Metal-Free All-Carbon Nanohybrid for Ultrasensitive Photoelectrochemical Immunosensing of alpha-Fetoprotein.

C can accept up to six electrons reversibly and show exceptional light absorption over the entire UV-vis spectrum, making it a potential photoactive probe for photoelectrochemical (PEC) bioassay. However, few successful works have been reported to apply fullerenes in PEC biosensing, partially because of the low electronic conductivity and poor interfacial interactions with targeted biomolecules. Herein, we report the addressing of these two obstacles by coupling high conductive graphite flake (Gr), graphene oxide (GO) with sufficient oxygen-containing functional groups, and an alkylated C (AC) into a metal-free all-carbon nanohybrid (AC-Gr-GO) via harnessing delicate noncovalent interactions among them through a facile mechanical grinding. It was revealed that the as-obtained AC-Gr-GO nanohybrid not only showed conspicuous enhancement of photocurrent up to 35 times but also offered rich anchors for bioconjugation. With detection of alpha-fetoprotein as an example, the AC-Gr-GO based PEC immunosensor demonstrated a broad linear detection range (1 pg·mL to 100 ng·mL) and a detection limit as low as 0.54 pg·mL, superior/competitive to PEC immunosensors for AFP in previous reports. By a proper reinforcement in conductivity and biointerface engineering, this work may provide a new way to use fullerenes as photoactive materials in more general PEC biosensing.