Quantitative Determination of Thiol Groups Modified Mesoporous Silica Nanoparticles by Ellman’s Reagent

Ellman's reagent 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) is found to be a sensitive tool for the assay of thiol groups. DTNB reacts with aliphatic thiols to form fluorescent derivative “2-nitro-5-thiobenzoate (TNB−)”. In this work, Ellman's reagent was used to determine mercapto groups modified Mesoporous Silica Nanoparticles (MSNs). Mesoporous silica materials were prepared with a pore size of 5-6 nm, high surface area ca. 930 m2/g and a large pore volume of 1.3 cm3/g. MSNs were fabricated with 3-mercaptopropyl groups in both inner and outer surfaces. Such materials were reacted with DTNB in PBS solution to determine the concentration of 2-nitro5-thiobenzoate (TNB−) by colorimetric method. The concentration of thiol groups in the outer surface was estimated to be ca. 
 0.02 mmol/g, while the total amount of mercapto groups coated outer/inner surfaces was calculated to be ca. 0.11 mmol/g. The results indicate that thiol groups in the inner surface Fare almost five times higher than the outer surface.