Fourier Transform Infrared Spectroscopy and Photoacoustic Spectroscopy for Saliva Analysis

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 mu L 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 1500-1750cm(-1) for proteins and 1050-1200cm(-1) for carbohydrates. In addition, the distinct spectral band at 2050cm(-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.