Figure 3.

Representative signals for the four nucleotides and d^meCMP after removal of the water signal. 10 μM nucleotide was dissolved in 1 mM phosphate buffer (pH=7) and the probe, functionalized with M scanned at 2nm/s over an Au(111) surface also functionalized with M. The tunnel gap was set under servo control to a baseline current of 6pA with a probe bias of 0.5V. The slew rate of the servo is much slower than the ms timescale of the pulses observed here. Approximate overall count rates are listed in Table 1 – these are much smaller than the pulse rates observed within the signal bursts shown here because the signals occur in clusters.