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. coli concentration from 104-107 CFU/mL (R2 = 0.9577). This method only requires the addition of 10 μL detection sample and 10 μL 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.