University of Alabama researchers have used an emerging submicron infrared (IR) technique, termed, optical photothermal infrared (O-PTIR) spectroscopic imaging to deepen understanding of cerebral amyloid angiopathy (CAA), a cerebrovascular disorder associated with the accumulation of amyloid-β (Aβ) proteins in blood vessel walls.
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Although CAA and Alzheimer’s disease share Aβ-related pathology, the structural characteristics of Aβ aggregates in CAA and how they change as the disease progresses remain poorly understood.
Conventional methods that depend on fibrils extracted from brain tissue may fail to capture the structural diversity and chemical associations within vascular amyloids. These limitations have left significant gaps in CAA research.
To address this issue, the research team applied label-free O-PTIR spectroscopic imaging, which offers spatial resolution of approximately 500nm, which is well beyond the traditional IR diffraction limit of ~10microns, to 80 vascular amyloid deposits. They probed the chemical structure and heterogeneity of vascular amyloid aggregates within human brain tissues from a range of CAA stages.
This study revealed that β-sheet content within vascular Aβ deposits increased alongside disease progression. The researchers also identified substantial amounts of antiparallel β-sheet structures, which were particularly prevalent in samples from moderate and severe CAA cases. This demonstrated a strong correlation with co-localized lipids, suggesting that lipids may influence the aggregation of these antiparallel structures.
Multivariate curve resolution analysis also revealed the relationship between lipids and amyloid structure. The researchers observed that lipids correlated specifically with antiparallel β-structures, but not with overall β-sheet populations.
These findings suggested that vascular amyloids comprise a heterogeneous mixture of parallel and antiparallel aggregates, with antiparallel structures forming due to the contributions of lipid-mediated pathways.
This study shows the benefits of the O-PTIR technique for this particular application. It offered unprecedented insights into amyloid structure directly within native tissue environments. Researchers could map chemical heterogeneities at the subcellular level without the risk of artifacts introduced by sample processing due to O-PTIR’s ~500nm sub-diffraction spatial resolution and label-free capabilities.
Additionally, this study shows how O-PTIR can reveal disease-relevant structural polymorphs that conventional approaches may overlook, offering crucial insights into pathogenic mechanisms and their potential therapeutic targets.
Acknowledgments
Produced from materials originally authored by Ana Pacheco de Oliveira, Divya Baghel, Brooke Holcombe, William Chase, Tyler Ward, Shih-Hsiu J. Wang, and Ayanjeet Ghosh.
References and further reading
- de Oliveira, A.P., Baghel, D., Holcombe, B. et al. Lipid mediated formation of antiparallel aggregates in cerebral amyloid angiopathy. Acta Neuropathologica, 150(3). (2025). https://doi.org/10.1007/s00401-025-02911-5.
About Photothermal Spectroscopy Corp
Photothermal Spectroscopy Corp (PSC) is a Santa Barbara, CA-based scientific equipment company that pioneered sub-micron IR microscopy and spectroscopy. PSC’s vision is to enable the power of sub-micron IR spectroscopy to be applied to high-value problems in both industry and academia via the adoption of O-PTIR and co-located multi-modal techniques.
O-PTIR is one of the highest growth IR microscopy techniques and addresses application areas in life science, microplastics, bioplastics, semiconductors, failure analysis, and chemical and polymeric materials.
mIRage-HSi IR Multimodal Microscope
mIRage-HSi combines sub-500 nm O-PTIR chemical imaging with laser-scanning speed, revealing label-free distributions of key macromolecules like lipids, proteins and nucleic acids while also resolving micro- and nanoplastic particles in complex biological samples.
Hyperspectral images are acquired in minutes and targeted single-wavenumber images in seconds, making detailed cellular studies and high-throughput particle workflows practical.
The mIRage-HSi supports multi-modal capabilities with simultaneous Raman, co-located fluorescence microscopy and optical microscopy making it a powerful instrument for high resolution life science research.
Optical Photothermal IR Spectroscopy
Multimodal Optical Photothermal infrared spectroscopy (O-PTIR) used on the mIRage microscope platforms is a result of nearly 2 decades of expertise in photothermal based IR spectroscopy.
O-PTIR: How it works
O-PTIR overcomes the IR diffraction limit by combining a mid-IR pulsed, tunable laser that heats the sample. When the IR laser is at a wavelength that excites a molecular vibration in the sample, absorption occurs, thereby creating photothermal effects including photothermal expansion. A visible probe laser, focused to 0.5 µm spot size, measures the photothermal response via the scattered light.
The component of the reflected visible laser signal that is modulated at the IR pump laser repetition rate is directly proportional to the absorption coefficient of the sample at that wavenumber. The IR pump laser can be tuned through the entire fingerprint region in one second or less, to obtain an IR spectrum.
By operating in reflection mode, O-PTIR eliminates several longstanding limitations and has substantial benefits for the IR community, including sub-micron resolution using a non-contact optical method.
Measurements are collected quickly and easily without need for sample contact, unlike ATR spectroscopy. Additionally, O-PTIR provides spectra comparable to FTIR without the dispersive artifacts observed in ATR. By operating in reflection mode, the need for thin samples is also eliminated, leading to dramatically easier sample preparation and faster turnaround times.
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