Optically Based Bacteria Hand-Held Sensor: From Fundamentals to Proof of Concept

Abstract

A prototype of a hand-held particle sensor based on digital inline holographic microscopy was developed to work as an early warning device to detect bacteria Escherichia coli (E. coli) in water within minutes. The aim of the device is to record holographic images of water samples and perform rapid analyses (less than 20 min) of these samples to give timely information about the levels of particulates, with the goal of detecting and quantifying pathogens such as E. coli in water samples. Using the hand-held sensor, laboratory trials were performed to compare the effectiveness of the sensor with traditional methods of detecting E. coli in water. To address the linearity of the sensor signal, a dilution series covering nine decades of bacterial suspensions were analyzed and a linear regression coefficient of determination (R2) of 86.4% was revealed. Preliminary studies have shown that the sensor can detect average values of E. coli levels from 7 colony forming units (CFU)/mL to 106 CFU/mL in deionized water spiked with the bacteria. The device can be essential for accurate and precise bacteria counts in drinking water systems inline or at home. The sensor’s major advantages are its portability, low cost, ease of operation, low power consumption rate, and no consumption of chemical reagents is needed to visualize and count E. coli.