Highly Sensitive and Selective Photoelectrochemical Aptasensors for Cancer Biomarkers Based on MoS2/Au/GaN Photoelectrodes

An Au/GaN photoelectrode was prepared by sputtering 30 nm thick Au film on the surface of n-type gallium nitride (GaN). When the electrode contacts with multilayered molybdenum disulfide (MoS2), photogenerated electrons and photogenerated holes transfer to MoS2 because of the band gap matching of MoS2 and GaN. The presence of Au promotes charge transfer and results in a greater recombination of electrons and holes; by this means, a more significant suppression of photocurrent can be detected. This characteristic has been coupled with the high selectivity of an aptamer and applied to develop a novel photoelectrochemical aptasensor for cancer biomarkers (alpha-fetoprotein (AFP) as a model). The aptamer of AFP was modified on the surface of the Au/GaN photoelectrode by Au–S bonds, which can bind to the target protein with high selectivity. Then, the transfer process of the charge carriers of GaN to MoS2 can be blocked by the target protein so that the suppression of photocurrent is reduced. The difference of the photocurrent in the presence and absence of AFP (ΔI) showed a linear relationship with AFP concentration that ranged from 1.0–150 ng/mL (R2 = 0.9995), and the detection limit was 0.3 ng/mL. The standard addition recovery rates ranged from 85.2 to 91.7%. The method possessed good sensitivity and high selectivity for AFP detection. The developed biosensor can be modified to detect other cancer biomarkers by simply replacing the aptamer used.