Triangular Nanoprisms Research Articles

Facet-selective asymmetric functionalization of anisotropic gold nanoprisms for Janus particle synthesis

Janus particles, which possess asymmetric structures and/or multiple surface chemistries, have attracted intense interest due to their capability of multiple distinct interactions with their environment. Most Janus particles synthesis techniques rely on applying coating molecules on isotropic particles. Herein, we demonstrate a method to controllably functionalize both major facets of geometrically anisotropic triangular gold nanoprisms in the size range of 100–200 nm with two distinct molecular coatings (hexadecane thiol or thiolated poly (ethylene) glycol and thiol-modified oligonucleotide), giving rise to the formation of Janus gold nanoprisms. Janus particles orient themselves on the interface of water-chloroform mixture and exhibit variable interaction with both hydrophilic and hydrophobic surfaces due to their amphiphilicity and undergo asymmetric self-assembly behavior with other nanoparticles.

Bottom-Up Fabrication of Plasmonic Nanoantenna-Based High-throughput Multiplexing Biosensors for Ultrasensitive Detection of microRNAs Directly from Cancer Patients' Plasma.

There is an unmet need in clinical point-of-care (POC) cancer diagnostics for early state disease detection, which would greatly increase patient survival rates. Currently available analytical techniques for early stage cancer diagnosis do not meet the requirements for POC of a clinical setting. They are unable to provide the high demand of multiplexing, high-throughput, and ultrasensitive detection of biomarkers directly from low volume patient samples ("liquid biopsy"). To overcome these current technological bottle-necks, herein we present, for the first time, a bottom-up fabrication strategy to develop plasmonic nanoantenna-based sensors that utilize the unique localized surface plasmon resonance (LSPR) properties of chemically synthesized gold nanostructures, gold triangular nanoprisms (Au TNPs), gold nanorods (Au NRs), and gold spherical nanoparticles (Au SNPs). Our Au TNPs, NRs, and SNPs display refractive index unit (RIU) sensitivities of 318, 225, and 135 nm/RIU respectively. Based on the RIU results, we developed plasmonic nanoantenna-based multiplexing and high-throughput biosensors for the ultrasensitive assay of microRNAs. MicroRNAs are directly linked with cancer development, progression, and metastasis, thus they hold promise as next generation biomarkers for cancer diagnosis and prognosis. The developed biosensors are capable of assaying five different types of microRNAs at an attomolar detection limit. These sets of microRNAs include both oncogenic and tumor suppressor microRNAs. To demonstrate the efficiency as a POC cancer diagnostic tool, we analyzed the plasma of 20-bladder cancer patients without any sample processing steps. Importantly, our liquid biopsy-based biosensing approach is capable of differentiating healthy from early ("non-metastatic") and late ("metastatic") stage cancer with a p value <0.0001. Further, receiver operating characteristic analysis shows that our biosensing approach is highly specific, with an area under the curve of 1.0. Additionally, our plasmonic nanoantenna-based biosensors are regenerative, allowing multiple measurements using the same biosensors, which is essential in low- and middle-income countries. Taken together, our multiplexing and high-throughput biosensors have the unmatched potential to advance POC diagnostics and meet global needs for early stage detection of cancer and other diseases (e.g., infectious, autoimmune, and neurogenerative diseases).

Green synthesis of non-spherical gold nanoparticles using Solidago canadensis L. extract

In the present article, we reported the application of the extract of leaves from Solidago canadensis L. for the green synthesis of triangular and hexagonal gold nanoparticles (AuNPs). The phytochemical characterization, by reaction with HAuCl4 solutions, showed that the extract of Solidago canadensis L. contained the secondary metabolites that can act both as reducing and as stabilizing agents. For the synthesis of AuNPs, the effects of the HAuCl4 concentration (0.25–0.975 mM) and the reaction time (10–180 min) were investigated. The formation of AuNPs is confirmed by the color change from yellowish to purple-red. Photoluminescence measurements of Au nanocolloids showed a continuous emission band ranging from violet to red. UV–Vis characterization of AuNPs in the prepared nanocolloids showed surface plasmon resonance peaks at 530 and > 870 nm. TEM revealed that the AuNPs are in the range of 8–200 nm, they have spherical, triangular, and hexagonal forms of varying sizes. AFM and STM showed a non-ideal relief of large triangular and hexagonal gold nanoprisms. The EDX analysis, XRD and SAED patterns confirmed the face-center cubic structure of AuNPs.

Surfactant-Free Synthesis and Scalable Purification of Triangular Gold Nanoprisms with Low Non-Specific Cellular Uptake.

Gold nanoprisms possess remarkable optical properties that make them useful for medical biotechnology applications such as diagnosis and photothermal therapy. However, shape-selective synthesis of gold nanoprisms is not trivial and typically requires either toxic surfactants or time-consuming purification protocols, which can limit their applicability. Here, we show how triangular gold nanoprisms of different sizes can be purified by precipitation using the non-toxic glutathione ligand, thereby removing the need for toxic surfactants and bottleneck purification techniques. The protocol is amenable for direct scaling up as no instrumentation is required in the critical purification step. The new purification method provides a two-fold increased yield in gold nanoprisms compared to electrophoretic filtration, while providing nanoprisms of similar localized surface plasmon resonance wavelength. Crucially, the gold nanoprisms isolated using this methodology show fewer non-specific interactions with cells and lower cellular internalization, which paves the way for a higher selectivity in therapeutic applications.

Label-free, sensitive colorimetric detection of mercury(II) by target-disturbed in situ seeding growth of gold triangular nanoprisms

Gold nanomaterials have been used extensively in colorimetric detection of mercuric ions (Hg2+) due to their shape- and size-dependent, ultrastrong localized surface plasmon resonance (LSPR). Conventional detection was performed by first synthesizing the nanomaterials, and then applying them to signal-transducing reactions. We herein report a convenient method for detecting Hg2+ based on gold triangular nanoprisms (AuTNPs). During the seeding-growth process, Hg2+ added to the growth solution was co-reduced and deposited on the high-energy facets of the gold seeds, affecting the deposition patterns of the subsequently generated Au0 and ultimately leading to the formation of defective AuTNPs. Morphological changes were reflected by the in-plane dipole LSPR wavelength shift, which was proportionally related to the concentration of Hg2+. To improve the selectivity, the interference from Ag+ was eliminated by a stepwise preparation-selective precipitation approach. Under the optimized conditions, Hg2+ could be selectively detected with 20 min, with a detection limit of 0.12 nM. Finally, the method was successfully applied to detecting trace Hg2+ in fortified drinking, mineral and rain water samples, with recoveries ranging from 95.17% to 110.6%.

Ag/PVP/PAN nanocomposites with triangular nanoprisms of silver synthesized by UV-induced polymerization: Morphology manipulation and optical properties tuning

Solid nanocomposite films of “silver/polyvinylpyrrolidone/polyacrylonitrile” were synthesized for the first time by means of UV-induced polymerization. Structural characterization carried out by transmission electron microscopy revealed the presence of triangular silver nanoprisms with an edge length of ~40 nm and a thickness of ~15 nm in addition to spherical nanoparticles. The nanoparticles shape evolution process during synthesis and storage has been monitored in detail by UV-VIS-NIR spectroscopy and plasma resonance bands depending on the shape of the silver nanoparticles have been identified. Unlike spherical nanoparticles, which absorb light at 420–450 nm, the triangular nanoprisms demonstrate a clear absorption in the red range of the spectrum. The optical spectra of the composite films with incorporated silver nanoprisms manifest an intense in-plane dipole plasmon resonance band at 585–650 nm, as well as a weak out-of-plane quadrupole resonance band at 340 nm.

Plasmonic Effects on the Growth of Ag Nanocrystals in Solution.

The light-stimulated transformation of ensembles of spherical nanoparticles into anisotropic metal nanostructures mediated by localized surface plasmon resonance (LSPR) excitation is an elegant way of synthesizing triangular silver nanoprisms with extraordinary control over size and shape. Generally, the transformation occurs in oxidizing environments along a pathway that involves the oxidative etching of small preexisting Ag seeds, followed by plasmon-mediated reduction of the resulting Ag ions and Ag0 incorporation into the anisotropic nanocrystals. Here, we investigate pathways toward Ag nanoprisms from initially homogeneous AgNO3 solutions held under reducing conditions. Observations using in situ electron microscopy show that reducing environments and high Ag precursor concentrations in the presence of sodium citrate favor two alternative transformation routes of initial spherical nuclei into anisotropic nanoprisms: (i) the aggregation of spherical nanoparticles and plasmon-mediated conversion of small clusters into triangular prisms; (ii) shape fluctuations of individual small nanoparticles. Simulated field distributions confirm that the coupling of the LSPR excitation between closely spaced nanoparticles causes significant field enhancements near the local plasmonic hot spots, which facilitates accelerated Ag incorporation and thus supports the transformation into nanoprisms.

A novel liquid biopsy-based approach for highly specific cancer diagnostics: mitigating false responses in assaying patient plasma-derived circulating microRNAs through combined SERS and plasmon-enhanced fluorescence analyses.

Studies have shown that microRNAs, which are small noncoding RNAs, hold tremendous promise as next-generation circulating biomarkers for early cancer detection via liquid biopsies. A novel, solid-state nanoplasmonic sensor capable of assaying circulating microRNAs through a combined surface-enhanced Raman scattering (SERS) and plasmon-enhanced fluorescence (PEF) approach has been developed. Here, the unique localized surface plasmon resonance properties of chemically-synthesized gold triangular nanoprisms (Au TNPs) are utilized to create large SERS and PEF enhancements. With careful modification to the surface of Au TNPs, this sensing approach is capable of quantifying circulating microRNAs at femtogram/microliter concentrations. Uniquely, the multimodal analytical methods mitigate both false positive and false negative responses and demonstrate the high stability of our sensors within bodily fluids. As a proof of concept, microRNA-10b and microRNA-96 were directly assayed from the plasma of six bladder cancer patients. Results show potential for a highly specific liquid biopsy method that could be used in point-of-care clinical diagnostics to increase early cancer detection or any other diseases including SARS-CoV-2 in which RNAs can be used as biomarkers.

Dimers of triangular Ag nanoprisms: computer simulation of optical properties

In this paper the properties of a nanostructure comprised of a pair of distorted triangular Ag nanoparticles are studied using computer simulation. It is shown that upon excitation of localized surface plasmon resonance the electromagnetic field enhancement can reach the value | E | / | E0 | = 48.

Azimuthal vector beam exciting silver triangular nanoprisms for increasing the performance of surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy (SERS) with high-sensitivity performance is a very necessary detection technology. Here, we present a method for increasing the performance of SERS based on silver triangular nanoprism arrays (ATNAs) vertically excited via a focused azimuthal vector beam (AVB). The ATNA substrates with different structural parameters are prepared based on the traditional self-assembled and modified film lift-off technique. Based on a theoretical model established adopting the structural parameters of the ATNA substrates, theoretical simulation results show that AVB excitation can achieve greater electric-field enhancement than linearly polarized beam (LPB) excitation. Experimental result indicates that SERS sensitivity obtained via AVB excitation is 10−13 M (1 M = 1 mol/L) using rhodamine 6G (R6G) as the target analyte, which is 2 orders of magnitude lower than that of LPB excitation (10−11 M). Meanwhile, the uniformity and reproducibility of the ATNA substrates are examined using Raman mapping and batch-to-batch measurement, respectively, and the Raman enhancement factor is calculated to be ∼3.3×107. This method of vector light field excitation may be used to improve the SERS performance of the substrates in fields of ultra-sensitive Raman detection.

Reversible Tuning of the Plasmoelectric Effect in Noble Metal Nanostructures Through Manipulation of Organic Ligand Energy Levels.

Ligand-controlled tuning of localized surface plasmon resonance (LSPR) properties of noble metal nanostructures is fundamentally important for various optoelectronic applications such as photocatalysis, photovoltaics, and sensing. Here we demonstrate that the free carrier concentration of gold triangular nanoprisms (Au TNPs) can be tuned up to 12% upon functionalization of their surface with different para-substituted thiophenolate (X-Ph-S-) ligands. We achieve this unprecedentedly large optical response (plasmoelectric effect) in TNPs through the selective manipulation of electronic processes at the Au-thiolate interface. Interestingly, thiophenolates with electron withdrawing (donating) groups (X) produce λLSPR blue (red) shifts with broadening (narrowing) of localized surface plasmon resonance peak (λLSPR) line widths. Surprisingly, these experimental results are opposite to a straightforward application of the Drude model. Utilizing density functional theory calculations, we develop here a frontier molecular orbital approach of Au-thiophenolate interactions in the solid-state to delineate the observed spectral response. Importantly, all the spectroscopic properties are fully reversible by exchanging thiophenolates containing electron withdrawing groups with thiophenolates having electron donating groups, and vice versa. On the basis of the experimental data and calculations, we propose that the delocalization of electrons wave function controls the free carrier concentration of Au and thus the LSPR properties rather than simple electronic properties (inductive and/or resonance effects) of thiophenolates. This is further supported by the experimentally determined work functions, which are tunable over 1.9 eV in the X-Ph-S-passivated Au TNPs. We believe that our unexpected finding has great potential to guide in developing unique noble metal nanostructure-organic ligand hybrid nanoconjugates, which could allow us to bypass the complications associated with off-resonance LSPR activation of noble metal-doped semiconductor nanocrystals for various surface plasmon-driven applications.

Plasmonic Nanocavity Metasurface Based on Laser-Structured Silver Surface and Silver Nanoprisms for the Enhancement of Adenosine Nucleotide Photoluminescence

A reliable photoluminescence (PL) spectroscopy and imaging of biomolecules at room temperature is a challenging and important problem of biophysics, biochemistry, and molecular genetics. A unique effect of strong plasmonic enhancement of the PL by metal nanostructures is one of the most effective approaches for this purpose. The highest enhancement is provided by metal nanostructures with densely packed sharp tips, periodically arranged metal nanostructures, and plasmonic cavities. All of these features have been realized in the plasmonic cavity metasurface based on the silver (Ag) laser-induced periodic surface structure and Ag triangular nanoprisms studied in the present work. The strong plasmon-enhanced PL of 5′-deoxyadenosine monophosphate deposited on such metasurfaces has been revealed at room temperature. The observed enhancement of more than 1000-fold has been interpreted as a result of synergetic action of the generation of a high concentration of hot spots near the sharp edges of the laser-induc...

Colorimetric probe for Ni2+ based on shape transformation of triangular silver nanoprisms upon H2O2 etching

In this article, a highly sensitive and selective colorimetric method for the detection of Ni2+ ions is presented on the basis of hydrogen peroxide etching of triangular silver nanoprisms (AgNPrs). Triangular AgNPrs were synthesized by a modified seed-mediated growth method, and upon addition of Ni2+ ions these triangular AgNPrs showed a significant colorimetric change from blue to reddish brown, and eventually yellow to as a function of the Ni2+ ion concentration. Ni2+ ion do not act as a selective etchant to triangular AgNPrs, but instead serve as a catalyst for the generation of H2O2 in a citrate-capped triangular AgNPr colloidal solution. The oxidative etching with H2O2 formed in the colloidal solution sculptured the sharp corners/edges of the triangular AgNPrs to produce circular Ag nanodisk. Selectivity tests for Ni2+ ions by the triangular AgNPr probe were performed in the presence of other various cations and anions at the optimized conditions (pH 8, 15 °C, and 30 min of reaction time). The probe showed a high linearity between absorption ratio (A475/A750) and concentration in the range of 0 to 30 μM of Ni2+, with a limit of detection of 21.6 nM in aqueous solution. The color and UV–vis absorption spectrum of the triangular AgNPr probe indicated that it is quite stable for two weeks in ambient temperature and pH ranges of 4.0˜10.0. This triangular AgNPr probe was successfully employed for the detection of Ni2+ ions in spiked tap and pond water samples.

Electrochemical immunosensor based on MoS2 NFs/Au@AgPt YNCs as signal amplification label for sensitive detection of CEA

Medically, the dynamic change of carcinoembryonic antigen (CEA) concentration has been an important indicator for monitoring and diagnosing tumors. The sensitive and early detection of CEA plays a momentous role in the prevention and diagnosis of cancer and the evaluation of treatment efficiency. In this work, a sensitive sandwich-type electrochemical immunosensor was fabricated for the quantitative detection of CEA. The trimetallic yolk-shell Au@AgPt nanocubes (Au@AgPt YNCs) loaded on amino-functionalized MoS2 nanoflowers (MoS2 NFs/Au@AgPt YNCs) were used as the labels to conjugate with secondary antibodies. The Au@AgPt YNCs with internal space and permeable shell improved catalytic active surface area. The nanosheet-based MoS2 NFs with good catalytic activity were used as carriers to load Au@AgPt YNCs effectively. Due to the biphasic synergistic catalysis, MoS2 NFs/Au@AgPt YNCs catalyzed the reduction of H2O2 effectually to amplify the current signal. Besides, Au triangular nanoprisms (Au TNPs) were used as substrate material to increase the effective contact areas with the surface of electrode and accelerate the interface electron transfer. Under the optimal conditions, a broad linear range from 10 fg mL−1 to 100 ng mL−1 with low detection limit of 3.09 fg mL−1 (S/N = 3) for detecting CEA was obtained. Moreover, the detection results of the human serum samples were satisfactory, indicating the fabricated immunosensor had potential application values in the early clinical analysis.

Resonant light absorption and plasmon tunability of lateral triangular Au nanoprisms array

Optical characteristics and electric field distribution of triangular Au nanoprism in a unit and units array under polarized light irradiation were systematically studied by numerical simulation with finite difference time domain method. It is found that the plasmonic properties of the triangular nanoprism are dominated by the electric polarization rather than the wave propagation. The triangular nanoprism presents similar optical response with a strong dipole band under different wave propagations if the electric polarization vectors are parallel to the triangular cross section. The lateral triangular Au nanoprisms array possesses a large tunability of the plasmonic properties contributed from the combined influence of inter-particle distance, particles size, polarization angle and even environmental medium. From the plasmon band shift versus the refractive index, ultra-high local surface plasmon resonance sensitivity (509.96 nm/RIU, figure of merit=5.55) is reached at ∼850nm, making this array promising for biochemical sensing applications.

Photocurrent Enhancements of TiO2-Based Nanocomposites with Gold Nanostructures/Reduced Graphene Oxide on Nanobranched Substrate

In this work, we studied three-dimensional (3D) highly branched TiO2 nanorod (b-NR) arrays decorated with plasmonic Au triangular nanoprisms (TNPs) and reduced graphene oxide (rGO) sheets for photo...

Tip-Patched Nanoprisms from Formation of Ligand Islands.

We apply the concept of "island formation" established for planar substrates, where ligands laterally cluster as they adsorb, to preparing nanoparticles (NPs) with precisely sized surface patches. Using gold triangular nanoprisms and 2-naphthalenethiols (2-NAT) as a prototypical system, we show that the preferential adsorption of 2-NAT on the prism tips leads to formation of tip patches. The patches are rendered visible for direct transmission electron microscopy and atomic force microscopy imaging upon attaching polystyrene-b-poly(acrylic acid). Using this method, the shape of patchy prisms is varied from small lobed, big lobed, trefoil, T-shaped to a reuleaux triangle by increasing the 2-NAT-to-prism concentration ratio. This trend matches with predictions of island formation as elucidated by our self-consistent field theory modeling, from which we exclude Langmuir adsorption. The tip-patched prisms assemble into unexpected twisted dimers due to the patch-patch interactions. We expect the island formation as a generalizable strategy to make patchy NPs of various shapes for emergent assemblies and applications.

The Synthesis Conditions Influence on Silver Nanostructures Formation Under the Effect of Electromagnetic Radiation

In the present work the influence of the synthesis conditions, particularly the effect of used surrounding media on the silver nanostructures formation with various spatial configuration under the effect of the visible electromagnetic radiation has been studied. Silver nanoparticles were synthesized by photostimulated reduction of silver ions from the silver nitrate water solution in aqueous medium and in water yeast extract. The modification of the configuration of resulting nanoobjects was carried out by irradiating the testing samples with red, green, and blue photon flows under the similar conditions. For this task the unique devise with three isolated cells for irradiating silver colloids under the room temperature was developed. The parameters of obtained silver nanostructures were characterized by spectrophotometry and their optical properties have been researched. For the obtained silver colloids the polydispersity indexes were also determined. Besides, the changes in morphology were confirmed by transmission electron microscopy. The shift of the absorption spectra of the testing colloids to the long-wavelength spectral region and their splitting in some cases after irradiation by different wavelength has been showed. For nanoparticles synthesized in the distilled water after irradiating by red, green, and blue photon flows the additional absorption peaks appeared in the longer-wavelength spectral region. Moreover, the colloidal solutions changed the colors after the electromagnetic radiation effect. This indicates the change in nanostructures shapes. The formation of triangular nanoprisms under the influence of red and green photon flows and formation of decahedral nanostructures under the influence of blue light was found. It has been shown that this method can be successfully used to obtain the large silver nanostructures in aqueous solution of the known spatial and optical parameters. The absorption spectrum of the silver nanostructures obtained in water yeast extract shows one clearly expressed peak. But, after irradiation of this colloid with red and green light, the absorption curves are very close in shape to the initial one. Only under the blue light irradiation an additional weak absorption peak can be observed at the wavelength of 523 nm, which might indicates a partial change in the nanostructures shapes. It has been shown that the use of water yeast extract as a surrounding medium for the synthesis of nanoparticles with different spatial morphology minimizes the photoinduced effect of the shape transformation, which was observed in pure aqueous colloids. The effectiveness and the ability to use of different surrounding media for the silver nanoparticles synthesis by photostimulated reduction for obtaining nanostructures with the predetermined spatial parameters and to shift their absorption peaks to the visible and near infrared spectral region has been shown.Ref. 17, fig. 7, tabl. 1.

Wavelength-dependent nonlinear absorption and ultrafast dynamics process of Au triangular nanoprisms.

The nonlinear absorption and ultrafast dynamics process of Au triangular nanoprisms were investigated by using broadband (ranging from 550 to 700 nm) nanosecond Z-scan measurements and femtosecond time-resolved transient absorption spectrum, respectively. We found that Au triangular nanoprisms exhibit saturation absorption (SA) at low excitation intensities. With the increase of incident intensity, a switch from SA to reverse saturation absorption (RSA) occurs. Photo-dynamics process was found to be a double-exponential energy relaxation with a fast and a slow decay component. Interestingly, when probe wavelength is away from the plasma resonance peak, the decay of relaxation also shows the modulation due to the vibration mode of the coherent excitation.

Copper Sulfide Nanodisks and Nanoprisms for Photoacoustic Ovarian Tumor Imaging.

Transvaginal ultrasound is widely used for ovarian cancer screening but has a high false positive rate. Photoacoustic imaging provides additional optical contrast to supplement ultrasound and might be able to improve the accuracy of screening. Here, we report two copper sulfide (CuS) nanoparticles types (nanodisks and triangular nanoprisms) as the photoacoustic contrast agents for imaging ovarian cancer. Both CuS nanoprisms and nanodisks were ~6 nm thick and ~26 nm wide and were coated with poly(ethylene glycol) to make them colloidally stable in phosphate buffered saline (PBS) for at least 2 weeks. The CuS nanodisks and nanoprisms revealed strong localized surface plasmon resonances with peak maxima at 1145 nm and 1098 nm, respectively. Both nanoparticles types had strong and stable photoacoustic intensity with detection limits below 120 pM. The circular CuS nanodisk remained in the circulation of nude mice (n=4) and xenograft 2008 ovarian tumors (n=4) 17.9-fold and 1.8-fold more than the triangular nanoprisms, respectively. Finally, the photoacoustic intensity of the tumors from the mice (n=3) treated with CuS nanodisks was 3.0-fold higher than the baseline. The tumors treated with nanodisks had a characteristic peak at 920 nm in the spectrum to potentially differentiate the tumor from adjacent tissues.