The most common methods are those based on O2 uptake. Respirometric assays are affected by a number of parameters
including temperature, humidity and incubation and
The ultimate fuel
In three years a new type of battery may be available, using urine as an energy source.
The battery consists of a strip of filter paper containing cupric chloride. A cathode is sandwiched between a magnesium film (the anode) and a thin layer of copper. As soon as a drop of urine touches the magnesium, the capillary effect makes the urine, containing many atoms with electric charges, penetrate the filter paper. There it reacts with the cupric chloride which releases electrons.
The electrons pass into the copper and magnesium. The entire device is enclosed between two sheets of plastic and urine enters through a small hole.
The battery is half the size of a credit card (8x3 cm). Over the last month its power output has been increased to 10 mW. It can be connected to a biosensor to measure the blood or urine characteristics of a patient. There already many test kits on the market, but most need an external energy source such as a conventional battery.
The most powerful prototype produced a maximum current of 1.5V, comparable to an AA battery. It was able to supply 1 V for over two hours.
Lee says his invention is suitable for any application that uses small amounts of electricity, such as a small GSM phone. This is very convenient for raising the alarm in emergencies.
“I chose urine as an energy source because everyone produces plenty. It's the ultimate biofuel. But in emergencies other bodily secretions (blood, tears, saliva, and even sperm) are usable.”
(Milieu Direct, Belgium, www.kluwer.be/kluwer/home.asp?doelid=3)
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