Paper Strips Functionalized with a Mixture of ZnO Nanotubes and Mn₃O₄ Nanoparticles for Simultaneous Separation of Blood Plasma and Detection of Physiological Iron Levels

Deviations in iron levels in human blood beyond normal physiological thresholds can signify more than just iron deficiency anemia; they may also indicate serious conditions such as hemochromatosis, acute iron poisoning, active cirrhosis, or hepatitis, necessitating precise estimation of iron levels in vulnerable individuals. While bone-marrow-based detection is considered the gold standard, its procedural complexity makes it impractical. Thus, there is a critical need for alternative methods, particularly in resource-limited settings. Addressing these challenges, we introduce a paper-microfluidics integrated fast cyclic voltammetry kit capable of on-site plasma separation and simultaneous iron detection. This approach employs a single scanning rate of approximately 200 V/s across a nanomaterial-coated screen-printed electrode. The redox-active manganese component of the nanomaterial enables rapid peak determination due to its variable oxidation states and high redox potential. Moreover, the nanomaterial-coated electrode coupled to the porous architecture of the paper matrix enhances electron transfer rates, resulting in amplified cathodic currents. The sensor exhibits high selectivity, with cyclic voltammetry demonstrating a noticeable reduction in redox potential (approximately −0.8 V) and a high limit of detection. For a reference iron concentration of 27 μmol/L, the sensor generates a current of about 110 μA with minimal background noise. It boasts a rapid response time of 0.1 s (yielding an overall sample-to-answer detection time of around 2 min) and a sensitivity of 0.3 μg/dl, making it suitable for rapid point-of-care diagnostics. Furthermore, this approach offers broader applicability beyond iron detection, providing a platform for the highly sensitive, specific, and rapid detection of various target analytes in blood plasma without requiring complex device architecture or external fields.