A microarray substrate including a piece of fluoropolymer whose surface is modified with polydopamine, in which the polydopamine forms an array of microspots on the surface of the fluoropolymer piece, and allows immobilization of molecules or cells. A microarray including the substrate, a microfluidic system designed for dispensing reagents onto selected locations on the surface of substrates, and a method for preparing the substrate and the microarray, in which a dopamine solution is dispensed onto the fluoropolymer piece using the microfluidic system, and forms an array of polydopamine microspots serving as the reaction sites for microarray analysis.