Electrochemical Biosensor Based on Dual-Ligand Functionalized Lanthanide-Encapsulated Polyoxometalate Conductive Polymer Film for Detecting Broad-Spectrum Tumor Marker MicroRNA-155

In this work, a dual-ligand functionalized lanthanide-encapsulated selenotungstate [H₂N(CH₃)₂]₁₆Na₂H₁₀[Ho₆(H₂O)₁₀(HPACA)₄W₁₀O₂₈(Ac)₂][SeW₉O₃₃]₆ · 60H₂O (1, HPACA = 2-pyrazinecarboxylic acid, HAc = acetic acid) was successfully acquired by simultaneously incorporating rigid HPACA and flexible Ac^– ligands to one reaction system. Interestingly, the polyanion [Ho₆(H₂O)₁₀(HPACA)₄W₁₀O₂₈(Ac)₂][SeW₉O₃₃]₆^28– of 1 is composed of six trivacant Keggin-type [B-α-SeW₉O₃₃]^8– units interconnected through an organic–inorganic hybrid dual-ligand bimetallic [Ho₆(H₂O)₁₀(HPACA)₄W₁₀O₂₈(Ac)₂]²⁰⁺ cluster. Moreover, the 1@PNMPy film (PNMPy = poly(N-methylpyrrole)) was successfully prepared through an electrochemical polymerization strategy. The doping of 1 significantly narrows the bandgap in the 1@PNMPy film, which enables the 1@PNMPy film to exhibit remarkable conductivity and rapid electron transfer capability. Then, the 1@PNMPy film-modified glassy carbon electrode was used to construct a 1@PNMPy-based electrochemical biosensor (ECBS), which achieves sensitive electrochemical detection (a low limit of detection of 0.108 fM and a wide concentration detection range of 10^–8–10^–15 M) for broad-spectrum tumor marker microRNA-155. Also, the 1@PNMPy-based ECBS has a good specific recognition performance for microRNA-155 in a variety of interfering media. The research not only contributes to a deeper understanding of the synthetic chemistry of multicomponent polyoxometalate (POM)-based materials but also can further expand innovative applications of multicomponent POM-based materials in electrochemical detection and electrochemical devices.