Naked eye colorimetric detection of Escherichia coli using aptamer conjugated graphene oxide enclosed Gold nanoparticles

• Successfully generated aptamers against E. coli bacterial cells through Cell-SELEX. • Aptamer-nanoprobe based sensitive and selective visual detection assay for E. coli was developed. • Graphene oxide enhances the loading capacity of aptamer on nanoprobe making it more sensitive. • Limit of detection using this nanoprobe was 10 2 cells/mL in Mili Q water and spiked coconut water. • The proposed detection assay was performed in glass capillary to mimic microfluidic channel. E. coli is the most common foodborne bacteria causing illnesses including diarrhea, fever, and death if left undiagnosed and untreated, which makes its detection most important. Traditional detection methods such as culture methods, PCR, or ELISA are time-consuming and require skilled manpower. To overcome the disadvantages of traditional detection methods, a fast, easy, and cost-effective platform is required. ssDNA aptamer is a stable, sensitive, and selective biomolecule used extensively for detection. To provide naked eye visible detection, gold nanoparticles (AuNPs) were used, and to increase the aptamer conjugation, AuNPs were covered with Graphene Oxide. Thus, the overall sensitivity of the designed nanoprobe was also augmented. Therefore, exploiting the properties of gold nanoparticles and graphene oxide, a detection platform with aptamer conjugation has been developed in this study. In the manifestation of E. coli cells, the visible color change was observed from red to blue within an hour incubation. The limit of detection observed visually was 10 2 cells/mL with GO coating and 10 3 cells/mL without GO. The detection limit in real time coconut water samples was also 10 2 cells/mL. This platform was found to be applicable in glass capillary which provides opportunities for making a point of care detection device.