A Non-Contact Colorimetric Sensor Based on Bromocresol Green-Nafion Composite for Rapid Pre-Screening of Urinary Tract Infections

Urinary tract infections (UTIs) are among the most prevalent bacterial infections and require timely detection to prevent complications such as acute kidney injury and bloodstream infections. Conventional diagnostic methods, such as bacterial culture, are time-consuming and resource-intensive, necessitating more efficient alternatives. To address this, a noncontact colorimetric sensor is developed for rapid UTI prescreening based on volatile organic compounds (VOCs) emitted from Escherichia coli (E. coli) - contaminated urine. This system employs a bromocresol green-Nafion composite for the selective detection of E. coli-associated VOCs. Mechanistic studies reveal that E. coli growth increases urinary ammonia concentration, inducing a pH-dependent colorimetric shift in bromocresol green. Nafion enhances specificity by lowering the solution's pH via sulfonic acid (-SO₃H) group dissociation, mitigating background ammonia interference while maintaining sensitivity to E. coli-derived VOCs. For practical use, a dual-strip configuration (bromocresol green and bromocresol green + Nafion) is integrated into a chamber accommodating urine-absorbing diapers, enabling real-time, non-contact detection. Experimental results demonstrated that 1.25 wt.% Nafion optimized selectivity, ensuring clear differentiation between normal and E. coli-contaminated urine through colorimetric changes. This sensor provides a simple, rapid, and non-invasive UTI pre-screening tool, especially suitable for infants and individuals with limited access to healthcare.