Stimuli‐Responsive Donor–Acceptor and DNA‐Crosslinked Hydrogels: Application as Shape‐Memory and Self‐Healing Materials

Carboxymethyl cellulose (CMC) chains are functionalized with self‐complementary nucleic acid tethers and electron donor or electron acceptor functionalities. The polymer chains crosslinked by the self‐complementary duplex nucleic acids and the donor–acceptor complexes as bridging units, yield a stiff stimuli‐responsive hydrogel. Upon the oxidation of the electron donor units, the donor–acceptor bridging units are separated, leading to a hydrogel of lower stiffness. By the cyclic oxidation and reduction of the donor units, the hydrogel is reversibly transformed across low and high stiffness states. The controlled stiffness properties of the hydrogel are used to develop shape‐memory hydrogels. In addition, CMC hydrogels crosslinked by donor–acceptor complexes and K⁺‐stabilized G‐quadruplexes reveal stimuli‐responsive properties that exhibit dually triggered stiffness functions. While the hydrogel bridged by the two crosslinking motifs reveals high stiffness, the redox‐stimulated separation of the donor–acceptor complexes or the crown‐ether‐stimulated separation of the G‐quadruplex bridges yields two alternative hydrogels exhibiting low stiffness states. The control over the stiffness properties of the dually triggered hydrogel is used to develop shape‐memory hydrogels, where the donor–acceptor units or G‐quadruplex bridges act as “memories”, and to develop triggered self‐healing process of the hydrogel.     

Stimuli‐Responsive DNA‐Gated Nanoscale Porous Carbon Derived from ZIF‐8

Stimuli‐responsive nanoscale porous carbon derived from ZIF‐8 (NCZIF) gated by DNA capping units is reported. The NCZIF is first obtained by calcination of nano‐ZIF‐8 crystals under an inert atmosphere. It is further conjugated with amine‐modified single‐stranded DNA after carboxylation (DNA/NCZIF). The guest molecules are sealed in the pore of NCZIF by the formation of a DNA duplex structure on the surface of NCZIF. As proof of principle, two systems that can be, respectively, used for controlled drug delivery and biosensing are introduced. In the first system, the drug model (rhodamine 6G, Rh6G) is locked in the NCZIF by the DNA capping units composed of rich‐G sequences and its complementary DNA strand. The in vitro cellular experiments reveal that DNA/NCZIF has good biocompatibility and can controllably release Rh6G upon the K⁺‐stimuli in cells. In the second system, the signal probe (methylene blue, MB) is locked in the NCZIF and then released after the unlocking of the pores triggered by the dissociation of the aptamer‐hybrid capping units. The MB‐loaded DNA/NCZIF can linearly respond to target molecules in the range from 1 × 10^?9 to 10 × 10^?6 m and has good specificity.     

Conjugated Polyelectrolyte and Aptamer Based Potassium Assay via Single‐ and Two‐Step Fluorescence Energy Transfer with a Tunable Dynamic Detection Range

A new potassium ion detection assay was developed using a dye‐labeled aptamer and conjugated polyelectrolyte (CPE) as a signaling platform via 1‐step and 2‐step fluorescence resonance energy transfer. Guanine‐rich K⁺‐specific aptamers were designed as K⁺ ion recognition species with 6‐carboxyfluorescein (6‐FAM) and 6‐carboxytetramethylrhodamine (6‐TAMRA) at both termini. In the presence of K⁺ ions, the aptamers undergo a conformational change from an unfolded to folded form by forming a G‐quadruplex with K⁺, bringing two dyes in proximity. FRET‐induced 6‐TAMRA emission was proportional to [K⁺] in a range of 22.5 μm –100 mm in water without interference by the presence of excess Na⁺ ions (100 mm ). Upon the addition of CPE, a two‐step FRET process from CPE to 6‐TAMRA via 6‐FAM was enabled, showing an intensified 6‐TAMRA signal with K⁺ ions. The dynamic detection range and limit of detection (LOD) was fine‐tuned from ～millimolar to ～nanomolar concentrations of K⁺ by modulating the signal amplification effect of CPE. The LOD was determined to be ≈3.0 nm . This detection assay also showed high selectivity against other metal ions. This sensing scheme can be extended to the detection of a wide range of target materials by simply modifying the recognition aptamer sequence.     

Positively K+‐Responsive Membranes with Functional Gates Driven by Host–Guest Molecular Recognition

A novel positively K⁺‐responsive membrane with functional gates driven by host‐guest molecular recognition is prepared by grafting poly(N‐isopropylacrylamide‐co‐acryloylamidobenzo‐15‐crown‐5) (poly(NIPAM‐co‐AAB₁₅C₅)) copolymer chains in the pores of porous nylon‐6 membranes with a two‐step method combining plasma‐induced pore‐filling grafting polymerization and chemical modification. Due to the cooperative interaction of host‐guest complexation and phase transition of the poly(NIPAM‐co‐AAB₁₅C₅), the grafted gates in the membrane pores could spontaneously switch from “closed” state to “open” state by recognizing K⁺ ions in the environment and vice versa; while other ions (e.g., Na⁺, Ca²⁺ or Mg²⁺) can not trigger such an ion‐responsive switching function. The positively K⁺‐responsive gating action of the membrane is rapid, reversible, and reproducible. The proposed K⁺‐responsive gating membrane provide a new mode of behavior for ion‐recognizable “smart” or “intelligent” membrane actuators, which is highly attractive for controlled release, chemical/biomedical separations, tissue engineering, sensors, etc.     

Tailoring Amino‐Functionalized Graphitic Carbon‐Encapsulated Gold Core/Shell Nanostructures for the Sensitive and Selective Detection of Copper Ions

The effective transfer of strong electromagnetic field from the gold core through the coating shell represents the most significant challenge for the applications of plasmonic nanoparticles. This study applies a one‐step arc discharge method to synthesize graphitic carbon‐encapsulated gold nanoparticles (Au@G NPs) functionalized with amino groups uniformly via adding NH₃ into He background gas. By tailoring the coating shell into few‐layered graphene, a strong localized surface plasmon resonance (LSPR) absorption band is achieved. The NH₃ introduces H radicals to strengthen the LSPR characteristic by etching the coating graphitic shell, as well as provides dissociated NH or NH₂ species to functionalize the surfaces with amino groups. With an LSPR‐based colorimetric method, it is demonstrated that trace Cu²⁺ ions can be detected rapidly with excellent sensitivity (as low as 10 × 10^‐9m linearly) and selectivity against other metal ions (Na⁺, K⁺, Mg²⁺, Ca²⁺, Co²⁺, Fe²⁺, Cd²⁺, Pb²⁺, and Hg²⁺ ions) by amino‐functionalized Au@G NPs in water samples.     

Suppressing Manganese Dissolution in Potassium Manganate with Rich Oxygen Defects Engaged High‐Energy‐Density and Durable Aqueous Zinc‐Ion Battery

The manganese dissolution leading to sharp capacity decline as well as the sluggish reaction kinetic are still major issues for manganese‐based materials as aqueous zinc‐ion batteries (ZIBs) cathodes. Here, a potassium‐ion‐stabilized and oxygen‐defect K_0.8Mn₈O₁₆ is reported as a high‐energy‐density and durable cathode for neutral aqueous ZIBs. A new insight into suppressing manganese dissolution via incorporation of K⁺ ions to intrinsically stabilize the Mn‐based cathodes is provided. A comprehensive study suggests that oxygen defects improve electrical conductivity and open the MnO₆ polyhedron walls for ion diffusion, which plays a critical role in the fast reaction kinetics and capacity improvement of K_0.8Mn₈O₁₆. In addition, direct evidence for the mechanistic details of simultaneous insertion and conversion reaction based on H⁺‐storage mechanism is demonstrated. As expected, a significant energy output of 398 W h kg^?1 (based on the mass of cathode) and an impressive durability over 1000 cycles with no obvious capacity fading are obtained. Such a high‐energy Zn‐K_0.8Mn₈O₁₆ battery, as well as the basic understanding of manganese dissolution and oxygen defects may open new opportunities toward high‐performance aqueous ZIBs.     

Understanding the Host–Guest Interaction Between Responsive Core‐Crosslinked Hybrid Nanoparticles of Hyperbranched Poly(ether amine) and Dyes: The Selective Adsorption and Smart Separation of Dyes in Water

The host–guest interaction between polymer nanoparticles and guest molecules plays a key role in fields such as controlled drug delivery, separation, and nanosensors. To understand this host–guest interaction, a series of hybrid polymer nanoparticles (SiO_1.5‐hPEA NPs) are designed and prepared based on hyperbranched poly(ether amine) (hPEA) with the different hydrophobicity and functional groups. Their adsorption behavior to twelve hydrophilic dyes in aqueous solution is studied. The core‐crosslinked hybrid nanoparticles (SiO_1.5‐hPEA NPs) are prepared by direct dispersion of hPEA containing trimethoxysilyl moieties (TMS‐hPEA) in aqueous solution, which exhibit sharp multiresponse to temperature, pH, and ionic strength in aqueous solution. The effect of molecular structure of TMS‐hPEA on the host–guest interaction between SiO_1.5‐hPEA NPs and hydrophilic dyes is investigated in detail. The obtained SiO_1.5‐hPEA NPs interact selectively with different hydrophilic dyes in aqueous solution. The distribution coefficient (K) for partitioning of dyes between SiO_1.5‐hPEA NPs and water is proposed to define the strength of the host‐guest interaction between the nanoparticles and dyes. K increases with the increasing hydrophobicity of the hPEA backbone regardless of their charge states of SiO_1.5‐hPEA NPs and dyes. A methodology is demonstrated for the smart separation of a mixture of dyes in water using SiO_1.5‐hPEA NPs.     

Red‐ to NIR‐Emitting,BODIPY‐Based,K+‐Selective Fluoroionophores and Sensing Materials

Optical sensing materials for the selective measurement of potassium ions (K⁺) in water are presented. The indicator dyes are based on an aza‐crown ether as a receptor and borondipyrromethenes (BODIPY) dyes as fluorophores. Fluorescence enhancement is caused by the reduction of photoinduced electron transfer (PET) upon complexation with K⁺ ions. The family of new indicators possesses tuneable optical properties (green to red excitation, red to NIR emission) and PET efficiencies. They exhibit high brightness with quantum yields between 0.20 and 0.47 in the “on” state and a molar absorption coefficient between 30 000 and 290 000 m ^?1 cm^?1. The new indicator dyes are immobilized in biocompatible hydrogel matrices to obtain stable nonleaching and fast responding (t₉₀ ≈ 10 s) sensing materials for continuous measurements of potassium. They are realized in various formats such as planar optodes, fiber‐optic sensors, and water‐dispersible polymer‐based nanoparticles. Apart from fluorescence intensity measurements, self‐referenced read‐out of fluorescence decay time is demonstrated. All sensor materials display a high K⁺/Na⁺ selectivity and are not influenced by pH within the physiologically relevant range. Practical applicability of the materials is emphasized by application of a fiber‐optic sensor to quantification of K⁺ in serum, which shows excellent correlation with the reference measurements.     

Room‐Temperature Ion‐Exchange‐Mediated Self‐Assembly toward Formamidinium Perovskite Nanoplates with Finely Tunable,Ultrapure Green Emissions for Achieving Rec. 2020 Displays

Delicate engineering of chromaticity is required to faithfully reproduce colors in a backlit display, this is extremely difficult for green downconverters because the human eye is highly sensitive to green colors. The central challenge is to achieve finely tunable green emissions in the narrow range of 525–535 nm while keeping the full width at half maximum (FWHM) <25 nm at the same time. Here, a room‐temperature ion‐exchange‐mediated self‐assembly strategy for preparing FAPbBr₃ (FA = CH(NH₂)₂⁺) nanoplates (NPs) to fulfill this goal is introduced. 2D layered OA₂PbBr₄ (OA is octadecylamine) NPs are first synthesized by spontaneous reprecipitation, and are then transformed into FAPbBr₃ NPs through a OA⁺‐to‐FA⁺ exchange induced self‐assembly of HP monolayers. A c‐axis contraction in this process makes a relative large thickness variation in OA₂PbBr₄ NPs, which can be realized by simply varying the precursor concentration, only result in a small thickness change in subsequent FAPbBr₃ NPs, thereby enabling finely tunable emissions in the range of 525–535 nm along with FWHM <25 nm and a quantum yield up to 85%. As a downconverter, the FAPbBr₃ NPs realize an ultrapure green backlight that covers ≈95% Rec. 2020 standard in the CIE 1931 color space.     

Single‐Crystalline p‐Type Zn3As2 Nanowires for Field‐Effect Transistors and Visible‐Light Photodetectors on Rigid and Flexible Substrates

Zn₃As₂ is an important p‐type semiconductor with the merit of high effective mobility. The synthesis of single‐crystalline Zn₃As₂ nanowires (NWs) via a simple chemical vapor deposition method is reported. High‐performance single Zn₃As₂ NW field‐effect transistors (FETs) on rigid SiO₂/Si substrates and visible‐light photodetectors on rigid and flexible substrates are fabricated and studied. As‐fabricated single‐NW FETs exhibit typical p‐type transistor characteristics with the features of high mobility (305.5 cm² V^?1 s^?1) and a high I_on/I_off ratio (10⁵). Single‐NW photodetectors on SiO₂/Si substrate show good sensitivity to visible light. Using the contact printing process, large‐scale ordered Zn₃As₂ NW arrays are successfully assembled on SiO₂/Si substrate to prepare NW thin‐film transistors and photodetectors. The NW‐array photodetectors on rigid SiO₂/Si substrate and flexible PET substrate exhibit enhanced optoelectronic performance compared with the single‐NW devices. The results reveal that the p‐type Zn₃As₂ NWs have important applications in future electronic and optoelectronic devices.     

Dendrimer‐Functionalized Iron Oxide Nanoparticles for Specific Targeting and Imaging of Cancer Cells

We demonstrated a unique approach that combines a layer‐by‐layer (LbL) self‐assembly method with dendrimer chemistry to functionalize Fe₃O₄ nanoparticles (NPs) for specific targeting and imaging of cancer cells. In this approach, positively charged Fe₃O₄ NPs (8.4 nm in diameter) synthesized by controlled co‐precipitation of Fe^II and Fe^III ions were modified with a bilayer composed of polystyrene sulfonate sodium salt and folic acid (FA)‐ and fluorescein isothiocyanate (FI)‐functionalized poly(amidoamine) dendrimers of generation 5 (G5.NH₂‐FI‐FA) through electrostatic LbL assembly, followed by an acetylation reaction to neutralize the remaining surface amine groups of G5 dendrimers. Combined flow cytometry, confocal microscopy, transmission electron microscopy, and magnetic resonance imaging studies show that Fe₃O₄/PSS/G5.NHAc‐FI‐FA NPs can specifically target cancer cells overexpressing FA receptors. The present approach to functionalizing Fe₃O₄ NPs opens a new avenue to fabricating various NPs for numerous biological sensing and therapeutic applications.     

Mechanical Restoration of Damaged Polymer Films by “Repair‐and‐Go”

A microencapsulation and nanoparticle deposition technique, termed “repair‐and‐go,” is employed for inducing mechanical restoration of damaged polymer films. In “repair‐and‐go,” polymer‐stabilized emulsion droplets, containing surface‐functionalized SiO₂ nanoparticles, traverse a substrate and deposit their nanoparticle contents selectively into the damaged regions. Surface‐oxidized poly(dimethylsiloxane) is employed as the substrate, and dynamic mechanical analysis reveals the enhanced mechanical properties of the film following nanoparticle deposition. Healing efficiency is optimal when using thinner test substrates, repeated deposition cycles, and functional SiO₂ nanoparticles that afford access to postdeposition curing.     

Solar Cells with Enhanced Photocurrent Efficiencies Using Oligoaniline‐Crosslinked Au/CdS Nanoparticles Arrays on Electrodes

Different configurations of CdS nanoparticles (NPs) are linked to Au electrodes by electropolymerization of thioaniline‐functionalized CdS NPs onto thioaniline‐functionalized Au‐electrodes. In one configuration, thioaniline‐functionalized CdS NPs are electropolymerized in the presence of thioanline‐modified Au NPs to yield an oligoaniline‐crosslinked CdS/Au NPs array. The NP‐functionalized electrode generates a photocurrent with a quantum yield that corresponds to ca. 9%. The photocurrent intensities are controlled by the potential applied on the electrode, and the redox‐state of the oligoaniline bridge. In the oxidized quinoide state of the oligoaniline units, the bridges act as electron acceptors that trap the conduction‐band electrons that are transported to the electrode and lead to high quantum yield photocurrents. The reduced π‐donor oligoaniline bridges act as π‐donor sites that associate N,N′‐dimethyl‐4,4′‐bipyridinium, MV²⁺, by donor/acceptor interactions, K_a = 5270 M^?1. The associated MV²⁺ acts as an effective trap of the conduction‐band electrons, and in the presence of triethanolamine (TEOA) as an electron donor, high photocurrent values are measured (ca. 12% quantum yield). The electropolymerization of thioaniline‐functionalized Au NPs and thioaniline‐modified CdS NPs in the presence of MV²⁺ yields a MV²⁺‐imprinted NP array. The imprinted array exhibits enhanced affinities toward the association of MV²⁺ to the oligoaniline π‐donor sites, K_a = 2.29 × 10⁴ M^?1. This results in the effective trapping of the conduction‐band electrons and an enhanced quantum yield of the photocurrent, ca. 34%. The sacrificial electron donor, TEOA, was substituted with the reversible donor I₃^?. A solar cell consisting of the imprinted CdS/Au NPs array, with MV²⁺ and I₃^?, was constructed. The cell generated a photocurrent with a quantum yield of 4.7%.     

Fast Potassium Storage in Hierarchical Ca0.5Ti2(PO4)3@C Microspheres Enabling High‐Performance Potassium‐Ion Capacitors

Hybrid potassium‐ion capacitors (KICs) show great promise for large‐scale storage on the power grid because of cost advantages, the weaker Lewis acidity of K⁺ and low redox potential of K⁺/K. However, a huge challenge remains for designing high‐performance K⁺ storage materials since K⁺ ions are heavier and larger than Li⁺ and Na⁺. Herein, the synthesis of hierarchical Ca_0.5Ti₂(PO₄)₃@C microspheres by use of the electrospraying method is reported. Benefiting from the rich vacancies in the crystal structure and rational nanostructural design, the hybrid Ca_0.5Ti₂(PO₄)₃@C electrode delivers a high reversible capacity (239 mA h g^?1) and superior rate performance (63 mA h g^?1 at 5 A g^?1). Moreover, the KIC employing a Ca_0.5Ti₂(PO₄)₃@C anode and activated carbon cathode, affords a high energy/power density (80 W h kg^?1 and 5144 W kg^?1) in a potential window of 1.0–4.0 V, as well as a long lifespan of over 4000 cycles. In addition, in situ X‐ray diffraction is used to unravel the structural transition in Ca_0.5Ti₂(PO₄)₃, suggesting a two‐phase transition above 0.5 V during the initial discharge and solid solution processes during the subsequent K⁺ insertion/extraction. The present study demonstrates a low‐cost potassium‐based energy storage device with high energy/power densities and a long lifespan.     

Nanostructured Alkaline‐Cation‐Containing δ‐MnO2 for Photocatalytic Water Oxidation

Oxygen evolution from water is one of the key reactions for solar fuel production. Here, two nanostructured K‐containing δ‐MnO₂ are synthesized: K‐δ‐MnO₂ nanosheets and K‐δ‐MnO₂ nanoparticles, both of which exhibit high catalytic activity in visible‐light‐driven water oxidation. The role of alkaline cations in oxygen evolution is first explored by replacing the K⁺ ions in the δ‐MnO₂ structure with H⁺ ions through proton ion exchange. H‐δ‐MnO₂ catalysts with a similar morphology and crystal structure exhibit activities per surface site approximately one order of magnitude lower than that of K‐δ‐MnO₂, although both nanostructured H‐δ‐MnO₂ catalysts have much larger Brunauer–Emmett–Teller (BET) surface areas. Such a low turnover frequency (TOF) per surface Mn atom might be due to the fact that the Ru²⁺(bpy)₃ sensitizer is too large to access the additional surface area created during proton exchange. Also, a prepared Na‐containing δ‐MnO₂ material with an identical crystal structure exhibits a TOF similar to that of the K‐containing δ‐MnO₂, suggesting that the alkaline cations are not directly involved in catalytic water oxidation, but instead stabilize the layered structure of the δ‐MnO₂.     

Ultrafine Nickel‐Nanoparticle‐Enabled SiO2 Hierarchical Hollow Spheres for High‐Performance Lithium Storage

The high theoretical capacity and natural abundance of SiO₂ make it a promising high‐capacity anode material for lithium‐ion batteries. However, its widespread application is significantly hampered by the intrinsic poor electronic conductivity and drastic volume variation. Herein, a unique hollow structured Ni/SiO₂ nanocomposite constructed by ultrafine Ni nanoparticle (≈3 nm) functionalized SiO₂ nanosheets is designed. The Ni nanoparticles boost not only the electronic conductivity but also the electrochemical activity of SiO₂ effectively. Meanwhile, the hollow cavity provides sufficient free space to accommodate the volume change of SiO₂ during repeated lithiation/delithiation; the nanosheet building blocks reduce the diffusion lengths of lithium ions. Due to the synergistic effect between Ni and SiO₂, the Ni/SiO₂ composite delivers a high reversible capacity of 676 mA h g^?1 at 0.1 A g^?1. At a high current density of 10 A g^?1, a capacity of 337 mA h g^?1 can be retained after 1000 cycles.     

Bright Blue Photo‐ and Electroluminescence from Eu2+‐Doped GaN/SiO2 Nanocomposites

In this article we demonstrate the synthesis of Eu²⁺‐doped GaN/SiO₂ nanocomposites using a simple solid state reaction and their use in light‐emitting devices. The nanocomposite exhibits a bright blue luminescence when excited in the UV region (quantum yield = 23 %). The origin of the blue emission is attributed to the presence of europium ions in the +2 oxidation state in the GaN/SiO₂ nanocomposites. Analysis of the EPR spectrum of europium‐doped GaN/SiO₂ nanocomposites confirms the existence of Eu²⁺ in the nanocomposites. Various control experiments show that the blue emission arises from these europium ions and that the interface of GaN and silica plays a crucial role. The Eu²⁺‐doped GaN/SiO₂ nanocomposite also exhibits a bright blue electroluminescence. Furthermore, the nanocomposites can be coated with a polymer to tune their dispersibility in organic medium.     

Membrane‐Free Detection of Metal Cations with an Organic Electrochemical Transistor

Alkali‐metal ions, particularly sodium (Na⁺) and potassium (K⁺), are the messengers of living cells, governing a cascade of physiological processes through the action of ion channels. Devices that can monitor, in real time, the concentrations of these cations in aqueous media are in demand not only for the study of cellular machinery, but also to detect conditions in the human body that lead to electrolyte imbalance. In this work, conducting polymers are developed that respond rapidly and selectively to varying concentrations of Na⁺ and K⁺ in aqueous media. These polymer films, bearing crown‐ether‐functionalized thiophene units specific to either Na⁺ or K⁺, generate an electrical output proportional to the cation type and concentration. Using electropolymerization, the ion‐selective polymers are integrated as the gate electrode of an organic electrochemical transistor (OECT). The OECT current changes with respect to the concentration of the ion to which the polymer electrode is selective. Designed as a single, miniaturized chip, the OECT enables the selective detection of the cations within a physiologically relevant range. These electrochemical ion sensors require neither ion‐selective membranes nor a reference electrode to operate and have the potential to surpass existing technologies for the detection of alkali‐metal ions in aqueous media.     

Highly Fluorescent Conjugated Polyelectrolyte Nanostructures: Synthesis,Self‐Assembly,and Al3+ Ion Sensing

A highly fluorescent triazine‐bridged polymer, poly[(diphenylamino‐s‐triazine)‐co‐(2‐methoxy‐5‐propyloxysulfonate‐1,4‐phenylene vinylene)] (DTMSPV), is synthesized from Wittig polycondensation of a triazine monomer with a water‐soluble p‐phenylene vinylene monomer. The fluorescent amphiphilic polymer in aqueous solution self‐assembled into nanoassemblies of micelle‐like nanostructure (MS) and π stacking nanostructure (πS), which have average sizes of 93 to 270 nm, depending on the concentration of DTMSPV. The micelle‐like nanostructure of DTMSPV (MS) shows blue emission at 457 and 488 nm with a high emission quantum yield (Φ_E) of 31% in aqueous solution. On the other hand, the Φ_E of π stacking structures (πS), formed in a highly concentrated solution, is lower than the MS. The MS exhibits fluorescence quenching as well as color change from blue to green/yellow, depending on the kinds of metal ions. The metal ion sensitivity is larger in the order of the main group ions (Na⁺, K⁺) < dicationic transition metal ions (Zn²⁺, Cd²⁺, Pb²⁺, Cu²⁺, Pd²⁺) < trivalent transition metal ions (Fe³⁺, Ru³⁺), with an exception of Al³⁺. In particular, the fluorescence of MS is dramatically quenched with color change to yellow in response to Al³⁺ concentrations. The selectivity and sensitivity of MS to Al³⁺ are unusually high even in the presence of competitive metal ions, which can be attributed to the specific interaction of triazine units with Al³⁺.     

pH, pK and pNa detection properties of SiO2/Si3N4 ISFET chemical sensors

This article reports the technological fabrication and the electrical characterisation of SiO₂/Si₃N₄ ion sensitive field effect transistors (ISFET) for the detection of H⁺, K⁺ and Na⁺ ions. ISFET chemical sensors show quasi-nernstian pH response with sensitivities around 54 mV/pH. pK and pNa measurements are also investigated, evidencing sensitivities lower than 20 mV/pH and non-nernstian pH-dependent phenomena for the highest K⁺ or Na⁺ concentrations (pK and pNa, respectively, lower than 4 and 3). It is shown that the detection properties of H⁺, K⁺ and Na⁺ ions are dependent on each other, being responsible for saturation effects for the highest concentrations. It is finally concluded that SiO₂/Si₃N₄ ISFETs are well adapted for the pH measurement, can be used for the pK or pNa measurements in the case of buffered solutions but are not fully suitable for multi-ion detection in the case of medical analysis.