Amy W. Wang

A silicon-based ultrasonic immunoassay for detection of breast cancer antigens

We report on a silicon-based immunosensor package that has direct application to the diagnostic detection of a breast cancer antigen in the sera of breast cancer patients. We couple the flexural plate wave (FPW) gravimetric sensor with a novel mass-amplifying label that increases sensor signal level (a shift of resonant frequency) from that of previous acoustic immunoassays, in which frequency shifts were due solely to the weight of the immunoglobulins. The use of a gravimetric immunoassay with a mass-amplifying label provides an alternative to radioimmunoassay, eliminating the need for radioactive labels that require costly disposal.

Gel-coated Lamb wave sensors

Initial experiments and theory describing the operation of gel-coated Lamb wave sensors are described. The lowest-order flexural Lamb wave can propagate in gel-coated plates with low attenuation. This allows some novel sensing approaches to be investigated, such as: using gels as filters for larger particles and molecules, while allowing smaller analytes to diffuse through to the sensor surface, and realizing sensors based on gel density and viscoelastic changes. The authors develop two theories to predict the response of the sensor to the viscoelastic properties of the gel, and find excellent agreement predictions from these theories and those from a numerical simulation program for waves in multilayered media. One uses a Rayleigh-type solution with modified boundary conditions to derive the mechanical radiation impedance presented to the plate surface by the gel, and from this impedance calculates the phase velocity. The other uses a transmission line theory originally developed by A. Oliner et al.<<ETX>>

A flexural-plate-wave microbial sensor

Flexural-plate-wave sensors have been used for the monitoring of the metabolism of gel-immobilized yeast. In one configuration, gel layers directly on the sensor contain the microbes and also prevent non-specific adsorption of proteins and cells onto the sensor surface. In other experiments, sensors have measured the density of solution flowing into and out of a test tube filled with yeast-containing gel beads. From the theoretical sensitivity of flexural-plate-wave sensors to perturbations in liquid density, the authors have related observed frequency shifts to physiological variables.<<ETX>>

Thin-film anodized aluminum on an acoustic sensor

An empirical model has been developed to predict the effect of a thin, porous anodized aluminum film on a solid-state flexural plate wave (FPW) chemical vapor sensor. A method of defining a precise anodization region using photolithography was developed. Initial experiments have shown through static measurements that a downward shift on the order of 100 kHz in the 4 MHz resonant frequency of the FPW device can be detected after aluminum anodization. Linear regression techniques were used to develop a model to predict frequency shift for given anodization parameters. Anodization variables investigated were anodization voltage and electrolyte concentration. The measured device frequency can be used to determine material properties of the anodized film.