparation method used here is relatively simple, hence such composite can be served as a potential candidate for effective microwave absorption in S-band.

Colorimetric determination of glutathione in human serum and cell lines by exploiting the peroxidase-like activity of CuS-polydopamine-Au composite.

In this study, we developed a simple colorimetric approach to detect glutathione (GSH). The proposed approach is based on the ability of CuS-PDA-Au composite material to catalytically oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to ox-TMB to induce a blue color with an absorption peak centered at 652 nm. However, the introduction of GSH can result in a decrease in oxidized TMB; similarly, it can combine with Au nanoparticles (Au NPs) on the surface of CuS-PDA-Au composite material. Both approaches can result in a fading blue color and a reduction of the absorbance at 652 nm. Based on this above, we proposed a technique to detect GSH quantitatively and qualitatively through UV-Vis spectroscopy and naked eye, respectively. This approach demonstrates a low detection limit of 0.42 µM with a broad detection range of 5 × 10-7-1 × 10-4 M with the assistance of UV-Vis spectroscopy. More importantly, this approach is convenient and rapid. This method was successfully applied to GSH detection in human serum and cell lines. Graphical abstract A colorimetric approach has been developed by exploiting the peroxidase-like activity of CuS-polydopamine-Au composite for sensitive glutathione detection.

Colorimetric determination of dopamine by exploiting the enhanced oxidase mimicking activity of hierarchical NiCo2S4-rGO composites.

A composite consisting of NiCo2S4 and reduced graphene oxide (rGO) was prepared via a hydrothermal process. Compared to individual NiCo2S4 nanomaterials or reduced graphene oxide, the composite exhibits enhanced oxidase-like activity. It is found that dopamine (DA) inhibits the ability of NiCo2S4-rGO to oxidize the substrate 3,3',5',5'-tetramethylbenzidine (TMB) to form blue colored ox-TMB. Based on these findings, a colorimetric method for determination of DA was worked out. The absorption, best measured at 652 nm, increases linearly in the 0.5-100 µM DA concentration range, and the limit of detection is 0.42 µM. This method was successfully applied to the detection of DA in spiked human serum samples. Graphical abstract A hierarchical NiCo2S4-rGO composite was prepared through two-step hydrothermal process. It exhibits enhanced oxidase-like activity which, however, is inhibited by dopamine (DA). Hence, less blue colored ox-TMB is formed by oxidation of 3,3',5,5'-tetramethylbenzidine in the presence of dopamine.

A ratiometric fluorometric and colorimetric probe for the ß-thalassemia drug deferiprone based on the use of gold nanoclusters and carbon dots.

A turn-on fluorometric probe is described for the ß-thalassemia drug deferiprone (DFP). The probe is making use of carbon dots (C-dots) and gold nanoclusters (AuNCs) which, under 340-nm excitation, display dual emission with peaks at 445 and 592 nm. The orange fluorescence of AuNCs is quenched after the addition of Fe(III), but recovered on addition of DFP. The blue fluorescence of the C-dots, in contrast, remains unchanged. The Fe(III)-DFP complex undergoes intermolecular electron transfer under UV excitation and displays only weak peaks in the UV region. The ratio of the two fluorescences is measured which makes the probe intrinsically self-calibrated. Colorimetry is best performed at a wavelength of 280 nm. The ratio of fluorescences increases linearly in the 0.1-80 µM DFP concentration range, and the detection limit is 0.1 µM. The respective figures for colorimetry are 2.5-120 µM and 0.3 µM. The probe is highly selective for DFP. Thus, it possesses a large potential for detection of DFP in serum. Graphical abstract The orange fluorescence of gold nanoclusters (AuNCs) is quenched by Fe3+ ions but recovered on addition of deferiprone (DFP), while the change of blue fluorescence in carbon dots (C-dots) is minimal. Moreover, the Fe(III)-DFP complex undergoes intermolecular electron transfer under ultraviolet (UV) irradiation, and absorption spectra can be observed in the presence of Fe(III)-DFP detected by UV scanning. Thus, a ratiometric fluorometric and colorimetric assay is developed for DFP.

Colorimetric and fluorometric determination of uric acid based on the use of nitrogen-doped carbon quantum dots and silver triangular nanoprisms.

A dual-read detection system is described for non-enzymatic and non-aggregation based analysis of uric acid (UA). Silver triangular nanoprisms (AgTNPs) were used as colorimetric probes, while the reduction in the fluorescence of nitrogen-doped carbon quantum dots (N-CQDs) served as the fluorometric readout. The absorption band of the AgTNPs overlaps the emission band of N-CQDs (with a peak at 440 nm). Therefore, fluorescence is reduced owing to an inner filter effect. The AgTNPs are etched if exposed to H2O2, and round nanodiscs are formed. In the presence of UA, etching of the AgTNPs is suppressed because the facets of the AgTNPs are coated with UA. The absorbance, best measured at 683 nm, increases with the concentration of the pre-added UA. The colorimetric assay works in the 0.1-45 µM UA concentration range, and the fluorometric assay between 1 and 42 µM of UA. The respective detection limits are 50 and 200 nM, respectively. The probe can be used for direct visualization of UA. The method was successfully applied to the determination of UA in urine samples. Graphical abstract The fluorescence of nitrogen-doped carbon quantum dots (N-CQDs) is quenched by AgTNPs (silver triangular nanoprisms). As the AgTNPs are etched by H2O2, fluorescence recovers in the system after H2O2 is added, and also undergoes a color change. Uric acid (UA) protects the AgTNPs from etching because the facets of the AgTNPs are coated with UA. The fluorescence of N-CQDs decreases. Thus, a dual-read probe is developed for determination of UA.