Here, we report a catalytic beacon sensor for uranyl (UO 2 2؉ ) based on an in vitro-selected UO 2 2؉ -specific DNAzyme. The sensor consists of a DNA enzyme strand with a 3 quencher and a DNA substrate with a ribonucleotide adenosine (rA) in the middle and a fluorophore and a quencher at the 5 and 3 ends, respectively. The presence of UO 2 2؉ causes catalytic cleavage of the DNA substrate strand at the rA position and release of the fluorophore and thus dramatic increase of fluorescence intensity. The sensor has a detection limit of 11 parts per trillion (45 pM), a dynamic range up to 400 nM, and selectivity of >1-million-fold over other metal ions. The most interfering metal ion, Th(IV), interacts with the fluorescein fluorophore, causing slightly enhanced fluorescence intensity, with an apparent dissociation constant of Ϸ230 M. This sensor rivals the most sensitive analytical instruments for uranium detection, and its application in detecting uranium in contaminated soil samples is also demonstrated. This work shows that simple, cost-effective, and portable metal sensors can be obtained with similar sensitivity and selectivity as much more expensive and sophisticated analytical instruments. Such a sensor will play an important role in environmental remediation of radionuclides such as uranium.DNA ͉ DNAzyme ͉ fluorescence ͉ deoxyribozyme ͉ catalytic DNA

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 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+, and Cs+ and the complex, [Co(NH3)6]3+. Only Li+, NH4+ and to a lesser extent Na+ showed detectable activity. The observed rate constants (kobs ~10−3 min−1 for Li+ and NH4+) are ~1000-fold lower than that in the presence of 10 mM Mg2+, and ~200,000-fold slower than the estimated rate in the presence of 100 µM Pb2+. Since the hammerhead ribozyme displays monovalent ion-dependent activity that is often within ~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 Pb2+ 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 (Kd ~0.35 M for Rb+ and Cs+), while those that confer DNAzyme activity possess stronger affinity (Kd ~0.22 M for Li+, Na+ and NH4 +). In addition, a correlation between metal ion charge density, binding affinity and enzyme activity was found among mono- and divalent metal ions except Pb2+; 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, Zn2+ and Mg2+; the Kd 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 Pb2+. These results indicate that Pb2+-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.

Covalent-organic frameworks (COFs) have been recognized as a new type of promising photocatalysts for hydrogen evolution. To investigate how different functional groups attached in the backbone of COFs affect the overall photocatalytic H 2 evolution, for the first time, we selected and synthesized a series of ketoenamine-based COFs with the same host framework as model system. It includes TpPaÀ COFÀ X (X =À H, À (CH 3 ) 2 , and À NO 2 ) with three different groups attached in the backbone of TpPaÀ COF. We systematically investigated the differences in morphology, light-absorption intensity and band gap of these 2D COFs. The results of photocatalytic H 2 evolution measurements indicate that the TpPaÀ COFÀ (CH 3 ) 2 shows the best activity, while the activity of TpPaÀ COFÀ NO 2 is relatively low compared to that of other two COFs in the system. Moreover, the separation ability of photogenerated charge was also followed the order of TpPaÀ COFÀ (CH 3 ) 2 > TpPaÀ COF > TpPaÀ COFÀ NO 2 . The best photocatalytic H 2 production performance of TpPaÀ COFÀ (CH 3 ) 2 in these systems should be mainly attributed to the better electron-donating ability of À CH 3 groups compared to À H or À NO 2 group, which result in more efficient charge transferring in the inner of the material. This work demonstrates that reasonably adding electrondonating group in TpPaÀ COFs can lead to a better photocatalytic H 2 evolution activity, and which is meaningful for further design of efficient COF-based photocatalysts for H 2 evolution.[a] J.

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