A thread-based microfluidic electrochemical platform for whole-blood protein sensing using endogenous uric acid as a...

Electrochemical protein sensing in whole blood remains challenging because many existing assays rely on external redox probes, washing steps, and off-chip pretreatment such as plasma separation. Here, we present a thread-based microfluidic electrochemical platform for protein-related sensing in whole blood without external redox reagents by exploiting endogenous uric acid (UA) as a redox mediator. The device integrates capillary-driven plasma separation and electrochemical detection in a compact format. Within the thread network, blood cells are retained through a Ca²⁺-induced aggregation mechanism, enabling plasma delivery to the electrode interface without centrifugation. Target recognition is established through a blocking-type mechanism in which antigen-antibody complex formation suppresses the oxidation current of UA. Using C-reactive protein (CRP) as a model target, the platform showed concentration-dependent responses over a clinically relevant range. The limit of detection was 0.091 mg dL^-1 in PBS and 0.106 mg dL^-1 in the integrated blood-based device configuration. In a stepwise CRP spike-and-recovery experiment, recoveries of 103.9%, 99.6%, and 99.8% were obtained for three concentration levels, with all relative standard deviation (RSD) values below 1.20%. These results demonstrate excellent analytical accuracy and reproducibility of the proposed sensing platform. The inhibition-based signal was preserved across the physiologically relevant range of uric acid concentrations tested, suggesting that the sensing response is relatively insensitive to moderate variations in endogenous uric acid levels. In a preliminary porcine inflammation model, the CRP-related sensor response showed a delayed temporal association with WBC count, with a maximum cross-correlation of R = 0.85 at a lag of approximately 180 min. Together, these results validate the feasibility of reagent-free protein sensing directly from whole blood using endogenous electroactive molecules. This study introduces a simple sample-to-answer thread-based microfluidic platform and highlights a new strategy for decentralized biochemical analysis without external redox mediators.