A low-cost paper and solution based colorimetric detection of bacteria using glucose-functionalized gold nanoparticles

Colorimetric bacterial detection based on functionalized gold nanoparticles (AuNPs) is simple, fast, and highly sensitive, and has been applied in real-time on-site monitoring and rapid testing. In this study, a paper- and solution-based colorimetric sensor for the direct detection of bacteria was developed using glucose-functionalized phyto-synthesized AuNPs (Glu-AuNPs) as a transducer. The proposed paper-based colorimetric assay was investigated for six different bacterial strains, three gram-negative bacteria namely E. coli (ATCC 11229), Pseudomonas aeruginosa (ATCC 10231), and Klebsiella pneumonia (ATCC 13884) and three gram-positive bacterial pathogens namely Staphylococcus aureus (ATCC 25923), Streptococcus pneumoniae (ATCC 49619), and Bacillus subtilis (ATCC 21332). The color intensity variation and color shifts in the affordable paper-based and solution-based sensors respectively could be observed with the naked eye. The sensing performance was evaluated using Adobe Photoshop, which exhibited an increase in color intensity with increasing bacterial concentration, with a recovery of 96 % for E.coli. Solution-based sensor exhibiting blue-shifted absorbance relies on the mechanism of repulsive interactions between negatively charged bacteria and negatively charged Glu-AuNPs. This assay is suitable for the detection of bacteria in the real sample. The direct detection of bacteria by simple colorimetric assay utilizing functionalized AuNPs has tremendous potential for bacterial detection in contaminated water.