Microarrays are classified into 3 types based on the mode of preparation. 

1. Spotted arrayson glass are created on glass slides coated with poly-lysine, which helps DNA stick to the surface. DNA is deposited using specialized pins, and fluorescent labels can be used to mark the samples. 
2. In-situ synthesized arrays are made directly on a solid surface using chemical synthesis. This process combines special light-sensitive chemicals with photolithography techniques to create the array. 
3. Self-assembled arraysinvolve fiber optic arrays where DNA is attached to small polystyrene beads. The beads are placed onto the ends of a fiber optic cable, with different DNA types on different beads. When a mixture of these beads is applied, they form a randomly assembled array.