WASHINGTON — Spectral images, which contain more color information than is obtainable with a typical camera, reveal characteristics of tissue and other biological samples that can’t be seen by the naked eye. A new smartphone-compatible device that is held like a pencil could make it practical to acquire spectral images of everyday objects and may eventually be used for point-of-care medical diagnosis in remote locations.

Potential applications of the new device include detecting oxygen saturation in a person’s blood, determining the freshness of meat in the grocery store and identifying fruit that is the perfect ripeness. The spectrometer could also make it easier to acquire spectral data in the field for scientific studies.

In The Optical Society (OSA) journal Biomedical Optics Express, the researchers describe how to make the new pencil-like spectrometer and demonstrate its ability to acquire spectral images of bananas, pork and a person’s hand. The new device can detect wavelengths from 400 to 676 nanometers at 186 spots simultaneously.


“The easiest way to use a spectrometer is to wave it over the part of the body or object being examined,” said first author Fuhong Cai, Hainan University, China. “However, many home-made portable spectrometers use a smartphone camera to acquire data and a phone cradle that contains other necessary optics. The cradle can be hard to align correctly and makes it awkward to wave the smartphone over the body."

Rather than using a smartphone camera to acquire images, the new spectrometer uses a commercially available complementary metal-oxide-semiconductor (CMOS) camera that wirelessly transmits images to a smartphone. This approach allowed the researchers to assemble a cylindrical spectral imaging device weighing just 140 grams (about 5 ounces) that is about the length of smartphone and just over 3 centimeters in diameter.

Using off-the-shelf components
The new pencil-like spectrometer uses all commercially-available components that can be purchased for less than $300 (US). The light source is an array of white LEDs, which connects to an off-the-shelf optical lens tube with the CMOS detector and other optical components necessary for spectral imaging.

One can use the pencil-like spectrometer simply by moving it across the target area by hand. This manual push-broom scanning process builds up a series of spectral images that are sent to a smartphone or computer where software stitches the spectral images together into a 3D spectral image data cube.

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