Due to the quantum size and surface eﬀect, noble metal nanoparticles have optical, electromagnetic and chemical properties that are different from those of their bulk-material counterparts. Transmission electron microscopy (TEM) image of spherical gold nanoparticles is shown in Figure 1. They show high efficiency in absorbing and scattering light with their absorbance spectrum tunable by their shape and size.
Nobel metal nanoparticles show enhanced physical properties, Local Surface Plasmon Resonance (LSPR) effects, which result in enhanced absorption, high chemical stability, catalytic activity and nonlinear optical effects as a result. These properties make them of value in microelectronics, sensors utilizing their LSPR properties, in biomedical imaging and diagnostics at the cellular and molecular level as well as in therapy in pharmaceutical applications and in cosmetics.
PHORNANO offers manufactured monodisperse gold nanoparticles with highest precision, which are free from agglomeration, ready to unfold their full potential in your research, development, and use in industrial scale in your demanding applications. Each single batch of 4nGold nanoparticles is precisely characterized using UV/VIS spectroscopy, regularly calibrated with Transmission Electron Microscopy (TEM), dynamic light scattering (DLS, particle size analysis) and/or Zeta potential measurements.
Figure 2: Plasmon resonance where the free electrons in the metal nanoparticle are driven into oscillation due to a strong coupling with a specific wavelength of incident light.
Figure 1: Transmission electron microscopy (TEM) images of gold nanoparticles with diameters of 20 nm (Item Number AUNS020)
Gold Nanoparticle Optical Properties
In contrast to dyes and pigments, optical properties of noble metal nanoparticles are mainly dependent on their sizes and geometries. The strong interaction of the noble metal nanoparticles with light occurs because the conduction electrons on the metal surface undergo a collective oscillation when excited by light at specific wavelengths (Figure 2). Known as a plasmon resonance, this oscillation results in unusually strong scattering and absorption properties. That allows noble metal nanoparticles to show effective absorbance (scattering & absorption) cross sections several times larger than their physical cross section. By selecting the size of spherical gold nanoparticles, their plasmon resonance peak wavelength can be tuned from ≈500 nm (blue-green light) to ≈600 nm (red light) and influences the appearance of the sample under visible light (Figure 3). By manufacturing rod shaped gold nanoparticles, the spectrum will be modified in shape. The plasmon resonance peak wavelength can be shifted to longer wavelength and a multi-peak structure of the spectrum can be observed, determined by the dimension of the nanorods (Figure 4).
Figure 3: Cuvettes containing gold nano-spheres of diameters ranging from 20 nm to 80 nm (Item AUNS020 - AUNS080).
Figure 4: Absorbance (scattering + absorption) spectra of gold nanoparticles. The graph represents the plasmon resonance peak of AUNS040 spherical nanoparticles of 40 nm in diameter.
Physicochemical assessment techniques
Qualitative and quantitative physicochemical characterization of silver nanoparticles provides:
of the manufactured nanoparticles.
Gold Nanoparticle Surface Chemistry
When nanoparticles are in solution, molecules associate with the nanoparticle surface to establish a double layer of charge that stabilizes the particles and prevents aggregation. PHORNANO offers several gold nanoparticles suspended in aqueous medium. A citrate-based agent was selected as a stabilizer, because the weakly bound capping agent provides long term stability and is readily displaced by various other molecules including thiols, amines, polymers, antibodies, and proteins.
Gold Nanoparticle Applications
Gold nanoparticles are being used in a large variety of technologies and incorporated into applications ranging from consumer products to high end biomedical applications that take advantage of their desirable optical and electronic properties.
Diagnostic Applications: Gold nanoparticles are used in bio-imaging, biosensors and as biological tags for quantitative detection.
Conductive Applications: Gold nanoparticles are used in conductive inks and integrated into composites to enhance thermal and electrical properties.
Optical Applications: Gold nanoparticles are used to efficiently harvest light and for enhancement of optical properties including metal-enhanced fluorescence (MEF) and surface-enhanced Raman scattering (SERS).
Table 1: Applications:
red = more significant,
blue = less significant.
FM: Fluorescence microscopy
PA: Photo acoustics
FLIM: Fluorescence lifetime imaging
SERS: Surface enhanced Raman spectroscopy
PHORNANO offers a portfolio of gold nanoparticles and elongated rods with predefined dimensions, as well as customized nanoparticles on demand. All nanoparticles are prepared in aqueous medium with a citrate-stabilized surface. A correlation of mass concentration to particle concentration is displayed below in Table 2
Table 2: Nanoparticle diameter, Item number, mass concentration, and particle concentration.
*) Dimensions can be customized between 20 and 80 nm in diameter, in case of nano-spheres, and between 50 and 100 nm in length, in case of rods. For nano-spheres of e.g.: 80 nm in diameter, please ask for AUNS080. For nano-rods of e.g.: 75 nm in length, please ask for AUNR10075. Other dimensions available upon request.
4cast online tool determines the LSPR peak wavelength for AUNS nano-spheres:
PHORNANO offers the PHORCAST tool to determine the dimension of the AUNS nano-spheres required for a specific LSPR peak wavelength.
Adjust the size of the AUNS nano-spheres with the slider and receive the LSPR peak wavelength below: