Handheld Microscope Detects Melanomas

It can be held by hand without blurring the resulting picture.

The new microscope examines to a resolution of five µm–for results with comparable resolution values, a conventional microscope would either be restricted to a tiny field forced to scan the surface: conventional equipment slowly sweeps the surface, point by point, recording countless images before combining them to create a complete picture. The drawback–it takes quite a while before the image is complete.

Designed by researchers at the Fraunhofer Institute for Applied Optics and Precision Engineering IOF (Jena, Germany), the new microscope combines the best of both types of microscope: because it foregoes the grid, it needs to make just a single measurement, and that is what makes it very fast.

"Our ultrathin microscope consists of not just one but a multitude of tiny imaging channels, with lots of tiny lenses arrayed alongside one another. Each channel records a tiny segment of the object at the same size for a 1:1 image," explained IOF group manager Dr. Frank Wippermann. Each slice is roughly 300 µm x 300 µm in size and fits seamlessly alongside the neighboring slice; a computer program then assembles these to generate the overall picture. The difference between this technology and a scanner microscope: all of the image slices are recorded simultaneously.

The imaging system consists of three glass plates with the tiny lenses applied to them, both on top and beneath. These three glass plates are then stacked on top of one another. Each channel also contains two achromatic lenses, so the light passes through a total of eight lenses. Several steps are involved in applying the lenses to glass substrates: first, the scientists coat a glass plate with photoresistant emulsion and expose this to UV light through a mask. The portions exposed to the light become hardened. If the plate is then placed in a special solution, all that remains on the surface are lots of tiny cylinders of photoresist; the rest of the coating dissolves away. Now, the scientists heat the glass plate: the cylinders melt down, leaving spherical lenses. Working from this master tool, an inverse tool is developed that can be used use as a die. A die like this can then be used to launch mass production of the lenses: simply take a glass substrate, apply liquid polymer, press the die down into it, and expose the polymer layer to UV light. In a process similar to the dentist's method of using UV light to harden fillings, here, too, the polymer hardens in the shape the die has printed into it. What remains are tiny lenses on the glass substrate. "Because we can mass-produce the lenses, they're really pretty low-cost," Wippermann added.

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Fraunhofer Institute for Applied Optics and Precision Engineering IOF