The catalytic enlargement of aptamer-functionalized Au nanoparticles amplifies the optical detection of aptamer-thrombin complexes in solution and on surfaces.

DNA and telomerase activity are detected by a DNAzyme generated upon hybridization and opening of a functional catalytic beacon.

A G-rich nucleic acid sequence binds hemin and yields a biocatalytic complex (DNAzyme) of peroxidase activity, namely, the biocatalyzed generation of chemiluminescence in the presence of H(2)O(2) and luminol. The DNAzyme is used as a label for the amplified detection of DNA, or for the analysis of telomerase activity in cancer cells, using chemiluminescence as an output signal. In one configuration, the analyzed DNA is hybridized with a primer nucleic acid that is associated with a Au surface, and the DNAzyme label is hybridized with the surface-confined analyte DNA. The DNA is analyzed with a detection limit of approximately 1 x 10(-)(9) M. In the second system, telomerase from HeLa cancer cells induces telomerization of a primer associated with a Au surface and the complementary DNAzyme units are hybridized with the telomere to yield the chemiluminescence. The detection limit of the system corresponds to 1000 HeLa cells in the analyzed sample.

DNAzyme-functionalized Au−NPs act as catalytic labels for the amplified detection of DNA and telomerase activity on nucleic acid-functionalized gold surface. The DNAzyme stimulates, in the presence of hemin, H 2 O 2 , and luminol, the generation of chemiluminescence. For DNA analysis, a nucleic acid unit complementary to the analyzed DNA is tethered to the DNAzyme structure associated with the Au−NPs. For telomerase activity, a nucleic acid complementary to the telomer repeat units generated on the surface is tethered to the DNAzyme structure associated with the Au−NPs. The detection limit for the detection of DNA is 1 × 10 -10 M. The method enables the detection of telomerase activity originating from 1000 HeLa cells.

The acetylcholine esterase, AChE, mediated hydrolysis of acetylthiocholine (1) yields a reducing agent thiocholine (2) that stimulates the catalytic enlargement of Au NP seeds in the presence of AuCl(4)(-). The reductive enlargement of the Au NPs is controlled by the concentration of the substrate (1) and by the activity of the enzyme. The catalytic growth of the Au NPs is inhibited by 1,5-bis(4-allyldimethylammoniumphenyl)pentane-3-one dibromide (3) or by diethyl p-nitrophenyl phosphate (paraoxon; 4), thus enabling a colorimetric test for AChE inhibitors. The colorimetric assay was also developed on glass supports.

Illuminating DNA: The assembly of two tailored nucleic acids (colored blue and brown in the scheme) in the presence of hemin yields a G‐quadruplex that exhibits peroxidase‐like activity and catalyzes the generation of chemiluminescence in the presence of H2O2 and luminol. The DNAzyme is employed for the analysis of DNA (green) in solution and on surfaces.

Aminoferrocene-based prodrugs are activated under cancer-specific conditions (high concentration of reactive oxygen species, ROS) with the formation of glutathione scavengers (p-quinone methide) and ROS-generating iron complexes. Herein, we explored three structural modifications of these prodrugs in an attempt to improve their properties: (a) the attachment of a -COOH function to the ferrocene fragment leads to the improvement of water solubility and reactivity in vitro but also decreases cell-membrane permeability and biological activity, (b) the alkylation of the N-benzyl residue does not show any significant affect, and (c) the attachment of the second arylboronic acid fragment improves the toxicity (IC50) of the prodrugs toward human promyelocytic leukemia cells (HL-60) from 52 to 12 μM. Finally, we demonstrated that the prodrugs are active against primary chronic lymphocytic leukemia (CLL) cells, with the best compounds exhibiting an IC50 value of 1.5 μM. The most active compounds were found to not affect mononuclear cells and representative bacterial cells.

Increasing efforts are directed to the application of metal and semiconductor nanoparticles (NPs) for the development of electronic or optical sensory systems.[1] Metal or semiconductor NPs functionalized with nucleic acids were employed as amplifying labels for the detection of DNA; the dissolution of the nanoparticles was used to follow DNA hybridization events.[2] Also, charge injection from semiconductor nanoparticles into electrodes and the generation of photocurrents was used to follow hybridization processes [3] and biocatalytic transformations.[4] The catalytic deposition of metals onto metal nanoparticles conjugated to DNA-hybridized complexes on surfaces was used as a sensor for DNA through conductivity [5] or microgravimetric quartz crystal microbalance [6] measurements. The optical detection of processes in the presence of metal and semiconductor NPs has become a common practice in analysis. Besides the use of semiconductor quantum dots as fluorescence labels in sensors, [7] the fluorescence quenching of semiconductor quantum dots has been employed in different sensing paths.[8] The plasmon absorbance of metal nanoparticles, such as Au NPs, and specifically the interparticlecoupled plasmon absorbance of aggregated NPs was extensively used to follow molecular [9] and biomolecular [10] recognition processes. The use of semiconductor or metallic NPs as probes to follow biocatalytic processes is less established, with only a few reports for these applications. [4,11] Nicotinamide adenine dinucleotide (NAD + )-and nicotinamide adenine dinucleotide phosphate (NADP + )-dependent enzymes are important in biocatalyzed synthesis.[12] Extensive efforts have been directed towards the development of electrochemical sensors based on NAD(P) + -dependent enzymes.[13] Herein, we report the catalyzed growth of gold nanoparticles in the presence of NAD(P)H cofactors. We apply the process to the quantitative optical analysis of NAD(P)H cofactors and to the analysis of NAD(P) + -dependent biocatalyzed reactions in solutions and on surfaces.The solution for the growth of the particles consisted of citrate-stabilized Au NPs (4.0 10 À10 m in 13 nm AE 1-nm particles), HAuCl 4 (1.8 10 À4 m), and CTAB (7.4 10 À2 m) as a surfactant. Figure 1 shows the changes in the UV/Vis spectra of the growth solution upon interaction with different concentrations of NADH. In the absence of NADH, the solution displays an absorbance band at l = 392 nm, characteristic of the AuCl 4 À component (Figure 1, curve a). Upon addition of NADH, this band disappears instantaneously and the characteristic orange color of the system is depleted (curve b), and then the slow buildup of the absorbance of the particle plasmon is observed. As the concentration of NADH increases, the absorbance of the Au particles increases and is shifted to longer wavelengths (from 523 to 530 nm; Figure 1, curves c-h). The inset in Figure 1 shows the calibration curve derived from the changes in the absorbance at l = 524 nm as the concentration of NADH increases. Figure 2 shows...