ZnO Nanotip-based QCM Biosensors

The medical diagnostics laboratories are showing an urgent need for accurate, fast and inexpensive biosensors. A zinc oxide (ZnO) nanotip-based quartz crystal microbalance (QCM) sensor is developed as a solution for accurate and inexpensive biosensors. The QCM sensor composed of single crystalline ZnO nanotips grown on top of a gold electrode using metal-organic chemical vapor deposition (MOCVD). Scanning electron microscopy (SEM) shows that the ZnO nanotips are uniformly aligned with their c-axis normal to the gold surface, giving a large surface area for sample up-taking. The ZnO nanotip coated QCM sensor shows a 10-time larger frequency shift than that of regular QCM sensors, when measuring the same DNA oligonucleotide (5´-AGAAAATCTTAGTGTC-3´) solution. In addition, the hydrophilic behaviors of the nanotip array significantly reduce the required liquid volume for effective detection. 0.5 mul solution fully covers the QCM sensor area (0.2047 cm²), while a minimum of 16 mul liquid is required to cover a flat surface of the conventional QCM. ZnO nanotips show superhydrophilicity with a contact angle of ~0deg under ultraviolet (UV) illumination. The superhydrophilic sensor surface significantly boosts the solution taking up ability; therefore, enhances the sensitivity of the QCM sensor. The effects of ZnO nanostructure on the bulk acoustic wave (BAW) are also discussed