Surface Of Platinum Nanoparticles Research Articles

Reaction Mechanisms in Platinum‐Mediated Electrodynamic Therapy

AbstractElectrodynamic therapy (EDT) has emerged as an alternative stimuli‐responsive approach for tumor treatment. The current understanding of its mechanism is that an electric field activates water dissociation on platinum nanoparticles (PtNPs) to produce toxic hydroxyl radicals. Nevertheless, the argument here remains that, if without direct contact with electrodes, the equipotential surfaces of PtNPs may hardly trigger electrocatalytic reactions and thus the induction of any radicals. Clearly, the limited understanding of EDT has considerably hindered its current and further explorations. Herein, the fundamental mechanism of EDT is revealed from the view of heterogeneous catalysis. First and foremost, the free chlorine generated during electrolysis is identified as the crucial reactant, which is not observed previously. Through experimental examinations and density functional theory (DFT) calculations, the fundamental reaction is confirmed to be the catalytic activation of HOCl by PtNPs, resulting in the production of oxygen anion radicals and the corrosion of PtNPs. Moreover, the cytotoxicity and intracellular abnormalities further verify the findings and provide new insight into its in vitro anti‐cancer mechanism. This study not only assists in re‐recognizing the nature of EDT, but also provides core knowledge in guiding its future investigations in catalytic medicine and medical technologies.

Homogeneous Pt nanostructures surface functionalized with phenylboronic acid phosphonic acid derivatives as potential biochemical nanosensors and drugs: SERS and TERS studies.

Here, surface-enhanced Raman scattering (SERS) and tip-enhanced Raman scattering (TERS) were used to characterize the selective adsorption of N-substituted 4-[(NH-R)(phosphono)-S-methyl]phenylboronic acids on the surface of platinum nanoparticles (PtNPs) from an aqueous solution and from air. The nature of the interaction of the studied compounds with the PtNPs/H2 O and PtNPs/air interfaces was discussed and compared. For this purpose, 4-[(N-anilino)(phosphono)-S-methyl]phenylboronic acid (1-PBA-PA) and its two analogs (2-PBA-PA and bis{1-PBA-PA}) as well as the PtNPs were synthesized in surfactant/ion-free solution via a synthetic route that allows control of the size and morphology of the NPs. The positively charged PtNPs with a size of ~12 nm were characterized by ultraviolet-visible spectroscopy (UV-Vis), dynamic light scattering (DLS), scanning electron microscopy (SEM), and X-ray powder diffraction (XRD).

Zwitterionic Sulfhydryl Sulfobetaine Stabilized Platinum Nanoparticles for Enhanced Dopamine Detection and Antitumor Ability.

Herein, three kinds of molecules were used to modify the surface of platinum nanoparticles (Pt NPs) to tune their surface charge. Zwitterionic thiol-functionalized sulfobetaine (SH-SB) stabilized Pt NPs (SH-SB/Pt NPs) had the highest oxidase activity and peroxidase activity in the prepared platinum nanozymes due to the generation of reactive oxygen species. In addition, a colorimetric dopamine detection method was established based on the peroxidase activity of SH-SB/Pt NPs. This method had a wide range (0-120 μM), a low detection limit (0.244 μM), and high specificity. More importantly, SH-SB/Pt NPs displayed little hemolysis and good stability in the presence of proteins. SH-SB/Pt NPs demonstrated high cytotoxicity in vitro and good antitumor ability in vivo, which was attributed to the photothermal conversion ability of SH-SB/Pt NPs and the generation of reactive oxygen species in the acidic environment. The surface modification of nanozymes using zwitterionic molecules opens a new method to improve the catalytic activity and antitumor ability of nanozymes.

Ultrasensitive electrochemical biosensor for protein detection based on target-triggering cascade enzyme-free signal amplification strategy

Herein, a cost-effective, simple and sensitive electrochemical sensing platform was established based on aptamer - target recognition and target-triggering signal amplification strategy for protein detection. Due to the high affinity between the aptamer and target, the assistant DNA1 (a1) could release from a1-aptamer duplex and trigger the following DNA circuits. The strand displacement and branch migration reaction brought assistant DNA3 (a3) released. Eventually, a large number of duplex structures of a3−Hairpin DNA3 were formed on the surface of electrode. Consequently, the capture DNA on the surface of platinum nanoparticles could hybridize with the unfolded DNA fragment of Hairpin DNA3 on the sensor surface, resulting in the electrochemical signal readout of H2O2 reduction. Using thrombin as a model target, under the optimal conditions, this method exhibited a linear detection range from 0.5 pM to 300 nM with a detection limit of 0.17 pM. The proposed detection strategy was enzyme-free and exhibited good selectivity and sensitivity for a variety of protein targets detection by using corresponding DNA-based affinity probes, which makes it possible to apply the sensor for sensitivity detection of analytes in bioassays.

Develepment of Catalystic Systems for Electroreduction of Highly Inert Reactants Such As Arsenate, Nitrite and Oxohalogenates

Noble metal nanoparticles (Pt, Rh, Ir Pd), when deposited on an inert electrode substrates, exhibit electrocatalytic properties during both oxidation of As(III) and reduction of As(V) in acid medium (e.g. 0.5 mol dm-3 H2SO4). For example, upon application of the appropriate potential, both As(III) and As(V) are preconcentrated on surfaces of Pt nanoparticles. Consequently, their presence can monitored under voltammetric conditions. Population of protons does affect the systems’ electrochemical characteristics. The nature of arsenic voltammetric peaks is strongly dependent on the preconcentration potential. While the reduction and deposition of As(III) is induced by adsorbed hydrogen on Pt formed at potentials lower than 0.25 V (vs. RHE), the adsorption and preconcentration of As(V) can be readily achieved at Pt oxides generated at Pt nanoparticles at potentials higher than 0.85 V (vs. RHE). From mechanistic point of view, voltammetric oxidation of bulk As(III) is catalyzed by Pt oxo species but electrocatalytic reduction of As(V) requires its prior adsorption. Electroreduction of the resulting As(V) adsorbates is catalyzed by both metallic platinum and by platinum on which hydrogen atoms are adsorbed; the resulting voltammetric peak current densities are dependent on concentration of As(V) in solution. A unique feature of the adsorbed As(III) and As(V) oxo species is the ability to agglomerate and form stable polynuclear electroactive films on Pt nanoparticles. Their performance resembles behavior of redox conducting polymers, and their redox transitions are fast and reversible. Electrochemical experiments are supported by the data from scanning and transmission electron microscopies and Raman spectroscopy.In conclusion, the present observations demonstrate the utility of Pt nanoparticles as the catalytic system for inducing of (otherwise highly inert) electrode processes of As(III) and As(V) in acid medium. While the electrocatalytic activity of platinum (particularly PtO) toward electrooxidation of As(III) was previously postulated, we clearly show here that arsenates(V) can be adsorbed, preconcentrated, and electrocatalytically reduced (without prior chemical treatment) and, thus, detected on surfaces of Pt nanostructures. On mechanistic grounds, As(V) must be first adsorbed on bare (metallic) Pt surface before the actual electron transfer can take place. In addition to the structural importance, ivolvement of protons is crucial to effective electrocatalysis. It is also noteworthy that the current signals can be correlated to concentration of As(V) in bulk solution. The present study also provides evidence of obtaining a stable redox-polymer-like As(III,V) oxo film capable of fast charge propagation (electron-self exchange rate on the level 8*106 dm3 mol-1 s-1) within the adsorbed layer existing on surfaces of platinum nanoparticles. The latter observation is of both fundamental and analytical significance. Observations made during electrocatalytic and photoelectrochemical reductions of bromates, nitrites and carbon dioxide with use of various metal nanoparticles and nanostructured metal oxides can serve as guides for such research.

Mesoporous silica decorated with platinum nanoparticles for drug delivery and synergistic electrodynamic-chemotherapy

Electrodynamic therapy (EDT) is a conceptually new cancer treatment approach recently proposed by our group. During EDT, the electro-driven catalytic reaction would occur on the surface of platinum nanoparticles (PtNPs) to produce reactive oxygen species (ROS) under the direct current (DC) or square-wave alternating current (AC) electric field. To further extend the potential of EDT, we hereby designed mesoporous silica-based nanocomposites decorated with PtNPs and loaded with anticancer drug doxorubicin (DOX) for synergistic electrodynamic-chemotherapy. Such silica-based nanocomposites could enable homogenous killing of large-sized tumors (over 500 mm3) and realize remarkable tumor destruction efficacy at a relatively low quantity of electricity. To our best knowledge, this is the first study to combine EDT and chemotherapy to develop a synergetic nanoplatform, openning a new dimension for the design of other EDT-based anticancer strategies.

(Invited) Develepment of Electrocatalystic Systems for Highly Inert Reactants: Reduction of Arsenic(V), Nitrite, Oxohalogenates and CO2 in Acid Medium

Noble metal nanoparticles (Pt, Rh, Ir Pd), when deposited on an inert electrode substrates, exhibit electrocatalytic properties during both oxidation of As(III) and reduction of As(V) in acid medium (e.g. 0.5 mol dm-3 H2SO4). For example, upon application of the appropriate potential, both As(III) and As(V) are preconcentrated on surfaces of Pt nanoparticles. Consequently, their presence can monitored under voltammetric conditions. Population of protons does affect the systems’ electrochemical characteristics. The nature of arsenic voltammetric peaks is strongly dependent on the preconcentration potential. While the reduction and deposition of As(III) is induced by adsorbed hydrogen on Pt formed at potentials lower than 0.25 V (vs. RHE), the adsorption and preconcentration of As(V) can be readily achieved at Pt oxides generated at Pt nanoparticles at potentials higher than 0.85 V (vs. RHE). From mechanistic point of view, voltammetric oxidation of bulk As(III) is catalyzed by Pt oxo species but electrocatalytic reduction of As(V) requires its prior adsorption. Electroreduction of the resulting As(V) adsorbates is catalyzed by both metallic platinum and by platinum on which hydrogen atoms are adsorbed; the resulting voltammetric peak current densities are dependent on concentration of As(V) in solution. A unique feature of the adsorbed As(III) and As(V) oxo species is the ability to agglomerate and form stable polynuclear electroactive films on Pt nanoparticles. Their performance resembles behavior of redox conducting polymers, and their redox transitions are fast and reversible. Electrochemical experiments are supported by the data from scanning and transmission electron microscopies and Raman spectroscopy.In conclusion, the present observations demonstrate the utility of Pt nanoparticles as the catalytic system for inducing of (otherwise highly inert) electrode processes of As(III) and As(V) in acid medium. While the electrocatalytic activity of platinum (particularly PtO) toward electrooxidation of As(III) was previously postulated, we clearly show here that arsenates(V) can be adsorbed, preconcentrated, and electrocatalytically reduced (without prior chemical treatment) and, thus, detected on surfaces of Pt nanostructures. On mechanistic grounds, As(V) must be first adsorbed on bare (metallic) Pt surface before the actual electron transfer can take place. In addition to the structural importance, ivolvement of protons is crucial to effective electrocatalysis. It is also noteworthy that the current signals can be correlated to concentration of As(V) in bulk solution. The present study also provides evidence of obtaining a stable redox-polymer-like As(III,V) oxo film capable of fast charge propagation (electron-self exchange rate on the level 8*106 dm3 mol-1 s-1) within the adsorbed layer existing on surfaces of platinum nanoparticles. The latter observation is of both fundamental and analytical significance. Observations made during electrocatalytic and photoelectrochemical reductions of bromates, nitrites and carbon dioxide with use of various metal nanoparticles and nanostructured metal oxides can serve as guides for such research.

Importance of Interfacial Activation and Proton Transfers during Redox Processes of Highly Inert Systems: Electrocatalytic Detection of As(III) and As(V) in Acid Medium

Noble metal nanoparticles (Pt, Rh, Ir Pd), when deposited on an inert electrode substrates, exhibit electrocatalytic properties during both oxidation of As(III) and reduction of As(V) in acid medium (e.g. 0.5 mol dm-3 H2SO4). For example, upon application of the appropriate potential, both As(III) and As(V) are preconcentrated on surfaces of Pt nanoparticles. Consequently, their presence can monitored under voltammetric conditions. Population of protons does affect the systems’ electrochemical characteristics. The nature of arsenic voltammetric peaks is strongly dependent on the preconcentration potential. While the reduction and deposition of As(III) is induced by adsorbed hydrogen on Pt formed at potentials lower than 0.25 V (vs. RHE), the adsorption and preconcentration of As(V) can be readily achieved at Pt oxides generated at Pt nanoparticles at potentials higher than 0.85 V (vs. RHE). From mechanistic point of view, voltammetric oxidation of bulk As(III) is catalyzed by Pt oxo species but electrocatalytic reduction of As(V) requires its prior adsorption. Electroreduction of the resulting As(V) adsorbates is catalyzed by both metallic platinum and by platinum on which hydrogen atoms are adsorbed; the resulting voltammetric peak current densities are dependent on concentration of As(V) in solution. A unique feature of the adsorbed As(III) and As(V) oxo species is the ability to agglomerate and form stable polynuclear electroactive films on Pt nanoparticles. Their performance resembles behavior of redox conducting polymers, and their redox transitions are fast and reversible. Electrochemical experiments are supported by the data from scanning and transmission electron microscopies and Raman spectroscopy. In conclusion, the present observations demonstrate the utility of Pt nanoparticles as the catalytic system for inducing of (otherwise highly inert) electrode processes of As(III) and As(V) in acid medium. While the electrocatalytic activity of platinum (particularly PtO) toward electrooxidation of As(III) was previously postulated, we clearly show here that arsenates(V) can be adsorbed, preconcentrated, and electrocatalytically reduced (without prior chemical treatment) and, thus, detected on surfaces of Pt nanostructures. On mechanistic grounds, As(V) must be first adsorbed on bare (metallic) Pt surface before the actual electron transfer can take place. In addition to the structural importance, involvement of protons is crucial to effective electrocatalysis. It is also noteworthy that the current signals can be correlated to concentration of As(V) in bulk solution. The present study also provides evidence of obtaining a stable redox-polymer-like As(III,V) oxo film capable of fast charge propagation (electron-self exchange rate on the level 8*106 dm3 mol-1 s-1) within the adsorbed layer existing on surfaces of platinum nanoparticles. The latter observation is of both fundamental and analytical significance. Although the experimental approaches are not optimized here, the detection of As(V) and As(III) down 5*10-6 and 2*10-6 mol dm-3, respectively, is feasible. The main drawback is that the baseline uncertainty limits its routine use in static solutions to concentrations above 2-5*10-6 mol dm-3. This level is not sufficient for practical purposes. For example, the US Environmental Protection Agency (EPA) defines the permissible level of arsenic in drinking water in the United States as 10 μg dm-3 (ca. 1.3*10-7 mol dm-3). Further research is being continued along this line.

Activity and Stability of Carbide Derived Carbon Supports in PEMFC Application

Polymer electrolyte membrane fuel cells (PEMFCs) are regarded as a promising alternative energy conversion devices for both mobile and stationary applications. Main problems hindering the wide-scale commercialization of PEMFCs are high overpotential for oxygen electroreduction reaction (ORR) at the cathode decreasing the efficiency as well as the instability of porous carbon supports in fuel cell working conditions. Therefore, novel catalyst materials are being sought for PEMFC applications [1, 2]. Hierarchical microporous-mesoporous carbon supports were prepared from molybdenum carbide using the high temperature chlorination method. Prepared materials exhibited high specific surface area and large mesopore volume [3-4]. Thermogravimetric analysis, X-ray diffraction, low temperature nitrogen sorption and high resolution transmission electron microscopy methods were used to characterize the structure of the synthesized catalyst materials. Prepared catalysts were used in the single cell measurements. Catalyst coated membrane method was used to prepare the MEAs using ultrasonic spaying technique. The polarization curves and chronopotentiometric measurements were conducted to evaluate the activity and stability of the catalyst materials synthesized. From cyclic voltammetry the electrochemically active surface area values were calculated and used to estimate the contact surface of platinum nanoparticles and Nafion electrolyte. The series resistance of electrolyte, polarization resistance and activation energy values have been calculated from electrochemical impedance spectroscopy data. It was established that prepared carbon materials with well-defined properties are excellent objects to study the impact of the catalyst support properties on the performance of a PEM fuel cell. It was found that the novel synthesized catalyst materials are very stable and catalytically active towards ORR. Therefore, prepared materials are suitable for PEMFC applications. Acknowledgements. This work was supported by Estonian target research project IUT20-13, Personal Research Grant PUT1033, Estonian Centre of Excellence Project No. 2014-2020.4.01.15-0011. References S. Sepp, K. Vaarmets, J. Nerut, I. Tallo, E. Tee, H. Kurig, J. Aruväli, R. Kanarbik, E. Lust, Electrochim. Acta 2016, 203, 221−229.S. Sepp, K. Vaarmets, J. Nerut, I. Tallo, E. Tee, H. Kurig, J. Aruväli, R. Kanarbik, E. Lust, J. Solid State Electrochem. 2016, 21(4), 1035–1043.S. Sepp, E. Härk, P. Valk, K. Vaarmets, J. Nerut, R. Jäger, E. Lust, J. Solid State Electrochem. 2014, 18(5), 1223 – 1229.E. Lust, K. Vaarmets, J. Nerut, I. Tallo, P. Valk, S. Sepp, E. Härk, Electrochim. Acta 2014, 140, 294-303.

Unsupported platinum nanoparticles as effective sensors of neurotransmitters and possible drug curriers

Herein, surface-enhanced Raman scattering (SERS) activity of positively charged unsupported platinum nanoparticles (PtNPs) with ∼12nm size and narrow size distribution, in an aqueous solution, towards neurotransmitters was monitored at 785nm excitation wavelength. The pure PtNPs were synthetized by polyol method. Their morphology and structure were checked by scanning electron microscopy (SEM) and X-ray diffraction spectroscopy (XRD) measurements. As a neurotransmitter bombesin (BN), which exhibits autocrine effect on the growth of normal and tumour tissues, and its fragments from the C-terminal end: BN13−14, BN12−14, BN11−14, BN10−14, BN9−14, and BN8−14 (X-14 fragments of the BN amino acid sequence) were chosen. The collected spectra were interpreted and discussed. This is to determine the adsorption mode of bombesin onto the PtNPs surface and changes in this mode as a result of the bombesin backbone shortening from the N-terminal end. This is important from the point of using PtNPs as potential BN carrier into the cancerous tissue and antitumor drug.

Electrocatalytic performance enhanced of the electrooxidation of gamma-hydroxybutyric acid (GHB) and ethanol on platinum nanoparticles surface. A contribution to the analytical determination of GHB in the presence of ethanol

The electrooxidation of GHB and ethanol on a glassy carbon/platinum nanoparticles/polyvinyl alcohol modified electrode (GC/PtNPs/PVA) in weakly acidic medium has been investigated by cyclic voltammetry and chronoamperometry. The study with the concentration, the scan rate and the analyses of j-t curves at several potentials for both compounds showed an enhanced electrocatalytic performance on the GC/PtNPs/PVA electrode.Cyclic Voltammetry of ethanol-GHB mixtures was also performed observing that the presence of GHB in ethanol solutions significantly suppressed the oxidation peak currents of ethanol. This fact has been discussed in different experimental conditions and suggests that this behaviour is due to a competition of both alcohols for the active sites of the platinum surface according to a Langmuir-type expression. Depression of the current density of ethanol in the presence of GHB opens up new prospects for the development of strategies for the determination of GHB. The interval of detectable concentrations comprises between 1 and 75mM (0.125 and 9.15mg/mL) within the known toxic dose for GHB that is 0.5mg/mL (4mM). Detection limit of GHB, under these experimental conditions, was 0.872mM (0.110mg/mL). Analyses of test samples including typical recreational alcoholic beverages (vodka, lemonade+vodka, gin, rum, tequila and whisky) on the surface with the modified electrode have been successfully carried out. Precision (% RSD) values of alcoholic drinks and spiked GHB samples were tested in intra-assay and inter-assay.

A Simple Assay for Ultrasensitive Colorimetric Detection of Ag⁺ at Picomolar Levels Using Platinum Nanoparticles.

In this work, uniformly-dispersed platinum nanoparticles (PtNPs) were synthesized by a simple chemical reduction method, in which citric acid and sodium borohydride acted as a stabilizer and reducer, respectively. An ultrasensitive colorimetric sensor for the facile and rapid detection of Ag+ ions was constructed based on the peroxidase mimetic activities of the obtained PtNPs, which can catalyze the oxidation of 3,3’,5,5’-tetramethylbenzidine (TMB) by H2O2 to produce colored products. The introduced Ag+ would be reduced to Ag0 by the capped citric acid, and the deposition of Ag0 on the PtNPs surface, can effectively inhibit the peroxidase-mimetic activity of PtNPs. Through measuring the maximum absorption signal of oxidized TMB at 652 nm, ultra-low detection limits (7.8 pM) of Ag+ can be reached. In addition to such high sensitivity, the colorimetric assay also displays excellent selectivity for other ions of interest and shows great potential for the detection of Ag+ in real water samples.

Aqueous platinum nanoparticles solution for the detection of pyridine derivatives of aminophosphinic acid. Influence of positional isomerism

Unsupported platinum nanoparticles (PtNPs) (∼12nm in diameter) were synthetized by the polyol method and ultraviolet-visible spectroscopy (UV–vis), scanning electron microscope (SEM), and X-ray powder diffraction (XRD) characteristic of their agglomerates were examined. Then, three pyridine α−aminophosphinic acid isomers (α–, β–, and γ–) were synthetized and assembled on the surface of PtNPs. Differences in adsorption and thus, in the spectral response resulting from positional isomerism, were checked by surface-enhanced Raman scattering (SERS) at 785nm excitation wavelength. The manner of interaction of the investigated isomers with PtNPs were discussed and compared. General conclusions were drowned.

Catalytic Duality of Platinum Surface Oxides in the Oxygen Reduction and Hydrogen Oxidation Reactions

In polymer electrolyte membrane fuel cells (PEMFCs), the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) take place on the surface of platinum nanoparticles (Pt-NPs) residing on carbon support. Polycrystalline platinum (Pt(poly)) serves as a model polyoriented system due to its randomly oriented grains separated by grain boundaries, and research using Pt(poly) creates important background knowledge that is used to identify and understand electrochemical phenomena occurring in fuel cells. In this study, we report new results on the electrochemical behavior of Pt(poly) in 0.50 M H2SO4 aqueous solution saturated with reactive gases, namely O2(g) and H2(g). We analyze the influence of the potential scan rate over a broad range of values (1.00–50.0 mV s−1) on the cyclic voltammetry (CV) behavior of Pt(poly). A comparative analysis of the impact of dissolved O2 and H2 on the electrochemical behavior of Pt(poly) is performed using CV profiles and capacitance transients. Their analysis reveals the existence of new features that are observed in the potential range corresponding to the Pt surface oxide formation and reduction. The results indicate that the Pt surface oxide reveals catalytic duality because it acts both as an inhibitor and a catalyst in both the ORR and HOR. In the case of the ORR, the anodic-going transients reveal that the process becomes inhibited as the Pt surface oxide develops, while in the cathodic-going transients, the reduction of Pt surface oxide significantly (ca. 65%) increases the reaction rate. In the case of the HOR, the anodic-going transients also reveal that the process becomes inhibited as the Pt surface oxide develops, while in the cathodic-going transients, the reduction of Pt surface oxide increases (ca. 15%) the reaction rate. The catalytic effect can be attributed either to changes in the surface electronic structure that accompanies the surface oxide reduction or to short-lived increase in the electrochemically active surface area.

Enhanced Stability of Novel Hierarchical Carbon Supports in PEMFC Application

Proton exchange membrane fuel cell (PEMFC) is one of the most promising candidates as an environmentally clean power source in various applications. The efficiency of a catalyst depends strongly on the selection of an appropriate support material. The instability of carbon supports in fuel cell working conditions is the major obstacle hindering the commercialization of PEMFCs. Therefore, novel carbon supports are being sought for fuel cell application [1, 2]. Hierarchical microporous-mesoporous carbon supports were prepared from molybdenum carbide using the high temperature chlorination method at different synthesis temperatures within the range from 600 °C to 1000 °C. Prepared materials exhibited high specific surface area, but they differed from one another in their structural properties, such as pore size distribution and the ratio of micro- and mesopores volumes [1, 3-4]. The platinum nanoparticles were deposited onto the carbon support using the sodium borohydride method. Thermogravimetric analysis, X-ray diffraction, low temperature nitrogen sorption and high resolution transmission electron microscopy methods were used to characterize the structure of the synthesized materials. Prepared catalysts were used in the single cell measurements. The polarization curves and chronopotentiometric measurements were conducted to evaluate the activity and stability of the catalyst materials synthesized. The electrochemically active surface area values were calculated and used to estimate the contact surface of platinum nanoparticles and Nafion electrolyte. The resistance of electrolyte, polarization resistance and activation energy values have been established from electrochemical impedance spectroscopy data. Prepared materials with well-defined properties are excellent objects to study the impact of the carbon catalyst support properties on the performance and stability of a PEMFC single cell. The main aim of this work was to study the time stability (Fig. 1) of Pt nanoclusters activated microporous-mesoporous carbon supports in fuel cell application and to compare the properties of these materials with commercial carbon Vulcan XC72 used as catalyst support. It was found that the novel synthesized carbon supports are very stable and thus suitable for PEMFC application. Acknowledgements. This work was supported by Estonian target research project IUT20-13, Personal Research Grant PUT55, Estonian Centre of Excellence Projects No. 2014-2020.4.01.15-0011 and 3.20101.11-0030. References S. Sepp, K. Vaarmets, J. Nerut, I. Tallo, E. Tee, H. Kurig, J. Aruväli, R. Kanarbik, E. Lust, Electrochim. Acta 2016, doi:10.1016/j.electacta.2016.03.158M. Uchida, Y. Fukuoka, Y. Sugawara, N. Eda, A. Ohta J. Electrochem. Soc. 1996, 143, 2245–2252.S. Sepp, E. Härk, P. Valk, K. Vaarmets, J. Nerut, R. Jäger, E. Lust, J. Solid State Electrochem. 2014, 18(5), 1223 – 1229.E. Lust, K. Vaarmets, J. Nerut, I. Tallo, P. Valk, S. Sepp, E. Härk, Electrochim. Acta 2014, 140, 294-303. Figure 1. Galvanostatic life-time measurements for single cells with synthesized and commercial carbon used as catalyst support. Figure 1

Electrochemical Study of Oxygen Reduction on a Carbon‐Supported Core–Shell Platinum–Gold Electrocatalyst with Tuneable Gold Surface Composition

AbstractThe presence of gold on the surface of platinum nanoparticles can have profound effects on the activity in the electrochemical oxygen reduction reaction (ORR). In this work, the ORR activity is studied at different surface coverage of gold on two types of core–shell platinum–gold catalysts. Surface‐limited redox reaction and redox transmetalation methods are used to synthesize core–shell catalysts with varying degrees of gold coverage on their surface. Experimental results indicate that the presence of gold on the surface intrinsically decreases the ORR activity. Furthermore, the effect of the core on the activity for ORR has been studied.

Electrocatalytic amplification of DNA-modified nanoparticle collisions via enzymatic digestion.

We report a new and general approach that will be useful for adapting the method of electrocatalytic amplification (ECA) to biosensing applications. In ECA, individual collisions of catalytic nanoparticles with a noncatalytic electrode surface lead to bursts of current. In the work described here, the current arises from catalytic electrooxidation of N2H4 at the surface of platinum nanoparticles (PtNPs). The problem with using ECA for biosensing applications heretofore, is that it is necessary to immobilize a receptor, such as DNA (as in the case here) or an antibody on the PtNP surface. This inactivates the colliding NP, however, and leads to very small collision signatures. In the present article, we show that single-stranded DNA (ssDNA) present on the PtNP surface can be detected by selectively removing a fraction of the ssDNA using the enzyme Exonuclease I (Exo I). About half of the current associated with collisions of naked PtNPs can be recovered from fully passivated PtNPs after exposure to Exo I. Experiments carried out using both Au and Hg ultramicroelectrodes reveal some mechanistic aspects of the collision process before and after treatment of the ssDNA-modified PtNPs with Exo I.

Enhancing the Oxygen Reduction Reaction Performance by Modifying the Surface of Platinum Nanoparticles

AbstractThe depressing oxygen reduction reaction (ORR) performance has impeded the commercialization of proton exchange membrane fuel cells. As a surface‐sensitive reaction, the surface structure of the electrocatalyst has a crucial impact on the ORR. Herein, Pt nanoparticle surfaces were modified with the aid of Ag, which was deposited on the surface of Pt nanoparticles and was etched away through cyclic voltammetry (CV). After surface modification, the step density of the Pt nanoparticles was observed to decrease, according to high‐resolution transmission electron microscopy images, which could contribute to the positive shift of the Pt 4f binding energy and the improved ability to prevent Pt from being oxidized, as seem by using X‐ray photoelectron spectroscopy. Furthermore, the peak potential increase for the surface metal‐oxide reduction during CV was consistent with the impact of the step density reduction. After surface modification, the Pt nanoparticles showed improved ORR performance, according to half‐cell tests. At the atomic scale, the decrease in the number of low‐coordination atoms on the surface steps, which exhibit stronger interactions with Oads/OHads compared with atoms on terraces, could lead to the enhanced ORR performance.

Detection of prostate specific antigen based on electrocatalytic platinum nanoparticles conjugated to a recombinant scFv antibody

Highly sensitive and label free detection of prostate specific antigen (PSA) still remains a challenge in prostate cancer diagnosis. In this paper, we propose a sensitive electrochemical immunosensor based on electrocatalytic platinum nanoparticles conjugated to a recombinant scFv antibody. Gold disc electrodes functionalised with a l-Cysteine (Cys) self-assembled monolayer (SAM) were used to covalently bind PSA specific monoclonal antibody (anti-PSA) using N-ethyl-N′-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide (EDC/NHS) chemistry. Immunosensing was completed using sandwich-type immunoreaction of the PSA–antigen (1–30ng/mL) between anti-PSA immobilized on the l-Cys modified electrode using label free electrochemical impedance (EIS) technique. Furthermore, highly specific in-house generated scFv fragments as receptor proteins were utilised for one step site-directed immobilisation on the surface of platinum nanoparticles (PtNPs). To improve the sensitivity of the immunoassay, these scFV labelled electrocatalytic PtNPs were then used for covalent hybridisation to the PSA modified electrode and then applied in a hybridisation assay to determine the concentration of the PSA by measuring the faradaic current associated with reduction of peroxide in solution. Semi-log plots of the PSA concentration vs. faradaic current are linear from 1 to 30ng/mL and pM concentrations can be detected without the need for molecular, e.g., PCR or NASBA, amplification.

Design of New Catalytic Architectures for Proton Exchange Membrane Fuel Cell

The Proton-exchange membrane fuel cell (PEMFC) will become a mature technology, and several car manufacturers in Asia, United State and Europe are communicating on the commercialization of Fuel Cell cars in the near future. The materials which will be used for the first generation of this technology of energy conversion are currently known: the solid electrolyte will consist in a perfluorinated membrane with attached pendant sidechains and sulfonic acid groups (–SO3H) at the sidechain terminals, which Nafion® is the mostly recognized representative and the electrodes will be composed of platinum-based nanoparticles (NPs) in the diameter range 1 - 10 nm dispersed on a high surface area electron conductive carbon black powder impregnated with proton conducting ionomer. Although such electrode formulation led to a significant increase of the catalyst efficiency, and therefore to a drastic decrease of Pt loading in electrodes, more efforts have still to be done to bring the state-of-the-art specific Pt power value (ca. 0.5 gPt kW−1) down to 0.2 gPt kW−1 for a large scale implementation of the PEMFCs for vehicle propulsion. In order to achieve this breakthrough, it is necessary to improve the platinum utilization efficiency. It was indeed estimated by Eikerling et al. that Pt activity in conventional catalytic layers reached at most 10 - 20 % of its full potential [[i]]. The limitation in the effectiveness factor of Pt utilization, determined as the ratio of the current delivered and the maximum theoretical current expected, is due to several reasons, particularly to mass transport and ohmic losses [[ii]]. So that, the performance improvement of the catalytic layers requires optimizing factors allowing maximizing the fraction of Pt surface atoms, and those allowing improving mass and charge transport properties of the layers. The optimizations of the catalytic support and of the catalytic layer architecture could greatly contribute to the enhancement of the effectiveness of the PEMFC catalytic layers, and thus enable further reduction of the Pt content, but classical architectures involve their impregnation by an ionomer in order to achieve the three-phase boundaries. A three-phase boundary corresponds to a confined spatial site where the reactant, the ionic conducting polymer and the electronic conductive substrate are present on the same platinum particle [[iii]], allowing the electrochemical reaction to occur with higher efficiency. However, Eikerling et al. also estimated that ca. 60% of unutilized Pt was that not located at the active three-phase boundary [1]. The grafting of ionic conducting polymer to the surface of platinum nanoparticles allows the creation of new catalyst layer architectures (Figure 1 and Figure 2) that promote both the ionic conduction to the solid electrolyte. The synthesis of polyfunctional catalyst, whose properties can be adjusted depending on synthesis parameters, allows optimize the electrical, chemical and mass transfer to electrodes and also reduce the overhead platinum. In this communication, we will report the synthesis of complex architecture of platinum supported on carbon, their physico-chemical characteristic, electrocatalytic properties (Figure 3) and fuel cell tests (Figure 4). [[i]] M. Eikerling, A. Korhyshev, A. Kulikovsky, The Fuel Cell Review 15 (20004/2005) FCR.IOP.org. [[ii]] H. A. Gasteiger, W. Gu, R. Makharia, M. F. Mathias, B. Sompalli, in: W. Vielstich, A. Lamm, H. A. Gasteiger (Eds.), Handbook of Fuel Cells – Fundamentals, Technology and Applications, Wiley, Chichester, Vol. 3, 2003, p. 593-610. [[iii]] R. O’Hayre, D. M. Barnett, F. B. Prinz, J. Electrochem. Soc. 152 (2005) A439-A444. Figure 1