Abstract
Modern tools for the analysis of cellular function aim for the quantitative measurement of all members of a given class of biological molecules. Of the analyte classes, nucleic acid measurements are typically the most tractable, both on an individual analyte basis and in parallel. Thus, tools are being sought to enable measurement of other cellular molecules using nucleic acid biosensors. Of the variety of potential nucleic acid biosensor strategies, structure-switching aptamers (SSAs) present a unique opportunity to couple sensing and readout of the target molecule. However, little has been characterized about the parameters that determine the fidelity of the signal from SSA biosensors. In this study, a small molecule biosensor based on a SSA was engineered to detect the model small molecule, theophylline, in solution. Quantitative theophylline detection over nearly three orders-of-magnitude was achieved by scintillation counting and quantitative PCR. Further analysis showed that the biosensor fidelity is primarily controlled by the relative stability of the two conformations of the SSA.