Complex refractive index spectra of whole blood and aqueous solutions of anticoagulants, analgesics and buffers in the mid-infrared

Abstract

Mid-infrared (MIR) spectroscopy is a powerful tool for characterising the vibrations of molecular bonds and is therefore ideal for label-free detection of chemical species. Recent research into thin-film deposition and etching techniques for mid-infrared materials shows potential for realising miniaturised bedside biosensors for clinical diagnostics exploiting MIR spectroscopy, to replace laboratory based-techniques. However, lack of refractive index information for commonly encountered biological media and analytes hampers optimisation of biosensor performance for maximum sensitivity, especially for devices exploiting evanescent spectroscopy. Here we present refractive index data for human whole blood and several aqueous solutions of general interest to the clinical community: anticoagulants, analgesics and buffers. The refractive indices are generally dominated by the water content of each sample and the whole blood spectra exhibit additional strong features due to protein content. Furthermore, we present a generalised method for extracting complex refractive indices of aqueous solutions in the mid-infrared region using conventional attenuated total reflection Fourier transform spectroscopy (ATR-FTIR) without the need for collimated or polarised incident light, as is required for existing methods.

Infrared Spectroscopy with a Fiber-Coupled Quantum Cascade Laser for Attenuated Total Reflection Measurements Towards Biomedical Applications

“…In addition, the spectral distortions are almost independent of glucose concentration, contrary to the concentration-dependent distortion expected from AD effects. This is in agreement with previous results, as e.g., Rowe et al [34] found a change in refractive index of <0.01 in whole blood as compared to water. Band distortions are also found in other spectroscopy techniques that involve reflections, e.g., transflection spectroscopy [35].…”

Blood refractive index modelling in the visible and near infrared spectral regions

“…Thus, the determination of optical dispersion of blood and its components in the visible and near infrared spectral regions is an urgent problem, since there are no complete data in the literature. Moreover, the known data on blood refractive index strongly differ among themselves [8][9][10][19][20][21][22], which additionally motivates the studies.…”

“…The quantitative and qualitative information on the blood optical properties, in particular, on the refractive index, is of great interest for many fields of biomedical studies and practical medicine, since the noninvasive or lowinvasive optical technologies become wider and wider used in diagnostics and therapy [1][2][3][4][5][6]. It is well known that the optical properties of blood are determined by such physiologic and biologic parameters as haematocrit, temperature, osmolarity, saturation with oxygen or other gases, membrane rigidity of the red blood cells, and depend on the wavelength in a complex way [1,[4][5][6][7][8][9][10][11][12]. The visible and near infrared spectral regions are often referred to as "therapeutic/diagnostic window", since just in this wavelength range water, which is a major component of many biological tissues, absorbs weakly.…”

“…Since the blood is a biological extremely turbid medium with high anisotropy of scattering (g = 0.9996) [3], possessing strong scattering and absorption in the visible region, different models of light scattering by particles and other indirect methods are used to determine the refractive index and its dispersion dependence. They include, e.g., the empirical methods based on the calculation of blood refractive index from the experimental values of the refractive indices of the components [10] or the theoretical methods that allow for calculation of the real part of the refractive index from the measured spectra of its imaginary part (absorption spectra) using the Kramers-Kronig relations [10,11,12].…”

CORNERSTONE’s Silicon Photonics Rapid Prototyping Platforms: Current Status and Future Outlook

“…The future outlook for MIR sensing using the suspended Si platform is broadly similar to that of Ge-on-Si discussed above, albeit with the additional benefits of offering simpler integration with Si MEMS and polydimethylsiloxane (PDMS) microfluidics. One exemplar application would be exploiting the bioanalytical data we have obtained using Fourier-transform infrared spectroscopy (FTIR), including a detailed study of the MIR properties of blood [149]. When combined with comprehensive knowledge of the MIR performance of the GOS and suspended Si platforms, sensitivity can be maximized for blood-based medical diagnostics.…”