Patterned self-assembled beads in silicon channels

A novel technique enabling selective bead trapping in microfluidic devices without the use of physical barriers is presented in this paper. It is a fa st, convenient and simple method, involving microcontact printing and self- assembly, that can be applied to silicon, quartz or plastic substrates. In the first step, channels are etched in the substrate. The surface chemistry of the internal walls of the channels is then modified by microcontact pri nting. The chip is submerged in a bead slurry where beads self-assemble bas ed on surface chemistry and immobilize on the internal walls of the channel s. Silicon channels (100 mum wide and 50 mum deep) have been covered with m onolayers of streptavidin-, amino- and hydroxy-functionalized microspheres and resulted in good surface coverage of beads on the channel walls. A high -resolution pattern of lines of self-assembled streptavidin beads, as narro w as 5 mum, has also been generated on the bottom of a 500 mum wide and 50 mum deep channel. Flow tests were performed in sealed channels with the dif ferent immobilized beads to confirm that the immobilized beads could withst and the forces generated by water flowing in the channels. The presented re sults indicate that single beads can be precisely positioned within microfl uidic devices based on self-assembly which is useful as screening and analy sis tools within the field of biochemistry and organic chemistry.