Power Spectrum Density Analysis of Electrical Noise in Glass Microelectrodes

Experiments were performed on glass microelectrodes in order to obtain quantitative estimates of the power spectrum density of their current and voltage noises. The effects of current injection (under voltage or current clamp), and ion concentration gradients, were studied separately or concurrently. It was observed that the spectral distribution of the fluctuations is of the 1/f¿type, with ¿values close to unity. The excess noise values measured, relative to specific Nyquist levels, depend approximately on the square value of the current injected through the microtip and on the absolute value of the tip potential of the microelectrode. Dependence of these spontaneous fluctuations as a function of the nature of the external solution was also investigated.