Fig. 1

Steady-state fluorescence intensity (FI) response to K⁺ was measured as a function of the magnesium concentration in the buffer used to hybridize DNA nanosensors. Fluorescence intensity was normalized with respect to the DNA nanosensor fluorescence signal in the presence of the control buffer (PB + MgCl₂), without K⁺. To optimize the concentration of magnesium in buffer, K⁺ was added at concentrations of 0, 1, 10, and 25 mM to 1 µM DNA nanosensor samples, each prepared with a buffer containing a different magnesium concentration: 0.85 mM (large circle), 1.05 mM (white up-pointing triangle), and 5 mM (figure dash)