Klaus edited Discussion.tex  over 8 years ago

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SAXS and SANS are also popular methods for the size measurement of macromolecules. While they can be used with higher particle concentrations than DLS ($\sim$1-100~mg/ml) and are applicable to a large MW range from few kDa to hundreds of MDa, they have low resolution, and structural information can only be obtained through complex model building.\cite{Pecora_1985} Similar to DLS, SAXS and SANS measure scattering from unlabelled molecules which simplifies sample preparation but makes the results susceptible to artefacts arising from dust and other contamination in the sample solution, and makes these techniques impossible to be used with scattering media, such as tissue.  The measurement time interval of 5~$\mu$s used in these experiments is ideal for measuring the rotational correlation times of these drugs with this ruthenium-based dye at low viscosities. However, if this approach is combined with imaging, to perform Phosphorescence Lifetime Imaging (PLIM) \cite{Baggaley2015} the long lifetime of the dye will require long pixel dwell times, making scanning-based data acquisition slow. We have recently developed wide-field lifetime imaging approaches \cite{Hirvonen2014_ol, Hirvonen2015_njp} that are ideally suited for measuring lifetimes at this time scale, and could image several wells containing different drugs and/or different viscosity solutions simultaneously. If these microsecond-resolution wide-field time-correlated single photon counting approaches were to be combined with polarization-resolved excitation and detection, one could perform time-resolved anisotropy imaging \cite{Suhling2004} on a microsecond time scale. This would benefit the measurement of similar or higher MW drugs in several wells of a multiwell plate simultaneoulsly, and also  enable imaging these drugs \textit{in vitro}.