Under the chip

A small microscope that can study various samples at one go

since its invention in the 16th century, the microscope has been improved many times. With better magnification, the size too increased and its use got limited to labs. But now, this basic tool has been designed about the size of a fingertip. Instead of using lenses, the new microscope uses computer chips.

Developed by the California Institute of Technology (Caltech), the optofluidic microscope can simplify diagnostics such as blood fraction analysis, screening urine for infection cells and counting tumour cells. The microscope can also be taken to the field and can be of great help to biologists. The resolution of the microscope is 0.8 micron. This helps distinguish two separate characters at this distance. An added advantage is the microscope does not need a specific source of light.

The new instrument combines traditional computer-chip technology with microfluidics--the channelling of very small volumes of fluids. A layer of metal is coated on a charge coupled devise sensor (ccd) to make the chip. The ccd sensors are the same as the ones used in digital camera. A line of tiny holes, less than one micron in diameter, is punched into the metal. The sample can be added through the microfluidic channel on top of the metal and sensor array. It flows horizontally under the line of holes and as cells or small organisms pass under the holes, they block the light from above onto the sensor below. This produces a series of images.

Caltech is trying to figure out ways to mass-produce the chip. The platform into which the chip is integrated needs to be made according to the object that needs to be magnified. Hundreds of microscopes are possible on a single chip so that many organisms can be imaged and analyzed. "Our system is tiny, it takes up an area of around 1mm x 50 microns on a chip. There is plenty of real estate on a chip to add more microscopes," says Changhuei Yang, assistant professor of Bioengineering and Electrical Engineering, Caltech. The cost of one microscope is around us $10 and it may take around 10 cents to add another microscope onto the same chip. "Our technology will replace the conventional microscope for a range of applications. For example, if a scientist needs to process a large number of samples, our technology will be advantageous as we can implement and operate hundreds or thousands of such microscope systems in parallel," he adds.

The chips can also be incorporated into devices that are implanted into the human body. "This is an exciting and promising new technology with the potential to provide low cost, high throughput automated imaging. It's not quite time to throw away all of our optical microscopes yet; resolution is not the same as some other optical imaging systems," says Renee Dickie, scientist with the Department of Environmental Health, Harvard School of Public Health.

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