DNA Encapsulation of 10 Silver Atoms Producing a Bright, Modulatable, Near-Infrared-Emitting Cluster

Abstract

Photostability, inherent fluorescence brightness, and optical modulation of fluorescence are key attributes distinguishing silver nanoclusters as fluorophores. DNA plays a central role both by protecting the clusters in aqueous environments and by directing their formation. Herein, we characterize a new near infrared-emitting cluster with excitation and emission maxima at 750 and 810 nm, respectively that is stabilized within C 3 AC 3 AC 3 TC 3 A. Following chromatographic resolution of the near infrared species, a stoichiometry of 10 Ag/oligonucleotide was determined. Combined with excellent photostability, the cluster's 30% fluorescence quantum yield and 180,000 M −1 cm −1 extinction coefficient give it a fluorescence brightness that significantly improves on that of the organic dye Cy7. Fluorescence correlation analysis shows an optically accessible dark state that can be directly depopulated with longer wavelength co-illumination. The coupled increase in total fluorescence demonstrates that enhanced sensitivity can be realized through Synchronously Amplified Fluorescence Image Recovery (SAFIRe), which further differentiates this new fluorophore. Keywordsnear infrared fluorescence; few-atom silver clusters; DNA templates; Ag nanodot; optical modulation Improved fluorescence sensitivity, largely through background reduction, continues to motivate the development of fluorescence contrast agents in the near infrared spectral region. 1 From 700-1000 nm, not only is scattering diminished relative to shorter wavelengths, but light absorption by hemoglobin, lipids, and water is also minimized. [2][3] Furthermore, endogenous chromophores typically have electronic transitions in the ultraviolet and visible spectral regions, so background autofluorescence is also drastically reduced using near infrared excitation. 1 These spectroscopic features in conjunction with cost-effective instrumentation suggest the great promise of near-infrared based molecular diagnostics. 4 However, the true potential of near infrared contrast agents is restricted by fluorophores with low sustained emission rates at low excitation (brightness), small numbers of emitted photons (photostability), and/or limited compatibility with biological environments. 5 jeff.petty@furman.edu and dickson@chemistry.gatech.edu. Supporting Information Available: Detailed experimental procedures and supplemental figures. This material is available free of charge via the Internet at http://pubs.acs.org. Due to their small size (~1 kDa), organic, transition metal, and lanthanide fluorophores both minimize perturbation of biomolecular interactions and enable high labeling densities to increase detection sensitivity. 6 Also contributing to their prevalence is amenability to synthetic modifications, thereby permitting covalent attachment to specific biomolecules, enhanced aqueous solubility, and modified spectral properties. 5,7-9 Genetically expressed fluorescent proteins are also attractive fluorophores that enable direct and specific correlations of fluores...

Ten-Atom Silver Cluster Signaling and Tempering DNA Hybridization

“…Silver and phosphorus standards (High Purity Standards) were used to generate calibration curves, and control samples containing oligonucleotide and Ag + were used to account for matrix effects. 50 A peristaltic pump delivered the samples to the nebulizer and the argon plasma. To relate the phosphorus and oligonucleotide concentrations, the lengths were derived from the DNA sequences, after accounting for the absence of the 3′ terminal phosphate.…”

Research Update: Density functional theory investigation of the interactions of silver nanoclusters with guanine

“…It has been shown that the emission wavelength can be varied from violet to near infrared in DNA-AgNCs. [19][20][21][22] Therefore, DNA-AgNCs have been identified as potential candidates to be utilized in various applications such as bioimaging, biolabeling, catalytic reactions, and analyte and ligand sensing. [4][5][6][7]14,[23][24][25][26] The emission tunability can also be altered through experimental conditions, 19,20,27,28 but changing the DNA template itself is considered superior due to the higher functionality in the DNA-AgNCs through emission tuning.…”

Single‐Molecule Characterization of Near‐Infrared‐Emitting Silver Nanoclusters

“…In this case, we focus on the nearinfrared emitters using 633 nm as the excitation wavelength. Although a number of single molecule studies have been performed on AgNC to investigate specifi c photophysical parameters, [ 5,6,8,10,14,25,[27][28][29][30][31][32][33] we simultaneously measure several photophysical properties for each individual cluster, including decay times, emission spectra, and antibunching. This allows us to compare and correlate these photophysical properties within a sample to better understand the photophysical behavior and heterogeneity of these complex as-synthesized AgNC samples.…”