Polyaniline nanoparticle based colorimetric sensor for monitoring bacterial growth

A simple, rapid and label free method for monitoring bacterial growth using polyaniline nanoparticle based colorimetric sensor has been demonstrated herein. The colorimetric response of the sensor relies on estimation of acidic by-products released by the bacteria during their growth. •A simple, rapid and label free method for monitoring bacterial growth demonstrated.•Visible color change of the sensor from blue to green during bacterial growth.•Sensor utilizes polyaniline nanoparticles and is generic in nature.•Sensor has potential for real life application in the form of a patch sensor.•Can be used on food/beverage carton to monitor bacterial contamination in real time. Detection of pathogens in food and water is important for quality monitoring and disease prevention. Herein, we report a simple and novel colorimetric sensor for detection of bacterial growth relying on estimation of its metabolic products. As a proof of the concept, utility of the sensor for detection of Escherichia coli (E. coli) is demonstrated. All major groups of microorganisms including E. coli commonly use the glycolytic pathway for glucose degradation in the presence or absence of oxygen, eventually releasing mixed acids like succinate, acetate, malate, etc. as by-products. Polyaniline, a conducting polymer, is highly sensitive to the presence of protons in its microenvironment and its protonic doping results in a visible color change. Hence, polyaniline nanoparticles were synthesized and the sensor films were fabricated by incorporating these nanoparticles in agarose gel. The films when used for real time monitoring of bacterial growth exhibited a visible color change from blue to green. Since no specific antibodies or receptors are used, the sensor is generic in nature and has potential for adaptation to real life applications in the form of patch sensor on cartons to gauge integrity and freshness of food items and beverages in real time.