May Tom-Moy

STW chemical sensors

A new kind of chemical sensor which is based on the surface transverse wave (STW) delay line is reported. This sensor is ideally suited to measurements of surface-attached mass under fluid immersion, and it is demonstrated operating under these conditions at 250 MHz. The mass sensitivity of an STW sensor is approximately 10 times greater than that of a thickness shear mode (TSM) or shear horizontal acoustic plate mode (SH-APM) sensor. The sensitivity is roughly comparable to that of a flexural plate wave (FPW) sensor, but it does suffer from the FPW sensors fragility. The STW device is applied to biosensing. By directly immobilizing antibodies on the surface, the sensor is used to detect human immunoglobulin G at a level of 33 nanomoles/liter.<<ETX>>

Environmental Measurements Using Surface Transverse Wave (STW) Biosensors

This chapter elaborates the environmental measurements using surface transverse wave (STW) biosensors. The development of bioanalytical sensors to make chemical measurements rapidly, at low cost, and at the site is described. The biosensors being developed at HP Laboratories derive their specificity, and selectivity using antibodies. The physical transducer that enables the measurement of the selective biological recognition event is an HP proprietary STW device. This biosensor can be configured to be field portable, and is potentially targeted for environmental analysis. The analyte of interest is covalently immobilized to the surface of the STW device, and a sample containing a fixed concentration of antibody is flowed across the surface. It is found that since this is a competitive assay, the response decreases with increasing analyte concentration. The measurement system is fully automated, and controlled by a PC. The performance specifications of the STW Biosensor measurement system were demonstrated using antibodies directed against atrazine, an herbicide. Atrazine was bound to the surface of the STW device using an HP proprietary chemistry.