Researchers at the California Institute of Technology have developed a super-compact high-resolution microscope, small enough to fit on a finger tip. The ‘microscopic microscope’ operates without lenses, but has the magnifying power of a top quality optical microscope.

The new instrument combines traditional computer-chip technology with microfluidics – the channelling of flow fluid flow at incredibly small scales. An entire optofluidic chip is about the size of a quarter, although the part of the device that images objects is only size of Washington’s nose on that quarter.

Changhuei Yang, assistant professor of electrical engineering and bioengineering at Caltech, who was among those who developed the device, explained: “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 up to do away with lenses and bulky optical elements.”

The fabrication of the microscopic chip is simple. A layer of metal is coated onto a grid of charge-coupled device (CCD) sensor. 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 by 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 flow – 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 of the images are then pieced together to create a surprisingly precise two-dimensional picture of the object.

Yang is now is discussion with biotech companies to mass-produce the chip. The platform into which the chip is integrated can vary depending on the needs of the user. In the future, the microscope chips could be incorporated into devices that are implanted in the human body.

Yang explained: “An implantable microscope analysis system can autonomously screen for and isolate rogue cancer cells in blood circulation, thus providing important diagnostic information and helping arrest the spread of cancer.”