Drug and nanoparticle mediated rapid naked eye water test for pathogens detection

•A novel drug based colloidal assay for rapid detection pathogen detection was developed.•Colistin, a commonly used drug molecule was used for detecting bacteria based upon Plasmon changes of Gold nanoparticles.•The assay show visible colorimetric response up to 10 Cells mL−1.•The assay was also tested on tap and lake water samples. Inspired by the interaction of colistin with lipopolysaccharides (LPS) of the bacterial outer membrane, we describe a simple, cost effective and rapid assay for the detection of bacterial contamination in water samples. Colistin, a bactericidal drug, has been used by us in a receptor configuration for detection of pathogenic microorganisms without involving any tedious sample preparation step. The approach employs the cationic antibiotic drug for dual purpose, firstly, as a primary binder for pathogens and secondly, as an aggregator for negatively charged Gold nanoparticles (GNPs). The former consists of colistin binding to bacteria in water that renders GNPs free in solution thus depicting red color and the latter shows colistin driven aggregation of GNPs producing blue colored solution. The assay works in a two-step procedure that involves addition of colistin and GNPs to the water sample before results can be visualized based on color change. The assay is sensitive at a concentration up to 10 bacterial cells·mL−1 in a time frame of 5 min without requiring any expensive reagents and instruments.