Design of a system to measure light scattering from individual cells excited by an acoustic wave.

A system to measure light scattering from individual cells excited by an acoustic wave was designed, and tests were performed on live Jurkat cells. Cells passing in a laminar stream within a water bath were excited by a focused ultrasound pulse, while the scattered light from a laser beam was monitored at various scattering angles. The cells were modeled as viscoelastic liquid drops, which return to equilibrium via shape oscillations after an acoustically-induced deformation. The Fast Fourier Transform of the scattered light signal was used to extract information about the highly-damped resonant frequencies of the cells, and the detected frequencies are consistent with theoretical predictions.

Particle sizing with a fast polar nephelometer.

We reported previously the design of a polar nephelometer that uses a rotational confocal imaging setup to enable fast scanning of the scattering phase function within a field of view of 55 degrees . The full dynamic range of the detection system can be used by increasing the signal-to-noise ratio by means of averaging successive scans. The calibration of the angular response of the instrument is achieved by obtaining the transfer function of the optical detection system using Rayleigh scatterers. Accurate particle sizing of individual polystyrene spheres (ranging from 1.5 to 9 micro m in diameter) in aqueous suspension is achieved by maximizing a correlation coefficient between precalculated tables of Mie phase functions and data obtained from the polar nephelometer. Good correlation is achieved between experimental and theoretical data, proving the functioning of the instrument as a fast and convenient particle sizer.

Polar nephelometer based on a rotational confocal imaging setup.

Rapid measurement of the angular distribution of light scattered by particles, the scattering phase function, is achieved by using a new type of polar nephelometer, a device for measuring the angular scattered-light intensity distribution, with a high angular precision and across many orders of magnitude of intensity. The design offers high-speed measurements and avoids many of the problems often associated with traditional goniometers when they are used for measurements of light scattering from small particles or biological cells in suspension. Our system relies on confocal imaging of the test space with off-axis parabolas, using a rotating mirror to scan the angular field of view at the second focus of a pair of conjugated parabolic mirrors, with the test space located at the first focus. The angular resolution of the system is limited mainly by the data-acquisition sampling frequency. In this proof-of-principle demonstration the system performs multiple scans of a 55 deg field of view in a very short time (<1 s). To significantly increase the signal-to-noise ratio, we averaged the successively acquired scans during this time. Polystyrene spheres dispersed in water at low concentrations were used to test the system. The scattering patterns obtained were found to be in good agreement with Mie theory calculations.