Attenuation of wastewater-derived contaminants in an effluent-dominated river

Although wastewater-derived chemical contaminants undergo transformation through a variety of mechanisms, the relative importance of processes such as biotransformation and photolysis is poorly understood under conditions representative of large rivers. To assess attenuation rates under conditions encountered in such systems, samples from the Trinity River were analyzed for a suite of wastewater-derived contaminants during a period when wastewater effluent accounted for nearly the entire flow of the river over a travel time of approximately 2 weeks. While the concentration of total adsorbable organic iodide, a surrogate for recalcitrant X-ray phase contrast media in wastewater, was approximately constant throughout the river, concentrations of ethylenediamine tetraacetate, gemfibrozil, ibuprofen, metoprolol, and naproxen all decreased between 60% and 90% as the water flowed downstream. Comparison of attenuation rates estimated in the river with rates measured in laboratory-scale microcosms suggests that biotransformation was more important than photolysis for most of the compounds. Further evidence for biotransformation in the river was provided by measurements of the enantiomeric fraction of metoprolol, which showed a gradual decrease as the water moved downstream. Results of this study indicate that natural attenuation can result in significant decreases in concentrations of wastewater-derived contaminants in large rivers.     

Surface acoustic wave velocity in single-crystal AlN substrates

The surface acoustic wave velocity has been measured on a-plane (c-propagation) and c-plane oriented bulk aluminum nitride (AlN) single crystals using the S11-parameter method in the frequency range 160-360 MHz. The SAW velocity is 5760 m/s for both orientations. From comparison of this value with the simulations using various elastic constants of AlN available in literature, we estimated the elastic constant C44 to be 122 +/- 1 GPa.     

Localized surface plasmon resonance spectroscopy of single silver triangular nanoprisms

The plasmonic properties of single silver triangular nanoprisms are investigated using dark-field optical microscopy and spectroscopy. Two distinct localized surface plasmon resonances (LSPR) are observed. These are assigned as in-plane dipolar and quadrupolar plasmon excitations using electrodynamic modeling based on the discrete dipole approximation (DDA). The dipole resonance is found to be very intense, and its peak wavelength is extremely sensitive to the height, edge length, and tip sharpness of the triangular nanoprism. In contrast, the intensity of the quadrupole resonance is much weaker relative to the dipole resonance in the single particle spectra than in the ensemble averaged spectrum. Several parameters relevant to the chemical sensing properties of these nanoprisms have been measured. The dependence of the dipole plasmon resonance on the refractive index of the external medium is found to be as high as 205 nm RIU(-1) and the plasmon line width as narrow as approximately 0.17 eV. These data lead to a sensing figure of merit (FOM), the slope of refractive index sensitivity in eV RIU(-1)/line width (eV), as high as 3.3. In addition, the LSPR shift response to alkanethiol chain length was found to be linear with a slope of 4.4 nm per CH2 unit. This is the highest short-range refractive index sensitivity yet measured for a nanoparticle.     

Modeling of scanning laser polarimetry images of the human retina for progression detection of glaucoma

The development of methods to detect slowly progressing diseases is often hampered by the time-consuming acquisition of a sufficiently large data set. In this paper, a method is presented to model the change in images acquired by scanning laser polarimetry, for the detection of glaucomatous progression. The model is based on image series of 23 healthy eyes and incorporates colored noise, incomplete cornea compensation and masking by the retinal blood vessels. Additionally, two methods for detecting progression, taking either one or two follow-up visits into account, are discussed and tested on these simulated images. Both methods are based on Student's t-tests, morphological operations and anisotropic filtering. The images simulated by the model are visually pleasing, show corresponding statistical properties to the real images and are used to optimize the detection methods. The results show that detecting progression based on two follow-up visits greatly improves the sensitivity without adversely affecting the specificity.     

Broadband coherent anti-Stokes Raman spectroscopy characterization of polymer thin films

Broadband coherent anti-Stokes Raman spectroscopy (CARS) is demonstrated as an effective probe of polymer thin film materials. A simple modification to a 1 kHz broad bandwidth sum frequency generation (SFG) spectrometer permits acquisition of CARS spectra for polymer thin films less than 100 nm thick, a dimension relevant to organic electronic device applications. CARS spectra are compared to the conventional Raman spectra of polystyrene and the resonance-enhanced Raman spectra of poly(3-hexylthiophene). The CARS spectra obtained under these conditions consistently demonstrate enhanced signal-to-noise ratio compared to the spontaneous Raman scattering. The sensitivity of the CARS measurement is limited by the damage threshold of the samples. The dielectic properties of the substrate have a dramatic effect on the detected signal intensity. For ultrathin films, the strongest signals are obtained from fused silica surfaces. Similar to surface-enhanced Raman scattering (SERS), Au also gives a large signal, but contrary to SERS, no surface roughening is necessary.     

Hydrolysis of Chlorella by Cellulomonas sp. YJ5 cellulases and its biofunctional properties

Both 10% and 20% (w/w) Chlorella suspensions were hydrolyzed by 150 to 350 U/mL of cellulases from a 3-d cultivation of Cellulomonas sp. YJ5. Higher chlorophyll, reducing sugars and soluble proteins, and lower residual insoluble solid were observed on both samples after 30-min hydrolysis by various concentrations of cellulases at 50 °C. Decrease in insoluble solid, increases in soluble proteins, peptides and chlorophyll contents, and microscopic observation indicated obvious lysis of cell walls occurred during 60- to 180-min hydrolysis. Significant increases in soluble proteins, peptides, Fe(2+) chelating ability, trolox equivalent antioxidation capacity (TEAC), and reducing power was obtained after 3-h hydrolysis by 150 U/mL of cellulase. These data suggested that cellulolysis technology has high application potential in Chlorella industry.     

Steroids in a typical swine farm and their release into the environment

The occurrence and fate of fourteen androgens, four estrogens, five glucocorticoids and five progestagens were investigated by rapid resolution liquid chromatography-tandem mass spectrometry (RRLC-MS/MS) in a typical swine farm with lagoon waste disposal systems, in south China. Nineteen, 22 and 8 of 28 steroids were detected at concentrations ranging from 2.2 ± 0.1 ng/g (androsta-1,4-diene-3,17-dione) to 14,400 ± 394 ng/g (progesterone) in the feces samples, from 6.1 ± 2.3 ng/L (17β-boldenone) to 10,800 ± 3190 ng/L (norgestrel) in the flush water samples, and from 5.0 ± 0.2 ng/g (progesterone) to 225 ± 79.4 ng/g (5α-dihydrotestosterone) in the suspended particles, respectively. By comparing the types and concentrations of steroids in different treatment stages of the lagoon systems, it demonstrated that the lagoon systems used in the farm were not effective method to reduce various steroids in wastewater. Among the thirteen synthetic steroids detected in the swine feces and flush water, only seven (methyl testosterone, 17α-trenbolone, 17β-trenbolone, 17α-ethynyl estradiol, dexamethasone, medroxyprogesterone, and norgestrel) were regarded as the parent/metabolite compounds of animal exogenous usage. According to the estimated masses of steroids from feces and flush water, the excretion of steroids for sows were mainly from feces, but for piglets or barrows, most excreted steroids were through flush water rather than feces. The total daily excreted masses of androgens, estrogens, glucocortcoids and progestagens in the sow feces were in the range of 90.7-6310 μg/d, which were up to a thousand fold of those in the feces of other growth stages indicating that the proportion of sow number in the swine farm directly influenced the total excretion mass of steroids. In addition, two natural steroids 4-androstene-3,17-dione and progesterone were worth notice due to their relatively high concentrations per sow excretion, 277 μg/d and 6380 μg/d, respectively, which are approximately equivalent to the daily excretion of 100 persons. Some steroids were also detected in the well water, vegetable field and receiving stream, and may pose potential high risks to some sensitive organisms in the receiving environment.     

High-throughput droplet digital PCR system for absolute quantitation of DNA copy number

Digital PCR enables the absolute quantitation of nucleic acids in a sample. The lack of scalable and practical technologies for digital PCR implementation has hampered the widespread adoption of this inherently powerful technique. Here we describe a high-throughput droplet digital PCR (ddPCR) system that enables processing of ~2 million PCR reactions using conventional TaqMan assays with a 96-well plate workflow. Three applications demonstrate that the massive partitioning afforded by our ddPCR system provides orders of magnitude more precision and sensitivity than real-time PCR. First, we show the accurate measurement of germline copy number variation. Second, for rare alleles, we show sensitive detection of mutant DNA in a 100,000-fold excess of wildtype background. Third, we demonstrate absolute quantitation of circulating fetal and maternal DNA from cell-free plasma. We anticipate this ddPCR system will allow researchers to explore complex genetic landscapes, discover and validate new disease associations, and define a new era of molecular diagnostics.     

Spatially resolved plasmonically enhanced photocurrent from Au nanoparticles on a Si nanowire

Semiconducting nanowires have been demonstrated as promising light-harvesting units with enhanced absorption compared to bulk films of equivalent volume. However, for small diameter nanowires, the ultrahigh aspect ratio constrains the absorption to be polarization selective by responding primarily to the transverse magnetic (TM) light. While this effect is useful for polarization-sensitive optoelectronic devices, practical light-harvesting applications demand efficient light absorption in both TM and transverse electric (TE) light. In this study, we engineer the polarization sensitivity and the charge carrier generation in a 50 nm Si nanowire by decorating the surface with plasmonic Au nanoparticles. Using scanning photocurrent microscopy (SPCM) with a tunable wavelength laser, we spatially and spectrally resolve the local enhancement in the TE photocurrent resulting from the plasmonic near-field response of individual nanoparticles and the broad-band enhancement due to surface-enhanced absorption. These results provide guidance to the development and the optimization of nanowire-nanoparticle light-harvesting systems.