A paper-based microfluidic biosensor integrating zinc oxide nanowires for electrochemical glucose detection

This paper reports an electrochemical microfluidic paper-based analytical device (EμPAD) for glucose detection, featuring a highly sensitive working electrode (WE) decorated with zinc oxide nanowires (ZnO NWs). In addition to the common features of μPADs, such as their low costs, high portability/disposability, and ease of operation, the reported EμPAD has three further advantages. (i) It provides higher sensitivity and a lower limit of detection (LOD) than previously reported μPADs because of the high surface-to-volume ratio and high enzyme-capturing efficiency of the ZnO NWs. (ii) It does not need any light-sensitive electron mediator (as is usually required in enzymatic glucose sensing), which leads to enhanced biosensing stability. (iii) The ZnO NWs are directly synthesized on the paper substrate via low-temperature hydrothermal growth, representing a simple, low-cost, consistent, and mass-producible process. To achieve superior analytical performance, the on-chip stored enzyme (glucose oxidase) dose and the assay incubation time are tuned. More importantly, the critical design parameters of the EμPAD, including the WE area and the ZnO-NW growth level, are adjusted to yield tunable ranges for the assay sensitivity and LOD. The highest sensitivity that we have achieved is 8.24 μA·mM−1·cm−2, with a corresponding LOD of 59.5 μM. By choosing the right combination of design parameters, we constructed EμPADs that cover the range of clinically relevant glucose concentrations (0−15 mM) and fully calibrated these devices using spiked phosphate-buffered saline and human serum. We believe that the reported approach for integrating ZnO NWs on EμPADs could be well utilized in many other designs of EμPADs and provides a facile and inexpensive paradigm for further enhancing the device performance. A paper-based microfluidic biosensor with an electrode decorated with zinc oxide nanowires is used for sensitive detection of glucose. Microfluidic paper-based analytical devices (μPADs) are attractive platforms for diagnostic biosensing, particularly in areas lacking sophisticated medical resources, because they are inexpensive and easy to operate. Now, Xiao Li, Chen Zhao and Xinyu Liu at McGill University in Canada have produced a high-sensitivity electrochemical μPAD that incorporates a working electrode decorated with zinc oxide nanowires. The μPAD has enhanced biosensing performance and stability, and can be produced by a simple, low cost process. By judicial selection of the design parameters, the researchers produced μPADs that can accurately detect glucose in a clinically relevant concentration range (0—15 millimolar) in human serum. They consider that the performance of other electrochemical μPADs could be enhanced through the integration of zinc oxide nanowires.

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