Cu-porphyrin PCN-222 MOF Hybridized with Au Nanoclusters to Accelerate Electron Transfer for Ultrasensitive Detection of 25-Hydroxyvitamin D3.

The present work reports the development of an electrochemical immunosensor using a metal-organic framework (MOF)/metallic nanocluster electrode surface for the detection of 25-hydroxy vitamin D3 (VitD3). The copper metal-coordinated organic porphyrin linker, 4,4,4,4-(Porphine-5, 10, 15, 20-tetrayl) tetrakis (benzoic acid) (Cu-TCPP) was prepared and utilized for the synthesis of Zirconium-based PCN-222(Cu) MOF, which was further conjugated to gold nanoclusters (AuNC). The fluorine-doped tin oxide (FTO) was sequentially modified with this nanoconjugate, p-phenylenediamine (PDA), bioreceptor antibodies (anti-VitD3), and blocking agent, 6-mercaptohexanol (MCH) to achieve the biosensor electrode, i.e., FTO/AuNC@PCN-222(Cu)/PDA/anti-VitD3/MCH. The electrode was used to detect VitD3 in a wide linear range, i.e., 1 to 108 fg/ml via electrochemical impedance spectroscopy. The detection limit and analytical sensitivity were found to be 0.088 fg/ml and 1.35 × 102 Ω/fgml-1 cm-2, respectively, with retained ∼91.9% of the actual response till 42 days in the presence of 103 fg/ml VitD3. The ultra-sensitivity of the biosensor in spiked human serum and real samples, was validated with the standard ELISA. Its outstanding selectivity and analytical performance open up new avenues for integrating AuNC@PCN-222(Cu)-based electrochemical sensors into miniaturized, cheaper, and real-time diagnostics.