Tip-enhanced Raman spectroscopy of amyloid ß at neuronal spines.

The early stages of Alzheimer's disease pathogenesis are thought to occur at the synapse level, since synapse loss can be directly correlated with memory dysfunction. Considerable evidence has suggested that amyloid beta (Aß), a secreted proteolytic derivative of amyloid precursor protein, appears to be a critical factor in the early 'synaptic failure' that is observed in Alzheimer's disease pathogenesis. The identification of Aß at neuronal spines with high spatial resolution and high surface specificity would facilitate unraveling the intricate effect of Aß on synapse loss and its effect on neighboring neuronal connections. Here, tip-enhanced Raman spectroscopy was used to map the presence of Aß aggregations in the vicinity of the spines exposed to Aß preformed in vitro. Exposure to Aß was of 1 and 6 hours. The intensity variation of selected vibrational modes of Aß was mapped by TERS for different exposure times to Aß. Of interest, we discuss the distinct contributions of the amide modes from Aß that are enhanced by the TERS process and in particular the suppression of the amide I mode in the context of recently reported observations in the literature.