Calibration-free disposable electrochemical sensor with co-facing electrodes for viscosity monitoring of plasma samples.

Plasma viscosity measurement is crucial in clinical diagnostics, providing insights into blood rheology and health status. Traditional methods, such as capillary and rotational viscometers, require large sample volumes and complex calibration. This study presents a novel disposable electrochemical sensor with co-facing electrodes for viscosity monitoring of plasma samples. The sensor independently determines the diffusion coefficient (D) of the electroactive test molecule ferrocyanide, eliminating the need for calibration curves. This enables the subsequent calculation of the solution's viscosity via the Stokes-Einstein relation. The sensor's performance was validated against a standard quartz-crystal microbalance method, demonstrating high accuracy and reliability. It maintained consistent measurements despite the presence of common electroactive plasma interferents such as ascorbic acid (≤160 μM), dopamine (<9.0 nM), uric acid (<1.0 mM), and urea (<15.6 mM). Although these interferents impacted D at concentrations exceeding twice the maximum levels typically present in plasma, the sensor exhibited robust performance under normal physiological conditions and standard interferent concentrations. The sensor offers rapid response times of less than 20 s, requires only 7 μL of sample, and is cost-effective, making it suitable for point-of-care applications. Bland-Altman plot analysis confirmed its precision, showing a mean difference of 0.00877 and narrow limits of agreement compared to the standard method used.