Development of determination of di-n-octyl phthalate (DOP) residue by an indirect enzyme-linked immunosorbent assay

A review on solution- and vapor-responsive sensors for the detection of phthalates

Phthalic acid esters, largely referred to as phthalates, are today acknowledged as important pollutants used in the manufacture of polyvinyl chloride (PVC)-based plastics, whose use extends to almost every aspect of modern life. The risk of exposure to phthalates is particularly relevant as high concentrations are regularly found in drinking water, food-contact materials and medical devices, motivating an immense body of research devoted to methods for their detection in liquid samples. Conversely, phthalate vapors have only recently been acknowledged as potentially important atmospheric pollutants and as early fire indicators; additionally, deposition of these vapors can pose significant problems to the proper functioning of spacecraft and diverse on-board devices, leading to major space agencies recognizing the need of developing vapor-responsive phthalate sensors. In this manuscript we present a literature survey on solution- and vapor-responsive sensors and analytical assays for the detection of phthalates, providing a detailed analysis of a vast array of analytical data to offer a clear idea on the analytical performance (limits of detection and quantification, linear range) and advantages provided by each class of sensor covered in this review (electrochemical, optical and vapor-responsive) in the context of their potential real-life applications; the manuscript also gives detailed fundamental information on the various physicochemical responses exploited by these sensors and assays that could potentially be harnessed by new researchers entering the field.

Multiple bioanalytical methods reveal a thyroid-disrupting mechanism related to the membrane receptor integrin αvβ3

Di(2-ethylhexyl) phthalate (DEHP), a manufactured chemical, is suitable for large-scale production and has extensive applications. Although restricted for use, DEHP is still ubiquitous in the environment and shows potential to disrupt the structure or function of the thyroid system. However, its toxic mechanism is complex and not clearly understood. In this study, a battery of methods was employed to investigate DEHP-induced thyroid-disrupting effects and their mechanism of action, focusing on a newly discovered membrane receptor-mediated mechanism. The results showed that DEHP promoted rat pituitary tumor (GH3) cell proliferation and c-fos gene expression at environment level concentrations (2 and 5 μmol/L) in a manner similar to that of the natural thyroid hormone 3,3',5-triiodo-L-thyronine (T3). The macromolecule DEHP-BSA cannot pass through the cell membrane to interact with nuclear receptors but upregulated the c-fos gene expression when administered at concentrations comparable to DEHP concentrations; molecular docking demonstrated that DEHP has affinity for the membrane receptor integrin α_vβ₃; DEHP at 2 μmol/L upregulated the β₃ gene expression in GH3 cells; after the addition of integrin α_vβ₃-inhibiting RGD peptide, DEHP-induced c-fos gene upregulation decreased. All of these findings support the supposition that DEHP-induced thyroid-disrupting effects might be mediated by the membrane receptor integrin α_vβ₃. Moreover, DEHP activated the downstream extracellular regulated protein kinase (ERK1/2) pathway, upregulating the gene expression of raf-1, MEK-1 and MAPK1 and increasing the protein levels of p-ERK; interestingly, ERK1/2 activation and c-fos upregulation induced by DEHP were attenuated by PD98059 (an ERK1/2 inhibitor). Taken together, the data suggest that the membrane receptor integrin α_vβ₃ and the downstream ERK1/2 pathway might be involved in DEHP-induced thyroid-disrupting effects. This study provides new insight into the thyroid-disrupting effect and the underlying mechanism and will advance the effort to construct adverse outcome pathways of DEHP and other thyroid hormone disrupting chemicals.

Development of non-equilibrium rapid replacement aptamer assay for ultra-fast detection of phthalic acid esters

In this paper, we developed a non-equilibrium rapid replacement aptamer (NERRA) assay that performed ultra-fast (in 30 s) quantitative detection of phthalic acid esters (PAEs) without waiting for the reaction to reach equilibrium. NERRA assay employed fluorescence PoPo3 dye intercalated in an ssDNA aptamer to selectively detect and quantify the PAEs in water. As the intercalated dye was replaced by the PAEs and quenched in the water, the rate of fluorescence change became proportional to PAEs concentration. The sensitivity of NERRA assay was first evaluated with a commercial spectrofluorometer. The selectivity for PAE mixture, individual PAEs, and non-phthalate compounds were also investigated. NERRA assay was also able to quantitatively detect the PAEs in a common plastic product (picnic mat), and the results were compared with those of gas chromatography mass spectrometry. Finally, a custom analyzer (8.5 cm × 8.5 cm × 16.5 cm) was built to demonstrate the portability of the NERRA assay. Using a commercial spectrofluorometer, NERRA assay was able to quantitatively detect a PAE mixture in 30 min with an LOQ of 0.1 μg/L. Using the portable custom analyzer, the detection time was shortened to 30 s with a tradeoff in the LOQ (1 μg/L). In both cases, the LOQs remain within the environmentally relevant PAE concentrations of 0.1-1472 μg/L.

DnBP-induced thyroid disrupting activities in GH3 cells via integrin αvβ3 and ERK1/2 activation

Di-n-butylphthalate (DnBP) exhibits alarming thyroid disrupting activities. However, the toxic mechanism of DnBP is not completely understood. In this study, we investigated the mechanism of DnBP in thyroid disruption. Rat pituitary tumor cell lines (GH3) were treated with DnBP in different scenarios, and cell viabilities, target gene transcriptions and protein levels were measured accordingly. The results showed that after treatment with DnBP (20 μmol/L), cell proliferation increased to 114.69% (p < 0.01) and c-fos gene was up-regulated by 1.57-fold (p < 0.01). Both nuclear thyroid hormone receptor β (TRβ) and membrane TR (integrin α_v and integrin β₃) genes were up-regulated by 1.31-, 1.08- and 2.39-fold (p < 0.01), respectively, the latter was inhibited by Arg-Gly-Asp (RGD) peptides; the macromolecular DnBP-BSA was unable to bind nuclear TRs, but still promoted cell proliferation to 104.18% and up-regulated c-fos by 2.99-fold (p < 0.01); after silencing TRβ gene, cell proliferation (106.64%, p < 0.05) and up-regulation of c-fos (1.23-fold, p < 0.01) were also observed. All of these findings indicated the existence of non-genomic pathway for DnBP-induced thyroid disruption. Finally, DnBP activated the downstream extracellular regulated protein kinases (ERK1/2) pathway, up-regulating Mapk1 (1.15-, p < 0.05), Mapk3 (1.26-fold, p < 0.01) and increasing protein levels of p-ERK (p < 0.01); notably, DnBP-induced ERK1/2 activation along with c-fos up-regulation were attenuated by PD98059 (ERK1/2 inhibitor). Taken together, it could be suggested that integrin α_vβ₃ and ERK1/2 pathway play significant roles in DnBP-induced thyroid disruption, and this novel mechanism warrants further investigation in living organisms.

Selection of Group-Specific Phthalic Acid Esters Binding DNA Aptamers via Rationally Designed Target Immobilization and Applications for Ultrasensitive and Highly Selective Detection of Phthalic Acid Esters

Phthalic acid esters (PAEs) are ubiquitous in the environment, and some of them are recognized as endocrine disruptors that cause concerns on ecosystem functioning and public health. Due to the diversity of PAEs in the environment, there is a vital need to detect the total concentration of PAEs in a timely and low-cost way. To fulfill this requirement, it is highly desired to obtain group-specific PAE binders that are specific to the basic PAE skeleton. In this study, for the first time we have identified the group-specific PAE-binding aptamers via rationally designed target immobilization. The two target immobilization strategies were adopted to display either the phthalic ester group or the alkyl chain, respectively, at the surface of the immobilization matrix. The former enabled the rapid enrichment of aptamers after four rounds of selection. The top 100 sequences are cytosine-rich (44.7%) and differentiate from each other by only 1-4 nucleotides at limited locations. The top two aptamers all display the nanomolar dissociation constants to both the immobilized target and the free PAEs [dibutyl phthalate (DBP), butyl benzyl phthalate (BBP), bis(2-ethylhexyl) phthalate (DEHP)]. We further demonstrate the applications of the aptamers in the development of high-throughput PAE assays and DEHP electrochemical biosensors with exceptional sensitivity [limit of detection (LOD), 10 pM] and selectivity (>10⁵-fold). PAE aptamers targeting one of the most sought for targets thus offer the promise of convenient, low-cost detection of total PAEs. Our study also provides insights on the aptamer selection and sensor development of highly hydrophobic small molecules.

Development of a Highly Specific Fluorescence Immunoassay for Detection of Diisobutyl Phthalate in Edible Oil Samples

The diisobutyl phthalate (DiBP) hapten containing an amino group was synthesized successfully, and the polyclonal antibody against 4-amino phthalate-bovine serum albumin (BSA) was developed. On the basis of the polyclonal antibody, a rapid and sensitive indirect competitive fluorescence immunoassay (icFIA) has been established to detect DiBP in edible oil samples for the first time. Under the optimized conditions, the quantitative working range of the icFIA was from 10.47 to 357.06 ng/mL (R(2) = 0.991), exhibiting a detection limit of 5.82 ng/mL. In this assay, the specific results showed that other similar phthalates did not significantly interfere with the analysis, with the cross-reactivity less than 1.5%, except for that of DiBAP. Thereafter, DiBP contamination in edible oil samples was detected by icFIA, with the recovery being from 79 to 103%. Furthermore, the reliability of icFIA was validated by gas chromatography-mass spectrometry (GC-MS). Therefore, the developed icFIA is suitable for monitoring DiBP in some edible oil samples.

Sensitive, fast, and specific immunoassays for methyltestosterone detection

An indirect competitive enzyme-linked immunosorbent assay (icELISA) and an immunochromatographic strip assay using a highly specific monoclonal antibody, were developed to detect methyltestosterone (MT) residues in animal feed. The optimized icELISA had a half-inhibition concentration value of 0.26 ng/mL and a limit of detection value of 0.045 ng/mL. There was no cross-reactivity with eight analogues, revealing high specificity for MT. Based on icELISA results, the recovery rate of MT in animal feed was 82.4%–100.6%. The results were in accordance with those obtained by gas chromatography-mass spectrometry. The developed immunochromatographic strip assay, as the first report for MT detection, had a visual cut-off value of 1 ng/mL in PBS, 2.5 ng/g in fish feed, and 2.5 ng/g in pig feed. Therefore, these immunoassays are useful and fast tools for MT residue detection in animal feed.

Development of an enzyme-linked immunosorbent assay for dibutyl phthalate in liquor

A monoclonal antibody specifically recognizing dibutyl phthalate (DBP) was prepared based on a hapten (di-n-butyl-4-aminophthalate). After optimizing various parameters such as concentrations of antibody, coating antigen and composition of the assay buffer, an inhibition curve was plotted with the 50% inhibition concentration value (IC₅₀) 33.6 ± 2.5 ng/mL. A low level of cross-reactivity (<5%) was found for other phthalate esters. Recovery tests were conducted using liquor simulant (a mixture of water and ethanol) at two fortification levels (100 ng/mL and 300 ng/mL). The recovery rates ranged from 84.7% to 94.5% with a coefficient of variation between 7.1% and 12.8%. Nine liquor samples of different alcoholic strengths were detected using the proposed measure and confirmatory analysis was performed using liquid chromatography-mass spectroscopy (LC-MS). The detection results showed good consistency between the two measures and all the data above indicated that the proposed ELISA could be applied in DBP screening.

A simple, sensitive, rapid and specific detection method for Bisphenol A based on Fluorescence Polarization Immunoassay

A rapid, sensitive, specific and simple method based on Fluorescence Polarization Immunoassay (FPIA) was developed for the quantitative detection of Bisphenol A in water. 4, 4-Bis (4-hydroxyphenyl) valeric acid (BHPVA) was selected as the hapten to produce the immunogen. Fluorescein-labeled Bisphenol A derivatives (tracers) with different structures were synthesized and purified by thin layer chromatography. Based on the polyclonal antibody and tracers, an optimized FPIA method was developed with a detection limit (10% inhibition) of 2 μg L(-1) and a linear working range of 20 to 800 μg L(-1). FPIA was suitable for screening a large number of samples. The recoveries of fortified Tai lake water samples ranged from 91.85 to 102.78%, and tap water samples ranged from 90.36 to 96.01%. The coefficients of variation were all less than 20%. This FPIA method, which did not require a complicated cleanup process, proved to be very useful for the screening of Bisphenol A in environmental water samples.