Vibrational spectroscopic analysis of peripheral blood plasma of patients with Alzheimer's disease.

Using Raman and infrared spectroscopy, we monitored spectral changes occurring in the blood plasma of patients with Alzheimer's disease (AD) in relation to healthy controls. The protein secondary structure as reflected by amide I band involves β-sheet enrichment, which may be attributable to Aβ peptide formation and to increasing proportion of the globulins that are β-sheet rich. Likewise, the behavior of the infrared 1200-1000-cm(-1) region and the Raman 980-910- and 450-400-cm(-1) regions can be explained in terms of the said plasma composition change. Further, the 744-cm(-1) Raman band from healthy control plasma shows frequency upshifting in the course of AD, which may be generated by the platelets collected in blood plasma. Linear discrimination analysis and receiver operating characteristic (ROC) analysis have been used to distinguish between patients with AD and age-matched healthy controls with a diagnostic accuracy of about 94%.