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9 pages, 2135 KiB

Open AccessArticle

Surface-Enhanced Raman Spectroscopy Based on a Silver-Film Semi-Coated Nanosphere Array

by Wending Zhang, Tianyang Xue, Lu Zhang, Fanfan Lu, Min Liu, Chao Meng, Dong Mao and Ting Mei

Sensors 2019, 19(18), 3966; https://doi.org/10.3390/s19183966 - 14 Sep 2019

Cited by 16 | Viewed by 6223

Abstract

In this paper, we present a convenient and economical method to fabricate a silver (Ag)-film semi-coated polystyrene (PS) nanosphere array substrate for surface-enhanced Raman spectroscopy (SERS). The SERS substrate was fabricated using the modified self-assembled method combined with the vacuum thermal evaporation method. [...] Read more.

In this paper, we present a convenient and economical method to fabricate a silver (Ag)-film semi-coated polystyrene (PS) nanosphere array substrate for surface-enhanced Raman spectroscopy (SERS). The SERS substrate was fabricated using the modified self-assembled method combined with the vacuum thermal evaporation method. By changing the thickness of the Ag film, the surface morphology of the Ag film coated on the PS nanospheres can be adjusted to obtain the optimized localized surface plasmonic resonance (LSPR) effect. The 3D-finite-difference time-domain simulation results show that the SERS substrate with an Ag film thickness of 10 nm has tens of times the electric field intensity enhancement. The Raman examination results show that the SERS substrate has excellent reliability and sensitivity using rhodamine-6G (R6G) and rhodamine-B (RB) as target analytes, and the Raman sensitivity can reach 10⁻¹⁰ M. Meanwhile, the SERS substrate has excellent uniformity based on the Raman mapping result. The Raman enhancement factor of the SERS substrate was estimated to be 5.1 × 10⁶. This kind of fabrication method for the SERS substrate may be used in some applications of Raman examination. Full article

(This article belongs to the Special Issue Optical Sensors for Nuclear, Physical, Biological and Chemical Sensing)

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11 pages, 5077 KiB

Open AccessArticle

Monitoring of Carbon Dioxide Using Hollow-Core Photonic Crystal Fiber Mach–Zehnder Interferometer

by Farid Ahmed, Vahid Ahsani, Kaveh Nazeri, Ehsan Marzband, Colin Bradley, Ehsan Toyserkani and Martin B. G. Jun

Sensors 2019, 19(15), 3357; https://doi.org/10.3390/s19153357 - 31 Jul 2019

Cited by 23 | Viewed by 5498

Abstract

Monitoring of greenhouse gases is essential to understand the present state and predict the future behavior of greenhouse gas emissions. Carbon dioxide (CO₂) is the greenhouse gas of most immediate concern, because of its high atmospheric concentration and long lifetime. A [...] Read more.

Monitoring of greenhouse gases is essential to understand the present state and predict the future behavior of greenhouse gas emissions. Carbon dioxide (CO₂) is the greenhouse gas of most immediate concern, because of its high atmospheric concentration and long lifetime. A fiber-optic Mach–Zehnder interferometer (MZI) is proposed and demonstrated for the laboratory-scale monitoring of carbon dioxide concentration. The interferometric sensor was constructed using a small stub of hollow-core photonic crystal fiber between a lead-in and lead-out standard single mode fiber, with air-gaps at both interfaces. At room temperature and atmospheric pressure, the sensor shows the sensitivity of 4.3 pm/% CO₂. The device was packaged to demonstrate the laboratory-scale leakage detection and measurement of CO₂ concentration in both subsurface and aqueous environments. The experimental study of this work reveals the great potential of the fiber-optic approach for environmental monitoring of CO₂. Full article

(This article belongs to the Special Issue Optical Sensors for Nuclear, Physical, Biological and Chemical Sensing)

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8 pages, 1122 KiB

Open AccessArticle

Orthogonal Demodulation Pound–Drever–Hall Technique for Ultra-Low Detection Limit Pressure Sensing

by Jinliang Hu, Sheng Liu, Xiang Wu, Liying Liu and Lei Xu

Sensors 2019, 19(14), 3223; https://doi.org/10.3390/s19143223 - 22 Jul 2019

Cited by 7 | Viewed by 4004

Abstract

We report on a novel optical microcavity sensing scheme by using the orthogonal demodulation Pound–Drever–Hall (PDH) technique. We found that larger sensitivity in a broad range of cavity quality factor (Q) could be obtained. Taking microbubble resonator (MBR) pressure sensing as an example, [...] Read more.

We report on a novel optical microcavity sensing scheme by using the orthogonal demodulation Pound–Drever–Hall (PDH) technique. We found that larger sensitivity in a broad range of cavity quality factor (Q) could be obtained. Taking microbubble resonator (MBR) pressure sensing as an example, a lower detection limit than the conventional wavelength shift detection method was achieved. When the MBR cavity Q is about 10⁵–10⁶, the technique can decrease the detection limit by one or two orders of magnitude. The pressure-frequency sensitivity is 11.6 GHz/bar at wavelength of 850 nm, and its detection limit can approach 0.0515 mbar. This technique can also be applied to other kinds of microcavity sensors to improve sensing performance. Full article

(This article belongs to the Special Issue Optical Sensors for Nuclear, Physical, Biological and Chemical Sensing)

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13 pages, 5896 KiB

Open AccessArticle

Application of Sapphire-Fiber-Bragg-Grating-Based Multi-Point Temperature Sensor in Boilers at a Commercial Power Plant

by Shuo Yang, Daniel Homa, Hanna Heyl, Logan Theis, John Beach, Billy Dudding, Glen Acord, Dwyn Taylor, Gary Pickrell and Anbo Wang

Sensors 2019, 19(14), 3211; https://doi.org/10.3390/s19143211 - 21 Jul 2019

Cited by 46 | Viewed by 6006

Abstract

Readily available temperature sensing in boilers is necessary to improve efficiencies, minimize downtime, and reduce toxic emissions for a power plant. The current techniques are typically deployed as a single-point measurement and are primarily used for detection and prevention of catastrophic events due [...] Read more.

Readily available temperature sensing in boilers is necessary to improve efficiencies, minimize downtime, and reduce toxic emissions for a power plant. The current techniques are typically deployed as a single-point measurement and are primarily used for detection and prevention of catastrophic events due to the harsh environment. In this work, a multi-point temperature sensor based on wavelength-multiplexed sapphire fiber Bragg gratings (SFBGs) were fabricated via the point-by-point method with a femtosecond laser. The sensor was packaged and calibrated in the lab, including thermally equilibrating at 1200 °C, followed by a 110-h, 1000 °C stability test. After laboratory testing, the sensor system was deployed in both a commercial coal-fired and a gas-fired boiler for 42 days and 48 days, respectively. The performance of the sensor was consistent during the entire test duration, over the course of which it measured temperatures up to 950 °C (with some excursions over 1000 °C), showing the survivability of the sensor in a field environment. The sensor has a demonstrated measurement range from room temperature to 1200 °C, but the maximum temperature limit is expected to be up to 1900 °C, based on previous work with other sapphire based temperature sensors. Full article

(This article belongs to the Special Issue Optical Sensors for Nuclear, Physical, Biological and Chemical Sensing)

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9 pages, 1388 KiB

Open AccessArticle

A Simple All-Optical Water Level Monitoring System Based on Wavelength Division Multiplexing with an Arrayed Waveguide Grating

by Hoon-Keun Lee, Jaeyul Choo and Gangsig Shin

Sensors 2019, 19(14), 3095; https://doi.org/10.3390/s19143095 - 13 Jul 2019

Cited by 9 | Viewed by 3142

Abstract

We propose and demonstrate a simple water level monitoring system based on the wavelength division multiplexing (WDM) for the spent fuel pool (SFP) at a nuclear power plant. The basic principle is based on the measurement of the optical power spectra by the [...] Read more.

We propose and demonstrate a simple water level monitoring system based on the wavelength division multiplexing (WDM) for the spent fuel pool (SFP) at a nuclear power plant. The basic principle is based on the measurement of the optical power spectra by the Fresnel reflection according to the change of the refractive index at the end facet of the optical fiber tip (OFT). An arrayed waveguide grating (AWG) is employed to achieve multi-channel sensing capability with a C-band broadband light source (BLS) based on amplified spontaneous emission (ASE). The feasibility of the proposed scheme is investigated with a simulation and experimentation. We also investigate the limiting factor for remote transmission. The system performance is degraded by the Rayleigh backscattering of the BLS light, but it can be operated over long distances within 10 km with 5 dB of difference peak power margin. Full article

(This article belongs to the Special Issue Optical Sensors for Nuclear, Physical, Biological and Chemical Sensing)

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14 pages, 4406 KiB

Open AccessArticle

Malaria-Infected Red Blood Cell Analysis through Optical and Biochemical Parameters Using the Transport of Intensity Equation and the Microscope’s Optical Properties

by Marcel Akpa Agnero, Kouakou Konan, Zan Guy Christian Stephane Tokou, Yao Taky Alvarez Kossonou, Bienvenue Sylvère Dion, Kenneth Amiga Kaduki and Jérémie Thouakesséh Zoueu

Sensors 2019, 19(14), 3045; https://doi.org/10.3390/s19143045 - 10 Jul 2019

Cited by 23 | Viewed by 5091

Abstract

The accuracy, reliability, speed and cost of the methods used for malaria diagnosis are key to the diseases’ treatment and eventual eradication. However, improvement in any one of these requirements can lead to deterioration of the rest due to their interdependence. We propose [...] Read more.

The accuracy, reliability, speed and cost of the methods used for malaria diagnosis are key to the diseases’ treatment and eventual eradication. However, improvement in any one of these requirements can lead to deterioration of the rest due to their interdependence. We propose an optical method that provides fast detection of malaria-infected red blood cells (RBCs) at a lower cost. The method is based on the combination of deconvolution, topography and three-dimensional (3D) refractive index reconstruction of the malaria-infected RBCs by use of the transport of intensity equation. Using our method, healthy RBCs were identified by their biconcave shape, quasi-uniform spatial distribution of their refractive indices and quasi-uniform concentration of hemoglobin. The values of these optical and biochemical parameters were found to be in agreement with the values reported in the literature. Results for the malaria-infected RBCs were significantly different from those of the healthy RBCs. The topography of the cells and their optical and biochemical parameters enabled identification of their stages of infection. This work introduces a significant method of analyzing malaria-infected RBCs at a lower cost and without the use of fluorescent labels for the parasites. Full article

(This article belongs to the Special Issue Optical Sensors for Nuclear, Physical, Biological and Chemical Sensing)

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11 pages, 1872 KiB

Open AccessArticle

CYTOP Fibre Bragg Grating Sensors for Harsh Radiation Environments

by Christian Broadway, Damien Kinet, Antreas Theodosiou, Kyriacos Kalli, Andrei Gusarov, Christophe Caucheteur and Patrice Mégret

Sensors 2019, 19(13), 2853; https://doi.org/10.3390/s19132853 - 27 Jun 2019

Cited by 30 | Viewed by 3301

Abstract

We present a polymer fibre Bragg grating sensor and its sensitivity to gamma radiation by observing the reflected spectral profile. The Bragg grating is femtosecond inscribed within a perfluorinated CYTOP fibre and the alteration of the Bragg wavelength corresponds to the total radiation [...] Read more.

We present a polymer fibre Bragg grating sensor and its sensitivity to gamma radiation by observing the reflected spectral profile. The Bragg grating is femtosecond inscribed within a perfluorinated CYTOP fibre and the alteration of the Bragg wavelength corresponds to the total radiation dose received. Over a total dose of 41

k

Gy, the fibre demonstrates a sensitivity of

- 26.2

p

m

/

k

Gy and a resolution of 40 Gy. Under active consideration for the instrumentation of nuclear waste repositories, this study gives a better understanding of the effects of gamma radiation upon Bragg gratings in CYTOP fibres. Full article

(This article belongs to the Special Issue Optical Sensors for Nuclear, Physical, Biological and Chemical Sensing)

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18 pages, 1552 KiB

Open AccessArticle

Hybrid Analytical Platform Based on Field-Asymmetric Ion Mobility Spectrometry, Infrared Sensing, and Luminescence-Based Oxygen Sensing for Exhaled Breath Analysis

by L. Tamina Hagemann, Stefan Repp and Boris Mizaikoff

Sensors 2019, 19(12), 2653; https://doi.org/10.3390/s19122653 - 12 Jun 2019

Cited by 7 | Viewed by 3971

Abstract

The reliable online analysis of volatile compounds in exhaled breath remains a challenge, as a plethora of molecules occur in different concentration ranges (i.e., ppt to %) and need to be detected against an extremely complex background matrix. Although this complexity is commonly [...] Read more.

The reliable online analysis of volatile compounds in exhaled breath remains a challenge, as a plethora of molecules occur in different concentration ranges (i.e., ppt to %) and need to be detected against an extremely complex background matrix. Although this complexity is commonly addressed by hyphenating a specific analytical technique with appropriate preconcentration and/or preseparation strategies prior to detection, we herein propose the combination of three different detector types based on truly orthogonal measurement principles as an alternative solution: Field-asymmetric ion mobility spectrometry (FAIMS), Fourier-transform infrared (FTIR) spectroscopy-based sensors utilizing substrate-integrated hollow waveguides (iHWG), and luminescence sensing (LS). By carefully aligning the experimental needs and measurement protocols of all three methods, they were successfully integrated into a single compact analytical platform suitable for online measurements. The analytical performance of this prototype system was tested via artificial breath samples containing nitrogen (N₂), oxygen (O₂), carbon dioxide (CO₂), and acetone as a model volatile organic compound (VOC) commonly present in breath. All three target analytes could be detected within their respectively breath-relevant concentration range, i.e., CO₂ and O₂ at 3-5 % and at ~19.6 %, respectively, while acetone could be detected with LOQs as low as 165-405 ppt. Orthogonality of the three methods operating in concert was clearly proven, which is essential to cover a possibly wide range of detectable analytes. Finally, the remaining challenges toward the implementation of the developed hybrid FAIMS-FTIR-LS system for exhaled breath analysis for metabolic studies in small animal intensive care units are discussed. Full article

(This article belongs to the Special Issue Optical Sensors for Nuclear, Physical, Biological and Chemical Sensing)

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22 pages, 6986 KiB

Open AccessArticle

The Detection of the Pipe Crack Utilizing the Operational Modal Strain Identified from Fiber Bragg Grating

by Zechao Wang, Mingyao Liu, Yongzhi Qu, Qin Wei, Zude Zhou, Yuegang Tan, Liu Hong and Han Song

Sensors 2019, 19(11), 2556; https://doi.org/10.3390/s19112556 - 4 Jun 2019

Cited by 21 | Viewed by 4249

Abstract

The small and light-weight pipeline is widely used in hydraulic system for aerospace engineering. The crack is one of the most common failures in the pipelines so that its incipient detection can further avoid the catastrophic damage of the piping system. The electrical [...] Read more.

The small and light-weight pipeline is widely used in hydraulic system for aerospace engineering. The crack is one of the most common failures in the pipelines so that its incipient detection can further avoid the catastrophic damage of the piping system. The electrical and piezoelectric sensors are conventionally used for the structural health monitoring (SHM), while these are not suitable for the cascaded pipelines in harsh environment because the added mass will change the modal characteristics of the cascaded pipelines. The Fiber Bragg Grating (FBG) sensor with light-weight, multiplexed, and anti-electromagnetic interference properties, are employed to obtain the modal strain transmissibility with a novel diagram of the operational modal analysis (OMA). Based on the OMA an enhanced damage indicator is proposed to detect the crack. After going through analytical modeling, finite element modeling (FEM) and its corresponding experiments, it is concluded that the presented method is effective and accurate to detect and locate the crack. Full article

(This article belongs to the Special Issue Optical Sensors for Nuclear, Physical, Biological and Chemical Sensing)

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15 pages, 3668 KiB

Open AccessArticle

Perfusion Microfermentor Integrated into a Fiber Optic Quasi-Elastic Light Scattering Sensor for Fast Screening of Microbial Growth Parameters

by Marco César Prado Soares, Franciele Flores Vit, Carlos Kenichi Suzuki, Lucimara Gaziola de la Torre and Eric Fujiwara

Sensors 2019, 19(11), 2493; https://doi.org/10.3390/s19112493 - 31 May 2019

Cited by 10 | Viewed by 3983

Abstract

This research presents a microfermentor integrated into an optical fiber sensor based on quasi-elastic light scattering (QELS) to monitor and swiftly identify cellular growth kinetic parameters. The system uses a 1310 nm laser light that is guided through single-mode silica optical fibers to [...] Read more.

This research presents a microfermentor integrated into an optical fiber sensor based on quasi-elastic light scattering (QELS) to monitor and swiftly identify cellular growth kinetic parameters. The system uses a 1310 nm laser light that is guided through single-mode silica optical fibers to the interior of perfusion chambers, which are separated by polycarbonate membranes (470 nm pores) from microchannels, where a culture medium flows in a constant concentration. The system contains four layers, a superior and an inferior layer made of glass, and two intermediate poly(dimethylsiloxane) layers that contain the microchannels and the perfusion chambers, forming a reversible microfluidic device that requires only the sealing of the fibers to the inferior glass cover. The QELS autocorrelation decay rates of the optical signals were correlated to the cells counting in a microscope, and the application of this microsystem to the monitoring of alcoholic fermentation of Saccharomyces cerevisiae resulted in the kinetic parameters of K_M = 4.1 g/L and μ_m = 0.49 h⁻¹. These results agree with both the data reported in the literature and with the control batch test, showing that it is a reliable and efficient biological monitoring system. Full article

(This article belongs to the Special Issue Optical Sensors for Nuclear, Physical, Biological and Chemical Sensing)

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14 pages, 4574 KiB

Open AccessArticle

Fiber Reshaping-Based Refractive Index Sensor Interrogated through Both Intensity and Wavelength Detection

by Peng Ji, Shiru Jiang and Sang-Shin Lee

Sensors 2019, 19(11), 2477; https://doi.org/10.3390/s19112477 - 30 May 2019

Cited by 4 | Viewed by 4370

Abstract

A fiber reshaping-based refractive index (RI) sensor is proposed relying on both optical intensity variation and wavelength shift. The objective of this study is to completely reshape the core and to ultimately mimic a coreless fiber, thereby creating a highly efficient multimode interference [...] Read more.

A fiber reshaping-based refractive index (RI) sensor is proposed relying on both optical intensity variation and wavelength shift. The objective of this study is to completely reshape the core and to ultimately mimic a coreless fiber, thereby creating a highly efficient multimode interference (MMI) coupler. Thus, propagation modes are permitted to leak out into the cladding and eventually escape out of the fiber, depending on the surrounding environment. Two interrogation mechanisms based on both the intensity variation and wavelength shift are employed to investigate the performance of the RI sensor, with the assistance of leaky-mode and MMI theories. By monitoring the output intensity difference and the wavelength shift, the proposed RI sensor exhibits high average sensitivities of 185 dB/RIU and 3912 nm/RIU in a broad range from 1.339 to 1.443, respectively. The operating range and sensitivity can be adjusted by controlling the interaction length, which is appealing for a wide range of applications in industry and bioscience research. Full article

(This article belongs to the Special Issue Optical Sensors for Nuclear, Physical, Biological and Chemical Sensing)

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12 pages, 4762 KiB

Open AccessArticle

A VCSEL-Based NIR Transillumination System for Morpho-Functional Imaging

by Sabina Merlo, Valentina Bello, Elisabetta Bodo and Sara Pizzurro

Sensors 2019, 19(4), 851; https://doi.org/10.3390/s19040851 - 19 Feb 2019

Cited by 11 | Viewed by 4364

Abstract

Transillumination with non-ionizing radiation followed by the observation of transmitted and diffused light is the simplest, and probably the oldest method to obtain qualitative information on the internal structure of tissues or body sections. Although scattering precludes formation of high-definition image (unless complex [...] Read more.

Transillumination with non-ionizing radiation followed by the observation of transmitted and diffused light is the simplest, and probably the oldest method to obtain qualitative information on the internal structure of tissues or body sections. Although scattering precludes formation of high-definition image (unless complex techniques are employed), low resolution pictures complemented by information on the functional condition of the living sample can be extracted. In this context, we have investigated a portable optoelectronic instrumental configuration for efficient transillumination and image detection, even in ambient day-light, of in vivo samples with thickness up to 5 cm, sufficient for visualizing macroscopic structures. Tissue illumination is obtained with an extended source consisting in a matrix of 36 near infrared Vertical Cavity Surface Emitting Lasers (VCSELs) that is powered by a custom designed low-voltage current driver. In addition to the successful acquisition of morphological images of the hand dorsal vein pattern, functional detection of physiological parameters (breath and hearth rate) is achieved non-invasively by means of a monochrome camera, with a Complementary Metal Oxide Semiconductor (CMOS) sensor, turned into a wavelength selective image detector using narrow-band optical filtering. Full article

(This article belongs to the Special Issue Optical Sensors for Nuclear, Physical, Biological and Chemical Sensing)

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8 pages, 4681 KiB

Open AccessArticle

Fiber Vector Bend Sensor Based on Multimode Interference and Image Tapping

by Ziyang Zhang, Aashia Rahman, Julia Fiebrandt, Yu Wang, Kai Sun, Jiajun Luo, Kalaga Madhav and Martin M. Roth

Sensors 2019, 19(2), 321; https://doi.org/10.3390/s19020321 - 15 Jan 2019

Cited by 5 | Viewed by 4200

Abstract

A grating-less fiber vector bend sensor is demonstrated using a standard single mode fiber spliced to a multimode fiber as a multimode interference device. The ring-shaped light intensity distribution at the end of the multimode fiber is subject to a vector transition in [...] Read more.

A grating-less fiber vector bend sensor is demonstrated using a standard single mode fiber spliced to a multimode fiber as a multimode interference device. The ring-shaped light intensity distribution at the end of the multimode fiber is subject to a vector transition in response to the fiber bend. Instead of comprehensive imaging processing for the analysis, the image can be tapped out by a seven-core fiber spliced to the other end of the multimode fiber. The seven-core fiber is further guided to seven single mode fibers via a commercial fan-out device. By comparing the relative light intensities received at the seven outputs, both the bend radius and its direction can be determined. Experiment has shown that a slight bend displacement of 10 µm over a 1.2-cm-long multimode fiber in the X direction (bend angle of 0.382°) causes a distinctive power imbalance of 4.6 dB between two chosen outputs (numbered C4 and C7). For the same displacement in the Y direction, the power ratio between the previous two outputs C4 and C7 remains constant, while the imbalance between another pair (C3 and C4) rises significantly to 7.0 dB. Full article

(This article belongs to the Special Issue Optical Sensors for Nuclear, Physical, Biological and Chemical Sensing)

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12 pages, 4553 KiB

Open AccessArticle

Sensing Performance and Efficiency of Two Energy Transfer-Based Two-Photon Fluorescent Probes for pH

by Yujin Zhang and Wei Hu

Sensors 2018, 18(12), 4407; https://doi.org/10.3390/s18124407 - 13 Dec 2018

Cited by 4 | Viewed by 2940

Abstract

The design and synthesis of fluorescent probes for monitoring pH values inside living cells have attracted great attention, due to the important role pH plays in many biological processes. In this study, the optical properties of two different two-photon fluorescent probes for pH [...] Read more.

The design and synthesis of fluorescent probes for monitoring pH values inside living cells have attracted great attention, due to the important role pH plays in many biological processes. In this study, the optical properties of two different two-photon fluorescent probes for pH are studied. The ratiometric sensing of the probes are theoretically illustrated. Meanwhile, the recognitional mechanisms of the probes are investigated, which shows the energy transfer process when react with H⁺. Specially, the calculated results demonstrate that Probe1 possesses a higher energy transfer efficiency and a larger two-photon absorption cross-section than Probe2, indicating it to be a preferable pH fluorescent probe. Therefore, the influence of connection between the donor and the acceptor on the sensing performances of the probe is demonstrated. Our results help to understand the experimental observations and provide a theoretical basis to synthesize efficient two-photon fluorescent probes for monitoring pH changes. Full article

(This article belongs to the Special Issue Optical Sensors for Nuclear, Physical, Biological and Chemical Sensing)

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