Low-cost technology developed by IIT Bombay can be used to detect imprints on currency notes, blood cells

Researchers from the Indian Institute of Technology (IIT) Bombay have devised low-cost lenses that will elevate smartphone cameras to the power of a microscope.

The lens with a resolution of 1.4 micrometre, which has been prepared by using natural interface, has been successfully tested to verify the authenticity of currency notes and in biomedical applications like identifying infected blood cells and contaminants in water.

Led by professor Soumyo Mukherji and Debjani Paul from the department of bioscience and bioengineering, the lens was developed by Bhuvaneshwari Karunakaran as part of her PhD at the institute.

The idea, researchers said, was to build a microscope that could be used through a mobile phone and solve problems caused by spherical lenses. “Spherical disruptions is a phenomenon where light rays that strike the edges of the lens do not focus at the same location as the light that comes through the centre of the lens. We developed an alternative technology to make aspherical lenses. This lens could be used with a mobile phone and see things that a naked eye or a magnifying glass misses,” Ms. Karunakaran said.

Mr. Mukherji said traditionally, lenses have been fabricated by polishing and grinding glass or moulding plastic against a template. “These methods are expensive as they require skilled workmanship and costly equipment. An alternative technique is to make them using fluids,” he said.

Researchers have never used plastic solution and water, and this enables a controlled curvature of the lens. While the lenses become reproducible using the technology, Ms. Karunakaran said their cost is as low as ₹1 or ₹2 with it taking 30 minutes to be made.

To develop the lens, the researchers took a plastic sheet and made a small hole in it, following which the sheet was put on a surface of water in a little bowl. On top of the plastic sheet, polymer polydimethylsiloxane, which is a hydrophobic substance, was poured.

“While the gravity tries to pull the polymer into the water through the hole, the surface tension pushes it up. If you cure the polymer for it to solidify, there is a sheet with round shapes — the lens. The lens will then have to be positioned properly on the mobile camera’s lens,” Mr. Mukherji said.

“One can use this ‘smartphone microscope’ technology to verify notes. A currency note has imprints at various places that one can see through this and verify the note. It can also be used to identify infected cells in a stained malaria-infected human blood smear, sperm counting, dental examination, and minimally invasive surgical procedures, besides designing optical systems for identifying contaminants in water such as microalgae and forensic applications,” Ms. Karunakaran said.