User-friendly lab-on-paper optical sensor for the rapid detection of bacterial spoilage in packaged meat products

A lab-on-paper colorimetric sensor for detection and quantification of bacterial meat spoilage is reported. Bromocresol purple (BCP) and bromothymol blue (BTB) were used for the construction of the proposed sensor. An Android application allowing fast detection and accurate quantification of bacteria in the spoiled chicken meat samples was developed. The sensor was applied to the determination of spoilage in real chicken-meat samples, at chiller and room temperatures, and can be used for producing smart meat-packaging films. Linearity ranges were found to be 11.2 × 10³ to 1.12 × 10⁶ and 38.0 × 10³ to 1.12 × 10⁶ CFU g^-1 for BTB and BCP, respectively. The calibration plots showed correlation coefficients (r) of 0.9998 (slope: 2.48 g CFU^-1) and 0.9999 (slope: 1.95 g CFU^-1) in case of bromothymol blue and bromocresol purple, respectively. The Android application uses standard images to plot a calibration curve for calculating the microbial count in the samples and relates it to the standard limits. Thereafter, the application shows a message with the product's freshness degree ranging from excellent to poor.