Raman Spectroscopy Of Human Skin For Kidney Failure Detection

INTRODUCTION

Among the non-communicable diseases, chronic kidney disease stands out as a prevalent condition. According to the World Health Organization, approximately 10% of the global population suffers from this ailment, resulting in millions of annual deaths attributed to kidney pathologies. The failure of the kidneys contributes to disruptions in the body's water, electrolyte, and nitrogen balance, as well as other metabolic disorders. These physiological and pathological characteristics of internal organs have a direct impact on the condition of the skin and its constituent composition. Various biochemical and immunochemical methods of laboratory analysis are applied in studying skin component composition. However, these methods are invasive and require additional reagents. Currently, Raman spectroscopy (RS) has been used in clinical experimental studies to determine skin composition. In skin analysis, RS is used to quantify the content of a specific component in the skin, determine dermal drug delivery, identify biophysical links between vibrational characteristics and specific compositional and chemical changes associated with aging, screen for skin cancer, etc.

METHOD

RS is based on the inelastic scattering of light by polarizable molecules, revealing the vibrational energy levels of the chemical bonds of molecules. The skin tissues for the in vivo analysis were selected using a stratified random sampling method.

Figure 1 The raw spectrum of human skin

The obtained experimental dataset of human skin was analyzed with smart algorithms. When constructing the regression model, the informative spectra bands were defined by analyzing the variable importance in the projection (VIP) distribution. VIP makes it possible to assess the impact of individual variables of the predicate matrix array on the model. The most informative Raman spectral bands were 1315–1330 cm⁻¹ (amide III, δ(CH2) in α-helicx collagen), 1450–1460 cm⁻¹ (δ(CH) in proteins and lipids) and 1700–1800 cm⁻¹ (ν(CO), ν(COO) in lipids and phospholipids). Changes in collagen structure, lipid content, or metabolite concentrations are specific and characteristic biological markers to identify kidney failure.

Figure 2 VIP-scores of the Raman spectra PLS-DA model

The results in Figure 2 are the results of an actual survey conducted on three groups of subjects: a target group consisting of 85 hemodialysis patients with kidney failure (90 spectra), the adult control group constituted by 40 healthy volunteers (80 spectra) without systemic diseases and the young control group constituted by 84 healthy volunteers (168 spectra). All examined subjects were Caucasians with skin phototypes I and II. The specificity, sensitivity, and accuracy of the model for detecting patients with kidney failure by analyzing the raw skin spectral properties were 0.99, 1, and 0.99, respectively. The correlation coefficients between the VIP values of the model “kidney failure VS whole healthy group” and the VIP values of the model “young healthy group VS adult healthy group” showed a lack of significant correlation, ranging up to 0.033. Therefore, the multivariate analysis of the Raman components of the skin spectrum is particularly suitable for detecting spectral features associated with changes in skin metabolism in kidney failure. The age factor did not significantly affect the analysis.

SYSTEM

For measurements, we used a modular Raman system comprising the QE Pro spectrometer, a 785 nm laser for Raman excitation and sampling optics. The 785 nm excitation produces excellent Raman spectra for most chemicals, with limited interference from fluorescence. These systems also offer very good spectral resolution, making them a preferred wavelength choice for Raman spectroscopy of chemicals and organic materials.

The QE Pro is a versatile, high-sensitivity spectrometer ideal for general-purpose and low light level applications such as fluorescence and Raman analysis. The spectrometer has a back-thinned CCD detector with high quantum efficiency and onboard spectral buffering to ensure data integrity at high collection rates. An optional internal shutter is available for effective management of dark measurements, and the interchangeable slit design allows users to switch between measurements easily. QE Pro has low-noise electronics and delivers great sensitivity for all sorts of applications. Setups are available using Raman excitation lasers ranging from 532 nm to 1064 nm.

Figure 3 QE Pro Spectrometer

Ocean Insight 785 nm Raman lasers, with their high power output, narrow spectral line width (only 0.2 nm), and advanced features like Thermo-Electric Cooler (TEC), low power consumption, and robust safety mechanisms, are well-suited for a wide range of applications in scientific research, industrial monitoring, and forensic analysis. The user-friendly interface and adjustable power settings further enhance their versatility, making them a reliable and efficient choice for demanding Raman spectroscopy applications.

Figure 4 Ocean Insight 785 nm Raman Lasers

CONCLUSIONS