1. A method for detecting Alzheimer's disease in a subject, said method comprising: providing a sample from the subject; subjecting different regions of the sample individually to a Raman spectroscopic analysis to produce a separate Raman spectrum for each of the different regions of the sample; producing a representation of each separate Raman spectrum; preparing a Raman spectroscopic signature for the sample based on the representation for each separate Raman spectrum; determining whether the Raman spectroscopic signature for the sample corresponds to an Alzheimer's disease spectroscopic signature; and identifying a subject as having Alzheimer's disease where the Raman spectroscopic signature for the sample from that subject corresponds to the Raman spectroscopic signature for Alzheimer's disease.