Ascorbic Acid Assay Research Articles

Hydrogen-Bonded Organic Framework Enhanced Antifouling Property for Efficient In Situ Electrochemical Assay of Cerebral Ascorbic Acid.

Accurate determination of cerebral ascorbic acid (AA) is crucial for understanding ischemic stroke (IS) related pathological events. Carbon fiber microelectrodes (CFEs) have proven to be robust tools with high sensitivity toward AA, however, they face ongoing challenges for in situ measurement due to the non-specific adsorption of proteins in brain tissue. In this study, the hydrogen-bonded organic framework PFC-71 is synthesized and modified on CFEs through π-π stacking interactions with carboxylated carbon nanotubes (CNT-COOH). It is found that the gating effect and hydrophilicity of PFC-71 provided the CFE with excellent antibiofouling properties. As a result, AA exhibited a low oxidation potential of -30mV on the CFE/CNT-COOH/PFC-71, even in the presence of 20mgmL-1 bovine serum albumin. Given the structural advantages of CFE/CNT-COOH/PFC-71, a ratiometric electrochemical strategy for AA is established, enabling the in situ assay of cerebral AA in a middle cerebral artery occlusion (MCAO) model with high accuracy and stability.

Chemical speciation and oxidative potential of PM10 in different residential microenvironments: Bedroom, living room and kitchen

Exposure to particulate matter (PM) and its chemical constituents in residential microenvironments has become a major health concern worldwide. The oxidative potential (OP) has been proposed as a metric for estimating the PM capacity to induce oxidative stress and, consequently, health effects. In the present study, PM10 was daily monitored simultaneously in the bedroom, living room and kitchen of three dwellings for one week in a small town of Portugal, to perform a detailed characterisation of its organic and inorganic constituents and the determination of the OP. Bedrooms (B) were found to be a hotspot of PM10 concentrations (B1 = 22.7 μg m−3; B2 = 19.5 μg m−3; B3 = 68.1 μg m−3). PM10-bound elements varied significantly between microenvironments in all dwellings. Lower molecular weight polycyclic aromatic hydrocarbons (PAHs) were found to be between 14 and 72 times higher than high molecular weight PAHs in bedrooms. The mean volume-normalised OP determined by the dithiothreitol and ascorbic acid assays varied within the 0.01–0.38 nmol min−1 m−3 and 0.03–0.53 nmol min−1 m−3 ranges, respectively. Quinones, oxy-aromatic, aromatic and alkyl-aromatic compounds stood out in bedrooms. Strong and significantly positive relationship between OP and black carbon, Cu and Br were observed, indicating common redox active species mainly associated with traffic emissions. Sr, Fe, Zn and Zr presented higher concentrations in dwelling 3, exhibiting excellent positive correlation with OP, indicating that the Sahara dust intrusion recorded in that house may have contributed to the formation of more redox active species thought to drive antioxidant depletion responses.

Gaseous and aerosol emissions from open burning of tree pruning and hedge trimming residues: Detailed composition and toxicity

Gaseous and PM10 samples were collected during the open burning of pruning residues (olive branches and garden waste) and characterised by distinct analytical techniques to obtain comprehensive chemical emission profiles. Oxidative potential (dithiothreoitol and ascorbic acid assays) and cell viability tests were also performed with the aim of evaluating aerosol toxicity. Emission factors (EFs) were as follows (g kg−1 biofuel, dry basis): 1537–1672 for CO2, 41.9–80 for CO, 2.74–6.6 for CH4, 0.89–3.51 for ethane, 0.79–1.78 for ethylene and 0.56–3.47 for formaldehyde. Emissions of PM10, organic carbon (OC) and elemental carbon (EC) were in the ranges 8–41, 3–18, and 0.4–1.5 g kg−1 biofuel, dry basis, respectively. OC accounted for 35–45% of the total PM10 mass, while EC contributed between around 3% and 5%. WSOC/OC ratios varied from 0.4 to 0.6, revealing that a substantial portion of the carbon emitted was hydrosoluble. Water soluble ions constituted around 8–21% of the PM10 mass, with potassium and chloride as the most abundant ions in all samples. Levoglucosan, widely used a reliable biomass burning tracer, was found in significant amounts in all samples (up to 1.2% of the PM10 mass). Retene, generally pointed out as a biomass combustion biomarker, was the predominant PAH. WSOC and some PAHs showed significant positive correlations with the intrinsic OP measured with the DTT assay, while the OPAA was significantly correlated with some trace metals, such as Fe or Ni. All samples significantly reduced the viability of alveolar epithelial cells.

Fe7S8 nanosheets- catalyzed colorimetric and fluorescence dual ratio sensing for high selectivity detection of ascorbic acid

By using Fe7S8 nanosheets (NSs) as catalyst, O-phenylenediamine (OPD) as chromogenic substrate, H2O2 as oxidant, and ascorbic acid (AA) as regulator, a dual ratio colorimetric and fluorescence sensing system for determining AA was constructed. The inherent peroxidase like activity of Fe7S8 NSs enables it to catalyze the oxidation of OPD in the existence of H2O2, resulting in the formation of yellow-colored 2, 3-diaminophenazine (DAP) with a characteristic absorption peak at 450 nm and a fluorescence emission peak at 560 nm. However, the presence of AA could suppress the oxidation of OPD and induce the generation of quinoxaline derivative (QXD) 3-(dihydroxyethyl) furo [3,4-b] quinoxaline-1-one with absorption and fluorescence emission peaks located at 345 and 435 nm, respectively. Thus, employing the absorption of QXD at 345 nm and emission at 435 nm as the reporting signals, and the absorption of DAP at 450 nm and emission at 560 nm as the reference signals, a ratio colorimetric (A345/A450) and ratio fluorescence (F435/F560) dual signal detection method for AA was developed. Under the optimized conditions, the value of A345/A450 was found to be linear with AA concentration in the ranges of 1.0–40 μM and 40–100 μM, and the value of F435/F560 was strongly correlated with AA concentration in the ranges of 1.0–30 μM and 30–100 μM. When applied for the assay of AA in human serum samples, an acceptable recovery ranging from 93.1 to 106.6 % was obtained, confirming the potential of the sensing system in practical applications.

Intrinsic Peroxidase-like Activity of Polystyrene Nanoplastics Mediates Oxidative Stress.

Nanoplastics represent a global environmental concern due to their ubiquitous presence and potential adverse impacts on public and environmental health. There is a growing need to advance the mechanistic understanding of their reactivity as they interact with biological and environmental systems. Herein, for the first time, we report that polystyrene nanoplastics (PSNPs) have intrinsic peroxidase-like activity and are able to mediate oxidative stress. The peroxidase-like activity is dependent on temperature and pH, with a maximum at pH 4.5 and 40 °C. The catalytic activity exhibits saturation kinetics, as described by the Michaelis-Menten model. The peroxidase-like activity of PSNPs is attributed to their ability to mediate electron transfer from peroxidase substrates to H2O2. Ozone-induced PSNP aging can introduce oxygen-containing groups and disrupt aromatic structures on the nanoplastic surface. While ozonation initially enhances peroxidase-like activity by increasing oxygen-containing groups without degrading many aromatic structures, extended ozonation destroys aromatic structures, significantly reducing this activity. The peroxidase-like activity of PSNPs can mediate oxidative stress, which is generally positively correlated with their aromatic structures, as suggested by the ascorbic acid assay. These results help explain the reported oxidative stress exerted by nanoplastics and provide novel insights into their environmental and public health implications.

Strong synergistic and antagonistic effects of quinones and metal ions in oxidative potential (OP) determination by ascorbic acid (AA) assays

A key challenge in oxidative potential (OP) assays is to accurately assess the cumulative impact of redox-active aerosol species rather than only their individual effects. This study investigates the OP of single and combined mixtures of 1,2-naphthoquinone (1,2-NQ), 1,4-naphthoquinone (1,4-NQ), 9,10-phenanthrenequinone (9,10-PQ), 1,4-benzoquinone (1,4-BQ), Cu, Fe, Mn, and Zn in standard ascorbic acid (OPAA) and the synthetic respiratory tract lining fluid (OPRTLF) assays. In both OPAA and OPRTLF, binary mixtures showed additive and synergistic effects in the presence of 1,2-NQ. The mixture of Cu and Zn showed substantial synergisms in both assays, while the mixtures in the absence of 1,2-NQ primarily induced antagonistic effects. For the first time, we propose linear equations to improve the prediction of OP values by considering the impacts of synergistic and antagonistic effects. Under this approach, we observed that the potential effects caused by binary mixtures in ambient particulate matter (PM) samples could account for up to 68 % of the PM-OP values in Fez, Morocco (OPmAA: 0.34 nmol min−1 µg−1 and OPmRTLF: 0.18 nmol min−1 µg−1). The present study improves the understanding of effects of chemical interaction of potentially toxic substances that are important in the understanding of PM-induced oxidative stress in the human body.

Understand the Stabilization Engineering of Ascorbic Acid, Mapping the Scheme for Stabilization, and Advancement.

Vitamin C is extensively used in cosmetic formulation, howbeit stability is the supreme demerit that limits its use in beautifying products. Numerous techniques are being employed to inhibit the degradation of vitamin C caused by formulation components to facilitate the use in skin rejuvenating products. Diverse materials are being exercised in formulation to stabilize the ascorbic acid and ingredients selected in this formulation composition help for stabilization. The initial stable prototype is developed and further optimization is accomplished by applying the design of experiment tools. The stable pharmaceutical formulations were evaluated for the evaluation parameters and designated as two optimized formulations. The analytical method for the assay of ascorbic acid from the United States pharmacopeia and the related substance method from European pharmacopeia has been modified to be used for cream formulation. The DoE design exhibited that the stability of formulation is impacted by citric acid and tartaric acid but not by propylene glycol and glycerin. The analysis results of topical formulations for the evaluation parameter exhibited satisfactory results. The in-vitro release study method has been developed, optimized, and validated to fit the analysis. The in-vitro studies have been performed for selected compositions and both the formulation has similar kinds of release patterns. The stability study as per ICH guidelines exhibited that the product is stable for accelerated, intermediate, and room-temperature storage conditions. The optimized formulation shows constant release and permeation of ascorbic acid through the skin. The formulation with the combinations of citric acid, tartaric acid, and tocopherol is more stable and the degradation of vitamin C has been reduced significantly. The beaucoup strategies in the unique composition help to protect the degradation by inhibiting the multitudinous degradation pathways.

Unveiling the optimal regression model for source apportionment of the oxidative potential of PM10

Abstract. The capacity of particulate matter (PM) to generate reactive oxygen species (ROS) in vivo leading to oxidative stress is thought to be a main pathway in the health effects of PM inhalation. Exogenous ROS from PM can be assessed by acellular oxidative potential (OP) measurements as a proxy of the induction of oxidative stress in the lungs. Here, we investigate the importance of OP apportionment methods for OP distribution by PM10 sources in different types of environments. PM10 sources derived from receptor models (e.g., EPA positive matrix factorization (EPA PMF)) are coupled with regression models expressing the associations between PM10 sources and PM10 OP measured by ascorbic acid (OPAA) and dithiothreitol assay (OPDTT). These relationships are compared for eight regression techniques: ordinary least squares, weighted least squares, positive least squares, Ridge, Lasso, generalized linear model, random forest, and multilayer perceptron. The models are evaluated on 1 year of PM10 samples and chemical analyses at each of six sites of different typologies in France to assess the possible impact of PM source variability on PM10 OP apportionment. PM10 source-specific OPDTT and OPAA and out-of-sample apportionment accuracy vary substantially by model, highlighting the importance of model selection according to the datasets. Recommendations for the selection of the most accurate model are provided, encompassing considerations such as multicollinearity and homoscedasticity.

Biogenic synthesis of silver nanoparticle from flower extract of Wedelia chinensis and their antibacterial and antioxidant activity

Wedelia chinensis is a medicinal herb of the family Asteraceae. Green synthesis of silver nanoparticles (AgNPs) was done by using flower extract of Wedelia chinensis. Optimum conditions for AgNPs synthesis were as such: flower extract and AgNO3 (0.1 M) were taken in 1:9 ratio; temperature- 30 °C; reaction time- 12 h. UV-Visible spectra of the synthesized nanoparticle showed maximum absorption at 400 nm. Crystalline nature of silver nanoparticle was confirmed by XRD pattern. Through TEM, average size of AgNPs was observed as 51.2 nm. FTIR indicated participation of various functional groups of flower extract in the formation of nanoparticles. In DLS study, AgNPs of size 121 nm showed 100% intensity. Zeta potential was recorded as −1.24 mV. Strong peak of silver was observed in EDX study. AgNPs alone showed effective inhibition against all pathogenic bacteria taken as test organisms, but its combination with the antibiotics showed considerable enhancement in antibacterial activity. Inhibition for methicillin resistant Staphylococcus aureus (MRSA) was maximum when nanoparticles were taken in the combination of antibiotics and the extract. Significant antioxidant potential of AgNPs were observed in DPPH, ascorbic acid and DNA nicking assays. Thus, AgNPs of Wedelia chinensis flower extract showed significant medicinal efficacy as antioxidant and antibacterial.

Iron modified hydrogen-bonded organic framework as fluorescent sensor for ascorbic acid detection

Herein, iron modified hydrogen-bonded organic framework (Fe-HOF) was successfully prepared by introducing the yellow-green fluorescent ligand 2,5-dihydroxyterephthalic acid into HOF and then modifying Fe3+. A simple turn-on fluorescence strategy is proposed for the detection of ascorbic acid (AA) based on Fe-HOF. Fe3+ could effectively quench fluorescence emission of HOF. In the presence of AA, Fe3+ was reduced to Fe2+, which led to the fluorescence recovery of HOF, thus realizing the fluorescence quantitative detection of AA. These fluorescence responsive behaviors of Fe-HOF ensure fluorescence assay of AA within 0.5 − 8 μM, along with a limit of detection (LOD) of 0.14 μM. The sensing platform could realize the rapid detection of ascorbic acid in vitamin C pills, tablets and beverages in the detection of ascorbic acid with good recoveries.

Oxidative potential of the inhalation bioaccessible fraction of PM10 and bioaccessible concentrations of polycyclic aromatic hydrocarbons and metal(oid)s in PM10

Atmospheric particulate matter (PM) has been related to numerous adverse health effects in humans. Nowadays, it is believed that one of the possible mechanisms of toxicity could be the oxidative stress, which involves the development of reactive oxygen species (ROS). Different assays have been proposed to characterize oxidative stress, such as dithiothreitol (DTT) and ascorbic acid (AA) acellular assays (OPDTT and OPAA), as a metric more relevant than PM mass measurement for PM toxicity. This study evaluates the OP of the bioaccessible fraction of 65 PM10 samples collected at an Atlantic Coastal European urban site using DTT and AA assays. A physiologically based extraction (PBET) using Gamble’s solution (GS) as a simulated lung fluid (SLF) was used for the assessment of the bioaccessible fraction of PM10. The use of the bioaccessible fraction, instead of the fraction assessed using conventional phosphate buffer and ultrasounds assisted extraction (UAE), was compared for OP assessment. Correlations between OPDTT and OPAA, as well as total and bioaccessible concentrations of polycyclic aromatic hydrocarbons (PAHs) and metal(oid)s, were investigated to explore the association between those compounds and OP. A correlation was found between both OP (OPDTT and OPAA) and total and bioaccessible concentrations of PAHs and several metal(oid)s such as As, Bi, Cd, Cu, Ni, and V. Additionally, OPDTT was found to be related to the level of K+.

Electrochemical Sensing of Vitamin C Using Graphene/Poly-Thionine Composite Film Modified Electrode

Background: Gastric irritation and kidney problems occur due to excess ascorbic acid content, whereas the lack of ascorbic acid in the human body leads to poor wound healing, muscle degeneration, and anemia. Objectives: Herein, we report the development of an electrochemical sensor for the detection of ascorbic acid using poly-thionine/ graphene (P-Th/Gr) modified glassy carbon electrode (GCE) in 0.1 M phosphate buffer solution (PBS) (pH 7.4). Electrostatically fused graphene affixed with poly-thionine was successfully illustrated for effective voltammetric sensing of ascorbic acid. Methodology: FE-SEM indicated the blended edge of a 2D graphene sheet with a deposited thin layer of polymer, which confirmed the formation of a poly-thionine/graphene composite. The cyclic voltammetry (CV) technique was utilized for the electrochemical assay of ascorbic acid (AsA, Vitamin C). Results: With the increased concentrations of AsA, the oxidation peak current of ascorbic acid increased at 0.0 V, and the overpotential showed a decrease compared to bare GCE. The effect of scan rate on cyclic voltammograms was recorded with 500 μM of ascorbic acid from 10 mV/s to 250 mV/s, which indicated that AsA oxidation is a diffusion-controlled process on poly-thionine/ graphene-modified electrode. Conclusion: It was concluded that a poly-thionine/graphene composite-based sensor could be useful for the determination of ascorbic acid in various biological samples.

Levels of Dry Deposition Submicron Black Carbon on Plant Leaves and the Associated Oxidative Potential

There is a need for monitoring air pollution associated with black carbon (BC) using a passive monitor is required in remote areas where the measurements are absent. In this pilot study, we developed a quantitative method to determine dry deposition submicron BC using dual-wavelength ultraviolet–visible spectroscopy. Furthermore, we measured the levels of dry deposition BC on plant leaves from 30 plant species located in urban Nanjing using the established method. The oxidative potential of BC on plant leaves as passive bio-monitoring samplers was assessed. The concentrations of black carbon (BC) on tree leaves varied from 0.01 to 1.6 mg m−2. Significant differences in levels of BC across leaves from different tree types were observed. The values of oxidative potential in deposited particles of leaf samples were observed to be in the range of 33–46 nmol min−1 mg−1 using the dithiothreitol (DTT) assay and 18–32 nmol min−1 mg−1 using the ascorbic acid (AA) assay, respectively. In comparison, the oxidative potential of BC-dominated mass in water extracts of leaf samples was in the range of 5–35 nmol min−1 mg−1 measured using the DTT assay and 2 to 12 nmol min−1 mg−1 using the AA assay, respectively. We found variations in the levels of OP across the leaves of different tree types were not large, while the levels of OP in terms of BC-dominated mass varied greatly. These results indicate that the established method with dual-wavelength ultraviolet–visible spectroscopy could provide a simple tool to determine submicron BC in plant leaves of the passive monitor.

Miniaturized ascorbic acid assay platform based on point discharge atomic emission spectrometry coupling with gold filament enrichment

BackgroundMiniaturized microplasma-based atomic emission spectrometry (AES) has been extensively used for element analysis in recent years due to the advantages of low power consumption, low gas consumption, relatively low manufacturing and running cost, and the potential for real-time and field analysis. However, few applications in bioassay detection have been reported based on microplasma AES systems because of their relatively low sensitivity and the absence of indirect analytical strategies. It is still a challenge to develop a simple, sensitive, and portable microplasma-based AES bioassay approach. ResultsIn this work, a portable analytical system was designed based on point discharge chemical vapor generation atomic emission spectrometry (PD-CVG-AES) coupling with gold filament enrichment. The detection of ascorbic acid (AA) was realized indirectly by means of the highly sensitive analysis of Hg2+. The measurement was based on Ag + can decrease the concentration of Hg2+ by forming Ag–Hg amalgam in the presence of the reductant SnCl2, while AA can pre-reduce Ag + to Ag0, leading to the generation of silver nanoparticles (Ag NPs). The pre-reduce procedure can decrease the generation of Ag–Hg amalgam, resulting in the recovery of Hg2+ signal. The dissociative Hg2+ was further detected by PD-CVG-AES combination of gold filament enrichment, which significantly improved the detection sensitivity for both Hg2+ and AA. Under optimal conditions, the limit of detection (LOD) of AA is as low as 19 nM with a relative standard deviation (RSD, n = 5) of 0.7 %. SignificanceThe developed novel analytical strategy obviously broadens the application of microplasma-based AES, and it is well demonstrated by the determination of AA in several traditional Chinese medicines (TCMs), offering a higher level of sensitivity compared to current AA detection techniques. It has potential for future application in point-of-care testing (POCT) assays.

Contribution of chemical composition to oxidative potential of atmospheric particles at a rural and an urban site in the Po Valley: Influence of high ammonia agriculture emissions

The present study investigates the chemical composition and oxidative potential (OP) of PM10 particles at two sites in the Po Valley (Norther Italy), with the aim of evidence the impact of high level of atmosphere ammonia (NH3). Field measurements were conducted in a rural location (Bertonico) close to farms strongly impacted by high ammonia emissions from agriculture and livestock husbandry. The urban site was in the metropolitan area of Milan. The NH3 concentrations observed at the rural site were about 5 times higher than those at the urban location, generating higher levels of secondary inorganic aerosol (ΣSIA) at Bertonico (16.6 ± 6.33 μg m−3) than at Milan 12.6 ± 4.93 μg m−3. The oxidative potential measured with the ascorbic acid assay (OPAAV) was almost triple in Milan than at Bertonico, namely 1.48 ± 1.08 nmol min−1 m−3 and 0.44 ± 0.23 nmol min−1 m−3, respectively, while the measured OPDTTV responses were similar at both sites, close to ∼ 0.5 ± 0.3 nmol min−1 m−3. These results suggested that the SIA components don't significantly contribute to the PM10 oxidative reactivity, although they account for most of the PM10 mass. Despite such an OP-inactivity, the SIA components resulted significantly correlated with both OPAAV and OPDTTV responses. This may be likely due to their inter-correlation with other redox-active components, such as the secondary organic species, which are synergically produced along with the SIA formation. In addition, an increase in the metals reactivity towards the OP assays, may be associated with the PM10 acidic environment produced by enhanced HNO3 and H2SO4 levels. Therefore, the contribution of the SIA to PM oxidative toxicity cannot be ignored in assessing health risk associated with PM exposure.

Oxidative potential in rural, suburban and city centre atmospheric environments in central Europe

Abstract. Oxidative potential (OP) is an emerging health-related metric which integrates several physicochemical properties of particulate matter (PM) that are involved in the pathogenesis of the diseases resulting from exposure to PM. Daily PM2.5-fraction aerosol samples collected in the rural background of the Carpathian Basin and in the suburban area and centre of its largest city of Budapest in each season over 1 year were utilised to study the OP at the related locations for the first time. The samples were analysed for particulate matter mass, main carbonaceous species, levoglucosan and 20 chemical elements. The resulting data sets were subjected to positive matrix factorisation to derive the main aerosol sources. Biomass burning (BB), suspended dust, road traffic, oil combustion mixed with coal combustion and long-range transport, vehicle metal wear, and mixed industrial sources were identified. The OP of the sample extracts in simulated lung fluid was determined by ascorbic acid (AA) and dithiothreitol (DTT) assays. The comparison of the OP data sets revealed some differences in the sensitivities of the assays. In the heating period, both the OP and PM mass levels were higher than in spring and summer, but there was a clear misalignment between them. In addition, the heating period : non-heating period OP ratios in the urban locations were larger than for the rural background by factors of 2–4. The OP data sets were attributed to the main aerosol sources using multiple linear regression with the weighted least squares approach. The OP was unambiguously dominated by BB at all sampling locations in winter and autumn. The joint effects of motor vehicles involving the road traffic and vehicle metal wear played the most important role in summer and spring, with considerable contributions from oil combustion and resuspended dust. In winter, there is temporal coincidence between the most severe daily PM health limit exceedances in the whole Carpathian Basin and the chemical PM composition causing larger OP. Similarly, in spring and summer, there is a spatial coincidence in Budapest between the urban hotspots of OP-active aerosol constituents from traffic and the high population density in central quarters. These features offer possibilities for more efficient season-specific air quality regulations focusing on well-selected aerosol sources or experimentally determined OP, rather than on PM mass in general.

Effects of personal exposure to the oxidative potential of PM2.5 on oxidative stress biomarkers in pregnant women

Oxidative stress is a prominent pathway for the health effects associated with fine particulate matter (PM2.5) exposure. Oxidative potential (OP) of PM has been associated to several health endpoints, but studies on its impact on biomarkers of oxidative stress remains insufficient. 300 pregnant women from the SEPAGES cohort (France) carried personal PM2.5 samplers for a week and OP was measured using ascorbic acid (AA) and dithiothreitol (DTT) assays, and normalized by 1) PM2.5 mass (OPm) and 2) sampled air volume (OPv). A pool of three urine spots collected on the 7th day of PM sampling was analyzed for biomarkers, namely 8-hydroxy-2-deoxyguanosine (8-OHdG), malondialdehyde (MDA) and 8-isoprostaglandin-F2α (8-isoPGF2α). Associations were investigated using adjusted multiple linear regressions. OP effects were additionally investigated by stratifying by median PM2.5 concentration (14 μg m−3). In the main models, no association was observed with 8-isoPGF2α, nor MDA. An interquartile range (IQR) increase in OPmAA exposure was associated with increased 8-OHdG (percent change: 6.2 %; 95 % CI: 0.2 % to 12.6 %). In the stratified analysis, exposure to OPmAA was associated with 8-OHdG for participants exposed to low levels of PM2.5 (percent change: 11.4 %; 95 % CI: 3.3 % to 20.1 %), but not for those exposed to high levels (percent change: −1.0 %; 95 % CI: −10.6 % to 9.6 %). Associations for OPmDTT also followed a similar pattern (p-values for OPmAA-PM and OPmDTT-PM interaction terms were 0.12 and 0.11, respectively). Overall, our findings suggest that OPmAA may be associated with increased DNA oxidative damage. This association was not observed with PM2.5 mass concentration exposure. The effects of OPmAA in 8-OHdG tended to be stronger at lower (below median) vs. higher concentrations of PM2.5. Further epidemiological, toxicological and aerosol research are needed to further investigate the OPmAA effects on 8-OHdG and the potential modifying effect of PM mass concentration on this association.

Photogeneration of reagent radicals for detection of ascorbic acid by using highly photoluminescent nitrogen-doped carbon quantum dots

An efficient and new hydrothermal method was established to prepare nitrogen-doped carbon quantum dots (N-CQDs) in an autoclave, using citric acid and 3,4-diaminobenzoic acid as precursors. The characterization of N-CQDs was performed by using various spectroscopic and microscopic techniques. The photoluminescence studies revealed that N-CQDs had a high quantum yield of 45.6 %. N-CQDs were used to develop a novel and exciting turn-off–on photoluminescence method for trace detection of ascorbic acid (AA). The photoluminescence of a mixture of N-CQDs and persulfate drastically decreased under UV irradiation in a flow injection setup. When AA was added to the mixture, the reagent radicals were scavenged. Therefore, the photoluminescence intensity was enhanced. Through the competitive mechanism, an efficient method was born to detect AA in some fruits, vegetables, and supplements. The sensing condition was optimized by a univariate procedure and a central composite design (CCD) approach. Under optimum conditions, the photoluminescence response was linear in the range of 0.3–11.5 µmol/L of AA. The AA sensing method exhibited a limit of detection of 0.05 µmol/L. It showed satisfactory sensitivity, repeatability, and accuracy. The AA assay method presented a sample throughput equal to 70 h−1.

Quantifying the levels and oxidative potential of submicron carbon black in plant leaves

Large amounts of the submicron carbon black are emitted in urban areas. Here, we developed a quantitative method using dual-wavelength ultraviolet–visible spectroscopy and Raman spectroscopy (respectively) for carbon black with amorphous structures and with ordering in a graphene sheet. Further, the dithiothreitol (DTT) assay and the ascorbic acid (AA) assay, were used to assess the oxidative potential (OP) of water extracts of leaf samples. Humic acids were adopted as a reference for the OP comparisons with carbon black in both assays. Using dual-wavelength ultraviolet–visible spectroscopy to determine carbon black with amorphous structures, our results achieved coefficients of determination greater than 0.99 in the linear range between 0.5 and 200 μg mL−1. Determination of carbon black with ordering in a graphene sheet using dual-wavelength Raman spectroscopy showed a linear in the range from 2 to 200 μg mL−1. The contents of carbon black with amorphous structures in tree leaves of passive bio-monitoring samplers were found to be in the range of 0.27–0.32 mg m−2, while the carbonaceous particles ordered with a graphene sheet were undetected. The OP of water extracts of leaves varied from 29 to 38 nmol min−1 mg−1 determined by DTT assay, and 16–30 nmol min−1 mg−1 by AA assay, respectively. The water-soluble ions enhanced the OP of submicron carbon black due to the presence of sp2-hybridized carbon atoms. These findings can help frame measures to mitigate health risks from nano-carbon black emitted from varied sources.

Size distribution and lung-deposition of ambient particulate matter oxidative potential: A contrast between dithiothreitol and ascorbic acid assays

Particulate matter (PM) inhaled into human lungs causes oxidative stress and adverse health effects through antioxidant depletion (oxidative potential, OP). However, there is limited knowledge regarding the association between the lung-deposited dose (LDD) of PM and OP in extrathoracic (ET), tracheobronchial (TB), and pulmonary (P) regions of human lungs. Dithiothreitol (DTT) and ascorbic acid (AA) assays were employed to measure the OP of PM size fractions to investigate OP distribution in human lungs and identify the chemical drivers. Quasi-ultrafine particles (quasi-UFP, ≤0.49 μm) exhibited high OP deposition in the TB and P regions, while coarse particles (CP, ≥3.0 μm) dominated in the ET region. A plot of extrinsic (per air volume) and intrinsic (per PM mass) OP versus LDD revealed that the OP for fine and coarse particles was greatest in the ET region, whereas the OP of quasi-UFP was greatest in alveoli. The study also demonstrated that extrinsic OP and PM doses are not strongly related. The decline in OP with increasing PM dose reveals the need for further investigation of the antagonistic effects of the chemical compositions. Overall, the results presented herein help address the gap in knowledge regarding the association between the OP and LDD of ambient particles in specific regions of human lungs.