a microfluidic structure comprising a thermoplastic portion defining a microfluidic recess , a bonding layer on the thermoplastic portion and a siloxane elastomer portion covalently bonded to the bonding layer to seal the microfluidic recess . the microfluidic recess can therefore be formed simply , quickly and cheaply using known injection molding techniques , which are not hampered by the need for a curing step . however , the positive qualities associated with elastomers can be brought to the structure by using this to seal the microchannels . the bonding layer can be formed by silica deposited on the thermoplastic portion using techniques known in the field of optics .