Determination of the absolute handedness of single enantiomer at small quantities is essential in chiral drug developments. Here we provide theoretical insights, numerical analysis and experimental demonstrations of high sensitivity to zepto moles of chiral molecules using optical metasurfaces. We introduce a figure of merit (FoM) for metasurfaces that can be extracted from simple far-field scattering measurements at visible to near-infrared frequencies, establishing the optimal performance to detect molecular handedness. Our results experimentally show opposite signs of FoM for different molecular chirality. The properly designed metamaterial serves as an ultra-sensitive probe to enhance circular dichroism measurements at frequencies for which these signals would be otherwise undetectable.