There is a critical need of a fast, specific and reliable assay for biological species. To address this need, long period fiber gratings (LPFG) among other fiber optic sensors can be used because of their high sensitivity to changes in surrounding medium. In this work we fabricated and used two over-etched LPFGs. One of them was covered with T4 Phage and the other was covered with MS2 phage that both specifically bind with Escherichia coli (E. coli) bacteria. This bacterium is a major cause of the food contaminations and outbreaks. We showed achieving a highest sensitivity region of the LPFG and the way to fine tune to that region by over-etching the grating. Finally, using the highly sensitive LPFG platform we could detect E. coli at concentrations as low as 100 colony forming units (CFU), by covering the LPFG with an optimized bio-functionalization of the fiber surface with MS2 bacteriophage.
Optical fiber fluorescence sensors are widely used for chemical sensing. Intrinsic fluorescence sensors such as evanescent-wave sensors can be used for surface sensing while extrinsic sensors are used for bulk sensing. In intrinsic/ extrinsic fluorescence sensors, typically the side-wall/end-face of a single/multi-mode fiber is used. In this paper we introduce a novel intrinsic optical fiber fluorescence sensor which uses the side-wall of a large-core multi-mode fiber to collect the fluorescence from the bulk of samples. The method is to use a corrugated long period fiber grating, fabricated by a CO2 laser, to couple radiating modes to the core modes. Using the side-wall of a fiber helps to fabricate a multitarget or a distributed sensor. We also report the sensing of lead ions with concentration as low as few ppb in water using a novel fluorescence turn-on polymer as a chemical probe.
Tracing of the specific chemicals and biological agents in a solution is becoming a vital interest in health, security and
safety industries. Although a number of standard laboratory-based testing systems exists for detecting such targets, but
the fast, real-time and on-site methods could be more efficient and cost-effective. One of the most common ways to
detect a target in the solution is to use the fluorophore molecules which will be selectively attached to the targets and
will emit or quench the fluorescence in presence of the target. The fiber-optic fluorometers are developed for
inexpensive and portable detection. In this paper, we explain a novel multi-segment fiber structure which uses the
periodic perturbation on the side-wall of a highly multi-mode fiber to enhance collecting the fluorescent light. This
periodic perturbation is fabricated and optimized on the core of the fiber using a CO2 laser. The theoretical explanation
to show the physical principle of the structure is followed by the experimental evidence of its functioning.
This paper is devoted to examining the ability of a coaxial fiber-optic sensor (FOS) in detecting weak fluorescent light
and weak fluorescence “turn-on” in the presence of trace heavy metal ion Pb2+. The captured fluorescent signal is
detected by the Ocean Optics QE65000 spectrometer. The stock solutions include Pb2+ acetate in water (0.01 M) and a
small molecule probe in water. The preliminary experiment shows that this FOS offers the Pb2+ detection limit (DL) of
1.26×10-4 mg/mL. The advantages, limitations and further improvements of this coaxial FOS are discussed in
comparison with the bench-top instruments in terms of the abilities of signal light capture and stray excitation light
suppression.
It is commonly accepted that light captured by the fiber core sidewall is from a depth of less than 1 μm limited by the
evanescent-wave (EW) field. Yet we demonstrate in this paper that, with some simple modifications, the fiber core
sidewall is also able to capture light from an adjustable depth beyond the EW field. The key elements are an air-clad
fiber core cylinder; a liquid sample droplet surrounding a short segment of the core; a narrow, collimated and position-tunable
excitation beam perpendicular to the fiber axis to excite the sample. A theoretical investigation of the operation
of the mechanism is given, which is verified by a preliminary experiment.
In this article the enhancement of the novel fiber-optic fluorescent sensor is demonstrated. The novel sensor that was
developed by our group is based on the collection of the fluorescence from the sidewall of the multimode optical fiber
which is partly de-cladded and covered by the sample under the test (SUT). The most part of the fluorescent intensity is
carried by the leaky rays which are inaccessible in traditional evanescent-wave fluorescence fiber sensors. In our
previous structure, some part of a refracting power is collected in the de-cladded segment and used to excite the lower
order lossless modes in the cladded part by an end-face mode-mixer. In the enhanced type of our sensor we discovered
that the mode-mixer on the side-wall, rather than on the end-face, is more efficient. The fluorescence efficiency
increased in this type of enhanced sensor by about 88%. Moreover, the capability of multiplexing of the different SUT
on one fiber is a promising advantage of this architecture with a view to develop the multi-channel chemical detection
system with inexpensive simple fiber-optic.
In this article a novel advanced fiber-optic fluorescent sensor is demonstrated. The sensor is based on collection of the
fluorescence from the sidewall of the multimode optical fiber which is partly de-cladded and covered by the sample
under the test (SUT). The most part of the fluorescent intensity is carried by the leaky rays which are inaccessible in
traditional evanescent-wave fluorescence fiber sensors. In the proposed structure, some part of a refracting power is
collected in the de-cladded segment and used to excite the lower order lossless modes in cladded part by a sidewall mode
mixer. In addition to the higher level of fluorescence collection, the architecture allows us to multiplex several different
channels along one fiber, since we use only a small segment of the normal (not tapered) sidewall for each channel.A
highly efficient fluorescence turn-on molecular probe is applied to this advanced fiber-optic structure, for sensitive and
selective detection of Cu+2 in water. The fluorescence turn-on molecular probe is a mixture of a fluorophore polymer
P1and M1 as a Cu receptor and a fluorescent quencher. The P1 is used as an indicator which generates the fluorescence
centered at the wavelength of 650 nm and then, with a proper amount of M1 solution, the fluorescence is quenched up to
53% of its maximum intensity. The P1-M1 pair is broken by absorption of Cu with the M1 and the fluorescence is
released again. This turn-on effect is used for detection of Cu with a low detection limit of 0.02689 g/ml.
In this paper, the enhancement of collection efficiency in fiber-optic evanescent-wave (EW) sensors is studied. Both
theory and experimental results are presented. The theory is based primarily on ray optics, but for the sake of simplicity
and accuracy, wave optics is also considered. Fluorescent light is coupled into the core of a partly unclad multimode
fiber via EW. Most power is carried to the unclad end-face by tunneling modes. Reflection from this rough end-face,
which is modeled as a diffuse source, mixes the initial modes. Bound rays also play an important role, carrying the
power to the other end-face. The amount of output power of the bound rays there is calculated. We also study the output
power when the end-face is smooth. The comparison of these two cases of output power shows that the rough end-face
enhances the collection of coupled evanescent waves.
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