A team of interdisciplinary researchers have created "smart" holograms that can monitor health conditions or diagnose diseases, by changing color in the presence of disease indicators in a person's breath or bodily fluids. When developed into a portable medical test, these responsive holograms could make testing for medical conditions and monitoring one's health very easy, the scientists claim.

A person would just have to check the hologram's color against a chart or use a camera phone to read the results. As these holographic sensors don't require batteries, electricity or lasers to function, it's possible to create inexpensive portable tests for healthcare workers to use or people to self-administer, that could help them potentially diagnose diseases in their earliest stages.

"We often see holograms on banknotes, credit cards, as security features, or artwork," Ali Yetisen, a PhD student at the University of Cambridge, UK, who led the research, tells Gizmag. "However, these type of holograms do not response when they encounter a health condition indicator such as glucose or blood electrolytes. We have developed techniques to make these holograms 'smart,' so that they can respond to a wide range of disease markers."

The holographic sensors are made out of hydrogels (a highly absorbent material) that are doped with silver nanoparticles. These silver nanoparticles are then organized into three-dimensional holograms of predetermined shapes using a multi-megawatt laser. The final sensors resemble the iridescent hardened forewings of beetles, and normally diffract light in a green color.

However, when the holographic sensor is exposed to a person's breath, urine, tears or a drop of their blood or saliva, the hydrogel in the sensor, which is sensitive to specific disease indicators, reacts if any of them are present. The hydrogel either swells or shrinks, causing a change in the hologram's color in the entire visible spectrum. It's the first time, the researchers claim, that they've been able to achieve such a result with a colorimetric sensor.

"It's pretty much like a butterfly wing," says Dr. Haider Butt, a Lecturer in Micro Engineering and Nanotechnology, at the University of Birmingham and a co-author of the study. "But this is a butterfly wing that changes color depending on the solution we dip it in."

The color changes can be checked against a color reference chart or read by a smartphone camera, making it simple for anyone to identify or monitor conditions like diabetes, an electrolyte imbalance, infections, cardiac functions and other important medical conditions. It took around three years,Yetisen says, for the multidisciplinary team of researchers from the University of Cambridge, to fabricate and optimize the holographic sensing mechanism. While they aren't a substitute for doctors, these smart holograms, they state, could offer patients an inexpensive alternative to costly laboratory tests.

"The most important advantage of holographic sensors is that it is equipment free," Yetisen tells us. "Meaning that you don't need a handheld reader to interpret the results. It also doesn't have any sharp components to harm or infect the patient, and it can be discarded by incineration. The tests have the potential to be used at point-of-care as well as centralized hospitals and can be used by the healthcare workers for screening health conditions."

The smart holograms are easy to mass produce and can be made in a fraction of a second. It costs less than 10 cents to make these small, lightweight and easy-to-carry sensors. The team is working on integrating them with paper-based microfluidics and smartphone readers, to make things more user-friendly. The sensing process is also reversible, which means that these smart holograms can be reused many times before they are discarded.

The researchers' ultimate goal is to provide to people in under-served communities in developing nations with an inexpensive alternative to costly medical tests. Aside from medical diagnostics, the technology could also be used to create security features to identify counterfeit medicine, according to Dr. Fernando da Cruz Vasconcellos, another team member. Potential environmental sensing applications, which could allow people to assess air or water quality by observing the hologram's color, are also in the works. In addition, the team is working on veterinary testing kits that could allow farmers to monitor their livestock's health and also check for contaminants in milk.

The team is currently carrying out clinical trials of these sensors to monitor glucose levels and urinary tract infections in diabetic patients at the Wolfson Diabetes and Endocrine Clinic, Addenbrooke's Hospital, UK. They hope to see these portable medical tests enter the market in around three to five years time. A paper on their research was recently published in the journal Advanced Optical Materials.

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