Nitrogen and Sulfur Co-doped Carbon Quantum Dots for Detecting Fe3+, Ascorbic Acid and Alkaline Phosphatase Activities.

A method utilizing nitrogen-doped and sulfur-doped carbon quantum dots (N, S-CQDs) as fluorescent probes for the rapid detection of Fe3+, L-ascorbic acid (AA), and alkaline phosphatase (ALP) was presented. The fluorescence intensity of N, S-CQDs nanoprobes can be rapidly and efficiently quenched by Fe3+ and based on the fluorescence "turn off-on" characteristic of N, S-CQDs nanoprobes, the fluorescence signals of the N, S-CQDs/Fe3+can be recovered after the addition of AA. By coupling a fluorescent nanoprobe to an enzyme and L-ascorbic acid-2-phosphate (AA2P), a green, simple, rapid and effective fluorescent analytical method for the determination of ALP was developed. The prepared N, S-CQDs showed high sensitivity and selectivity to Fe3+, AA and ALP with the detection limit of 0.42 µM, 12.7 nM and 0.017 U·L-1 and their optimal concentration ranges were10-600 µM, 10-200 µM, 0.18-54 U·L-1, respectively. The fluorescence quantum yield of N, S-CQDs (0.2 mg·mL-1) at 393 nm excitation wavelength was 4.41%. Additionally, the fluorescent nanoprobes have been employed to successfully measure ALP in serum samples. It is expected that the established method may offer a new approach for biomolecular detection in clinical diagnosis and pharmaceutical analysis.

Colorimetric determination of cholesterol based on the peroxidase-like activity of Cu-Salt-Fe nanozyme with multiple active sites.

A strategy to enhance the peroxidase-like activity of the hemin composite is presented. The Cu-Salt-Fe with enhanced activity was synthesized by one-step heat treatment and applied to the colorimetric determination of free cholesterol in human serum. Phosphate can act in complexing Cu2+ to form a carrier Cu-Floc with a large specific surface area. The coordination effect of Cu-Floc with hemin was used to disperse and load hemin to form Cu-Floc-Hemin from which Cu-Salt-Fe was prepared. The Cu-Salt-Fe exhibits a synergistic catalytic effect of Cu-Salt, Fe2+, Fe3+, or Fe-Nx active sites in amplification of H2O2 oxidation. As expected, Cu-Salt-Fe triggered H2O2-mediated oxidation of 3,3',5,5'-tetramethylbenzidine (TMB), resulting in H2O2-dependent absorbance changes at 652 nm. A cholesterol oxidase (ChOx)/Cu-Salt-Fe-TMB colorimetric sensing system exhibited excellent cholesterol determination performance in the range 5-1200 µM with a detection limit of 2.73 µM. Cholesterol recoveries from the three-level spiked serum ranged from 92.2 to 98.9% (RSD ≤ 5.4). This colorimetric sensing system not only provided a strategy for the determination of endogenous substances with H2O2 as an intermediate, but also provided a new design idea (carrier selection, activity enhancement method) for the development of other artificial enzymes with the same catalytic core.

CuCo2S4 nanozyme-based stimulus-responsive hydrogel kit for rapid point-of-care testing of uric acid.

An efficient analysis platform composed of nanozyme-based hydrogel kit and smartphone was constructed for on-site detection of uric acid (UA) in a rapid and realiable manner. CuCo2S4 nanoparticles (CuCo2S4 NPs) as a peroxidase mimic were successfully prepared and the peroxidase-like activity and catalytic mechanism were studied in detail. The hydrogen peroxide (H2O2) stimulus-responsive nanozyme-based hydrogel kit was manufactured by integrating agarose, CuCo2S4 NPs, and 3,3',5,5'-tetramethylbenzidine (TMB) into the cap of centrifuge tube. H2O2 generated via UA oxidation acts as stimulus signal, which triggers the oxidation of TMB to form blue product (oxTMB) under the catalysis of CuCo2S4 NPs, resulting in the color response of the constructed kit. The color image of the kit was captured by a smartphone built-in camera and converted into color intensity using ImageJ software, thus achieving the quantitative determination of UA. The portable kit possesses high selectivity and was used to monitor UA in human serum with satisfactory results (recovery was in the range 95.8-107.3% and RSD was not greater than 4.6%). The established sensing platform is convenient and reliable, which provides a new strategy for point-of-care testing of UA and has a broad prospect in the fields of chemical sensing and biomedical.

Smartphone-assisted ratiometric fluorescence sensing platform and logical device based on polydopamine nanoparticles and carbonized polymer dots for visual and point-of-care testing of glutathione.

As a crucial biothiol, glutathione (GSH) plays a key role in the organisms. Monitoring GSH level is of great significance for disease diagnosis and biomedical research. In this work, polydopamine (PDA) nanoparticles-red fluorescent carbonized polymer dots (r-CPDs) based ratiometric fluorescence sensing platform was constructed and employed for GSH assay. Dopamine (DA) could be oxidized by cobalt oxyhydroxide (CoOOH) nanosheets and further polymerized into PDA nanoparticles with green fluorescence. However, in the presence of GSH, CoOOH nanosheets were reduced and decomposed, which prevented the production of PDA nanoparticles. In the sensing system, green-emitting PDA nanoparticles were employed as a response unit and r-CPDs were used as an internal reference unit. With the addition of GSH, the green fluorescence of PDA nanoparticles decreased as well as the red fluorescence of system remained relatively stable. Importantly, a distinct fluorescence color evolution from green to red was presented with a serious of GSH concentrations. Based on this, a portable smartphone-assisted ratiometric chromaticity analytical method was developed to achieve the on-site visual detection of GSH. Both the established ratiometric fluorescence and ratiometric chromaticity sensing methods for GSH assay have the merits of wide linear range, high sensitivity and excellent accuracy, which are suitable for the determination of GSH in human serum and exhibit great application potential in rapid and accurate monitoring of the GSH levels in clinical. Moreover, an ingenious logical device reflecting GSH levels was designed based on the two different fluorescence signals, which provided a new strategy for the intelligent online detection of GSH in complex biological matrices.

Nitrogen-Doped Carbon Dot and CdTe Quantum Dot Dual-Color Multifunctional Fluorescent Sensing Platform: Sensing Behavior and Glucose and pH Detection.

A novel fluorescent probe based on a nitrogen-doped carbon dot (N-CD) and CdTe quantum dot (CdTe QD) platform has been constructed for H2O2/glucose detection and pH sensing. In this work, H2O2-tolerant blue fluorescence N-CDs were added to the H2O2-mediated yellow fluorescence quenching of CdTe QDs to construct a dual-color ratiometric fluorescent H2O2 probe. H2O2-induced passivated group detachment and action on deep nanocrystals promoted CdTe QD fluorescence quenching. Meanwhile, the addition of the blue fluorescent background of N-CDs sharply reflected the color change in CdTe QDs. Under the optimized experimental conditions, the platform was effectively applied to the detection of H2O2 produced by the enzymatic reaction of glucose, showing high sensitivity (limit of detection 7.86 µM) and wide linear range (26-900 µM) for glucose detection. The pH-sensing behavior of CdTe QDs and N-CDs was attributed to the displacement of a weak acid (3-mercaptopropionic acid) by a strong acid (HCl) and the acid titration process of two coexisting bases (N-CDs and NH3·H2O), respectively. The loss of passivation and doping effects led to a decrease in the fluorescence intensity of CdTe QDs and N-CDs. Moreover, utilizing the ability of bimaterial system fluorescence to pH sensing, a semiquantitative pH detection based on the linear response was developed. The pH range was analyzed by three kinds of N-CD (Fex = 440 nm) and CdTe QD (Fex = 548 nm) typical emission spectral shapes. In addition, the recovery results showed that the bimaterial system was proved to be appropriate for the assay of glucose in spiked serum samples.

Dummy molecularly imprinted membranes based on an eco-friendly synthesis approach for recognition and extraction of enrofloxacin and ciprofloxacin in egg samples.

In this work, novel dummy molecularly imprinted membranes (MIMs) were fabricated using the nylon-66 (NY-66) membranes as the subtracts based on an eco-friendly "sandwich" technology with less consumption of organic reagents at mild conditions for recognition and extraction of enrofloxacin (ENR) and ciprofloxacin (CIP) in egg samples. The prepared MIMs were characterized by SEM, ATR-FTIR and TGA, showing the successful construction of uniform and porous polymers on the surface of membranes. A series of adsorption affinity tests were investigated, indicating the prepared materials had specific recognition capacity and excellent stability as novel sorbents. Furthermore, Box-Benhnken design (BBD) and single factor investigations were applied to optimize pretreatment procedures, coupling with Ultra High Performance Liquid Chromatograph (UHPLC) detection. The method showed a good correlation (r2>0.9999) within the linear range of 5.0~5000.0 µg kg-1, and limit of detection (LOD) of ENR and CIP were 0.3 and 0.7 µg kg-1, respectively. The mean recovery ranged from 84.5% to 97.0% within relative standard deviations (RSDs) of 10.2%. Finally, ENR and CIP were not detected in 3 batches of egg samples. The current study developed the dummy MIMs as sorbents combined with UHPLC analysis for extraction and detection of target analytes in food matrices.

Redox-induced target-dependent ratiometric fluorescence sensing strategy and logic gate operation for detection of α-glucosidase activity and its inhibitor.

A target-dependent ratiometric fluorescence sensing strategy was designed and fabricated based on a redox reaction for highly sensitive detection of α-glucosidase (α-Glu) activity and its inhibitor. In this study, silicon quantum dots (SiQDs) with excellent optical properties and two-dimensional (2D) cobalt oxyhydroxide (CoOOH) nanosheets were successfully prepared and exploited for the detection of analytes. The CoOOH nanosheets are able to oxidize o-phenylenediamine (OPD), and the product 2,3-diaminophenazine (oxOPD) not only quenches the blue fluorescence of SiQDs (440 nm) by the inner filter effect (IFE) but also emits orange fluorescence (565 nm). α-Glu can catalytically hydrolyze l-ascorbic acid-2-O-α-d-glucopyranosyl (AA2G) to produce ascorbic acid (AA). The redox between AA and CoOOH could lead to the damage of CoOOH nanosheets, thereby inhibiting the oxidization of OPD and effectively preserving the fluorescence of SiQDs. Thus, ratiometric detection of α-Glu activity was achieved according to the AA-dependent dual-fluorescence signal responses. Under the optimal conditions, good linearity was obtained in the range of 0.01-6 U mL-1 with a detection limit of 0.004 U mL-1. The IC50 of α-Glu inhibitor acarbose was estimated to be 0.216 µM. The method provides high sensitivity and selectivity for the determination of α-Glu activity and its inhibitor, which has great application potential in clinical diagnosis and anti-diabetic drug screening. Furthermore, a logic gate analytical device was successfully established based on double fluorescence signals, which makes it possible to monitor α-Glu activity by intelligence equipment.

Fe3O4/graphene molecularly imprinted composite for selective separation of catecholamine neurotransmitters and their analysis in rat brain tissues.

In this study, a novel of magnetic molecularly imprinted polymers (Fe3O4/GO/DMIPs) with multi-targets recognizing function were prepared by surface molecular imprinting technique adopting isoprenaline as the dummy-template molecule and graphene oxide (GO) as the carrier. The morphology, structures and magnetic properties of nanosorbents were characterized and assessed in detail and the results indicated that the 3D recognition cavities and matching functional groups with catecholamine neurotransmitters (CNs) were successfully fabricated on Fe3O4/GO surface. Moreover, the kinetic, isothermal and selective adsorption experiments were conducted to further reveal the adsorption behavior of adsorbent toward CNs and the results showed that the Fe3O4/GO/DMIPs possessed high adsorption capacity, rapid binding rate and excellent selectivity for CNs. On this basis, the Fe3O4/GO/DMIPs were further applied as adsorbent of magnetic solid-phase extraction (MSPE) for selective recognition and separation of CNs (dopamine, epinephrine, norepinephrine) followed by UPLC-MS/MS detection. The crucial parameters affecting the extraction efficiency were systematically optimized by Box-Behnken statistical design. Under the optimum conditions, satisfactory linearity (r > 0.99) was obtained with the lower limit of quantification from 0.53 to 1.93 ng mL-1. The accuracy (RE) ranged from -7.6% to 6.4% and the intra- and inter-day precisions were not more than 8.7% and 10.2%, respectively. Hence, the strategy proposed in this study might be used for high selectivity recognition and determination of CNs in complex biological matrices, which would provide a basis and reference for its application in the fields of separation and clinical monitoring.

Magnetic dummy-template molecularly imprinted polymers based on multi-walled carbon nanotubes for simultaneous selective extraction and analysis of phenoxy carboxylic acid herbicides in cereals.

A novel of magnetic dummy-template molecularly imprinted polymers (mag-MWCNTs-DMIPs) were prepared by surface molecular imprinting technique. The structure of polymers were characterized and the binding properties were assessed by adsorption experiments. The synthetic mag-MWCNTs-DMIPs exhibit satisfying adsorption capacity, excellent selectivity and fast adsorption rate toward phenoxy carboxylic acid (PCA) herbicides. Afterwards, a reliable analytical method for selective separation and determination of trace PCA herbicides in cereals was established by using magnetic solid-phase extraction (mag-MWCNTs-DMIPs as magnetic adsorbent) and UPLC-MS/MS detection. A series of requisite factors were optimized in detail to achieve expected extraction performance. Under the optimum MSPE parameters, the mean spiked recoveries for analytes in different cereals ranged from 86.7% to 95.2% with intra- and inter-day precision not greater than 8.5% and 10.6%, respectively. At last, the developed method was successfully utilized for determination the four PCA herbicides in actual cereals.

Dummy-surface molecularly imprinted polymers as a sorbent of micro-solid-phase extraction combined with dispersive liquid-liquid microextraction for determination of five 2-phenylpropionic acid NSAIDs in aquatic environmental samples.

A highly binding dummy template surface of molecularly imprinted polymers (MWNTs-MIPs) was synthesized on multi-walled carbon nanotubes surface using 2-phenylpropionic acid as dummy template, 4-vinylpyridine as the functional monomer, ethylene glycol dimethacrylate as the cross-linker, and DMF as porogen by precipitation polymerization method. MIPs were characterized by FT-IR spectroscopy, scanning electron microscope, thermo-gravimetric analysis, and nitrogen adsorption-desorption experiment. Adsorption and selectivity experiments of MIPs and non-imprinted polymers (NIPs) verified that the MIPs had a good selectivity and adsorption properties for five 2-phenylpropionic acid nonsteroidal anti-inflammatory drugs (NSAIDs). Imprinted polymer was used as a sorbent material for µSPE in current work and µSPE-DLLME method was selected for pretreatment of water samples. The µSPE-DLLME method was successfully used for the pre-concentration of five non-steroidal anti-inflammatory drugs in different environmental water samples prior to ultra-high performance liquid chromatography-tandem mass spectrometry. Efficiencies of µSPE and DLLME were thoroughly investigated and optimized in this study. The optimal results were obtained by using 3 mL of 1% formic acid-acetonitrile as elution solvent and dichloroethane and acetonitrile as extractant and disperser solvent, respectively. Limits of detection and quantification of five NSAIDs for different water matrices varied from 0.50 to 1.10 ng L-1 and 0.93 to 2.20 ng L-1, respectively. Each target analyte had a good linearity in its corresponding concentration range. Enrichment factors of target analytes ranged from 91 to 215. Recoveries of the target analytes were between 72.43 and 113.99% at the concentration levels of 0.02, 0.1, and 0.5 µg L-1. The developed method was successfully applied to extraction and analysis of NSAIDs in different water samples with satisfactory results which could help us better understand their environmental fate and risk to ecological health. Graphical abstract Dummy-surface molecularly imprinted polymers as a sorbent of micro-solid-phase extraction combined with dispersive liquid-liquid microextraction for determination of five 2-phenylpropionic acid NSAIDs in aquatic environmental samples.

Trace determination of five triazole fungicide residues in traditional Chinese medicine samples by dispersive solid-phase extraction combined with ultrasound-assisted dispersive liquid-liquid microextraction and UHPLC-MS/MS.

A novel and reliable method for determination of five triazole fungicide residues (triadimenol, tebuconazole, diniconazole, flutriafol, and hexaconazol) in traditional Chinese medicine samples was developed using dispersive solid-phase extraction combined with ultrasound-assisted dispersive liquid-liquid microextraction before ultra-high performance liquid chromatography with tandem mass spectrometry. The clean up of the extract was conducted using dispersive solid-phase extraction by directly adding sorbents into the extraction solution, followed by shaking and centrifugation. After that, a mixture of 400 µL trichloromethane (extraction solvent) and 0.5 mL of the above supernatant was injected rapidly into water for the dispersive liquid-liquid microextraction procedure. The factors affecting the extraction efficiency were optimized. Under the optimum conditions, the calibration curves showed good linearity in the range of 2.0-400 (tebuconazole, diniconazole, and hexaconazole) and 4.0-800 ng/g (triadimenol and flutriafol) with the regression coefficients higher than 0.9958. The limit of detection and limit of quantification for the present method were 0.5-1.1 and 1.8-4.0 ng/g, respectively. The recoveries of the target analytes ranged from 80.2 to 103.2%. The proposed method has been successfully applied to the analysis of five triazole fungicides in traditional Chinese medicine samples, and satisfactory results were obtained.