A sensitive and selective assay of nucleic acids by measuring enhanced total internal reflected resonance light scattering signals deriving from the evanescent field at the water/tetrachloromethane interface

A total internal reflected resonance light scattering (TIR-RLS) technique, the coupling of resonance light scattering (RLS) technique with total internal reflected light at the interface of two immiscible liquids, where the steep change of the refractive indexes occurs to result in an evanescent field, is proposed with the characteristics of separation and enrichment properties of analytes and direct use of oil-soluble reagents free from surfactants. At pH 8.69 and ion strength 0.008, ternary amphiphilic species formed by the interaction of nucleic acids, including calf thymus DNA (ctDNA), fish sperm DNA (fsDNA), and yeast RNA (yRNA), with Eu(III) in the presence of oil-soluble trioctylphosphine oxide (TOPO), are adsorbed to the water/tetrachloromethane (H2O/CCl4) interface, giving rise to significantly enhanced TIR-RLS signals. It has been found that the enhanced TIR-RLS intensity at 348.0 nm is proportional to the concentration of thermally denatured ctDNA, fsDNA and yRNA in the range 0.002-2.5 mug ml(-1), 0.002-2.5 mug ml(-1) and 0.003-2.0 mug ml(-1), respectively and their limits of determination (3sigma) are 0.16 ng ml(-1), 0.19 ng ml(-1) and 0.28 ng ml(-1), correspondingly. Complicated artificial samples with highly interfering backgrounds were determined satisfactorily.