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
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]
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