Nanoscience/nanotechnology has emerged as one the fastest growing fields of science this decade.1Various nanoparticles, including carbon nanotubes, quantum dots, and gold nanoparticles, are extensively studied for biomedical applications. The inertness and biocompatibility of gold nanoparticles (Au-NPs) make them very promising for specific applications such as medical imaging, drug delivery, gene delivery, and molecular sensing.2
In each of these applications the particle size of Au-NPs is critical. The distinct absorption peak from the surface plasmon absorption of the gold nanoparticles is located between 510 and 530 nm.
Surface plasmon is a collective excitation of electrons at the interface between the conductor and insulator.3 Absorption of light by surface plasmon of Au-NPs accounts for the colorful appearance of these solutions, which in turn is a direct characteristic of their size and aggregation.
The majority of applications with Au-NPs involve conjugating these molecules with DNA, protein, or active pharmaceutical ingredients. Conjugation of biological molecules to Au-NPs is mainly due to the electrostatic and hydrophobic interactions between the protein-Au-NP complexes.4 Thus, there is always a need to analyze the size of Au-NPs to ensure there is proper conjugation without aggregation of Au-NPs.
Characterization of Au-NPs with protein or DNA is optimized in multiple levels, starting with selecting the right size particles, pH, and protein concentration. Figure 2 shows an example of four proteins conjugated to Au-NP-80 nm. It is evident that similar concentrations of different proteins result in unique interaction with the same particle, indicating the importance of spectroscopic optimization studies prior to developing any Au-NP-based therapeutic system.
The advent of improved near-infrared (NIR) probes has resulted in more nanomedical research being focused on the NIR spectral range. In addition, cancer therapies and drug-delivery systems based on an NIR trigger mechanism of Au-NP are currently being explored. As research advances, spectroscopic characterization with high-end spectrophotometers that can deliver resolution and very high absorbance accuracy will become increasingly important.
1. Chen PC, et al. Gold Nanoparticles: From nanomedicine to nanosensing.Nanotechnology, Science and Applications. 2008; 1:45.
2. De Jong WH, Borm PJ. Drug delivery and nanoparticles: Applications and hazards.Int J Nanomedicine. 2008;3(2):133.
3. Rayford CE, et al. Optical properties of gold nanoparticles. Nanoscape. 2005; 2(3):33.
4. Chah W, et al. Gold Nanoparticles as colorimetric sensors for protein conformational changes. Chem Biol. 2005; 12(3):323.