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Holographic Sensor for Water in Solvents
Abstract
The diffraction color of a gelatin holographic diffraction grating changed as a function of the water activity when immersed in a "wet" hydrophobic liquid. Quantification of the absorption maximum of the diffracted light showed that it was related, after calibration, to either the water content or the water activity of the solvent. The holographic diffraction grating measured water contents of hydrocarbon solvents at sensitivities comparable to that of the Karl Fischer coulometric titrator and over a wide range of water contents. A grating immersed in xylene revealed a visible color change when the water content was increased from 47 to 120 ppm. Conversely, the holographic grating responded to ethanol in water in the range 0-1% (w/w). The inexpensiveness and simplicity of silver halide holographic reflection gratings, combined with their relatively high sensitivity, suggests that these devices might find widespread application as immersible water activity sensors for hydrophobic liquids.
... The process of detection involves a change in the optical characteristics of the hologram caused by the interaction of the analyte with the support medium. The main effort in the development of holographic sensors for visual detection has been focused on reflection holographic sensors [1][2][3][4][5][6][7][8][9] and on optimisation of the support medium. The optimisation of the support medium targets the achievement of selectivity towards a specific analyte. ...
... The optimisation of the support medium targets the achievement of selectivity towards a specific analyte. Reflection holographic sensors sensitive to trypsin [1], water in hydrophobic liquids [2], alcohol levels [3], pH [4], glucose [5,6], l-lactate [7,8] and bacterial spores [9] have been developed. The principle of operation of these holographic sensors [1][2][3][4][5][6][7][8][9] relies mainly on swelling /shrinking of the hologram support medium when it is exposed to the analyte. ...
... Reflection holographic sensors sensitive to trypsin [1], water in hydrophobic liquids [2], alcohol levels [3], pH [4], glucose [5,6], l-lactate [7,8] and bacterial spores [9] have been developed. The principle of operation of these holographic sensors [1][2][3][4][5][6][7][8][9] relies mainly on swelling /shrinking of the hologram support medium when it is exposed to the analyte. Other mechanisms such as changes of the average refractive index and of the refractive index modulation are also possible. ...
This chapter presents holographic devices for sensing the relative humidity in the environment. The principle of operation of two main types of holographic sensors based on transmission and refection holograms is described and their properties are theoretically modelled. The effect of different factors such as change of the overall refractive index, change of the hologram’s thickness due to swelling/shrinkage of the layer and change in the refractive index modulation due to absorption/desorption of moisture are considered. In the experimental studies an emphasis is given to the reflection holographic humidity sensors which can provide a visual indication of the relative humidity observed as a change of the colour of the reflected light. The work presented focuses on holograms recorded in acrylamide based photopolymers. The results from studies of their sensitivity, reversibility, relative humidity range of operation and response time are summarised. The operational temperature range is also studied.
The potential use of the humidity sensors as user-verifiable security holograms is described as well as applications in packaging and environmental sensing.
... Although the first sensing holograms were recorded on commercially available silver bromide gelatin films [40,70,71], their posterior fabrication was based on thin films of hydrogels synthesized mainly with two groups of monomers and cross-linkers: acrylamide (AAm) and N,Nmethylenbisacrylamide (MBA [72][73][74] and 2-hydroxyethyl methacrylate (HEMA) and ethylene dimethacrylate (EDMA) [58,[75][76][77][78][79][80][81][82][83]. Different components, such as NPs [84][85][86][87] or liquid crystals [88], were later included in the formulations to either gain stability or improve the DE of holograms. ...
... The holographic system's water sensitivity was firstly demonstrated by Lowe using gelatin as the holographic support [71]. However, gelatin recorded by the silver halide process has a strong hysteresis toward humidity sensing and new materials and recording modes were later proposed by other authors. ...
Hydrogel-based holographic sensors consist of a holographic pattern in a responsive hydrogel that diffracts light at different wavelengths depending on the dimensions and refractive index changes in the material. The material composition of hydrogels can be designed to be specifically responsive to different stimuli, and thus the diffraction pattern can correlate with the amount of analyte. According to this general principle, different approaches have been implemented to achieve label-free optical sensors and biosensors, with advantages such as easy fabrication or naked-eye detection. A review on the different approaches, sensing materials, measurement principles, and detection setups, and future perspectives is offered.
... The detection of trace water in organic solvents is an important analytical tool in several elds of industry and chemistry. [1][2][3][4][5][6][7] The existence of water may cause hydrolysis of organic solvents and increase the formation of oxidation products during storage of organic solvents. [8][9][10][11][12][13][14] At present, water content is usually measured by a classic Karl-Fisher titration. ...
... Therefore, the determination of the water content in the organic solvent is one of the most important and most commonly encountered analytical problems. 2,3,5,7,13 In order to explore the possibility for application of the asprepared CQDs in the detection of water content in organic solvents, the uorescence emission spectra excited by the light of 440 nm of CQDs dispersed in ethanol were further examined. As shown in Fig. 5(a), when 10% v/v water was added into the ethanol solution of CQDs, the uorescent intensity decreased signicantly for one minute and then tends to be stable. ...
The quantitative analysis of trace water in organic solvents has always been a research hotspot, and it is still in the development stage and needs to be continuously developed. In this study, a facile and rapid approach was developed for the preparation of carbon quantum dots (CQDs) with yellow fluorescence emission and ultrahigh absolute fluorescence quantum yields (92.6%). Compared to traditional organic fluorescent molecules, the preparation of CQDs is simpler, faster and more environmentally friendly. It is found that the fluorescent properties of CQDs are excellent in organic solvents and could be quenched by trace water, which makes them a promising material used without any modification for the detection of water in organic solvents. As a result, the as-prepared CQDs were adopted as fluorescent probes for the detection of water in organic solvents (ethanol, tetrahydrofuran, and 1,4-dioxane). The limit of detection was as low as 0.01%. To the best of our knowledge, this is the first time that CQDs have been used as water sensing fluorescent probes in organic solvents. The possible mechanism for trace water detection of the as-prepared CQDs in organic solvents is attributed to the specific water-fluorophore interaction and partially to the increase in polarity of the solvent caused by an increase in water concentration.
... Interaction of the analyte with the hologram causes a change in the swelling state or cross-linking density of the polymer, which in turn results in a change in the recorded hologram. A range of sensors have been designed using these principles including systems for detecting pH [2], ionic strength [3], sodium ions, potassium ions [4], calcium ions [5], alcohol [6], water [7], glucose [8][9][10], a variety of enzymes [11,12], bacterial cells [13] and physical stimuli. ...
... Highly sensitive water sensors can be fabricated which respond rapidly to small amounts of water in solvents [7] or even to moisture saturated air ( Figure 1). By tailoring the hydrophobicity of the holographic film, it is possible to tailor the response of the sensors to solvents other than water [6] as well. ...
Smart" holograms are novel sensor systems which utilise diffraction as the transduction method for the detection of physical stimuli or (bio)chemical analytes. Interaction of these sensors with a specific analyte or stimulus changes the colour, image or brightness of the hologram and these changes can be visualised directly by the user or quantified using a simple colour reader. Sensor holograms are inexpensive, robust, label-free, format flexible systems which can be engineered to be sensitive to a wide range of analytes.
... Any physical, chemical or biological mechanism that changes the spacing of the fringes (d) or the average refractive index (n) will generate observable changes in the wavelength (colour) of the reflection hologram. For example, if a holographic grating is immersed in an aqueous sample, absorption of water by the hydrogel layer causes the grating to swell perpendicular to the plane of the substrate layer [13]. This swelling increases the holographic fringe separation and consequently red-shifts the diffraction wavelength with the embedded holographic grating acting as a sensitive reporter of film thickness, which can be easily quantified using a spectrometer and a white light source. ...
... Given their swelling behaviour in water, holographic gratings have been proposed for the direct measurement of water activity in liquids [13]. Immersion of gelatine holograms in 'wet' hydrophobic liquids results in swelling due to the absorption of water. ...
Analyte-responsive holograms comprise a holographic grating embedded in a smart hydrogel film. The grating acts as a reporter that enables analyte induced changes in the thickness of the associated polymer film to be accurately determined. Interaction of these materials with a specific analyte or stimuli leads to a change in the colour, image or brightness of the hologram and these changes can be visualised directly or quantified using a simple colour reader. Analyte-responsive holograms are inexpensive, robust and have proven suitable for detection of a wide range of clinically and industrially important analytes.
... The resultant recording of the interference pattern acts as a diffraction grating with tunable characteristics based on material and recording conditions. Holographic sensors have been demonstrated for numerous analytes such as temperature [69], humidity [70], pH [71], water [72], and gasses [73]. Holographic sensors are based on the change in the properties of the hologram when exposed to the analyte and the analysis of the resultant variation in the hologram's diffractive properties [25]. ...
The term optomechanical sensors describes devices based on coupling the optical and mechanical sensing principles. The presence of a target analyte leads to a mechanical change, which, in turn, determines an alteration in the light propagation. Having higher sensitivity in comparison with the individual technologies upon which they are based, the optomechanical devices are used in biosensing, humidity, temperature, and gases detection. This perspective focuses on a particular class, namely on devices based on diffractive optical structures (DOS). Many configurations have been developed, including cantilever- and MEMS-type devices, fiber Bragg grating sensors, and cavity optomechanical sensing devices. These state-of-the-art sensors operate on the principle of a mechanical transducer coupled with a diffractive element resulting in a variation in the intensity or wavelength of the diffracted light in the presence of the target analyte. Therefore, as DOS can further enhance the sensitivity and selectivity, we present the individual mechanical and optical transducing methods and demonstrate how the DOS introduction can lead to an enhanced sensitivity and selectivity. Their (low-) cost manufacturing and their integration in new sensing platforms with great adaptability across many sensing areas are discussed, being foreseen that their implementation on wider application areas will further increase.
... The disadvantage is that the smart polymer has to be tailored for each individual application. These kinds of sensors have been used to detect, for example, divalent metal ions (González et al., 2005) that are important in biological processes, pH (Marshall et al., 2003), water content, solvents in water (Blyth et al., 1996), proteases (Millington et al., 1995) and glucose (Kabilan et al., 2005;Domschke et al., 2004). No publications on the integration of sensor holograms with fibre or paper-like products were found in this study. ...
In this patent and literary survey bioactive papers and fibre products, i.e. paper-like products, cardboard, fabrics and their combinations, etc., with active recognition and/or functional material capabilities are reviewed. The focus is on materials that specifically react with the target entity or environmental condition, and this reaction initializes different events, like a discharge of molecules or signalling function, in the product. The aim of this publication is to review and provide basic information on biomolecules and their potential utilisation for functional purposes, embedded signalling - concentrating especially on conducting polymers and optics - low-cost manufacturing on a large scale, modification of fibres and grafting or immobilisation of bioactive components. In addition, some application scenarios for bioactive paper products are presented.
... Water is an essential substance, not only in human life, but also in chemistry [1][2][3][4][5][6][7] . It is also a common impurity in most of the organic solvents [8] . ...
The quantitative analysis of trace water in organic solvents remains a hotspot in current research because of the importance in both industrial and laboratory scale chemistry. This study introduced a fluorescence chemosensor (L3) for the detection of trace water in dimethyl sulfoxide (DMSO). Addition of water into the DMSO solution of L3 resulted a significant fluorescence enhancement at 533 nm with a detection limit of 0.002 wt %. The fluorescence turn-on response is occurred due to the formation of aggregates of L3. Also, other possible mechanism for trace water detection by L3 in DMSO is attributed to the specific water-L3 interaction and partially to the increase in polarity of the solvent caused by an increase in water concentration. Dynamic light scattering (DLS), ¹H NMR, scanning electron microscope (SEM), transmission electron microscope (TEM) and quantum mechanical studies were performed to support the water sensing by L3 in DMSO.
... The holographic photonic structures were recorded in different materials, and this allowed the group to create a variety of different sensors. The first examples were for detection of proteases [17], water in solvents [18], trypsin [19], and alcohol [20]. At about the same time, two other groups reported the first sensors based on transmission holographic gratings for detection of moisture [21] and salinity of water [22]. ...
... To our knowledge, this is the first time that an optical fiber sensor based on LMR for ethanol concentration in water is reported so it is difficult to establish a comparison for these values. However, as a reference, recent works based on other phenomena showed rise and fall times of 40 and 70 s [25], 13 and 6 s [26], more than 10 min [37]. Authors could just find a work presenting similar dynamic times [27]. ...
The influence of graphene oxide (GO) over the features of an optical fiber ethanol sensor based on lossy mode resonances (LMR) has been studied in this work. Four different sensors were built with this aim, each comprising a multimode optical fiber core fragment coated with a SnO2 thin film. Layer by layer (LbL) coatings made of 1, 2 and 4 bilayers of polyethyleneimine (PEI) and graphene oxide were deposited onto three of these devices and their behavior as aqueous ethanol sensors was characterized and compared with the sensor without GO. The sensors with GO showed much better performance with a maximum sensitivity enhancement of 176% with respect to the sensor without GO. To our knowledge, this is the first time that GO has been used to make an optical fiber sensor based on LMR.
... The polyHEMA-co-EDMA polymers were synthesised according to the protocol of Marshall et al. [5]. A 0.3 M silver perchlorate (AgClO 4 ) solution (300 ml) was pipetted onto the surface of a clean glass plate in a longitudinal strip. ...
Conventional volume holographic gratings (VHGs) fabricated in photosensitive emulsions such as gelatin containing silver salts enable the facile visualization of the holographic image in ambient lighting. However, for the fabrication of holographic sensors, which require more defined and chemically-functionalised polymer matrices, laser ablation has been introduced to create the VHGs and thereby broaden their applications, although the replay signal can be challenging to detect in ambient lighting. When traditional photochemical bleaching solutions used to reduce light scattering and modulate refractive index within the VHG are applied to laser ablated volume holographic gratings, these procedures decrease the holographic peak intensity. This is postulated to occur because both light and dark fringes contain a proportion of metal particles, which upon solubilisation are converted immediately to silver iodide, yielding no net refractive index modulation. This research advances a hypothesis that the reduced intensity of holographic replay signals is linked to a gradient of different sized metal particles within the emulsion, which reduces the holographic signal and may explain why traditional bleaching processes result in a reduction in intensity. In this report, a novel experimental protocol is provided, along with simulations based on an effective medium periodic 1D stack, that offers a solution to increase peak signal intensity of holographic sensors by greater than 200%. Nitric acid is used to etch the silver nanoparticles within the polymer matrix and is thought to remove the smaller particles to generate more defined metal fringes containing a soluble metal salt. Once the grating efficiency has been increased, this salt can be converted to a silver halide, to modulate the refractive index and increase the intensity of the holographic signal. This new protocol has been tested in a range of polymer chemistries; those containing functional groups that help to stabilize the metal nanoparticles within the matrix yield more intense holographic signals as the integrity of the fringe is more protected with increasing metal solubility.
... A colorimetric sensor, using a periodic array inside the gel, was another system used to make the PBA-derived hydrogel system. This system can be prepared using three different methods, including the formation of an array via hydrogels in the case of a hologram, [76] a periodic array of voids, [77][78][79] and the inclusion of a colloidal crystal within the gel. [80,81] In comparison to inverse opal hydrogels, which possess a high porous network, the crystalline colloidal array (CCA) is more accurately correlated with the diffraction wavelength of the incorporated photonic crystal. ...
Recent advances and applications of biomolecule-responsive hydrogels, namely, glucose-responsive hydrogels, protein-responsive hydrogels, and nucleic-acid-responsive hydrogels are highlighted. However, achieving the ultimate purpose of using biomolecule-responsive hydrogels in preclinical and clinical areas is still at the very early stage and calls for more novel designing concepts and advance ideas. On the way toward the real/clinical application of biomolecule-responsive hydrogels, plenty of factors should be extensively studied and examined under both in vitro and in vivo conditions. For example, biocompatibility, biointegration, and toxicity of biomolecule-responsive hydrogels should be carefully evaluated. From the living body's point of view, biocompatibility is seriously depended on the interactions at the tissue/polymer interface. These interactions are influenced by physical nature, chemical structure, surface properties, and degradation of the materials. In addition, the developments of advanced hydrogels with tunable biological and mechanical properties which cause no/low side effects are of great importance.
... The polyHEMA-co-EDMA polymers were synthesised according to the protocol of Marshall et al. [5]. A 0.3 M silver perchlorate (AgClO 4 ) solution (300 ml) was pipetted onto the surface of a clean glass plate in a longitudinal strip. ...
Conventional volume holographic gratings (VHGs) fabricated in photosensitive emulsions such as gelatin containing silver salts enable the facile visualisation of the holographic image in ambient lighting. However, for the fabrication of holographic sensors, which require more defined and chemically-functionalised polymer matrices, laser ablation has been introduced to create the VHGs and thereby broaden their applications, although the replay signal can be challenging to detect in ambient lighting. When traditional photochemical bleaching solutions used to reduce light scattering and modulate refractive index within the VHG are applied to laser ablated volume holographic gratings, these procedures decrease the holographic peak intensity. This is postulated to occur because both light and dark fringes contain a proportion of metal particles, which upon solubilisation are converted immediately to silver iodide, yielding no net refractive index modulation. This research advances a hypothesis that the reduced intensity of holographic replay signals is linked to a gradient of different sized metal particles within the emulsion, which reduces the holographic signal and may explain why traditional bleaching processes result in a reduction in intensity. In this report, a novel experimental protocol is provided, along with simulations based on an effective medium periodic 1D stack, that offers a solution to increase peak signal intensity of holographic sensors by greater than 200%. Nitric acid is used to etch the silver nanoparticles within the polymer matrix and is thought to remove the smaller particles to generate more defined metal fringes containing a soluble metal salt. Once the grating efficiency has been increased, this salt can be converted to a silver halide, to modulate the refractive index and increase the intensity of the holographic signal. This new protocol has been tested in a range of polymer chemistries; those containing functional groups that help to stabilise the metal nanoparticles within the matrix yield more intense holographic signals as the integrity of the fringe is more protected with increasing metal solubility.
... Holography has become an area of great interest with application in many fields including holographic digital microscopy [1,2], holographic tweezers [3], holographic optical elements (HOEs) for solar concentrators [4,5], sensors [6][7][8][9][10], and data storage (HDS) [11,12]. A large range of photosensitive media are available for holographic recording, each with its inherent advantages and disadvantages. ...
Polymerisation-induced shrinkage is one of the main reasons why many photopolymer materials are not used for certain applications including holographic optical elements and holographic data storage. Here, two compositional changes for the reduction of shrinkage in an acrylamide-based photopolymer are reported. A holographic interferometric technique was used to study changes in the dynamics of the shrinkage processes occurring in the modified photopolymer during holographic recording in real time. Firstly, the effect of the replacement of the acrylamide monomer in the photopolymer composition with a larger monomer molecule, diacetone acrylamide, on polymerisation-induced shrinkage has been studied. A reduction in relative shrinkage of 10–15% is obtained using this compositional change. The second method tested for shrinkage reduction involved the incorporation of BEA-type zeolite nanoparticles in the acrylamide-based photopolymer. A reduction in relative shrinkage of 13% was observed for acrylamide photopolymer layers doped with 2.5% wt. BEA zeolites in comparison to the undoped photopolymer.
... alcohol, lactate, glucose, pH, ions, etc. Examples of holographic sensors are reported in literature. Holograms recorded in gelatin by traditional methods have been used for sensing proteases, watersolvent mixtures, alcohol content and humidity [94,[126][127][128][129][130][131][132][133]. Also, in aqueous solutions coupled with biomolecules, cells or organisms expand their capabilities and detection ranges [134][135][136][137][138]. Holograms produced in polymer hydrogels, such as acrylate, acrylamide and vinyl alcohol, have been used for holographic sensing of glucose, lactate, toluene, pH and different types of ions by introducing extra functional groups [25,[139][140][141][142][143][144]. ...
Holographic sensors are photonic layered structures contained in analyte sensitive lms that upon illumination produce monochromatic reflections (λ). The present work reports the fabrication of oxygen and ammonia sensors in Nafi on membranes and hydrocarbon and volatile organic compound sensors in poly(dimethylsiloxane) (PDMS) films. A holographic recording technique was developed to suit these materials consisting of the in situ formation of nanoparticles of 18nm average diameter and their subsequent ordered ablation with a 300mJ laser. The wavelength of the monochromatic reflections depends principally on the refractive index of the resulting layers (n) and the separation between them (Λ). Changes in these parameters are generated by the analyte-sensor interactions and their magnitude can be correlated to the analyte concentration. The strength of these interactions is determined by the thermodynamic properties of the analytes, such as the cohesive energy density (δ^2), and this, was coupled with a photonic model for the prediction of the holographic response. After exposure to different concentrations of the analytes, the kinetics of the responses were determined and the lowest detection limits (LDL) established as follows: Hydrocarbons in PDMS holograms 1% (v/v) in 3s for a range of concentrations from 0-100%; ammonia in Nafi on holograms 0.16% in 100s in the 0-12.5% range; the LDL for oxygen sensing could not be determined although the response was recorded down to 12.5% and up to 100% in 100s. Holographic sensors show competitive responses comparable to commercially available gas sensors for biomedical diagnostics and industrial process monitoring because of their facile fabrication and their shared sensing platform allowing multiplexing.
... Sensor holograms utilize the diffraction principle of transmitting volume holographic grating (VHG) recorded within a photopolymer appositely functionalized to detect a specific stimulus or analyte. Holographic sensors sensitive to a wide range of analytes, such as pH [2], alcohol [3], water [4], glucose [5], a variety of enzymes [6], bacterial cells [7] and physical stimuli have been designed. ...
Sensor holograms utilize the diffraction principle of transmitting volume holographic grating (VHG) recorded within a photopolymer appositely functionalized to detect a specific stimulus or analyte. A change in the swelling or shrinking state or cross-linking density of the polymer can be caused by the hologram interaction with an analyte. This leads to a change in the recorded hologram sensor and thus, considering an incident monochromatic light and the VHG angular selectivity, to an angle shift of the diffracted maximum intensity. In this work, two new photopolymers based on a sol-gel matrix opportunely functionalized to be sensitive to transition metals or heavy metals were used as sensitive material to record VHGs. An interferometric set up with a laser source at 532nm was used to record VHGs and gratings of 1000 lines/mm were realized. When exposed to a solution of water and lead, an angle shift of about 3° of the first order diffraction of the grating was measured, demonstrating its capability to reveal the presence of heavy metal in water.
... Holograms can be used as analytical devices to quantify the humidity content and biomolecule concentration (Blyth et al. , 1996, Lowe, Millington, 1995, Millington et al. , 1996, Spooncer et al. , 1992). Holographic sensors incorporate multilayer Bragg diffraction gratings in functionalized hydrogel matrixes. ...
Analyte-sensitive hydrogels that incorporate optical structures have emerged as sensing platforms for point-of-care diagnostics. The optical properties of the hydrogel sensors can be rationally designed and fabricated through self-assembly, microfabrication or laser writing. The advantages of photonic hydrogel sensors over conventional assay formats include label-free, quantitative, reusable, and continuous measurement capability that can be integrated with equipment-free text or image display. This review explains the operation principles of photonic hydrogel sensors, presents syntheses of stimuli-responsive polymers, and provides an overview of qualitative and quantitative readout technologies. Applications in clinical samples are discussed, and potential future directions are identified.
... alcohol, lactate, glucose, pH, ions, etc. Examples of holographic sensors are reported in literature. Holograms recorded in gelatin by traditional methods have been used for sensing proteases, watersolvent mixtures, alcohol content and humidity [94,[126][127][128][129][130][131][132][133]. Also, in aqueous solutions coupled with biomolecules, cells or organisms expand their capabilities and detection ranges [134][135][136][137][138]. Holograms produced in polymer hydrogels, such as acrylate, acrylamide and vinyl alcohol, have been used for holographic sensing of glucose, lactate, toluene, pH and different types of ions by introducing extra functional groups [25,[139][140][141][142][143][144]. ...
Holographic sensors are photonic layered structures contained in analyte sensitive lms that upon illumination produce monochromatic reflections (?). The present work reports the fabrication of oxygen and ammonia sensors in Nafi on membranes and hydrocarbon and volatile organic compound sensors in poly(dimethylsiloxane) (PDMS) films. A holographic recording technique was developed to suit these materials consisting of the in situ formation of nanoparticles of 18nm average diameter and their subsequent ordered ablation with a 300mJ laser. The wavelength of the monochromatic reflections depends principally on the refractive index of the resulting layers (n) and the separation between them (?). Changes in these parameters are generated by the analyte-sensor interactions and their magnitude can be correlated to the analyte concentration. The strength of these interactions is determined by the thermodynamic properties of the analytes, such as the cohesive energy density (?^2), and this, was coupled with a photonic model for the prediction of the holographic response. After exposure to different concentrations of the analytes, the kinetics of the responses were determined and the lowest detection limits (LDL) established as follows: Hydrocarbons in PDMS holograms 1% (v/v) in 3s for a range of concentrations from 0-100%; ammonia in Nafi on holograms 0.16% in 100s in the 0-12.5% range; the LDL for oxygen sensing could not be determined although the response was recorded down to 12.5% and up to 100% in 100s. Holographic sensors show competitive responses comparable to commercially available gas sensors for biomedical diagnostics and industrial process monitoring because of their facile fabrication and their shared sensing platform allowing multiplexing.
... Holograms can be used as analytical devices to quantify the humidity content and biomolecule concentration (Blyth et al. , 1996, Lowe, Millington, 1995, Millington et al. , 1996, Spooncer et al. , 1992). Holographic sensors incorporate multilayer Bragg diffraction gratings in functionalized hydrogel matrixes. ...
Inkjet printing and patterning strategies have been developed for fabrication of hybrid holographic sensors using zeolite nanocrystals on glass-supported photopolymers. The flexibility of the proposed techniques was demonstrated by fabrication and characterization of two types of holographic sensors. The first type, which is a reversible sensor, is based on a transmission hologram recorded in a hydrophobic MFI-type zeolite doped layer with high sensitivity toward alcohols. In this type of sensor the patterning of the zeolite nanocrystals in the volume of the polymer layer is achieved by holographic recording; the pattern periodicity is in the submicrometer range. The second type of sensor is based on a reflection hologram, and it is produced by inkjet printing of zeolite nanocrystals on photopolymer layer before holographic recording. The resulting localized presence of zeolite nanocrystals in the layer is key for the performance of the sensor. Irreversible humidity sensors based on photopolymer layers doped with hydrophilic EMT-type zeolite are fabricated using the second approach and characterized in a controlled humidity environment. We demonstrate that the inkjet printing approach enables fabrication of a variety of patterns with high precision and uniformity, using zeolite nanocrystals (10-50 nm sizes). Limitations and future directions of this fabrication technique are discussed. (Graph Presented).
... The sensing element is a bead of anion exchange resin formed by derivatizing porous crosslinked polystyrene with a quaternary ammonium salt. Blyth et al. [2] proposed a gelatin holographic diffraction grating sensor, making use of the diffraction color of a gelatin holographic diffraction grating changed as a function of the water content of the solvents. The optode membranes prepared by Hisamoto et al. [3], used so-called multi-information and site-controlled' dyes of the merocyanine type. ...
An optical chemical sensor for determining water content in organic solvents has been developed based on a fluorescent dye, 10-allyl-acridine orange, which is covalently bound to supporting matrix. After chemical modification of the glass slide surface with olefin units, the fluorescent dye is copolymerized with olefin units in the presence of a hydrophilic monomer, 2-hydroxypropyl methacrylate, and a dye-incorporating optode membranes tightly immobilized on the glass surface is thus obtained. The optode membrane was used for the measurement of water content in organic solvents. Being resistant to swelling, the membrane possesses relatively long lifetime and short response and recovering time. The reversibility and reproducibility of the sensor are adequate for practical measurements.
... It is because of these reasons that development of new approaches for the measurement has never stopped during the past few decades. Continuous exploration upon IR spectroscopy, 5,6 potentiometry, 7 solid-phase extraction, 8 Raman spectroscopy, 9 holographic method, 10 flow-injection, 11 absorbance-based film sensors, 12,13 and the recently reported approach of cathodic stripping voltammetry at a gold electrode 14 has existed. These methods, however, are not perfect, and they also suffer from their own limitations: requirement of sophisticated equipment and limited application toward specific solvents. ...
A butterfly-shaped pyrene derivative of cholesterol, namely N,N'-(ethane-1, 2-diyl)-bis(N-(2- (chol-amino)ethyl)pyrene-1-sulfonamide)(ECPS), has been designed and synthesized. Solvent effect studies revealed that in good solvents such as n-hexane, benzene and 1,4-dioxane, the profile of the fluorescence emission of the compound is characterized by pyrene monomer emission, but in poor solvent such as water, the emission is dominated by pyrene excimer emission. Quantitatively speaking, the ratio of the excimer emission to monomer emission changes from 50 to 0 when ECPS is dissolved in water and n-hexane, respectively. In contrast, for a commonly used polarity probe pyrene, the ratio of I3/I1 varies only from ~0.6 to ~1.7, where I3 and I1 stand for the intensities of the fluorescence emission at peak 3 and peak 1, respectively. This value suggests that a more powerful discriminating ability of the new compound in polarity sensing. Furthermore, unlike the main components of the compound, pyrene and cholesterol, its main chain is composed of multiple hydrophilic structures, and it is this structure that makes the emission of the compound in organic solvents sensitive to the presence of water. Accordingly, the applicability of the compound in determination of the trace amount of water in some organic solvents was evaluated. As expected, the detection limit of the compound toward water in acetonitrile reaches 7 ppm, a result never reached before. Furthermore, the fluorescence emission of the compound is also sensitive to viscosity variation. Therefore, it is assumed that ECPS may be used both as a polarity probe and a viscosity probe. On the bases of a series of steady-state and time-resolved fluorescence, as well as dynamic light scattering studies, a structural model was proposed to rationalize the fluorescence behavior of the compound in different solvents and its polarity and viscosity probing performances.
This chapter discusses current developments concerning recent advances and applications of biomolecule‐responsive hydrogels in medicine via emphasizing this research area with novel literature studies. The discussion is categorized into three main types, namely, glucose‐responsive hydrogels, protein‐responsive hydrogel, and nucleic acid‐responsive hydrogels. The chapter describes their potential applications in drug delivery, cell and cancer research, regenerative medicine and biosensor, and presents some problems as well as the new directions on future developments. Enzyme‐responsive hydrogels are used in the fabrication of degradable biomaterials and native extracellular matrices. Although the ribonucleic acid (RNA), deoxyribonucleic acid (DNA), and the natural nucleic acid‐responsive hydrogels provide the advantages of biocompatibility, they are not stable against temperature and enzymatic cleavage. Peptide nucleic acid, serving as a synthetic nucleic acid not only solved these issues but also indicated stronger binding properties than RNA and DNA.
Holographic sensors are an exciting and versatile new addition to the analysts armamentarium which offer a number of advantages over conventional sensor technologies: They are an inexpensive and scalable platform amenable to mass production, configurable in multiple formats, including miniaturization, arrays and free standing flakes, and are able to output the results qualitatively or quantitatively as changes in color, intensity, two- and three-dimensional images and alpha-numeric displays and can be assessed visually and using smartphones. This review describes the basics of holography, how relatively simple holographic sensors were first developed and how the field has developed such that a plethora of key analytes including ions, gases, volatiles, metabolites, drugs, proteins, enzymes, inhibitors and whole cells could be monitored with holograms constructed with novel bespoke hydrophilic and apolar matrices and suitable embedded recognition-response systems. More recent developments such as molecular imprinting, combinatorial chemistry, increased reflectivity, new photopolymer materials, micro array technologies and improved modelling greatly enhance their selectivity, sensitivity and general acceptability. Nevertheless, despite a requirement for further research, this holographic sensor platform is highly versatile and can be configured to create visual or instrumentally monitored responses in discreet or real-time at macro, micro and nano scales.
Herein, a novel type of environment‐sensitive carbon dots (ES‐CDs) has been synthesized via ethanothermal reaction using 1,6‐naphthalenediol as a carbon source and sulfuric acid as a catalyst. The morphology and structure of ES‐CDs are characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT‐IR) and X‐ray photoelectron spectra (XPS). ES‐CDs exhibit green and excitation wavelength independent emission in different solvents. Using the optical response of ES‐CDs towards acetone‐water binary mixtures with different composition, the sensitive detection of solvent polarity is realized based on the inner filter effect (IFE). The ink‐jet printed patterns of ES‐CDs show a blue‐to‐green conversion as exposure to external vapor from hydrogen chloride to ammonia, and enable information to hide assisting with a laser direct writing. We believe that the environment‐sensitive carbon dots developed in this study are potential candidates for solvent sensing and fluorescence anti‐counterfeiting.
Advancements in hybrid sol‐gel technology have provided a new class of holographic materials as photopolymerizable glasses. Recently, a number of photosensitive glass compositions with high dynamic range and high spatial resolution have been reported and their excellent capability for volume holography has been demonstrated. Nevertheless, challenges remain, particularly in relation to the processing time and environmental stability of these materials, that strongly affect the performance and durability of the fabricated holograms. State‐of‐the‐art photopolymerizable glasses possess long curing times (few days) required to achieve thick films, thus limiting the industrial implementation of this technology and its commercial viability. This article presents a novel, fast curing, water‐resistant, photopolymerizable hybrid sol‐gel (PHSG) for holographic applications. Due to introducing an amine‐based modifier that increases the condensation ability of the sol‐gel network, this PHSG overcomes the problem of long curing time and can readily produce thick (up to a few hundred micrometers) layers without cracking and breaking. In addition, this PHSG exhibits excellent water‐resistance, providing stable performance of holographic gratings for up to 400 h of immersion in water. This finding moves photopolymerizable glasses to the next development stage and renders the technology attractive for the mass production of holographic optical elements and their use across a wide number of outdoor applications.
Anthraquinone functional zinc phthalocyanine sensor platform was utilized for ultra-trace amount of water determination in THF and DMF. Using the fluorometric method, the water content in THF was determined with a LOD of 2.27 × 10⁻⁴ M and a response time of 1 s. The sensor is based on the mechanism of aggregation depended on quenching of emission. Although the aggregation is known as an undesirable property in the application of phthalocyanine, this property has been successfully applied in the quantification of water content in THF. By using the shift of the third reduction wave of the sensor, the water content in DMF was measured with a LOD value of 5.64 × 10⁻⁷ M. The voltammetric response mechanism is based on the hydrogen bonding depended shifting of the reduction potential of quinone moiety on phthalocyanine. Redox potentials of phthalocyanine are used as a calibrant for accurate quantification of water content in DMF. Water molecules (n and m) and equilibrium constants (K¹ and K²) for the formation of hydrogen bonding for the first and third reduction processes were calculated as 1.18 (n), 10.4 (m) and 19.3 (K¹), 1.6 × 1011 (K²) M−(m-n), which demonstrated why the third reduction process was chosen to set the calibration plots.
In this work, we report fast and low-cost fluorimetric system for the determination of trace amounts of water in both aprotic and protic organic solvents. The analytical signal of the proposed method is based on the quenching effects of water on the fluorescence emission spectrum of (4, 4′-diamino-4″-methoxytriphenylamine) molecule. It was found that physical interactions such as hydrogen bonding are responsible for the observed quenching effect. The limit of detection values for the determination of water in DMSO, acetonitrile, ethanol and methanol were 0.0727, 0.0636, 0.0761 and 0.0631 (W/W%), respectively. The limit of quantitation values in DMSO, acetonitrile, ethanol and methanol were 0.2734, 0.2546, 0.2540 and 0.2531 (W/W%), respectively. Simplicity, low cost and high speed of the proposed water sensing system make it a valuable candidate to be used in industrial applications such as quality control procedures. In addition, it can be used for the determination of water in redox active solvents such as DMSO, where the standard Karl Fischer method gives problematic results.
Water acts as the solvent for natural biotic and abiotic processes and in many technological contexts. The availability of water to participate in chemical and physical processes is captured by thermodynamic variables which track the energetic state of water such as water activity, water potential, and the chemical potential of water. Our understanding of the energetic state of water in relevant processes is limited by a lack of sensors capable of providing accurate and reliable ex-situ and in-situ measurements of water activity. To address this technology gap, we present applications of a microtensiometer (μTM): a biomimetic microelectromechanical system (MEMS) sensor capable of measuring water activity in liquid, vapor and semi-solid (e.g., hydrogels, cheese) phases. We developed packaging, experimental apparatuses and methodology to enable us to make water activity measurement previously inaccessible to tensiometry. We present measurements in two contexts: 1) a small benchtop unit for ex-situ measurements and 2) a probe format for in-situ measurements. We demonstrate that the μTM can accurately measure water activity in a diversity of complex samples and agrees with chilled mirror hygrometry, an industry standard for water activity measurement.
Novel N-doped green-emitting carbon dots (N-GCDs) that were responsive to various external stimuli and had high quantum yields (QYs) for multifaceted applications were synthesized from β-resorcylic acid and ethylenediamine using a hydrothermal process followed by a reflux method. The QYs of the N-GCDs were in the range of 17.36%–48.4% and were associated with different photoluminescent color emission in different solvents. Interestingly, the as-synthesized N-GCDs exhibited strict solvent polarity-dependent switchability (solvatochromism) and multicolor excitation-wavelength-independent emission in different solvents. Sensing of an analyte based on the switching of the photoluminescence (PL) emission maxima (λ max ) is always preferred over that based on fluorescence quenching to avoid complexity and confusion regarding the initial fluorescence intensity (I 0 ) and thus make the sensing process simple, rapid, ordered, and reliable. The N-GCDs exhibited blue emission in low-polarity organic solvents, but with the increase of the trace water content in the system, the PL emission peak gradually shifted to a higher wavelength (bathochromic shift) at a single-wavelength excitation. Thus, the N-GCDs are sensitive visual probes for the fluorescence detection of the trace water content in organic solvents without sophisticated processes. They also indicate the pH-response behavior. When the pH decreased from 7.6 to 2.4, the fluorescence emission intensity decreased, with a particularly good linear relationship (R ² = 0.990) in the range of 3.8–6.2. Moreover, the polarity-dependent-emission property was observed in the solid state polymer matrices. Multicolor-emissive N-GCD/polymer films were prepared by integrating N-GCDs with the polymer matrices of different polarity, demonstrating the application of carbon dots for solid-state lighting.
A novel composition for a low-toxicity, water-soluble, holographic photopolymer capable of recording bright reflection gratings with diffraction efficiency of up to 50% is reported. The unique combination of two chemical components, namely, a chain transfer agent and a free radical scavenger, is reported to enhance the holographic recording ability of a diacetone acrylamide (DA)-based photopolymer in reflection mode by 3-fold. Characterization of the dependence of diffraction efficiency of the reflection gratings on spatial frequency, recording intensity, exposure energy, and recording wavelength has been carried out for the new low-toxicity material. The use of UV postexposure as a method of improving the stability of the photopolymer-based reflection holograms is reported. The ability of the modified DA photopolymer to record bright Denisyuk holograms which are viewable in different lighting conditions is demonstrated.
Optical devices that reversibly respond to external stimuli can provide fast, quantitative, visual colorimetric readouts in real-time. They may consist of bioactive recognition elements that can transmit the signal through a transducer embedded within the system. Responsive photonic structures may have applications in chemical, biological and physical sensors for medical diagnostics, veterinary screening, environmental monitoring, pharmaceutical bioassays, optomechanical sensing and security applications. This chapter provides an overview of the fabrication of optical devices, and highlights holography as a practical approach for the rapid construction of optical sensors that operate in the visible spectrum and near infrared. It begins with describing the fundamentals of holography and origins of holographic sensors. The chapter also explains the principle of operation of these devices and discusses the design parameters that affect the readouts. The principles of laser light interference during sensor fabrication and photochemical patterning are discussed. Furthermore, computational readout simulations of a generic holographic sensor through a finite element method are demonstrated. Studied design parameters include optical effects due to lattice spacing, nanoparticle (NP) size and concentration, number of stacks, their distribution, and lattice deficiencies within the sensor. Computational simulations allow designing holographic sensors with predictive optical characteristics.
The concept of using a simple reflection hologram as both an analyte-sensitive polymer matrix and an optical interrogation and reporting transducer to generate inexpensive, mass-producible biochemical sensors is descibed. The system is exemplified with holographic sensors for water and enzyme activity and the value of rationally designed holographic matrices promoted.
A study is conducted to establish a theoretical framework for holographic sensing, define terminology in holographic sensing, demonstrate how holographic sensing fits into the existing body of sensing mechanisms, and highlight gaps in the previous research. The study aims at integrating and summarizing what is known in holographic sensing, identifying where the major questions remain, and enabling others in the field to be able to replicate the existing experimental setups for fabricating and interrogating holographic sensors. It scope consists of the latest techniques for producing holographic sensors, and their potential applications in research, industrial settings, and among the public. The study also discusses the need for optical sensing, the fundamentals of holography, the origins of holographic sensors, holographic media and materials, fabrication techniques, sensing capabilities, readouts, and relevant theoretical studies.
Colourimetric sensors and indicators are widely used because of their low cost and simplicity. A significant challenge associated with the design of this type of device is that the sensing mechanism must be simultaneously optimised for the sensitivity of the response and a visually perceptible colour change. Structural colour, derived from coherent scattering rather than molecular absorption, is a promising route to colourimetric sensor design because colour shifts are tied to changes in one of many physical properties of a material, rather than a specific chemical process. This Feature Article presents an overview of the development of low-cost sensors and indicators that exploit structural colour. Building upon recent advances in structurally adaptive materials design, structural colour sensors have been developed for a wide variety of previously inaccessible physical (e.g. temperature, strain, electric fields) and chemical stimuli (e.g. small organic molecules, charged species, biomacromolecules and metabolites). These devices, often exceeding the state of the art in performance, simplicity or both, have bright prospects for market impact in areas such as environmental monitoring, workplace hazard identification, threat detection, and point-of-care diagnostics. Finding the ideal balance between performance (e.g. sensitivity, specificity, reproducibility, etc.) and simplicity (e.g. colourimetric vs. spectroscopic readout) will be one of the most critical elements in the further development of structural colour sensors. This balance should be driven largely by the market demands and competing technologies.
Hierarchical structuring of materials offers exciting opportunities to construct functional devices that exploit the ordering at different length scales to impart key functional properties. Herein, multiple processes are combined to create complex materials organized at the molecular, nano, and microscales for selective detection of testosterone by label‐free opto‐chemical sensing. Molecular imprinting is used to construct molecular scale analyte‐selective cavities. Microphase separation produces a porous polymer film within which sensitized silver halide nanocolloids are dispersed by a process of infusion and controled precipitation, then converted to periodic layers of silver nanoparticles by holographic patterning followed by chemical development. Testosterone binding is followed via wavelength changes of the holographic reflection peak as a function of testosterone concentration and incubation time. Polymer cross‐linking and film porosity are optimized with respect to the needs of both molecular recognition and hologram quality. The silver halide infusion step does not destroy the molecular selectivity of the molecularly imprinted polymers (MIP). Selective, label‐free sensing of testosterone is possible at concentrations down to 1 μm. The approach is generic and should be applicable to many types of molecules and conventional MIP formulations, individually or in multiplexed arrays. Reflection holograms are fabricated in a molecularly imprinted polymer (MIP) film by periodic photoreduction of silver‐halides using a standing wave originating from two interfering laser beams. The MIP‐based holographic film is used as a label‐free opto‐chemical sensor for the specific detection of testosterone.
Here we report the fabrication and characterization of photonic structures in Nafion membranes sensitive to ammonia in the 0.19% to 12.5% concentration range. The photonic structures were recorded by laser ablation of silver nanoparticles synthesized in situ by diffusion. The particles showed an average diameter of 17nm with a narrow size distribution. After ablation, the nanoparticles generated a diffracting structure giving colorful reflections at defined peak wavelengths. The reflectivity at these wavelengths was directly proportional to concentration after ammonia exposure. The concentration range that can be measured with these membranes encompasses the fatal limit of exposure and the lower flammable limit of gaseous ammonia. Interrogation by reflection spectroscopy makes them suitable for remote sensing and real-time monitoring of gases.
Poly[1-phenyl-2-(p-trimethylsilyl) phenylacetylene] (PTMSDPA) with microporous and intramolecular stack structures in the bulk solid state can be used as a fluorescent water sensor for on-line real-time monitoring. A solubility parameter (delta) of PTMSDPA is estimated from the degree of swelling and solvation of the polymer in various organic solvents. When the PTMSDPA film is immersed in organic solvents with a range of d values, the fluorescence (FL) intensity increases significantly due to swelling, whereas the FL intensity decreases gradually upon the addition of water in the solvents due to deswelling. The FL decreasing ratios are quite different according to the solvents. The hydrogen-bonding strength of the solvents toward water plays a key role in determining the FL responsivity of the polymer. The FL response is very specific to water in organic solvents. The PTMSDPA film responds quickly to water within several seconds. A fluidic channel of which the inner wall is coated with PTMSDPA is fabricated to demonstrate the on-line, real-time monitoring of water in fl owing solvents. The development of more facile and convenient devices, such as microfluidic lab-on-chip and optode sensors, using PTMSDPA as an active layer will advance practical applications.
This article describes an optical chemical sensor based on a fluorescent dye 1-allyloxy-4-hydroxyanthracene-9, 10-dione (AHD) with terminal double bond, which is covalently bonded to quartz glass plate surface treated with a silanizing agent to prevent its leakage. The purpose of this work was to characterize and optimize the sensor for determining the water content in the acetone organic solvent. The sensor is resistant to swelling; the membrane possesses relatively long lifetime, short response and recovering time. The reversibility and reproducibility of the sensor are adequate for practical measurements.
Ultrasonic decomposition of (4-Chloro-2-methyl phenoxy)acetic acid (MCPA) in aqueous solution was performed at a frequency of 500 kHz under an argon atmosphere. We investigated the mechanism of ultrasonic degradation of MCPA by observing the decomposition time evolution of MCPA and the behaviors of chloride ion, TOC (total organic carbon), and byproducts formed through the ultrasonic degradation process of MCPA. At a constant power of 21.4 W, MCPA was completely decomposed after 180-min sonication and the ultrasonic decomposition of MCPA followed a pseudo first order reaction kinetics. Much of its chlorine atoms were mineralized in solution after 360-min sonication. On the other hand, it was difficult to achieve complete mineralization of carbon, and about 60% of the initial TOC remained in aqueous solution after 360 min. Based on the GC-MS analysis, byproducts such as 4-chloro-2-methyl phenol (CMP), 4-chlorocathecol, methylhydroquinone, cresol, acetic acid and formic acid were detected in the aqueous solution to which ultrasonic irradiation was applied. The CMP concentration increased during the early period of irradiation reaching a maximum concentration at about 60 min followed by its decrease until CMP became undetectable at 180 min. Decomposition of MCPA by ultrasonic irradiation resulted in the increase in acetic acid concentration until 120 min, after which no further increase was observed. Conversely, formic acid concentration was observed to increase only during the duration of sonication experiment.
A derivative of benzothioxanthene, N-(2-methacryloxyethyl)benzo[k,l] thioxanthene-3,4-dicarboximide (MBTD), was used as a fluorescent indicator for determination of water content in organic solvents. MBTD was photocopolymerization-immobilized on a glass surface. The prepared sensor system possesses relatively long lifetime, short response, and recovering time. The reversibility and reproducibility are also adequate for practical measurement.
Holographic sensors for monitoring ionic strength have been fabricated from charged sulphonate and quaternary ammonium monomers, incorporated into thin, polymeric hydrogel films which were transformed into volume holograms. The diffraction wavelength or reflected colour of the holograms was used to characterise their swelling or de-swelling behaviour as a function of ionic strength in various media. The effects of co-monomer structure, buffer composition, ion composition, pH and temperature were evaluated, whilst the reversibility and reproducibility of the sensor was also assessed. An acrylamide-based hologram containing equal molar amounts of negatively and positively charged monomers was shown to be able to quantify ionic strength independent of the identity of the ionic species present in the test solution. The sensor was fully reversible, free of hysteresis and exhibited little response to pH between 3 and 9 and temperature within the range 20–45°C. The system was successfully used to quantify the ionic strength of milk solutions, which contain a complex mixture of ions and biological components.
A simple liquid-phase alcohol sensor based on a reflection hologram distributed throughout the volume of a cross-linked poly(hydroxyethyl methacrylate) film is described. The sensor is interrogated optically through the back of the film, by measuring the peak wavelength of the narrow-band reflection spectrum when the hologram is illuminated with white light. This procedure makes it possible to measure thickness changes in the film with great precision. The presence of alcohol in the sample medium causes the polymer film to swell in a concentration-dependent manner, whence the alcohol content can be determined by measurement of the wavelength of the reflected spectral peak. The sensor exhibits a wide dynamic range, which can easily be tuned for specific applications, and is unaffected by highly colored and turbid samples, since the light path does not pass through the sample. The sensor is relatively insensitive to pH in the range 3−6.5 and is highly stable, both in use and in storage. The performance of the sensor was demonstrated by measuring the alcohol contents of a wide range of alcoholic beverages such as wines and beers, with no sample pretreatment. Most alcohol concentrations were determined to be within approximately ±0.3 vol % of their stated values.
IntroductionSRP Architectures for Biosensor ApplicationsMechanisms of ResponseSensing and Transduction MechanismsLimitations and ChallengesConclusion and OutlookAcknowledgementsReferences
Photonic crystal (PC) based bioassay techniques have many advantages in sensitive biomolecular screening, label-free detection, real-time monitoring of enzyme activity, cell morphology research, and so on. This study provides an overall survey of the basic concepts and up-to-date research concerning the very promising use of PC materials for bioassays. It includes the design and application of PC films, PC microcarriers, PC fibers, and PC optofluidics for fluorescence enhancement or label-free bioassays. Emphasis is given to the description of the functional structures of different PC materials and their respective sensing mechanisms. Examples of detecting various types of analytes are presented. This article promotes communication among chemistry, biology, medicine, pharmacy, and material science.
The holographic sensor is actually a thick hologram plane mirror about the size of a square centimeter. By placing such plate in a special cell containing 24 cells of 2 mm diameter each of which contains 50 ul of fluid being analyzed, we can create chips for the simultaneous determination of several tens of samples.
The use of holographic elements as biochemical sensors is suggested and exemplified with a device for monitoring protease activity. A quantitative optical response of a holographic element constructed in gelatin is demonstrated for a range of trypsin concentrations down to 25 nM with a response time within 20 min, These data demonstrate the principle for a general protease sensor which has particular relevance to the measurement of trypsin activity below normal physiological duodenal levels. The holographic devices respond with a change in wavelength (color) and/or a change in brightness. The possibility of creating a family of specific, reagentless, low-cost holographic sensors with direct visual output is outlined.
It has been shown that the rate constant for the Karl Fischer reaction in methanolic reagents buffered with pyridine or imidazole at pH 6.6 is independent of the base used. Reagents buffered with imidazole at pH>7 showed a different behavior than reported previously for reagents buffered with this or other buffer substances. The reaction rate constant in the pH range 7-10 was found to increase with the square of the nonprotonated imidazole concentration in the reagent. The reaction rate constant, k3, in a 2 mol/L imidazole reagent was found to be as high as 81 000 ± 1400 L2mol-2s-1. Using a reagent prepared from 4 mol/L imidazole, 0.6 mol/L SO2, 0.05 mol/L I2, and 0.15 mol/L KI, coulometric titration of 12.7 μg of water could be performed in less than 1 min with the concentration of iodine at the end point as low as 5 × 10-6 mol/L.
General rules for the optimization of different biocatalytic systems in various types of media containing organic solvents are derived by combining data from the literature, and the logarithm of the partition coefficient, log P, as a quantitative measure of solvent polarity. (1) Biocatalysis in organic solvents is low in polar solvents having a log P < 2, is moderate in solvents having a log P between 2 and 4, and is high in a polar solvents having a log P > 4. It was found that this correlation between polarity and activity parallels the ability of organic solvents to distort the essential water layer that stabilizes the biocatalysts. (2) Further optimization of biocatalysis in organic solvents is achieved when the polarity of the microenvironment of the biocatalyst (log P(i)) and the continuous organic phase (log P(cph)) is tuned to the polarities of both the substrate (log P(s)) and the product (log P(p)) according to the following rules: |log P(i) - log P(s)| and |log P(cph) - log P(p)| should be minimal and |log P(cph) - log P(s)| and |log P(i) - log P(p)| should be maximal, with the exception that in the case of substrate inhibition log P(i), should be optimized with respect to log P(s) In addition to these simple optimization rules, the future developments of biocatalysis in organic solvents are discussed.