Spherical Nucleic Acid Probes on Floating-Gate Field-Effect Transistor Biosensors for Attomolar-Level Analyte Detection

Field-effect transistor (FET) sensors are attractive for the label-free detection of target biomolecules, offering ultrahigh sensitivity and a rapid response. However, conventional methods for modifying biomolecular probes on sensors often involve intricate and time-consuming procedures that require specialized training. Herein, we propose a simple and versatile approach to functionalize floating-gate (FG) FET sensors by exploiting the strong binding ability of polyvalent interactions and the three-dimensional structure of densely functionalized spherical nucleic acids (SNAs). Crucially, the SNAs can be easily deposited onto a dielectric layer under mild conditions, ensuring stable immobilization of the probes. Further, the SNAs show efficient and robust immobilization on various dielectric layers including Y₂O₃, Ta₂O₅, and HfO₂, forming conjugates that resist denaturation by various agents. By modifying the DNA sequence within the SNAs, we achieved highly sensitive FG-FET biosensors for DNA, adenosine triphosphate, and viral nucleic acids at the attomolar level. For clinical samples detection, unamplified enterovirus 71 RNA at levels as low as 0.13 copies μL^-1 was detected within 100 s. Moreover, the sensor attained 100% accuracy for analyte detection in both positive and negative samples. Our findings provide a general and simple method for fabricating FET-based biochemical sensors and demonstrate that the SNA-modified FG-FET biosensor is a versatile and reliable integrated platform for ultrasensitive biomarker detection.