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

This paper reports an electrochemical microfluidic paper-based analytical device (E mu PAD) for glucose detection, featuring a highly sensitive working electrode (WE) decorated with zinc oxide nanowires (ZnO NWs). In addition to the common features of mu PADs, such as their low costs, high portability/disposability, and ease of operation, the reported E mu PAD has three further advantages. (i) It provides higher sensitivity and a lower limit of detection (LOD) than previously reported mu PADs 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 E mu PAD, 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 mu A center dot mM(-1)center dot cm(-2), with a corresponding LOD of 59.5 mu M. By choosing the right combination of design parameters, we constructed E mu PADs 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 E mu PADs could be well utilized in many other designs of E mu PADs and provides a facile and inexpensive paradigm for further enhancing the device performance.