Development and evaluation of colorimetric <scp>pH</scp> determination methods as a potential tool for biomarkers monitoring

Abstract BACKGROUND pH plays a critical role in biomedical applications due to its influence on biological processes, particularly the stability and functionality of protein biomarkers. Conventional pH measurement methods have limitations, including the need for frequent calibration, high cost, and susceptibility to temperature. Therefore, novel, accessible, and reliable strategies are required. This study aimed to compare two colorimetric methods – spectrophotometry with bromothymol blue (BTB) and pH test strips combined with image analysis (scanner and smartphone) – for pH determination in saliva samples as a potential tool for biomarker monitoring. RESULTS Calibration curves demonstrated a linear fit for the BTB spectrophotometric method and a sigmoidal fit for the pH test strips. In buffer solutions, the coefficient of determination was 0.987 (BTB), 0.999 (scanner), and 0.998 (smartphone), with an error below 5% for all methods. In saliva samples, pH values ranged from 6.3 to 7.64 (BTB, error &lt; 15%) and 6.47 to 8.31 (smartphone, error &lt; 5%). CONCLUSION The studied methods performed comparably to the potentiometer in buffer solutions, but only the smartphone‐based pH test strip method achieved similar accuracy in saliva. Commercial pH test strips are widely available and overcome semi‐quantitative and subjective limitations when combined with image analysis. This novel approach enhances accessibility and affordability, positioning smartphone‐assisted pH analysis as a promising alternative for real‐time biomarker monitoring and point‐of‐care applications. © 2025 Society of Chemical Industry (SCI).