POTENTIAL TOXINS DETECTED BY COLORIMETRIC SENSORS

Thursday, July 22, 2010 - 03:46PM

July 16, 2010 - appearing in Highlights in Chemical Technology

Highlights in Chemical Technology

Colourimetric sensor detects pesticide toxins

16 July 2010

A paper-based colourimetric dipstick bioassay that can detect low levels of pesticides has been developed by Canadian chemists.

Organophosphate pesticides can be toxic to both humans and animals as they inhibit important enzymes such as acetylcholinesterase (AChE) in the nervous system. But are still in widespread use so there is a need for a simple method to detecting their residues. Bioactive paper sensors using a biorecognition element such as DNA aptamers, enzymes or antibodies have gained widespread interest as paper is inexpensive, disposable and environmentally friendly. But, so far, these devices have not been amenable to traditional dip tests that would make them easier to use in remote locations.

Now John Brennan and colleagues at McMaster University in Hamilton, Canada have created a dipstick test to identify inhibitors of the acetylcholinesterase enzyme. Brennan combined acetylcholinesterase with gold nanoparticles in a sol-gel derived coating deposited on a hydrophobically modified paper. Inhibitors present in test solutions decrease the growth of gold nanoparticles and causes a colour change that can be detected by eye.

Brennan explains that 'the use of gold nanoparticles was based on a need to retain colour within the dipstick. Small organic chromophores would leach when dipped into solutions; the larger gold particles remain on the sensor surface and produce a very intense colour that makes detection of organophosphates easy'.

This assay is sufficiently sensitive to allow detection of low levels of organophosphate pesticides such as Paraoxon. Brennan adds that 'organophosphates that inhibit acetylcholinesterase are also of interest to the military as they can be used as nerve agents or for bioterrism therefore simple methods to detect inhibitors can aid in these situations'.

Karen Faulds an expert in bioanalytical chemistry at the University of Strathclyde in the UK comments that this system is 'very significant as it could easily be used in the field to detect insecticides (or other acetylcholinesterase inhibitors) without complex instrumentation using a low cost, disposable assay'. She continues to say that 'the assay format shows stability over 90 days which is also a great advantage over current solution based methods.'

Brennan hopes to develop this system by 'integrating the various reagents involved in the assay into a single lateral flow device, which should avoid the need for adding external reagents'. They are also 'investigating other enzymes that are known to support catalytic growth of gold nanoparticles to further evaluate this sensor platform'.

Nicola Wise

Journal article

Bioactive paper dipstick sensors for acetylcholinesterase inhibitors based on sol–gel/enzyme/gold nanoparticle composites
Roger E. Luckham and John D. Brennan, Analyst, 2010, 135, 2028