Opto-chemical sensors are prepared by self-assembly of SiO/SiO2 nanomembranes into microtube structures. Dynamic molecular processes of H2O and C2H5OH are detected on the surface of sub-wavelength-thin nanomembranes. Based on the perturbation theory, quantitative information of molecule layer changes is acquired. The nanomembrane-based molecular-sensing ability constitutes a versatile platform for the detection of diverse surface phenomena in a label-free fashion.