Selective Detection of Deoxyribonucleic Acid at Ultralow Concentrations by SERRS

Genetic research programs such as the human genome project have demonstrated the need for selective detection of nucleic acids at ultralow concentrations (McKusik, V. A. FASEB J. 1991, 5, 12-20. Cui, X.; et al. Proc. Natl. Acad. Sci. U.S.A. 1989, 89, 9389-9393). Current detection techniques require amplification of the genetic material by the polymerase chain reaction (PCR) and detection of the amplified product by fluorescence. A new reliable method for DNA detection has been developed based on adsorption of DNA on colloidal silver and subsequent signal detection using surface-enhanced resonance Raman scattering (SERRS). It uses specifically designed primers and can be applied directly to genetic analysis. Improved surface and aggregation chemistry, utilizing modified DNA and a novel aggregating agent, has resulted in acceptable reproducibility for biological detection. DNA was detected down to 8 × 10^-13 M, which equates to less than one molecule in the interrogation volume at any one time, and an RSD of 10% was obtained. The increased sensitivity compared to fluorescence circumvents the need for an amplification step, and much greater selectivity is obtained due to the sharp vibrational spectra observed, thus reducing the need for separation procedures. The method is potentially sensitive enough to eliminate the need for time-consuming amplification steps and provide a new dimension to labeling chemistry and multiplex analysis of DNA.