Unusually large Stokes shift for a near-infrared emitting DNA-stabilized silver nanocluster

Sidsel Ammitzbøll Bogh,Steven M Swasey,Elisabeth G Gwinn,Cecilia Cerretani,Stacy M Copp,Tom Vosch,Miguel R Carro-Temboury

doi:10.1088/2050-6120/aaa8bc

Abstract

In this paper we present a new near-IR emitting silver nanocluster (NIR-DNA-AgNC) with an unusually large Stokes shift between absorption and emission maximum (211 nm or 5600 cm−1). We studied the effect of viscosity and temperature on the steady state and time-resolved emission. The time-resolved results on NIR-DNA-AgNC show that the relaxation dynamics slow down significantly with increasing viscosity of the solvent. In high viscosity solution, the spectral relaxation stretches well into the nanosecond scale. As a result of this slow spectral relaxation in high viscosity solutions, a multi-exponential fluorescence decay time behavior is observed, in contrast to the more mono-exponential decay in low viscosity solution.

Highlights

Due to its sensitivity and versatility, fluorescence spectroscopy has found many applications in both materials and life science imaging [1, 2]
The formation kinetics of the NIR-DNA-AgNC is slow: to obtain a good synthesis yield, it is best to perform the HPLC purification at least three days after synthesis
The same trend is evident from time-resolved measurements of NIR-DNA-AgNC in high viscosity solution, where time-resolved spectral relaxation is stretched to the nanosecond time scale

Summary

Introduction

Due to its sensitivity and versatility, fluorescence spectroscopy has found many applications in both materials and life science imaging [1, 2]. DNA-stabilized silver nanoclusters (DNA-AgNCs) are a new class of emitters that were introduced in 2004 [3]. DNA-AgNCs exhibit a wide range of emission properties that can be tuned by changing the stabilizing DNA sequence [4,5,6,7,8]. The DNA-AgNCs usually contain below 25 silver atoms [9] and in some cases form bright and photo-stable emitters, though dark clusters are often formed as well [10,11,12]. For most fluorescence imaging applications, bright emitters with high photo-stability and a reasonable Stokes shift are used to create contrast. The Stokes shift in particular is useful for spectrally separating the excitation light from the probe emission [25]

Methods

Results

Conclusion