Colloidal Nanoparticles Research Articles

The concentration limit of stability for individual gold nanoparticles in aqueous colloid during water evaporation

The work established the presence of a concentration limit for the stability of aqueous colloids of gold nanoparticles obtained using laser ablation. It has been shown that in aqueous colloid of gold nanoparticles with a size of 15 nm, upon evaporation of water, the concentration of nanoparticles monotonically increases to a certain limit. When the limit is reached (the concentration of nanoparticles is about 1013 NPs/ml), a threshold process of decreasing the concentration of nanoparticles due to aggregation is observed. In this case, the ζ-potential of the entire colloid does not change. It has been shown that the aggregation process for some gold nanoparticles is irreversible; linear aggregates in the form of dimers, trimers and chain aggregates of greater length are observed in the colloid.

Three-dimensional nanoporous gold/gold nanoparticles substrate for surface-enhanced Raman scattering detection of illegal additives in food

Owing to their nanoscale size and porous structure, both colloidal gold nanoparticles (AuNPs) and nanoporous gold (NPG) have demonstrated good and stable surface-enhanced Raman scattering (SERS) activity, and are therefore widely used as SERS substrates for the rapid detection of various components in food, environmental, biological, and other samples. In this study, we fabricated a novel, sensitive, and reproducible composite three-dimensional (3D) substrate for rapid SERS-based detection of illegal additives in food products. AuNPs and NPGs were prepared by chemical reduction and chemical dealloying methods, with the particle size of AuNPs about 60 nm and the pore size of NPG in the range of 5–36 nm. The AuNPs were then assembled on the surface of NPG to form the composite substrate 3D-NPG/AuNPs, which was characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and other methods. Finally, the new SERS substrate combined with a portable Raman spectrometer was used to detect the illegal food additives 6-benzylaminopurine and melamine, with detection limits of 1 × 10−9 M and 5 × 10−7 M respectively. We further analyzed the relationship between the dealloying time-controlled morphology and the SERS properties of NPG, demonstrating that 3D-NPG/AuNPs as a novel SERS substrate have strong practical application potential in the rapid detection of food additives and other substances.

Water-Soluble Lead Sulfide Nanoparticles: Direct Synthesis and Ligand Exchange Routes.

Colloidal semiconductor nanoparticles (NPs) represent an emergent state of matter with unique properties, bridging bulk materials and molecular structures. Their distinct physical attributes, such as bandgap and photoluminescence, are intricately tied to their size and morphology. Ligand passivation plays a crucial role in shaping NPs and determining their physical properties. Ligand exchange (LE) offers a versatile approach to tailoring NP properties, often guided by Pearson's Hard-Soft Acid-Base theory. Lead sulfide (PbS), a semiconductor of considerable interest, exhibits size-dependent tunable bandgaps from the infrared to the visible range. Here, we present two methods for synthesizing water-soluble, polyvinylpyrrolidone (PVP)-coated PbS NPs. The first involves direct synthesis in an aqueous solution while utilizing PVP as the surfactant for the formation of nano-cubes with a crystal coherence length of ~30 nm, while the second involves LE from octadecylamine-coated PbS truncated nano-cubes to PVP-coated PbS NPs with a crystal coherence length of ~15 nm. Multiple characterization techniques, including X-ray diffraction, transmission electron microscopy, Fourier-transform infrared spectroscopy, and thermal gravimetric analysis, confirmed the results of the synthesis and allowed us to monitor the ligand exchange process. Our findings demonstrate efficient and environmentally friendly approaches for synthesizing PVP-coated PbS NPs.

Thiol-polyethylene glycol-folic acid (HS-PEG-FA) induced aggregation of Au@Ag nanoparticles: A SERS and extinction UV–Vis spectroscopy combined study

Plasmonic colloidal nanoparticles (NPs) functionalised with polymers are widely employed in diverse applications, offering advantages demonstrated over non-functionalised NPs such as enhanced colloidal stability or increased biocompatibility. However, functionalisation with polymers does not always increase the stability of the colloidal system. This work explores the intricate relationship between the functionalisation of plasmonic core@shell Au@Ag nanoparticles (NPs) with thiol-polyethylene glycol-folic acid (HS-PEG-FA) polymer chains and the resulting stability and spectral characteristics of Surface-Enhanced Raman Scattering (SERS) nanotags based on these NPs. We demonstrate that varying levels of HS-PEG-FA grafting influence nanotag stability, with a low level of grafting causing aggregation and subsequently affecting the spectral signature of Raman-reporter molecules attached to the surface of the NP. Electrostatic destabilisation is identified as the primary mechanism driving aggregation, impacting the SERS spectrum of Malachite Green isothiocyanate (MGITC) whose spectral shape is different between the aggregated and non-aggregated NPs. The findings provide valuable insights into NPs stability under different conditions, offering essential considerations for the design and optimisation of SERS nanotags in bio-analytical applications, particularly those involving data processing based on spectral shape, such as in multiplex approaches where experimental spectra are decomposed with several reference components.

Colloidal Titanium Nitride Nanoparticles by Laser Ablation in Solvents for Plasmonic Applications.

Titanium nitride (TiN) is a candidate material for several plasmonic applications, and pulsed laser ablation in liquids (PLAL) represents a rapid, scalable, and environmentally friendly approach for the large-scale production of nanomaterials with customized properties. In this work, the nanosecond PLAL process is developed, and we provide a concise understanding of the process parameters, such as the solvent and the laser fluence and pulse wavelength, to the size and structure of the produced TiN nanoparticles (NPs). TiN films of a 0.6 μm thickness developed by direct-current (DC) magnetron sputtering were used as the ablation targets. All laser process parameters lead to the fabrication of spherical NPs, while the laser pulse fluence was used to control the NPs' size. High laser pulse fluence values result in larger TiN NPs (diameter around 42 nm for 5 mJ and 25 nm for 1 mJ), as measured from scanning electron microscopy (SEM). On the other hand, the wavelength of the laser pulse does not affect the mean size of the TiN NPs (24, 26, and 25 nm for 355, 532, and 1064 nm wavelengths, respectively). However, the wavelength plays a vital role in the quality of the produced TiN NPs. Shorter wavelengths result in NPs with fewer defects, as indicated by Raman spectra and XPS analysis. The solvent type also significantly affects the size of the NPs. In aqueous solutions, strong oxidation of the NPs is evident, while organic solvents such as acetone, carbides, and oxides cover the TiN NPs.

Insights into the Engineered Gold Nanoparticle-Based Remedy for Supplementation Therapy of Ovarian Carcinoma.

Chronic diseases, notably cancer, pose a significant global threat to human life. Oncologists and medical professionals addressing malignancies confront challenges such as toxicity and multidrug resistance. To tackle these issues, the focus has shifted toward the employment of multifunctional colloidal gold nanoparticles. This study aims to design pH-sensitive doxorubicin-loaded gold nanoparticles using polyvinylpyrrolidone. The cytotoxic efficacy of the designed gold nanoarchitecture and its doxorubicin counterpart was assessed in an in vitro model using the HeLa cell. In comparison to the free drug, experimental evaluations showed that the gold nanoarchitecture outperformed significantly lower unspecific drug leaching and efficiently delivered the payload in a controlled manner, boosting the chemotherapy outcomes. This work opens a streamlined approach for engineering gold nanoarchitecture that could be further expanded to incorporate other therapeutics and/or functional moieties that require optimized controlled delivery, offering a one-size-fits-all solution and paving the revolutionary adjustments to healthcare procedures.

The ion-activated attractive patchy particle model and its application to the liquid-vapor phase transitions.

Patchy particles are an intriguing subject of study and indeed a model system in the field of soft matter physics. In recent years, patchy particle models have been applied to describe a wide variety of systems, including colloidal crystals, macromolecular interactions, liquid crystals, and nanoparticle assemblies. Given the importance of the topic, rationalizing and capturing the basic features of these models is crucial to their correct application in specific systems. In this study, we extend the ion-activated attractive patchy particles model previously employed to elucidate the phase behavior of protein solutions in the presence of trivalent salts. Our extension incorporates the effect of repulsion between unoccupied and occupied binding sites, depicted as patches. Furthermore, we examine the influence of model parameters on the liquid-vapor coexistence region within the phase diagram, employing numerical methods. A deeper understanding of this model will facilitate a better comprehension of the effects observed in experiments.

Engineering FeOOH/Fe2O3@Carbon Interfaces With Biomass-Derived Carbon Nanodot/Iron Colloids for Efficient Redox-Modulated Dopamine Voltammetric Detection.

The Fe2+/Fe3+ redox couple is effective for voltammetric detection of trace dopamine (DA). However, achieving adequate concentrations with high electroactive surface area (ECSA), DA affinity, and fast interfacial charge transfer is challenging. Consequently, most reported Fe-based sensors have a high nanomolar range detection limit (LOD). Herein, we address these limitations by manipulating the phase and morphology of FeOOH/Fe2O3 heterojunctions anchored on sp2-carbon. FeOOH/Fe2O3 is synthesized by variable temperature aging of unique Fe5H9O15/Fe2O3@sp2-carbon colloidal nanoparticles, which form via chelation between biomass-derived carbon nanodots (CNDs) and Fe2+ ions. At 27 °C and 120 °C, Fe5H9O15/Fe2O3@sp2-carbon transforms into β-FeOOH/Fe2O3 nanoparticles and α-FeOOH/Fe2O3 nanosheet, respectively. The β-FeOOH/Fe2O3 interface exhibits higher eg orbital electron occupancy than α-FeOOH/Fe2O3, thereby facilitating oxygen adsorption and the generation of Fe2+/Fe3+ sites near the polarization potential of DA. This facilitates interfacial electron transfer between Fe3+ and DA. Moreover, its nanoparticle morphology enhances ECSA and DA adsorption compared to α-FeOOH/Fe2O3 nanosheets. With a LOD of ~3.11 nM, β-FeOOH/Fe2O3 surpasses the lower threshold in humans (~10 nM) and matches noble-metal sensors. Furthermore, it exhibits selective detection of DA over 10 biochemicals in urine. Therefore, the β-FeOOH/Fe2O3@sp2-C platform holds promise as a low-cost, easy-to-synthesize, and practical voltammetric DA monitor.

A Rapid and Interference-Resistant Formaldehyde Detection Method Based on Surface-Enhanced Raman Spectroscopy with a Reaction-Induced Self-Amplification Strategy

Formaldehyde is widely utilized across various industries such as food, textiles, and leather, yet its presence raises significant health concerns due to its irritation and carcinogenicity. Numerous methods have been developed to probe it in solution and gas states. Among them, absorption spectroscopy-based methods commonly employed. However, these methods require complex preprocessing for colored solutions to avoid interference. In response to this challenge, a novel interference-resistant detection kit leveraging surface-enhanced Raman spectroscopy (SERS) coupled with reaction-induced self-amplification for rapid and direct detection of formaldehyde was developed. The kit needed only ten minutes and achieved a limit of detection lower than 10−4 μg/mL with a handheld Raman spectrometer. Thanks to the kit’s reaction with formaldehyde, colloidal nanoparticles were linked to form “hot-spots” to further enhance the SERS signals. The signal demonstrated outstanding resistance to interference, including different dyes, ensuring a practical tool for direct detection of formaldehyde in complex solutions.

Structural Color Enhancement through Synchronizing Natural Convection and Marangoni Flow in Pendant Drops.

Structural color, renowned for its enduring vibrancy, has been extensively developed and applied in the fields of display and anticounterfeiting. However, its limitations in brightness and saturation hinder further application in these areas. Herein, we propose a pendant evaporation self-assembly method to address these challenges simultaneously. By leveraging natural convection and Marangoni flow synchronization, the self-assembly process enhances the dynamics and duration of colloidal nanoparticles, thereby enhancing the orderliness of colloidal photonic crystals. On average, this technique boosts the brightness of structural color by 20% and its saturation by 35%. Moreover, pendant evaporation self-assembly is simple and convenient to operate, making it suitable for industrial production. We anticipate that its adoption will remarkably advance the industrialization of structural color, facilitating its engineering applications across various fields, such as display technology and anticounterfeiting identification.

Facile Synthesis of Novel Short-Chain Ligand-Capped Colloidal Metal Oxide Nanoparticles for Printed Flexible Devices.

Colloidal metal oxide nanoparticles are key materials for achieving cost-effective and large-scale production of flexible devices, as they enable the formation of functional oxide thin films at low temperatures (<400 °C) through printing techniques such as inkjet printing, gravure coating, and microcontact printing. The conventional solvothermal synthesis of colloidal metal oxide nanoparticles through the thermal decomposition of precursors results in particles with bulky, long-chain ligands on their surfaces, which hinder the formation of dense oxide films when depositing the colloidal metal oxide nanoparticles. Herein, we have developed a simple and versatile method for synthesizing colloidal metal oxide nanoparticles using base-induced hydrolysis and the condensation of metal acetates as precursors. Various binary and ternary colloidal metal oxide nanoparticles (CuO, Mn3O4, Co3O4, CeO2, In2O3, Co1.8Mn1.2O4) were synthesized using short-chain acetate ligands on their surfaces. The thin acetate ligand-containing colloidal Co1.8Mn1.2O4 nanoparticle film exhibited lower resistivity than the same with long-chain oleate ligands. The films coated onto a polyimide substrate formed a flexible negative temperature coefficient thermistor that exhibited the temperature dependence of resistance comparable to bulk materials with a bending durability of up to 5 mm radius. These findings highlight the effectiveness of utilizing colloidal metal oxide nanoparticles with short-chain ligands in flexible devices.

Impact of colloidal silver nanoparticles (AgNPs) added for their antimicrobial efficacy on the compressive strength of poly(methyl methacrylate)-based acrylic denture base resin subjected to two different curing cycles: An in vitro study

Abstract Introduction: Colloidal silver nanoparticles (AgNPs) have been incorporated into acrylic resins to induce antimicrobial properties. However, as additives, they can influence the mechanical properties of the final product. The aim of the present study was to evaluate compressive strength of acrylic denture base resin incorporated with different concentrations of AgNPs subjected to two different curing cycles. Materials and Methods: Lucitone 199 acrylic denture base resin was used in the present in vitro study design because of its high-impact strength, while AgNPs were incorporated at 0.5% and 5% concentration by polymer mass. Specimens devoid of AgNPs were used as controls. The specimens were fabricated according to the American Dental Association specification No. 12 for denture base resin: Second revision, BS specification 2482 and tested for compressive strength using universal testing machine. Statistical analysis was done using Statistical Package for Social Sciences (SPSS) version 19 (SPSS Inc., Chicago, IL, USA). Descriptive statistics was used to compare two different curing cycles; while one-way analysis of variance and Kruskal–Wallis H-test were used for statistical analysis. P &lt;0.05 was considered statistically significant. Results: Colloidal silver nanoparticles (AgNPs) incorporation at 0.5% concentration increased the mean compressive strength in both the short and long curing cycles by 5.3% and 8.3% respectively when compared with the control group. Conclusions: The findings of the present study suggested that the mean compressive strength of acrylic denture base resin modified with 0.5% concentration of AgNPs was above the control group, both in the short and long curing cycles. However, at 5% concentration of AgNPs, decrease in compressive strength compared to the control group was observed, both in short and long curing cycles, giving it a questionable prognosis, while the results were found to be statistically significant. The following core competencies are addressed in this article: Practice-based learning and improvement, Patient care and procedural skills, Systems-based practice, Medical knowledge.

Plasmonic magnesium arrays with nanosphere lithography

Magnesium is a rising alternative plasmonic metal that is potentially cheaper, more biocompatible, and less lossy in the ultraviolet-blue region of the visible spectrum than the commonly used gold and silver. Recent studies of colloidal magnesium nanoparticles demonstrated the plasmonic resonances of a variety of faceted shapes. However, applications such as refractive index sensing benefit from well-defined arrays, which have been developed for all other plasmonic metals. Here, we implement nanosphere lithography to fabricate metallic magnesium arrays that display attractive plasmonic properties. The deposition process was found to be highly vulnerable to oxidation, recrystallization, kinetic energy of the metal vapor, and substrate properties. The resulting structures obtained with 350, 500, and 750 nm hexagonally packed nanosphere masks exhibit the hallmark light–matter interactions of plasmonic metals, including strong extinction and resonance energy dependence on feature size, further securing Mg’s place as an alternative plasmonic metal.

The mechanism of the influence of ultrasound on the nucleation and growth of A2B6 nanoparticles in a colloidal solution

The mechanism of the influence of ultrasound on the nucleation and growth of A2B6 nanoparticles in a colloidal solution was investigated. The proposed theory is based on an increase in the temperature of the colloidal solution and the diffusion coefficient of the monomer under the influence of ultrasonic cavitation. It was established that ultrasound leads to a decrease in the critical radius of colloidal nanoparticles. And when the radius of nanoparticles exceeds this critical value, their growth is observed. The dependence of the growth rate of CdSe nanoparticles on their radius at different temperatures and intensities of ultrasound was researched. It is shown that at the beginning of nanocrystal growth, an increase in intensity of ultrasound leads to an increase in the growth rate, followed by a sharp decrease. This makes it possible to synthesize colloidal quantum dots that are more uniform in size with the help of ultrasonic treatment.

Spin echo small-angle neutron scattering using superconducting magnetic Wollaston prisms.

We show the implementation of superconducting magnetic Wollaston prisms for spin echo small-angle neutron scattering. Two calibration methods for the spin echo length are presented: one utilizing spin echo modulated small-angle neutron scattering and the other based on the neutron refraction by quartz wedge crystals. Our experimental results with polystyrene nano-particle colloids showcase the system's efficacy in measuring both dilute and concentrated colloidal systems. Additionally, investigations into the pore diameter and pitch of a nano-porous alumina membrane demonstrate its capability in analyzing nano-porous materials. Furthermore, we discuss potential optimizations to further extend the accessible spin echo length.

Synthetic Roadmap to a Large Library of Colloidal High-Entropy Rare Earth Oxyhalide Nanoparticles Containing up to Thirteen Metals.

Nanoparticles of high-entropy materials that incorporate five or more elements randomized on a crystalline lattice often exhibit synergistic properties that can be influenced by both the identity and number of elements combined. These considerations are especially important for structurally and compositionally complex materials such as multimetal multianion compounds, where cation and anion mixing can influence properties in competitive and contradictory ways. Here, we demonstrate the synthesis of a large library of colloidal high-entropy rare earth oxyhalide (REOX) nanoparticles. We begin with the synthesis of (LaCePrNdSmEuGdDyHoErYbScY)OCl, which homogeneously incorporates 13 distinct rare earth elements. Through time point studies, we find that (LaNdSmGdDy)OCl, a 5-metal analogue, forms through in situ generation of compositionally segregated core@shell@shell intermediates that convert to homogeneously mixed products through apparent core-shell interdiffusion. Assuming that all possible combinations of 5 through 13 rare earth metals are synthetically accessible, we propose the existence of a 7099-member REOCl nanoparticle library, of which we synthesize and characterize 40 distinct members. We experimentally validate the incorporation of a large number of rare earth elements using energy dispersive X-ray spectra, despite closely spaced and overlapping X-ray energy lines, using several fingerprint matching strategies to uniquely correlate experimental and simulated spectra. We confirm homogeneous mixing by analyzing elemental distributions in high-entropy nanoparticles versus physical mixtures of their constituent compounds. Finally, we characterize the band gaps of the 5- and 13-metal REOCl nanoparticles and find a significantly narrowed band gap, relative to the constituent REOCl phases, in (LaCePrNdSmEuGdDyHoErYbScY)OCl but not in (LaNdSmGdDy)OCl.

One-step fabrication of a self-driven point-of-care chip by femtosecond laser direct writing and its application in cancer cell H2O2 detection via semiconductor-based SERS

Self-driven microfluidic systems have attracted significant attention and demonstrated great potential in the field of point-of-care (POC) testing due to their device simplicity, low power consumption, increased portability, and reduced sample consumption. To develop POC detection chips with diverse characteristics that meet different requirements, there is a strong demand for feasible strategies that enable easy operation and reduce processing time. Here, a one-step processing approach using femtosecond laser direct writing technology was proposed to fabricate a capillary-actuated POC microfluidic chip. The driving force of the chip is highly dependent on its surface wettability, which can be easily adjusted by changing the laser processing parameters. This POC microfluidic chip allowed for the detection of intracellular H2O2 through a catalytic reaction system that incorporated 5-aminosalicylic acid -sensitized colloidal TiO2 nanoparticles and horse radish peroxidase, with integrating semiconductor-based surface-enhanced Raman scattering (SERS) quantitative technique. The concentration of H2O2 was determined by the SERS signal of the catalytic products in the microfluidic chip, resulting in rapid detection with minimal sample consumption. Our method provides a simple, feasible, and alternative strategy for POC testing of H2O2, with a linear range of 10−2∼10−6 M and a limit of detection of 0.55 μM. This approach was successfully applied to rapid detection of intracellular H2O2 in MCF-7 breast cancer cells with high sensitivity and minimal sample consumption. Additionally, this study not only demonstrates the exceptional advantages of femtosecond laser processing technology in fabricating diverse microfluidic chips for various applications, but also presents an efficient POC testing strategy for detecting cell signaling molecules.

Direct visualization of ligands on gold nanoparticles in a liquid environment.

The interactions between gold nanoparticles, their surface ligands and the solvent critically influence the properties of these nanoparticles. Although spectroscopic and scattering techniques have been used to investigate their ensemble structure, a comprehensive understanding of these processes at the nanoscale remains challenging. Electron microscopy makes it possible to characterize the local structure and composition but is limited by insufficient contrast, electron beam sensitivity and the requirement for ultrahigh-vacuum conditions, which prevent the investigation of dynamic aspects. Here we show that, by exploiting high-quality graphene liquid cells, we can overcome these limitations and investigate the structure of the ligand shell around gold nanoparticles and at the ligand-gold interface in a liquid environment. Using this graphene liquid cell, we visualize the anisotropy, composition and dynamics of ligand distribution on gold nanorod surfaces. Our results indicate a micellar model for surfactant organization. This work provides a reliable and direct visualization of ligand distribution around colloidal nanoparticles.

Multiple Fano Resonances Enabled by the Interference between an Out‐of‐Plane Plasmon Mode and Fabry–Pérot Cavity Modes

AbstractMultiple Fano resonances (mFRs) are arising as a promising optical platform to achieve precise sensing and detection. However, experimentally achieving mFRs by simple structures has remained challenging, which impedes the widespread applications of mFRs. Herein a simple structure composed of a single colloidal metal nanoparticle and a transition metal dichalcogenide flake to simultaneously achieve up to 8 FRs in experiments is demonstrated. Combining theoretical and experimental techniques, that an out‐of‐plane plasmon mode of the metal nanoparticle interferes with the Fabry–Pérot cavity modes from the WS2 flake to form mFRs in the visible region is proved. The simplicity and generality of the method further allow us to systematically study the tunability of the mFRs, in terms of the peak/dip positions and the number of FRs, by changing the structural parameters, which include the thickness of the WS2 flake, size and shape of the plasmonic nanoparticle. In addition, the quality of the mFRs is proved to be adjustable by tuning the reflectivity of the substrate in the system. The highest quality factor and spectral contrast of the achieved resonances are up to ≈180 and ≈0.95, respectively. The simple structure and high‐quality optical modes will prosper applications in precise sensing and light modulation.

Interactions between prokaryotic polysaccharides and colloidal magnetic nanoparticles for bacteria removal: A strategy for circumventing antibiotic resistance

Highly stable, colloidal iron oxide nanoparticles with an oxyhydroxide-like surface were used as bacteria-capturing nano-baits. Peptidoglycan isolated from Listeria spp was used as bacteria polysaccharide model, and the nanoparticle binding was characterized showing a Langmuir isotherm constant, KL, equal to 50 ± 3 mL mg−1. The chemical affinity was further supported by dynamic light scattering, transmission electron microscopy, and infrared and UV–Vis data, pointing at the occurrence of extended, coordinative multiple point bindings. The interaction with Gram (+) (Listeria spp) and Gram (−) (Aeromonas veronii) bacteria was shown to be effective and devoid of any toxic effect. Moreover, a real sample, containing a population of several oligotrophic bacteria strains, was incubated with 1 g L−1 of nanoparticle suspension, in the absence of agitation, showing a 100 % capture efficiency, according to plate count. A nanoparticle regeneration method was developed, despite the known irreversibility of such bacterial-nanosurface binding, restoring the bacteria capture capability. This nanomaterial represents a competitive option to eliminate microbiological contamination in water as an alternative strategy to antibiotics, aimed at reducing microbial resistance dissemination. Finally, beyond their excellent features in terms of colloidal stability, binding performances, and biocompatibility this nanoparticle synthesis is cost effective, scalable, and environmentally sustainable.