Fluorescent bacteria detection in water using cell imprinted polymer (CIP) coated microparticles in a magnetophoretic microfluidic device

Molecular imprinting has advanced towards synthesizing whole-cell imprints of microorganisms such as bacteria on various sensor surfaces including wire electrodes, quartz crystal microbalances, and microparticles (MPs). We recently introduced cell-imprinted polymers (CIPs) coated on MPs, called CIP-MPs, for bacteria recovery from water. In this paper, we have advanced towards rapid fluorometric Escherichia coli (E. coli) detection by applying fluorescent magnetic CIP-MPs, which were captured by soft ferromagnetic microstructures integrated into a microfluidic channel. The shape of ferromagnetic microstructures was optimized numerically to enhance the magnetophoretic accumulation of CIP-MPs in the microchannel. The device was then fabricated and the flow rate required to enhance bacteria capturing efficiency by CIP-MPs was determined. Decreasing the flow rate reduced the flow-induced drag and increased the interactions between the bacteria and imprinted CIP cavities. Fluorescent imaging of the accumulated CIP-MPs was done before and after bacteria capturing to quantify the changes in the fluorescence intensity as E. coli cells were captured by CIP-MPs in the microchannel. The doseresponse curve of the sensor at 0-109 CFU/mL bacterial counts was obtained. Using the 3- and 10-sigma methods on the dose-response curve, the limits of detection (LOD) and quantification (LOQ) of the sensor were determined to be 4 x 102 and 3 x 103 CFU/mL, respectively, within a dynamic range of 102-107 CFU/mL. Lastly, the specificity of the CIP-MPbased sensor towards E. coli was tested and confirmed using Sarcina as a nonspecific target bacterium. In summary, our developed sensor offers a promising approach for rapid and low-cost detection of bacteria in water and is suitable for development of portable and durable all-polymeric sensors for point-of-need detection.

Automated summary

This paper introduces a new sensor for rapid and low-cost detection of bacteria in water, which utilizes fluorescent magnetic CIP-MPs and a microfluidic channel for quick detection of Escherichia coli. The shape of the magnetic microstructures is optimized to enhance the accumulation of CIP-MPs in the microchannel. The sensor has low detection and quantification limits, and exhibits specificity towards Escherichia coli.