A biosensor is an analytic device that employs biological reactions to detect target analytes and convert these reactions into quantifiable signals. Colorimetric biosensors, such as the PANI-PEC strip, represent a rapid, simple, accurate, and cost-effective detection method. The PANI-PEC strip, composed of polyaniline (a conducting polymer) and pectin (a stabilizer), is distinguished by its eco-friendly properties, excellent conductivity, strong biomolecule interactions, and multiple color transitions. This biosensor can detect food spoilage organisms like E. coli, coliforms, and total bacterial counts, identifying bacterial levels ranging from 10⁸ to 10⁴ in just 20 minutes.
The developed assay is based on the principle that bacterial growth in a carbohydrate-rich medium produces acidic metabolites. These metabolites interact with pH-sensitive polyaniline nanoparticles on paper strips, which enhances conductivity through proton doping, causing a color shift from blue to green as the base form transitions into the salt form.
For detection, the developed paper strip sensor was dipped into 500 µL of raw milk (after milking) and incubated at 37°C for 20 minutes. To validate the sensor's effectiveness, it was tested on 150 raw milk samples and 50 pasteurized milk samples.
Observed color changes on the paper strips were graded as being of very good (blue), good (bluish green), fair (greenish-blue), and poor (green) quality with microbial loads of ≤ 10⁴, 10⁵ – 10⁶, 10⁷– 10⁸, and ≥10⁸ cfu/ml, respectively.
This newly developed sensor provides a sensitive, cost-effective, and user-friendly method for evaluating raw milk quality at the reception dock, offering an alternative to traditional methods like the methylene blue reduction test (MBRT), direct microscopic count, and aerobic plate count (APC). It facilitates real-time analysis, reduces testing time, and is applicable to raw milk, pasteurized and dried milk. Incorporating this sensor into routine testing can enhance product quality, ensure regulatory compliance, and streamline operations, thereby improving overall dairy product safety and quality.
