ABSTRACT
The present study aims at fabricating a laccase (LAC) based amperometric biosensor for detection of phenolic compounds. LAC was immobilized into the porous matrix of polyaniline nanofibers (PANFs) in a three-step process, consisting of enzyme adsorption, precipitation, and crosslinking (EAPC). Immobilized LAC on PANF in the form of EAPC was highly active and stable when compared to control samples of 'enzyme adsorption (EA)' and 'enzyme adsorption and crosslinking (EAC)' samples. For example, the activity of EAPC was 19.7 and 15.1 times higher than those of EA and EAC per unit weight of PANF, respectively. After 6days at room temperature, EAPC maintained 100% of its initial activity, while EA and EAC retained only 7.7% and 11% of their initial activities, respectively. When the samples were subjected to the heat treatment at 60°C over 3h, EAPC maintained 74% of its initial activity, while EA and EAC retained around 1% of their initial activities, respectively. To demonstrate the feasible application of EAPC in biosensors, the enzyme electrodes were prepared and used for detection of phenolic compounds, which are environmentally hazardous chemicals. The sensitivities of biosensors with EA, EAC, and EAPC were 20.3±5.9, 26.6±5.4 and 518±11µAmM(-1)cm(-2), respectively. At 50°C for 5h, EAPC electrode maintained 80% of its initial sensitivity, while EA and EAC electrode showed 0% and 19% of their initial sensitivities, respectively. Thus, LAC-based biosensor using EAPC protocol with PANFs showed a great promise for developing a highly sensitive and stable biosensor for detection of phenolic compounds.
Subject(s)
Aniline Compounds/chemistry , Biosensing Techniques , Laccase/chemistry , Nanofibers/chemistry , Adsorption , Catechols/chemistry , Cross-Linking Reagents/chemistry , Electrochemistry , Electrodes , Environmental Monitoring/methods , Enzymes, Immobilized/chemistry , Microscopy, Electron, Scanning , Phenol/chemistry , Phenols , TemperatureABSTRACT
Raman spectroscopy is used to characterize the composition of toroids formed in an aprotic Li-O2 cell based on an activated carbon cathode. The trends in the Raman data as a function of discharge current density and charging cutoff voltage provide evidence that the toroids are made up of outer LiO2-like and inner Li2O2 regions, consistent with a disproportionation reaction occurring in the solid phase. The LiO2-like component is found to be associated with a new Raman peak identified in the carbon stretching region at â¼1505 cm(-1), which appears only when the LiO2 peak at 1123 cm(-1) is present. The new peak is assigned to distortion of the graphitic ring stretching due to coupling with the LiO2-like component based on density functional calculations. These new results on the LiO2-like component from Raman spectroscopy provide evidence that a late stage disproportionation mechanism can occur during discharge and add new understanding to the complexities of possible processes occurring in Li-O2 batteries.
