Ascorbic Acid Assay Research Articles

Enhancing enzymatic activity of Mn@Co3O4 nanosheets as mimetic nanozyme for colorimetric assay of ascorbic acid

In nanozyme-based assays, increasing enzymatic activity is very desirable for enhancing sensitivity and lowering the detection limit. In this study, novel Mn doped cobalt oxide nanosheets (Mn@Co3O4 NSs) were synthesized by hydrothermal process. The obtained Mn@Co3O4 possessed enhanced dual-enzyme mimetic, oxidase and peroxidase, and can catalytically oxidize of 3, 3′, 5, 5′-tetramethylbenzidine (TMB), to a blue product of oxidized TMB. The enzyme kinetics were well-described mathematically using a common Michaelis-Menten and Lineweaver Burk model. The enzyme kinetics constant (Km) was found to be 0.15 mM, which is relatively low comparing with pure Co3O4 nanosheets (0.35 mM) and natural enzyme HRP (0.434 mM). Therefore, the efficient colorimetric method was achieved for determination of H2O2 and ascorbic acid. The limit of detection (LOD) of H2O2 was 8.0 μM and the linear range was 20–200 μM based on direct turn on of the peroxidase-like activity of Mn@Co3O4. While, for ascorbic acid detection based on turn-off approach, the linearity range for the ascorbic acid was 1–8 μM with LOD of 0.4 μM. Moreover, the colorimetric system exhibited good stability and selectivity toward the detection of ascorbic acid effectively in real samples (vitamin C tablets) with satisfactorily accuracy and precision.

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.

Modification of Microfluidic Paper-Based Devices with an Oxidant Layer for Distance Readout of Reducing Substances.

We developed a novel strategy for modification of paper cellulose with water-insoluble oxidants for distance readout of reducing substances on microfluidic paper-based analytical devices (μPADs). Water-insoluble oxidants were formed and modified onto paper cellulose through the redox reaction that occurred between paper cellulose and potassium permanganate deposited on the paper channel, developing a yellowish-brown color on the channel. As aqueous solutions containing reducing substances flowed along the channel, reducing substances were consumed owing to the redox reaction that occurred between oxidants and reducing substances until the reducing substances were depleted, forming a discolored zone on the yellowish-brown channel. The redox reaction between insoluble oxidants and reducing substances on the paper cellulose could be used for distance-based detection of a wide variety of reducing substances, which is similar to the classical potassium permanganate titration that employs the redox reaction that occurred between potassium permanganate and reducing substances. We believe that this method will broaden the analytical applications of distance-based detection on μPADs. This method was applied to ascorbic acid assay and captopril assay in real samples with analytical results comparing well with the labeled values, demonstrating its great potential in real sample analysis.

Integrating In Silico and In Vitro Approaches to Screen the Antidiabetic Properties from Tabernaemontana divaricata (Jasmine) Flowers.

The purpose of this study was to assess different in vitro biological activities such as phytochemical constituents, enzymatic antioxidant status, cytotoxicity through hemolytic activity, and antidiabetic potential of plant methanolic extract through glucose uptake by yeast cells. Further, using in silico approach by the SwissADME technique the drug-likeness rules for bioactive components were characterized, while potential interactions were identified via molecular docking of a ligand with target proteins by GOLD 5.3.0. The results showed that T. divaricata was rich in TPC and TFC, i.e., 62.32 ± 4.02 and 24.53 ± 0.61, respectively, and the cytotoxic potential was 10% towards human RBCs, while protein estimation revealed the presence of protein in the extract, which was 22.82 ± 4.6. DPPH assay in comparison with ascorbic acid and several enzymatic assays, such as CAT, SOD, and POD, showed maximum antioxidant potential, i.e.,15.9 ± 2.33%, 65.57 ± 13.4%, 3.02 ± 3.4, 15.87 ± 0.5, and 0.74 ± 0.2, respectively. Glucose uptake by yeast cells, i.e., α-amylase and α-glucosidase, showed a maximum antidiabetic potential such as 75.11 ± 1.44%, 41.81 ± 3.75%, and 35.9 ± 1.24%, respectively. Our results indicate that the methanolic extract of T. divaricata has antioxidant potential and inhibits α-amylase and α-glucosidase activity and possesses maximum antidiabetic potential. The results provide scientific proof that the medicinal plant being studied is a powerful source of natural antioxidant, antidiabetic, and medicinally significant substances. In silico study, using a molecular docking, unveiled that two compounds showed good interactions with 5kzw protein with considerable binding affinities and fulfilled docking parameters. It may conclude that T. divaricata is an important vegetable with a potent source of natural antioxidants and antidiabetic activity justifying its traditional use in green therapeutics.

Characterization of deposited dust and its respirable fractions in underground coal mines: Implications for oxidative potential-driving species and source apportionment

Oxidative potential (OP) is considered to be an efficient indicator of particulate matter (PM) to induce oxidative stress in the lungs and is increasingly considered to be a relevant health metric. In this study, two complementary OP assays were deployed, including dithiothreitol (DTT) and ascorbic acid (AA) assays, to investigate the potential toxicity (as generators of oxidative stress) of respirable fractions (DD4, < 4 μm) of deposited dust (DD500, < 500 μm) in underground low-S and low-pyrite coal mines in Henan Province, Central China. The OPDTT of DD4 is higher than that reported for other types of atmospheric PM, whereas the OPAA of DD4 is similar and/or slightly higher. Cross-correlation and multilinear regression analyses are applied using datasets of major mineral and geochemical patterns in the DD4 samples and the respective OP values to identify the major drivers for OP in respirable coal dust. Thereafter, the patterns of DD4 are compared with those of DD500 and the parent coals to determine the sources of OP-relevant substances. OPDTT is mainly governed by some trace elements (Sb, As, Li, B, Sr, and Pb) and minor minerals (anatase, quartz, siderite), and their synergistic effect may be one of the reasons for the high DTT consumption. For OPAA, quartz, total clay (sum of illite, kaolinite, tobelite, and clinochlore) and Ni, Cr, Co, Si, and S, play an important role in regulating the OPAA of pyrite-free DD4 samples. These OP-relevant substances have three sources: coal dust, which has a similar composition in DD4, DD500, and the parent coal (such as siderite and its associated elements); gangue dust, which does not occur in the parent coal but is widely detected in DD4 and DD500 (such as quartz, kaolinite, and relevant elements); and cement dust (from gunite galleries), which is mainly calcite- and calcite-associated elements.

Simple colorimetric paper assay of acetaminophen, ascorbic acid and phenylephrine in pharmaceutical samples

Simple colorimetric paper assay of acetaminophen, ascorbic acid and phenylephrine in pharmaceutical samples

Polycyclic aromatic hydrocarbons and their oxygenated derivatives in urban aerosol: levels, chemical profiles, and contribution to PM2.5 oxidative potential

The concentrations of polycyclic aromatic hydrocarbons (PAHs) and quinones, a subgroup of oxygenated PAHs (oxy-PAHs), were measured in PM2.5 samples collected during warm (May–June 2019) and cold (February–March 2020) seasons in the city of Bologna, Italy. Total PAHs concentration was nearly double in winter (6.58 ± 1.03 ng m−3) compared with spring (3.16 ± 0.53 ng m−3), following the trend of the PM2.5 mass concentration. Molecular diagnostic ratios suggested that, together with traffic, biomass burning was the dominant emission source contributing to the peaks of concentration of PM2.5 registered in the cold season. Quinone level was constant in both seasons, being 1.44 ± 0.24 ng m−3, that may be related to the increased secondary formation during warm season, as confirmed by the higher Σoxy-PAHs/ΣPAHs ratio in spring than in winter. The oxidative potential (OP) of the PM2.5 samples was assessed using acellular dithiothreitol (DTT) and ascorbic acid (AA) assays. The obtained responses showed a strong seasonality, with higher volume-normalized (OPV) values in winter than in spring, i.e., OPVDTT: 0.32 ± 0.15 nmol min−1 m−3 vs. 0.08 ± 0.03 nmol min−1 m−3 and OPVAA: 0.72 ± 0.36 nmol min−1 m−3 vs. 0.28 ± 0.21 nmol min−1 m−3. Both OPVDTT and OPVAA responses were significantly associated with total PAHs, as a general descriptor of redox-active PAH derivatives, associated with co-emission from burning sources or secondary atmospheric oxidation of parent PAHs. Otherwise, only winter OPVDTT responses showed a significant correlation with total Ʃoxy-PAHs concentration.

Smartphone-assisted multiple-mode assay of ascorbic acid using cobalt oxyhydroxide nanoflakes and carbon quantum dots

A multi-mode detection platform for ascorbic acid (AA) based on cobalt oxyhydroxide nanoflakes (CoOOH) was designed in this study. CoOOH has enzyme-mimicking properties and can oxidize 3,3′,5,5′-tetramethyl benzidine (TMB) into a blue colored oxidation product (TMBox). CoOOH nanoflakes are selectively reduced to Co2+ by AA, which results in the loss of oxidation of CoOOH and a gradual color evolution from blue to colorless and a UV–vis absorption decrease of TMBox. The AA can be detected in the range of 0.2–20 μM with a limit of detection (LOD) of 0.067 μM (UV–vis model). In addition, carbon quantum dots (CQDs) with blue fluorescence were prepared using a one-step hydrothermal method and employed as the signal output. When nanocomposites of CoOOH nanoflakes and CQDs were formed by hybridization, the fluorescence of CQDs was quenched by CoOOH nanoflakes via fluorescence resonance energy transfer (FRET) and readily recovered by AA, representing an “on–off-on” response and a variation in color from black to light blue under a 365-nm UV lamp. The calibration curve was linear in the range of 0.1–30 μM with a limit of detection (LOD) of 0.031 μM (Fluorescence model). Two smartphone-based colorimetric devices were designed for analyzing the chromogenic solutions. The red, green, and blue values of the colored solutions were obtained directly using an Android application (Color Grab). The LOD of two smartphone colorimetry models are 0.16 μM and 0.19 μM, and linear range are 0.5–16 μM, 0.75–20 μM respectively. The multi-mode detection platform was successfully applied to the detection of AA in fruits with acceptable recoveries from 90.5% to 107%, a relative standard deviation (RSD) ranging from 1.6% to 5.0%. Compared with the fluorescence and UV–vis modes, the smartphone-integrated colorimetric platform was found to be simple, portable, fast, and inexpensive.

The oxidative and neurotoxic potentials of the ambient PM2.5 extracts: The efficient multi-solvent extraction method

The health effects of ambient air particulate matter with a diameter of ≤2.5 μm (PM2.5) on the central nervous system are well known and the induced oxidative stress has been shown as their main neuropathologic outcome. Ambient air PM2.5 sampling methods mostly use air sampler systems that collect PM2.5 on filters, which is followed by a PM2.5 extraction approach. Inefficient extraction may lead to compositional bias and unreal interpretation of the results. This study aimed to compare our proposed multi-solvent extraction (MSE) approach for PM2.5 extraction with a conventional aqueous extraction (AqE) method using the analysis of oxidative effects and cytotoxicity in the human neuroblastoma SH-SY5Y cell line. Ambient PM2.5 samples were collected from an urban traffic location in Tehran city, the capital of Iran, using a high-volume sampler. The developed MSE method was proved to have superior advantages over the AqE method including an increased extraction efficiency (as much as 96 against 48% for PMms and PMaq, respectively), and decreased artifacts and compositional biases. Ambient PM2.5, besides PMms and PMaq were analyzed for water-soluble ions, metals, and major elements. Dithiothreitol, ascorbic acid, lipid peroxidation, and cell viability assays on SH-SY5Y cells represented the significantly higher oxidative potential for PMms compared to PMaq. The increased cytotoxicity may occur because of the increased oxidative potential of PMms and possibly is associated with higher efficiency of the MSE over the AqE method for removal of total redox-active PM components.

Ascorbic acid ameliorates corneal endothelial dysfunction and enhances cell proliferation via the noncanonical GLUT1-ERK axis

BackgroundThe pumping function of corneal endothelial cells (CECs) plays a pivotal role in the maintenance of corneal water homeostasis. Corneal endothelial dysfunction (CED) leads to corneal edema and opacity, but with the exception of keratoplasty, no optimal therapeutic strategies have been established for CED. In this study, we aimed to investigate the ameliorative effect of ascorbic acid (AA) on CED and the underlying mechanism of action in the corneal endothelium. MethodsRabbit corneal endothelial damage was induced by anterior chamber injection of benzalkonium chloride (BAK). AA was topically administered to the corneal surface, and the transparency and thickness of the cornea were assessed by external eye photography, slit-lamp photography, and ultrasonic pachymetry. To further analyze the mechanism, rabbit CECs and immortalized human CECs (B4G12 cells) were cultured. A ferric reducing/antioxidant and AA (FRASC) assay was performed to measure the AA concentration. Cell proliferation was evaluated by cell counting and bromodeoxyuridine (BrdU) labeling assays, and protein expression was examined by liquid chromatography–mass spectrometry (LC/MS) and immunoblotting. The involvement of glucose transporter 1 (GLUT1) and phospho-ERK was evaluated via GLUT1-siRNA and phospho-ERK inhibitor (PD98059) treatment. InterpretationWe observed that topical AA ameliorates BAK-induced rabbit corneal endothelial damage. Furthermore, we demonstrated that AA is transported into B4G12 cells via GLUT1, and afterward, AA increases ERK phosphorylation and promotes cell proliferation. Our findings indicate that CEC proliferation stimulated via the noncanonical AA-GLUT1-ERK axis contributes to AA-enhanced healing of CED.

A colorimetric and ratiometric photometric sequential assay for ascorbic acid and alkaline phosphatase in serum based on valence states modulation

The photometric method is widely used in real clinical tests due to its simple operation, low cost and convenient. Many of the reported colorimetric ALP assays so far are non- ratiometric because the detection was based on changes in absorbance at a single wavelength. The development of novel colorimetric and ratiometric assay is of importance for quantitatively measuring target with high accuracy. The challenge in the design of ratiometric photometric assay is that the chromophore must have a significant spectral shift before and after binding to the target. Here, we report a colorimetric and ratiometric photometric sequential assay of AA and ALP based on the complexation between ARS and Cu2+ and redox reaction between AA and Cu2+. The absorption band of ARS centered at 425 nm (yellow color), which could be shifted to 510 nm (red color) upon Cu2+ binding. However, as far as we know, this classic color reaction has not been used to develop a ratiometric photometric method to sequentially detect AA and ALP, although photometric methods based on the regulation of other color reagents with oxidizing metal ions have been reported. The proposed sensing system shows a limit of detection for ALP at 0.24 U L−1 and could be applied for detecting ALP in newborn calf serum. The established sensing system makes a useful contribution to the detection of ALP in complex clinical samples.

"Light-on" Colorimetric Assay for Ascorbic Acid Detection via Boosting the Peroxidase-like Activity of Fe-MIL-88

A label-free "light-on" colorimetric assay for ascorbic acid (AA) determination is unprecedentedly devised by regulating the intrinsic peroxidase-mimetic activity of the Fe-MIL-88. AA can reduce Fe(III) presented in Fe-MIL-88 to Fe(II), which will dramatically promote the hydroxyl radicals (·OH) conversion efficiency of H2O2 through a Fenton reaction, and effectually accelerate the Fe-MIL-88 catalyzed chromogenic reaction of 3,3′,5,5′-tetramethylbenzidine (TMB)-H2O2. Redox reaction between AA and H2O2 also can produce ·OH and promote this chromogenic reaction. Thus, quantification of AA is realized via determining the enhanced colorimetric signals. The linear range is 0.5 − 40 μM with a detection limit of 0.12 μM. Furthermore, the straightforward yet effective colorimetric strategy with the merits of simplicity, cost-effectiveness, high accuracy, specificity, and sensitivity is widely utilized to determine the concentrations of AA in serological tests.

Atmospheric conditions and composition that influence PM2.5 oxidative potential in Beijing, China.

Epidemiological studies have consistently linked exposure to PM2.5 with adverse health effects. The oxidative potential (OP) of aerosol particles has been widely suggested as a measure of their potential toxicity. Several acellular chemical assays are now readily employed to measure OP; however, uncertainty remains regarding the atmospheric conditions and specific chemical components of PM2.5 that drive OP. A limited number of studies have simultaneously utilised multiple OP assays with a wide range of concurrent measurements and investigated the seasonality of PM2.5 OP. In this work, filter samples were collected in winter 2016 and summer 2017 during the atmospheric pollution and human health in a Chinese megacity campaign (APHH-Beijing), and PM2.5 OP was analysed using four acellular methods: ascorbic acid (AA), dithiothreitol (DTT), 2,7-dichlorofluorescin/hydrogen peroxidase (DCFH) and electron paramagnetic resonance spectroscopy (EPR). Each assay reflects different oxidising properties of PM2.5, including particle-bound reactive oxygen species (DCFH), superoxide radical production (EPR) and catalytic redox chemistry (DTT/AA), and a combination of these four assays provided a detailed overall picture of the oxidising properties of PM2.5 at a central site in Beijing. Positive correlations of OP (normalised per volume of air) of all four assays with overall PM2.5 mass were observed, with stronger correlations in winter compared to summer. In contrast, when OP assay values were normalised for particle mass, days with higher PM2.5 mass concentrations (μgm−3) were found to have lower mass-normalised OP values as measured by AA and DTT. This finding supports that total PM2.5 mass concentrations alone may not always be the best indicator for particle toxicity. Univariate analysis of OP values and an extensive range of additional measurements, 107 in total, including PM2.5 composition, gas-phase composition and meteorological data, provided detailed insight into the chemical components and atmospheric processes that determine PM2.5 OP variability. Multivariate statistical analyses highlighted associations of OP assay responses with varying chemical components in PM2.5 for both mass- and volume-normalised data. AA and DTT assays were well predicted by a small set of measurements in multiple linear regression (MLR) models and indicated fossil fuel combustion, vehicle emissions and biogenic secondary organic aerosol (SOA) as influential particle sources in the assay response. Mass MLR models of OP associated with compositional source profiles predicted OP almost as well as volume MLR models, illustrating the influence of mass composition on both particle-level OP and total volume OP. Univariate and multivariate analysis showed that different assays cover different chemical spaces, and through comparison of mass- and volume-normalised data we demonstrate that mass-normalised OP provides a more nuanced picture of compositional drivers and sources of OP compared to volume-normalised analysis. This study constitutes one of the most extensive and comprehensive composition datasets currently available and provides a unique opportunity to explore chemical variations in PM2.5 and how they affect both PM2.5 OP and the concentrations of particle-bound reactive oxygen species.

Stabilization and attributive amelioration of sugarcane juice by naturally derived preservatives using aonla and moringa extract.

Sugarcane juice (SCJ) is a cheap, popular, and very nutritious beverage served at roadside stalls in many countries during harvesting season. The juice is normally consumed immediately after extraction as fermentation sets within a few hours of extraction. Preserving the raw sugarcane juice is always challenging because it spoils within a few hours of extraction due to fermentation. Therefore, the bottling, distribution, and marketing of sugarcane are difficult tasks. The present study was designed to investigate the effect of naturally derived preservatives using aonla extract (AE) and moringa extract (ME) in different proportions (0%, 3%, 5%, and 7%) for the preservation of SCJ during 21 days of the storage period at 4 ± 2°C temperature. The effect of extracts and storage time were analyzed on physicochemical parameters, bioactive compounds, enzymatic, microbiological, and sensory analyses of SCJ. A significant improvement in pH of 5% AE (5.30 ± 0.06) and 5% ME (5.36 ± 0.02) was observed at 21 days as compared to control (5.89 ± 0.02). The total phenolic contents in 7% ME were also observed to be retained (4.4 ± 0.02 mg GAE/mL) at 21 days as compared to control (2.65 ± 0.03 mg GAE/mL). Other physicochemical and phytochemical analyses including titratable acidity, total soluble solids, total flavonoids, ascorbic acid, 2,2‐Diphenyl‐2‐picrylhydrazyl (DPPH), and ferric reducing antioxidant power assay (FRAP) also indicated that SCJ treated with ME was significantly stable (p < .05) regarding quality parameters, nutritional and sensory attributes at different storage intervals. These findings may be practical for the large‐scale production, storage, and marketing of SCJ products.

Dip-Type Paper-Based Analytical Device for Straightforward Quantitative Detection without Precise Sample Introduction.

The development of low-cost, user-friendly paper-based analytical devices (PADs) that can easily measure target chemicals is attracting attention. However, most PADs require manipulation of the sample using sophisticated micropipettes for quantitative analyses, which restricts their user-friendliness. In addition, immobilization of detection molecules to cellulose fibers is essential for achieving good measuring ability as it ensures the homogeneity of color development. Here, we have described a dip-type PAD that does not require pipette manipulation for sample introduction and immobilization of detection molecules to cellulose fibers and its application to ascorbic acid (AA) and pH assays. The PAD consisted of a dipping area and two channels, each with two detection zones. The developed PADs show color distribution in the two detection zones depending on the sample flow from the dipping area. In comparison with a PAD that has one detection zone at the end of the channel, our developed device achieved higher sensitivity (limit of detection (LOD), 0.22 mg/mL) and reproducibility (maximum coefficient of variation (CV), 2.4%) in AA detection. However, in pH detection, the reproducibility of the PAD with one detection zone at the end of the channel (maximum CV, 21%) was worse than that with two zones (maximum CV, 11%). Furthermore, a dipping time over 3 s did not affect color formation or calibration curves in AA detection: LODs at 3 and 30 s dipping time were 18 and 5.8 μg/mL, respectively. The simultaneous determination of AA and pH in various beverages was performed with no significant difference compared to results of the conventional method.

Effect of filter extraction solvents on the measurement of the oxidative potential of airborne PM2.5

Solvent extraction of PM2.5 samples collected on the filter is a preliminary step for assessing the PM2.5 oxidative potential (OP) using cell-free assays, as the dithiothreitol (DTT) and the ascorbic acid (AA) assays. In this study, we evaluated the effect of the solvent choice by extracting ambient PM2.5 samples with different solvents: methanol, as organic solvent, and two aqueous buffers, i.e., phosphate buffer (PB) and Gamble’s solution (G), as a lung fluid surrogate solution. Both the measured volume-based OPVDTT and OPVAA responses varied for the different extraction methods, since methanol extraction generated the lowest values and phosphate buffer the highest. Although all the tested solvents produced intercorrelated OPVDTT values, the phosphate buffer resulted the most useful for OPDTT assessment, as it provided the most sensible measure (nearly double values) compared with other extractions. The association of the measured OPV values with PM chemical composition suggested that oxidative properties of the investigated PM2.5 samples depend on both transition metals and quinones, as also supported by additional experimental measurements on standard solutions of redox-active species.

Poly(methacrylic acid)‐Stabilized Silver Nanoclusters as Colorimetric Sensors for the Rapid and Sensitive Detection of Ascorbic Acid

AbstractA simple, rapid, and sensitive colorimetric assay for ascorbic acid (AA) was developed based on poly(methacrylic acid)‐stabilized silver nanoclusters (PMAA‐AgNCs). The AgNCs were prepared via a single‐step synthesis exploiting PMAA as both a reducing agent and a stabilizer. The sensing capability of this method is based on the color change associated with the growth in size of AgNCs, which turn into nanoparticles, resulting from the reduction of free Ag+ present in AgNCs solution to Ag0 by AA. In the presence of AA, an apparent surface plasmon resonance absorption peak of the silver nanoparticles was observed at 430 nm, and its intensity increased linearly with AA concentration, so that a solution color change could be observed with the naked eye. The proposed method exhibited a linear working concentration range of 0.25–100 μM and a detection limit of 95 nM. The sensor was employed to determine AA concentration in fruit juice and vitamin C tablet samples, affording results of high accuracy.

Electrochemical synthesis of carbon dots with a Stokes shift of 309 nm for sensing of Fe3+ and ascorbic acid

Preparation of carbon dots (C dots) with strong emission at long wavelengths is an ongoing goal to their advanced applications, especially in bioanalysis. For sensing Fe3+ and ascorbic acid (AA), we prepared C dots with a large Stokes shift using o-phenylenediamine (OPD) as the carbon source through an electrochemical method. During the electrolysis, OPD undergoes polymerization, carbonization, and passivation at the platinum anode to form C dots. These C dots were characterized by UV–Vis spectroscopy, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and FT-IR spectroscopy. They are composed of C, N, O, H elements, having a maximum of emission at 570 nm and a supreme excitation at 261 nm, with a Stokes shift of 309 nm. A new emission at 350 nm emerged with their exposure to Fe3+ and the intensity rises upon increasing Fe3+, while the emission intensity at 570 nm decreases. Thus, dissimilar to the usual quenching strategy, a novel ratiometric fluorescent sensor based on the fluorescence intensity ratio (F350/F570) of the C dots at 350 nm and 570 nm has been developed for quantitation of Fe3+ with a limit of detection (LOD) of 0.16 μM and high selectivity toward Fe3+ against K+, Cu2+, and Fe2+. With evidence of decreased C–NC and C–O/N–O in XPS and increased content of CO/NO and N–H, we suggested the complexation of Fe3+ with the surface groups led to the changes in chemical bonds accounting for their optical property variation. Furthermore, AA can quench the fluorescence of C dots at 570 nm and Fe3+-treated C dots (incubated with 50 μM Fe3+) at 350 nm by a static mechanism. Accordingly, two assays toward AA were developed with LODs of 0.12 μM and 0.32 μM by using C dots and Fe3+-treated C dots, respectively. Especially, both AA assays exhibited excellent selectivity under various substances including those with strong reducing ability such as pyrogallic acid, sodium citrate, tea polyphenol, and dithiothreitol. The applications of the assays were validated with the quantitation of Fe3+ in urine and AA in beverages. Electrochemical method is a significant approach to develop novel C dots even using the same carbon sources as in other methods.

Spatial mapping and size distribution of oxidative potential of particulate matter released by spatially disaggregated sources

The ability of particulate matter (PM) to induce oxidative stress is frequently estimated by acellular oxidative potential (OP) assays, such as ascorbic acid (AA) and 1,4-dithiothreitol (DTT), used as proxy of reactive oxygen species (ROS) generation in biological systems, and particle-bound ROS measurement, such as 2′,7′-dichlorodihydrofluorescein (DCFH) assay. In this study, we evaluated the spatial and size distribution of OP results obtained by three OP assays (OPAA, OPDCFH and OPDTT), to qualitative identify the relative relevance of single source contributions in building up OP values and to map the PM potential to induce oxidative stress in living organisms. To this aim, AA, DCFH and DTT assays were applied to size-segregated PM samples, collected by low-pressure cascade impactors, and to PM10 samples collected at 23 different sampling sites (about 1 km between each other) in Terni, an urban and industrial hot-spot of Central Italy, by using recently developed high spatial resolution samplers of PM, which worked in parallel during three monitoring periods (February, April and December 2017). The sampling sites were chosen for representing the main spatially disaggregated sources of PM (vehicular traffic, rail network, domestic heating, power plant for waste treatment, steel plant) present in the study area. The obtained results clearly showed a very different sensitivity of the three assays toward each local PM source. OPAA was particularly sensitive toward coarse particles released from the railway, OPDCFH was sensible to fine particles released from the steel plant and domestic biomass heating, and OPDTT was quite selectively sensitive toward the fine fraction of PM released by industrial and biomass burning sources.

Extension of postharvest shelf life of strawberries (Fragaria ananassa) using a coating of chitosan-whey protein isolate conjugate.

Chitosan and whey protein isolate (WPI) conjugate films were prepared as a novel matrix for encapsulating and extending the postharvest shelf life of strawberries. Film forming solutions of chitosan, WPI, and chitosan-WPI conjugate were mixed with glycerol, casted for films at 60±2°C and assessed for their colour, water vapour and oxygen transfer rate, textural, functional groups and secondary structure, thermal, crystallinity, and antioxidant properties. Chitosan-WPI conjugate films were applied as an edible coating on strawberries, and studied for storage stability at 5°C and 20°C by assessing physical and biochemical parameters. A considerable reduction in colour indices, weight loss, pH and titratable acidity, reducing sugars, ascorbic acid, total phenolics, DPPH and ABTS assay was noted in the coated strawberries over the control at both the studied temperatures. The control strawberries had a shelf life of 5 and 3days, whereas coating enhanced the shelf life of strawberries to 8 and 5days when stored at 5°C and 20°C, respectively.