Spherical\nNucleic Acid Probes on Floating-Gate Field-Effect\nTransistor Biosensors for Attomolar-Level Analyte Detection

Field-effect\ntransistor (FET) sensors are attractive for the label-free\ndetection of target biomolecules, offering ultrahigh sensitivity and\na rapid response. However, conventional methods for modifying biomolecular\nprobes on sensors often involve intricate and time-consuming procedures\nthat require specialized training. Herein, we propose a simple and\nversatile approach to functionalize floating-gate (FG) FET sensors\nby exploiting the strong binding ability of polyvalent interactions\nand the three-dimensional structure of densely functionalized spherical\nnucleic acids (SNAs). Crucially, the SNAs can be easily deposited\nonto a dielectric layer under mild conditions, ensuring stable immobilization\nof the probes. Further, the SNAs show efficient and robust immobilization\non various dielectric layers including Y<sub>2</sub>O<sub>3</sub>,\nTa<sub>2</sub>O<sub>5</sub>, and HfO<sub>2</sub>, forming conjugates\nthat resist denaturation by various agents. By modifying the DNA sequence\nwithin the SNAs, we achieved highly sensitive FG-FET biosensors for\nDNA, adenosine triphosphate, and viral nucleic acids at the attomolar\nlevel. For clinical samples detection, unamplified enterovirus 71\nRNA at levels as low as 0.13 copies μL<sup>–1</sup> was\ndetected within 100 s. Moreover, the sensor attained 100% accuracy\nfor analyte detection in both positive and negative samples. Our findings\nprovide a general and simple method for fabricating FET-based biochemical\nsensors and demonstrate that the SNA-modified FG-FET biosensor is\na versatile and reliable integrated platform for ultrasensitive biomarker\ndetection.