Determination of Hydrodynamic Properties of Bare Gold and Silver Nanoparticles as a Fluorescent Probe Using its Surface-Plasmon-Induced Photoluminescence by Fluorescence Correlation Spectroscopy

Abstract

Noble-metal nanoparticles labeled with fluorescent molecules are used in a variety of applications requiring the measurement of size and diffusion properties of single nanoprobes. We have successfully used intrinsic surface-plasmon-induced photoluminescence (SPPL) signatures of monodispersed bare gold and silver nanoparticles in water to detect and measure their precise diffusion coefficient, concentration and hydrodynamic radius by fluorescence correlation spectroscopy (FCS). Measurement of the effective hydrodynamic radius confirms particle size to be 80 ± 8 and 64 ± 14 nm for gold and silver, respectively, which is in excellent agreement with scanning electron microscopic measurements made on the same particles. Detection of bare gold and silver nanoparticles at the single-molecule level with moderately high value of "per particle brightness" (PPB) confirms those particles to be used as fluorescent probes in biological research and in different medical and biotechnology applications where fluorescence detection plays a vital role. Additionally, these results demonstrate an alternative method for measuring hydrodynamic properties, particularly the size-distribution of bare noble-metal nanoparticles in solution using data-fitting algorithm for FCS based on the maximum entropy method (MEMFCS).

Scattering Correlation Spectroscopy and Raman Spectroscopy of Thiophenol on Gold Nanoparticles: Comparative Study between Nanospheres and Nanourchins

“…This method relies on scattered intensity fluctuations within a confocal volume to determine the hydrodynamic radius of GNPs. ,, The correlation curve is mathematically represented by the equation where N is the average number of particles, s is the ratio of transverse (ω xy ) to axial (ω z ) dimensions of the analysis volume ( s = 0.3), and τ D is the diffusion time of the GNP crossing the focal volume. This time is directly related to the hydrodynamic radius ( R h ) through the Stokes–Einstein equation , where η is the water viscosity (10 –3 kg m –1 s –1 ), k if the Boltzmann constant, and T is the temperature (all measurements were done at room temperature, 21 °C).…”

Potential therapeutic and diagnostic applications of one-step in situ biosynthesized gold nanoconjugates (2-in-1 system) in cancer treatment

“…The hydrodynamic radius of AuNP-OX-500 is measured by onephoton luminescence, which has been used to measure the unconstrained Brownian motion and the size of gold nanoparticles through FCS according to our earlier report. 46 The hydrodynamic size of as-synthesized AuNP-OX-500 calcu- lated by FCS analysis is y28.6 nm ¡ 4 nm (radius = y14.3 nm ¡ 4 nm) for almost 85-90% of AuNPs. The size of AuNPs-OX-500 obtained from FCS results (Fig.…”

Spherical and Flower-Shaped Gold Nanoparticles Characterization by Scattering Correlation Spectroscopy

“…where N is the average number of particles crossing the focal volume and s is the ratio of transversal (w xy ) to axial (w z ) dimensions of the analysis volume (s = 0.3, see Figure S3 in the Supporting Information). Numerical fit of the SCS data following eq 1 provides the diffusion time τ D , and this time is directly related to both translational diffusion coefficient (D) and hydrodynamic radius (R h ) of the GNPs by the Stokes− Einstein equation: 28,31,54,55 τ…”

“…One of the recent powerful techniques used to characterize GNPs is the scattering correlation spectroscopy (SCS). − As fluorescence correlation spectroscopy (FCS), the SCS technique is based on the analysis of intensity fluctuations within a well-defined confocal volume (∼1 fL). The correlation curve is directly related to the hydrodynamic radius of molecules or nanoparticles, − to their diffusion coefficient, concentration and shape. ,− The SCS is very sensitive to GNPs morphology and brightness since the scattering intensity depends on the GNPs volume. − …”