Klaus edited Method.tex  over 8 years ago

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The Ru(bpy)$_2$(mcbpy-O-Su-ester)(PF$_6$)$_2$-labelled drugs in buffer were mixed with glycerol in different proportions to produce solutions with different viscosities up to $\sim$70\% volume fraction glycerol. Glycerol is known to cause preferential hydration of proteins,\cite{Gekko1981} and at higher concentrations the rotational correlation times do not follow the linear model. A drop of each mixture was placed in a multiwell plate with \#1.5 coverslip glass bottom. The refractive index of each solution was measured with a refractometer (Bellingham+Stanley, U.K.) before and after the fluorescence measurement and converted to viscosity using a function fitted to a conversion chart.\cite{Glycerine1963}  A simplified diagram of the experimental setup is shown in Fig~\ref{fig:setup}a. The anisotropy measurements were performed with a Leica TCS SP2, a standard confocal inverted microscope. A pulsed diode laser (PLP-10 470, Hamamatsu, Japan; optical pulse width 90~ps) was used as the excitation source at 200~kHz repetition rate (5~$\mu$s between pulses). The beam was focused in the middle of the well containing the sample solution with a 20$\times$ NA0.5 air objective (Leica HC PL Fluotar). The emission was collected with the same objective through a 550~nm long-pass emission filter. A polariser was inserted in the emission path and parallel and perpendicular polarisation components of the fluorescence emission were recorded sequentially with a photomultiplier tube (PCM-100, hybrid detector (Becker & Hickl, Germany, based on xxx by  Hamamatsu, Japan) connected to a time-correlated single photon counting (TCSPC) acquisition card (SPC 150, Becker\&Hickl GmbH, Berlin, Germany). The measurement time window was 5~$\mu$s, with xxx time channels and xx ps/ch, and a  data acquisition time of 30-60~min per data set. \subsection{Calculation of hydrodynamic radii}