Low-Coherence Reflectometry for Refractive Index Measurements of Cells in Micro-Capillaries

Abstract

The refractive index of cells provides insights into their composition, organization and function. Moreover, a good knowledge of the cell refractive index would allow an improvement of optical cytometric and diagnostic systems. Although interferometric techniques undoubtedly represent a good solution for quantifying optical path variation, obtaining the refractive index of a population of cells non-invasively remains challenging because of the variability in the geometrical thickness of the sample. In this paper, we demonstrate the use of infrared low-coherence reflectometry for non-invasively quantifying the average refractive index of cell populations gently confined in rectangular glass micro-capillaries. A suspension of human red blood cells in plasma is tested as a reference. As a use example, we apply this technique to estimate the average refractive index of cell populations belonging to epithelial and hematological families.

Spectral Optical Readout of Rectangular–Miniature Hollow Glass Tubing for Refractive Index Sensing

“…The best sensitivity value found in the experimental verification was slightly lower than that expected theoretically: probably, this result can be explained by a mismatch between the nominal and effective geometrical dimensions of the device. To estimate the actual dimensions, we characterized the tubing employed for refractometric detection through low-coherence interferometric measurements, that give the optical thickness as OT g = n g · x, where n g is the group refractive index of the material and x its geometrical thickness, as explained in [ 37 , 38 ]. We thus found the device geometrical dimensions by placing n g,glass = 1.4752 RIU [ 39 ] and n g,air = 1 RIU, obtaining t f = 22.40 µm t d = 22.30 µm and d = 29.84 µm.…”

Testing of Piezo-Actuated Glass Micro-Membranes by Optical Low-Coherence Reflectometry

“…The same basic optical setup was successfully employed for static and dynamic characterization. In addition to static measurements of optical thickness, also reported in previous papers on different devices [22,23,28], we investigated out-of-plane large displacements of the micro-membrane at low frequency to identify hysteretic effects induced by positive and negative slopes of the driving voltage. Given the applied instantaneous voltage, it is possible to immediately quantify the hysteresis, thanks to the amplitude modulation of the sinusoidal interferometric signal induced by the Gaussian broad emission spectrum of the SLED.…”

Flow-through micro-capillary refractive index sensor based on T/R spectral shift monitoring

“…To verify the agreement between experimental and theoretical results, we measured on the tested devices the effective value of channel depth, d eff , as well as of the optical path of the front glass wall, n glass • t f,eff , and of the back glass wall, n glass • t b,eff , by means of low-coherence reflectometry in the near-infrared, presented in our previous works [35,36]. Table 1 summarizes the values of the highest sensitivity, the widest Δλ and the specific D value for all the tested capillaries.…”