Effect of DNA Density on Nucleic Acid Detection Using Cross-Linking Aggregation of DNA-Modified Gold Nanoparticles

Gold nanoparticles (AuNPs) have been utilized as colorimetric biosensors by which target molecule-induced AuNP aggregation is recognized by a color change from red to blue. Particularly, single-stranded DNA (ssDNA)-immobilized AuNPs (ssDNA-AuNPs) have been applied to genetic diagnosis. Herein, we investigated the effect of the density of immobilized ssDNA on the sensitivity of the target ssDNA detection using two different cross-linking aggregation models of ssDNA-AuNPs, i.e., the unidirectional (UD) type and bidirectional (BD) type. We demonstrated that target ssDNA detection was more sensitive in both types of aggregation models when smaller amounts of immobilized ssDNA were used. Interestingly, the UD type was more sensitive in detecting the target than the BD type possibly due to the number of cross-links. It was also shown that the sensitivity differed depending upon the number of bases between the AuNPs at higher DNA density. Our results indicate that control of immobilized probe ssDNA density improves the detection sensitivity and duplex formation ratio in cross-linking aggregation.