Ascorbic Acid In Real Samples Research Articles

Manganese Oxide-Doped Graphitic Carbon Nitride-Based 2D Material as Nanozyme for the Colorimetric Sensing of Ascorbic Acid

Ascorbic acid is a key player in the human body, pharmaceutical industry, and food industry. It is involved in many physiological processes, and its deficiency or excess amount is linked to many pathological conditions, which makes it essential to monitor its concentration. In the current work, graphitic carbon nitride (g-C3N4) and manganese oxide-doped graphitic carbon nitride (g-C3N4@MnO2) were synthesized through the pyrolysis process. Various characterization techniques, including spectroscopic, diffraction, thermal, and imaging methods, were employed to analyse the material's structural, compositional, and morphological properties. The surface chemical state of the material through X-ray photoelectron spectroscopy confirmed that manganese was present in its tetravalent state, anchoring with nitrogen in the two-dimensional g-C3N4. The synthesized g-C3N4@MnO2 demonstrated intrinsic peroxidase-like activity visualized through the naked eye by the transformation of 3,3′,5,5′-tetramethylbenzidine (TMB) to oxiTMB and confirmed through a UV-Vis spectrophotometer. The detection of ascorbic acid was performed through the peroxidase inhibitory action of the analyte through a chromogenic substrate, which reduced the oxiTMB to a colorless form. Under the optimized conditions, the sensor system was able to detect the analyte in the linear range of 1 to 80µM with a 0.16μM LOD, 0.53µM LOQ, and an R2 value of 0.9982. The sensor system, along with its sensitivity and linearity, was very selective in the presence of various potential interfering species. The sensor was successfully employed for the sensing of ascorbic acid in real samples with excellent reproducibility. The proposed sensor can be used in diagnosis, pharmaceutical applications, and the food industry.

Aggregation-disaggregation regulated fluorescence resonance energy transfer of perovskite nanocrystals for the detection of ascorbic acid

Fluorescence resonance energy transfer (FRET) from fluorescent nanoparticles to small molecules is an attractive approach for bioanalysis. It remains challenging to reversibly regulate the FRET, let alone use reversible FRET to detect ions or molecules. Here we demonstrate an aggregation/disaggregation strategy for reversible regulation of FRET based on metal–ligand coordination chemistry and redox reactions. An amino-functionalized red fluorescent (∼668 nm) perovskite nanocrystals (PNCs) was prepared as the energy donor. Fe3+ can coordinate with the amino groups on PNCs, resulting in the aggregation of PNCs and enhanced absorption from 600 to 700 nm on the surface of PNCs. Aggregation can reduce the distance between PNCs and Fe3+–amino complexes, as well as restrict rotational and translational diffusion of PNCs or Fe3+–amino complexes, consequently enhancing the FRET between PNCs and Fe3+–amino complexes. Interestingly, reductive ascorbic acid can reduce Fe3+ to Fe2+ in the complexes, leading to a weakening of absorption at 668 nm and dispersion of PNCs, resulting in the disappearance of the FRET process involved in PNCs. Based on the FRET switch, we have realized consecutive quantitative analysis of Fe3+ and ascorbic acid in real samples. We expect that reversible FRET process can be regulated by aggregation-disaggregation instructed by coordination and redox reactions, and that the regulation strategy could significantly expand the application scope of PNCs in fluorescence detection.

Electrochemical determination of ascorbic acid using palladium supported on N-doped graphene quantum dot modified electrode

To precise screening concentration of ascorbic acid (AA), a novel electrochemical sensor was prepared using palladium nanoparticles decorated on nitrogen-doped graphene quantum dot modified glassy carbon electrode (PdNPs@N-GQD/GCE). For this purpose, nitrogen doped GQD nanoparticles (N-GQD) were synthesized from a citric acid condensation reaction in the presence of ethylenediamine and subsequently modified by palladium nanoparticles (PdNPs). The electrochemical behavior of AA was investigated, in which the oxidation peak appeared at 0 V related to the AA oxidation. Considering the synergistic effect of Pd nanoparticles as an active electrocatalyst, and N-GQD as an electron transfer accelerator and electrocatalytic activity improving agent, PdNPs@N-GQD hybrid materials showed excellent activity in the direct oxidation of AA. In the optimal conditions, the voltammetric response was linear in the range from 30 to 700 nM and the detection limit was calculated to be 23 nM. The validity and the efficiency of the proposed sensor were successfully tested and confirmed by measuring AA in real samples of chewing tablets, and fruit juice.

Highly efficient determination of trace ascorbic acid in vitamin C tablets by boronate affinity-modified magnetic metal–organic frameworks

Ascorbic acid (AA) plays an important role in many life processes. The chronic nutritional deficiency of AA will lead to the symptoms of scurvy. Therefore, the sensitive quantitative detection of AA is most important in the pharmaceutical analysis, food industry and diagnostic application. In this study, a dual-functional magnetic metal–organic frameworks (Fe3O4@SiO2@UiO-PBA) nanoparticles was synthesized by modifying phenylboronic acid to the surface of magnetic UiO-66-NH2 via postsynthetic modification for selectively and sensitively florescent detection of AA. Due to the abundant amino groups and grafted phenylboronic acid, the proposed nanoparticles have the dual properties of hydrophilicity and boronate affinity. Under optimum conditions, the obtained Fe3O4@SiO2@UiO-PBA nanoparticles can detect AA within 30 s, and has a good linear relationship with the concentration of AA in the range of 5.0–60 μM with a detection limit of 2.5 μM (S/N = 3). In addition, the prepared Fe3O4@SiO2@UiO-PBA nanoparticles showed excellent selectivity and great potential application in the highly efficient determination of trace AA in vitamin C tablets. These results indicated that a convenient method was proposed to develop fluorescent probes for rapid and sensitive detection of trace AA in real samples.

2D Phthalocyanine-Assembled Porous Nanostructure-Based Electrochemical Platform for High-Efficiency Detection of Ascorbic Acid

In this work, a novel two-dimensional (2D) porous nanostructure is constructed upon air/water interfacial assembly of 12-crown-ether-4-incorporated double-decker phthalocyanine (Pc2). The combination of the good electroconductivity of phthalocyanine and the great surface area of the porous structure endows the assembled film with excellent chemical sensing property for ascorbic acid (AA). The low limit of detection can be 0.15 μM with a large linear concentration range and strong anti-interfering ability, which can be comparable to the best results of tetrapyrrole-based electrochemical sensors for AA. Furthermore, the obtained 2D porous assembled film sensor can be applied in real-time monitoring of AA in commercial drinks, indicating its application potential in accurate detection of AA in real samples.

Liquid-phase microextraction of ascorbic acid in food and pharmaceutical samples using ferrofluid-based on cobalt ferrite (CoFe2O4) nanoparticles

Quantitation of ascorbic acid is extremely desired in the food, cosmetic, and pharmaceutical samples. In this study, liquid-phase microextraction using ferrofluid (LPME-FF) based on the cobalt ferrite nanoparticles (CoFe2O4) coupled with a green, precise, accurate, and robust spectrofluorometric approach was used for extraction and determination of ascorbic acid. The procedure is based on the reaction between ascorbic acid (AA) and methylene blue (MB) as an inexpensive and readily available fluorescence quenching reagent. The native fluorescence intensity of MB was quenched using ascorbic acid. The CoFe2O4 magnetic nanoparticles were synthesized and confirmed by Fourier transform infrared (FT-IR) spectroscopy, vibrating sample magnetometer (VSM), field emission scanning electron microscopy (FE-SEM), and energy dispersive X-ray spectroscopy (EDXS). Three parameters of pH, ferrofluid volume, and ultrasonic time were selected as influential factors on the process and optimized by central composite design (CCD). Under optimal conditions, linear range, detection limit, and the relative standard deviation were obtained 0.26–5.70 μM, 0.074 μM and, 2.0 %, respectively. Finally, the proposed method was successfully employed for the quantification of ascorbic acid in real samples of lemon juice, orange juice, and vitamin C tablets.

A sensitive and simple electrochemical technique for detecting ascorbic acid content in pharmaceutical and biological compounds

In the current study, a glassy carbon electrode (GCE) modified with graphene-CoS2 nanocomposite was investigated for electrochemical sensing of ascorbic acid. The electrochemical performance of the modified electrode was examined using differential pulse voltammetry (DPV), linear sweep voltammetry (LSV) and chronoamperometry (CHA) techniques. The electrochemical behavior of ascorbic acid at the graphene-CoS2/GCE displayed a higher oxidation current and lower oxidation potential than bare GCE. Under the optimal experimental conditions, the sensor presented a good linear response between the current and the ascorbic acid concentration range of 0.15–245.0 μM, with a low detection limit of 0.05 μM. Finally, the graphene-CoS2 nanocomposite-modified GCE was applied for the determination of ascorbic acid in real samples and displayed excellent recoveries.

Modulation of inner filter effect between persistent luminescent particles and 2, 3-diaminophenazine for ratiometric fluorescent assay of ascorbic acid and ascorbate oxidase activity

Ascorbate oxidase (AAO) and ascorbic acid (AA) play an important role in delaying lives senescence and metabolism. In this study, a sensitive ratiometric fluorescence sensing system based on the inner filter effect (IFE) between persistent luminescent particles (PLPs) and 2, 3-diaminophenazine (DAP), was designed for the detection of AA and AAO activity. Wherein, PLPs emit blue fluorescence at 475 nm with an excitation wavelength of 370 nm. CoOOH nanosheets with oxidase-like activity can oxidize o-phenylenediamine (OPD) to produce 2, 3-diaminophenazine (DAP) with orange fluorescence at 558 nm. The generated DAP quenched the fluorescence of PLPs by an inner filter effect (IFE). When AA was introduced to the system, CoOOH nanosheets were destroyed and reduced to Co2+, thereby inhibiting the oxidization of OPD and effectively preserving the blue fluorescence of PLPs at 475 nm. Besides, AAO can catalyse AA to produce the oxided dehydroascorbic acid (DHA). The dissipative AA can recover orange fluorescence of DAP with weakening the blue fluorescence of PLPs. Therefore, a sensitive ratio fluorescence sensing strategy was established by using PLPs as the reference signal and DAP as a reported signal for the detection of AA and AAO activity. Under optimal conditions, the obtained linear ranges were 1–45 μM and 1–20 mU/mL, and detection limits were 0.2 μM and 0.25 mU/mL, respectively. Finally, this proposed ratiometric fluorescent analytical strategy was used to detect AA in real samples (lemon, orange, tomato), which exhibited satisfactory results comparing with commercial kit.

Voltammetric Determination of Ascorbic Acid Content in Cabbage Using Anthraquinone Modified Carbon Paste Electrode

In this study, a low-cost, sensitive, and efficient voltammetric method based on anthraquinone modified carbon paste electrode was developed for determination of ascorbic acid in cabbage samples. After cyclic voltammetry was used to investigate the electrochemical behavior of ascorbic acid and to study dependence of oxidative peak current on scan rate and pH, square wave voltammetric method was developed for direct determination of ascorbic acid in cabbage samples. In contrast to the unmodified carbon paste electrode, a remarkable enhancement in oxidative peak current at anthraquinone modified carbon paste electrode confirmed electrocatalytic property of the modifier towards oxidation of ascorbic acid. A better correlation coefficient for the dependence of peak current on the square root of scan rate (R2=0.9963) than on the scan rate (R2=0.9781) indicated that the oxidation of ascorbic acid at anthraquinone modified carbon paste electrode is predominantly governed by diffusion-controlled process. Square wave amplitude, square wave step potential, and square wave frequency are optimized for the investigation of AA in cabbage. The optimized values are 30 mV, 7 mV, and 35 Hz, respectively. Under the optimized method and solution parameters, an excellent linear response was observed between square wave voltammetric peak current of AQMCPE and concentration of ascorbic acid in the range5×10−5to4×10−3 M with a better correlation coefficient (R2=0.9993) and detection limit (LOD=1.84×10−6 M). The ascorbic acid content of the three cabbage samples from three different cabbage growing areas was found in the range3.686±0.026–8.298±0.011 mg/g of powdered cabbage. Excellent recovery results between 95.042 and 96.139% for spiked ascorbic acid in cabbage samples confirmed the potential applicability of the developed method based on AQMCPE for the determination of ascorbic acid in real samples like cabbage.

Fe3O4@Au-metal organic framework nanozyme with peroxidase-like activity and its application for colorimetric ascorbic acid detection.

A free radical scavenging system based on Fe3O4@Au/MOF-ABTS˙+ has formed the basis of a novel method for the highly sensitive and specific spectrophotometric determination of ascorbic acid (AA). The Fe3O4@Au/MOF nanozyme with magnetic separation properties was effectively prepared and evaluated using an environmentally friendly technique. Nanomaterials have the advantages of superparamagnetism, biocompatibility, chemical stability, and enhanced synergistic peroxidase-like activity, which can be utilized in catalysis to oxidise the peroxidase substrate 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) into a green-colored product in the presence of H2O2. AA as an antioxidant has scavenging effects on ABTS radicals and can reduce green ABTS˙+ to uncolored ABTS2-, contributing to a substantial reduction in green color. Based on such a premise, a highly selective and sensitive chromogenic sensing method depending on the peroxidase-like activity of the nanocomposites was developed in order to achieve the efficient detection of AA in real samples. Under optimum conditions, the proposed technique had a detection range of 0.001-0.1 mmol L-1, a limit of detection of 0.098 μmol L-1, and a detection time of only 30 seconds. The newly proposed colorimetric analysis method devoid of enzymes has broad application potential in the areas of quality control and quality and safety detection.

Cobalt-Doped Carbon Quantum Dots with Peroxidase-Mimetic Activity for Ascorbic Acid Detection through Both Fluorometric and Colorimetric Methods.

In this work, we fabricated cobalt-doped carbon quantum dots (Co-CQDs) by a one-pot hydrothermal method with cobalt tetraphenylporphyrin and 1,2-ethanediamine as precursors. The morphology and structure of the Co-CQDs were characterized through transmission electron microscopy, X-ray diffraction spectra, Fourier transform infrared, and X-ray photoelectron spectra. The Co-CQDs emitted intense blue luminescence under ultraviolet irradiation and exhibited a typical excitation-dependent emission property. Moreover, they can act as a fluorescent probe for the detection of Fe3+ and ascorbic acid (AA) with high selectivity and sensitivity through an "on-off-on" mode. The limit of detection (LOD) of Fe3+ was measured as 38 μM (S/N = 3). The quenched emission of carbon quantum dots can be recovered with the addition of ascorbic acid (AA) to the Co-CQDs/Fe3+ system. The change of fluorescence was linear with the concentration of AA (0.6-1.6 mM) with the LOD of 18 μM. Furthermore, the Co-CQDs exhibited high oxidase-like catalytic behavior, which could convert transparent 3,3',5,5'-tetramethylbenzidine (TMB) into blue ox-TMB by dissolved oxygen. After adding ascorbic acid to the Co-CQDs/TMB system, the blue color of the solution faded due to the reduction of blue ox-TMB to colorless TMB. Based on this phenomenon, the Co-CQDs were capable of detecting AA (10-400 μM) with the LOD of 0.27 μM. The fluorometric and colorimetric assays based on the Co-CQDs for the AA detection were then successfully applied in fresh fruits. Furthermore, the high biocompatibility of the Co-CQDs against HeLa cells was verified by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. Thus, the Co-CQDs could be used as a powerful tool for the detection of AA in real samples through a dual-mode method.

Application of a Simple and Sensitive Electrochemical Sensor in Simultaneous Determination of Paracetamol and Ascorbic Acid

A new electrochemical sensor for the quick determination of both paracetamol (ACOP) and ascorbic acid (AA) was prepared using an acetylene black paste electrode modified with polyvinylpyrrolidone and graphene composite (PVP-GR/ABPE). Second derivative linear sweep voltammetry (SDLSV) and cyclic voltammetry (CV) were then used to investigate the electrochemical behavior of both ACOP and AA on this PVP-GR/ABPE. The results demonstrate that the two analytes have good resolution and strong electrochemical signal responses. Due to the interconnected effects of PVP, GR, and AB ternary composite, the designed electrode has several beneficial characteristicsincluding good adsorption ability, significant specific surface area, and good conductivity. The voltammetric responses of ACOP and AA on the PVP-GR/ABPE show that the modified electrode displayed good electrocatalytic properties for the chemical reactions of both ACOP and AA, with the linear range of 0.01–100 μM for ACOP and the linear range of 6–1000 μM for AA. The detection limits of 6.0 nM (ACOP) and 1.0 μM (AA) were obtained, respectively. The sensor has successfully been used in the measurement of ACOP and AA in real samples, indicating that this method is potentially applicable for routine biomedical and chemical sensing in vitro diagnostically.

One-pot microwave-assisted synthesis of blue emissive multifunctional N-S-P co-doped carbon dots as a nanoprobe for sequential detection of Cr(VI) and ascorbic acid in real samples, fluorescent ink and logic gate operation

In this communication, blue light-emitting fluorescent N-S-P co-doped carbon dots (PGP-CDs) were synthesized by a simple, yet rapid procedure using microwave charring. Low cost, easily accessible precursors like glutathione, polyethylene glycol (PEG-400), and o-phosphoric acid (H3PO4) were used in the synthesis following which PGP-CDs obtained with a good quantum yield (15%) were well characterized. The HRTEM analysis showed that PGP-CDs were well distributed and spherical, with an average size of 4.5 nm. XPS analysis confirmed the chemical composition of doped N-S-P-CDs, and fluorescence spectroscopy revealed that they exhibit pH-independent and excitation wavelength-dependent fluorescence with excitation/emission maxima at 380/455 nm. Blue fluorescence of the PGP-CDs was exclusively quenched by the addition of carcinogenic Cr(VI) in the presence of other metal ions within a linear range of 0.1–100 µM which can be explained by the inner filter effect (IFE). The regeneration of carbon dots could be achieved by the addition of ascorbic acid (AA) and thus, PGP-CDs act as a sensitive fluorescent turn “on–off-on” nano-sensor in water. The limit of detection (LOD) for Cr(VI) was found to be 4 nM which is lesser than the permissible limit (0.9 µM) as prescribed by World Health Organisation (WHO) in drinking water. PGP-CDs show reversibility up to four cycles and on this basis, a combinatorial molecular logic gate consisting of a special combination of logic functions NAND & NOT has been constructed. Furthermore, PGP-CDs were also utilized as fluorescent ink without any chemical alteration. For real sample applications, PGP-CDs were also successfully applied to determine Cr(VI) in real water samples and PGP-CD + Cr(VI) complex to detect AA levels in food samples. Results obtained from real sample analysis suggest that PGP-CDs can be used as a potential nanoprobe that offers outstanding precision in detecting the trace amount of Cr(VI) and AA with a low detection limit.

Voltammetric Determination of Ascorbic Acid in Pharmaceutical Formulations Using Modified Iodine-Coated Platinum Electrode

Background: Despite the high reactivity of the platinum electrode, the iodine-coated platinum electrode shows obvious inertness toward adsorption and surface processes. For that, iodine-coated platinum electrodes accommodate themselves to interesting voltammetric applications. Objectives: This study reports using the modified iodine-coated polycrystalline platinum electrode as a voltammetric sensor for ascorbic acid determination in pharmaceutical formulations. Methods: The developed voltammetric method based on recording cyclic voltammograms of ascorbic acid at iodine-coated electrode The optimized experimental parameters for the determination of ascorbic acid were using 0.1 M KCl as a supporting electrolyte with a scan rate of 50mV/s. Results: The anodic peak related to ascorbic acid oxidation was centered at nearly 0.28V. An excellent and extended linear dependence of the oxidative peak current on the concentration of ascorbic acid was observed in the range 2.84x10-3 - 5.68 mM. The limit of detection (LOD) and limit of quantitation (LOQ) were 1.0 µM and 3.01 µM, respectively, attesting to the method’s sensitivity. The investigation for the effect of potential interference from multivitamin tablet ingredients (vitamins B1, B6, B12, folic acid, citric acid, sucrose, glucose, and zinc) indicated specific selectivity toward ascorbic acid and the absence of any electrochemical response toward these components. Recovery results in the range 98.93±2.78 - 99.98±5.20 for spiked standard ascorbic acid in pharmaceutical formulations further confirmed the potential applicability of the developed method for the determination of ascorbic acid in real samples. Conclusions: The developed method was successfully applied to the analysis of ascorbic acid (vitamin C), and the obtained results were in good agreement with the labeled values; besides, the statistical tests indicated no significant difference at p=0.05 with a 95% confidence level.

Porous silicon-mesoporous carbon nanocomposite based electrochemical sensor for sensitive and selective detection of ascorbic acid in real samples

Ascorbic acid (AA) is one of the vital water-soluble antioxidants in blood serum and can function as a key blood serum biomarker for oxidative stress. Therefore, we have developed a highly sensitive and selective AA electrochemical sensor based on novel porous silicon-mesoporous carbon nanocomposites (PSi-MC NCs) modified glassy carbon electrode (GCE). The structural properties and morphological investigation of the PSi-MC NCs were systematically studied by different techniques. This newly designed PSi-MC/GCE-based non-enzymatic electrochemical sensor can measure an extremely wide range of AA (0.5–2473 μM) in phosphate buffer solution (PBS) with a sensitivity 0.1982 μAμM−1cm−2 and a logical limit of detection (LOD) 30.0±0.1 nM. The proposed AA sensor was also applied to detect possible interference from common interfering substances that are present in human blood, showing highly selective performance. The proposed AA sensor also showed highly acceptable results towards the detection of AA levels in human blood serum and vitamin C tablets. This new combination of active material PSi-MC NCs provided steady, excellent reproducibility, repeatability, and long-term stability.

Simple and eco-friendly synthesis of crude orange-peel-derived carbon nanoparticles for detection of Fe3+ and ascorbic acid.

Although fluorescence sensors based on carbon dots (CDs) have been developed widely, multicomponent detection using CDs without extra and tedious surface modification remains a challenge. Here, the crude carbon nanoparticles (CPs) as a fluorescence sensor were prepared through one-pot hydrothermal process using orange peel as the precursor. The method was simple, rapid, economical, and eco-friendly given that such extra steps as dialysis and lyophilization were not required. By adding ethanol into the reaction solvent, the fluorescence properties of orange-peel-derived CPs as well as their sensitivity of detecting Fe3+ with a limit of detection of 0.25 μM were improved. Additionally, orange-peel-derived CPs could be used as a fluorescence sensor for detection of ascorbic acid (AA) with a LOD of 5 μM. More importantly, the proposed fluorescence methods were successfully used to qualitatively and quantitatively analyze Fe3+ and AA in real samples. Recovery of Fe3+ from tap water was within the range 97.2-105.4%. Conversely, recovery of AA from vitamin C tablets and orange juices laid within the ranges 97.7-99.3% and 93.2-97.6%, respectively.

An electrochemical sensor based on the modification of platinum nanoparticles and ZIF-8 membrane for the detection of ascorbic acid

In this manuscript, a layer of 2-methylimidazole zinc salt (ZIF-8) membrane is deposited on the surface of glassy carbon electrode (GCE) modified with platinum nanoparticles (Pt NPs) by reduction electrochemical method to obtain ZIF-8/Pt NPs/GCE, and then used for the detection of ascorbic acid (AA). The deposition of Pt NPs on the surface of GCE can not only guide the nucleation and growth of ZIF-8 membrane, but also exert a synergistic effect with it to enhance conductivity. For ZIF-8 membrane, it can increase the active area of electrode and thus improve the electrochemical response of the sensor for AA. Influence factors such as the deposition current density, deposition time on the surface morphology of the modified electrode, and the detection performance of the modified electrode during the electrochemical deposition of ZIF-8 membrane were explored to get the best performance. In addition, influence of conditions such as sweep speed and pH of the test solution on the electrochemical response signal of AA were also studied. Under the best conditions, the linear range of AA detection by this sensor is from 10 μmol L−1 to 2500 μmol L−1, and the detection limit is 5.2 μmol L−1 based on S/N = 3. What's more, the modified electrode also has good anti-interference ability, reproducibility and stability, and has achieved satisfactory results in the detection for AA in real samples.

Hydrogen peroxide assisted synthesis of sulfur quantum dots for the detection of chromium (VI) and ascorbic acid.

Sulfur quantum dots (SQDs), heavy-metal-free quantum dots, are regarded as the next generation promising green nanomaterials compared with traditional heavy-metal-based quantum dots. However, there have been few reports on the synthesis and application of SQDs for analytical detection. Herein, an H2O2-assisted top-down method is used to synthesize SQDs. The as-obtained SQDs have good water dispersion, stability, photoluminescence (PL) properties and achieving a quantum yield (QY) to 11%. After adding Cr (VI) in SQDs, the fluorescence intensity decreases base on inner filter effect (IFE). Moreover, Cr (VI) can be reduced to Cr(III) when ascorbic acid (AA) is introduced into the SQDs - Cr (VI) system, accompanying the recovery of the fluorescence intensity. The fluorescence sensor displays high sensitivity and quickly response toward Cr (VI) and AA in a range of 10-120μmol L-1 and 20-500μmol L-1 with a detection limit of 0.36μmol L-1 and 1.21μmol L-1, respectively. In addition, the fluorescence sensor has been applied for the determination of Cr (VI) and AA in real samples.

A turn-off-on near-infrared photoluminescence sensor for sequential detection of Fe3+ and ascorbic acid based on glutathione-capped gold nanoclusters.

Many reports have suggested that near-infrared (NIR) fluorescent probes are one of the most promising molecules for improving the sensitivity of fluorescence sensing and imaging. Herein, gold nanoclusters with excellent near-infrared photoluminescence (PL) were synthesized by a simply hydrothermal treatment of hydrogen tetrachloroaurate(III) trihydrate and glutathione (GSH). The NIR PL of GSH-capped gold nanoclusters (GSH-AuNCs) can be significantly quenched by Fe3+, which follows a dynamic quenching mechanism. However, the NIR PL of the GSH-AuNCs/Fe3+ system can be recovered after the addition of ascorbic acid (AA). The decrease and increase of NIR PL intensities of GSH-AuNCs were linearly correlated with the concentration of Fe3+ and AA, respectively. Therefore, a turn-off-on NIR PL sensing strategy can be constructed for sequential detection of Fe3+ and AA with the linear range of 0.7-180μM and 0.5-120μM, respectively. The proposed NIR PL sensor exhibits excellent sensing performance and has been applied to the determination of Fe3+ and AA in real samples with satisfactory results.

Non-enzymatic simultaneous detection of acetylcholine and ascorbic acid using ZnO·CuO nanoleaves: Real sample analysis

A facile wet-chemical technique used to prepare the zinc oxide doped copper oxide nanoleaves (ZnO·CuO nanoleaves) in alkaline phase. ZnO·CuO nanoleaves were examined using a variety of conventional techniques for example UV–Visible, FTIR, XRD, FESEM equipped XEDS, and XPS. A non-enzymatic sensor was prepared with modification of a slightly deposited of ZnO·CuO nanoleaves onto a flat GCE, which fabricated through a conducting nafion polymer matrix in order to detect selective acetylcholine and ascorbic acid simultaneously. Analytical performances such as sensitivity, LOD, LOQ, LDR, and durability of the selective acetylcholine and ascorbic acid sensors were examined through a conventional current–voltage method. Calibration graphs of acetylcholine and ascorbic acid sensors were found linear (R2 = 0.9049 and 0.9201) over a good concentration range (100.0 pM–100.0 mM) respectively. Sensitivity (317.0 and 94.94 pAμM-1cm−2), LOD (14.7 and 12.0 pM), and LOQ (490.0 and 367.0 mM) of acetylcholine and ascorbic acid sensors were calculated correspondingly from the slope of the linear portion of calibration graph. Preparation of ZnO·CuO nanoleaves using wet-chemical technique is an excellent approach for the advancement of nanomaterial based on sensor development in support of enzyme free detection of biological molecules for the safety in healthcare and biomedical fields. This expected sensor applied for the specific determination of acetylcholine and ascorbic acid in real samples (Human, mouse, and rabbit serum, orange juice, and urine) and found satisfactory and acceptable results.