183 research outputs found
Efficiency of integrated waveguide probes in the detection of fluorescence and backscattered light
No full textIntegrated optical probes for detecting backscattered light in, e.g., Raman spectroscopy show desirable characteristics compared to conventional optical fiber probes, although the latter ones may have better collection efficiency in many cases. Major advantages of integrated probes include reduced size; reduced background noise due to scattering in the probe because of reduced propagation length; potential for monolithic integration with filters and spectrometers; very small collection volume, providing high spatial resolution; and polarization maintenance. We demonstrate that when scattered light needs to be collected from a thin layer close to the probe surface, integrated probes can have better collection efficiency than fiber probes do. We modeled a multimode integrated waveguide probe by adapting an analytical model that had been developed for fiber probes. The model was extended in order to account for arbitrary waveguide geometries and a low number of discrete waveguide modes compared to the quasi-continuum of modes in a typical multimode fiber. Using this model we compared the collection efficiencies of integrated and fiber probes for a thin scattering sample. We found that the integrated probe has a higher collection efficiency for scattering layer thickness and probe-to-layer distance both smaller than ~100 um
Improving health outcomes: innovation, coverage, quality and adherence.
No full textThe Israeli health system has made considerable progress in reducing deaths amenable to medical care but has more to do. This commentary describes how progress in this area results from innovation, coverage, quality, and adherence to treatment. It describes what is being done in Israel and beyond to address each of these factors but concentrates on the often poorly recognised problem of adherence to treatment, describing the growing evidence that it is often sub-optimal and reviewing evidence on what can be done to improve it
Fiber optic lossy mode resonance sensors for chemical sensing
No full textThis work presents the fabrication and characterization of a fiber optic gas sensor utilizing Lossy Mode Resonances (LMR) achieved with a nanoscale polyphenylene oxide (PPO) coating. The PPO coating is applied to the cladding removed region of a multi-mode silica fiber, simultaneously serving as both the LMR support layer and the sensing material. The PPOcoated LMR sensor is exposed to various concentrations of ammonia as a case study. The sensor demonstrates a high sensitivity of 0.25 nm/ppm within the ammonia concentration range of 2.5 to 37.5 ppm. These results highlight the potential of this PPO-based fiber optic sensor for efficient and sensitive detection of hazardous compounds in different settings, ranging from medical to industrial
Ion-selective optical sensor for continuous on-line monitoring of dialysate sodium during dialysis
No full textPatients with end stage renal disease are dependent on dialysis. In most outpatient centers, the dialysate is prepared with a fixed electrolyte concentration without taking into account the inter-individual differences of essential electrolytes (sodium, potassium and calcium). This one-size fits all approach can lead to acute and chronic cardiovascular complications in dialysis patients. On-line monitoring of these essential electrolytes is an important physiological step towards patient specific dialysate leading to individualized treatment. Currently, changes in electrolyte concentrations are indirectly measured by conductivity measurements, which are not ion- specific. In this paper, we present a novel optical sensor for on-line monitoring of sodium concentrations in dialysate. This sensor is ion-specific and can detect up to a single ion. The working principle is based on the selective fluorescence quenching of photo-induced electron transfer (PET) molecules. The PET molecules when complexed with sodium ions start fluorescing upon laser excitation. The emission intensity is directly correlated to the sodium concentration. To prove the working principle, a micro-optofluidic device has been fabricated in polydimethylsiloxane (PDMS) with integrated optical fibers for fluorescence light collection. The PET molecules are covalently grafted in the PDMS microchannel for continuous monitoring of the sodium dialysate concentrations. The experimental setup consists of a laser module (λ=450nm) operating at 4.5mW, a syringe pump to precisely control the sample flow and a spectrometer for fluorescence collection. The performance of the sensor has been evaluated for sodium ions ranging from 0-50mM. A clear signal and good response time was observed
Flexible delivery of Er:YAG radiation at 2.94 μm with novel hollow-core silica glass fibres:demonstration of tissue ablation
No full textIn this work we present the delivery of high energy Er:YAG laser pulses operating at 2.94 mu m through a hollow-core negative curvature fibre (HC-NCF) and a hollow-core photonic crystal fibre (HC-PCF) and their use for the ablation of biological tissue. In HC-NCF fibres, which have been developed recently, the laser radiation is confined in a hollow core and by an anti-resonant or reflection principle (also known as ARROW). Both fibres are made of fused silica which has high mechanical and chemical durability, is bio-inert and results in a fibre with the flexibility that lends itself to easy handling and minimally invasive procedures. The HC-NCF structure consists of only one ring of capillaries around a realtively large core, followed by a protecting outer layer, hence the preform is relatively easy to build compared to traditional HC-PCF. The measured attenuation at 2.94 mu m is 0.06 dB/m for the HC-NCF and 1.2 dB/m for the HC-PCF. Both fibres have a single mode output beam profile which can be advantageous for surgical applications as the beam profile is maintained during fibre movement. We demonstrate delivery of high energy pulses through both fibres, well above the thresholds needed for the ablation of biological tissue in non-contact and contact mode. Delivered energy densities reached > 750 J/cm(-2) after 10 m of HC-NCF and > 3400 J/cm(2) through a 44 cm HC-PCF.This flexible high energy delivery system offers an alternative to existing beam delivery systems such as articulated arms and large core multi-mode fibres with enhanced capabilities.</p
Cost-effective optical coherence tomography spectrometer based on a tilted fiber Bragg grating
No full textA compact, fiber-based spectrometer for biomedical application utilizing a tilted fiber Bragg grating (TFBG) as integrated dispersive element is demonstrated. Based on a 45° UV-written PS750 TFBG a refractive spectrometer with 2.06 radiant/μm dispersion and a numerical aperture of 0.1 was set up and tested as integrated detector for an optical coherence tomography (OCT) system. Featuring a 23 mm long active region at the fiber the spectrum is projected via a cylindrical lens for vertical beam collimation and focused by an achromatic doublet onto the detector array. Covering 740 nm to 860 nm the spectrometer was optically connected to a broadband white light interferometer and a wide field scan head and electronically to an acquisition and control computer. Tomograms of ophthalmic and dermal samples obtained by the frequency domain OCT-system were obtained achieving 2.84 μm axial and 7.6 μm lateral resolution
Noise characterization of a 512 x 16 SPAD line sensor for time-resolved spectroscopy applications
No full textTime-resolved spectroscopy in the presence of noise is challenging. We have developed a new 512 pixel line sensor with 16 single-photon-avalanche (SPAD) detectors per pixel and ultrafast in-pixel time-correlated single photon counting (TCSPC) histogramming for such applications. SPADs are near shot noise limited detectors but we are still faced with the problem of high dark count rate (DCR) SPADs. The noisiest SPADs can be switched off to optimise signal-to-noiseratios (SNR) at the expense of longer acquisition/exposure times than would be possible if more SPADs were exploited. Here we present detailed noise characterization of our array. We build a DCR map for the sensor and demonstrate the effect of switching off the noisiest SPADs in each pixel. 24% percent of SPADs in the array are measured to have DCR in excess of 1kHz, while the best SPAD selection per pixel reduces DCR to 53+/-7Hz across the entire array. We demonstrate that selection of the lowest DCR SPAD in each pixel leads to the emergence of sparse spatial sampling noise in the sensor.</p
Label-free single-molecule all-optical sensor
No full textRecently, quality factors greater than 100 million were demonstrated using planar arrays of silica microtoroid resonators. These high Q factors allow the toroidal resonators to perform very sensitive detection experiments. By functionalizing the silica surface of the toroid with biotin, the toroidal resonators become both specific and sensitive detectors for Streptavidin. One application of this sensor is performing detection in lysates. To mimic this type of environment, additional solutions of Streptavidin were prepared which also contained high concentrations (nM and μM) of tryptophan
Label-free oligonucleotide biosensor based on dual-peak long period fiber grating
No full textWe report the simplification and development of biofunctionalization methodology based on one-step 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)-mediated reaction. The dual-peak long period grating (dLPG) has been demonstrated its inherent ultrahigh sensitivity to refractive index (RI), achieving 50-fold improvement in RI sensitivity over a standard LPG sensor used in low RI range. With the simple and efficient immobilization of unmodified oligonucleotides on sensor surface, dLPG-based biosensor has been used to monitor the hybridization of complementary oligonucleotides showing a detectable oligonucleotide concentration of 4 nM with the advantages of label-free, real-time, and ultrahigh sensitivity
Fibre optic time-resolved spectroscopy using CMOS-SPAD arrays
No full textIn vivo fibre optic fluorescence-based sensing is the use of synthesised fluorophores which interrogate the local environment via variation in their fluorescence emission, addressed through an optic fibre. However, the emission intensity is influenced by intrinsic factors such as photobleaching, quantitative factors like concentration dependency and background signals from autofluorescence of tissue and the delivery optical fibre. Many of these problems can be addressed by using time-resolved spectroscopy which measures variations in the fluorescent lifetime. We present a versatile fibre-based time-resolved spectrograph based on a CMOS SPAD line sensor capable of acquiring time and spectral resolved fluorescent lifetime data in a single measurement exploiting the time-correlated single photon counting (TCSPC) technique. It is shown that these TCSPC histograms enable the differentiation between autofluorescence of tissue and synthesized fluorophores, as well as the removal of unwanted fibre background through post-processed time-gating. As a proof-of-principle application the pH- dependent changes in fluorescent lifetime of 5-carboxyuorescein (FAM) are measured.</p
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