Optical Trapping of Extracellular Vesicles for Diagnosis of Prostate Cancer

As an older male, I’m concerned with prostate cancer. I also had experience 30 years ago with laser tweezers for selecting and holding particles in an optical trap. The trapping concept was invented by Arthur Ashkin of Bell Labs, who was awarded the Nobel Prize in Physics in 2018.

Extracellular vesicles (EVs) are released from mammalian cells to circulate in body fluids. The composition of EVs depends upon their origin and cell state. Lee et al. reported that the composition is potentially useful in diagnosis and therapy, in this case, prostate cancer.

EVs are spherical particles in the range of 30 nm to 1 µm. This is the sweet spot for optical trapping (Figure 1). The apparatus consists of a laser illuminating a high-numerical-aperture lens, which produces a focused force field (the waist of the red beam). When an EV enters the light beam, light is refracted, which changes its momentum. Momentum must be conserved, so the illuminated particle is forced backward to the center of the trap.

ImageFigure 1 – Illustration of optical trapping holding several extracellular vesicles (EVs), which are found in body fluids and may be useful in diagnosis and therapy of cancer. From the top, gray represents the bottom of a high-numerical-aperture lens on a fluorescence microscope with laser illumination in red. The darker red waist illustrates the high-intensity light at the focal point. Particles such as EVs that are in the field of view of the laser light are drawn to the focal point and trapped (green and yellow dots in beam waist). The content of the EVs is determined by Raman spectrophotometry, which is illustrated by the four spectra on the right.

While in the trap, the Raman spectra of the EVs in the trap are recorded. Samples were red blood cell and platelet EVs from healthy donors and EVs from the prostate cancer cell lines, PC3 and LNCaP. Principal component analysis of 300 data sets maps the spectra to the EV origin (normal or cancer) with accuracy better than 90%.

When I was involved with optical trapping in the 1980s, I wondered how quickly it would find a practical application. Thirty years later, applications are starting to appear. This is a long gestation from dream to use.

Robert L. Stevenson, Ph.D., is Editor Emeritus, American Laboratory/Labcompare; e-mail: [email protected]

Related Products

Comments