Growth of gold-aryl nanoparticles in lysozyme crystals

Hen egg-white lysozyme crystals are an exemplary system for the growth of gold-aryl nanoparticles within proteins. We investigated the growth of AuNPs functionalized with carboxyl groups in a single protein crystal of lysozyme (Lys@AuNPs) by the protein reduction of aryldiazonium tetrachloroaurate(III) salt [COOH-4C(6)H(4)N = N]AuCl4 over 30, 60, and 90 days. We studied the time-dependent, in situ, and gradual growth of AuNPs within single crystals of lysozyme in precipitant solution of 6.5% NaCl in 0.1 M sodium acetate at pH 4.5. The growth and incorporation of AuNPs inside the lysozyme crystals were confirmed by HR-TEM measurements and microscopy imaging. Investigation of TEM images indicates that AuNPs matured progressively beginning with an average size of 48.5 +/- 5.7 nm after 30 days. More numbers of AuNPs of 20.8 +/- 4.4 nm and 19.2 +/- 5.4 nm after 60 and 90 days, respectively, were formed within the lysozyme crystals. Furthermore, we observed that the addition of Hg2+ can expedite the formation of Lys@AuNPs crystals. The color of the gold nanoparticles was developed after 8 days in the presence of Hg2+. The formed AuNPs were mostly spherical with an average size of 13.9 +/- 5.2 nm.