304 research outputs found
Optical diffraction for measurements of nano-mechanical bending
Micromechanical transducers such as cantilevers for AFM often rely on optical
readout methods that require illumination of a specific region of the
microstructure. Here we explore and exploit the diffraction effects that have
been previously neglected when modeling cantilever bending measurement
techniques. The illumination of a cantilever end causes an asymmetric
diffraction pattern at the photodetector that significantly affects the
calibration of the signal in the popular optical beam deflection technique
(OBDT). Conditions for optimized linear signals that avoid detection artifacts
conflict with small numerical aperture illumination and narrow cantilevers
which are softer and therefore more sensitive. Embracing diffraction patterns
as a physical measurable allows a richer detection technique that decouples
measurements of tilt and curvature and simultaneously relaxes the requirements
on the alignment of illumination and detector. We show analytical results,
numerical simulations and physiologically relevant experimental data
demonstrating the usefulness of these diffraction features. We offer
experimental design guidelines and identify and quantify possible sources of
systematic error of up to 10% in OBDT. We demonstrate a new nanometre
resolution detection method that can replace OBDT, where Frauenhofer and Bragg
diffraction effects from finite sized and patterned cantilevers are exploited.
Such effects are readily generalized to arrays, and allow transmission
detection of mechanical curvature, enabling in-line instruments. In particular,
a cantilever with a periodic array of slots produces Bragg peaks which can be
analyzed to deduce the cantilever curvature. We highlight the comparative
advantages over OBDT by detecting molecular activity of antibiotic Vancomycin,
with an RMS noise equivalent to less than (1.5 nm), as example of
possible multi-maker bio-assays.Comment: 9 pages, 8 figure
Rapid antimicrobial sensitivity testing by single cell nanoscale optical interference
Growing antimicrobial resistance (AMR) is a serious global threat to human health, with estimates of AMR leading to 10 million deaths per year and costing the global economy $100tn by 20501,2. Current methods to detect resistance include phenotypic antibiotic sensitivity testing (AST) which measures bacterial growth and is therefore hampered by slow time to result (~12-24 hours). Therefore new rapid phenotypic methods for AST are urgently needed3. Here we describe a novel method for detecting phenotypic antibiotic resistance in ~45 minutes, capable of detecting single bacteria. The method uses a sensitive laser and detector system to measure nanoscale optical interference of single bacterial cells present in media, with simple sample preparation. This provides a read out of bacterial antibiotic resistance by detecting growth (resistant) or death (sensitive), much faster than current methods. We demonstrate the potential of this technique by determining resistance in both lab and clinical strains of E. coli, a key species for clinically burdensome urinary tract infections. This work provides the basis for a simple and fast diagnostic tool to detect antibiotic resistance in bacteria, reducing the health and economic burdens of AMR
Cantilever sensors for rapid optical antimicrobial sensitivity testing
Growing antimicrobial resistance (AMR) is a serious global threat to human health. Current methods to detect resistance include phenotypic antibiotic sensitivity testing (AST), which measures bacterial growth and is therefore hampered by a slow time to obtain results (∼12–24 h). Therefore, new rapid phenotypic methods for AST are urgently needed. Nanomechanical cantilever sensors have recently shown promise for rapid AST but challenges of bacterial immobilization can lead to variable results. Herein, a novel cantilever-based method is described for detecting phenotypic antibiotic resistance within ∼45 min, capable of detecting single bacteria. This method does not require complex, variable bacterial immobilization and instead uses a laser and detector system to detect single bacterial cells in media as they pass through the laser focus. This provides a simple readout of bacterial antibiotic resistance by detecting growth (resistant) or death (sensitive), much faster than the current methods. The potential of this technique is demonstrated by determining the resistance in both laboratory and clinical strains of Escherichia coli (E. coli), a key species responsible for clinically burdensome urinary tract infections. This work provides the basis for a simple and fast diagnostic tool to detect antibiotic resistance in bacteria, reducing the health and economic burdens of AMR
Ground-based remote sensing of an elevated forest fire aerosol layer at Whistler, BC: implications for interpretation of mountaintop chemistry
On 30 August 2009, intense forest fires in interior British Columbia (BC)
coupled with winds from the east and northeast resulted in transport of a
broad forest fire plume across southwestern BC. The physico-chemical and
optical characteristics of the plume as observed from Saturna Island
(AERONET), CORALNet-UBC and the Whistler Mountain air chemistry facility
were consistent with forest fire plumes that have been observed elsewhere in
continental North America. However, the importance of three-dimensional
transport in relation to the interpretation of mountaintop chemistry
observations is highlighted on the basis of deployment of both a <i>CL31</i> ceilometer
and a single particle mass spectrometer (SPMS) in a mountainous setting. The
SPMS is used to identify the biomass plume based on levoglucosan and
potassium markers. Data from the SPMS are also used to show that the
biomass plume was correlated with nitrate, but not correlated with sulphate
or sodium. This study not only provides baseline measurements of biomass
burning plume physico-chemical characteristics in western Canada, but also
highlights the importance of lidar remote sensing methods in the
interpretation of mountaintop chemistry measurements
Trans-Pacific dust events observed at Whistler, British Columbia during INTEX-B
International audienceThe meteorology and physico-chemical characteristics of aerosol associated with two new cases of long range dust transport affecting western Canada during spring 2006 are described. Each event showed enhancements of both sulfate aerosol and crustal material of Asian origin. However, the events were of quite different character and demonstrate the highly variable nature of such events. The April event was a significant dust event with moderate sulfate enhancement while the May event was a weak dust event with very significant sulfate enhancement. The latter event was interesting in the sense that it was of short duration and was quickly followed by significant enhancement of organic material likely of regional origin. Comparison of these two events with other documented cases extending back to 1993, suggests that all dust events show coincident enhancements of sulfate and crustal aerosol. However, events vary across a wide continuum based on the magnitude of aerosol enhancements and their sulfate to calcium ratios. At one extreme, events are dominated by highly significant crustal enhancements (e.g. the well-documented 1998 and 2001 "dust" events) while at the other are events with some dust transport, but where sulfate enhancements are of very high magnitude (e.g. the 1993 event at Crater Lake and the 15 May 2006 event at Whistler). Other events represent a "mix". It is likely that this variability is a function of the comparative strengths of the dust and anthropogenic SO2 sources, the transport pathway and in particular the extent to which dust is transported across industrial SO2 sources, and finally, meteorological and chemical processes
A review of gallium nitride LEDs for multi-gigabit-per-second visible light data communications
The field of visible light communications (VLC) has gained significant interest over the last decade, in both fibre and free-space embodiments. In fibre systems, the availability of low cost plastic optical fibre (POF) that is compatible with visible data communications has been a key enabler. In free-space applications, the availability of hundreds of THz of the unregulated spectrum makes VLC attractive for wireless communications. This paper provides an overview of the recent developments in VLC systems based on gallium nitride (GaN) light-emitting diodes (LEDs), covering aspects from sources to systems. The state-of-the-art technology enabling bandwidth of GaN LEDs in the range of >400 MHz is explored. Furthermore, advances in key technologies, including advanced modulation, equalisation, and multiplexing that have enabled free-space VLC data rates beyond 10 Gb/s are also outlined
Heterogeneous integration of gallium nitride light-emitting diodes on diamond and silica by transfer printing
We report the transfer printing of blue-emitting micron-scale light-emitting diodes (micro-LEDs) onto fused silica and diamond substrates without the use of intermediary adhesion layers. A consistent Van der Waals bond was achieved via liquid capillary action, despite curvature of the LED membranes following release from their native silicon growth substrates. The excellence of diamond as a heat-spreader allowed the printed membrane LEDs to achieve optical power output density of 10 W/cm2 when operated at a current density of 254 A/cm2. This high-currentdensity operation enabled optical data transmission from the LEDs at 400 Mbit/s
Impacts of an intense wildfire smoke episode on surface radiation, energy and carbon fluxes in southwestern British Columbia, Canada
A short, but severe, wildfire smoke episode in July 2015, with an aerosol
optical depth (AOD) approaching 9, is shown to strongly impact radiation
budgets across four distinct land-use types (forest, field, urban and
wetland). At three of the sites, impacts on the energy balance are also
apparent, while the event also appears to elicit an ecosystem response with
respect to carbon fluxes at the wetland and a forested site. Greatest impacts on
radiation and energy budgets were observed at the forested site where the
role of canopy architecture and the complex physiological responses to an
increase in diffuse radiation were most important. At the forest site, the
arrival of smoke reduced both sensible and latent heat flux substantially
but also lowered sensible heat flux more than the latent heat flux. With
widespread standing water, and little physiological control on
evapotranspiration, the impacts on the partitioning of turbulent
fluxes were modest at the wetland compared to the physiologically dominated
fluxes at the forested site. Despite the short duration and singular nature
of the event, there was some evidence of a diffuse radiation fertilization
effect when AOD was near or below 2. With lighter smoke, both the wetland
and forested site appeared to show enhanced photosynthetic activity (a
greater sink for carbon dioxide). However, with dense smoke, the forested site
was a strong carbon source. Given the extensive forest cover in the Pacific
Northwest and the growing importance of forest fires in the region, these
results suggest that wildfire aerosol during the growing season potentially
plays an important role in the regional ecosystem response to smoke and
ultimately the carbon budget of the region.</p
Integrated dual-color InGaN light-emitting diode array through transfer printing
We demonstrate an integrated dual-color InGaN light-emitting diode (LED) array by transfer printing blue LED structures from their silicon growth substrate in between the pixels of a pre-processed green LED array on a sapphire substrate
Visible Light Communication Using a Blue GaN μLED and Fluorescent Polymer Color Converter
This letter presents a novel technique to achieve high-speed visible light communication (VLC) using white light generated by a blue GaN mu LED and a yellow fluorescent copolymer. We generated white light suitable for room illumination by optimizing the ratio between the blue electroluminescence of the mu LED and yellow photoluminescence of the copolymer color converter. Taking advantage of the components' high bandwidth, we demonstrated 1.68 Gb/s at a distance of 3 cm (at 240 lx illumination). To the best of our knowledge, this is the fastest white light VLC results using a single blue LED/color converter combination.PostprintPeer reviewe
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