Remote-point photonic sensors are fabricated and evaluated. They are based on nanocomposite thin films comprising $\mathrm{Ni}{\mathrm{Cl}}_2$ nanocrystals embedded in sol-gel silica matrix and are patterned using direct UV laser microetching techniques to form surface relief structures, which exhibit environment sensitive optical diffraction effects. A strong response to ammonia is detected via the alteration of diffraction efficiency of its orders upon exposure to the analyte. Detection of ammonia in the $2\mathrm{ppm}$ level with a typical response time of about $30\mathrm{s}$ in the ambient, 50% RH $20°\mathrm{C}$ , room environment is demonstrated.