Abstract: A review with 40 references. Silk fibroin derived from Bombyx mori cocoon is being developed and utilized for purposes besides traditional textile material. Fibroin can be easily made up into various forms, several of which can serve as enzyme-immobilized supports. There are numerous reports on immobilized enzymes using these forms of silk fibroin as supports in which the enzyme-immobilized fibroin membranes were characterized in detail by means of spectrophotometry, IR spectra, NMR, ESR. Enzyme-immobilized fibroin membranes have been successfully used in several biosensors for the determinations of glucose, hydrogen peroxide and uric acid in which glucose and urate biosensors in a flow injection system were able rapidly to analyze various biosamples including human whole blood or serum.

Abstract: The biosensors based on the enzyme electrode in a flow injection analysis suffer an interference from hemacyte, macromolecules and some lower molecular weight species in whole blood, plasma, serum or urine, besides endogenous electroactive species such as ascorbate. This often results in an increasingly serious tailing phenomenon in the response current peak of substrates. A unique method used daily is to cover the outer enzyme membrane with a porous ultrafilter film to isolate it from hemacyte and macromolecules but not from some smaller molecules. In the present paper, we first introduce a tailing inhibitor-ion pair reagent into the flowing buffer system for eliminating the tailing phenomenon from the complex matrices on biosensors. When 0.25 or 0.5% tetrabutylammonium chloride (V/V) was added to 0.02 M phosphate buffer, serious lags of whole blood, plasma, serum and urine on the two biosensors for uric acid and glucose disappeared entirely so that their response time was shortened to about 50 seconds; their base lines also became more smooth and stable. Thus, the resulting two biosensors were capable of detecting over 60 biosamples per hour. The reported experiment shows that the tailing inhibitor has effects on the response current and response time of various biosamples and on the concentration of the dissolved oxygen in buffer, with no evident effect on the recoveries of glucose and mate in biosamples with both sensors. The finding confirmed that some lower molecular weight species with negative charge result in the serious tailing phenomenon in the response current peaks of various biosamples on the glucose and mate biosensors in a now injection system.

Abstract: An amperometric urate sensor based on a uricase-immobilized silk fibroin membrane and an O electrode in flow injection analysis are described. The biosensor shows that recoveries of uric acid in human serum and urine are at 94.2-102.6% and 92.5-97.9%, respectively. The relative standard deviations (RSDs) for repeatedly monitoring standard urate solution, human serum and urine are 2.37, 3.72 and 2.95%, respectively., based on 100 measurements. The urate sensor based on the uricase-immobilized membrane is capable of detecting 60-70 human serum samples per h. Also, a piece of uricase-immobilized fibroin membrane used at the sensor could not only be stored for over 2 yr, but also repeatedly monitored >1000 times for biosamples such as human serum or urine.