Small‐Molecule Probes Enhance in Vivo Field‐Effect Transistor‐Based Biosensing by Overcoming Debye Length Limitations

Field-effect transistor (FET) biosensors have garnered extensive interest in biomedical detection, while their high sensitivity is maintained only when the targets are within the Debye length. In high-ionic-strength biological environments, the Debye length could be reduced to ca. 1 nm, but the size of traditional recognition probes such as antibodies and aptamers far exceeds the Debye length, therefore significantly compromising the sensitivity. Here, inspired by fluorescent probes, we designed and synthesized small molecules (approximately 1 nm in size) as the recognition probes to overcome the Debye length limitation and maintain the sensor's sensitivity in biological environments. Upon binding to target molecules, the probe triggers a change in the surface charge of the FET sensing channel and generate a quantifiable electronic signal. As a proof of concept, an ATP-responsive Small Molecules probe functionalIzed needLE (SMILE) FET biosensor was developed, which exhibited excellent affinity, selectivity and sensitivity with a detection limit of 82 fM toward detection of ATP in physiological solution. This allowed real-time monitoring of ATP level and its dynamic variations in both normal and depressed mice, providing a new solution of FET sensor for in vivo applications.