Smartphone Detection of Escherichia coli From Field Water Samples on Paper Microfluidics

Smartphone detection of Escherichia coli from field water samples is successfully demonstrated using paper microfluidics. A three-channel paper chip is designed and fabricated, with a negative control channel preloaded with bovine serum albumin (BSA)-conjugated beads and two E. coli detection channels preloaded with anti-E. coli-conjugated beads, for low- and high-concentration detection. Field water samples are introduced to the paper chip by dipping or pipetting, and the antigens from E. coli travel through the paper fibers by capillary action while the dust/soil or algae particles are effectively filtered. Antibody-conjugated beads, confined within the paper fibers, immunoagglutinate in the presence of E. coli antigens, while BSA-conjugated beads do not. The extent of immunoagglutination is quantified by evaluating Mie scatter intensity from the digital images taken at an optimized angle and distance using a smartphone. The assay results show excellent agreement with the MacConkey plate results, i.e., the count of viable E. coli. The scatter simulation procedure is introduced to substitute for experimental optimization, such that the proposed method can be easily adapted to the other types of samples. A smartphone application is developed, incorporating the internal gyroscope of a smartphone, to allow the user to position the smartphone at an optimized angle of scatter detection. The detection limit is single-cell-level and the total assay time is 90 s.