New paper-based biosensor to detect water toxicity

Researchers have developed an inexpensive paper-based biosensor covered with bacteria to detect water toxicity which can be easily used in economically restricted areas or developing countries.
The detection of toxic contaminants is an essential element of analysis and control of water quality, something very needed in an increasingly urbanised and industrialised world.
Chemical analysis techniques are of great utility in determining specific substances, but are limited when used to analyse complex samples which can contain multiple contaminants, researchers said.
In this sense, the use of biosensors is appropriate, in which they measure the effect samples have on a biological element, such as enzymes or proteins, or on a vital parametre of an indicator organism, they said.

"The innovation provided by our sensor is based on the use of absorbent paper matrices with entrapped bacteria with the aim of conducting colorimetric measures of toxicity," said Ferran Pujol from Autonomous University of Barcelona in Spain.
The detection technique proposed and validated by researchers is quick and simple. Its mechanism is similar to that of paper strips used to measure the pH of water.

The samples analysed are added to the matrices together with the colouring agent ferrocyanide, which ranges from yellow to transparent when breathed in by the microorganisms, researchers said.
The paper changes colours according to the intensity of the cell metabolism of the bacteria, inversely proportional to the toxicity of the sample - the more the colour changes, the less contamination detected, they said.

These changes can be measured with optical techniques, by analysing the image or with the naked eye.
The bioassay detects any contaminant which can be toxic for the microorganisms after some 15 to 30 minutes of coming into contact with the cells (time taken to conduct the test), such as heavy metals or hydrocarbons such as petroleum or benzene, researchers said.
The technique can be applied to both natural waters and urban and industrial wastewater.
Using a material such as paper and without the need of complex tools makes this biosensor a simple and inexpensive technique which can be used to detect toxicity in contexts of economic restrictions or in developing countries, researchers said.

The findings were published in the journal Analytica Chimica Acta.