What is claimed is: 1. A method of modifying fluid flow in a channel formed in a substrate which comprises: exposing only one or more discrete, isolated portions of the channel to light at a fluence which is sufficient to change a surface charge at the one or more discrete, isolated exposed portions of the channel. 2. A method of modifying fluid flow in a channel formed in a substrate according to claim 1, wherein the one or more discrete, isolated portions of the channel is exposed to light at a fluence and wavelength(s) which are sufficient to alter the surface charge at the exposed portion of the channel, and wherein the substrate is not ablated by the light. 3. A method of modifying fluid flow in a channel formed in a substrate according to claim 1, wherein the fluence causes ablation of the substrate. 4. A method of modifying fluid flow in a channel formed in a substrate according to claim 3, wherein the one or more discrete, isolated portions of the channel which is exposed to light comprises at least one of a wall of the channel, a bottom of the channel, and one or more portions thereof. 5. A method of modifying fluid flow in a channel formed in a substrate according to claim 3, wherein the channel is linear. 6. A method of modifying fluid flow in a channel formed in a substrate according to claim 3, wherein the channel is non-linear. 7. A method of modifying fluid flow in a channel formed in a substrate according to claim 3, wherein the one or more discrete, isolated portions of the channel is exposed to at least one of a linear and non-linear pattern of light. 8. A method of modifying fluid flow in a channel formed in a substrate according to claim 3, wherein the substrate is a member selected from the group consisting of polymeric, glass, silica, ceramic, and composites thereof. 9. A method modifying fluid flow in a channel formed in a polymeric substrate according to claim 3, wherein the substrate is selected from the group consisting of a poly(methyl methacrylate) substrate, a polycarbonate substrate, a poly(ethylene terephthalate glycol) substrate, a polystyrene substrate, and a poly(vinyl chloride) substrate. 10. A method of modifying fluid flow in a channel formed in a substrate according to claim 3, wherein the substrate comprises a microfluidic system. 11. A method of modifying fluid flow in a channel formed in a substrate according to claim 2, wherein the one or more discrete, isolated portions of the channel which is exposed to light comprises at least one of a wall of the channel, a top of the channel, a bottom of the channel, and portions thereof. 12. A method of modifying fluid flow in a channel formed in a substrate according to claim 3, wherein the channel is linear. 13. A method of modifying fluid flow in a channel formed in a substrate according to claim 3, wherein the channel is non-linear. 14. A method of modifying fluid flow in a channel formed in a substrate according to claim 3, wherein the portion of the channel is exposed to at least one of a linear and non-linear pattern of light. 15. A method of modifying fluid flow in a channel formed in a substrate according to claim 3, wherein the substrate is a member selected from the group consisting of polymeric, glass, silica, ceramic, or composites thereof. 16. A method of modifying fluid flow in a channel formed in a polymeric substrate according to claim 3, wherein the substrate is selected from the group consisting of a poly(methyl methacrylate) substrate, a polycarbonate substrate, a poly(ethylene terephthalate glycol) substrate, a polystyrene substrate, and a poly(vinyl chloride) substrate. 17. A method of modifying fluid flow in a channel formed in a substrate according to claim 3, wherein the substrate comprises a microfluidic system. 18. A method of immobilizing a chemical species in a channel formed in a substrate which comprises: exposing the one or more discrete, isolated portions of the channel to light at a fluence which is sufficient to change a surface charge at the exposed portion of the channel; and applying a chemical species to the exposed portion of the channel. 19. A method of immobilizing a chemical species in a channel formed in a substrate according to claim 18, wherein the chemical species comprises a chemical compound. 20. A method of immobilizing a chemical species in a channel formed in a substrate according to claim 18, wherein the chemical species comprises a biological species. 21. A method of immobilizing a chemical species in a channel formed in a substrate according to claim 18, wherein the one or more discrete, isolated portions of the channel that is exposed to the light comprises at least one of a wall of the channel, a bottom of the channel, and portions thereof. 22. A method of immobilizing a chemical species in a channel formed in a substrate according to claim 18, wherein the substrate is a member selected from the group consisting of polymeric, glass, silica, ceramic, or composites thereof. 23. A method of immobilizing a chemical species in a channel formed in a polymeric substrate according to claim 22, wherein the substrate is selected from the group consisting of a poly(methyl methacrylate) substrate, a polycarbonate substrate, a poly(ethylene terephthalate glycol) substrate, a polystyrene substrate, and a poly(vinyl chloride) substrate. 24. A method of immobilizing a chemical species in a channel formed in a substrate according to claim 18, wherein the substrate comprises a microfluidic system. 25. A method for immobilizing a chemical species in a channel formed in a substrate according to claim 24, wherein a microarray is formed in the microfluidic system.