“Precipitation on Nanoparticles”: Attractive Intermolecular Interactions Stabilize Specific Ligand Ratios on the Surfaces of Nanoparticles

Short Zwitterionic Sulfobetaine-Modified Silica Nanoparticles: Is Neutrality Possible?

Zwitterionic coatings are an efficient strategy for preventing biomolecule adsorption and enhancing nanoparticle stability in solution. The properties of zwitterions and other antifouling materials, including suppression of nonspecific adsorption and improved colloidal stability of nanoparticles, are believed to derive from their electroneutral and highly hydrophilic nature. Among different zwitterions, short sulfobetaines have been demonstrated to be effective in preventing protein adsorption onto several nanoparticles and providing enhanced colloidal stability. Although zwitterionic sulfobetaine silane (ZS) is electrically neutral, the negatively charged zwitterionic sulfobetaine-functionalized silica nanoparticles (ZS@SiO2NPs) exhibit a similar ζ-potential to nonfunctionalized silica nanoparticles (SiO2NPs). In this work, we present a thorough comprehension of the surface properties of ZS@SiO2NPs, which encompasses the development of meticulous functionalization procedures, detailed characterization approaches, and cutting-edge modeling to address the questions that persist regarding the surface features of ZS@SiO2NPs. The negative charge of ZS@SiO2NPs is due to the stabilization of siloxide from residual surface silanols by the quaternary amine in the sulfobetaine structure. Consequently, we infer that zero-charge ZS@SiO2NPs are unlikely to be obtained since this stabilization increases the dissociation degree of surface silanols, increasing the overall structure negative charge. Additionally, colloidal stability was evaluated in different pH and ionic strength conditions, and it was found that ZS@SiO2NPs are more stable at higher ionic strengths. This suggests that the interaction between ZS and salt ions prevents the aggregation of ZS@SiO2NPs. Together, these results shed light on the nature of the ZS@SiO2NP negative charge and possible sources for the remarkable colloidal stability of zwitterionic nanoparticles in complex media.

Solution-Processed Inorganic Thermoelectric Materials: Opportunities and Challenges

Thermoelectric technology requires synthesizing complex materials where not only the crystal structure but also other structural features such as defects, grain size and orientation, and interfaces must be controlled. To date, conventional solid-state techniques are unable to provide this level of control. Herein, we present a synthetic approach in which dense inorganic thermoelectric materials are produced by the consolidation of well-defined nanoparticle powders. The idea is that controlling the characteristics of the powder allows the chemical transformations that take place during consolidation to be guided, ultimately yielding inorganic solids with targeted features. Different from conventional methods, syntheses in solution can produce particles with unprecedented control over their size, shape, crystal structure, composition, and surface chemistry. However, to date, most works have focused only on the low-cost benefits of this strategy. In this perspective, we first cover the opportunities that solution processing of the powder offers, emphasizing the potential structural features that can be controlled by precisely engineering the inorganic core of the particle, the surface, and the organization of the particles before consolidation. We then discuss the challenges of this synthetic approach and more practical matters related to solution processing. Finally, we suggest some good practices for adequate knowledge transfer and improving reproducibility among different laboratories.

Chirality Inversion in Self-Assembled Nanocomposites Directed by Curvature-Mediated Interactions

Nanoscale curvature-dependent interactions are of paramount importance in biological systems. Here, we report that nanoscale curvature plays an important role in regulating the chirality of self-assembled nanocomposites from chiral organic molecules and achiral nanoparticles. Specifically, we show that the supramolecular chirality of the nanocomposites markedly depends on the nanoparticle curvature, where small-sized nanoparticles of high curvature and large-sized nanoparticles of low curvature lead to nanocomposites with opposite chirality. Quantitative kinetic experiments and molecular dynamics simulations reveal that nanoparticle curvature plays a key role in promoting the pre-nucleation oligomerization of chiral molecules, which consequently regulates the supramolecular chirality of the nanocomposites. We anticipate that this study will aid in rational design of an artificial cooperative system giving rise to emergent assembling phenomena that can be surprisingly rich and often cannot be understood by studying the conventional noncooperative systems.

Viscoelasticity Investigation of Semiconductor NP (CdS and PbS) Controlled Biomimetic Nanoparticle Hydrogels

The viscoelastic properties of colloidal nanoparticles (NPs) make opportunities to construct novel compounds in many different fields. The interparticle forces of inorganic particles on colloidal NPs are important for forming a mechanically stable particulate network especially the NP-based soft matter in the self-assembly process. Here, by capping with the same surface ligand L-glutathione (GSH), two semiconductor NP (CdS and PbS) controlled biomimetic nanoparticle hydrogels were obtained, namely, CdS@GSH and PbS@GSH. The dependence of viscoelasticity of colloidal suspensions on NP sizes, concentrations, and pH value has been investigated. The results show that viscoelastic properties of CdS@GSH are stronger than those of PbS@GSH because of stronger surface bonding ability of inorganic particles and GSH. The hydrogels formed by the smaller NPs demonstrate the higher stiffness due to the drastic change of GSH configurations. Unlike the CdS@GSH hydrogel system, the changes of NP concentrations and pH value had great influence on the PbS@GSH hydrogel system. The higher the proportion of water in the small particle size PbS@GSH hydrogel system, the greater the mechanical properties. The stronger the alkalinity in the large particle size PbS@GSH hydrogel system, the greater the hardness and storage modulus. Solution˗state nuclear magnetic resonance (NMR) indicated that the ligand GSH forms surface layers with different thickness varying from different coordination modes which are induced by different semiconductor NPs. Moreover, increasing the pH value of the PbS@GSH hydrogel system will dissociate the surface GSH molecules to form Pb²⁺ and GSH complexes which could enhance the viscoelastic properties.

An Organometallic Strategy for Assembling Atomically Precise Hybrid Nanomaterials

For decades, chemists have strived to mimic the intricate design and diverse functions of naturally occurring systems through the bioinspired synthesis of programmable inorganic nanomaterials. The development of thiol-capped gold nanoparticles (AuNPs) has driven advancement in this area; however, although versatile and readily accessible, hybrid AuNPs are rarely atomically precise, which limits control over their surface topology and therefore the study of complex structure-function relationships. Here, we present a bottom-up approach to the systematic assembly of atomically precise hybrid nanoclusters employing a strategy that mimics the synthetic ease with which thiol-capped AuNPs are normally constructed, while producing well-defined covalent nanoscale assemblies with diverse surface topologies. For the first time, using a structurally characterized cluster-based organometallic building block, we demonstrate the systematic synthesis of nanoclusters with multivalent binding capabilities to complex protein targets.

Simultaneous and Reversible Triggering of the Phase Transfer and Luminescence Change of Amidine-Modified Carbon Dots by CO2

The ability to reversibly manipulate the surface nature of luminescent nanoparticles upon external stimulation enables the development of advanced optical probes for biological sensing and data encoding. Herein, we report the synthesis of a new class of smart carbon dots (CDs) via surface modification of amine-enriched CDs with CO₂-responsive groups of amidine. We present that alternative CO₂ and N₂ bubbling can not only lead to a reversible phase transfer of the CDs between an organic phase and an aqueous phase but also give rise to a corresponding reversible luminescence change between blue and cyan-green. We attribute these observations to changes in both the surface chemistry and the emission states of the CDs triggered by the alternative CO₂/N₂ introduction. We also find a similar luminescence change of the CDs upon alternative exposure to a humid vapor of CO₂ and a mixture of NH₃ and N₂ at room temperature, allowing them to be used as a new class of optical materials for optical encoding.

Label-free gold nanorods sensor array for colorimetric detection and discrimination of biothiols in human urine samples

Biothiols play important roles in regulating redox balance in biological systems, but their discrimination is challengeable. In this work, a colorimetric nanosensing array for biothiols was established, which was composed of gold nanorods (AuNRs) and metal ions (Hg²⁺, Pb²⁺, Cu²⁺, Ag⁺). By employing label-free AuNRs as the colorimetric probe, and the color and spectral changes of AuNRs as the output signal, principal component analysis (PCA) was applied to processing the signal and generating a clustering map. Due to the different binding affinity between biothiols and metal ions, AuNRs exhibited a unique pattern to form a fingerprint-like colorimetric array, which was able to discriminate five biothiols by the naked eyes. This strategy combines PCA and sensor array to achieve rapid and accurate discrimination and detection of biothiols. In addition, the method shows the great potential in analysis of biothiols in human urine samples.

Simple and rapid detection of bisphenol A using a gold nanoparticle-based colorimetric aptasensor

A colorimetric aptasensor was developed for the simple and rapid detection of bisphenol A (BPA). The aptasensor was designed to consist of colloidal gold nanoparticles (AuNPs) and a BPA-specific 24-bp aptamer. The AuNP-aptamer conjugates underwent an electrolyte-induced aggregation in the presence of sub-ppb levels of BPA. The surface plasmon resonance shift of AuNPs facilitated a color change from red to blue upon aggregation, which was visually observed by the naked eye. The corresponding visual limit of detection of BPA was as low as 1 pg/mL (0.004 nM). The aptasensor also achieved a selective detection of BPA over a variety of BPA analogs. The applicability of the aptasensor was verified via a successful detection of BPA in a single grain of rice. This result indicates that the colorimetric aptasensor can be used in a screening procedure for food and environmental monitoring, with reliable performance to sub-ppb levels of BPA detection.

A Versatile AuNP Synthetic Platform for Decoupled Control of Size and Surface Composition

While a plethora of protocols exist for the synthesis of sub-10-nm gold nanoparticles (AuNPs), independent control over the size and surface composition remains restricted. This poses a particular challenge for systematic studies of AuNP structure-function relationships and the optimization of crucial design parameters. To this end, we report on a modular two-step approach based on the synthesis of AuNPs in oleylamine (OAm) followed by subsequent functionalization with thiol ligands and mixtures thereof. The synthesis of OAm-capped AuNPs enables fine-tuning of the core size in the range of 2-7 nm by varying the reaction temperature. The subsequent thiol-for-OAm ligand exchange allows a reliable generation of thiol-capped AuNPs with target surface functionality. The compatibility of this approach with a vast library of thiol ligands provides detailed control of the mixed ligand composition and solubility in a wide range of solvents ranging from water to hexane. This decoupled control over the AuNP core and ligand shell provides a powerful toolbox for the methodical screening of optimal design parameters and facile preparation of AuNPs with target properties.