Synthesis of Gold Nanoparticle

Synthesis of Nanoparticles for Bioimaging

Abstract

The goal was to prepare nanoparticles in microemulsions. The experimental procedure was learned by preparing silica and gold nanoparticles. Particle characterization was done using Dynamic Light Scattering. The size of the silica and gold nanoparticles was found to decrease with increased w/o. The aim of this experiment was to synthesis fluorescent nanoparticles and gold nanoparticles. These are commonly used in bioimaging.

Introduction

As researchers continue to develop a wide range of nanoparticle-enabled technologies for bioimaging, there is a growing need to understand how the basic physical properties of a particular nanoparticle affect biologically relevant behavior such as cellular uptake.

The most popular microemulsion system for preparation of nanoparticle is “water-in-oil” (w/o) microemulsion system, and commonly referred to as reverse micelles. W/o microemulsions have tremendous scope for manipulation of reaction conditions to suit the nanoparticle design.

Dynamic light scattering (DLS) theory is a well-established technique for measuring particle size over the size range from a few nanometers to a few microns. A source of light (such as a laser) having known frequency is directed at the moving particles and the light is scattered at a different frequency. This difference in the frequency of scattered light among particles of different sizes is used to determine the sizes of the particles present.

Gold nanoparticles have been used extensively as specific staining agents in biological electron microscopy. According to the Mie Scattering Theory, particle size, shape and agglomeration can cause gold colloids to appear red, violet or blue (Feldheim et al). These nanoparticles of gold have a high backscatter coefficient, so they appear bright in a scanning electron microscope image.

In 1956, the formation of silica particles was observed by reacting TEOS in alkali solution with water in the presence of certain bases (Kolbe). Silica nanoparticles are used to make electronic substrates, thermal insulators and humidity sensors. The quality of some of these products is highly dependent on the size and size distribution of the silica particles (Vacassy).

Fluorescent dyes absorb light at certain wavelengths and in turn emit their fluorescence energy at a higher wavelength. Each dye has a distinct emission spectrum, which can be exploited for multicolor analysis. Fluorenscein-5-isothiocyanate (FITC) has an excitation and emission frequency of approximately 480nm and 520nm respectively. These dyes can be entrapped inside the silica particles (Vanblaaderen) and the spectral characteristics of the dye molecules remains almost intact. Silica encapsulation provides a protective layer around dye molecules, reducing oxygen molecule penetration both in air and in aqueous medium (Santra et al). As a result, photo stability of dye molecules increases substantially in comparison to bare dyes in solution.

Materials and Methods

Materials

Triton x100, Cyclohexane, n-hexanol, nanopure water, tetraethylorthosilicate (TEOS), chlorauric acid (HAuCl4), Ammonium