A vibrational spectroscopy method for diagnosing Alzheimer's disease in a subject is disclosed, said method comprising the steps of a) determining in a Raman spectrum of a biofluid retrieved from said subject or in a sample derived from said biofluid the intensity of a Raman band around 1256 cm-1； and b) comparing the intensity value obtained in step a) with a reference value, wherein an increase in the value of said Raman band intensity with respect to the reference value is indicative that the subject suffers Alzheimer's disease. Also disclosed are an apparatus for plasma sample analysis, a computer program, and a data carrier.
