Improved Gold Nanoprobes for Detection of Single Nucleotide Polymorphisms: The Influence of Size

Gold nanoparticles (AuNPs) are widely used in biomedical diagnostics due to their unique plasmonic properties, with larger AuNPs showing higher extinction coefficients for the plasmon band and, consequently, more intense colors than the more commonly used spherical 20 nm AuNPs. Other factors can be important in the performance of different-sized AuNPs, including surface area, colloidal stability, and curvature effects. Here, the properties of spherical 20 nm AuNPs and 35 nm AuNPs functionalized with a specific thiol-modified oligonucleotide–Au nanoprobes are compared when used on a colorimetric assay for the detection of a single nucleotide polymorphism related to lactose intolerance in humans. Successful functionalization of AuNPs is assessed by UV–vis spectroscopy, agarose gel electrophoresis, dynamic and electrophoretic light scattering, and nanoparticle tracking analysis. Statistical differences between Au-nanoprobe DNA target groups are calculated using analysis of variance and a post hoc Tukey's test. These results show that both 35 and 20 nm Au nanoprobes have similar detection limits using a 0.15 nmol dm⁻³ nanoprobe concentration compared to 2.5 nmol dm⁻³. Interestingly, the use of 35 nm Au nanoprobes allows a reduction of 80% and 48% in the amount of gold and oligonucleotide used in the assay, respectively.