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Optical biosensors for fast determination of toxicity in water

Scientists at the CSIC’s Microelectronics Institute of Barcelona are working in the development of biosensors for a quick control of water toxicity. These biosensors, which are not restricted to individual pollutants in the sample, can detect the synergy of all of them and enable controlling the general toxicity of water.

Part of the core of the biosensor. Right, a solution with the bacteria, a reactive to trigger the colour change. A LED light (at the left, the blue light) beam pass trough this solution. Depending on the bacterial reaction, the liquid will change its colour which, in turn, affects the wavelength of the beam light. The latter is detected by the photodetector. Control of pollutants and pathogens in water requires, usually, bringing samples to a laboratory to be analyzed, which means a delay between collection and measurement. This is not a good strategy when a quick answer is required, like when it is necessary to know if water is drinkable or measures have to be taken to avoid environmental disasters.

In the last years, several scientific teams have started to develop portable systems for the fast analysis of water in situ. Nevertheless, these new systems don’t always detect all pollutants which are in a sample. Or, another possible problem, they require complex portable instruments which are economically expensive or heavy or relatively big.

Another approach to this issue are biosensors. Scientists at the CSIC’s Microelectronics Institute of Barcelona have been working on them for some years. Recently they chose an ingenious strategy.  

The core of biosensors is molecules or organisms whose reaction shows the presence of the compounds or pollutants. In this case, the scientists of the IMB-CNM are using bacteria from the same group of human gut-bacteria: if the sample is toxic for the bacteria in the sensor, it will be toxic therefore for our gut-bacteria and, also, for us.

One of the firsts developments based on this idea is a paper bioassay to assess water toxicity, created in collaboration with the Universitat Autònoma de Barcelona. The bioassay can detect in 15-30 minutes any pollutant or molecule toxic for the microorganisms, such as heavy metals and hydrocarbons like fuel or benzene. In this bioassay, the organisms are on the paper. When the water sample is applied on them, the paper changes its colour depending on the intensity of bacterial cellular metabolism in an inverse proportion to the toxicity of the sample: the more colour change the less toxicity in water detected. This change can be red with optical techniques, image analyses or at naked eye.

Now, the scientists at the IMB-CNM are working to transform the same idea into an optical biosensor which can be more accurate and quantify the result. The team has already developed a prototype, which is based on several elements: a solution with the bacteria, a reactive to trigger the colour change –which depends on the bacteria reaction-, a LED light emitter and a photo detector. The latter is controlled by a control-unit, developed also by the same team, which corrects the possible interference of the ambient light and allows therefore using the device and obtaining a correct measure in any place.

The sample to be analyzed is placed into the solution where the bacteria are. Depending on the bacterial reaction, the liquid will change its colour which, in turn, affects the wavelength of the beam light that passes through (as part of the light is absorbed by the colour of the liquid. The photo-detector quantifies the wavelength change of the beam light. 

The biosensor enables to find out if the interaction of all the pollutants is toxic, something which is not always possible to know with other methods

Xavier Muñoz, scientists at the IMB-CNM, says that this optic biosensor detects the general toxicity of water. “Most interesting the biosensor enables to find out if the interaction of all the pollutants is toxic, something which is not always possible to know with other methods. Sometimes, several pollutants, which independently are not harmful, together interact and become toxics”.

The biosensor detects anything that inhibits the bacteria, whatever it is: chemical products, viruses, antibiotics, pathogenic bacteria... if the compounds synergy is harmful for the bacteria, it will be detected by the biosensor. This is essential when the cases where water in rivers, lakes or treatment plants has to be quickly analyzed and a quick decision has to be taken in order to know if water is drinkable.

The first prototype includes batteries, which makes it a little bigger, but the final device will have other ways to get the power and will be smaller than a cigarette box. The firsts results, published in the journal Sensors and Actuators B: Chemical, are very promising. The scientists have been able to analyze and quantify toxicity of water samples in less than 10 minutes.

This research team has specialized in the development of optical and electrochemical sensors, which are produced by them for small and medium companies. The technology used in some of these sensors, such as the ISFET, says Muñoz, is complex and cannot easily be produced by a conventional microelectronics factory. The IMB-CNM has in its facilities a Clean Room with capacity to produce chips and microdevices for small and medium companies in quantities of thousands.

The research group has recently received the TECNIO accreditation as an expert group in technology transfer. A recent development by them is the electrochemical sensor of the Devicare’s lithiasis control.

Reference article:

Portable and miniaturized optofluidic analysis system with ambient light correction for fast in situ determination of environmental pollution. Ferran Pujol-Vila et al. Sensors and Actuators B: Chemical Volume 222, January 2016, Pages 55–62. doi:10.1016/j.snb.2015.07.095