fluidic methods and devices for conducting parallel chemical reactions are disclosed . the methods are based on the use of in situ photogenerated reagents such as photogenerated acids , photogenerated bases , or any other suitable chemical compounds that produce active reagents upon light radiation . the present invention describes devices and methods for performing a large number of parallel chemical reactions without the use of a large number of valves , pumps , and other complicated fluidic components . the present invention provides microfluidic devices that contain a plurality of microscopic vessels for carrying out discrete chemical reactions . other applications may include the preparation of microarrays of dna and rna oligonucleotides , peptides , oligosacchrides , phospholipids and other biopolymers on a substrate surface for assessing gene sequence information , screening for biological and chemical activities , identifying intermolecular complex formations , and determining structural features of molecular complexes .