Improved photoelectrochemical performance of TiO2-in-MIL-101(Cr)@CDs@AgNPs and application for the detection of ultralow level AβO

TiO2 was successfully synthesized within the internal pores of MIL-101(Cr), leading to the formation of a TiO2-in-MIL-101(Cr) composite. This heterojunction structure significantly improved the photogenerated electron-hole separation within the metal-organic framework (MOF) composite. Subsequently, carbon dots (CDs) and silver nanoparticles (AgNPs) were introduced to further modify the TiO2-in-MIL-101(Cr), resulting in a multimodified MIL-101(Cr) composite. The integration of CDs enhanced the light absorption capabilities of the composite, thereby boosting the photocurrent. Meanwhile, AgNPs not only enhanced the absorption of visible light through the local surface plasmon resonance effect (LSPR) but also facilitated efficient electron transport. This multimodal modification strategy led to a remarkable enhancement in the photoelectrochemical (PEC) performance of MIL-101(Cr), with the photocurrent density (J) increasing by approximately a factor of 19. To further expand the functionality of this composite, AβO capture DNA (cDNA) and CuS-binding aptamer were grafted onto the TiO2-in-MIL-101(Cr)@CDs@AgNPs, creating a sandwich-like structure. Based on this multimodified MIL-101(Cr) composite, an "on-off-on" type PEC biosensor was constructed. The p-type semiconductor CuS served as a signal amplifier, capturing photogenerated electrons and effectively reducing the photocurrent. When cDNA hybridized with AβO, the Apt-CuS moiety detached from the MIL-101(Cr) composite, leading to the restoration of the photocurrent. The PEC biosensor for the detection of AβO exhibited optimal performance at a pH of 7.00, an incubation temperature of 37 °C, and an incubation time of 45 min. Under these conditions, the biosensor demonstrated a wide detection range of 5 fM to 1 μM, with an ultralow detection limit of 4.36 fM. This method exhibits high sensitivity, robust anti-interference capabilities, and holds great promise for applications in tracing the detection of AβO in human serum.