Review of Synthesis and Functionalization of Gold Nanobipyramids

Abstract

Nanoparticles, as one of the nanotechnology implementations, have a potential application due to their advantages compared to bulk size. The type of nanoparticle widely used for many applications such as sensing, imaging, photothermal therapy and optical devices is a metal nanoparticle through their properties. The advantages of metal nanoparticles are unique plasmonic properties, size and shape control flexibility, low toxicity and the ability to be functionalized with other substances. Besides silver and platinum, gold become the most popular in recent decades because it is highly stable and does not quickly oxidize or corrode. Also, gold nanoparticles have a high extinction coefficient and efficient energy transfer properties, so they can enhance the detection signals, resulting in increased sensitivity and lower detection limits. Then gold nanoparticles are also biocompatible in the biomedical field. Several researchers successfully synthesize gold nanoparticles with different shapes for various applications using bottom-up methods, i.e., chemical reduction, electrochemical deposition, sol-gel and seed-mediated growth and top-down methods, i.e., mechanical milling, laser ablation, lithography, template-assisted synthesis, high-energy ball milling and plasma-based techniques. But, gold with a bipyramid shape is rarely reported, causing limited literature sources that discuss gold nanobipyramids (GNBPs). GNBPs have a stronger electric field enhancement than other shapes, so GNBPs are highly sensitive to surrounding medium change marked with the high value of Refractive Index Sensitivity (RIS) and Figure of Merit (FOM). Therefore, GNBPs have excellent potential to be implemented in various fields. This work discusses and overviews the synthesis method to produce GNBPs for further application. GNBPs can be fabricated through a synthesis process using microwave-assisted, one-pot, galvanic replacement and seed-mediated growth, with seed-mediated growth being the popular method. Then, GNBPs can be functionalized with several substances such as polymers, biomolecules, amine and thiol to bind with specific targeted analytes. Hence, due to their plasmonic properties, GNBPs are promising materials for many fields, especially sensing applications.