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Submitted to 2 fabrication of holographic sensors that display improved versatility and scalability. This platform utilizes an efficient approach to produce off-axis chemical-stimuli responsive holographic sensors with a large, reversible narrow-band tunability, using metallic nanoparticles that can be organized in density-concentrated 3D regions. Our sensor employs a simultaneous lateral and vertical periodic diffraction grating of silver nanoparticles dispersed within a poly (hydroxyethyl methacrylate)-based (pHEMA) matrix with a dry thickness of approximately 10 μm. The diffracted light is spectrally concentrated at a specific narrowband color due to the vertically-ordered periodicity.

We use 6 ns-pulsed laser (λ= 532 nm) standing waves to order the density of silver nanoparticles into regions with a periodicity of approximately half of the wavelength distributed throughout the cross section of the polymer matrix. The fabrication of the holographic sensors begins with UV-initiated free radical polymerization of the pHEMA-based hydrogel on a O2-plasma-treated poly (methyl methacrylate)(PMMA) substrate (Figure 1 (a)). Subsequently, Ag+ ions are perfused into the pHEMA polymer matrix (Figure 1 (b)), and reduced with a photographic developer to form silver nanoparticles (Ag0)(Figure 1 (c)). The Ag nanoparticles within the hydrogel matrix are selectively and photochemically patterned at the areas where laser light constructively interferes to form a well-ordered photonic structure (Figure 1 (d))(see Supporting Information). The resulting hologram is instantaneously useable and it acts as a sensor by undergoing changes in diffraction properties during …