Sensitive Dual-Mode Biosensors for CYFRA21‑1 Assay Based on the Dual-Signaling Electrochemical Ratiometric Strategy and “On–Off–On” PEC Method

Herein, an electrochemical (EC)–photoelectrochemical (PEC) dual-mode biosensor was constructed for cytokeratin 19 fragment 21-1 (CYFRA21-1) assay based on the dual-signaling electrochemical ratiometric strategy and “on–off–on” PEC method. The indium tin oxide (ITO) electrode was modified by 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA)@C₆₀ and gold nanoparticles (Au NPs), and the double-stranded DNA composed of thiol/methylene blue (MB)-labeled single-stranded DNA (ssDNA) (S0-MB) and antibody/ferrocene (Fc)-labeled ssDNA (Ab1-S1-Fc) was immobilized on the Au NPs/PTCDA@C₆₀/ITO electrode via the Au–S bond between Au NPs and thiol of S0-MB. With the help of another antibody-labeled ssDNA (Ab2-S2), the presence of CYFRA21-1 triggered a typical antigen–antibody sandwich immune reaction (Ab1, CYFRA21-1, and Ab2) and proximity hybridization between Ab1-S1-Fc and Ab2-S2. This caused the release of Ab1-S1-Fc from the modified electrode and the change of S0-MB to a hairpin structure, resulting in a decrease (an increase) of the oxidation peak current of Fc (MB) and an increase of the photocurrent due to the enhancing (inhibiting) effect of MB (Fc) on the photoelectric performance of the Au NPs/PTCDA@C₆₀/ITO electrode. Thus, CYFRA21-1 was detected by the developed EC–PEC dual-mode sensing platform sensitively, and the linear response ranges of 0.001–40 ng/mL with a detection limit of 0.3 pg/mL for the EC technique and 0.0001–4 ng/mL with a detection limit of 0.03 pg/mL for the PEC method were obtained. Furthermore, by changing the specific antibodies of disease-related biomarkers, the developed dual-mode biosensing platform could be readily extended to detect other antigens, implying its great potential applications in biological analysis and early disease diagnosis.