This thesis focuses on modifying the surface interactions of photonic crystals (PhCs) for sensors and hybrid hydrogels for atmospheric water harvesting. PhCs are known for manipulating the light flow and are used in bio- and chemical-sensing. However, detecting small molecules like drugs and volatile organic compounds (VOCs) at very low concentrations remains challenging. Therefore, we develop a sensor using one-dimensional (1D) PhCs, modifying the surface layer to enhance sensitivity to changes in refractive index (RI) for detecting opioids. The PhC-based opioid sensor offers label-free, rapid and quantitative measurements, with optimized incident light angles achieving the highest sensitivity of 5688.8 nm/refractive index unit and limit of detections (LODs) of 7 ng/mL and 6 ng/mL for morphine and fentanyl, respectively. Additionally, we enhance the sensitivity of VOC detection by casting VOC-reactive dyes on PhC surfaces, utilizing PhCs to enhance dye light absorption. This approach enables color change upon VOCs exposure more pronounced, achieving distinct color difference maps for acetaldehyde, acetone, and acetic acid, with LODs of 1 ppm, 0.1 ppm, and 0.02 ppm, respectively. Atmospheric water harvesting is a promising method for obtaining fresh water and sustainable energy from moisture in the air. Hybrid hydrogels, specifically those incorporating hygroscopic salts, have shown potential for this purpose. However, the conventional desorption process often requires additional energy for sample heating. To address this, we present charged network, poly(acrylic acid) (PAA) hydrogels embedded with lithium chloride, that shows different surface interactions with atmospheric moisture. Unlike neutral hydrogels, where water droplets nucleate on the hybrid hydrogel surface and are immediately absorbed into the hydrogel network, there is a delay in water diffusion in PAA hydrogel, due to charge-charge interactions, leading to self-release of captured moisture as water in the liquid from. This allows harvesting atmospheric moisture without any energy input. Therefore, this thesis highlights the importance of understanding PhC properties and the hybrid hydrogel behavior in water absorption processes to modify their surface or surface interactions to pave the next directions for sensors and water harvesters.