Development of a sensor instrument that is responsive to minute mass loadings on a nanoscale, while exhibiting a mass sensitivity profile that is independent of material placement on the sensor platform, would enable nanogram measurements of a broad range of materials, a necessity in chemical and biological research. Mass sensitivity of current commercial analytical balances is limited to the microgram scale which is inadequate as scientific and technological research continues to progress towards further minute magnitudes. Fortunately, significant research into the utilization of thickness shear mode (TSM) quartz resonators as nanoscale mass balances is well documented1. However, a substantial shortcoming of past research is the establishment of a flat radial sensitivity distribution across the sensor platform. Non-uniformity of mass sensitivity on the TSM resonator surface prohibits the utilization of this technology in the measurement of absolute mass. To achieve a uniform distribution requires the design and testing of various electrode patterns. Presented in this study are the radial sensitivity distributions of TSM devices having different electrode geometries. In conducting the experiments, the electrodes were deposited on blank AT-cut quartz wafers and the wafers placed inside a G1 mass/heat flow instrument developed by Masscal Scientific Instruments. This instrument permits the extraction of the frequency signal of the crystal, either bare or solvent droplet loaded, and the associated thermal power which enter as parameters in the mathematical models describing mass sensitivity. Additionally, a computer simulation of the mass sensitivity was conducted for each electrode using finite element method (FEM) analysis to corroborate the experimental results, and to discover the best possible design.

References:

[1] Josse, F.; Lee, Y.; Martin, S. J.; Cernosek, R. W. Analysis of the radial dependence of mass sensitivity for modified-electrode quartz crystal resonators. Analytical Chemistry 1998, 70, 237-247.

[2] Smith, A. Gravimetric analysis of the non-volatile residue from an evaporated droplet, using the quartz crystal microbalance/heat conduction calorimeter. J. ASTM Intl. 2006, 3, 1-5.