Optical coherence tomography for blood glucose monitoring in vitro through spatial and temporal approaches.

As diabetes causes millions of deaths worldwide every year, new methods for blood glucose monitoring are in demand. Noninvasive approaches may increase patient adherence to treatment while reducing costs, and optical coherence tomography (OCT) may be a feasible alternative to current invasive diagnostics. This study presents two methods for blood sugar monitoring with OCT in vitro. The first, based on spatial statistics, exploits changes in the light total attenuation coefficient caused by different concentrations of glucose in the sample using a 930-nm commercial OCT system. The second, based on temporal analysis, calculates differences in the decorrelation time of the speckle pattern in the OCT signal due to blood viscosity variations with the addition of glucose with data acquired by a custom built Swept Source 1325-nm OCT system. Samples consisted of heparinized mouse blood, phosphate buffer saline, and glucose. Additionally, further samples were prepared by diluting mouse blood with isotonic saline solution to verify the effect of higher multiple scattering components on the ability of the methods to differentiate glucose levels. Our results suggest a direct relationship between glucose concentration and both decorrelation rate and attenuation coefficient, with our systems being able to detect changes of 65 mg/dL in glucose concentration.

Color center production by femtosecond pulse laser irradiation in LiF crystals.

We report the production of color centers in LiF single crystals by ultrashort high intensity laser pulses (60fs, 10 GW). An intensity threshold for color centers creation of 2 TW/cm(2) was determined, which is slightly smaller than the continuum generation threshold. We could identify a large amount of F centers that gave rise to aggregates such as F(2), F(2) (+) and F(3) (+). The proposed mechanism of formation is based on multiphoton excitation that also produce short lived F(2) (+) centers. It is also shown that it is possible to write tracks in the LiF crystals with dimensional control.