Chapter 4 - Derivatization of Colloidal Gold Nanoparticles Toward Their Application in Life Sciences

Abstract

In this chapter, the derivatization of colloidal gold nanoparticles (Au NPs) in terms of functionalization and characterization is described. This chapter hereby focuses in particular on Au NPs which consist of an inorganic Au core of approximately 5 nm diameter, and which is stabilized by hydrophobic surface molecules. Transfer of the nanoparticles to aqueous environments (an indispensable necessity for biomedical applications) has been achieved by coating them with an amphiphilic polymer, which generates water solubility and moreover gives the ability for further functionalization. The physicochemical properties of such nanoparticles are verified within different purposes. First, several fundamental intrinsic surface properties are quantified, including the establishment of pH titration as characterization tool. It is found that the carboxylic groups, responsible for the colloidal stabilization, partly have different properties (like their pK a ) compared to free-standing carboxylic acids. These findings are crucial for the colloidal stabilization of nanoparticles, as well as for their further functionalization. Second, two species of fluorescently labeled Au NPs, which differ in first order only in their net surface charge, are employed to study charge-dependent interaction of nanoparticles with biological systems, including protein adsorption as well as in vitro internalization by living cells. For these nanoparticles, polymers with variable charge have been developed. The formation of the so-called protein corona around the nanoparticles is described, which has far-reaching impacts on cell internalization abilities. The data demonstrate that positively charged nanoparticles show higher cell internalization as well as higher toxicity. Third, in order to highlight one potential application, Au NPs are modified toward sensing applications by surface functionalization with ion-sensitive dyes. Positively charged nanoparticles are modified with a Cl − -sensitive dye and negatively charged nanoparticles are modified with a Zn 2+ -sensitive dye. In summary, this chapter will describe an extension of existing techniques for nanoparticle derivatization, particularly regarding new types of functional polymers for tuning the surface charge of particles, as it will outline the techniques for a fundamental and comprehensive characterization of nanoparticles ranging from the verification of intrinsic, physicochemical properties to biomedical applications.