Cluster Plasmonics: Dielectric and Shape Effects on DNA-Stabilized Silver Clusters

Abstract

This work investigates the effects of dielectric environment and cluster shape on electronic excitations of fluorescent DNA-stabilized silver clusters, AgN-DNA. We first establish that the longitudinal plasmon wavelengths predicted by classical Mie-Gans (MG) theory agree with previous quantum calculations for excitation wavelengths of linear silver atom chains, even for clusters of just a few atoms. Application of MG theory to AgN-DNA with 400-850 nm cluster excitation wavelengths indicates that these clusters are characterized by a collective excitation process and suggests effective cluster thicknesses of ∼2 silver atoms and aspect ratios of 1.5 to 5. To investigate sensitivity to the surrounding medium, we measure the wavelength shifts produced by addition of glycerol. These are smaller than reported for much larger gold nanoparticles but easily detectable due to narrower line widths, suggesting that AgN-DNA may have potential for fluorescence-reported changes in dielectric environment at length scales of ∼1 nm.

Optical properties and charge distribution in rod-shape DNA–silver cluster emitters

“…Another broad band appears at 1.7 eV that corresponds to the plasmon-like longitudinal excitation of the metal cluster as was also reported before. 8,20,33,34 In accordance with the charge distribution proposed for this type of systems, the features of this visible band remains practically unchanged when the system is charged. Also, a small red shift of this band is observed when increasing the neutral core-Ag length, as was also reported before experimentally by Gwinn and coworkers.…”

“…The tunability of this band may be governed by the length of the neutral silver-core and the DNA bases sequence, but could also be modified by charge environment and cluster shape. [8][9][10] More interestingly, for emitting DNA Ag n clusters, the excitation on the UV band leads to the same fluorescence spectrum as in the case of the visible band excitation. This phenomena could be due to a charge transfer from the DNA-base to the silver-core when exciting the UV band.…”

“…19 They also found that the visible band experiments show a red-shift as the number of neutral silver atoms increases, along with an enhancement of its intensity. 8 This results led the authors to propose a rod-shape like DNA Ag n model with a zigzag neutral silver-core structure as a way to explain the inner charge of the metal-core, as well as the "magic numbers" of Ag 0 and the tuning of the visible band. This model is based on the idea that a neutral rod is generated with Ag + acting as "glue" in between the neutral rod and the DNA bases.…”

Addressing the properties of “Metallo-DNA” with a Ag(i)-mediated supramolecular duplex

“…7,[10][11][12][13][14][15][16][17][18] Consequently, the combination of silver chemistry with DNA-based structure building is particularly promising for the synthesis of nanomaterials, e.g. nanowires, [19][20][21][22][23] quantum-conned metal clusters [24][25][26][27][28][29][30][31] and plasmonic materials 32,33 as well as the development of a bottom-up approach to functional molecular systems. While most common with cytidine, other silver-mediated pairings including Watson-Crick purinepyrimidine combinations are possible (Scheme 2).…”

Predicting absorption spectra of silver‐ligand complexes

“…Various techniques have been developed for the synthesis of stable, water‐soluble silver NCs by using dendrimers, polymers, polypeptides, thiols, DNA, thiolated DNA, and other ligands to stabilize silver ions . The influence of various thiolates on binding energy with silver NCs has been studied in details .…”