Fourier Transform Infrared Spectroscopy and Photoacoustic Spectroscopy for Saliva Analysis

Abstract

Saliva provides a valuable tool for assessing oral and systemic diseases, but concentrations of salivary components are very small, calling the need for precise analysis methods. In this work, Fourier transform infrared (FT-IR) spectroscopy using transmission and photoacoustic (PA) modes were compared for quantitative analysis of saliva. The performance of these techniques was compared with a calibration series. The linearity of spectrum output was verified by using albumin-thiocyanate (SCN(-)) solution at different SCN(-) concentrations. Saliva samples used as a comparison were obtained from healthy subjects. Saliva droplets of 15 µL were applied on the silicon sample substrate, 6 drops for each specimen, and dried at 37 ℃ overnight. The measurements were carried out using an FT-IR spectrometer in conjunction with an accessory unit for PA measurements. The findings with both transmission and PA modes mirror each other. The major bands presented were 1500-1750 cm(-1) for proteins and 1050-1200 cm(-1) for carbohydrates. In addition, the distinct spectral band at 2050 cm(-1) derives from SCN(-) anions, which is converted by salivary peroxidases to hypothiocyanate (OSCN(-)). The correlation between the spectroscopic data with SCN(-) concentration (r > 0.990 for transmission and r = 0.967 for PA mode) was found to be significant (P < 0.01), thus promising to be utilized in future applications.

Pathology-specific molecular profiles of saliva in patients with multiple dental caries—potential application for predictive, preventive and personalised medical services

“…Preliminary analysis of the data obtained by FTIR demonstrated that the spectra of all samples within a certain experimental group involved one and the same set of vibration modes. The use of FTIR for the analysis qualitatively demonstrated that the molecular composition of the mixed saliva was characterised by a specific set of vibration modes in the IR spectra, in agreement with published data on biological fluids [21,[27][28][29][30][31].…”

“…The most intensive vibration in this group of bands is a mode in the range of 2150-1950 cm −1 . According to the data of [29], this mode is related to the −N=C=S bond of thiocyanate anions that are present in mixed saliva. Visual analysis of the intensity for this vibration in the spectrum of the oral fluid obtained from those with multiple caries demonstrated that it is considerably more intensive than for the healthy subjects.…”

“…Non-stimulated mixed saliva was sampled during daylight, to minimise circadian rhythm, 5 min after the preliminary rinsing of the oral cavity with pure water. The saliva was placed into 15-ml sterile test tubes for subsequent laboratory investigation according to the standard technique [29] as shown in the inset Bа^in Fig. 1.…”

“…Changes in the molecular composition of saliva associated with cariogenesis can be used as efficient tissue markers of dental caries development [7,19,24,26]. Such an approach requires the precise analysis of the biological fluid composition; in this case, the most suitable technique is Fourier transform infrared spectroscopy (FTIR) [21,[27][28][29][30][31]. FTIR is non-invasive, rapid, precise and highly selective allowing the investigation of erosion in hard dental tissue, its attrition, as well as for the study of different forms of caries [23,32,33].…”

“…Also, infrared spectroscopy can be employed as a preventive and predictive method to define tooth and gum disease (gingivitis/periodontitis) [31,34,35]. IR spectroscopy has been successfully applied for the detection of tissue marker pathologies [21,27,29,36]. With the development of spectroscopic express methods of human saliva analysis, screening of diseases at the molecular level at any early stage is possible [13,28,29,37].…”