Parameter-Free Determination of Au Nanorod Dimensions Using Depolarized DLS and Genetic Optimization

Area of Science:

• Nanotechnology and Materials Science
• Optical Physics
• Biomedical Engineering

Background:

• Gold nanorods (AuNRs) exhibit unique optical properties and precise dimensions, making them valuable for imaging, sensing, and disease treatment.
• Characterizing AuNRs in solution, especially with surface coatings, is challenging for conventional methods like TEM, DLS, and small-angle scattering due to limitations in sample size, element detection, and analytical frameworks.
• Existing techniques often require prior knowledge of particle dimensions, hindering comprehensive analysis of functionalized nanoparticles.

Purpose of the Study:

• To evaluate the effectiveness of multiangle depolarized dynamic light scattering (DDLS) for characterizing surfactant-coated gold nanorods in solution.
• To compare the performance of two analytical approaches and a genetic algorithm (GA) for analyzing DDLS data and determining AuNR dimensions.
• To assess the GA's ability to accurately predict AuNR dimensions without requiring a priori information, such as aspect ratio.

Main Methods:

• Multiangle depolarized dynamic light scattering (DDLS) measurements were performed on three distinct surfactant-coated AuNR samples.
• DDLS data were analyzed using two standard analytical methods and a genetic algorithm (GA) approach.
• The GA optimized particle dimensions to best match relaxation rates derived from DDLS measurements, comparing results with TEM/SEM data.

Main Results:

• For high-quality DDLS data, all three analytical approaches provided length estimates consistent (within 10-20%) with TEM/SEM results.
• The GA approach demonstrated superior performance with noisy DDLS data, yielding dimensions more closely aligned with TEM/SEM values than traditional analytical methods.
• The GA successfully determined AuNR dimensions solely from rotational and translational relaxation rates, without needing additional parameters like aspect ratio.

Conclusions:

• Multiangle DDLS combined with a genetic algorithm provides a robust method for characterizing gold nanorods in solution, even with surface modifications.
• The GA approach offers a significant advantage over traditional methods, particularly when dealing with complex or noisy scattering data.
• This analytical strategy holds promise for advancing the characterization of anisotropic nanoparticles, facilitating their application in diverse scientific and medical fields.