An optical biosensor for dichlovos using stacked sol–gel films containing acetylcholinesterase and a lipophilic chromoionophore

An optical biosensor consisting of a chromoionophore (ETH5294) (CM) doped sol–gel film interfaced with another sol–gel film immobilized with acetylcholinesterase (AChE) was employed to detect the insecticide dichlorvos. The main advantage of this optical biosensor is the use of a sol–gel layer with immobilized CM that possesses lipophilic property. The highly lipophilic nature of the CM and its compatibility with the sol–gel matrix has prevented leaching, which is frequently a problem in optical sensor construction based on pH indicator dyes. The immobilization of the indicator and enzyme was simple and need no chemical modification. The CM layer is pH sensitive and detects the pH changes of the acetylcholine chloride (AChCl) substrate when hydrolyzed by AChE layer deposited above. In the absence of the AChE layer, the pH response of the CM layer is linear from pH 6 to 8 (R2 = 0.98, n = 3) and it showed no leaching of the lipophilic chromoionophore. When the AChE layer is deposited on top, the optical biosensor responds to AChCl with a linear dynamic range of 40–90 mM AChCl (R2 = 0.984, n = 6). The response time of the biosensor is 12 min. Based on the optimum incubation time of 15 min, a linear calibration curve of dichlorvos against the percentage inhibition of AChE was obtained from 0.5 to 7 mg/L of dichlorvos (17–85% inhibition, R2 = 0.991, n = 9). The detection limit for dichlorvos was 0.5 mg/L. The results of the analysis of 1.7–6.0 mg/L of dichlorvos using this optical biosensor agreed well with a gas chromatography–mass spectrometry detection method.