Colorimetric and photographic detection of bacteria in drinking water by using 4-mercaptophenylboronic acid functionalized AuNPs

Water-borne bacterial infection is a growing problem worldwide. Rapid and reliable contamination detection method for drinking-water is in high demand. Herein, a colorimetric bacteria detection strategy based on 4-mercaptophenylboronic acid (4-MPBA) functionalized gold nanoparticles (AuNPs) is introduced. The immobilization of 4-MPBA-AuNPs on the surface of bacteria cells via covalent bonds impedes NaCl induced aggregation of 4-MPBA-AuNPs. The color shift due to AuNPs aggregation is observable with the naked eye and quantifiable through UV-Vis absorbance spectrum or digital-camera-based RGB analysis. This platform is validated with five strains of bacteria, including gram-positive and gram-negative strains, which demonstrated its capability for broad-spectrum bacteria detection. By using UV-Vis absorbance spectrum for bacteria quantification, a linear relationship is observed between absorbance intensity at 524 nm and E. tort concentration from 10(4)-10(7) CFU/mL (R-2 = 0.9577). This method only requires the addition of 10 mu L detection sample and 10 mu L NaCl, and the results are obtainable within 20 min. This study is the first documented report to utilize bacterial inhibition of salt-induced aggregation of 4-MPBA-AuNPs for broad-spectrum bacteria detection. The proposed colorimetric method offers a cost-effective solution for drinking-water quality control.