Engineering a lifetime-based activatable probe for photoacoustic imaging

Challenging a Preconception: Optoacoustic Spectrum Differs from the Optical Absorption Spectrum of Proteins and Dyes for Molecular Imaging

“…However, the vibronic relaxation following ISC, regularly occurring in the long microseconds range, was considered too slow to contribute to detectable OA signals (Visser et al, 2002) in our observation time window of sub-microseconds range, and thus would not explain the higher PGE of the H-aggregate. Interestingly, the ISC for MB is very fast (ns vs. µs) (Morgounova et al, 2013), suggesting that we can indeed detect the resultant vibronic relaxations. Consequently, we can show here that the formation of H-aggregates by MB results in fast ISC, which contributes to the observed strengthening of the OA signal.…”

“…The sensitivity of some natural chromophores and organic dyes to aggregation and other environmental changes has been exploited for various sensing applications in OA imaging (Jiang and Pu, 2017;Lovell et al, 2011;Morgounova et al, 2013;Peters et al, 2019;. However, the photophysics underlying the changes in the OA signals of these chromophores have never been thoroughly understood or described, precluding efficient and rational exploitation of such effects for the design of next-generation functional OA labels.…”

“…Conversely, the OA spectrum shows a comparably stronger signal for the H-aggregate band (610 nm), reflecting a higher OA signal generation (thus PGE) for this transition compared to the monomer (slope of 0.61 at 610 nm vs. 0.37 at 665 nm in Figure 2b). It is generally accepted that the loss of fluorescence in highly symmetric H-aggregates, like the one formed by MB, stems from a favored ISC (Kasha et al, 1965;Morgounova et al, 2013) (Supplementary Figure 4). This is corroborated by our photo-fatigue analysis of the different transitions, which shows faster bleaching for the Haggregate at 610 nm (Supplementary Figure 5) than for the monomer at 665 nm.…”