Biomedical diagnostic techniques and imaging based on photothermal thermophysics: Blood glucose biosensor and early dental enamel caries imager

A. Mandelis1, X. Guo1 and N. Tabatabaei1

1University of Toronto, Canada

Keywords: photothermal thermophysics, instrumentation and measurements
property: biosensors
material: biomaterials

This talk will present an overview of the development of two biomedical photoacoustic and photothermal (thermophotonic) instrumentation and analytical techniques introduced in the CADIFT.

 1. Wavelength-modulated differential laser photothermal radiometry (WMPTR) for non-invasive blood glucose measurements. The WM-DPTR method consists of the out-of-phase modulated excitation at two discrete wavelengths, 9.5 mm and 10.4 mm (near the peak and the baseline, respectively, of a mid-IR glucose absorption band), generated from a dual quantum cascade laser system and detected through differential absorption and blackbody (thermophotonic) emissions using a HgCdZnTe detector. The differential method suppresses the strong background water absorption and reduces source-detector interference, thus enhancing glucose detection sensitivity by ~ 2 orders of magnitude over conventional FTIR spectroscopy.  Results from aqueous glucose phantoms in the human blood concentration range (0 – 300 mg/dl) demonstrate that WM-DPTR comprises the most sensitive non-invasive glucose biosensor to-date, capable of  monitoring changes in glucose concentration across the hypo-glycemic, normal and hyper-glycemic ranges.   

 2. Thermophotonic lock-in and radar imaging of early carious lesions in dental enamel. Using photothermal wave principles, two novel dental imaging modalities, thermophotonic lock-in imaging (TPLI) and thermophotonic radar imaging (TPRI), have been developed. They both use a mid-IR camera and distinct image modulation waveforms. In-vitro dental samples with natural and artificially-generated demineralization caries were examined and the results were validated with the destructive “gold standard” transverse microradiography density profiles. TPLI images provide thermal-diffusion-length-integrated information from subsurface enamel regions, whereas TPRI images are depth-resolved. Phase images are emissivity normalized and therefore insensitive to the presence of enamel stain. Amplitude images provide information from deeper enamel regions. These non-invasive, non-ionizing imaging methodologies exhibit significantly higher sensitivity to very early demineralization than dental radiographs and are serious contenders for supplementing or replacing the ubiquitous radiographs in Dentistry.

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