Lichens have long been used as biomonitors of environmental pollution. We therefore investigated the application of lichen-modified carbon paste electrodes (CPEs) for the determination of lead( 11) and copper( 11) using differential pulse anodic stripping voltammetry. These electrochemical biosensors incorporate the biological selectivity of lichen species such as Cladonia portentosa and Lobaria pulmonauia, and the genus Koccelh, with the sensitivity of electrochemical detection. As such, they may offer new reactivity patterns that could be exploited in the determination of trace metal ions in environmental samples and in speciation studies. The voltammetric responses were evaluated with respect to pH of accumulation (carried out under open circuit conditions), pH of electrolyte solution, metal ion concentration, percentage lichen loading in the carbon paste, interferences, and surface renewal. lNTRODUCTIONLichens are plants formed by the symbiotic association of an alga and a fungus. Their general structure is that of an upper cortex, a protective central fungal medulla (of loosely packed hyphae), and a lower cortex. The algae may form a distinct layer beneath the upper cortex, or they can be dispersed throughout. Most lichens have an extracellular matrix which is a gelatinous secretion containing polysaccharides such as lichenan and isolichenan together with glucans, galactomannose, and lichen acids.For years, lichens have been known to accumulate metal ions and have been used extensively as biomonitors of environmental pollution [ 1, 21. The diversity of lichen species close to a suspected pollution source has been used to assess the levels of gaseous air pollutants, with fewer lichen species being found closer t o the emission source 13, 41. These plants are considered to be useful biomonitors of sulfur dioxide A review by Richardson [22] on the pollution sensitivity of lichens discusses the effects of sulfur dioxide and acid rain on the lichens, along with the mechanism of airborne elemental accumulation by these plants. Since then, Beck and Ramelow [ 231 have used lichens enclosed in porous polyvinyl chloride (PVC) tubes as monitors of dissolved metals in natural waters. The W C tubes were suspended at drfferent sampling points along a river. After 2 weeks, the lichens were analyzed by atomic absorption spectroscopy for a wide variety of metals ions includng Pb(I1) and Cu(I1).Kecently, Wang et al. [ 241 reported on experiments at algae-modified electrodes to investigate the incorporation of anionic and cationic metal complexes by algae. GardeaTorresday et al. [ 2 5 , 261 then reported on voltammetric measurements at algae-modified electrodes capable of preconcentrating Cu(I1) and Au( I). These studies suggested that the development of lichen-modified electrodes might open up a new area of sensor development based on the nonelectrochemical bioaccumulation of metal ions.This article describes the development of lichenmodified carbon paste electrodes (CPEs) for the detection of lead( 11) and copper( 1...
An approach to the construction of amperometric biosensors based on the incorporation of an enzyme in silicone grease and using the grease to fill micropores on a graphite surface is described. The enzyme-grease electrode concept, illustrated with the enzyme tyrosinase, offers a very simple, rapid and inexpensive approach to the fabrication of enzyme electrodes. The tyrosinase electrode responds very rapidly to dynamic changes in the concentration of phenolic compounds. A response time (t95%) as low as 5 s has been determined. With flow injection, 120 samples per hour can be processed with a relative standard deviation of 2.4%. The electrode remains active for about 12 d. The detection limit for dopamine is 6 x 10(-6) M. This method of biosensor construction should be applicable to other enzyme-substrate systems.
Gas samples were obtained during colonoscopy for analysis. Patients were prepared with polyethylene glycol (PEG) (N = 23), phosphate enema (N = 34) and mannitol (N = 4). Air insufflation was used in all procedures. High concentrations of hydrogen were detected in 3 out of 38 gas samples in the PEG group, in 2 of 41 samples in the phosphate enema group and in one of the 8 samples in the mannitol group. All patients had a coexisting intracolonic oxygen concentration > 5%. The results suggest that potentially explosive concentrations of hydrogen may occur after conventional bowel preparations, and that insufflation of carbon dioxide during polypectomy should be a routine.
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