In-depth interpretation of aptamer-based sensing on electrode: Dual-mode electrochemical-photoelectrochemical sensor for the ratiometric detection of patulin

•Four aptamers of patulin were selected to explore their sensing behaviors at electrode with EC and PEC methods.•Ratiometric strategy by coupling EC and PEC methods was used to select optimal aptamer for aptasensing.•The resultant aptasensor offered attracting analytical performance for patulin. Electrochemical aptasensors have been extensively used to quantify food contaminants (e.g., mycotoxin) by using high-affinity aptamer for target recognition. Yet, analytical performance of aptasensors using different aptamers can be varied for the same target. Here, four aptamers with different sequences (i.e., A22, A34, A42, and A45) of patulin (PAT) were selected to estimate sensing behaviors at electrodes with electrochemical (EC) and photoelectrochemical (PEC) assays. Synergistic effect of steric hindrance and electron transfer distance was found to significantly affect EC and PEC response for PAT at aptasensors fabricated with A22, A34, A42, or A45. Eventually, A22 emerged to be the optimal aptamer for aptasensing, despite the highest affinity of A42 to PAT. The A22-based EC-PEC dual-mode ratiometric aptasensor offered a linear range of 50 fg mL−1 – 500 ng mL−1 with a detection limit of 30 fg mL−1 for PAT, and it was applied to apple product (i.e., juice, puree) analysis.