The effect of pH and ionic strength on the fluorescence properties of a red emissive DNA-stabilized silver nanocluster

Abstract

DNA-stabilized silver nanoclusters (DNA-AgNCs) are a class of promising fluorophores for imaging and sensing applications. All aspects of their spectroscopic properties are not yet fully characterized, leaving this field still with a number of fundamental studies to be addressed. In this work, we studied the spectroscopic properties of red-emitting DNA-AgNCs at different pH (5 to 9) and ionic strength μ (0.005 to 0.5). The photophysical properties of high performance liquid chromatography (HPLC) purified DNA-AgNCs proved to be constant over a large range of pH and μ, with absorption, emission and fluorescence decay times only being affected at very high pH and μ values. Non-purified DNA-AgNCs were also unaffected by pH and/or μ variations, but significant differences can be observed between the rotational correlation times of purified and non-purified DNA-AgNCs.

Studies on the interactions of Ag(i) with DNA and their implication on the DNA-templated synthesis of silver nanoclusters and on the interaction with complementary DNA and RNA sequences

“…27 Other studies, however, have not observed this decrease in long cytosine-rich sequences. 61 By using a DNA sequence similar to the ones used in this work, Shah et al…”

Probing the Fluorescence Behavior of DNA‐Stabilized Silver Nanoclusters in the Presence of Biomolecules

“…Synthesis and purification of DNA-AgNCs DNA-templated silver nanoclusters (DNA-AgNCs) were synthesized as described elsewhere. [29,30] Briefly, ss-DNA (5'-TTCCCACC-CACCCCGGCCC-3', IDT) dissolved in nuclease-free water (IDT) and AgNO 3 (> 99.998 %, Fluka Analytical) were mixed (1 : 10 ratio) in a 10 mM ammonium acetate (NH 4 OAc) solution. After 10 minutes at room temperature, NaBH 4 was added ([NaBH 4 ] : [AgNO 3 ] = 1 : 2) and the resulting sample was stored overnight at 4°C.…”

“…The emissive state of the DNA-AgNCs has an average decay time of 2.5 ns when probed at 640 nm and 25°C, while the sample displays a limiting anisotropy value of 0.4 and a rotational correlation time of 2.6 ns at 25°C (Table 1). [29,30] Rotational correlation times [31,32] measured at different temper-atures (10, 25, 37 and 45°C) were used to calculate the hydrodynamic volume of the DNA-AgNCs, yielding a value of about 12 nm 3 . Based on this value and the arrangement proposed for other types of DNA-AgNCs, [1,33] it can be assumed that the DNA-AgNCs comprise a single oligonucleotide strand surrounding a metal core of about 10 to 30 Ag atoms.…”

“…[28] Recently, we have demonstrated that the luminescence properties of a red emitting DNA-AgNCs, stabilized with a cytosine-rich sequence (5'-TTC CCA CCC ACC CCG GCC C-3') are relatively stable in the pH range from 5 to 9 and ionic strengths from 0.005 to 0.05. [29] To deepen the knowledge of DNA-AgNCs in environments with progressively more complex composition and evaluate their accurate applicability in bio-sensing, we investigated the interactions between DNA-AgNCs and selected biomolecules, with a particular attention to the influence on the photophysical properties of the DNA-AgNCs. The cytosine-rich sequence (5'-TTC CCA CCC ACC CCG GCC C-3') has been chosen as stabilizing strand for the AgNCs: this sequence yields very stable and highly fluorescent red-emitting AgNCs, which can be used as fluorescence decay time-based nanothermometers.…”

“…Recently, we have demonstrated that the luminescence properties of a red emitting DNA‐AgNCs, stabilized with a cytosine‐rich sequence (5’‐TTC CCA CCC ACC CCG GCC C‐3’) are relatively stable in the pH range from 5 to 9 and ionic strengths from 0.005 to 0.05 [29] …”