Figure 3From: In vitro detection of adrenocorticotropic hormone levels by fluorescence correlation spectroscopy immunoassay for mathematical modeling of glucocorticoid-mediated feedback mechanismsFCS studies of a single and two diffusion species. (a) The two autocorrelation functions were calculated from intensity fluctuations of the free antibody and that of the ACTH-bound ones. The shift of the autocorrelation curve (a, blue line) to the right indicates that the diffusion time of the ACTH-bound particles through the focus is higher than that of the free antibody. To eliminate the amount of unbound from the ACTH-bound forms in the sample, a two-component fit over the autocorrelated data points of the ACTH-bound form (a, blue line) was performed with a fixed diffusion time for the unbound antibodies (220 μs, previously calculated with a one-component fit to obtain the average diffusion time of free unbound fluorescent antibodies) and a variable one for quantifying different ACTH concentrations. (b) A double-logarithmic plot of calculated concentrations versus related diffusion times over 50 measurements shows the accuracy of the results obtained by FCS for different ACTH concentrations.Back to article page