The functional DNA molecules with non-Watson-Crick structures can undergo structure transformation in a controllable and reversible manner upon the external stimuli.Elucidating the mechanisms of the structure transformation is the key to understand their medical applicability and function feasibility.The secondary structure transformation and functioning processes of these functional DNA molecules mostly occur in an interfacial environment,which are difficult to be characterized by the common used techniques.In this study,we investigated the molecular structure and kinetics of guanine-rich DNA molecules at model cell membrane interface using sum frequency generation vibrational spectroscopy (SFG-VS).We systematically studied the influence of ions on the kinetics of DNA secondary structure transformation and deduced the orientation of DNA molecules by analyzing the SFG spectra in "finger-print" region (1200-1800cm-1).Results fiom this study will help the researchers to control the DNA secondary structures in a desired manner and to guide the design of anticancer drugs,as well as improve the reproductivity,stability,reversibility of DNA-based functional materials.