Monitoring patients’ vital signs is standard medical practice in health care facilities. What happens when people want or need to monitor their vital signs on their own, outside of a hospital or doctor’s office? Researchers from several labs and universities in Israel and the Netherlands have developed two noninvasive, wearable devices containing sensors that can monitor people’s biometrics; they are worn like a wristwatch. The sensors detect changing patterns of scattered light — one of the sensors tracks a person’s glucose concentration and hydration levels, while the other monitors pulse. While less sensitive to errors while the person is in motion, the devices are not 100 percent accurate. Researchers are working to reduce margin of error. The optical configuration for remote measuring of glucose levels from the subject’s wrist. The subject’s hand is under laser illumination. Images courtesy of Biomedical Optics Express. “Around 96 percent of our in vivo measurements were within a range of 15 percent deviation from the readout of a medical reference glucometer device,” said Zeev Zalevsky a bioengineer at Israel’s Bar-Ilan University. “The main factor for errors now is the stability of our device on the wrist of the user.” Both sensors use a grainy interference pattern — a speckle effect — which is produced on images when laser light reflects from an uneven surface or scatters from an opaque material. The light-scattering material moves, prompting the speckle pattern to alter with changes in the flow. Such light variations provide valuable information, according to Mahsa Nemati, lead researcher and biomedical engineer and graduate student in the Optics Research group at Delft University of Technology. The glucose sensor detects changes in glucose concentration by analyzing changing patterns in back-scattered light produced by laser-generated wavefronts of light that illuminate skin on the wrist near an artery; a camera measures the changes over time. “Glucose is the holy grail of the world of biomedical diagnostics, and dehydration is a very useful parameter in the field of wellness, which is one of our main commercial aims,” Zalevsky said. The same glucose sensor can also be used to reveal a person’s dehydration level as it changes. With the pulse-tracking device, the researchers found they can use speckle changes to more accurately track blood flow in simulated heartbeats, even when the light source is also moving. The artifacts are generated by the motion of the laser beam, which creates a different penetration depth and distance to the detector. The speckle contrast has been calculated over the entire illuminated area. “This … shows for the first time that a speckle pattern generated from a flowing liquid can give us the pulsation properties of the flow in spite of motion-induced artifacts,” Nemati said. The research is featured in two papers, one focusing on the glucose sensor and the other on the pulse sensor. Both are published in Biomedical Optics Express (doi: 10.1364/BOE.5.001926) and (doi: 10.1364/BOE.5.002145). For more information, visit www.osa.org.