Optofluidic Microscope Is the Size of a Computer Chip

It combines traditional computer-chip technology with microfluidics--the channeling of fluid flow at extremely small scales. The method, called Optofluidic Microscopy (OFM), enables the imaging of fluid-immersible objects with microscope-level resolution.

The microscope operates without lenses but has the magnifying power of a top-quality optical microscope, can be used in the field to analyze blood samples for malaria or check water supplies for Giardia and other pathogens, and can be mass-produced for around US$10.

Developed by the California Institute of Technology (Caltech; Pasadena, CA, USA) bioengineers, the manufacture of the microscope was very simple. A layer of metal was coated onto a grid of charge-coupled device (CCD) sensor (similar to sensors used in digital cameras). A line of tiny holes less than one-millionth of a meter in diameter and spaced five µm apart was punched into the metal. Each hole corresponded to one pixel on the sensor array. A microfluidic channel, through which the liquid containing the sample to be analyzed flows, was added on top of the metal and sensor array. The entire chip can be 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, the objects block the passage of light from above onto the sensor below. This produces a series of images, consisting of light and shadow, resembling the output of a pinhole camera. The holes are slightly skewed, so that they create a diagonal line with respect to the direction of flow. Therefore, the images overlap slightly. All of the images are then pieced together to create a precise two-dimensional picture of the object.

"The whole thing is truly compact--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, assistant professor of electrical engineering and bioengineering at Caltech, who developed the device together with his colleagues at Caltech.


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