Development of sensitive direct and indirect enzyme-linked immunosorbent assays (ELISAs) for monitoring bisphenol-A in canned foods and beverages

Bisphenol A contamination in aquatic environments: a review of sources, environmental concerns, and microbial remediation

The production of polycarbonate, a high-performance transparent plastic, employs bisphenol A, which is a prominent endocrine-disrupting compound. Polycarbonates are frequently used in the manufacturing of food, bottles, storage containers for newborns, and beverage packaging materials. Global production of BPA in 2022 was estimated to be in the region of 10 million tonnes. About 65-70% of all bisphenol A is used to make polycarbonate plastics. Bisphenol A leaches from improperly disposed plastic items and enters the environment through wastewater from plastic-producing industries, contaminating, sediments, surface water, and ground water. The concentration BPA in industrial and domestic wastewater ranges from 16 to 1465 ng/L while in surface water it has been detected 170-3113 ng/L. Wastewater treatment can be highly effective at removing BPA, giving reductions of 91-98%. Regardless, the remaining 2-9% of BPA will continue through to the environment, with low levels of BPA commonly observed in surface water and sediment in the USA and Europe. The health effects of BPA have been the subject of prolonged public and scientific debate, with PubMed listing more than 17,000 scientific papers as of 2023. Bisphenol A poses environmental and health hazards in aquatic systems, affecting ecosystems and human health. While several studies have revealed its presence in aqueous streams, environmentally sound technologies should be explored for its removal from the contaminated environment. Concern is mostly related to its estrogen-like activity, although it can interact with other receptor systems as an endocrine-disrupting chemical. Present review article encompasses the updated information on sources, environmental concerns, and sustainable remediation techniques for bisphenol A removal from aquatic ecosystems, discussing gaps, constraints, and future research requirements.

Electrochemical (bio)sensors based on carbon quantum dots, ionic liquid and gold nanoparticles for bisphenol A

Electrochemical (bio)sensors were developed for bisphenol A (BPA) determination. Screen printed carbon electrode (SPCE) was modified with ionic liquid 1- butyl-3-methylimidazolium tetrafluoroborate (IL), carbon quantum dots (CQD) and gold nanoparticles (AuNP) for the fabrication of the BPA sensor. Electrode surface composition was optimized for the deposition time of AuNP, amount of CQD and percentage of IL using the central composite design (CCD) method. The results of the CCD study indicated that maximum amperometric response was recorded when 9.8 μg CQD, 3% IL and 284 s AuNP deposition time were used in modification. Tyrosinase (Ty) was further modified on the AuNP/CQD-IL/SPCE to fabricate the biosensor. Analytical performance characteristics of the BPA sensor were investigated by differential pulse anodic adsorptive stripping voltammetry and the AuNP/CQD-IL/SPCE sensor exhibited a linear response to BPA in the range of 2.0 × 10^-8 - 3.6 × 10^-6 M with a detection limit of 1.1 × 10^-8 M. Amperometric measurements showed that the linear dynamic range and detection limit of the Ty/AuNP/CQD-IL/SPCE were 2.0 × 10^-8 - 4.0 × 10^-6 M and 6.2 × 10^-9 M, respectively. Analytical performance characteristics such as sensitivity, reproducibility and selectivity were investigated for the presented (bio)sensors. The analytical applicability of the (bio)sensors to the analysis of BPA in mineral water samples was also tested.

A paper-analytical device for detecting bisphenol-A in foods

Bisphenol A (BPA) is a plastic monomer that can leach into food and cause adverse health effects with long-term exposure. In this study, we developed simple paper-analytical devices (PADs) for detecting BPA in food. The PADs were designed with hydrophilic and hydrophobic areas via wax printing. The hydrophilic areas were designed as a detection zone and modified with carboxymethyl cellulose (CMC) for the immobilisation of BPA-bovine serum albumin (BSA). The monoclonal antibodies against BPA were generated and modified with quantum dots (QDs) to synthesise QD-antibody (QD-Ab) probes. Detection conditions of the assay were optimized, with results of 0.1 μg of BPA-BSA and 30-fold diluted QD-Ab probes. The detection limit was 0.098 μg L^-1 using ImageJ analysis. Samples of drinking water, green tea beverage and peanut cooking oil were selected to conduct the matrix effect study. The recovery rates of BPA in different samples ranged from 78.77% to 118.96%, proving that the PADs were a simple and sensitive detection method for easy, low-cost analysis of real food samples.

Indirect Competitive ELISA for the Determination of Total Chromium Content in Food, Feed and Environmental Samples

Background: This study aimed to prepare monoclonal antibodies (mAbs) with high immunoreactivity, sensitivity, and specificity for the chelate (Cr(III)-EDTA) of trivalent chromium ion (Cr(III)) and ethylenediamine tetraacetic acid (EDTA). Further, the study established an indirect competitive enzyme-linked immunosorbent assay (icELISA) for detecting the total chromium content in food, feed, and environmental samples. Methods: Hapten Cr(III)-iEDTA was synthesized by chelating Cr(III) with isothiocyanatebenzyl-EDTA (iEDTA). Immunogen Cr(III)-iEDTA-BSA formed by chelating Cr(III)-iEDTA with bovine serum albumin (BSA), and coating antigen Cr(III)-iEDTA-OVA formed by chelating Cr(III)-iEDTA with ovalbumin (OVA) were prepared using the isothiocyanate method and identified by ultraviolet spectra (UV) and inductively coupled plasma optical emission spectrometry (ICP-OES). Balb/c mice were immunized with the Cr(III)-iEDTA-BSA, and the anti Cr(III)-EDTA mAb cell lines were screened by cell fusion. The Cr(III)-EDTA mAbs were prepared by induced ascites in vivo, and their immunological characteristics were assessed. Results: The immunogen Cr(III)-iEDTA-BSA was successfully synthesized, and the molecular binding ratio of Cr(III) to BSA was 15.48:1. Three hybridoma cell lines 2A3, 2A11, and 3D9 were screened, among which 2A3 was the best cell line. The 2A3 secreted antibody was stable after six passages, the affinity constant (Ka) was 2.69 × 109 L/mol, its 50% inhibition concentration (IC50) of Cr(III)-EDTA was 8.64 μg/L, and it had no cross-reactivity (CR%) with other heavy metal ion chelates except for a slight CR with Fe(III)-EDTA (1.12%). An icELISA detection method for Cr(III)-EDTA was established, with a limit of detection (LOD) of 1.0 μg/L and a working range of 1.13 to 66.30 μg/L. The average spiked recovery intra-assay rates were 90% to 109.5%, while the average recovery inter-assay rates were 90.4% to 97.2%. The intra-and inter-assay coefficient of variations (CVs) were 11.5% to 12.6% and 11.1% to 12.7%, respectively. The preliminary application of the icELISA and the comparison with ICP-OES showed that the coincidence rate of the two methods was 100%, and the correlation coefficient was 0.987. Conclusions: The study successfully established an icELISA method that meets the requirements for detecting the Cr(III)-EDTA chelate content in food, feed, and environmental samples, based on Cr(III)-EDTA mAb, and carried out its preliminary practical application.

The hazardous threat of Bisphenol A: Toxicity, detection and remediation

Bisphenol A (or BPA) is a toxic endocrine disrupting chemical that is released into the environment through modern manufacturing practices. BPA can disrupt the production, function and activity of endogenous hormones causing irregularity in the hypothalamus-pituitary-gonadal glands and also the pituitary-adrenal function. BPA has immuno-suppression activity and can downregulate T cells and antioxidant genes. The genotoxicity and cytotoxicity of BPA is paramount and therefore, there is an immediate need to properly detect and remediate its influence. In this review, we discuss the toxic effects of BPA on different metabolic systems in the human body, followed by its mechanism of action. Various novel detection techniques (LC-MS, GC-MS, capillary electrophoresis, immunoassay and sensors) involving a pretreatment step (liquid-liquid microextraction and molecularly imprinted solid-phase extraction) have also been detailed. Mechanisms of various remediation strategies, including biodegradation using native enzymes, membrane separation processes, photocatalytic oxidation, use of nanosorbents and thermal degradation has been detailed. An overview of the global regulations pertaining to BPA has been presented. More investigations are required on the efficiency of integrated remediation technologies rather than standalone methods for BPA removal. The effect of processing operations on BPA in food matrices is also warranted to restrict its transport into food products.

Multilayered iron oxide/reduced graphene oxide nanocomposite electrode for voltammetric sensing of bisphenol-A in lake water and thermal paper samples

A multilayered iron oxide/reduced graphene oxide (ION-RGO) nanocomposite electrode is reported for the voltammetric sensing of bisphenol-A (BPA). Structural characterizations reveal the nanocomposite features RGO sheets decorated with nanometric spherical ION in a mixture of maghemite and magnetite phases. ITO substrate modified with the ION-RGO multilayered film exhibits strong electrocatalytic effect toward BPA oxidation, which is made possible by Fe(III) catalysts generated at the ION's surface after scanning the electrode potential from below 0 V (vs Ag/AgCl) and followed by the RGO phase conducting the transferred electrons. Under optimized differential pulse voltammetry conditions, the proposed sensor shows three linear working ranges 0.09-1.17 (r² = 0.999), 1.17-3.81 (r² = 0.995) and 3.81-8.20 (r² = 0.998), with the highest sensitivity equaling 7.76 μA cm^-2/μmol L^-1 and the lowest limit of detection of 15 nmol L^-1. A single electrode can be used for at least twenty consecutive runs loosing less than 15% of sensitivity, whereas electrodes fabricated in different bacthes exhibit almost identical perfomances. Determination of BPA in a thermal paper sample shows no difference (at 95% confidence level) between the proposed sensor and HPLC/UV. The sensor is neither influenced by the matrix composition nor by other emerging contaminants.

Effects of a Plastic-Free Lifestyle on Urinary Bisphenol A Levels in School-Aged Children of Southern Italy: A Pilot Study

Bisphenol A (BPA) is an endocrine disruptor (ED) frequently used in food packaging. BPA is used as a monomer in the manufacture of some food packaging. This study aimed to evaluate the urinary BPA concentration in an Italian pediatric cohort, testing the levels of this ED over a period of 6 months, evaluating the effects of a diet regimen with a reduction of Plastic Food Packaging (PFP). One hundred thirty Italian children were enrolled and divided into two groups "School Canteen" and "No School Canteen." The first group consumed one meal at school using a plastic-free service for 5 days/weeks, while the other group did not modify their normal meal-time habits. The BPA levels were tested in urine samples at three time points: T0, is the time before the application of the plastic-free regimen diet; T3, 3 months later; and T6, 6 months later. A reduction of urine BPA levels was detected in the "School Canteen" group. In particular, the reduction was significant analyzing both the intra (among the three testing times) group and inter (between "School Canteen" and "No School Canteen") group variability. Our results show the effects of a diet regimen with a reduction of PFP, demonstrating a connection between urinary BPA levels and food packaging.

Fluorescent enzyme-linked immunoassay based on silane-doped carbon dots for sensitive detection of microcystin-LR in water and crucian samples

In this work, a fluorescent nanoparticles labeling-free fluorescence enzyme-linked immunoassay (FELISA) has been established for the ultrasensitive detection of microcystin-LR (MC-LR) in water and fish samples. Polyclonal antibody against MC-LR was labeled with horseradish peroxidase (HRP) and used as signal probe for binding with analyte in sample or for coating antigen. After washing of the unbound antibody, the substrate system (2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS)/H₂O₂) was added. The oxidation product of ABTS (ox-ABTS) catalyzed by HRP effectively caused the fluorescence quenching of subsequently added silane-doped carbon dots (Si-CDs), and the change in fluorescence intensity of Si-CDs was used to realize the quantitative detection of MC-LR. Under the optimum conditions, the Si-CDs based FELISA method showed a good linear relationship from 0.001 to 3.20 μg L^-1 (R² = 0.994) and provided a low detection limit of 0.6 ng L^-1, which was approximately 30-fold lower than that of traditional indirect competitive ELISA. Average recovery values from 79.9% to 109.2% was obtained from spiked water and crucian samples, suggesting its potential application on the monitoring of MR-LR at a trace level.

A facile synthesis of nanostructured CoFe2O4 for the electrochemical sensing of bisphenol A

This work reports a novel, highly sensitive and cost-effective electrochemical sensor for the detection of bisphenol A in environmental water samples. Attractive non-noble transition metal oxide CoFe₂O₄ nanoparticles were successfully synthesized using a sol–gel combustion method and further characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. Under optimal conditions, the CoFe₂O₄ nanoparticle modified glassy carbon electrode exhibits high electrochemical activity and good catalytic performance for the detection of bisphenol A. The linear calibration curves are obtained within a wide concentration range from 0.05 μmol L⁻¹ to 10 μmol L⁻¹, and the limit of detection is 3.6 nmol L⁻¹ for bisphenol A. Moreover, this sensor also demonstrates excellent reproducibility, stability, and good anti-interference ability. The sensor was successfully applied to determine bisphenol A in practical samples, and the satisfactory recovery rate was between 95.5% and 102.0%. Based on the great electrochemical properties and practical application results, this electrochemical sensor has broad application prospects in the sensing of bisphenol A.

A new electrochemical sensor for bisphenol A is reported. CoFe₂O₄ nanoparticles were synthesized by a sol–gel combustion method. A nanoparticle-modified glassy carbon electrode exhibited outstanding electrochemical performance for the detection of bisphenol A.

Fluorescence Polarization Immunoassay for Determination of Enrofloxacin in Pork Liver and Chicken

Enrofloxacin (ENR) is a widely used fluoroquinolone (FQ) antibiotic for antibacterial treatment of edible animal. In this study, a rapid and highly specific fluorescence polarization immunoassay (FPIA) was developed for monitoring ENR residues in animal foods. First, ENR was covalently coupled to bovine serum albumin (BSA) to produce specific polyclonal antibodies (pAbs). Three fluorescein-labeled ENR tracers (A, B, and C) with different spacers were synthesized and compared to obtain higher sensitivity. Tracer C with the longest arm showed the best sensitivity among the three tracers. The developed FPIA method showed an IC₅₀ (50% inhibitory concentration) of 21.49 ng·mL⁻¹ with a dynamic working range (IC₂₀–IC₈₀) of 4.30–107.46 ng·mL⁻¹ and a limit of detection (LOD, IC₁₀) of 1.68 ng·mL⁻¹. The cross-reactivity (CR) of several structurally related compounds was less than 2%. The recoveries of spiked pork liver and chicken samples varied from 91.3% to 112.9%, and the average coefficients of variation were less than 3.83% and 5.13%, respectively. The immunoassay took only 8 min excluding sample pretreatment. This indicated that the established method had high sensitivity, specificity, and the advantages of simplicity. Therefore, the proposed FPIA provided a useful screening method for the rapid detection of ENR residues in pork liver and chicken.

Integration of black phosphorus and hollow-core anti-resonant fiber enables two-order magnitude enhancement of sensitivity for bisphenol A detection

Hollow core anti-resonant fiber (HARF) has found a handful applications in optical communications, nonlinear optics and high power delivery. The intrinsic property of the fiber also renders it an ideal candidate for biosensing, which has not been explored intensively. Herein, we demonstrate an optical fiber sensing platform, taking advantages of the state-of-the-art HARF technology and superior physicochemical properties of 2D material black phosphorus, for ultra-sensitive detection of bisphenol A (BPA) in blood and environmental samples. The specially designed HARF can not only achieve broadband transmission of light, but also confine light in the low refractive-index liquid core, ensuring maximum overlap of light and liquid core. Modification of the inner surface of HARF with 2D black phosphorus nanoflakes functionalized with fluorescently labeled BPA-specific aptamer provides a smart sensing interface enabling highly selective detection of BPA via measuring the fluorescence. The limit of detection is 1.69pM, which is more than two orders of magnitude enhancement compared to the conventional plate assay. The proposed assay is not interfered with the BPA analogues BPB and BPS. The long optical path with tight optical confinement greatly enhances the analyte-light interaction and improves the sensitivity of the sensing platform. The proposed sensing platform can be further developed for versatile applications.

Au-polythionine nanocomposites: a novel mediator for bisphenol A dual-signal assay based on imprinted electrochemical sensor

In this work, a novel electrochemical sensor was developed by the modification of poly(p-aminobenzene sulfonic acid) (pABSA), Au-polythionine (Au-pTH) nanowires, and molecularly imprinted polymer (MIP) on glassy carbon electrode surface for bisphenol A (BPA) detection. The results of characterizations including scanning electron microscope, transmission electron microscopy, Fourier transform infrared spectra, and X-ray diffraction showed the successful synthesis of helical structural Au-pTH nanowires, which acted as an electro-active probe for BPA detection. Cyclic voltammetry results illustrated that the modified pABSA, Au-pTH, and MIP endowed the sensor with good electrocatalytic activity, the second current signal, and recognition ability, respectively. Since the imprinted cavities provided electron transfer channels for thionine (TH) redox, the peak current of TH can be found in a blank electrolyte. The added BPA molecules can be rebound in imprinted cavities, which are oxidized and then display its current. The rebound BPA molecules in turn blocked the electron transfer channels for TH redox, resulting in the decrease of TH current. A double signal defined, as the sum of the changes of TH current (∆i_TH|) and BPA current (|∆i_BPA|) (|∆i_TH|+|∆i_BPA|), was employed as the detected signal for BPA sensitive detection, which was linearly proportional to the logarithm of concentration of BPA ranging from 8.0 × 10^-8 to 1.0 × 10^-4 mol/L with a limit of detection of 3.8 × 10^-8 mol/L (S/N = 3) in a weakly acidic solution. Moreover, the natural recognition ability of MIP enabled the sensor to selectively detect BPA from its analogues. The proposed dual-signal strategy-based sensor provided a feasible tool for rapid, sensitive, and selective determination of BPA. Graphical abstract.

Carbon-dot-based dual-emission silica nanoparticles as a ratiometric fluorescent probe for Bisphenol A

A simple and effective strategy for designing a ratiometric fluorescent nanosensor is described in this work. A carbon dots (CDs) based dual-emission nanosensor for Bisphenol A (BPA) was prepared by coating CDs on the surface of dye-doped silica nanoparticles. The fluorescence of dual-emission silica nanoparticles was quenched in hydrochloric acid by potassium bromate (KBrO₃) oxidation; BPA inhibited KBrO₃ oxidation, resulting in the ratiometric fluorescence response of dual-emission silica nanoparticles. Several important parameters affecting the performance of the nanosensor were investigated and optimized. The detection limit of this nanosensor was 0.80ng mL^-1 with a linear range from 10 to 500ng mL^-1. This was applied successfully to determine BPA in the leached solution of different plastic products with satisfactory results.

Highly Uniform Gold Nanobipyramids for Ultrasensitive Colorimetric Detection of Influenza Virus

Gold nanoparticles (AuNPs) have been frequently utilized for the construction of diverse colorimetric biosensors. Normally, AuNPs with sharp edges could have better sensitivity. However, the poor monodipersity of AuNPs with sharp edges seriously confines their utility for colorimetric biosensing. Herein, we demonstrate the utility of highly uniform gold nanobipyramids (Au NBPs) for ultrasensitive colorimetric detection of H₅N₁ virus. The proposed method is based on the fact that alkaline phosphatase (ALP) could catalyze the decomposition of 4-aminophenyl phosphate (4-APP) to generate 4-aminophenol (4-AP), which would then reduce silver nitrate to metal silver and then deposited on Au NBPs. The metal silver shell coated on the Au NBPs changed the refractive index of gold and thus resulted in a blue shift of longitudinal localized surface plasmon resonance (LSPR) and accompanied a vivid color change. This method exhibited a higher sensitivity than that of other Au NPs such as gold nanorods due to the high-index-faceted on the tips of the Au NBPs. This method was used to detect the activity of ALP. It exhibited a linear range of 0.1-5 mU/mL with a limit of detection (LOD) of 0.086 mU/mL. Finally, the proposed method was used in immunoassay to detect H₅N₁ virus. The results showed that the corresponding linear range for the detection of H₅N₁ virus antigen was 0.001-2.5 ng/mL, and the LOD was determined to be 1 pg/mL, which is more sensitive than those in most of the colorimetric biosensors reported previously.

Aptamer-based electrochemical biosensor by using Au-Pt nanoparticles, carbon nanotubes and acriflavine platform

Herein, an ultrasensitive electrochemical aptasensor for quantitative detection of bisphenol A (BPA) was fabricated based on a novel signal amplification strategy. This aptasensor was developed by electrodeposition of gold-platinum nanoparticles (Au-PtNPs) on glassy carbon (GC) electrode modified with acid-oxidized carbon nanotubes (CNTs-COOH). In this protocol, acriflavine (ACF) was covalently immobilized at the surface of glassy carbon electrode modified with Au-PtNPs/CNTs-COOH nanocomposite. Attachment of BPA-aptamer at the surface of modified electrode was performed through the formation of phosphoramidate bonds between the amino group of ACF and phosphate group of the aptamer at 5'end. By interaction of BPA with the aptamer, the conformational of aptamer was changed which lead to retarding the interfacial electron transfer of ACF as a probe. Sensitive quantitative detection of BPA was carried out by monitoring the decrease of differential pulse voltammetric (DPV) responses of ACF peak current with increasing the BPA concentration. The resultant aptasensor exhibited good specificity, stability and reproducibility, indicating that the present strategy was promising for broad potential application.

Effects of Surface Epitope Coverage on the Sensitivity of Displacement Assays that Employ Modified Nanoparticles: Using Bisphenol A as a Model Analyte

With the ever-increasing use of nanoparticles in immunosensors, a fundamental study on the effect of epitope density is presented herein, with a small molecule epitope, on the performance of the displacement assay format in an enzyme-linked immunosorbent assay (ELISA). Thiolated bisphenol A (BPA) functionalized gold nanoparticles (cysBPAv-AuNPs) and specific anti-BPA antibodies are employed for this purpose. It is shown that the displacement of cysBPAv-AuNPs bound to the immobilized antibodies was influenced by both the avidity of bound cysBPAv-AuNPs and the concentration of free BPA to displace it. The importance of surface epitope density was that it changed the number of epitopes in close proximity to the antibody-binding site. This then influenced the avidity of cysBPAv-AuNPs bound to the immobilized antibody. Furthermore, the molar epitope concentration in an assay appears to affect the degree of antibody binding site saturation. Controlling surface epitope density of the functionalized nanoparticles and molar epitope concentration in an assay leads to a decrease of the concentration of free BPA required to displace the bound cysBPAv-AuNP, and hence better assay performance with regards to the D50 value and dynamic range in the displacement assay.

Recent advances and progress in the detection of bisphenol A

Bisphenol A (BPA) is an important industrial chemical used as a plasticizer in polycarbonate and epoxy resins in the plastic and paper industries. Because of its estrogenic properties, BPA has attracted increasing attention from many researchers. This review focuses primarily on analytical methods for BPA detection that have emerged in recent years. We present and discuss the advantages and disadvantages of sample preparation techniques (e.g., solvent extraction, solid-phase extraction, molecularly imprinted polymer solid-phase extraction, and micro-extraction techniques) and analytical methods (e.g., liquid chromatography, liquid chromatography-mass spectrometry, gas chromatography-mass spectrometry, capillary electrophoresis, immunoassay, and several novel sensors). We also discuss expected future developments for the detection of BPA. Graphical Abstract This review focuses primarily on the recent development in the detection of bisphenol A including sample pre-treatment and analytical methods.

A competitive fluorescence quenching-based immunoassay for bisphenol A employing functionalized silica nanoparticles and nanogold

A competitive fluorescence quenching-based immunoassay was constructed for bisphenol A, employing functionalized silica nanoparticles and nanogold.

A microfluidic indirect competitive immunoassay for multiple and sensitive detection of testosterone in serum and urine

We demonstrate a microfluidic-based indirect competitive chemiluminescence enzyme immunoassay (MIC) for multiple, sensitive, reliable and rapid detection of testosterone in human serum and urine samples. As MIC can detect biomarkers in a cost-effective and easy-to-operate manner, it may have great potential for clinical diagnosis and point-of-care testing (POCT).

A novel electrochemical aptasensor for bisphenol A assay based on triple-signaling strategy

Based on a triple-signaling strategy, a novel electrochemical aptasensor has been developed for sensitive and selective detection of bisphenol A (BPA). The thiolated ferrocene (Fc)-modified BPA-binding aptamer probe (Fc-P) was immobilized on the gold electrode and then hybridized with the methylene blue (MB)-modified complementary DNA probe (MB-P) to form a rigid double-stranded DNA (ds-DNA). The specific interaction between BPA and Fc-P led to the release of MB-P from the sensing interface and the conformational change of Fc-P. As a result, the oxidation peak currents of Fc and BPA increased with the increase of the concentration of target (BPA) according to the "signal-on" mode while that of MB decreased with the increase of the BPA concentration according to the "signal-off" mode. By superimposing the triple signal changes, BPA was detected sensitively with a linear range from 1 pM to 100 pM. The detection limit is 0.19 pM, and much lower than that obtained by most of the reported electrochemical methods. The aptasensor also exhibited satisfactory specificity, selectivity, reproducibility and stability. By changing the specific aptamers, this strategy could be easily extended to detect other redox targets, showing promising applications in environmental analysis, food safety monitoring, and bioanalysis.

Development of a surface plasmon resonance immunosensor for detecting melamine in milk products and pet foods

A sensitive and stable surface plasmon resonance (SPR) immunosensor based on the inhibition format was developed and validated for detecting melamine (MEL) in milk products and pet foods. The sensitivity and the limit of detection (LOD) of the proposed method for MEL were 2.32 × 10(-2) and 1.4 × 10(-3) μg/mL, respectively. The immunosensor was highly specific to MEL, which displayed only low cross-reactivity (CR) (<0.01%) for cyanuric acid, cyanuric chloride, and atrazine. The assay was validated for the detection of MEL in full-cream milk, skim milk powder, infant formula, dog food, and cat food. Most of the recovery results ranged between 76 and 115%. The sensitivities of the assay in each type of sample were 2.57 × 10(-2) μg/mL, 2.32 × 10(-2) μg/kg, 2.51 × 10(-2) μg/kg, 2.66 × 10(-2) μg/kg, and 2.68 × 10(-2) μg/kg, respectively, which were much lower than the maximum residue levels (MRLs) of MEL.

Development of an indirect competitive ELISA for the detection of ABO blood group antigens

We developed an indirect competitive enzyme-linked immunosorbent assay (ELISA) for the detection of ABO blood group antigens in human samples; in particular for blood stains. ABO blood group antigens conjugated to polyacrylamide were used for immobilized antigen. ABO blood group antigens were extracted from blood stains using a novel method involving pre-incubation with proteinase K (PK), followed by heat treatment. The extracts (analytes) were combined with either anti-A or -B monoclonal antibodies (mAbs), and added directly to the antigen-coated wells. The anti-A and -B mAbs were captured by either ABO blood group antigens present in the analyte or by the immobilized blood group antigens. Peroxidase-conjugated anti-mouse IgM antibody was used to detect anti-A and -B mAbs complexed with immobilized blood group antigens, and a colorimetric reaction using o-phenylenediamine/H2O2 used for its measurement. The ELISA developed in this study was able to detect blood group antigens in blood, saliva and blood stains. The detection limit for unknown blood, saliva and blood stain were determined as 1:200, 1:32 and 1:16. Overall the ABO blood grouping ELISA can be used with relative ease for the high throughput screening of biological samples for the detection of ABO blood group antigens.

Facile synthesis of chitosan-capped ZnS quantum dots as an eco-friendly fluorescence sensor for rapid determination of bisphenol A in water and plastic samples

Quantitative detection of BPA in water and plastic samples was developed based on fluorescence quenching of eco-friendly chitosan-capped ZnS QDs.

Resonance light scattering determination of trace bisphenol A with signal amplification by aptamer-nanogold catalysis

HAuCl4 was reduced by sodium citrate to prepare 10 nm gold nanoparticles (AuNPs) that were modified by the bisphenol A aptamer (Apt) to obtain an aptamer-nanogold probe (Apt-AuNP) for bisphenol A (BPA). The probes were aggregated nonspecifically to form large clusters, which showed a strong resonance light scattering (RLS) peak at 520 nm, under preparation conditions (pH 7.6 Na2HPO4-NaH2PO4 buffer and ultrasonication). Upon addition of BPA, the probe reacted specifically to form dispersed BPA-Apt-AuNP conjugates that exhibited strong catalysis of the two particle reactions of glucose-Cu(II) and hydrazine hydrochloride-Cu(II) with a strong RLS peak at 360 nm and 510 nm respectively. When the BPA concentration increased, the RLS intensity at 360 nm and 510 nm increased respectively. Accordingly, two new and highly-sensitive RLS methods were established for the detection of BPA, using the Apt-AuNP catalytic amplification.

A testosterone specific competitive enzyme immunoassay for monitoring water quality

Testosterone, an androgen and a primary male sex hormone, migrates through the environment in ways which could pose a threat to water quality and, subsequently, environmental and human health. This paper describes the development of a direct competitive enzyme-linked immunosorbent assay (ELISA) that is capable of measuring testosterone with high specificity. The testosterone ELISA displayed the IC20 (as the limit of detection) and IC50 values of 0.05 ± 0.01 μg L(-1) and 0.33 ± 0.18 μg L(-1), respectively. In addition, the assay showed <0.1 % cross-reactivity against structurally related steroidal compounds. However, this assay was found to be sensitive to environmental matrices such as certain metal ions, pH, and high humic acids, and sample clean-up to remove such interference was necessary before analysis. The analyses of 50 surface water samples collected in rural and urban areas in New South Wales, Australia showed that ELISA results correlated well with the androgenic activity measured by the recombinant yeast-based androgen screen assay.