Evaluation of thiodiglycolic acid as a urinary biomarker for exposure to vinyl chloride monomer: Development and analytical validation of a colorimetric method based on metal-organic frameworks

Vinyl Chloride Monomer (VCM) is an industrial contaminant and carcinogen classified in IARC group 1. Chronic exposure to VCM may lead to serious health problems. Thiodiglycolic acid (TDGA) acts as a biomarker for exposure to VCM; hence, its quantitative estimation in urine provides precise information about exposure level. In this study, the authors propose a newly developed colorimetric assay based on metal-organic framework (MOFs), specifically MIL-100(Fe), acting as a nanozyme. In particular, it shows strong peroxidase-like activity; as such, it generates blue color in response to hydrogen peroxide (H₂O₂) and 3,3',5,5'-Tetramethylbenzidine (TMB). The optimum reaction conditions were determined via response surface methodology (RSM) to maximize the assay's sensitivity and performance. Under optimal conditions, the method achieved a limit of detection (LOD) of 2.48 ppm and a linear range of 1 to 200 ppm. The assay demonstrated high accuracy and precision in spiked urine samples, with recoveries ranging from 93.74% to 96.81% relative to theoretical values. The proposed test provides ease of performance, scalability, and cost efficiency as well as acceptable specificity and sensitivity; hence, it would be an ideal method for estimating exposure levels to VCM in human workers. The developed colorimetric assay, in contrast to present gold standard techniques such as GC-MS, is transportable, and the analysis can be done either by an inexpensive UV-Vis spectrophotometer or a smartphone. The whole process can be accomplished in less than 15 min, which makes it amenable to site-specific biologic monitoring in the petrochemical industry. This can be especially relevant in developing nations. The proposed method bridges an important gap for biological monitoring in occupational health surveillance where a need for immediate, cost-effective, and transportable methods for testing TDGA exists.