Optimized Approach to Synthesize Ultra Small Gold Nanorods to Target Nanospaces

Optimized Approach to Synthesize Ultra Small Gold Nanorods to Target Nanospaces

Priya Prabakaran, Ming Cheng, Eno Ebong

Abstract

Nanoparticles have recently become very important in the biomedical field due to their ability to deliver therapeutics to difficult areas. These areas include nanospaces which are nano-scale voids that are difficult to access. Depending on their application, nanoparticles can be made of different types of materials. For drug delivery applications, the surface of the gold particles can be modified since gold is highly reactive with thiols which forms strong bonds with drugs.¹ Other advantages of gold nanoparticles include applications for imaging and photothermal therapy.² Gold is also useful due to its high biocompatibility. In addition, many different shapes can be synthesized including spheres and rods both of which can be used for different applications.³ Spheres and rods are useful because their size allows access to nano-sized voids in tissue. Rods have been found to be better for drug delivery due to their high surface area. The higher surface area, allows for more interaction between the binding sites and the membrane receptors. The size and shape of nanoparticles can be controlled using specific experimental conditions. However, little is known about how exactly different parameters affect the dimensions of nanorods or how to create consistently small rods in order to target nanospaces such as those found in cells and the extracellular matrix.Filling this gap is our main focus. This experiment aims to find a repeatable approach to synthesize nanorods to be used to target nanospaces.

For this experiment, the seed growth method was used to synthesize gold nanorods. A seed solution consisted of 25mM HAuCl₄, 0.1M CTAB solutions, and cold NaBH₄. A growth solution was comprised of 0.5 mM HAuCl₄, ascorbic acid, 0.12 mM AgNO₃, and 0.1M CTAB solutions. The ascorbic acid concentrations that were used were 0.6 M, 1.0M, and 1.2 M. The seed solution was then added to the growth solution which was placed in a water bath. The temperatures of the water bath were tested at 30, 33, and 35°C and the growth time was tested at 1hr, 2hr, 3hr, and 4hr. The nanorods were extracted by centrifugation and imaged using Transmission Electron Microscopy (TEM). This experiment quantifies the length and width of the nanorods relative to the growth temperature, growth time, and ascorbic acid concentration.

At the reference condition with a growth temperature of 33°C, a growth time of 1 hr, and an ascorbic acid concentration of 0.1 M, particles were synthesized with dimensions around 25nm by 55nm. All methods described above synthesized dimensions that were less than 8nm by 25nm. It was also determined that 35°C and 1.2 M of ascorbic acid gave the smallest dimensions. Time is not a factor that affects dimensions.

Future studies will be done to incorporate drugs and imaging agents to these small nanorods.

References

(1) Huang, X., et al. Advanced Materials, (2009)  (2) Burrows, N. D., et al. Langmuir (2016)

(3) Pérez-Juste, J., et al. Coordination Chemistry Reviews (2009)