We have developed an acoustic immunoassay that couples a mass-amplifying label with a silicon-micromachined gravimetric sensor, the Flexural Plate Wave (FPW) device. This assay has direct application to the diagnostic detection of a breast cancer antigen in the sera of breast cancer patients. The use of an acoustic immunoassay provides an alternative to radioimmunoassay, eliminating the need for radioactive labels that pose health hazards to technicians and require costly disposal.
In this work, we discuss protein immobilization methods and compare methods of attaching proteins to the FPW device surface. We describe a liquid-tight micromachined flow cell package with a 20 ul sample size that allows the introduction of multiple reagents. In addition, we develop a mass label using colloidal gold particles and a silver developer solution that results in a mass amplification of five orders of magnitude over the mass of immunoglobulins alone. Our label can be applied to a variety of gravimetric assays and provides flexibility in choosing the desired size and mass of the label. With this mass label, we demonstrate the ability to detect with the FPW device breast epithelial mucin antigens at levels present in women with active breast cancer.
We also explore methods of providing on-chip sample mixing during protein binding steps. Using the FPW device as an acoustic source, we are able to generate an ultra- sonic form of sample volume agitation that results in faster protein binding. This ability to increase the reaction rate allows us to reduce the total time necessary to perform a measurement to less than a sixth of the time for the original radioimmunoassay. With this reduced assay time, we are still able to detect antigen concentrations at the level of the radioimmunoassay (0.1 ug/ml). We have also found that the use of ultrasonic agitation results in the concentration of proteins due to the nature of the acoustic waves. From our success in detecting breast cancer antigens acoustically, and with the additional benefits of ultrasound. We believe our prototype immunosensor holds promise as a safe replacement for radioimmunoassay methods.
December 31, 1997
Wang, A. W. (1998). A Micromachined Acoustic Immunosensor for the Detection of Breast Cancer Antigens. United States: University of California, Berkeley.