A SERRS way to determine blood sugar levels

Lynn Savage lynn.savage@photonics.com

Surface-enhanced resonance Raman spectroscopy (SERRS) has proved to be an astute determiner of how much HbA1c is held in blood samples, which could lead to better diagnosis and treatment of people with diabetes.

When sugars attach themselves to the main blood protein, hemoglobin, they remain for the life of the cell that contains the molecules. Chemical analysis of these glycated proteins, called HbA1c, provides an indication of how well one’s body processes sugar intake. Normal blood contains 6 percent or less of HbA1c – 9 percent or more points to someone with poor sugar metabolism. Tests of HbA1c are performed routinely on people with diabetes to see how well diet, exercise or insulin intake helps with the disease.

As with many chemical tests, however, the sensitivity can be less than ideal, and there is much ongoing research to improve HbA1c test results. Now, scientists at the National Institute of Advanced Industrial Science and Technology (AIST) in Japan have found that SERRS may provide a highly sensitive way to determine blood glucose levels.

SERRS is used to study other biomolecules of interest and is better than standard Raman scattering experiments at culling the spectra from weak signals emitted by molecules such as DNA, cytochrome and, of course, hemoglobin. However, although hemoglobin has been studied using SERRS techniques, differentiating it from HbA1c had not been attempted successfully until now.

The AIST researchers, led by Mitsuru Ishikawa of the institute’s Health Technology Research Center, incubated hemoglobin A (HbA) and HbA1c with 60-nm silver particles, which provided signal enhancement. They deposited the colloidal solutions via spin-coating onto slides and then mounted the slides onto an inverted microscope from Olympus of Tokyo. They then illuminated the samples with a 532-nm continuous-wave diode laser made by Coherent Inc. of Palo Alto, Calif. Using a CCD camera made by Nikon, a CCD sensor made by Andor fitted with a polychromator made by Acton, and a holographic notch filter to block Rayleigh scattering, the researchers captured Raman scattering and SERRS imaging data.

The group found that HbA1c exhibits a SERRS band at about 770 to 830 cm^–1 (predominantly at 827 cm^–1), whereas the HbA showed bands at 1403 and 1652 cm^–1. The investigators reason that the band at 827 cm^–1 appears because of the presence of a glucose moiety on the hemoglobin molecule – not from free glucose nearby – thus making the band a major determinant of HbA1c.

In addition, they saw that both HbA and HbA1c induced aggregation of the silver nanoparticles in solution, with HbA causing larger formations. Again, they found that the presence of the glucose moiety on the HbA1c was the cause of the different aggregation patterns.