Formation Of Self-assembled Monolayers Research Articles

Anchoring groups for ordered and highly stable monomolecular films on naturally oxidized aluminum – phosphonate versus carboxylate

Modification of metal oxide surfaces by self-assembled monolayers (SAMs) is attracting growing attention. Carboxylic (CA) and phosphonic (PA) acids are most popular anchoring groups in this context, applied to create hydrophobic coatings, biosensors, and organic field-effect transistors. The efficiency of these devices is crucially affected by the structural quality and stability of the SAM. In this context, we studied the effect of the preparation procedure (solvent, incubation time, and temperature) on the quality of PA SAMs on naturally oxidized aluminum. We demonstrate formation of PA SAMs matching structural quality of archetypical alkanethiols on gold. Next, we compare their stability with analogue CA SAMs. Our data show that PA SAMs not only exhibit much higher hydrolytic stability but are also capable to protect aluminum substrate from oxidation and degradation. Importantly, even small improvement of the PA SAMs quality, translates into enormous increase of their hydrolytic stability crucial for majority of applications. Finally, we demonstrate that the thermal stability of PA on oxidized aluminum is by ∼250 K higher than CA SAMs, and by ∼200 K higher than for thiols on gold, which makes PA SAMs an excellent candidate for organic electronics, where overheating problems and high-temperature fabrication procedures are common issues.

A healable amino silane self-assembled monolayer incorporating polymer capped palladium nanoclusters and its application as the copper diffusion barrier layer on silicon wafer

Self-assembled monolayers (SAMs) with short organic chains terminated with specific functional groups are attractive for modifying surface properties for a variety of applications, including being a copper diffusion barrier layer on Si wafer. However, SAM formation is process-sensitive and ideal SAM is difficult to obtain, both of which need to carefully deal with before practical use. Herein we developed a system to achieve seamless electroless deposited copper (ELD Cu) film on an amino-terminated silane SAM modified Si wafer with the help of a bifunctional polyvinyl alcohol-capped Pd nanocluster (PVA-Pd) catalyst. The PVA-Pd acts as a catalyst for ELD Cu as well as a healing agent to fix defects of the amino silane SAM. The sheet resistance, cross-sectional morphology analysis and adhesion of ELD Cu on the Si wafer are extensively studied. By controlling the abundancy of PVA in PVA-Pd, the diffusion barrier property of a flawed amino-terminated silane SAM remains reliably effective even after a 500 °C rapid thermal annealing (RTA), evidencing the superior healing function of PVA. The whole thickness of the PVA-Pd/amino-terminated silane SAM before and after RTA is 〜6 nm and 〜2 nm, respectively, which is applicable for advanced microelectronic manufacturing.

Clicked BODIPY-Fullerene-Peptide Assemblies: Studies of Electron Transfer Processes in Self-Assembled Monolayers on Gold Surfaces.

Two BODIPY-C60 -peptide assemblies were synthesized by CuAAC reactions of BODIPY-C60 dyads and a helical peptide functionalized with a terminal alkyne group and an azide group, respectively. The helical peptide within these assemblies was functionalized at its other end by a disulfide group, allowing formation of self-assembled monolayers (SAMs) on gold surfaces. Characterizations of these SAMs, as well as those of reference molecules (BODIPY-C60 -alkyl, C60 -peptide and BODIPY-peptide), were carried out by PM-IRRAS and cyclic voltammetry. BODIPY-C60 -peptide SAMs are more densely packed than BODIPY-C60 -alkyl and BODIPY-peptide based SAMs. These findings were attributed to the rigid peptide helical conformation along with peptide-peptide and C60 -C60 interactions within the monolayers. However, less dense monolayers were obtained with the target assemblies compared to the C60 -peptide, as the BODIPY entity likely disrupts organization within the monolayers. Finally, electron transfer kinetics measurements by ultra-fast electrochemistry experiments demonstrated that the helical peptide is a better electron mediator in comparison to alkyl chains. This property was exploited along with those of the BODIPY-C60 dyads in a photo-current generation experiment by converting the resulting excited and/or charge separated states from photo-illumination of the dyad into electrical energy.

Enhancement of Ligand Immobilization on Gold Surface by Optimizing Monolayer Concentration and Pre‐Concentration Studies for Surface Plasmon Resonance Analysis of Rutin‐Lysozyme Interaction

AbstractSurface plasmon resonance (SPR) is a versatile tool for real time monitoring of molecular interactions, providing biophysical data such as affinity and kinetics. Rutin is found in various plants and fruits and is utilized in several industries. Because of its therapeutic and industrial importance, the binding of rutin to one of the major proteins found in blood and saliva, lysozyme (LZM), was investigated to determine the affinity constants of the rutin‐LZM interaction. Chicken egg white lysozyme (CEWLZM) was selected as a model ligand. 11‐mercaptoundecanoic acid (MUA) was chosen for the self‐assembled monolayer (SAM) design on the gold chip surface. After optimizing MUA concentration and pre‐concentration studies to enhance ligand immobilization, optimum MUA concentration in SAM formation, ideal running and coupling buffers, flow rate and ligand concentration were determined to perform SPR analysis. Various concentrations of rutin (20–300 μM) were injected into the SPR for kinetic analysis. The association (ka), dissociation (kd) rate constants, and equilibrium constant (KD) were calculated from the kinetics of the binding curves. SPR binding results indicated that the KD value of rutin‐CEWLZM binding was determined as 80.07±1.22 μM. This study demonstrates the binding affinity of rutin to CEWLZM, offering potential insights for medical and pharmaceutical sciences.

The Conductance Isotope Effect in Oligophenylene Imine Molecular Wires Depends on the Number and Spacing of 13C-Labeled Phenylene Rings.

We report a strong and structurally sensitive 13C intramolecular conductance isotope effect (CIE) for oligophenyleneimine (OPI) molecular wires connected to Au electrodes. Wires were built from Au surfaces beginning with the formation of 4-aminothiophenol self-assembled monolayers (SAMs) followed by subsequent condensation reactions with 13C-labeled terephthalaldehyde and phenylenediamine; in these monomers the phenylene rings were either completely 13C-labeled or the naturally abundant 12C isotopologues. Alternatively, perdeuterated versions of terephthalaldehyde and phenylenediamine were employed to make 2H(D)-labeled OPI wires. For 13C-isotopologues of short OPI wires (<4 nm) in length where the charge transport mechanism is tunneling, there was no measurable effect, i.e., 13C CIE ≈ 1, where CIE is defined as the ratio of labeled and unlabeled wire resistances, i.e., CIE = Rheavy/Rlight. However, for long OPI wires >4 nm, in which the transport mechanism is polaron hopping, a strong 13C CIE = 4-5 was observed. A much weaker inverse CIE < 1 was evident for the longest D-labeled wires. Importantly, the magnitude of the 13C CIE was sensitive to the number and spacing of 13C-labeled rings, i.e., the CIE was structurally sensitive. The structural sensitivity is intriguing because it may be employed to understand polaron hopping mechanisms and charge localization/delocalization in molecular wires. A preliminary theoretical analysis explored several possible explanations for the CIE, but so far a fully satisfactory explanation has not been identified. Nevertheless, the latest results unambiguously demonstrate structural sensitivity of the heavy atom CIE, offering directions for further utilization of this interesting effect.

Exploring alkyl-diamine chain length effects on electrochemical behavior of AuNPs fabricated electrodes: Influence of linkers on the sensitive detection of hydrazine

In this electrochemical exploration, we scrutinized the influence of alkyl-diamine (AD) chain length as crucial linkers between glassy carbon electrodes (GCE) and citrate-capped gold nanoparticles (Cit-AuNPs), focusing on their conductive behavior and sensing proficiency, particularly in hydrazine detection. Meticulous examination of self-assembled monolayers (SAMs) formed by three distinct ADs, namely 1,6-hexanediamine (HDA), 1,8-octanediamine (ODA) and 1,10-decanediamine (DDA) unfolded over GC surfaces revealed a precise adherence to Langmuir adsorption kinetics during the SAM formation process. Utilizing cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), the electrochemical activity of the [Ru(NH₃)₆]³⁺/²⁺ redox pair at electrodes modified with ADs was investigated. The proposed mechanism involves a Michael-like nucleophilic addition process at the GC surface/diamine solution interface during the SAM formation. Analysis across various techniques underscored the compact nature of the DDA-formed SAM in comparison to HDA and ODA. Exploiting the free amine functional groups on the SAMs, the as-synthesized Cit-AuNPs were attached on the electrode surface and investigated comprehensively through CV, EIS, attenuated total reflection Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. Remarkably, Cit-AuNPs attached DDA-SAM/GC electrode offered superior electro active surface area, establishing an advanced electrochemical platform for carcinogenic hydrazine determination. The DDA/Cit-AuNPs electrode demonstrated a linear determination range of 0.003–1 mM, limits of detection at 11 nM, and sensitivity of 1080 µA mM−1 cm−2. This study gives a complete picture of how AD chain lengths, SAM formation, Cit-AuNPs attachment, and electrocatalytic performance work together to make an advanced electrochemical sensing scaffold for environmental pollutants determination.

Phosphonic acid anchored tripodal molecular films on indium tin oxide.

Whereas monopodal self-assembling monolayers (SAMs) are most frequently used for surface and interface engineering, tripodal SAMs are less popular due to the difficulty in achieving a reliable and homogeneous bonding configuration. In this context, in the present study, the potential of phosphonic acid (PA) decorated triptycene (TripPA) for formation of SAMs on oxide substrates was studied, using indium tin oxide (ITO) as a representative and application-relevant test support. A combination of several complementary experimental techniques was applied and a suitable monopodal reference system, benzylphosphonic acid (PPA), was used. The resulting data consistently show that TripPA forms well-defined, densely packed, and nearly contamination-free tripodal SAMs on ITO, with the similar parameters and properties as the monopodal reference system. Modification of wetting properties and work function of ITO by non-substituted and cyano-decorated TripPA SAMs was demonstrated, showing a potential of this tripodal system for surface engineering of oxide substrates.

Concentration gradients probed in microfluidics by gate-array electrolyte organic transistor

We propose a device architecture termed gate-array electrolyte gated organic transistor (GA-EGOFET) that quantitatively measures the solute concentration gradient created in a spatially inhomogeneous solution, for instance a (biological) fluid. The integrated H-cell microfluidics yields a diffusive concentration profile along the microfluidics channel according to the flow rate of the input streams. We demonstrate this concept by monitoring the formation of self-assembly monolayers (SAMs) on top of an array of parallel Au gate electrodes exposed to a different local concentration of alkanethiols. The deposition rate and the coverage both increase from the entrance towards the H-cell end. The voltage change at each gate is transduced in the transfer curve acquired with the specific gate electrode. For short chain length SAMs (n = 3), the trend of the current hints to a diffusion-limited surface reaction. For longer thiols (n = 6, 9), instead, the slower surface diffusion or incorporation in the more stable and compact SAM yields a current that is independent of the longitudinal gradient. The microfluidics/GA-EGOFET platform is viable for constructing dose curves in reproducible manner and for validating different electrode functionalization strategies where the deposition rates are different at each substrate site.

Comparison of Barrier Efficiency for Self-Assembled Monolayers on SiO2 by Using Decyltrimethoxysilane or 3-Aminopropyltrimethoxysilane Vapor Treatment

Self-assembled monolayers (SAMs) are the emerging materials as the candidate of barriers used in back-end-of–line interconnects for future generation. In this study, SAMs were formed on the SiO2 film by using decyltrimethoxysilane (DTMOS) or 3-aminopropyltrimethoxysilane (APTMS) in the vapor phase at a temperature of 100 °C. Barrier efficiency of the formation SAMS at the surface of SiO2 films under thermal and electrical stress was investigated from the perspective of the electrical characteristics. The formation of SAMs onto the SiO2 films by DTMOS and APTMS vapor treatment enhanced the adhesion, dielectric breakdown field and barrier against Cu migration under thermal stress. Additionally, APTMS-SAMs had a larger improvement. Under electrical stress with field larger than 6.5 MV cm−1, DTMOS-SAMs lost barrier effectiveness due to weak bonding structure. APTMS-SAMs still had the barrier capacity.

Compact Hole-Selective Self-Assembled Monolayers Enabled by Disassembling Micelles in Solution for Efficient Perovskite Solar Cells.

Self-assembled monolayers (SAMs) are widely employed as effective hole-selective layers (HSLs) in inverted perovskite solar cells (PSCs). However, most SAM molecules are amphiphilic in nature and tend to form micelles in the commonly used alcoholic processing solvents. This introduces an extra energetic barrier to disassemble the micelles during the binding of SAM molecules on the substrate surface, limiting the formation of a compact SAM. To alleviate this problem for achieving optimal SAM growth, a co-solvent strategy to disassemble the micelles of carbazole-based SAM molecules in the processing solution is developed. This effectively increases the critical micelle concentration to be above the processing concentration and enhances the reactivity of the phosphonic acid anchoring group to allow densely packed SAMs to be formed on indium tin oxide. Consequently, the PSCs derived from using MeO-2PACz, 2PACz, and CbzNaph SAM HSLs show universally improved performance, with the CbzNaph SAM-derived device achieving a champion efficiency of 24.98% and improved stability.

Hydrogen Gas Generation Using Self-Assembled Monolayers (SAMs) of 5,10,15,20-Tetrakis (p-Thiophenol) Porphyrin on a Gold Electrode

A novel approach was used to synthesize the 5,10,15,20-tetrakis (p-thiophenol) porphyrin (TPTH-P) (2), which involved the demethylation of tetra (p-anisole) porphyrin (1) in the presence of ZnCl2 as a catalyst and DMF as a solvent at 100 °C. The demethylation step was followed by an acidification step with concentrated H2SO4 to yield the desired TPTH-P (2) in an almost quantitative yield (95%). The chemical structure of the synthesized porphyrin thiol (TPTH-P) (2) was verified through spectroscopic techniques (NMR, IR, UV-Vis). The catalytic activity of TPTH-P in the hydrogen evolution reaction (HER) was investigated in 0.1 M of H2SO4 and 1 M of KNO3. A self-assembled monolayer (SAM) of TPTH-P was formed on a gold electrode. The immersion time during SAM formation and the electrochemical activation cycles in H2SO4 were found to be important to enhancing the activity of the Au-TPTH-P electrode in the HER. Contact angle measurements and electrochemical techniques, including cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and chronoamperometry, were used to characterize and evaluate the electrochemical activities of the SAM.

Efficient formation of poly(ethylene glycol) polymer brushes on gold electrodes via surface-initiated electrochemically mediated ATRP (SI-eATRP)

Electrochemically mediated surface-initiated atom transfer radical polymerization (SI-eATRP) is an interesting grafting from technique used to grow, in a controlled way, polymeric films from a wide range of surfaces, including metal substrates. Aqueous SI-eATRP offers an appealing strategy for the preparation of polymers by using water-soluble monomers, employing an oxidatively stable catalyst complex. The goal of this work is to tailor compact poly-(oligo(ethylene glycol)methacrylate) (p-OEGMA) brushes on gold electrodes by combining the formation of self-assembled monolayers (SAMs) containing a suitable ATRP initiator molecule, and the SI-eATRP polymerization approach. We have investigated the effects of the SAM-initiator nature, the applied potential, and the duration of the polymerization process on the properties of the grafted p-OEGMA-brushes. In addition, we employed electrochemical quartz crystal microbalance measurements to evidence the living character of the polymerization. The final properties of the tailored p-OEGMA-brush were studied by cyclic voltammetry and electrochemical impedance spectroscopy, obtaining information on the electronic and ionic blocking behaviour of these films, under different experimental conditions. Further information on structural conformation, composition, and organization was obtained from different characterization techniques: IRRAS and XPS spectroscopies, contact angle measurements, and SEM and AFM microscopies. These techniques confirmed that an efficient formation of p-OEGMA-brushes via SI-eATRP was achieved. Thus, the designed SI-eATRP system offers an interesting option to functionalize a wide variety of substrates with water-soluble and biocompatible monomers. Such coatings present potential applications in various fields, including biomedical applications.

Influence of Temperature-Guided SAM Growth on Wetting and Its Mass Transfer Models.

The formation and growth of self-assembled monolayers (SAMs) composed of amphiphiles have garnered significant attention due to their diverse technical applications. This article reports the findings of molecular dynamics simulations aimed at elucidating the intricate relationship between the wetting behavior of amphiphiles, specifically n-alkanols, and the growth of their SAMs on a mica surface under varying temperature conditions. The investigation quantifies the structural characteristics of the formed SAMs, including density profiles, in-plane radial distribution functions, order parameters, and end-to-end length distributions of n-alkanol molecules within the SAM. Thermodynamic properties, such as the second virial coefficient and excess entropy, are examined in relation to temperature and time. The growth of the SAM is assessed by analyzing characteristic time scales at different temperatures and in-plane diffusion of n-alkanol molecules and utilizing classical theories of mass transfer to quantify the growth rate as a function of temperature. These results are then correlated with changes in the contact angle and spreading coefficient of n-alkanol droplets on the mica surface over time, providing insights into the impact of SAM growth on the wetting behavior and the mass transfer model of such systems.

Self‐Assembled Monolayers of Bi‐Functionalized Porphyrins: A Novel Class of Hole‐Layer‐Coordinating Perovskites and Indium Tin Oxide in Inverted Solar Cells

AbstractSelf‐assembled monolayers (SAMs) offer the advantage of facile interfacial modification, leading to significant improvements in device performance. In this study, we report the design and synthesis of a new series of carboxylic acid‐functionalized porphyrin derivatives, namely AC‐1, AC‐3, and AC‐5, and present, for the first time, a strategy to exploit the large π‐moiety of porphyrins as a backbone for interfacing the indium tin oxide (ITO) electrode and perovskite active layer in an inverted perovskite solar cell (PSC) configuration. The electron‐rich nature of porphyrins facilitates hole transfer and the formation of SAMs, resulting in a dense surface that minimizes defects. Comprehensive spectroscopic and dynamic studies demonstrate that the double‐anchored AC‐3 and AC‐5 enhance SAMs on ITO, passivate the perovskite layer, and function as conduits to facilitate hole transfer, thus significantly boosting the performance of PSCs. The champion inverted PSC employing AC‐5 SAM achieves an impressive solar efficiency of 23.19 % with a high fill factor of 84.05 %. This work presents a novel molecular engineering strategy for functionalizing SAMs to tune the energy levels, molecular dipoles, packing orientations to achieve stable and efficient solar performance. Importantly, our comprehensive investigation has unraveled the associated mechanisms, offering valuable insights for future advancements in PSCs.

Self-Assembled Monolayers of Bi-Functionalized Porphyrins: A Novel Class of Hole-Layer-Coordinating Perovskites and Indium Tin Oxide in Inverted Solar Cells.

Self-assembled monolayers (SAMs) offer the advantage of facile interfacial modification, leading to significant improvements in device performance. In this study, we report the design and synthesis of a new series of carboxylic acid-functionalized porphyrin derivatives, namely AC-1, AC-3, and AC-5, and present, for the first time, a strategy to exploit the large π-moiety of porphyrins as a backbone for interfacing the indium tin oxide (ITO) electrode and perovskite active layer in an inverted perovskite solar cell (PSC) configuration. The electron-rich nature of porphyrins facilitates hole transfer and the formation of SAMs, resulting in a dense surface that minimizes defects. Comprehensive spectroscopic and dynamic studies demonstrate that the double-anchored AC-3 and AC-5 enhance SAMs on ITO, passivate the perovskite layer, and function as conduits to facilitate hole transfer, thus significantly boosting the performance of PSCs. The champion inverted PSC employing AC-5 SAM achieves an impressive solar efficiency of 23.19% with a high fill factor of 84.05%. This work presents a novel molecular engineering strategy for functionalizing SAMs to tune the energy levels, molecular dipoles, packing orientations to achieve stable and efficient solar performance. Importantly, our comprehensive investigation has unraveled the associated mechanisms, offering valuable insights for future advancements in PSCs.

Cooperativity at the Solution/Solid Interface: Formation and Reactivity of Self-Assembled Monolayers

Cooperativity is a molecular phenomenon, in which multiple interactions participate synchronously to significantly affect the activity and/or selectivity of the interacting components by accelerating (or impeding) their chemical or physical processes. Cooperative effects are prevalent in biology and can be observed in chemistry and materials science. Synthesis of functional materials frequently requires surfaces and interfaces where cooperative interactions can propagate with substrate assistance. In this context, of great interest is the characterization and control of ligands binding to metal centers, given their rich chemistry and prevalence in functional materials. In addition, self-assembly of compounds on surfaces can be steered by cooperative effects, and supramolecular polymerization can also proceed in a cooperative manner. Essential for these kinds of chemistries is the availability of highly resolving analysis methods to investigate reaction and adsorption outcomes directly at the surface. Scanning tunneling microscopy (STM) is particularly well suited to the study of such processes on surfaces and interfaces by offering both molecular resolution and real time and space information regarding changes in the electronic structure of materials upon adsorption and/or reaction.In this contribution, we present quantitative STM experimental results and supporting theoretical calculations of the binding dynamics of neutral ligands (heteroaromatics, O2) to metal porphyrins adsorbed on solid substrates as well as self-assembly of polyaromatics on metallic supports. Single molecule level STM imaging was accomplished in-situ under ambient solution conditions. We measured binding affinities and uncovered surface modulated cooperativity both in coordination reactions and in molecular self-assembly -- results essential for understanding adsorbate-surface interactions. Computations corroborate our experimental findings. The high-resolution, quantitative knowledge gained at the molecular level combined with theoretical studies offer not only insights into chelation, adsorption, and cooperativity but also into control parameters for surface-driven synthesis, tunable surface functionalization, and catalysis selectivity control.

N-Heterocyclic carbene-based gold etchants.

N-Heterocyclic carbenes (NHCs) are an emerging alternative to thiols for the formation of stable self-assembled monolayers (SAMs) on gold. We examined several different species that have been used to produce NHC-based monolayers on gold, namely 1,3-diisopropyl-5-nitrobenzimidazolium iodide, 1,3-diisopropyl-5-nitrobenzimidazolium hydrogen carbonate, bis(1,3-diisopropyl-5-nitrobenzimidazolium)gold(I) iodide, and 1,3-diisopropyl-5-nitrobenzimidazole-2-ylidene. Contrary to expectation, solutions containing the first two species in tetrahydrofuran and dichloromethane caused visible loss of gold from thin-film-coated glass slides. The use of toluene solutions of all species resulted in no apparent dissolution of gold. We present scanning electron micrographs and elemental imaging analyses by energy dispersive X-ray spectroscopy to examine the effect of solutions of each species on the gold film. This work highlights the risk of unwanted etching during some routes to NHC-based surface functionalization but also the potential for deliberate etching, with the outcome determined by choice of chemically synthesized organic species and solvent.

Soft removal of stearic acid self-assembled monolayer for area-selective atomic layer deposition

Stearic acid (SA) self-assembled monolayer (SAM) is proposed as a soft-removal passivating agent for area-selective atomic layer deposition (AS-ALD) applications. First, the SAM formation kinetics and its thermal stability were evaluated on a copper surface. We observed a highly packed, hydrophobic, and ordered monolayer. The transition temperature from order to disorder was observed above 160 °C. Next, the SA/copper was evaluated as a non-growth surface for ZnO ALD and monitored by X-ray Photoelectron Spectroscopy (XPS). The optimal ALD parameters were found at 70 °C, dosing 25 ms of diethyl zinc precursor and water, while purge was 10 s for each. In these conditions, the attenuation growth remained for at least 40 ALD cycles; despite zinc deposition after the first three cycles. Finally, the removal of the SA monolayer was investigated with water, acetone, and ethanol at room temperature. According to infrared and water contact angle, ethanol was the most effective, showing a complete removal after 30 min immersion time (without sonication or agitation). We conclude that SA SAM is an efficient removable copper passivating agent for area-selective atomic layer deposition without exposing samples to harsh conditions, like etching or acid treatments.

Defect Mapping and Densification in Self-Assembled Monolayers of Octadecyltrichlorosilane on SiO&lt;sub&gt;2&lt;/sub&gt;

Self-assembled monolayers (SAMs) can be used for surface functional control to assist with pattern collapse prevention and as a protective layer to enable Area Selective Deposition (ASD). To be successful, these applications require the formation of a high-density, defect-free, so-called well-packed SAM at the nm scale. In this paper, we describe a method to map the nm scale defects of octadecyltrichlorosilane (ODTS) SAMs using a post-etching AFM analysis of the surface of the substrate and used this technique to develop a process to form high-density, defect-free SAM layer at the nm scale. This was achieved by optimizing the water concentration in the solvent for the precursor solution and annealing after SAM formation.

Fast analysis of Staphylococcus aureus in food products using disposable label-free nano-electrochemical immunosensor chips

Rapid analysis and early detection of food poisoning has become an important factor for the recognition and prevention of problems associated with food safety and public health. Accordingly, a number of different methods have been developed and applied for the detection and identification ofS. aureus. However, these methods are not suitable for on-site applications as they are time-consuming and laborious. Thus, a label-free impedimetric immunosensor was constructed using the self-assembling monolayer formation of the lipoic at the AuNPs@Fe3O4-screen printed electrode. The formed layer of the lipoic acid supported the covalent immobilization of anti-S. aureusantibody as the selective bio-recognition element. As a result, a specific immune reaction between the whole pathogen cells and the immobilized antibody was monitored under optimized conditions. Electrochemical impedance spectroscopy along with other chemical assessments were used to verify the stepwise assembly of the immunosensor fabrication. Accordingly, the newly developed impedimetric immunosensor showed high sensitivity and selectivity towards the targeting bacterial strain with the limit of detection and limit of quantification of 0.10, and 0.34 CFU/mL, respectively. Eventually, the designed immunosensor was successfully implemented to analyze theS. aureus contamination in milk and meat samples, whereas the obtained results were validated.