Significant Elevation in Potassium Concentration Surrounding Stimulated Excitable Cells Revealed by an Aptamer-Modified Nanowire Transistor.

Recording ion fluctuations surrounding biological cells with a nanoelectronic device offers seamless integration of nanotechnology into living organisms and is essential for understanding cellular activities. The concentration of potassium ion in the extracellular fluid ( C K + ex ) is a critical determinant of cell membrane potential and must be maintained within an appropriate range. Alteration in C K + ex can affect neuronal excitability, induce heart arrhythmias, and even trigger seizure-like reactions in the brain. Therefore, monitoring local fluctuations in real time provides an early diagnosis of the occurrence of the K + -induced pathophysiological responses. Here, we modified the surface of a silicon nanowire field-effect transistor (SiNW-FET) with K + -specific DNA-aptamers (Apt K + ) to monitor the real-time variations of C K + ex in primary cultured rat embryonic cortical neurons or human embryonic stem cell-derived cardiomyocytes. The binding affinity of Apt K + to K + , determined by measuring the dissociation constant of the Apt K + -K + complex ( K d = 10.1 ± 0.9 mM), is at least 38-fold higher than other ions (e.g., Na + , Ca 2+ , and Mg 2+ ). By placing cultured cortical neurons over an Apt K + /SiNW-FET device, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) stimulation raised the C K + ex dose-dependently to 16 mM when AMPA concentration was >10 μM; this elevation could be significantly suppressed by an AMPA receptor antagonist, 6,7-dinitroquinoxaline-2,3-dione. Likewise, the stimulation of isoproterenol to cardiomyocytes raised the C K + ex to 6-8 mM, with a concomitant increase in the beating rate. This study utilizing a robust nanobiosensor to detect real-time ion fluctuations surrounding excitable cells underlies the importance of ion homeostasis and offers the feasibility of developing an implant device for real-time monitoring.