Dielectric Constant Measurements Research Articles

Degradation of anti-rust oil film in a simulated coastal atmosphere: Inhibition mechanism and in-situ monitoring

Anti-rust oils (ARO) are widely used to inhibit atmospheric corrosion of metal structures, but their degradation mechanisms are unclear, particularly in coastal environments. In this work, we first prepared a kind of ARO made of sodium petroleum sulfonate (SPS) and white oil, then coated the ARO on a mild steel plate to investigate its deterioration process beneath saline water droplets by Quartz crystal microbalance (QCM) and electrochemical mapping techniques. It shows that the SPS concentration is crucial to the ARO inhibition property. When the SPS content is lower than its critical micelle concentration (CMC), saline droplets may intrude the barrier formed by the nonpolar paraffin groups of SPS and then adsorb on the steel surface, resulting in localised corrosion. However, once the SPS content exceeds its CMC, the saline droplets will be emulsified and captured in the oil phase by the reverse micelle effect, thus inhibiting the corrosion of steel substrates. Moreover, the atmospheric corrosion rate of mild steel obeys a power decaying under ARO film. Finally, a capacitive sensor was invented to evaluate the degree of degradation of ARO in situ by dielectric constant measurement.

Dielectric And Mechanical Properties Of PLA-Carbon Composites

This study focuses on the development and characterization of Carbon-based Polylactide (PLA) composites for 3D printer filaments. The aim is to enhance the electrical and mechanical properties of PLA by incorporating recovered carbon black (RCB) in different mesh sizes (500, 1000, 1500, and 2000 mesh). Electrical impedance spectroscopy and dielectric constant measurements were performed to investigate the electrical properties of the composites. Results showed that the addition of RCB increased the dielectric constant, with values ranging from 2.5 to 7.1, indicating improved electrical performance. Scanning electron microscopy (SEM) analysis revealed the dispersion of carbon particles within the composites, enhancing their electrical conductivity. The effect of RCB particle size on electrical properties was also explored, with smaller particle sizes (2000 mesh) resulting in the highest conductivity of 6.2 S/m. Tensile testing demonstrated that the addition of RCB increases the tensile strength of PLA, with values ranging from 28.6 MPa to 47.2 MPa, and the elastic modulus, ranging from 832 MPa to 1.56 GPa, depending on the mesh size. The optimal combination of RCB content and mesh size resulted in a composite with a tensile strength of 43.8 MPa. Overall, this research provides insights into the development of Carbon-based PLA composites with improved electrical and mechanical properties.

Breast Cancer-Related Lymphedema Assessed via Tissue Dielectric Constant Measurements.

This review describes the use of tissue dielectric constant (TDC) measurements mainly in the assessment of breast cancer-related lymphedema (BCRL). PubMed, Web of Science, and EMBASE databases were initially searched using criteria that included the terms "dielectric" and "lymphedema." The initial search yielded a total of 131 titles. After removing studies not focused on upper extremity lymphedema, 56 articles remained. These articles, together withrelevant articles from their bibliographies, formed the basis of the review. The findings show the potential utility and applications of TDC measurements to help detect and track BCRL, whether present in limbs, breasts, or trunks. It is reported as a non-invasive, simple-to-use method, with each measurement requiring less than 10 seconds, suggesting its practicality and useability as an in-office or in-clinic screening and tracking method. Although there are various ways to quantitatively evaluate lymphedema, most, if not all, are restricted to measurements on limbs. Thus, one significant advantage of the TDC approach is that almost any local region of interest can be effectively measured and tracked, which, for BCRL, could include specific regions of arms or hands, breasts, and truncal areas.

Design of a Transformer Oil Viscosity, Density, and Dielectric Constant Simultaneous Measurement System Based on a Quartz Tuning Fork.

Transformer oil, crucial for transformer and power system safety, demands effective monitoring. Aiming to address the problems of expensive and bulky equipment, poor real-time performance, and single parameter detection of traditional measurement methods, this study proposes a quartz tuning fork-based simultaneous measurement system for online monitoring of the density, viscosity, and dielectric constant of transformer oil. Based on the Butterworth-Van Dyke quartz tuning fork equivalent circuit model, a working mechanism of transformer oil density, viscosity, and dielectric constant was analyzed, and a measurement model for oil samples was obtained. A miniaturized simultaneous measurement system was designed based on a dedicated chip for vector current-voltage impedance analysis for data acquisition and a Savitzky-Golay filter for data filtering. A transformer oil test platform was built to verify the simultaneous measurement system. The results showed that the system has good repeatability, and the measurement errors of density, viscosity, and dielectric constant are lower than 2.00%, 5.50%, and 3.20%, respectively. The online and offline results showed that the system meets the requirements of the condition maintenance system for online monitoring accuracy and real-time detection.

Structural, morphological, electrical, and dielectric properties of Na2Cu5(Si2O7)2 for ASSIBs.

Solid inorganic electrolyte materials are fundamental components for constructing all-solid-state sodium-ion batteries. These solid electrolytes offer considerable benefits related to safety, electrochemical performance, and mechanical stability in comparison to liquid organic electrolyte systems. This study investigates the sodium ion conduction mechanism and relaxation kinetics in the sorosilicate material Na2Cu5(Si2O7)2, a potential solid electrolyte, using impedance spectroscopy. Analysis of the DC conductivity data demonstrates that sodium ion mobility follows Arrhenius behavior with a thermal activation energy barrier of 1.21 eV. This work highlights the importance of carefully choosing an appropriate equivalent circuit model to extract DC conductivity parameters from impedance data, given the contributions from both grain and grain boundary effects. Analysis of the AC conductivity and dielectric constant as a function of frequency and temperature demonstrates that ionic conduction takes place in this material through a process in which charge carriers overcome correlated energy barriers, known as correlated barrier hopping. The neutron diffraction patterns were analyzed using soft bond valence sum (BVS) techniques to map the possible ionic conduction pathways within the unit cell. Examination of the data points to obstructions in the sodium ion diffusion routes along the a-axis and diagonal of the bc plane within the triclinic unit cell. These bottlenecks likely contribute to the high activation energy and correspondingly low ionic conductivity observed. Analysis of dielectric properties by modulus verified that the ionic conduction relaxation phenomena exhibit thermal activation and a distribution of relaxation times. In summary, this work elucidates the microscopic ionic conduction mechanism in Na2Cu5(Si2O7)2 through extensive analysis encompassing DC/AC conductivity, electric modulus, and dielectric constant measurements. The insights gained into the ionic conduction mechanism will aid in engineering optimized ionic conductor materials for battery technologies.

Exploring the possibilities of lead-free 0.98NaNbO3-0.02BiSmKZrO3 for electrical and optical applications using solid-state method

A new lead-free ceramic materials 0.98NaNbO3 - 0.02 (Bi(1-x)Smx)0.5K0·5ZrO3, are developed with varying levels of x (mole) (x = 0.01, 0.02, 0.03, and 0.04). The conventional sintering process involves adjusting the ratio of the constituent elements to optimize the material's properties. This results enhanced electrical conductivity and improved optical properties. Our findings show that the material exhibits an orthorhombic phase at x (mole) levels between 0.01 and 0.04. The FESEM and TEM analysis provided detailed information about the surface morphology and internal structure of the NaNbO3 ceramic materials. Additionally, the UV–Vis absorption spectra indicated that the band-gap range of 3.3 eV (± 0.04) (at x = 0.01–0.04) makes these materials suitable for various optoelectronic applications Furthermore, the luminescence behaviors of Sm3+ doped NaNbO3 materials were found to be influenced by the co-doping of Bi3+. Additionally, the dielectric constant (εr) and dielectric loss (tan δ) measurements indicated that the material undergoes two phase transitions from antiferroelectric to paraelectric within a temperature range of 120–250 °C. The investigation also compared the material's electric features, such as piezoelectricity and ferroelectricity, with its leakage current. The results showed that the co-doping of Bi3+ not only influenced the luminescence behaviors but also had an impact on the material's electrical properties. The synthesized proposed system 0.98 NaNbO3 - 0.02BiSmKZrO3 material also demonstrates excellent optical properties, with a high color purity of 80–81 % at x-0.02 under a 407 nm excitation wavelength. Additionally, the estimated color coordinates of the material fall within the reddish-orange domain, further enhancing its visual appeal.

Mineral composition, crystallinity and dielectric evaluation of Bamboo Salt, Himalaya Salt, and Ba’kelalan salt content

The mineral composition, crystallinity, and dielectric properties of salts can provide valuable insights into the quality and suitability of different types of salt for various applications. In this study, comprehensive analysis of the X-Ray Diffraction (XRD), X-ray fluorescence (XRF) and dielectric analysis of the Ba'kelalan salt, Himalaya salt and Bamboo salt have been investigated. The mineral composition of these salts, encompassing vital elements such as iodine and other trace minerals, significantly influences the salt's nutritional profile and overall excellence. Nonetheless, gauging the dispersion and density of these minerals poses difficulties due to conventional techniques that can be arduous, damaging, and expensive. Sample preparation is carried out before conducting X-ray diffraction (XRD), X-ray fluorescence (XRF), and dielectric analysis. XRD measurements are performed using the Bruker D2 Phaser to identify crystalline material phases. XRD operates on the principle of constructive X-ray interference within crystalline samples. For elemental analysis across a broad spectrum of materials, XRF is employed. Elemental peaks are scanned, starting from the lowest to the highest angle of incidence. The X-ray intensity at characteristic peaks is compared to the standard series. Dielectric spectroscopy analysis examines the dielectric behaviour of Ba'kelalan salt, Himalaya salt, and Bamboo salt. The setup involves a vector network analyser (VNA) paired with an open-ended coaxial probe, utilizing the microwave method. This approach ensures rapid, efficient, and non-destructive measurements of dielectric constants (ε′) and loss factors (ε”). The dielectric permittivity spectra are acquired within the frequency range of 4 GHz–20 GHz. ε′ of these salts increase with frequency. Meanwhile, ε” seem varies insignificantly over frequency. Mineral contents and crystallinity are the crucial factors lead to these responses. Based on the study, the quality and suitability of the selected salts for specific applications can be determined by considering their mineral composition, crystallinity, and dielectric properties in the context of the intended use. This gives an insight for some applications that may benefit from certain minerals or crystalline structures, others may require specific dielectric properties for effective use. Therefore, understanding these properties allows for decision-making in choosing the right type of salt for a given purpose, whether it's for foods, medical, industrial, healthcare, and technological applications.

Medical Applications of Skin Tissue Dielectric Constant Measurements.

Tissue dielectric constant (TDC) values assess certain skin properties that are dependent on multiple factors but mainly on the relative amount of water content within a locally measured tissue volume. Because of the non-invasive nature of these measurements and their ease of use, the method has been widely used in various medically related applications. The goal of this paper was to review and describe the uses and findings of such TDC measurements, considering and including the wide array of medical applications. The review is in part based on information derived from an analysis of published material obtained via literature searches of four major electronic databases and, in part, based on the author's experience with the TDC measurement methods and their various applications and his professional experiences. The databases searched were PubMed, Web of Science, EMBASE, and CINAHL Complete. Based on the initial search criteria, a total of 1257 titles were identified. After removing duplicates and filtering according to relevancy, 160 remained for detailed further review. In some cases, the bibliography of these retrieved articles provided additional sources. The findings demonstrate multiple research and medical uses and applications of TDC measurements, focusing on detecting and quantifying localized edema and lymphedema in multiple target sites. These include the upper and lower extremities, breasts, and trunk as regions involved in medical conditions causing lymphedema. In addition, the findings suggest that TDC evaluations are a convenient, non-invasive method to study and evaluate other conditions impacting skin, including diabetes mellitus and skin wounds or ulcers. Its ability to detect aspects of tissue changes simply and rapidly at almost any anatomical location makes it a useful tool for investigating multiple dermatological conditions and their treatment as future applications of this method.

Dielectric and structural properties of double-sintered (Na1-xKx)NbO3, (0.460 ≤ x ≤ 0.485) ceramics

Ceramic samples of Na1-xKxNbO3, (0.460 ≤ x ≤ 0.485) were prepared by using the double sintering solid-state reaction method. The grain size and porosity were found to vary with composition. The dielectric constant of the material phase was obtained from the measured dielectric constant of the prepared ceramic pellets by applying porosity correction. Among the prepared compositions, the dielectric constant was observed to be minimum for x = 0.475. The temperature variation of the dielectric constant and lattice parameters was measured for the samples with x = 0.475, in the range from room temperature (RT) to 500 °C. Three distinct phase transitions, monoclinic to tetragonal, at about 205 °C; tetragonal to tetragonal, at about 410 °C; and tetragonal to cubic, at 460 °C, were observed from the dielectric constant and high-temperature X-ray diffraction (HT-XRD) measurements of the prepared compositions.

Biomass fly ash as nanofiller to improve the dielectric properties of low-density polyethylene for possible high-voltage applications

Flexible capacitive energy storage applications require polymer nanocomposites with high dielectric properties, which can be accomplished by addition of inorganic nanofillers to the polymer matrix. Low-density polyethylene (LDPE), known for its good dielectric characteristics and wide use in electrical insulation have been investigated for the desired applications. However, the improvement of its breakdown strength still continues with the use of various nanomaterials employed as nanofillers. In this study, a waste-derived material known as biomass fly ash (BFA) as a nanofiller to improve the dielectric properties of LDPE has been explored. BFA exhibits versatility in its composition with various metal oxides, making it an attractive choice as a nanofiller. The BFA-LDPE sheets were prepared using a conventional solvent mixing and subsequent hot-pressing process, incorporating BFA loadings ranging from 1 % to 4 wt%. The effects of different BFA loadings were carefully examined, and the synthesized nanocomposites were extensively characterized using various characterization methods, such as XRD, SEM, FTIR, TGA and dielectric constant measurements, to investigate the crystallographic properties, morphology, chemical composition, and thermal stability. Among all the nanocomposites, 4 wt%BFA-LDPE exhibited the highest dielectric constant, with a value of 11.58, compared to simple LDPE that had a dielectric constant of 8.33. This improvement is ascribed to the synergistic effects of different inorganic metal oxides (SiO2, MgO, and Fe2O3) present in BFA. The results showed a significant enhancement in dielectric properties, indicating that the waste-derived BFA can be purposefully applied as an effective nanofiller in the LDPE-based composites with even less than 4% loading for electrical insulating applications in future studies.

3D Imaging and Quantitative Subsurface Dielectric Constant Measurement Using Peak Force Kelvin Probe Force Microscopy

AbstractNoninvasive and depth‐sensitive measurements of dielectric properties are becoming of great interest in advanced and complex nanostructured architectures. Here, a straightforward parallel approach applicable in peak force Kelvin probe force microscopy for a 3D measurement of dielectric constants at the nanoscale is demonstrated. The proposed approach features a simultaneous measurement of the mechanical, electrical, and depth‐dependent dielectric properties applied to embedded nanostructures. The findings provide initial elements for further development of experimental dielectric nano‐tomography methods for characterizing buried and embedded systems and dielectric interfaces.

To study the synthesis and characterization of SrO–MgO–SiO2 system in biological and dielectric applications

Ternary ceramic samples comprising SrO–MgO–SiO2 with varying element concentrations were synthesized using the solid-state method and sintered at 800°C. To characterize the properties of the samples, several analysis techniques were employed. X-ray Diffraction (XRD) was utilized for structural analysis, FTIR spectroscopy was used to identify bonds, SEM provided morphological analysis, biocompatibility was assessed through Vitro testing, microhardness was evaluated using Vickers testing, and dielectric analysis was performed to investigate electrical properties. The XRD spectra confirmed the presence of a ternary phase known as Magnesium Strontium Di-silicate [MgSr2Si2O7], with no impurity peaks detected. FTIR spectroscopy indicated the formation of Magnesium silicate, displaying vibrational bands corresponding to SiO4 and MgO, which further confirmed the existence of MgSr2Si2O7 in the samples. The Vitro test results revealed that all samples exhibited biocompatible behavior, with moderate pH and weight loss. SEM images provided insights into the morphology of the system and confirmed the development of an appetite layer on the sample surfaces. The particle size of the samples was measured to be approximately 116.48±9 nm. Vickers hardness testing yielded microhardness values ranging from 378.1 to 400.2 HV. Dielectric constant measurements demonstrated that the AC conductivity of the SrO–MgO–SiO2 system increased as the percentage of Mg doping increased.

Test-Retest Reliability of a Protocol for Assessment of Local Tissue Water in the Head and Neck Area.

Background: Lymphedema measurement is vital to select appropriate treatment and monitor its progress. Quantifying lymphedema in the head and neck area is challenging. The use of tissue dielectric constant (TDC) measurements has shown promising results in other body areas. This study aims to determine the test-retest reliability of a TDC measurement protocol developed for the head and neck area. Methods and Results: A detailed measurement protocol, including eight measurement points per side, was developed. Subsequently, the reliability of the protocol was tested in a sample of healthy participants (n = 50, 28 males). Using the LymphScanner (Delfin, Finland), participants were subjected to two measurement sessions. Each measurement point was measured three times per session. Test-retest reliability for each point was evaluated using intraclass correlation coefficients (ICCs) and standard errors of measurement (SEMs). Using the average of three measurements, reliability was good to excellent for all points (ICCs 0.81-0.95), with small measurement errors (SEMs 1.51-2.86). The reliability of a single measurement was moderate to excellent for all measurement points (ICCs 0.58-0.87), with larger, but still small, measurement errors (SEMs 1.65-3.39). When using single measurements, the lowest ICCs were found for the temporal (left 0.73 and right 0.67) and submandibular (left 0.58 and right 0.77) locations. Conclusion: Measurements with the LymphScanner, taken according to the developed protocol, are reliable in healthy participants. We recommend using the average of three measurements to optimize reliability. The protocol is fit for further testing in patient populations and for determining normal values in a larger scale study with healthy subjects.

Phase transitions and magnetoelectricity in Fe implanted TlInS2 and TlGaSe2 ferroelectric crystals

The dielectric constant measurements of Fe implanted TlInS2 and TlGaSe2 crystals without and under application of constant magnetic field have been performed. It has been observed that the implantation of the crystals with Fe ions caused the formation of ferromagnetic layer in the irradiated region, which leads to considerable shifts of the successive incommensurate and commensurate phase transitions to high temperatures in the heating regime. Remarkable shifts of the phase transition temperatures back to the low temperature region on heating of the samples were observed on applying the magnetic field perpendicularly to the implanted surface. None changes of the phase transition temperature points on measurements of the samples have been observed in cooling regime. The obtained results are interpreted as magnetodielectric effects that resulted from magnetoelectric coupling between ferromagnetic and ferroelectric constituents of the composite structure.

Dielectric constant measurement sensitivity in electrostatic force and force gradient microscopy-based modes

Understanding the nanoscale electrostatic interaction between a conductive atomic force microscopy (AFM) probe and a dielectric film is central to the operation of various nanoscale dielectric microscopies and determination of dielectric properties of the film. There is no simple analytical description of the electrostatic interaction generated in the confined probe-sample geometry for neither static nor dynamic AFM modes used in dielectric measurements. An accurate description of the involved physics is obtained only by means of a finite element analysis modeling of the system. However, the alternative to using the numerical analysis is not very popular due to being slower and requiring relatively high computation resources. In this work, we revised the contributions from different parts of the AFM probe to the probe-sample capacitance by both analytical and numerical methods. We tried to reconciliate the two approaches and observed the differences as a function of geometry and material parameters. Under various noise levels, the efficiency of an analytical model was tested against a finite element analysis that captures in detail the electrostatic interaction in AFM-based dielectric measurements. The investigation was performed in both spectroscopic force-distance curves and constant height scans with measurements for deflection and frequency of the AFM probe. The obtained measurement sensitivities are relevant in selecting the optimal scanning mode and its operational parameters for a given film thicknesses and dielectric constants but also show the critical role of the numerical analysis to the correct interpretation of the measurements.

OPTICAL AND DIELECTRIC PROPERTIES OF EPOXY RESIN FILLED WITH TITANIUM DIOXIDE PARTICLES

This work studies the electrical properties for pure epoxy, and epoxy with (0, 1, 1.5, 2 wt%) titanium dioxide powder composites. The effects of titanium dioxide contents on optical and dielectrically properties of the epoxy/ titanium dioxide have investigated by several techniques were used to characterize the epoxy/titanium dioxide: UV-visible spectrophotometer reveals a new absorption band in the wavelength range (350-600) nm. The findings of this investigation show that when the proportion of titanium dioxide added increases, the absorbance increases which are ascribed to interchain interaction. The absorption coefficient (α), extinction coefficient (k), refractive index (n), the real and imaginary permittivity (εr, εi), and energy gap (Eg) of epoxy/titanium dioxide samples were effectively determined from the recorded data optical transmission technique. In addition, these epoxy have been examined in the wavenumber range (4000-500 cm-1) using an FT-IR spectrometer and also a dielectric constant measurement. The thickness of all the samples is 1.2 mm ± 0.1 mm.

Broadband Measurements of Soil Complex Permittivity.

Agriculture is a major consumer of freshwater and is often associated with low water productivity. To prevent drought, farmers tend to over-irrigate, putting a strain on the ever-depleting groundwater resources. To improve modern agricultural techniques and conserve water, quick and accurate estimates of soil water content (SWC) should be made, and irrigation timed correctly in order to optimize crop yield and water use. In this study, soil samples common to the Maltese Islands having different clay, sand, and silt contents were, primarily, investigated to: (a) deduce whether the dielectric constant can be considered as a viable indicator of the SWC for the soils of Malta; (b) determine how soil compaction affects the dielectric constant measurements; and (c) to create calibration curves to directly relate the dielectric constant and the SWC for two different soil types of low and high density. The measurements, which were carried out in the X-band, were facilitated by an experimental setup comprising a two-port Vector Network Analyzer (VNA) connected to a rectangular waveguide system. From data analysis, it was found that for each soil investigated, the dielectric constant increases notably with an increase in both density and SWC. Our findings are expected to aid in future numerical analysis and simulations aimed at developing low-cost, minimally invasive Microwave (MW) systems for localized SWC sensing, and hence, in agricultural water conservation. However, it should be noted that a statistically significant relationship between soil texture and the dielectric constant could not be determined at this stage.

Flexible microwave sensor films based on nested-complementary split ring resonator for liquid dielectric constant detection

This paper proposes a flexible double-sided attached microwave sensor film for real-time measurement of the liquid dielectric constant, and proposes a nested-complementary split ring resonator（NCSRR）structure with high sensitivity and quality factor values that is based on the structure evolution of a complementary split ring resonator（CSRR）. The sensor films are composed of a ground film with an NCSRR structure and a U-shaped microstrip line film. By taking a borosilicate glass beaker and a polypropylene beaker as examples, two types of microwave sensors are formed by attaching films to both sides of the beakers. Lubricating oil with 0%− 25% water content is added to the beakers separately, and the dielectric constants of the mixture are characterized nondestructively by the transmission coefficient (S21) of the device. According to the mathematical model established from the measurement results, the resonant frequencies of both sensors are linearly and negatively correlated with the dielectric constant of the liquid to be measured, which proves that the sensor film can be attached to a substrate with arbitrary curvature to form a microwave resonant sensor.

Effect of Gamma Irradiation on Dielectric and AC Conductivity Studies of Bismuth Borate Glasses Doped with V2O5

Objectives: To study gamma ray irradiation effect on dielectric and AC conductivity of V2O5 doped bismuth borate glasses designed with the compositions 50B2O3-(50-X)Bi2O3-XV2O5 where, X = 0, 0.2, 0.4, 0.6, 0.8, 1.0 and establishing the conduction mechanism. Methods: Glasses were synthesized by traditional melt quenching technique at 1323K. The prepared samples were subjected to annealing at 623K, which helps to remove strain in the samples. Absence of crystalline phases in the samples was confirmed by X-ray diffraction studies. An independent measurement of dielectric constant, dielectric loss and AC conductivity was carried out for temperature range from 300Kto 493K by impedance analyzer. Findings: The physical properties of glass were achieved by studying the density and the molar volume. Dielectric constant (e ’) and dielectric loss (e ”) were measured as a function of temperatures in the range from 300K to 493K, over the frequencies 102 Hz – 106 Hz before and after gamma ray irradiation. AC conductivity (s AC) of the glasses was measured as a function of frequency for different temperatures before and after gamma ray irradiation. Novelty: For the first time, it was attempted that the effect of gamma ray irradiation on dielectric and AC conductivity properties of bismuth-borate glasses doped with vanadium oxide has been investigated. Here we have observed the change in the variation of dielectric constant, dielectric loss and AC conductivity with frequency and temperature before and after gamma ray irradiation. The borate network becomes more compact after being exposed to gamma rays, and the energy band gap may even narrow. Furthermore, it has been found that the composition of the glass influences how radiation impacts conductivity. Keywords: Oxide Glasses; XRD; Gamma Ray Irradiation; Dielectric Properties; AC Conductivity

Multi-parametric sensing by multi-channel molecular fluorescent probes based on excited state intramolecular proton transfer and charge transfer processes

Considering the applications of fluorescent probes and the information they provide, their brightness of fluorescence and photostability are of paramount importance. However, in the case of steady-state fluorescence spectroscopy and fluorescence microscopy, the amount of information can be increased by the application of multi-channel probes, via a multi-band fluorophore introduced in the probe molecule. In most cases, the use of such a multi-band (or multi-channel) fluorophore can also be combined with the concomitant introduction of one or several analyte receptors. Most often, the design of ratiometric probes with multi-band fluorescence emission are based on phenomena such as photoinduced intramolecular charge transfer (ICT) or excited state intramolecular proton transfer (ESIPT). Although ICT probes were up to recently the most popular, ESIPT probes and among them 3-hydroxyflavone derivatives, were shown to be the most productive. Several general problems were resolved by this family of probes, as for example the measurement of local dielectric constant, local H-bond accepting ability, water local concentration and ATP concentration in small volumes.Incorporation of such multi-channel probes into lipid membranes allowed to measure the different membrane potentials and to detect cell apoptosis. Also, it enabled to recognize and characterize the rafts formation in different lipid bilayers and peculiar features of the charged membrane interface. Such probes are also able to provide a concentration-dependent fluorescence signals upon binding of H+, Mg2+and Ba2+ions, and thus to recognize these different cations.The multi-channel probes are effective tools in the study of interactions of macromolecules such as peptides, proteins and nucleic acids. The most useful feature is that they inform simultaneously about several physical parameters, in this way giving a better insight in the investigated system. Thus, by comparing the reviewed probes with other modern fluorescent approaches, it can be concluded they are more informative and accurate tools.