Saliva preparation method exploration for ATR-FTIR spectroscopy: Towards bio-fluid based disease diagnosis.

Saliva has garnered a lot of interest as a non-invasive, easy to collect, and biochemical rich sample for attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) based disease diagnosis. Although a large number of studies have explored its potential, the preparation methods used differ greatly. For large scale clinical studies to aid translation into clinics, the collection/processing methodology needs to be standardized. Therefore, in this study, we explored different saliva collection (spitting, method A/cotton soaking, method B) and processing protocols (unprepared, TS; supernatant from the centrifugation, CS; and drying, C) to find which gives the best ATR-FTIR signals. Analysis showed highest proteins, carbohydrates, amino acids, and nucleic acid + proteins/lipids in BTS, BCS, ACS, and BC, respectively. Notably, only BC shows a 1377 cm-1 nucleic acid band that is also uniquely identified in multivariate analysis. We conclude that the collection-processing protocol should be based on a biochemical component that best gives a differential diagnosis.