Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) was used to detect DNA hybridization on gold surfaces. Mixed monolayers of 6-mercapto-1-hexanol (MCH) and single-stranded DNA (ssDNA) with a C6-SH 5' modifier were first formed on the gold surface by co-deposition. Then hybridization with the complementary ssDNA strand was performed to obtain double-stranded DNA (dsDNA). The PM-IRRAS spectra obtained contained absorptive features indicative of DNA arising from the phosphodiester backbone and the purine and pyrimidine rings. An infrared signature of dsDNA was observed at 1655 cm(-1) that was absent in the ssDNA spectra. This band permitted the distinction between ssDNA and dsDNA to be made thus allowing for the detection of DNA hybridization on gold surfaces by PM-IRRAS.