A spatially multiplexed voltammetric magneto-sandwich assay involving Fe₃O₄/Fe-based metal-organic framework for dual liver cancer biomarkers

Voltammetric sandwich assays were constructed by integrating capture bioreceptors-conjugated magnetic nanocomposites, namely Fe₃O₄/MIL-101(Fe)-(NH)(CO)-COOH (FO/MOF) and alkaline phosphatase (ALP)-labeled detection antibodies on an eight-well screen-printed carbon ink electrode (SPCIE) for the simultaneous detection of liver cancer biomarkers, human tissue transglutaminase 2 (TGM2) and heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1). Magnetic FO/MOF nanocomposites were prepared via a simple microwave-assisted method; these not only provided large surface areas for covalently attaching capture bioreceptors, but also acted as a separator for the sandwich nanocomposites magnetically isolated from solutions. TGM2 and hnRNP A1 were first adsorbed onto anti-TGM2 (JU30–02)- and hnRNP A1 aptamer-FO/MOF conjugates, respectively, in buffer or serum followed by the corresponding adsorption of ALP-anti-TGM2 (2F4) and ALP-anti-hnRNP A1 to form the sandwich complexes of anti-TGM2 (JU30–02)-FO/MOF/TGM2/ALP-anti-TGM2 (2F4) and hnRNP A1 aptamer-FO/MOF/hnRNP A1/ALP-anti-hnRNP A1. After being magnetically accumulated on each well of the SPCIE surface, eight different voltammetric responses due to the reaction of ALP in the sandwich nanocomplex with 4-aminophenyl phosphate to produce 4-aminophenol and subsequently oxidize to 4-quinoneimine were concurrently measured for the quantitative analyses of both biomarkers. TGM2 and hnRNP A1 dynamic ranges in a buffer were 0.05–1.5 and 0.1–5 nM, respectively, with sensitivity of 0.331 and 0.104 μA/nM and detection and quantification limits of 6.7 and 22.3 and 19.6 and 65.3 pM, respectively. The performance was much less sensitive for undiluted serum samples, possibly due to the unavoidable matrix effect. Finally, the magneto-sandwich sensor was employed to directly analyze TGM2 and hnRNP A1 concentrations in various clinical serum samples.