Nanoimprinted Holographic MOF Diffraction Gratings─Advancing Selective Volatile Organic Compound Detection at Low Concentrations.

Metal-organic frameworks (MOFs) hold remarkable potential for detecting volatile organic compounds (VOCs) in applications ranging from indoor air quality monitoring to breath-based diagnostics. However, the integration of MOFs into optical sensors remains a significant challenge. In this study, we present an optimized soft lithographic approach for fabricating high-quality surface relief diffraction gratings composed entirely of MOF nanoparticles, as replicas of holographic structures. By increasing the height amplitude of the gratings, we significantly enhanced the sensitivity, as predicted by the Raman-Nath theory. For instance, a ZIF-71 grating with a depth of 530 nm demonstrated exceptional sensitivity to six VOCs, achieving a detection limit of 60 ppb for toluene. The general applicability of the approach was demonstrated by integrating other porous materials, resulting in an improved sensitivity to acetone. This work represents a step toward developing an optical VOC sensor array.