09-01-2014, 12:28 PM
Non-invasive Glucose Sensor
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Introduction
Blood glucose monitoring is a way of testing the concentration of glucose in blood.
Particularly important in the care of diabetes mellitus, a blood glucose test is performed by piercing the skin (typically, on the finger) to draw blood, then applying the blood to a chemically active disposable 'test-strip‘.
Blood glucose monitoring reveals individual patterns of blood glucose changes, and helps in the planning of meals, activities, and at what time of day to take medications.
Blood glucose monitoring reveals individual patterns of blood glucose changes, and helps in the planning of meals, activities, and at what time of day to take medications.
Also, testing allows for quick response to high blood sugar (hyperglycemia) or low blood sugar (hypoglycemia). This might include diet adjustments, exercise, and insulin (as instructed by the health care provider).
Blood Glucose Meters
A blood glucose meter is an electronic device for measuring the blood glucose level.
A relatively small drop of blood is placed on a disposable test strip which interfaces with a digital meter.
Within several seconds, the level of blood glucose will be shown on the digital display.
Needing only a small drop of blood for the meter means that the time and effort required for testing is reduced and the compliance of diabetic people to their testing regimens is improved.
‘Alternate site testing', the use of blood drops from places other than the finger, usually the palm or forearm. This testing uses the same test strips and meter, is pain free, and gives the real estate on the finger tips a needed break if they become sore. The disadvantage is that there is usually less blood flow to alternate sites, which prevents the reading from being accurate when the blood sugar level is changing.
Continuous Glucose Monitoring
A continuous glucose monitor (CGM) determines glucose levels on a continuous basis (every few minutes). A typical system consists of:
a disposable glucose sensor placed just under the skin, which is worn for a few days until replacement
a link from the sensor to a non-implanted transmitter which communicates to a radio receiver
an electronic receiver worn like a pager (or insulin pump) that displays glucose levels with nearly continuous updates, as well as monitors rising and falling trends.
1. Reverse Iontophoresis
The principle is based on the method of iontophoresis, where two electrodes are placed on the skin.
In the solution is (NaCl) in the form of ions. The sodium ion is positively charged and the chlorine ion is negative.
When a voltage is applied, the sodium ion migrates with the blood sugar to the negative electrode.
It then provides 12 hours of a blood sugar every 20 minutes.
2. Impedance Spectroscopy
Impedance spectroscopy has been proposed as possible approach for non-invasive glycaemia monitoring.
There is a relation between the dielectric parameters and the sensor impedance embedded in blood medium.
This sensor allows the detection of the blood glucose level through the variation of the sensor impedance that depends on the dielectric parameters of blood, in particular the conductivity.
3. Optical Spectroscopy
The difference between the colour of the different hemoglobin components like oxyhemoglobin, reduced hemoglobin, carboxyhemoglobin and methemoglobin is obvious.
Blood sugar shows very low light absorption in visible and NIR, so that it cannot be distinguished from water using absorption spectroscopy.
Glucose in water shows no fluorescence.
4. Elastic (Diffuse) Scattering
Elastic scattering due to Rayleigh and Mie scattering is dependent on glucose concentrations in blood.
Scatter measurement monitors the changes in tissue reduced scattering coefficient and is used for the determination of glucose.
Increased glucose in the sample is proportional to an increase in the refractive index of the sample and thus the particle scattering properties of the sample are changed.
Conclusion
Optical methods are valuable and promising for the non-invasive detection of blood glucose.
Raman scattering can have a very high sensitivity and resolution, but the development of an in-vivo simple device till now, seems to be very difficult.
IR-spectroscopy is promising for the development of an easy cost effective sensor for home monitoring.
Tiny perturbations such as temperature, humidity and applied pressure variations can adulterate the measurements.