Coupling metal-organic framework nanosphere and nanobody for boosted photoelectrochemical immunoassay of Human Epididymis Protein 4.

A "signal-on" photoelectrochemical (PEC) immunosensor for highly sensitive detection of Human Epididymis Protein 4 (HE4), a new serum biomarker of ovarian cancer with small molecular weight, was fabricated by coupling the porphyrin-based metal-organic framework (MOF) nanosphere (nPCN-224) and Nanobody (Nb). To label the Nb, the nPCN-224 with an average size of 160-200 nm was prepared by solvothermal method. The mechanism for the photocurrent generation of nPCN-224 was systematically investigated, showing that the dissolved O2 in aqueous solution participated in the charge separation and transport during the photoelectric conversion by generating O2˙-, which resulted in a 6-fold enhanced photocurrent by using ascorbic acid as the O2 ˙- scavenger. Moreover, the inherent structural porosity of nPCN-224 demonstrated advantage for reactant accessibility. Due to the superior properties of nPCN-224, and the high specificity and affinity of Nbs, the immunosensor exhibited a broad detection range from 1.00 pg mL-1 to 10.0 ng mL-1 and a detection limit of 0.560 pg mL-1, lower than most methods reported before. The immunosensor could clearly distinguish ovarian cancer patients in different stages from healthy individuals, and the as-obtained results matched well with those by traditional electrochemiluminescence immunoassay method from the hospital. This work would open a new avenue for PEC immunosensors in clinical diagnostics and evaluation of potential clinical efficacy.