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The susceptibility of Escherichia coli and Helicobacter pylori to pH and the effect of pepsinmediated proteolysis were investigated. This was to establish the relative importance of their bacterial killing properties in gastric juice. Solutions in the pH range 1?5-7?4 with or without pig pepsin A were used, together with seven gastric juice samples obtained from patients undergoing routine gastric collection. Escherichia coli C690 (a capsulate strain), E. coli K-12 (a rough mutant) and Helicobacter pylori E5 were selected as the test organisms. Suspensions of bacteria (1610 6 E. coli ml "1 and 1610 8 H. pylori ml) were pre-incubated with test solutions at 37 6C for up to 2 h, and then cultured to establish the effect on subsequent growth. Survival of bacteria was diminished at pHs of less than 3?5, whereas killing required a pH of less than 2?5. Preincubation with pig pepsin at 0?5, 1?0 and 2?0 mg ml "1 at pH 3?5 reduced viable counts by 100 % for E. coli 690 and E. coli K-12 after 100 min incubation. With H. pylori, the viable counts decreased to 50 % of the control after 20 min incubation in 1 mg pepsin ml "1 at pH 2?5, 3?0 and 3?5. The gastric juices showed bactericidal activity at pH 3?5, and the rate of killing was juice dependent, with complete death of E. coli 690 occurring between 5 and 40 min post-incubation. Thus, killing of E. coli and H. pylori occurs optimally at pHs of less than 2?5. At pH 3?5, little effect is observed, whereas addition of pepsin alone or in gastric juice causes a marked increase in bacterial susceptibility, suggesting an important role for proteolysis in the killing of bacteria.

The development of a high-throughput single-cell metabolic rate monitoring system relies on the use of transparent substrate material for a single cell-trapping platform. The high optical transparency, high chemical resistance, improved surface quality and compatibility with the silicon micromachining process of fused silica make it very attractive and desirable for this application. In this paper, we report the results from the development and characterization of a hydrofluoric acid (HF) based deep wet-etch process on fused silica. The pin holes and notching defects of various single-coated masking layers during the etching are characterized and the most suitable masking materials are identified for different etch depths. The dependence of the average etch rate and surface roughness on the etch depth, impurity concentration and HF composition are also examined. The resulting undercut from the deep HF etch using various masking materials is also investigated. The developed and characterized process techniques have been successfully implemented in the fabrication of micro-well arrays for single cell trapping and sensor deposition. Up to 60 μm deep micro-wells have been etched in a fused silica substrate with over 90% process yield and repeatability. To our knowledge, such etch depth has never been achieved in a fused silica substrate by using a non-diluted HF etchant and a single-coated masking layer at room temperature.

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In this note, we present our results from process development and characterization of reactive ion etching (RIE) of fused silica using a single-coated soft masking layer (KMPR R 1025, Microchem Corporation, Newton, MA). The effects of a number of fluorine-radical-based gaseous chemistries, the gas flow rate, RF power and chamber pressure on the etch rate and etching selectivity of fused silica were studied using factorial experimental designs. RF power and pressure were found to be the most important factors in determining the etch rate. The highest fused silica etch rate obtained was about 933 Å min −1 by using SF 6 -based gas chemistry, and the highest etching selectivity between the fused silica and KMPR R 1025 was up to 1.2 using a combination of CF 4 , CHF 3 and Ar. Up to 30 μm deep microstructures have been successfully fabricated using the developed processes. The average area roughness (R a ) of the etched surface was measured and results showed it is comparable to the roughness obtained using a wet etching technique. Additionally, near-vertical sidewalls (with a taper angle up to 85 • ) have been obtained for the etched microstructures. The processes developed here can be applied to any application requiring fabrication of deep microstructures in fused silica with near-vertical sidewalls. To our knowledge, this is the first note on deep RIE of fused silica using a single-coated KMPR R 1025 masking layer and a non-ICP-based reactive ion etcher.

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