For the signal transduction pathway to function, in the absence of the target nucleic acid sequences, aptamers should aggregate gold nanoparticles. However, in their presence, aptamers must hybridise with target nucleic acid sequences and dissociate from gold nanoparticles, thus triggering their disaggregation. This was achieved by designing an aptamer that demonstrates strong affinity for the target nucleic acid sequence, whilst demonstrating partial affinity for nucleotides linked to the surface of gold nanoparticles, which were used to facilitate their aggregation. Therefore, nucleotide bases specific and complementary to the target nucleic acid were selected for the aptamer sequence-5' GA AAC ACG GAC ACC CAA AGT 3'. This aptamer was used to bridge and aggregate gold nanoparticles by partially hybridising two different nucleotide sequences, Sequence-A (SH-5' A12 CCC AGG ACT AC T TTC 3') and Sequence-B (Biotin-5' GTG TTT CGG GAA G 3'-SH), which were linked to gold nanoparticle surfaces, via stable thiol-gold bonds (Figure ). Sequence-A consisted of a thiol functionalisation at 5', to bind gold nanoparticle surfaces, a polyadenylated tail (n=12), to minimise the interaction with signal transduction components, and 9 nucleotide bases complementary to the 3' aptamer strand. Whereas, Sequence-B was composed of a thiol functionalisation at 3', to bind to gold nanoparticle surfaces, and 7 nucleotide bases complementary to the 5' aptamer strand. The lateral flow device was engineered by biotinylating Sequence-B at 5' (Figure ), such that it could be trapped by streptavidin functionalised membranes (Figure ).