Surface-enhanced Raman spectroscopy of tears: toward a diagnostic tool for neurodegenerative disease identification

Abstract

Significance: A noninvasive method based on surface-enhanced Raman spectroscopy (SERS) of tears was proposed as a support for diagnosing neurodegenerative pathologies, including different forms of dementia and Alzheimer's disease (AD). In this field, timely and reliable discrimination and diagnosis are critical aspects for choosing a valid medical therapy, and new methods are highly required. Aim: The aim is to evince spectral differences in SERS response of human tears from AD affected, mild cognitive impaired (MCI), and healthy control (Ctr) subjects. Approach: Human tears were characterized by SERS coupled with multivariate data analysis. Thirty-one informed subjects (Ctr, MCI, and AD) were considered. Results: Average SERS spectra from Ctr, MCI, and AD subjects evidenced differences related to lactoferrin and lysozyme protein components. Quantitative changes were also observed by determining the intensity ratio between selected bands. We also constructed a classification model that discriminated among AD, MCI, and Ctr subjects. The model was built using the scores obtained by performing principal component analysis on specific spectral regions (i-PCA). Conclusions: The results are very encouraging with interesting perspectives for medical applications as support of clinical diagnosis and discrimination of AD from other forms of dementia.

Raman Spectroscopic Study of Amyloid Deposits in Gelatinous Drop-like Corneal Dystrophy

“…As to the peaks present in both the specimens, even with differences in their height, we found a prominent shift for the peaks located at ~855 cm −1 and at ~1173 cm −1 and assigned to tyrosine [ 28 , 32 , 34 ], an amino acid present in amyloid deposits [ 41 ].…”

“…Particular relevance can be attributed to the peaks at ~1200–1300 cm −1 related to the Amide III band [ 34 ]. They were particularly high in GDCD cornea when compared to normal and are considered typical of the amyloid material [ 45 ], and in particular to lactoferrin [ 36 ].…”

Methods in Raman spectroscopy for saliva studies – a review

“…[1,2] However, other biofluids are being investigated, which may have different accessibility, risk, and content profiles than blood or urine. [3][4][5][6] Optical methods show promise in biosensing, and specifically, there is an increasing interest in spectroscopic means that may confer benefits of speed, increased accuracy, and multiplexing. Alongside this, the development of smaller instruments needing low sample volumes for benchtop clinical or bedside use, or in-field applications at a roadside accident or a crime scene, is desirable.…”

“…As an exception, D'Elia et al [105] uses stimulated resonance Raman at 239 nm excitation, establishing a LoD of 10 lg/mL for cocaine in artificially mixed saliva-cocaine samples while pointing out that a laser excitation at 200 nm could decrease the LoD further with significant sensitivity improvement required for forensic drug detection (8 ng/mL). The movement toward shorter excitation wavelengths confers a significant benefit in terms of signal due to the 1/(wavelength) 4 dependence of the Raman scattering intensity. Perhaps just as important, UV excitation avoids the need for any pre-concentration or other preparatory step by mitigating the inherent, and masking, effect of absorption from the native oral fluid.…”

“…In SERS measurements, plasmonically driven chemical or thermal effects may further need to be considered. [87] While surface powers of 5mW are sufficient for laser interrogation in the green region [39,257] and even for 633 nm laser excitation, [47,60,234] higher laser power (!10mW) is often necessary in the infrared range, [50,145,152,[154][155][156]304] due to the 1/ (wavelength) 4 Raman scattering signal dependence. The exact power density relies not only on the laser power at the surface but also on the numerical aperture (NA) of the objective lens and the excitation wavelength.…”