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We report that silver ion ([Ag.sup.+]) uptake is enhanced by 4-aminopyridine (4-AP), a well known voltage-sensitive potassium ion channel ([K.sub.v]) blocker. Both bacterial (Escherichia coli) and mammalian (3T3 fibroblast) cells were used as model systems. [Ag.sup.+] uptake was monitored with a scanning electrochemical microscope with an amperometric [Ag.sup.+] ion-selective electrode ([Ag.sup.+]-ISE) and the respiration rates of E. coli cells were measured by oxygen reduction at an ultramicroelectrode. The results showed that not only the amount but also the rate of silver uptake by the cells increased significantly when 4-AP was added to the solution. For fibroblasts, the [Ag.sup.+] uptake rate was 4.8 x [10.sup.7] ions per cell per sec without 4-AP compared with 1.0 x [10.sup.8] ions per cell per sec with 0.2 mM 4-AP. For E. coli cells, the uptake rate was 1.5 x 104 ions per cell per sec without 4-AP vs. 3.5 x [10.sup.4] ions per cell per sec with 0.5 mM 4-AP and 5.9 x [10.sup.4] ions per cell per sec with 1 mM 4-AP. Thus, 4-AP might be useful where silver is used as antimicrobial agent to speed its uptake. E. coli | scanning electrochemical microscope | silver ion

We report the use of a micropipet-supported ITIES (interface between two immiscible electrolyte solutions, also called a liquid/liquid (L/L) or water/oil (W/O) interface) as a scanning electrochemical microscopy (SECM) tip to detect silver ion and explore [Ag.sup.+] toxicity in living cells. A 1,2-dichloroethane solution containing a commercially available calixarene-based [Ag.sup.+] ionophore (IV) was injected into a micrometer-size glass pipet to construct an [Ag.sup.+]-selective SECM tip. The local [Ag.sup.+] concentration, down to the micromolar level, in the vicinity of living fibroblast cells, was monitored by SECM approach curves and through imaging of the uptake and efflux of [Ag.sup.+] by living fibroblast cells in real time. The results show that several stages of interaction between [Ag.sup.+] and fibroblast cells exist. Since a number of biological processes of cells are involved with non-redox-active ions, the work presented here provides a new way to explore cell metabolism, drug delivery, and toxicity assessment by SECM.

Electrochemical, spectroscopic, and mass spectrometric (MS) methods were used to probe the interaction (complexation) of silver ions and zerovalent silver species with polyamidoamine generation 1 amine-terminated (PAMA-MG1N[H.sub.2]) and generation 2 hydroxy-terminated (PAMA-MG2OH) dendrimers (DDMs). Stability constants ([K.sup.+.sub.q]) and stoichiometries (q) (i.e., the number of silver ions complexed per DDM molecule) were determined from the voltammetric data, that is, shifts in potential and changes in peak or limiting current with addition of DDM. When the mole ratio of DDM to [Ag.sup.+] is [greater than or equal to] 1, [Ag.sup.+] binds with PAMAMG2OH to form a dominant 1:1 complex with a [K.sup.+.sub.1] value of 1.1 x [10.sup.7] [M.sup.-1]. Under similar conditions, [Ag.sup.+] binds with PAMAMG1N[H.sub.2], yielding a 1:1 complex with [K.sup.+.sub.1] = 4 x [10.sup.9] [M.sup.-1], which is consistent with the finding of the MS experiments. When the mole ratio is

The bipolar conductance, BICON, technique for the measurement of solution resistance, based on the application of microsecond current pulses, as originally described by Enke and co-workers for measurements with conventional electrodes, was extended for use with ultramicroelectrodes, with a focus on its application in scanning electrochemical microscopy (SECM). When the plateau time used to make the measurement lies within the BICON conditions, the solution conductance can be obtained directly from the output without the need for calibration curves. However, decreasing the size of the ultramicroelectrode decreases the range of values that satisfy these conditions, and one must resort to calibration curves to obtain solution conductance from the measured current, which was nevertheless found to be proportional to electrolyte concentration with electrodes as small as 5 [micro]m in diameter. BICON/SECM approach curves over insulating substrates followed SECM negative feedback theory and approach curves in the presence of low (micromolar) or no added electrolyte are possible once the background conductivity is taken into account. Approach curves to a conducting substrate at open circuit potential are influenced by the solution time constant (solution resistance at the electrode tip x electrode double layer capacitance), which is a function of the tip/substrate distance, as well as the substrate size.

The use of the scanning electrochemical microscope (SECM) to probe the kinetics of charge-transfer processes at bilayer lipid membranes (BLM) is presented. Analysis of the SECM tip response demonstrates that an unmodified BLM behaves as an insulator, whereas a BLM doped with iodine shows some positive feedback. The SECM technique thus allows one to probe processes at BLM and determine the kinetics of the charge-transfer process. The SECM can also be used to determine the shape of the BLM.

A study was conducted to analyze the ion transport characteristics of two gels made from polyacrylate and polyacrylamide using scanning electrochemical microscopy (SECM). A platinum microdisk was utilized as the SECM tip while a platinum wire was used as a quasi-reference electrode. Results indicated that the transient SECM response can be utilized to obtain the diffusion coefficient of a redox species from the critical transient time as a function of tip displacement.

Electrogenerated chemiluminescence (ECL) at a scanning electrochemical microscope (SECM) tip as the tip was moved in the vicinity of insulating and conductive substrates was studied either by ion annihilation or with a coreactant. The SECM/ECL approach curves (intensity vs tip-substrate distance, d) with both insulating and conducting substrates showed a decrease in ECL intensity with a decrease in d. Modes of operation that produced sufficiently intense and stable ECL for optical imaging are possible. The needed improvements for higher resolution and the potential application of this technique for the studies of the kinetics and mechanisms of coreactant ECL reactions are discussed.

Electrochemical measurements on single molecules of [(trimethylammonio)methyl]ferrocene ultramicrotips insulated at the tip with Apiezon wax. Rapid heterogeneous electron transfer reactions at the electrodes produced a current of approximately 0.6 pA/molecule. Analyses revealed that fluctuations in the tip current are influenced by cell geometry and nature of the substrate.

The electrochemical detection of single iridium oxide nanoparticle (Ir[O.sub.x] NP) collisions on a NaB[H.sub.4]-treated Pt ultramicroelectrode (UME) is described. The observed current is very sensitive to the material and surface state of the measuring electrode, a NaB[H.sub.4]-treated Pt UME is significant for obtaining reproducible results.

The electrical properties of self-assembled monolayers (SAMs) on a gold surface is explored, to address the relation between the conductane of a molecule and its electronic structure. The rectifying behavior of the electric conduction of a fresh SAM, of these molecules is explained.