A digital microfluidic platform for the automation of quantitative, multi-step biomolecular assays is developed and optimized. The platform consists of a 2-dimensional array of microvalves that can be programmed to perform reagent routing, mixing, rinsing, serial dilution, and many other operations using nanolitre scale volumes of sample. Discrete transfer of fluid between microvalves is characterized using gravimetric flow analysis and optimized to achieve maximum efficiency. Protocols for on-chip reagent mixing and serial dilution are optimized to achieve linearity over a 1000-fold dilution range. These optimized programs are used to develop a rapid, quantitative assay for hydrogen peroxide, a biomarker of oxidative stress. A sub-micromolar limit of detection is demonstrated with an 8.5 min program runtime, thus establishing this platform as an effective tool for the automation of multi-step bioassays. The programmability of this system enables rapid development of diverse assay protocols on a common chip format.