Today's smartphones come chock-full of technological capability, intended to help us with everything from taking holiday snaps, finding our way around a new town or staying connected with people around the world. As it turns out, the hardware inside is starting to show huge promise in the world of medical diagnostics, with smartphones repurposed as blood-scanning microscopes, HIV testers and sleep apnea detectors. The latest advance in this area comes in the form of a fiber optic sensor for smartphones that monitors bodily fluids, a tool that could be used for biomolecular tests such as pregnancy or diabetes monitoring.
Surface plasmon resonance (SPR) is a process where a stream of light is directed onto a metallic film, with most, but not all of it being reflected. Some of the light is absorbed by electrons on the film's surface which causes them to jostle. When a fluid is then brought into contact with the metallic film, it affects how the light is absorbed and reflected, allowing scientists to deduce critical information about the composition of the sample, along with the presence of certain trace gases and biomolecules. This has seen SPR commonly used in biosensing, though it usually involves large and expensive lab equipment. 
Researchers at the Hanover Centre for Optical Technologies figured that a modern smartphone contained much of what they needed to pack an SPR device into pocket-sized package, namely a light detector and light source. The scientists fixed a 400 micrometer fiber optic cable curved into a U-shape across the phone's camera and LED light. The camera was fitted with a diffraction grating to separate the light beam into an emission spectrum and a small well to store fluid samples was added.
In testing the small SPR device, the team used different concentrations of glycerol and found that its sensitivity was equal to that of conventional equipment. The tool could be used to monitor body fluids such as blood, urine, saliva, sweat or breath. The team says the sensor's readings could then be processed by a smartphone application to turn out real-time results. 
"We have the potential to develop small and robust lab-on-a-chip devices for smartphones," says Kort Bremer, inventor and co-author of the study. "So, surface plasmon resonance sensors could become ubiquitous now."
The research is published in the journal Optics Express.