Figure 1.

Incident visible (green) and infrared (red) beams produce a second-order SFG signal (blue) at the buried surface-bound DNA/water interface. The inset shows click chemistry linking the DNA to a SiO₂-coated CaF₂ prism. The SFG beam’s polarization is rotated 45° by an achromatic waveplate (AW). The beam is then split into vertical and horizontal polarizations by a beam displacer (BD). Finally, the +45° and −45° polarized SFG responses are collected simultaneously (CCD). The difference between the measured +45° and −45° polarized SFG responses across the OH stretch region shown in the graph proves the existence of a chiral water superstructure surrounding DNA.