Trapping of single extracellular vesicles in the evanescent field of an optical cavity

Type:
Oral presentation
Authors:
E. van der Pol, F.A.W. Coumans, J. Wilke, C. Earhart, B. DiPaolo, R. Hart, B. Cordovez, A. Sturk, R. Nieuwland, and T.G. van Leeuwen
Location: 
SPIE Photonics West 2015, San Francisco, United States
Date:
February 9, 2015

Summary

Extracellular vesicles (EV) are present in all bodily fluids and are potential biomarkers for metastatic carcinomas. However, due to their small size (30-1000 nm), EV detection remains challenging. For the first time, we have trapped single submicron EV in the evanescent field of an optical cavity on an integrated photonic device (Nanotweezer, Optofluidics, USA). A 1064 nm 322 mW laser was used to excite the cavity, resulting in an irradiance inside the optical trap of ~0.1 MW/mm2. The combination of a switchable optical trap and the high irradiance inside the trap is attractive for Raman microspectroscopy on single EV.

Abstract

Background: Extracellular vesicles (EV) are present in all bodily fluids and play a role in intercellular communication. Therefore, EV are potential biomarkers for metastatic carcinomas. However, due to their small size (30-1000 nm), detection and characterization of single EV remains a major challenge.

Method: EV were isolated from human urine and guided through an optical trap at a flow rate of 0.5 μL/min. The trap was formed by the evanescent field of an optical cavity on an integrated photonic device (Nanotweezer, Optofluidics, USA). A 1064 nm 322 mW laser was used to excite the cavity, which had a resonance frequency of 9400 cm-1. The irradiance inside the optical trap was ~0.1 MW/mm2. Scattering of single EV was imaged onto a CCD camera by a 0.5 NA microscope objective. To estimate the EV diameter, we analytically described the relation between the diameter, refractive index, and light scattering of polystyrene beads and EV by Mie theory.

Results: EV were optically trapped for 0.25-5 seconds, with three EV remaining trapped until the laser was turned off. The trapped EV had a diameter of 760 ± 90 nm (mean ± standard deviation) and their light scattering intensity was on average 24-fold higher than the background intensity.

Conclusions: For the first time, we have trapped single submicron EV in the evanescent field of an optical cavity. The combination of a switchable optical trap and the high irradiance inside the trap is attractive for Raman microspectroscopy on single EV.

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