We demonstrate a self-assembled reagentless biosensor based on a modular design strategy that functions in the detection of TNT and related explosive compounds. The sensor consists of a dye-labeled anti-TNT antibody fragment that interacts with a cofunctional surface-tethered DNA arm. The arm consists of a flexible biotinylated DNA oligonucleotide base specifically modified with a dye and terminating in a TNB recognition element, which is an analogue of TNT. Both of these elements are tethered to a Neutravidin surface with the TNB recognition element bound in the antibody fragment binding site, bringing the two dyes into proximity and establishing a baseline level of fluorescence resonance energy transfer (FRET). Addition of TNT, or related explosive compounds, to the sensor environment alters FRET in a concentration-dependent manner. The sensor can be regenerated repeatedly through washing away of analyte and specific reformation of the sensor assembly, allowing for subsequent detection events. Sensor dynamic range can be usefully altered through the addition of a DNA oligonucleotide that hybridizes to a portion of the cofunctional arm. The modular design of the sensor demonstrates that it can be easily adapted to detect a variety of different analytes.