Sensitivity Limit of Nanoparticle Biosensors in the Discrimination of Single Nucleotide Polymorphism

Detection of single nucleotide polymorphism (SNP) by selective aggregation of nanoparticles offers a rapid determination of cancer biomarkers, detectable by the naked eye. The main factor limiting the sensitivity of such colloidal sensors is the number of available target DNA molecules that can induce aggregation and thereby transduce an optical output signal. Although particle size is an obvious parameter of choice toward the modulation of the target-to-particle ratio at constant metal concentration, it is often omitted due to difficulties in the synthesis of particles with suitable size or to the limited colloidal stability of large particles stabilized with DNA. We present here a systematic study of SNP detection using gold nanoparticles of various sizes (13, 46, and 63 nm), using a conventional sandwich assay. We found that a 5-fold increase in particle size, at constant gold concentration, leads to an improvement in the limit of detection by 3 orders of magnitude, which is 5, 0.1, and 0.05 nM for 13, 46, and 63 nm, respectively. This assay allows the SNP detection down to 10.85 fmol within less than 10 min. We conclude that a target-to-particle ratio equal to 4 sets the limit of detection and sensitivity of the assay, regardless of particle size.