FIGURE 7.

The low-frequency spectral density of current noise versus pH dependence has a pronounced peak at ∼pH 2.5. Noise at the maximum exceeds noise at neutral pH by approximately three orders of magnitude. As pH is shifted from 6 to 9 (inset), the noise stays at its lowest; however, subsequent pH increase leads to the increase in noise spectral density. The spectral density of the background (curve 1 in Fig. 6) was subtracted. Applied voltage was 100 mV. 1 M KCl was used as a bathing solution.