No abstract

Systematic evolution of ligands by exponential enrichment (SELEX) was used to develop DNA ligands (aptamers) to cholera whole toxin and staphylococcal enterotoxin B (SEB). Affinity selection of aptamers was accomplished by conjugating the biotoxins to tosyl-activated magnetic beads. The use of magnetic beads reduces the volumes needed to perform aptamer selection, thus obviating alcohol precipitation and allowing direct PCR amplification from the bead surface. Following five rounds of SELEX, 5'-biotinylated aptamers were bound to streptavidin-coated magnetic beads and used for the detection of ruthenium trisbypyridine [Ru(bpy)3(2+)]-labeled cholera toxin and SEB by an electrochemiluminescence methodology. A comparison of control (double-stranded) aptamer binding was made with aptamers that were heat denatured at 96 degrees C (single-stranded) and allowed to cool (conform) in the presence of biotoxin-conjugated magnetic beads. Results suggest that control aptamers performed equally well when compared to heat-denatured DNA aptamers in the cholera toxin electrochemiluminescence assay and a colorimetric microplate assay employing peroxidase-labeled cholera toxin and 5'-amino terminated aptamers conjugated to N-oxysuccinimide-activated microtiter wells. Interestingly, however, in the SEB electrochemiluminescence assay, double-stranded aptamers exceeded the performance of single-stranded aptamers. The detection limits of all aptamer assays were in the low nanogram to low picogram ranges.

A novel assay was developed for the detection of Bacillus thuringiensis (BT) spores. The assay is based on the fluorescence observed after binding an aptamer-quantum dot conjugate to BT spores. The in vitro selection and amplification technique called SELEX (Systematic Evolution of Ligands by EXponential enrichment) was used in order to identify the DNA aptamer sequence specific for BT. The 60 base aptamer was then coupled to fluorescent zinc sulfide-capped, cadmium selenide quantum dots (QD). The assay is semi-quantitative, specific and can detect BT at concentrations of about 1,000 colony forming units/ml.

No abstract

To better understand the cellular and molecular responses to overexposure to millimeter waves, alterations in the gene expression profile and histology of skin after exposure to 35 GHz radiofrequency radiation were investigated. Rats were subjected to sham exposure, to 42 degrees C environmental heat, or to 35 GHz millimeter waves at 75 mW/cm(2). Skin samples were collected at 6 and 24 h after exposure for Affymetrix GeneChip analysis. The skin was harvested from a separate group of rats at 3-6 h or 24-48 h after exposure for histopathology analysis. Microscopic findings observed in the dermis of rats exposed to 35 GHz millimeter waves included aggregation of neutrophils in vessels, degeneration of stromal cells, and breakdown of collagen. Changes were detected in 56 genes at 6 h and 58 genes at 24 h in the millimeter-wave-exposed rats. Genes associated with regulation of transcription, protein folding, oxidative stress, immune response, and tissue matrix turnover were affected at both times. At 24 h, more genes related to extracellular matrix structure and chemokine activity were altered. Up-regulation of Hspa1a, Timp1, S100a9, Ccl2 and Angptl4 at 24 h by 35 GHz millimeter-wave exposure was confirmed by real-time RT-PCR. These results obtained from histopathology, microarrays and RT-PCR indicate that prolonged exposure to 35 GHz millimeter waves causes thermally related stress and injury in skin while triggering repair processes involving inflammation and tissue matrix recovery.

No abstract

Electromagnetic fields at millimeter wave lengths are being developed for commercial and military use at power levels that can cause temperature increases in the skin. Previous work suggests that sustained exposure to millimeter waves causes greater heating of skin, leading to faster induction of circulatory failure than exposure to environmental heat (EH). We tested this hypothesis in three separate experiments by comparing temperature changes in skin, subcutis, and colon, and the time to reach circulatory collapse (mean arterial blood pressure, 20 mmHg) in male Sprague-Dawley rats exposed to the following conditions that produced similar rates of body core heating within each experiment: (1) EH at 42 degrees C, 35 GHz at 75 mW/cm, or 94 GHz at 75 mW/cm under ketamine and xylazine anesthesia; (2) EH at 43 degrees C, 35 GHz at 90 mW/cm, or 94 GHz at 90 mW/cm under ketamine and xylazine anesthesia; and (3) EH at 42 degrees C, 35 GHz at 90 mW/cm, or 94 GHz at 75 mW/cm under isoflurane anesthesia. In all three experiments, the rate and amount of temperature increase at the subcutis and skin surface differed significantly in the rank order of 94 GHz more than 35 GHz more than EH. The time to reach circulatory collapse was significantly less only for rats exposed to 94 GHz at 90 mW/cm, the group with the greatest rate of skin and subcutis heating of all groups in this study, compared with both the 35 GHz at 90 mW/cm and the EH at 43 degrees C groups. These data indicate that body core heating is the major determinant of induction of hemodynamic collapse, and the influence of heating of the skin and subcutis becomes significant only when a certain threshold rate of heating of these tissues is exceeded.

The existence of specific bioeffects due to high peak power microwaves and their potential health hazards are among the most debated but least explored problems in microwave biology. The present study attempted to reveal such effects by comparing the bioeffects of short trains of extremely high power microwave pulses (EHPP, 1 μs width, 250–350 kW/g, 9.2 GHz) with those of relatively low power pulses (LPP, 0.5–10 s width, 3–30 W/g, 9.2 GHz). EHPP train duration and average power were made equal to those of an LPP; therefore both exposure modalities produced the same temperature rise. Bioeffects were studied in isolated, spontaneously beating slices of the frog heart. In most cases, a single EHPP train or LPP immediately decreased the inter‐beat interval (IBI). The effect was proportional to microwave heating, fully reversible, and easily reproducible. The magnitude and time course of EHPP‐ and LPP‐induced changes always were the same. No delayed or irreversible effects of irradiation were observed. The same effect could be repeated in a single preparation numerous times with no signs of adaptation, sensitization, lasting functional alteration, or damage. A qualitatively different effect, namely, a temporary arrest of preparation beats, could be observed when microwave heating exceeded physiologically tolerable limits. This effect also did not depend on whether the critical temperature rise was produced by LPP or EHPP exposure. Within the studied limits, we found no indications of EHPP‐specific bioeffects. EHPP‐ and LPP‐induced changes in the pacemaker rhythm of isolated frog heart preparation were identical and could be entirely attributed to microwave heating. Bioelectromagnetics 21:245–254, 2000. © 2000 Wiley‐Liss, Inc.