Gold nanoparticles (AuNPs), including spherical particles, nanorods, and nanoshells with sizes ranging from 10s to 100s nm, have attracted enormous attention in the recent years due to their unique properties, such as the quantum size effect, remarkably enhanced surface-to-volume ratio, and surface plasmon resonance [1
The light-scattering cross section of gold nanoparticles (AuNPs) with a diameter of 60 nm is 4 to 5 orders of magnitude stronger than that of a strong fluorescence dye, e.g., fluorescein [4
]. Plasmonic nanoparticles, such as AuNPs and silver nanoparticles, can be used for colorimetric detection, and its color change can be easily observed with the naked eye [5
]. This results in a color change providing a simple, sensitive colorimetric method useful for many applications, such as metal cation [7
], small molecule [9
], protein [11
], and cell imaging [13
Dynamic light scattering (DLS), known as photon correlation spectroscopy, is a well-established noninvasive technique for measuring the size of particles in the range from 0.5 nm to 6 μm [14
]. This technique is based on the Brownian motion of spherical particles which causes a Doppler shift of incident laser light. The diffusion constant of particles is measured, and the size of the particles is calculated according to the Stokes-Einstein relation [19
]. DLS is a powerful tool for determining small changes in the size of particles. This technique couples the use of AuNPs probes as a light-scattering enhancer and DLS as a read-out system. The subsequent average particle size increase was then measured by DLS and correlated to the analyte concentration. Therefore, it is a potential analytical tool for quantitative immunoassay.
In this paper, we reported a facile and convenient method for the detection of deoxyribonucleic acid (DNA) based on the aggregation of AuNPs from a well-dispersed state. DNA functionalized AuNPs have been often used as colorimetric probes for DNA detection [20
]. DLS is a sensitive method to determine small changes in the size of AuNPs, and the size distribution of Au nanoclusters has a linear response to DNA concentration in a wide range. Therefore, DLS can be a very sensitive technique for quantitative detection of DNA, and it opens many more possibilities in biomolecular analysis.