Flow Dynamics and Probe Positioning Effects in Microfluidic Optical Fiber Meta-Tip Biosensors

Optical fiber (OF)-based biosensors are increasingly attracting attention due to their high sensitivity and compatibility with minimally invasive diagnostics. In this work, we investigate the integration of a plasmonic metasurface-assisted Lab-on-Tip (LoT) OF probe within a microfluidic platform for the detection of the breast cancer biomarker ErbB2. The biosensor response was evaluated over a concentration range of 1-1000 ng/mL under controlled flow conditions. Experimental results reveal a strong dependence of sensing performance on probe positioning within the microfluidic channel, with reduced response observed near the channel center. Numerical simulations demonstrate that this behavior is governed by local flow velocity, which inversely affects analyte-probe interaction time. Additional experiments at different flow rates confirm that higher velocities reduce detection efficiency due to limited interaction time. These findings provide practical guidelines for optimizing microfluidic-assisted LoT biosensors. Furthermore, the proposed platform, owing to its compactness and compatibility with minimally invasive tools, represents a promising candidate for integration into point-of-care (PoC) diagnostic systems and Internet-of-Things (IoT)-enabled sensing networks.