Figure 4.
Electrochemistry and enzymatic activity on various DNA films. a, Illustration of the chip layout for measuring the electrochemical characteristics and RsaI activity with four DNA films (from top left to bottom right) including the well matched 100-mer which contains the RsaI binding site, a well matched 17-mer that does not contain the RsaI binding site, the single stranded, Nile Blue modified 25-mer, and the 100-mer missing the central 36-mer segment. As illustrated, the 25-mer and 100-mer without the central 36-mer are expected to be reduced through direct surface adsorption and contact. In a is also illustrated restriction of the well matched 100-mer DNA films upon addition of RsaI and Mg2+. b, CV scans of the four DNA films prior to addition of enzyme (blue) and after addition of RsaI (red). The enzyme reaction was carried out in 10 mM tris-HCl, 50 mM NaCl, 10 mM MgCl2, 4 mM spermidine, pH 7.9. Scans were taken before and after the enzyme reaction in phosphate buffer (5 mM phosphate, 50 mM NaCl, 4 mM MgCl2, 4 mM spermidine, 10% glycerol, pH 7). CV scans were measured versus Ag/AgCL at a 100 mV/s scan rate. For the 100-mer, 17-mer and single stranded 25-mer, respectively, the peak splittings are 80 mV, 60 mV, and 15mV; the midpoint potentials are −180 mV, −180mV, and −170mV; k100 = k17 = 39 kss25. Values could not be determined accurately for the 100-mer lacking the 36-mer strand.