Non-covalent labeling of human serum albumin with indocyanine green: a study by capillary electrophoresis with diode laser-induced fluorescence detection.

Indocyanine green (ICG) is a negatively charged, water-soluble, tricarbocyanine dye used primarily for medical imaging. ICG is only weakly fluorescent in the near-infrared region in its free (unbound) state in dilute aqueous solution. However, when non-covalently bound to protein, its fluorescence is greatly enhanced, making it a candidate for diode laser-induced fluorescence (diode-LIF) detection of proteins in capillary electrophoresis (CE). This paper investigates the suitability of ICG as a fluorescent label for the separation and detection of human serum albumin (HSA) by CE with diode-LIF detection. Specifically, we have considered the separation conditions necessary to resolve free ICG from ICG-HSA complexes; the limits of detection for free and HSA-bound ICG; the stability of aqueous ICG and ICG-HSA solutions over time; and the stoichiometry of the ICG-HSA complex.