Blood Glucose Test By Spectrophotometer

[Hadi Sapre]

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We describe further development of a novel method for non-invasive measurement of blood glucose concentration (BGL), named Pulse Glucometry, based on differential near infrared spectrophotometry. Sequential temporal differences of infrared transmittance spectra from the radiation intensity (I(lambda)) emerging from a fingertip containing an arterial pulse component (DeltaI(lambda)) are analysed. To perform the measurements we developed a new high-speed spectrophotometer, covering the wavelength range from 900 to 1700 nm, scanning at a maximum spectral rate of 1800 spectra/s, with a minimum exposure time of 20 micros. Spectra related only to the pulsatile blood component are derived, thus minimising influences of basal components such as resting blood volume, skin, muscle and bone. We have now improved the performance of the spectrophotometer and in the present paper we describe new in vivo measurements carried out in 23 healthy volunteers undergoing glucose tolerance tests. Blood samples were collected from the cephalic vein simultaneously with radiation intensity measurements in the fingertip every 10 min before and after oral administration of glucose solution for 120 min. BGL values were then predicted using a PLS calibration model and compared with blood values determined by colorimetric assay. The precision and accuracy of the non-invasive determinations are encouraging.

Loss of consciousness, seizures and even death can occur if the blood glucose level is very low. The complications that can occur as a result of very high blood glucose level include infections, kidney damage and cardiovascular disease4.

Standard glucose monitoring procedures involve collecting a drop of blood by stabbing the finger using a needle, or invasively. This process not only causes pain to the patient, but is also expensive due to a new test strip being needed for each measurement. Moreover, these measurements have to be carried out on patients several times a day5.

Since standard glucose monitoring procedures are both painful and costly, extensive efforts have been taken to develop non-invasive (and pain-free) methods that do not require the finger to be pricked. Ideally, these methods should also not require consumable items. This would be more convenient for diabetics and would reduce costs for treatment providers.

Although non-invasive techniques have been studied for several decades, no true solution has been reached so far, and as a result, conventional, and invasive, blood glucose level monitoring methods remain the standard6.

The past few years have seen the development of several non-invasive methods, including transdermal techniques such as reverse iontophoresis and skin impedance spectroscopy, and optical methods like optical coherence tomography and Raman spectroscopy.

However, to design a laser with a high tuning speed, one has to compromise in other areas. For sensitive (high signal-to-noise ratio) detection of glucose molecules, the quality of the light from the laser must not be compromised for the tuning speed. The laser should possess high beam quality and high spectral repeatability (low variability in wavelength and spectral content of the laser output) to enable highly consistent and accurate measurements.

According to the authors, since the measurements performed in this study were representative of the level of blood glucose, their method of using mid-IR photoacoustic spectroscopy holds potential for monitoring the levels of blood glucose in diabetics conveniently, without causing any pain to the patient5. Hence, it can be concluded that this technique represents a highly potential non-invasive glucose monitoring method.

For the first time, fast and broad tuning, Continuous Wave (CW) or pulsed output, high spectral repeatability, high power and power stability, and high beam quality are available from a compact, robust mid-IR laser.

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This application note describes how to determine the glucose content in wine using a sample and reagent kit along with a UV/VIS Excellence Spectrophotometer. To find out more, please proceed to download the application note below.

Glucose measurement is an important part of the wine production process as the amount of sugar in wine is indicative of the final alcohol content. Glucose, one of the primary sugars found in wine grapes, is a six-carbon sugar molecule derived from the breakdown of sucrose. These sugars are broken down during the fermentation process to form ethanol and carbon dioxide.

In this experiment, a kit for the quantitative, enzymatic determination of glucose in wine and other materials is used in conjunction with the UV7 Excellence Spectrophotometer from METTLER TOLEDO. A spectrophotometer is a popular glucose measurement device due to its speed and ease of use. The absorbance of standard and sample solutions are both measured at 340nm. The difference in absorbance is directly proportional to the concentration of glucose in wine.

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Non-invasive blood glucose sensing can be achieved using mid-infrared spectroscopy, although no practical device based on this method has yet been developed. Here, we propose mid-infrared passive spectroscopic imaging for glucose measurements from a distance. Spectroscopic imaging of thermal radiation from the human body enabled, for the first time in the world, the detection of glucose-induced luminescence from a distance. In addition, glucose emission spectra of the wrist acquired at regular intervals up to 60 min showed that there was a strong correlation between the glucose emission intensity and blood glucose level measured using an invasive sensor. Thus, the new technology proposed here is expected to be applied to real-time monitoring of diabetic patients to detect hypoglycemic attacks during sleep and to detect hyperglycemia in a population. Moreover, this technology could lead to innovations that would make it possible to remotely measure a variety of substances.

With lifestyle changes, the number of people diagnosed with diabetes continues to increase, becoming a major problem worldwide1. Furthermore, in pre-diabetic subjects with metabolic syndrome and obesity, postprandial hyperglycemia is associated with increased cardiovascular events2. Therefore, real-time monitoring of glucose levels is highly desirable, but despite advancements made globally, a non-invasive technique has not yet been developed3.

Glucose sensors have been developed using a variety of approaches. For example, low-frequency reverse iontophoresis has been exploited to develop very thin devices attached to the skin, which must be worn throughout the day, to monitor glucose levels. The GlucoWatch Biographer, a device based on this method, was approved by the US Food and Drug Administration (FDA), but was discontinued in 2008 owing to problems with long warm-up time, skin irritation, and sweating. Since then, no device based on this method has appeared on the market4,5,6,7. Microwave-based glucose sensors are cost-effective and can be miniaturized. Importantly, they have excellent penetration depth, especially in the low frequency range. Skin reflection, transmission, and absorption are closely related to the dielectric properties or permittivity of the skin, which can be correlated with glucose variations. However, the dielectric constant is strongly affected by other blood components. Therefore, this method provides an indirect correlation between the dielectric constant and blood component changes and cannot directly detect changes in glucose8,9. There are numerous studies using near-infrared spectroscopy for biological measurements. However, methods using near-infrared spectroscopy generally require multivariate analyses to extract information about glucose from the overall spectrum. Therefore, an effective method with sufficient accuracy has not yet been established3. Other technologies have been widely investigated in recent years, although the resulting devices have yet to meet the requirements for practical applications. For example, devices with improved biocompatibility have been developed using 3D printing10, magnetohydrodynamics has been exploited to enhance the sensitivity of glucose detection11, and analyses have been improved by implementing neural networks12. In contrast, mid-infrared spectroscopy operates in the wavelength band known as the fingerprint region of a substance to provide molecule-specific spectra. Attenuated total reflection13 (ATR), high-power quantum cascade lasers14, and ytterbium-doped YAG lasers15 have been proposed to measure glucose levels in living organisms using mid-infrared spectroscopy. However, owing to its measurement principle, ATR can only measure to a shallow depth of approximately 5 μm from the surface, and light reaches only the stratum corneum in normal skin16. Therefore, the measurement site is limited to the oral mucosa13. Our proposed mid-infrared passive spectroscopic imaging method uses the synchrotron radiation of the substance as a spectroscope to obtain information from greater measurement depths (approximately 1.2 mm). Therefore, we believe that it is possible to measure glucose from a depth corresponding to the dermal layer of normal skin using mid-infrared spectroscopy, which is excellent for component identification.

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