Functionalisation of hollow gold nanospheres for use as stable, red-shifted SERS nanotags

Abstract

Hollow Gold Nanospheres (HGNs) exhibit a unique combination of properties which provide great scope for their use in many biomedical applications. However, they are highly unstable to changes in their surrounding environment and have a tendency to aggregate, particularly when exposed to high salt concentrations or changes in pH which is not ideal for applications such as cell imaging and drug delivery where stable solutions are required for efficient cellular uptake. Therefore there is a significant need to find a suitable stabilising agent for HGNs, however potential stabilising agents for these nanostructures have not previously been compared. Within this work we present an improved method for stabilising HGNs which simultaneously shifts the SPR from around 700 nm to 800 nm or greater. Herein, we compare three different materials which are commonly used as stabilising agents; polymers, sugars and silica in order to determine the optimum stabilising agent for HGNs. Analysis was performed using extinction spectroscopy and dynamic light scattering, supported with SEM imaging. Results showed PEG to be the most suitable stabilising agent for HGNs displaying both an increased stability to changes in salt concentration and pH as well as increased long term stability in solution. Furthermore, we demonstrate that in addition to increased stability, SERS detection can be achieved at both 1064 nm and 785 nm excitation. This combination of improved stability with a SPR in the NIR region along with SERS detection demonstrates the great potential for these nanostructures to be used in applications such as biological SERS imaging and drug delivery.

Surface enhanced resonance Raman spectroscopy (SERRS) for probing through plastic and tissue barriers using a handheld spectrometer

“…We have previously reported the use of red-shifted chalcogenpyrylium based Raman reporters for both SERS 1,28,26 and surface enhanced spatially offset Raman spectroscopy (SESORS) applications using NIR Raman excitation. 22 By controlling the length of the number of sp 2 carbons in the aliphatic backbone and the choice of chalcogen atoms in the ring system, it is possible to tune the absorption maximum of the Raman reporter into the near infrared (NIR).…”

Unique optical properties and applications of hollow gold nanospheres (HGNs)

“…Here, NIR absorbing HGNs with an average outer diameter of ~43.5 nm and a shell thickness of 3-4 nm were stabilized with polyethylene glycol (PEG) and attached to an ∝melanocyte-stimulating hormone (MSH) analog, [Nle4,D-Phe7]a-MSH (NDP-MSH), targeting the melanocortin type-1 receptor overexpressed in melanoma. PEG has shown to be the most effective capping agent for HGNs, stabilizing the nanoparticles against aggregation, caused by both increased salt concentration (up to 5 M) and changes in pH [222][223]. The intracellular uptake of bioconjugated HGNs was confirmed by both excised tissue and by [18F] fluorodeoxyglucose positron emission tomography [72].…”

Controllable Cobalt Oxide/Au Hierarchically Nanostructured Electrode for Nonenzymatic Glucose Sensing

“…Here, NIR absorbing HGNs with an average outer diameter of ∼43.5 nm and a shell thickness of 3-4 nm were stabilized with polyethylene glycol (PEG) and attached to an ∝-melanocyte-stimulating hormone (MSH) analog, [Nle4,D-Phe7]a-MSH (NDP-MSH), targeting the melanocortin type-1 receptor over-expressed in melanoma. PEG has shown to be the most effective capping agent for HGNs, stabilizing the nanoparticles against aggregation, caused by both increased salt concentration (up to 5 M) and changes in pH [222,223]. The intracellular uptake of bioconjugated HGNs was confirmed by both excised tissue and by (18F)-fluorodeoxyglucose positron emission tomography [72].…”