Lens Realizes Nanoscale Imaging

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A*STAR researchers and collaborators at the National University of Singapore have developed a non-invasive optical microscope that can image smaller objects than conventional microscopes, and does not require samples to be dyed.

It is hard to overestimate the incredible contribution the humble optical microscope has made to science and industry. But microscopes suffer from a fundamental limitation that prevents them from distinguishing between two objects that are closer than about 200 nanometers. In recent years, various ingenious ways to overcome this limit have been demonstrated, but most of them require either placing the lens extremely close to the sample — both of which could be damaged during focusing — or staining the sample with fluorescent dyes, reducing the usefulness of these so-called super-resolution microscopes.

Now, Jinghua Teng of the A*STAR Institute of Materials Research and Engineering and colleagues have developed a super-resolution microscope that can distinguish objects separated by just 65 nanometers and does not suffer from either disadvantage.

The microscope has a specially engineered lens, known as a supercritical lens. This flat lens has transparent concentric rings at certain radii and focuses down to a much narrower spot than a conventional lens. By using this lens to focus a laser beam and then scanning the focused beam across a sample, it is possible to build up a high-resolution image of the sample. While other research groups have fabricated supercritical lenses in the past five years, they have various drawbacks. Teng and his team have overcome these disadvantages through improved lens design based on computer simulations.

Besides enabling super-resolution imaging, the lens has several other important advantages. It is easy and inexpensive to make because, unlike previous supercritical lenses, it has micrometer-scale features rather than nanometer-scale features. It also has a long, needle-like focal region, meaning that samples will remain in focus even if they move slightly up or down relative to the lenses. Furthermore, the distance between the lens and the sample is about ten times greater than that for previous supercritical lenses. Finally, since the imaging process is completely physical and captured in real time, there is no need for special sample preparation or mathematical post-processing of images, making the microscope quick and easy to use.

The team compared the performance of their microscope with those of a conventional optical microscope and a confocal laser scanning microscope, and found that theirs had superior resolution to both.

“This technique is highly attractive for developing the next generation of confocal laser scanning microscopes. There are huge potentials for planar-lens technology in general,” notes Teng. “We hope to commercialize the planar-lens technology within three to five years. We’re already having discussions with optic companies,” he adds. The researchers are working on optimizing the specifications of their microscope in preparation for commercialization.