A liquid crystal biosensor for detecting organophosphates through the localized pH changes induced by their hydrolytic products

We report a biosensor for detecting organophosphates (OPs) by using liquid crystal (LC). The mechanism of the biosensor is based on detection of minute pH changes during the enzymatic hydrolysis of OPs. To hydrolyze OPs, paraoxonase 1 (PON1) is immobilized on a copper grid which also hosts pH-sensitive LC, 4-cyano-4′-pentylbiphenyl (5CB) doped with 0.3% of 4′-pentyl-biphenyl-4-carboxylic acid (PBA). Proximity of enzyme and LC ensures that H+ can be detected by the pH-sensitive LC before it is neutralized by buffer. Thus, the presence of OPs can be reported as color change in LC when they undergo enzymatic hydrolysis. For paraoxon detection, we can reach a limit of detection (LOD) of 1 μM by using the naked eye. This type of LC-based biosensor also shows high specificity and does not respond to imidacloprid and ampicillin.