Gold Nanotriangles Research Articles

Circularly Polarized Light-Induced Chiral Growth of Achiral Plasmonic Nanoparticles Dispersed in a Solution.

Plasmonic nanoparticles (NPs) with chiral geometries have wide applications from chiral molecular sensing to enantioselective catalysis. The synthesis of chiral plasmonic nanoparticles using circularly polarized light (CPL) has attracted a considerable amount of attention because it eliminates the need for chiral molecules. However, NPs need to be immobilized on a solid substrate during synthesis. Here, we successfully synthesized colloidal chiral plasmonic NPs by depositing silver on the surface of achiral gold nanoparticles dispersed in a solution using CPL. Circular dichroism (CD) signals corresponding to the handedness of the irradiated CPL were observed when gold nanorods or gold nanotriangles were used. In contrast, no clear CD signal was observed when gold nanospheres were used. The morphological anisotropy of the gold nanoparticles was a key factor in the synthesis of chiral plasmonic nanoparticles using CPL. Furthermore, we demonstrated the tuning of chiroptical properties according to the CPL wavelength.

The Role of Iodide in the Formation of Gold Nanotriangles

The Role of Iodide in the Formation of Gold Nanotriangles

Temperature Sensitive PNIPAm-g-PEI/Gold Nanotriangle for Gene Delivery Promotion.

As a two-dimensional material, gold nanotriangles (GNTs) are rarely studied in the field of gene delivery. In this study, a temperature-responsive GNTs was developed as a novel carrier for gene delivery. The temperature-sensitive copolymer PNIPAm-g-PEI was grafted onto the surface of GNTs to construct a PNIPAm-g-PEI/GNTs composite controllable release platform. The lower critical solution temperature (LCST) of PNIPAm-g-PEI/GNTs was found to be 42°C, and the particle size of PNIPAm-g-PEI/GNTs was 150nm at this temperature. Gel electrophoresis experiments showed that PNIPAm-g-PEI/GNTs completely condensed DNA at 20μg/mL, and PNIPAm-g-PEI/GNTs promoted the release of DNA under laser irradiation. Luciferase and green fluorescent protein reporter gene assays demonstrated that the transfection efficiency of PNIPAm-g-PEI/GNTs was 1.5 and 7.2 times that of PEI, respectively. These results demonstrated the promising potential of temperature-responsive GNTs as effective and safe gene delivery vectors.

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.

Synthesis of thermosensitive hybrid structure gold nanotriangles coated with poly(N-isopropylacrylamide) for reversible confinement of molecules

In this work, we investigate a synthesis method for novel systems that involve the use of gold nanotriangles arrays (AuNTs) coated with poly(N-isopropylacrylamide) (pNIPAM) brushes, designed as smart platforms for the reversible confinement of bio-particles. Initially, we employed cost-effective nanosphere lithography to fabricate gold nanotriangles arrays. Next, polymer initiator groups were attached to the AuNTs surface through a spontaneous reduction approach, enabling exclusive functionalization of pNIPAM on the gold surface. Finally, we utilized surface-initiated atom transfer radical polymerization to graft pNIPAM brushes onto the gold surface. We systematically investigated the polymer initiator groups’ grafting time and the polymerization time to control the thickness of the grafted pNIPAM brushes. Subsequently, we characterized the thermoresponsive properties of these hybrid structures using Atomic Force Microscopy (AFM) measurements, evaluating their ability to undergo on/off adsorption and desorption of polystyrene (PS) beads on their surface. Indeed, the combination of the thermosensitive pNIPAM polymer with AuNTs arrays results in the development of a precisely regulated two-dimensional active device which exhibits tunable properties with external temperature changes, making it a versatile platform suitable for a wide range of applications.

Customizable ligand exchange on the surface of gold nanotriangles enables their application in LSPR-based sensing.

Nanomaterials made of noble metals have been actively utilized in sensorics and bioanalytics. Nanoparticles of anisotropic shapes are promising for increasing sensitivity due to the generated hotspots of electron density. Such structures can be effectively manufactured by a relatively accessible colloidal synthesis. However, the shape control requires the attachment of a surfactant on specific crystal facets during their growth. Commonly used cetrimonium halides form a closely packed bilayer, lowering the surface accessibility for subsequent (bio)functionalization steps. While there are numerous studies on functionalizing gold nanospheres, novel materials, such as nanotriangles (AuNTs), often require thorough studies to adapt the existing procedures. This is mainly caused by the incomplete characterization of initial nanoparticle colloids in empirically developed protocols. Herein, we report a rational approach utilizing the surface area of AuNTs as a function of both their dimensions and concentration, determined with an express UV-VIS analysis. We demonstrate its efficiency for the exchange of cetyltrimethylammonium chloride (CTAC) with polystyrene sulfonate (PSS) and with biocompatible citrate using direct and indirect methods, respectively. Fourier-transform infrared spectroscopy unequivocally proves the ligand exchange. Such functionalization allows evaluating the bulk refractive index sensitivity of AuNTs as a measure of their potential in LSPR-based sensing.

Simultaneous detection of Pb2+ and Cu2+ based on catalytic etching of AgNTs@AuNHs colorimetric nanoprobe

A colorimetric gold nanohexagonals coated silver nanotriangles (AgNTs@AuNHs) nanoprobe has been constructed for the ultrasensitive detection of trace Pb2+ and Cu2+, based on the fact that Pb2+ and Cu2+ as the catalyzer can selectively enhance the etching rate of AgNTs@AuNHs by S2O32−. In the presence of Pb2+, the inner AgNTs within the AgNTs@AuNHs undergo complete etching to form the hollow AuNHs, leading to the marked decrease in both absorbance and chrominance at 585 nm. In contrast, Cu2+ initiates an etching reaction on the AgNTs, subsequently extending to the AuNHs. These transformations give rise to the formation of hollow gold nanotriangles, accompanied by pronounced red-shifts in the absorption peaks of the detection system. The distinct optical responses induced by Pb2+ and Cu2+ in the AgNTs@AuNHs nanoprobe enable the sensitive and selective detection and quantification of these heavy metal ions. Furthermore, we successfully extracted RGB data from the color changes of AgNTs@AuNHs nanoprobe, enabling a straightforward visual readout for detection of Pb2+ and Cu2+. This method yields satisfactory recoveries when applied to the analysis of Pb2+ and Cu2+ in river water, rice, and onion samples, with detection results closely matching those obtained using ICP-MS. These results collectively underscore the practical applicability of the AgNTs@AuNHs nanoprobe.

Oxidative Stress Sensing System for 8-OHdG Detection Based on Plasma Coupled Electrochemistry by Transparent ITO/AuNTAs/PtNPs Electrode.

8-Hydroxydeoxyguanosine (8-OHdG) is the most widely used oxidative stress biomarker of the free radical-induced oxidative damage product of DNA, which may allow a premature assessment of various diseases. This paper designs a label-free, portable biosensor device to directly detect 8-OHdG by plasma-coupled electrochemistry on a transparent and conductive indium tin oxide (ITO) electrode. We reported a flexible printed ITO electrode made from particle-free silver and carbon inks. After inkjet printing, the working electrode was sequentially assembled by gold nanotriangles (AuNTAs) and platinum nanoparticles (PtNPs). This nanomaterial-modified portable biosensor showed excellent electrochemical performance for 8-OHdG detection from 10 μg/mL to 100 μg/mL by our self-developed constant voltage source integrated circuit system. This work demonstrated a portable biosensor for simultaneously integrating nanostructure, electroconductivity, and biocompatibility to construct advanced biosensors for oxidative damage biomarkers. The proposed nanomaterial-modified ITO-based electrochemical portable device was a potential biosensor to approach 8-OHdG point-of-care testing (POCT) in various biological fluid samples, such as saliva and urine samples.

Seedless and non-thermal liquid-phase reduction synthesis of gold nanotriangles

Seedless and non-thermal liquid-phase reduction synthesis of gold nanotriangles

Behind the Optimization of the Sensor Film: Bioconjugation of Triangular Gold Nanoparticles with Hemoproteins for Sensitivity Enhancement of Enzymatic Biosensors.

Electrochemical biosensors are widely used in a multitude of applications, such as medical, nutrition, research, among other fields. These sensors have been historically used and have not undergone many changes in terms of the involved electrochemical processes. In this work, we propose a new approach on the immobilization and enhancement of the electrochemical properties of the sensing layers through the control and bioconjugation of hemoproteins (hemoglobin, myoglobin, and cytochrome C) on anisotropic gold nanoparticles (gold nanotriangles (AuNTs)). The hemeproteins and the AuNTs are mixed in a solution, resulting in stable bioconjugates that are deposited onto the electrode surface to obtain the biosensors. All the systems proposed herein exhibited direct well-defined redox responses, highlighting the key role of the AuNTs acting as mediators of such electron transfers. Several protein layers surrounding the AuNTs are electroactive, as demonstrated from the charge measured by cyclic voltammetry. The retention of the stability of the hemeproteins once they are part of the bioconjugates is evidenced towards the electrocatalytic reduction of hydrogen peroxide, oxygen, and nitrite. The parameters obtained for the proposed biosensors are similar or even lower than those previously reported for similar systems based on nanomaterials, and they exhibit attractive properties that make them potential candidates for the latest developments in the field of sensing devices.

Flexible SERS sensor using AuNTs-assembled PDMS film coupled chemometric algorithms for rapid detection of chloramphenicol in food

The misuse of chloramphenicol (CAP) has led to the development of drug-resistant strains that pose significant threats to public health. Here, we propose a universal flexible surface-enhanced Raman spectroscopy (SERS) sensor utilizing gold nanotriangles (AuNTs) and polydimethylsiloxane (PDMS) film for rapid detection of CAP in food samples. Initially, AuNTs@PDMS with unique optical and plasmonic properties were used to collect spectra of CAP. Afterward, four chemometric algorithms were executed and compared. Accordingly, random frog-partial least squares (RF-PLS) exhibited optimum results with correlation coefficient of prediction (Rp = 0.9802) and the lowest root-mean-square error of prediction (RMSEP = 0.348 µg/mL). Furthermore, the sensor's efficacy to detect CAP in milk samples was confirmed, and the findings were compatible with the conventional HPLC approach (P > 0.05). Therefore, the proposed flexible SERS sensor could effectively be used to monitor milk quality and safety.

Onsite detection of cadmium and nickel using gold nanospheres and nanotriangles capped with Cyclea peltata phytochemicals

Small-sized gold nanospheres and nanotriangles (CPAuNPs) were synthesized to visually identify low concentrations of cadmium and nickel (20 ppm) in polluted water samples. Three factors i.e Cyclea peltata extract concentration (X1), temperature (X2), pH (X3) and agitation speed (X4) were optimized for maximum CPAuNPs synthesis by central composite design. The optimized conditions were found to be CP extract concentration of 24.20%, pH of 7.68 and agitation speed of 43 RPM at which maximum yield of 0.412 g/L was obtained with a fold increase of 1.42 as compared to unoptimized conditions. Gold nanospheres were in the size range of 25–36 nm and nano triangles of 100–140 nm with zetapotential of −31.8 mV. The synthesized CPAuNPs demonstrated good selectivity for visual detection of cadmium and nickel at ppm levels, where the colour of CPAuNPs changed from pink to purple. Upon interaction of CPAuNPs with Cd+3 and Ni+2 in the varied concentration ranges, a maximum red shift was seen at 20 ppm, which confirmed agglomeration. The variation in absorbance ratio (A640nm/A523nm) for Cd+3 and (A610nm,/A523nm) for Ni+2 showed linearity upto 50 ppm with respect to increased concentration in both the cases with R2 = 0.926 in case of Cd+3 and R2 = 0.950 for Ni+2. Hence, a portable low-cost detection kit for specific heavy metals could be constructed, employing this plant reduced nanospheres, for on-site detection sensing of cadmium and nickel in industrial effluents upto 20 ppm limits.

Gold Nanotriangle-Assembled Nanoporous Structures for Electric Field-Assisted Surface-Enhanced Raman Scattering Detection of Adenosine Triphosphate.

A reliable, rapid, cost-effective, and simple method for the detection of biomolecules would greatly promote the research of analytical detection of single molecules. A nanopore-based analytical technique is promising for detecting biomolecules. Conventional electrochemical nanopores cannot distinguish biomolecules precisely because of their fast translocation speed and limited electrochemical information. Therefore, it is highly desirable to develop electrochemical surface-enhanced Raman scattering (SERS) nanopores to obtain multidimensional information. Herein, we designed and fabricated gold nanotriangle (AuNT)-assembled porous structures at the tip of a glass capillary using dithiol adenosine triphosphate (ATP) aptamers as cross-linking molecules. The AuNTs exhibited an edge length of 57.3 ± 6.2 nm and thickness of about 15 nm. The gold nanoporous structure (GPS) showed a strong ion rectification even at a high concentration of electrolyte (2 M) and a high SERS activity. Based on these designed structures, SERS and electrochemistry techniques were combined to control the rapid movement of ATP to the vicinity of the GPS by an applied potential of +1 V, where ATP was concentrated by ATP aptamers and the molecular signals were amplified by SERS. As a result, the GPS successfully detected ATP at a concentration as low as 10-7 M.

SERS-fluorescence dual-mode nanoprobe for the detection and imaging of Bax mRNA during apoptosis.

Adual-mode nanoprobe was constructed to detect Bax messenger RNA (mRNA), consisting of gold nanotriangles (AuNTs), a Cy5-modified recognition sequence, and a thiol-modified DNA sequence. Bax mRNA is one of the key pro-apoptotic factors in the apoptosis pathway. Raman enhancement and fluorescence quenching of the signal group Cy5 were performed using AuNTs as substrates. The thiol-modified nucleic acid chain is partially complementary to the Cy5-modified nucleic acid chain to form a double strand and is linked to the AuNTs by the Au-S bond. When Bax mRNA is present, the Cy5-modified strand specifically binds to it to form a more stable duplex, making Cy5 far away from AuNTs, and SERS signal is weakened while fluorescence signal is enhanced. The nanoprobe can be used for the quantitative detection of Bax mRNA in vitro. Combined with the high sensitivity of SERS and the visualization of fluorescence, this method has good specificity and can be used for in situ imaging and dynamic monitoring of Bax mRNA during deoxynivalenol (DON) toxin-induced apoptosis of HepG2 cells. DON plays a pathogenic role mainly by inducing cell apoptosis. Theresults confirmed that the proposed dual-mode nanoprobe has good versatility in various human cell lines.

Microfluidic-Generated Seeds for Gold Nanotriangle Synthesis in Three or Two Steps.

Nanoparticle synthesis has drawn great attention in the last decades. The study of crystal growth mechanisms and optimization of the existing methods lead to the increasing accessibility of nanomaterials, such as gold nanotriangles which have great potential in the fields of plasmonics and catalysis. To form such structures, a careful balance of reaction parameters has to be maintained. Herein, a novel synthesis of gold nanotriangles from seeds derived with a micromixer, which provides a highly efficient mixing and simple parameter control is reported. The impact of the implemented reactor on the primary seed characteristics is investigated. The following growth steps are studied to reveal the phenomena affecting the shape yield. The use of microfluidic seeds led to the formation of well-defined triangles with a narrower size distribution compared to the entirely conventional batch synthesis. A shortened two-step procedure for the formation of triangles directly from primary seeds, granting an express but robust synthesis is further described. Moreover, the need for a thorough study of seed crystallinity depending on the synthesis conditions, which - together with additional parameter optimization - will bring a new perspective to the use of micromixers which are promising for scaling up nanomaterial production is highlighted.

Triphenylphosphonium conjugated gold nanotriangles impact Pi3K/AKT pathway in breast cancer cells: a photodynamic therapy approach

Although gold nanoparticles based photodynamic therapy (PDT) were reported to improve efficacy and specificity, the impact of surface charge in targeting cancer is still a challenge. Herein, we report gold nanotriangles (AuNTs) tuned with anionic and cationic surface charge conjugating triphenylphosphonium (TPP) targeting breast cancer cells with 5-aminoleuvinic acid (5-ALA) based PDT, in vitro. Optimized surface charge of AuNTs with and without TPP kill breast cancer cells. By combining, 5-ALA and PDT, the surface charge augmented AuNTs deliver improved cellular toxicity as revealed by MTT, fluorescent probes and flow cytometry. Further, the 5-ALA and PDT treatment in the presence of AuNTs impairs cell survival Pi3K/AKT signaling pathway causing mitochondrial dependent apoptosis. The cumulative findings demonstrate that, cationic AuNTs with TPP excel selective targeting of breast cancer cells in the presence of 5-ALA and PDT.

Three-dimensional building of anisotropic gold nanoparticles under confinement in submicron capsules.

The low collision rate and contact time of gold nanoparticles (NPs) in solution afford a low welding probability, which hinders their welding structure, orientation, and dimension. Encapsulated anisotropic NPs, gold nanotriangles (AuNTs), were successfully assembled into a three-dimensional structure inside a permeable silica nanocapsule under light illumination to generate localized surface plasmon resonance (LSPR). AuNTs were trapped in the permeable silica nanocapsules and diffused in the nanospace because of copolymer release, which increased the contact probability of AuNTs and promoted the three-dimensional building of AuNTs. Electron energy loss mapping simulations revealed that the obtained three-dimensional AuNT structure exhibited spatially separated multiple LSPR modes with different energies of incident light, which are photophysically attractive beyond the facet-selective chemical growth of NPs, and postmodification for anchoring substances with site-selective attachment to the obtained structure will be applicable to expand the sensing design and class of substances for sensing.

Depletion force optimization for high-purity gold nanotriangles prepared using different growth methods.

A homogeneous structural distribution in metal nanoparticle is commonly required for their application, and despite high-yield growth techniques, unavoidable structural heterogeneity remains a concern in metal nanoparticle synthesis. Gold nanotriangles (AuNTs) were synthesized using seed-mediated and seedless growth methods. Recent advancements in high-yield synthesis processes have enabled easy handling of AuNTs, which exhibit unique localized surface plasmon resonance characteristics due to their anisotropic triangular form. The flocculation and subsequent precipitation technique was used to purify AuNTs of different sizes synthesized using seed-mediated and seedless growth methods. The optimal conditions for obtaining high-purity AuNTs were explored by introducing a high concentration of cetyltrimethylammonium chloride. Additionally, the depletion force necessary for achieving high-purity AuNTs was calculated to reveal variations in the required depletion forces for AuNTs synthesized using different growth techniques. The alternations in the size distribution of AuNTs during the flocculation step were tracked using dynamic light scattering, and the surface charge of AuNTs synthesized through different growth methods was evaluated by ζ-potential. The high purity of the AuNTs produced using the seedless growth method required a larger depletion force than the seed-mediated grown AuNTs. The difference in the required depletion forces results from the difference in the electrostatic forces caused by the different growth methods.

Tunable reactivity of silver nanoclusters: a facile route to synthesize a range of bimetallic nanostructures.

Quantized energy levels and unique optoelectronic properties of atomically precise noble metal nanoclusters (NCs) have made them important in materials science, catalysis, sensors, and biomedicine. Recent studies on the profound chemical interactions of such NCs within themselves and with ultrasmall plasmonic nanoparticles (NPs) indicate that depending on the size, shape, and composition of the second reactant, NCs can either take part in colloidal assembly without any chemical modifications or lead to products with atoms exchanged. Anisotropic NPs are a unique class of plasmonic nanomaterials as their sharp edges and protrusions show higher chemical reactivity compared to flat surfaces, often leading to site-specific growth of foreign metals and metal oxide shells. Here, using chemical interactions between gold nanotriangles (AuNTs) and Ag NCs of different compositions, we show for the first time that metal atom etching, alloying/atom exchange, and colloidal assembly can all happen at a particular length scale. Specifically, Ag25(DMBT)18 NCs (denoted as 1), upon reacting with AuNTs of ∼57 nm edge length, etch gold atoms from their sharp tips and edges. Simultaneously, the two nanosystems exchange metal atoms, resulting in Ag-doped AuNTs and AuxAg24-x(DMBT)18 (x = 1, 2). However, another Ag NC with the same metallic core, but a different ligand shell, namely, Ag25H22(DPPE)8 (denoted as 2), creates dendritic shells made of Ag, surrounding these AuNTs under the same reaction conditions. Furthermore, we show that in the case of a more reactive thiol-protected Ag NC, namely, Ag44(pMBA)30 (denoted as 3), gold etching is faster from the edges and tips, which drastically alters the identities of both the reactants. Interestingly, when the AuNTs are protected by pMBA, 3 systematically assembles on AuNTs through H-bonding, resulting in an AuNT core-Ag NC shell nanocomposite. Thus, while shedding light on various factors affecting the reactivity of Ag NCs towards AuNTs, the present study proposes a single strategy to obtain a number of bimetallic nanosystems of targeted morphology and functionality.

A Review on Gold Nanotriangles: Synthesis, Self-Assembly and Their Applications.

Gold nanoparticles (AuNPs) with interesting optical properties have attracted much attention in recent years. The synthesis and plasmonic properties of AuNPs with a controllable size and shape have been extensively investigated. Among these AuNPs, gold nanotriangles (AuNTs) exhibited unique optical and plasmonic properties due to their special triangular anisotropy. Indeed, AuNTs showed promising applications in optoelectronics, optical sensing, imaging and other fields. However, only few reviews about these applications have been reported. Herein, we comprehensively reviewed the synthesis and self-assembly of AuNTs and their applications in recent years. The preparation protocols of AuNTs are mainly categorized into chemical synthesis, biosynthesis and physical-stimulus-induced synthesis. The comparison between the advantages and disadvantages of various synthetic strategies are discussed. Furthermore, the specific surface modification of AuNTs and their self-assembly into different dimensional nano- or microstructures by various interparticle interactions are introduced. Based on the unique physical properties of AuNTs and their assemblies, the applications towards chemical biology and sensing were developed. Finally, the future development of AuNTs is prospected.