Directed Modification of Reaction Centers from Purple Bacteria

Abstract

In a hybridized microchannel made of poly(dimethylsiloxane) (PDMS)and glass, nonuniform electroosmotic flow (EOF) was created whenan electric field was applied. PDMS and glass pieces were bondedat room temperature after oxidization with oxygen plasma. After oxidization,the PDMS surface has a higher zeta (zeta) potential than that ofglass, which results in faster EOF at that surface. When the channelhas a large aspect ratio (width ≫ depth), the EOF can be consideredas a two-dimensional gradient shear flow. By using a scanning confocalfluorescence microscope, we demonstrated that negatively chargedDNA molecules were focused by the nonuniform EOF and the electricfield into a thin layer at the glass surface of about one-fifth ofthe channel depth. This phenomenon was applied to selectively detecttarget DNA molecules using evanescent-field excitation. Streptavidin-conjugatedquantum dots (QD) were used to selectively bind biotinylated DNA.After applying an electric field, free QD remained randomly distributedwithin the channel. Nonbiotinylated DNA molecules were focused ontothe glass surface, but they were not labeled and thus nonfluorescent.Therefore, the increase in molecule count after application of theelectric field can be solely attributed to QDDNA complexes whichwere focused onto the glass surface. This method does not requirethe separation of excessive probes (QD) and can be operated continuouslyto achieve high throughput.