Oxidation signals, label-free electrochemical

Fig. 6 Label-free electrochemical detection of DNA hybridization. The inosine (I) substituted probe shows no electrochemical signals, since inosine is not electroactive (a) After hybridization with the target DNA, the appearance of the guanine (G) oxidation signal (around + 1 V vs. Ag/AgCl) provides specific detection (b)...

Kerman et al, 2004 also described the label-free electrochemical detection of DNA based on the direct attachment of adenine probes to the sidewall and end of functionalized MWCNTs. The MWCNTs were attached onto the carbon paste electrode surface modified with thymine probes by hybridization between adenine and thymine. The combination of sidewall and end functionalization of MWNT showed enhancement of the guanine oxidation signal in the direct measurement compared to the ones from only end-modified MWCNT. 

Figure 7.1 Label-free voltammetric detection of aptamer-protein interactions. (A) The electrochemical oxidation response from the guanine bases in the aptamer is observed at about 1 V (peak G) on the surface of the screen-printed electrodes. (The inset shows gold and carbon-based screen-printed electrodes with a three-electrode system.) (B) After the binding event with the target protein, an oxidation signal appears at about 0.6 V (peak P), and the oxidation signal of the aptamer decreases.

DNA oxidation at carbon electrodes is associated with the irreversible oxidation of guanine and adenine [33], For example, the G oxidation signal observed at -i-1.0 V, without external labels, has been used to monitor telomerase activity by using a carbon graphite electrode (CGE) as an electrochemical transducer [5], Telomerase activity has been detected in cell extracts containing as low as 100 ng pl of protein. This label-free assay is practical in the quantitative determination of telomerase activity providing a cheap and simple detection protocol for the diagnosis of cancer that can also be extended to the analysis of food related to DNA. 

Eskiocak, U., Ozkan-ariksoysal, D., Ozsoz, M. and Oktem, H.A. (2007) Label-free detection of telomerase activity using guanine electrochemical oxidation signal. Anal. Chem.,19 (22), 8807-8811. 

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