Medical And Non-Medical Area Spectroscopic Glucose Measurement With Infrared Spectroscopy

Related Vendors

FAULHABER Drive Systems

Wuxi InfiMotion Technology Co., Ltd.

Shortwave infrared spectroscopy (SWIR) offers a promising approach for quantitative glucose measurement in biological fluids and tissues. The greater molecular specificity, greater penetration depth and stronger absorption properties of SWIR lead to higher analytical accuracy. But there are limitations.

Insulin-dependent diabetes is a major global health threat, affecting over 537 million adults worldwide, with this number expected to rise significantly by 2045. Non-invasive glucose monitoring is essential for diabetes management, but traditional methods such as finger prick blood tests are uncomfortable for the patient and pose a risk of infection.

These limitations have led to an increasing interest in optical spectroscopic glucose measurement, in particular shortwave infrared spectroscopy (SWIR), which offers a promising approach for quantitative glucose measurement in biological fluids and tissues. SWIR spectroscopy operates in the spectral range of 700-2500 nm, where glucose exhibits strong harmonic absorption bands, enabling quantitative detection in complex biological environments.

Compared to near-infrared spectroscopy (NIR), which has already been extensively researched for glucose measurement, SWIR offers greater molecular specificity, greater penetration depth and stronger absorption properties, resulting in higher analytical accuracy.

Relevance Also in the Non-Medical Sector

In addition to biomedical applications, glucose quantification is also relevant in non-medical areas such as food science, biotechnology and industrial monitoring. Glucose is an important component of food. Its measurement is essential for the evaluation of the glycemic index, food quality control, fermentation monitoring and industrial bioprocessing. At a wavelength of 1050 nm, the biological penetration depth of SWIR reaches its peak.

The spectral sensitivity of human skin is characterized by peaks and troughs. The reflectivity of human skin is relatively high at a wavelength of 1050 nm at approx. 50 to 60 % and relatively low at a wavelength of 1450 nm at approx. 5 to 10 %.

Optical spectroscopic glucose measurement with short-wave infrared spectroscopy (SWIR) attempts to determine the glucose content in blood non-invasively from the interaction of light with tissue. The basic idea is that molecules absorb light at specific wavelengths and that glucose has characteristic vibrational bands in the SWIR range.SWIR utilizes overtones and combination bands of the fundamental molecular vibrations that are unique to glucose. The detector measures the spectral intensity after the passage or reflection through the tissue and attempts to extract the glucose component from it.

Typical SWIR systems consist of a light source. This can be a laser or broadband SWIR LEDs. The measurement method can be transmissive, e.g. on the earlobe, or reflective on the finger, arm or palm. Detection is carried out using InGaAs sensors, spectrometers or, in the case of inexpensive systems, photodiode arrays.

Glucose is difficult to measure because the glucose absorption band is very weak and is often overlaid by water, lipids, proteins and collagen. In addition, the measurement is strongly influenced by factors such as skin thickness, blood flow, hydration, temperature, scattering and melanin. Therefore, statistical models and calibration via machine learning are needed. Calibration is required individually per person, which is the most common reason for the failure of commercial devices. It drifts over time due to skin changes, hydration and age.

Theoretically, SWIR is the most promising of all optical methods, but in practice there are still errors that are too high for medical approval. Good laboratory set-ups can cope much better, but are usually not suitable for everyday use. The basic problem is that glucose is a weak absorber and tissue is a highly complex scattering medium.

Nevertheless, research continues as SWIR offers many advantages. It has higher glucose-specific absorption bands than NIR and less interference from melanin. In addition, InGaAs sensors are becoming cheaper and AI-based unmixing of multidimensional spectra is improving.

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