With the development of medical laboratory science, sensitive biomarkers detection has a prime role in the early diagnosis of diseases. The rapid diagnosis is crucial in acute diseases to lower mortality, e.g., acute myocardial infarction (AMI). Additionally, the dual-biomarker detection is highlighted in the bioassays. Compared to the gold standard immunoassay—enzyme-linked immunosorbent assay (ELISA) with extensive pretreatment and extended duration, the turbidimetric inhibition immunoassay (TIIA) is an ideal candidate for the fast detection with simple procedure and short reaction time. However, the low sensitivity limits its applications. Here, we presented an optofluidic laser immunosensor based on the latex-enhanced TIIA. With the dual-amplification of latex particles and laser, a fast and sensitive detection of cardiac troponin I (cTnI) was achieved. Furthermore, a dual-biomarker immunoassay was demonstrated with the optofluidic laser immunosensor by a two-step strategy to produce two types of immune complexes in the optofluidic laser. With the low minimum distinguishable detection (~fM) of dual-biomarkers of cTnI and immunoglobulin G (IgG) was achieved by the two-step strategy within 25 min. Thanks to the various commercial immunoassay kits, this method shows the potential to be employed in immunoassays for a variety of proteins, providing a unique platform for rapid and ultrasensitive dual-biomarker biosensing and an effective tool for clinical diagnosis of diseases.
In the field of acoustic sensing, compared with traditional acoustic sensors, fiber-optic distributed acoustic sensing (DAS) system is a revolutionary technology with many unique capabilities, such as high sensitivity, large sensing scale, real-time dynamic strain detection, excellent compatibility to standard optical fibers. However, DAS is limited by the single-component sensing characteristic of fiber itself, 3-component (3C) DAS technology is still a major challenge to date. 3C-DAS is of great significance to acoustic target tracking aloft and underwater, as well as seismic exploration underground. In this paper, we demonstrate a 3C fiber-optic quasi-distributed acoustic sensing (QDAS) system to detect 3C strains applied to optical fibers, which are mounted on 3C elastomers. 3C strain changes when placing the acoustic source at different positions. We use an ultra-sensitive DAS (uDAS) system with ~5 pε/√Hz strain sensitivity to detect the acoustic field. When the acoustic source is placed 0.5m away from the elastomers, 3C strain detected by uDAS are 5.70 nε, 6.37 nε and 35.88 nε, respectively. The experimental results verify the feasibility of the proposed 3C-QDAS scheme.
Optofluidic bio-lasers are currently of high interest for sensitive, intra-cavity, biochemical analysis. In comparison with conventional methods such as fluorescence and colorimetric detection, lasers provide us with a method for amplifying small concentration differences in the gain medium, thus achieving high sensitivity. Our previous research has demonstrated that sandwich IL-6 ELISA performed in capillary-based optofluidic laser cavity was able to achieve ultrahigh detection sensitivity (LOD between 1-10 fg/ml) with a small sample volume (~20 μL). However, such approach has several limitations such as low repeatability and long assay time (~8 hours in total, 7 hours for laser measurements). Here, we developed a novel on-chip ELISA laser platform by directly fabricating micro-wells on dielectric mirrors for immunosorbent reactions. Polystyrene microbeads of 30 μm in diameter were placed in the wells to optically enhance the resonance cavity during laser measurement, thus significantly improving reliability, shortening assay time (~1.5 hours, 30 minutes for laser measurements) while maintaining the attractive features such as small sample volume and very high sensitivity (LOD ~0.1 pg/mL for IL-6). This work pushes the ELISA laser one step closer to solving problems in realworld biochemical analysis.
We report a novel donor-acceptor-donor conjugated organic dye as the liquid gain material for the sensing of nitryl aromatic explosives by optofluidic laser. The red emissive dye with high quantum yield and large stokes shift can afford the low threshold optofluidic lasing to achieve a large dynamic range with 4 orders of magnitude and a lower limit of detection (10 nM).
Forward phase-matched Brillouin optomechanical resonance, excited by a tapered fiber, in a graphene inner-deposited whispering-gallery-mode microfluidic cavity, is demonstrated for the first time. The generated Brillouin optomechanical modes with Q factor ≈ 47000 show extremely high sensitivity (200kHz/ppm) for absolute gas detection based on frequency variation, achieving a detection limit down to 1 ppb and a dynamic range >105 orders of magnitude.
We demonstrate an optofluidic flow rate sensor based on the heat transfer effect in a microfluidic channel for the lab-on-a-chip applications. By employing an optofluidic ring resonator (OFRR), the wavelength shift of the resonant dip of the whispering gallery mode is detected as a function of the flow rate when the flow is heated by a 1480 nm laser. A measurement range of 2 μL/min - 100 μL/min, a minimum detectable change of 30 nL/min for the flow rate detection are achieved. Experimental results indicate that the OFRR flow rate sensor has good repeatability and the inverse sensitivity is beneficial for detecting the low flow rate with high sensitivity.
A dual-mode optofluidic flow rate sensor with a large dynamic range of 4 orders of magnitude is developed. The sensing mechanism is based on the force balance on an optically trapped polystyrene microparticle. As the optical force is very small, the flow rate sensor is very sensitive. In the open-loop mode, the manipulation length is used as the sensing signal. The sensor has an inverse sensitivity, that is, the manipulation length decreases as the flow rate increases, so that it has high sensitivity at low flow rate. In the closed-loop mode, the manipulation length is set to be constant and a feedback signal to tune the laser power for force balance is used as the sensing signal. The closed-loop mode is helpful for extending the upper limit of flow rate and also enhancing the sensitivity at high flow rate.
An all-fiber graphene oxide (GO) based 'FRET on Fiber' concept is proposed and applied in biochemical detections. This method is of both good selectivity and high sensitivity, with detection limits of 1.2 nM, 1.3 μM and 1 pM, for metal ion, dopamine and single-stranded DNA (ssDNA), respectively.
The enzyme horseradish peroxidase (HRP) has been extensively used in biochemistry for its ability to amplify a weak signal. By using HRP catalyzed substrate as the gain medium, we demonstrate sensitive ion concentration detection based on the optofluidic laser. The enzyme catalyzed reaction occurs in bulk solution inside a Fabry-Perot laser cavity, where the colorless, non-fluorescent 10-Acetyl-3,7-dihydroxyphenoxazine (ADHP) substrate is oxidized to produce highly fluorescent resorufin. Laser emission is achieved when pumped with the second harmonic wave of a Q-switched YAG laser. Further, we use sulfide anion (S2-) as an example to investigate the sensing performance of enzyme catalyzed optofluidic laser. The laser onset time difference between the sample to be tested and the reference is set to be the sensing output. Thanks to the amplification effects of both the enzymatic reaction and laser emission, we achieve a detection limit of 10 nM and a dynamic range of 3 orders of magnitude.
Sensitive flowmeter with a large dynamic range is highly desirable for microfluidic applications. We developed an optofluidic flow rate sensor, with a dynamic range of about 3 orders of magnitude, based on the optical manipulation of a microparticle by a single mode fiber (SMF) with a flat endface. A single polystyrene microsphere was trapped on the optical axis by the 980 nm laser emitting from SMF and the force balance between the optical force and flow force was used for sensing. The manipulation distance was detected as a function of the flow rate. The measurement range of the flow rate can cover 20 - 22000 nL/min with a laser power of 11.4 mW to 146.3 mW. The maximum manipulation length is about 715 μm. The experimental results indicate that the sensor has a good repeatability for the flow rate measurement.
The successful regeneration of fibre Bragg gratings (FBGs) inscribed in an inline fibre etalon is demonstrated. The etalon is formed by UV-micromaching of the fibre end-face to form a cylindrical hole, the fibre is then fusion spliced to seal the cavity. Such a fibre device has excellent potential for the simultaneous measurement of ultra-high temperatures and strain.
The excitation of surface field and evanescent enhancement in the graphene based optical waveguide have shown sensitive to the refractive index of surrounding media and potential applications in high-sensitivity biochemical sensing. In this paper, we investigate the graphene-coated microfiber Bragg gratings (GMFBGs) with different diameters for ammonia gas sensing. The maximum sensitivity with 6 pm/ppm is achieved experimentally when the microfiber’s diameter is ~10 μm. Moreover, by adjusting the diameter of the GMFBG, the sensing performance of the GMFBGs can be optimized. Experimental results indicate, when the diameter is range of 8~12 μm, the GMFBG shows the characteristics of high sensitivity, relative low attenuation, and large dynamic range.
KEYWORDS: Graphene, Fiber Bragg gratings, Sensors, Reflection, Chemical analysis, Gas sensors, Refractive index, Adsorption, Biological and chemical sensing, Signal attenuation
In this paper, a novel graphene-coated microfiber Bragg grating (GMFBG) sensor is proposed and demonstrated for detection of gas concentration, for the first time. Taking advantage of the surface field enhancement and polar molecular adsorption by the graphene film, we find that this structure is very sensitive to local chemical gas concentration, and the obtained sensitivities are 0.2 and 0.5ppm for NH3 and Xylene gas for tiny gas variation, respectively. Such a miniature GMFBG sensor could find applications in biological or chemical sensing, such as for trace analysis.
A high sensitivity NH3 gas sensor based on graphene/microfiber hybrid waveguide (GMHW) is reported for the first time. Enhanced by the graphene, a very high sensitivity of 0.3ppm is achieved for GMHW-based NH3 gas sensing. This work may open a window for development of novel GMHW-based gas sensors with high sensitivity, small footprint, easy fabrication and low cost.
In this paper, a novel method to sensing the complex refractive index (CRI) of graphene waveguide (GW) is demonstrated. Theoretical analysis and simulated results indicate the spectral properties of evanescent wave guided by microfiber would be modulated by the GW nearby. In experiment, evanescent waves with wavelength from 1510nm to 1590nm transimitting on the surface of the GW for a few centimeters, which are launched and collected by specially designed microfiber knot sensors (MFKSs). Repeated experiments and statistic results verifie that the CRI of the GW varies from 2.59-i2.66 to 2.51-i2.84 for 1510nm-1590nm band. Such an application of MFKS is suitable not only for the GW, but also for other thin films, which would be significant for the design and research of state-of-art optical devices.
Capacity of the sensor network is always a bottleneck problem for the novel FBG-based quasi-distributed fiberoptical defending system. In this paper, a highly sensitive sensing network with FBG vibration sensors is presented to relieve stress of the capacity and the system cost. However, higher sensitivity may cause higher Nuisance Alarm Rates (NARs) in practical uses. It is necessary to further classify the intrusion pattern or threat level and determine the validity of an unexpected event. Then an intelligent identification method is proposed by extracting the statistical features of the vibration signals in the time domain, and inputting them into a 3-layer Back-Propagation(BP) Artificial Neural Network to classify the events of interest. Experiments of both simulation and field tests are carried out to validate its effectiveness. The results show the recognition rate can be achieved up to 100% for the simulation signals and as high as 96.03% in the real tests.
Optical fiber tweezers based on a graded-index multimode fiber (GIMMF) tip is proposed. Light propagation characteristics and gradient force distribution near the GIMMF tip are numerically investigated, which are further compared with that of optical fiber tips based on conventional single mode fibers. The simulated results indicated that by selecting optimal GIMMF length, the gradient force of the GIMMF tip tweezers is about 4 times higher than that of the SMF tip tweezers with a same shape. To prove the feasibility of such a new concept, optical trapping of yeast cells with a diameter of ~5 μm using the chemically-etched GIMMF tip is experimentally demonstrated and the trapping force is also calculated.
Phase-sensitive Optical-Time-Domain Reflectometry (OTDR) system is a typical distributed fiber-optic sensing technology to detect and locate multiple dynamic disturbances from the outside, which provides a cost-effective and highly sensitive solution especially for monitoring long or ultra-long perimeters. However, the system is liable to be interfered by laser frequency drifts and environmental noises due to its phase sensitivity. The fluctuant and time-varying backgrounds severely obscure real intrusion signals, which always cause bad detection results or high Nuisance Alarm Rates (NARs). In this paper, an effective signal separation method is proposed to extract true intrusion information from the complicated noisy backgrounds of phase-sensitive OTDR system. The sensing signal in the time-domain at each spatial point is obtained by accumulating the changing trails at different moments. Multi-scale wavelet decomposition is employed on the temporal signal to get the detailed components at different scales. By selectively recombining the scale components, it can easily extract the real intrusion signal, and separate the fluctuant frequency-drift induced phase noises, and the time-varying sound or other interferences caused by the air movements, which are respectively located at different time-frequency components. Moreover, the experimental results show that the event type could be divided and discerned from the time-frequency energy distribution at different scale. Thus nuisance and false alarms in practical applications of phase-sensitive OTDR system can be decreased significantly by this way of signal separation and extraction. This technique provides a useful solution for the intrusion detection and identification of the phase-sensitive OTDR in complicated environments, and paves the way for many important applications such as long perimeter security, oil or gas pipe safety monitoring, large-scale structure health detection and fault diagnosis and so on.
A fiber Bragg grating (FBG) sensor packaged with a thin-wall alloy tube for simultaneous measurement of temperature and pressure is proposed. The influence of the structural parameters on the pressure sensitivity is investigated both numerically and experimentally. Experimental results agree well with the simulations. The pressure sensitivities of 7.8 pm/MPa and temperature sensitivity of 20.1 pm/°C are obtained in the measurement range of 0-60 MPa and 0-150°C, respectively. High repeatability and high linearity of the pressure measurement are confirmed by the experiment. By changing the materials with different elastic modulus, the inner diameter and thickness of the alloy tube, the measuring range and sensitivity of the sensor can be further optimized. The sensing performance of the sensor is also compared with a FBG sensor with another packaging structure. Preliminary results indicates that the sensor has good sensing performance and is promising to be used for long-term pressure sensing in harsh environments.
Graphene's featureless optical absorption, ultrahigh carrier mobility and optical modulation capacity would enable a new
breed of optical devices with novel photonics characteristics. The complex refractive index (CRI) of graphene can be
modulated by its local boundary conditions when molecules are attaching on the surface of the graphene layer, leading to
change in the CRI of graphene, which would induce altered properties of the evanescent wave propagating between the
graphene film and optical waveguide. In this paper, a novel fiber-optic sensor concept that integrates the graphene film
onto a microfiber is proposed to detect the molecular concentration based on TE intensity measurement. The theoretical
investigation shows that such a sensor could offer a solution for realization of a variety of high sensitivity and fast
response molecular sensing in biological, medical and chemical fields.
Novel fiber Bragg gratings (FBG) based settlement sensors are developed and the sensing performance is evaluated in
both the lab and field environments. The settlement is determined by precisely measuring the pressure of the water level
difference. The experimental results indicated that the sensor has good linearity, good repeatability and high accuracy in
the settlement measurements. The influence of temperature fluctuations on the sensor's performance is eliminated and
long-term test results proved the good stability of better than ±0.1% of the sensor. Such a FBG sensing system has been
applied to monitor the settlement of high-speed railways in practice.
In this paper, a novel graphene-based microfiber sensor is proposed and demonstrated for detection of gas concentration for the first time. As the complex refractive index (CRI) of graphene can be modulated by gas molecules in the surrounding environment, the propagating light along the graphene layer coupled by the microfiber would be altered to induce the attenuation of polarization mode intensity. Based on such a unique TE-polarization mode attenuation feature of graphene, experimental results showed that the acetone concentration can be measured accurately and quickly. Such an approach could open a window for realization of a variety of highly sensitive and fast gas or liquid sensors based on graphene, for wide applications in biological, medical and chemical fields.
A fiber-optic curvature sensor based on the singlemode-multimode-singlemode (SMS) fiber structure is developed.
Several notches in the transmitted spectrum of the SMS fiber structure are generated due to the multimode interference
effect. The dependence of the wavelength shifts and intensity changes of three transmission notches on the applied
curvature are different from each other. The maximum sensitivities of wavelength-curvature and intensity-curvature
relationships are - 10.38 nm/m-1 and - 130.37 dB/m-1, respectively. By properly choosing to measure wavelength shifts or
intensity changes, high sensitivity measurement of curvature over a large scale can be obtained. The wavelength of the
second notch is insensitive to the curvature change, offering the possibility for simultaneous measurement of curvature
and other parameters such as temperature or strain.
Numerical simulations based on the ray-transfer-matrix (RTM) method is realized for explaining the principle of a
graded-index multimode fiber (GI-MMF) based hybrid fiber Fabry-Perot (GI-FFP) sensor. It is verified by the
numerical simulations and experimental results that the high fringe contrast of the reflective spectrum of the
sensor is due to the periodic focusing effect of the GI-MMF. Experimental results are in good agreement with the
theory. A typical GI-FFP sensor is fabricated and its response to the external refractive index is measured with a
maximum sensitivity of ~160 dB/RIU.
A novel fiber-optic sensor structure fabricated by cascading two optical microfiber knot resonators (MKRs) is
proposed and demonstrated in this paper. A theoretical analysis for describing the principle of such a microfiber
double-knot resonators (MDKRs) based sensing structure is given while an experiment is carried out to verify the
design. Experimental results show that high-precision and simultaneous multi-point temperature sensing in
micro-scale can be achieved by using this structure. Such a MDKRs based sensor also shows the potential for
achieving dual-parameter measurement to eliminate the cross-talk in small scale.
In this paper, three fiber-optic interferometric humidity sensors based on silica/polymer microfiber knot resonators
(SMKR/PMKR) are reported. These tiny humidity sensors are directly fabricated by using silica/polymer microfibers
without any humidity-sensitive coating. The silica MKR has a humidity sensitivity of ~12pm/10% RH over a range from
14% RH to 60% RH, while the PMMA (poly-methyl methacrylate) MKR has a humidity sensitivity of ~88pm/10% RH,
over a range from 17% RH to 95% RH, and the PAM (Polyacrylamide) MKR with the highest sensitivity of ~270pm/%
RH over the range of 10% to 62%.
Micro extrinsic fiber-optic Fabry-Perot interferometers (MEFPI) are fabricated by chemically etching Er-doped
fiber and then splicing the etched fiber to a single-mode fiber, for the first time to our knowledge. By using the
mixture of Hydrochloric (HCl) acid and Hydrofluoric (HF) acid as etching solution, a cavity length of up to ~27 μm
and a maximum fringe contrast of ~24dB are obtained. Experimental results show that the MEFPI is insensitive to
temperature change but highly sensitive to strain, with temperature and strain sensitivities of ~0.65 pm/°C and 3.15
pm/ με, respectively. Such type of MEFPI sensors based on the etched Er-doped fiber is compact, cost-effective and
especially suitable for mass production, offering great potential for a wide range of applications.
A novel miniature fiber-optic Fabry-Perot (F-P) refractive-index (RI) sensor machined by 157nm laser is proposed. The
sensor head consists of a micro air F-P cavity near the tip of a single-mode fiber with a micro channel on the fiber tip. The
micro channel is used as the entrance for medium under test. Two thin films are coated at reflective interfaces of the F-P
cavity as mirrors to ensure high optical contrast, respectively. A RI resolution of 1130.887nm/RI unit (RIU) is achieved
by experiment. Such a sensor has a number of outstanding advantages when compared with other fiber-optic RI sensors,
such as very small, rigid, high resolution, excellent linearity, wide measurement range, et al. It is anticipated that this
miniature sensor could meet the requirements for practical applications and find important applications in any case where
small sensor size is essential, such as in biomedical diagnostic.
Highly reflective mirrors have been widely used in high power lasers, laser gyros, and gravitational-wave detection, etc.
However, reliable measurement of high reflectivity (R>99.99%) is difficult. In this paper a novel optical feedback cavity
ring-down technique (OF-CRD) by re-injecting the strong optical feedback from the ring-down cavity (RDC) into the
oscillator cavity of a Fabry-Perot diode laser is developed for the ultra-high reflectivity measurement. The laser line is
narrowed and occasionally in resonance with one or more ring-down cavity modes. The amplitude of the RDC output
signal is enhanced by a factor of over two orders of magnitude, compared with the conventional phase-shift CRD
technique. Four pairs of cavity mirrors with different reflectivity are used to investigate the sensitivity and
reproducibility of the OF-CRD technique. The accuracy is greatly enhanced from about 0.003% to 0.00003% as the
reflectivity of cavity mirrors increases from about 99.8% to 99.996%. A folded RDC with cavity length of 70cm is
constructed by inserting a planar test mirror into the linear RDC and the reflectivity of the test mirror is statistically
determined to be 99.9526±0.0004%. The OF-CRD is simple, reliable, highly-sensitive and cost efficient.
A simple and sensitive photothermal technique-photothermal detuning (PTDT), which is based on the absorption-induced shift of reflectance or transmission spectrum of an optical coating, is developed to measure the absorption of coated optical components. A PTDT theory is developed to describe the signal's dependence on the structural parameters of the optical coatings and on the geometric parameters of the experimental configuration. An experiment is performed to measure the PTDT signal of a highly reflective multilayer coating used in 532nm by using a probe beam with a wavelength of 632.8nm. By optimizing the incident angle of the probe beam, the measurement sensitivity is maximized. Good agreements between the theoretical predictions and experimental results are obtained.
Exponential-decay based cavity ring-down (CRD) techniques, such as the pulsed-CRD and continuous-wave (cw) CRD employing a fast switch to shut down the laser beam, are widely used for high reflectivity measurement. In this paper the influence of the response time of the experimental apparatus on the high reflectivity measurement is investigated theoretically and experimentally. Theoretical expressions taking into account the instrumental response time are given for both pulsed- and cw-CRD techniques, respectively. By establishing a simple cw-CRD setup employing detectors with different response time, the influence of the instrumental response time on the high reflectivity measurement is experimentally investigated. By applying a multi-parameter estimation technique to determine simultaneously the cavity decay time and the overall response time of the experimental apparatus via fitting the experimental CRD signal to the corresponding theoretical model, the influence of a long instrumental response time on the reflectivity determination is eliminated. The reflectivities of the cavity mirror measured with detectors with different rise time are in excellent agreement. On the other hand, the error of high reflectivity measurement increases with the increasing rise/fall time of the apparatus in cases that the CRD signals obtained by detectors with relatively slow rise time are simply treated with a single exponential decay fitting procedure.
A continuous-wave cavity ring-down (CRD) technique, in which a diode laser is employed as light source, is developed to determine the high reflectivity of optical dielectric mirrors. Based on on-axis alignment, large resonant peaks are obtained for CRD signal. When the amplitude of signal exceeds the predefined threshold, laser beam is switched off and a single exponential decay signal is obtained to fit the cavity decay time. The reflectivity of the cavity mirror, measured at several cavity lengths, is statistically determined to be 0.99737 at 1064 nm, with an uncertainty of 6×10-5. On the other hand, with off-axis geometry, a steady signal is obtained to make a sensitive lock-in measurement and the steady signal itself fitted with appropriate theories to determine the cavity decay time. The reflection of the cavity mirror obtained by three methods and at different cavity lengths are in excellent agreement.
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