Abstract
No reliable non-invasive glucose monitoring devices are currently available. We implemented a mid-infrared (MIR) photoacoustic (PA) setup to track glucose in vitro in deep epidermal layers, which represents a significant step towards non-invasive in vivo glucose measurements using MIR light. An external-cavity quantum-cascade laser (1010–1095 cm−1) and a PA cell of only 78 mm3 volume were employed to monitor glucose in epidermal skin. Skin samples are characterized by a high water content. Such samples investigated with an open-ended PA cell lead to varying conditions in the PA chamber (i.e., change of light absorption or relative humidity) and cause unstable signals. To circumvent variations in relative humidity and possible water condensation, the PA chamber was constantly ventilated by a 10 sccm N2 flow. By bringing the epidermal skin samples in contact with aqueous glucose solutions with different concentrations (i.e., 0.1–10 g/dl), the glucose concentration in the skin sample was varied through passive diffusion. The achieved detection limit for glucose in epidermal skin is 100 mg/dl (SNR=1). Although this lies within the human physiological range (30–500 mg/dl) further improvements are necessary to non-invasively monitor glucose levels of diabetes patients. Furthermore spectra of epidermal tissue with and without glucose content have been recorded with the tunable quantum-cascade laser, indicating that epidermal constituents do not impair glucose detection.
Highlights
Diabetes mellitus is a widespread human disease with worldwide 346 million persons concerned and an estimated 3.4 million deaths due to high blood glucose level per year [1]
The therapy of diabetes mellitus so far consists in monitoring the blood glucose (BG) level of a patient to avoid the danger of hypo- and hyperglycemia and to assist in adjusting the diet and medical treatment
If biological samples with a high water content are investigated with an open-ended PA cell the evaporation of water causes a steady increase in relative humidity (RH) until saturation is reached
Summary
Diabetes mellitus is a widespread human disease with worldwide 346 million persons concerned and an estimated 3.4 million deaths due to high blood glucose level per year [1]. To monitor the blood sugar level as accurate as possible frequent measurements are required. The blood sample is placed on a test strip and usually analyzed via an electrochemical reaction This expensive procedure is uncomfortable especially if frequently performed, it bears the risk of infections and does not represent a continuous measurement technique, which would be ideal for glycemic control [2]. Glucose absorption in this wavelength region is weak and interferes strongly with other blood and tissue components [23,24,25], which hampered a breakthrough to non-invasive glucose monitoring. Metabolites and proteins diffuse into the ISF on their way from capillaries to cells This leads to a strong correlation of BG levels and ISF glucose concentration within the physiological range as confirmed in clinical trails [32].
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