Monitoring of Aqueous Fullerene Dispersions by Thermal-Lens Spectrometry

Abstract

Aqueous fullerene solutions (dispersions) are very promising materials of biomedicine and biotechnology. Of importance are the traceability of their production and characterization of their optical and colloidal properties. Thermal-lens spectrometry, as a method suitable for both optical and thermophysical studies, was used to elucidate the forms of non-modified fullerenes in their aqueous dispersions and to determine low concentrations of $$\hbox {C}_{60}$$ and $$\hbox {C}_{70}$$ fullerenes. It was shown that the residual amounts of toluene in aqueous fullerene dispersions made according to the solvent-exchange protocol could be detected by thermal lensing. As a result, the technique for the production of aqueous fullerene dispersions was improved compared to the existing data providing higher fullerene concentrations. The limits of detection of $$\hbox {C}_{60}$$ and $$\hbox {C}_{70}$$ fullerenes are approximately $$100\,\hbox {ng}{\cdot }\hbox {mL}^{-1}$$ , which are 20-fold lower compared to conventional spectrophotometry. The distinction between aqueous fullerene dispersions in comparison with organic solutions of fullerenes caused by the formation of large clusters is shown by the comparison of transient and steady-state calibration curves for aqueous and organic fullerene solutions and model reference systems under various thermal-lens excitation conditions. The advantages of thermal lensing for such colloidal systems are discussed.