Abstract
Gold nanoparticles have been available for many years as a research tool in the life sciences due to their electron density and optical properties. New applications are continually being developed, particularly in nanomedicine. One drawback is the need for an easy, real-time quantitation method for gold nanoparticles so that the effects observed in in vitro cell toxicity assays and cell uptake studies can be interpreted quantitatively in terms of nanoparticle loading. One potential method of quantifying gold nanoparticles in real time is by chemisorption of iodine-125, a gamma emitter, to the nanoparticles. This paper revisits the labelling of gold nanoparticles with iodine-125, first described 30 years ago and never fully exploited since. We explore the chemical properties and usefulness in quantifying bio-functionalised gold nanoparticle binding in a quick and simple manner. The gold particles were labelled specifically and quantitatively simply by mixing the two items. The nature of the labelling is chemisorption and is robust, remaining bound over several weeks in a variety of cell culture media. Chemisorption was confirmed as potassium iodide can remove the label whereas sodium chloride and many other buffers had no effect. Particles precoated in polymers or proteins can be labelled just as efficiently allowing for post-labelling experiments in situ rather than using radioactive gold atoms in the production process. We also demonstrate that interparticle exchange of I-125 between different size particles does not appear to take place confirming the affinity of the binding.
Highlights
Gold nanoparticles have been in use as a research tool in the life sciences for over 40 years
As part of a research team developing the use of colloidal gold particles as an imaging agent in immunoelectron microscopy, we developed a way of quantifying gold particles by radiolabelling the gold with iodine-125 (Beardmore et al 1987)
The preparations of nominal sizes 5 and 15 nm gold resulted in mean sizes of 6.6 and 16.4 nm, respectively, after measuring diameters of TEM images of the particles (n = 100) (Fig. 1)
Summary
Gold nanoparticles have been in use as a research tool in the life sciences for over 40 years. The original application was that of an electron dense marker for immunoelectron microscopy (Faulk and Taylor 1971). The second wave of applications of gold nanoparticles developed when the optical properties of these nanomaterials were exploited in a number of in vitro assays whereby the macroscopic signal generated by the red colour of gold nanoparticles was utilised. Other assays have exploited surface plasmon resonance properties by using the colour shift from red to blue when the nanoparticles are aggregated (Aslan et al 2004). DNA assays have been developed utilising the optical properties of gold nanoparticles (Stofhoff et al 2004) which can be silver enhanced for greater sensitivity (Nam et al 2004)
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