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

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.

High Specific and Rapid Detection of Cannabidiol by Gold Nanoparticle-Based Paper Sensor

In order to facilitate monitoring of cannabidiol (CBD), we devised a gold immunochromatographic sensor based on a specific monoclonal antibody (mAb). To prepare the antigen, a novel hapten with CBD moiety and a linear carbon chain was employed. By utilizing hybridoma technology, a specific mAb was screened and identified that exhibited a 50% maximal inhibitory concentration against CBD ranging from 28.97 to 443.97 ng/mL. Extensive optimization led to the establishment of visual limits of detection for CBD, achieving a remarkable sensitivity of 8 μg/mL in the assay buffer. To showcase the accuracy and stability, an analysis of CBD-spiked wine, sparkling water, and sports drink was conducted. The recovery rates observed were as follows: 88.4-109.2% for wine, 89.9-107.8% for sparkling water, and 83.2-95.5% for sports drink. Furthermore, the coefficient of variation remained impressively low, less than 4.38% for wine, less than 2.07% for sparkling water, and less than 6.34% for sports drink. Importantly, the developed sensor exhibited no cross-reaction with tetrahydrocannabinol (THC). In conclusion, the proposed paper sensor, employing gold nanoparticles, offers a user-friendly and efficient approach for the precise, rapid, and dependable determination of CBD in products.

Development of Lateral Flow Test-System for the Immunoassay of Dibutyl Phthalate in Natural Waters

The use of a large amount of toxic synthetic materials leads to an increase in the pollution of environmental objects. Phthalates are compounds structurally related to esters of phthalic acid that are widely used in the manufacturing of synthetic packaging materials as plasticizers. Their danger is conditioned by leaching into the environment and penetrating into living organisms with negative consequences and effects on various organs and tissues. This work presents the first development of lateral flow immunoassay to detect dibutyl phthalate, one of the most common representatives of the phthalates group. To form a test zone, a hapten-protein conjugate was synthesized, and gold nanoparticles conjugated with antibodies to dibutyl phthalate were used as a detecting conjugate. The work includes the preparation of immunoreagents, selectivity investigation, and the study of the characteristics of the medium providing a reliable optical signal. Under the selected conditions for the analysis, the detection limit was 33.4 ng/mL, and the working range of the determined concentrations was from 42.4 to 1500 ng/mL. Time of the assay-15 min. The developed technique was successfully applied to detect dibutyl phthalate in natural waters with recovery rates from 75 to 115%.

Ultrasensitive detection of four organic arsenic compounds at the same time using a five-link cardboard-based assay

In order to effectively control the excessive use of organic arsenic reagents in livestock and poultry products, there is an urgent need to develop a method for rapid detection of multiple organic arsenic reagents. In this study, two haptens were designed and derivatized around the structural formula of roxarsone, and a highly-sensitive group-selective mAb 3F2 was prepared, which can simultaneously detect roxarsone, 4-aminophenylarsonic acid, 2-aminophenylarsonic acid and phenylarsonic acid. We further developed a colloidal gold immunochromatographic test strip (ICS) and prepared a five-link card that can simultaneously detect four organic arsenics in chicken and pork samples. Its quantitative detection limits (LOQ) for the four compounds in chicken and pork samples were 0.06 and 0.32 ng/mL, 0.11 and 0.29 ng/mL, 0.34 and 0.99 ng/mL, and 0.88 and 1.5 ng/mL, respectively. This multi-ICS detection provides a powerful tool for the on-site detection and rapid screening of organic arsenic reagents in actual samples.

Clustered Detection of Eleven Phthalic Acid Esters by Fluorescence of Graphene Quantum Dots Displaced from Gold Nanoparticles

A gold nanoparticle-quenched graphene quantum dot-based aptasensor was developed to perform clustered detection of 11 phthalic acid esters (PAEs). The binding of the target PAEs to the aptasensor frees the graphene quantum dots that are otherwise quenched by the carrier gold nanoparticle. The resultant fluorescence upon excitation is proportional to the number of freed graphene quantum dots and hence the target PAE concentration. The synthesis of the proposed aptasensor was first verified step-by-step via FT-IR measurement, scanning electron microscopy, and fluorescence measurement. Selectivity was evaluated for individual and combined target PAEs and compared against seven non-PAE endocrine disrupting compounds. The proposed aptasensor successfully quantified 11 PAEs in test samples with varying concentrations of 0.001-50 ng PAEs/mL and demonstrated a limit of detection of ∼4 pg./mL. Finally, the AuNP-gQD aptasensor was employed to detect multiple combinations of commonly regulated PAEs (DBP, DIBP, DEHP, and BBP). The recovery (%) for all four PAEs combination in environmentally relevant concentrations of 0.5, 1, 5, and 10 ng/mL were ∼100%.

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.

Competitive binding assays for measuring the binding affinity of thyroid-disrupting chemicals for integrin αvβ3

Some thyroid-disrupting chemicals (TDCs) affect thyroid function by activating the pathways mediated by a typical thyroid hormone (TH) membrane receptor, integrin α_vβ₃. The present study introduces improved competitive binding assays for the rapid and sensitive evaluation of the binding affinities of TDCs for integrin α_vβ_3. Based on different probes, two assays were modified: a fluorescence competitive binding assay and a radioligand competitive binding assay. The chemicals tested included the known TH, 3,3',5,5'-tetraiodo-l-thyronine (T4); a deaminated analog of T4, tetraiodothyroacetic acid (tetrac); and phthalate esters (PAEs). The relative binding potency of T4 was studied, and the concentration required to displace 50% of the ligands from their receptors (RIC50) of T4 was 4.9 × 10⁵ and 9.7 × 10⁴ nM for the fluorescence and radioligand competitive binding assays, respectively, suggesting that the radioligand competitive binding assay might be more sensitive for the evaluation of the binding affinity for integrin α_vβ₃. The three PAEs, including diethyl hexyl phthalate (DEHP), benzyl butyl phthalate (BBP) and dibutyl phthalate (DnBP), demonstrated binding affinities for integrin α_vβ₃ in the following order of potency: DnBP > DEHP > BBP tested by the radioligand competitive binding assay. A docking simulation of each of the three PAEs with integrin α_vβ₃ confirmed the calculated binding energies, which had a strong positive relationship with the log RIC20 values of the 3 PAEs (R = 0.99, p < 0.001). The present study shows that the established radioligand competitive binding assay could be used as a valuable tool for quantifying the affinity of TDCs for integrin α_vβ₃.

Colloidal Gold Immunochromatographic Assay for Rapid Detection of Carbadox and Cyadox in Chicken Breast

Abused or misused carbadox (CBX) and cyadox (CYA) in animal feed may cause food safety concerns, threatening human health. Here, we describe the design of a novel hapten for preparation of a monoclonal antibody against CBX and CYA simultaneously. Using this antibody, colloidal gold immunochromatographic assay (GICA) was developed for screening of CBX and CYA residues in chicken breast. Under optimal conditions, semiquantitative analysis results were visible by eye, with a visual limit of detection of 8 μg/kg for CBX and CYA, and cut-off values of 20 μg/kg for CBX and 40 μg/kg for CYA in chicken breast. Quantitative analysis could be performed using a hand-held strip scanner, with a calculated limit of detection of 2.92 μg/kg for CBX and 2.68 μg/kg for CYA in chicken breast. Validated by liquid chromatography-MS/MS, the developed GICA provides a useful tool for rapid on-site CBX and CYA residue screening in chicken breast.

A one-step incubation ELISA kit for rapid determination of dibutyl phthalate in water, beverage and liquor

A one-step incubation ELISA kit based on monoclonal antibody against dibutyl phthalate (DBP) was developed. After optimizing concentrations of coating antigen, antibody and composition of the assay buffer, an inhibition curve was plotted. The IC50 is 29.6 ng·mL-1, and the detection limit for DBP is 3.6 ng·mL-1. Compared with other ELISA methods, this ELISA kit had a simpler sample preparation, costed less time for detection and could detect more types of sample. The recoveries of DBP in water, beverage and liquor samples were range from 78% to 110.4%, the range of coefficient of variations is 7.7-15.3%. The cross reactivity was very low (&1%) except that for butyl benzyl phthalate (3.9%) and the di-isobutyl phthalate (12.5%). The detection results in liquor showed good correlation with those from GC-MS. All data above indicated that this kit could be used as the fast and high-throughput screening of DBP in water, beverage and liquor.

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.

Gold Nanoparticle-Based Paper Sensor for Simultaneous Detection of 11 Benzimidazoles by One Monoclonal Antibody

A colloidal gold immunochromatographic assay based on a generic monoclonal antibody is developed for the simultaneous detection of benzimidazoles and metabolite residues in milk samples. The monoclonal antibody is prepared using 2-(methoxycarbonylamino)-3H-benzimidazole-5-carboxylic acid as the hapten, and it can recognize 11 types of benzimidazoles simultaneously. The immunochromatographic strip is assembled and labeled using gold nanoparticles. This strip can detect 11 benzimidazoles including albendazole, albendazole s-oxide, albendazole sulfone, fenbendazole, fenbendazole sulfone, flubendazole, mebendazole, parbendazole, oxfendazole, oxibendazole, and carbendazim within 15 min in milk samples. Results are obtained visually with the naked eye, and the cutoff values and the visual limit of detection values for these benzimidazoles are 25, 6.25, 12.5, 12.5, 50, 25, 50, 50, 50, 6.25, and 25 ng mL^-1 , and 6.25, 3.125, 3.125, 1.56, 12.5, 6.25, 12.5, 12.5, 6.25, 0.78, and 12.5 ng mL^-1 , respectively. Results are also obtained using a hand-held strip scan reader, with calculated limit of detection values for these benzimidazoles of 0.83, 0.77, 1.83, 0.98, 7.67, 3.50, 3.96, 5.71, 0.92, 0.59, and 1.69 ng mL^-1 , respectively. In short, the developed paper sensor is a useful tool for rapid and simple screening of residues of benzimidazoles in milk samples.

Development of an immunochromatographic assay as a screen for detection of total phthalate acid esters in cooking oil

Phthalate acid esters (PAEs) contamination raised concerns as a result of migration from food packaging and environmental exposure. Because of the adverse effects of PAE reported in humans, the aim of this study was to examine the ability to screen for the detection these chemicals as an indicator of potential exposure. Too develop a sensitive screening test to determine PAE, a specific polyclonal antibody against phthalic acid (PA), the hydrolysate of PAEs, was used as a marker of total PAEs. This method involved the use of 4-aminophthalic acid (APA) as an immunizing hapten to generate antibody. Subsequently, this antibody conjugated with labeled gold nanoparticles (GNPs) was then used to develop an immunochromatographic assay (ICA) for visually detecting PA. After establishing optimal assay conditions, the ICA strip detected visually PA at 3 μg/ml rapidly in less than 5 min. Further, this assay exhibited reliable specificity for PA with no apparent cross-reactivity with structurally related PAEs. A significant correlation between data obtained with the ICA strip and high-performance liquid chromatography (HPLC) analysis was achieved using cooking oils as model spiked samples. The proposed use of ICA offers an effective tool for rapid on-site screening for total PAEs in cooking oils.

An ultra-sensitive monoclonal antibody-based enzyme-linked immunosobent assay for dibutyl phthalate in human urinary

Dibutyl phthalate (DBP) has been extensively used as a plasticizer in many daily products, which is highly toxic to human, notably affecting the reproductive and developmental function. As the previous method is expensive, time-consuming, low sensitivity and just focused on the environment. Present study was aimed to establish an ultra-sensitive and simple method based on good quality monoclonal antibody, applying to evaluate excretion level of DBP in urine samples of Chinese population directly. A monoclonal antibody was generated and characterized after fusion of myeloma cells with spleen cells isolated from BALB/c mouse. The mouse was previously immunized using a specially designed amino derivative of DBP conjugated with bovine serum albumin (BSA) as immunogen. Cross-reactivity values of the monoclonal antibody against DBP, di-isobutyl phthalate (DIBP) were observed 100% and 1.25%, while for dimethyl phthalate (DMP), butyl benzyl phthalate (BBP) and didecyl phthalate (DDP) the values were <0.06%. The standard curve was constructed at 0-50 ng mL(-1) and good linearity (R(2)=0.994) was achieved. The observed IC50 (7.34 ng mL(-1)) and LOD (0.06 ng mL(-1)) values was improved 1000-fold to polyclonal antibody and 5-fold to other monoclonal antibodies. A total 1246 urine samples were analyzed and the detection frequency of DBP was observed 72.87% by ic-ELISA. The 95th percentile and mean concentration of DBP were 12.07 and 3.00 ng mL(-1). Acceptable recovery rates of DBP were 97.8-114.3% and coefficients variation 5.93-11.09%. The concentrations of DBP in females were found significantly higher (p<0.05) than males. Similarly, the DBP in middle aged and low educated individuals was found higher (p<0.001) than the others. Considering the adverse health effects, DBP internal exposure in the Chinese population should be reduced. The ic-ELISA method has been proved as a cost effective, specific, and highly sensitive screening tool to detect DBP in urinary samples.

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.