Experimental System of FCS

The Principle of the Method of Measurement of Local Temperature Using PCS 

The autocorrelation function, G(x), of the temporal fluctuation of the fluorescence intensity at the confocal volume is analytically represented by the following equation [8, 9]  

Under the condition that the Stokes-Einstein model holds, the translational diffusion coefficient, D, can be represented by Eq. (8.3). the diffusion time, Xd, obtained through the analysis is given by Eq. (8.4). 

T is the absolute temperature, kthe Boltzmarm constant, Ti(T) the viscosity of the solution at temperature, f and a is the hydrodynamic radius of a probe molecule in the sample solution. Erom Eqs. (8.2) and (8.3), we obtain Eq. (8.4). 

The q(T) can be independently measured by a viscometer and the value of y is determined by the PCS measurement at a certain temperature (typically 21 22 °C). Under the condition that the hydrodynamic diameter of the probe molecule is constant in the temperature range examined, we can obtain the temperature of the confocal area. It is worth noting that the present method estimates average temperature inside the confocal volume of the microscopic system because ECS provides the average value of the translational diffusion velocity over multiple fluorescent molecules passing through the sampling area. 

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