Accurate sizing of nanoparticles using confocal correlation spectroscopy.

Area of Science:

• Nanotechnology
• Spectroscopy
• Physical Chemistry

Background:

• Accurate sizing of low-concentration nanoparticles in small volumes is crucial across scientific disciplines.
• Existing methods struggle with nanoparticle sizing in the 11-300 nm range, particularly in microfluidic applications.

Purpose of the Study:

• To characterize Confocal Correlation Spectroscopy (CCS) for accurate nanoparticle sizing.
• To investigate and overcome challenges like biased diffusion and detector saturation in CCS measurements.
• To demonstrate CCS's utility for sizing particles in microscale volumes.

Main Methods:

• Utilized Confocal Correlation Spectroscopy (CCS) to measure particle sizes.
• Investigated the impact of laser power on diffusion times and autocorrelation curves.
• Compared resonant and nonresonant conditions for biased diffusion effects.
• Employed simulations to determine the trapping potential depth causing biased diffusion.

Main Results:

• Successfully sized nanoparticles (11-300 nm) including quantum dots, gold colloids, and latex spheres.
• Identified and addressed artifacts from detector saturation at low laser powers.
• Observed changes in autocorrelation curves at higher laser powers (>1 mW) indicative of particle trapping.
• Found minimal differences in biased diffusion between resonant and nonresonant conditions.
• Simulations indicated trapping potentials > 1 k(B)T are necessary for biased diffusion.

Conclusions:

• CCS accurately sizes nanoparticles in the 11-300 nm range, overcoming previous limitations.
• The method effectively mitigates artifacts from detector saturation and biased diffusion.
• CCS is highly advantageous for sizing nanoparticles in small volumes, such as microfluidic channels and microdroplets.
• The technique shows significant potential for broad applications in nanoparticle and macromolecular system analysis.