Particle Size Analysis of Gold Nanoparticles

By AZoNano

Table of Contents

Overview
Introduction
Why are Gold Nanoparticles of So Much Interest?
Synthesis of Gold Nanoparticles
Colloid or Nanoparticle?
NIST Reference Materials
Experimental Procedure
Results and Discussion
Conclusions
About Horiba

Overview

There has been a great interest in uniformly dispersed suspensions of colloidal gold or nanoparticles right from ancient times. Colloidal gold was initially used in stained glass, potions and other artistic expressions. Presently researchers are studying gold nanoparticle  dispersions and one needs to note that control of morphology and size of particles is highly critical. The National Institute of Standards and Technology (NIST) has developed reference materials (RMs) of gold nanoparticles that are around 10, 30, and 60 nm. This application note discusses a technique and shows results from a study analyzing the NIST RM samples.

Introduction

Colloidal gold or "nanogold", as it is commonly called is a colloid or suspension of sub-micron particles of gold in a liquid such as water. The liquid is normally either an intense red color for particle sizes below 100 nm as shown in the figure, or a dirty yellow color for larger particles.

Why are Gold Nanoparticles of So Much Interest ?

As gold nanoparticles have distinct electronic, optical and molecular-recognition characteristics, they are being researched substantially and can be used for different applications such as electronics, nanotechnology, and for synthesising innovative materials having unique properties.

Synthesis of Gold Nanoparticles

Chloroauric acid (H[AuCl4]) is reduced in a liquid to form gold nanoparticles though there are more accurate and sophisticated methods available. H[AuCl4] is dissolved, a reducing agent is added and the solution is rapidly mixed. This results in Au3+ ions being reduced to neutral gold atoms. As a large number of these gold atoms form, the solution becomes supersaturated, and gold slowly begins precipitating to sub-nanometer particles. The remaining gold atoms stick to the existing particles, and when the solution is mixed very vigorously, the particles will be uniform in size. In order to prevent aggregation of the particles, some sort of stabilizing agent that sticks to the nanoparticle surface is added. They can be functionalized with several organic ligands to create organic-inorganic hybrids with advanced functionality.

Colloid or Nanoparticle?

The NIST Reference Material (RM) samples are suspensions of gold particles in the range of 10 to 60 nm. The sample may be called as colloidal gold or nanoparticles. A colloidal suspension may be defined as any dispersed and continuous two phase system where the dispersed phase exists at a length scale from 1 nm – 1 µm. Nanoparticles are now defined at a length scale of 1 to 100 nm. Hence, the NIST RM samples 8011, 8012, and 8013 are both colloids and nanoparticles and both terms are used in this document.

NIST Reference Materials

Three NIST Reference Materials (RMs), 8011, 8012, & 8013 were analyzed for this study. The RMs were created primarily for evaluating and qualifying instrument performance and/or methodology linked to the physical/dimensional characterization of nanoscale particles often used in pre-clinical biomedical research. The RMs are also be useful for developing and evaluating in vitro assays and interlaboratory test comparisons. Each sample consists of approximately 5 mL of citrate stabilized gold nanoparticles in an aqueous suspension in hermetically sealed prescored glass ampoules sterilized by gamma irradiation. The suspension contains primary particles (monomers) and a small percentage of clusters of monomers. The 8011 sample is nominally 10 nm, the 8012 sample is 30 nm, and 8013 sample is 60 nm.

The reference values provided on the Report of Investigation supplied with each sample are an ideal estimate of the true value provided by NIST where all suspected or known sources of bias have not been fully investigated by NIST. The reference values and images by SEM and TEM for samples 8011, 8012, and 8013 are shown in the Table 1 and Figures 1, 2 and 3.

Figure 1. SEM (above) and TEM (below) images for RM 8011

Figure 2. SEM (above) and TEM (below) images for RM 8012

Figure 3. SEM (above) and TEM (below) images for RM 8013

Table 1. Reference Values for RM 8011, 8012 and 8013

Material Technique Size nm
RM 8011 Atomic Force Microscopy 8.5 ± 0.3
Scanning Electron Microscopy 9.9 ± 0.1
Transmission Electron Microscopy 8.9 ± 0.1
Differential Mobility Analysis 11.3 ± 0.1
Dynamic Light Scattering 13.5 ± 0.1
Small-Angle X-ray Scattering 9.1 ± 1.8
RM 8012
Atomic Force Microscopy 24.9 ± 1.1
Scanning Electron Microscopy 26.9 ± 0.1
Transmission Electron Microscopy 27.6 ± 2.1
Differential Mobility Analysis 28.4 ± 1.1
Dynamic Light Scattering 173° scattering angle 11.3 ± 0.1
Dynamic Light Scattering 90° scattering angle 26.5 ± 3.6
Small-Angle X-ray Scattering 24.9 ± 1.2
RM 8013
Atomic Force Microscopy 55.4 ± 0.3
Scanning Electron Microscopy 54.9 ± 0.4
Transmission Electron Microscopy 56.0 ± 0.5
Differential Mobility Analysis 56.3 ± 1.5
Dynamic Light Scattering 173° scattering angle 56.6 ± 1.4
Dynamic Light Scattering 90° scattering angle 55.3 ± 8.3
Small-Angle X-ray Scattering 53.2 ± 5.3

Experimental Procedure

The NIST reference materials were examined on the HORIBA SZ-100 DLS system (see Figure 4). The following sample preparation and measurement procedure was employed:

  • Power up the instrument 30 minutes in advance of measurements
  • Clean measurement cuvettes w/filtered DI water and dry
  • Pre-rinse cuvette w/dilution medium before loading sample
  • Dilution medium, 50 mL filtered 2 mM (2x10-3 mol/L) NaCl
  • Dilute sample 1 part in 10 using dilution medium
  • Diluted sample then filtered using 0.45 µm syringe filter
  • Set temperature to 20° C
  • Perform five repeat measurements
  • Record the average values of the measurements

Figure 4. SZ-100 Nanoparticle Size Analyzer

Results and Discussion

The results from these measurements are shown in Tables 4-6 and typical graphs shown in Figures 5-7. The HORIBA results for samples 1 and 2 (in table 2) are reported in Intensity mean (Z average) and polydispersity index (PDI). ASTM results from an ASTM interlaboratory study where 13 labs measured the same NIST RMs are also provided.

Table 2. DLS results for RM 8011, 8012 and 8013

Material Testing Sample Size-1 Size-2
RM 8011 HORIBA Average St dev
Sample 1 13.4 nm 1.8
Sample 2 12.6nm 1.9
ASTM Z ave st dev
Combined 15.8 nm 4.2
RM 8012 HORIBA Average St dev
Sample 1 31.5nm 3.9
Sample 2 32.4 nm 5.9
ASTM Z ave st dev
Combined 31.2 nm 3.6
RM 8013 HORIBA Average St dev
Sample 1 57.6 nm 3.5
Sample 2 58.4 nm 3.9
ASTM Z ave st dev
Combined 59.8 nm 5.0

Conclusions

Gold nanoparticles are of great interest for researchers in many fields. The size distribution of the particles is an important physical characteristic that influences particle behavior. The most common technique to measure the size of gold nanoparticles is DLS. The HORIBA SZ-100 system has proven to be a great choice for precise and reproducible particle size analysis of gold nanoparticles.

About Horiba

HORIBA Scientific is the new global team created to better meet customers’ present and future needs by integrating the scientific market expertise and resources of HORIBA. HORIBA Scientific offerings encompass elemental analysis, fluorescence, forensics, GDS, ICP, particle characterization, Raman, spectral ellipsometry, sulfur-in-oil, water quality, and XRF. Prominent absorbed brands include Jobin Yvon, Glen Spectra, IBH, SPEX, Instruments S.A, ISA, Dilor, Sofie, SLM, and Beta Scientific. By combining the strengths of the research, development, applications, sales, service and support organizations of all, HORIBA Scientific offers researchers the best products and solutions while expanding our superior service and support with a truly global network.

This information has been sourced, reviewed and adapted from materials provided by Horiba.

For more information on this source, please visit Horiba.

Date Added: Oct 21, 2011 | Updated: Jan 16, 2014
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