Seed-mediated Synthesis Research Articles

Ocimum basilicum seed-mediated green synthesis of silver nanoparticles: characterization and evaluation of biological properties

Ocimum basilicum seed-mediated green synthesis of silver nanoparticles: characterization and evaluation of biological properties

Seed-Mediated Growth and Advanced Characterization of Chiral Gold Nanorods.

The controlled growth of gold nanostructures with complex shapes and reduced symmetry, exemplified by chiral gold nanorods and nanoparticles, is one of the most dynamic fields of nanochemistry. A timely summary of underlying concepts, including growth mechanisms and redefined chirality measures, would further promote this research area. In this perspective, we aim to establish qualitative connections between the chiral shapes and growth conditions, specifically for the seed-mediated synthesis of chiral gold nanorods as a convenient case of chiral morphogenesis. The crystallographic and morphological features of achiral nanorods used as seeds, the experimental conditions during chiral growth, and the symmetry of the chiral inducers, can all be exploited to obtain nanorods with intricate chiral shapes. Chirality characterization (such as electron tomography techniques) and quantification (including chirality measures) emerge as critical aspects to comprehensively explore and understand such structures, enabling optimization of their geometric and optical features. We conclude by discussing relevant challenges to be addressed toward a better controlled synthesis of chiral plasmonic nanostructures.

Vachelia nilotica seed-mediated green synthesis of sulfur nanoparticles (SNPs) and evaluation of anticancer & antifungal activities

Sulfur nanoparticles (SNPs) have been successfully synthesized by applying Vachelia nilotica seed extract as a bioactive aqueous material by a disproportionation reaction of sodium thiosulfate pentahydrate (Na2S2O3 .5H2O) with a 10% hydrochloric acid (HCl) at room temperature. The synthesized SNPs were characterized by UV–Visible, Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy-Dispersive X-ray Spectroscopy (EDS), and X-ray Diffraction (XRD) techniques. The usual size of SNPs was determined by an XRD study and calculated with the Debye–Scherrer formula. The SNPs are crystalline with a calculated average size of 45 nm. The SEM and TEM analyses revealed spherical shape and size around 55 nm of SNPs. The synthesized SNPs were screened for their antifungal activity against M. furfur species and for anticancer activities against (MCF-7, HepG2) cell lines. The obtained results suggested towards moderate to good antifungal and excellent anticancer activities.

Enhanced OSL emission from α- Al2O3 produced in the presence of halloysite nanocrystals

Aluminum oxide (Al2O3) compounds are extensively used in ionizing radiation dosimetry due to their high sensitivity when doped with carbon. However, their production is difficult and expensive, leading to much research on alternative ways to increase its sensitivity. This paper proposes a seed-mediated synthesis of α-Al2O3 by the combustion method with halloysite nanocrystals as seeds, which also have the ability to scavenge heavy metal ions. The dosimetric features were studied by radioluminescence (RL), thermoluminescence (TL), and optically stimulated luminescence (OSL). Scanning electron microscopy images and X-ray diffraction patterns pointed to the halloysite nanotubes (HNT) acting as heterogeneous nucleation seeds, and as adsorber centers for the chromium ions (Cr3+), as evidenced by the decreased crystallite size and Cr3+ RL emission. Decreased TL intensity upon increasing HNT content in addition to the RL data suggested that the Cr3+ ions strongly participate in the TL emission process as a luminescent center. Remarkable 6-fold enhanced OSL area intensity and 69-fold OSL initial intensity enhancement were registered from the samples seed-mediated by HNT, revealing that, by scavenging Cr3+, the HNT eliminated a luminescent center that competes with the OSL emission. Therefore, HNTs are promising nanomaterials to enhance the sensitivity of Al2O3 dosimeters with potential application in medical physics, where a decrease in the density of concurrent luminescent centers and an increase in OSL intensity were evidenced by the presence of HNT in Al2O3.

Variations in CTAC batches from different suppliers highly affect the shape yield in seed-mediated synthesis of gold nanotriangles

The rapidly developing miniaturization in numerous fields require low-demanding but robust methods of nanomaterial production. Colloidal synthesis provides great flexibility in product material, size, and shape. Gold nanoparticle synthesis has been thoroughly studied, however, recent reports on mechanistic insights of crystal formation have been hindered by the numerous procedures and parameter optimization works. With every new study, scientists fill another blank space on the map of understanding anisotropic growth and find out the critical parameters. In the current work, we highlight the choice importance for surfactant supplier in achieving the gold nanotriangle formation. We systematically study the variation in the shape yield when utilizing five batches of cetyltrimethylammonium chloride (CTAC) from varied suppliers. Using analytical techniques, we search for deviations causing such variation, e.g. different impurity content. We found only a marginal effect of iodine contamination on the studied system, excluding this factor as decisive in contrast to what was proposed earlier in the literature, and leaving the high dependency of the yield to originate from yet unknown reagent characteristics. A deeper understanding of these factors would provide highly effective protocols lowering the reagent consumption and increasing the accessibility of nanomaterials manufactured in a sustainable manner.

Exploring the Complex Chemistry and Degradation of Ascorbic Acid in Aqueous Nanoparticle Synthesis.

Ascorbic acid (AA) is the most widely used reductant for noble metal nanoparticle (NP) synthesis. Despite the synthetic relevance, its aqueous chemistry remains misunderstood, due in part to various assumptions about its reduction pathway which are insufficiently supported by experimental evidence. This study aims to provide an understanding of the complex chemistry associated with AA under aqueous conditions. We demonstrate that (i) AA undergoes appreciable degradation in alkaline solution on a timescale relevant to NP synthesis, (ii) contrary to popular belief, AA does not degrade into dehydroascorbic acid (DHA), nor is DHA the oxidized product of AA under noble metal NP synthetic conditions, (iii) DHA, which readily degrades under alkaline conditions, can also effectively reduce metal salt precursors to metal NPs, (iv) neither ascorbate nor dehydroascorbate act as surface capping agents post-synthetically on the NPs (v) AA degradation time greatly affects the morphology and polydispersity of the resultant NP. Results from our mechanistic investigation enabled us to utilize purposefully-aged reductants to achieve control over shape yield and monodispersity in the seed-mediated synthesis of Au nanorods. Our findings have important implications for achieving monodispersed products in the many metal NP synthesis reactions that make use of AA as a reducing agent.

Evolution-guided Bayesian optimization for constrained multi-objective optimization in self-driving labs

The development of automated high-throughput experimental platforms has enabled fast sampling of high-dimensional decision spaces. To reach target properties efficiently, these platforms are increasingly paired with intelligent experimental design. However, current optimizers show limitations in maintaining sufficient exploration/exploitation balance for problems dealing with multiple conflicting objectives and complex constraints. Here, we devise an Evolution-Guided Bayesian Optimization (EGBO) algorithm that integrates selection pressure in parallel with a q-Noisy Expected Hypervolume Improvement (qNEHVI) optimizer; this not only solves for the Pareto Front (PF) efficiently but also achieves better coverage of the PF while limiting sampling in the infeasible space. The algorithm is developed together with a custom self-driving lab for seed-mediated silver nanoparticle synthesis, targeting 3 objectives (1) optical properties, (2) fast reaction, and (3) minimal seed usage alongside complex constraints. We demonstrate that, with appropriate constraint handling, EGBO performance improves upon state-of-the-art qNEHVI. Furthermore, across various synthetic multi-objective problems, EGBO shows significative hypervolume improvement, revealing the synergy between selection pressure and the qNEHVI optimizer. We also demonstrate EGBO’s good coverage of the PF as well as comparatively better ability to propose feasible solutions. We thus propose EGBO as a general framework for efficiently solving constrained multi-objective problems in high-throughput experimentation platforms.

Seed-mediated growth synthesis and tunable narrow-band luminescence of quaternary Ag-In-Ga-S alloyed nanocrystals.

Silver-based I-III-VI-type semiconductor nanocrystals have received extensive attention due to their narrow-band luminescence properties. Herein, we demonstrated a seed-mediated growth of quaternary Ag-In-Ga-S (AIGS) nanocrystals (NCs) with narrow-band luminescence. By conducting partial cation exchange with In3+ and Ga3+ based on Ag2S NCs and controlling the Ag/In feeding ratios (0.25 to 2) of Ag-In-S seeds as well as the inventory of 1-dodecanethiol, we achieved optimized luminescence performance in the synthesized AIGS NCs, characterized by a narrow full width at half maximum of less than 40 nm. Meanwhile, narrow-band luminescent AIGS NCs exhibit a tetragonal AgGaS2 crystal structure and a gradient alloy structure, rather than a core-shell structure. Most importantly, the kinetics decay curves of time-resolved photoluminescence and the ground state bleaching in transient absorption generally agree with each other regarding the lifetime of the second decay component, which indicates that the narrow-band luminescence is due to the slow radiative recombination between trapped electrons and trapped holes located at the edge of the conduction band and the deep silver-related trap states (e.g., silver vacancy), respectively. This study provides new insights into the correlation between the narrow-band luminescence properties and the structural characteristics of AIGS NCs.

Heterostructure seed-mediated synthesis of zinc phosphide quantum dots for bright band-edge emission.

This study explores the synthesis of colloidal zinc phosphide quantum dots (QDs) by a novel In(Zn)P cluster seed-mediated approach, addressing the challenge of achieving low-cost, high-quality, nontoxic QDs suitable for optoelectronic applications. By intentionally limiting the amount of In precursor added to a hot solvent containing Zn and P precursors, In-rich In(Zn)P cluster seeds were formed. Subsequently, these clusters served as seeds for the growth of zinc phosphide nanocrystals, effectively using the remaining Zn and P precursors for further crystal growth. The synthesized QDs exhibited a tetragonal-like Zn3P2 structure and exceptional optical properties, including band-edge photoluminescence (PL) emission under ambient conditions. A ZnS shell was applied to further enhance the PL intensity, achieving a PL quantum yield of 40% and an average PL decay lifetime of 74 ns, while significantly improving the stability of the QDs. Temperature-dependent PL spectroscopy revealed significant resistance to thermal quenching with an exciton dissociation energy of 62 meV, underscoring the potential of this approach for advancing the field of optoelectronics. This method provides a pathway to fabricate zinc phosphide-based QDs with controlled optical properties and highlights the effective use of earth-abundant materials in the development of environmentally benign photonic materials.

The influence of the reducing agent used during the synthesis of gelatin-coated gold nanorods on its thermal properties for photothermal application

The development of Gold nanorods (AuNRs) as phototherapeutic agents (PTAs) has attracted much interest from researchers in recent decades. The majority of their synthetic methods use Hydroquinone (HQ) and Ascorbic acid (AA) as the reducing agent, and these have been shown to affect the properties of AuNRs. However, no study has been conducted on how these two reducing reagents can affect their application, especially after coating. Therefore, we herein report a seed-mediated synthesis of AuNRs using two reducing agents and coating them with gelatin at different volume ratios (1:5, 1:2, 1:1,2:1, and 5:1). The HQ-reduced AuNRs and AA-reduced AuNRs absorbed at TSPR of 512 nm and 514 nm and LSPR of 914 nm and 847 nm, respectively. The gelatin-coated HQ-reduced and AA-reduced AuNRs did not show significant LSPR wavelength changes for all the volume ratios. However, a slight increase in the TSPR and the absorbance at regions below 550 nm was seen for volume ratios 1:1, 2:1, and 5:1. The thermal stability studies at 70 ℃ for the coated materials revealed that AA-reduced AuNRs were more thermally stable than HQ-reduced AuNRs, with the less optical shift. The coated AA-reduced AuNRs were further tested for photothermal responses. The results show that the high gelatin volume during coating affects the photothermal response of the AuNRs. This study indicates volume ratio of 1:5 and 1:2 has good stability while maintaining the good photothermal profiling needed in PTT applications. Hence Gel@AuNRs synthesised with AA is an excellent PTT agent for phototherapy applications.

Synthesis of small-sized gold nanorod using catechol as a reducing agent

Facile preparation of small gold nanorod with controllable and large surface plasmon resonance band is of great value for applications in especially the biomedical and sensing fields. In this work, we propose that without addition of additive to complicate the experimental system catechol of a very weak reducibility can be used as reducing agent for seed-mediated synthesis of gold nanorod. Under a temperature of 40 °C and a catechol concentration of 17.5 mM, monodisperse gold nanorod with a high shape yield, a largest plasmon wavelength of 918 nm, and especially a small diameter of 9.8 nm can be acquired simultaneously. A good tune over the plasmon wavelength is also shown by varying the amount of silver ion. Besides, the effects of experimental parameters including silver ion, cetyltrimethylammonium bromide, gold seed and catechol have also been carefully studied, and the morphological and structural evolutions of the particle have been discussed based on reported growth mechanism.

Synthesis of Au-Ag bimetallic nanoparticles using Korean red ginseng (Panax ginseng Meyer) root extract for chemo-photothermal anticancer therapy.

Green synthesis strategies have been widely applied for the preparation of versatile nanomaterials. Gold nanospheres with an average size of 6.95 ± 2.25nm were green synthesized by using a 70% ethanol extract of Korean red ginseng (Panax ginseng Meyer) root as a reducing agent. A seed-mediated synthesis was conducted to prepare Au-Agbimetallic nanoparticles using gold nanospheres as seeds. Remarkably, Au-Ag bimetallic nanoparticles with an average size of 80.4 ± 11.9nm were synthesized. Scanning transmission electron microscopy, energy dispersive X-ray spectroscopy and elemental mappings revealed bimetallic nanoparticles with Au-Ag alloy core and Au-rich shells. A face-centered cubic structure of Au-Ag bimetallic nanoparticles was confirmed by X-ray diffraction analysis. For Au-Ag bimetallic nanoparticles, the ratio of Ag/Au was 0.20 which was detected and analyzed by inductively coupled plasma-mass spectrometry. Gold nanospheres and Au-Ag bimetallic nanoparticles were functionalized by PEGylation, folic acid conjugation and grafting onto graphene oxide. Finally, docetaxel was loaded for evaluating the in vitro cell viability on cancer cells. Successful functionalization was confirmed by Fourier-transform infrared spectra. The anticancer activity of the docetaxel-loaded nanoparticles was higher than that of their non-docetaxel-loaded counterparts. The highest anticancer activity on human gastric adenocarcinoma cells (AGS) was observed in the docetaxel-loaded gold nanospheres that were functionalized by PEGylation, folic acid conjugation and grafting onto graphene oxide. Additionally, grafting onto graphene oxide and docetaxel loading induced high intracellular reactive oxygen species generation. For chemo-photothermal (PTT) anticancer therapy, cell viability was investigated using near-infrared laser irradiation at 808nm. The highest chemo-PTT anticancer activity on AGS cells was observed in the docetaxel-loaded Au-Ag bimetallic nanoparticles. Therefore, the newly prepared docetaxel-loaded Au-Ag bimetallic nanoparticles in the current report have potential applications in chemo-PTT anticancer therapy.

Atomically precise nanoclusters predominantly seed gold nanoparticle syntheses

Seed-mediated synthesis strategies, in which small gold nanoparticle precursors are added to a growth solution to initiate heterogeneous nucleation, are among the most prevalent, simple, and productive methodologies for generating well-defined colloidal anisotropic nanostructures. However, the size, structure, and chemical properties of the seeds remain poorly understood, which partially explains the lack of mechanistic understanding of many particle growth reactions. Here, we identify the majority component in the seed solution as an atomically precise gold nanocluster, consisting of a 32-atom Au core with 8 halide ligands and 12 neutral ligands constituting a bound ion pair between a halide and the cationic surfactant: Au32X8[AQA+•X-]12 (X = Cl, Br; AQA = alkyl quaternary ammonium). Ligand exchange is dynamic and versatile, occurring on the order of minutes and allowing for the formation of 48 distinct Au32 clusters with AQAX (alkyl quaternary ammonium halide) ligands. Anisotropic nanoparticle syntheses seeded with solutions enriched in Au32X8[AQA+•X-]12 show narrower size distributions and fewer impurity particle shapes, indicating the importance of this cluster as a precursor to the growth of well-defined nanostructures.

Elucidating the role of seed structure in the heterometallic seeded growth of copper-based nanocrystals

Seed-mediated synthesis is a versatile method to prepare multimetallic nanocrystals for diverse applications. However, many fundamental questions remain on how the structural and chemical properties of nanocrystal seeds control the reaction pathways, especially for nonaqueous synthesis at elevated temperatures. Herein, we elucidate the role of surface ligands and crystallinity of Au nanocrystal seeds on the heterometallic seeded growth of Cu-based nanocrystals. We found that weakly coordinating ligands are critical to facilitate the diffusion between Au and Cu, which enables subsequent one-dimensional growth of Cu. Replacing multiple-twinned Au seeds with single-crystalline ones switched the growth pathway to produce heterostructured nanocrystals. Our work illustrates the importance of precise control of seed characteristics for the predictive synthesis of structurally complex multimetallic nanocrystals.

Seed-mediated synthesis of gold nanorods by using dopamine as the weak reducing agent in a binary surfactant mixture

Gold nanorods were prepared by using a modified seed-mediated wet chemical growth method at reduced concentrations of hexadecyltrimethylammonium bromide and sodium oleate. The weak reducing agent used in the growth solution was dopamine. Gold nanorods with longitudinal surface plasmon resonance wavelength ranging from 780 to 1115 nm were obtained by varying the amounts of hexadecyltrimethylammonium bromide, silver nitrate, and hydrochloric acid in the growth solution. Moreover, the photothermal properties of the gold nanorods at 1064 nm were studied, indicating the potential applications of gold nanorods as photothermal agents in the second near-infrared window.

Smart Anisotropic Colloidal Composites: A Suitable Platform for Modifying the Phase Transition of Diblock Copolymers by Gold Nanoparticles

Surface modification of metallic nanoparticles (NPs) by stimuli-responsive polymers is a benign method to prepare smart colloidal composites which tune the characteristic properties of individual systems. The temperature-dependent transition of diblock copolymer poly(N-isopropylacrylamide)-block-poly(N-vinylcaprolactam) (PNIPMA-b-PVCL) synthesized using reversible addition-fragmentation chain transfer polymerization was studied by incorporating anisotropic gold NPs (AGPs) such as spheres (AuNSs), rods (AuNRs), cubes (AuNCs), and rhombic dodecahedrals (AuRDs). Shape-dependent physiochemical properties of nanostructures alter the lower critical solution temperature (LCST) of the chemical inhomogeneous diblock copolymer. Heterogeneous nucleation of AuNPs was facilitated by seed-mediated synthesis for incorporating uniformity. In the mixed system, the presence of PNIPAM-b-PVCL modifies the surface of AGPs through physisorption which is supported by transmission electron microscopy and field emission scanning electron microscopy showing the NPs embedding in the polymeric matrix. Furthermore, steady state fluorescence spectroscopy and Fourier transform infrared spectroscopy were performed to examine the phase transition behavior of PNIPAM-b-PVCL in AGPs. The formation of a smart polymer nanocomposite alters the physiochemical properties of the diblock copolymer as demonstrated from the variation of LCST in the dynamic light scattering measurement. Henceforth, functionalizing the surfaces of AGPs with a thermoresponsive diblock copolymer provides combinatorial benefits in the properties of smart polymeric colloidal systems with potential applications in bioimaging and drug delivery.

Universal Solid-Phase Seed-Mediated Synthesis of Monodisperse and Ultrasmall L10-PtM Intermetallic Nanocrystals

Intermetallic compounds have emerged as a class of promising electrocatalysts for fuel cells; however, it is still a great challenge to synthesize monodisperse and small intermetallic phases by an economical and scalable method. Herein, we demonstrate a generally applicable solid-phase seed-mediated diffusion strategy for controllable synthesis of ordered L10-PtM (M = Mn, Fe, Co, and Zn) nanoparticles, where the preprepared monodispersed Pt seeds are used as the growth sites. The freeze-drying procedure produces monodisperse metal precursors on Pt/C, and the subsequent annealing process in a H2/Ar atmosphere obtains highly dispersed and ultrasmall PtM intermetallic nanocrystals (∼3 nm) on carbon supports. More importantly, such a strategy is also applicable to the preparation of a high-loaded PtMn intermetallic catalyst (50 wt %). Taking PtMn/C catalysts as examples, we illustrate their synthetic details and formation mechanism of the desired ordered phases. This approach eliminates the need for energy-consuming filtering and washing procedures, which makes it very promising for large-scale production.

Seed-mediated synthesis of a modified micro-mesoporous MIL-101(Cr) for improved benzene and toluene adsorption at room conditions

The modification of metal-organic frameworks (MOFs) for enhanced volatile organic compounds (VOCs) removal is a huge challenge. Therefore, it is of great importance to find a proper strategy to tune the porosity of MOFs and their VOCs removal performance. In this study, we report a novel seed-mediated synthesis strategy using a low-cost and heteroatom-rich carbon structure (MIC-COOH) to prepare hierarchical micro-mesoporous MIL-101(Cr). Different amounts of MIC-COOH were applied to investigate the efficiency of seed concentration on the fundamental specification of the created hierarchical MIL-101(Cr) and its benzene and toluene uptake. The results showed that the increase of MIC-COOH significantly enhanced the mesoporous volume in the MOF structure, resulting in the creation of large surface area (up to 2971.5 m2/g) and high pore volume (up to 2.21 cm3/g). MIL@MIC-4% nanostructure exhibited 235.3 ± 0.05 and 291.6 ± 0.04 wt% adsorption efficiency for benzene and toluene, respectively, which are ⁓3.0 and 4.1 times greater than those of pristine MIL-101(Cr). It also exhibited higher cyclic adsorption efficiency than that of the pristine MIL-101(Cr) after five consecutive adsorption-desorption cycles. The uptake behavior of benzene and toluene on the modified MIL@MIC structure was also perused by applying density functional theory (DFT) calculations. According to the findings, it was revealed that the cooperative charge transfers between MIL-101(Cr) and MIC-COOH through the structure can play an efficient role in the enhanced uptake of benzene and toluene molecules.

Seed-Mediated Synthesis of Thin Gold Nanoplates with Tunable Edge Lengths and Optical Properties

Thin Au nanoplates show intriguing localized surface plasmon resonance (LSPR) properties with potential applications in various fields. The conventional synthesis of Au nanoplates usually involves the formation of spherical nanoparticles or produces nanoplates with large thicknesses. Herein, we demonstrate a synthesis of uniform thin Au nanoplates by using Au-Ag alloy nanoframes obtained by the galvanic replacement of Ag nanoplates with HAuCl4 as the seeds and a sulfite (SO32-) as a ligand. The SO32- ligand not only complexes with the Au salt for the controlled reduction kinetics but also strongly adsorbs on Au {111} facets for effectively constraining the crystal growth on both basal sides of the Au nanoplates for controlled shape and reduced thicknesses. This seed-mediated synthesis affords Au nanoplates with a thickness of only 7.5 nm, although the thickness increases with the edge length. The edge length can be customizable in a range of 48-167 nm, leading to tunable LSPR bands in the range of 600-1000 nm. These thin Au nanoplates are applicable not only to surface-enhanced Raman spectroscopy with enhanced sensitivity and reliability but also to a broader range of LSPR-based applications.

Validating and Utilizing Machine Learning Methods to Investigate the Impacts of Synthesis Parameters in Gold Nanoparticle Synthesis

The control over the synthesis of gold nanoparticles is crucial to ensure optimal optical and processing properties, but synthesis is complex and interdependent on many variables such as reducing agent, capping agent, and the amount of gold seeds and precursor. Machine learning offers the prospect of giving insight into this multidimensional problem, but the reason for selecting a certain model is often unclear. Here, we apply tree-based machine learning algorithms on the semi-batch, seed-mediated synthesis of gold nanoparticles in the size range of 20–120 nm to analyze the correlation between synthesis parameters, optical spectra, and size. After testing the validity of the machine learning models by nested cross-validation, the Random Forest model is selected as a simple model that can reproduce the outcome of the synthesis well. In a further analysis by SHAP (SHapley Additive exPlanations), chemical relationships that were not explicitly taught to the model but purely derived from the data analysis are revealed.