Stimuli-responsive polymers have been attracted increasing attention over the years for their ability of altering physiochemical properties upon external stimuli. However, many stimuli-responsive polymer-based sensors require specialised and expensive equipment which limits their applications. Here, an inexpensive and portable sensing platform of novel microarray films made of stimuli-responsive polymers is introduced for real-time sensing of various environmental changes. When illuminated by laser light, microarray films generate diffraction patterns which can real-time reflect and magnify variations of the periodical microstructure induced by surrounding invisible parameters. Stimuli-responsive polyelectrolyte complexes (PEC) are structured into micropillar arrays to monitor the pH variation and the presence of calcium ions based on reversible swelling/shrinking behaviours of the polymers. A pH hysteretic effect of the selected polyelectrolyte pair is determined and explained. Further, polycaprolactone (PCL) microchamber arrays are fabricated and display a thermal driven structural change, which is exploited for photonic threshold temperature detection. Experimentally observed diffraction patterns are additionally compared with Rigorous Coupled Wave Analysis (RCWA) simulations which prove, that induced diffraction pattern alterations are solely caused by geometrical microstructure changes. Microarray-based diffraction patterns are a novel sensing platform with versatile sensing capabilities which will likely pave a way to use microarray structures as photonic sensors.