Rapid and Quantitative Detection of Bacteria by Smartphone-based Colorimetric Analysis System

An efficient, convenient and rapid method for quantitative detection of bacteria was established with the self-developed smartphone-based colorimetric analysis system in this work. The boric acid group in 4-mercaptophenylboronic acid modified gold nanoparticles (4-MPBA-AuNPs) could be covalently bonded with the polysaccharides on the surface of bacteria, so as to achieve the identification of bacteria. When the concentrations of bacteria in 4-MPBA-AuNPs solution was different, the aggregation degree of 4-MPBA-AuNPs was different after adding excess amount of NaCI, and accordingly, the color of the solution was different. So, the quantitative detection of bacteria could be realized by using the smartphone-based colorimetric analysis system to take photos of 4-MPBA-AuNPs solution and performed digital colorimetric analysis of bacteria. 4-MPBA-AuNPs nanoprobes was easy to prepare with low cost, and had broad-spectrum for bacteria identification, which could meet the testing requirements for large quantities of samples. The application of smartphone based colorimetric analysis system could effectively reduce the interference of external environment and human subjective factors, improve the accuracy of bacterial colorimetric analysis. More importantly, by analyzing the RGB values of the image using this custom designed mobile phone App, the concentration of bacteria could be obtained directly, which further improved the effectiveness of bacterial detection. The detection time of this method was short (40 min), and it had a wide linear range (104-109 CFU/mL) with a detection limit of 5.74x102 CFU/mL. Besides, the recoveries of spiked pork samples were 103.2%-115.7%, and the relative standard deviations were 3.3%-7.3%. In summary, this method was low-cost, easy to operate and popularized, which provided a new method to food safety supervision.