Nandini Nagraj

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTMaterials and Transducers Toward Selective Wireless Gas SensingRadislav A. Potyrailo*, Cheryl Surman, Nandini Nagraj, and Andrew BurnsView Author Information General Electric Global Research Center, Niskayuna, New York, USAE-mail: [email protected].Cite this: Chem. Rev. 2011, 111, 11, 7315–7354Publication Date (Web):September 7, 2011Publication History Received7 February 2011Published online7 September 2011Published inissue 9 November 2011https://pubs.acs.org/doi/10.1021/cr2000477https://doi.org/10.1021/cr2000477review-articleACS PublicationsCopyright © 2011 American Chemical SocietyRequest reuse permissionsArticle Views10036Altmetric-Citations243LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Carbon nanotubes,Humidity,Materials,Polymers,Sensors Get e-Alerts

Market demands for new sensors for food quality and safety stimulate the development of new sensing technologies that can provide an unobtrusive sensor form, battery-free operation, and minimal sensor cost. Intelligent labeling of food products to indicate and report their freshness and other conditions is one important possible application of such new sensors. This study applied passive (battery-free) radio frequency identification (RFID) sensors for the highly sensitive and selective detection of food freshness and bacterial growth. In these sensors, the electric field generated in the RFID sensor antenna extends from the plane of the RFID sensor and is affected by the ambient environment, providing the opportunity for sensing. This environment may be in the form of a food sample within the electric field of the sensing region or a sensing film deposited onto the sensor antenna. Examples of applications include monitoring of milk freshness, fish freshness, and bacterial growth in a solution. Unlike other food freshness monitoring approaches that require a thin film battery for operation of an RFID sensor and fabrication of custom-made sensors, the passive RFID sensing approach developed here combines the advantages of both battery-free and cost-effective sensor design and offers response selectivity that is impossible to achieve with other individual sensors.

The 8-17 DNAzyme is a DNA metalloenzyme catalyzing RNA transesterification in the presence of divalent metal ions, with activity following the order Pb2+ >> Zn2+ >>Mg2+. Since the DNAzyme has been used as a metal ion sensor, its metal-induced global folding was studied by fluorescence resonance energy transfer (FRET) by labeling the three stems of the DNAzyme with the Cy3/Cy5 FRET pair two stems at a time in order to gain deeper insight into the role of different metal ions in its structure and function. FRET results indicated that, in the presence of Zn2+ and Mg2+, the DNAzyme folds into a compact structure, stem III approaching a configuration defined by stems I and II without changing the angle between stems I and II. Correlations between metal-induced folding and activity were also studied. For Zn2+ and Mg2+, the metal ion with higher affinity for the DNAzyme in global folding (Kd(Zn) = 52.6 microM and Kd(Mg) = 1.36 mM) also displays higher affinity in activity (Kd(Zn) = 1.15 mM and Kd(Mg) = 53 mM) under the same conditions. Global folding was saturated at much lower concentrations of Zn2+ and Mg2+ than the cleavage activities, indicating the global folding of the DNAzyme occurs before the cleavage activity for those metal ions. Surprisingly, no Pb2+-dependent global folding was observed. These results suggest that for Pb2+ global folding of the DNAzyme may not be a necessary step in its function, which may contribute to the DNAzyme having the highest activity in the presence of Pb2+.

The effect of monovalent ions on both the reactivity and global folding of the 8-17 DNAzyme is investigated, and the results are compared with those of the hammerhead ribozyme, which has similar size and secondary structure. In contrast to the hammerhead ribozyme, the 8-17 DNAzyme activity is not detectable in the presence of 4 M K(+), Rb(+), or Cs(+) or in the presence of 80 mM, [Co(NH(3))(6)](3+). Only 4 M Li(+), NH(4)(+) and, to a lesser extent, Na(+) conferred detectable activity. The observed rate constants (k(obs) approximately 10(-3) min(-1) for Li(+) and NH(4)(+)) are approximately 1000-fold lower than that in the presence of 10 mM Mg(2+), and approximately 200,000-fold slower than that in the presence of 100 microM Pb(2+). Since the hammerhead ribozyme displays monovalent ion-dependent activity that is often within approximately 10-fold of divalent metal ion-dependent activity, these results suggest that the 8-17 DNAzyme, obtained by in vitro selections, has evolved to have a more stringent divalent metal ion requirement for high activity as compared to the naturally occurring ribozymes, making the 8-17 DNAzyme an excellent choice as a Pb(2+) sensor with high selectivity. In contrast to the activity data, folding was observed in the presence of all the monovalent ions investigated, although those monovalent ions that do not support DNAzyme activity have weaker binding affinity (K(d) approximately 0.35 M for Rb(+) and Cs(+)), while those that confer DNAzyme activity possess stronger affinity (K(d) approximately 0.22 M for Li(+), Na(+) and NH(4)(+)). In addition, a correlation between metal ion charge density, binding affinity and enzyme activity was found among mono- and divalent metal ions except Pb(2+); higher charge density resulted in stronger affinity and higher activity, suggesting that the observed folding and activity is at least partially due to electrostatic interactions between ions and the DNAzyme. Finally, circular dichroism (CD) study has revealed Z-DNA formation with the monovalent metal ions, Zn(2+) and Mg(2+); the K(d) values obtained using CD were in the same range as those obtained from folding studies using FRET. However, Z-DNA formation was not observed with Pb(2+). These results indicate that Pb(2+)-dependent function follows a different mechanism from the monovalent metal ions and other divalent metal ions; in the presence of latter metal ions, metal-ion dependent folding and structural changes, including formation of Z-DNA, play an important role in the catalytic function of the 8-17 DNAzyme.