The role of ligands in coinage-metal nanoparticles for electronics

Ligands of Nanoparticles and Their Influence on the Morphologies of Nanoparticle-Based Films

Nanoparticle-based thin films are increasingly being used in various applications. One of the key factors that determines the properties and performances of these films is the type of ligands attached to the nanoparticle surfaces. While long-chain surfactants, such as oleic acid, are commonly employed to stabilize nanoparticles and ensure high monodispersity, these ligands often hinder charge transport due to their insulating nature. Although thermal annealing can remove the long-chain ligands, the removal process often introduces defects such as cracks and voids. In contrast, the use of short-chain organic or inorganic ligands can minimize interparticle distance, improving film conductivity, though challenges such as incomplete ligand exchange and residual barriers remain. Polymeric ligands, especially block copolymers, can also be employed to create films with tailored porosity. This review discusses the effects of various ligand types on the morphology and performance of nanoparticle-based films, highlighting the trade-offs between conductivity, structural integrity, and functionality.

Paper-Based DNA Biosensor for Rapid and Selective Detection of miR-21

Cancer is the second leading cause of death globally, with 9.7 million fatalities in 2022. While routine screenings are vital for early detection, healthcare disparities persist, highlighting the need for equitable solutions. Recent advancements in cancer biomarker identification, particularly microRNAs (miRs), have improved early detection. MiR-21 is notably overexpressed in various cancers and can be a valuable diagnostic tool. Traditional detection methods, though accurate, are costly and complex, limiting their use in resource-limited settings. Paper-based electrochemical biosensors offer a promising alternative, providing cost-effective, sensitive, and rapid diagnostics suitable for point-of-care use. This study introduces an innovative electrochemical paper-based biosensor that leverages gold inkjet printing for the quantitative detection of miR-21. The biosensor, aimed at developing cost-effective point-of-care devices for low-resource settings, uses thiolated self-assembled monolayers to immobilize single-stranded DNA-21 (ssDNA-21) on electrodeposited gold nanoparticles (AuNPs) on the printed gold surface, facilitating specific miR-21 capture. The hybridization of ssDNA-21 with miR-21 increases the anionic barrier density, impeding electron transfer from the redox probe and resulting in a current suppression that correlates with miR-21 concentration. The biosensor exhibited a linear detection range from 1 fM to 1 nM miR-21 with a sensitivity of 7.69 fM µA-1 cm2 and a rapid response time (15 min). With a low detection limit of 0.35 fM miR-21 in serum, the biosensor also demonstrates excellent selectivity against interferent species. This study introduces an electrochemical paper-based biosensor that uses gold inkjet printing to precisely detect miR-21, a key biomarker overexpressed in various cancers. This innovative device highlights the potential for cost-effective, accessible cancer diagnostics in underserved areas.

In Situ Growth of Gold Nanofilms with Branched Structures in the Presence of Organosulfur for High-Performance Flexible Electronics

Herein, a novel method is presented for the in situ growth of gold nanofilms with branched structures in the presence of organosulfur. The key feature in this approach is the Rayleigh instability of ultrathin gold nanowires (AuNWs) without oleylamine (OAm), which allows the ultrathin AuNWs to decompose into gold nanoparticles (AuNPs) and the AuNPs to in situ grow into branched structures for high-performance stability and electrical conductivity. The sheet resistance of the gold nanofilms initially sharply decreased, whereas it subsequently slightly increased with the concentration of CS(NH2)2 until it exceeded the optimal range. After undergoing a 10 min heat treatment at 150 °C, the sheet resistance of the nanofilms was further reduced to 18 Ω/sq, which could be maintained for more than five months. The internal structure becomes fully grown and denser, forming a branched structure after heat treatment. Only certain organosulfurs can improve the electrical properties of the gold nanofilms, and the mechanism of organosulfur in the in situ growth of gold nanofilms with branched structures has also been presented. Overall, this novel method provides a straightforward and convenient approach to obtaining gold nanomaterials with branched structures, holding great potential promise for applications in flexible electronics, catalysis, and energy fields.

Role of transition metals in coinage metal nanoclusters for the remediation of toxic dyes in aqueous systems

A difficult issue in chemistry and materials science is to create metal compounds with well-defined components. Metal nanoclusters, particularly those of coinage groups (Cu, Ag, and Au), have received considerable research interest in recent years owing to the availability of atomic-level precision via joint experimental and theoretical methods, thus revealing the mechanisms in diverse nano-catalysts and functional materials. The textile sector significantly contributes to wastewater containing pollutants such as dyes and chemical substances. Textile and fabric manufacturing account for about 7 × 105 tons of wastewater annually. Approximately one thousand tons of dyes used in textile processing and finishing has been recorded as being discharged into natural streams and water bodies. Owing to the widespread environmental concerns, research has been conducted to develop absorbents that are capable of removing contaminants and heavy metals from water bodies using low-cost technology. Considering this idea, we reviewed coinage metal nanoclusters for azo and cationic dye degradation. Fluorometric and colorimetric techniques are used for dye degradation using coinage metal nanoclusters. Few reports are available on dye degradation using silver nanoclusters; and some of them are discussed in detailed herein to demonstrate the synergistic effect of gold and silver in dye degradation. Mostly, the Rhodamine B dye is degraded using coinage metals. Silver nanoclusters take less time for degradation than gold and copper nanoclusters. Mostly, H2O2 is used for degradation in gold nanoclusters. Still, all coinage metal nanoclusters have been used for the degradation due to suitable HOMO-LUMO gap, and the adsorption of a dye onto the surface of the catalyst results in the exchange of electrons and holes, which leads to the oxidation and reduction of the adsorbed dye molecule. Compared to other coinage metal nanoclusters, Ag/g-C3N4 nanoclusters displayed an excellent degradation rate constant with the dye Rhodamine B (0.0332 min-1). The behavior of doping transition metals in coinage metal nanoclusters is also reviewed herein. In addition, we discuss the mechanistic grounds for degradation, the fate of metal nanoclusters, anti-bacterial activity of nanoclusters, toxicity of dyes, and sensing of dyes.

Enhancing Conductivity of Silver Nanowire Networks through Surface Engineering Using Bidentate Rigid Ligands

Solution processable metallic nanomaterials present a convenient way to fabricate conductive structures, which are necessary in all electronic devices. However, they tend to require post-treatments to remove the bulky ligands around them to achieve high conductivity. In this work, we present a method to formulate a post-treatment free conductive silver nanowire ink by controlling the type of ligands around the silver nanowires. We found that bidentate ligands with a rigid molecular structure were effective in improving the conductivity of the silver nanowire networks as they could maximize the number of linkages between neighboring nanowires. In addition, DFT calculations also revealed that ligands with good LUMO to silver energy alignment were more effective. Because of these reasons, fumaric acid was found to be the most effective ligand and achieved a large reduction in sheet resistance of 70% or higher depending on the nanowire network density. The concepts elucidated from this study would also be applicable to other solution processable nanomaterials systems such as quantum dots for photovoltaics or LEDs which also require good charge transport being neighboring nanoparticles.

Nanotechnology Applications in Sepsis: Essential Knowledge for Clinicians

Sepsis is a life-threatening condition caused by a dysregulated host response to an invading pathogen such as multidrug-resistant bacteria. Despite recent advancements, sepsis is a leading cause of morbidity and mortality, resulting in a significant global impact and burden. This condition affects all age groups, with clinical outcomes mainly depending on a timely diagnosis and appropriate early therapeutic intervention. Because of the unique features of nanosized systems, there is a growing interest in developing and designing novel solutions. Nanoscale-engineered materials allow a targeted and controlled release of bioactive agents, resulting in improved efficacy with minimal side effects. Additionally, nanoparticle-based sensors provide a quicker and more reliable alternative to conventional diagnostic methods for identifying infection and organ dysfunction. Despite recent advancements, fundamental nanotechnology principles are often presented in technical formats that presuppose advanced chemistry, physics, and engineering knowledge. Consequently, clinicians may not grasp the underlying science, hindering interdisciplinary collaborations and successful translation from bench to bedside. In this review, we abridge some of the most recent and most promising nanotechnology-based solutions for sepsis diagnosis and management using an intelligible format to stimulate a seamless collaboration between engineers, scientists, and clinicians.

Nanoparticle Self-Assembly: From Design Principles to Complex Matter to Functional Materials

The creation of matter with varying degrees of complexities and desired functions is one of the ultimate targets of self-assembly. The ability to regulate the complex interactions between the individual components is essential in achieving this target. In this direction, the initial success of controlling the pathways and final thermodynamic states of a self-assembly process is promising. Despite the progress made in the field, there has been a growing interest in pushing the limits of self-assembly processes. The main inception of this interest is that the intended self-assembled state, with varying complexities, may not be "at equilibrium (or at global minimum)", rendering free energy minimization unsuitable to form the desired product. Thus, we believe that a thorough understanding of the design principles as well as the ability to predict the outcome of a self-assembly process is essential to form a collection of the next generation of complex matter. The present review highlights the potent role of finely tuned interparticle interactions in nanomaterials to achieve the preferred self-assembled structures with the desired properties. We believe that bringing the design and prediction to nanoparticle self-assembly processes will have a similar effect as retrosynthesis had on the logic of chemical synthesis. Along with the guiding principles, the review gives a summary of the different types of products created from nanoparticle assemblies and the functional properties emerging from them. Finally, we highlight the reasonable expectations from the field and the challenges lying ahead in the creation of complex and evolvable matter.

New Water-Soluble Magnetic Field-Induced Drug Delivery System Obtained Via Preferential Molecular Marriage over Narcissistic Self-Sorting

Nanomaterials that respond to stimuli are of considerable interest for drug delivery applications. Drug delivery has been a leading challenge when it comes to the externally triggered controlled release of hydrophobic drugs. The present paper describes a unique arrangement of polymers in a competitive environment derived from the dynamic self-sorting behavior of the hydrophobic chains of amphiphilic mPEG-PLLA and poly-l-lactic acid (PLLA)-coated iron oxide nanoparticles IONP@PLLA to achieve a core-shell structure in which the hydrophobic PLLA part acts as a dense core and poly(ethylene glycol) (PEG) as an uncrowded shell. By using irreversible covalent interactions created by hydrophobic polymer-functionalized IONPs, it was possible to selectively form socially self-sorted nanocarriers (SS-NCs) with a higher hydrophobic core than the hydrophilic shell over narcissistic self-sorted nanocarriers (NS-NCs), that is, homo-micelles of amphiphilic polymers. The higher hydrophobic core of SS-NCs is indeed helpful in achieving higher drug [doxorubicin (DOX)] loading and encapsulation efficiencies of around 17 and 90%, respectively, over 10.3 and 65.6% for NS-NCs. Furthermore, due to the presence of IONPs and the densely packed hydrophobic compartments, the controlled release of DOX was facilitated by direct magnetism and temperature stimulation when an alternating magnetic field (AMF) was applied. An appreciably higher rate of drug release (∼50%) than that without AMF (∼18%) was achieved under ambient conditions in 24 h. The present study, therefore, proposes a new drug delivery system that exceeds homo-micelles and adds an extra feature of manipulating drug release through magnetism and temperature, that is, hyperthermia.

The Effect of Capping Agents on Gold Nanostar Stability, Functionalization, and Colorimetric Biosensing Capability

Capping agents (organic ligands, polymers, and surfactants) are pivotal for stabilizing nanoparticles; however, they may influence the surface chemistry, as well as the physico-chemical and biological characteristics, of gold nanostar (AuNS)-based biosensors. In this study, we proved that various capping agents affected capped and bioconjugated AuNS stability, functionality, biocatalysis, and colorimetric readouts. Capped and bioconjugated AuNSs were applied as localized surface plasmon resonance (LSPR)-based H2O2 sensors using glucose oxidase (GOx) as a model enzyme. Furthermore, our analyses revealed that the choice of capping agent influenced the properties of the AuNSs, their stability, and their downstream applications. Our analyses provide new insights into factors governing the choice of capping agents for gold nanostars and their influences on downstream applications with conjugated enzymes in confined environments.

Metal-Polymer Heterojunction in Colloidal-Phase Plasmonic Catalysis

Plasmonic catalysis in the colloidal phase requires robust surface ligands that prevent particles from aggregation in adverse chemical environments and allow carrier flow from reagents to nanoparticles. This work describes the use of a water-soluble conjugated polymer comprising a thiophene moiety as a surface ligand for gold nanoparticles to create a hybrid system that, under the action of visible light, drives the conversion of the biorelevant NAD⁺ to its highly energetic reduced form NADH. A combination of advanced microscopy techniques and numerical simulations revealed that the robust metal-polymer heterojunction, rich in sulfonate functional groups, directs the interaction of electron-donor molecules with the plasmonic photocatalyst. The tight binding of polymer to the gold surface precludes the need for conventional transition-metal surface cocatalysts, which were previously shown to be essential for photocatalytic NAD⁺ reduction but are known to hinder the optical properties of plasmonic nanocrystals. Moreover, computational studies indicated that the coating polymer fosters a closer interaction between the sacrificial electron-donor triethanolamine and the nanoparticles, thus enhancing the reactivity.

Switchable Binding Energy of Ionic Compounds and Application in Customizable Ligand Exchange for Colloid Nanocrystals

The ability to engineer the surface ligands or adsorbed molecules on colloid nanocrystals (NCs) is important for various applications, as the physical and chemical properties are strongly affected by the surface chemistry. Here, we develop a facile and generalized ionic compound-mediated ligand-exchange strategy based on density functional theory calculations, in which the ionic compounds possess switchable bonding energy when they transfer between the ionized state and the non-ionized state, hence catalyzing the ligand-exchange process. By using an organic acid as the intermediate ligand, ligands such as oleylamine, butylamine, polyvinylpyrrolidone, and poly(vinyl alcohol) can be freely exchanged on the surface of Au NCs. Benefiting from this unique ligand-exchange strategy, the ligands with strong bonding energy can be replaced by weak ones, which is hard to realize in traditional ligand-exchange processes. The ionic compound-mediated ligand exchange is further utilized to improve the catalytic properties of Au NCs, facilitate the loading of nanoparticles on substrates, and tailor the growth of colloid NCs. These results indicate that the mechanism of switchable bonding energy can be significantly expanded to manipulate the surface property and functionalization of NCs that have applications in a wide range of chemical and biomedical fields.

Polarizability is a key parameter for molecular electronics

Identifying descriptors that govern charge transport in molecular electronics is of prime importance for the elaboration of devices. The effects of molecule characteristics, such as size, bulkiness or charge, have been widely reported. Herein, we show that the molecule polarizability can be a crucial parameter to consider. To this end, platinum nanoparticle self-assemblies (PtNP SAs) are synthesized in solution, including a series of polyoxometalates (POMs). The charge of the POM unit can be modified according to the nature of the central heteroatom while keeping its size constant. POM hybrids that display remote terminal thiol functions strongly anchor the PtNP surface to form robust SAs. IV curves, recorded by conductive AFM, show a decrease in Coulomb blockade as the dielectric constant of the POMs increases. In this system, charge transport across molecular junctions can be interpreted as variations in polarizability, which is directly related to the dielectric constant.

N-Functionalised Imidazoles as Stabilisers for Metal Nanoparticles in Catalysis and Anion Binding

Metal nanoparticles (NPs) have physicochemical properties which are distinct from both the bulk and molecular metal species, and provide opportunities in fields such as catalysis and sensing. NPs typically require protection of their surface to impede aggregation, but these coatings can also block access to the surface which would be required to take advantage of their unusual properties. Here, we show that alkyl imidazoles can stabilise Pd, Pt, Au, and Ag NPs, and delineate the limits of their synthesis. These ligands provide an intermediate level of surface protection, for which we demonstrate proof‐of‐principle in catalysis and anion binding.

Use of Photoacids and Photobases To Control Dynamic Self-Assembly of Gold Nanoparticles in Aqueous and Nonaqueous Solutions

Dynamic self-assembly of nanoparticles (NPs) for the formation of aggregates takes place out of thermodynamic equilibrium and is sustained by external energy supply. Herein, we present light energy driven dynamic self-assembly process of AuNPs, decorated with pH sensitive ligands. The process is being controlled by the use of photoacids and photobases that undergo excited state proton or hydroxide transfer, respectively, due to their large p K_a change between their ground and excited electronic states. The unique design is underlined by record subsecond conversion rates between the assembled and disassembled AuNPs states, and the ability to control the process using only light of different wavelengths. Measurements in both aqueous and nonaqueous solutions resulted in different self-assembly mechanisms, hence showing the wide versatility of photoacids and photobases for dynamic processes.

Role of Stabilizing Surfactants on Capacitance, Charge, and Ion Transport in Organic Nanoparticle-Based Electronic Devices

Deposition of functionalized nanoparticles onto solid surfaces has created a new revolution in electronic devices. Surface adsorbates such as ionic surfactants or additives are often used to stabilize such nanoparticle suspensions; however, little is presently known about the influence of such surfactants and additives on specific electronic and chemical functionality of nanoparticulate electronic devices. This work combines experimental measurements and theoretical models to probe the role of an ionic surfactant in the fundamental physical chemistry and electronic charge carrier behavior of photodiode devices prepared using multicomponent organic electronic nanoparticles. A large capacitance was detected, which could be subsequently manipulated using the external stimuli of light, temperature, and electric fields. It was demonstrated that analyzing this capacitance through the framework of classical semiconductor analysis produced substantially misleading information on the electronic trap density of the nanoparticles. Electrochemical impedance measurements demonstrated that it is actually the stabilizing surfactant that creates capacitance through two distinct mechanisms, each of which influenced charge carrier behavior differently. The first mechanism involved a dipole layer created at the contact interfaces by mobile ions, a mechanism that could be replicated by addition of ions to solution-cast devices and was shown to be the major origin of restricted electronic performance. The second mechanism consisted of immobile ionic shells around individual nanoparticles and was shown to have a minor impact on device performance as it could be removed upon addition of electronic charge in the photodiodes through either illumination or external bias. The results confirmed that the surfactant ions do not create a significantly increased level of charge carrier traps as has been previously suspected, but rather, preventing the diffusion of mobile ions through the nanoparticulate film and their accumulation at contacts is critical to optimize the performance.

Mono and dual hetero-structured M@poly-1,2 diaminoanthraquinone (M = Pt, Pd and Pt–Pd) catalysts for the electrooxidation of small organic fuels in alkaline medium

Oxidation of some small organic fuels such as methanol (MeOH), ethanol (EtOH) and ethylene glycol (EG) was carried out in an alkaline medium using palladium (Pd)–platinum (Pt) nanoparticles/poly1,2-diaminoanthraquinone/glassy carbon (p1,2-DAAQ/GC) catalyst electrodes. Pd and Pt were incorporated into the p1,2-DAAQ/GC electrode using the cyclic voltammetry (CV) technique. The obtained Pd/p1,2-DAAQ/GC, Pt/p1,2-DAAQ/GC, Pt/Pd/p1,2-DAAQ/GC and Pd/Pt/p1,2-DAAQ/GC nanocatalyst electrodes were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and CV methods. Real active surface area (A_real) achieved by carbon monoxide (CO) adsorption using differential electrochemical mass spectroscopy (DEMS) technique. The electrochemical activity was evaluated and normalized to A_real per metal loading mass. The electrocatalytic oxidation of the small organic fuels at the prepared nanocatalyst electrodes was studied in 1.0 M NaOH solutions by CV and chronoamperometric (CA) techniques. Pt/Pd/p1,2-DAAQ/GC nanocatalyst electrode exhibited enhanced catalytic activity, better durability and higher tolerance to carbon monoxide generated in the oxidation reaction when compared with the other three studied nanocatalysts. The present investigation suggests that the studied nanocatalysts can be successfully applied in direct oxidation of small organic fuels, especially MeOH.

Oxidation reaction of some small organic fuels such as methanol, ethanol and ethylene glycol was carried out in alkaline medium at palladium (Pd)–platinum (Pt) nanoparticles/poly1,2-diaminoanthraquinone/glassy carbon catalyst electrodes.

Stimuli-responsive self-assembly of nanoparticles

Ligand-protected nanoparticles can serve as attractive building blocks for constructing complex chemical systems.

A Novel Method for the Metallization of 3D Silicon Induced by Metastable Copper Nanoparticles

The development of efficient copper deposition processes in high-aspect-ratio silicon structures is still a key technological issue for the microelectronic industry. We describe here a new process for the deposition of copper thin films in three-dimensional (3D) structures induced by the decomposition of a copper amidinate precursor in solution under a moderate H₂ pressure. The reduction of a metal precursor under soft conditions (3 bar, 110 °C) affords the preparation of a high-purity, conformal metallic layer. We unveil a novel deposition mechanism driven by colloidal copper nanoparticles (NPs) in solution that behave as a reservoir of metastable metallic NPs that eventually condense as a solid film on all immersed surfaces. The film growth process is characterized by time-resolved analyses of the NPs in the colloidal state (nuclear magnetic resonance NMR and UV-vis spectra) and of the NPs and metallic layer on substrates (transmission electron microscopy TEM, and scanning electron microscopy SEM). Major deposition stages of this process are proposed and the conformal metallization of 3D silicon substrates is successfully achieved. This method is transposable to other metallic layers such as silver or nickel.