Combined optical intensity and polarization methodology for analyte concentration determination in simulated optically clear and turbid biological media

Tuning and hybridization of surface phonon polaritons in α-MoO3 based metamaterials

We propose an effective medium approach to tune and control surface phonon polariton dispersion relations along the three main crystallographic directions of α-phase molybdenum trioxide. We show that a metamaterial consisting of subwavelength air inclusions into the α-MoO₃ matrix displays new absorption modes producing a split of the Reststrahlen bands of the crystal and creating new branches of phonon polaritons. In particular, we report hybridization of bulk and surface polariton modes by tailoring metamaterials' structural parameters. Theoretical predictions obtained with the effective medium approach are validated by full-field electromagnetic simulations using finite difference time domain method. Our study sheds light on the use of effective medium theory for modeling and predicting wavefront polaritons. Our simple yet effective approach could potentially enable different functionalities for hyperbolic infrared metasurface devices and circuits on a single compact platform for on-chip infrared photonics.

Review of Non-invasive Glucose Sensing Techniques: Optical, Electrical and Breath Acetone

Annual deaths in the U.S. attributed to diabetes are expected to increase from 280,210 in 2015 to 385,840 in 2030. The increase in the number of people affected by diabetes has made it one of the major public health challenges around the world. Better management of diabetes has the potential to decrease yearly medical costs and deaths associated with the disease. Non-invasive methods are in high demand to take the place of the traditional finger prick method as they can facilitate continuous glucose monitoring. Research groups have been trying for decades to develop functional commercial non-invasive glucose measurement devices. The challenges associated with non-invasive glucose monitoring are the many factors that contribute to inaccurate readings. We identify and address the experimental and physiological challenges and provide recommendations to pave the way for a systematic pathway to a solution. We have reviewed and categorized non-invasive glucose measurement methods based on: (1) the intrinsic properties of glucose, (2) blood/tissue properties and (3) breath acetone analysis. This approach highlights potential critical commonalities among the challenges that act as barriers to future progress. The focus here is on the pertinent physiological aspects, remaining challenges, recent advancements and the sensors that have reached acceptable clinical accuracy.

Broadband polarimetric glucose determination in protein containing media using characteristic optical rotatory dispersion

One of the major challenges during polarimetric determination of glucose concentration is the spectral superposition with other optically active molecules, especially proteins like albumin. Since each of those substances has a characteristic optical rotatory dispersion (ORD), we developed a broadband polarimeter setup to distinguish between glucose and albumin. A partial least squares (PLS) regression with 5 components was applied to the polarimeter signal in the wavelength range of 380 - 680 nm . To verify the efficacy of the proposed method, different glucose levels of 0 - 500 mg/dl were spiked with varying albumin concentrations up to 1000 mg/dl . A standard error of prediction of ± 16.0 mg/dl was achieved compared to ± 128.3 mg/dl using a two-wavelength system with 532 nm and 635 nm under the same conditions.

Real-time compensation method for robust polarimetric determination of glucose in turbid media

Polarimetric determination of glucose is known to be strongly affected by scattering in turbid media. Other effects like fluctuations of light source emission and sample absorption also deteriorate glucose predictability. This work presents a measurement setup using a real-time data processing method to address these problems. The approach uses the frequency-dependent intensity components created when the polarization of the incident light is periodically modulated by a Faraday rotator. The efficacy of the proposed method was verified experimentally for a glucose range of 0 - 500 mg/dl. It was shown that the approach reduces the prediction errors in slightly turbid media from 35.7 mg/dl down to 1.17 mg/dl. In a similar way, the glucose predictability for fluctuating light source emission was improved from ±16.16 mg/dl to ±1 mg/dl and for varying sample absorbance from ±15.69 mg/dl to ±1.23 mg/dl, respectively. Therefore, considerable improvement of robustness and reproducibility of glucose determination was demonstrated.

Low-coherence interferometry for phase-sensitive measurement of optical rotation

We present phase-sensitive measurement of optical rotation using spectral-domain and time-domain low-coherence interferometry. The method utilizes two decorrelated polarization states and simultaneous dual-channel detection provided by polarization-maintaining fiber-based implementation. The sample is placed between polarization optics to control and switch left- and right-handed circular states that experience the sample in forward and backward directions. Phase difference between two interferometric signals yields the optical rotation. Results from glucose and fructose samples are presented for validation.

Design of a simple non-destructive detection system using P-wave lasers for determining the soluble solids content of apples

The simple and nondestructive detection system studied in this work uses a near-infrared (NIR) detector and parallel-polarized (P-wave) NIR lasers to determine the soluble solids content (SSC) of apples. The P-wave NIR laser in this system is incident into the apple's pulp at the Brewster angle to minimize the interference caused by interfacial reflections. After the apple has been illuminated by four P-wave NIR lasers that correspond to the specified wavelengths of the SSC chemical bonds (880, 940, 980, and 1064 nm), the prediction of correlation (rp2) and the root-mean-square error for prediction (RMSEP) of the SSC are determined via partial least square regression analysis of the reflectance. Our results indicate that the use of P-wave lasers at the Brewster angle (as the angle of incidence) and the above specified wavelengths for the prediction set measurement of the SSC of apples obtained an rp2 of 0.88 and an RMSEP of 0.47°Brix. These rp2 are 6% higher, and the RMSEPs are 9% lower, than those obtained using non-polarized lasers.

Polarized light imaging in biomedicine: emerging Mueller matrix methodologies for bulk tissue assessment

Polarized light point measurements and wide-field imaging have been studied for many years in an effort to develop accurate and information-rich tissue diagnostic methods. However, the extensive depolarization of polarized light in thick biological tissues has limited the success of these investigations. Recently, advances in technology and conceptual understanding have led to a significant resurgence of research activity in the promising field of bulk tissue polarimetry. In particular, with the advent of improved measurement, analysis, and interpretation methods, including Mueller matrix decomposition, new diagnostic avenues, such as quantification of microstructural anisotropy in bulk tissues, have been enabled. Further, novel technologies have improved the speed and the accuracy of polarimetric instruments for ex vivo and in vivo diagnostics. In this paper, we review some of the recent progress in tissue polarimetry, provide illustrative application examples, and offer an outlook to the future of polarized light imaging in bulk biological tissues.

Quantitative correlation between light depolarization and transport albedo of various porcine tissues

We present a quantitative study of depolarization in biological tissues and correlate it with measured optical properties (reduced scattering and absorption coefficients). Polarized light imaging was used to examine optically thick samples of both isotropic (liver, kidney cortex, and brain) and anisotropic (cardiac muscle, loin muscle, and tendon) pig tissues in transmission and reflection geometries. Depolarization (total, linear, and circular), as derived from polar decomposition of the measured tissue Mueller matrix, was shown to be related to the measured optical properties. We observed that depolarization increases with the transport albedo for isotropic and anisotropic tissues, independent of measurement geometry. For anisotropic tissues, depolarization was higher compared to isotropic tissues of similar transport albedo, indicating birefringence-caused depolarization effects. For tissues with large transport albedos (greater than ~0.97), backscattering geometry was preferred over transmission due to its greater retention of light polarization; this was not the case for tissues with lower transport albedo. Preferential preservation of linearly polarized light over circularly polarized light was seen in all tissue types and all measurement geometries, implying the dominance of Rayleigh-like scattering. The tabulated polarization properties of different tissue types and their links to bulk optical properties should prove useful in future polarimetric tissue characterization and imaging studies.

Tissue polarimetry: concepts, challenges, applications, and outlook

Polarimetry has a long and successful history in various forms of clear media. Driven by their biomedical potential, the use of the polarimetric approaches for biological tissue assessment has also recently received considerable attention. Specifically, polarization can be used as an effective tool to discriminate against multiply scattered light (acting as a gating mechanism) in order to enhance contrast and to improve tissue imaging resolution. Moreover, the intrinsic tissue polarimetry characteristics contain a wealth of morphological and functional information of potential biomedical importance. However, in a complex random medium-like tissue, numerous complexities due to multiple scattering and simultaneous occurrences of many scattering and polarization events present formidable challenges both in terms of accurate measurements and in terms of analysis of the tissue polarimetry signal. In order to realize the potential of the polarimetric approaches for tissue imaging and characterization/diagnosis, a number of researchers are thus pursuing innovative solutions to these challenges. In this review paper, we summarize these and other issues pertinent to the polarized light methodologies in tissues. Specifically, we discuss polarized light basics, Stokes-Muller formalism, methods of polarization measurements, polarized light modeling in turbid media, applications to tissue imaging, inverse analysis for polarimetric results quantification, applications to quantitative tissue assessment, etc.

Mueller matrix decomposition for polarized light assessment of biological tissues

The Mueller matrix represents the transfer function of an optical system in its interactions with polarized light and its elements relate to specific biologically or clinically relevant properties. However, when many optical polarization effects occur simultaneously, the resulting matrix elements represent several "lumped" effects, thus hindering their unique interpretation. Currently, no methods exist to extract these individual properties in turbid media. Here, we present a novel application of a Mueller matrix decomposition methodology that achieves this objective. The methodology is validated theoretically via a novel polarized-light propagation model, and experimentally in tissue simulating phantoms. The potential of the approach is explored for two specific biomedical applications: monitoring of changes in myocardial tissues following regenerative stem cell therapy, through birefringence-induced retardation of the light's linear and circular polarizations, and non-invasive blood glucose measurements through chirality-induced rotation of the light's linear polarization. Results demonstrate potential for both applications.