High-performance photoelectrochemical immunosensor based on featured photocathode-photoanode operating system

Highlights

• An efficient photocathode-photoanode integrating strategy was reported to fabricate PEC immunosensor.

• The integrated PEC operating system was composed of TiO₂/AIS photoanode and CNT/CIS photocathode.

• The photocathode-photoanode platform owned excellent photoelectric property and anti-interference ability.

• The PEC immunosensor exhibited high sensitivity and good specificity for target biomarker detection.

Abstract

Photocathodic immunosensors generally exhibit fortified anti-interference abilities than photoanodic ones against the detection in biological specimens. Yet, the weak photocurrent signals of the photocathodes have limited evidently the detection performance. Herein, an efficient and feasible photoelectrochemical (PEC) immunosensor was developed on the basis of the featured photocathode-photoanode operating system. In the proposal, the elaborated PEC immunosensor integrated photocathode with photoanode, and the immune recognition occurred just on the photocathode. To illustrate the performance, α-fetoprotein (AFP) was selected as a target antigen (Ag) for detection. TiO₂ nanoparticles were decorated with AgInS₂ quantum dots (AIS QDs) to fabricate the TiO₂/AIS photoanode, and the carbon nanotubes (CNTs) were modified with CuInS₂ nanoflowers (CIS NFs) to prepare the CNT/CIS photocathode for the capture AFP antibody (Ab) anchoring. Target Ag detection depended on significant decrease of the photocurrent signal produced by large steric hindrance of the captured AFP molecules. Coupling excellent photoelectric property with anti-interference ability in this elegant PEC immunosensor, sensitive and specific probing of target Ag was realized. The proposed photocathode-photoanode integrating strategy provides a promising way to explore other high-performance PEC immunosensors against the detection in biological matrixes.

Introduction

Accurate and sensitive measuring of important biomarkers is of great significance for early diagnosis and surveillance of major diseases or cancers [[1], [2], [3]]. Photoelectrochemical (PEC) immunosensing as a booming analytical technique has aroused widespread interest, benefiting from its fascinating features of high sensibility, low background noise, simple instrument, easy operation, and low cost [[4], [5], [6]]. These distinct merits endow PEC immunosensing with rapid, real-time and high-throughput detection. PEC immunosensing generally combines photoactive material with immune bioprobe. With light illumination, an evident change on the photocurrent signal of the PEC immunosensor would be produced when the specific immunoreaction between immune bioprobe and target biomarker [[7], [8], [9]]. On the basis of the change extent of photocurrent signal, quantitative determination of the target biomarker could be realized. Since photocurrent signals are rooted from photoactive materials, photoactive materials as one of the two core components of PEC immunosensors play a crucial role in the sensing performance [[10], [11], [12]].

According to the nature of the photoactive materials (p-type and n-type), the build PEC immunosensors could be divided into photocathodic and photoanodic ones. Photocathodic immunosensors fabricated on p-type photoelectrodes are demonstrated to show better anti-interference abilities to reductive species [[13], [14], [15], [16]]. However, the weak photocurrent signals of photocathodes have impeded the enhancement of the sensing performances. Photoanodic immunosensors fabricated on n-type photoelectrodes usually exhibit pleased photocurrent signals, but easily tend to be interfered by possible reductive species in biological matrixes [[15], [16], [17]]. As a result, false signals might be generated because of oxidizing properties of the photoanodes. In order to realize accurate probing of target biomarkers with low abundances in biological matrixes, advanced and feasible PEC immunosensors that own both evident photocurrent signals and favorable anti-interference abilities are highly pursued.

Stimulated by the above-mentioned distinct merits of photocathodic and photoanodic immunosensors, an advanced and efficient PEC immunosensor that integrated photocathode with photoanode was reported, as shown in Scheme 1. This featured operating system was composed mainly of CNT/CIS photocathode and TiO₂/AIS photoanode. Typical antigen (Ag) of α-fetoprotein (AFP) was selected as a model target for detection, and its capture AFP antibody (Ab) was anchored on the CNT/CIS photocathode with chitosan (CS) as linking molecule and bovine serum albumin (BSA) as blocking reagent. Target Ag detection was based on remarkable decrease of the photocurrent signal generated by significant steric hindrance of the formed immunocomplex between capture Ab and target Ag. With evident photocurrent response and good anti-interference ability of the outlined two-photoelectrode PEC immunosensor, the target Ag was finally probed with high sensitivity and specificity in the biological matrix.