Pulse Radiolysis Investigation of Radicals Derived from Water-Soluble Cyanine Dyes: Implications for Super-resolution Microscopy

Abstract

Light-induced blinking, an inherent feature of many forms of super-resolution microscopy, has been linked to transient reduction of the fluorescent cyanine dye used as an imaging agent. There is, however, only scant literature information related to one-electron reduced cyanine dyes, especially in an aqueous environment. Here, we examine a small series of cyanine dyes, possessing disparate π-conjugation lengths, under selective reducing or oxidizing conditions. The experiment allows recording of both differential absorption spectra and decay kinetics of the resultant one-electron reduced or oxidized transient species in water. Relative to the ground state, absorption transitions for the various radicals are weak and somewhat broadened but do allow correlation with the π-conjugation length. In all cases, absorption maxima lie to the blue of the main ground-state transition. Under anaerobic conditions, the transient species decay on the microsecond to millisecond time scale, with the mean lifetime depending on molecular structure, radiation dose, and dye concentration. The experimental absorption spectra recorded for the one-electron reduced radicals and the presumed dimer cation radical compare well to spectra obtained from time-dependent density functional theory calculations. The results allow conclusions to be drawn regarding the plausibility of the reduced species being responsible for light-induced blinking in direct stochastic optical reconstruction microscopy.

Photoswitching fingerprint analysis bypasses the 10-nm resolution barrier

“…While a recent study identified the formation of a Cy5-thiol adduct with absorption maximum at 310 nm as off-state in dSTORM experiments 21 another study proposed the formation of a radical formed by one-electron reduction of the cyanine dye absorbing at roughly 450 nm (ref. 22 ). But, Cy5 fluorescence can be restored from the off-state also on irradiation with red light demonstrating that the off-state exhibits a very broad absorption spectrum 21 .…”

Deuterated Indocyanine Green (ICG) with Extended Aqueous Storage Shelf‐Life: Chemical and Clinical Implications

“…[ 53 , 64 ] Likewise, deuterated polymethine cyanine dyes with a low propensity for photooxidative dimerization are promising future candidates for optimized super‐resolution microscopy. [65] …”

Near‐Infrared Self‐Assembled Hydroxyl Radical Generator Based on Photoinduced Cascade Electron Transfer for Hypoxic Tumor Phototherapy

“…However, when the Cy5 •− feature is isolated from the one‐peak mix PIA features at 480 nm, the remaining signals closely match the signals of Cy5 •+ (Figure S10d, Supporting Information) reported in the literature through transient capturing. [ 20 ] Accordingly, one photon‐excited S 1 molecule can rapidly transfer charge to another nearby molecule in the ground state through SB‐CS in the molecular assembly, producing the Cy5 •− –Cy5 •+ CSS1. To further prove the SB‐CS charge transient mechanism, the TAS for Cy5 solid film was also measured (Figure S11a, Supporting Information).…”