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.

Utilization of a novel PVC- optical sensor for high sensitive and selective determination of zinc ion in real samples

A novel and highly specific bulk membrane optode was developed for the ultra-sensitive detection of zinc(II) in biological, pharmaceutical, and water samples. The polymer inclusion membrane (PIM) utilized in this study consists of 50% polyvinyl chloride (PVC) as a base polymer, 9.00% DOP (dioctylphthalate) as the plasticizer, and 40.0% D2EHPA (di(2-ethlyhexyl)phosphoric acid) as the carrier. To facilitate the spectrophotometric determination of zinc(II), a colorimetric reagent, namely 4-(2-arsonophenylazo) salicylic acid (APASA) {1.00%, m/v}, was employed. When Zn(II) was extracted into the PIM, it led to the creation of the zinc-D2EHPA complex. This complex then underwent a reaction with APASA, resulting in the formation of a red Zn - APASA complex with a maximum absorption wavelength (λmax) of 558 nm. To optimize the response of the optode, a central composite design was employed, considering variables such as the amount of additive and reagent, response time, and pH. When operated under the specific optimal conditions, the sensor demonstrated a limit of quantification (LOQ) of 0.74 ng/mL (equivalent to 1.17 × 10-8 M) and a limit of detection (LOD) of 0.22 ng/mL (equivalent to 3.44 × 10-9 M). The optode membrane demonstrated excellent reproducibility, stability, and a relatively long lifespan, making it suitable for precise and accurate monitoring of Zn(II) ion content. Regeneration of the optode was achieved effectively using 0.25 nitric acid solution, and its response exhibited reversibility and reproducibility, showed a relative standard deviation of less than 1.33%. Moreover, the PIM-APASA optode exhibited a high level of effectiveness in accurately determining the presence of Zn(II) ions in real environmental samples.

Effect on Improving CO2 Sensor Properties: Combination of HPTS and γ-Fe2O3@ZnO Bioactive Glass

8-Hydroxypyrene-1,3,6-trisulfonic acid (HPTS) dye, a fluorescent dye often used as a pH indicator, is embedded within the bioactive glass matrix and undergoes changes in its fluorescent properties when exposed to carbon dioxide (CO2). The aim of the current study is to investigate the use of bioactive glass (BG) particles containing γ-Fe2O3@ZnO to enhance the CO2 sensitivity of HPTS. X-ray diffraction, Fourier transform infrared, scanning electron microscopy, and photoluminescence spectroscopies were used to characterize the sol-gel synthesized powders. The sensing slides were prepared in the form of a thin film by immobilizing the fluorescent dye and γ-Fe2O3@ZnO-based additives into the poly(methyl methacrylate) matrix. The addition of γ-Fe2O3@ZnO nanoparticles with bioactive glass additives to the HPTS improves the performance characteristics of the sensor, including the linear response range, relative signal variation, and sensitivity. Meanwhile, the CO2 sensitivities were measured as 10.22, 7.73, 16.56, 17.82, 19.58, and 42.40 for the undoped form and M, M@ZnO, 5M@ZnO-BG, 10M@ZnO-BG, and 20M@ZnO-BG NP-doped forms of the HPTS-based thin films, respectively. The response and recovery times of the HPTS-based sensing slide along with 20M@ZnO-BG NPs have been measured as 44 and 276 s, respectively. The γ-Fe2O3/ZnO-containing BG particle-doped HPTS composites can be used as a promising sensor agent in the detection of CO2 gas in various fields such as environmental monitoring, medical diagnostics, and industrial processes.

Utility of 5-(2',4'-dimethylphenylazo)-6-hydroxy-pyrimidine-2,4-dione in PVC membrane for a novel green optical chemical sensor to detect zinc ion in environmental samples

In plasticized (2-nitro-phenyloctyl ether (o-NPOE)) and polyvinyl chloride (PVC) membrane incorporating (N,N-diethyl-5-(octadecanoylimino)-5H-benzo[a] phenolxazine-9-amine (ETH 5294) and sodium tetraphenyl borate (NaTPB), an ionophore 5-(2',4'-dimethylphenylazo)-6-hydroxy-pyrimidine-2,4-dione (DMPAHPD) form an optical chemical sensor for zinc determination is ascribed. The sensor response is based on selective complexation of Zn²⁺ with DMPAHPD in the designed membrane phase, resulting in an ion exchange process between H⁺ in the membrane and Zn²⁺ in the sample solution. The influences of several experimental parameters, as membrane composition, pH, and type and concentration of the regenerating reagent, were demonstrated. The sensor has a response range of 5.0 × 10^-9 to 2.5 × 10^-5 M Zn²⁺ with detection and quantification limits of 1.6 × 10^-9 and 4.9 × 10^-9 M, respectively. The response time of 1 min at 0.1 M phosphate buffer solution of pH 5.0 with recording repeatability and sensor-to sensor reproducibility is reported. The proposed sensor signifies high selectivity for Zn²⁺ over various transition metal ions, alkali, and alkaline earth ions. The sensor membrane can be simply regenerated with 0.5 M HNO₃. The sensor has been used to assess Zn²⁺ in river, waste, tap, sea, well, and spring waters samples, serum of diabetic patients, powdered milk, hair, red meat, pharmaceutical formulations, and talc powder samples.

A double helix-shaped optical fiber sensor for non-endoscopic diagnosis of gastrin-17

Non-endoscopic tools for the diagnostic evaluation of patients should be promoted in the field of biomedical assay and the need for highly sensitive, efficient, low-cost, and user-friendly sensors must be considered.

A New Optical Fiber Probe-Based Quantum Dots Immunofluorescence Biosensors in the Detection of Staphylococcus aureus

Staphylococcus aureus (S. aureus) is one of the most common clinical pathogenic bacteria with strong pathogenicity and usually leads to various suppurative infections with high fatality. Traditional bacterial culture for the detection of S. aureus is prone to diagnosis and antimicrobial treatment delays because of its long-time consumption and low sensitivity. In this study, we successfully developed a quantum dots immunofluorescence biosensor for S. aureus detection. The biosensor combined the advantages of biosensors with the high specificity of antigen-antibody immune interactions and the high sensitivity and stability of quantum dots fluorescence. The results demonstrated that the biosensor possessed high specificity and high sensitivity for S. aureus detection. The detection limit of S. aureus reached 1 × 10⁴ CFU/ml or even 1 × 10³ CFU/ml, and moreover, the fluorescence intensity had a significant positive linear correlation relationship with the logarithm of the S. aureus concentration in the range of 10³–10⁷ CFU/ml (correlation coefficient R² = 0.9731, P = 0.011). A specificity experiment showed that this biosensor could effectively distinguish S. aureus (1 × 10⁴ CFU/ml and above) from other common pathogenic (non-S. aureus) bacteria in nosocomial infections, such as Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii and Escherichia coli. Additionally, the whole detection procedure spent only 2 h. In addition, the biosensor in this study may not be affected by the interference of the biofilm or other secretions since the clinical biological specimens are need to be fully liquefied to digest and dissolve viscous secretions such as biofilms before the detection procedure of the biosensor in this study. In conclusion, the biosensor could meet the need for rapid and accurate S. aureus detection for clinical application.

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.

Synthesis and spectroscopic characterization of a fluorescent phenanthrene-rhodamine dyad for ratiometric measurements of acid pH values

Ratiometric pH sensing by multichannel emission response utilizing excimer/monomer emissions of phenanthrene and rhodamine emission at single excitation wavelength.

Optical sensor film for metribuzin pesticide detection

We present a new ratiometric and colorimetric optical sensor film for detection one of the most prevalent pesticide metribuzin. The detection proceeds within the low concentration range between 0 and 1.5 μM. The optical film is based on (a) near infrared (NIR) dye 2-[2-[2-Chloro-3-[2-[1,3-dihydro-3,3-dimethyl-1-(4-sulfobutyl)-2H-indol-2-ylidene]-ethylidene]-1-cyclopen-ten-1-yl]-eth-enyl]-3,3-di-methyl-1-(4-sulfobutyl)-3H-indolium hydroxide and (b) upconverting nanoparticles UCNPs of the NaYF₄:Yb,Er type (diameter ~40-100 nm) that can be emitted a dual (green and red) emission under 980 nm laser diode excitation. Commercially available polyvinyl chloride (PVC) was utilized as a homogeneous matrix for immobilizing NIR dye and UCNPs. The color of the NIR dye in the PVC matrix is based on the concentration of the metribuzin. When the sensor film is exposed to metribuzin the color changes from green to blue with a significant blue shift in the absorption peak (656 nm) of the NIR dye. Furthermore, the quenching of the red emission (659 nm) of the UCNPs is proceeded due to an inner filter effect. Thus, increasing the metribuzin concentration causes the red emission of UCNPs to be reduced. Conversely, the green emission (545 nm) of the UCNPs persists uninfluenced by metribuzin and can act as a reference signal. This optical sensor film provides great sensitivity based on their unique luminescence properties of UCNPs and recognition abilities within a very low detection limit for the metribuzin LOD 6.8 × 10^-8 M with a linear range of 0.23 to 1.5 μM and a relative standard deviation RSD_r (1%, n = 3). The novel optical sensor was applied to the detection of metribuzin in real water samples (surface and ground waters). The sensor film exhibits great selectivity in presence of different types of ions and pesticide molecules. But, atrazine pesticide interferes the analytical signal of the sensor film due to the presence of reactive amino groups in its structure. Memorably, we report the first optical chemical sensor film based on polymer film for metribuzin detection.

Enzyme-based optical biosensors for organophosphate class of pesticide detection

A systematic review of enzyme based optical detection schemes for the detection and analysis of organophosphate pesticides has been presented.

Recent advances in immunodiagnostics based on biosensor technologies-from central laboratory to the point of care

Immunological methods are widely applied in medical diagnostics for the detection and quantification of a plethora of analytes. Associated analytical challenges usually require these assays to be performed in a central laboratory. During the last several years, however, the clinical demand for rapid immunodiagnostics to be performed in the immediate proximity of the patient has been constantly increasing. Biosensors constitute one of the key technologies enabling the necessary, yet challenging transition of immunodiagnostic tests from the central laboratory to the point of care. This review is intended to provide insights into the current state of this transition process with a focus on the role of biosensor-based systems. To begin with, an overview on standard immunodiagnostic tests presently employed in the central laboratory and at the point of care is given. The review then moves on to demonstrate how biosensor technologies are reshaping this landscape. Single analyte as well as multiplexed immunosensors applicable to point of care scenarios are presented. A section on the areas of clinical application then creates the bridge to day-to-day diagnostic practice. Finally, the depicted developments are critically weighed and future perspectives discussed in order to give the reader a firm idea on the forthcoming trends to be expected in this diagnostic field.

Hydrogel-Based Fluorescent Dual pH and Oxygen Sensors Loaded in 96-Well Plates for High-Throughput Cell Metabolism Studies

In this study, we developed fluorescent dual pH and oxygen sensors loaded in multi-well plates for in-situ and high-throughput monitoring of oxygen respiration and extracellular acidification during microbial cell growth for understanding metabolism. Biocompatible PHEMA-co-PAM materials were used as the hydrogel matrix. A polymerizable oxygen probe (OS2) derived from PtTFPP and a polymerizable pH probe (S2) derived from fluorescein were chemically conjugated into the matrix to solve the problem of the probe leaching from the matrix. Gels were allowed to cure directly on the bottom of 96-well plates at room-temperature via redox polymerization. The influence of matrix’s composition on the sensing behaviors was investigated to optimize hydrogels with enough robustness for repeatable use with good sensitivity. Responses of the dual sensing hydrogels to dissolved oxygen (DO) and pH were studied. These dual oxygen-pH sensing plates were successfully used for microbial cell-based screening assays, which are based on the measurement of fluorescence intensity changes induced by cellular oxygen consumption and pH changes during microbial growth. This method may provide a real-time monitoring of cellular respiration, acidification, and a rapid kinetic assessment of multiple samples for cell viability as well as high-throughput drug screening. All of these assays can be carried out by a conventional plate reader.

Unusual PLS application for Pd(ii) sensing in extremely acidic solutions

Tazoc-Mar@: a simple device that turns into a deep blue colour in presence of Pd(ii) at very low concentration.

Refractometric detection of liquids using tapered optical fiber and suspended core microstructured fiber: a comparison of methods

Detecting explosive, flammable, or toxic industrial liquids reliably and accurately is a matter of civic responsibility that cannot be treated lightly. Tapered optical fibers (TOFs) and suspended core microstructured optical fibers (SC MOFs) were separately used as sensors of liquids without being compared to each other. We present a highly sensitive time-stable TOF sensor incorporated in the pipeline system for the in-line regime of measurement. This paper is furthermore focused on the comparison of this TOF and SC MOF of similar parameters for the detection of selected liquids. A validated method that incorporates TOF and SC MOF of small core (waist) diameter for refractometric detection is presented. The principle of detection is based on the overlap of an enhanced evanescent wave with a liquid analyte that either fills the cladding holes of the SC MOF or surrounds the waist area of the TOF. Optical power within the evanescent wave for both sensing structures and selected liquid analytes is analyzed. Measurement results concerning TOF and SC MOF are compared. Calculations to ascertain the limit of detection (LOD) for each sensor and the sensitivity (S) to refractive indices of liquid analytes in the range of 1.4269 to 1.4361 were performed at a wavelength of 1550 nm with the lowest refractive index step of 0.0007. Results affirming that S=600.96  dB/RIU and LOD=0.0733  RIU for the SC MOF and S=1143.2  dB/RIU and LOD of 0.0026 RIU for the TOF sensor were achieved, clearly illustrating that TOF-based sensors can reach close to two times greater sensitivity and 30 times higher limit of detection. This paper extends the comparison of the fiber sensors by discussing the potential applications.

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.

Two-dimensional photonic crystal chemical and biomolecular sensors

We review recent progress in the development of two-dimensional (2-D) photonic crystal (PC) materials for chemical and biological sensing applications. Self-assembly methods were developed in our laboratory to fabricate 2-D particle array monolayers on mercury and water surfaces. These hexagonal arrays strongly forward Bragg diffract light to report on their array spacings. By embedding these 2-D arrays onto responsive hydrogel surfaces, 2-D PC sensing materials can be fabricated. The 2-D PC sensors utilize responsive polymer hydrogels that are chemically functionalized to show volume phase transitions in selective response to particular chemical species. Novel hydrogels were also developed in our laboratory by cross-linking proteins while preserving their native structures to maintain their selective binding affinities. The volume phase transitions swell or shrink the hydrogels, which alter their 2-D array spacings, and shift their diffraction wavelengths. These shifts can be visually detected or spectrally measured. These 2-D PC sensing materials have been used for the detection of many analytes, such as pH, surfactants, metal ions, proteins, anionic drugs, and ammonia. We are exploring the use of organogels that use low vapor pressure ionic liquids as their mobile phases for sensing atmospheric analytes.

Highly selective and sensitive fluorescence optode membrane for uranyl ion based on 5-(9-anthracenylmethyl)-5-aza-2,8-dithia[9],(2,9)-1,10-phenanthrolinophane

A highly sensitive and selective fluorimetric optode membrane based on the enhancement in fluorescence emission of 5-(9-anthracenylmethyl)-5-aza-2,8-dithia[9],(2,9)-1,10-phenanthrolinophane (L) for subnanomolar detection of uranyl ion is presented.

A surface-enhanced Raman scattering optrode prepared by in situ photoinduced reactions and its application for highly sensitive on-chip detection

A surface-enhanced Raman scattering (SERS)-active optical fiber sensor combining the optical fiber waveguide with various SERS substrates has been a powerful analytical tool for in situ and long-distance SERS detection with high sensitivity. The design and modification of a high-quality SERS-active sensing layer are important topics in the development of novel SERS-active optical fiber sensors. Here, we prepared a highly sensitive SERS-active optrode by in situ fabrication of a three-dimensional porous structure on the optical fiber end via a photoinduced polymerization reaction, followed by the growth of photochemical silver nanoparticles above the porous polymer material. The fabrication process is rapid (finished within 1 h) and can be on line under light control. The porous structure supports vast silver nanoparticles, which allows for strong electromagnetic enhancement of SERS. Interestingly, the preparation of this SERS optrode and its utilization for SERS detection can all be conducted in a microfluidic chip. The qualitative and quantitative on-chip SERS sensing of organic pollutants and pesticides has been achieved by this SERS optrode-integrated microfluidic chip, and its high detection sensitivity makes it a promising factor in the analysis of liquid systems.

Optical methods for sensing and imaging oxygen: materials, spectroscopies and applications

We review the current state of optical methods for sensing oxygen. These have become powerful alternatives to electrochemical detection and in the process of replacing the Clark electrode in many fields. The article (with 694 references) is divided into main sections on direct spectroscopic sensing of oxygen, on absorptiometric and luminescent probes, on polymeric matrices and supports, on additives and related materials, on spectroscopic schemes for read-out and imaging, and on sensing formats (such as waveguide sensing, sensor arrays, multiple sensors and nanosensors). We finally discuss future trends and applications and summarize the properties of the most often used indicator probes and polymers. The ESI† (with 385 references) gives a selection of specific applications of such sensors in medicine, biology, marine and geosciences, intracellular sensing, aerodynamics, industry and biotechnology, among others.

Fluorescence-based biosensors

The field of optical sensors has been a growing research area over the last three decades. A wide range of books and review articles has been published by experts in the field who have highlighted the advantages of optical sensing over other transduction methods. Fluorescence is by far the method most often applied and comes in a variety of schemes. Nowadays, one of the most common approaches in the field of optical biosensors is to combine the high sensitivity of fluorescence detection in combination with the high selectivity provided by ligand-binding proteins. In this chapter we deal with reviewing our recent results on the implementation of fluorescence-based sensors for monitoring environmentally hazardous gas molecules (e.g. nitric oxide, hydrogen sulfide). Reflectivity-based sensors, fluorescence correlation spectroscopy-based (FCS) systems, and sensors relying on the enhanced fluorescence emission on silver island films (SIFs) coupled to the total internal reflection fluorescence mode (TIRF) for the detection of gliadin and other prolamines considered toxic for celiac patients are also discussed herein.

Design, Synthesis and Electrospinning of a Novel Fluorescent Polymer for Optical Sensor Applications

This work describes the synthesis and electrospinning of new fluorescent polymers and their use for the fabrication of optical chemical sensors. A new fluorescent monomer was first synthesized by coupling reactions between methacryloyl chloride and a pyrene derivative, 1-pyrene butanol. Fluorescent polymers containing pyrene molecules were then obtained by the copolymerization of this monomer with methylmethacrylate using 2,2'-azobisisobutyronitrile as the initiator. These polymers show distinct and well-defined fluorescence that is characteristic of the pyrene chromophores. Electrospinning was used to process these polymers into high surface area nanofibrous membranes for optical sensing. The resulting membranes show a high sensitivity to 2,4-dinitro toluene based on the fluorescence quenching of the pyrene chromophores. Fluorescence intensities decreased with increasing concentration of the 2,4-dinitro toluene. The quenching behavior follows Stern-Volmer bimolecular quenching kinetics. The synthesis, characterization, electrospinning fabrication, and sensing capability of these polymers will be discussed.

Fast quantitative single-molecule detection at ultralow concentrations

The applicability of single-molecule fluorescence assays in liquids is limited by diffusion to concentrations in the low picomolar range. Here, we demonstrate quantitative single-molecule detection at attomolar concentrations within 1 min by excitation and detection of fluorescence through a single-mode optical fiber in presence of turbulent flow. The combination of high detectability and short measurement times promises applications in ultrasensitive assays, sensors, and point-of-care medical diagnostics.

Optoelectronic capillary sensors in microfluidic and point-of-care instrumentation

This paper presents a review, based on the published literature and on the authors' own research, of the current state of the art of fiber-optic capillary sensors and related instrumentation as well as their applications, with special emphasis on point-of-care chemical and biochemical sensors, systematizing the various types of sensors from the point of view of the principles of their construction and operation. Unlike classical fiber-optic sensors which rely on changes in light propagation inside the fiber as affected by outside conditions, optical capillary sensors rely on changes of light transmission in capillaries filled with the analyzed liquid, which opens the possibility of interesting new applications, while raising specific issues relating to the construction, materials and instrumentation of those sensors.

Optical colorimetric sensor strip for direct readout glucose measurement

A novel direct readout colorimetric optical glucose sensor strip was constructed based on a three-layer film, including a green-emitted CdTe/CdS quantum dots (QDs) layer as a stable color background, a red-fluorescent platinum-porphyrin oxygen-sensing layer and a glucose oxidase layer. The sensor achieved high resolution (up to 0.2 mmol L(-1)) glucose determination with a detection range from 0 to 3.0 mmol L(-1). A "glucose ruler" which acts as a glucose standard colorimetric card was obtained. Glucose concentration could easily be directly readout using the "glucose ruler", which made the glucose determination rapid, convenient and easy. The effects of pH, salinity and temperature were systematically investigated. The prepared sensor was finally applied for glucose sample analysis, compared with the "glucose ruler", accurate results could be directly readout.

Special Engineering Aspects

The specific characteristics of mammalian cells discussed in Chap. 2 require adapted solutions for bioreactor design and operation. Especially, cell damage by shear stress and aeration has to be considered. Therefore this chapter starts with a detailed discussion of shear stress effects on mammalian cells (anchorage-dependent and suspendable cells) in model systems and bioreactors, respectively, and consequences for reactor design. Appropriate oxygen supply is another critical issue, as adapted oxygen supply systems are required. Techniques for immobilization of cells, either grown on microcarriers in suspension culture or within macroporous carriers in fixed bed or fluidized bed reactors, are discussed as well. With respect to the operation of bioreactors, the characteristics of different culture modes (batch, fed-batch, chemostat, perfusion) are introduced and practical examples are given. Finally, concepts for monitoring of bioreactors, including offline and online methods as well as control loops (e.g. O₂, pH), are considered.

Aspects of recent development of immunosensors

This chapter focuses on the recent developments in the field of immunosensors. Immunosensors incorporate the specific immunochemical reaction with the modern transducers including electrochemical (potentiometric, conductometric, capacitative, impedance, amperometric), optical (fluorescence, luminescence, refractive index), and microgravimetric transducers. These immunosensor devices with dramatic improvements in the sensitivity and selectivity possess the abilities to investigate the reaction dynamics of antibody–antigen binding and the potential to revolutionize conventional immunoassay techniques. With the rapid development of immunological reagents and detection equipments, immunosensors have allowed an increasing range of analytes to be identified and quantified and in particular, simple-to-use, inexpensive, and reliable immunosensing systems have been developed for areas such as outpatient monitoring, large screening programs, and remote environmental surveillance. Immunosensors with lowered detection limits and increased sensitivities have been developed in various fields, particularly in clinical analysis. A noticeable development trend is also observed in the development of immunosensors combining with other techniques such as flow injection analysis (FIA) or capillary electrophoretic (CE) analysis, which complement and improve the present immunoassay methods. Belov et al. have proposed a novel immunophenotyping method for leukemias which uses a cluster of differentiation antibody microarray, and a microarray of enzyme-linked immunosorbent assay has been developed for autoimmune diagnosis of systematic rheumatic disease. Development of microfluidic immunosensor systems for proteomics and drug discovery have also been reported in recent years where the microfluidic system integrates multiple processes in a single device to improve analytical performance by reducing the reagent consumption and the analysis time, and increasing reliability and sensitivity through automation.

Optical Fiber Sensing Using Quantum Dots

Recent advances in the application of semiconductor nanocrystals, or quantumdots, as biochemical sensors are reviewed. Quantum dots have unique optical properties thatmake them promising alternatives to traditional dyes in many luminescence basedbioanalytical techniques. An overview of the more relevant progresses in the application ofquantum dots as biochemical probes is addressed. Special focus will be given toconfigurations where the sensing dots are incorporated in solid membranes and immobilizedin optical fibers or planar waveguide platforms.

Chloride selective calix[4]arene optical sensor combining urea functionality with pyrene excimer transduction

A neutral 2-site chloride selective compound has been developed (3), based on a 1,3-alternate tetrasubstituted calix[4]arene providing a preorganized supramolecular scaffold. The resultant supramolecular cavity is among the first to combine urea functional groups bridged with single methylene spacers to pyrene moieties. It combines a naturally and synthetically proven H-bonding system with the elegant ratiometric fluorescent signaling properties of an intramolecular pyrene excimer system, triggered by conformational changes upon anion coordination. The excimer emission of 3 is quenched, with a simultaneous rise in the monomer emission solely by the chloride anion among a wide variety of anions tested. 3 has an association constant of 2.4 x 10(4) M(-1) with chloride. The suitability and advantages of ratiometric optical sensor compounds like 3 for use in practical sensor devices is discussed. 3 has an LOD of 8 x 10(-6) M with chloride in acetonitrile-chloroform (95:5 v/v). A dynamic fluorescence study revealed a response time of < 3 s. A recently developed and simple HPLC-based purification method complimented conventional organic work up methods to yield pure product.

Development of a disposable mercury ion-selective optode based on trityl-picolinamide as ionophore

A disposable ion-selective optode for mercury based on trityl-picolinamide (T-Pico) as neutral ionophore was developed. The sensing layer consist of plasticised PVC incorporating T-Pico as a selective ionophore for Hg2+, ETH 5418 as a chromoionophore, and potassium tetrakis[3,5-bis(trifluoromethyl)phenyl] borate as lipophilic salt. The measurement principle is based on an ion-exchange mechanism. When the optode membrane is introduced into a water sample for 5 min, there is a colour change from red to blue, depending on the mercury concentration (pH 4.7), making it possible to use the absorbance at 665 nm as the analytical signal. The optode membrane response to Hg2+ was not fully reversible; however, it reveals a very good selectivity to many cations including alkali, alkaline earth, transition, and heavy metal ions. The detection limit for Hg2+ is 5.0x10(-7) M at pH 4.7. The response characteristics of the sensor including dynamic range, reproducibility, response time, and lifetime are discussed in detail. This sensor was used for the determination of mercury in environmental water samples with satisfactory recovery.

Proteins from extremophiles as stable tools for advanced biotechnological applications of high social interest

Extremophiles are micro-organisms adapted to survive in ecological niches defined as 'extreme' for humans and characterized by the presence of adverse environmental conditions, such as high or low temperatures, extreme values of pH, high salt concentrations or high pressure. Biomolecules isolated from extremophiles possess extraordinary properties and, in particular, proteins isolated from extremophiles represent unique biomolecules that function under severe conditions, comparable to those prevailing in various industrial processes. In this article, we will review some examples of recent applications of thermophilic proteins for the development of a new class of fluorescence non-consuming substrate biosensors for monitoring the levels of two analytes of high social interest, such as glucose and sodium.