Strong enzyme immobilization associated by anatase TiO2 sputtered on platinum black nanoclusters to improve sensitivity and long-term stability of electrochemical cholesterol sensor

Abstract

Enzyme immobilization is one of the essential features to achieve a high-performance, enzyme-based electrochemical sensor. Here, we developed a simple and strong immobilization strategy that provides a sensitive, selective, and stable cholesterol sensor fabricated by conventional MEMS processes. As the immobilization strategy, pure anatase TiO2 film was sputtered on platinum black (BPt) nanoclusters as a working electrode for large effective surface areas, since TiO2 has various surface OH groups, including Ti OH, that can be used as linkers to immobilize enzyme molecules. We prepared BPt, TiO2/BPt, and annealed TiO2/BPt and analyzed using quantitative XPS and FTIR measurement. It was demonstrated that TiO2/BPt achieved solid enzyme immobilization (our quantified score = 1.23) compared to BPt (score = 0.04) and annealed TiO2/BPt (score =-0.02) electrodes. This is due to its large amount of reactive OH groups (reactive I-OH/ITi-O 23.8 % of TiO2/BPt vs. inactive I-O1s/I-Pt4f similar to 17.7 % of BPt) and high surface energy. Accordingly, TiO2/BPt exhibited superior sensitivity (81.2 mu A-mu M-1 cm(-2); LOD = 0.96 mu M) and a low KM value (9.21 mu M) compared to other electrodes. Notably, TiO2/BPt provided great stability (similar to 96.4 %) for 30 days as well as selectivity and reusability. We believe this study provides new insights that could allow simpler and better immobilization methods for industrial applicable biosensors.