DNA-Templated Molecular Silver Fluorophores

Abstract

Conductive and plasmon-supporting noble metals exhibit an especially wide range of sizedependent properties, with discrete electronic levels, strong optical absorption, and efficient radiative relaxation dominating optical behavior at the ~10-atom cluster scale. In this Perspective, we describe the formation and stabilization of silver clusters using DNA templates and highlight the distinct spectroscopic and photophysical properties of the resulting hybrid fluorophores. Strong visible to near-IR emission from DNA-encapsulated silver clusters ranging in size from 5-11 atoms has been produced and characterized. Importantly, this strong Ag cluster fluorescence can be directly modulated and selectively recovered by optically controlling the dark state residence, even when faced with an overwhelming background. The strength and sequence sensitivity of the oligonucleotide-Ag interaction suggests strategies for fine tuning and stabilizing cluster-based emitters in a host of sensing and biolabeling applications that would benefit from brighter, more photostable, and quantifiable emitters in high background environments. KeywordsNoble metals; clusters; modulation; fluorescence; biolabel; imaging; photophysics Few-atom metal clusters exhibit distinctive, size-dependent behaviors along the transition from bulk to molecular scales. For example, as electron mean free path and Fermi screening length scales are approached, the excellent conductivity and optical reflectivity characterizing bulk metals morph into shape-dependent plasmon excitations, size-dependent redox potentials and chemical/biological reactivities, with discrete optical transitions emerging at even smaller sizes. [1][2][3][4] Resulting from their relative inertness and highly polarizable electronic transitions, molecular-scale noble metals have emerged as a promising class of fluorophores for materials and biological imaging. Characterized by excellent brightness and photostability, gold and silver clusters encapsulated by coordinating ligands feature strong optical transitions that vary not only with stoichiometry, charge, and geometry, but can also be strongly influenced by interactions with their encapsulating matrix. [5][6][7][8] As the molecular size scale is approached, few-atom metallic cluster sizes exhibit an insufficient density of states to close the "band gap" as occurs in bulk or nanoparticulate metals, leading to strong size-dependent optical and catalytic properties that in many cases are well-explained by the nuclear shell model for free electron energies and magic cluster sizes. [9][10][11] This approach has led to the extended atom description of metallic clusters and an effective expansion of the periodic table with size-dependent cluster behaviors when metalmetal interactions dominate cluster stability. 12, 13 * dickson@chemistry.gatech.edu. Although the protoplasmonic electronic structure of metal clusters is best observed in bare, unsolvated and isolated clusters, 9, 10, 14 ligands are essential to constrain growth, stabilize, an...

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

“…[1][2][3] Small sized metal nanoclusters (with diameters up to around 2 nm) are considered to be brighter and more photostable fluorophores [4][5][6][7][8][9][10][11] compared to existing organic dyes as well as smaller and less toxic compared to quantum dots. 12 In particular, silver nanoclusters (AgNCs) are of interest, and these systems involve stabilizing ligands to prevent them from oxidation and aggregation.…”

“…Many studies have been performed to understand the effects from the DNA base pairs on the small AgNCs (∼Ag 2 -Ag 30 ) 18,[29][30][31][32] and some provide insights into creating AgNCs using different DNA platforms. 4,5,8,10 Their findings indicate that it is possible to manipulate the size and formation of these nanomaterials by employing strands of DNA with specific sequences. 3,18,29,30,32 Dickson, Petty, and coworkers have shown that very small (n < 10) AgNCs can be synthesized by exploiting the DNA sequence.…”

“…30 Gwinn's group and Dickson's group have done studies especially on short singlestranded DNA. 8,9,[33][34][35][36] Yeh, Martinez, Werner, and co-workers have carried out investigations on DNA detection probes with a greater focus on guanine bases. 12,23,[37][38][39] In addition to the experimental work, theoretical investigations have also been performed on DNA-AgNCs by several groups.…”

DNA-stabilized, fluorescent, metal nanoclusters for biosensor development

“…This is a rapidly growing field and the number of publications is increasing exponentially. A number of review papers have already covered the physical chemistry [20][21][22][23], synthesis [24], DNA sensing [25][26][27], and other applications [28,29]. Herein, we review recent progress in using DNAtemplated metal NCs for biosensor development.…”

Communication: UV photoionization of cytosine catalyzed by Ag+

“…20 One of the most interesting examples is Ag + whose AgNO 3 salt has been considered as mutagen class I; 21 however, silver is extensively used as an antimicrobial agent, 22 e.g., by coating the surface of prostheses with silver layers and for wound dressings, or as a water cleaning agent in swimming pools or even in drinkable water filters. In addition, highly fluorescent silver nanoparticles can be synthesized in cytosine (Cyt) and/or guanine rich DNA templates [23][24][25][26] due to the high affinity and site specificity of Ag + upon interaction with these two bases. 27,28 The fast development of nanoscience and nanotechnology and the fact that silver nanoparticles can be easily synthesized have spread their use in many technological applications in which medicine and biology are not the exception.…”