Split photoelectrochemistry for the immunoassay of α-fetoprotein based on graphitic carbon nitride

Herein we introduce a novel, split protocol for the photoelectrochemical (PEC) immunoassay of a-fetoprotein (AFP) (taken as a model) without the need for fixing antibody/antigen on the surface of electrode. Alkaline phosphatase (ALP), as a catalytic label tracer, catalyzed the hydrolysis of the substrate of o-phosphonoxyphenol (OPP) to in situ generated an electron donor of catechol (CA), which greatly promoted the photocurrent intensity of graphitic carbon nitride (g-C3N4). High-throughput and improved sensitivity was achieved through a split-type PEC protocol, which separated the enzyme reaction (conducted in microwell plates) and the PEC detecting (made in a PEC cell) in different sites, avoiding the steric hindrance for the reaction between the electron donor and the immobilized g-C3N4. This signal-on PEC sensor showed excellent analytical performance to the activity of ALP. The activity of ALP was detected from 0.07 to 110 U/L. On the basis of the high sensitivity of the response of the method to ALP, immunoassay of AFP was realized with a detection linear range from 0.5 pg/mL to 100 ng/mL. A detection limit of 0.2 pg/mL was achieved for AFP. This methodology was also applied to detect AFP in serum samples with satisfactory results. (C) 2016 Elsevier B.V. All rights reserved.