Optochemical Sensors Research Articles

Colorimetric photosensing of solvent polarity using photochromic spironaphthoxazine dye and its stimuli-responsive acrylic copolymer: A physico-chemical study

Stimuli-responsive devices containing photoswitchable compounds have received a great deal of attention for constructing portable opto-chemical sensors in detection of solvent polarities. Here, photochromic and solvatochromic behavior of the synthesized spironaphtooxazine (SNO) and its acrylic copolymer (PCSN-3) in various protic and aprotic solvents were investigated experimentally and theoretically; and the results were exploited to fabricate a portable probe for colorimetric and spectroscopic detection of solvent polarity. The incorporation of SNO-based comonomer into the poly(methyl methacrylate) chains was approved by observing its functional groups in FTIR spectra and the efficiency of chemical incorporation was evaluated as 98.2% using 1HNMR analysis. DLS and SEM analyses demonstrated particles sizes of below 100 nm with spherical morphology and narrow size distributions. DFT calculation was used to predict plausible meronaphtooxazine (MNO) conformations and they were compared with the experimental results. UV–vis analyses showed that the maximum absorption intensity of MNO increased up to 20 folds in protic and aprotic solvents at −20 °C compared to those at room temperature. Hansen solubility parameter and solute-solvent interaction for SNO, MNO and PCSN-3 in different protic and aprotic solvents were measured by group contribution method for the first time. It was found that hydrogen bonding and solvent polarity are the determining parameters for solvatochromic behavior of SNO in protic solvents, while dispersibility parameter is dominant in aprotic solvents. Photochromism and solvatochromism of PCSN-3 film in aprotic solvents were studied similar to SNO. Interestingly, PCSN-3 film showed definite visual color change and spectroscopic feature for each solvent after UV irradiation at 365 nm, which establishes a promising solid-state portable probe for colorimetric photosensing of solvents polarity.

Flexible sensor patch for continuous carbon dioxide monitoring.

Monitoring and measurement of carbon dioxide (CO2) is critical for many fields. The gold standard CO2 sensor, the Severinghaus electrode, has remained unchanged for decades. In recent years, many other CO2 sensor formats, such as detection based upon pH-sensitive dyes, have been demonstrated, opening the door for relatively simple optical detection schemes. However, a majority of these optochemical sensors require complex sensor preparation steps and are difficult to control and repeatably execute. Here, we report a facile CO2 sensor generation method that suffers from none of the typical fabrication issues. The method described here utilizes polydimethylsiloxane (PDMS) as the flexible sensor matrix and 1-hydroxypyrene-3,6,8-trisulfonate (HPTS), a pH-sensitive dye, as the sensing material. HPTS, a base (NaOH), and glycerol are loaded as dense droplets into a thin PDMS layer which is subsequently cured around the droplet. The fabrication process does not require prior knowledge in chemistry or device fabrication and can be completed as quickly as PDMS cures (∼2 h). We demonstrate the application of this thin-patch sensor for in-line CO2 quantification in cell culture media. To this end, we optimized the sensing composition and quantified CO2 in the range of 0–20 kPa. A standard curve was generated with high fidelity (R 2 = 0.998) along with an analytical resolution of 0.5 kPa (3.7 mm Hg). Additionally, the sensor is fully autoclavable for applications requiring sterility and has a long working lifetime. This flexible, simple-to-manufacture sensor has a myriad of potential applications and represents a new, straightforward means for optical carbon dioxide measurement.

Advanced multimodal solid-state optochemical pH and dual pH/O2 sensors for cell analysis

Optochemical sensors are actively used in cell analysis, however existing systems have limitations with respect to their robustness and analytical performance. We have developed advanced multimodal and multi-parametric solid-state pH sensors for cell analysis based on hydrophobic protonable metal-free porphyrins, such as octaethylporphine (OEP), and octaethylporphine-ketone (OEPK), as fluorescent pH indicators. The internally referenced ratiometric intensity and nanosecond lifetime-based versions of the pH sensors were developed and also multiplexed with the O2 sensors based on phosphorescent PtOEP dye. We optimised the key parameters of the pH sensor, including: dye encapsulation matrix, the type and concentration of proton transfer reagent, measurement pH range and pKa, dye concentrations and cross-talk with the O2 sensor. Subsequently, sensor coatings were deposited on common substrates used in cell analysis (96-well plates), fine-tuned for their operational performance, dual O2/pH sensing functionally and the ability to measure Extracellular Acidification (ECAR) and Oxygen Consumption (OCR) rates in biological samples containing cells. The optimised sensors with stable internally referenced calibrations, convenient spectral characteristics and low cytotoxicity, were demonstrated with cultured cells and 3D spheroid structures, measuring their ECAR, OCR and responses to stimulation. These pH and dual pH/O2 sensors are well-suited for detailed metabolic studies of biological samples on widely available laboratory equipment.

Opto-Chemical pH Detection of Myocardial Ischaemia Using Fluorescent Hydrogels

In this research fluorescent optochemical pH probes for the detection of ischaemia have been investigated. Myocardial ischaemia is the most prominent risk during heart surgery. During open heart surgery the heart is temporarily arrested and, since there no blood flowing, oxygen supply and removal of waste products is stopped and heart cells can be damaged. In this paper we propose a novel method to monitor the condition of the heart by placing optochemical pH sensors on several strategic places around the heart during surgery. Low cost opto-chemical pH sensors, using a HPTS (8-hydroxy-1,3,6-pyrene trisulfonic acid trisodium salt) fluorescent dye encapsulated in a thin bio-compatible hydrogel layer, were investigated for this application. Our research started with an extensive optical characterization of several types of hydrogel layers at different pH levels. Secondly a reflection probe prototype using several of these layers was designed, built and tested. Dual wavelength excitation and ratiometric detection of the fluorescent signals was used to detect the pH level. Typical output signals of 35% to 53% per pH in the range from 6.5-8.0 pH have been measured and a response time of typically 400 seconds was obtained for the prototypes. Finally based on our measurements on the HPTS layers and the reflection probe we propose an improved type of pH probe for the detection of ischaemia during open heart surgery.

A cuvette-compatible Zn2+ sensing tool for conventional spectrofluorometers prepared by copolymerization of macrocyclic fluoroionophores on quartz glass surface

We report here the development of a surface-modified quartz glass sheet, which affords an opportunity for converting conventional spectrofluorometers to ion-selective optochemical sensors by placing it diagonally into a photometric cuvette. Moreover, we describe a generalizable technique, which allows the usage of any polymerizable ionophores for developing multiple-use fluorescent chemosensors of various selectivity. A fluorescent bis(acridino)-crown ether containing allyl groups was photocatalytically copolymerized with a methacrylate-acrylamide-based monomer mixture to obtain an ion-selective sensor membrane layer on the surface of the cuvette-compatible glass sheet. This glass membrane-based direct optode enabled the analysis of Zn2+ above a lower limit of detection of 2.2 × 10–7 mol·l−1 with an excellent reusability. Limiting factors, like pH and competing ionic or organic agents were thoroughly investigated. Moreover, spiked river-water samples were measured to demonstrate applicability. The proposed sensor placed in any conventional spectrofluorometer provides an innovative method for perturbation-free analysis of Zn2+ for all the chemists in need of a fast, easy-to-use, portable and regenerable analyzer without the requirement of an analyte-specific instrumentation.

Oscillation and Sensor Properties of Integrated Opto-Chemical Sensors in Different Solvents

Oscillation and Sensor Properties of Integrated Opto-Chemical Sensors in Different Solvents

Fabrication of graphene-based sensor for exposure to different chemicals.

Opto-chemical sensors are the most significant type of sensors that are widely used to detect a variety of volatile organic compounds and chemicals. This research work demonstrates the fabrication and characterization of an opto-chemical sensor based on a graphene thin film. A 300 nm graphene thin film was deposited on clean glass with the help of RF magnetron sputtering. The structure, surface and quality of the graphene thin film were characterized using XRD, SEM and Raman spectroscopy. For optical characterization, the thin film was exposed to IPA, acetone and toluene (separately) for five, ten and fifteen minutes. The optical transmission was then observed via UV-NIR spectroscopy in the near-infrared range (900 to 1450 nm). The thin film of graphene has expressed a sharp response time and recovery time with high sensitivity for each chemical. However, by comparing the output of the graphene thin film in response to each chemical, it was observed that graphene thin film has a better transmission and sensing rate for exposure to toluene.

Spiropyran and spironaphthoxazine based opto-chemical probes for instant ion detection with high selectivity and sensitivity to trace amounts of cyanide

Colorimetric chemical sensors with instant detection of cyanide ion, as a dangerous effluent from various industries and high toxicity, are nowadays of significant importance. Here, photochromic spironaphthoxazine (SNO) and hydroxyethyl spiropyran (SPOH) were synthesized and employed to detect some cations as well as trace amount of cyanide ion with reasonable selectivity and sensitivity among different anions. Their spiro forms were not triggered by metal cations, while their UV-induced open-ring isomers became susceptible to establish a dye-cation complex. The opto-chemical results demonstrated that neither SPOH nor SNO could make reliable discrimination between different metal cations, even after UV irradiation. However, both SPOH and SNO were selectively attached to CN− with a 1:1 stoichiometric ratio (from Job’s plot), even in the presence of several other anions and in the absence of UV irradiation. This was approved by 1HNMR and UV–vis spectroscopies. Besides, the interaction of CN− with SPOH and SNO was approved by visual color change from colorless (λmax of 345 nm for both) to dark yellow with λmaxs of 416 and 412 nm for those linked to hydroxyethyl merocyanine (MC-CN) and meronaphthoxazine (MNO-CN), respectively. The detection limits of SPOH (0.091 µM) and SNO (0.094 µM) sensors toward CN− were lower than its permitted level in drinking water by WHO (1.9 µM). These were also checked and compared with other spiro-based sensors. The obtained results demonstrate the potentiality of SNO and SPOH as promising colorimetric and opto-chemical sensors with wide linear dynamic detection range for determining trace amount of CN−.

Sol-Gel Thin Film Processing for Integrated Waveguide Sensors

Integrated opto-chemical sensors present great advantages in comparison to the current lab equipment. They bring portability, reduced costs, facilitate in-situ measurements, as well as largely reduced sample volumes. In this quest, standard processing protocols over established materials, such as silicon nitride, silicon, silicon dioxide, titanium oxide, and even a wide variety of polymers have so far been the key toward on-chip devices. However, if very specific materials in terms of composition and tailored properties are required, the deposition via a solution represents a viable alternative. In this review, we highlight the role of sol-gel chemistry and top-down processing of sol-gel thin film layers in the design of waveguide-based optical sensors. In particular, we stress the advantages of porous sol-gel based materials as a new approach to increase sensitivity and selectivity, first when used as claddings, and, more recently, as waveguides with enhanced light–analyte interaction. We finally discuss the future perspectives of such devices to increase specificity in complex matrices, which is of utmost importance for bio-sensing.

Functionalization of carbon dots and their applications in food safety

Almost two decades have passed since the discovery of carbon nanodots (CDs). As a promising family of optical nanomaterials, CDs have high emission efficiency, excellent water solubility, and good bio-compatibility; in addition, they are inexpensive and can be produced by a facile synthesis process. Because of these advantages, CDs have drawn tremendous attention for use in the development of novel optochemical sensors. However, the application scope of chemical sensors based on pristine CDs is restricted because the synthetic methods and starting materials for the CDs give rise to a great limitation of their surface chemical structures. Therefore, pristine CDs need to be functionalized so that they can be employed in sensing applications, with high sensing capability. Typically, functionalization can be classified into two types: doping and surface modification. Doping, as an effective method for introducing new elements to the skeleton of CDs, not only helps manipulate the energy bang-gap of pristine CDs, but also brings the specific acceptor of the target analyte to the CD matrix. Surface modification is a conventional functionalization method that allows one to manipulate the surface chemical structure of CDs in a covalent or non-covalent fashion, so that the selectivity and sensitivity of pristine CDs can be sequentially improved. In this paper, we review the research progress in the functionalization of CDs over the last eight years based on the publications from Web of Science, and systematically summarize the applications of CD-based sensors in the area of food safety. Although this review is incomprehensive due to space restrictions, it can shed fresh light on the development of CD-based rapid sensors for food safety applications in the near future.

Biobased, Internally pH-Sensitive Materials: Immobilized Yellow Fluorescent Protein as an Optical Sensor for Spatiotemporal Mapping of pH Inside Porous Matrices.

The pH is fundamental to biological function and its measurement therefore crucial across all biosciences. Unlike homogenous bulk solution, solids often feature internal pH gradients due to partition effects and confined biochemical reactions. Thus, a full spatiotemporal mapping for pH characterization in solid materials with biological systems embedded in them is essential. In here, therefore, a fully biocompatible methodology for real-time optical sensing of pH within porous materials is presented. A genetically encoded ratiometric pH sensor, the enhanced superfolder yellow fluorescent protein (sYFP), is used to functionalize the internal surface of different materials, including natural and synthetic organic polymers as well as silica frameworks. By using controlled, tailor-made immobilization, sYFP is homogenously distributed within these materials and so enables, via self-referenced imaging analysis, pH measurements in high accuracy and with useful spatiotemporal resolution. Evolution of internal pH is monitored in consequence of a proton-releasing enzymatic reaction, the hydrolysis of penicillin by a penicillin acylase, taking place in solution or confined to the solid surface of the porous matrix. Unlike optochemical pH sensors, which often interfere with biological function, labeling with sYFP enables pH sensing without altering the immobilized enzyme's properties in any of the materials used. Fast response of sYFP to pH change permits evaluation of biochemical kinetics within the solid materials. Thus, pH sensing based on immobilized sYFP represents a broadly applicable technique to the study of biology confined to the internally heterogeneous environment of solid matrices.

Photodetector with superior functional capabilities based on monolayer WO3 developed by atomic layer deposition

Photodetector based on monolayer of tungsten trioxide (WO3) was fabricated by atomic layer deposition (ALD) and its structure and properties were analyzed by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), ellipsometry, atomic force microscopy (AFM), transmission electron microscopy (TEM) and spectrophotometry techniques. The as-developed photodetector exhibited high sensitivity, wide-range photoresponse, extremely fast response time of ∼2.5–2.7ms and superior long-term stability over more than 250 cycles. ALD-enabled Angstrom-precision development of monolayer WO3 with thickness of ∼0.74±0.07nm was done by utilizing (tBuN)2W(NMe2)2 as tungsten precursor and H2O as oxygen precursor, respectively, without affecting the underlying silicon substrate. The performance of monolayer WO3-based photodetector was much better than that of photodetectors based on other nanostructured WO3, monolayers and few layers of MoS2, MoSe2, GaSe and two-dimensional (2D) ZnO/ZnS nanocomposites. Its fast response speed also enables great application potential in high-frequency light-wave communications, various opto-chemical sensors, photo-switches and optoelectronic circuits.

Online monitoring of priority and dangerous pollutants in natural and urban waters

Purpose – Advancements in real-time water monitoring technologies permit rapid detection of water quality, and threats from waste loads. Water Framework Directive mandating the establishment of Member States’ water resources monitoring, presence of hazardous contaminants in effluents, and perception of vulnerability of water distribution system to attacks, have spurred technical and economic interests. The paper aims to discuss these issues. Design/methodology/approach – As alternative to traditional analyzers, chemosensors, operate according to physical principles, without sample collection (online), and are capable of supplying parameter values continuously and in real-time. Their low selectivity and stability issues have been overcome by technological developments. This review paper contains a comprehensive survey of existing and expected online monitoring technologies for measurement/detection of pollutants in water. Findings – The state-of-the-art in online water monitoring is presented. Application examples are reported. Monitoring costs will become a lesser part of a water utility budget due to the fact that automation and technological simplification will abate human cost factors, and reduce the complexity of laboratory procedures. Originality/value – An overview of applicable instrumentation, and forthcoming developments, is given. Technological development in this field is very rapid, and astonishing advances are anticipated in several areas (fingerprinting, optochemical sensors, biosensors, molecular techniques). Online monitoring is becoming an ever-important tool not only for compliance control or plant management purposes, but also as a useful approach to pollution control and reduction, minimizing the environmental impact of discharges.

Monolithic Integration of a Silicon-Based Photonic Transceiver in a CMOS Process

This work presents the design, fabrication, and characterization of a monolithic and complementary-metal–oxide–semiconductor (CMOS)-based integrated optical system, including the light emitter working in the visible range, waveguide, and photodetector. The presented system aims to be applied for the development of optochemical sensors. The work presents the proposed concept and the integration strategy, as well as the fabrication process. The individual elements of the system are theoretically evaluated to assure compatibility among them. Then, the fabrication and studies to the complete system are presented. The response of the light sensor is shown to be caused by optical stimulation of light originated in the integrated light source and transmitted through a dielectric waveguide, thus validating the integration procedure.

Application of phosphorescent oxygen sensors in in-package dielectric barrier discharge plasma environment

Abstract Dielectric barrier discharge plasma treatment of two different types of phosphorescent oxygen sensors under different in-package gas mixture has been studied. Commercial Optech™-O2 platinum and microporous polypropylene (PP) membrane sensors impregnated with platinum benzoporphyrin (PtBP) dye were found effective for oxygen sensing when DBD plasma treated under modified atmospheric conditions. When treated under DBD air plasma, PP sensors were largely degraded and found incompatible with the plasma processing. Although some changes in the lifetime signals were observed after air plasma treatment, Optech™-O2 platinum sensors were found effective as oxygen sensors. This study indicates that in-package gas composition of food products plays an important role in selection of right intelligent optochemical sensors for plasma processing. Industrial Relevance In-package cold plasma processing is emerging as a novel and innovative approach for the decontamination of food products with significant potential for commercial application. This paper studies the compatibility of phosphorescent oxygen sensors with this technology. This study demonstrates that the package gas composition has huge impact on the accuracy and usability of sensors. The work described in this research is relevant to all food industries which uses intelligent sensors for monitoring gas composition.

Porous Silicon Structures as Optical Gas Sensors.

We present a short review of recent progress in the field of optical gas sensors based on porous silicon (PSi) and PSi composites, which are separate from PSi optochemical and biological sensors for a liquid medium. Different periodical and nonperiodical PSi photonic structures (bares, modified by functional groups or infiltrated with sensory polymers) are described for gas sensing with an emphasis on the device specificity, sensitivity and stability to the environment. Special attention is paid to multiparametric sensing and sensor array platforms as effective trends for the improvement of analyte classification and quantification. Mechanisms of gas physical and chemical sorption inside PSi mesopores and pores of PSi functional composites are discussed.

Optochemical sensors using electrodeposited polyaniline films: Electrical bias enhancement of reflectance response

A bias-enhanced reflective optochemical pH sensor with electrochromic polyaniline is presented. Polyaniline films were prepared by electrodeposition process, controlling the total amount of deposited charge by varying the deposition time. The electrochromic property of polyaniline was the main parameter for sensor development. A quick and easy reflective spectra measurement process was obtained using a handset spectrophotometer in the visible region. A film deposited for 120min presented a linear response (sensitivity of 25/pH and linearity of 97%) for the integrated reflectance in the green band of the spectrum after insertion in buffer solutions with pH ranging from 2 to 8. The reflectance intensity increased by 92% for the applied bias voltage of 1000mV. Sensitivity of the sensors increased by about 28% (32/pH) with applied bias voltage of 700mV, and decreased by about 9% (29/pH) with applied bias voltage of 1000mV. A corresponding slight decrease in linearity by about 4% (93%) was observed with applied bias voltage of 700mV, which preserves the linearity value within a good range for use. The linearity decreases by about 20% (78%) with applied bias voltage of 1000mV. Both facts together indicate the presence of an optimal operation point. The improvement in sensor performance is related to the bias effect over polyaniline protonation/deprotonation. The electrochromic property of the polyaniline films were investigated using the CIE L*a*b* color scale. The data indicated changes from the emeraldine base oxidation state of polyaniline, which is blue, in alkali medium, to the emeraldine salt conducting, which is green, in acid medium. Handset spectrophotometers can be used with PANI optochemical pH sensors working with reflective spectra.

Ultra-fast opto-chemical sensors by using electrospun nanofibers as sensing layers

Optical sensors based on the principle of luminescence quenching of analyte-sensitive dyes gain increasing importance in numerous sensing applications, especially for oxygen detection. In general, the actual sensing element of these sensors consists of a specifically selected, analyte-sensitive luminescent dye immobilized in a compact polymer layer. The luminescence intensity and decay time change as a function of the analyte concentration and can be evaluated by appropriate equipment. The response dynamics of such opto-chemical sensors are limited by the rates of diffusion and equilibration of the analyte between the sample medium and the bulk of the sensor matrix material. The thicker the matrix layer, the slower the response. The appropriate sensor thickness therefore is a trade-off between response characteristics and signal intensity, i.e. general sensor performance.By means of electrospinning, many polymers can be processed to nanofibers, resulting in a non-woven fleece with a high surface-to-volume ratio and excellent analyte accessibility. Doped with fluorescent dyes, such fiber layers are well suited for fast sensing applications where the response time is a critical issue.In this work we replaced the compact oxygen-sensing layer of a standard oxygen sensor (oxygen-sensitive dye Pt-tetra(pentafluorophenyl) porphyrine (PtTFPP) immobilized in a polystyrene (PS) matrix) with a highly porous nanofiber layer electrospun from the same dye/matrix formulation. The response time t90 decreased by two orders of magnitude (from several seconds to less than 40ms) while other sensor characteristics like sensitivity and signal intensity were maintained.

Sensor monitoring of organotypic human tumor short term cultures may reveal profiles of metabolism and chemosensitivity

Event Abstract Back to Event Sensor monitoring of organotypic human tumor short term cultures may reveal profiles of metabolism and chemosensitivity Martin Brischwein1*, Regina Kleinhans1, Marina Haas1 and Bernhard Wolf1 1 Technische Universitaet Muenchen, Germany Background and aim. There is an urgent clinical demand for improved stratification of cancer patients and allocation into distinct therapeutic regimens. In this proof-of-principle study we analyse the feasibilty of a sensor-based profiling of metabolism and chemosensitivity on an organotypic human breast cancer model preserving the native, heterogeneous character of the tumor tissue. Methods. The approach is based on surgically explanted human breast cancer tissue samples which were subjected to careful slicing preparation (Kleinhans, 2012). These organotypic slices in a size of ≈ 4 µl were subsequently cultured for 3-5 days in an automated assay platform (Wolf, 2013). This platform analyzes the pH and dissolved oxygen values with optochemical sensors in the close vicinity of the tumor slices. Acid extrusion and oxygen consumption rates are determined before, during and after treatments with pharmaceutical compounds. Results . A number of 23 surgical samples was analysed. After the introduction of a careful vibratome slicing protocol the success rate of generating viable short term tumor cultures was generally good. The optimum slice thickness was found to be at 200-250 µm. Both a recording of pre-treatment metabolic profiles (i.e. ratios of extracellular acidification rates and oxygen consumption rates) and assessments of chemoresponses to drugs such as chloracetaldehyde and doxorubicine is feasible. Additionally, a computational reaction-diffusion modelling (Grundl, 2013) allows an estimation of pH and dissolved oxygen values in temporal and spatial resolution for an improved control about physico-chemical conditions of the cellular microenvironment. Conclusions / Discussion. A non-interventional, prospective clinical study should be initiated on the basis of this proof-of-principle research. In such a study, the microphysiometric, sensor-based approach should be complemented by data from histopathological, metabolomic and genomic profiling.

Detection of Soluble Organic and Inorganic Compounds with an Array of Pure and Blended Optical Reporters

The issue of detecting harmful compounds in water may be approached in different ways, ranging from analytical methods to chemical sensor arrays. Optochemical sensors offer the advantage of being a simple and effective method for online monitoring of the parameters of interest in water solution. The core of an optochemical sensor is represented by a dye that changes colour upon the interaction with analytes. In this work, we used porphyrins, pH indicators and their mixtures to prepare the colorimetric sensor array for the analysis of ionic salts and organic compounds in water. The colour changes of sensing dyes exposed to an aqueous solution containing target compounds were read out with a system consisting of a computer screen (light source) and a digital camera (detector). Beyond the detection of metallic salts, nitrites, nitrates, phosphates, and organic compounds, we found that the array can recognize creatinine and urea, two markers of kidney functionalities.