Photoinduced Fluorescence Activation and Nitric Oxide Release with Biocompatible Polymer Nanoparticles

A viable strategy to encapsulate a fluorophore/photochrome dyad and a nitric oxide photodonor within supramolecular assemblies of a cyclodextrin‐based polymer in water was developed. The two photoresponsive guests do not interact with each other within their supramolecular container and can be operated in parallel under optical control. Specifically, the dyad permits the reversible switching of fluorescence on a microsecond timescale for hundreds of cycles, and the photodonor enables the irreversible release of nitric oxide. Furthermore, these supramolecular assemblies cross the membrane of human melanoma cancer cells and transport their cargo in the cytosol. The fluorescence of one component allows the visualization of the labeled cells, and its switchable character could, in principle, be used to acquire super‐resolution images, while the release of nitric oxide from the other induces significant cell mortality. Thus, our design logic for the construction of biocompatible nanoparticles with dual functionality might evolve into the realization of valuable photoresponsive probes for imaging and therapeutic applications.     

Light‐Controlled Ion Transport through Biomimetic DNA‐Based Channels

Light‐controlled nanochannels are fabricated through self‐assembling azobenzene‐incorporated DNA (Azo‐DNA) strands to regulate ion transport. By switching between collapsed and relaxed states using visible and ultraviolet light alternately, the Azo‐DNA channels can be opened and closed because the conformation of Azo‐DNA changes, that is, Azo‐DNA is used as switchable controlling unit. In addition to sharing short response time and reversibility with other photoresponsive apparatuses, the Azo‐DNA‐based nanochannel system has advantages in good biocompatibility and versatile design, which could potentially be applied in light‐controlled drug release, optical information storage, and logic networks.     

Neutral-carrier-type potassium ion-selective electrodes based on polymer-supported liquid-crystal membranes for practical use.

Polymer-supported liquid-crystal membranes have been designed for neutral-carrier-type potassium ion-selective electrodes, aiming for practical applications of high-performance liquid-crystalline membrane ion sensors. Two types of polymer-supported liquid-crystal membranes were tested for their usefulness; one is microporous poly(tetra fluoroethylene) (PTFE) membranes impregnated by thermotropic liquid-crystalline compounds, and another is poly(methyl methacrylate) (PMMA) membrane dispersing the same liquid-crystalline compounds. Both of the polymer-supported liquid-crystal membranes containing a liquid-crystalline benzo-15-crown-5 neutral carrier as well as a lipophilic anion excluder work well as ion-sensing membranes for potassium ion-selective electrodes, the ion selectivities of which can be switched by the measurement temperatures. Specifically, PTFE-impregnated liquid-crystal membranes are better than the PMMA-dispersed ones in the sensitivity and selectivity of the resulting ion electrodes. A potassium ion assay in blood sera has proved that neutral-carrier-type ion-selective electrodes based on the polymer-supported liquid-crystal membranes are reliable for practical uses.     

新型杯芳烃为载体的铅离子选择电极

报道了5,11,17,23-四（1,1-二甲基乙基）-25,27-二羟基-26,28-二[（2-丙酰胺）乙氧基]杯[4]芳烃1的合成及以此化合物为载体研制了PVC膜铅离子选择电极。研究了不同极性的膜增塑剂和亲脂性阴离子位点对铅离子选择电极响应性能的影响,测定了铅离子选择电极的性能。铅离子选择电极对铅离子表现出优良的能斯特响应和高选择性,能在pH4.0-6.5的范围内使用,该电极可作为电位滴定的指示电极。     

Kinetic considerations of ion selectivity coefficients of ion-selective electrodes based on neutral carriers

Ion selectivity coefficients of ion-selective electrodes based on neutral carriers are described by means of a mixed potential model of ion transport reactions at the aqueous solution/ion-sensitive membrane interface. The decrease in ion selectivity can be explained by the deviations from the equilibrium conditions, which arise from the ionic partial current across the interface, but the proposed correspondence of the exchange current density of ion transfer reactions with the ion selectivity coefficients is rationalized only for certain conditions of the kinetic parameters. The ion selectivity for liquid membrane transport is discussed starting from three different rate-determining steps. It is shown that the potentiometric selectivities of ion-selective electrodes and the transport selectivities are correlated when the ionic transfer across the aqueous solution/ membrane interface is fast compared with the complex ion transport through the membrane. The significance of a kinetic approach for the design of neutral carriers for ion-selective electrodes is stressed.     

Electrochemical analysis based on nanoporous structures

Analytical applications and the underlying principles of unique electrochemistry in nanoporous structures are reviewed and discussed. In addition to the conventional concept of enlarged surface area, the structural effects of nanoporous materials can play significant roles such as discriminative electrokinetics, the nano-confinement effect, electrical double layer overlapping, ion-selective impedance, etc. The applications described in this review article include solid-state pH sensors, miniaturized pseudo-reference electrodes, nonenzymatic glucose monitoring, ion diodes, transistors, extracellular neural probes, and a few more. Further intensive research is required to develop creative analytical tools based on nanoporous structures and to unravel the underlying physicochemical principles.     

Recent developments in the field of metal complexes containing photochromic ligands: Modulation of linear and nonlinear optical properties

Organic photochromic molecules are important for the design of photoresponsive functional materials, as switches and memories. Over the past 10 years, research efforts have been directed towards the incorporation of photoresponsive molecules into metal systems, in order either to modulate the photochromic properties, or to photoregulate the redox, optical and magnetic properties of the organometallic moieties. This review article focuses on some of the recent work reported within the last few years in the area of organometallic and coordination complexes containing photochromic ligands for the photoregulation of optical and nonlinear optical properties. The first part is related to photochromic 1,2-diarylethene (DAE)-containing metal complexes, examples of mono- and multi-DAE metal-based will be discussed. The second part deals with metal complexes incorporating spiropyran and spirooxazine derivatives.     

Construction and application of photoresponsive smart nanochannels

In living organisms, many biological processes are inextricably linked with light, such as the photosynthesis systems and rhodopsin. Hence, construction of light-sensitive biomimetic-nanochannels, which can realize the functions of cells and other membrane structures with high degree of spatial and temporal control, is particularly attractive and challenging. As a cornerstone of light-sensitive nanochannels, the photoresponsive materials are a big family and at their mature stage after several decades of development, which can provide different strategies to construct biomimetic photoresponsive nanochannels. In this review, we mainly summarize the construction and applications of photoresponsive nanochannels on the basis of various photoresponsive materials. The construction of photoresponsive nanochannels can be classified into four categories: photoresponsive inorganic nanochannels based on inorganic-compound-based photonic sensitive materials; photoresponsive organic nanochannels based on organic-compound-based photonic sensitive materials; photoresponsive polymers nanochannel based on photoresponsive polymers materials and potential photoresponsive nanochannels based on other photoresponsive materials. After introducing the construction of photoresponsive nanochannels, the review highlights some of the most recent applications of photoresponsive nanochannels in separation, energy conversion and storage, drug delivery and so on.     

Iodide Ion-Selective Electrode and Its Application to the Determination of Organic Compounds

The mixture of silver iodide and ferrocene is used to prepare the membrane of iodide ion-selective electrode. The interference of sulfide can be reduced by the addition of cupric ion in the test solution. Ethylene glycol is determined by potentiometric titration using iodine ion-selective electrode as an indicator electrode.     

The effect of electric field on potentiometric Scanning Electrochemical Microscopic imaging

Potentiometric Scanning Electrochemical Microscopy (SECM) is a powerful tool in corrosion science. It allows the selective imaging of a particular ionic species released at the anodic sites in a corrosion microcell, by using ion-selective microelectrodes (ISMEs) as scanning probes. Galvanic corrosion is a particularly often studied process. The measured potential of the ISME is thought to depend only on the activity of the primary ion. However, an electric field is also formed as a result of the potential difference between the surfaces of the galvanic pair, which has a direct influence on the potential of the sensing microelectrode; the measured potential is the sum of these two contributions. The potential difference caused by the electric field can be substantially large, exceeding that of the potential difference associated with the activity of the primary ion. In this paper, we present experimental evidence of this feature, and investigate the extent to which it influences the final chemically-resolved image.     

Electrochemical methods for the determination of the diffusion coefficient of ionophores and ionophore-ion complexes in plasticized PVC membranes

The diffusion coefficients of active components in ion-selective membranes have a decisive influence on the life-time and detection limit of the respective ion-selective electrodes, as well as influencing the rate of polarization and relaxation processes of electrically perturbed ion sensors. Therefore, the rational design of mass transport controlled ion-selective electrodes with sub-nanomolar detection limits requires reliable data on the diffusion coefficients. We have implemented electrochemical methods for the quantitative assessment of both the diffusion coefficients of free ionophores and ion-ionophore complexes. The diffusion coefficients of the pH-sensitive chromoionophore ETH 5294 and the calcium-selective ionophore ETH 5234 were determined in plasticized PVC membranes with different PVC to plasticizer ratios. The diffusion coefficient of the free chromoionophore determined by a chronoamperometric method was validated with optical methods for a variety of membrane compositions. The calcium-selective ionophore ETH 5234 was used as a model compound to assess the diffusion coefficient of the ion-ionophore complex calculated from the time required for the complexes to cross a freshly prepared membrane during potentiometric ion-breakthrough experiments. The difference between the diffusion coefficients of the free ionophore ETH 5234 and the ion-ionophore complex was found to be significant and correlated well with the geometry of the respective species.     

Optical sensors: An ion-selective optrode for potassium

A new type of sensor (called ion-selective optrode) for the continuous determination of electrolytes is presented that can be exploited in optical and fibre-optic sensors. It is based on the ability of certain fluorescent dyes to respond to an electrical potential at the interface between a lipid phase and an aqueous phase. The potential is created by addition of a neutral ion-carrier, and its magnitude is measured with an appropriate potential-sensitive dye. An opto-sensor for potassium is described. A lipid bilayer is formed on a glass support by applying the Langmuir-Blodgett film technique. A lipid-soluble rhodamine dye is incorporated into this layer together with valinomycin as the ion-carrier. When exposed to potassium ion solutions in the 0.01–100 mM range, fluorescence intensity is continuously diminished. It is shown that two kinds of response towards potassium solutions occur: one is selective for this ion, but the other is unselective, being evident with other metal ions. the unselective response can be compensated for by a reference optrode. The signal change of the ion-selective optrode depends on the nature of the layer and the concentration of dye and valinomycin. The relationship between ΔI/I (i.e., the reduction in intensity relative to the total signal) and the logarithmic analyte concentration is linear over a wide range, typically 0.01–10 mM. The selectively factor over sodium varies from 2.5 to 5.     

PVC膜离子选择电极检测下限的优化

价格低廉、携带方便、适用浓度宽、操作简单快捷、能耗低的离子选择电极在医院、分析实验室、野外等领域得到了越来越广泛的应用。尽管如此,由于PVC膜中存在的离子流严重破坏了更低检测下限的获取,限制了离子选择电极的进一步发展。因此,本文从减小甚至消除PVC膜中存在的离子流角度出发,系统论述了优化PVC膜离子选择电极检测下限的原理和优良策略,根据收集归纳的大量数据定量阐述传感膜组成的优化、电极组装和调制、应用旋转电极以及电流极化处理等对检测下限的优化提升作用,进一步总结出各种方法的改善规律,分析它们的优势和面临的问题。提出在PVC铸膜液中要突破传统配方,减小增塑剂和离子交换剂用量,以抑制传感膜两侧的离子流,同时外加电流补偿处理等也是降低电极检测下限的有效方法,对检测下限的改善最好的可降低5个数量级。这一总结为PVC膜离子选择电极的高性能化明确了研究方向。     

Potassium-ion-selective sensing based on selective reflection of cholesteric liquid crystal membranes

It is well-known that cholesteric liquid crystals have an optical property, selective reflection, due to changes in the pitch of their helical structure. This unique property of cholesteric liquid crystals can be used to attain a visual sensing system showing color changes as the detection signal. In this paper, we report a visual sensing membrane comprising cholesteric liquid crystals, in which a 15-crown-5 derivative was incorporated as ion recognizing sites, for K⁺ in aqueous solution. The resulting CLC membrane showed a shift of the reflection peak sensitive to K⁺ in water. We have also designed polymer-dispersed liquid crystal membranes that showed ion-selective reflection peak shifts with improved response time.     

Amperometric determination of hydrogen and hydroxyl ion concentrations in unbuffered solutions in the pH range 5–9

Hydrogen and hydroxyl ion concentrations can be determined by ion-selective amperometry in the pH range 5–9 in unbuffered solutions. The working electrode is a plasticized PVC membrane electrode loaded with the neutral hydrogen ion carrier tridodecylamine. Measurements are made in a flow-injection system.     

Optical and Electrochemical Probes for Monitoring Cytochrome c in Subcellular Compartments During Apoptosis

Cytochrome c (Cyt. c) is a key initiator of the caspases that activate cell apoptosis. The spatiotemporal evaluation of the contents of Cyt. c in cellular compartments and the detection of Cyt. c delivery between cellular compartments upon apoptosis is important for probing cell viabilities. We introduce an optical probe and an electrochemical probe for the quantitative assessment of Cyt. c in cellular compartments at the single cell level. The optical or electrochemical probes are functionalized with photoresponsive o-nitrobenzylphosphate ester-caged Cyt. c aptamer constituents. These are uncaged by light stimuli at single cell compartments, allowing the spatiotemporal detection of Cyt. c through the formation of Cyt. c/aptamer complexes at non-apoptotic or apoptotic conditions. The probes are applied to distinguish the contents of Cyt. c in cellular compartments of epithelial MCF-10A breast cells and malignant MCF-7 and MDA-MB-231 breast cells under apoptotic/non-apoptotic conditions.     

Application of amalgam electrodes in studies of heavy metals under natural water conditions

The application of amalgam electrodes for measuring the degree of complexation of metal ions is described with respect to natural water conditions. The amalgam electrodes are compared with the corresponding capabilities of ion-selective electrodes. A special cell is described for preparing the amalgam and for filling a hanging amalgam drop electrode. Factors affecting the reproducibility of the standard potentials and slopes, the response time and detection limits are discussed. Complexation measurements are described with lead and zinc amalgam electrodes. Triethylenetetramine, carbonate and nitrolotriacetic acid are used as ligands, to test the ability of these electrodes to measure correctly8 the degree of complexation even at low total-metal. concentrations (down to ca. 10^?7 M) and at very low concentrations of free metal ion (10^?15 M). Results obtained with well-characterized fulvinc compound and an algal culture medium (AAP) are also reported. The observed results are in compl;ete accordance with theoretical predictions (based on Nernstian behaviour), evven at the lowest concentrations of tltal and free metal ion used. An important limitation is that any oxidant in the solution can interfere by oxidizing the amalgma. Solutions must be carefully degassed to eliminate oxygen. It is shown that the interfering actin of oxidants can be corrected for by means of equations which are theoretically sound, even when the nature of the oxidant is unknown, provided that its content is not too high. Compared to ion-selective electrodes, amalgam electrodes are more reproducible, inexpensive and readily prepared for various metal ions which cannot be measured with ion-selective electrodes.     

Polymethacrylate polymers with appended aluminum(III)-tetraphenylporphyrins: Synthesis, characterization and evaluation as macromolecular ionophores for electrochemical and optical fluoride sensors

The synthesis and characterization of a novel polymethacylate polymer with covalently linked Al(III)-tetraphenylporphyrin (Al(III)-TPP) groups is reported. The new polymer is examined as a potential macromolecular ionophore for the preparation of polymeric membrane-based potentiometric and optical fluoride selective sensors. To prepare the polymer, an Al(III) porphyrin monomer modified with a methacrylate functionality is synthesized, allowing insertion into a polymethacrylate block copolymer (methyl methacrylate and decyl methacrylate) backbone. The resulting polymer can then be incorporated, along with appropriate additives, into conventional plasticized poly(vinyl chloride) films for testing electrochemical and optical fluoride response properties. The covalent attachment of the Al(III)-TPP ionophore to the copolymer matrix provides potentiometric sensors that exhibit significant selectivity for fluoride ion with extended lifetimes (compared to ion-selective membrane electrodes formulated with conventional free Al(III)-TPP structure). However, quite surprisingly, the attachment of the ionophore to the polymer does not eliminate the interaction of Al(III)-TPP structures to form dimeric species within the membrane phase in the presence of fluoride ion. Such interactions are confirmed by UV/visible spectroscopy of the blended polymeric films. Use of the new polymer-Al(III)-TPP conjugates to prepare optical fluoride sensors by co-incorporating a lipophilic pH indicator (4′,5′-dibromofluorescein octadecyl ester; ETH7075) is also examined and the resulting optical sensing films are shown to exhibit excellent selectivity for fluoride, with the potential for prolonged operational lifetime.     

A calcium-selective optrode based on fluorimetric measurement of membrane potential

An ion-selective optrode for the continuous determination of calcium ions is presented. It is based on measurement of the fluorescence intensity of a potential-sensitive dye (the C-18 ester of rhodamine B) incorporated into a lipid membrane constructed by the Langmuir-Blodgett film technique. The membrane potential depends on the calcium ion concentration in the sample solution, when a calcium-selective ionophore (ETH 1001) is incorporated into the lipid membrane. The fluorescence of the potential-sensitive dye is reduced with increasing calcium ion concentrations. Interferences by other cations can be compensated for by using a reference optrode. The relation between the negative logarithm of the calcium ion concentration and the decrease in relative fluorescence is linear over the range 0.1–10 mM calcium and can be described by an optical “Nernst” equation. The selectivity factors over magnesium, sodium and potassium are better than 1×10⁵ when the reference optrode is used. The maximal signal change caused by 10 mM calcium ion is ?8%. The membranes are stable for more than six months when stored in the dark. The analytical data are compared with those obtained with potassium- and sodium-selective optrodes, and the photophysical principles underlying the selective and unselective responses are discussed.