Colloidally stable gold nanoparticles were synthesised via sodium citrate reduction. Disaggregated gold nanoparticles exhibit a characteristic deep red colour with an UV absorption maximum at 524 nm (Figure ). Aggregation of citrate stabilised gold nanoparticles, with a concentrated salt solution, red shifts the wavelength of their absorbance maxima to 544 nm and their appearance to a dark purple colour (Figure ). Functionalisation of gold nanoparticle surfaces with Sequence-A and Sequence-B was performed by independently reducing the thiol groups on the nucleic acid sequences in the presence of gold nanoparticle suspensions. Gold-aptamer-nanoconstructs were assembled through incubating gold nanoparticles functionalised with Sequence-A and Sequence-B in a 1:1 ratio, with an initial molar excess of the aptamer strand overnight. Unbound aptamers and disaggregated gold nanoparticles were removed, with washing and centrifugation, to produce gold-aptamer-nanoconstructs aggregated suspended in a buffer solution, composed of sodium chloride (600 mM) and tris acetate (25 mM).