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Biosensing Paraoxon in Simulated Environmental Samples by Immobilized Organophosphorus Hydrolase in Functionalized Mesoporous Silica

Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352

^* Corresponding author (Eric.Ackerman{at}pnl.gov)

Received for publication May 31, 2006. There is a critical need for highly sensitive, cost-effective sensors to conduct ecological analyses for environmental and homeland security-related applications. Enzyme biosensors, which are currently gaining acceptance for environmental monitoring applications, need improvements to deliver faster measurements with stabilized sensing elements, e.g., enzymes. We report here on a method which significantly overcomes this difficulty, and demonstrate its application in a biosensor for aquatic environmental applications. A fast-responding and stable biosensor was developed via immobilization of organophosphorus hydrolase (OPH) in functionalized mesoporous silica (FMS) with pore sizes in tens of nanometers. The OPH-FMS composite was held on glassy carbon electrode by a dried Nafion gel and FMS protected OPH from Nafion-resulted activity loss. The resulting enzyme biosensor, when integrated with an electrochemical instrument, responded rapidly to low paraoxon concentration and achieved steady-state current in less than 10 s, with a detection limit of 4.0 x 10^–7 M paraoxon. The biosensor was tested for detection of paraoxon in simulated environmental samples, under wide-ranging physicochemical conditions. Results clearly indicate high recovery efficiencies in aqueous solutions (96 to 101%) at different pH, total organic carbon, total dissolved solids, and total suspended solids, and demonstrate the ability of the biosensor unit to continuously monitor paraoxon in aqueous conditions similar to those found in river and lake systems.

Abbreviations: OPH, organophosphorus hydrolase • FMS, functionalized mesoporous silica • GDAH, glutaric dialdehyde • GCE, glassy carbon electrode • TDS, total dissolved solids • TOC, total organic carbon • BTC, simulated breakthrough curve