On-chip Interferometry

Texas Tech University, Lubbock TX

Investigators

Abstract

This award supports the development of a device for on-chip, interferometric backscatter detection (OCIBD) for universal on-chip solute determinations. The primary usage of the device will be for protein detection during capillary electrophoresis carried out in channels etched in chips made of glass, such as a microscope slide, or similar substrate. The PI has already shown OCIBD can be used for refractive index measurements of sub-nanoliter volumes of liquids. The liquid passes through an etched channel with the general shape of a half cylinder. The detection system consists of a simple, folded optical train based and a low power laser beam. The laser light backscattered from the channel takes on the form of a high contrast interference pattern; the pattern varies with the bulk properties of the fluid contained within the channel. In preliminary efforts, positional changes in the fringes of the pattern allow the detection of test proteins at micromolar concentrations (0.2-1.0 mg/ml). The PI has also developed a preliminary theoretical model for OCIBD that is in good agreement with this experimental data. The model can be used to predict general system performance as a function of proposed optical train modifications including the chip's wall thickness and channel diameter. Improvements realized for OCIBD, under the proposed investigations, are predicted to result in detection limits for proteins at concentrations in the range of 150-250 nanomolar and in volumes of much less than a nanoliter. The result of this research is expected to be a sensitive universal detector system that will be broadly applicable to miniature bioanalytical devices, often referred to as "lab-on-a-chip" devices. These are of increasing interest in biological research because they minimize the amounts of material needed for separation and analysis, and are amenable to electronic, rather than mechanical, control. Detection of individual proteins and other cellular components at these low levels should make analysis of individual cells possible; availability of detection schemes that do not require chemical modification of cellular components will increase the potential utility of on-chip devices for a variety of uses.