A cheap holographic microscope capable of detecting E. coli and other bacteria has been developed by researchers in the US.
The handheld device uses a laser instead of lenses to identify bugs in water, food or blood, and costs less than $100 (£60) to build.
Images can be uploaded to remote computers for further analysis.
Scientists hope the technology will improve healthcare in areas that lack sophisticated diagnostic equipment.
Details of the microscope - created at the University of California, Los Angeles (UCLA) - were published in the journal Biomedical Optics Express.
The device has two modes of operation: a "transmission" mode which can analyse liquids such as blood and water, and a "reflection" mode which produces holographic images of denser surfaces.
"Transmission mode is great for looking at optically transparent things like cells or very thin slices," explained Dr Karl Ryder of Leicester University's Advanced Microscopy Centre.
"However, if you want to look at more solid surfaces, you can't use transmission mode, because the light wouldn't get through."
In reflection mode, the microscope used holography to create a 3D image of the sample being studied.
"You take a laser and you split the beam in two using a mirror. Then you use one of these beams to illuminate your sample," said Dr Ryder.
"You can then recombine these two beams using clever mathematics to build a 3D image of your object."
A key advantage of the design is that it employs cheap electrical components instead of heavy and expensive lenses.
"There are no optics at all in this system. They've made it really small, and they're looking at small sample sizes, so you don't need complex focusing," said Dr Ryder.
Instead, the microscope uses digital photo sensors commonly found in devices like iPhones and Blackberrys. These can cost less than $15 each to produce.
Despite its price, researchers claim that the microscope can help to monitor outbreaks of difficult-to-detect bacteria such as E. coli.
"It's a very challenging task to detect E. coli in low concentrations in water and food. This microscope could be part of a solution for field investigation," said Prof Aydogan Ozcan from UCLA.
The device captures raw data, but its simple design means that processing needs to be done on an external device with more computing power.
A user in the field can forward the image data to their mobile phone, a laptop PC, or even upload it to an internet server.
Prof Ozcan believes the microscope could prove invaluable for medics working in developing countries.
"With just a small amount of training, doctors could use devices like these to improve healthcare in remote areas of the world with little access to diagnostic equipment."