Aptamer-based sensors

Kirby R, Cho EJ, Gehrke B, Bayer T, Park YS, Neikirk DP, McDevitt JT, Ellington AD (2004) Aptamer-based sensor arrays for the detection and quantitation of proteins. Anal Chem 76 4066-4075... 

It is not surprising that wide range of aptamer-based sensors (aptasensors) have been reported in the literature.118-120 Recently, electrochemical aptamer sensors gained considerable attention.121,122 Since, nucleic acids aptamers fold their structure upon binding to the target molecule, formation of the aptamer-target complex can be... 

The advantageous properties of PNA-based biosensors represent an appealing alternative to DNA and aptamer based sensors under some circumstances. They offer advantages of increased sensitivity, selectivity, and stability, therefore they present valuable alternative to DNA/aptamer based sensors but have problems associated with solubility and synthetic procedure. 

Fig. 3 Electrochemical aptamer-based sensor of redox-tagged DNA against specific targets, (a) When the aptamer comes in contact with a small molecule, in this case cocaine, it folds, and the redox tag is brought closer to the electrode, increasing the current, (b) When the aptamer comes in contact with thrombin, the tag moves away from the surface, decreasing the electrochemical signal. Reproduced from [85] with permission. Copyright Langmuir, 2007...

To demonstrate a way of the use of aptamers in design of biomimetic sensors, two examples will be cited from the recent literature. The piezoelectric sensor for protein IgE has been developed with the use of commercially available anti-IgE aptamer oligonucleotide.167 The obtained sensor shows specificity and sensitivity equivalent to these of immunosensor, but for aptamer-based sensor a less decrease of sensitivity after consecutive cycles of analyte binding and regeneration, as well as relative heat resistance and stability over several weeks was shown. A more complex mechanism of sensing was employed in adenosine aptamer-based sensor.168 Detection was based on enzymatic activity measurements by fluorescence polarization with the use of aptameric enzyme subunit, which was a DNA aptamer composed of enzyme-inhibiting aptamer and adenosine-binding aptamer. 

The above results indicate that it is likely to construct tailor-made biosensors for biogenic amines by the RNP-based strategy. Aptamer-based sensors or RNP-based sensors would enable selective and reliable simultaneous measurements of biogenic amines at physiological concentrations. 

Label-free protein biosensors witnessed great advance in recent years. An impedometric label-free detection was proposed to conduct immunoassay with high sensitivity and specificity [140]. Aptamers that were immobilized on solid substrates received appreciable attention because they have high permanent charge density, which is possibly exploited for label-free detection such electrochemical impedance spectroscopy (EIS) [141]. There are many cases of aptamers-based sensors, which are separately described in Sect. 4.4. 

Willner, L, Zayats, M. (2007). Electronic aptamer-based sensors. Aw ew Chem Int Ed Engl 46(34), 6408-6418. 

Xiao, Y., Lubin, A. A., Heeger, A. J., Plaxco, K. W. (2005a). Label-free electronic detection of thrombin in blood serum by using an aptamer-based sensor. Angew Chem Int Ed Engl 44, 5456-5459. 

De-los-Santos Alvarez, N., Lobo-Castanon, M. J., Miranda-Ordieres, A. J., Tunon-Blanco, P. (2007). Modified-RNA aptamer-based sensor for competitive impedimetric assay of neomycin B. J Am Chem Soc 129, 3808-3809. 

Zayats, M., Huang, Y., Gill, R., Ma, C. A., Willner, I. (2006). Label-free and reagentless aptamer-based sensors for small molecules. J Am Chem Soc 128, 13666-13667. 

However, although countless examples of fluorescence or electrochemical labels have been demonstrated as signal-generating components of aptamer-based sensors, the specific nucleic acid structure of these novel binders has so far not been used sufficiently to improve the sensitivities, and thus the detection limit, of sensorial approaches. A combination of aptamers and DNA machines might take the field to new heights. 

Figure 2.8. (a) The microfluidic electrochemical aptamer-based sensor chip, (b] The syringe pumps connected to a four-input, single-output multiplexed valve, (c) The detection mechanism of the switch on sensor. 

Y. Xiao, D. Piorek, K. W. Plaxco, and A. J. Heeger, A reagentless slgnal-on architecture for electronic, aptamer-based sensors via target-induced strand displacement,/. Am. Chem. Soc., 127[51], 17990-17991 [2005b]. 

Aptamer recognition has been described for the development of biosensors and applied to biomedical and environmental studies [46]. As illustrated in Fig. 5.7, an electrochemical aptamer-based sensor (E-AB) for specific recognition of thrombin was constructed. Zhang and co-workers [46] used immobilization of a Fe304-nanoparticles/tagged aptamer via a self-assembly method. In this case, bifunctional aptamer was covalently linked to both Fe304-NPs and gold electrode. Certainly... 

Fig. 5.7 a Schematic representation and thrombin recognition by an electrochemical aptamer-based sensor and b voltammogram curves of the E-AB sensor before and after deposition of 40 nM of thrombin. Reproduced with permission from [46]... 

Zhang, S., Zhou, G., Xu, X., Cao, L., Liang, G., Chen, H., Liu, B., Kong, J. Development of an electrochemical aptamer-based sensor with a sensitive Fc304 nanopaticle-redox tag for reagentless protein detection. Electrochem. Commun. 13, 928-931 (2011). doi 10.1016/ j. elecom.2011.06.002... 

Swensen, J. S., Xiao, Y., Ferguson, B. S. et al. 2009. Continuous, real-time monitoring of cocaine in undiluted blood serum via a microfluidic, electrochemical aptamer-based sensor. J. Am. Chem. Soc. 131 4262 266. 

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