A Sensitive Colorimetric and Near-Infrared Fluorescent Probe for Tracing Slight pH Variation in Food Samples

Measurement of slight pH variation in food samples is valuable for assessing food freshness and quality. Herein, a novel colorimetric and near infrared (NIR) fluorescent probe, Hx, was developed to measure slight pH variation in various food samples. Probe Hx showed fluorescence response to pH in the NIR fluorescence region. Moreover, based on the unique transformation of the ring-opened form and ring-closed form, probe Hx displayed highly sensitive response to slight pH variation (0.1-0.2 pH units) near neutral pH. Also, probe Hx exhibited obvious colorimetric changes to pH. Probe Hx has been applied for accurately detecting pH in freshly squeezed juices. Importantly, upon fabricating the test paper, probe Hx was employed as a simple and sensitive tool to on-site monitor slight pH variation in packed meat in the process of spoilage. Additionally, upon detecting slight pH variation in potato tissues, the probe could be served for assessment of potato infected by silver scurf.