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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

View larger version (15K): [in this window] [in a new window]   Fig. 1. Schematic of the biosensor testing unit. (a) the modified YSI electrochemical chamber (reactor); (b) YSI sipper tube; (c) glassy carbon electrode (GCE); (d) Ag/AgCl reference electrode; (e) Pt wire auxiliary electrode is separately drawn, whose position on the chamber is marked. The body of the auxiliary electrode was vertical to the plane of the drawing paper and the Pt wire spring was immersed in the working solution; (f) the flowing direction for the flushed solution; (g) the stirring bar; (h) the organophosphorus hydrolase functionalized mesoporous silica (OPH-FMS) layer held on GCE by a Nafion gel. The three electrodes are connected with Autolab PSTAT12. The sipper tube is driven by a YSI mechanism system so that the sipper tube can descend into or ascend from the chamber, or rotate above the chamber. Thus, the samples can be injected into the chamber and the tested solution can be flushed by refilling the working buffer solution via the sipper tube.

View larger version (16K): [in this window] [in a new window]   Fig. 2. Cyclic voltammetry of 0.25 mM 4-nitrophenol (solid line) and paraoxon (dotted line) in pH 8.5, 0.1 M HEPES/0.1 M NaCl at glassy carbon electrode (GCE). Scan rate: 0.1 V s–1.

View larger version (14K): [in this window] [in a new window]   Fig. 3. (A) Dynamic response of the paraoxon biosensor. Step = 10 µM; (B) Calibration plot of the paraoxon biosensor.

View larger version (16K): [in this window] [in a new window]   Fig. 4. Amperometric response of the paraoxon biosensor in simulated aqueous samples at different pH. The concentration of paraoxon in the testing solutions was 15.0 µM.

View larger version (16K): [in this window] [in a new window]   Fig. 5. Continuous mode testing of the paraoxon biosensor on a simulated breakthrough curve. The samples contained 1 mM NaOH, 10 mM NaNO3, 50 mg L–1 clay colloid, 500 mg L–1 NaCl, and 5 mg L–1 humic acid.