Aptamer-Modified Extended-Gate Field-Effect Transistor Allows Direct Detection of Minute Cell Surface Charge for Early Diagnosis of Leukemia

A miniaturized and inexpensive biosensor should be developed for the early and rapid diagnosis of leukemia. In this study, we have demonstrated a direct electrical detection of leukemia cells such as CCRF-CEM using an extended-gate field-effect transistor (FET) sensor modified with the sgc8c aptamer. As a result, we found that the FET signal intensity quantitatively increased with cell density, resulting from CCRF-CEM cell–sgc8c aptamer-specific interactions. In particular, the increase in the amount of the sgc8c aptamer immobilized on the gate electrode contributed to the increase in cell density on it, resulting in quantitative detection of CCRF-CEM cells on the gate electrode. Moreover, the surface charge of a CCRF-CEM cell was analyzed in accordance with the detection principle of FET sensors. Indeed, slight changes in molecular charges on CCRF-CEM cells that would have entered the Debye screening layer were detected owing to the amplification of electrical signals by the capacitive gate structure in the front-end junction-type FET system, which was composed of the extended-gate FET sensor in this study. The analysis further suggests that only a limited fraction of the cell surface charge near the gate interface contributes to the FET response.