Near-Infrared-to-Ultraviolet Light-Mediated Photoelectrochemical Aptasensing Platform for Cancer Biomarker Based on Core–Shell NaYF4:Yb,Tm@TiO2 Upconversion Microrods

Titanium dioxide (TiO2; as a potential photosensitizer) has good photocurrent performance and chemical stability but often exhibits low utilization efficiency under ultraviolet (UV) region excitation. Herein, we devised a near-infrared light-to-UV light-mediated photoelectrochemical (PEC) aptasensing platform for the sensitive detection of carcinoembryonic antigen (CEA) based on core–shell NaYF4:Yb,Tm@TiO2 upconversion microrods by coupling with target-triggered rolling circle amplification (RCA). The upconversion microrods synthesized through the hydrothermal reaction could act as a photosensing platform to convert the near-infrared (near-IR) excitation into UV emission for generation of photoinduced electrons. The target analyte was determined on a functional magnetic bead by using the corresponding aptamers with a sandwich-type assay format. Upon target CEA introduction, a complex was first formed between capture aptamer-1-conjugated magnetic bead (Apt1-MB) and aptamer-2-primer DNA (Apt2-pDNA). Thereafter, the carried primer DNA by the aptamer-2 paired with linear padlock DNA to trigger the RCA reaction. The guanine (G)-rich product by RCA reaction was cleaved by exonuclease I and exonuclease III (Exos I/III), thereby resulting in the formation of numerous individual guanine bases to enhance the photocurrent of core–shell NaYF4:Yb,Tm@TiO2 upconversion microrods under near-IR illumination (980 nm). Under optimal conditions, the near-IR light-mediated PEC aptasensing system could exhibit good photoelectrochemical response toward target CEA and allowed for the detection of target CEA as low as 3.6 pg mL–1. High reproducibility and good accuracy were achieved for analysis of human serum specimens. Importantly, the near-IR-activated PEC aptasensing scheme provides a promising platform for ultrasensitive detection of other biomolecules.