Multifunctional tunable Cu2O and CuInS2 quantum dots on TiO2 nanotubes for efficient chemical oxidation of cholesterol and ibuprofen

Abstract

In this study, a CuInS2/Cu2O/TiO2 nanotube (TNT) heterojunction-based hybrid material is reported for the selective detection of cholesterol and ibuprofen. Anodic TNTs were co-decorated with Cu2O and CuInS2 quantum dots (QDs) using a modified chemical bath deposition (CBD) method. QDs help trigger the chemical oxidation of cholesterol by cathodically generating hydroxyl radicals ((OH)-O-center dot). The small size of QDs can be used to tune the energy levels of electrode materials to the effective redox potential of redox species, resulting in highly improved sensing characteristics. Under optimal conditions, CuInS2/Cu2O/TNTs show the highest sensitivity (similar to 12 530 mu A mM(-1) cm(-2), i.e. up to 11-fold increase compared to pristine TNTs) for cholesterol detection with a low detection limit (0.013 mu M) and a fast response time (1.3 s). The proposed biosensor was successfully employed for the detection of cholesterol in real blood samples. In addition, fast (4 s) and reliable detection of ibuprofen (with a sensitivity of similar to 1293 mu A mM(-1) cm(-2)) as a water contaminant was achieved using CuInS2/Cu2O/TNTs. The long-term stability and favourable reproducibility of CuInS2/Cu2O/TNTs illustrate a unique concept for the rational design of a stable and high-performance multi-purpose electrochemical sensor.