Photoelectrochemical Immunosensor for Carcinoembryonic Antigen Detection: An Attempt for Early Cancer Screening

Metal organic framework (MOF) is a porous material assembled by organic ligands or metals. Due to its large volume, specific surface area, high porosity, and adjustability, MOF is widely used in catalysis, pollutant adsorption, detection, drug transport, and other fields. MIL-101 (Cr) is a typical MOF based on Cr. However, its wide band gap (2.38 eV) will lead to lower photogenerated carrier density. Quantum dots (QDs), metal oxide semiconductors, and composite nanomaterials can promote the transfer of photogenerated electrons and amplify the photoelectrochemical (PEC) signal due to their narrow band gaps. Therefore, we focused on the study of combining CdTe-QDs of narrow band gap material, with MIL-101 (Cr) of a wide band gap material, to form a p-n heterostructure. The active carboxyl and amino groups on the surface of MIL-101 (Cr) can be covalently coupled with carcinoembryonic (CEA) antibody (Ab). The nonspecific binding site was blocked by bovine serum albumin (BSA). CEA was further captured by its Ab and due to the steric hindrance blocking the electron transfer between CdTe-QDs and MIL-101 (Cr), the photocurrent signal of M&C composites decreased. In the presence of M&C, the band gap, valence band, conduction band, flat band position, and Fermi level of CdTe-QDs and MIL-101 (Cr) were studied, and the process of photoinduced electron transfer was discussed in depth. Organic inorganic nanocomposites inherited the high charge mobility of organic materials and the strong photosensitivity of inorganic materials. A well-matched band gap further improved the separation of photogenerated carriers. According to the characteristics of the sensitive detecting CEA, it was further developed into a small detection instrument. Firstly, a pulse width modulation (PWM) digital signal with a specific duty cycle was generated from the external clock signal of the minimum system of stm32f103 single-chip microcomputer, and the external power supply was 12 V. The analog digital conversion module was used to control the digital output voltage at 0.3 V. 510 k Ω transimpedance amplifier was used for signal amplification. The input signal was the current in the range of 0–3 mA. In the process of inverse transformation, the corresponding voltage signal was divided by the amplification factor in the microcontroller program. The microcontroller and the transimpedance amplifier were powered by the 5 V voltage stabilizing module. The whole system was fixed with the shell printed by 3D. The 3D printing material was polylactic acid, which is a biodegradable corn plastic. At present, the detector model still has challenges in realizing commercial application, and more research investment is needed in the production process, which is expected to play a wider application in CEA detection in clinical serum and urine samples.