FIXED POLARIZER ELLIPSOMETRY FOR SIMPLE AND SENSITIVE DETECTION OF THIN-FILMS GENERATED BY SPECIFIC MOLECULAR-INTERACTIONS - APPLICATIONS IN IMMUNOASSAYS AND DNA-SEQUENCE DETECTION

Biological thin films may form on a surface by specific molecular inte ractions. The fixed polarizer ellipsometer (FPE) is a sensitive instru ment that detects biological thin films either qualitatively or quanti tatively. The design is simple and inexpensive. The assays are formatt ed on an optical surface, and the FPE detection is based on the phase shift of linearly polarized light after reflection through a thin film . We have constructed mathematical models of the FPE response to refle ction through single-layer and two-layer films that agree closely with experimental data. Several biological assays have been measured with the FPE to demonstrate the application of this technology to clinical targets, including ultrasensitive immunoassays for hepatitis B surface antigen (0.1 ng/mL) and alpha-fetoprotein (0.01 ng/mL) and DNA hybrid ization (0.5 fmol/mu L target probe). A clinical study for detection o f group A streptococcus from patient throat swabs demonstrated the qua litative application of the FPE to infectious disease targets. The fle xibility and sensitivity of the FPE makes this technology suitable for numerous target analytes and applications.