Gold Surface Research Articles

Label-free determination of diffusion coefficients at the nanoscale through modelling of the Surface Plasmon Resonance signal.

Surface plasmon resonance (SPR) is normally used to measure the kinetic parameters of biomolecular interactions between a molecule immobilized on a gold surface and another one flowing in a microfluidic channel above the surface. During the SPR measurements, convection-diffusion phenomena occur inside the microfluidic channels, but they are generally minimized by appropriate experimental setup in order to obtain diffusion free kinetic parameters of the molecular interactions. In this work, for the first time, a commercial SPR apparatus has been used to obtain non canonical scientific parameters. Indeed, a specifically designed SPR experimental setup is described for carrying out measurements of the diffusion coefficient (D) of molecules in solutions. The high precision and reproducibility of the approach, as well as the wide applicability of the newly proposed SPR based method for the measurement of D of many different molecules and biomolecules, are here demonstrated and illustrated in detail.

A versatile gold leaf immunosensor with a novel surface functionalization strategy based on protein L and trastuzumab for HER2 detection

Although various sensors specifically developed for target analytes are available, affordable biosensing solutions with broad applicability are limited. In this study, a cost-effective biosensor for detecting human epidermal growth factor receptor 2 (HER2) was developed using custom-made gold leaf electrodes (GLEs). A novel strategy for antibody immobilization on a gold surface, for the first time mediated by protein L and HER2-specific antibody trastuzumab, was examined using commercial screen-printed gold electrodes and GLEs. A self-assembled monolayer of 11-mercaptoundecanoic acid (MUA) was formed on the gold surface, which was used to covalently immobilize protein L. Further binding of trastuzumab to the protein L was employed and HER2 detection was achieved through electrochemical impedance spectroscopy (EIS). The HER2 detection was examined in phosphate-buffered saline (PBS) and supplemented cell culture medium. The modified GLEs showed good specificity and high sensitivity of HER2 detection without any enrichment steps, achieving a limit of detection (LOD) of 1 ng mL− 1 in PBS and 2.7 ng mL− 1 in cell culture medium, making the proposed immunosensor a cost-effective and sensitive solution for detection in complex biological matrices.

Spontaneous switching and fine structure of donor-acceptor Stenhouse adducts on Au(111).

We present the spontaneous isomerization of donor-acceptor Stenhouse adducts anchored onto a gold surface, visualized using scanning tunneling spectroscopy. Our investigation reveals a palette of molecular arrangements, including those with ferroelectric-like ordering, evolving over time into a fine pattern consisting of both open and closed forms of the photoswitch.

Binding mechanism of oligopeptides on solid surface: assessing the significance of single-molecule approach.

This paper addresses the complementarity and potential disparities between single-molecule and ensemble-average approaches to probe the binding mechanism of oligopeptides on inorganic solids. Specifically, we explore the peptide/gold interface owing to its significance in various topics and its suitability to perform experiments both in model and real conditions. Experimental results show that the studied peptide adopts a lying configuration upon adsorption on the gold surface and interacts through its peptidic links and deprotonated thiolate extremities, in agreement with theoretical predictions. Single-molecule force spectroscopy (SMFS) measurements revealed the existence of a wide panel of adhesion forces, resulting from the interaction between individual peptide moieties and the abundant surface sites. We therefore propose methodological developments for sorting the events of interest to understand the peptide adsorption mechanism. Thermodynamic and kinetic aspects of the peptide adsorption are probed using both static and dynamic force spectroscopy measurements. Specifically, we show the possibility of providing a reasonable estimate of the peptide free energy of adsorption ΔadsG° by exploring the fluctuations of the adhesion work, based on the Jarzynski equality, and by using a parametric Gamma estimator. The proposed approach offers a relevant method for studying the different factors influencing the peptide adsorption and evaluating their impact on ΔadsG° as an alternative to exploring adhesion forces that may lead to misinterpretations. This is illustrated by the comparison of the adsorption of two peptides with specific amino acids substitution. Our method provides insights into the overall mechanism by which peptides interact with the surface and allows an integration of the single-molecule versus ensemble-average points of view.

A novel method for detecting genetic biomarkers in blood-based liquid biopsies using surface plasmon resonance imaging and magnetic beads shows promise in cancer diagnosis and monitoring.

Directly detecting biomarkers in liquid biopsy for diagnosis and personalized treatment plays a crucial role in managing cancer relapse and increasing survival rates. Typically, the standard analysis of circulating tumour DNA requires lengthy isolation, extraction, and amplification steps, leading to sample contamination, longer turnaround time and higher assay costs. Surface plasmon resonance is an emerging and promising technology for rapid and real-time dynamic biomarker monitoring in liquid biopsy. Here, we propose a new SPR imaging biosensing approach to detect tumour DNA circulating in the blood of colorectal cancer patients by exploiting the unique properties of superparamagnetic particles. Micrometer beads functionalized with a biotinylated oligonucleotide can directly capture DNA target sequences bearing single-nucleotide variations of KRAS oncogene in human blood plasma. Mutated and wild-type peptide nucleic acid probes immobilized on an SPR gold surface recognize complementary and non-complementary DNA targets by discriminating a single nucleotide mismatch. The new assay allows for detecting p.G13D mutated DNA in buffer and spiked human plasma at attomolar level (down to 300 copies mL-1) with minimal sample manipulation and in just a few microliters. The assay was validated using plasma samples from colorectal cancer patients and healthy donors, by discriminating mutated DNA circulating in patients and wild-type DNA found in healthy blood donors. This feature underscores the potential of the liquid biopsy assay as a valuable tool for the diagnosis and monitoring of cancer.

Mechanism of electrochemical oxidation of gold surfaces in a novel cobalt(II)-glycine-thiosulfate leaching system: An electrochemical experiments and DFT study

The thiosulfate gold leaching system is a promising alternative to cyanide gold leaching because of its low cost, environmental friendliness, and selectivity for gold ore. However, in the traditional thiosulfate leaching gold system, copper(II)–ammonia–thiosulfate (Cu2+–NH3–S2O32-), copper ions increase the consumption of thiosulfate, and excessive ammonia causes water eutrophication and other problems. Therefore, this paper investigated the redox mechanism of gold electrodes in the cobalt(Ⅱ)-glycine-thiosulfate (Co2+-Gly-S2O32-) composite system by electrochemical techniques. The reaction on the surface of the gold electrode was inferred by CV, and the anodic oxidation of the gold electrode was studied by LSV, i-t, and thermodynamic and kinetic parameters obtained from Tafel plots and kinetic parameters obtained from EIS. Finally, the products on the surface of the gold electrode were analyzed by SEM, AFM, FT-IR, and XPS. In addition, the oxidation mechanism was discussed by quantum chemical calculation using DFT method. The results show that thiosulfate concentration does not alter the oxidation mechanism but affects the kinetic process. High concentration of thiosulfate favors the oxidation tendency of gold, therefore, the concentration of thiosulfate should not be too low. In addition, when additional driving force (high potential) is provided will favor the oxidation of S0 and reduce the hindrance to the oxidation of the gold surface. Meanwhile, we also obtained a model of the electrochemical oxidation mechanism of the gold surface.

Dimer Is Not Double: The Unexpected Behavior of Two-Floor Peptide Nanosponge.

Using the framework of an investigation of the stimuli-responsive behavior of peptide assembly on a solid surface, this study on the behavior of a chemisorbed peptide on a gold surface was performed. The studied peptide is a dimeric form of the antimicrobial peptide Trichogin GAIV, which was also modified by substituting the glycine with lysine residues, while the N-terminus octanoyl group was replaced by a lipoic one that was able to bind to the gold surface. In this way, a chemically linked peptide assembly that is pH-responsive was obtained because of the protonation/deprotonation of the sidechains of the Lys residues. Information about the effect of protonation/deprotonation equilibria switching the pH from acid (pH = 3) to basic (pH = 11) conditions was obtained macroscopically by performing Quartz crystal microbalance with dissipation monitoring (QCM-D), Surface Plasmon Resonance (SPR), Nanoplasmonic Sensing (NPS), and FTIR techniques. Using molecular dynamics (MD) simulations, it is possible to explain, at the molecular level, our main experimental results: (1) pH changes induce a squeezing behavior in the system, consisting in thickness and mass variations in the peptide layer, which are mainly due to the pH-driven hydrophilic/hydrophobic character of the lysine residues, and (2) the observed hysteresis is due to small conformational rearrangements from helix to beta sheets occurring mainly on the first half of the peptide, closer to the surface, while the second half remains almost unaffected. The latter result, together with the evidence that the layer thickness is not simply double the assembly of the monomeric analog, indicates that the dimeric peptide does not behave as a double monomer, but assumes very peculiar features.

Tailoring DNA Surface Interactions on Single-Layer Graphene: Comparative Analysis of Pyrene, Acridine, and Fluorenyl Methyl Linkers.

This study investigates the effect of different linkers and solvents on the immobilization of DNA probes on graphene surfaces, which are crucial for developing high-performance biosensors. Quartz crystal microbalance with dissipation (QCM-D) measurements were used to characterize in situ and real-time the immobilization of ssDNA and hybridization efficiency on model graphene surfaces. The DNA probes immobilization kinetics and thermodynamics were systematically investigated for all the pairings between three bifunctional linkers─1-pyrenebutyric acid succinimidyl ester (PBSE), Fluorenylmethylsuccinimidyl carbonate (FSC), and Acridine Orange (AO) succinimidyl ester─and three organic solvents (DMF, DMSO, and 10% DMF/ethanol). The linker's spatial orientation and effective surface modification for DNA probe attachment were also evaluated based on footprints and DNA probe surface coverage. Graphene surfaces functionalized with PBSE in DMF achieved the highest DNA probe surface density (up to 1.31 × 1013 molecules cm-2) and fastest kinetic, p values above 4, and hybridization efficiencies of at least 70%, with 20 to 30% of ssDNA directly adsorbed nonspecifically on the functionalized graphene surface, which has significant implications for the design of sensitive biosensors. The efficiency of the ethanolamine-NHS blocking reaction was estimated to be 80%. The surface packing density of the linker was estimated at 25% of the entire surface coverage for PBSE, and about 22 and 13% for AO and FSC, respectively. Overall, the surface coverage achieved for probe DNA was in the same order of magnitude as that obtained on flat gold surfaces (≥1013 molecules cm-2), typically used in biosensors. These findings highlight the importance of the selected conditions for graphene surface modification to achieve high DNA probe surface density on graphene materials. These results underscore the critical role of interface engineering in achieving target functional outcomes in biosensing technology.

Water Uptake, Thin-Film Characterization, and Gravimetric pH-Sensing of Poly(vinylphosphonate)-Based Hydrogels.

Herein, novel, superabsorbent, and pH-responsive hydrogels obtained by the photochemical cross-linking of hydrophilic poly(vinylphosphonates) are introduced. First, statistical copolymers of diethyl vinylphosphonate (DEVP) and diallyl vinylphosphonate (DAlVP) are synthesized via rare earth metal-mediated group-transfer polymerization (REM-GTP) yielding similar molecular weights (Mn,NMR = 127-142 kg/mol) and narrow polydispersities (Đ < 1.12). Subsequently, polymer analogous transformations of P(DEVP-stat-DAlVP) introduced vinylphosphonic acid (VPA) units into the polymers. In this context, the partial dealkylation of the polymers revealed a preference for DAlVP hydrolysis, which was observed via 1H NMR spectroscopy and explained mechanistically. Furthermore, the P(DEVP-stat-DAlVP-stat-VPA) polymers were cross-linked under photochemical reaction conditions (λ = 365 nm) via thiol-ene click chemistry, yielding superabsorbent hydrogels with water uptakes up to 150 ± 27 g (H2O)/g (hydrogel). Regarding water absorption, evident structure-property relationships between cross-linking density, polarity, and swelling behavior were found. Finally, the pH-responsiveness of thin films of these hydrogels was investigated. In this regard, films with a thickness of 39.4 ± 2.33 nm determined via profilometry were spin-coated on sensors of a quartz crystal microbalance with dissipation monitoring (QCM-D) and thoroughly characterized by atomic force microscopy (AFM). QCM-D measurements exposing the hydrogel films to different aqueous media revealed different swelling states of the hydrogels depending on the pH values (1, 6, 10, and 13) of the surrounding environment, as reflected by corresponding frequency and dissipation values. The hydrogels exhibited fully reversible swelling and deswelling upon switching between pH 1 and 13 (three cycles), sustaining the harsh conditions without erosion from the gold surface and thus acting as a gravimetric sensor discriminating between the two pH values. The high stability of the films on the gold surfaces of QCM-D sensors was explained by anchoring of the P(DEVP-stat-DAlVP-stat-VPA) networks through the dithiol cross-linker as confirmed by detailed X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) studies.

Multivalent GCase Enhancers: Synthesis and Evaluation of Glyco-Gold Nanoparticles Decorated with Trihydroxypiperidine Iminosugars.

The present study reports the preparation of the first multivalent iminosugars built onto a glyco-gold nanoparticle core (glyco-AuNPs) capable of stabilizing or enhancing the activity of the lysosomal enzyme GCase, which is defective in Gaucher disease. An N-nonyltrihydroxypiperidine was selected as the bioactive iminosugar unit and further functionalized, via copper-catalyzed alkyne-azide cycloaddition, with a thiol-ending linker that allowed the conjugation to the gold core. These bioactive ligands were obtained with either a linear monomeric or dendritic trimeric arrangement of the iminosugar. The concentration of the bioactive iminosugar on the gold surface was modulated with different amounts of a glucoside bearing a short thiol-ending spacer as the inner ligand. The new mixed-ligand coated glyco-AuNPs were fully characterized, and those with the highest colloidal stability in aqueous medium were subjected to biological evaluation. Glyco-AuNPs with trimeric iminosugar bioactive units showed the ability to stabilize recombinant GCase in a thermal denaturation assay, while Glyco-AuNPs with monomeric iminosugar bioactive units were able to enhance the activity of mutant GCase in Gaucher patient's fibroblasts by 1.9-fold at 2.2 μM.

Enhanced Electrochemiluminescence by Knocking Out Gold Active Sites.

Electrochemiluminescence (ECL) of the conventional system of [Ru(bpy)3]2+ luminophore and amine-based coreactants is particularly inefficient on noble metal electrodes. This is due to the formation of a passivating oxide layer on the metal surface inhibiting the electro-oxidation of amines like tri-n-propylamine (TPrA) coreactant, Herein, we demonstrated the enhancement of ECL emission on gold surface by hydroxyl radicals attack that are chemically generated with Cu-Fenton reagent. These radicals selectively deactivate the gold active sites and knockout the metal surface asperities that counterintuitively led to an amplification of the ECL emission. Atomic Force Microscopy shows a massive smoothening of the surface. The electrochemical characterization proves that the involved ECL reaction mechanism switches from direct oxidation to catalytic route, where the kinetics of indirect TPrA oxidation is facilitated on deactivated gold surface. Besides, in situ smoothening of a rough electrode in presence of tandem [Ru(bpy)3]2+/TPrA, the ECL enhancement enables Cu2+ sensing with good reliability and limit of detection. Such atomically smoothened and corrosion-resistant gold surface readily tuned the ECL reactivity and opened new directions on influence of topography and reactivity on ECL mechanisms, thus will be extremely useful for the future development of ECL imaging strategies and highly sensitive ECL sensors.

Enhanced Electrochemiluminescence by Knocking Out Gold Active Sites

Electrochemiluminescence (ECL) of the conventional system of [Ru(bpy)3]2+ luminophore and amine‐based coreactants is particularly inefficient on noble metal electrodes. This is due to the formation of a passivating oxide layer on the metal surface inhibiting the electro‐oxidation of amines like tri‐n‐propylamine (TPrA) coreactant, Herein, we demonstrated the enhancement of ECL emission on gold surface by hydroxyl radicals attack that are chemically generated with Cu‐Fenton reagent. These radicals selectively deactivate the gold active sites and knockout the metal surface asperities that counterintuitively led to an amplification of the ECL emission. Atomic Force Microscopy shows a massive smoothening of the surface. The electrochemical characterization proves that the involved ECL reaction mechanism switches from direct oxidation to catalytic route, where the kinetics of indirect TPrA oxidation is facilitated on deactivated gold surface. Besides, in situ smoothening of a rough electrode in presence of tandem [Ru(bpy)3]2+/TPrA, the ECL enhancement enables Cu2+ sensing with good reliability and limit of detection. Such atomically smoothened and corrosion‐resistant gold surface readily tuned the ECL reactivity and opened new directions on influence of topography and reactivity on ECL mechanisms, thus will be extremely useful for the future development of ECL imaging strategies and highly sensitive ECL sensors.

Use of Laccase Enzymes as Bio-Receptors for the Organic Dye Methylene Blue in a Surface Plasmon Resonance Biosensor.

Methylene blue is a cationic organic dye commonly found in wastewater, groundwater, and surface water due to industrial discharge into the environment. This emerging pollutant is notably persistent and can pose risks to both human health and the environment. In this study, we developed a Surface Plasmon Resonance Biosensor employing a BK7 prism coated with 3 nm chromium and 50 nm of gold in the Kretschmann configuration, specifically for the detection of methylene blue. For the first time, laccases immobilized on a gold surface were utilized as bio-receptors for this organic dye. The enzyme was immobilized using carbodiimide bonds with EDC/NHS crosslinkers, allowing for the analysis of samples with minimal preparation. The method demonstrated validation with a limit of detection (LOD) of 4.61 mg L-1 and a limit of quantification (LOQ) of 15.37 mg L-1, a working range of 0-100 mg L-1, and an R2 value of 0.9614 during real-time analysis. A rainwater sample spiked with methylene blue yielded a recovery rate of 122.46 ± 4.41%. The biosensor maintained a stable signal over 17 cycles and remained effective for 30 days at room temperature.

Disulfide-Containing Nitrosoarenes: Synthesis and Insights into Their Self-Polymerization on a Gold Surface.

Disulfide-containing nitrosoarenes with [bis(4-nitrosobenzyl) disulfide, NOBnDS (1)] or without [4-nitrosophenyl disulfide, NOPDS (2), and 1,2-bis(4'-nitroso-[1,1'-biphenyl]-4-yl)disulfane, NOBPDS (3)] an alkyl spacer between the sulfur headgroup and the aromatic moiety (phenyl in NOPDS (2) or biphenyl in NOBPDS (3)) were synthesized and used as precursors to form azodioxy thiolate films on Au(111) substrates. Due to the incorporated disulfide functionalities, these specifically designed nitrosoarenes are enabled to self-polymerize through azodioxy bonds on a gold surface. Thin films of NOBnDS (1), NOPDS (2), and NOBPDS (3) were prepared at different adsorption times via the solution-phase self-assembly of molecules onto the Au(111) surface and characterized by Raman spectroscopy, ellipsometry, water contact angle measurements, atomic force microscopy (AFM), and scanning tunneling microscopy (STM). For comparison, films of structurally analogous disulfide-containing nitro derivatives on Au(111), which can form only monolayer films, thus serving as a reference, were also fabricated and characterized. Raman spectra of NOBnDS (1), NOPDS (2), and NOBPDS (3) films on the Au(111) substrates revealed the presence of a N═N stretching band of the E-azodioxy group. Ellipsometry showed that nitrosoarenes form thicker films compared with their nitro counterparts, indicating the formation of azodioxy oligomer films. AFM revealed an island-like morphology of the nitrosoarene films, in contrast to the rather homogeneous one observed for the monolayer films of nitro derivatives. STM images of nitrosoarene films indicated the formation of poorly organized surface structures in which oligomer chains are possibly interdigitated and substantially tilted relative to the surface normal, which agrees with the relatively low values of the ellipsometry-derived thicknesses. The obtained results emphasized the influence of the substituent electronic effects on the on-surface formation of azodioxides and could be used for the future design of azodioxy thiolate films on gold surfaces.

Effect of End-Tethered Methoxy-PEO Chain Density on Uremic Toxin Adsorption.

In 2023, around 850 million people globally were affected by chronic kidney disease, which leads to the retention of uremic toxins and excess fluid in the blood. This study examines the adsorption of these toxins to poly(ethylene oxide) (PEO) films, known for their low-fouling properties. The gold surfaces were treated with 5 mM end-thiolated methoxy-terminated PEO (m-PEO) and analyzed using dynamic contact angle measurements, X-ray photoelectron spectroscopy, and spectroscopic ellipsometry to confirm the PEO film's presence and determine chain density. The adsorption of 25 different uremic toxins to m-PEO films was evaluated by using liquid chromatography-mass spectrometry (LC/MS), focusing on their binding affinity and adsorption dynamics. Results showed the effective modification of surfaces with m-PEO, with a notable change in contact angles and chain density (∼0.5 and 0.8 chains/nm2). Interestingly, pyruvic acid showed significant adsorption, whereas other toxins, such as hippuric acid, creatinine, and xanthosine had minimal interactions with the film. This indicates that the adsorption of these toxins is not primarily concentration driven and is rather dependent on the chemical structure of each toxin. These findings provide important insights for designing low-fouling coatings for biomedical devices.

Planar and Curved π-Extended Porphyrins by On-Surface Cyclodehydrogenation.

Recent advancements in on-surface synthesis have enabled the reliable and predictable preparation of atomically precise low-dimensional materials with remarkable properties, which are often unattainable through traditional wet chemistry. Among these materials, porphyrins stand out as a particularly intriguing class of molecules, extensively studied both in solution and on surfaces. Their appeal lies in the ability to fine-tune their unique chemical and physical properties through central metal exchange or peripheral functionalization. However, the synthesis of π-extended porphyrins featuring unsubstituted anthracenyl groups has remained elusive. Herein, we report an in vacuo temperature-controlled cyclodehydrogenation of bis- and tetraanthracenyl Zn(II) porphyrins on a gold(111) surface. By gradually increasing the temperature, sequential dehydrogenation leads to the formation of fused anthracenyl porphyrin products. Notably, at high molecular coverage, the formation of bowl-shaped porphyrins occurs, along with transmetalation of Zn with Au. These findings open the door to a variety of π-extended anthracenyl-containing porphyrin products via cyclodehydrogenation and transmetalation, offering significant potential in the fields of molecular (photo/electro)catalysis, (opto)electronics, and spintronics.

Investigation of the modification of gold electrodes by electrochemical molecularly imprinted polymers as a selective layer for the trace level electroanalysis of PAH

Electrochemical molecularly imprinted polymers (e-MIPs) were grafted for the first time as a thin layer to the surface of a gold electrode to perform trace level electroanalysis of benzo(a)pyrene (BaP). This was achieved by controlled/living radical photopolymerization of a redox tracer monomer (ferrocenylmethyl methacrylate, FcMMA) with ethylene glycol dimethacrylate in the presence of benzo(a)pyrene as the template molecule. For that purpose, a novel photoiniferter-derived SAM was first deposited on the gold surface. The SAM formation was monitored by cyclic voltammetry and electrochemical impedance spectroscopy. Then, the “grafting from” of the e-MIP was achieved upon photoirradiation during a controlled time. Differential pulse voltammetry was used to quantify BaP in aqueous solution by following the modification of the signal of FcMMA. A limit of detection of 0.19 nM in water and a linear range of 0.66 nM to 4.30 nM, were determined, thus validating the enhancement of sensitivity induced by the close contact between the e-MIP and the electrode, and the improved transfer electron.

Silica Nanoparticles Tailored with a Molecularly Imprinted Copolymer Layer as a Highly Selective Biorecognition Element.

Molecularly imprinted silica nanoparticles (SP-MIP) are synthesized for the real-time optical detection of low-molecular-weight compounds. Azo-initiator-modified silica beads are functionalized through reversible addition-fragmentation chain transfer (RAFT) polymerization, which leads to efficient control of the grafted layer. The copolymerization of methacrylic acid (MAA) and ethylene glycol dimethacrylate (EDMA) on azo initiator-coated silica particles (≈100nm) using chain transfer agent (2-phenylprop-2-yl-dithiobenzoate) is carried out in the presence of a target analyte molecule (l-Boc-phenylalanine anilide, l-BFA). The chemical and morphological properties of SP-MIP are characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller surface analysis, and thermogravimetric analysis. Finally, SP-MIP is located on the gold surface to be used as a biorecognition layer on the surface plasmon resonance spectrometer (SPR). The sensitivity, response time, and selectivity of SP-MIP are investigated by three similar analogous molecules (l-Boc-Tryptophan, l-Boc-Tyrosine, and l-Boc-Phenylalanine) and the imprinted particle surface showed excellent relative selectivity toward l-Boc-Phenylalanine (l-BFA) (k=61), while the sensitivity is recorded as limit of detection=1.72×10-4m.

Electrochemically induced release of a model dye from a pH-sensitive and electroactive microgel monolayer attached to an electrode surface

We present a novel electrochemically-induced release system featuring a pH-responsive and electroactive microgel monolayer specifically designed to enhance drug delivery mechanisms. This microgel, synthesized from acrylic acid and a ferrocene derivative, was formed on a conductive electrode surface, providing a robust platform for controlled release applications. The physical and chemical properties of the microgel were meticulously characterized using dynamic light scattering (DLS), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), nuclear magnetic resonance (NMR), and electrochemical techniques. The microgel particles modified the electrode surface by forming a monolayer through interactions between the sulfur present in the crosslinking agent and the gold surface of the electrode. Cyclic voltammetry was used to analyze the properties of the modified electrode, and the morphology of the monolayer was confirmed by scanning electron microscopy (SEM). Notably, we demonstrated that the incorporation of positively charged crystal violet (CV) dye molecules was facilitated through electrostatic interactions with the negatively charged carboxylic groups of the microgel, resulting in effective dye retention. Our investigation revealed that the electrochemical oxidation of the ferrocene groups significantly weakens the interactions between the crystal violet (CV) dye and the polymer chains within the microgel network, facilitating controlled dye release. The release process was successfully monitored using quartz crystal microbalance with dissipation monitoring (QCM-D), confirming the system's potential for innovative drug delivery platforms and implant construction.

Investigating the Effect of Copper Ion Impurities on the Structural Evolution and Electrocatalytic Activity of Catalysts for HER

Seawater splitting has garnered significant research interest recently as a method to produce green hydrogen at reduced costs1. One major limitation is the effect of naturally present impurities on all parts of an electrolyzer2– from the membranes to the catalysts. Transition metal cations with reduction potentials in the range of the hydrogen evolution reaction (HER) could interfere with the electrocatalytic reaction. Although this effect has been investigated in the context of underpotential deposition3, there is limited understanding of how competitive redox processes involving impurity ions can influence HER on electrocatalytic electrodes. Here, we study the effect of copper as an impurity ion in the presence of electrocatalytic (platinum) and non-electrocatalytic (gold) electrodes to understand the dynamic competition between electrodeposition and HER. We find that copper deposition competes with HER on both platinum and gold surfaces, leading to a significant decrease in current density with increasing copper concentration. The electrode surfaces are characterized with scanning electron microscopy and atomic force microscopy to understand morphological evolution of the growing copper metal, and X-ray photoelectron spectroscopy is used to quantify the nanoscale thickness of deposited copper. At relatively high dissolved Cu2+ concentrations, copper metal is observed to electrodeposit uniformly on gold electrodes, whereas platinum features nonuniform copper growth with pits and channels likely due to the influence of hydrogen evolution. In situ atomic force microscopy is also used to gain insight into the nucleation and growth behavior of copper on these different electrodes. Together, the results clearly show that redox competition of copper impurities can occur even at the relatively low concentrations of Cu2+ found in seawater (~1 μM)4, highlighting the importance of studying the effect of different impurities on the catalyst under consideration. This work is intended to eventually lead to robust electrolyzers that can be used to efficiently produce hydrogen under impure input stream conditions, potentially lowering costs.REFERENCES: Tong, W., et al., Nature Energy (2020) 5 (5), 367Becker, H., et al., Sustainable Energy & Fuels (2023) 7 (7), 1565Cadle, S. H., and Bruckenstein, S., Analytical Chemistry (1971) 43 (13), 1858Leal, P. P., et al., Sci Rep (2018) 8 (1), 14763