Daniel Mandler

Exciting new directions in the intersection of functionalized sol–gel materials with electrochemistry

The implications of organically-modified silica-based materials in electrochemical science is reviewed along with some selected recent trends in the field of functionalized and sol–gel silica electrochemistry. These recent trends include the electro-assisted generation of organosilica films on solid electrode surfaces, the preparation and applications of sol–gel derived composite (carbon, gold, nanotubes) electrodes, the electrochemical characterisation of mass transfer reactions in porous functionalized silicas, solid-state electrochemistry and gas sensors involving sol–gel materials, imprinted functionalized silica, and the electrochemical characterisation and applications of ordered mesoporous organosilicas.

Selective Determination of Cr(VI) by a Self-Assembled Monolayer-Based Electrode.

We have developed a selective electrode for chromium(VI), based on a self-assembled monolayer of 4-(mercapto-n-alkyl)pyridinium on gold surfaces, which exhibits unique speciation capabilities. Cr(VI) levels as low as 1 parts per trillion can be detected using a 4-(mercaptoethyl)pyridinium monolayer. The different parameters that govern the analytical performance of these electrodes have been studied in detail and optimized. In addition, the organization of the monolayers has been examined by a variety of surface techniques such as XPS, FT-IR, and electrochemistry. Our results show that structuring and understanding the solid-liquid interface at the molecular level are essential for designing probes with superior analytical characteristics.

Scanning Electrochemical Microscopy: The Application of the Feedback Mode for High Resolution Copper Etching

Dissolution electrochimique du cuivre dans une solution acide (pH=4). Caracterisation du phenomene de mordancage par microscopie electrochimique a balayage

Electrochemically controlled drug-mimicking protein release from iron-alginate thin-films associated with an electrode.

Novel biocompatible hybrid-material composed of iron-ion-cross-linked alginate with embedded protein molecules has been designed for the signal-triggered drug release. Electrochemically controlled oxidation of Fe(2+) ions in the presence of soluble natural alginate polymer and drug-mimicking protein (bovine serum albumin, BSA) results in the formation of an alginate-based thin-film cross-linked by Fe(3+) ions at the electrode interface with the entrapped protein. The electrochemically generated composite thin-film was characterized by electrochemistry and atomic force microscopy (AFM). Preliminary experiments demonstrated that the electrochemically controlled deposition of the protein-containing thin-film can be performed at microscale using scanning electrochemical microscopy (SECM) as the deposition tool producing polymer-patterned spots potentially containing various entrapped drugs. Application of reductive potentials on the modified electrode produced Fe(2+) cations which do not keep complexation with alginate, thus resulting in the electrochemically triggered thin-film dissolution and the protein release. Different experimental parameters, such as the film-deposition time, concentrations of compounds and applied potentials, were varied in order to demonstrate that the electrodepositon and electrodissolution of the alginate composite film can be tuned to the optimum performance. A statistical modeling technique was applied to find optimal conditions for the formation of the composite thin-film for the maximal encapsulation and release of the drug-mimicking protein at the lowest possible potential.

Fabrication of nanoelectrode ensembles by electrodepositon of Au nanoparticles on single-layer graphene oxide sheets

Nanoelectrode ensembles (NEEs) have been fabricated by the electrodeposition of Au nanoparticles (AuNPs) on single-layer graphene oxide (GO) sheets coated on a glassy carbon electrode (GCE). The fabricated NEEs show a typical sigmoidal shaped voltammetric profile, arising from the low coverage density of AuNPs on GCE and large distance among them, which can be easily controlled by varying the electrodeposition time. As a proof of concept, after the probe HS-DNA is immobilized on the NEEs through the Au-S bonding, the target DNA is detected with the methylene blue intercalator. Our results show that the target DNA can be detected as low as 100 fM, i.e. 0.5 amol DNA in 5 μL solution.

Visualization of Latent Fingermarks by Nanotechnology: Reversed Development on Paper—A Remedy to the Variation in Sweat Composition†

Paper is one of the most frequently tested surfaces for the detection of latent fingermarks in criminal and terroristrelated investigations. Despite the plethora of modern physical and chemical fingerprint-detection techniques, a considerable portion of the latent fingermarks still escape detection. A plausible explanation is the remarkable difference in sweat composition between individual persons. A potential remedy to this problem could be achieved by reversing the roles, that is, developing a fingerprint-detection technique in which paper serves as the substrate for the interaction with the reagent, while the latent fingermarks will serve as a mask. In this work, “negative” fingermarks have been developed on paper, even after soaking in water, by the application of a new bifunctional reagent attached to gold nanoparticles (AuNPs), and then a silver physical developer (Ag-PD). The bifunctional reagent is composed of an active head, that is, a polar group with high affinity to cellulose, attached by a long chain to an active tail containing a sulfur group, which can stabilize AuNPs. Through the active head, the AuNPs, which are stabilized by the active tail, adhere preferentially to the paper cellulose rather than to the fingerprint material, to which they conventionally bind. Consequently, Ag-PD, which normally develops sebaceous fingermarks by precipitating dark silver on the sebaceous material, precipitate preferentially on the gold-coated areas giving rise to the appearance of uncoloured ridge detail on a dark background. In this competing process, the paper itself serves as the substrate, whereas the fingermarks serve as a mask. This process may increase the overall yield of developed fingermarks as it bypasses the issue of the remarkable differences in sweat composition between individual persons. Functionalized nanoparticles have drawn great interest during the past decade not only in potential applications as biomedical, electronic, catalytic, and optical materials, but also in forensic science, as visualizing reagents for latent fingermarks. Accumulative results on a large number of paper items such as used checks, all of which are supposed to bear latent fingemarks, have shown that over 50% escape detection of identifiable marks. Such observations have led to intensive research into more-sensitive fingerprint detection techniques. Paper that has been wetted is a particular challenge since the amino acids, which are the main substrate for chemical enhancement of latent fingermarks, are dissolved and removed by the water. A silver physical developer (Ag-PD), comprising an aqueous solution of silver nanoparticles (AgNPs) stabilized by cationic surfactants, is required to achieve satisfactory development of such fingermarks. Silver slowly deposits on the water-insoluble components of the sweat, forming dark grey to black impressions (Figure 1). Although the technique is quite sensitive, it suffers from several inconveniences, including complexity, lack of reproducibility, solution instability, and often poor contrast. 6] As a result, many forensic laboratories refrain from using this technique on a routine basis. Latent fingermark enhancement by gold nanoparticles stabilized by citrate ions in aqueous medium, and then a modified Ag-PD, is currently used in a process known as colloidal gold or multimetal deposition (MMD). AuNPs adhere to the fingermark residue and catalyze the precipitation of metallic silver from the Ag-PD solution. The gold adherence to the fingermark material is explained by an ionic interaction between the negatively charged gold colloids and the positively charged components of the fingermark residue at low pH. In a modification known as SMD (singlemetal deposition), the enhancement of gold colloids by precipitation of silver, was replaced by gold-based growth of the nanoparticles. Several other fingerprint techniques that are also based on nanochemical processes, have been suggested recently; all of these suggestions involve the adherence of nanoparticles to the fingerprint material. 3, 8] Previously we showed that good quality fingermarks were developed by treatment with an organic solution of hydrophobic AuNPs stabilized by long chain thiols, and then with Figure 1. Sebaceous fingermark developed by Ag-PD.

Preparation and characterization of octadecylsilane monolayers on indium–tin oxide (ITO) surfaces

Abstract The preparation and characterization of octadecylsilane, C 18 , monolayers on indium–tin oxide (ITO) have been studied carefully. A reproducible procedure was developed for the formation of C 18 /ITO employing octadecyltrimethoxysilane (OTMS) as a monomer. The films were studied by means of electrochemistry, wettability, infrared and atomic force microscopy. All these measurements provide evidence for the formation of a disorganized, ‘brush-type’ monolayer with a maximum surface fractional coverage of 0.90±0.04. The surface coverage can be controlled through the silanization time. The applications and implications of such disorganized monolayers in electroanalytical chemistry are discussed.

Studying thiol adsorption on Au, Ag and Hg surfaces by potentiometric measurements

The adsorption of thiols on different metal surfaces has been studied using potentiometric measurements. The adsorption is a complex process that comprises a few steps. The first involves negative charge transfer to the electrode surface as evidenced by a sharp negative shift of the open circuit potential (ocp). The charge that is accumulated on the electrode surface is discharged through a reduction process that involves either water or oxygen reduction. The rate of the discharging process depends strongly on the overpotential of the electrode material for water reduction, the medium, and to some extent, on additional functional groups that the thiol bears. A detailed general mechanism that is in agreement with our findings is proposed and discussed.

Self-assembled monolayers on mercury surfaces

Abstract The formation and organization of self-assembled monolayers of alkanethiols and ω-mercaptocarboxylic acids on mercury surfaces have been studied. The organization process was examined in-situ and ex-situ by cyclic voltammetry. Charging current measurements as well as electron transfer experiments with Ru(NH 3 ) 6 3+/2+ indicate that the adsorption of homologous alkanethiols and ω-mercaptocarboxylic acids on mercury is followed by the formation of a densely packed array.

Microwriting of Gold Patterns with the Scanning Electrochemical Microscope

The deposition of gold patterns on indium-tin-oxide (ITO) with the scanning electrochemical microscope (SECM) has been accomplished by the controlled dissolution of a gold microelectrode. The continuous anodic dissolution of gold at the microelectrode in the presence of bromide while maintaining the potential of the ITO constant resulted in the deposition of microcrystalline structures of gold. The unique advantages of the SECM made it possible to suggest a mechanism for the process based on the structures as well as the parameters that control the deposition process.