We report the discovery of a DNA sequence that templates a highly stable fluorescent silver nanocluster. In contrast to other DNA templated silver nanoclusters that have a relatively short shelf-life, the fluorescent species templated in this new DNA sequence retains significant fluorescence for at least a year. Moreover, this new silver nanocluster possesses low cellular toxicity and enhanced thermal, oxidative, and chemical stability.
We report that extended exposure to broad-spectrum terahertz radiation results in specific changes in cellular functions that are closely related to DNA-directed gene transcription. Our gene chip survey of gene expression shows that whereas 89% of the protein coding genes in mouse stem cells do not respond to the applied terahertz radiation, certain genes are activated, while other are repressed. RT-PCR experiments with selected gene probes corresponding to transcripts in the three groups of genes detail the gene specific effect. The response was not only gene specific but also irradiation conditions dependent. Our findings suggest that the applied terahertz irradiation accelerates cell differentiation toward adipose phenotype by activating the transcription factor peroxisome proliferator-activated receptor gamma (PPARG). Finally, our molecular dynamics computer simulations indicate that the local breathing dynamics of the PPARG promoter DNA coincides with the gene specific response to the THz radiation. We propose that THz radiation is a potential tool for cellular reprogramming.
Conspectus Metal nanoclusters containing a few to several hundred atoms with sizes ranging from sub-nanometer to ∼2 nm occupy an intermediate size regime that bridges larger plasmonic nanoparticles and smaller metal complexes. With strong quantum confinement, metal nanoclusters exhibit molecule-like properties. This Account focuses on noble metal nanoclusters that are synthesized within a single stranded DNA template. Compared to other ligand protected metal nanoclusters, DNA-templated metal nanoclusters manifest intriguing physical and chemical properties that are heavily influenced by the design of DNA templates. For example, DNA-templated silver nanoclusters can show bright fluorescence, tunable emission colors, and enhanced stability by tuning the sequence of the encapsulating DNA template. DNA-templated gold nanoclusters can also serve as excellent cocatalysts, which are integratable with other biocatalysts such as enzymes. In this Account, DNA-templated silver and gold nanoclusters are selected as paradigm systems to showcase their emergent properties and unique applications. We first discuss the DNA-templated silver nanoclusters with a focus on the creation of a complementary palette of emission colors, which has potential applications for multiplex assays. The importance of the DNA template toward enhanced stability of silver nanoclusters is also demonstrated. We then introduce a special class of activable fluorescence probes that are based on the fluorescence turn-on phenomena of DNA-templated silver nanoclusters, which are named nanocluster beacons (NCBs). NCBs have distinct advantages over molecular beacons for nucleic acid detection, and their emission mechanisms are also discussed in detail. We then discuss a universal method of creating novel DNA–silver nanocluster aptamers for protein detection with high specificity. The remainder of the Account is devoted to the DNA-templated gold nanoclusters. We demonstrate that DNA–gold nanoclusters can serve as enhancers for enzymatic reduction of oxygen, which is one of the most important reactions in biofuel cells. Although DNA-templated metal nanoclusters are still in their infancy, we anticipate they will emerge as a new type of functional nanomaterial with wide applications in biology and energy science. Future research will focus on the synthesis of size selected DNA–metal nanoclusters with atomic monodispersity, structural determination of different sized DNA–metal nanoclusters, and establishment of structure–property correlations. Some long-standing mysteries, such as the origin of fluorescence and mechanism for emission color tunability, constitute the central questions regarding the photophysical properties of DNA–metal nanoclusters. On the application side, more studies are required to understand the interaction between nanocluster and biological systems. In the foreseeable future, one can expect that new biosensors, catalysts, and functional devices will be invented based on the intriguing properties of well-designed DNA–metal nanoclusters and thei...
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