Microneedle Combined with an Electrochemical Lateral Flow Immunoassay Strip for Highly Sensitive and Wide-Range Detection of Protein Biomarkers by Increasing the Reaction Contact Area

Electrochemical lateral flow immunoassay (eLFIA) strips have been widely used in sensitive, rapid, and quantitative detection of the disease biomarkers. However, due to the short electron tunneling distance (<10 nm), the traditional planar electrode (PE)-based eLFIA strip is blind to electroactive probes distributed in the micrometer-thick immunoreaction-completed nitrocellulose (NC) membrane. Herein, a microneedle electrode (MNE) was prepared and served as the working electrode in eLFIA. With a unique sharp needle structure, the MNE can easily pierce the NC membrane to reinforce the contact between the electrode and the NC membrane, thus spatially increasing the detection deepness and reaction area. Compared with PE-based eLFIA, this design enables more electroactive probes embedded in the NC membrane to participate in the electrochemical reaction, generating a larger current signal. In conjunction with using an electrochemical signal amplification strategy based on horseradish peroxidase, a low limit of detection (LOD) (0.96 pg mL^-1) and a wide linear range (25-300 pg mL^-1) were obtained in the detection of C-reactive protein. Furthermore, the MNE-based eLFIA strip behaved well in the analysis of clinical samples. We believe it holds great promise as a next-generation point-of-care platform with high sensitivity and a wide detection range for fast and quantitative disease biomarker detection.