Sabbir Liakat

Noninvasive in vivo glucose sensing on human subjects using mid-infrared light.

Mid-infrared quantum cascade laser spectroscopy is used to noninvasively predict blood glucose concentrations of three healthy human subjects in vivo. We utilize a hollow-core fiber based optical setup for light delivery and collection along with a broadly tunable quantum cascade laser to obtain spectra from human subjects and use standard chemo-metric techniques (namely partial least squares regression) for prediction analysis. Throughout a glucose concentration range of 80-160 mg/dL, we achieve clinically accurate predictions 84% of the time, on average. This work opens a new path to a noninvasive in vivo glucose sensor that would benefit the lives of hundreds of millions of diabetics worldwide.

In vivo measurement of mid-infrared light scattering from human skin

Two mid-infrared light sources, a broadband source from a Fourier Transform Infrared Spectrometer (FTIR) and a pulsed Quantum Cascade (QC) Laser, are used to measure angle-resolved backscattering in vivo from human skin across a broad spectral range. Scattering profiles measured using the FTIR suggest limited penetration of the light into the skin, with most of the light interacting with the stratum corneum layer of the epidermis. Scattering profiles from the QC laser show modulation patterns with angle suggesting interaction with scattering centers in the skin. The scattering is attributed to interaction of the laser light with components such as collagen fibers and capillaries in the dermis layer of the skin.

In vitro measurements of physiological glucose concentrations in biological fluids using mid-infrared light

Mid-infrared transmission spectroscopy using broadband mid-infrared or Quantum Cascade laser sources is used to predict glucose concentrations of aqueous and serum solutions containing physiologically relevant amounts of glucose (50-400 mg/dL). We employ partial least squares regression to generate a calibration model using a subset of the spectra taken and to predict concentrations from new spectra. Clinically accurate measurements with respect to a Clarke error grid were made for concentrations as low as 30 mg/dL, regardless of background solvent. These results are an important and encouraging step in the work towards developing a noninvasive in vivo glucose sensor in the mid-infrared.

Mid-infrared (λ = 8.4–9.9 μm) light scattering from porcine tissue

Back-scattering of mid-infrared light from porcine skin is studied versus wavelength and angle for a Quantum Cascade laser and a broadband infrared light source. Scattering is detected over 30° away from the specular angle for both sources, and modulation patterns with angle are seen when using the laser. A nonlinear increase in scattered light intensity versus input power indicates that directional scattering from within the skin is dominant. Collagen fibers in the dermis layer, over 200 μm deep into the skin, are conducive to such scattering. We conclude that mid-infrared light penetrates deep enough for potential glucose detection in dermal interstitial fluid.

Mid-infrared noninvasive in vivo glucose detection in healthy human subjects

A novel hollow-core fiber based mid-infrared noninvasive in vivo sensor, capable of clinically accurate predictions of glucose concentrations ranging from 80 - 160 mg/dL in healthy humans, is presented.

In vitro measurements of physiological glucose concentrations in biological fluids using mid-infrared spectroscopy

Predictions of glucose concentrations throughout the physiological range are obtained in vitro using partial least squares regression analysis of mid-infrared transmission spectra. Concentrations as low as 30 mg/dL are predicted to clinical accuracy.