Specular reflectance of monochromatic linearly polarized light, reflected on the interface of a prism coupled to a transparent medium at the critical angle of the transition to total internal reflection, has been long utilized to accurately determine optical constants, such as the refractive index and the dielectric constant, by the so-called ‘derivative method’. However, in its original formulation, the derivative method does not account for the imaginary part of the complex optical constants that chararacterize attenuating media and becomes increasingly inaccurate even for the real part when attenuation grows. We therefore derive a proper analytic extension of the derivative method for attenuating media. Reflectance and angle of incidence at the derivative maximum are the experimental input quantities that yield both parts of the complex dielectric constant for both linear polarizations.

Assessment of regional lymph node status in breast cancer is of important staging and prognostic value. Even though formal histological examination is the currently accepted standard of care, optical imaging techniques have shown promising results in disease diagnosis. In the present article, we review six spectroscopic techniques and focus on their use as alternative tools for breast cancer lymph node assessment. Elastic scattering spectroscopy (ESS) seems to offer a simple, cost-effective, and reproducible method for intraoperative diagnosis of breast cancer lymph node metastasis. Optical coherence tomography (OCT) provides high-resolution tissue scanning, along with a short data acquisition time. However, it is relatively costly and experimentally complex. Raman spectroscopy proves to be a highly accurate method for the identification of malignant axillary lymph nodes, and it has been further validated in the setting of head and neck cancers. Still, it remains time-consuming. Near-infrared fluorescence imaging (NIRF) and diffuse reflectance spectroscopy (DFS) are related to significant advantages, such as deep tissue penetration and efficiency. Fourier-transform infrared spectroscopy (FTIR) is a promising method but has significant drawbacks. Nonetheless, only anecdotal reports exist on their clinical use for cancerous lymph node detection. Our results indicate that optical imaging methods can create informative and rapid tools to effectively guide surgical decision-making.

The search for more sustainable alternatives to traditional organic solvents, in the frame of the green chemistry approach, is leading to an increasing interest toward the exploration of deep eutectic solvents (DESs), especially natural-based ones (NADESs). The great ferment in the use of DESs as innovative media for many applications and in the research of novel types of DESs is not matched by an equal rigor in their characterization and in the study of their physico-chemical characteristics. Nevertheless, it is evident how comparative studies encompassing the investigation of a wide range of properties in relationship with the DESs structures would be beneficial for a rational development of the field. In this work a panel of DESs featuring choline acetate, L-carnitine and L-proline as hydrogen bond acceptor constituents (HBAs) and ethylene glycol, glycerol and levulinic acid as hydrogen bond donor constituents (HBDs) in 1:2 and 1:3 molar ratios have been prepared and characterized. Their density, viscosity and optical properties have been thoroughly investigated at various temperatures, analyzing the influence of their composition in terms of type of HBA, type of HBD and molar ratio on their properties. All the proposed DESs have also been thermally characterized by TGA and DSC, providing a description of their thermal behavior in a wide range of temperature and determining their thermal stability and thermal degradation profile.

Background: Breast malignancy is the most common cancer type and the second leading cause of cancer-related death for women all ages. Axillary surgery provides prognostic and predictive information, but carries significant morbidity. Imaging techniques are a promising field, providing the characterization of biological tissues using the interaction between the light and a medium, and may offer an accurate cancerous diagnosis without the need for formal histopathological examination. Methods: In this study, using a prism couple refractometer, we sought to determine tissues’ reflection profiles in freshly excised human lymph nodes from female patients with breast cancer, in whom axillary lymph node dissection was performed. Results: Thirty-four patients were included, contributing a total number of 90 lymph nodes and, according to our results, the median refractive indices were significantly higher in cancerous lymph nodes compared to normal lymph nodes in 450 nm, 964 nm, and 1551 nm wavelengths (p < 0.05). Conclusions: Results from this small experimental study imply that the use of a prism couple refractometer may aid in the discrimination between benign and malignant axillary lymph nodes in female patients with breast cancer.

At a critical angle of incidence, Fresnel reflectance at an interface between a front transparent and a rear lossy medium exhibits sensitive dependencies on the complex refractive index of the latter. This effect facilitates the design of optical sensors exploiting single (or multiple) reflections inside a prism (or a parallel plate). We determine an empirical framework that captures performance specifications of this sensing scheme, including sensitivity, detection limit, range of linearity and—what we define here as—angular acceptance bandwidth. Subsequently, we develop an optimization protocol that accounts for all relevant optical or geometrical variables and that can be utilized in any application.