Surface-modified ZnSe waveguides for label-free infrared attenuated total reflection detection of DNA hybridization

This communication presents a novel label-free biosensing method to monitor DNA hybridization via infrared attenuated total reflection (IR-ATR) spectroscopy using surface-modified ZnSe waveguides. Well-defined carboxyl-terminated monolayers were formed at H-terminated ZnSe by direct photochemical activation. Chemical activation of the acidic function was obtained by using succinimide/carbodiimide linkers. The sequential surface modification reactions were characterized by XPS and IR-ATR spectroscopy. Finally, a single stranded DNA probe with a C6-NH(2) 5' modifier was coupled to the ester-terminated surface via peptide bonding, and the hybridization of the immobilized DNA sequence with its complementary strand was directly evaluated by IR-ATR spectroscopy in the mid-infrared (MIR) spectral regime (3-20 μm) without requiring an additional label. A shift of the vibrational modes corresponding to the phosphodiester and deoxyribose structures of the DNA backbone was observed. Hence, this approach substantiates a novel strategy for label-free DNA detection utilizing mid-infrared spectroscopy as the optical sensing platform.