Photoelectrochemical Aptasensor for the Sensitive Detection of Microcystin-LR Based on Graphene Functionalized Vertically-aligned TiO2 Nanotubes

In this work, a visible-light driven photoelectrochemical (PEC) aptasensor with high sensitivity and selectivity for cyanobacterial toxin Microcystin-LR (MC-LR) has been developed. MC-LR aptamers, serving as the specific recognition element, were conveniently immobilized onto vertically-aligned titanium dioxide nanotubes (TiO 2 NTs) photoanode substrate with the aid of graphene via π–π stacking interactions between the graphene hexagonal cells and the nucleobases of the DNA. The functionalization of graphene further endowed the constructed aptasensor visible-light response activity. The aptasensor was used for the label-free analysis of MC-LR by monitoring the increase in photocurrent that resulted from the binding of MC-LR and its aptamers. Results showed that the photocurrent increment had a linear relationship with logarithm of MC-LR concentration in the range from 1.0 to 500 fM and the limit of detection reached as low as 0.5 fM. Furthermore, the aptasensor exhibited high selectivity while used to detect 100-fold concentration other several potential coexisting interferents. A promising PEC aptasensing platform for highly sensitive and selective monitoring of MC-LR has thus been established.