A miniaturized, disposable microbial culture chip has been fabricated by microengineering a highly porous ceramic sheet with up to one million growth compartments. This versatile culture format, with discrete compartments as small as 7 ؋ 7 m, allowed the growth of segregated microbial samples at an unprecedented density. The chip has been used for four complementary applications in microbiology. (i) As a fast viable counting system that showed a dynamic range of over 10,000, a low degree of bias, and a high culturing efficiency. (ii) In high-throughput screening, with the recovery of 1 fluorescent microcolony in 10,000. (iii) In screening for an enzyme-based, nondominant phenotype by the targeted recovery of Escherichia coli transformed with the plasmid pUC18, based on expression of the lacZ reporter gene without antibiotic-resistance selection. The ease of rapid, successive changes in the environment of the organisms on the chip, needed for detection of -galactosidase activity, highlights an advantageous feature that was also used to screen a metagenomic library for the same activity. (iv) In high-throughput screening of >200,000 isolates from Rhine water based on metabolism of a fluorogenic organophosphate compound, resulting in the recovery of 22 microcolonies with the desired phenotype. These isolates were predicted, on the basis of rRNA sequence, to include six new species. These four applications suggest that the potential for such simple, readily manufactured chips to impact microbial culture is extensive and may facilitate the full automation and multiplexing of microbial culturing, screening, counting, and selection. microdish ͉ microcolony ͉ cellular assay ͉ nanoporous aluminum oxide
Nanoscale ISFET (ion sensitive field-effect transistor) pH sensors are presented that produce the well-known sub-nernstian pH-response for silicon dioxide (SiO(2)) surfaces and near ideal nernstian sensitivity for alumina (Al(2)O(3)) surfaces. Titration experiments of SiO(2) surfaces resulted in a varying pH sensitivity ∼20 mV/pH for pH near 2 and >45 mV/pH for pH > 5. Measured pH responses from titrations of thin (15 nm) atomic layer deposited (ALD) alumina (Al(2)O(3)) surfaces on the nanoISFETs resulted in near ideal nernstian pH sensitivity of 57.8 ± 1.2 mV/pH (pH range: 2-10; T = 22 °C) and temperature sensitivity of 0.19 mV/pH °C (22 °C ≤ T ≤ 40 °C). A comprehensive analytical model of the nanoISFET sensor, which is based on the combined Gouy-Chapman-Stern and Site-Binding (GCS-SB) model, accompanies the experimental results and an extracted ΔpK ≈ 1.5 from the measured responses further supports the near ideal nernstian pH sensitivity.
Microstreaming from oscillating bubbles is known to induce vigorous vortex flow. Here we show how to harness the power of bubble streaming in an experiment to achieve directed transport flow of high velocity, allowing design and manufacture of microfluidic MEMS devices. By combining oscillating bubbles with solid protrusions positioned on a patterned substrate, solid beads and lipid vesicles are guided in desired directions without microchannels. Simultaneously, the flow exerts controlled localized forces capable of opening and reclosing lipid membranes.
We report a new low-cost top-down silicon nanowire fabrication technology requiring only conventional microfabrication processes including microlithography, oxidation, and wet anisotropic plane-dependent etching; high quality silicon nanowire arrays can be easily made in any conventional microfabrication facility without nanolithography or expensive equipment. Silicon nanowires with scalable lateral dimensions ranging from 200 nm down to 10-20 nm and lengths up to approximately 100 microm can be precisely formed with near-perfect monocrystalline cross sections, atomically smooth surfaces, and wafer-scale yields greater than 90% using a novel size reduction method where silicon nanowires can be controllably scaled to any dimension and doping concentration independent of large contacting regions from a continuous layer of crystalline silicon.
Measurements are shown indicating that the drying rate of nanochannels can be enhanced by up to 3 orders of magnitude relative to drying by vapor diffusion, and that the drying rate is independent of the relative humidity of the environment up to a relative humidity of more than 90%. Micromachined Pyrex glass nanochannels of 72 nm height and with sharp corners (corner angles 7 degrees) were used. Available theory shows that the sharp corners function as a low-resistance pathway for liquid water, siphoning (wicking) the water to a location close to the channel exit before it evaporates. The described phenomena are of importance for the understanding of drying processes in industry and agriculture. The introduction of sharp corners or grooves can furthermore be beneficial for the functioning of microheat pipes and capillary-pumped loops. DOI: 10.1103/PhysRevLett.95.256107 PACS numbers: 68.03.Fg Understanding the drying mechanism of porous materials is of importance in many industries such as the food, paper, pharmaceutical, and textile industry [1][2][3]. It has previously been observed that microporous media dried approximately 1 order of magnitude faster than can be expected from vapor diffusion alone [4,5]. Flow in liquid water films held on surfaces and flow of water held in corners or grooves were thought to cause this acceleration [6]. The contribution of film flow to drying has been experimentally investigated in cylindrical nanocapillaries, where it caused a tenfold increase of drying rate, [7] but the contribution of corner flow has never been investigated. Here we report on experiments using noncylindrical micromachined nanochannels to quantify corner flow.Drying results from three water transport mechanisms: vapor diffusion, film flow, and corner flow. To specifically investigate corner flow we designed an array of high aspect ratio (widthheight) noncylindrical channels of equal height but different width (Fig. 1). The three water transport mechanisms schematically are shown in Fig. 2. When corner flow dominates the drying process in a channel, the drying rate will depend on the inverse of the channel width, because the number of corners is independent of width but the total water volume inside the channel proportional with width. Drying due to film flow (for widthheight) and vapor diffusion in contrast does not depend on the channel width. Arrays of Pyrex channels, open on two sides, were manufactured in a clean room. Channels were wet etched (hydrofluoric acid) into one Pyrex wafer using a photolithographic mask. This wafer was bonded by thermal fusion to a second wafer which had access holes for filling. The channels were 4 mm long, 72:4 0:8 nm high (determined by AFM) and the width in the array differed from 2 to 30 m. The channel shape was an isosceles trapezoid of very high aspect ratio (width=height > 40) (Fig. 1 bottom). The angle of the sharp corner was determined to be 6:6 0:7 degrees by SEM measurements of bonded chips and by AFM measurements prior to bonding of the Pyrex plates. The shar...
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