Formation and analysis of shallow arsenic profiles

Shallow arsenic implants were activated by furnace and rapid thermal annealing (RTA). Comparisons of junction depths measured by secondary ion mass spectrometry (SIMS) and spreading resistance (SR) showed SIMS values 50-90 nm deeper than SR values, due to ion knock-on during SIMS profiling     

Prof. Dr. Robert Weigel elected an IEEE Fellow

SciencenewsIEEE MTT-S

Prof. Dr. Robert Weigel elected an IEEE Fellow     

Development of a set of simple bacterial biosensors for quantitative and rapid measurements of arsenite and arsenate in potable water

Testing for arsenic pollution is commonly performed with chemical test kits of unsatisfying accuracy. Bacterial biosensors are an interesting alternative as they are easily produced, simple, and highly accurate devices. Here, we describe the development of a set of bacterial biosensors based on a nonpathogenic laboratory strain of Escherichia coli, the natural resistance mechanism of E. coli against arsenite and arsenate, and three reporter proteins: bacterial luciferase, beta-galactosidase and Green Fluorescent Protein (GFP). The biosensors were genetically optimized to reduce background expression in the absence of arsenic. In calibration experiments with the biosensors and arsenite-amended potable water, arsenite concentrations at 4 microg of As/L (0.05 microM) were routinely and accurately measured. The currently most quantitative system expressed the bacterial luciferase as reporter protein, responding proportional with a concentration range between 8 and 80 microg of As/L. Sensor cells could be stored as frozen batches, resuspended in plain media, and exposed to the aqueous test sample, and light emission was measured after 30-min incubation. Field testing for arsenite was achieved with a system that contained beta-galactosidase, producing a visible blue color at arsenite concentrations above 8 microg/L. For this sensor, a protocol was developed in which the sensor cells were dried on a paper strip and placed in the aqueous test solution for 30 min after which time color development was allowed to take place. The GFP sensor showed good potential for continuous rather than end point measurements. In all cases, growth of the biosensors and production of the strip test was achieved by very simple means with common growth media, and quality control of the sensors was performed by isolating the respective plasmids with the genetic constructs according to simple standard genetic technologies. Therefore, the biosensor cells and protocols may offer a realistic alternative for measuring arsenic contamination in potable water.     

Effect of fungal hyphae on the access of bacteria to phenanthrene in soil

The effect of fungal hyphae on the mobilization of soil-dwelling bacteria and their access to hydrophobic phenanthrene in soil was tested in columns containing air-filled agricultural soil. The experimental design included a spatial separation between zones of bacterial inoculation and contamination. Motile Pseudomonas putida PpG7 (NAH7) and fast-growing, hydrophilic Pythium ultimum were used as the model phenanthrene-degrading and vector organisms, respectively. Efficient translocation of strain PpG7 in the range of centimetres in presence of P. ultimum indicated that the fungal mycelia bridged air-filled pores and thereby provided a continuous network of water-paths that enabled bacteria to spread in the soil. Biodegradation of the soil-associated phenanthrene was found only in the presence of the fungal mycelia, hence proving that the fungal network facilitated the access of the bacteria to the contaminant. Our data suggest that the specific stimulation of indigenous fungi is a promising method to mobilize pollutant degrading bacteria and thereby improve soil bioremediation in-situ.     

High-mobility organic thin-film transistors based on a small-molecule semiconductor deposited in vacuum and by solution shearing

The small-molecule organic semiconductor 2,9-di-decyl-dinaphtho-[2,3-b:2′,3′-f]-thieno-[3,2-b]-thiophene (C₁₀-DNTT) was used to fabricate bottom-gate, top-contact thin-film transistors (TFTs) in which the semiconductor layer was prepared either by vacuum deposition or by solution shearing. The maximum effective charge-carrier mobility of TFTs with vacuum-deposited C₁₀-DNTT is 8.5 cm²/V s for a nominal semiconductor thickness of 10 nm and a substrate temperature during the semiconductor deposition of 80 °C. Scanning electron microscopy analysis reveals the growth of small, isolated islands that begin to coalesce into a flat conducting layer when the nominal thickness exceeds 4 nm. The morphology of the vacuum-deposited semiconductor layers is dominated by tall lamellae that are formed during the deposition, except at very high substrate temperatures. Atomic force microscopy and X-ray diffraction measurements indicate that the C₁₀-DNTT molecules stand approximately upright with respect to the substrate surface, both in the flat conducting layer near the surface and within the lamellae. Using the transmission line method on TFTs with channel lengths ranging from 10 to 100 μm, a relatively small contact resistance of 0.33 kΩ cm was determined. TFTs with the C₁₀-DNTT layer prepared by solution shearing exhibit a pronounced anisotropy of the electrical performance: TFTs with the channel oriented parallel to the shearing direction have an average carrier mobility of (2.8 ± 0.3) cm²/V s, while TFTs with the channel oriented perpendicular to the shearing direction have a somewhat smaller average mobility of (1.3 ± 0.1) cm²/V s.     

Calcite Reinforced Silica–Silica Joints in the Biocomposite Skeleton of Deep‐Sea Glass Sponges

The hierarchically structured glass sponge Caulophacus species uses the first known example of a silica and calcite biocomposite to join the spicules of its skeleton together. In the stalk and body skeleton of this poorly known deep‐sea glass sponge siliceous spicules are modified by the addition of conical calcite seeds, which then form the basis for further silica secretion to form a spinose region. Spinose regions on adjacent spicules are then joined by siliceous crosslinks, leading to unusually strong cross‐spicule linkages. In addition to the biomaterials implications it is now clear, from this first record of a biomineral other than silica, that the hexactinellid sponges are capable of synthesizing calcite, the ancestral skeletal material. We propose that, while the low concentrations of calcium in deep sea waters drove the evolution of silica skeletons, the brittleness of silica has led to retention of the more resilient calcite in very low concentrations at the skeletal joints.     

“To Catch or Not to Catch”: Microcapsule‐Based Sandwich Assay for Detection of Proteins and Nucleic Acids

The development of new assays that specifically detect intermediate or final products of biotechnological processes or multiple analytes in biomedical research is important for diagnostics and biotechnology. This study presents a microcapsule‐based sandwich assay for detection of proteins and nucleic acids using flow cytometry as an optical readout. The main component of the assay are robust chemically cross‐linked microcapsules that are coated with adaptor proteins such as protein A or streptavidin. In the first approach, the ability of detecting the blood cancer biomarker beta‐2 microglobulin in the fM to pM concentration range with the help of protein A‐coated capsules is demonstrated. In the second approach, streptavidin‐coated capsules are used for detection of nucleic acids in the nM concentration range. The developed assay allows rapid quantitative analyte measurement, while providing high sensitivity and selectivity at very small sample quantities. In the future, protein A‐ and streptavidin‐coated microcapsules can be used as universal tools for detection of a broad range of analytes.