Fiber-Optic Chemical Sensors and Biosensors

Fiber-optics based fluorescence detection. Part I: Basic concepts

Continuous in-line detection and process monitoring are essential for industrial, analytical, and biomedical applications. Lightweight, highly flexible, and low-cost fiber optics enable the construction of compact and robust hand-held devices forin situchemical and biological species analysis in both industrial and biomedicalin vitro/in vivodetection. Despite the broad range of fiber-optic based applications, we lack a good understanding of the parameters that govern the efficiency of light collection or the sensitivity of detection. Consequently, comparing samples of different optical density and/or geometry becomes challenging and can lead to misinterpretation of results; especially when we lack the approaches necessary to correct the detected signal (spectra) for artifacts such as inner-filter effect or scattering. Hence, in this work, we discuss factors affecting the signal detected by the fiber optic in the bare and lens-coupled flat-tipped configurations that lead to signal/spectral distortions. We also present a simple generic model describing the excitation profile and emission collection efficiency that we verify with experimental data. Understanding the principles governing the signal collected by the fiber will provide rationales for correcting the measured emission spectra and recovering the true emission profile of optically dense samples.

Ferritin Single-Electron Transistor

We report on the fabrication of a single-electron transistor based on ferritin using wide self-aligned nanogap devices. A local gate below the gap area enables three-terminal electrical measurements, showing the Coulomb blockade in good agreement with the single-electron tunneling theory. Comparison with this theory allows extraction of the tunnel resistances, capacitances, and gate coupling. Additionally, the data suggest the presence of two separate islands coupled in series or in parallel: information that was not possible to distinguish by using only two-terminal measurements. To interpret the charge transport features, we propose a scenario based on the established configuration structures of ferritin involving either iron sites in the organic shell or two dissimilar clusters within the core.

Organosilica Nanosensors for Monitoring Spatiotemporal Changes in Oxygen Levels in Bacterial Cultures

Oxygen plays a central role in aerobic metabolism, and while many approaches have been developed to measure oxygen concentration in biological environments over time, monitoring spatiotemporal changes in dissolved oxygen levels remains challenging. To address this, we developed a ratiometric core-shell organosilica nanosensor for continuous, real-time optical monitoring of oxygen levels in biological environments. The nanosensors demonstrate good steady state characteristics (KpSV = 0.40 L/mg, R2 = 0.95) and respond reversibly to changes in oxygen concentration in buffered solutions and report similar oxygen level changes in response to bacterial cell growth (Escherichia coli) in comparison to a commercial bulk optode-based sensing film. We further demonstrated that the oxygen nanosensors could be distributed within a growing culture of E. coli and used to record oxygen levels over time and in different locations within a static culture, opening the possibility of spatiotemporal monitoring in complex biological systems.

Rapid and quantitative detection of DNA hybridization using a simplified Fabry-Perot interferometric biosensor

This study introduces a miniaturized fiber-optic Fabry-Perot (FP) interferometric biosensor, distinctively engineered for cost-effective, rapid, and quantitative DNA sequence detection. By leveraging the interference patterns generated within a Fabry-Perot microcavity, our sensor precisely monitors DNA hybridization events in real-time. We have verified the sensor's biofunctionalization via fluorescent labeling and have extensively validated its performance through numerous hybridization and regeneration cycles with 1 μM single-stranded DNA (ssDNA) solutions. Demonstrating remarkable repeatability and reusability, the sensor effectively discerns ssDNA sequences exhibiting varying degrees of mismatches. Its ability to accurately distinguish between sequences with 2 and 7 mismatches underscores its potential as a valuable asset for swift DNA analysis. Characterized by its rapid response time-typically yielding results within 6 minutes-and its adeptness at mismatch identification, our biosensor stands as a potent tool for facilitating accelerated DNA diagnostics and research.

Recent Trends in Chemical Sensors for Detecting Toxic Materials

Industrial development has led to the widespread production of toxic materials, including carcinogenic, mutagenic, and toxic chemicals. Even with strict management and control measures, such materials still pose threats to human health. Therefore, convenient chemical sensors are required for toxic chemical monitoring, such as optical, electrochemical, nanomaterial-based, and biological-system-based sensors. Many existing and new chemical sensors have been developed, as well as new methods based on novel technologies for detecting toxic materials. The emergence of material sciences and advanced technologies for fabrication and signal-transducing processes has led to substantial improvements in the sensing elements for target recognition and signal-transducing elements for reporting interactions between targets and sensing elements. Many excellent reviews have effectively summarized the general principles and applications of different types of chemical sensors. Therefore, this review focuses on chemical sensor advancements in terms of the sensing and signal-transducing elements, as well as more recent achievements in chemical sensors for toxic material detection. We also discuss recent trends in biosensors for the detection of toxic materials.

Optical sensors (optodes) for multiparameter chemical imaging: classification, challenges, and prospects

Chemical gradients and uneven distribution of analytes are common in natural and artificial systems. As a result, the ability to visualize chemical distributions in two or more dimensions has gained significant importance in recent years. This has led to the integration of chemical imaging techniques into all domains of analytical chemistry. In this review, we focus on the use of optical sensors, so-called optodes, to obtain real-time and multidimensional images of two or more parameters simultaneously. It is important to emphasize that multiparameter imaging in this context is not confined solely to multiple chemical parameters (analytes) but also encompasses physical (e.g., temperature or flow) or biological (e.g., metabolic activity) parameters. First, we discuss the technological milestones that have paved the way for chemical imaging using optodes. Later, we delve into various strategies that can be taken to enable multiparameter imaging. The latter spans from developing novel receptors that enable the recognition of multiple parameters to chemometrics and machine learning-based techniques for data analysis. We also explore ongoing trends, challenges, and prospects for future developments in this field. Optode-based multiparameter imaging is a rapidly expanding field that is being fueled by cutting-edge technologies. Chemical imaging possesses the potential to provide novel insights into complex samples, bridging not only across various scientific disciplines but also between research and society.

Leveraging a smartphone to perform time-gated luminescence measurements

Empowered by advanced on-board sensors, high-performance optics packages and ever-increasing computational power, smartphones have democratized data generation, collection, and analysis. Building on this capacity, many platforms have been developed to enable its use as an optical sensing platform for colorimetric and fluorescence measurements. In this paper, we report the ability to enable a smartphone to perform laboratory quality time-resolved analysis of luminescent samples via the exploitation of the rolling shutter mechanism of the native CMOS imager. We achieve this by leveraging the smartphone's standard image capture applications, commercially available image analysis software, and housing the device within a UV-LED containing case. These low-cost modifications enable us to demonstrate the smartphone's analytical potential by performing tasks ranging from authentication and encryption to the interrogation of packaging, compounds, and physical phenomena. This approach underscores the power of repurposing existing technologies to extend the reach and inclusivity of scientific exploration, opening new avenues for data collection and analysis.

Identification of Volatile Organic Liquids by Combining an Array of Fiber-Optic Sensors and Machine Learning

In this paper, we report an array of fiber-optic sensors based on the Fabry-Perot interference principle and machine learning-based analyses for identifying volatile organic liquids (VOLs). Three optical fiber tip sensors with different surfaces were included in the array of sensors to improve the accuracy for identifying liquids: an intrinsic (unmodified) flat cleaved endface, a hydrophobic-coated endface, and a hydrophilic-coated endface. The time-transient responses of evaporating droplets from the optical fiber tip sensors were monitored and collected following the controlled immersion tests of 11 different organic liquids. A continuous wavelet transform was used to convert the time-transient response signal into images. These images were then utilized to train convolution neural networks for classification (identification of VOLs). We show that diversity in the information collected using the array of three sensors helps machine learning-based methods perform significantly better. We explore different pipelines for combining the information from the array of sensors within a machine learning framework and their effect on the robustness of models. The results showed that the machine learning-based methods achieved high accuracy in their classification of different liquids based on their droplet evaporation time-transient events.

Direct Identification of Label-Free Gram-Negative Bacteria with Bioreceptor-Free Concentric Interdigitated Electrodes

This investigation demonstrates an electrochemical method for directly identifying unlabeled Gram-negative bacteria without other additives or labeling agents. After incubation, the bacterial cell surface is linked to the interdigitated electrode through electroadsorption. Next, these cells are exposed to a potential difference between the two electrodes. The design geometry of an electrode has a significant effect on the electrochemical detection of Gram-negative bacteria. Therefore, electrode design geometry is a crucial factor that needs to be considered when designing electrodes for electrochemical sensing. They provide the area for the reaction and are responsible for transferring electrons from one electrode to another. This work aims to study the available design in the commercial market to determine the most suitable electrode geometry with a high detection sensitivity that can be used to identify and quantify bacterial cells in normal saline solutions. To work on detecting bacterial cells without the biorecognition element, we have to consider the microelectrode's design, which makes it very susceptible to bacteria size. The concentration-dilution technique measures the effect of the concentration on label-free Gram-negative bacteria in a normal saline solution without needing bio-recognized elements for a fast screening evaluation. This method's limit of detection (LOD) cannot measure concentrations less than 102 CFU/mL and cannot distinguish between live and dead cells. Nevertheless, this approach exhibited excellent detection performance under optimal experimental conditions and took only a few hours.

Cu2+-imprinted optical fiber SPR sensor for intelligent recognition

An optical fiber surface plasma resonance (SPR) sensor with MMF-TCF-MMF structure was designed to realize intelligent recognition of copper ions (Cu²⁺), and the selective adsorption sensitization was achieved by plating a layer of Cu²⁺-imprinted film on the surface of gold film excitation layer. Combining the principle of optical fiber interference and SPR, the proposed sensor realized the detection of the copper ions concentration through measuring the refractive index changes caused by ions adsorption on imprinted film. The Cu²⁺-imprinted optical fiber SPR sensor can realize the intelligent recognition and detection of copper ions in the complex environment and exhibits a detection sensitivity of -10.05 pm/ppm. The proposed sensor has tremendous development potential in practical application, and provides new ideas for the field of metal ions detection.

Robust Dual Optical Sensor for pH and Dissolved Oxygen

As part of moving our optical pH and dissolved oxygen (DO) optical chemosensors toward industrial applications, we decided to explore a many-sensors-in-one principle. It was tested if physical segregation of the optical sensor components in a single sensor polymer could remove cross-talk and quenching. It was found that a design concept with an oxygen-responsive dye in polymer nanoparticles and a pH-responsive dye in an organically modified siloxane polymer resulted in a robust pH/O₂ dual optical sensor. Individually, the O₂-sensitive nanoparticles, a known component for optical DO sensing, and the pH sensor are operational. Thus, it was decided to test if nanoparticles enclosed within the pH-sensitive responsive sol-gel (i) could work together if segregated and (ii) could operate with a single intensity signal that is without a reference signal; developments within industrial optical sensor technology indicate that this should be feasible. The prototype optode produced in this work was shown to have a negligible drift over 60 h, bulk diffusion-limited DO response, and independent response to pH and O₂. On the individual optode, pH calibration was found to show the expected sigmoidal shape and pK_a, while the complexity of the calibration function for the DO signal was significant. While the engineering of the sensor device, optics, and hardware are not robust enough to attempt generic sensor calibration, it was decided to demonstrate the design concept in simple fermentation experiments. We conclude that the dual sensor design with the physical segregation of components is viable.

Advances in Optical Sensors for Persistent Organic Pollutant Environmental Monitoring

Optical chemical sensors are widely applied in many fields of modern analytical practice, due to their simplicity in preparation and signal acquisition, low costs, and fast response time. Moreover, the construction of most modern optical sensors requires neither wire connections with the detector nor sophisticated and energy-consuming hardware, enabling wireless sensor development for a fast, in-field and online analysis. In this review, the last five years of progress (from 2017 to 2021) in the field of optical chemical sensors development for persistent organic pollutants (POPs) is provided. The operating mechanisms, the transduction principles and the types of sensing materials employed in single selective optical sensors and in multisensory systems are reviewed. The selected examples of optical sensors applications are reported to demonstrate the benefits and drawbacks of optical chemical sensor use for POPs assessment.

Preparation of Notch-4 Receptor Containing Quartz Crystal Microbalance Biosensor for MDA MB 231 Cancer Cell Detection

Quartz crystal microbalance (QCM) is a highly sensitive system that is used as a biosensor for biomolecules and cells. Detection and characterization of cancer cells in circulation or biopsy samples is of crucial importance for cancer diagnosis. Here, we introduce approaches for breast cancer cell detection via their surface molecules. The sensor system is based on preliminary coating of QCM chip with polymeric nanoparticles to increase the surface area and allow for the attachment of proteins to the chip surface. This is followed by the attachment of a specific protein in order to functionalize the chip. Breast cancer cells and fibroblast cells as control are cultured and applied to this chip. The functionalized QCM system can detect breast cancer cells with high affinity and selectivity. Here, we present the preparation methods of QCM-based sensors for selective detection of MDA MB 231 cancer cells. Selectivity of QCM-based sensor is carried out in the presence of L929 mouse fibroblast cells.

Biocompatible and Biodegradable Polymer Optical Fiber for Biomedical Application: A Review

This article discusses recent advances in biocompatible and biodegradable polymer optical fiber (POF) for medical applications. First, the POF material and its optical properties are summarized. Then, several common optical fiber fabrication methods are thoroughly discussed. Following that, clinical applications of biocompatible and biodegradable POFs are discussed, including optogenetics, biosensing, drug delivery, and neural recording. Following that, biomedical applications expanded the specific functionalization of the material or fiber design. Different research or clinical applications necessitate the use of different equipment to achieve the desired results. Finally, the difficulty of implanting flexible fiber varies with its flexibility. We present our article in a clear and logical manner that will be useful to researchers seeking a broad perspective on the proposed topic. Overall, the content provides a comprehensive overview of biocompatible and biodegradable POFs, including previous breakthroughs, as well as recent advancements. Biodegradable optical fibers have numerous applications, opening up new avenues in biomedicine.

Thermal equilibria between conformers enable highly reliable single-fluorophore ratiometric thermometers

Fluorescent thermometers based on organic dyes play an important role in the visualization of dynamic temperature topography with high resolution. Many molecular thermometers contain two fluorophores with different temperature responses to achieve ratiometric temperature detection. However, the stability and reliability of such ratiometric thermometers are highly dependent on the susceptibility of the fluorophores towards photobleaching. Despite the use of single-fluorophore ratiometric thermometers in previous reports, the difficulty and complexity in their molecular design and synthesis severely hinder their widespread applicability. In this work, we have investigated the use of commercially available dyes (i.e., BD140 and LD688) with conformational isomers as ratiometric thermometers. Each of these dyes consists of a mixture of conformers with distinct UV-vis absorption and emission spectra. The thermal equilibrium of these conformers successfully enabled the development of ratiometric thermometers with good stability and reliability.

Recent progress in surface plasmon resonance based sensors: A comprehensive review

In the recent years, researchers have contributed substantially in the field of Surface Plasmon Resonance (SPR) sensors and its applications. SPR sensors show the salient features, such as label-free detection, real-time monitoring, small sample size, furnish accurate outcomes at low cost, and smooth handling. Moreover, the SPR sensors are also well-known because of its quantitative and qualitative excellent performance in real-time applications, including drug discovery, environment monitoring, food safety, medical diagnosis, clinical diagnosis, biological studies, and biomolecule interactions. This paper exhibits a comprehensive review of SPR based sensors, such as prism-based SPR with the applications (e.g., biomolecule interaction, medical diagnostic, etc.), fiber-based SPR, and waveguide-based SPR. Furthermore, we summarized the modern designs and techniques with their limitations and challenges in detail. The erudition outlined in this paper can be given an exceptional benefit for the researchers and industry people in the field of SPR based sensors.

Cultivation of Saccharomyces cerevisiae with Feedback Regulation of Glucose Concentration Controlled by Optical Fiber Glucose Sensor

Glucose belongs among the most important substances in both physiology and industry. Current food and biotechnology praxis emphasizes its on-line continuous monitoring and regulation. These provoke increasing demand for systems, which enable fast detection and regulation of deviations from desired glucose concentration. We demonstrated control of glucose concentration by feedback regulation equipped with in situ optical fiber glucose sensor. The sensitive layer of the sensor comprises oxygen-dependent ruthenium complex and preimmobilized glucose oxidase both entrapped in organic–inorganic polymer ORMOCER^®. The sensor was placed in the laboratory bioreactor (volume 5 L) to demonstrate both regulations: the control of low levels of glucose concentrations (0.4 and 0.1 mM) and maintenance of the glucose concentration (between 2 and 3.5 mM) during stationary phase of cultivation of Saccharomyces cerevisiae. Response times did not exceed 6 min (average 4 min) with average deviation of 4%. Due to these regulation characteristics together with durable and long-lasting (≥2 month) sensitive layer, this feedback regulation system might find applications in various biotechnological processes such as production of low glucose content beverages.

Raposo MM. Optical Fiber Sensors for Biocide Monitoring: Examples, Transduction Materials, and Prospects

Antifouling biocides are toxic to the marine environment impacting negatively on the aquatic ecosystems. These biocides, namely, tributyltin (TBT) and Cu(I) compounds, are used to avoid biofouling; however, their toxicity turns TBT and Cu(I) monitoring an important health issue. Current monitoring methods are expensive and time-consuming. This review provides an overview of the actual state of the art of antifouling paints' biocides, including their impact and toxicity, as well as the reported methods for TBT and Cu(I) detection over the past decade. The principles of optical fiber sensors (OFS) applications, with focus on environmental applications, and the use of organic chemosensors in this type of sensors are debated. The multiplexing ability of OFS and their application on aquatic environments are also discussed.

Combining Chemometrics and Sensors: Toward New Applications in Monitoring and Environmental Analysis

For many years, an extensive array of chemometric methods have provided a platform upon which a quantitative description of environmental conditions can be obtained. Applying chemometric methods to environmental data allows us to identify and describe the interrelations between certain environmental drivers. They also provide an insight into the interrelationships between these drivers and afford us a greater understanding of the potential impact that these drivers can place upon the environment. However, an effective marriage of these two systems has not been performed. Therefore, it is the aim of this review to highlight the advantages of using chemometrics and sensors to identify hidden trends in environmental parameters, which allow the state of the environment to be effectively monitored. Despite the combination of chemometrics and sensors, to capture new developments and applications in the field of environmental sciences, these methods have not been extensively used. Importantly, although different parameters and monitoring procedures are required for different environments (e.g., air, water, soil), they are not distinct, separate entities. Contemporary developments in the use of chemometrics afford us the ability to predict changes in different aspects of the environment using instrumental methods. This review also provides an insight into the prevailing trends and the future of environmental sensing, highlighting that chemometrics can be used to enhance our ability to monitor the environment. This enhanced ability to monitor environmental conditions and to predict trends would be beneficial to government and research agencies in their ability to develop environmental policies and analysis procedures.

Surface plasmon resonance based fiber-optic nanosensor for the pesticide fenitrothion utilizing Ta2O5 nanostructures sequestered onto a reduced graphene oxide matrix

A surface plasmon resonance study was carried out for the identification and determination of the organophosphate pesticide fenitrothion via an optical fiber sensor. A thin layer of silver was deposited on the unclad core of silica optical fiber for plasmon generation. This was followed by the deposition of a sensing surface comprising a layer of tantalum(V) oxide nanoparticles sequestered in a nano-scaled matrix of reduced graphene oxide. The sensing mechanism is due to the interaction of fenitrothion with the silver film which leads to a change in refractive index.. Characterized by a wavelength interrogation scheme, the fiber-optic sensor exhibited a red shift equalling 56 nm corresponding to fenitrothion concentration in the range 0.25-4 μM including the blank solution. The spectral sensitivity is 24 nm μM^-1, the limit of detection is 38 nM, and the response time is as short as 23 s. The sensor is selective, repeatable and works at ambient temperature. Graphical abstractSchematic representation of the sensing mechanism of an SPR based fiber-optic fenitrothion sensor utilizing modification in refractive index of sensing surface comprising of tantalum(V) oxide (Ta₂O₅) nanoparticles embedded in reduced graphene oxide (rGO) caused by interaction with fenitrothion entities.

A unified approach for investigating chemosensor properties - dynamic characteristics

Chemosensors are a group of sensors-responsive sensor chemistry, sensor hardware, and software-that report on the composition of solutions and gaseous samples. Dynamic properties are fundamental for all sensor characterization. While electrochemical chemosensors have seen a century of research and are well-described, research on chemosensors using other modes of transductions are still at an early stage. The dynamic properties of chemosensors-independent of their mode of transduction-are not reported consistently in the literature. This makes it impossible to compare sensor performance of chemosensors from different manufacturers and laboratories. To remedy this, standardized experimental methods that exclude the influence of drift and any dependence on activity step change must be used. Subsequently, the resulting data must be treated using a unifying analysis formalism, and robust values must be used to describe chemosensor characteristics. Characterizing the sensor properties in turn enables rationalizing the link between sensor performance and sensor chemistry. Following a review of sensor theory, a thorough discussion of experimental methods and data analysis models for determining dynamic sensor properties, we arrive at evidence-based recommendations for good practice when describing new chemosensors. Adhering to these recommendations, sensor performance can be compared between laboratories, and information on the sensor chemistry may be revealed in the data analysis. This topic is particularly relevant in the rapidly maturing field of optical chemosensors.

Label-free detection of Staphylococcus aureus bacteria using long-period fiber gratings with functional polyelectrolyte coatings

Highly sensitive long-period fiber gratings (LPFG) was developed for label-free and rapid detection of Staphylococcus aureus (S. aureus). Specifically, the LPFG was functionalized with antibody and nanopitted polyelectrolyte coatings to facilitate bacterial adhesion and thus enhance the sensitivity of bacteria detection. The kinetics of S. aureus adhesion on functional coatings were tracked by surface morphology evolution and time-resolved resonance wavelength shift of the coated LPFG at a flow rate of 30 μl/ml and 37 °C in the concentration range of 10⁴-10⁸ colony forming unit (CFU)/ml. S. aureus detection at concentrations as low as 224 CFU/ml can be achieved within a short time span of 30 min. The LPFG-based biosensor can be readily adapted to a variety of biophotonic platforms, for applications such as food safety inspection, environmental monitoring, clinical diagnostics, and medical applications.

Life sensors: current advances in oxygen sensing by lanthanide complexes

Oxygen is essential for life. Inspired by the importance of oxygen, we present this critical and current review on lanthanide-based oxygen sensors.

A Fiber Optic Biosensor Based on Hydrogel-Immobilized Enzyme Complex for Continuous Determination of Cholesterol and Glucose

A multiparameter fiber optic biosensor for continuous determination of cholesterol and glucose was developed. This sensor was based on poly(N-isopropylacrylamide) (PNIPAAm)-immobilized glucose oxidase (GOx) complex (PIGC) and immobilized cholesterol oxidase (COD). The immobilized COD catalysis to the oxidation of cholesterol and PIGC catalysis to the oxidation of glucose could be performed at different temperatures. Therefore, the sensor could detect cholesterol and glucose continuously by changing temperature. The optimal detection conditions for glucose were achieved with pH 6.5, 30 °C, and 10 mg GOx (in 100-mg carrier), and those for cholesterol were achieved with pH 7.5, 33 °C, and 25 mg COD (in 250-mg carrier). The sensor has the cholesterol detection range of 20-250 mg/dL and the glucose detection range of 50-700 mg/dL. This biosensor has outstanding repeatability and selectivity, and the detection results of the practical samples are satisfactory.

Plasma dye coating as straightforward and widely applicable procedure for dye immobilization on polymeric materials

Here, we introduce a novel concept for the fabrication of colored materials with significantly reduced dye leaching through covalent immobilization of the desired dye using plasma-generated surface radicals. This plasma dye coating (PDC) procedure immobilizes a pre-adsorbed layer of a dye functionalized with a radical sensitive group on the surface through radical addition caused by a short plasma treatment. The non-specific nature of the plasma-generated surface radicals allows for a wide variety of dyes including azobenzenes and sulfonphthaleins, functionalized with radical sensitive groups to avoid significant dye degradation, to be combined with various materials including PP, PE, PA6, cellulose, and PTFE. The wide applicability, low consumption of dye, relatively short procedure time, and the possibility of continuous PDC using an atmospheric plasma reactor make this procedure economically interesting for various applications ranging from simple coloring of a material to the fabrication of chromic sensor fabrics as demonstrated by preparing a range of halochromic materials.

A luminescent europium complex for wide-range pH sensors and sensor microtiterplates

Luminescent sensor membranes and sensor microplates are presented for continuous or high-throughput wide-range measurement of pH based on a europium probe.

Synthesis and spectral evaluation of 5,10,15,20-tetrakis(3,4-dibenzyloxyphenyl)porphyrin

Porphyrins are of interest in many applications that involve electron transfer and absorption of light, such as solar energy and photodynamic cancer therapy. The newly synthesized 5,10,15,20-tetrakis(3,4-dibenzyloxyphenyl)porphyrin, TDBOPP, was characterized using 1H NMR, 13C NMR, UV-vis and fluorescence spectroscopy and MALDI-TOF/TOF high resolution mass spectrometry. Standard 1H NMR and 13C NMR experiments coupled with nuclear Overhauser effect (NOE) experiments confirmed the structure of the compound. The expected M+ and [M+H]+ ions are observed in the MALDI-TOF/TOF mass spectrum. The UV-vis absorption spectrum of TDBOPP shows a Soret band at 424 nm and three Q bands at 519 nm, 556 nm, and 650 nm with molar absorptivity 3.6×105 cm−1m−1, 1.6×104 cm−1m−1, 1.0×104 cm−1m−1 and 5.3×103 cm−1m−1, respectively. Excitation at 424 nm gives emission at 650 nm. The quantum yield of the porphyrin is 0.11.

Thymine based copolymers: feasible sensors for the detection of persistent organic pollutants in water

A multidisciplinary approach for understanding properties of thymine-based copolymer sensors.

Luminescence materials for pH and oxygen sensing in microbial cells - structures, optical properties, and biological applications

Luminescence including fluorescence and phosphorescence sensors have been demonstrated to be important for studying cell metabolism, and diagnosing diseases and cancer. Various design principles have been employed for the development of sensors in different formats, such as organic molecules, polymers, polymeric hydrogels, and nanoparticles. The integration of the sensing with fluorescence imaging provides valuable tools for biomedical research and applications at not only bulk-cell level but also at single-cell level. In this article, we critically reviewed recent progresses on pH, oxygen, and dual pH and oxygen sensors specifically for their application in microbial cells. In addition, we focused not only on sensor materials with different chemical structures, but also on design and applications of sensors for better understanding cellular metabolism of microbial cells. Finally, we also provided an outlook for future materials design and key challenges in reaching broad applications in microbial cells.

Some New Observations on Activation Energy of Crystal Growth for Thermally Activated Crystallization

Calorimetric study of glass/crystal phase transformation in disordered semiconductors is a significant tool for understanding their crystallization kinetics. Such studies provide the basis for practical application of glasses. Differential scanning calorimetry (DSC) is one of the advanced techniques for the analysis of thermally induced crystallization in glassy or amorphous systems. We are reporting the nonisothermal DSC measurements on four amorphous systems of Se70Te30 alloy with Ag, Cd, Sb, and Zn as chemical modifiers. In general, the rate constant (K) shows Arrhenian dependence on temperature (T), i.e., K = K0 exp (-Eg/RT) where Eg is the activation energy of crystal growth and K0 is called the pre-exponential factor of rate constant. In the present work, an experiment is designed to see the effect of composition on the activation energy of crystal growth. We have found Meyer-Neldel relation (MNR) between Eg and K0 for present systems. Another interesting feature of present work is the observation of further relation between Meyer-Neldel prefactor and Meyer-Neldel energy.

Microwave-assisted ionothermal synthesis of a water-stable Eu-coordination polymer: a Ba2+ ion detector and fluorescence thermometer

Presented is a water-stable Eu-coordination polymer, namely [HMIm]Eu(DHBDC)₂, capable of detecting Ba²⁺ in aqueous solution and acting as a two-PL transition fluorescence thermometer.

Double remote electrochemical addressing and optical readout of electrochemiluminescence at the tip of an optical fiber

A double remote strategy based on wireless addressing and remote readout of electrochemiluminescence at the tip of an optical fiber is reported.

Fiber-Optic Chemical Sensors and Fiber-Optic Bio-Sensors

This review summarizes principles and current stage of development of fiber-optic chemical sensors (FOCS) and biosensors (FOBS). Fiber optic sensor (FOS) systems use the ability of optical fibers (OF) to guide the light in the spectral range from ultraviolet (UV) (180 nm) up to middle infrared (IR) (10 μm) and modulation of guided light by the parameters of the surrounding environment of the OF core. The introduction of OF in the sensor systems has brought advantages such as measurement in flammable and explosive environments, immunity to electrical noises, miniaturization, geometrical flexibility, measurement of small sample volumes, remote sensing in inaccessible sites or harsh environments and multi-sensing. The review comprises briefly the theory of OF elaborated for sensors, techniques of fabrications and analytical results reached with fiber-optic chemical and biological sensors.

Gas sensing using porous materials for automotive applications

The use of zeolites and metal–organic frameworks in the sensing of gases emitted from automobile exhausts is reviewed.

Genotyping single nucleotide polymorphisms using different molecular beacon multiplexed within a suspended core optical fiber

We report a novel approach to genotyping single nucleotide polymorphisms (SNPs) using molecular beacons in conjunction with a suspended core optical fiber (SCF). Target DNA sequences corresponding to the wild- or mutant-type have been accurately recognized by immobilizing two different molecular beacons on the core of a SCF. The two molecular beacons differ by one base in the loop-probe and utilize different fluorescent indicators. Single-color fluorescence enhancement was obtained when the immobilized SCFs were filled with a solution containing either wild-type or mutant-type sequence (homozygous sample), while filling the immobilized SCF with solution containing both wild- and mutant-type sequences resulted in dual-color fluorescence enhancement, indicating a heterozygous sample. The genotyping was realized amplification-free and with ultra low-volume for the required DNA solution (nano-liter). This is, to our knowledge, the first genotyping device based on the combination of optical fiber and molecular beacons.

An enhanced LSPR fiber-optic nanoprobe for ultrasensitive detection of protein biomarkers

A miniaturized, localized surface plasmon resonance (LSPR)-coupled fiber-optic (FO) nanoprobe is reported as a biosensor that is capable of label-free, sensitive detection of a cancer protein biomarker, free prostate specific antigen (f-PSA). The biosensor is based on the LSPR at the reusable dielectric-metallic hybrid interface with a robust, gold nano-disk array at the fiber end facet that is directly fabricated using EBL and metal lift-off process. The f-PSA has been detected with a mouse anti-human PSA monoclonal antibody (mAb) as a specific receptor linked with a self-assembled monolayer at the LSPR-FO facet surfaces. Experimental investigation and data analysis found near field refractive index (RI) sensitivity at ~226 nm/RIU with current LSPR-FO nanoprobe, and demonstrated the lowest limit of detection (LOD) at 100 fg/mL (~3 fM) of f-PSA in PBS solutions. The control experimentation using 5mg/mL bovine serum albumin in PBS and nonspecific surface test shows the excellent specificity and selectivity in the detection of f-PSA in PBS. These results present important progress towards a miniaturized, multifunctional fiber-optic technology that integrates informational communication and sensing function for developing a high performance, label-free, point-of-care (POC) device.

Synthesis and Spectroscopic and Biological Activities of Zn(II) Porphyrin with Oxygen Donors

Results of investigation of the physicochemical properties of zinc complexes containing substituted phenols as axial ligand having general formula [X-Zn-t(p-CH₃) PP] [where X = different phenolates as axial ligand] in impurity-free organic solvent are presented. The four-coordinated zinc porphyrin accepts one axial ligand in 1 : 1 molar ratio to form five-coordinated complex, which is purified by column chromatography and characterized by physicochemical, biological evaluation and TGA/DTA studies. Absorption spectra show two principal effects: a red shift for phenols bearing substituted electron releasing groups (−CH₃, −NH₂) and blue shift for phenols bearing electron withdrawing groups (−NO₂, −Cl) relative to Zn-t(p-CH₃) PP, respectively. ¹H NMR spectra show that the protons of the phenol ring axially attached to the central metal ion are merged with the protons of the porphyrin ring. Fluorescence spectra show two fluorescence peaks in the red region with emission ranging from 550 nm to 700 nm. IR spectra confirm the appearance of Zn-N_Por and Zn-O vibrational frequencies, respectively. According to the thermal studies, the complexes have a higher thermal stability and the decomposition temperature of these complexes depends on the axial ligation. The respective complexes of X-Zn^II-t(p-CH₃) PP were found to possess higher antifungal activity (up to 90%) and higher in vitro cytotoxicity against human cancer cells lines.