Electrochemical aptasensors assays

In its simplest, QCM, format, protein-aptamer interactions were analyzed by Liss et al. (2002). They compared the interaction of IgE with DNA aptamer as well as with anti-IgE antibodies. Although the detection limit was similar in the two cases, the advantage of the aptasensor was its possibility of surface regeneration, which was impossible for an antigen-based biosensor. However, recently it has been shown that immobilization of anti-IgE on the dendrimer surface also allows us to regenerate an immunosensor (Svobodova et al., 2006). The QCM method was recently compared with the electrochemical biosensor assay of thrombin detection (Hianik et al., 2005, 2007). It has been shown that the sensitivity of thrombin detection was similar for the two methods. Mascini and co-workers showed that similar results in sensitivity and selectivity in the detection of Tat peptide with RNA aptamer can be obtained by the QCM and SPR methods (Tombelli et al., 2005b). 

Ikebukuro et al. [12] first reported an electrochemical aptasensor for the detection of thrombin based on a sandwich-based assay. Two different aptamers specific for thrombin were used the 29-mer thiolated aptamer and the 15-mer aptamer labeled with glucose dehydrogenase [GDH]. The thiolated aptamer was immobilized onto gold electrodes thrombin at different concentrations and then the enzyme-labeled aptamer was added to the aptamer-modified electrodes. The electric current generated by the addition of glucose was measured at 0.1 V vs. Ag/AgCl in a buffer containing... 

Another example of electrochemical aptasensor based on Au-NPs as labels for the detection of thrombin is reported by Zheng et al. [28]. The assay was based on a sandwich format, in which the aptamerl (15-mer DNA aptamer with an amino group at its 5 end) was immobilized onto carboxyl functionalized magnetic beads. Such aptamer-coated magnetic beads were used for capturing and separation. Thrombin and Au-NP-labeled aptamerll were then added to... 

Electrochemical methods of detection affinity interactions at the surfaces are rather effective due to their relative simplicity and low cost. Amperometric aptasensor based on sandwich assay was proposed by Ikebukuro et al. [42]. They used two aptamers selective to thrombin. 

In literature no many examples of electrochemical enz5mie-labeled aptasensors based on a competitive assay are present. The advantages of a competitive format (direct and indirect) are mainly related to the fact that only one aptamer is required (considering that two or more aptamers are not selected for many target anal ftes) and the time necessary for the assay is faster. 

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