Generation of Regularly Ordered 2D Ultrathin Covalent Organic Framework Films for Highly Sensitive Photoelectrochemical Bioanalysis.

Developing new photoactive materials and electrode preparation technology with high stability, repeatability, easy fabrication, and a low electron-hole recombination rate is promising for ideal photoelectrochemical (PEC) biosensors, but it remains a great challenge. Here, a porous and crystalline oriented two-dimensional (2D) ultrathin covalent organic framework film (D-TA COF film) was formed on indium-doped tin oxide (ITO) substrates under very mild conditions. The structure and morphology of D-TA COF film were characterized by means of Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and powder X-ray diffraction. Compared with the randomly oriented D-TA COF powder drop-coated on ITO, the photocurrent of the D-TA COF film grown on the ITO surface achieved as high as ∼333-fold increase. This photocurrent can be further amplified by O (acting as electron acceptors). Benefiting from the fabrication , D-TA COF film also exhibited tough adhesion, assuring the film was difficult to separate from the electrode. Accordingly, D-TA COF film was applied as the photoactive material to build a PEC biosensor for HO detection based on coupling with large amounts of catalase (CAT) through simple adsorption. The introduced CAT catalyzed the decomposition of HO to O, leading to an enhancement of the photocurrent response. As a result, a "signal-on" PEC biosensor was fabricated with good sensitivity, rapid response, and high stability, and it can also detect HO released from living cells. Taking into account these advantages, the D-TA COF film is expected to be an ideal photoactive material to construct various PEC biosensors, which as far as we know have not been reported.