Electrochemical electrode/SAW system for metal ions and glucose in solutions

An electrochemical electrode/surface acoustic wave (ESAW) system was developed to explore the possibility of the application of UHF waves, 300–3000 MHz for chemical analysis in solution. The ESAW system with a ST-cut SAW quartz transducer was prepared for detection of metal ions and glucose in aqueous solutions. The ESAW system has the advantages of very low cost, easy fabrication. A set of electrodes welded with long-distance wires and coaxial cables was used to contact to the metal shell of the 315 MHz SAW quartz resonator. The ESAW system was applied to detect various metal ions, e.g., alkaline metal, alkaline-earth metal and transition-metal ions. Without pre-concentration technique, the detection limit of Cu2+ ion with the ESAW detection system was estimated to be 1.2 × 10−4 mol/L (7.6 ppm), from an analytical sensitivity of 2.55 × 105 Hz/(mol/L) and the standard deviation of the blank signal of 10 Hz with a confidence level of 99.86%. The ESAW detection system was also applied as a biosensor for glucose to detect gluconic acid, a product of glucose oxidation by glucose oxidase (GOD) in aqueous solution. The glucose ESAW biosensor with glucose oxidase exhibited a linear frequency response to the log concentration of glucose with a slope of approximately 9.3 × 102 Hz decade−1 (ΔHz/Δlog M). The ESAW detection system also showed a good selectivity and a good detection limit of <10−3 M for glucose in aqueous solution. Furthermore, the ESAW detector showed much more sensitive than QCM crystal sensor for glucose.