Construction of a Dye-Sensitized and Gold Plasmon-Enhanced Cathodic Photoelectrochemical Biosensor for Methyltransferase Activity Assay.

DNA methyltransferases may function as important biomarkers of cancers and genetic diseases. Herein, we develop a dye-sensitized and gold plasmon-enhanced cathodic photoelectrochemical (PEC) biosensor on the basis of p-type covalent organic polymers (COPs) for the signal-on measurement of M.SssI methyltransferase (M.SssI MTase). The cathodic PEC biosensor is constructed by the in situ growth of p-type COP films onto a glass coated with indium tin oxide and the subsequent assembly of biotin- and HS-labeled double-stranded DNA (dsDNA) probes onto the COP film via biotin-streptavidin interaction. The dsDNA probe contains the recognition sequence of M.SssI MTase. The COP thin films possess a porous ultrathin nanosheet structure with abundant active sites, facilitating the generation of a high photocurrent compared with the hydrothermally synthesized ones. The presence of DNA methyltransferases can prevent the digestion of restriction endonuclease HpaII, consequently inducing the introduction of gold nanoparticles (AuNPs) to the dsDNA probes via the S-Au bond and the intercalation of rhodamine B (RhB) into the DNA grooves to produce a high photocurrent due to the dye-photosensitized enhancement and AuNP-mediated surface plasmon resonance. However, in the absence of M.SssI MTase, HpaII digests the dsDNA probes, and neither AuNPs nor RhB can be introduced onto the electrode surface, leading to a low photocurrent. This cathodic PEC biosensor possesses high sensitivity and good selectivity, and it can screen the inhibitors and detect M.SssI MTase in serum as well.

In-situ synthesis of covalent organic polymer thin film integrates with palladium nanoparticles for the construction of a cathodic photoelectrochemical cytosensor.

Sensitive detection of cancer cells is essential to early clinic diagnosis, and the photoelectrochemical (PEC) sensors with high sensitivity and good selectivity may provide new approaches for cytosensing. Herein, we demonstrate the development of a new cathodic PEC cytosensor based on the integration of covalent organic polymer (COP) with palladium nanoparticles (PdNPs). The COP films are in-situ grown at room temperature on the transparent indium tin oxide-coated glass substrates, and they subsequently assemble with PdNPs to immobilize aptamers via palladium-sulfur chemistry. PdNPs can catalyze the oxidation of dopamine to produce aminochrome and its derivative, which may function as the electron acceptors of COP for the generation of an enhanced photocurrent. In the absence of cancer cells, the electrons on the conduction band of COP on the electrode transfer to the aminochrome and O2, while the electrons on the electrode transfer to the hole of valence band, resulting in a high cathodic photocurrent. In the presence of cancer cells, the trapped cancer cells efficiently cover the electrode to reduce the surface of COP/PdNPs, resulting in the decrease of catalytic precipitation on the electrode and consequently the generation of a low PEC signal. This PEC cytosensor exhibits high sensitivity with a detection limit of 8 cells mL-1 and a large dynamic range from 10 to 106 cells mL-1. Moreover, this PEC cytosensor has distinct advantages of high selectivity, good reproducibility and excellent stability, and it can be extended to directly detect various cancer cells through the integration with corresponding specific aptamers.