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The rapid, inexpensive, and on-site detection of bacterial contaminants using highly sensitive and specific microfluidic sensors is attracting substantial attention in water quality monitoring applications. Cell-imprinted polymers (CIPs) have emerged as robust, cost-effective, and versatile recognition materials with selective binding sites for capturing whole bacteria. However, electrochemical transduction of the binding event to a measurable signal within a microfluidic device to develop easy-to-use, compact, portable, durable, and affordable sensors remains a challenge. For this paper, we employed CIP-functionalized microwires (CIP-MWs) with an affinity towards E. coli and integrated them into a low-cost microfluidic sensor to measure the conductometric transduction of CIP–bacteria binding events. The sensor comprised two CIP-MWs suspended perpendicularly to a PDMS microchannel. The inter-wire electrical resistance of the microchannel was measured before, during, and after exposure of CIP-MWs to bacteria. A decline in the inter-wire resistance of the sensor after 30 min of incubation with bacteria was detected. Resistance change normalization and the subsequent analysis of the sensor's dose-response curve between 0 to 109 CFU/mL bacteria revealed the limits of detection and quantification of 2.1 × 105 CFU/mL and 7.3 × 105 CFU/mL, respectively. The dynamic range of the sensor was 104 to 107 CFU/mL where the bacteria counts were statistically distinguishable from each other. A linear fit in this range resulted in a sensitivity of 7.35 μS per CFU/mL. Experiments using competing Sarcina or Listeria cells showed specificity of the sensor towards the imprinted E. coli cells. The reported CIP-MW-based conductometric microfluidic sensor can provide a cost-effective, durable, portable, and real-time solution for the detection of pathogens in water. [ABSTRACT FROM AUTHOR]

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 dose-response 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 × 102 and 3 × 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 non-specific 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. [Display omitted] • Magnetic cell imprinted polymer microparticles (CIP-MPs) and their capturing optimization in a microchannel. • Rapid E. coli detection by fluorescent magnetic CIP-MPs in a microfluidic device. • Low-cost and durable all-polymeric sensor for bacteria detection in water. • Sensor limit of detection at 4 × 102 CFU/mL and limit of quantification at 3 × 103 CFU/mL. • Sensor specificity towards E. coli , providing a reliable tool for targeted bacterial quantification. [ABSTRACT FROM AUTHOR]

Molecularly imprinted polymers (MIPs) have been utilized as biorecognition elements in various fields such as separation, sensing and imaging due to their easy accessibility and high binding capacity to target molecular analytes. To expand the application scope of MIPs and widen their range of targets to microorganisms, we have developed a methodology for the synthesis of MIP shells on the surface of polystyrene microparticles (MPs) with a binding affinity towards E. coli OP50 as a bacterial surrogate. Monodisperse MIP-based core–shell microparticles (MIP-MPs) with controllable shell thickness ranging from 0.25 μm to nearly 3.5 μm were produced using a stepwise polymerization method. Optical and fluorescence microscopy as well as scanning electron microscopy were used for characterization of MIP-MPs and MPs coated with non-imprinted polymers (i.e., NIP-MPs) under various timing and temperature settings. E. coli OP50 imprinting and rebinding experiments were conducted using the MIP-MPs with a suitable MIP shell thickness of 2–3 μm. Capturing experiments were carried out with different concentrations of NIP- and MIP-MPs (i.e., 102, 103 and 104 particles/mL) to investigate the uptake ratio of bacteria (104 cells/mL) and its particle dose-dependency. The optimum uptake ratio of E. coli was approximately 74%, which was achieved using 103 MIP-MPs/mL. NIP-MPs had reduced bacteria recovery and results were statistically lower than MIP-MPs, showing the affinity of our MIP shells towards microorganisms. The results reported here provide a new fabrication methodology and binding efficiency of core–shell MIP-MPs to bacteria, and can create the basis for the fabrication of various imprinted coating layers on spherical substrates with potential applications in bioseparation and point-of-care sensing. [Display omitted] • Polystyrene microparticles (MPs) with molecularly imprinted polymer (MIP) shells. • MIPs composed of four monomers for enhanced imprinting of bacteria cells on MPs. • Two-step temperature-dependent polymerization to control MIP shell thicknesses. • Optimum MIP-MPs to bacteria ratio of 1–10, showing high-level MIP imprinting. • MIP-MPs reached 74% bacteria capturing efficacy improving the state of the art. [ABSTRACT FROM AUTHOR]