Scientists at more than a hundred labs around the world will be gearing up this week for a competition to build the best machine. There is only one condition. All the parts must come from living organisms.

To the scientists involved, the competition is an exercise in extreme, not to say minuscule, DIY. Instead of hinges and door knobs, they must use the microscopic components found inside biological cells. Instead of screwdrivers and hammer-drills, the tools of the trade are those of the genetic engineer.

The aim of the competition, now in its sixth year, is to take the basic building blocks of life and turn them into useful technology. Along the way, scientists hope to create the biological equivalent of a hardware store, in which strands of DNA and cellular machinery will line the shelves, ready to be pieced together by anyone with the know-how.

"Our mission has been to see if we can use biological parts to build things and operate them. A lot of people said it's too complex and can't be done, but every year we have systems that show it can work," said Meagan Lizarazo, a former biologist and assistant director of the International Genetically Engineered Machine competition at the Massachusetts Institute of Technology in Boston.

This week, the last of the teams, most of whom are students, will register for the competition. From June, they will spend three months building their machines from components ordered from MIT's registry, which already contains around 3,200 biological spare parts. The parts are refered to as "biobricks", which explains why the trophy for first prize, to be awarded in the first week of November, is a metal lego brick the size of a shoebox. Any new parts the scientists use must be deposited in the public registry when the competition is over.

By pitting the world's best up-and-coming scientists against one another, the competition's organisers aim to accelerate progress in what has become a powerful and controversial field known as synthetic biology. One leading advocate of the technology is the American scientist and entrepreneur Craig Venter, who hopes not only to make bugs that produce hydrogen for environmentally friendly vehicles, but to create new life from scratch.

Critics of the field raise concerns that scientists could make dangerous new organisms by accident, or that the knowledge could fall into the hands of terrorists, who could resurrect long-contained viruses, or fashion more deadly strains.

The competition has already produced some promising ideas. Last year, a team led by Roland Eils at the University of Heidelberg in Germany, re-engineered Escherichia coli bacteria so that instead of swimming towards food, they homed in on substances released by dangerous pathogens. When they get close, the bacteria turn themselves into microscopic suicide bombers by churning out a natural toxin, killing both themselves and the pathogens around them. The team's entry was called "E.colicense to kill."

Since then, the team has created E. coli that hunt down cancer cells, and have used them to destroy tumours in mice. This year, Eils says the team is considering building a machine out of parts taken from human cells for the first time.

A previous entry from scientists at Edinburgh University involved bacteria that could detect arsenic in contaminated water supplies. In a freeze-dried form, the bacteria can be used in water testing kits for use in Bangladesh, where arsenic in water from bore holes has killed countless people.

The competition began in 2004 with only five entrants. A year later, it went international and attracted 13 teams. This year, more than 100 teams from all over the world have already signed up. The teams come from all over the world, with entrants from Mumbai and Beijing, Tokyo and Melbourne, Stanford and Sheffield.

Paul Freemont, who co-founded the Institute of Systems and Synthetic Biology at Imperial College London, is heading one of Britain's best hopes this year, but confesses his team has yet to decide what to build. One of the ideas would involve using vats of bacteria to make clothing. They have already shown that they can control the movement of bacteria by switching the motors that drive their whip-like tails on and off at will.

"Our team is due to meet in a few weeks' time and they will start with a blank sheet of paper," said Freemont. "They've got to brainstorm from scratch, and that makes it a really interesting way of doing research."