Facile fabrication of visible light photoelectrochemical immunosensor for SCCA detection based on BiOBr/Bi₂S₃ heterostructures via self-sacrificial synthesis method

Highlights

• Bi₂S₃ firstly formed on hierarchical BiOBr microflowers by self-sacrificial method.

• BiOBr/Bi₂S₃ heterostructures showed excellent PEC activity.

• The smart PEC immunosensor realized the ultrasensitive detection of SCCA.

Abstract

A novel visible light photoelectrochemical immunosensor based on BiOBr/Bi₂S₃ heterostructures was fabricated to detect squamous cell carcinoma antigen (SCCA). Bi₂S₃ nanoparticles formed on the BiOBr microflowers by the self-sacrificial synthesis method based on the facile reaction between BiOBr and S^2- ions. The BiOBr/Bi₂S₃ composites exhibited excellent visible light photoelectrochemical activity, when ascorbic acid (AA) was employed as a perfect electron donor. The photocurrent intensity of BiOBr/Bi₂S₃ modified ITO electrode arrived at around 20 µA, which was approximately 30 times than that of pure BiOBr. Dopamine formed easily polydopamine film via self-polymerization on the surface of BiOBr/Bi₂S₃ composites to immobilize SCCA antibody. Under the optimal condition, this photoelectrochemical immunosensor realized the ultrasensitive determination of SCCA. With the logarithm of SCCA concentration in the range of 0.001–75 ng mL⁻¹, the specific binding between SCCA and antibody led to the linearly decrease of photocurrent signal with a low detection limit of 0.3 pg mL⁻¹ (S/N = 3). This facilely constructed photoelectrochemical immunosensor maybe have promising practical application in photocatalysis, analytical detection and biosensor, etc.

Introduction

With the high morbidity and mortality, lung cancer increasingly threatens the health of people. Therefore, exploring effective tumor markers is crucial. According to the previous reports, Tong et al. studied the application of squamous cell carcinoma antigen (SCCA) in the diagnosis of lung cancer [1]. They found that SCCA was related with the development condition of lung cancer, which can be used to detect the clinically recurrence and metastasis of malignant tumors. Zhao et al. found that the content of SCCA was significantly increased in the lung cancer group [2]. And the level of squamous cell carcinoma was higher than other pathological types of lung cancer, suggesting that SCCA played an important role in the determination of the pathological types of lung cancer. Therefore, SCCA is generally applied as a dependable tumor marker for the early diagnosis of lung cancer [3], [4], [5].

Nowadays, photoelectrochemical (PEC) immunosensor has been extensively focused in the fields of analysis and detection [6], [7], [8], [9]. PEC immunosensor detects target accurately by transforming light signals into electrical signals, and possesses many advantages, such as strong specificity, fast analysis speed, high accuracy, simple operating system and excellent selectivity for the target [10], [11], [12], [13]. Therefore, a novel and facile visible light PEC immunosensor is fabricated to detect SCCA in our work. As the crucial factor of the preparation of PEC immunosensor, the selection of PEC material needs to be carefully treated, which is benefit to enhancing the sensitivity of PEC immunosensor.

Recently, as a typical p-type semiconductor material, bismuthyl bromide (BiOBr) has attracted significant interest in various fields, such as photocatalytic activity [14], sensor [9], electrocatalytic alcohol oxidation [15] and so on. BiOBr has unique and excellent electrical, magnetic and optical properties, such as excellent chemical stability, good photoelectric activity and suitable band-gap [16], [17], [18]. The wide band-gap of BiOBr about 2.7 eV could inhibit the recombination of electron-hole (e^-/h⁺), which is benefit to the strengthening of photoelectric activity. According to the previous references, the photoelectric activity of BiOBr is diverse due to their different morphology, for example, 2-dimensional flaky structure, 3-dimensional floral structure, hollow microspheres and spherical microflowers [19]. In our work, the BiOBr with hierarchical microsphere structure is prepared by hydrothermal synthesis method. The smooth surface and the larger specific surface of BiOBr increase the binding sites, promoting the combination of BiOBr with more particles.

Moreover, the construction of heterojunction is an effective technique to improve the photoelectric activity of PEC immunosensor. For example, Guo et al. prepared BiOBr/Bi heterojunctions [20], Hu et al. fabricated a Z-scheme Bi₂MoO₆/BiOBr photocatalyst [21], Di et al. prepared N-CQDs/BiOBr [22]. Recently, bismuth sulfide (Bi₂S₃) with a narrow band-gap (1.30–1.70 eV) has attracted intensive attention in the fields of photocatalytic degradation [23], electrochemical determination [24] and so on. The most important thing is that the valence band (VB) and conduction band (CB) of Bi₂S₃ are higher than that of BiOBr. The satisfying match of band-gap accelerates efficiently the electron transfer under the visible light irradiation, which improves the conductivity of PEC immunosensor. Therefore, as the matrix, the BiOBr/Bi₂S₃ heterostructures were fabricated via self-sacrificial synthesis method in our work.

Most importantly, it is the first time that Bi₂S₃ nanoparticles formed on the BiOBr microflowers by the self-sacrificial synthesis method. Comparing with other references [25], [26], [27], [28], the self-sacrificial synthesis method is simple and quick. The obtained BiOBr/Bi₂S₃ composites exhibit excellent photoelectric activity, when ascorbic acid (AA) is employed as a perfect electron donor. Based on the above discussion, a novel visible light PEC immunosensor based on BiOBr/Bi₂S₃ heterostructures is designed via self-sacrificial synthesis method to detect SCCA.