Biophotonics enables easier detection of malaria

UEF Bulletin 2016

Biophotonics is one of the latest trends in photonics. In the future, pocket-size measuring devices will allow biophotonics to be used in diagnosing diseases and detecting counterfeit food products and drugs.

The Department of Physics and Mathematics at the University of Eastern Finland is currently carrying out biophotonics research that makes use of nanostructures in enhancing measurement accuracy.

“The idea of our research is to use nanostructures to optically strengthen signals that can be measured from samples. We are currently investigating how to make biological measurements increasingly sensitive,” says Postdoctoral Researcher and Biochemist Tarmo Nuutinen, who defended his dissertation last year.

“Molecules are formed by atoms which have thermal movement towards one another. Each molecule vibrates in a unique manner, so in a way they have their own fingerprints,” Professor Pasi Vahimaa says.

“Surface-enhanced Raman spectroscopy, SERS, enables us to study these fingerprints. Light condenses onto the surface of the nanosturcture, increasing interaction between its molecules and light. This allows us to detect signals even from a small sample, and the different wavelengths of the scattered light tell us which substances the sample contains.”

By coating silicon wafers with surface structures invisible to the naked eye, it is easier to make different substances visible, as nanostructures can enhance the detection of substances put on their surface.

“Nanostructures can be created on the surface of the sample material in different ways – our way is to dip the sample in two different liquids: silver nitrate and table salt. The method is based on traditional photographic processing. This allows us to create crystals on the surface of the sample randomly, yet evenly,” Vahimaa explains.

“Silver chloride is better than silver, which darkens quickly and loses its signal enhancement capacity in SERS – rendering samples unusable in just one day. Samples treated with silver chloride, on the other hand, are practically permanent, as silver chloride is converted into silver only in the measuring device right before the measurement,” says Early Stage Researcher Antti Matikainen, who will defend his dissertation this autumn.

The advantages of a technique that is based on creating nanostructures include speed, easiness and cost efficiency: with proper equipment, anyone can make them. According to Vahimaa, the idea has potential for swift commercialisation.

The silver chloride-based measurement method is new and has several applications, including the detection of counterfeit drugs and food products, as well as the monitoring of the environment and its chemicalisation.

“Our idea is to look for molecules that are indicative of diseases, such as malaria pigment. This information can then be used in biomedicine. Our method is a lot simpler than the traditional antibody analysis, which requires fluorescent markers, for example. Here, the target of interest gets bounds directly to the sample surface, and that’s the strength of this technique,” Nuutinen says.

“SERS can also be used to analyse food products for added substances such as melamine, which is illegally added to milk in China. This technique enables easy verification of substance concentrations, unlike some other traditional methods that can be intentionally confounded by the sample’s nitrogen concentration,” Matikainen says.

Applications of this measurement method could be useful for customs, police and the security sector in general. Small, portable measuring devices are already being tested in these fields.

“SERS and optical fibre can also be used in optical biopsy, which provides information on the progression of cancer or atherosclerosis, for example,” Vahimaa says.

“For future applications, it is important to verify, characterise and test various devices, sample platforms and substances.”

“SERS has long been regarded as an unreliable measurement method and many have failed in attempts to utilise it. However, we have succeeded in replicating the method, and this gives an additional boost for motivation,” Matikainen and Nuutinen say.

“We’ve made a breakthrough in this research. There are plenty of publications on the topic, though, and the technology is slow to spread. That makes it difficult to stand out,” adds Matikainen.

Text Marianne Mustonen Photo Varpu Heiskanen