BPA Endocrine Disruptor Detection at the Cutting Edge: FPIA and ELISA Immunoassays

Sensitive and rapid detection of bisphenol A using signal amplification nanoparticles loaded with anti-bisphenol A monoclonal antibody

Bisphenol A has been reported to be a ubiquitous contaminant, and exposure to this compound can lead to adverse effects in human health. In the study, monoclonal antibody against BPA (anti-BPA mAb) with high affinity (3.74 × 109 L/mol) secreted by cell line 2E3 was successfully screened. Inspired by the signal amplification of nanoparticles, anti-BPA mAbs were labeled with nano-materials including colloidal gold (AuNP) and gold nanoflowers (AuNF) for preparation of immunoprobes and AuNP-/AuNF-based test strips. The developed AuNP- and AuNF-based test strips achieved the rapid and sensitive detection of BPA within 10 min, with the limit of detection (LOD) of 25 μg/mL and 3.125 μg/mL, respectively. The detection result in BPA spiked samples measured by the proposed methods was consistent with that detected by LC-MS method. The preparation process of as-prepared test strip is time-saving and considered as ideal candidates method for rapid screening BPA in real samples.

Comparison of Conjugates Obtained Using DMSO and DMF as Solvents in the Production of Polyclonal Antibodies and ELISA Development: A Case Study on Bisphenol A

When developing immunochemical test systems, it is necessary to obtain specific antibodies. Their quality depends, among other things, on the immunogen used. When preparing hapten-protein conjugates to obtain antibodies for low-molecular-weight compounds, the key factors are the structure of the hapten itself, the presence of a spacer, the size of the carrier protein and the degree of its modification by hapten molecules. This work shows that one additional factor-the conditions for obtaining the hapten-protein conjugate-is overlooked. In this work, we have synthesized conjugates of bisphenol A derivative 4,4-bis(hydroxyphenyl)valeric acid (BVA), the protein carrier soybean trypsin inhibitor (STI), and bovine serum albumin (BSA) in reaction media combining water with two organic solvents: dimethylformamide (DMF) or dimethyl sulfoxide (DMSO). Namely, BSADMF-BVA, STIDMF-BVA, BSADMSO-BVA and STIDMSO-BVA conjugates were obtained. Rabbit polyclonal antibodies against the BSADMF-BVA conjugate demonstrated basically different interactions in the developed ELISA systems using either STIDMF-BVA or STIDMSO-BVA conjugates. The use of the STIDMF-BVA conjugate demonstrated the absence of competition in combination with antisera obtained from BSADMF-BVA in an ELISA. A competitive interaction was observed only with the use of the STIDMSO-BVA conjugate. Under the selected conditions, the detection limit of bisphenol A was 8.3 ng/mL, and the working range of determined concentrations was 18.5-290.3 ng/mL. The obtained data demonstrate the possibility of achieving sensitive immunoassays by simply varying the reaction media for the hapten-protein conjugation, which could provide an additional tool in the development of immunoassays for other low-molecular-weight compounds.

Immunodetection of Poorly Soluble Substances: Limitations and Their Overcoming

Immunoassays based on the specific antigen-antibody interactions are efficient tools to detect various compounds and estimate their content. Usually, these assays are implemented in water-saline media with composition close to physiological conditions. However, many substances are insoluble or cannot be molecularly dispersed in such media, which objectively creates problems when interacting in aquatic environments. Thus, obtaining immunoreactants and implementing immunoassays of these substances need special methodological solutions. Hydrophobicity of antigens as well as their limited ability to functionalization and conjugation are often overlooked when developing immunoassays for these compounds. The main key finding is the possibility to influence the behavior of hydrophobic compounds for immunoassays, which requires specific approaches summarized in the review. Using the examples of two groups of compounds-surfactants (alkyl- and bisphenols) and fullerenes, we systematized the existing knowledge and experience in the development of immunoassays. This review addresses the challenges of immunodetection of poorly soluble substances and proposes solutions such as the use of hydrotropes, other solubilization techniques, and alternative receptors (aptamers and molecularly imprinted polymers).

Snowflake Cu2S@ZIF-67: A novel heterostructure substrate for enhanced adsorption and sensitive detection in BPA

Developing semiconductor substrates with superior stability and sensitivity is challenging in surface-enhanced Raman scattering (SERS) research. Here, a snowflake Cu2S@ZIF-67 heterostructure was fabricated using a straightforward method, exhibiting a notable enhancement factor of 9.0 × 109 and a limit of detection (LOD) of 10-14 M for methylene blue (MB). In addition, the Cu2S@ZIF-67 heterostructure substrate demonstrates outstanding homogeneity (relative standard deviation (RSD) = 9.2%) and stability (120 days). Employing Cu2S generates highly sensitive hotspots via an electromagnetic (EM) mechanism, and the growth of ZIF-67 on its surface augments the adsorption capacity and charge transfer capability (chemical mechanism, CM), thereby enhancing the SERS detection sensitivity. Furthermore, the Cu2S@ZIF-67 heterostructure, which was used as a SERS substrate, facilitated the detection of bisphenol A (BPA) with an LOD of 10-11 M. The Cu2S@ZIF-67 heterostructure substrate has excellent selectivity and anti-interference, which is very suitable for BPA detection in complex environment applications. The accuracy of the Cu2S@ZIF-67 heterostructure as a SERS substrate for detecting BPA in real water samples (water bottles, tap water, and pure milk) was confirmed by comparison with high-performance liquid chromatography (HPLC). These results demonstrate that through the rational design of heterostructures can achieve the quantitative and accurate detection of hazardous substances in food and the environment can be achieved.

Molecularly imprinted photopolymers combined with smartphone-based optical sensing for selective detection of bisphenol A in foods

Bisphenol A (BPA), known for its endocrine-disrupting properties and potential to leach into food products, has led to significant food safety concerns. Therefore, the development of sensitive and selective BPA rapid detection methods is crucial. In this study, molecularly imprinted solid-phase extraction coupled to a colorimetric method was adopted for the smartphone-based determination of BPA. The molecularly imprinted polymer (MIP) was prepared via photopolymerization and used as a selective adsorbent material for SPE columns. The solid-phase extraction (SPE) columns with multiple cycles significantly reduced the extraction time to only 30 min. The developed method demonstrates useful sensitivity for BPA (LOD = 30 ppb). Furthermore, BPA migration from plastic packaging was evaluated under different storage conditions, revealing that microwave treatment for 5 min led to BPA release from polycarbonate packaging in juice and basic solutions. The MIP selective extraction/clean-up and smartphone-based optical sensor were successfully applied to BPA standard solutions and complex food samples (e.g., juice and tap water), resulting in reproducible and selective BPA determination (RSD ≤ 6%, n = 3). This rapid and cost-effective method of producing MIPs for BPA offers a promising solution for fast and low-cost sensing for on-site fresh food analysis.

Detection of Dibutyl Phthalate in Surface Water by Fluorescence Polarization Immunoassay

Dibutyl phthalate (DBP) is widely used as a plasticizer in the production of polymeric materials to give them flexibility, strength and extensibility. However, due to its negative impact on human health, in particular reproductive functions and fetal development, the content of DBP must be controlled in food and the environment. The present study aims to develop a sensitive, fast and simple fluorescence polarization immunoassay (FPIA) using monoclonal antibodies derived against DBP (MAb-DBP) for its detection in open waters. New conjugates of DBP with various fluorescein derivatives were obtained and characterized: 5-aminomethylfluorescein (AMF) and dichlorotriazinylaminofluorescein (DTAF). The advantages of using the DBP-AMF conjugate in the FPIA method are shown, the kinetics of binding of this chemical with antibodies are studied, the analysis is optimized, and the concentration of monoclonal antibodies is selected for sensitivity analysis-16 nM. The calibration dependence of the fluorescence polarization signal for the detection of DBP was obtained. The observed IC50 (DBP concentration at which a 50% decrease in the fluorescence polarization signal occurs, 40 ng/mL) and the limit of detection (LOD, 7.5 ng/mL) values were improved by a factor of 45 over the previously described FPIA using polyclonal antibodies. This technique was tested by the recovery method, and the high percentage of DBP discovery in water ranged from 85 to 110%. Using the developed method, real water samples from Lake Onega were tested, and a good correlation was shown between the results of the determination of DBP by the FPIA method and GC-MS. Thus, the FPIA method developed in this work can be used to determine DBP in open-water reservoirs.