Colorimetric paper strip sensor for the detection of total bacterial count in milk

Background:

Due to its perishable nature, milk is quite vulnerable to microbial contamination. To guarantee the quality and safety of milk and milk products, it is crucial to evaluate the microbiological load of milk. It represents the hygienic conditions upheld during procurement and processing and acts as a preliminary indicator of milk’s keeping quality. Even though they are regarded as the gold standard, conventional microbiological testing procedures rely on time-consuming and labour-intensive pour plate techniques. Flow cytometry (D-Count), and the direct epifluorescent filter technique (DEFT) are examples of rapid detection techniques that can yield data in 8–24 hours. Additionally, the widely utilized MBRT exam takes at least 30 minutes. However, these methods are frequently inappropriate for ordinary industrial analysis and require costly equipment and skilled workers. As a result, there is an increasing demand for innovative, quick, accurate, user-friendly, economical, and sensitive techniques for figuring out the number of bacteria in milk.

Technology Details:

Colorimetric sensors are straightforward, accurate, portable, inexpensive, quick, dependable, user-friendly, and non-invasive instruments that don’t need sophisticated equipment or specialist staff. One of the most promising conducting polymers for creating colorimetric biosensors for identifying foodborne microbes is polyaniline (PANI). This is explained by its extreme sensitivity to variations in the pH and electrical conductivity of its microenvironment. The invention of a paper strip-based colorimetric sensor that uses polyaniline nanoparticles to measure the aerobic plate count in milk has been shown in earlier research. The detection principle is based on detecting changes in the optimal growth medium’s pH and conductivity brought on by the generation of ionic and acidic metabolites during bacterial growth. Through proton doping, these metabolites interact with the immobilized pH-sensitive polyaniline nanoparticles on the paper strips, boosting their conductivity. This process causes the emeraldine base form to convert into the emeraldine salt form, which is followed by a noticeable shift in color from blue to green. Polyaniline nanoparticles, a pH- and conductivity-responsive substance that changes colour in the presence of microbial metabolites, are used in the developed colorimetric paper-strip sensor. When bacteria proliferate in milk or enriched medium, they release ionic and acidic by-products that interact with the polyaniline matrix, resulting in a measurable and visible colour shift from blue to green. In milk with a high microbial load, this transition occurs within 20 minutes. The sensor also produces distinct colour grades corresponding to different milk quality levels: green for poor quality, greenish-blue for fair quality, bluish-green for good quality, and blue for very good quality. This method makes it possible to quickly determine the microbial load without the use of costly equipment, incubation plates, or specialist expertise. This invention overcomes the drawbacks of traditional

microbiological techniques, which are labour-intensive, cumbersome, and require specialized staff and laboratory equipment, by offering a quick, easy-to-use, and affordable way to evaluate the microbial quality of milk. Novelty Features of the Colorimetric Paper-Strip Sensor § Rapid detection: Compared to traditional procedures, MBRT methods, and other quick techniques like D-count, DEFT, etc., it provides results within 20 minutes, allowing for almost real-time milk quality testing. § Cost-effective and low-resource compatible: It works without electricity, equipment, or trained workers, which makes it ideal for small-scale processors, cooperative dairies, dairy farms, and collecting centres. § Easy to use and portable: Even inexperienced users can easily conduct on-site testing thanks to the lightweight paper-strip style. § The distinct colorimetric readout eliminates the need for sophisticated analytical equipment by producing a clear, observable color shift (from blue to green) in response to microbial metabolites. Visual observation can be used to further quantify detection. § High sensitivity to microbial activity: Polyaniline pectin (PANI-PEC) nanoparticles can detect spoiling early because they react quickly to minute changes in conductivity and pH caused by bacterial metabolism. § Environmentally robust: PANI-PEC has a long shelf life, constant performance in field circumstances, and outstanding thermal and environmental stability. § Scalable and adaptable platform: The sensor may be customized for different food matrices and microbial targets or altered with different medium formulations, making it adaptable and deployable in a variety of applications.