Ti₃C₂/Cu₂O heterostructure based signal-off photoelectrochemical sensor for high sensitivity detection of glucose

Highlights

• Ti₃C₂/Cu₂O material with high photoelectrochemical (PEC) performance was synthesized by simple oil bath heating method.

• Ti₃C₂/Cu₂O was used as photocathode to construct a non-enzymatic PEC sensor for the detection of glucose.

• The sensor was highly sensitive to glucose with a wide linear range of 0.5 nM to 0.5 mM and a detection limit of 0.17 nM.

• The PEC non-enzymatic sensor was applied in standard samples and human serum successfully.

Abstract

Photoelectrochemical (PEC) sensing has emerged as a simple and practical method for the analysis and detection, its separated optical signal and detection electrical signal give it the advantages of reduced background noise and outstanding sensitivity. Here, we synthesized a Ti₃C₂/Cu₂O composite through simple oil bath heating process, whose excellent PEC performance and sensitive photoelectric response to glucose make it a propitious substitution to glucose oxidase. On this basis, we construct a PEC non-enzymatic sensor based on the Ti₃C₂/Cu₂O heterostructure for the detection of glucose. Under the optimal conditions, the photocurrent of Ti₃C₂/Cu₂O is linear with the logarithm value of glucose concentration in the wide range of 0.5 nM to 0.5 mM with a detection limit of 0.17 nM. Furthermore, the successful detection of glucose in standard samples and human serum by the proposed Ti₃C₂/Cu₂O based PEC non-enzymatic sensor demonstrates the application prospect of heterostructure material in PEC sensor, which provides a new thought for the design and construction of PEC non-enzymatic sensing platform.

Introduction

Glucose is an indispensable component in human body, providing energy for cell metabolism and ensuring normal work of body functions. In addition, glucose in blood is a clinical indicator of diabetes, excess or deficiency will induce diabetes and hypoglycemia, respectively (Gopalan et al., 2017). Thus, quantitative determination of glucose in blood serum is of great meaningfulness. To date, researches on glucose detection have been varied and mature, such as fluorometric (Liu et al., 2015b), colorimetric (Li et al., 2018), electrochemical (Chaiyo et al., 2017) and photoelectrochemical methods (Dai et al., 2017). Among these detection methods, glucose oxidase is adopted for its outstanding selectivity and sensitivity. Unfortunately, the limitations of glucose oxidase in terms of storage, cost, reproducibility and chemical stability have affected the practical application of biosensors to some extent. Recent years, various nanomaterials have been studied as the substitution to glucose oxidase to construct non-enzymatic glucose sensors (Nallal et al., 2017). The widely studied non-enzymatic methods are simple in operation and low in cost, but still suffer from one or more weaknesses of low sensitivity and poor selectivity. Therefore, the exploration of a non-enzymatic method with high sensitivity and selectivity toward glucose detection has been an urgent concern.

MXenes is a novel family of 2D transition-metal carbides and/or carbonitrides material, which has ignited much interest of researchers since it was prepared. Gogotsi and his group obtained the Ti₃C₂ via etching away Al from Ti₃AlC₂ using aqueous HF solution in room temperature, and thus, the formation of this new 2D material was reported since then (Naguib et al., 2011). Ti₃C₂ was one of the most widely used MXenes, exhibiting a variety of distinguished properties including good conductivity, small diffusion barrier, high volumetric capacitance and superior photothermal conversion efficiency, which make it a promising material in energy storage (Anasori et al., 2017), lithium ions batteries (Er et al., 2014), cell imagining (Xue et al., 2017) and photothermal treatment (Li et al., 2017; Liu et al., 2017). Obviously, Ti₃C₂ is mainly applied in the field of electrochemistry and photochemistry. But Ti₃C₂ also exhibits the potential application prospect in photoelectric fields. For example, the large surface area and exposed metal sites of Ti₃C₂ provide more active sites for the growth of semiconductors (Michael et al., 2014; Zhou et al., 2017). Furthermore, Ti₃C₂ is conductive to the separation and transmission of photo-induced carriers in Ti₃C₂/semiconductor heterostructure because of the built-in electric field formed in the interface of Ti₃C₂ and semiconductor, which is caused by the difference between valance band and Fermi levels (E_F) (Kang et al., 2017; Peng et al., 2016). Particularly, Hefei Wand etc. reported that the OH-functionalized Ti₃C₂ was an excellent electrode material for semiconductors to construct heterojunctions whose Schottky barrier nears to zero by first principle calculations (Wang et al., 2017). Zhe Kang etc. prepared Ti₃C₂T_X/n-Si Schottky junction heterostructures by van der Waals forces and fabricated a self-driven vertical junction photodetector with high response and recovery speed (Kang et al., 2017). On the basis of the theoretical calculations and experimental researches, it can be concluded that the Ti₃C₂ is anticipated to function as an ideal supporting material in PEC sensors. In addition, the combination of Ti₃C₂ with photoactive material such as semiconductors can well overcome the drawback of the short lifetime of the photo-induced electrons.

Cu₂O, as a nontoxic and abundant p-type semiconductor with narrow bandgap of 2.0-2.2 eV, is much popular in photoelectric material for its broad light harvest range and stable photocurrent (Kecsenovity et al., 2017). But the Cu₂O inevitably has the disadvantage of a high recombination rate of electron-hole pairs, which is the inherent limitation nature of pure semiconductors. Doping with metals and bonding with energy band matched semiconductors are both common and effective strategies to obtain an improvement of charge transfer rate (Lingmei et al., 2015; Wang et al., 2015). Unfortunately, doping methods are suffering from complicated operation and limited economic benefits, while the high contact resistance between photoactive material and electrode limits the migration of electrons. Therefore, it's of great importance to have a contact material combining with Cu₂O to construct a heterostructure in which the migration of electrons is less obstructed.

Herein, the well-defined Ti₃C₂/Cu₂O heterostructure was synthesized by a simple oil bath heating process. Cu₂O with a regular octahedron shape is a photoactive material in the PEC sensing system. After the introduction of Ti₃C₂, the large surface area of Ti₃C₂ offers mounts of active sites for the growth of Cu₂O, thus the prepared Ti₃C₂/Cu₂O heterostructure is of high carrier separation rate, which ultimately results in an enhanced PEC performance compared with pure Cu₂O. Particularly, the Ti₃C₂/Cu₂O was found to be sensitive to dissolved oxygen and the photocurrent of Ti₃C₂/Cu₂O decreased in the presence of glucose due to the consumption of the dissolved O₂ in the redox process of glucose. On this basis, a non-enzymatic PEC sensor based on the Ti₃C₂/Cu₂O heterostructure is constructed for the detection of glucose. The PEC sensor shows a wide range and low detection limit toward glucose and is applied to the detection of human serum successfully.