Self-assembled Monolayers Research Articles

Monitoring the On-Surface Boronic Acid Condensation Process at the Nanoscale Using Tip-Enhanced Raman Spectroscopy.

The on-surface condensation of boronic acids is a key step in fabricating functional interfaces with tailored properties; yet, a clear understanding of the molecular structural transformations involved remains a significant challenge. Here, we directly monitor the condensation reaction in a self-assembled monolayer of 4-mercaptophenylboronic acid (MPBA) on Au(111) using tip-enhanced Raman spectroscopy (TERS). The structural evolution in the MPBA adlayer is tracked via the emergence of new peaks, blue shifts, and intensity changes in characteristic Raman bands. Hyperspectral TERS imaging provides comprehensive insight into molecular transformations, including B-O-B bond formation, increased molecular constraints, and an evolution in molecular orientation. Furthermore, density functional theory simulations confirm that the boroxine trimer is the primary product of the on-surface condensation reaction. This study provides significant insights into on-surface boronic acid condensation chemistry for the rational design of functionalized surfaces with targeted chemical properties.

Cholesterol Functionalized Nanoparticles Are Effective against Helicobacter pylori, the Gastric Bug: A Proof-of-Concept Study.

Helicobacter pylori chronic infection is the highest risk factor for the development of gastric cancer, being this Gram-negative bacterium classified as carcinogenic. The mounting resistance of H. pylori to antibiotics calls for innovative therapeutic strategies. Here, the proof-of-concept studies that support the development of a "trojan horse" therapeutic strategy based on cholesterol-grafted nanoparticles (Chol-NP) to counteract H. pylori infection are depicted. The bacterium ability to specifically recognize and bind to surface grafted cholesterol is demonstrated by its adhesion to cholesterol(Chol)-functionalized self-assembled monolayers (SAMs) on gold substrates (2D Chol-SAMs) in a concentration dependent manner, with optimal Chol-SAMs prepared with 25% Chol-polyethylene glycol (PEG)-thiol in solution (75% tetra(ethylene glycol)-thiol). These results further show that cholesterol functionalized gold nanoparticles (3D Chol-SAMs, Chol-NP) eradicate H. pylori at a minimum bactericidal concentration of 125 µg mL-1. Chol-NP kill H. pylori through internalization and membrane rupture, as observed by transmission electron microscopy (TEM). Chol-NP are cytocompatible (human gastric adenocarcinoma (AGS) cell line), non-hemolytic and innocuous to bacteria representative of the gut microbiota (Escherichia coli and Lactobacillus acidophilus). This study supports the further development of cholesterol functionalized biomaterials as an advanced and targeted treatment for H. pylori infection.

Leaf-Face Dendrobium Classifier Based on an Integrated Electrochemical Tongue and Machine Learning.

Botanical sourcing seriously impacts the safety and potency of herbal medicines, restricting the development of the traditional Chinese medicinal industry. Rapid and convenient identification of plant resources is important to address this problem. Herein, we innovated a portable, intelligent, and integrated platform, termed the Smart Electronic Tongue (SET), for right recognizing Dendrobium bonsai of different subspecies and origins. The device is miniaturized with a hollow microneedle array for leaf-face extraction, a press-pumping pipeline for on-demand sample sap suction, plus a five-electrode chip for electrochemical readout. Differential pulse voltammograms on three simplexes of self-assembled monolayers as well as their multiplexed configurations are specialized to generate high-dimensional fingerprinting of Dendrobium subtypes. Taking advantage of machine learning algorithms, the platform achieves automatic authentication over eight varieties with a discriminatory accuracy of 95%. Given this, we anticipate that such a bionic sensing setup would offer a versatile solution toward the classification of diverse officinals at the point of need.

Rational Design and Visualization of Multifunctional Phenothiazine-Based Self-Assembled Monolayers for Better Interface Contact in High-Efficiency and Stable Perovskite Solar Cells.

Interfacial modification using self-assembled monolayers (SAMs) is crucial for defect passivation and energy level alignment in perovskite solar cells (PSCs), yet scaling SAMs remains a challenge. Organic SAMs are often too thin for large-area homogeneous layers through spin-coating and their hydrophobic nature complicates solution-based perovskite fabrication, hindering uniform film formation. This study introduces SAM based on phenothiazine core that involves synergistic co-adsorption of a hydrophilic phosphonic acid with phenothiazine core unit for use as a hole transport layer in p-i-n PSCs. The PTZ-PA SAM improves film formation, energy alignment, and hole extraction, achieving a power conversion efficiency above 23.2%. It also maintains stable performance for over 500h under continuous illumination, indicating its potential for durable PSCs. PTZ-PA increases surface energy, overcoming non-wetting issues and enabling the formation of high-quality perovskite films with improved morphology and crystallinity. The phosphonic acid group coordinates with lead iodide in the perovskite, enhancing electronic charge transfer and mechanical absorption, which facilitates effective p-type charge-selective contacts.

Electron transfer kinetics in ferrocene-terminated self-assembled monolayers: The effect of ferrocene surface coverage variation

Electron transfer kinetics in ferrocene-terminated self-assembled monolayers: The effect of ferrocene surface coverage variation

The Role of Self-Assembly Monolayers (SAM) on Schottky Diode Performance

This study investigates the electrical and charge transport properties of Schottky diodes with a p-Si/TiO2/SAM/Al structure, incorporating the self-assembly monolayers (SAMs) 4", 4""-[biphenyl-4,4" diylbis(phenylimino)]dibiphenyl-4-carboxylic acid (MZ187) onto a titanium dioxide (TiO2) layer synthesized via the sol-gel method. The impact of the MZ187 molecule on diode performance was evaluated based on parameters such as the barrier height (∅b), ideality factor (n), and series resistance (Rs). Experimental results reveal that the MZ187 monolayers on TiO2 substantially enhanced diode performance, reducing the n from 3.7 for the control diode to 2.7 for the MZ187-modified diode. The Rs was also significantly reduced, while the ∅b increased. The rectification ratio increased from 1.3x102 for the control diode to 2.2x103 for the MZ187 modified diode. These improvements are attributed to the ability of MZ187 molecules to minimize interface states (Nss) and improve surface quality. These findings underscore the critical role of SAMs in optimizing Schottky diode performance and demonstrate how the MZ187 molecule enhances diode efficiency by altering interface properties. The effectiveness of SAM coatings in enhancing Schottky diode performance makes a significant contribution to the field of nanoelectronics. This research paves the way for future studies on the use of SAMs in various nano electronic applications and offers promising potential for improving the performance and reliability of these technologies.

Self-Assembly of Mycolic Acid in Water: Monolayer or Bilayer.

The enduring pathogenicity of Mycobacterium tuberculosis can be attributed to its lipid-rich cell wall, with mycolic acids (MAs) being a significant constituent. Different MAs' fluidity and structural adaptability within the bacterial cell envelope significantly influence their physicochemical properties, operational capabilities, and pathogenic potential. Therefore, an accurate conformational representation of various MAs in aqueous media can provide insights into their potential role within the intricate structure of the bacterial cell wall. We have carried out MD simulations of MAs in an aqueous solution and shed light on various structural properties such as thickness, order parameters, area-per-MAs, conformational changes, and principle component (PC) in the single-component and mixture MAs monolayer. The different conformational populations in the monolayer were estimated using the distance-based analysis between the function groups represented as W, U, and Z conformations that lead to the fold of the MAs chain in the monolayer. Additionally, we have also simulated the mixture of alpha-MA (α-MA or AMA), methoxy-MA (MMA), and keto-MA (KMA) with 50.90% AMA, 36.36% MMA, and 12.72% KMA composition. The thickness of the MAs monolayer was observed to range from 5 to 7 nm with an average 820 kg/m3 density for α-MA, MMA, and KMA quantitative agreement with experimental results. The mero chain (long chain), consisting of a functional group at the proximal and distal positions, tends to fold and exhibit a more disordered phase than the short chain. The keto-MA showed the greatest WUZ total conformations (35.32%) with decreasing trend of eZ > eU > aU > aZ folds in both single component and mixture. Our results are in quantitative agreement with the experimental observations. The sZ folds show the lowest conformational probability in monolayer assembly (0.75% in a single component and 1.1% in a mixture). However, eU and aU folds are most probable for AMA and MMA. One striking observation is the abundance of MA conformers beyond the known WUZ convention because of the wide range distribution of intramolecular distances and change in dihedral angles. From a thermodynamic perspective, all mycolic acid monolayers in this study within the microsecond-long simulation, MA molecules self-assembled, and the self-assembled monolayer was found to be stable. The conformation of MAs corresponding to lower free energy minima in the monolayer gives rise to tighter packing and a highly dense self-assembly. Such a highly packed assembly shows higher resistance for drug permeability. Therefore, we concluded that the monolayer formed by AMA will be more densely packed and may cause more resistance for the drug molecules.

Selective On-Surface Metalation and Uncommon Reordering of Self-Assembled Macrocyclic Biquinazoline Ligands on Ag(111).

The macrocyclic biquinazoline ligand, H-Mabiq, presents a central and a peripheral site for the coordination of metal ions, making the adsorption on solid surfaces promising for the creation of self-assembled bimetallic two-dimensional platforms. Here, we apply an on-surface metalation strategy under ultra-high vacuum conditions to guide the synthesis of metalated species and study sequential metalation patterns. We find that cobalt (as well as iron) metalation on the Ag(111) surface preferentially occurs at the macrocyclic centre without further metal coordination to the peripheral site. Nevertheless, starting from a densely packed, self-assembled H-Mabiq monolayer, the modification of the central cavity by Co is accompanied by an unusual, metalation-induced phase transformation which gives evidence of modified lateral / interfacial interactions. The selective metalation of one molecular site opens up an on-surface route to create bimetallic networks incorporating select metal ions at different locations.

High-Security Data Encryption Enabled by DNA Multi-Strand Solid-Phase Hybridization and Displacement in Inkjet-Printed Microarrays.

Multicolor fluorescent encryption systems that respond to specific stimuli have drawn widespread attention to data storage and encryption due to their low cost and facile data access. However, existing encryption systems are limited by encryption materials, restricting their encryption depth. This study uses DNA molecules as encryption materials that offer exceptional specificity and encryption depth within sequences. With inkjet-printed microarrays on a solid-phase interface, a multicolor fluorescent data storage system based on DNA hybridization and strand displacement is developed, achieving an encryption system with high encryption depth and flexibility. DNA strands, modified with different fluorescent labels, are delivered onto solid-phase interfaces containing a DNA self-assembled monolayer (SAM) via inkjet printing, forming multicolor fluorescent data microarrays. Data storage and encryption are achieved through the hybridization of fluorescent DNA strands for data presentation and interference with the DNA SAM at the interface between the solid phase and droplets. Interference DNA strands can be removed by DNA strand displacement for decryption. The encryption depth of this system is determined by the design of the DNA sequences and the combination of multiple DNA strands, showcasing its outstanding encryption ability. Meanwhile, high-throughput inkjet printing accelerates the data writing process, further enhancing the system efficiency. With DNA solid-phase reaction in inkjet-printed microarrays, this system provides a scalable and robust strategy for high-depth and efficient data encryption.

Capillary Wave-Assisted Colloidal Assembly.

The self-assembly of nanoparticle colloids into large-area monolayers with long-range order is a grand challenge in nanotechnology. Using acoustic energy, i.e., acoustic annealing, to improve the crystal quality of self-assembled colloidal monolayers is a new solution to this challenge, but the characterization of the capillary waves driving the annealing process is lacking. We use a laser Doppler vibrometer and optical diffraction to uncover the frequency-dependent effects of capillary waves on the real-time self-assembly of submicrometer diameter polystyrene nanospheres at an air-water interface. Our study unambiguously demonstrates that low-frequency, e.g., sub-100 Hz, capillary waves are key to improving the long-range order of colloidal monolayers on an air-water interface. Furthermore, we demonstrate how a simple immersion transducer can generate capillary waves and how transducer placement and design affect vibrational spectra. Lastly, we show that frequency-shift keying of a high-frequency focused transducer provides a straightforward method of exciting low-frequency capillary waves that are effective at forming colloidal monolayers with excellent crystal quality, exhibited by grains over 3.5 cm2.

Self‐Assembled Monolayers for Highly Efficient All‐Polymer Solar Cells Sequentially Processed from Hydrocarbon Solvent

AbstractAll‐polymer solar cells (all‐PSCs), comprising polymer donors and polymerized small‐molecule acceptors (PSMAs), hold significant promise for industrial production owing to their superior device efficiencies and stability. However, the lower molecular weights and weaker crystallinity of PSMAs lead to low electron mobility, while achieving high efficiencies in all‐PSCs typically rely on the use of the highly volatile chloroform. These challenges have been addressed through the development of self‐assembled monolayers (SAMs) as a novel interfacial layer, offering improved transparency, stability, sensitivity and surface passivation. This research investigates SAMs, specifically 2PACz, as a hole transporting layer (HTL) in all‐PSCs, employing a sequential processing strategy with toluene solvent to mitigate the aforementioned challenges. This study achieves highly efficient 2PACz‐based all‐PSC cells at 19.19% (certificated at 18.51%), which is a new record for all‐PSCs by non‐halogen solvents. Compared to PEDOT:PSS‐based solar cells, the improved performance of 2PACz‐based devices can be attributed to enlarged charge carrier mobility, prolonged carrier lifetime, and constrained recombination traps. Good generality of 2PACz as HTL is observed for PM6:PYF‐T‐o and PM6:PJ1‐γ systems as 2PACz‐based devices outperform PEDOT:PSS counterparts. These results demonstrate that SAMs are a promising candidate for hole transport engineering in high‐performance all‐PSCs.

Self-Assembled Monolayer Materials with Multifunction for Antimony Selenosulfide Solar Cells

Self-Assembled Monolayer Materials with Multifunction for Antimony Selenosulfide Solar Cells

Electrochemical capacitance-based aptasensor for HER2 detection.

The overexpression of Human Epidermal Growth Factor Receptor 2 (HER2) protein is specifically related to tumor cell proliferation in breast cancers. Its presence in biological serum samples indicates presence or progression of cancer, becoming a promise biomarker. However, their detection needs a simple and high accuracy platform. In this study, we report the develop and optimization of a simple highly sensitive electrochemical platform for HER2. Gold electrode surface was modified with a self-assembled monolayer composed by DNA aptamer, 6-(ferrocenyl) hexanethiol and 6-mercapto-1-hexanethiol. Electrochemical impedance spectroscopy was used to quantify the changes in capacitance on the interface due to the presence ferrocene, whether acting as a redox charge or its behavior under different HER2 concentration in PBS and undiluted human serum. As a result, the approach allows detection of HER2 with a limit of detection of 3.61 pg/mL, 12.28 nF sensitivity per decade and a linear range from 1 pM to 1 [Formula: see text]M in serum. This electrochemical aptasensor can be applied to different arrays for aptamer screening and has a significant importance to interaction study of biological systems.

Transforming Polymers: Innovative Physical and Chemical Modification Techniques for Advanced Functional Applications

Abstract: Polymer modification encompasses a diverse array of techniques aimed at enhancing the physical and chemical properties of polymers, thereby expanding their applicability across various fields. Physical modification methods include self-assembled monolayers, radiation-induced surface modifications, UV irradiation, γ-irradiation, and laser-induced surface modifications. These techniques primarily focus on altering surface properties and enhancing characteristics such as strength, toughness, and thermal stability through non-chemical means. Chemical modification methods, on the other hand, involve reactions that change the polymer’s chemical structure. Common chemical reactions used in polymer modification include PEGylation, conjugation, wet chemical oxidation treatments, and plasma treatments. These processes introduce new functional groups, improve compatibility with other materials, and tailor properties like solubility, adhesion, and biodegradability. Despite the significant advancements in polymer modification techniques, challenges such as maintaining polymer integrity, controlling modification precision, and ensuring scalability persist. This review provides a comprehensive overview of both physical and chemical polymer modification methods, discussing their mechanisms, applications, and the challenges involved, thereby highlighting their critical role in the development of advanced materials for industrial, biomedical, and environmental applications.

Investigating Benzoic Acid Derivatives as Potential Atomic Layer Deposition Inhibitors Using Nanoscale Infrared Spectroscopy

Area-selective atomic layer deposition (AS-ALD) is a technique utilized for the fabrication of patterned thin films in the semiconductor industry due to its capability to produce uniform and conformal structures with control over thickness at the atomic scale level. In AS-ALD, surfaces are functionalized such that only specific locations exhibit ALD growth, thus leading to spatial selectivity. Self-assembled monolayers (SAMs) are commonly used as ALD inhibiting agents for AS-ALD. However, the choice of organic molecules as viable options for AS-ALD remains limited and the precise effects of ALD nucleation and exposure to ALD conditions on the structure of SAMs is yet to be fully understood. In this work, we investigate the potential of small molecule carboxylates as ALD inhibitors, namely benzoic acid and two of its derivatives, 4-trifluoromethyl benzoic acid (TBA), and 3,5-Bis (trifluoromethyl)benzoic acid (BTBA) and demonstrate that monolayers of all three molecules are viable options for applications in ALD blocking. We find that the fluorinated SAMs are better ALD inhibitors; however, this property arises not from the hydrophobicity but the coordination chemistry of the SAM. Using nanoscale infrared spectroscopy, we probe the buried monolayer interface to demonstrate that the distribution of carboxylate coordination states and their evolution is correlated with ALD growth, highlighting the importance of the interfacial chemistry in optimizing and assessing ALD inhibitors.

A Brief Review on Self-Assembled Monolayers in Organic Solar Cells: Progress, Challenges, and Future Prospects

A Brief Review on Self-Assembled Monolayers in Organic Solar Cells: Progress, Challenges, and Future Prospects

Carboxylate-Terminated Electrode Surfaces Improve the Performance of Electrochemical Aptamer-Based Sensors.

Electrochemical aptamer-based (EAB) sensors are a molecular measurement platform that enables the continuous, real-time measurement of a wide range of drugs and biomarkers in situ in the living body. EAB sensors are fabricated by depositing a thiol-modified, target-binding aptamer on the surface of a gold electrode, followed by backfilling with an alkanethiol to form a self-assembled monolayer. And while the majority of previously described EAB sensors have employed hydroxyl-terminated monolayers, a handful of studies have shown that altering the monolayer headgroup can strongly affect sensor performance. Here, using 4 different EAB sensors, we show that the mixed monolayers composed of mixtures of 6-carbon hydroxyl-terminated thiols and varying amounts of either 6- or 8-carbon, carboxylate-terminated thiols lead to improved EAB sensor performance. Specifically, the use of such mixed monolayers enhances the signal gain (the relative change in the signal seen upon target addition) for all tested sensors, often by several fold, both in buffer and whole blood at room temperature or physiological temperatures. Moreover, these improvements in gain are achieved without significant changes in the aptamer affinity or the stability of the resulting sensors. In addition to proving a ready means of improving EAB sensor performance, these results suggest that exploration of the chemistry of the electrode surface employed in such sensors could prove to be a fruitful means of advancing this unique in vivo sensing technology.

Strong Hydrophobic Interaction of High Molecular Weight Chitosan in Aqueous Solution.

Chitosan is a versatile bioactive polysaccharide in various industries, such as pharmaceuticals and environmental applications, owing to its abundance, biodegradability, biocompatibility, and antibacterial properties. To effectively harness its potential for various purposes, it is crucial to understand the mechanisms of its interaction in water. This study investigates the interactions between high molecular weight (HMW, >150 kDa) chitosan and four different functionalized self-assembled monolayers (SAMs) at three different pHs (3.0, 6.5, and 8.5) using a surface forces apparatus (SFA). We report that HMW chitosan exhibits the strongest adhesion to methyl-terminated SAM (CH3-SAM) at all pHs, showing potential for strong hydrophobic interactions against other molecules containing hydrophobic moieties. Noting that hydrogen bonding has been considered the dominating interaction mechanism of chitosan, the consequence of this study provides valuable insights into its applications in developing chitosan-based eco-friendly materials.

Molecular ferroelectric self-assembled interlayer for efficient perovskite solar cells

The interfacial molecular dipole enhances the photovoltaic performance of perovskite solar cells (PSCs) by facilitating improved charge extraction. However, conventional self-assembled monolayers (SAMs) face challenges like inadequate interface coverage and weak dipole interactions. Herein, we develop a strategy using a self-assembled ferroelectric layer to modify the interfacial properties of PSCs. Specifically, we employ 1-adamantanamine hydroiodide (ADAI) to establish robust chemical interactions and create a dipole layer over the perovskite. The oriented molecular packing and spontaneous polarity of ferroelectric ADAI generate a substantial interfacial dipole, adjusting band bending at the anode, reducing band misalignment, and suppressing charge recombination. Consequently, our formamidinium lead iodide-based conventional PSC achieves efficiencies of 25.13% (0.06 cm2) and 23.5% (1.00 cm2) while exhibiting enhanced stability. Notably, we demonstrate an impressive efficiency of 25.59% (certified at 25.36%) in a 0.06 cm2 area for the inverted champion device, showcasing the promise of ferroelectric SAMs for PSCs performance enhancement.

Prof. George Whitesides’ Contributions to Self-Assembled Monolayers (SAMs): Advancing Biointerface Science and Beyond

Prof. George Whitesides’ pioneering contributions to the field of self-assembled monolayers (SAMs) have profoundly influenced biointerface science and beyond. This review explores the development of SAMs as highly organized molecular structures, focusing on their role in advancing surface science, biointerface research, and biomedical applications. Prof. Whitesides’ systematic investigations into the effects of SAMs’ terminal group chemistries on protein adsorption and cell behavior culminated in formulating “Whitesides’ Rules”, which provide essential guidelines for designing bioinert surfaces. These principles have driven innovations in anti-fouling coatings for medical devices, diagnostics, and other biotechnological applications. We also discuss the critical role of interfacial water in SAM bioinertness, with studies demonstrating its function as a physical barrier preventing protein and cell adhesion. Furthermore, this review highlights how data science and machine learning have expanded the scope of SAM research, enabling predictive models for bioinert surface design. Remarkably, Whitesides’ Rules have proven applicable not only to SAMs but also to polymer-brush films, illustrating their broad relevance. Prof. Whitesides’ work provides a framework for interdisciplinary advancements in material science, bioengineering, and beyond. The enduring legacy of his contributions continues to inspire innovative approaches to addressing challenges in biomedicine and biotechnology.