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Raman tweezers probe red blood cells

10 Jun 2008

Researchers move closer to understanding devastating haemoglobin-related blood disorders thanks to a combination of optical tweezers and Raman spectroscopy.

A system that combines optical tweezers with Raman spectroscopy is helping researchers in Italy gain a deeper understanding of blood disorders such as thalassemia. The team hopes that its findings will pave the way for Raman tweezers to be used as a diagnostic tool for other haemoglobin(Hb)-related disorders (Optics Express 16 7943).

"Our main goal was to demonstrate that Raman tweezers can provide quantitative information on thalassemia," researcher Guilia Rusciano from the University of Naples Federico II told optics.org. "Unlike traditional diagnostic tools, our apparatus studies both chemical and mechanical properties, even at the single cell level."

Thalassemia is a hereditary blood disorder that is widespread in Mediterranean and Asian countries. The disease creates an abnormality in the protein part of the Hb molecule, meaning that affected cells cannot function properly. In the worst cases, the sufferer requires blood transfusions on a monthly basis to provide a supply of healthy red blood cells (RBCs).

The team investigated three specific properties: the oxygenation capability of haemoglobin, the elastic properties of RBCs and photodamage to cells at different wavelengths.

"Our results confirm medical predictions such as reduced oxygenation capability of thalassemic RBCs (t-RBCs) and their higher rigidity," explained Rusciano. "We induced cell deformation using a double trap system to study the mechanical response of cells. We saw an increased membrane rigidity of more than 40%, showing that the genetic defect associated with thalassemia also affects the RBC's mechanical properties."

The optical set-up uses an Nd:YAG laser operating at 1064 nm to trap the cells and a frequency-doubled Nd:YVO laser emitting at 532 nm to excite the Raman signals. To create the double trap system, the team applied a square voltage signal to a galvo-mirror in the trapping beam path.

"There is a strong Hb absorption band in the visible region, which gives rise to a resonant enhancement of the Hb signal," said Rusciano. "It is possible to acquire a Raman spectrum of Hb inside a single RBC without the influence of any other parts of the cell."

Rusciano believes that the approach could provide an insight into other disorders such as iron-deficiency anaemia. "Our system opens new opportunities to correlate the higher rigidity to the membrane protein arrangement, which can be obtained by Raman imaging of the cell membrane. Improvements in our set-up are in progress to reach this goal."

Author
Jacqueline Hewett is editor of Optics & Laser Europe magazine.

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