Ion Sensor Research Articles

A Highly Sensitive, Low Creep Hydrogel Sensor for Plant Growth Monitoring

Ion−conducting hydrogels show significant potential in plant growth monitoring. Nevertheless, traditional ionic hydrogel sensors experience substantial internal creep and inadequate sensitivity, hindering precise plant growth monitoring. In this study, we developed a flexible hydrogel sensor composed of polyvinyl alcohol and acrylamide. The hydrogel sensor exhibits low creep and high sensitivity. Polyvinyl alcohol, acrylamide, and glycerol are crosslinked to create a robust interpenetrating double network structure. The strong interactions, such as van der Waals forces, between the networks minimize hydrogel creep under external stress, reducing the drift ratio by 50% and the drift rate by more than 60%. Additionally, sodium chloride and AgNWs enrich the hydrogel with conductive ions and pathways, enhancing the sensor’s conductivity and demonstrating excellent response time (0.4 s) and recovery time (0.3 s). When used as a sensor for plant growth monitoring, the sensor exhibits sensitivity to small strains and stability for long−term monitoring. This sensor establishes a foundation for developing plant health monitoring systems utilizing renewable biomass materials.

Ion sensors based on organic semiconductors acting as quasi-reference electrodes

Thin-film devices that transduce the chemical activity of ions into electronic signals are essential components in various applications, including healthcare diagnostics and environmental monitoring. Combinations of organic semiconductors (OSCs) and ion-selective materials have been explored for developing solution-processable ion sensors. However, the necessity of reference electrodes (REs) and operational stability in ion-permeable OSCs have posed questions regarding whether reliable measurements with thin-film components are attainable with OSCs. Herein, we report electric double-layer transistors (EDLTs) with OSCs in single-crystal forms for ion sensing. Our EDLTs demonstrated high operational stability, with a one-to-one relationship between the source electrode potential and device resistance, and served as quasi-REs (qRE). When our EDLT is served as qRE, its drift was as small as 0.5 mV/h and comparable to that of commonly employed REs. In our system, the semiconductor-electrolyte interface is self-passivated by the alkyl chains of OSCs in single-crystal structures, with the two-dimensional transport layer appearing unaltered upon gating. EDLT arrays with ion-selective and nonselective liquid junctions enable ion concentration sensing without a conventional RE. These findings provide opportunities to develop thin-film devices based on OSCs for easy integration and reliable measurements.

3D-Printed Transducers for Solid Contact Potentiometric Ion Sensors: Improving Reproducibility by Fabrication Automation.

3D printing technology has become attractive in the development of electrochemical sensors as it offers automation in fabrication, customization on-demand, and reproducibility, among other features. Nonetheless, to date, solid contact potentiometric ion sensors have remained overlooked using this technology. Thus, the novelty of this work relies on demonstrating for the first time the usefulness of the multimaterial 3D printing approach to manufacture potentiometric ion-selective electrodes. The significance is indeed twofold. First, we discovered that by using the polyethylene terephthalate glycol (PETg) and polylactic acid-carbon black (PLA-CB) filaments together with a rational electrode design containing a well to accommodate the ion-selective membrane, a tight seal among all of the sensing materials is obtained. Importantly, this has mainly impacted the electrode-to-electrode reproducibility (ERSD0 ± 3 mV). Second, 75 ready-to-use electrodes can be printed in less than 3.5 h in a completely automated manner at a cost of ∼0.32 €/sensor. This feature may positively impact the suitability of further scaled-up production as well as the possibility of application in low-resource contexts. Overall, the presented outcomes are expected to encourage certain research directions to adopt using multimaterial 3D-printing approaches for producing highly reproducible solid contact potentiometric ion-selective electrodes, but are not restricted to them.

Synthesis of fluorometric carbon nano dots(CNDs) for selective sensing of biologically important Fe3+ and Cu2+ metal ions and evaluating their antioxidant capacity.

In this research, CNDs were prepared by a green and cost effective method using Cinnamomum Tamala (bay leaf) as carbon sources. TEM, UV, FTIR, ZETA Potential, PL and Fluorescence methods were used to characterize the produced CNDs and the average particle size is 3.42nm. This research was conducted on the development of fluorescent sensors for various metal ions, including Fe3+, Cu2+, Zn2+, Ni2+, Pb2+, Cr3+, Mg2+, Na+ 1 and Cd2+. The CNDs demonstrated selective sensing of biologically important Fe+ 3 and Cu+ 2 metal ions. The CNDs antioxidant assay was tasked with DPPH• radical scavenging properties. CNDs made from Cinnamomum Tamala had the highest DPPH free radical scavenging activity at 100mg/L (42.06%) with the IC50 of 130.68mg/L. The outcome implies that Indian spices are among the best materials for optical metal ion detection and sensing, and they also have therapeutic benefits.

Preparation of glutathione-Cu/Ag bimetallic nanoparticles for temperature and metal ion Co2+ sensing

In this work, copper silver bimetallic nanoparticles (Cu/Ag BNPs) with strong fluorescence were prepared using glutathione (GSH) as a reductant and protectant. The range of fluorescence signal of GSH-Cu/Ag BNPs to ambient temperature is 30∼90 °C has a sensitive response and can be used as a temperature sensor. The high fluorescence intensity of GSH-Cu/Ag BNPs at around 30 °C indicates that the detection of Co2+ does not require harsh temperature conditions, which could be very convenient for future practical detection work. In addition, glutathione in Cu/Ag BNPs and the synergistic effect of Cu and Ag nanoparticles in Cu/Ag BNPs can be used as a metal ion sensor for Co2+ fluorescence detection.

A comprehensive investigation of cholesteric liquid crystal interpenetrating polymer networks for metal ion sensor technology

This study outlines the fabrication process of a photonic polymer cholesteric liquid crystal (PCLC) engineered for dynamic response to external stimuli. The methodological framework includes the precise templating of PCLC onto an interpenetrating polymer network (IPN) following selective UV crosslinking and the careful removal of nonreactive mesogens. The sensor component of the PCLC film is composed of poly(acrylic acid) hydrogel. A key aspect of the process involves the formation of micro-holes through acetone treatment to enhance sensitivity. Additionally, functionalization with potassium hydroxide (KOH) improves the detection of calcium ions (Ca2+) by disrupting hydrogen bonds and facilitating the formation of potassium carboxylate salt. Combining the inherent properties of PCLC with the hydrogel’s responsiveness to metal ions results in a sophisticated sensor designed to detect Ca2+ ions through the modulation of PCLC pitch, creating distinct transmission bands. The manuscript provides a detailed quantitative analysis of stimulus-induced changes in PCLC wavelength, using measured spectra to refine and optimize process conditions. The resulting PCLC sensor demonstrates exceptional sensitivity (9.30 nm/mM) within the 1–15 mM Ca2+ ion concentration range, along with excellent specificity. This cost-effective, user-friendly, and colorimetric sensing modality holds significant promise for various applications in analytical chemistry.

Heterocyclic Hemipiperazines: Multistimuli-Responsive Switches and Sensors for Zinc or Cadmium Ions.

Advance in the design of molecular photoswitches - adapters that convert light into changes at molecular level - opens up exciting possibilities in preparing smart polymers, drugs photoactivated inside humans, or light-fueled nanomachines that might in the future operate in our bloodstream. Hemipiperazines are recently reported biocompatible molecular photoswitches based on cyclic dipeptides. Here we report a multistimuli-responsive hemipiperazine-based switch that reacts on light, solvents, acidity, or metal ions. Its photoequilibration is controlled by the intramolecular hydrogen bonding pattern. The compound can be used as a mid-nanomolar photoswitchable fluorescent sensor for zinc and cadmium ions, applicable to monitor environmental pollution in real time.

Effect of oxygen content in CuO x nanofilms on chloride ion detection for ion sensor applications

Sensors for detecting chloride ions have been required for routine monitoring of industry and human health. This study proposes a concept of an ion sensor based on CuO x nanofilms with different oxygen contents. The CuO x -based sensors exhibited an increase in DC current for those with low oxygen content and a decrease for those with high oxygen content following exposure to a chloride ion solution. AC impedance analysis suggested differential reactions of chloride ions in the bulk and surface regions of CuO x , dependent on the oxygen content. For the CuO x -based sensors with a ratio of 0.78 oxygen to copper atoms at chloride ion concentrations of 10−1000 ppm, the sensitivity in the bulk region calculated from AC impedance was 61−2926, which was higher than the sensitivity of 1.3−2.6 calculated from DC impedance. Finally, CuO x -based sensors demonstrated identifiability for chloride ions compared to sodium and calcium ions.

A novel organic chromo-fluorogenic optical sensor for detecting chromium ions

Sensing trivalent chromium ion (Cr(III)) is widely applied in different areas, such as clinical analysis, marine, environmental monitoring, or even chemical industry applications. Cr(III) has a significant role in the physiological process of human life. It is classified as an essential micronutrient for living organisms. Herein, we developed and designed a novel optical Cr(III) ions sensor film. The investigated sensor has a relatively small dynamic range of 1.24 × 10−3 to 0.5 μM. We report a highly sensitive optical sensor film for Cr(III) ions based on diethyl 3,4-diaminothieno[2,3-b]thiophene-2,5-dicarboxylate (3D) probe. The optical characteristics of the chemical probe exhibit substantial emission at 460 nm under 354 nm excitation. Besides, the interaction of the Cr(III) ions with 3D involves a complex formation with a 2:1 (metal: ligand) ratio, which is convoyed by the main peak enhancement that centered at 460 nm of 3D, and the main peak is red-shifted to 480 nm. The easily discernible fluorescence enhancement effect is a defining characteristic of the complexation reaction between the 3D probe and Cr(III). On the basis of the substantial fluorescence mechanism caused by the formation of a (Cr(III)-3D complex, which inhibits the photo-induced electron transfer (PET) process, the devised optical sensor was proposed. This film exhibits exceptional sensitivity and selectivity due to its notable fluorescence properties, stock shift of less than 106 nm, and detection capabilities at a significantly low detection limit of 0.37 × 10−3 μM. The detection procedure is executed by utilizing a physiological pH medium (pH = 7.4) with a relative standard deviation RSDr (1 %, n = 3). In addition, the 3D sensor demonstrates a high degree of affinity for Cr(III), as determined by the calculation of its binding constant to be 1.40 × 106. We present an impressive optical sensor that is constructed upon a three-dimensional molecule.

A 1H-imidazo[4,5-f][1,10]phenanthroline based ligand and its binuclear Cu(I) complexes: Syntheses, structures and luminescence sensing for Cr2O72− and MnO4−

Dichromate (Cr2O72−) and permanganate (MnO4−) ions have been important targets for sensing and detection in the field of luminescent complexes and their corresponding ligands due to their significant impact on the ecological environment and human health. However, many Cu(I) complexes with good room-temperature phosphorescence are rarely used as luminescent sensors for ions in water due to the insolubility and the disproportionation of the Cu(I) ion. Herein, 2,6-di-1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl-4-tertbutylphenol (diptpH3) and its two luminescent binuclear Cu(I) complexes, [Cu(diptpH3)(POP)]ClO4 (1) and [Cu(diptpH3)(xantphos)]ClO4 (2), were designed and synthesized (POP = bis[(2-diphenylphosphino)phenyl] ether, and xantphos = 9,9-dimethyl-4,5-bis(diphenylphosphino)-9H-xanthene). All compounds in DMSO/H2O (1: 9, v: v) show high stability to water, which was confirmed by the results of electrospray ionization mass spectrometry (ESI-MS). Cr2O72− and MnO4− ions showed high luminescence quenching coefficients (Cr2O72−: 3.042 × 104 − 2.946 × 105 M−1; MnO4−: 1.476 × 104 − 2.254 × 105 M−1) for all the three compounds. DiptpH3, complexes 1 and 2 exhibited good luminescent sensing properties toward Cr2O72− and MnO4− ions with short response times, good selectivity and low detection limits (Cr2O72−: 1.845 × 10−7 − 2.359 × 10−6 mol⋅L−1; MnO4−: 1.850 × 10−7 − 6.221 × 10−6 mol⋅L−1) in DMSO/H2O. The plausible sensing mechanisms were fully discussed.

Biocompatible bright orange emissive carbon dots: Multifunctional nanoprobes for highly specific sensing toxic Cr(VI) ions and mitochondrial targeting cancer cell imaging

Although several luminescent-based nanostructured materials are used as cellular imaging probes, creating a biocompatible subcellular imaging probe can be challenging. Instantaneously, it is crucial and urgently needed for certain fluorescent nanoprobes to identify possibly harmful heavy metal ions. We present a straightforward one-pot preparation of bright orange emissive (quantum yield approximately 16 %) Nitrogen/Sulfur co-doped carbon dots (N/S CDs) from citric acid and methylene blue as raw materials that will serve as a specific Cr(VI) ions sensor and an effective mitochondrial labeling in cancer cells. They had several benefits including low ecological impact, facile synthesis, good water solubility, photostability, and high stability. We found that N/S CDs photoluminescence (PL) could be reduced when Cr(VI) ions were present near them, and the PL reduction occurred highly sensitively to the presence of Cr(VI) compared to other metal ions including Cr(III) ions. This specific reduction of PL was due to the non-fluorescent complex formation through the inner filter effect (IFE). The established fluorescence-based sensing technique could serve for Cr(VI) ion quantification with exceptional sensing efficiency in the wide linear range of 7 to 70 μM (R2 = 0.9873), with the limit of detection of 53.5 nM. It was also revealed that the current fluorescent probe could be encouragingly utilized to quantify the concentration of Cr(VI) ions in various water specimens such as tap water. In addition, they were shown to function as a mitochondria-targeting nanoprobe in human cancer cells (ME 180 cells and Hela cells) for cell imaging. Concludingly, it was envisioned that these fluorescent nanoprobes could find a use in real-time monitoring of Cr(VI) ions in water-based ecosystems with ultrahigh sensitivity and cell image tracking via mitochondria labeling as biocompatible nanoprobes.

Mass Production of Carbon Nanotube Transistor Biosensors for Point-of-Care Tests.

Low-dimensional semiconductor-based field-effect transistor (FET) biosensors are promising for label-free detection of biotargets while facing challenges in mass fabrication of devices and reliable reading of small signals. Here, we construct a reliable technology for mass production of semiconducting carbon nanotube (CNT) film and FET biosensors. High-uniformity randomly oriented CNT films were prepared through an improved immersion coating technique, and then, CNT FETs were fabricated with coefficient of performance variations within 6% on 4-in. wafers (within 9% interwafer) based on an industrial standard-level process. The CNT FET-based ion sensors demonstrated threshold voltage standard deviations within 5.1 mV at each ion concentration, enabling direct reading of the concentration information based on the drain current. By integrating bioprobes, we achieved detection of biosignals as low as 100 aM through a plug-and-play portable detection system. The reliable technology will contribute to commercial applications of CNT FET biosensors, especially in point-of-care tests.

Synthesis, structure of a new bimetallic-organic framework film sensor and fluorescence detection of histamine and metal ions

A novel bimetallic organic framework material based on 3,5-di (2′, 4′ - dicarboxylphenyl) benozoic acid (H5L) ligand, named {[Tb9CoL6(H2O)6 (H3O)]·4DMF·2H2O}n [L = C23H9O10, DMF = N, N- Dimethylformamide) (Tb-Co-MOF), had been successfully synthesized by solvothermal method. The structure and properties of Tb-Co-MOF were characterized by single-crystal X-ray diffraction, elemental analysis, thermogravimetric analysis, powder X-ray diffraction, ultraviolet spectrum, infrared spectrum and fluorescence spectrum. This results indicated that Tb-Co-MOF was crystallized in the trigonal system with the R3 space group and it was a novel three-dimensional structure, good thermal stability and luminous performance. Fluorescent film was prepared with Tb-Co-MOF powders by polymer embedding method. This film had high fluorescence recognition ability for histamine (HIS), Fe3+ ion and Cr2O72− anion, so it could be used as a selective fluorescence sensor for them. Their detection limits were 1.43 μmol·L−1, 0.94 μmol·L−1 and 0.96 μmol·L−1, respectively. Compared with the powder MOFs, the fluorescence film had the advantages of high sensitivity, good selectivity, fast response speed, high stability and strong reversibility, which provided a certain reference for the application of metal-organic framework materials in environmental detection.

High performance PVC/ [AMI]mNTF2 ionic gel sensors for smart wearable applications

Plasticized polyvinyl chloride (PVC) gel as an electroactive polymer material has attracted increasing interest for the construction of flexible devices with the integration of actuation and self-sensing. However, the insufficient sensing ability of traditional PVC gels limits their applications. In this paper, a PVC ionic gel sensor based on the physical blending of PVC gel and the ionic liquid 1-allyl-3-methylimidazolium bisimide ([AMI]mNTF2) is presented. With the addition of ionic liquids, the PVC molecular chains and ions formed stable conductive pathways, resulting in increased conductivity and sensing performance of the PVC gel. The proposed sensor exhibits excellent sensing properties of high resolution (0.12 %) and fast response time (95 ms), along with high sensitivity (GF=27.8), which is more than seven times that of the traditional PVC gel. Furthermore, it was successfully utilized for human motion detection and remote control of a robotic hand, demonstrating the feasibility of the sensor for smart wearable applications in the future.

Stretchable Anisotropic Conductive Film with Position‐Registered Conductive Microparticles Used for Strain‐Insensitive Ionic Interfacing in Stretchable Ionic Sensors

AbstractNumerous approaches are explored to achieve precise position registry of microparticles (MPs) with minimal defects; however, MP assembly in a periodic pattern or an arbitrary manner has been a challenging issue over the past several decades. Utilizing the position‐registered conductive MPs, polymer composites of the MPs are used as anisotropic conductive film (ACF) and soft interfacing. One of the remaining challenges is maintaining the MP positions while producing or utilizing the ACF. This study proposes a simple strategy to produce a stretchable ACF (S‐ACF) by mechanical rubbing, without disturbing the MP positions during the production and use. A practical means of precise MP positioning on a ultraviolet (UV)‐patternable soft template is investigated first. This study investigates, through both experiment and finite element method calculation, the relationship between local adhesion of the template and mechanical rubbing variables (pressure, rubbing velocity, and MP size). Based on this exploration, a fast and simple method to fabricate large‐area S‐ACF is presented. This study demonstrates that the S‐ACF can be used for electronic interfacing in stretchable devices and for ionic interfacing to remove the effect of external mechanical force in ionic sensors.

Structure-property relationship between different molecular precursors and the final properties of carbon dots: Preparation, characterization and applications as sensors for metal ions

Carbon dots (CDs) have attracted significant attention in recent years due to their interesting properties, such as photoluminescence, biocompatibility, excellent water dispersibility, as well as their potential applications in different fields. Despite these features, the complexity of their photoluminescent properties remains a subject of ongoing research and still presents unresolved questions. In this work, we investigated the preparation of various CDs from different low molecular mass starting materials containing carbon, nitrogen and/or sulfur, using hydrothermal carbonization as the preparation method. The CDs were characterized using various techniques, including TEM, FTIR, photoluminescence, UV–Vis, Raman and XPS. A detailed analysis of the initial reactions between the precursors was conducted, and our main results suggest that the optical properties of the CDs are related to fluorophores formed during the initial Michael condensation reactions between the precursors. This process produces molecular fluorescence, which plays a pivotal role in the photoluminescence properties of the nanoparticles. In addition, two of the obtained CDs were used as selective and sensitive probes for metal ions, achieving a detection limit of 0.58 μM and 0.55 μM. Finally, the findings described here can guide future works in fine-tuning the design of CDs with desired properties and different potential applications.

A Platform for Ultra-Fast Proton Probing of Matter in Extreme Conditions.

Recent developments in ultrashort and intense laser systems have enabled the generation of short and brilliant proton sources, which are valuable for studying plasmas under extreme conditions in high-energy-density physics. However, developing sensors for the energy selection, focusing, transport, and detection of these sources remains challenging. This work presents a novel and simple design for an isochronous magnetic selector capable of angular and energy selection of proton sources, significantly reducing temporal spread compared to the current state of the art. The isochronous selector separates the beam based on ion energy, making it a potential component in new energy spectrum sensors for ions. Analytical estimations and Monte Carlo simulations validate the proposed configuration. Due to its low temporal spread, this selector is also useful for studying extreme states of matter, such as proton stopping power in warm dense matter, where short plasma stagnation time (<100 ps) is a critical factor. The proposed selector can also be employed at higher proton energies, achieving final time spreads of a few picoseconds. This has important implications for sensing technologies in the study of coherent energy deposition in biology and medical physics.

Position-induced differential aggregation behavior with red-shifted emission: A case study of the promising copper ion sensor skeleton-based regio-isomers

AIE-ESIPT active Schiff base luminescent organic materials (LOM) have significant advantages and applications. Still, tuning their emission in the long-wavelength region (>600 nm) while maintaining low molecular mass remains challenging for the research community. Recently, researchers have found excellent capabilities like high CT nature, red-shifted emission, and large stokes shift in meta-fluorophores. However, such studies on the role of meta substitution, especially in the case of AIE-ESIPT active Schiff base LOM, have just been explored. Herein, we have presented a case study on the malonitrile-substituted regioisomers (p-BK and m-BK) based on the SDPA skeleton, a promising copper ion-sensing skeleton. It was found that the emission in m-BK is almost ∼ 50 nm red-shifted with approx. ∼ 200 nm stoke shift, compared to the p-BK. Although changing substituents from para to meta changes the aggregation behavior but, the selectivity remains identical towards copper ions. The practical sensing applicability of both isomers was analyzed in various environments, and bioimaging analysis in HeLa cells were performed to prove the promising nature of the SDPA skeleton. In sum, this case study highlighted the potential of unexplored meta-fluorophores, which can open up new avenues for researchers to create and design new AIE-active LOMs with desired emission wavelengths.

Synthesis and functionalization of red-emissive carbon dots towards sensing of copper(II) and ATP in aqueous media

Red-emissive carbon dots, RCDs, were prepared in a bottom-up approach, from citric acid and urea, through a single solvothermal step, which were posteriorly surface-functionalized with di-(2-picolyl)amine (DPA) groups. The functionalized RCDs, henceforth named CD1, were analyzed through high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), dynamic light-scattering (DLS) and infrared spectroscopy (FTIR), and were found to be spherical, with diameter of circa 4 nm. UV-Vis and luminescence spectroscopic studies showed that CD1 display an absorption maximum at 550 nm, with emission maxima at around 640 nm. Fluorescence measurements indicated that Cu(II) induces the strongest changes in the emission of CD1 among eleven investigated metal ions, with a full quenching effect being observed. Further addition of an anionic species, adenosine 5-triphosphate (ATP), resulted in a recovery of the luminescence, which suggests that ATP is capable of sequestering metal ions from the surface of CD1. These results highlight the potential of simple and easy-to-make carbon nanomaterials as sensors for ions in aqueous media.

Traces of Ions Sensing and Tracking in Support of Green H2 Economy and Sustainability

Given the focus on a green H2 economy for a sustainable future, it is crucial to understand the degradation features of H2-focus electrochemical devices and systems, i.e., proton exchange membrane fuel cells and water electrolysis (PEM-based FC & WE). The current accelerated stress test and resulting degradation features are systematically investigated through comprehensive analysis, including a series of electrochemical, spectroscopic, tomographic, and microscopic characterization, assisted with a detailed structure examination of the electrode, membrane, and interface. However, numerous characteristic studies that aim to uncover these features under various dynamic operations are commonly employed to depend on the sophisticated laboratory stationary bulky facilities and instruments in the theater. Moving forward to real-world practical applications, i.e., H2 electrical vehicles, a miniaturized, mobile, low-cost, and user-friendly measurement and diagnostic tool is highly in demand. Considering the dependence of the performance and durability on the ion exchange/transport, and involvement of small particles, and the high possibility of dissolution, the time-dependent sensing and tracking of such traces of ions can provide fundamental insight into the activities and events within the PEM-based FC & WE devices and systems. Our recent efforts are dedicated to bridging the notable gap to develop electrochemical and transistor-based ion sensors integrated on a circuit chip towards real-time in-situ monitoring of the health and degradation status. This complementary work may also provide valuable guidelines for establishing a suitable accelerated stress test protocol to diagnose system durability, and for designing durable materials for long-term operation.