Enhanced oxygen detection using porous polymeric gratings with integrated recognition elements

The development of ordered porous nanostructured materials, such as polymeric Bragg gratings, offers an attractive platform for the encapsulation of chemical and biological recognition elements. To date, various types of polymer gratings have been developed with several demonstrated applications in switching, lasing, and display devices. Here, we focus on a new class of holographically ordered porous polymer (HOPP) gratings that are an extension of holographic polymer dispersed liquid crystal (H-PDLC) structures. We present biochemical sensing using HOPP gratings that include a volatile solvent as the phase separation fluid. The resulting HOPP gratings are simple to fabricate, chromatically tunable, highly versatile, and can be employed as a general template for the encapsulation of recognition elements. As a prototype, we developed an oxygen (O₂) sensor by encapsulating the fluorophore (tris(4,7-diphenyl-1,10-phenathroline)ruthenium(II) within these nanostructured materials. The resulting O₂ sensors performed across the full-scale range (0-100%) of oxygen in nitrogen, with a response time of less than 1 s. The O₂ sensor system uses a LED excitation source and a silicon photodiode detector. The ability of these HOPP reflection gratings to transmit or reflect a particular wavelength range, based on the grating spacing, enables us to selectively enhance the detection efficiency for the wavelengths of interest.