# Optical Characterization of Homogeneous and Heterogeneous Intralipid-Based Samples
## 4 Results and Discussion
### DLS Results  
The autocorrelation functions obtained for Intralipid solutions at different volume concentrations are shown in Figure 6a. The shape of the functions was similar for the low scattering samples (0.003-0.16% Intralipid concentration), while it was completely changed for the highest concentration  
Figure 5: (a) Relative scattered intensity corrected for volume effects (i.e., I\({}_{0}\) sin\(\theta\)/(I\({}_{0}\) sin (90\({}^{\circ}\)))) as a function of the scattering angle obtained for Intralipid suspensions at different concentrations. Intralipid volume concentrations of the considered suspensions are reported in the legend. At \(\theta=0^{\circ}\) the forward scattered light was detected, while at \(\theta=180^{\circ}\) the backscattered signal was detected. (b) Light intensity as a function of the scattering angle for Intralipid aqueous suspension at different concentrations (diamond (blue), square (red), triangle (green), and x (purple) in respect to 0.7%, 0.875%, 1.4%, and 2.175%). Reprinted from. [46].  
suspension. The correlation functions of the low-scattering samples well resembled the autocorrelation functions typically arising from single scattering samples with freely diffusing scatters (Brownian particles). On the contrary, the function evaluated for the high-scattering sample showed a different time dependence and the intensity signal was correlated over a time shorter than those characterizing the low-scattering samples. The correlation functions obtained for the suspensions with concentrations in the range of 2-10% show intermediate features. In addition, the characteristic time of the autocorrelation decreased as a function of the Intralipid concentration. These experimental findings confirm that the above-mentioned conditions (single scattering/free diffusion) did not hold for the high-scattering sample. The same results were obtained for Intralipid suspensions at higher concentrations (data not shown).  
Figure 6: (**a**) Normalized autocorrelation functions as obtained by dynamic light scattering (DLS) apparatus in right angle (\(\theta=90^{\circ}\)) collection geometry for suspensions at various volume concentrations of Intralipid. (**b**) Relative characteristic time (i.e., \(\Gamma\)/\(\Gamma_{0}\), where the subscript “0” indicates that the parameter is the one obtained for the first concentration reported in the figure that was used as reference) vs. Intralipid concentration is reported for the intermediate concentrations (see text). \(\Gamma\) and \(D\) values were obtained by analyzing the autocorrelation functions, also according to Equations (26) and (27). The red line is the line resulting by performing a linear fit on all the data but the highest concentration. Results of the fitting procedure: intercept = 0.83 \(\pm\) 0.16; slope = 1.23 \(\pm\) 0.04; [PERSON]’s linear correlation coefficient r = 0.998.  
For the solutions with intermediate concentrations, the characteristic time (\(\Gamma\) see Equation (26)) was obtained by analyzing the autocorrelation functions. The resulting values are reported in Figure 6b, where the value of the relative characteristic time of the particles (i.e., \(\Gamma/\Gamma_{0}\), where the subscript \"0\" indicates that the parameter is the one obtained for the lowest concentration reported in the figure that was used as reference) and the corresponding diffusion coefficients are shown, according to Equations (26) and (27).  
This suggests that some scattering information about turbid media can be obtained by using DLS even if it cannot be employed for the sizing of the sample components. In fact, it is worth noting that the linear behavior of the \(\Gamma/\Gamma_{0}\), as a function of the Intralipid concentration recalls the dependence observed for the reduced scattering coefficient as a function of Intralipid concentration [47].