This invention pertains to the design, fabrication, and uses of an electronic system which can actively carry out and control multi-step and multiplex reactions in macroscopic or microscopic formats. In particular, these reactions include molecular biological reactions, such as nucleic acid hybridizations, nucleic acid amplification, sample preparation, antibody/antigen reactions, clinical diagnostics, combinatorial chemistry and selection, drug screening, oligonucleotide and nucleic acid synthesis, peptide synthesis, biopolymer synthesis, and catalytic reactions. A key feature of the present invention is the ability to control the localized concentration of two or more reaction-dependant molecules and their reaction environment in order to greatly enhance the rate and specificity of the molecular biological reaction.