A novel approach based on ferricyanide-mediator immobilized in an ion-exchangeable biosensing film for the determination of biochemical oxygen demand

A novel biochemical oxygen demand (BOD) sensing method employing a ferricyanide (FC) mediator immobilized in an ion-exchangeable polysiloxane was developed. The ion-exchangeable polysiloxane containing alkylammonium groups (PAPS-Cl) was synthesized by sol-gel reaction of 3-(aminopropyl)trimethoxysilane (APTMOS) catalyzed by hydrochloric acid. FC was combined in PAPS-Cl via ion-association and the product was labeled as PAPS-FC, which was employed for a modified glassy carbon electrode. The apparent diffusion coefficient (D-app) of FC on the modified glassy carbon electrode was 9.8 X 10(-11) cm(2) S-1. In a three-electrode system, a linear relationship between the anodic current responses and glucose/glutamate (GGA) concentration was obtained up to 40 mg O-2 L-1 (r = 0.994) when the reaction mixture was incubated for 30 min. Single sensor and piece-to-piece reproducibility were less than 3.8 and 7.7%, respectively The effects of dissolved oxygen, pH, temperature and co-existing substances on the BOD responses were studied. The sensor responses to nine pure organic substances were compared with the conventional BOD5 method and other biosensor methods. Detection results of seawater samples were compared with those obtained from the BOD5 method and showed a good correlation (r = 0.988). (C) 2008 Elsevier B.V. All rights reserved

Rhodamine-based ratiometric fluorescence sensing for the detection of mercury(II) in aqueous solution

Novel ratiometric fluorescent silica nanoparticles with high selectivity towards Hg2+ were synthesized for the detection of Hg2+, Hg2+ promoted the ring opening of spirolactam in the rhodamine moiety grafted onto the silica nanoparticles, resulting in a change in the fluorescence intensity. The fluorescence intensity was proportional to the Hg2+ concentration, and the detection limit (S/N = 3) for Hg2+ was found to be 2.59 x 10(-9) mol L-1 with a linear range from 0.4 to 8 x 10(-7) mol L-1. In addition, the morphology of the silica nanoparticles, the effects of pH and co-existing substances, and the reversibility were investigated. The proposed approach was successfully applied to the determination of Hg2+ in water samples. (C) 2010 Elsevier B.V. All rights reserved.National Nature Scientific Foundation of China (NSFC) [20775064, 20735002]; National Basic Research Program of China [2010CB732402