Bioengineers develop ‘microscope on a chip’

July 29th, 2008 - 2:06 pm ICT by IANS  

Washington, July 29 (IANS) California Institute of Technology researchers have miniaturised microscope small enough to sit on a fingertip, but with the magnifying power of its high-resolution counterparts. The “microscopic microscope” operates without lenses and can be used for analysis of blood samples for malaria or to check water supplies for giardia and other pathogens.

“It could be put in a cell phone - and it can use just sunlight for illumination, which makes it very appealing for Third-World applications,” said Changhuei Yang of the California Institute of Technology (Caltech), member of the team that developed the device, dubbed optofluidic microscope.

The new instrument can be mass-produced for $10 and combines traditional computer-chip technology with micro-fluidics - the channelling of fluid flow at incredibly small scales.

An entire optofluidic microscope chip is about the size of a coin, although the part of the device that images objects takes up only a small fraction of that space.

“Our research is motivated by the fact that microscopes have been around since the 16th century, and yet their basic design has undergone very little change and has proven prohibitively expensive to miniaturise.”

“Our new design operates on a different principle and allows us to do away with lenses and bulky optical elements,” says Yang.

The fabrication of the microscopic chip is disarmingly simple. A layer of metal is coated onto a grid of charge-coupled device (CCD) sensors (used in digital cameras).

Then, a line of tiny holes, less than one-millionth of a metre in diameter, is punched into the metal, spaced five micrometers apart. Each hole corresponds to one pixel on the sensor array.

A microfluidic channel, through which the liquid containing the sample to be analysed will flow, is added on top of the metal and sensor array. The entire chip is illuminated from above; sunlight is sufficient.

When the sample is added, it flows - either by the simple force of gravity or drawn by an electric charge - horizontally across the line of holes in the metal.

As cells or small organisms cross over the holes, one hole after another, the objects block the passage of light from above onto the sensor below. This produces a series of images, consisting of light and shadow, akin to the output of a pinhole camera.

Because the holes are slightly skewed, so that they create a diagonal line with respect to the direction of flow, the images overlap slightly. All the images are then pieced together to create a surprisingly precise two-dimensional picture of the object.

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