Response Of Optical Sensors Research Articles

Tuning the Sensitivity of Photonic Sensors Toward Alkanes Through the Textural Properties of Hybrid Xerogel Coatings

AbstractThis work exemplifies how incorporating organosilane modifiers into silica matrices allows for tuning the optical response of reflection photonic sensors through customizing the textural properties of hybrid xerogel sensing films. Xerogels with propyl molar percentages 0, 5, and 10% are used to construct photonic probes (OFS0pTEOS, OFS5pTEOS and OFS10pTEOS, respectively) by dip‐coating upon optimizing film deposition parameters. The time response of these probes toward a battery of volatile organic compounds (VOCs) comprising species with different functionality, size‐shape, and polarity is systematically analyzed through ON/OFF experiments, revealing that a low propyl content makes the poor‐responding OFS0pTEOS film highly sensitive toward non‐aromatic, large molecules with low‐polar or non‐polar character in OFS5pTEOS. This sensor is particularly sensitive toward alkanes, with globular cyclohexane (cyHex) outperforming elongated n‐hexane. Variable‐temperature calibration curves obtained from step‐by‐step experiments and adsorption–desorption cycles corroborate these observations and allow hysteresis to be quantified. The response to cyHex closely follows VOC concentration changes with the most stable signal among analytes, leading to well‐defined curves with low‐to‐negligible hysteresis. The isosteric enthalpies of cyHex adsorption are obtained for both the bulk material and the sensor, demonstrating labile adsorbate‐adsorbent interactions ruling the sensor response and becoming more exothermic for larger VOC concentrations.

Integrated interferometers’ system for in situ real-time optical signal modulation

Improving the functionality of an optical sensor on a prefabricated platform relies heavily on an optical signal conditioning method that actively modulates optical signals. In this work, we present a method for active modulation of an optical sensor response that uses fiber modal interferometers integrated in parallel. Over a broad frequency range of 1 Hz to 1 kHz, the interferometers’ technology allows for adjustable amplification, attenuation, and filtering of dynamic signals. The suggested method is also used to enhance the real-time response of an optical fluid flowmeter. In order to keep tabs on different physical fields, the suggested approach promotes the creation of self-conditioning sensing systems.

Vernier effect-based optical fiber sensor for dynamic sensing using a coarsely resolved spectrometer.

Vernier effect-based optical fiber sensors have been demonstrated for high-sensitivity measurements of a diverse array of physical and chemical parameters. The interrogation of a Vernier sensor typically needs a broadband source and an optical spectrum analyzer to measure amplitudes over a broad wavelength window with dense sampling points, facilitating accurate extraction of the Vernier modulation envelope for sensitivity-improved sensing. However, the stringent requirement on the interrogation system limits the dynamic sensing capability of Vernier sensors. In this work, the possibility of employing a light source with a small wavelength bandwidth (35 nm) and a coarsely resolved spectrometer (∼166 pm) for the interrogation of an optical fiber Vernier sensor is demonstrated with the assistance of a machine learning-based analysis technique. Dynamic sensing of the exponential decay process of a cantilever beam has been successfully implemented with the low-cost and intelligent Vernier sensor. This work represents a first step towards a simpler, faster, and cheaper way to characterize the response of optical fiber sensors based on the Vernier effect.

Optical sensor response towards hydrogen peroxide in low fat and full cream milk

Fiber Optic Displacement Sensor (FODS) categorized as one of the optical sensor based reflective intensity modulation. An intensity based sensor have been widely used in detecting various substances due to their simplicity structures. Generally for sensing principle, a pair of fiber is used to construct FODS which one of optical fiber is the transmitting fiber and another one is receiving fiber. The objective of this current work is to introduce FODS to evaluate the optical response in terms of voltage reading at different concentration of hydrogen peroxide in two different types of milk. A real-time measurement, low cost, stability, high sensitivity and simplicity of design promote a well-developed sensor in providing useful parameters in detecting hydrogen peroxide in milk. Hydrogen peroxide is an adulterated agent added in milk that can harm the consumers. Transmitive optical sensor as a function of displacement technique was developed to study the hydrogen peroxide concentrations in the range of 0 %-10 % as consuming more than 3-10 % of hydrogen peroxide can cause mild allergies reactions, stomach upset and vomiting. The output from the receiving fiber in this designated system was measured in terms of voltage reading through multimeter. The sensor shows outstanding performances of delivering 0.0007 V/% sensitivity for low fat milk and with linearity of >98 %. Whereas, the sensitivity achieved for full cream milk was 0.0005 V/% with a good linearity >97 %. The simplicity and credibility of this system offer a good opportunity in this project and also foods industry applications.

Influence of the photopolymerization matrix on the indicator response of optical fiber pH sensors

Optical fiber pH sensors work by observing a change in the indicator’s optical signal caused by variations in pH and these indicators can be immobilized onto the surface of an optical fiber using a polymer matrix. How the composition of the polymer matrix changes pH detection range using the indicator (5(6)-carboxynaphthofluorescein (CNF)) has not been studied. Here we show that the composition of the polymer matrix affects the working pH ranges of optical fiber CNF sensors. We used acrylamide (AAm) or N-isopropylacrylamide (NIPAM) as the backbone monomer, and N, N’-methylenebisacrylamide (BIS) as the crosslinker for the polymer matrix. We found that AAm-based pH sensors showed rapid response over the pH range 6.6 – 8.0, while the dynamic ranges of NIPAM-based sensors shifted to basic pH compared with AAm-based pH sensors. Furthermore, we found that an increased ratio of the backbone monomer, NIPAM, over the crosslinker, BIS, significantly shifted the working range to more basic pH values, covering a pH range of 8.1 – 10.3. Our results demonstrate that the polymer matrix can be a powerful means to control the indicator response of optical pH sensors.

Cerium Bromide Single-Crystal X-Ray Detection and Spectral Compatibility Assessment with Various Optical Sensors

Scintillators with high light yield (LY) values are of interest for medical imaging applications, in harsh environments, nondestructive testing (NDT), etc. CeBr3 has a LY of 60000 photons per MeV, a value much higher than other efficient materials, such as Lu3Al5O12:Ce (25000 photons/MeV); thus, its X-ray detection properties would be of interest to be examined for medical imaging applications. The X-ray detection and absorption properties of a single crystal CeBr3 sample along with the compatibility of its produced light with various optoelectronic sensors were examined. In this study, the quantum detection (QDE) and the energy absorption efficiency (EAE) of CeBr3 were calculated. The findings were compared with data for 10 × 10 × 10 m m 3 Lu3Al5O12:Ce and CaF2:Eu single crystals. The measured optical spectrum produced by CeBr3 was well correlated with the spectral response of commercial optical sensors, yielding spectral matching higher than 93% for various photocathodes, e.g., GaAs (94%), E-S20 (95%), and bialkali and multialkali (95-97%), as well as with flat panel position-sensitive photomultipliers (95-99%). The energy absorption properties of CeBr3 were found higher than those of Lu3Al5O12:Ce and CaF2:Eu for X-ray tube voltages greater than 100 kVp. The quantum detection efficiency was 100% across the examined energy range. Even though CeBr3 is hygroscopic and has a mediocre 5.1 g/cm3 density, the QDE, EAE, and spectral correlation results are promising for medical imaging applications.

In Situ Synthesis of Gold Nanoparticles in Layer-by-Layer Polymeric Coatings for the Fabrication of Optical Fiber Sensors.

A new method is proposed to tune the interferometric response of wavelength-based optical fiber sensors. Using the nanoparticle in situ synthesis (ISS) technique, it is possible to synthesize gold nanoparticles (AuNPs) within a pre-existing polymeric thin film deposited at the end-face of an optical fiber. This post-process technique allows us to adjust the optical response of the device. The effect of the progressive synthesis of AuNPs upon polymeric film contributed to a remarkable optical contrast enhancement and a very high tuning capability of the reflection spectra in the visible and near-infrared region. The spectral response of the sensor to relative humidity (RH) variations was studied as a proof of concept. These results suggest that the ISS technique can be a useful tool for fiber optic sensor manufacturing.

Influence of the Photopolymerization Matrix on the Indicator Response of Optical Fiber Ph Sensors

Influence of the Photopolymerization Matrix on the Indicator Response of Optical Fiber Ph Sensors

Optical Oxygen Sensor Patch Printed with Polystyrene Microparticles-based Ink on Flexible Substrate.

Optical oxygen sensors based on photoluminescence quenching have gained increasing attention as a superior method for continuous monitoring of oxygen in a growing number of applications. A simple and low-cost fabrication technique was developed to produce sensor arrays capable of two-dimensional oxygen tension measurement. Sensor patches were printed on polyvinylidene chloride film using an oxygen-sensitive ink cocktail, prepared by immobilizing Pt(II) mesotetra(pentafluorophenyl)porphine (PtTFPP) in monodispersed polystyrene microparticles. The dispersion media of the ink cocktail, high molecular weight polyvinyl pyrrolidone suspended in 50% ethanol (v/v in water), allowed adhesion promotion and compatibility with most common polymeric substrates. Ink phosphorescence intensity was found to vary primarily with fluorophore concentration and to a lesser extent with polystyrene particle size. The sensor performance was investigated as a function of oxygen concentrations employing two different techniques: a multi-frequency phase fluorometer and smart phone-based image acquisition. The printed sensor patch showed fast and repetitive response over 0-21% oxygen concentrations with high linearity (with R2 >0.99) in a Stern-Volmer plot, and sensitivity of I0/I21 >1.55. The optical sensor response on a surface was investigated further using two-dimensional images which were captured and analyzed under different oxygen environment. Printed sensor patch along with imaging read-out technique make an ideal platform for early detection of surface wounds associated with tissue oxygen.

Application of the principal components analysis technique to optical fiber sensors for acetone detection

Generally, the data analysis of sensors based on spectral measurements, for instance, fiber Bragg gratings (FBG), long period fiber gratings (LPFG) is performed observing the shift or attenuation of a single wavelength. However, sometimes such spectrum variations are not evident or clearly perceptible; therefore, it becomes necessary to use other analysis techniques. One of them is principal components analysis (PCA) which allows to explore the behavior of the complete transmission spectrum pattern. In this work, we show the application of PCA to the response of fiber optical sensors for acetone detection. Two kinds of acetone sensors based upon single long period fiber gratings (LPFG) and Mach-Zehnder fiber interferometers (MZI), formed with a pair of cascaded LPFGs, coated with polydimethylsiloxane (PDMS) were developed. The sensor response was measured inside a Teflon chamber injecting a liquid acetone sample. The transmission spectrum variations at the devices output were measured with an optical spectrum analyzer, stored in a computer and analyzed by PCA. A comparison between the performance of both kinds of sensors was carried out and it was found that the sensitivity was increased up to 13 times (from 0.7 × 10−4 ppm−1 to 9.4 × 10−4 ppm−1) for the MZI sensors compared with that of single LPFG ones, which means, at best, a limit of detection (LOD) of 170 ppm.

Development of a Tuneable NDIR Optical Electronic Nose.

Electronic nose (E-nose) technology provides an easy and inexpensive way to analyse chemical samples. In recent years, there has been increasing demand for E-noses in applications such as food safety, environmental monitoring and medical diagnostics. Currently, the majority of E-noses utilise an array of metal oxide (MOX) or conducting polymer (CP) gas sensors. However, these sensing technologies can suffer from sensor drift, poor repeatability and temperature and humidity effects. Optical gas sensors have the potential to overcome these issues. This paper reports on the development of an optical non-dispersive infrared (NDIR) E-nose, which consists of an array of four tuneable detectors, able to scan a range of wavelengths (3.1–10.5 μm). The functionality of the device was demonstrated in a series of experiments, involving gas rig tests for individual chemicals (CO2 and CH4), at different concentrations, and discriminating between chemical standards and complex mixtures. The optical gas sensor responses were shown to be linear to polynomial for different concentrations of CO2 and CH4. Good discrimination was achieved between sample groups. Optical E-nose technology therefore demonstrates significant potential as a portable and low-cost solution for a number of E-nose applications.

Investigation of UV irradiation response of optical fiber sensors for radiation dosimetry

In this work, the investigation of radiation response for modified cladding multimode optical fibres exposed to UV radiation (N2 Laser) in terms of Radiation-Induced Attenuation (RIA) had been presented. The optical fibres were tapered to 65 and 60 μm then dipped into (5 wt % of Germanium to modify the cladding region. By exposing these fibres to different energies of UV irradiation, the transmission spectra were online monitored and recorded every ten seconds to analyze the attenuation changes with the increasing of the radiation dose. The experimental results revealed two points: the first point is that the sensor undergoes the RIA effect which is resulted from the interaction between the radiation and the dopant material, and the second point shows that the sensitivity increases as the diameter of the sensor decrease. From these outcomes, we can conclude that such a sensor can be employed in different dosimetry applications.

MoSe2-Au Based Sensitivity Enhanced Optical Fiber Surface Plasmon Resonance Biosensor for Detection of Goat-Anti-Rabbit IgG

Surface Plasmon resonance (SPR) provides an efficacious and label-free detection method for optical fiber bio-sensing. MoSe 2 is one of the transition metal dichalcogenides (TMDCs) which has broad applications in detecting specific reactions. Cysteamine hydrochloride with enriched groups can generate self-assemble films for tight attachment. In this study we aimed to combine the rapid response of optical fiber SPR sensors with the enhanced sensitivity of MoSe 2 nano-films. An optical fiber SPR biosensor with MoSe 2 -Au nanostructure was proposed and implemented, and a sensitivity of 2821.81 nm/RIU was achieved, which was approximately 98.7% higher than that of conventional SPR sensor without using MoSe 2 nanostructure. Furthermore, Bovine Serum Albumin (BSA) was utilized as the target molecule to test the bioaffinity of the biosensor with MoSe 2 deposition cycles from 0 to 8. Weighing the sensitivity and the figure of merit (FOM), the best deposition cycle of MoSe 2 was 4 with the sensitivity of 2793.36 nm/RIU and FOM of 37.24 RIU -1 . At last, immunization experiments were carried out using Goat-anti-Rabbit IgG and a detection limit of 0.33 μg/mL was achieved. The rapid response and the high bioaffinity showed a strong applicability of the proposed MoSe 2 -Au SPR immune-sensor in specific interactions and immunization therapy.

Templating colloidal sieves for tuning nanotube surface interactions and optical sensor responses

Surfactants offer a tunable approach for modulating the exposed surface area of a nanoparticle. They further present a scalable and cost-effective means for suspending single-walled carbon nanotubes (SWCNTs), which have demonstrated practical use as fluorescence sensors. Though surfactant suspensions show record quantum yields for SWCNTs in aqueous solutions, they lack the selectivity that is vital for optical sensing. We present a new method for controlling the selectivity of optical SWCNT sensors through colloidal templating of the exposed surface area. Colloidal nanotube sensors were obtained using various concentrations of sodium cholate, and their performances were compared to DNA-SWCNT optical sensors. Sensor responses were measured against a library of bioanalytes, including neurotransmitters, amino acids, and sugars. We report an intensity response towards dopamine and serotonin for all sodium cholate-suspended SWCNT concentrations. We further identify a selective, 14.1 nm and 10.3 nm wavelength red-shifting response to serotonin for SWCNTs suspended in 1.5 and 0.5 mM sodium cholate, respectively. Through controlled, adsorption-based tuning of the nanotube surface, this study demonstrates the applicability of sub-critical colloidal suspensions to achieve selectivities exceeding those previously reported for DNA-SWCNT sensors.

Model-based analysis of biocatalytic processes and performance of microbioreactors with integrated optical sensors

Design and development of scale-down approaches, such as microbioreactor (μBR) technologies with integrated sensors, are an adequate solution for rapid, high-throughput and cost-effective screening of valuable reactions and/or production strains, with considerably reduced use of reagents and generation of waste. A significant challenge in the successful and widespread application of μBRs in biotechnology remains the lack of appropriate software and automated data interpretation of μBR experiments. Here, it is demonstrated how mathematical models can be usedas helpful tools, not only to exploit the capabilities of microfluidic platforms, but also to reveal the critical experimental conditions when monitoring cascade enzymatic reactions. A simplified mechanistic model was developed to describe the enzymatic reaction of glucose oxidase and glucose in the presence of catalase inside a commercial microfluidic platform with integrated oxygen sensor spots. The proposed model allowed an easy and rapid identification of the reaction mechanism, kinetics and limiting factors. The effect of fluid flow and enzyme adsorption inside the microfluidic chip on the optical sensor response and overall monitoring capabilities of the presented platform was evaluated via computational fluid dynamics (CFD) simulations. Remarkably, the model predictions were independently confirmed for μL- and mL- scale experiments. It is expected that the mechanistic models will significantly contribute to the further promotion of μBRs in biocatalysis research and that the overall study will create a framework for screening and evaluation of critical system parameters, including sensor response, operating conditions, experimental and microbioreactor designs.

One Spot—Two Sensors: Porous Silicon Interferometers in Combination With Gold Nanostructures Showing Localized Surface Plasmon Resonance

Sensors composed of a porous silicon monolayer covered with a film of nanostructured gold layer, which provide two optical signal transduction methods, are fabricated and thoroughly characterized concerning their sensing performance. For this purpose, silicon substrates were electrochemically etched in order to obtain porous silicon monolayers, which were subsequently immersed in gold salt solution facilitating the formation of a porous gold nanoparticle layer on top of the porous silicon. The deposition process was monitored by reflectance spectroscopy, and the appearance of a dip in the interference pattern of the porous silicon layer was observed. This dip can be assigned to the absorption of light by the deposited gold nanostructures leading to localized surface plasmon resonance. The bulk sensitivity of these sensors was determined by recording reflectance spectra in media having different refractive indices and compared to sensors exclusively based on porous silicon or gold nanostructures. A thorough analysis of resulting shifts of the different optical signals in the reflectance spectra on the wavelength scale indicated that the optical response of the porous silicon sensor is not influenced by the presence of a gold nanostructure on top. Moreover, the adsorption of thiol-terminated polystyrene to the sensor surface was solely detected by changes in the position of the dip in the reflectance spectrum, which is assigned to localized surface plasmon resonance in the gold nanostructures. The interference pattern resulting from the porous silicon layer is not shifted to longer wavelengths by the adsorption indicating the independence of the optical response of the two nanostructures, namely porous silicon and nanostructured gold layer, to refractive index changes and pointing to the successful realization of two sensors in one spot.

The Impact of Exposed Surface Area on the Response of SWCNT Optical Sensors

Due to their distinct and advantageous fluorescence properties, semiconducting single-walled carbon nanotubes (SWCNTs) are being applied to a variety of optical sensing applications. Limitations in solubility and biocompatibility have been overcome by non-covalently functionalizing the surface of the SWCNT with wrappings using techniques that retain its inherent fluorescence. Though wrappings based on surfactants and single-stranded DNA (ssDNA) have been extensively studied for this purpose, they are limited by factors such as lack of selectivity and lower fluorescence quantum yield, respectively. In this study, we take advantage of the higher fluorescence emission of surfactant-coated SWCNTs and focus on new approaches that can tune their selectivity as sensors. Through the concomitant monitoring of both the fluorescence intensity and wavelength position of emission peaks, we demonstrate the ability to increase the selectivity of sensors based on surfactant-suspended SWCNTs while retaining their higher fluorescence intensity. These results provide not only a promising avenue for rationally designing SWCNT sensors, but also insight on the mechanisms governing the selectivity of existing SWCNT-based optical sensors.

Tuning the p Ka of a pH Responsive Fluorophore and the Consequences for Calibration of Optical Sensors Based on a Single Fluorophore but Multiple Receptors.

Since Sørensen and Bjerrum defined the pH scale, we have relied on two methods for determining pH, the colorimetric or the electrochemical. For pH electrodes, calibration is easy as a linear response is observed in the interesting pH range from 1 to ∼12. For colorimetric sensors, the response follows the sigmoidal Bjerrum diagram of an acid-base equilibrium. Thus, calibration of colorimetric sensors is more complex. Here, seven pH responsive fluorescent dyes based on the same diazaoxatriangulenium (DAOTA) fluorophore linked to varying receptor groups were prepared. Photoinduced electron transfer (PeT) quenching from appended aniline or phenol receptors generated the pH response of the DAOTA dyes, and the position of the p Ka value of the dye was tuned using the Hammett relationship as a guideline. The fluorescence intensity of the dyes in a sol-gel matrix environment was measured as a function of pH in universal buffer, and it was found that the dyes behave as perfect pH responsive probes under these conditions. The response of optical pH sensors is nonlinear and was found to be limited to 2-3 pH units for a precision of 0.01 pH unit. As sensors with a broader sensitivity range can be achieved by mixing multiple dyes with different p Ka values, mixtures of dyes in solution were investigated, and a broad range pH sensor with a precision of 0.006 pH units over a range of 3.6 pH units was demonstrated. Further, approximating the sensor response as linear was considered, and a limiting precision for this approach was determined. As the responses of the pH responsive DAOTA dyes were found to be ideally sigmoidal and as the six dyes were shown to have p Ka values scattered over a range from ∼2 to ∼9, this allows for design of a broad range optical pH sensor in the pH range from 1 to 10. This hypothesis was tested using quaternary mixtures of the different DAOTA dyes, and these were found to behave as a direct sum of the individual components. Thus, while linear calibration is limited to a precision of 0.02 in a range of 2-3 pH units, calibration using ideal sigmoidal functions is possible in the range of 1-10 with a precision better than 0.01, and as good as 0.002 pH units.

Application of modified mesoporous boehmite (γ-AlOOH) with green synthesis carbon quantum dots for a fabrication biosensor to determine trace amounts of doxorubicin.

An important form of carbon nanoparticles that are used for a wide range of applications, are carbon dots (CDs). In this study, a very easy, in expensive and green process was described for the preparation of CDs by using hydrothermal treatment of Tragacanth Gum (TG). A rapid assay for the determination of trace amounts of an anticancer medication doxorubicin (DOX) was developed, based on the quenching of the CDs derived from their aggregation. Electrostatic interaction between CDs and DOX could lead to fluorescence quenching. The optimized biosensor showed a detection range from 1 to 400ngmL-1 and a limit of detection of 0.4ngmL-1 . In the following, the synthesized CDs modified the Boehmite (Boh) mesoporous surface based on hydrogen bonding. The Boh has been used as supports and ideal hosts in this method, in which the particle size distribution of CDs in the pores of Boh is limited and they have controlled pore sizes. Accordingly, the surface-to-volume ratio and the presence of high-volume pores increased the longevity and sustainability of CDs; also prevented the aggregation of the CDs and improved their photo stability. The advantages of Boh are large pore volume, high surface area, and narrow size distribution. Variable factors influencing optical sensor response in DOX measurement were evaluated and optimized. In optimal conditions, the linear range was calculated from 1 to 500 ngmL-1 and the detection limit was 0.2 ng mL-1 . The sensors were used for measuring DOX in human blood plasma.

Effects of quantitative composition of the sensing phase in the response of ionophore-based optical sensors

The response characteristics of the optical chemical sensors (optodes), namely response range, response span and sensitivity are quantitatively related to the composition of the sensor phase for the first time. The dependence of the characteristics of ion-selective bulk optodes on the concentrations of the indicator, ionophore and ionic additive (ion-exchanger) are simulated numerically and experimentally verified with Na+- and K+-selective colorimetric optodes. It is shown how the response span, response range, median and sensitivity depend on the sensor membrane composition. Response curves with an intermediate plateau are predicted theoretically and obtained experimentally. It is shown that the inflection point in the response curve does not necessarily refers to α = 0.5. The results can be used for the fine tuning of the optical response of chemical sensors.