Au Nanobipyramids Research Articles

Metal–Organic-Frameworks-Isolated Au Nanobipyramids as Synergetic Surface-Enhanced-Raman-Scattering Substrates

Recently, mushrooming efforts in surface-enhanced Raman scattering (SERS) have been devoted to applying semiconductor-like metal–organic frameworks (MOFs) as a charge-transfer center rather than only a porous filter or stabilizing layer in a metal@MOF core–shell substrate. However, the influence of an enhanced electric field on the charge-transfer process of MOFs has not been quantitatively explored, leading to an elusive understanding of the synergetic effect of metal@MOF core–shell substrates. Here we reveal a synergetic effect through SERS measurements of gold nanobipyramid (Au NBP) @zeolitic-imidazolate-framework (ZIF) core–shell nanostructures with varied thickness and composition of the shell. The synergetic effect was confirmed by the stronger enhancement factors of some NBP@ZIFs than that of pure NBP-785 with methyl orange (MO) and rhodamine 6G as the probe. Moreover, a reorientation phenomenon of MO discovered in the ZIF shell probably also accounted for the higher intensity, given that the probe orientation could impact the SERS intensity. Besides elucidating the charge transfer and synergy effect of the metal@MOF core–shell SERS substrates, this work could also provide new ideas to enrich the family of the shell-isolated nanoparticle-enhanced Raman spectroscopy substrates by employing porous materials as the shell.

Plasmonic Hot-Electron-Painted Au@Pt Nanoparticles as Efficient Electrocatalysts for Detection of H2O2.

Plasmon-driven catalysis of metal nanostructures has garnered wide interest. Here, a photogenerated plasmonic hot-electron painting strategy was reported to form Au@Pt composite nanoparticles (Au@Pt NPs) with high catalytic reactivity without using reducing agents. Au nanoparticles, including Au nanospheres (Au NSs), Au nanorods (Au NRs), and Au nanobipyramids (Au NBPs), generated hot electrons under localized surface plasmon resonance (LSPR) excitation, which made the platinum precursor reduced as a consequence that Pt(0) atoms were painted on the surface of Au NPs to form an asymmetric Pt shell outside the plasmonic Au core. Compared with bare Au NPs, Au@Pt NPs exhibited significantly enhanced electrocatalytic activity toward reduction of H2O2 due to the bimetallic synergistic effect and great dispersion of Au@Pt NP-modified indium tin oxide (Au@Pt NPs/ITO). It exhibited a linear detection of H2O2 in a wide concentration range from 0.5 to 1000 μM with a low detection limit of 0.11 μM (S/N = 3). Therefore, the plasmonic hot-electron-painted Au@Pt NPs represent a novel and simple method for the design of advanced noble asymmetric metal nanomaterials.

Shining at the Tips: Anisotropic Deposition of Pt Nanoparticles Boosting Hot Carrier Utilization for Plasmon-Driven Photocatalysis.

Bimetallic nanostructures are a promising candidate for plasmon-driven photocatalysis. However, knowledge on the generation and utilization of hot carriers in bimetallic nanostructures is still limited. In this work, we explored Pt position-dependent photocatalytic properties of bimetallic Au nanobipyramids (Au NBPs) with single-molecule fluorescence imaging. Compared with all-deposited core-shell nanostructures (aPt-Au NBPs), single-molecule imaging and simulation results show that the end-deposited bimetallic nanostructures (ePt-Au NBPs) can maintain a strong electromagnetic (EM) field and further promote the generation and transfer of energetic hot electrons for photocatalysis. Even though the Pt lattice is more stable than Au, the strong EM field at the sharp tips can boost lattice vibration, where enhanced spontaneous surface restructuring for active reaction site generation takes place. Significantly enhanced catalytic efficiency from ePt-Au NBPs is observed in contrast to that of Au NBPs and aPt-Au NBPs. These microscopic evidences offer valuable guidelines to design plasmon-based photocatalysts, particularly for bimetallic nanostructures.

A plasmonic ELISA for multi-colorimetric sensing of C-reactive protein by using shell dependent etching of Ag coated Au nanobipyramids

The etching of gold nanorods/nanobipyramid, or silver-coated nanorods/nanobipyramid inducing plasmon changes represents an efficient strategy to improve the performance of enzyme-linked immunosorbent assay (ELISA). However, the effect of shape on the sensitivity was negligible, especially the thickness of coated silver shell. Here, we propose a plasmonic ELISA for multi-colorimetric detection of CRP based on the etching of Ag-coated Au nanobipyramid (Au NBP@Ag). The effect of silver shell thickness on the sensitivity of plasmon peak shifting was investigated by experiments and DDA calculations. The relationship between the Ag shell thickness and the sensitivity of plasmon peak shifting was obtained. Our results reveal that the thickness of coated Ag shell acts as a key factor in the multi-color change of Au NBP@Ag etching. It is found that Au NBP@Ag with medium Ag shell thickness and rod-like shape has the higher sensitivity and is suitable for sensing. At the optimized most sensitive Ag shell, the detection limit of proposed plasmonic ELISA for CRP was determined to be 0.09 ng/mL with a spectrometer in the range from 0.09 ng/mL to 25 ng/mL. Importantly, the visual detection limit was 0.78 ng/mL, which allows the differential diagnosis with the naked eye. Compared with traditional ELISA with the monochromatic intensity variations, the multi-color ELISA proposed in this study has a large linear range and rich color variation for high-sensitivity and naked-eye semi-quantitative detection.

A polarization-resolved ECL strategy based on the surface plasmon coupling effect of orientational Au nanobipyramids patterned structures

Here, we developed a polarization-resolved surface plasmon coupling electrochemiluminescence (ECL) strategy based on orientational Au nanobipyramids (Au NBPs) patterned structures. As the surface plasmonic materials, the Au NBPs with large localized electromagnetic field enhancement were used to construct the different patterned structures through the droplet evaporation induced assembly. The distinct morphology of the horizontal and vertical Au NBPs patterned structures provided the different plasmonic properties reflecting on resonance peak positions and polarized absorbance. As a result, the variations of the polarized ECL emission of SnS2 QDs have been regulated by the Au NBPs patterned structures via the surface plasmon coupling progress. Because of the superior polarization-resolved ECL performances, the sensing system was used to analyze the miRNA-21 and miRNA-205 expression level in tumor tissues of triple negative breast cancer patients. The satisfactory results indicated this polarization-resolved sensing strategy possessed great potential for clinical analysis.

Optimized plasmonic performances and derivate applications of Au nanobipyramids

Gold nanobipyramids (AuBPs) with narrow size distribution and high monodispersity have driven intensive attention because they display more advantageous plasmonic properties than gold nanorods (AuNRs). Applications of AuBPs based on tunable plasmonic properties and enhanced electromagnetic fields are being widely investigated in recent years. In this article, we focused on the preparation of well-defined AuBPs using the seed-mediated method, the plasmonic properties, and the exploration of AuBP-supported derivatives. The synergetic contributions of penta-twinned and appropriate growth environment could produce high-purity AuBPs. Systematic comparisons of plasmonic properties between AuBPs and AuNRs are illustrated. In addition, the well-defined AuBPs can be used as a template to synthesize multi-metallic nanostructures. The development of the epitaxial growth based on the AuBPs and corresponding applications are introduced. This study will provide a guide for the fabrication of composite nanostructures and advance their plasmonic applications.

Site-Selective Deposition of Metal–Organic Frameworks on Gold Nanobipyramids for Surface-Enhanced Raman Scattering

Site-selective deposition of metal-organic frameworks (MOFs) on metal nanocrystals has remained challenging because of the difficult control of the nucleation and growth of MOFs. Herein we report on a facile wet-chemistry approach for the selective deposition of zeolitic imidazolate framework-8 (ZIF-8) on anisotropic Au nanobipyramids (NBPs) and nanorods. ZIF-8 is selectively deposited at the ends and waist and around the entire surface of the elongated Au nanocrystals. The NBP-based nanostructures with end-deposited ZIF-8 exhibit the best surface-enhanced Raman scattering (SERS) performance, implying that molecules can be concentrated by ZIF-8 at the hot spots. In addition, the SERS signal exhibits good selectivity for small molecules because of the molecular sieving effect of ZIF-8. This study opens up a promising route for constructing plasmonic nanostructures with site selectively deposited ZIF-8, which hold enormous potential for molecular sensing, optical switching, and plasmonic catalysis.

Coherent Interference Fringes of Two-Photon Photoluminescence in Individual Au Nanoparticles: The Critical Role of the Intermediate State.

The interaction between light and metal nanoparticles enables investigations of microscopic phenomena on nanometer length and ultrashort timescales, benefiting from strong confinement and enhancement of the optical field. However, the ultrafast dynamics of these nanoparticles are primarily investigated by multiphoton photoluminescence on picoseconds or photoemission on femtoseconds independently. Here, we presented two-photon photoluminescence (TPPL) measurements on individual Au nanobipyramids (AuNP) to reveal their ultrafast dynamics by double-pulse excitation on a global timescale ranging from subfemtosecond to tens of picoseconds. Two orders of magnitude photoluminescence enhancement, namely, coherent interference fringes, has been demonstrated. Power-dependent measurements uncovered the transform of the nonlinearity from 1 to 2 when the interpulse delay varied from tens of femtoseconds to tens of picoseconds. We proved that the real intermediate state plays a critical role in the observed phenomena, supported by numerical simulations with a three-state model. Our results provide insight into the role of intermediate states in the ultrafast dynamics of noble metal nanoparticles. The presence of the intermediate states in AuNP and the coherent control of state populations offer interesting perspectives for imaging, sensing, nanophotonics, and in particular, for preparing macroscopic superposition states at room temperature and low-power superresolution stimulated emission depletion microscopy.

A multicolor immunosensor for point-of-care testing NTRK1 gene fusion

The gene fusion of Neurotrophic tropomyosin receptor kinase (NTRK) promotes the formation of tumors and is closely related to multiple cancers. Therefore, the detection of NTRK gene fusion markers has been a research hotspot in recent years. However, up to now, there is still lack of a fast and effective detection method for point-of-care testing (POCT). Herein, a multicolor immunosensor for point-of-care testing NTRK1 gene fusion by the naked eye was fabricated. Au nanobipyramids (Au NBPs) can be etched by 3, 3′, 5, 5′-tetramethylbenzidine ions (TMB2+) to produce a variety of aspect ratios, and the blue shift of its longitudinal plasmon band showed different color changes. So, the Au NBPs were combined with horseradish peroxidase (HRP)-TMB immunoassay system for achieving qualitative and semi-quantitative detection of NTRK1 gene fusion marker within 20 min by the naked eyes. The results shows that the relevant linear range for detection of TRKA protein was 7.5 pg/mL to 240 pg/mL. The constructed immunosensor will be expected to be used to quickly detect NTRK gene fusion markers in remote areas with underdeveloped medical conditions.

Machine learning: Assisted multivariate detection and visual image matching to build broad-specificity immunosensor

The machine learning based on image matching is presented to construct a broad-specificity immunosensor for the detection of multiple ochratoxins. During the immunoreaction, ascorbic acid 2-phosphate (AAP) is catalyzed by the immobilized alkaline phosphatase to form ascorbic acid (AA), which can initiate the following reactions. First, silver ions (Ag+) can be reduced by AA to form silver coating on Au nanobipyramids (Au NBPs), changing the diameter of Au NBPs and the color of the solution. Second, AA can act as a sacrificial reagent to enhance the photoelectrochemical (PEC) current of CdS. Third, Ce4+ can be reduced to form Ce3+ and an intense fluorescence was discovered. Thus, a three-dimensional signal including colorimetry, photoelectrochemistry and fluorescence is built and then transformed to color signals for image matching. Results show that this method can predict multiple ochratoxins, suggesting that machine learning has great potential in combining multi-signal detection and multi-target detection by immunosensors.

Development of FL/MR dual-modal Au nanobipyramids for targeted cancer imaging and photothermal therapy

Multifunctional nanodrugs have emerged as an effective platform to integrate multiple imaging and therapeutic functions for tremendous biomedical applications. However, the development of a simple potent theranostic nanoplatform is still an intractable challenge. Herein, a novel theranostic nanoplatform was developed by coupling prepared Au nanobipyramids with Gd2O3, Au nanoclusters and denatured bovine serum albumin (AuNBP-Gd2O3/Au-dBSA) for FL/MR dual-modal imaging guided photothermal therapy. AS1411 aptamers were conjugated to enhance its targetability towards breast cancer. The AS1411-AuNBP-Gd2O3/Au-dBSA suspension could be readily heated above 40 °C at a low concentration (2 mg/L) and NIR density (1 W/cm2). The AS1411-AuNBP-Gd2O3/Au-dBSA revealed a fluorescence quantum yield of 4.2% and higher longitudinal relaxivity rate of 6.75 mM−1 s−1 compared to Gd-DTPA of 4.45 mM−1 s−1. As a result, the AS1411-AuNBP-Gd2O3/Au-dBSA functions as a multimodal nanoprobe of photothermal, fluorescence and MR imaging for specific tumor diagnosis and guidance of therapy, which was validated via in vitro and in vivo tests. Moreover, AS1411-AuNBP-Gd2O3/Au-dBSA nanoparticles indicated excellent photothermal anticancer effect more than 95% in both in vitro and in vivo tests. Besides, the low toxicity of AS1411-AuNBP-Gd2O3/Au-dBSA nanocomposites was further confirmed in vitro and in vivo. Thus, these results demonstrated the AS1411-AuNBP-Gd2O3/Au-dBSA nanocomposites as a rational design of multifunctional nanoplatform to enable multimodal imaging guided photothermal therapy.

Symmetry‐Broken Au–Cu Heterostructures and their Tandem Catalysis Process in Electrochemical CO2 Reduction

AbstractSymmetry‐breaking synthesis of colloidal nanocrystals with desired structures and properties has aroused widespread interest in various fields, but the lack of robust synthetic protocols and the complex growth kinetics limit their practical applications. Herein, a general strategy is developed to synthesize the Au–Cu Janus nanocrystals (JNCs) through the site‐selective growth of Cu nanodomains on Au nanocrystals, which is directed by the substantial lattice mismatch between them, with the assistance of judicious manipulation of the growth kinetics. This strategy can work on Au nanocrystals with different architectures for the achievement of diverse asymmetric Au–Cu hybrid nanostructures. Of particular note, the obtained Au nanobipyramids (Au NBPs)‐based JNCs facilitate the conversion of CO2 to C2 hydrocarbon production during electrocatalysis, with the Faradaic efficiency and maximum partial current density being 4.1‐fold and 6.4‐fold higher than those of their monometallic Cu counterparts, respectively. The excellent electrocatalytic performances benefit from the special design of the Au–Cu Janus architectures and their tandem catalysis mechanism as well as the high‐index facets on Au nanocrystals. This research provides a new approach to synthesize various hybrid Janus nanostructures, facilitating the study of structure‐function relationship in the catalytic process and the rational design of efficient heterogeneous electrocatalysts.

Yolk-Shelled Gold@Cuprous Oxide Nanostructures with Hot Carriers Boosting Photocatalytic Performance.

Plasmonic Au nanoparticles (NPs) have been commonly used to enhance the photocatalytic activity of Cu2O. Till now, core-shell Au NP@Cu2O composites have been reported in previous studies. Yet, these Au@Cu2O composites only exhibit visible light response. Other special Au nanostructures, such as Au nanorods (NRs) or Au nanobipyramids (NBPs), which possess near-infrared light absorption, were rarely used to endow the near-infrared light response for Cu2O. In this work, for the first time, we used Au NPs, Au NRs, and Au NBPs and employed a handy and universal method to synthesize a series of yolk-shelled Au@Cu2O composites. The results showed that the yolk-shelled Au@Cu2O composites had much higher photocatalytic activity than their solid-shelled ones and pure Cu2O. More importantly, yolk-shelled Au NR@Cu2O and Au NBP@Cu2O composites indeed presented excellent near-infrared light-driven photocatalytic activity, which were impossible for Au NP@Cu2O and pure Cu2O. This outstanding performance for yolk-shelled Au NR@Cu2O and Au NBP@Cu2O could be attributed to the transfer of abundant hot electrons from Au NRs or Au NBPs to Cu2O, and the timely utilization of hot holes on Au through the rich pore channels on their yolk-shelled structure. Furthermore, yolk-shelled Au@Cu2O also showed better stability than pure Cu2O, owing to the migration of the oxidizing holes from Cu2O to Au driven by the built-in electric field. This work may give a guide to fabricate controllable and effective photocatalysts based on plasmonic metals and semiconductors with full solar light-driven photocatalytic activities in the future.

"Add on" Dual-Modal Optical Immunoassay by Plasmonic Metal NP-Semiconductor Composites.

Staphylococcus aureus enterotoxins (SEs, involving SEA, SEB, SEC, SED, and SEE) are considered to be the common toxins causing food poisoning and are not allowed to be detected in food. Accurate and anti-interfering SE detection in a complex food matrix is urgently required for food safety. Dual-modal optical sensors are able to avoid mutual interference of optical signals and possess the advantages of high accuracy and sensitivity. Herein, Au nanobipyramids (Au NBPs) and persistent luminescence ZnGeGaO:Cr,Er,Yb nanoparticle (ZGGO NP) nanocomposites are fabricated using the SEC antibody/antigen as templates, which display enhanced persistent luminescence (PL) and surface-enhanced Raman scattering (SERS) strength. The enhanced PL of Au NBP-ZGGO NP nanocomposites is ascribed to plasmon-enhanced radiative transitions. It is first found that ZGGO NPs display unique upconversion fluorescence, which can be absorbed by Au NBPs and that they largely excite the intensive electromagnetic field for SERS enhancement. Dual-model optical immunoassay achieved anti-interfering and specific SEC detection with a limit of detection of 7.5 pg/mL for the PL signal and 8.9 pg/mL for the SERS signal in the range of 10 pg/mL-100 ng/mL. Depending on the plasmon-enhanced PL mechanism and upconversion fluorescence-enhanced SERS principle, plasmonic NP-semiconductor composites show potential prospects in the establishment of multimodal optical biosensors for the quantitative and accurate evaluation of analytes in a complex food matrix.

Au nanobipyramids with Pt decoration enveloped in TiO2 nanoboxes for photocatalytic reactions.

Noble metal nanocrystals and core–shell nanocomposites have attracted particular interest due to their unique optical properties originating from surface plasmon resonance (SPR) and wide applications related to the SPR effect. In this work, we designed and fabricated a new Au–Pt@TiO2 nanocomposite, in which Au nanobipyramids (AuNBPs) decorated with platinum (Pt) clusters were enveloped in mesoporous TiO2 nanoboxes with nanocavities. AuNBPs provide strong SPR absorption and localized field enhancement restricted to the cavities of TiO2 nanoboxes. The Pt nanoclusters decorated on the surface of AuNBPs can effectively modulate the charge movement and energy transfer in the photocatalytic process. The enhanced electric field provides a local thermal effect for the photocatalytic reaction and promotes the injection process of hot electrons which facilitates carrier separation. The nanoboxes with nanocavities can effectively manage the usage of localized energy and provide space for reaction. Under the cooperative effects, the photocatalytic performance was remarkably improved along with durability and stability. For the AuNBP–Pt@TiO2 nanoboxes, the rhodamine-B degradation efficiency was ∼6.5 times that of AuNBP@TiO2 nanoboxes. The mechanism of the photocatalysis process was proposed based on experimental results and simulations. Benefiting from the excellent structure and properties, the obtained nanostructure is a promising candidate in the fields of pollutant degradation and chemical reaction catalysis.

Gold nanobipyramids integrated ultrasensitive optical and electrochemical biosensor for Aflatoxin B1 detection

This work reports the development of an electrical and optical biosensing for label-free detection of Aflatoxin B1 (AFB1) using gold (Au) nanobipyramids (NBPs). AuNBPs were synthesized through a two-step seed-mediated growth process followed by an exchange of capping agent from surfactant to lipoic acid. Pure and monodispersed AuNBPs of 70 nm base length were obtained and deposited on indium tin oxide (ITO)-coated glass substrate modified with self-assembled (3-Aminopropyl) triethoxysilane (APTES) film. The characterization of the obtained surfaces using spectroscopy, microscopy and diffractometry confirms the formation of AuNBPs, the conjugation to ITO electrode substrate and the immobilization of anti-AFB1 antibodies. AuNBPs modified ITO substrates were used for both electrochemical and Surface Plasmon Resonance biosensing studies. Localized Surface Plasmon Resonance (LSPR) local field enhancement was demonstrated. SPR based AFB1 detection was found to be linear in the 0.1–500 nM range with a limit of detection of 0.4 nM, whereas, impedimetric AFB1 detection was shown to be linear in the 0.1–25 nM range with a limit of detection of 0.1 nM. The practical utility of the impedimetric sensor was tested in spiked maize samples and 95–100% recovery percentage was found together with low relative standard deviation, proof of the robustness of this AFB1 sensor.

Hybrid Hydrogels for Synergistic Periodontal Antibacterial Treatment with Sustained Drug Release and NIR-Responsive Photothermal Effect.

BackgroundPeriodontal pathogenic bacteria promote the destruction of periodontal tissues and cause loosening and loss of teeth in adults. However, complete removal of periodontal pathogenic bacteria, at both the bottom of the periodontal pocket and the root bifurcation area, remains challenging. In this work, we explored a synergistic antibiotic and photothermal treatment, which is considered an alternative strategy for highly efficient periodontal antibacterial therapy.MethodsMesoporous silica (MSNs) on the surface of Au nanobipyramids (Au NBPs) were designed to achieve the sustained release of the drug and photothermal antibacterials. The mesoporous silica-coated Au NBPs (Au NBPs@SiO2) were mixed with gelatin methacrylate (GelMA-Au NBPs@SiO2). Au NBPs@SiO2 and GelMA-Au NBPs@SiO2 hybrid hydrogels were characterized, and the drug content and photothermal properties in terms of the release profile, bacterial inhibition, and cell growth were investigated.ResultsThe GelMA-Au NBPs@SiO2 hybrid hydrogels showed controllable minocycline delivery, and the drug release rates increased under 808 nm near-infrared (NIR) light irradiation. The hydrogels also exhibited excellent antibacterial properties, and the antibacterial efficacy of the antibiotic and photothermal treatment was as high as 90% and 66.7% against Porphyromonas gingivalis (P. gingivalis), respectively. Moreover, regardless of NIR irradiation, cell viability was over 80% and the concentration of Au NBPs@SiO2 in the hybrid hydrogels was as high as 100 µg/mL.ConclusionWe designed a new near-infrared light (NIR)-activated hybrid hydrogel that offers both sustained release of antibacterial drugs and photothermal treatment. Such sustained release pattern yields the potential to rapidly eliminate periodontal pathogens in the periodontal pocket, and the photothermal treatment maintains low bacterial retention after the drug treatment.

Detection of ferrous ion by etching-based multi-colorimetric sensing of gold nanobipyramids

Colorimetric sensing methods based on non-spherically symmetric gold (Au) nanoparticles have become a powerful tool in the field of biomedical detection due to their intriguing plasmonic properties. In this study, Au nanobipyramids (Au NBPs) were used as colorimetric sensing probes to detect ferrous ions (Fe2+) through tip etching. The quick etching of Au NBPs along the longitudinal direction by superoxide radicals generated by the reaction of Fe2+ and H2O2 led local surface plasmon resonance (LSPR) to blue shift and produced vivid color change that could be used for visual inspection. Under the optimal reaction conditions, the peak shift of the Au NBPs and the logarithm of the concentrations of Fe2+ had a linear relationship in the range of 10 nM to 10 μM, with a very low detection limit of 1.29 nM. During the etching process, a different end shape of the Au nanoparticles results in a different process for the morphology transition, which makes the degree of spectral change and detection sensitivity significantly different. In the presence of trace amounts of Fe2+ (<1000 nM), the detection sensitivity of Au NBPs with sharp ends which rely on aspect ratio and truncation is nine times higher than that of gold nanorods with round ends which only rely on aspect ratio. Although the color change of larger-sized Au NBPs was not clear during detection, the LSPR peak shift was more severe. Therefore, the system provides different modes for detecting Fe2+ according to Au NBPs with different sizes and characteristics.

Au decahedra with High yield for the improved synthesis of Au nanobipyramids

Penta-fold twinned (PFT) Au nanobipyramids (AuNBs) have outstanding optical properties compared with other PFT Au nanocrystals. The reproducible preparation of the seeds for synthesizing high quality of AuNBs still remains a challenging problem. In this work, we achieved the high-yield and reproducible preparation of small sized Au nanodecahedron (AuND) nanocrystals, and further used them as seeds in a controlled manner to synthesize monodispersed AuNBs and other shaped nanocrystals. The prepared AuNBs have better photothermal conversion performance than other shaped Au nanocrystals. This approach can promote the AuNB-based study and applications in optics, catalysis and therapy.

Detection of Chlortetracycline Hydrochloride in Milk with a Solid SERS Substrate Based on Self-assembled Gold Nanobipyramids.

This paper described how a high-yield, monodisperse Au nanobipyramids (Au NBs) sol was prepared by a seed-mediated method, and gold nanoparticles were assembled on the surface of a silicon wafer by self-assembly technology to obtain a solid SERS substrate. Scanning electron microscopy (SEM) showed that the average length of Au NBs was 34.31 nm, and the analysis enhancement factor (AEF) was approximately 7.3 × 105 with rhodamine 6G (R6G) used as a probe. SERS detection of chlortetracycline hydrochloride (CCH) in milk was performed utilizing the prepared Au NBs substrate, and the limit of detection was 0.01 mg/mL. In the range of 0.01 - 1 mg/mL, the mass concentration of CCH and the SERS signal intensity satisfied the linear relationship y = 258.467x + 150.501; the value of the correlation coefficient was 0.9785. In addition, the recovery of spiked samples fluctuated between 96.80 to 111.38%. These results proved that the method is simple and fast, and it is promising to be applied to the field detection of antibiotics in milk.