Today, my post is about a well known technique over many years with a very large potential for the measurement of blood sugar completely outside of the body – the spectroscopy. I’m waiting a long time for a blood glucose meter that works in this way. Spectroscopy is an infinitely wide field and there are really many approaches to the measurement of blood sugar. I once summarized the most important ways of spectroscopy. I even found a circuit and some devices, that might be soon available. I’m thrilled. Finally I tried to explain how these devices might work.
It is important to me that blood sugar measuring is as simple as possible. So that I can measure in any situation for example while running. The previous test strips are quite impractical.
The story in terms of spectroscopy
In the last decade there have been several approaches to build glucometers that work spectroscopically and don’t hurt the skin. In 2003 a Swiss, Dutch manufacturer build a blood sugar measuring watch named Pendra (1). It had initially a CE Declaration of Conformity, but seemed to have accuracy deficits. So there was no watch that measured the blood glucose with the spectroscopy. Ten years later a company called MediSensors brought a sensor, the C8, on the market. A real launch never happend.
(1) Two links to Pendra watch:
What is Spectroscopy at all
The operation of spectroscopy is easily explained. Mostly, the skin is irradiated with light. The light penetrates more or less into the skin and the result is then analyzed with the hope to find something that changes with the blood sugar level. There are endless possibilities and variations of spectroscopy in the science described, rather theoretical. But mostly these methods fail practical.
The light sources are usually laser diodes. These devices are small and conveniently available – similar to those found in a laser pointer. Light in the near and mid-infrared spectrum is being used for the spectroscopy. The near-infrared spectrum extends from the red light spectrum and is for us no longer visible. The mid-infrared light follows.
But there is also an increasingly work with a small alternating current or an electromagnetic wave. This kind of spectroscopy is not so popular yet. It is my favorite and is full of surprises.
The absorption spectroscopy
In this method, an earlobe or a finger is irradiated with a laser light. The light penetrates into the earlobe or finger and at the other end a sensor messures how much of the light has arrived. There already exists a device that is probably ready for the market (2). In Magdeburg is also built a similar device that uses a finger clip. Unfortunately I can’t find the link to it. Hopefully the work on this device is still going on. I find a finger or ear clip to measure the blood sugar somewhat impractical.
The function of this type of measurement:
The glucose in the blood absorbs the light when the light frequency matches the resonant frequency of the glucose. I think a device is designed in this way: The skin is irradiated with a light source whose light is constant distributed over a certain frequency range. On the other side it looks only for one frequency, the resonant frequency of glucose, and filters out the other frequencies. The less you find the frequency of glucose on the other end, the higher the glucose level in the blood. So you have a direct way to get the blood sugar levels.
(2) A link to the GlucoTrack blood glucose meter:
(12) And a possible circuit:
Near infrared spectroscopy, mid infrared spectroscopy, Raman spectroscopy
Then there are some infrared – methods that I would describe as a classic. They are quite complicated. In the mid-infrared spectroscopy the laser light does not penetrate far into the skin. It is rather scanned at the surface. The laser light lets the glucose molecule vibrate. This vibration is analyzed. A CCD sensor is located next to the laser diode that emits the light. The CCD sensor measures the returning radiation.
It is a problem that not only glucose starts to vibrate. Many other molecules such as Laktate and amino acids, and even water begin to vibrate too. Most molecules and water consist of the compounds oxygen and hydrogen or nitrogen and hydrogen, so that their vibrations are very close to the glucose molecule. A large computational effort is necessary to calculate the glucose from the measurement result.
In the near-infrared spectroscopy, the laser light penetrates deeper into the tissue. For a wide spectral range the tissue becomes quite transparent for the light.
There are still a lot of methods to analyze the light, for example by scattering. But these methods are all very complicated. Therefore there is also a trend towards simpler and very promising alternatives. The following two methods are studied extensively scientifically currently. I think the prospects are excellent that a device of this area will revolutionize the blood sugar measuring, and that makes me happy.
Photoacoustic spectroscopy is applied in many areas. But not yet for determining glucose. In Germany for instance were is intensive research going on in this area. A marketable product for measuring blood sugar seems not to be entered. But that could change in a few years. The range of the middle infrared spectrum is applied (3). But there are also numerous and promising approaches in the range of the near infrared spectrum (4).
Thermal expansion and elasticity of the molecules are used in this method. The tissue is shot from the outside with a light source, for example a laser diode. Especially modulated light pulses are emitted. The pulses are selected in a way that they bump into the glucose molecule. For this purpose also the pulse duration is important.
The glucose molecule absorbs the light pulses. The energie of the pulse is converted into temperature and the glucose molecule is heated thereby. By heating it expands. After the pulse has passed the glucose molecule cools down again and falls back into its primary size. This expansion and contraction generates an acustic wave. This acustic waves radiate out and can be dedected, for example with a microphone or a piezoelectric pressure sensor. The more glucose molecules are present, the louder is the acustic wave, that is generated by more glucose molecules. The acoustic wave can be used to measure of blood sugar.
Impedance spectroscopy or dielectric spectroscopy
If a current is put on on a resistor, the current through the resistor changes itself depending on, whether the resistance is large or not. The resistance is measured by the current. The impedance spectroscopy now uses alternating current. The alternating resistance – called impedance – is measured. The impedance can be quite complex. The dielectric is a material property, which is responsible for the impedance of the tissue. It is now measured the impedance of the tissue with an alternating current. There are several different options for the current frequency, that are documented. The range of some MHz to 200 MHz is very popular.
Not the capillary blood glucose is measured only the glucose concentration in the tissue. This requires a certain time to get the capillary blood sugar similarly to sensors such as in the CGMS. Finally the measured results can be inaccurate or unusable, for example by sweating. The measurement method is temperature sensitive.
The construction is possible with a few stand type semiconductor devices and is extremely cheap. Of course I’ve been experimenting and just going to. A few seconds I had the feeling it works, but I not got down so far something really smart. Otherwise I would have posted my results. I found a circuit description (7) which I added to the links.
(7) For technology freaks. The circuit description for the determination of glucose via impedance measurement
(8) Weitere Infos
The GlucoWise blood glucose meter
The GlucoWise blood glucose meter (9) is also based on the method of the dielectric glucose determination. It has a special feature. It operates at a frequency which is extremely high. This seems to bring immense benefits. The frequency is 65 GHz, making it about 30 times higher than that of a mobile phone.
With such a high frequency the current for measuring the impedance becomes an electromagnetic wave that is running through so called waveguide. In (10) you can see how a waveguide in the laboratory looks like. There is no clasical resistance, but the degree of how far the wave can propagate in the glucose is measured. The wave propagation dependents on the glucose in the blood (reflection of the wave). The device does not measure the glucose in the tissue, but the capillary blood glucose. There exists no delay of the measured blood sugar values. I suspect that the propagation of the electromagnetic wave continues in the blood vessel of the hand. The blood vessel become a waveguide for the electromagnetic wave and the wave propagates along the vessel. The wave propagation depends on the glucose in the vessel. The device seems to be in beta testing and will probably extensively tested clinically and is my absolute personal favorite.
(9) Homepage GlucoWise:
(11) For HF – Freaks: