Gold colloids with nanoparticles of different sizes were found to enhance the chemiluminescence (CL) of the luminol-H2O2 system, and the most intensive CL signals were obtained with 38-nm-diameter gold nanoparticles. UV-visible spectra, X-ray photoelectron spectra, and transmission electron microscopy studies were carried out before and after the CL reaction to investigate the CL enhancement mechanism. The CL enhancement by gold nanoparticles of the luminol-H2O2 system was supposed to originate from the catalysis of gold nanoparticles, which facilitated the radical generation and electron-transfer processes taking place on the surface of the gold nanoparticles. The effects of the reactant concentrations, the size of the gold nanoparticles. and some organic compounds were also investigated. Organic compounds containing OH, NH2, and SH groups were observed to inhibit the CL signal of the luminol-H2O2-gold colloids system, which made it applicable for the determination of such compounds.

Electrodes with three-dimensionally ordered macroporous (3DOM) carbon as the intermediate layer between an ionophore-doped solvent polymeric membrane and a metal contact are presented as a novel approach to solid-contact ion-selective electrodes (SC-ISEs). Due to the well-interconnected pore and wall structure of 3DOM carbon, filling of the 3DOM pores with an electrolyte solution results in a nanostructured material that exhibits high ionic and electric conductivity. The long-term drift of freshly prepared SC-ISEs with 3DOM carbon contacts is only 11.7 microV/h, and does not increase when in contact with solution for 1 month, making this the most stable SC-ISE reported so far. The electrodes show good resistance to the interference from oxygen. Moreover, in contrast to previously reported SC-ISEs with conducting polymers as the intermediate layer, 3DOM carbon is an electron conductor rather than a semiconductor, eliminating any light interference.

The effects of the architecture and surface chemistry of three-dimensionally ordered macroporous (3DOM) carbon solid contacts on the properties of ion-selective electrodes (ISEs) were examined. Infiltration of the plasticized PVC membrane into the pores of the carbon created a large interfacial area between the sensing membrane and the solid contact, as shown by cryo-SEM and elemental analysis. This large interfacial area, along with the high capacitance of the 3DOM carbon solid contacts (as determined by cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy) results in an excellent long-term stability of the potentiometric response, with drifts as low as 11.7 µV/h. The comparison of 3DOM carbon solid contacts with an untemplated carbon solid contact shows that the pore structure is an essential feature for the excellent electrode performance. However, the surface chemistry of the 3DOM carbon cannot be ignored. While there is no evidence for an aqueous layer forming between the sensing membrane and unoxidized 3DOM carbon, electrodes based on oxidized 3DOM carbon exhibit potentiometric responses with the typical hysteresis indicative of a water layer. A comparison of the different techniques to characterize the solid contacts confirms that constant-current charge-discharge experiments offer an intriguing approach to assess the long-term stability of solid-contact ISEs but shows that their results need to be interpreted with care.

Liquid-junction-free reference electrodes that contact the sample through an ionic-liquid-doped, hydrophobic polymer membrane have attracted attention because they offer an alternative to reference electrodes with conventional salt bridges. In this work, liquid-junction-free reference electrodes were developed using plasticized poly(vinyl chloride) membranes doped with the ionic liquid (IL) 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide. Three-dimensionally ordered macroporous (3DOM) carbon substrates infused with this ionic liquid phase were used as solid contacts for these reference membranes. As in prior work with ionophore-based 3DOM carbon-contact ion-selective electrodes, the long-term stability of the liquid-junction-free reference electrodes was excellent, with potential drifts as low as 42 μV/h over 26 days. Successful measurements of pH in milk were performed and, to the best of our knowledge, are the first example of the use of liquid-junction-free reference electrodes in complex real-life samples. A thorough analysis of their performance at low pH revealed protonation of the ionic liquid anion (L(-)) and formation of LHL(-) type of associates in the reference electrode membrane, effects not observed in prior work. Also, when reference membranes were mounted into conventional electrode bodies with inner filling solutions that contained no ionic liquid ions, zero-current ion fluxes across the sample/membrane interface occurred, as previously only seen for ionophore-doped ion-selective membranes. Understanding these effects will be crucial to the design of liquid-junction-free reference electrodes suitable for other applications.

Solid-contact ion-selective electrodes (SC-ISEs) can exhibit very low detection limits and, in contrast to conventional ISEs, do not require an optimization of the inner filling solution. This work shows that subnanomolar detection limits can also be achieved with SC-ISEs with three-dimensionally ordered macroporous (3DOM) carbon contacts, which have been shown recently to exhibit excellent long-term stabilities and good resistance to the interferences from oxygen and light. The detection limit of 3DOM carbon-contacted electrodes with plasticized poly(vinyl chloride) as membrane matrix can be improved with a high polymer content of the sensing membrane, a large ratio of ionophore and ionic sites, and conditioning with a low concentration of analyte ions. This permits detection limits as low as 1.6×10−7 M for K+ and 4.0×10−11 M for Ag+.