Nanoscale size dependence in the conjugation of amyloid beta and ovalbumin proteins onthe surface of gold colloidal particles

Abstract

Absorption spectroscopy was utilized to investigate the conjugation of amyloidβ proteinsolution (Aβ1−40) and chicken egg albumin (ovalbumin) with various sizes of gold colloidal nanoparticles forvarious pHs, ranging from pH 2 to pH 10. The pH value that indicates the colour change,pHo, exhibited colloidal size dependence for bothAβ1−40 and ovalbumin coated particles. In particular,Aβ1−40 coated gold colloidal particles exhibited non-continuous size dependence peakingat 40 and 80 nm, implying that their corresponding cage-like structures provideefficient net charge cancellation at these core sizes. Remarkably, only thepHo value for ovalbumin coated 80 nm gold colloid waspH>7, and a specific cage-like structure is speculated to have a positive net charge facingoutward when ovalbumin self-assembles over this particular gold colloid. Thepreviously reported reversible colour change between pH 4 and 10 took place only withAβ1−40 coated 20 nm gold colloids; this was also explored with ovalbumin coated goldcolloids. Interestingly, gold colloidal nanoparticles showed a quasi-reversible colourchange when they were coated with ovalbumin for all test sizes. The ovalbumincoated gold colloid was found to maintain reversible properties longer thanAβ1−40 coated gold colloid.