Live cell refractometry using microfluidic devices

Abstract

Using Hilbert phase microscopy for extracting quantitative phase images, we measured the average refractive index associated with live cells in culture. To decouple the contributions to the phase signal from the cell refractive index and thickness, we confined the cells in microchannels. The results are confirmed by comparison with measurements of spherical cells in suspension.

Tissue refractometry using Hilbert phase microscopy

“…Highly scattering tissue has been characterized in terms of an average refractive index by optical coherence tomography [5] and, more recently, total internal reflection [6]. Recently, we applied quantitative phase imaging to live cells flowing in microfluidic devices, which provides a high-throughput method for cytorefractometry [7].In this Letter, we present a direct method for measuring the refractive index of biological tissues. The method extends, for the first time to our knowledge, the concept of quantitative phase imaging [8][9][10][11][12] to unstained tissue sections that are relevant for pathology and can be characterized as transparent, i.e., weakly absorbing and scattering objects.…”

“…Highly scattering tissue has been characterized in terms of an average refractive index by optical coherence tomography [5] and, more recently, total internal reflection [6]. Recently, we applied quantitative phase imaging to live cells flowing in microfluidic devices, which provides a high-throughput method for cytorefractometry [7].…”

Quantitative phase microscopy with asynchronous digital holography

“…The fringe in each image is fit to a sine wave and analyzed to find both the phase shift between images, α, and the spatial frequency, q. Once the phase shift is known, the phase can then be found unambiguously: (2) In Eq. (2), I 1 and I 2 represent successive images with a phase shift α between them.…”

“…Quantitative phase measurements have merited great interest lately for measuring cellular dynamics [1,2]. One natural modality for studying these dynamics is digital holographic interferometry (DHI) [3], a simple interferometric configuration that can be used to assess subwavelength changes in an object by measuring the optical path length difference between each imaged point at two distinct times.…”

“…Feld and coworkers take the third approach; they created a system that uses only one image, isolating the phase term via image processing [7], similar to the Fourier transform evaluation method [8]. This system can be used for wide-field imaging and has no limitations on the spatial resolution; it has been successfully used to quantify cell structure and dynamics [2,9]. One possible disadvantage of this approach, among others [3], is that in using image processing to eliminate unwanted background, some desired signal may be eliminated as well.…”