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The kinetics of tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)) oxidation and reduction in acetonitrile were investigated by steady-state voltammetry using scanning electrochemical microscopy (SECM). The SECM setup was placed inside a drybox for carrying out experiments in an anhydrous atmosphere and in the absence of oxygen. The standard rate constant, k°, for Ru(bpy) oxidation at a Pt electrode (radius, a = 5 μm) was 0.7 ± 0.1 cm/s, which is smaller than k° for Ru(bpy) reduction measured under the same conditions (≥3 cm/s). This is attributed to the 2,2'-bipyridine ligands having an electron-transfer (ET) blocking effect on the oxidation of the ruthenium(II) center, as opposed to the reduction, which involves ET to the exposed ligands. Thus, tunneling effects may be important in considering the ET in this molecule.

Metal doping of the metal oxide photoelectrocatalyst, BiVO4, dramatically increases its activity for water oxidation. Scanning electrochemical microscopy (SECM) was used to screen various dopants for their photoelectrochemical performance and to optimize the used dopant material concentrations with this photocatalyst. For example, adding Mo to W-doped BiVO4 enhanced the performance. The photocatalytic activity was examined on larger electrodes by means of photoelectrochemical and electrochemical measurements. The developed photoelectrocatalyst, W- and Mo-doped BiVO4, shows a photocurrent for water oxidation that is more than 10 times higher than undoped BiVO4. Factors that affect performance are discussed, and enhanced separation of excited electron–hole pairs by doping onto the semiconductor is suggested by first-principles density-functional theory (DFT) calculations. Distortion of the crystal structure of monoclinic scheelite-like BiVO4 by addition of W and Mo doping predicted by DFT is also revealed b...

We report the synthesis, electrochemistry, spectroscopy, and electrogenerated chemiluminescence (ECL) of a donor (D)–acceptor (A) molecule of form D–A−π–A–D, 4,4′-(7,7′-(9,9-bis(6-azidohexyl)-9H-fluorene-2,7-diyl)bis(benzo[c][1,2,5]thiadiazole7,4-diyl))bis(N,N-diphenylaniline) (Azide-BTA), and its organic nanoparticles (NPs). Azide-BTA consists of two 2,1,3-benzothiadiazole (A) and triphenylamine (D) groups at the ends bridged by a fluorene (π) moiety. Cyclic voltammetry (CV) of Azide-BTA showed a single reversible reduction wave (Eored = −1.48 V vs SCE) and two reversible oxidation waves (Eo1,ox = 0.92 V, Eo2,ox = 1.34 V vs SCE). The first oxidation and reduction waves were assigned two reversible, closely spaced one-electron transfers. Azide-BTA exhibited a large solvatochromic effect in the emission ranging from yellow (580 nm) to red (633 nm). The ECL spectrum resulting from the annihilation reaction showed a bright and single peak with a maximum at 652 nm in mixed solvent of acetonitrile and benzene ...

This review discusses briefly the preparation, electrochemistry, and electrogenerated chemiluminescence (ECL) as well as spectroscopic properties of organic nanoparticles. Organic nanoparticles, ranging from several tens of nanometers to hundreds of nanometers in diameter, were successfully prepared by various methods. Using a simple reprecipitation method, organic nanoparticles of a very small size can be prepared and show unique electrochemical and ECL characteristics. As with inorganic nanoparticles, organic nanoparticles suggest possible applications, like labels for the analysis of biological materials with ECL.

Oxygen evolution reaction (OER) electrocatalyst arrays for photoelectrochemical (PEC) water oxidation were fabricated on a metal oxide semiconductor photoelectrode, W-doped BiVO4 (BiVW-O). The electrocatalysts (IrOx, Pt, Co3O4) were prepared on a drop cast film of BiVW-O on fluorine-doped tin oxide (FTO) with a picoliter solution dispenser or photodeposition with light irradiation through an optical fiber. The prepared arrays were tested for PEC water oxidation in 0.2 M sodium phosphate buffer (pH 6.8) using scanning electrochemical microscopy modified with an optical fiber. Pt and Co oxide electrocatalysts showed an enhanced photocurrent for PEC water oxidation, while the other metal oxide catalysts including IrOx, which is known as an excellent water oxidation electrocatalyst on a metal substrate, were not effective. These results were confirmed with bulk film studies. A cobalt phosphate (Co-Pi) electrocatalyst was also tested as a bulk film on BiVW-O and showed improvement for PEC water oxidation. Prel...

A new D-A-π-A-D molecule (Spiro-BTA) containing two 2,1,3-benzothiadiazole (BTA) as the acceptor (A) and triphenylamine as the donor (D) bridged by a spirobifluorene moiety has been synthesized. The novel D-A molecule shows intense red emission (612 nm) with a high PL quantum yield (Φ(PL) = 0.51) in a solid film. A cyclic voltammogram of Spiro-BTA in 1:2 MeCN:benzene/0.1 M Bu(4)NPF(6) shows two reversible oxidation waves and one reversible reduction wave. The first oxidation wave and reduction wave were assigned as two successive electron transfer peaks separated by ∼50 mV related to the oxidation of the two noninteracting donors and the reduction of the two noninteracting acceptors, respectively. Electrogenerated chemiluminescence (ECL) of Spiro-BTA upon cyclic oxidation and reduction in MeCN:benzene 1:2 shows a very bright and stable red emission that could be seen in a well-lit room. Using a reprecipitation method, well-dispersed organic nanoparticles (NPs) of the Spiro-BTA were prepared in aqueous solution. The nanoparticles were analyzed by dynamic light scattering (DLS) and scanning electron microscopy (SEM), yielding a NP size (without surfactant) of 130 ± 20 nm, while with surfactant, 100 ± 20 nm. Bathochromic shifts of absorption spectra (∼16 ± 2 nm), as compared to that of the dissolved Spiro-BTA in THF, were observed for both NPs in water and as a thin film. While blue shifts (14 ± 2 nm) were observed for the photoluminescence (PL). The PL intensity of the Spiro-BTA nanoparticles was slightly enhanced (Φ(PL) of nanoparticles in water = 48%) over that of the dissolved Spiro-BTA in THF. The ECL of the organic Spiro-BTA nanoparticles in aqueous solution could be observed upon oxidation with tri-n-propylamine as a coreactant.

Nanostructured BiVO4 films were synthesized by coevaporation of bismuth and vanadium in an oxygen ambient, a process referred to as reactive ballistic deposition (RBD). The films were tested in various electrolyte solutions to assess their activity for photoelectrochemical water oxidation. Deposition parameters, including the V/Bi atomic flux ratio and the incident angle of deposition, were adjusted. Films deposited with excess vanadium (V/Bi = 2) and incident angles of deposition at 65° showed the highest initial photocurrents with IPCE values above 21% for light wavelengths of 340−460 nm (in 0.5 M Na2SO4 at 1.0 V vs Ag/AgCl). With continued illumination the excess vanadium in these films dissolved into the electrolyte and the photocurrents dropped by 60−75% before reaching steady state. The steady-state photocurrent and IPCE values (above 14% for 340−460 nm light) were higher than the initial values for films synthesized with stoichiometric amounts of vanadium and bismuth (V/Bi = 1) and incident angles ...

A picoliter solution dispenser was used to fabric-ate photosensitizer arrays on mesoporous TiO2 electrodes. The scanning electrochemical microscopy (SECM) technique, modified by replacing the usual ultramicroelectrode (UME) with an optical fiber and using the photooxidation of iodide in acetonitrile in a photoelectrochemical (PEC) cell, was shown to be useful for the initial screening of potential PEC photosensitizers. This SECM technique allows for the rapid identification of new dyes and also can be used to investigate the synergetic effect of multiple dyes for application in dye-sensitized solar cells (DSSCs). This technique was specifically demonstrated via the synthesis and analysis of a new, bis-bithiophene functionalized porphyrin derivative, wherein the modified SECM technique was used to carry out an initial test of its PEC efficiency relative to other dyes. The PEC properties of bulk films based on this new porphyrin derivative were then investigated and the results shown to be in good agreement...

Photoelectrochemical (PEC) studies of CuInSe2 (CIS) and Cu(In1−xGax)Se2 (CIGS) thin films prepared by electrodeposition and spray coating of nanocrystals were carried out. PEC reductions of methyl viologen (MV) in aqueous solution and ethyl viologen (EV) in acetonitrile were used to evaluate the thin-film performance by measuring the photocurrent. Deposition of a CdS layer on CIS and CIGS films strongly enhanced the photocurrent; for example, a nanocrystal-CIS film showed about 100 times higher photocurrent with a thin CdS layer. Capacitance measurements and Mott−Schottky plots were obtained to find the flat band potential. Incident photon to current conversion efficiencies (IPCE) and absorbed photon to current conversion efficiencies (APCE) obtained from PEC measurements were about 20% and 40−70%, respectively.

Quaternary-alloyed ZnxCd1−xSySe1−y arrays were prepared from four precursor aqueous/glycerol (3:1) solutions with a robotic piezoelectric dispenser on fluorine-doped tin oxide (FTO) conductive glas...

The surface interrogation mode of scanning electrochemical microscopy (SI-SECM), an in situ method for the quantification of adsorbed intermediates at electrodes at open circuit, was used to evaluate the rate of reaction of four redox mediators of different reducing power (methyl viologen+ > Ru(NH3)62+ > Fe(II)[EDTA]2− > Fe(CN)64−) with electrogenerated platinum oxides (PtOx) at different pHs. The rate constant determined by SI-SECM was sensitive to the nature of the Pt oxide formed at different potentials. A simplified model with finite element method simulation was used to fit the SI-SECM experimental response. The extraction of kinetic constants and their comparison to the potential (reducing power) of the mediator yielded a Marcus-theory type relationship. Although these are clearly not outer sphere reactions, if subjected to the Marcus theory treatment, one can extract an estimated value of λ = 1.3 ± 0.3 eV for the reduction of “place exchanged” oxide, which forms with oxide coverage values larger th...

CuInSe2 and CuInMSe2 (M = Ga, Zn, Cd) arrays were prepared from precursor aqueous:glycerol (3:1) solutions with a robotic piezoelectric dispenser on fluorine-doped tin oxide (FTO) conductive glass. Studies of the photoresponse of spots on the array by scanning electrochemical microscopy (SECM) with an optical fiber tip showed that different annealing temperatures affected the position on the array of the optimal spot (the spot that showed the highest photocurrent). Depositing a thin layer of CdS on the CIS-250 array improved the photoactivity of the spots and also affected the optimal spot position. Adding 20−40% Ga into the CIS array increased the photocurrent, but addition of Zn or Cd did not.

Changes in HeLa cell morphology, membrane permeability, and viability caused by the presence of Triton X-100 (TX100), a nonionic surfactant, were studied by scanning electrochemical microscopy (SECM). No change in membrane permeability was found at concentrations of 0.15 mM or lower during an experimental period of 30 to 60 min. Permeability of the cell membrane to the otherwise impermeable, highly charged hydrophilic molecule ferrocyanide was seen starting at concentrations of TX100 of about 0.17 mM. This concentration level of TX100 did not affect cell viability. Based on a simulation model, the membrane permeability for ferrocyanide molecules passing though the live cell membrane was 6.5 ± 2.0 × 10 -6 m/s. Cells underwent irreversible permeabilization of the membrane and structural collapse when the TX100 concentration reached the critical micelle concentration (CMC), in the range of 0.19 to 0.20 mM. The impermeability of ferrocyanide molecules in the absence of surfactant was also used to determine the height and diameter of a single living cell with the aid of the approach curve and probe scan methods in SECM.

Recent experiments on the observation of colli- sions of single nanoparticles (NPs) with an electrode through amplification of the current by electrocatalysis are described. Systems in which the particles adhere to the elec- trode upon collision produce a step and staircase response, while those in which particles only interact for a short time with the electrode produce a spike or blip, with little change in the steady state current. Examples of both behaviors, e. g., Pt NPs on a Au electrode for hydrazine oxidation (staircase response) and IrOx NPs on a Pt electrode for water oxidation (blip response) are shown. Controlling the nature of the electrode surface is important in generating useful responses, for example, in the case of gold NPs on an oxidized Pt electrode for borohydride oxidation.

After growing a thin layer of oxide (PtOx) by anodization of a Pt electrode, it changed from catalytically active for electrochemical NaBH4 oxidation into an inactive electrode. When held at a potential where the oxide film was maintained, collisions of individual 14 nm diameter Au nanoparticles (NPs) that catalyzed NaBH4 oxidation were successfully observed as discrete current pulses (spikes or blips) for each NP interaction with the modified Pt electrode via amplification from NaBH4 oxidation. The current response is affected by NP concentration and the applied potential.

The electrochemistry and the electrogenerated chemiluminescence (ECL) of the BODIPY species (2,6-diethyl-1,3,5,7-tetramethyl-8-n-pentyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene, i.e., B8-n-pentyl), an aromatic monomer (B8-phenyl), and a closely related dimer were examined. The B8-n-pentyl species with the n-pentyl donor chain in the meso position shows good electrochemical behavior in MeCN with the formation of stable radical ions. The ECL emission is characterized by long-wavelength emission during consecutive oxidation and reduction steps. This is attributed to aggregate formation on radical ion annihilation, the extent of which increased with increasing concentration of the compound. The B8-phenyl electrochemistry also shows stable radical ions. However, B8-phenyl with the meso phenyl group ECL emission does not show any long-wavelength emission. The synthesized dimer closely related to this species shows two electrochemical oxidations with peak separations of 0.5 V and two reductions with peak separ...

The volume created by the positioning of two scanning electrochemical microscope (SECM) probes (tip and substrate) at a micrometric distance defines a "picoliter beaker" where homogeneous electron-transfer reactions are studied. The SECM is used to concurrently electrogenerate in situ two reactive species and to evaluate the possibility of detecting their reactivity. Two reaction cases are studied: the first, called the "reversible case", occurs when the electrochemically generated species at the substrate electrode can also react at the tip to yield the same product as the reaction in the gap. The second case, named the "irreversible case", occurs when the electrochemically generated species at the substrate are not able to react at the tip. Digital simulations are performed and compared to experimental studies. These show that an unusual compensation between collection and feedback effects render the analysis inapplicable in the "reversible case". The "irreversible case" is shown experimentally.

A picoliter solution dispenser was used to fabricate various n-type BiVO4 based photocatalyst arrays having different compositions and a scanning electrochemical microscopy (SECM) technique modified by replacing a normal ultramicroelectrode with an optical fiber was used for fast screening of the effective photocatalysts for Na2SO3 (as a sacrificial reductant) and water oxidation. Bi/V/W oxide with a ratio of 4.5:5:0.5 showed ∼4.6× higher photocurrent than Bi/V oxide without W and this result was confirmed with bulk film studies. Preliminary characterization (XRD, XPS, and EIS) was also performed for these catalysts. This material was tested for photoelectrochemical water oxidation with a Pt ring optical fiber to detect the product (O2) of photoelectrochemical oxidation reaction.

We report the synthesis, electrochemistry, and electrogenerated chemiluminescence of a series of star-shaped donor-acceptor (D-A) molecules. The star-shaped molecules consist of an electron-deficient 1,3,5-triazine core with three fluorene arms substituted with diarylamino (TAM1-TAM3) or carbazolyl (TAM4) electron donors. Cyclic voltammetry of TAM1-TAM3 shows that the reduction consists of one wave of single electron transfer to the core, while the oxidation exhibits a single peak of three sequential electron-transfer processes, with the formation of a trication. The carbazole-containing molecule TAM4 after oxidation undergoes a subsequent rapid chemical reaction to produce a dimer (via the overall coupling of two radical cations with the loss of two protons). The dimer electrooxidizes more easily than the monomer of TAM4. With continuous cycling on the oxidation side, a conductive polymer film is formed on the surface of the working electrode. Because of the presence of the acceptor (triazine) center and strong donors in the arms (diarylamine or carbazole), TAM1-TAM3 exhibit large solvatochromic effects with emissions ranging from deep blue (428 nm) to orange-red (575 nm) depending on the solvent polarity. These star-shaped molecules show high PL quantum yields of 0.70-0.81. The electrogenerated chemiluminescence (ECL) of TAM1-TAM3 in nonaqueous solutions showed strong ECL that could be seen with the naked eye in a well-lit room. Because the enthalpy of annihilation is higher than the energy required for formation of the singlet excited state, the ECL emission is believed to be generated via S-route annihilation. However, TAM4 shows weak annihilation ECL because of the production of polymer film on the electrode surface during oxidation cycles. However, by limiting the potential region only to the reduction side and using benzoyl peroxide (BPO) as a coreactant, strong ECL of TAM4 can be obtained.

Electrodeposition of Si on substrates such as Ni, Ag and GC from acetonitrile and tetrahydrofuran containing SiCl 4 and SiHCl 3 as precursors is reported. The deposits readily oxidize on exposure to air but XPS analysis of a deposit with minimum contact with air confirms that elemental Si (2p, 99.5 eV) is electrodeposited. The deposits contained C, O, N and Cl impurities; annealing under argon improved the quality of the deposits. Studies related to initial stages of Si growth using cyclic voltammetry and chronoamperometry suggest that growth occurs via four stages (1) nucleation and localized growth, (2) growth in between islands, (3) growth inhibition and (4) slow growth stage and the growth is inhibited after a layer (∼2 nm) of Si is electrodeposited on the substrate.

The surface interrogation mode of scanning electrochemical microscopy (SECM) is extended to the in situ quantification of adsorbed hydrogen, H(ads), at polycrystalline platinum. The methodology consists of the production, at an interrogator electrode, of an oxidized species that is able to react with H(ads) on the Pt surface and report the amounts of this adsorbate through the SECM feedback response. The technique is validated by comparison to the electrochemical underpotential deposition (UPD) of hydrogen on Pt. We include an evaluation of electrochemical mediators for their use as oxidizing reporters for adsorbed species at platinum; a notable finding is the ability of tetramethyl-p-phenylenediamine (TMPD) to oxidize (interrogate) H(ads) on Pt at low pH (0.5 M H(2)SO(4) or 1 M HClO(4)) and with minimal background effects. As a case study, the decomposition of formic acid (HCOOH) in acidic media at open circuit on Pt was investigated. Our results suggest that formic acid decomposes at the surface of unbiased Pt through a dehydrogenation route to yield H(ads) at the Pt surface. The amount of H(ads) depended on the open circuit potential (OCP) of the Pt electrode at the time of interrogation; at a fixed concentration of HCOOH, a more negative OCP yielded larger amounts of H(ads) until reaching a coulomb limiting coverage close to 1 UPD monolayer of H(ads). The introduction of oxygen into the cell shifted the OCP to more positive potentials and reduced the quantified H(ads); furthermore, the system was shown to be chemically reversible, as several interrogations could be run consecutively and reproducibly regardless of the path taken to reach a given OCP.

Electrostatic charges generated on polymer surfaces by contact electrification e.g. polyethylene (PE) contacted with polyamide (Nylon), are capable of carrying out redox reactions. For example, metal ions such as Pd 2+ , Ag + , and Cu 2+ were reduced, leading to a metal film deposition on the polymer, Fe ( CN ) 6 3 - was reduced to Fe ( CN ) 6 4 - , and chemiluminescence was produced. These results reinforce the electron transfer mechanism of contact electrification and the concept of ‘single electrode electrochemistry’ using PE or Nylon (or PTFE) as the source of charge. From the extent of the redox reactions, one estimates charge densities of up to about 10 14 /cm 2 .

Photocatalyst arrays of a number of metal oxides were prepared by dispensing metal precursor solutions onto fluorine-doped tin oxide-coated glass followed by annealing at 500 °C for 3 h. These were screened by scanning electrochemical microscopy with a scanning optical fiber, and the results showed that all Sn-doped Cd−In−Bi, Zn−In, and W−Cd oxide photocatalysts produced enhanced photocurrents for specific metal ratios. The products of the photoelectrochemical (PEC) reaction could be detected electrochemically by a Au ring on the optical fiber. The PEC properties of larger electrodes were investigated, and the Zn−In and W−Cd oxide photocatalysts showed a much higher photoactivity than Sn-doped Cd−In−Bi. Even without catalysts, they showed visible light response for water oxidation to oxygen.

Solid standards prepared by freeze-drying consistently showed a high degree of homogeneity. The freezing process, completed in fractions of a second, preserves the original homogeneous distribution of the dopants, and the subsequent sublimation step would minimize any disturbance. Compared to those prepared by conventional methods such as blending and spiking, freeze-dried standards exhibited superior lateral distribution and better uniform depth distribution. There is, however, a concentration constraint for achieving homogeneity. At 5% doping, segregation was observed in both lateral and depth distribution. Many tungsten standards doped with 10–28 elements ranging from 10 to 200 ppm were successfully prepared and used as controls for a number of analytical techniques including glow discharge mass spectrometry (GDMS) and d.c.-arc optical emission spectroscopy (OES). Copyright © 2009 John Wiley & Sons, Ltd.

Surfaces of dielectrics (insulators) often become charged following contact with metals, semiconductors, and dielectrics with or without rubbing. The mechanism and participants in the charge transfer (electrons or ions), although widely investigated, are still controversial. Whereas the identity of the charge carrier cannot be distinguished by electrostatic measurements, we have recently found that charges on a dielectric surface, e.g. for polymers like Teflon (polytetrafluoroethylene or PTFE) and Lucite [poly(methylmethacrylate) or (PMMA)], can carry out different chemical redox reactions, e.g. metal deposition, ion reduction, and chemiluminescence. This suggests that electron transfer occurs in electrification. This chemical approach allows determination of the surface density of electronic charge as well as processes involved in charging and discharging the dielectrics. An overview of this work is presented.

We report the electrogenerated chemiluminescence (ECL) of 2-oxa-bicyclo[3.3.0]octa-4,8-diene-3,6-dione ( OBDD ). Cyclic voltammetry at 100 mV/s shows two chemically reversible reduction waves but an irreversible oxidation wave. As opposed to the usual radical ion annihilation ECL, for this compound, ECL was observed in an acetonitrile solution just upon oxidation to the radical cation (D + ) in the absence of any additional coreactant. This suggests that OBDD can produce the needed reducing species upon its oxidation, so ECL is probably generated by the reaction of D + with a strongly-reducing free radical produced during OBDD electrooxidation. Production of CO 2 upon oxidation was found by bulk electrolysis and mass spectrometry.

Ag−Fe2O3 and Sn-doped Ag−Fe2O3 nanocomposite photocatalysts were optimized by scanning photoelectrochemical microscopy (SPECM) as a potential photoelectrochemical material for visible light irradiation (λ ≥ 420 nm). The photocurrent vs potential response and the action spectra were investigated in a three-electrode cell. Among different mole ratios, the composition of nanocomposite with 50% Ag−50% Fe (atomic percentage) showed a dramatic improvement in photocurrent on a thin film electrode under visible light (λ ≥ 420 nm). The addition of 2 atomic % Sn (relative to Fe) produced an Ag−Fe2O3 nanocomposite with the largest photocurrent in alkaline solution under visible light irradiation (λ ≥ 420 nm).

We present data for H2O2 production at eight different materials tested as electrocatalysts for the oxygen reduction reaction (ORR) in 0.5 M H2SO4 (Hg, Au, Ag, Cu, Pt, Pd, Pd80Co20, and Au60Cu40) using scanning electrochemical microscopy (SECM) as an alternative to the widely used rotating ring-disk electrode (RRDE) method. The amount of H2O2 is related to the total number of electrons, n, found in the O2 reduction reaction, with n = 2 showing only H2O2 production and n = 4 showing no H2O2 formation. From the SECM study Hg shows n close to 2, whereas Pt and Pd80Co20 show n-values near 4. The other materials show intermediate n-values as a function of potential.

The electrocatalytic properties of individual single Pt nanoparticles (NPs) can be studied electrochemically by measuring the current−time (i−t) responses during single NP collisions with a noncata...

A group of highly fluorescent 2,1,3-benzothiadiazole derivatives (BH0-BH3), including two fluorene derivatives (AB2 and C01) were synthesized and characterized. The electrochemical, spectroscopic, and electrogenerated chemiluminescence (ECL) properties of the compounds were determined. Benzothiadiazole derivatives BH1, BH2, and BH3 show reversible oxidation and reduction waves and produce strong green ECL in nonaqueous solutions. This ECL could be seen by the naked eye, even in a well lit room. The fluorene derivatives, C01 and AB2, also produce bright, easily observable ECL. Since the ECL spectra are at essentially the same wavelengths as the photoluminescence (PL) spectra, and the energies of the electron transfer reactions are greater than the singlet state energies, we propose direct formation of the excited singlet state during ion annihilation. BH0, which shows a quasi-reversible oxidation wave, only produced weak ECL via direct annihilation but gave strong ECL with benzoyl peroxide (BPO) as a coreactant. The ECL quantum efficiencies of the series, compared to that of 9,10-diphenylanthrace, was estimated to range from 0.05 to 7%. This series shows rare green photoluminescence (lambda(PL) = 490-556 nm) with a high PL quantum efficiency in solution (Phi = 5 to 90%).

We report the preparation, characterization, and electrogenerated chemiluminescence (ECL) of rubrene nanoparticles (NPs) and 9,10-diphenylanthracene (DPA) nanorods. The organic NPs were prepared in an aqueous phase using a simple reprecipitation method, i.e., injecting a solution of the hydrocarbon in an organic solvent into water. The resulting NPs can be collected and redispersed to form stable colloidal solutions in water. Rubrene forms spherical nanoparticles (NPs) (diameter ∼50 nm), while DPA initially forms nanorods with an average size of ∼500 nm in length and ∼50 nm in diameter. DPA nanorods grew gradually with time into wires with diameters of ∼1 μm and lengths of ∼10 μm. ECL emission from these NPs was observed upon electrochemical oxidation in aqueous solutions containing different co-reactants, such as tri-n-propylamine for rubrene and an oxalate ion for DPA NPs. The ECL intensity from rubrene NPs was significantly higher than that from DPA NPs because of the smaller size, and thus there is a ...

The viability and activity of HeLa cells were probed using scanning electrochemical microscopy (SECM). The feedback generated by HeLa cells during scanning depends on the electrochemical mediator. Living HeLa cells generated positive feedback when ferrocene methanol (FcMeOH) was oxidized at the tip, showing that the cells reduced FcMeOH + . The positive feedback with FcMeOH changed to negative feedback when the HeLa cells were exposed to toxic treatments, i.e. CN − or UVC radiation, suggesting that FcMeOH + reduction can be used to monitor cell activity. Living HeLa cells also accumulate FcMeOH after exposure times of a few h, but the presence of mM concentrations of FcMeOH has no apparent effect on the cell viability. The effect of Ag + (known to be toxic to bacteria at the 10 μM level) on HeLa cells was probed using the FcMeOH as an indicator. The activity of the HeLa cells was not affected in a culture medium containing Ag + up to 10 mM. The uptake of Ag + by living and dead HeLa cells was small and nearly the same, indicating that even at high Ag + concentrations in the culture medium, only a small amount of Ag + is accumulated within the cells.

Scanning electrochemical microscopy in the photoelectrochemical (PEC) mode was used to search for more efficient doped iron oxide photocatalysts under visible light irradiation (λ ≥ 420 nm). Iron oxide doped with one or two different metal cations was investigated to improve its PEC performance. Among various dopants, Sn or Ti as single dopants and Be or Al as codopants showed an improved photocurrent response of Fe2O3 under visible light irradiation (λ ≥ 420 nm). Fe2O3 doped with 4% Sn(IV) and 6% Be(II) showed the highest photocurrent as well as a good photosensitivity and stability in alkali solution (0.2 M NaOH) under UV and visible light irradiation.

Nanoscale bimetallic Pd-Ti catalysts on carbon supports were prepared in liquid using ammonium tetrachloropalladate and titanium isopropoxide. The size of the metal particles ranged from subnanometer to greater than 10 nm, and the X-ray diffraction pattern of metal particles was dominated by a cubic crystalline structure. Depending upon the preparation conditions, the catalysts were comprised of Pd and TiO2 or Pd3Ti-like alloy. The surface Ti/Pd ratio was much greater than the original metal loading. We propose that the bimetallic particles were comprised of short-range Pd and TiO2 or Pd-Ti alloy nanocrystal covered by a thin TiO2 layer.

Lingsheng Dong1, Andrew J Bard1, William G Richards1, Matthew D Nitz2, Dan Theodorescu2, Raphael Bueno1, Gavin J Gordon11The Thoracic Surgery Oncology laboratory and the Division of Thoracic Surgery, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA; 2Departments of Urology and Molecular Physiology, University of Virginia, Charlottesville, VA, USAPurpose: Bladder cancer is relatively common but early detection techniques such as cystoscopy and cytology are somewhat limited. We developed a broadly applicable, platform-independent and clinically relevant method based on simple ratios of gene expression to diagnose human cancers. In this study, we sought to determine whether this technique could be applied to the diagnosis of bladder cancer.Experimental design: We developed a model for the diagnosis of bladder cancer using expression profiling data from 80 normal and tumor bladder tissues to identify statistically significant discriminating genes with reciprocal average expression levels in each tissue type. The expression levels of select genes were used to calculate individual gene pair expression ratios in order to assign diagnosis. The optimal model was examined in two additional published microarray data sets and using quantitative RT-PCR in a cohort of 13 frozen benign bladder urothelium samples and 13 bladder cancer samples from our institution.Results: A five-ratio test utilizing six genes proved to be 100% accurate (26 of 26 samples) for distinguishing benign from malignant bladder tissue samples (P

The diffusion coefficient (D(O(2))), solubility (C(O(2))), and electrochemical behavior of oxygen reduction were investigated by cyclic voltammetry and transient amperometry on a Pt ultramicroelectrode in aqueous solutions containing various concentrations of NaOH (1-12 M). The results show that both D(O(2)) and C(O(2)) decrease as the solution viscosity (eta) increases significantly with increasing concentration of NaOH. The Stokes-Einstein relationship (D(O(2)) vs 1/eta) is followed, yielding a radius for the O(2) molecule, 2.8 A, that does not change over the concentration range of NaOH studied. From results reported previously for C(O(2)) in more dilute NaOH solutions and the new results here, the number of electrons, n, involved in the first step of the oxygen reduction reaction (ORR) was found to change with the concentration of NaOH, from n = 2 at low NaOH concentrations (1-2 M) to n = 1 at high concentrations (6 M), in line with the changing water activity. Scanning electrochemical microscopy (SECM) was employed as a sensitive tool to investigate the electrochemical behavior of the product of the ORR in 10 M NaOH solution, O(2)(*-), as a function of potential. The SECM approach curves depend on the substrate bias and state of the Pt substrate surface, and the apparent rate constant for the redox couple of O(2)/O(2)(*-) is determined to be about 2.6 x 10(-4) cm/s in this solution.

We report the electrochemistry, spectroscopy, and electrogenerated chemiluminescence (ECL) of donor−acceptor compounds containing a quinoxaline derivative as the central core coupled with fluorene (CFPQ, CFPP, and MFPQ) and triphenylamine moieties (MAPQ). Cyclic voltammetry of all four derivatives show reversible reduction waves (assigned to the formation of the radical anion) localized in the quinoxaline moiety (the acceptor group), whereas oxidation waves show behavior that depends upon the nature of the donor group. With a pair of strong donor groups, triphenylamine, (MAPQ), exhibits a two electron oxidation wave due to the two noninteracting donor moieties. The fluorene derivatives (CFPQ, CFPP, and MFPQ) show less reversible oxidation waves at scan rates of 100 mV/s, but CFPP and CFPQ become reversible at higher scan rates. In their absorbance and emission spectra, all of the compounds, except MFPQ, exhibit large Stokes shifts, which are related to the rearrangement of the excited-state and also to so...

We introduce a new in situ electrochemical technique based on the scanning electrochemical microscope (SECM) operating in a transient feedback mode for the detection and direct quantification of adsorbed species on the surface of electrodes. A SECM tip generates a titrant from a reversible redox mediator that reacts chemically with an electrogenerated or chemically adsorbed species at a substrate of about the same size as the tip, which is positioned at a short distance from it (ca.1 microm). The reaction between the titrant and the adsorbate provides a transient positive feedback loop until the adsorbate is consumed completely. The sensing mechanism is provided by the contrast between positive and negative feedback, which allows a direct quantification of the charge neutralized at the substrate. The proposed technique allows quantification of the adsorbed species generated at the substrate at a given potential under open circuit conditions, a feature not attainable with conventional electrochemical methods. Moreover, the feedback mode allows the tip to be both the titrant generator and detector, simplifying notably the experimental setup. The surface interrogation technique we introduce was tested for the quantification of electrogenerated oxides (adsorbed oxygen species) on gold and platinum electrodes at neutral pH in phosphate and TRIS buffers and with two different mediator systems. Good agreement is found with cyclic voltammetry at the substrate and with previous results in the literature, but we also find evidence for the formation of "incipient oxides" which are not revealed by conventional voltammetry. The mode of operation of the technique is supported by digital simulations, which show good agreement with the experimental results.

Electrochemical hydrazine oxidation and proton reduction occur at a significantly higher rate at Pt than at Au or C electrodes. Thus, the collision and adhesion of a Pt particle on a less active Au or C electrode leads to a large current amplification by electrocatalysis at single nanoparticles (NPs). At low particle concentrations, the collision of Pt NPs was characterized by current transients composed of individual current profiles that rapidly attained a steady state, signaling single NP collisions. The characteristic steady-state current was used to estimate the particle size. The fluctuation in collision frequency with time indicates that the collision of NPs at the detector electrodes occurs in a statistically random manner, with the average frequency a function of particle concentration and diffusion coefficient. A longer term current decay in single current transients, as opposed to the expected steady-state behavior, was more pronounced for proton reduction than for hydrazine oxidation, revealing microscopic details of the nature of the particle interaction with the detector electrode and the kinetics of electrocatalysis at single NPs. The study of single NP collisions allows one to screen particle size distributions and estimate NP concentrations and diffusion coefficients.

We report that silver ion (Ag + ) uptake is enhanced by 4-aminopyridine (4-AP), a well known voltage-sensitive potassium ion channel (K v ) blocker. Both bacterial ( Escherichia coli ) and mammalian (3T3 fibroblast) cells were used as model systems. Ag + uptake was monitored with a scanning electrochemical microscope with an amperometric Ag + ion-selective electrode (Ag + -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 + uptake rate was 4.8 × 10 7 ions per cell per sec without 4-AP compared with 1.0 × 10 8 ions per cell per sec with 0.2 mM 4-AP. For E. coli cells, the uptake rate was 1.5 × 10 4 ions per cell per sec without 4-AP vs. 3.5 × 10 4 ions per cell per sec with 0.5 mM 4-AP and 5.9 × 10 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.

A method for rapid screening of photocatalysts employing a form of scanning electrochemical microscopy (SECM) is described. A piezoelectric dispenser was used to deposit arrays composed of approximately 300-microm-size photocatalyst spots with different compositions onto conducting glass, fluorine-doped tin oxide substrate. The scanning tip of the SECM was replaced by a fiber optic connected to a xenon lamp and was rapidly scanned over the array. In this arrangement, the photocatalytic performance of the spots was evaluated by measuring the photocurrent at the substrate of the array. A fiber optic with a ring electrode can also be used to electrochemically detect products of the photoreaction. Several iron oxide-based bimetallic oxide combinations were found to exhibit enhanced photocatalytic activity, when compared to pure alpha-Fe2O3. These combinations included iron-palladium, iron-europium, and iron-rubidium in specific ratios. A trimetallic bismuth-vanadium-zinc oxide combination was also found to show a higher photocurrent, by approximately 40%, compared to BiVO3.

B8amide is a large molecule based on a derivative of the BODIPY laser dye PM567. Both molecules exhibit highly stable radical ions and similar absorbance and photoluminescence spectra. For B8amide,...

This review describes work done in scanning electrochemical microscopy (SECM) since 2000 with an emphasis on new applications and important trends, such as nanometer-sized tips. SECM has been adapted to investigate charge transport across liquid/liquid interfaces and to probe charge transport in thin films and membranes. It has been used in biological systems like single cells to study ion transport in channels, as well as cellular and enzyme activity. It is also a powerful and useful tool for the evaluation of the electrocatalytic activities of different materials for useful reactions, such as oxygen reduction and hydrogen oxidation. SECM has also been used as an electrochemical tool for studies of the local properties and reactivity of a wide variety of materials, including metals, insulators, and semiconductors. Finally, SECM has been combined with several other nonelectrochemical techniques, such as atomic force microscopy, to enhance and complement the information available from SECM alone.

We demonstrate a novel method of observing single particle collision events with electrogenerated chemiluminescence (ECL). A single event is characterized by the enhancement of ECL intensity during the collision of an individual platinum nanoparticle (Pt NP) on an indium tin oxide electrode, which catalyzes the oxidation of Ru(bpy)3(2+) and a coreactant, for example, tri- n-propylamine (TPrA), present in the solution. Every collision produces a unique photon spike whose amplitude and frequency can be correlated with the size and concentration of the Pt NPs. A large amplification of ECL intensity can occur by choosing an appropriate measuring electrode and using high concentrations of Ru(bpy)3(2+) and the coreactant.

The identity of charges generated by contact electrification on dielectrics has remained unknown for centuries and the precise determination of the charge density is also a long-standing challenge. Here, electrostatic charges on Teflon (polytetrafluoroethylene) produced by rubbing with Lucite (polymethylmethacrylate) were directly identified as electrons rather than ions by electrochemical (redox) experiments with charged Teflon used as a single electrode in solution causing various chemical reactions: pH increases; hydrogen formation; metal deposition; Fe(CN)(6)(3-) reduction; and chemiluminescence in the system of Teflon(-)/Ru(bpy)(3)(2+)/S(2)O(8)(2-) (analogous to electrogenerated chemiluminescence). Moreover, copper deposition could be amplified by depositing Pd first in a predetermined pattern, followed by electroless deposition to produce Cu lines. This process could be potentially important for microelectronic and other applications because Teflon has desirable properties including a low dielectric constant and good thermal stability. Charge density was determined using Faraday's law and the significance of electron transfer processes on charged polymers and potentially other insulators have been demonstrated.

We report the electrogenerated chemiluminescence (ECL) of 2,2'-bis(10-phenylanthracen-9-yl)-9,9'-spirobifluorene (spiro-FPA), a dichromophoric molecule composed of two phenylanthracenes linked by a spirobifluorene moiety (PA-X-PA). The results are compared to those for 9,10-diphenylanthracene (DPA), a related molecule with a single chromophore. Cyclic voltammetry (CV) of spiro-FPA shows two reversible, closely spaced, one-electron transfers on both reduction and oxidation, occurring at E(o)(1,red) = -2.02, E(o)(2,red) = -2.07 V vs SCE and E(o)(1,ox) = 1.14, E(o)(2,ox) = 1.20 V vs SCE. The potentials for each pair are close enough to appear as a single peak in CV, indicating that the spirobifluorene moiety interrupts conjugation between the redox centers. The potentials observed are similar to those of DPA, which shows E(o)(red) = -2.06 V vs SCE and E(o)(ox) = 1.15 V vs SCE. The absorbance spectrum of spiro-FPA shows lambda(max,abs) = 377 nm, with 377 = 25,700 M(-1) s(-1), while DPA exhibited lambda(max,abs) = 374 nm, with 374 = 13,800 M(-1) s(-1), demonstrating that spiro-FPA has twice the available chromophores as DPA. Photoluminescence (PL) data for spiro-FPA shows lambda(max,PL) = 434 nm, with Phi(PL) = 0.74, while DPA fluoresces at 420 nm with Phi(PL) = 0.91; thus, there is greater solvent or structural relaxation in the spiro-FPA excited state, which may account for the greater internal conversion. Unlike DPA, the ECL spectrum of spiro-FPA exhibits long-wavelength emission not observed in the PL. We attribute this emission to excimers formed during annihilation ECL. Steric hindrance prevents DPA from forming excimers, even in ECL, but spiro-FPA annihilation can occur between pairs of di-ions (PA(*-)-X-PA(*-) and PA(*+)-X-PA(*+)), which are electrostatically more strongly attracted to one another than the mono-ions. This greater electrostatic attraction may be sufficient to overcome the steric hindrance to excimer formation. Lowering the electrolyte concentration decreases the electrostatic shielding of the ions from one another; thus, the increase in longer wavelength ECL accompanying a decrease in electrolyte concentration supports the role of the di-ions in excimer formation. Additionally, simulations show, consistent with experiment, a more rapid decrease in excimer concentration than in excited monomer concentration as a function of time after each potential pulse. This is probably due to the greater number of scavenging reactions available for di-ions. The simulations are confirmed experimentally when lower potential pulsing frequencies yield lower relative excimer emission. Since an excited state created by one-electron transfer between two di-ions should be rapidly quenched via electron transfer by the other PA moiety, the existence of excimers suggests the possibility of simultaneous, two-electron transfer to generate the excimer.

Electron transfer (ET) rate kinetics through n-alkanethiol self-assembled monolayers (SAMs) of alkanethiols of different chain lengths [Me(CH2)nSH; n=8, 10, 11, 15] on Au and Hg surfaces and ferrocene (Fc)-terminated SAMs (poly-norbornylogous and HS(CH2)12CONHCH2Fc) on Au were studied using cyclic voltammetry and scanning electrochemical microscopy (SECM). The SECM results allow determination of the ET kinetics of solution-phase Ru(NH3)63+/2+ through the alkanethiol SAMs on Au and Hg. A model using the potential dependence of the measured rate constants is proposed to compensate for the pinhole contribution. Extrapolated values of koML for Ru(NH3)63+/2+ using the model follow the expected exponential decay (beta is 0.9) for different chain lengths. For a Fc-terminated poly-norbornyl SAM, the standard rate constant of direct tunneling (ko is 189+/-31 s(-1)) is in the same order as the ko value of HS(CH2)12CONHCH2Fc. In blocking and Fc SAMs, the rates of ET are demonstrated to follow Butler-Volmer kinetics with transfer coefficients alpha of 0.5. Lower values of alpha are treated as a result of the pinhole contribution. The normalized rates of ET are 3 orders of magnitude higher for Fc-terminated than for blocking monolayers. Scanning electron microscopy imaging of Pd nanoparticles electrochemically deposited in pinholes of blocking SAMs was used to confirm the presence of pinholes.