Electrochemical arrays for the detection of small molecule drugs Summary: Microarrays for the detection of DNA and RNA are well established, and protein microarrays are advancing rapidly. The development of arrays for the quantitative detection of small molecules, in contrast, has lagged significantly. Here we propose a reagentless, electrochemical method for monitoring a panel of small molecules in parallel, in real time, in blood and other complex media, an advance that should prove of significant utility in applications ranging from diagnostics through drug discovery to the basic biological sciences (e.g., metabolomics). Our approach is based on an electrochemical, aptamer-based (E-AB) platform that is sensitive, rapid, reagentless, and selective enough to employ directly in serum and other largely unprocessed biological materials. And while our long-term objective is the fabrication of E-AB devices for the real-time monitoring of effectively any small molecule, the proposed research focuses on specific, high-value examples of the drugs of abuse and aminoglycosidic antibiotics. The reagentless E-AB platform utilizes electrochemistry to monitor the target-induced folding of an electrode-bound aptamer. To date we have fabricated E-AB sensors against protein, small molecule and inorganic ion targets, each of which is sensitive (micromolar to picomolar detection limits) and selective enough to deploy directly in blood serum, saliva, and soil extracts. Moreover, our sensors are stable and equilibrate rapidly, allowing for the continuous, real-time detection of small molecules in an analyte stream, such as flowing blood serum. In support of this nascent approach, the proposed research program focuses on the top-to-bottom development E-AB arrays directed at the simultaneous, real-time quantification of suites of small-molecule drugs. Achieving this will require the development of improved schemes for the selection of high affinity, high-specificity DNA aptamers against small molecules, the selection of new aptamers and their adaptation in high gain, high- sensitivity E-AB sensors, further improvements in the E-AB platform itself and, finally, the fabrication and testing of micron-scale E-AB arrays, advances that will firmly establish the utility of this potentially promising and general sensing technology.Relevance. Microarrays for the simultaneous detection of multiple RNAs have revolutionized our understanding of transcription and gene regulation, and protein arrays are rapidly improving our understanding of translational regulation and protein-protein interactions. A quantitative, parallelizable means of monitoring small molecules would likely prove similarly transformative in applications including the basic biological sciences (e.g., metabolomics), diagnostics and drug discovery. Current methods for the detection of drugs, metabolites and other small molecules in blood, however, are generally limited to chromatographic or competition assays, techniques that are ill suited for rapid, parallel analyte detection. Here we propose the development of an electrochemical, aptamer-based (E-AB) technology for the quantification of multiple small molecule analytes in parallel, in real time, in blood and other complex media. And while our long-term objective is the development of E-AB arrays suitable for the continuous, real-time monitoring of effectively any small molecule, the efforts proposed here will focus on the drugs of abuse and the aminoglycosidic antibiotics as high-value, clinically relevant targets with which to develop this potentially promising and general sensing technology.