A wireless handheld spectrometer that is smartphone-compatible could make it easier and more economical to acquire spectral images of everyday objects and in the future could be used for point-of-care medical diagnosis in remote locations. The device can detect wavelengths from 400 to 676 nm. A white LED array lamp is used as the light source. The wavelength resolution of the spectrometer is about 17 nm. Rather than using a smartphone camera to acquire images, the new spectrometer uses a commercially available CMOS camera that wirelessly transmits images to a smartphone. Using this approach, researchers from Hainan University, Beijing University of Chemical Technology and Zhejiang University assembled a cylindrical, pencil-like spectral imaging device weighing just 140 grams (about 5 ounces). The device is 15.5 cm in length (about the length of a smartphone) and is just over 3 cm in diameter. A smartphone or network computer can serve as the data receiver and processor for this standalone device. Researcher Fuhong Cai said that many home-made portable spectrometers use a smartphone camera to acquire images and a phone cradle to contain the optics necessary for transmission. The cradle can be difficult to align, he said, and can make it difficult to wave the spectrometer over the part of the body or object that is being imaged. A new pencil-like wireless spectrometer can be used with a smartphone to collect 3D spectral images of the body and other objects. This design could make the device useful for point-of-care diagnostics. Courtesy of Dan Wang, Beijing University of Chemical Technology. The components used to assemble the spectrometer are all commercially available and can be purchased for less than $300 USD. The LED light source connects to the CMOS detector and other optical components via an off-the-shelf optical lens tube. The spectrometer is held like a pencil to scan and image an object. To activate the device, the user simply moves it across the target area by hand. Through this manual push-broom scanning process, a series of spectral images is accumulated. The images are sent to a smartphone or computer where software stitches the spectral images together into a 3D spectral image data cube. In experiments the spectrometer provided repeatable measurements of spatial 2D images at various wavelengths for various bio-samples. Researchers monitored the impacts of chlorophyll, myoglobin and hemoglobin on bananas, pork, and human hands, using the spectrometer to detect ripeness in bananas and myoglobin levels in a piece of pork. They obtained a 3D spectral image data cube from their scan of a human hand. The data cube was obtained within 16 seconds and exhibited good signal to background noise ratio. Due to the regional differences in blood concentration, the reflectance showed differences in optical intensity attenuation around 540 nm and 580 nm. Researchers believe that the spectral image at the 580 nm band could be used to predict the concentration of blood, and that by using an IR camera, the spectral range for their spectrometer could be expanded to study deep human tissue. The researchers are also interested in using their compact imaging spectrometer for environmental monitoring. “We’re developing distributed spectral cameras that could be used for a wide range of ocean surveys, such as detecting dissolved organic matter in water or pigments that indicate early signs of harmful algal blooms,” said Cai. “Since the imaging spectrometer can connect to any type of camera, we are also examining the idea of attaching it to the camera of an autonomous vehicle to create a remote ocean sensing system.” Although the use of commercially-available components to make the prototype means that anyone can assemble the device, it also places limits on the device’s resolution and sensitivity. For example, the prototype spectrometer can only resolve wavelengths that differ by at least 17 nm. “We expect significant spectral resolution improvements in the future by using an improved camera with a long focal length lens,” said researcher Dan Wang. “These improvements would expand the applications for the device.” The researchers also plan to develop software to make the spectral imager even more useful. “We want to develop ways to use machine learning algorithms to analyze the massive amounts of data that could be collected with the portable spectra imager,” said researcher Sailing He. “We also want to create software for smartphones that uses spectral imaging data to measure meat freshness, for example.” The research was published in Biomedical Optics Express, a publication of OSA, The Optical Society (doi: 10.1364/BOE.8.005427).