Transcription factor expression levels, which sensitively reflect cellular development and disease state, are typically monitored via cumbersome, reagent-intensive assays that require relatively large quantities of cells. Here, we demonstrate a simple, quantitative approach to their detection based on a simple, electrochemical sensing platform. This sensor sensitively and quantitatively detects its target transcription factor in complex media (e.g., 250 mu g/mL crude nuclear extracts) in a convenient, low-reagent process requiring only 10 mu L of sample. Our approach thus appears a promising means of monitoring transcription factor levels.