Ecological and human risk assessments of heavy metal contamination of surface soils of auto-mechanic shops at Bogoso Junction, Tarkwa, Ghana.

There is a growing recognition that activities at automobile mechanic shops could contribute to heavy metal contamination of soils. This study seeks to evaluate the ecological and human risk assessments of heavy metal contamination of surface soils of auto-mechanic shops at Bogoso Junction, Tarkwa, Ghana. Herein, 20 composite soil samples were taken, acid-digested, and the concentrations of Cu, Pb, Cd, Mn, Ni, Cr, and Fe were measured using a flame atomic adsorption spectrometer (SHIMADZU, AA 7000). Appraising metal pollution indices, the potential human and ecological risks associated with analyzed metals were carried out. Findings of the present study indicate that the levels of analyzed metals of soils exceeded the control soil sample and the European Union standards for soil quality. The mean metal concentration increased in the order Fe > Mn > Cu > Ni > Pb > Cr > Cd in the soils. Outcomes of enrichment factor, geo-accumulation index, and contamination factor revealed that the soil quality is deteriorated with Cu, Pb, and Cd. The potential ecological risk identified Cd and Pb as the richest elements and offered a high ecological risk in all sampling sites. Furthermore, hazard quotient of analyzed metals depicted that Ni and Mn in urban soils of Bogoso Junction automobile mechanic shops may pose a threat to children (HI > 1). Dermal contact and inhalation of soil particles are the main exposure routes for children susceptibility. Specifically, cancer risk associated with Cd inhalation was 10 times greater than oral ingestion of Pb, showing a relatively high carcinogenic hazard to humans. Altogether, artisanal activities such as engine repair, welding and soldering, vehicle overhauling, and oil exchange at the automobile mechanic shops could deteriorate the soil quality resulting in ecological and human health implications within the vicinity of automobile mechanic shops in Ghana.

Oxidative Stress and Apoptosis in Bisphenol AF-Induced Neurotoxicity in Zebrafish Embryos.

Bisphenol AF (BPAF) is a structural counterpart of bisphenol A that is utilized in the food and beverage industry. The present study investigated the potential mechanisms in BPAF-induced neurotoxicity in zebrafish embryos. The BPAF concentrations (0.03, 0.1, 0.3, and 1.0 µM) had no obvious effect on hatching, mortality, and body length of zebrafish larvae, while curved tail and pericardial edema were observed in the 1.0 µM group at 72 and 96 h postfertilization (hpf). Locomotor activity of the larvae (at 120 hpf) significantly decreased from dark to light but increased from light to dark transitions in BPAF groups (0.1, 0.3, and 1.0 µM). Acridine orange showed that BPAF significantly increased green fluorescence protein intensity (22.6%) in the 1.0 µM group. Consistently, the induced apoptosis significantly up-regulated caspase 3 at 0.3 µM (1.95-fold) and 1.0 µM (2.26-fold) and bax at 0.3 µM (1.60-fold) and 1.0 µM (1.78-fold), whereas bcl-2 expression was significantly decreased at 0.3 µM (0.72-fold) and 1.0 µM (0.53-fold). In addition, increased reactive oxygen species concentrations at 0.3 µM (27%) and 1.0 µM (61.4%) resulted in suppressed superoxide dismutase and catalase activities. Moreover, quantitative polymerase chain reaction results showed that BPAF (0.3 and 1.0 µM) significantly altered normal dopaminergic signaling where dat was up-regulated, while drd2a and th1 were down-regulated, in a concentration-dependent manner. Aberrations in dopamine-related genes were congruous with the dysregulations in neurodevelopment genes (sox11b, pax6a, syn2a, and rob2). Our findings suggest that BPAF-evoked oxidative stress and apoptosis could translate into phenotypical behavioral and neurodevelopmental abnormalities. These highlights could provide theoretical reference for risk assessment and act as an early indicator to BPAF exposure. Environ Toxicol Chem 2022;41:2273-2284. © 2022 SETAC.

Spatial distribution and eco-environmental risk assessment of heavy metals in surface sediments from a crater lake (Bosomtwe/Bosumtwi).

Thirty samples of sediments were taken from Bosumtwi Lake (also called Bosomtwe Lake) in Ghana and analyzed for the contents of Fe, As, Hg, Co, Cr, Ni, Cd, and Pb. Several pollution indices (enrichment factor (EF), contamination factor (CF), geoaccumulation (Igeo), and pollution load index (PLI)) were used to determine sedimentary pollution levels, and the risk of environmental exposure was calculated using Hakanson's potential ecological risk (PER) indices. The results from PER assessments have indicated that sediments from the Bosumtwi Lake present a moderate environmental risk. According to EF calculations, Hg in Bosumtwi lake sediments is the element of concern that is being severely enriched. Hg was the largest contributor to PER with a 97% risk contribution. Multivariate statistical analysis revealed that the main sources of Hg were agrochemicals and atmospheric deposition, whereas the sources of Fe, As, Co, Cr, and Ni to Bosumtwi Lake were natural processes and are derived from the local lithology. There was no strong significant correlation among the contents of the heavy metals, sediment grain sizes, and total organic carbon (TOC), suggesting their lack of control in the distribution of heavy metals, the source, and the transport pathway. Finally, it is strongly recommended to do a study on Hg bioavailability in Bosumtwi Lake sediments. These findings will be relevant to Bosumtwi Lake's profiling and historical development of heavy metal loads.

Cancer and non-cancer risks in humans exposed to trace elements in drinking water from a crater lake (Bosumtwi/Bosomtwe).

The total and dissolved lead, cadmium, mercury, nickel, chromium, cobalt, and arsenic in 30 water samples collected from Bosomtwe Lake were analyzed. Arsenic bioavailability was also determined using the ARSOlux test system. Except for chromium, their mean values in the study results exceeded the WHO permissible limit for potability. Cancer and non-cancer effects associated with exposure to dissolved and total metals by a child and an adult via oral and dermal routes were estimated. The hazard quotient (HQ) values obtained (except adult exposure to total arsenic of 1.71 × 1000 ) were less than unity. Between child and adult, the recorded hazard index (HI) was 0.82 and 1.75, respectively. The HI results indicate that the adult population is at risk for non-cancer health effects. Arsenic was the element of concern, and it remained biologically available for uptake by target groups. For child and adult, respectively, arsenic contributed 96.39% and 97.29% to HI values. The risk values for cancer in a child and an adult with oral and dermal exposure to dissolved and total arsenic were lower than the USEPA range. Principal component and cluster analysis identified atmospheric deposition, geogenic, and unregulated application of agrochemicals as plausible sources of water pollution in Bosomtwe Lake. PRACTITIONER POINTS: The hazard quotient (HQ) values obtained for adult exposure to total arsenic was 1.71 × 1000 . Arsenic remained biologically available for uptake by target groups. The calculated health index (HI) indicated that the adult population is at risk for non-cancer health effects. Arsenic contributed 96.39% and 97.29% to HI values for a child and an adult. Atmospheric deposition, geogenic, and unregulated application of agrochemicals were the plausible sources of water pollution in Bosomtwe Lake.

Embryonic Exposure to Low Concentrations of Bisphenol A and S Altered Genes Related to Pancreatic ß-Cell Development and DNA Methyltransferase in Zebrafish.

Bisphenol A (BPA) and bisphenol S (BPS) are implicated in the development of metabolic disorders, such diabetes mellitus. However, the epigenetic mechanism underlying the pancreatic ß-cell dysregulation for both BPA/BPS needs clarification. This exploratory study was designed to investigate whether embryonic exposure to low BPA/BPS concentrations impair early pancreatic ß-cell differentiation as well as DNA methylation in its gene expression profile using an in vivo model, zebrafish. Zebrafish embryos were exposed to 0, 0.01, 0.03, 0.1, 0.3, and 1.0 µM BPA/BPS at 4-h post fertilization (hpf) until 120 hpf. BPA/BPS-induced effects on pancreatic-related genes, insulin gene, and DNA methylation-associated genes were assessed at developmental stages (24-120 hpf), while glucose level was measure at the 120 hpf. The insulin expression levels decreased at 72-120 hpf for 1.0 µM BPA, while 0.32 and 0.24-fold of insulin expression were elicited by 0.3 and 1 µM BPS respectively at 72 hpf. Significant elevation of glucose levels; 16.3% (for 1.0 µM BPA), 7.20% (for 0.3 µM BPS), and 74.09% (for 1.0 µM BPS) higher than the control groups were observed. In addition, pancreatic-related genes pdx-1, foxa2, ptfla, and isl1 were significantly interfered compared with the untreated group. Moreover, the maintenance methylation gene, dnmt1, was monotonically and significantly decreased at early stage of development following BPA exposure but remained constant for BPS treatment relative to the control group. DNMT3a and DNMT3b orthologs were distinctively altered following BPA/BPS embryonic exposure. Our data indicated that embryonic exposure to low concentration of BPA/BPS can impair the normal expressions of pancreatic-associated genes and DNA methylation pattern of selected genes in zebrafish early development.

Developmental neurotoxicity of low concentrations of bisphenol A and S exposure in zebrafish.

The vulnerability to environmental insults is heightened at early stages of development. However, the neurotoxic potential of bisphenol A (BPA) and bisphenol S (BPS) at developmental windows remains unclear. To investigate the mechanisms mediating the developmental neurotoxicity, zebrafish embryos were treated with 0.01, 0.03, 0.01, 0.3, 1 µM BPA/BPS. Also, we used Tg(HuC:GFP) zebrafish to investigate whether BPA/BPS could induce neuron development. The reduction in body length, and increased heart rate were significant in 0.3 and 1 µM BPA/BPS groups. The green fluorescence protein (GFP) intensity increased at 72 hpf and 120 hpf in Tg(HuC:GFP) larvae which was consistent with the increased mRNA expression of elval3 following BPS treatments, an indication of the plausible effect of BPS on embryonic neuron development. Additionally, BPA/BPS treatments elicited hyperactivity and reduced static time in zebrafish larvae, suggesting behavioral alterations. Moreover, qRT-PCR results showed that BPA and BPS could interfere with the normal expression of development-related genes vegfa, wnt8a, and mstn1 at the developmental stages. The expression of neurodevelopment-related genes (ngn1, elavl3, gfap, α1-tubulin, mbp, and gap43) were significantly upregulated in BPA and BPS treatments, except for the remarkable downregulation of mbp and gfap elicited by BPA at 48 (0.03 µM) and 120 hpf (0.3 µM) respectively; ngn1 at 48 hpf for 0.1 µM BPS. Overall, our results highlighted that embryonic exposure to low concentrations of BPA/BPS could be deleterious to the central nervous system development and elicit behavioral abnormalities in zebrafish at developmental stages.

Hepatic oxidative stress, DNA damage and apoptosis in adult zebrafish following sub-chronic exposure to BDE-47 and BDE-153.

Polybrominated diphenyl ethers (PBDEs) are ubiquitous and prolific contaminant in both the abiotic and biotic environment because of the wide industrial applications of these chemicals. In the present study, the effects of 2,2',4,4'-tetrabrominateddiphenyl ether (BDE-47) and 2,2',4,4',5,5'-hexabromodiphenyl ether (BDE-153) exposure on the induction of hepatic oxidative stress, DNA damage, and the expression of apoptosis-related genes in adult zebrafish were investigated. The activities of antioxidant enzymes, such as catalase and superoxide dimutase, significantly increased when adult zebrafish was exposed to various concentrations of BDE-47 and BDE-153 for 7 and 15 days. BDE-47 and BDE-153 elicited significant alterations in zebrafish 7-Ethoxyresorufin-O-deethylase activity at 3, 7, or 15 days of exposure. In addition, the significant increase in comet assay parameters of zebrafish hepatocytes in a concentration-dependent manner indicated BDE-47 and BDE-153 induced DNA damage, probably due to observed oxidative stress. Furthermore, a monotonically upregulation of p53 and Caspase3, which are apoptotic-regulated genes, and decreased expression ratio of the anti-apoptotic B-cell lymphoma/leukaemia-2 and Bcl2-associated X protein genes for all BDE-47 and BDE-153 treatments at 7 and 15 days indicated apoptosis induction in zebrafish liver. Our findings help elucidate the mechanisms of BDE-47- and BDE-153-induced toxicity in zebrafish hepatocytes.

Chemiluminescence imaging immunoassay for simultaneous determination of TBBPA-DHEE and TBBPA-MHEE in aquatic environments.

The environmental concentration of tetrabromobisphenol A bis(2-hydroxyethyl) ether (TBBPA-DHEE) and tetrabromobisphenol A mono(hydroxyethyl) ether (TBBPA-MHEE), as some of the main derivatives and byproducts of tetrabromobisphenol A (TBBPA), are obscure due to lacking available analytical methods. In the present study, a multiplexed competitive chemiluminescent imaging immunoassay (CLIIA) based on specific monoclonal antibody respectively against TBBPA-MHEE and TBBPA-DHEE has been developed for the simultaneous detection of the two targets. To improve the sensitivity of immunoassay, Au nanoparticles (AuNPs) were utilized as solid support for loading horseradish peroxidase, labeled to obtain the multi-enzyme particles. Under the optimized conditions, the limits of detection (LODs) for TBBPA-MHEE and TBBPA-DHEE were 1.85 ng/mL and 2.05 ng/mL, respectively. After estimating its accuracy and precision, the established method was applied for investigation of the contaminants at the inner rivers in Zhenjiang, Jiangsu Province. Our results indicated that no TBBPA-MHEE was found in all 11 water samples and two samples of TBBPA-DHEE were detected up to 6.34 ng/mL, possibly ascribed to the dense population and slow flow rate around the sampling site. Graphical abstract.

A novel and facile immunosensor based on a barometer: Application for rapid analysis of Escherichia coli in waters.

A facile immunosensor was constructed based on a barometer indicator using a double-antibody- sandwich method for rapid and sensitive detection of Escherichia coli (E. coli) from water samples. At the present study, Anti- E. coli DH-5 polyclonal antibody was modified through enriching carboxylated magnetic beads and catalase functionalized gold nanoparticles (AuNPs)- loaded nanospheres. The functionalized AuNPs-loaded nanospheres exhibited an excellent catalysis towards decomposition of hydrogen peroxide (H2O2), generating a large volume of oxygen (O2) into waters, increasing the pressure inside the glass vial, which in turn raised the water level in barometer. Under the optimized experimental conditions, the proposed method showed wide linear ranges (102- 107 cfu mL-1), good accuracy and precision (recoveries, 86.7- 107%; CV, 3.2- 8.1%) with a limit of detection (LOD, S/N = 3) and the limit of quantification (LOQ, S/N = 10) were 80 cfu mL-1and 267 cfu mL-1, respectively. Furthermore, the fabricated portable immunosensor device showed some distinct features in low cost and visibility, suggesting great potential for rapid and on-site analysis of this bacteria from waters in less developed areas of developing countries.

Ratiometric fluorescence immunoassay based on FAM-DNA-functionalized CdSe/ZnS QDs for the sensitive detection of tetrabromobisphenol A in foodstuff and the environment.

A simple indirectly competitive ratiometric fluorescent immunoassay was designed based on fluorescein amidite (FAM)-DNA-functionalized CdSe/ZnS quantum dots (QDs) for the sensitive determination of tetrabromobisphenol A (TBBPA). At the detection system, catalase (CAT) was labeled on the secondary antibody (Ab2), which served as a controller of the H2O2 concentration. After the competitive binding step, the emitted red fluorescence (excitation at 490 nm) from FAM-DNA-functionalized CdSe/ZnS QDs could be effectively quenched by the H2O2 added. Under the optimized conditions, the limit of detection (LOD) reached 0.118 µg/L with a linear range of 0.34-45.34 µg/L, which was approximately 1 order of magnitude lower than that by HRP-based traditional ELISA. Furthermore, the combination of the dual-output ratiometric fluorescence assays with ELISA improved the inherent built-in rectification to the environment, which brought about satisfactory accuracy and precision (recoveries, 83.16-112.4%; CV, 2.42-7.28%), indicating great potential for the determination of trace TBBPA from food and environmental samples. Graphical abstract.

Sublethal concentrations of triclosan elicited oxidative stress, DNA damage, and histological alterations in the liver and brain of adult zebrafish.

Triclosan (TCS), an antimicrobial agent, has been a pollutant of increasing concern owing to its potential health risk on humans and aquatic animals. The present study seeks to test the hypothesis that TCS could alter the oxidative stress-related parameters in the brain and liver, as well as eliciting DNA damage in hepatocytes of adult zebrafish. On the basis of the 96 h LC50 (398.9 µg/L), adult zebrafish were separately exposed to 50, 100, and 150 µg/L TCS for 30 days. The brain and liver tissues from adult zebrafish were excised and assayed for a suite of antioxidant parameters and oxidative stress biomarkers including DNA damage in the liver. The induced effect by TCS on the activity of acetylcholinesterase (AChE) was also analyzed in the brain. Results showed a significant decrease in superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) in the brain and liver of adult zebrafish. Also, the contents of the glutathione system (GSH and GSSH), as well as the activity of the glutathione reductase (GR), assayed in the liver, were reduced while the contents of malondialdehyde (MDA) were elevated in the liver. A comet assay revealed dose-dependent DNA damage in zebrafish hepatocytes. The 8-hydroxy-2'-deoxyguanosine (8-OHdG), MDA, and carbonyl protein contents in brain tissues significantly increased. Moreover, the AChE in the zebrafish brain was induced. Apparently, no obvious histological changes in brain tissues of zebrafish were observed compared with those of the control whereas atrophy and necrosis of hepatocytes and increased hepatic plate gap were observed in zebrafish hepatocytes after TCS exposure. The obtained results highlight that sublethal concentrations of TCS may be deleterious to the liver and brain of adult zebrafish upon subchronic exposure.

High-throughput chemiluminescence immunoassay based on Co2+/hemin synergistic catalysis for sensitive detection tetrabromobisphenol A bis(2-hydroxyethyl) ether in the environments.

Here, a novel chemiluminescence (CL) immunoassay was fabricated for sensitive determination of tetrabromobisphenol A bis(2-hydroxyethyl) ether (TBBPA-DHEE), one of typical tetrabromobisphenol A derivatives. At the indirectly competitive method, the synthesized PS@hemin@Co2+ was labelled by secondary antibody (Ab2) instead of common natural enzymes, which showed excellent catalysis towards the decomposition of luminol-H2O2 for producing CL signal. Furthermore, the CL signal was greatly amplified owing to the synergistic catalysis of hemin and Co2+ in the detection system. Under the optimized conditions, the established method offered (i) low detection limit (LOD, 0.9 µg/L), which was almost 5 times lower than that using a conventional ELISA with the same antibody; (ii) a good linearity (1.6-14.3 µg/L); (iii) satisfactory accuracy and precision (recoveries, 89.67-125.33%; CV, 2.75-8.37%). The proposed CL immunoassay was applied for analysis of environmental samples from various sources collected from Jiangsu and Zhejiang province, China. And the detected concentrations were ranged in 2.4-3.7 µg/L in environmental waters and 1.8-2.4 ng/g (dry weight, dw) in soil samples, indicating great potential for trace TBBPA-DHEE detection from environmental samples.

A novel signal amplification strategy based on the competitive reaction between 2D Cu-TCPP(Fe) and polyethyleneimine (PEI) in the application of an enzyme-free and ultrasensitive electrochemical immunosensor for sulfonamide detection.

Nanozymes with peroxidase-like activity have been widely used as signal labels in electrochemical immunosensors. However, these sensors always suffer from some shortcomings during the processes underlying nanozyme labeling, including complex reactions, nanozyme inactivation after being decorated on the antibodies. To solve these problems, a novel electrochemical immunosensor was designed for ultrasensitive detection of sulfonamides (SAs), in which the synthesized 2D Cu-TCPP(Fe) with peroxidase-like property was used as a nanozyme that was directly modified on the electrode surface. Meanwhile, the structure of 2D Cu-TCPP(Fe) could be destroyed by the polyethyleneimine (PEI) from PEI-GO@Ab2 due to the stronger affinity between PEI and Cu2+, leading to an activity change of the prepared nanozyme. When H2O2 was introduced to the system, the electrochemical current was significantly declined owing to the peroxidase activity of 2D Cu-TCPP(Fe) decreased, which led to signal amplifications. Under the optimized conditions, this strategy had a wide detection range (1.186-28.051 ng/mL), satisfactory accuracy and precision (recoveries, 64-118%; CV, 2.16-7.27%) with a low detection limit of 0.395 ng/mL. The findings of this study indicate that the electrochemical immunosensor we developed has great potential and can be used for enzyme-free detection of SAs in environmental samples.

Electrochemical immunosensor based on Ag+-dependent CTAB-AuNPs for ultrasensitive detection of sulfamethazine.

An electrochemical biosensor was proposed utilizing an improved amplification strategy for the rapid detection of sulfamethazine (as a model target) in aquatic environments. In this competitive immunoassay, cetyltrimethylammonium bromide-capped gold nanoparticles (CTAB-AuNPs) were used as a signal amplifier and electrode matrix and coated with an antigen-antibody (Cag-Ab1) specific binding system as a recognition unit for the target compound. In addition, silver nanoparticle labels were functionalized with dendritic fibrous nanosilica (DFNS@AgNPs) and decorated onto chitosan/single walled carbon nanohorn (CS/SWCNH)-modified glass carbon electrodes (GCEs), which improved the electron transfer rate and increased the surface area, enabling more coating antigens to be captured. Under acidic conditions, massive amounts of the Ag+ bound to the surface of the AuNPs dissolved, and consequently, formed Ag+@CTAB-AuNP complexes, which resulted in a distinctly improved peroxidase-like activity and enhanced current response. Furthermore, the destroyed Ab1-Ab2-DFNS conjugation greatly decreased the impedance, bringing about the amplification of the electrochemical signals. After optimization of the parameters, the proposed approach exhibited excellent performance, including good sensitivity (LOD, 0.0655 ng/mL) and satisfactory accuracy (recoveries, 79.02%-118.39%; CV, 3.18%-9.82%), which indicates the great potential of this strategy for the rapid detection of trace pollutants in the environments.

Electrochemical Biosensor Based on Tetrahedral DNA Nanostructures and G-Quadruplex-Hemin Conformation for the Ultrasensitive Detection of MicroRNA-21 in Serum.

MicroRNAs (miRNAs) play important roles as significant biomarkers in disease diagnostics. Here, an electrochemical biosensor was developed for the quick, sensitive, and specific detection of miRNAs from human-serum samples using three-dimensional (3D) DNA tetrahedron-structured probes (TSPs) and duplex-specific nuclease (DSN). The designed TSPs were composed of a recognition sequence that corresponded to a target miRNA and a G-quadruplex sequence that was combined with hemin to mimic the biocatalytic functions for H2O2 reduction and l-cysteine oxidation. After hybridization with miRNA, the TSPs were immobilized on the Au electrode to shape the DNA-RNA double strands, which could be discriminated by DSN for hydrolysis of the DNA in the heteroduplexes to generate significant change in the reduction currents. Under optimal conditions, the biosensor showed a wide linear response ranging from 0.1 fM to 0.1 pM, with a low detection limit of 0.04 fM. Meanwhile, the method showed acceptable accuracy and precision for the determination of miRNAs in serum after a series of assessments.

A novel fluorescence immunoassay based on AgNCs and ALP for ultrasensitive detection of sulfamethazine (SMZ) in environmental and biological samples.

A novel indirect competitive fluorescence immunoassay based on the quenching of I- to silver clusters (AgNCs) was developed for the highly selective and ultrasensitive detection of sulfamethazine (SMZ). In this system, alkaline phosphatase (ALP) was labeled on the secondary antibody (Ab2). And after a competition step, magnesium ascorbyl phosphate could be catalyzed to produce ascorbic acid under the catalysis of ALP. Subsequently, I2 was introduced and further reduced to I- in the presence of ascorbic acid, triggering the fluorescence quenching of AgNCs dispersed in isopropanol (IPA) buffer. More importantly, trace I- could lead to an obvious reduction in fluorescence signal, indicating the sensitivity of this method would be greatly improved. Under the optimal condition, this improved method for the SMZ detection has a lower detection of limit (LOD, 0.05000 µg/L) with a wider range (0.1400-71.71 µg/L). After an evaluation, the fluorescence ELISA proposed in this work has satisfactory accuracy and reliability (recoveries, 84.18-118.6%; CV, 2.03-7.64%), illustrating good performance and great potential for the detection of trace SMZ in environmental and biological samples.

A competitive immunosensor for ultrasensitive detection of sulphonamides from environmental waters using silver nanoparticles decorated single-walled carbon nanohorns as labels.

A novel competitive electrochemical immunosensor based on Au nanodendrites (Au NDs)/silver nanoparticles (Ag NPs) @single-walled carbon nanohorns (SWCNHs) was established for sensitive determination of sulphonamides (SAs) in aquatic environments. The indirectly competitive binding system of the approach was composed of coating antigen that coated on Au NDs/glass carbon electrode (GCE), the target and primary antibody (Ab1). When Ab2@Ag NPs@SWCNHs was captured by coating antigen (Cag)- Ab1 complex, massive Ag+ will be released from electrode in the presence nitric acid (HNO3), consequently, the generated Ag+ will significantly amplify the electrochemical signal, which would be recorded by the linear sweep voltametry (LSV). Meanwhile, the used three-dimensional Au nanodendrites (Au NDs) could increase the conductivity of the electrode and the size of the active surface area to improve the antigen-loading. Under the optimal conditions, the immunosensor showed a good linear relationship for sulfamethazine (SMZ)ranged in 0.33-63.81 ng/mL with a detection limit of 0.12 ng/mL (LOD, based on 90% inhibition). In addition, the proposed approach exhibited satisfactory accuracy and precision (recoveries, 79.25-119.25%; CV, 2.14-9.58%), it can be applied for rapid analysis of the trace pollutants from environmental waters.

An ultrasensitive electrochemical biosensor for detection of microRNA-21 based on redox reaction of ascorbic acid/iodine and duplex-specific nuclease assisted target recycling.

A novel electrochemical biosensor was developed based on multiwall carbon nanotubes/graphene oxide nanoribbons (MWCNTs/GONRs) for sensitive analysis of microRNA-21. Signal-amplified strategy was achieved by duplex-specific nuclease assisted target recycling and alkaline phosphatase-induced redox reactions. At the fabrication process of the sensor, ssDNA capture probes were immobilized on the surface of the MWCNTs@GONRs/AuNPs modified electrode through the Au-S bond, and the streptavidin-conjugated alkaline phosphatase (SA-ALP) was attached to the end of the probe. In the absence of miRNA-21, SA-ALP catalysed the conversion of ascorbic acid 2-phosphate (AAP) into ascorbic acid (AA), triggered a redox reaction under iodine, producing a marked electrochemical response. When miRNA-21 was hybridized to the capture probe, the duplex would be cleaved by the duplex-specific nuclease (DSN), causing the electrochemical signals being significantly decreased as a result of SA-ALP detached from the electrode surface. Under the optimized conditions, our biosensor showed satisfactory sensitivity (detection limit, 0.034 fM), excellent selectivity and good accuracy (recoveries, 77.4-120.2%; RSD, 5.2-7.3%) after systematic evaluations. The proposed approach was applied to detect miRNA-21 from human serum samples, which indicated that it was reliable and could be widely used as an effective tool for rapid detection of the target in serums.

A novel electrochemical immunosensor based on catalase functionalized AuNPs-loaded self-assembled polymer nanospheres for ultrasensitive detection of tetrabromobisphenol A bis(2-hydroxyethyl) ether.

A competitive immunosensor was established using an electrochemical amperometric strategy for sensitive detection of tetrabromobisphenol A bis(2-hydroxyethyl) ether (TBBPA-DHEE), an important derivative of tetrabromobisphenol A (TBBPA). In this system, the amplified electrochemical signal towards the reduction of hydrogen peroxide (H2O2) was recorded by amperometric method. Meanwhile, the synthetized catalase functionalized AuNPs-loaded self-assembled polymer nanospheres showed an excellent electrocatalytic ability to catalyse H2O2, which was beneficial for strengthening the electrochemical signals. Under the optimized conditions, this method displayed: (i) low detection limits (0.12 ng/mL, 7 times lower than the traditional ELISA with the same antibody); (ii) satisfactory accuracy (recoveries, 78-124%; RSD, 2.1-8.3%) and good agreement with the corresponding ELISA; (iii) low sample consumption (6 µL) and low cost. The proposed approach was applied for investigation of TBBPA-DHEE from environmental waters, and our results indicated that this immunosensor has great potential to detect the trace pollutants in aquatic environments.