Active-site rich nanostructure with dual-enhanced electron transfer for ultra-sensitive electrochemiluminescence detection of DNA methylation in colon cancer.

Traditional DNA methylation assays for colon cancer still face challenges of insufficient sensitivity, limited specificity, and low cost-efficiency in clinical samples. Herein, we develop an electrochemiluminescence biosensor based on a dual-enhanced electron transfer mechanism using DNA tetrahedral nanostructure probes for the ultrasensitive detection of methylated DNA related to colon cancer. The DNA tetrahedral structure probe overcomes the shortcomings of poor adaptability caused by the low binding efficiency and high spatial steric hindrance in complex clinical samples. The electrochemiluminescence biosensor uses active-site-rich TiO2-Ti3C2 MXenes@AgNPs hybrid nanocomposites as the electro-active substrate. These nanocomposites exhibited accelerated electron transfer and shortened the reaction paths due to the intrinsic photoelectric activity of TiO2 and the surface plasmon resonance (SPR) effect between AgNPs and TiO2. Furthermore, the three-dimensional (3D) self-assembled AuNPs-ABEI nanoluminous spheres substantially improved the luminescence intensity by concentrating more AuNPs to accelerate electron transfer while immobilizing additional ABEI molecules. The dual-enhanced electron transfer strategy significantly accelerated the kinetics of interfacial electron transfer. Metal nanoparticles (such as AgNP, AuNP, and TiO2) generate SPR-induced local electric fields under electrochemical excitation. The electric fields enhance the electron transfer and amplify the electrochemiluminescence intensity, thereby achieving ultra-sensitive detection of the methylated Septin9 gene with a detection limit as low as 8.2 aM. Clinical sample validation using clinical serum samples from healthy controls (n = 100) and colon cancer patients (n = 100) has shown that the biosensor achieves comparable performance to the gold standard method in terms of both sensitivity and specificity, demonstrating equivalent detection efficacy to pyrosequencing.