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Special Issue "Spectroscopy Based Sensors"

A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Biosensors".

Deadline for manuscript submissions: closed (15 May 2018) | Viewed by 85438

Special Issue Editor

Dr. Frans J.M. Harren
E-Mail Website
Guest Editor
Department of Molecular and Laser Physics, Radboud University Nijmegen, Nijmegen, The Netherlands
Interests: laser-based spectroscopy; sensor development; trace gas detection; biological/medical applications; Frequency Comb Spectroscopy

Special Issue Information

Dear Colleagues,

Spectroscopic sensors have attracted intensive interest from many different field of applications, such as industrial/food process control, atmospheric monitoring, analysis of biological/medical processes, etc. In the future, integrated, miniaturized sensors, produced at reduced costs, should be able to operate under hazardous, remote field conditions, such as drones, production lines, and shipped containers, but also in high-end quality control in medical processes. This Special Issue focuses on both types of sensors, publishing the newest scientific developments and applications of spectroscopic sensors for in situ, real-time analysis of critical biological, chemical, and physical parameters of the process under investigation. It welcomes contributions utilizing the UV, visible, IR, THz wavelength regions sensing via direct absorption, Raman, fluorescence, or other spectroscopic processes.

Dr. Frans J.M. Harren
Guest Editor

Manuscript Submission Information

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Keywords

  • Bioprocess monitoring
  • Process analytical technology
  • Medical sensors
  • In-line monitoring
  • Real-time monitoring
  • Trace gas sensors
  • Laser-based sensors
  • Airborne sensors
  • Hyperspectral Imaging
  • Optical/Infrared/Terahertz sensors
  • Time resolved sensors

Published Papers (28 papers)

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Research

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Article
Utilization of Inexpensive Carbon-Based Substrates as Platforms for Sensing
Sensors 2018, 18(8), 2444; https://doi.org/10.3390/s18082444 - 27 Jul 2018
Cited by 5 | Viewed by 1762
Abstract
Gold (Au) has been widely used as a material for Surface Enhanced Raman Spectroscopy (SERS) due to its plasmonic properties, stability and biocompatibility. Conventionally for SERS application, Au is deposited on a rigid substrate such as glass or silicon. The rigid substrates severely [...] Read more.
Gold (Au) has been widely used as a material for Surface Enhanced Raman Spectroscopy (SERS) due to its plasmonic properties, stability and biocompatibility. Conventionally for SERS application, Au is deposited on a rigid substrate such as glass or silicon. The rigid substrates severely limit analyte collection efficiency as well as portability. Here, flexible substrates like carbon cloth and carbon paper were investigated as potential substrate candidates for SERS application. The flexible substrates were coated with Au nanostructures by electrodeposition. Model analyte, Rhodamine 6G was utilized to demonstrate the capabilities of the flexible SERS substrates. Additionally, the pesticide paraoxon was also detected on the flexible SERS substrates as well as on a real sample like the apple fruit. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Cholesterol-Bearing Fluorescent G-Quadruplex Potassium Probes for Anchoring at the Langmuir Monolayer and Cell Membrane
Sensors 2018, 18(7), 2201; https://doi.org/10.3390/s18072201 - 09 Jul 2018
Cited by 7 | Viewed by 2203
Abstract
The purpose of the present work was to design, synthesize and spectrally characterize cholesterol-anchored fluorescent oligonucleotide probes (Ch(F-TBA-T), Ch(py-TBA-py)), based on G-quadruplexes, which were able to incorporate into a lipid structure (Langmuir monolayer, living cell membrane). The probes, based on the thrombin-binding aptamer [...] Read more.
The purpose of the present work was to design, synthesize and spectrally characterize cholesterol-anchored fluorescent oligonucleotide probes (Ch(F-TBA-T), Ch(py-TBA-py)), based on G-quadruplexes, which were able to incorporate into a lipid structure (Langmuir monolayer, living cell membrane). The probes, based on the thrombin-binding aptamer (TBA) sequence, were labeled with fluorescent dyes which enabled simultaneous monitoring of the formation of G-quadruplex structures and visualization of probe incorporation into the cellular membrane. The combinations of fluorophores used included fluorescence resonance energy transfer (FRET) and excimer emission approaches. The structural changes of the probes upon binding with K+ or Na+ ions were monitored with fluorescence techniques. These systems showed a very high binding preference for K+ over Na+ ions. The use of confocal fluorescence microscopy indicated successful anchoring of the cholesterol-bearing fluorescent probes to the living cell membrane. These structurally simple cholesterol-based fluorescent probes have good potential for opening up new and exciting opportunities in the field of biosensors; e.g., in vivo detection of K+ ions. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
RES-Q-Trace: A Mobile CEAS-Based Demonstrator for Multi-Component Trace Gas Detection in the MIR
Sensors 2018, 18(7), 2058; https://doi.org/10.3390/s18072058 - 27 Jun 2018
Cited by 6 | Viewed by 2119
Abstract
Sensitive trace gas detection plays an important role in current challenges occurring in areas such as industrial process control and environmental monitoring. In particular, for medical breath analysis and for the detection of illegal substances, e.g., drugs and explosives, a selective and sensitive [...] Read more.
Sensitive trace gas detection plays an important role in current challenges occurring in areas such as industrial process control and environmental monitoring. In particular, for medical breath analysis and for the detection of illegal substances, e.g., drugs and explosives, a selective and sensitive detection of trace gases in real-time is required. We report on a compact and transportable multi-component system (RES-Q-Trace) for molecular trace gas detection based on cavity-enhanced techniques in the mid-infrared (MIR). The RES-Q-Trace system can operate four independent continuous wave quantum or interband cascade lasers each combined with an optical cavity. Twice the method of off-axis cavity-enhanced absorption spectroscopy (OA-CEAS) was used, twice the method of optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS), respectively. Multi-functional software has been implemented (i) for the general system control; (ii) to drive the four different laser sources and (iii) to analyze the detector signals for concentration determination of several molecular species. For the validation of the versatility and the performance of the RES-Q-Trace instrument the species NO, N2O, CH4, C2H4 and C3H6O, with relevance in the fields of breath gas analysis and the detection of explosives have been monitored in the MIR with detection limits at atmospheric pressure in the ppb and ppt range. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Sensitive Spectroscopy of Acetone Using a Widely Tunable External-Cavity Quantum Cascade Laser
Sensors 2018, 18(7), 2050; https://doi.org/10.3390/s18072050 - 27 Jun 2018
Cited by 20 | Viewed by 3225
Abstract
We employed a single-mode, widely tunable (~300 cm−1) external-cavity quantum cascade laser operating around 8 µm for broadband direct absorption spectroscopy and wavelength modulation spectroscopy where a modulation frequency of 50 kHz was employed with high modulation amplitudes of up to [...] Read more.
We employed a single-mode, widely tunable (~300 cm−1) external-cavity quantum cascade laser operating around 8 µm for broadband direct absorption spectroscopy and wavelength modulation spectroscopy where a modulation frequency of 50 kHz was employed with high modulation amplitudes of up to 10 GHz. Using a compact multipass cell, we measured the entire molecular absorption band of acetone at ~7.4 µm with a spectral resolution of ~1 cm−1. In addition, to demonstrate the high modulation dynamic range of the laser, we performed direct absorption (DAS) and second harmonic wavelength modulation spectroscopy (WMS-2f) of the Q-branch peak of acetone molecular absorption band (HWHM ~10 GHz) near 1365 cm−1. With WMS-2f, a minimum detection limit of 15 ppbv in less than 10 s is achieved, which yields a noise equivalent absorption sensitivity of 1.9 × 10−8 cm−1 Hz−1/2. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Hydrogen Sulfide Gas Detection via Multivariate Optical Computing
Sensors 2018, 18(7), 2006; https://doi.org/10.3390/s18072006 - 22 Jun 2018
Cited by 12 | Viewed by 2418
Abstract
Hydrogen-sulfide gas is a toxic, colorless gas with a pungent odor that occurs naturally as a decomposition by-product. It is critical to monitor the concentration of hydrogen sulfide. Multivariate optical computing (MOC) is a method that can monitor analytes while minimizing responses to [...] Read more.
Hydrogen-sulfide gas is a toxic, colorless gas with a pungent odor that occurs naturally as a decomposition by-product. It is critical to monitor the concentration of hydrogen sulfide. Multivariate optical computing (MOC) is a method that can monitor analytes while minimizing responses to interferences. MOC is a technique by which an analogue calculation is performed entirely in the optical domain, which simplifies instrument design, prevents the drift of a calibration, and increases the strength and durability of spectroscopic instrumentation against physical perturbation when used for chemical detection and identification. This paper discusses the detection of hydrogen-sulfide gas in the ultraviolet (UV) spectral region in the presence of interfering gaseous species. A laboratory spectroscopic measurement system was set up to acquire the UV spectra of H2S and interference gas mixtures in high-pressure/high-temperature (HPHT) conditions. These spectra were used to guide the design and fabrication of a multivariate optical element (MOE), which has an expected measurement relative accuracy of 3.3% for H2S, with a concentration in the range of 0–150 nmol/mL. An MOC validation system with the MOE was used to test three samples of H2S and mercaptans mixtures under various pressures, and the relative accuracy of H2S measurement was determined to be 8.05%. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Optical-Spectrometry-Based Method for Immunosuppressant Medicine Level Detection in Aqueous Solutions
Sensors 2018, 18(7), 2001; https://doi.org/10.3390/s18072001 - 22 Jun 2018
Cited by 1 | Viewed by 1831
Abstract
In this paper, an investigation into detecting immunosuppressive medicine in aqueous solutions using a spectrometry-based technique is described. Using optical transmissive spectrometry, absorbance measurements in the spectra range from 250 nm to 1000 nm were carried out for different cyclosporine A (CsA) concentrations [...] Read more.
In this paper, an investigation into detecting immunosuppressive medicine in aqueous solutions using a spectrometry-based technique is described. Using optical transmissive spectrometry, absorbance measurements in the spectra range from 250 nm to 1000 nm were carried out for different cyclosporine A (CsA) concentrations in aqueous solutions. The experiment was conducted for samples both with and without interferent substances—glucose and sodium chloride. Using a dedicated algorithm, the measured data was analyzed and a high correlation coefficient R2 = 0.8647 was achieved. The experiment showed that the described technique allowed for the detection of various CsA concentration levels in a selective, label-free and simple way. This method could be used in medicine, veterinary medicine and laboratory diagnostics. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Nitric Oxide Analysis Down to ppt Levels by Optical-Feedback Cavity-Enhanced Absorption Spectroscopy
Sensors 2018, 18(7), 1997; https://doi.org/10.3390/s18071997 - 22 Jun 2018
Cited by 16 | Viewed by 2667
Abstract
Monitoring nitric oxide at the trace level is required in a large range of applications. We report on a trace gas analyzer optimized for nitric oxide measurements by Optical Feedback Cavity Enhanced Absorption Spectroscopy with an interband cascade laser at 5.3 µm. The [...] Read more.
Monitoring nitric oxide at the trace level is required in a large range of applications. We report on a trace gas analyzer optimized for nitric oxide measurements by Optical Feedback Cavity Enhanced Absorption Spectroscopy with an interband cascade laser at 5.3 µm. The short response time of the instrument allows for reaching the level of 50 ppt in only 180 ms. Its stability enables averaging up to 12 min to reach a detection limit of 0.9 ppt. Absolute concentration calibration requires to account for the optical saturation effect that results from the intense absorption line intensity addressed here, in the mid infrared region, in contrast to instruments that are operating in the near infrared region. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Non-Destructive Methodology to Determine Modulus of Elasticity in Static Bending of Quercus mongolica Using Near-Infrared Spectroscopy
Sensors 2018, 18(6), 1963; https://doi.org/10.3390/s18061963 - 18 Jun 2018
Cited by 9 | Viewed by 2379
Abstract
This article presents a non-destructive methodology to determine the modulus of elasticity (MOE) in static bending of wood through the use of near-infrared (NIR) spectroscopy. Wood specimens were obtained from Quercus mongolica growing in Northeast of China. The NIR spectra of specimens were [...] Read more.
This article presents a non-destructive methodology to determine the modulus of elasticity (MOE) in static bending of wood through the use of near-infrared (NIR) spectroscopy. Wood specimens were obtained from Quercus mongolica growing in Northeast of China. The NIR spectra of specimens were acquired by using a one-chip NIR fiber optic spectrometer whose spectral range was 900~1900 nm. The raw spectra of specimens were pretreated by multiplication scatter correlation and Savitzky-Golay smoothing and differentiation filter. To reduce the dimensions of data and complexity of modeling, the synergy interval partial least squares and successive projections algorithm were applied to extract the characteristic wavelengths, which had closing relevance with the MOE of wood, and five characteristic wavelengths were selected from full 117 variables of a spectrum. Taking the characteristic wavelengths as input values, partial least square regression (PLSR) and the propagation neural network (BPNN) were implemented to establish calibration models. The predictive ability of the models was estimated by the coefficient of determination (rp) and the root mean square error of prediction (RMSEP) and in the prediction set. In comparison with the predicted results of the models, BPNN performed better results with the higher rp of 0.91 and lower RMSEP of 0.76. The results indicate that it is feasible to accurately determine the MOE of wood by using the NIR spectroscopy technique. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Laser Spectroscopic Sensors for the Development of Anthropomorphic Robot Sensitivity
Sensors 2018, 18(6), 1680; https://doi.org/10.3390/s18061680 - 23 May 2018
Cited by 9 | Viewed by 2571
Abstract
The development of underwater robotics sensitivity, which is based on the sensors of laser spectroscopy methods, have been discussed. The ways to improve Laser Induced Fluorescence (LIF) and Laser Induced Breakdown Spectroscopy (LIBS) methods were investigated in order to develop and create laser [...] Read more.
The development of underwater robotics sensitivity, which is based on the sensors of laser spectroscopy methods, have been discussed. The ways to improve Laser Induced Fluorescence (LIF) and Laser Induced Breakdown Spectroscopy (LIBS) methods were investigated in order to develop and create laser sensitivity for underwater robotics. A brief overview is done in the article, where LIF and LIBS spectroscopy in underwater robotics are used as spectroscopy sensors in order to investigate underwater environments by means of underwater vehicles. Limit of Detection (LoD) of oil and oil product solutions in the seawater have been detected by means of nanosecond and femtosecond spectroscopy LIF. All results, which had been received by laser pulses of different duration, were compared. The same experiments have been provided in order to measure concentrations of elements in the seawater and solutions by the LIBS method. It was discovered that the LoD of a group of elements was reduced when the femtosecond LIBS was used. Anthropomorphic complexes were under discussion in order to adopt laser spectroscopy sensors for underwater environments. The submersible module, which was constructed to investigate and examine laser spectroscopy sensors, has been described. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Non-Invasive Methodology to Estimate Polyphenol Content in Extra Virgin Olive Oil Based on Stepwise Multilinear Regression
Sensors 2018, 18(4), 975; https://doi.org/10.3390/s18040975 - 25 Mar 2018
Cited by 3 | Viewed by 1992
Abstract
Normally the olive oil quality is assessed by chemical analysis according to international standards. These norms define chemical and organoleptic markers, and depending on the markers, the olive oil can be labelled as lampante, virgin, or extra virgin olive oil (EVOO), the last [...] Read more.
Normally the olive oil quality is assessed by chemical analysis according to international standards. These norms define chemical and organoleptic markers, and depending on the markers, the olive oil can be labelled as lampante, virgin, or extra virgin olive oil (EVOO), the last being an indicator of top quality. The polyphenol content is related to EVOO organoleptic features, and different scientific works have studied the positive influence that these compounds have on human health. The works carried out in this paper are focused on studying relations between the polyphenol content in olive oil samples and its spectral response in the near infrared spectra. In this context, several acquisition parameters have been assessed to optimize the measurement process within the virgin olive oil production process. The best regression model reached a mean error value of 156.14 mg/kg in leave one out cross validation, and the higher regression coefficient was 0.81 through holdout validation. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Determination of Food Oxalates Using Silica–Titania Xerogel Modified with Eriochrome Cyanine R
Sensors 2018, 18(3), 864; https://doi.org/10.3390/s18030864 - 15 Mar 2018
Cited by 5 | Viewed by 2926
Abstract
The interaction of silica–titania xerogel with triphenylmethane dyes (pyrocatechol violet, chrome azurol S, eriochrome cyanine R) has been investigated to create a new sensor material for solid phase spectrophotometric determination of food oxalates. The complex forming reaction between xerogel incorporated titanium(IV) and triphenylmethane [...] Read more.
The interaction of silica–titania xerogel with triphenylmethane dyes (pyrocatechol violet, chrome azurol S, eriochrome cyanine R) has been investigated to create a new sensor material for solid phase spectrophotometric determination of food oxalates. The complex forming reaction between xerogel incorporated titanium(IV) and triphenylmethane dyes has been studied; half-reaction periods, complex composition, equilibrium constants, and xerogel sorption capacity have been calculated for each dye. Eriochrome cyanine R (ECR) is characterized by the shortest half-reaction period, the smallest equilibrium constant, and the greatest capacity; it has been chosen for the sensor material construction because titanium(IV)-ECR complex is formed faster and can be destroyed easier than other studied complexes. The interaction of this sensor material with oxalates has been described: the presence of oxalates causes sensor material discoloration and the absorbance is used as analytical signal. The analytical range is 35–900 mg/L (LOD 10.5 mg/L, n = 7). High concentrations of interfering inorganic anions, organic acids, and sucrose did not affect oxalate determination. Proposed solid phase spectrophotometric procedure has been successfully applied for the determination of oxalates in food samples (sorrel, spinach, parsley, ginger, and black pepper) and the results are in good agreement with HPLC oxalate determination. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Ppbv-Level Ethane Detection Using Quartz-Enhanced Photoacoustic Spectroscopy with a Continuous-Wave, Room Temperature Interband Cascade Laser
Sensors 2018, 18(3), 723; https://doi.org/10.3390/s18030723 - 28 Feb 2018
Cited by 14 | Viewed by 2117
Abstract
A ppbv-level quartz-enhanced photoacoustic spectroscopy (QEPAS)-based ethane (C2H6) sensor was demonstrated by using a 3.3 μm continuous-wave (CW), distributed feedback (DFB) interband cascade laser (ICL). The ICL was employed for targeting a strong C2H6 absorption line [...] Read more.
A ppbv-level quartz-enhanced photoacoustic spectroscopy (QEPAS)-based ethane (C2H6) sensor was demonstrated by using a 3.3 μm continuous-wave (CW), distributed feedback (DFB) interband cascade laser (ICL). The ICL was employed for targeting a strong C2H6 absorption line located at 2996.88 cm−1 in its fundamental absorption band. Wavelength modulation spectroscopy (WMS) combined with the second harmonic (2f) detection technique was utilized to increase the signal-to-noise ratio (SNR) and simplify data acquisition and processing. Gas pressure and laser frequency modulation depth were optimized to be 100 Torr and 0.106 cm−1, respectively, for maximizing the 2f signal amplitude. Performance of the QEPAS sensor was evaluated using specially prepared C2H6 samples. A detection limit of 11 parts per billion in volume (ppbv) was obtained with a 1-s integration time based on an Allan-Werle variance analysis, and the detection precision can be further improved to ~1.5 ppbv by increasing the integration time up to 230 s. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Cavity-Enhanced Raman Spectroscopy for Food Chain Management
Sensors 2018, 18(3), 709; https://doi.org/10.3390/s18030709 - 27 Feb 2018
Cited by 18 | Viewed by 3686
Abstract
Comprehensive food chain management requires the monitoring of many parameters including temperature, humidity, and multiple gases. The latter is highly challenging because no low-cost technology for the simultaneous chemical analysis of multiple gaseous components currently exists. This contribution proposes the use of cavity [...] Read more.
Comprehensive food chain management requires the monitoring of many parameters including temperature, humidity, and multiple gases. The latter is highly challenging because no low-cost technology for the simultaneous chemical analysis of multiple gaseous components currently exists. This contribution proposes the use of cavity enhanced Raman spectroscopy to enable online monitoring of all relevant components using a single laser source. A laboratory scale setup is presented and characterized in detail. Power enhancement of the pump light is achieved in an optical resonator with a Finesse exceeding 2500. A simulation for the light scattering behavior shows the influence of polarization on the spatial distribution of the Raman scattered light. The setup is also used to measure three relevant showcase gases to demonstrate the feasibility of the approach, including carbon dioxide, oxygen and ethene. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Fast Detection of Copper Content in Rice by Laser-Induced Breakdown Spectroscopy with Uni- and Multivariate Analysis
Sensors 2018, 18(3), 705; https://doi.org/10.3390/s18030705 - 27 Feb 2018
Cited by 28 | Viewed by 2802
Abstract
Fast detection of heavy metals is very important for ensuring the quality and safety of crops. Laser-induced breakdown spectroscopy (LIBS), coupled with uni- and multivariate analysis, was applied for quantitative analysis of copper in three kinds of rice (Jiangsu rice, regular rice, and [...] Read more.
Fast detection of heavy metals is very important for ensuring the quality and safety of crops. Laser-induced breakdown spectroscopy (LIBS), coupled with uni- and multivariate analysis, was applied for quantitative analysis of copper in three kinds of rice (Jiangsu rice, regular rice, and Simiao rice). For univariate analysis, three pre-processing methods were applied to reduce fluctuations, including background normalization, the internal standard method, and the standard normal variate (SNV). Linear regression models showed a strong correlation between spectral intensity and Cu content, with an R 2 more than 0.97. The limit of detection (LOD) was around 5 ppm, lower than the tolerance limit of copper in foods. For multivariate analysis, partial least squares regression (PLSR) showed its advantage in extracting effective information for prediction, and its sensitivity reached 1.95 ppm, while support vector machine regression (SVMR) performed better in both calibration and prediction sets, where R c 2 and R p 2 reached 0.9979 and 0.9879, respectively. This study showed that LIBS could be considered as a constructive tool for the quantification of copper contamination in rice. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
A Micro-Damage Detection Method of Litchi Fruit Using Hyperspectral Imaging Technology
Sensors 2018, 18(3), 700; https://doi.org/10.3390/s18030700 - 26 Feb 2018
Cited by 15 | Viewed by 2820
Abstract
The non-destructive testing of litchi fruit is of great significance to the fresh-keeping, storage and transportation of harvested litchis. To achieve quick and accurate micro-damage detection, a non-destructive grading test method for litchi fruits was studied using 400–1000 nm hyperspectral imaging technology. The [...] Read more.
The non-destructive testing of litchi fruit is of great significance to the fresh-keeping, storage and transportation of harvested litchis. To achieve quick and accurate micro-damage detection, a non-destructive grading test method for litchi fruits was studied using 400–1000 nm hyperspectral imaging technology. The Huaizhi litchi was chosen in this study, and the hyperspectral data average for the region of interest (ROI) of litchi fruit was extracted for spectral data analysis. Then the hyperspectral data samples of fresh and micro-damaged litchi fruits were selected, and a partial least squares discriminant analysis (PLS-DA) was used to establish a prediction model for the realization of qualitative analysis for litchis with different qualities. For the external validation set, the mean per-type recall and precision were 94.10% and 93.95%, respectively. Principal component analysis (PCA) was used to determine the sensitive wavelength for recognition of litchi quality characteristics, with the results of wavelengths corresponding to the local extremum for the weight coefficient of PC3, i.e., 694, 725 and 798 nm. Then the single-band images corresponding to each sensitive wavelength were analyzed. Finally, the 7-dimension features of the PC3 image were extracted using the Gray Level Co-occurrence Matrix (GLCM). Through image processing, least squares support vector machine (LS-SVM) modeling was conducted to classify the different qualities of litchis. The model was validated using the experiment data, and the average accuracy of the validation set was 93.75%, while the external validation set was 95%. The results indicate the feasibility of using hyperspectral imaging technology in litchi postpartum non-destructive detection and classification. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
A Spectral Reconstruction Algorithm of Miniature Spectrometer Based on Sparse Optimization and Dictionary Learning
Sensors 2018, 18(2), 644; https://doi.org/10.3390/s18020644 - 22 Feb 2018
Cited by 21 | Viewed by 2825
Abstract
The miniaturization of spectrometer can broaden the application area of spectrometry, which has huge academic and industrial value. Among various miniaturization approaches, filter-based miniaturization is a promising implementation by utilizing broadband filters with distinct transmission functions. Mathematically, filter-based spectral reconstruction can be modeled [...] Read more.
The miniaturization of spectrometer can broaden the application area of spectrometry, which has huge academic and industrial value. Among various miniaturization approaches, filter-based miniaturization is a promising implementation by utilizing broadband filters with distinct transmission functions. Mathematically, filter-based spectral reconstruction can be modeled as solving a system of linear equations. In this paper, we propose an algorithm of spectral reconstruction based on sparse optimization and dictionary learning. To verify the feasibility of the reconstruction algorithm, we design and implement a simple prototype of a filter-based miniature spectrometer. The experimental results demonstrate that sparse optimization is well applicable to spectral reconstruction whether the spectra are directly sparse or not. As for the non-directly sparse spectra, their sparsity can be enhanced by dictionary learning. In conclusion, the proposed approach has a bright application prospect in fabricating a practical miniature spectrometer. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Laser-Based Monitoring of CH4, CO2, NH3, and H2S in Animal Farming—System Characterization and Initial Demonstration
Sensors 2018, 18(2), 529; https://doi.org/10.3390/s18020529 - 09 Feb 2018
Cited by 15 | Viewed by 5015
Abstract
In this paper, we present a system for sequential detection of multiple gases using laser-based wavelength modulation spectroscopy (WMS) method combined with a Herriot-type multi-pass cell. Concentration of hydrogen sulfide (H2S), methane (CH4), carbon dioxide (CO2), and [...] Read more.
In this paper, we present a system for sequential detection of multiple gases using laser-based wavelength modulation spectroscopy (WMS) method combined with a Herriot-type multi-pass cell. Concentration of hydrogen sulfide (H2S), methane (CH4), carbon dioxide (CO2), and ammonia (NH3) are retrieved using three distributed feedback laser diodes operating at 1574.5 nm (H2S and CO2), 1651 nm (CH4), and 1531 nm (NH3). Careful adjustment of system parameters allows for H2S sensing at single parts-per-million by volume (ppmv) level with strongly reduced interference from adjacent CO2 transitions even at atmospheric pressure. System characterization in laboratory conditions is presented and the results from initial tests in real-world application are demonstrated. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Silver Eco-Solvent Ink for Reactive Printing of Polychromatic SERS and SPR Substrates
Sensors 2018, 18(2), 521; https://doi.org/10.3390/s18020521 - 09 Feb 2018
Cited by 4 | Viewed by 2557
Abstract
A new reactive ink based on a silver citrate complex is proposed for a photochemical route to surface-enhanced Raman spectroscopy active substrates with controllable extinction spectra. The drop-cast test of the ink reveals homogeneous nucleation of silver and colloid particle growth originating directly [...] Read more.
A new reactive ink based on a silver citrate complex is proposed for a photochemical route to surface-enhanced Raman spectroscopy active substrates with controllable extinction spectra. The drop-cast test of the ink reveals homogeneous nucleation of silver and colloid particle growth originating directly from photochemical in situ reduction in droplets, while the following evaporation of the deposited ink produces small nano- and micron-size particles. The prepared nanostructures and substrates were accurately characterized by electron microscopy methods and optical extinction spectroscopy. Varying the duration of UV irradiation allows tuning the morphology of individual silver nanoparticles forming hierarchical ring structures with numerous “hot spots” for most efficient Raman enhancement. Raman measurements of probe molecules of rhodamine 6G and methylene blue reached the largest signal enhancement of 106 by the resonance effects. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Determining Biogenic Content of Biogas by Measuring Stable Isotopologues 12CH4, 13CH4, and CH3D with a Mid-Infrared Direct Absorption Laser Spectrometer
Sensors 2018, 18(2), 496; https://doi.org/10.3390/s18020496 - 07 Feb 2018
Cited by 1 | Viewed by 2222
Abstract
A tunable laser absorption spectrometer (TLAS) was developed for the simultaneous measurement of δ13C and δD values of methane (CH4). A mid-infrared interband cascade laser (ICL) emitting around 3.27 µm was used to measure the absorption of the [...] Read more.
A tunable laser absorption spectrometer (TLAS) was developed for the simultaneous measurement of δ13C and δD values of methane (CH4). A mid-infrared interband cascade laser (ICL) emitting around 3.27 µm was used to measure the absorption of the three most abundant isotopologues in CH4 with a single, mode-hop free current sweep. The instrument was validated against methane samples of fossil and biogenic origin with known isotopic composition. Three blended mixtures with varied biogenic content were prepared volumetrically, and their δ13C and δD values were determined. Analysis demonstrated that, provided the isotopic composition of the source materials was known, the δ13C and δD values alone were sufficient to determine the biogenic content of the blended samples to within 1.5%. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Exploring the Efficacy of Platinum and Palladium Nanostructures for Organic Molecule Detection via Raman Spectroscopy
Sensors 2018, 18(1), 147; https://doi.org/10.3390/s18010147 - 07 Jan 2018
Cited by 12 | Viewed by 2699
Abstract
Noble transition metals, like palladium (Pd) and platinum (Pt), have been well-known for their excellent catalytic and electrochemical properties. However, they have been considered non-active for surface enhanced Raman spectroscopy (SERS). In this work, we explore the scattering contributions of Pd and Pt [...] Read more.
Noble transition metals, like palladium (Pd) and platinum (Pt), have been well-known for their excellent catalytic and electrochemical properties. However, they have been considered non-active for surface enhanced Raman spectroscopy (SERS). In this work, we explore the scattering contributions of Pd and Pt for the detection of organic molecules. The Pd and Pt nanostructures were synthesized on silicon substrate using a modified galvanic displacement method. The results show Pt nanoparticles and dendritic Pd nanostructures with controlled density and size. The influence of surfactants, including sodium dodecyl sulfate and cetyltrimethylammonium bromide, on the size and morphology of the nanostructures was investigated. The Pd and Pt nanostructures with a combination of large size and high density were then used to explore their applicability for the detection of 10−5 M Rhodamine 6G and 10−2 M paraoxon. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Identification of Coffee Varieties Using Laser-Induced Breakdown Spectroscopy and Chemometrics
Sensors 2018, 18(1), 95; https://doi.org/10.3390/s18010095 - 31 Dec 2017
Cited by 27 | Viewed by 2782
Abstract
We linked coffee quality to its different varieties. This is of interest because the identification of coffee varieties should help coffee trading and consumption. Laser-induced breakdown spectroscopy (LIBS) combined with chemometric methods was used to identify coffee varieties. Wavelet transform (WT) was used [...] Read more.
We linked coffee quality to its different varieties. This is of interest because the identification of coffee varieties should help coffee trading and consumption. Laser-induced breakdown spectroscopy (LIBS) combined with chemometric methods was used to identify coffee varieties. Wavelet transform (WT) was used to reduce LIBS spectra noise. Partial least squares-discriminant analysis (PLS-DA), radial basis function neural network (RBFNN), and support vector machine (SVM) were used to build classification models. Loadings of principal component analysis (PCA) were used to select the spectral variables contributing most to the identification of coffee varieties. Twenty wavelength variables corresponding to C I, Mg I, Mg II, Al II, CN, H, Ca II, Fe I, K I, Na I, N I, and O I were selected. PLS-DA, RBFNN, and SVM models on selected wavelength variables showed acceptable results. SVM and RBFNN models performed better with a classification accuracy of over 80% in the prediction set, for both full spectra and the selected variables. The overall results indicated that it was feasible to use LIBS and chemometric methods to identify coffee varieties. For further studies, more samples are needed to produce robust classification models, research should be conducted on which methods to use to select spectral peaks that correspond to the elements contributing most to identification, and the methods for acquiring stable spectra should also be studied. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Remotely Exploring Deeper-Into-Matter by Non-Contact Detection of Audible Transients Excited by Laser Radiation
Sensors 2017, 17(12), 2960; https://doi.org/10.3390/s17122960 - 20 Dec 2017
Viewed by 2179
Abstract
An acoustic spectroscopic approach to detect contents within different packaging, with substantially wider applicability than other currently available subsurface spectroscopies, is presented. A frequency-doubled Nd:YAG (neodymium-doped yttrium aluminum garnet) pulsed laser (13 ns pulse length) operated at 1 Hz was used to generate [...] Read more.
An acoustic spectroscopic approach to detect contents within different packaging, with substantially wider applicability than other currently available subsurface spectroscopies, is presented. A frequency-doubled Nd:YAG (neodymium-doped yttrium aluminum garnet) pulsed laser (13 ns pulse length) operated at 1 Hz was used to generate the sound field of a two-component system at a distance of 50 cm. The acoustic emission was captured using a unidirectional microphone and analyzed in the frequency domain. The focused laser pulse hitting the system, with intensity above that necessary to ablate the irradiated surface, transferred an impulsive force which led the structure to vibrate. Acoustic airborne transients were directly radiated by the vibrating elastic structure of the outer component that excited the surrounding air in contact with. However, under boundary conditions, sound field is modulated by the inner component that modified the dynamical integrity of the system. Thus, the resulting frequency spectra are useful indicators of the concealed content that influences the contributions originating from the wall of the container. High-quality acoustic spectra could be recorded from a gas (air), liquid (water), and solid (sand) placed inside opaque chemical-resistant polypropylene and stainless steel sample containers. Discussion about effects of laser excitation energy and sampling position on the acoustic emission events is reported. Acoustic spectroscopy may complement the other subsurface alternative spectroscopies, severely limited by their inherent optical requirements for numerous detection scenarios. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Detection of Water Content in Rapeseed Leaves Using Terahertz Spectroscopy
Sensors 2017, 17(12), 2830; https://doi.org/10.3390/s17122830 - 06 Dec 2017
Cited by 40 | Viewed by 3060
Abstract
The terahertz (THz) spectra of rapeseed leaves with different water content (WC) were investigated. The transmission and absorption spectra in the range of 0.3–2 THz were measured by using THz time-domain spectroscopy. The mean transmittance and absorption coefficients were applied to analyze the [...] Read more.
The terahertz (THz) spectra of rapeseed leaves with different water content (WC) were investigated. The transmission and absorption spectra in the range of 0.3–2 THz were measured by using THz time-domain spectroscopy. The mean transmittance and absorption coefficients were applied to analyze the change regulation of WC. In addition, the Savitzky-Golay method was performed to preprocess the spectra. Then, the partial least squares (PLS), kernel PLS (KPLS), and Boosting-PLS were conducted to establish models for predicting WC based on the processed transmission and absorption spectra. Reliable results were obtained by these three methods. KPLS generated the best prediction accuracy of WC. The prediction coefficient correlation (Rval) and root mean square error (RMSEP) of KPLS based on transmission were Rval = 0.8508, RMSEP = 0.1015, and that based on absorption were Rval = 0.8574, RMSEP = 0.1009. Results demonstrated that THz spectroscopy combined with modeling methods provided an efficient and feasible technique for detecting plant physiological information. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Monitoring the Wobbe Index of Natural Gas Using Fiber-Enhanced Raman Spectroscopy
Sensors 2017, 17(12), 2714; https://doi.org/10.3390/s17122714 - 24 Nov 2017
Cited by 26 | Viewed by 5214
Abstract
The fast and reliable analysis of the natural gas composition requires the simultaneous quantification of numerous gaseous components. To this end, fiber-enhanced Raman spectroscopy is a powerful tool to detect most components in a single measurement using a single laser source. However, practical [...] Read more.
The fast and reliable analysis of the natural gas composition requires the simultaneous quantification of numerous gaseous components. To this end, fiber-enhanced Raman spectroscopy is a powerful tool to detect most components in a single measurement using a single laser source. However, practical issues such as detection limit, gas exchange time and background Raman signals from the fiber material still pose obstacles to utilizing the scheme in real-world settings. This paper compares the performance of two types of hollow-core photonic crystal fiber (PCF), namely photonic bandgap PCF and kagomé-style PCF, and assesses their potential for online determination of the Wobbe index. In contrast to bandgap PCF, kagomé-PCF allows for reliable detection of Raman-scattered photons even below 1200 cm−1, which in turn enables fast and comprehensive assessment of the natural gas quality of arbitrary mixtures. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Fast, Low-Cost and Non-Destructive Physico-Chemical Analysis of Virgin Olive Oils Using Near-Infrared Reflectance Spectroscopy
Sensors 2017, 17(11), 2642; https://doi.org/10.3390/s17112642 - 16 Nov 2017
Cited by 15 | Viewed by 2827
Abstract
Near-Infrared (NIR) Spectroscopy was used for the non-destructive assessment of physico-chemical quality parameters in olive oil. At the same time, the influence of the sample presentation mode (spinning versus static cup) was evaluated using two spectrophotometers with similar optical characteristics. A total of [...] Read more.
Near-Infrared (NIR) Spectroscopy was used for the non-destructive assessment of physico-chemical quality parameters in olive oil. At the same time, the influence of the sample presentation mode (spinning versus static cup) was evaluated using two spectrophotometers with similar optical characteristics. A total of 478 olive oil samples were used to develop calibration models, testing various spectral signal pre-treatments. The models obtained by applying MPLS regression to spectroscopic data yielded promising results for olive oil quality measurements, particularly for acidity, the peroxide index and alkyl and ethyl ester content. The results obtained indicate that this non-invasive technology can be used successfully by the olive oil sector to categorize olive oils, to detect potential fraud and to provide consumers with more reliable information. Although both sample presentation modes yielded comparable results, equations constructed with samples scanned using the spinning mode provided greater predictive capacity. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Article
Electrochemical and Infrared Absorption Spectroscopy Detection of SF6 Decomposition Products
Sensors 2017, 17(11), 2627; https://doi.org/10.3390/s17112627 - 15 Nov 2017
Cited by 20 | Viewed by 4641
Abstract
Sulfur hexafluoride (SF6) gas-insulated electrical equipment is widely used in high-voltage (HV) and extra-high-voltage (EHV) power systems. Partial discharge (PD) and local heating can occur in the electrical equipment because of insulation faults, which results in SF6 decomposition and ultimately [...] Read more.
Sulfur hexafluoride (SF6) gas-insulated electrical equipment is widely used in high-voltage (HV) and extra-high-voltage (EHV) power systems. Partial discharge (PD) and local heating can occur in the electrical equipment because of insulation faults, which results in SF6 decomposition and ultimately generates several types of decomposition products. These SF6 decomposition products can be qualitatively and quantitatively detected with relevant detection methods, and such detection contributes to diagnosing the internal faults and evaluating the security risks of the equipment. At present, multiple detection methods exist for analyzing the SF6 decomposition products, and electrochemical sensing (ES) and infrared (IR) spectroscopy are well suited for application in online detection. In this study, the combination of ES with IR spectroscopy is used to detect SF6 gas decomposition. First, the characteristics of these two detection methods are studied, and the data analysis matrix is established. Then, a qualitative and quantitative analysis ES-IR model is established by adopting a two-step approach. A SF6 decomposition detector is designed and manufactured by combining an electrochemical sensor and IR spectroscopy technology. The detector is used to detect SF6 gas decomposition and is verified to reliably and accurately detect the gas components and concentrations. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Review

Jump to: Research

Review
Probe of Alcohol Structures in the Gas and Liquid States Using C–H Stretching Raman Spectroscopy
Sensors 2018, 18(7), 2061; https://doi.org/10.3390/s18072061 - 28 Jun 2018
Cited by 7 | Viewed by 1745
Abstract
Vibrational spectroscopy is a powerful tool for probing molecular structures and dynamics since it offers a unique fingerprint that allows molecular identification. One of important aspects of applying vibrational spectroscopy is to develop the probes that can characterize the related properties of molecules [...] Read more.
Vibrational spectroscopy is a powerful tool for probing molecular structures and dynamics since it offers a unique fingerprint that allows molecular identification. One of important aspects of applying vibrational spectroscopy is to develop the probes that can characterize the related properties of molecules such as the conformation and intermolecular interaction. Many examples of vibrational probes have appeared in the literature, including the azide group (–N3), amide group (–CONH2), nitrile groups (–CN), hydroxyl group (–OH), –CH group and so on. Among these probes, the –CH group is an excellent one since it is ubiquitous in organic and biological molecules and the C–H stretching vibrational spectrum is extraordinarily sensitive to the local molecular environment. However, one challenge encountered in the application of C–H probes arises from the difficulty in the accurate assignment due to spectral congestion in the C–H stretching region. In this paper, recent advances in the complete assignment of C–H stretching spectra of aliphatic alcohols and the utility of C–H vibration as a probe of the conformation and weak intermolecular interaction are outlined. These results fully demonstrated the potential of the –CH chemical group as a molecular probe. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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Review
Smartphone Spectrometers
Sensors 2018, 18(1), 223; https://doi.org/10.3390/s18010223 - 14 Jan 2018
Cited by 87 | Viewed by 9047
Abstract
Smartphones are playing an increasing role in the sciences, owing to the ubiquitous proliferation of these devices, their relatively low cost, increasing processing power and their suitability for integrated data acquisition and processing in a ‘lab in a phone’ capacity. There is furthermore [...] Read more.
Smartphones are playing an increasing role in the sciences, owing to the ubiquitous proliferation of these devices, their relatively low cost, increasing processing power and their suitability for integrated data acquisition and processing in a ‘lab in a phone’ capacity. There is furthermore the potential to deploy these units as nodes within Internet of Things architectures, enabling massive networked data capture. Hitherto, considerable attention has been focused on imaging applications of these devices. However, within just the last few years, another possibility has emerged: to use smartphones as a means of capturing spectra, mostly by coupling various classes of fore-optics to these units with data capture achieved using the smartphone camera. These highly novel approaches have the potential to become widely adopted across a broad range of scientific e.g., biomedical, chemical and agricultural application areas. In this review, we detail the exciting recent development of smartphone spectrometer hardware, in addition to covering applications to which these units have been deployed, hitherto. The paper also points forward to the potentially highly influential impacts that such units could have on the sciences in the coming decades. Full article
(This article belongs to the Special Issue Spectroscopy Based Sensors)
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