Two isosbestic points
are detectable, at 515 nm (Figure 5(b)) and 556 nm, respectively, indicating the formation of a certain complex between [beta]-carotene and gold nanoparticles.
The state of equilibrium between various protonated and deprotonated species was examined from the spectral changes like shifting of peaks and formation of isosbestic points
. The whole range of spectral data as shown in the Figure 5(a) was included in the calculations by nonlinear least square fitting program pHAb, which gave best fit for three species whose protonation constants agreed well with the potentiometric results.
Furthermore, spectroscopic titration studies for the interaction of these food additives with DNA showed that these dyes bind to calf thymus DNA and distinct isosbestic points
are observed clearly suggesting binding of the dyes to DNA.
The retina is illuminated through the pupil, preferably at isosbestic points
for oxy- and deoxyhemoglobin, using several discrete visible/NIR light bands while the reflected light from vessels overlying the optic disk is analyzed.