Other Aptasensors

Despite being relatively new technology, aptamers have a tremendous potential and can be envisioned to rival antibodies and other traditional recognition elements for molecular detection and recognition, due to their inherent affinity, selectivity, and ease of synthesis. In addition, the combination of aptasensors with electrochemical detection methods has the added advantage of further cost reduction and miniaturization of such systems. 

AQ/Qo = (Q - Qo)/Qo, where Q0 is charge consumption without analyte and Q is that at certain thrombin, concentration. An example of calibration curve for two independently prepared electrodes is shown in Fig. 47.3. It is seen, that results are well reproducible. Statistical analysis, performed earlier [4] revealed that standard error is approximately 11%. Interferences of this aptasensor with other compounds, human serum albumine (HSA) and human IgG are relatively low. An example is shown in Fig. 47.4, where calibration curve for thrombin is compared with those for HSA and IgG. Please note, that concentrations of HSA and IgG are much higher in comparison with that of thrombin. 

Comparison of the developed aptasensor with other Tat detection methods is very difficult since most of the published papers on this subject deal with Tat-derived peptides and not with the full length protein. Anyway, the results demonstrated that the use of a biosensor with a specific aptamer as biorecognition element could be an interesting approach in the detection of proteins, which has been examined here considering a model system. 

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. 

These aptasensors are based on the use of a redox probe such as methylene blue (MB) that undergoes an oxidation and reduction due to the electron transfer from an electrode surface to a probe. These redox probes are noncovalently bound to aptamers and intercalate or interact with aptamers mainly by electrostatic interactions. For example, MB, positively charged, interacts with negatively charged proteins or other negatively charged analytes. When... 

Hernandez EJ, Ozalp VC (2012) Graphene and other nanomaterial-based electrochemical aptasensors. Biosensors 2 1-14... 

On the other hand, Ocafia et al. (2012) reported a simple, label-free impedimetric aptasensor for the detection of THR in PBS buffer solutions. In the design of the aptasensor, a graphite epoxy composite was used and the aptamers were immobilized onto the electrode surface by physical adsorption. A detection limit of 4.5 pM was achieved using EIS in the presence of the [Fe(CN) ] " redox probe. The aptasensor was regenerated for several cycles. Recently, Liu et al. (2015) developed an impedimetric aptasensor, using AuNPs for signal amplification and the redox probe [Fe(CN) ] , for detection and quantification of MUCl in PBS buffer solutions. 

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