he test strip, a piece of plastic about an inch and a half long and familiar to virtually anyone with
diabetes, is actually plastic surrounding a strip of paper, coated with a soap-like chemical. This
chemical helps the liquid (the blood) quickly saturate the paper inside of the strip, where there
are organic chemicals that react with it, and give the glucose reading.
When the blood comes into contact with these organic chemicals they act as catalysts to the glucose molecules within the blood. Each individual glucose molecule will go through a number of steps
to reach the final result.
A glucose molecule will first react with an enzyme called Glucose Oxidase, or GOx. This is a huge
molecule, about 160,000 Da in molecular weight. However, the most important part of GOx in this
reaction is a structure called Flavin, also found in Vitamin B2. In the reaction, flavin is labeled ‘F’. The
first reaction between the glucose molecule, C6H12O6, and FAD, is shown below:
T
C6H12O6 + H2O + F ----->C6H12O7 + reduced F (FH2)
This reaction simply makes the F reduced, meaning two hydrogen atoms are added to the flavin,
and an oxygen atom is added to the glucose to make it gluconic acid.
Next, for a substance to act as a catalyst, it must only be temporarily changed. This means something must happen to change the reduced FAD back to oxidized F. AgaMatrix calls the next catalyst
a mediator. The mediator’s equation is not shown because it is frankly too large and unnecessary to
put into the equation. Mediators that are used often vary; they include ferrocene derivatives, ferricyanide, conducting organic salts, phenothiazine/phenoxazine compounds, and quinone compounds.
The first and second reactions are shown below:
C6H12O6 + H2O + F ----->C6H12O7 + reduced F (FH2)
Reduced F (FH2) + 2Oxidized Mediator ---->F + 2Reduced Mediator + 2H+
After these two reactions happen, the reduced F is returned to oxidized F, and on paper, you can
cancel the F out of the equations. The third and final reaction returns the mediator catalyst back to its
oxidized state.
After the second reaction, each mediator carries two electrons to what is called the electrode. The
electrode is a line of carbon that conducts these electrons (remember electrons are electricity) through
the strip and into the meter, where it is measured. The first, second, and last equations look like this:
C6H12O6 + H2O + F ----->C6H12O7 + reduced F (FH2)
Reduced F (FH2) + 2Oxidized Mediator ---->F + 2Reduced Mediator + 2H+
2Reduced Mediator----->2Oxidized Mediator + 2eFrom these three steps, you can derive a basic equation to describe what happens when the blood
goes into the strip. The glucose molecule reacts with catalysts that remove two electrons that are carried to the electrode, then into the meter to be measured (concise equation shown below). This is
where software engineers come in handy at AgaMatrix, and also where ham radio operators’ interest
should be piqued. The bridge from chemistry to electronics is made at the end of the strip, where the
electrons that are collected are carried to the electrode by the mediator, then measured to determine
the concentration of glucose in the blood.
C6H12O6 + H2O ----->C6H12O7 + 2H+ + 2e-
kids’ korner
In her "Kids' Korner" column this month, CQ Youth Editor Brittany Decker, KB1OGL, describes her
visit to a commercial chemistry lab as part of a school assignment and how the enthusiasm of her
host for the day, along with his explanations of all the chemistry involved in how the company's
products work, led her to see parallels with the value of similar enthusiasm in teaching about
amateur radio.
Brittany was so enthused herself by her visit to AgaMatrix, a company that tests and modifies diabetic test strips for blood glucose levels, that she couldn't resist sharing with CQ readers the chemical and electronic processes that go on "under the hood" on a test strip.
BY BRITTANY DECKER,* KB1OGL
Modern-Day Alchemy: Turning
Chemistry into Electronics
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At the AgaMatrix lab, a glucose test meter, test strips and an iPhone with a special module that lets it act as a meter. The small bottle contains a glucose solution of known concentration for testing meters' accuracy (the blue dots on the test
strips inserted in the meters are the glucose solution).
Now, knowing that two electrons are derived from each glucose molecule in the
blood, you can predict the reading by doing some simple equations. For example,
if the meter reads 100mg/L of glucose, you can find the number of glucose molecules in the blood and the number of electrons in the blood.
First, find the molarity (concentration) of the reading by converting mg/dL to
mmol/L (Shown below):
100mg 10dl
1g
1dl
1L 1000mg
1mol
1 000mmol = 5.55 mmol/L
180.15588gC6H12O6
1mol
Then, convert millimoles to molecules by using Avogadro’s Number,
6.022 x 1023:
Find how many mmol are in a molecule:
1mol 6.022 x 1023 molecules = 0.006022 x 1023 molec/mmol
1000mmol
1mol
5.55mmol
1L
.006022 x 1023 molecules = .0334 x 1023 molecules/L
1mmol
or 3.34 x 1021 molecules/L
Knowing that there are two electrons for every glucose molecule, we simply multiply by 2 to get the number of electrons in the blood drop:
3.34 x 1021 molecules x 2= 6.68 x 1021 electrons/L
While working out the math and conversions, Richard Williams - my host and
the company's head of scientific development - saw the way I did my math (fraction bars to keep my units straight) and was very surprised that a high school student could make those conversions so quickly and accurately. He had never seen
that method before, and said he’d have to keep it in mind for his own use.
Now you know how a chemical reaction generates a flow of electrons (also
known as an electric current) that allows the glucose meter to measure the concentration of glucose in the patient's blood. If you haven't read the rest of Brittany's
column, get a copy of CQ and read it! If you have, start thinking about how you
can pass along your knowledge and enthusiasm for amateur radio to the next
generation of hams.
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