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As per the post by giftiger_wunsch above there are two main methods (I used to work for a diagnostic company that designed and built them!).
You either put your sample onto a test strip (which contains chemical reagents), these change color depending on the level of glucose. You then either read the reflected or absorbed light at a given wavelength, and then calculate the glucose result. Alternatively you have a specially designed 'glucose cell' (containing such things as membranes, electrodes etc) and then you measure the voltage or current change produced in the measurement cell.
With either method you also need calibration solutions containing known levels of glucose to compare your result against. Commonly this calibration of performed on a batch (for strips) or daily for cell measurement devices. The calibration data being stored until either a new batch or cell is used.
Using the first method detection using something such as a photo-diode is relatively simple. Using the cell method is more difficult and depends of the dynamics of the cell and would require more signal processing to detect such things as peaks and plateaus.
If you have any more questions then please come back to me.
This is actually quite an interesting topic; I'm a biochemistry student so I'd be interested in finding out which 'chemical reagents' are used. There are simple chemical tests for glucose but I wonder if an ELISA (Enzyme-Linked Immunosorbent Assay) is a better option.
This is actually quite an interesting topic; I'm a biochemistry student so I'd be interested in finding out which 'chemical reagents' are used. There are simple chemical tests for glucose but I wonder if an ELISA (Enzyme-Linked Immunosorbent Assay) is a better option.
ELISA would not be better. Check out the Wikipedia article on glucometers. It gives the details you want. You also want to look up glycosylated hemoglobin (HgA1c).
I was also involved in the development and production of ELISA tests and microplate readers!
Some of the chemistry for the strip tests is in your previous post - it relies on the oxidation of glucose, which produces hydrogen peroxide. You can then use the peroxide to oxidize a suitable dye reagent, thus causing a color change. The produced color is then assessed photometrically.
I guess that you could produce an ELISA (I don't know of one) on the assumption that you could produce a suitable antibody to glucose and then successfully conjugate it to a suitable enzyme such as HRP. We then used to use Phenolphthalein Monophosphate as a color reagent. Of course if you got a suitable antibody then the world is open to any technique you like such as FIA or RIA.
The cell idea uses less reagents (or they are 'bound' into the cell) and produce a small amperometric changes depending on glucose concentration. As I said previously you have be be better at doing DSP than using other methods.
There are alot of patents on the subject so I suggest you have a look in the Uni. library for more information if you are interested.
Of course if you want to build an analyser or plate reader then let me know!
I guess that you could produce an ELISA (I don't know of one) on the assumption that you could produce a suitable antibody to glucose and then successfully conjugate it to a suitable enzyme such as HRP. We then used to use Phenolphthalein Monophosphate as a color reagent. Of course if you got a suitable antibody then the world is open to any technique you like such as FIA or RIA.
Indeed I haven't heard of an ELISA for glucose but a vast number of antibodies have been isolated or developed, I'm sure there's one for glucose somewhere. But the only real reason for using an ELISA over other methods would be specificity to avoid false positives, or to produce a more linear relationship between glucose conc. and the absorption of a specific wavelength on the EM spectrum once combined with a reagent. If an ELISA doesn't improve these factors then it's unnecessarily complicating the test.
@giftiger wunsch
My previous response was perhaps to short. So, to elaborate, the major problems in glucose monitoring are not the methodology for measuring glucose in a sample of plasma or blood. The methods we have are low cost, quick, precise, accurate, easily automated, and reasonably immune from interference. They have been in use for so long that most interferences with the principal methods are assumed to be known (obviously unprovable).
The main problems in management of patients are specimen collection and compliance. For the latter, hemoglobin A1c is most common today. There are some very interesting studies on compliance that show patients with diabetes, particularly those with Type I, play games with the glucose results and their insulin doses. It is a complex subject involving psychology, biochemistry, immunology, and genetics and well is beyond the scope here. Remember, diabetes in clinical practice is not simply "not enough insulin."
As for specimen collection, that is an area of great research activity. Everyone wants a less painful or non-invasive procedure for monitoring, and those will likely happen. There has been a lot of publicity about using the forearm for samples. That has simply not proved to be the best option for all patients. Methods using sweat and saliva continue to be worked on, and I believe a modified sweat method has been approved in the US by the FDA. Something similar to a pulse oximeter but for glucose is probably not too far distant, at least there is hope for it.
Thanks for the detailed explanation jpanhalt, that was what I had guessed would be the case; while an ELISA would be possible, it's unnecessary and is more complicated that it needs to be given the factors involved in the Hb A1c method that you mentioned.
I've had lectures on diabetes but they were mainly from a metabolic point of view, so this is certainly interesting. Anyway as you said it's also beyond the scope of these forums or this thread so I'll satisfy my curiosity through independent research. Thanks for sharing your knowledge on the subject though.
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