Density and structure of DNA immobilised on gold nanoparticles affect sensitivity in nucleic acid detection

Gold nanoparticles (AuNPs) are used as colorimetric biosensors that, combined with immobilised single-stranded DNA (ssDNA-AuNPs), can be used in genetic diagnosis because of their rapid and sequence-specific aggregation properties. Herein, we investigated the effect of the steric structure and density of immobilised DNA on AuNPs in non-crosslinking aggregation-based nucleic acid detection. Detection sensitivity improved with decreasing DNA density for linear conformations, but worsened for those with more rigid stem structures. We controlled the density of immobilised DNA using two different methods and investigated the aggregation behaviour of ssDNA-AuNPs. Interestingly, controlling the immobilised DNA density through ethylene glycol treatment had different effects on ssDNA-AuNP aggregation compared to those of alkanethiol substitution. This study suggests that the sensitivity of ssDNA-AuNPs for detecting target DNA could be affected by density and structure of the immobilised DNA.