Novel techniques for refractive index determination of single nanoparticles in suspension

Type:
Oral presentation
Authors:
E. van der Pol, F.A.W. Coumans, A.N. Böing, A. Sturk, R. Nieuwland, and T.G. van Leeuwen
Location: 
SPIE Photonics West 2015, San Francisco, United States
Date:
February 8, 2015
Attachment: 
San Fransisco 2015 Refractive index nanoparticles.pdf (1,202 kB)

Summary

The refractive index (RI) of nanoparticles (<500 nm) is an indispensable property in a wide range of applications, relating light scattering to the size, shape, and chemical composition of nanoparticles. However, currently no method is capable of determining the RI of single nanoparticles in suspension. We have demonstrated the first use of dark-field microscopy, multi-angle flow cytometry, and resistive pulse sensing to determine the RI of single nanoparticles in suspension. Based on the RI, we have distinguished 200 nm and 400 nm silica beads from similar-sized polystyrene beads and we have determined the RI of 100-500 nm human cell-derived vesicles.

Abstract

Background: The refractive index (RI) of nanoparticles (<500 nm) is an indispensable property in a wide range of applications. The RI relates light scattering to the size, shape, and chemical composition of nanoparticles. However, currently no method is capable of determining the RI of single nanoparticles in suspension.

Method: We have developed three novel methods to determine the RI of single nanoparticles in suspension. We measured the diameter and light scattering of nanoparticles by (1) dark-field microscopy, (2) multi-angle flow cytometry, and (3) resistive pulse sensing combined with backscattering microscopy. For each method, we quantified light scattering using beads of known properties and solved the inverse light scattering problem by Mie theory. The method was validated on a mixture of 200 nm, and a mixture of 400 nm polystyrene (RI = 1.63) and silica beads (RI = 1.45). We applied each method to derive the RI of human cell-derived vesicles.

Results: Based on the RI, we have distinguished 200 nm and 400 nm silica beads from similar-sized polystyrene beads. The RI of silica and polystyrene beads were in agreement with the specifications and had an uncertainty <3%. The mean RI of human urinary vesicles was 1.37 at 405 nm.

Conclusions: We have demonstrated the use of dark-field microscopy, multi-angle flow cytometry, and resistive pulse sensing to determine the RI of single nanoparticles in suspension, such as cell-derived vesicles. The RI of vesicles is essential to data interpretation and standardization and may be utilized to distinguish vesicles from similar-sized particles in body fluids.

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