This grant supports the development of a new ultrasensitive optical assay for biological macromolecules. Either protein or nucleic acid target molecules will be detected at the level of 1 femtogram. This level of sensitivity will allow the identification and quantification of the chosen macromolecule in a single cell. The sensitivity, speed, and accuracy of these assays will be optimized using a real-time in-vitro studies.
The reporter molecule for such an assay must be robust and nano-sized yet still have a very large light-scattering cross-section. Immmunolabelled plasmon resonant particles (PRPs) are ideal for this purpose. PRPs are small (40-80 nanometer) metal particles that scatter visible light elastically with extraordinary efficiency when excited at their plasmon resonance frequency. They are inexpensive, non-toxic, and are available in a variety of colors. The light scattered from PRPs under typical white light illumination is so large that each PRP is individually visible. At appropriate concentration, the actual number of PRPs in a field of view is simply the number of particles bound to the target macromolecule plus any particles that are non-specifically bound. An image of such a field of PRPs can be recorded using a CCD camera within milliseconds. This will allow for the rapid and ultrasensitive detection of the target macromolecules in the cell.
It is anticipated that commercialized versions of the PRP immunoassay will allow for low cost detection of a wide range of important molecules in the cell. Such an immunoassay should complement or replace standard ELISA or radio-immunoassays for cases where the concentration of the target molecules if very low and target amplification is not beneficial or practical.
