Oxidative Desorption Research Articles

Reversible oxidation of ethylene on ferroelectric BaTiO3(001): An X-ray photoelectron spectroscopy study

Adsorption and desorption of ethylene on BaO-terminated (001) barium titanate are investigated by X-ray photoelectron spectroscopy. Carbon is found in an oxidized state, at a binding energy similar to that resulting from CO adsorption on BaTiO3(001). The amount of carbon adsorbed on the surface is also similar to the case of CO/BaTiO3(001). Upon heating the substrate up to the loss of its ferroelectric polarization, the C 1s signal from the oxidized spectral region vanishes. At the same time, there was no noticeable oxygen depletion of the surface after repeated C2H4 adsorption and desorption. The substrate remains stable after repeated oxidative adsorption and desorption of ethylene. Desorption occurs at different temperatures, depending on the adsorption temperature, which suggests different adsorption geometries: non-dissociated adsorption at high temperature with ethylene bond on two surface oxygen atoms, and locally dissociated adsorption at lower temperatures, in “formaldehyde-like” local configurations.

A new look at metal–carbon hybrids: Molecular-scale study of covalently grafted gold

The reliable integration of new nanocarbons in future molecular and hybrid electronics requires mastery of chemical binding between dissimilar materials down to the individual bond. Here, we present a detailed study of covalent grafting of aryl radicals on single crystal Au(111), and investigate their electrochemical stability and oxidative desorption. Copper underpotential deposition and Gaussian deconvolution of its current–potential trace are used to map the thermodynamic and kinetic landscape of the modified Au surface. Scanning tunnelling microscopy in a high-boiling organic solvent suggests that grafting is accompanied by vacancy island formation on the Au surface, while iodide adsorption heals these vacancies and allows high-contrast imaging of individual covalent grafts.

Spectroelectrochemical determination of thiolate self-assembled monolayer adsorptive stability in aqueous and non-aqueous electrolytes.

Self-assembled monolayers (SAM) are ubiquitous in studies of modified electrodes for sensing, electrocatalysis, and environmental and energy applications. However, determining their adsorptive stability is crucial to ensure robust experiments. In this work, the stable potential window (SPW) in which a SAM-covered electrode can function without inducing SAM desorption was determined for aromatic SAMs on gold electrodes in aqueous and non-aqueous solvents. The SPWs were determined by employing cyclic voltammetry, attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), and surface plasmon resonance (SPR). The electrochemical and spectroscopic findings concluded that all the aromatic SAMs used displayed similar trends and SPWs. In aqueous systems, the SPW lies between the reductive desorption and oxidative desorption, with pH being the decisive factor affecting the range of the SPW, with the widest SPW observed at pH 1. In the non-aqueous electrolytes, the desorption of SAMs was observed to be slow and progressive. The polarity of the solvent was the main factor in determining the SPW. The lower the polarity of the solvent, the larger the SPW, with 1-butanol displaying the widest SPW. This work showcases the power of spectroelectrochemical analysis and provides ample future directions for the use of non-polar solvents to increase SAM stability in electrochemical applications.

Adsorption/Desorption Behaviors of Sulfur Species at Pt Single Crystal Surfaces

Platinum is an excellent electrocatalyst for polymer electrolyte membrane (PEM) fuel cells because it drives hydrogen oxidation and oxygen reduction with very high efficiency. However, when sulfur species contained as a trace amount of impurity in hydrogen fuel and/or pollutant in air adsorb on platinum surfaces, power output significantly decrease because of reduced electrochemically active surface area. Such negative effect caused by the adsorption of sulfur species, so-called sulfur poisoning, is a serious problem because interaction between sulfur species and platinum surfaces is very strong. Thus, understanding and control of adsorption behavior of sulfur species at platinum surfaces are very important to maintain the cell performance of PEM fuel cells. In the present study, adsorption/desorption behaviors of sulfur species at well-defined platinum single crystal surfaces in acidic aqueous solutions are studied by electrochemical measurements, x-ray photoelectron spectroscopy (XPS), and surface x-ray diffraction (SXRD).Prior to each experiment, platinum single crystal surfaces were annealed by induction heating method [1, 2, 3] at 1600°C more than 1 h under the flowing of Ar and H2 mixed gas, followed by cooling under the Ar and H2 flow for 7 min. The surface was immersed in a 1 mM Na2S aqueous solution saturated with Ar and H2 mixed gas, for 1 h. After rinsing with ultrapure water, electrochemical measurements were carried out in an aqueous solution of 0.1 M HClO4 or H2SO4 deaerated with pure N2 gas.At the bare Pt(111) surface, characteristic current responses such as adsorption/desorption of hydrogen and hydroxyl group were observed. After immersing in the sulfur-containing solution, however, those characteristic current responses disappeared, confirming the adsorption of sulfur species and decrease of electrochemically active surface area. XPS in the S 2p region of the Pt(111) surface immersed in the sulfur-containing solution showed three major adsorbed species; adsorbed hydrosulfide ion (Pt-HS- ad) at 161.8 eV, adsorbed sulfur (Pt-Sad) at162.7 eV, and adsorbed polysulfide (Pt-Sn) at 164.3 eV. While Pt-HS- ad reductively desorbed from the surface by the potential sweeping up to -0.2 V vs. Ag/AgCl, Pt-Sad and Pt-Sn oxidatively desorbed by the potential sweeping up to the potential more positive than 0.7 V vs. Ag/AgCl. SXRD showed that the sulfur species adsorbed at the Pt(111) surface in the (√3×√3)R30° structure.At the Pt(100) surface, the oxidative desorption of sulfur species occurred at more positive potential than that at the Pt(111) surface. This indicates that the recovery from sulfur poisoning at the Pt(100) surface is more difficult than that at the Pt(111) surface. Unlike the Pt(111)-(√3×√3)R30° structure, SXRD showed that the sulfur species adsorbed at the Pt(100) surface in the (√2×√2)R45° structure. While the sulfur species occupies a three-fold hollow site of the Pt(111)-(√3×√3)R30° structure, it occupies a four-fold hollow site of the Pt(100)-(√2×√2)R45° structure. The different coordination number of adsorbed sulfur species is considered as the origin of different oxidative desorption behaviors.

Oxidative Desorption of Adsorbed Sulfur on Platinum Surfaces Modified with Cerium Species

In polymer electrolyte membrane fuel cells, hydrogen oxidation and oxygen reduction reaction occur at platinum (Pt) catalyst surface. Pollutants in air and hydrogen fuel, especially, sulfur (S) species, often strongly adsorb on the Pt surface, resulting in reduced electrochemically active surface area, namely poisoning effect. Because such poisoning causes the significant deterioration of cell performance and durability, understanding and control of adsorption behavior of S species are very important. Thus, it is necessary to develop a new method or material for recovery from S poisoning in anode.In this study, a Pt(111) single crystal electrode was modified with a Ce species and its electrochemical property was compared with a bare Pt electrode. The modification with Ce species was accomplished by immersion in a Ce (NO3)3 + HClO4 aqueous solution with bubbling Ar + H2 gas through the solution for 1 h or applying the potential at -0.2 V in a Ce (NO3)3 + HClO4 aqueous solution. The modification of Pt(111) electrode with Ce species drastically changed the electrochemical responses; hydrogen adsorption/desorption waves become smaller and adsorption/desorption waves of hydroxy group disappeared because of the presence of adsorbed Ce species. Adsorbed species was identified as a Ce3+ ion by XANES spectrum.After the bare Pt(111) electrode was immersed in an aqueous solution containing sodium sulfide, three types of adsorbed S species, HS and S/Sn were detected by XPS. HS was reductively desorbed from Pt electrode surface at potential cycling between 0.0 and 0.2 V vs. RHE (-0.2 and 0.0 V vs. Ag/AgCl). S/Sn species remained during this potential cycling but oxidatively desorbed when the positive limit of potential cycling was 0.6 V vs. RHE (0.8 V vs. Ag/AgCl). The hydrogen adsorption/desorption current gradually increased as repeating potential cycling between 0.0 and 1.0 V vs. RHE (-0.2 V and 0.8 V vs. Ag/AgCl).After the Ce-modified Pt(111) electrode was immersed in an aqueous solution containing sodium sulfide, an anodic current assignable to the oxidative desorption of S species appeared at 0.3 V. The peak current decreased as repeating potential cycling between 0.0 and 0.7 V vs. RHE (-0.2 V and 0.5 V vs. Ag/AgCl). After this potential cycling, the peak area of S2p region of XPS spectra decreased as well as Ce 3d peak. The oxidative desorption of S and Sn on the Ce-modified Pt(111) electrode took place at 0.5 V vs RHE (0.3 V vs. Ag/AgCl) which is much more negative than that of bare Pt(111) electrode (1.0 V vs. RHE (0.8 V vs. Ag/AgCl)). Thus, modification of Pt(111) electrode with Ce species promoted the oxidative desorption of S species.

Amendment of palladium nanocubes with iron oxide nanowires for boosted formic acid electro−oxidation

To quickly move the formic acid (FA) fuel cells closer to a real commercialization, an inexpensive, efficient, and durable electrocatalyst for the direct FA electro-oxidation (FAEO) was developed. This involved a sequential modification of a glassy carbon (GC) substrate with palladium nanocubes (ca. 70 nm, nano-Pd) and iron oxide nanowires (nano-FeOx, ca. 40 nm and 150 nm in average diameter and length, respectively). The deposition sequence and loading level of nano-FeOx in the catalyst were optimized to minimize the catalyst's poisoning with CO that might probably release from a parallel dehydration of FA or from CO2 reduction. Surprisingly, the FeOx/Pd/GC catalyst exhibited a high (21.6 mA cm−2) specific activity for FAEO, which denoted ca. 7 times that of the “pristine” Pd/GC catalyst. This was synchronized with a better (up to fivefold increase in turnover frequency) “long-termed” stability that extended for 90 min of continuous electrolysis at room temperature. A successful effort was dedicated to improving more the catalyst's stability by activating the catalyst electrochemically at –0.5 V vs Ag/AgCl/KCl (sat.) in 0.2 mol L−1 NaOH. The CO stripping agreed perfectly with the impedance analysis in appending the observed enhancement in the catalytic efficiency of FAEO to a favorable electronic modulation at the Pd surface that boosted the oxidative desorption of poisoning CO species at a lower potential.

Effects of the potential and the electrolyte nature in the integrity of the O-(2-Mercaptoethyl)-O′-methyl-hexa(ethylene glycol) self-assembled monolayer by electrochemical impedance spectroscopy

• Electrochemical impedance spectroscopy in the absence of redox probes informs about the integrity of the monolayer. • The EG7-SAM resists the ingress of ions under certain experimental conditions. • The stability region of the EG7-SAMs is lower when defined by impedance in comparison with cyclic voltammetry. • The nature of the electrolyte and the solution pH influence the ability of ion ingress in the EG7-SAM. • Capacitance spectroscopy adds more insight into the EG7-SAM behavior in respect to ions conduction through the film. This work addresses an in-deep study of the ionic conductive properties of the O-(2-Mercaptoethyl)-O’-methyl-hexa(ethylene glycol)-self assembled monolayer (EG7-SAM) by electrochemical impedance spectroscopy in a range of experimental conditions including different aqueous electrolytes and wide potential intervals. The measurements are made in the absence of electroactive probes to get information about the ionic ingress or dynamics into the film. The SAMs stability potential regions comprised between both the potentials for reductive and oxidative desorption processes are here limited and re-defined as regions where ionic ingress occur and these where the ionic permeability does not take place. This distinction leads to a much smaller region where the SAM behaves as an ideal capacitor. Moreover, these features are dependent on the solution pH and electrolyte in contact with the SAM. The temperature effects on the ionic conductivity are also addressed resulting in differences in behavior of complementary parameters. Capacitance spectroscopy analysis of the EG7-SAM helps in the characterization of these films. Thus, information about processes occurring in different time scales (or frequencies) is obtained through the proposed analysis. Putting all the results together, a new perspective of the SAMs conductive properties can be obtained that will be very useful in the choice of a determined layer for specific applications.

Research on UO2 modification of a direct ethanol fuel cell Pt/C catalyst.

Radioactive UO2 powder was prepared by hydrothermal method and a set of Pt–xUO2/C catalysts were synthesized by impregnation method for solving the problem of low activity and easy poisoning of anode Pt/C catalysts for a direct ethanol fuel cell. XRD, TEM, EDS, XPS and ICP-MS characterization showed the successful loading of Pt and UO2 onto the carbon carrier. Electrochemical workstation and single cell test results confirm that the catalytic performance of Pt–10% UO2/C is significantly better than Pt/C-eg. It is speculated that the synergistic effect of Pt and U enhances the catalytic activity and UO2 improves the resistance to CO poisoning by releasing O2 stored in the lattice space, while the α-particles released by 235U can also generate radiolysis product OH and promote the oxidative desorption of CO from the Pt surface.

Coverage-dependent formic acid oxidation reaction kinetics determined by oscillating potentials

Abstract Establishing correlations between catalytic activity and dynamic surface properties of real catalysts, such as adsorbate coverage, is not straight-forward but crucial for the understanding of catalytic phenomena. The formic acid oxidation reaction comprises the non-Faradaic dehydration to CO when no potential is applied to the catalyst surface and the subsequent Faradaic oxidative desorption to form CO2. Here, we report a methodology based on applying oscillating potentials to various electrocatalytically active metal surfaces during the formic acid oxidation reaction. Moderate frequency oscillations (0.1–10 Hz) allow us to control the coverage of intermediates on the surface, thus enabling the quantification of the transient effects (on the time scale of up to 10−4 s) of coverage on the reaction rate. We determined different coverage-dependences of turnover frequencies for Pt metal plate and various carbon-supported metal nanoparticle catalysts (Pt/C, Pd/C and Rh/C). This method therefore constitutes a valuable and simple tool for the elucidation of adsorbate coverages on metal surfaces and their resulting catalytic performance. We also demonstrate that dynamic catalytic processes can be analysed semi-quantitatively with this new approach, allowing the design of catalytic processes under optimized conditions.

Application of Shungit for Neutralization of Toxic Components of Hydrazine Fuel

The neutralization of toxic hydrazine fuel accidents and spills is an urgent task of protecting the biosphere. The effectiveness of using shungite for sorption and catalytic destruction of unsymmetric dimethylhydrazine and its transformation products in the environment has been established. The interaction of shungite with unsymmetric dimethylhydrazine that has fallen into water and soil is investigated. The composition of the products of oxidative transformation and desorption was identified, and the kinetics of changes in their concentration on the surface of various sorbents was studied depending on the state of the environment and temperature, soil composition and the presence of shungite. According to the results, a technology has been created that allows efficiently and environmentally sound elimination of spills of hydrazine fuel. The reliability of this technology is based on the results of chromatographic and mass spectral methods for monitoring the neutralization degree of ecotoxicants.

On the kinetics and mechanism of simultaneous CO and NO oxidations on polyoriented and Pt nanoparticles

Simultaneous carbon and nitrogen monoxide oxidations were studied on different platinum surfaces to envisage the kinetics and mechanism of oxidations in acid media. Nanosized platinum specimens were prepared by an electrochemical method without chemical capping agents and platinum ion precursors. Crystalline oriented particles were obtained from a platinum surface by applying symmetric or asymmetric potential programs in concentrated sulfuric acid followed by cathodizations at very large negative potentials.Nitrogen monoxide arising from nitrite solutions showed synergetic oxidation profiles when first scanning the potential towards cathodic values in solutions containing carbon monoxide. Nitrite oxidative desorption to nitrate arose as a mass controlled process, whereas carbon monoxide oxidation to carbon dioxide occurred firstly from its adsorbate and then associated with carbon monoxide bulk solution.Tafel lines were derived including the potential dependence of surface coverages by oxygen containing adsorbates together with those by carbon and nitrogen monoxides. No changes for nitrogen oxide oxidation Tafel slopes were detected either in the presence or the absence of carbon monoxide (ca. 0.120 Vdec−1) above 1 V, whereas carbon monoxide oxidation varies the slope from 0.040 to ca. 0.060 Vdec−1 when nitrogen monoxide adsorbates were formed.

Electrocatalytic Properties of Rh/C and Pt-Rh/C Catalysts Fabricated by the Method of Electrochemical Dispersion

The Pt/C, Rh/C, and Pt-Rh/C catalytic systems with uniform distribution of metal phase over the surface of carbon support and an average size of Pt and Rh nanoparticles of 7.3 and 6.5 nm, respectively, are fabricated by the method of electrochemical dispersion of metals in the aqueous electrolytes containing Na+. It is shown that the double-layer potential E = 300 mV (RHE) is the optimal potential of CO adsorption for determining the electrochemically active surface area of Pt/C, Rh/C, and Pt-Rh/C catalysts by the method of oxidative desorption of CO. The introduction of Rh into the Pt/C catalyst enables us to increase the specific activity and reduce the potential of the onset of methanol oxidation.

Systematic Assessment of Benzenethiol Self-Assembled Monolayers on Au(111) as a Standard Sample for Electrochemical Tip-Enhanced Raman Spectroscopy

A molecular-scale understanding of electrolyte/electrode interfaces has long been a challenging issue in electrochemistry. Spectroscopic tools with high spatial resolution are required for advancing beyond conventional electrochemical measurements such as cyclic voltammetry (CV). In this study, we developed tip-enhanced Raman spectroscopy (TERS), which is based on an electrochemical scanning tunneling microscope (EC-STM), and demonstrated electrochemical TERS (EC-TERS) measurements of benzenethiol self-assembled monolayers (SAMs) on Au(111). A specially designed cell enables us to carry out reproducible CV, EC-STM, and EC-TERS measurements, which indicates consistent results among these techniques for the oxidative desorption of the SAMs. We also present direct evidence that the measured EC-TERS signals originate from molecules adsorbed on Au(111) and not from those on the STM tip.

Carbon monoxide oxidation assisted by interfacial oxygen-water layers

Based on the fact that oxygenated species promotes the oxidative desorption of carbon monoxide adsorbates, a simple methodology is described here to prepare platinum electrodes with oxygen/water ensembles. Platinum fast quenching (thermal shocking) in oxygenated water after flame annealing in an oxygen atmosphere offers features not seen before. We propose the formation of interfacial oxygen/water ensembles as partially soluble species between platinum rows at stepped n x (110) surfaces. Depending on the temperature of quenching and time of cooling, it is possible to almost completely oxidize carbon monoxide adsorbates, via two processes, i.e., chemical oxidation by molecular oxygen and Langmuir-Hinshelwood surface oxidation.

In-situ electrochemical surface-enhanced Raman spectroscopy study of formic acid electrooxidation at variable temperatures by high-frequency heating technology

The combination of in-situ electrochemical surface-enhanced Raman spectroscopy (EC-SERS) and high-frequency heating technology was used to investigate formic acid (HCOOH) electrooxidation at variable temperatures. Any preset temperature could be adjusted within 1 s on the surface of the working electrode (thermocouple microelectrode, TCME) by using the high-frequency heating technology. Cyclic voltammetry and EC-SERS were used to investigate the electrooxidation behavior of HCOOH on the surface of Au@Pt nanoparticles. Cyclic voltammetry showed that elevated temperatures improve the catalytic activity of Au@Pt/TCME toward HCOOH oxidation. The EC-SERS results showed that the intensity of the PtC band decreased with an increase in temperature, which indicates that a high temperature favors the oxidative desorption of CO from the Pt surface and improves the catalytic reaction. This work could be used to screen catalysts for HCOOH electrooxidation at high temperature, or for other investigations of EC-SERS at variable temperatures.

Enhanced Activity for Methanol Oxidation of Platinum Particles Supported on Iridium Oxide Modified Boron‐Doped Diamond Powder

AbstractElectrocatalytic activity toward methanol oxidation in alkaline media of platinum nanoparticles supported on iridium oxide modified boron‐doped diamond powder (Pt/IrO2/BDDP) was assessed, and was compared with that of Pt deposited on bare diamond particles (Pt/BDDP). Cyclic voltammetry attests that the presence of the iridium oxide intermediary layer promotes methanol oxidation and provides a more efficient reactivation of Pt particles. Linear sweep voltammetric experiments performed in methanol‐free solution indicated that, at Pt/IrO2/BDDP, oxygen evolution is preceded by the formation, within the potential range of CH3OH oxidation, of adsorbed oxygenated species. As expected, the presence in close proximity of Pt particles of such species and of an important amount of IrOx(OH)y (evidenced by XPS) assists in the oxidative desorption of CO species adsorbed on Pt active sites. Steady‐state polarization measurements carried out in a floating configuration with Pt/IrO2/BDDP gas‐diffusion‐type electrodes yielded for methanol oxidation overall process Tafel slope values of ca. 120 mV decade−1, which compare well with those reported for traditional electrocatalysts.

Anodic Desorption Monitored by Voltammetric and Gravimetric Measurements for Fast Estimation of Surface Coverage of Complex Organic Molecules on Au Electrodes

AbstractA methodology for fast determination of surface coverage of molecules or nanostructures assembled in monolayers at the surface of gold electrodes has been developed. The approach is based on anodic oxidative desorption of the molecules which is controlled by synchronized electrochemical gravimetric and voltammetric measurements. Successive anodic scans induce degradation and oxidative desorption of the assembled molecules resulting in a decrease in electrode mass. The completion of desorption is accurately controlled by the charge associated with adsorption of hydroxyl and oxygen species at the bare gold surface. The proposed method can be used to (i) complement the classical approaches or (ii) to estimate the surface coverage for nanostructures whose adsorption requirements, such as long‐time assembling, ex‐situ chemical treatment and other ex‐situ or in‐situ multistage procedures, complicate utilization of common approaches. Adsorbed nanostructures composed of poly(amido) amine dendrimers terminated with thiol functionalized viologen head groups were used as the model objects to evaluate the proposed methodology.

Fabrication of High‐aspect Ratio (HAR) Palladium Nanorod‐modified Electrodes for Raman Spectroelectrochemical Studies of Thiolate Desorption from HAR Nanomaterials

AbstractWe describe a method to fabricate electrodes modified with high‐aspect ratio (HAR) palladium (Pd) nanorods derived from the electrochemical reduction of Pd salts in polycarbonate track‐etched membranes. The HAR Pd nanorod‐modified electrode platform enables direct spectroscopic observation of electrochemical processes particular to HAR forms of nano‐Pd using Raman spectroelectrochemistry. In the present study, we use this platform to observe an anomalous mechanism of oxidative electrochemical desorption of the probe molecule benzenethiol (BT) from the HAR Pd surface. At HAR Pd, the Pd−S bond between the Pd nanorods and BT severs upon oxidation of the Pd surface, whereas on the surface of spherical nano‐Pd, the C−S bond in BT is broken, as is more typically observed for sulfur‐containing organic molecules adsorbed to Pd surfaces. Using this probe reaction, we demonstrate the suitability of this HAR nanorod‐modified electrode platform for the investigation of anomalous electrochemical phenomena observed at HAR Pd for reactions that involve adsorbed intermediates in general – including not only adsorbed sulfur – but in principle also for the electrochemical oxidation of alternative fuels such as ethanol and methanol.

Size dependent lattice constant change of thiol self-assembled monolayer modified Au nanoclusters studied by grazing incidence x-ray diffraction

Size and lattice constant of thiol self-assembled monolayer (SAM)-modified gold nanoclusters (GNCs) assembled on Au(111) surfaces after each electrochemical treatment were investigated using grazing incidence x-ray diffraction (GIXRD). When the potential was swept between 0 and 1.3V (vs. Ag/AgCl), the size and lattice constant of GNCs slightly decreased due to the oxidative desorption of the SAMs. As the number of potential cycles increased, the size of GNCs started to increase due to the aggregation, while the lattice constant continued to decrease due to further desorption of the SAMs from the GNCs. After most of the SAMs were removed from the GNCs, the size and lattice constant monotonically increased with the number of potential cycles. The size dependent lattice constant change was observed when GNCs were smaller than ~35Å.

A Novel Method of Immobilizing Antigens on Gold Electrode for Immunosensing

An antigen modified gold electrode based on a self-assembled lipoic acid monolayer has been developed. The contact angle measurement and cyclic voltammetry confirm the formation of a dense self-assembled monolayer on gold from 100 mM lipoic acid in ethanol. The electrochemical behavior shows a stable activity in a range of potential from -0.2 V to 0.65 V vs. Ag/AgCl. By applying a potential of 1 V vs. Ag/AgCl the monolayer is completely removed by oxidative desorption and a clean gold surface re-established. This allows for an easy renewal of the gold surface and recycling of modified immunosensor chips. This lipoic acid monolayer was covalently functionalized with a small molecule antigen synthesized from progesterone-3-(O-carboxymethyl)oxime and 4,7,10-trioxa-1,13 tridecanediamine to form a well ordered, low unspecific binding, antigen layer for an antibody-antigen interaction study.The effectiveness of antigen - antibody binding reaction was demonstrated by fluorescence imaging using a fluorescence-labeled anti-progesterone antibody as the binding partner. The new approach represents a way of improving the surface chemistry of electrochemical, surface-plasmon resonance and QCM-based immunosensors for which reusability, simplicity and sensitivity in flow-injection mode are required.