Electrochemical aptasensors, detection

There is a limited number of studies on aptasensors (aptamer sensors), particularly for the detection of small organic molecules. An electrochemical aptasensor was developed by Kim et al. " for the detection of tetracycline using an ssDNA aptamer that selectively binds to tetracycline as the recognition element. The aptamer was highly selective for tetracycline and distinguishes minor structural... 

Li, B. L., Du, Y., Wei, H., Dong, S. J. (2007b). Reusable, label-free electrochemical aptasensor for sensitive detection of small molecules. Chem Commun 3780-3782. 

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... 

Centi et al [18] described various approaches for the development of electrochemical aptasensors for the detection of thrombin using magnetic beads as solid support and carbon... 

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... 

A detection limit of 0.55 fM of thrombin was calculated. Authors attribute the significant improvement of the sensitivity of such aptasensors with respect to others present in literature to the use of a nanoelectrode, formed by immobilization of Au-NPs on the surface of a gold electrode, to the use of NPs as labels, and to the use of DPV technique for the detection of the dissolved Cd + in the solution. Moreover, the electrochemical aptasensor was successfully tested in some serum samples. 

DNA probes, the first one linked with paramagnetic beads and the second one modified with Au-NPs via biotin-streptavidin affinity reactions. Zheng et al. [67] employed this detection methodology for the development of a specific electrochemical aptasensor for the detection of thrombin. The sensor was based on a sandwich format of magnetic nanoparticle/thrombin/Au-NP and signal amplification by forming network-like thiocyanuric acid/Au-NPs. A detection limit of 7.82 aM was achieved. 

Feng, L. Chen, Y Ren, J. Qu, X. A graphene functionalized electrochemical aptasensor for selective label-free detection of cancer cells. Biomaterials 2011,32, 2930-2937. 

Here we describe two types of label-free electrochemical aptasensors for small molecule detection based on gold nanoparticle (AuNP) amplification (13,14). These sensors are designed with either signal-off or signal-on modes, respectively (see Fig. 1). 

Zhang H, Han Y, Guo Y, Dong C. Porphyrin funcUonalized graphene nanosheels-based electrochemical aptasensor fo" label-free ATP detection. J Mater Chem 2012 22 23900-5. 

Zhou, L., Li, D.-J., Gai, L. et al. (2012) Electrochemical aptasensor for the detection of tetracycline with multi-walled carbon nanotubes amplification. Sens. Actuators, B, 162, 201-208. 

As an example of application of electrochemical aptasensor to medical diagnosis. Sun et al. developed a label-free electrochemical aptasensor for thrombin detection in whole blood. For the fabrication of this aptamers, self-assembled multilayers of carboxymethyl-polyethylene glycol-carboxymethyl (CM-PEG-CM) and thrombinbinding aptamer (TBA) were used. The thrombin molecules in the medium bound onto the TBA which leads to current decrease. This current decrease was monitored by differential pulse voltammetry. A linear range of 1 pM to 160nM was obtained for thrombin with LOD value of 1.56 x (Sun et al., 2013). 

Sun, C., Wang, X., Yang, X., Xing, L., Zhao, B., Yang, X., Mao, C., 2013. A label-free electrochemical aptasensor for sensitive thrombin detection in whole blood. Electrochimica Acta 106, 327-332. 

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