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.
5-(2-bromoethyl)phenanthridinium bromide (BEP) undergoes a 3-step-one-pot cyclisation reaction with primary amines allowing the facile synthesis of a vast library of heterocycles. A diverse range of primary aryl amines were explored as reactants to gain insight into the product isolated as a result of the steric and electronic effects of the aryl precursors. Analysis and reaction monitoring with UV-vis and NMR spectroscopy revealed that excessively electron withdrawing groups and sterically hindered amines do not allow for isolation of the common neutral tetrahydroimidazophenanthridine (TIP) structure but allow either the isolation of the charged dihydroimadazophenanthridinium (DIP) or aminoethylphenanthridinium (AEP) products.
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