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 their composites. Overall, DNA–metal nanoclusters can add additional spotlights into the highly vibrant field of ligand protected, quantum sized metal nanoclusters.
We report the synthesis and characterization of a new DNA-templated gold nanocluster (AuNC) of ∼1 nm in diameter and possessing ∼7 Au atoms. When integrated with bilirubin oxidase (BOD) and single ...walled carbon nanotubes (SWNTs), the AuNC acts as an enhancer of electron transfer (ET) and lowers the overpotential of electrocatalytic oxygen reduction reaction (ORR) by ∼15 mV as compared to the enzyme alone. In addition, the presence of AuNC causes significant enhancements in the electrocatalytic current densities at the electrode. Control experiments show that such enhancement of ORR by the AuNC is specific to nanoclusters and not to plasmonic gold particles. Rotating ring disk electrode (RRDE) measurements confirm 4e– reduction of O2 to H2O with minimal production of H2O2, suggesting that the presence of AuNC does not perturb the mechanism of ORR catalyzed by the enzyme. This unique role of the AuNC as enhancer of ET at the enzyme-electrode interface makes it a potential candidate for the development of cathodes in enzymatic fuel cells, which often suffer from poor electronic communication between the electrode surface and the enzyme active site. Finally, the AuNC displays phosphorescence with large Stokes shift and microsecond lifetime.
DNA-templated silver nanoclusters (DNA/Ag NCs) are an emerging set of fluorophores that are smaller than semiconductor quantum dots and can have better photostability and brightness than commonly ...used organic dyes. Here we find the red fluorescence of DNA/Ag NCs can be enhanced 500-fold when placed in proximity to guanine-rich DNA sequences. On the basis of this new phenomenon, we have designed a DNA detection probe (NanoCluster Beacon, NCB) that “lights up” upon target binding. Since NCBs do not rely on Förster energy transfer for quenching, they can easily reach high (>100) signal-to-background ratios (S/B ratios) upon target binding. Here, in a separation-free assay, we demonstrate NCB detection of an influenza target with a S/B ratio of 175, a factor of 5 better than a conventional molecular beacon probe. Since the observed fluorescence enhancement is caused by intrinsic nucleobases, our detection technique is simple, inexpensive, and compatible with commercial DNA synthesizers.
We have synthesized an intrinsically fluorescent recognition ligand that combines the high fluorescence quantum yield (>50%) of oligonucleotide templated AgNCs with the specificity and strong binding ...affinity of DNA aptamers for their target proteins, to develop a new strategy for detection of specific proteins.
Rapid and precise screening of small genetic variations, such as single-nucleotide polymorphisms (SNPs), among an individual’s genome is still an unmet challenge at point-of-care settings. One ...crucial step toward this goal is the development of discrimination probes that require no enzymatic reaction and are easy to use. Here we report a new type of fluorescent molecular probe, termed a chameleon NanoCluster Beacon (cNCB), that lights up into different colors upon binding SNP targets. NanoCluster Beacons (NCBs) are collections of a small number of Ag atoms templated on single-stranded DNA that fluoresce strongly when placed in proximity to particular DNA sequences, termed enhancers. Here we show the fluorescence emission color of a NCB can change substantially (a shift of 60–70 nm in the emission maximum) depending upon the alignment between the silver nanocluster and the DNA enhancer sequence. Chameleon NCBs exploit this color shift to directly detect SNPs, based on the fact that different SNPs produce a different alignment between the Ag nanocluster and the enhancer. This SNP detection method has been validated on all single-nucleotide substitution scenarios in three synthetic DNA targets, in six disease-related SNP targets, and in two clinical samples taken from patients with ovarian serous borderline tumors. Samples with single-nucleotide variations can be easily identified by the naked eye under UV excitation, making this method a reliable and low-cost assay with a simple readout format.
We report the synthesis and photophysical properties of silver-nanoclusters templated on DNA, with fluorescence excitation and emission at distinct wavelengths that are tuned to common laser ...excitation wavelengths.
Optical phenomena such as fluorescence, phosphorescence, polarization, interference and non-linearity have been extensively used for biosensing applications. Optical waveguides (both planar and ...fiber-optic) are comprised of a material with high permittivity/high refractive index surrounded on all sides by materials with lower refractive indices, such as a substrate and the media to be sensed. This arrangement allows coupled light to propagate through the high refractive index waveguide by total internal reflection and generates an electromagnetic wave-the evanescent field-whose amplitude decreases exponentially as the distance from the surface increases. Excitation of fluorophores within the evanescent wave allows for sensitive detection while minimizing background fluorescence from complex, "dirty" biological samples. In this review, we will describe the basic principles, advantages and disadvantages of planar optical waveguide-based biodetection technologies. This discussion will include already commercialized technologies (e.g., Corning's EPIC(®) Ô, SRU Biosystems' BIND(™), Zeptosense(®), etc.) and new technologies that are under research and development. We will also review differing assay approaches for the detection of various biomolecules, as well as the thin-film coatings that are often required for waveguide functionalization and effective detection. Finally, we will discuss reverse-symmetry waveguides, resonant waveguide grating sensors and metal-clad leaky waveguides as alternative signal transducers in optical biosensing.
Purpose
Perifoveal exudative vascular anomalous complex (PEVAC) was initially described as an isolated aneurysmal lesion in healthy eyes. Similar aneurysmal abnormalities may occur in association ...with retinal vascular diseases such as diabetic retinopathy or retinal vein occlusions (PEVAC‐resembling). The aim of this study was to compare several imaging characteristics of PEVAC and PEVAC‐resembling lesions.
Methods
Ten eyes with a PEVAC and 27 eyes with a PEVAC‐resembling lesion were included in this cross‐sectional study. They were all imaged with optical coherence tomography (OCT), OCT angiography (OCT‐A) and colour fundus photography (CFP). Several clinical, morphological and vascular characteristics were assessed and compared between both PEVAC types.
Results
All PEVAC lesions were unilateral, while PEVAC‐resembling lesions appeared bilateral in 23% of patients (p > 0.05). Unilateral multifocal PEVAC‐resembling lesions were more frequently observed (56%) than unilateral multifocal PEVAC lesions (10%, p < 0.01). Furthermore, 90% of the PEVAC lesions were located within 500 µm from the centre of the fovea, while this was only true for 56% of the PEVAC‐resembling lesions (p > 0.05). No notable differences were observed in other studied characteristics.
Conclusions
The clinical, morphological and vascular features of PEVAC and PEVAC‐resembling lesions are similar based on multimodal imaging. Given the bilaterality and multifocality seen in PEVAC‐resembling lesions, an underlying retinal vascular disease may stimulate the quantity of aneurysmal abnormalities. Due to the similarities with PEVAC‐resembling lesions, PEVAC may also be considered a microangiopathy but with an unknown origin.
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.
PDF
