Ag Nanorod Arrays Research Articles

Bimetallic nanoplasmonic gap-mode SERS substrate for lung normal and cancer-derived exosomes detection

Abstract Surface-enhanced Raman scattering (SERS) has received significant attention for analytical and diagnostic applications in cancer research due to its potency for detecting low abundance of biomarkers at high sensitivity. Cell-secreted exosomes play an important role is not only physiological but also pathological conditions by carrying various key biomolecules such as proteins, lipids, and nucleic acid of their cells of origin and are involved in intercellular transport. They are thus possible biomarkers for many diseases, including cancer. Herein, we fabricated a strong plasmonic gap-mode SERS substrate using Ag nanocubes (NCs) on an Au nanorod (NR) array substrate in order to investigate exosomes. A strong plasmonic cavity effect was obtained from individual Ag NCs assembled on the hot-ring diameter (HR) area on the NR surface. The SERS signal of a low concentration of Rhodamine 6 G upon NCs on NR substrate was amplified. The enhancement factor of the optimized Ag NCs on Ag NR array substrate reached 9.11 × 10 8 . The developed SERS substrate was applied to investigate exosomes derived from lung normal (from NL-20, BEAS-2B, and L929) and cancer (from PC-9, H1975, and HCC827) cell lines with limited sample input. A significant difference was found in the SERS signals from proteins, lipids, and nucleic acid not only between lung normal and cancer exosomes but also between fibroblast and epithelium exosomes. For the lung cancer exosomes, a strong protein SERS signal was observed under time-dependent SERS analysis, whereas for the normal exosomes, the SERS signal mostly corresponded to proteins, lipids, and nucleic acid. The attachment of Ag NCs on the HR area of Au NRs is presumably key for enhancing the electromagnetic effect and thus the SERS signal of exosomes.

Multi-angle ZnO microstructures grown on Ag nanorods array for plasmon-enhanced near-UV-blue light emitter

Metal enhanced ultraviolet light emission has been explored in ZnO/Ag hybrid structures prepared by hydrothermal growth of multi-angled ZnO nanorods on slanted Ag nanorods array fabricated by the thermal evaporation technique. Slanted Ag nanorods are realized to be the stacking of non-spherical Ag nanoparticles, resulting in asymmetric surface plasmon resonance spectra. The surface roughness of Ag nanorod array films significantly influences the growth mechanism of ZnO nanorods, leading to the formation of multi-angled ZnO microflowers. ZnO/Ag hybrid structures facilitate the interfacial charge transfer from Ag to ZnO with the realization of negative shift in binding energy of Ag 3d orbitals by ∼0.8 eV. These high quality ZnO nanorods in ZnO/Ag hybrid nanostructures exhibit strong ultraviolet emission in the 383–396 nm region without broad deep level emission, which can be explained by a suitable band diagram. The metal enhanced photoluminescence is witnessed mainly due to interfacial charge transfer with its dependence on surface roughness of bottom layer Ag nanorods, number density of ZnO nanorods and diversity in the interfacial area between Ag and ZnO nanorods. The existence of strong ultraviolet light with minor blue light emission and appearance of CIE shade in strong violet-blue region by ZnO/Ag hybrid structures depict exciting possibilities towards near UV-blue light emitting devices.

Localized surface plasmon resonance properties of Ag nanorod arrays on graphene-coated Au substrate

Localized surface plasmon resonance (LSPR) on silver nanorod (SNR) arrays deposited on a graphene-coated Au substrate is investigated by the discrete dipole approximation (DDA) method. The resonance peaks in the extinction spectra of the SNR/graphene/Au structure show significantly different profiles as SNR height, and refractive index of the surrounding medium are varied gradually. Numerical simulation reveals that the shifts in the resonance peaks arise from hybridization of multiple plasmon modes as a result of coupling between the SNR arrays and graphene-coated Au substrate. Moreover, the LSPR modes blue-shifts from 800 nm to 700 nm when the thickness of the graphene layer in the metal nanoparticle (NP) - graphene hybrid nanostructure increases from 1 nm to 5 nm, which attribute to charge transfer between the graphene layer and SNR arrays. The results provide insights into metal NP-graphene hybrid nanostructures which have potential applications in plasmonics.

Enhancement of Surface Raman Spectroscopy Performance by Silver Nanoparticles on Resin Nanorods Arrays from Anodic Aluminum Oxide Template

The surface enhanced Raman spectroscopy (SERS) substrates were fabricated by many methods including the AAO molding and high-cost nanolithography-etching-deposition process. In this article, we have demonstrated the SERS substrate fabricated with silver nanoparticles (Ag-NP) electroless deposition on highly ordered dense hexagonal arrays of UV curable resin nanorods (R-NR) arrays which was reproducible from a precisely controlled anodic aluminum oxide (AAO) template. This method could improve the non-flatness induced defect problem in the conventional nanoimprinting technique and form high-quality duplications of nanometer templates. The periodic hierarchical double-structured nanorods arrays with small nanorods (diameter about 30∼40 nm) in large nanorods (diameter about 100∼110 nm) were obtained by the UV curable resins molding from the AAO template. Two kinds of electroless deposition i.e. self-assembly and ultrasonic vibration methods were performed for Ag-NP formation on R-NR. The enhancement factors of SERS using 10−5 M methylene blue (MB) as probing molecules were 104∼106 for the self-assembled method and 105∼107 for the ultrasonic vibration one, respectively. This was because the ultrasonic vibration deposition could result in Ag nanorods arrays with higher regularity and contact area than the self-assembly one.

Highly Sensitive Detection of Melamine Using a One-Step Sample Treatment Combined with a Portable Ag Nanostructure Array SERS Sensor.

There is an urgent need for rapid and reliable methods able to detect melamine in animal feed. In this study, a quick, simple, and sensitive method for the determination of melamine content in animal feed was developed using surface-enhanced Raman spectroscopy on fabricated Ag nanorod (AgNR) array substrates with a one-step sample extraction procedure. The AgNR array substrates washed by HNO3 solvent (10−7 M) and methanol and showed the good stability within 6 months. The Raman shift at △ν = 682 cm−1 was used as the characteristic melamine peak in the calculations. Sufficient linearity was obtained in the 2–200 μg·g−1 range (R2 = 0.926). The limits of detection and quantification were 0.9 and 2 μg·g−1, respectively. The recovery rates were 89.7–93.3%, with coefficients of variation below 2.02%. The method showed good accuracy compared with the tradition GC-MS analysis. This new protocol only need 2 min to fininsh the detection which could be developed for rapid onsite screening of melamine contamination in quality control and market surveillance applications.

Metal enhanced fluorescence improved protein and DNA detection by zigzag Ag nanorod arrays

As metal nano-arrays show great potential on metal enhanced fluorescence (MEF) than random nanostructures, MEF of Ag zigzag nanorod (ZNR) arrays made by oblique angle deposition has been studied for biomolecule-protein interaction and DNA hybridization. By changing the folding number and the deposition substrate temperature, a 14-fold enhancement factor (EF) is obtained for biotin-neutravidin detection. The optimal folding number is decided as Z=7, owing to the high scattering intensity of Ag ZNRs. The substrate temperature T=25°C and 0°C slightly alters the morphology of Ag ZNRs but has no big difference in EF. Further, Ag ZNRs deposited on a layer of Ag film have been introduced to the DNA hybridization and a significant signal enhancement has been observed through the fluorescence microscope. Through a detailed quantitative EF analysis, which excludes the enhancing effect from the increased surface area of ZNRs and only considers the contribution of MEF, an EF of 28 is achieved for the hybridization of two single-stranded oligonucleotides with 33 bases. Furthermore, a limit of detection is determined as 0.01pM. We believe that the Ag ZNR arrays can serve as a universal and sensitive bio-detection platform.

Highly Sensitive and Selective Surface-Enhanced Raman Spectroscopy Label-free Detection of 3,3',4,4'-Tetrachlorobiphenyl Using DNA Aptamer-Modified Ag-Nanorod Arrays.

An improved label-free approach for highly sensitive and selective detection of 3,3',4,4'-tetrachlorobiphenyl (PCB-77), a type of polychlorinated biphenyl, via surface-enhanced Raman spectroscopy (SERS) using DNA aptamer-modified Ag-nanorod arrays as the effective substrate is reported. The devised system consists of Ag-nanorod (Ag-NR) arrays with the PCB-77 binding aptamers anchored covalently to the Ag surfaces through a thiol linker. The aptamers are made of single-stranded DNA (ssDNA) oligomers, with one end standing on the Ag surface, and upon conjugation with PCB-77, the ssDNA molecules can change their conformation to hairpin loops, so that the Raman intensity of guanines at the other end of the DNA strand increases accordingly. As such, the intensity ratio I(656 cm(-1))/I(733 cm(-1)) increases concomitantly with the increase of the concentration of PCB-77, making the quantitative evaluation of trace amounts of PCB-77 attainable. Moreover, it is found that the DNA aptamer-based Ag-NR arrays can be more responsive with a lower and optimal density of the DNA molecules modified on the substrate surface, and the best sensitivity for detection of PCB-77 can be achieved with the lower detection limit approaching 3.3 × 10(-8) M. This work therefore demonstrates that the design of aptamer-modified Ag-NRs can be used as a practically promising SERS substrate for label-free trace detection of persistent organic pollutants (POPs) in the environment.

Z-shape nanostructured array deposited by substrate cooling method

The substrate cooling method was used in glancing angle deposition to grow a slanted silver nanorod array (NRA). Liquid nitrogen was allowed to flow under the substrate during deposition, and we compared the morphologies of Ag NRAs deposited with and without cooling. The cooling reduced the average width of the nanorods. A Z-shaped nanostructure array composed of three sections of silver NRAs was then deposited under the same cooling conditions. The average tilt angle of the nanorods from the surface normal was varied from the bottom section to the top section with the nanorods of the top section made to lie almost parallel to the substrate. Under normal illumination, the rods in the top section exhibit distinct longitudinal and transverse plasmon modes that cause strong polarization-dependent transmittance and reflectance.

An advance Towards the Synthesis of Ag Nanorod Arrays with Controlled Surface Roughness for SERS Substrates

An innovative approach to produce silver nanorod (NRs) arrays with controlled morphological parameters and surface roughness is presented. The Ag NRs were obtained using a three-stage fabrication process based on the electron beam exposure of a metal-polymer nanocomposite resist on a transparent substrate and development, a post bake and then a series of non-electrochemical metallization steps. After each step the evolution of the Ag NRs was characterized by scanning electron microscopy (SEM) for morphology and optical transmittance (T) measurements for Localized Surface Plasmon Resonance (LSPR). The transmittance measurements were interpreted using models based on the Finite Element Method (FEM).

An ultrasensitive SERS sensor for simultaneous detection of multiple cancer-related miRNAs.

Simultaneous detection of multiple trace cancer associated serum miRNA biomarkers is considered as a feasible method for early cancer screening and diagnosis. In the present work, an ultrasensitive SERS sensor was prepared based on an Ag nanorod array SERS substrate by assembling special hairpin-shaped molecular beacons (MBs) for the detection of multiple lung cancer-related miRNA biomarkers. The portable SERS sensor exhibits excellent performance for the qualitative and quantitative detection of miRNAs, with advantages of ultra-sensitivity, good specificity, uniformity, reproducibility and stability, as well as remarkable reusability. By monitoring the SERS signal quenching of the MBs in the presence of target miRNA biomarkers, three lung cancer related-miRNAs (miRNA-21, miRNA-486, and miRNA-375) in buffer and human serum were simultaneously assayed using the SERS sensor array, and the limits of detection of the three miRNAs in human serum are 393 aM, 176 aM, and 144 aM, respectively. The reliable results demonstrate that the proposed SERS sensor array can be a promising candidate with great potential for the screening and clinical diagnosis of cancer in the early stage.

Silicon nanowire arrays coated with electroless Ag for increased surface-enhanced Raman scattering

The ordered Ag nanorod (AgNR) arrays are fabricated through a simple electroless deposition technique using the isolated Si nanowire (SiNW) arrays as the Ag-grown scaffold. The AgNR arrays have the single-crystallized structure and the plasmonic crystal feature. It is found that the formation of the AgNR arrays is strongly dependent on the filling ratio of SiNWs. A mechanism is proposed based on the selective nucleation and the synergistic growth of Ag nanoparticles on the top of the SiNWs. Moreover, the special AgNR arrays grown on the substrate of SiNWs exhibit a detection sensitivity of 10−15M for rhodamine 6G molecules, which have the potential application to the highly sensitive surface-enhanced Raman scattering sensors.

Mechanical Strain Induced Tunable Anisotropic Wetting on Buckled PDMS Silver Nanorods Arrays.

We report the fabrication of anisotropic superhydrophobic surface with dual-scale roughness by the deposition of silver nanorods arrays on prestretched poly(dimethylsiloxane) (PDMS) using oblique angle deposition and subsequent release of strain after the deposition, which resulted in the formation of microbuckles/wrinkles. The amplitude and periodicity of the wrinkles were tuned by varying the prestretching mechanical strain (ε) applied to the PDMS film from 0 to 30% prior to Ag nanorods deposition. The peaks and valleys in the surface topography of Ag nanorods arrays covered PDMS films lead to anisotropic wetting by water droplet. The droplet is free to move along the direction parallel to the wrinkles, but the droplet moving perpendicular to the wrinkles confront energy barrier leading to wetting anisotropy. The anisotropic wettability was tuned from 22 to 37° for 10-30% prestretched PDMS film. The dual scale roughness (nanorods on micro wrinkles) was found to be responsible for the superhydrophobicity (contact angle ∼155°) of the sample prepared for 30% prestretched PDMS film in perpendicular direction. The wetting behavior of the Ag nanorods PDMS film surface was reversibly tuned by applying the mechanical strain, which induces the change in the microscale roughness determined by amplitude (A) and periodicity (λ) of the buckles. Most interestingly, the water droplet also displayed the anisotropy in the roll-off angle. The effect of different A and λ on anisotropic wettability of Ag nanorods arrays/PDMS film was also demonstrated by lattice Boltzmann (LB) modeling. These findings may produce a promising way of controlling the direction of liquid flow such as in microfluidic devices and transportation of the microliter water droplets in a preset direction.

Power-Dependent Luminescence of CdSe/ZnS Nanocrystal Assembled Layer-by-Layer on a Silver Nanorod Array**Supported by the National Natural Science Foundation of China under Grant Nos 11174229, 11374236 and 11204221, and the National Basic Research Program of China under Grant No 2011CB922201.

We investigate the power-dependent luminescence of CdSe/ZnS semiconductor quantum dots closely packed layer-by-layer in the proximity of a silver nanorod array cavity. It is found that the emission peak shifts significantly to the longer wavelengths as the excitation power increases, especially when the longitudinal surface plasmon resonance of the Ag nanorod array cavity is adjusted to be close to the emission wavelength. The equivalent gain varies with the coating layer of CdSe/ZnS semiconductor quantum dots and the excitation power is also studied to explain this interesting spectrum-shifting effect. These findings could find applications in the dynamic information processing of active plasmonic and photonic nanodevices.

Ag Nanorod Arrays for SERS: Aspects of Spectral Reproducibility, Surface Contamination, and Spectral Sensitivity

Ag nanorod arrays prepared by oblique angle vapor deposition (OAD) represent regular, large area substrates for surface‐enhanced Raman scattering (SERS) spectroscopy. We studied uniformity and spectral reproducibility of silver OAD‐fabricated substrates (AgOADs) by spectral mapping of methylene blue. The results demonstrate good reproducibility apart from occasional “hot‐spot” sites where the intensity is higher. The number of “hot‐spots” represents 2%–6% of SERS‐active sites of mapping substrate area. We were able to obtain good SERS spectra of testing amino acid tryptophan at 1 × 10−5 M concentration and three different free‐base porphyrins down to ∼10−7 M concentration. We found out that keeping the AgOADs in a vacuum chamber overnight prevents the surface from binding any contaminants from the ambient atmosphere, without significant reduction in the SERS enhancement. Such substrates provide stable SERS enhancement even when stored for 1 year after preparation.

The Study of Surface Plasmon Enhanced Emission of ZnO Nanorods on Plasmonic Ag Nanorods Array

Ag islands and nanorods (NRs) array were fabricated through glancing angle deposition (GLAD) method at an angle of 85°C by using thermal evaporation technique. Subsequently, ZnO NRs were grown along the side of Ag NRs arrays through hydrothermal reaction. The crystal structure of ZnO/Ag hybrid structure was studied by Glancing Incident X-Ray Diffraction (GIXRD). The surface morphologies of Ag NRs arrays and ZnO NRs were studied through AFM and SEM techniques. The presence of different vibrational energy modes of ZnO structure was studied through confocal Raman spectrometer. The surface plasmon enhanced fluorescence of ZnO NRs was probed through fluorescence spectrophotometer. The presence of strong UV emission and the absence of intense visible emission of ZnO NRs are due to the existence of fewer crystal defects which could make the hybrid structure precious for UV LEDs.

Strong light coupling effect for a glancing-deposited silver nanorod array in the Kretschmann configuration.

In this work, three slanted silver nanorod arrays (NRAs) with different thicknesses are fabricated using the glancing angle deposition method. Each silver NRA in the Kretschmann configuration is arranged to form a prism/NRA/air system. Attenuated total reflection occurs over the visible wavelengths and wide incident angles of both s- and p-polarization states. The extinctance is inversely proportional to the thickness of the Ag NRA. The thinnest NRA, with a thickness of 169 nm, exhibits strong extinctance of more than 80% over the visible wavelengths. The associated forward scatterings from the three NRAs are measured and compared under illumination with a laser beam with a wavelength of 632.8 nm.

Surface plasmon-enhanced nanoporous GaN-based green light-emitting diodes with Al2O3 passivation layer.

A surface plasmon (SP)-enhanced nanoporous GaN-based green LED based on top-down processing technology has been successfully fabricated. This SP-enhanced LED consists of nanopores passing through the multiple quantum wells (MQWs) region, with Ag nanorod array filled in the nanopores for SP-MQWs coupling and thin Al(2)O(3) passivation layer for electrical protection. Compared with nanoporous LED without Ag nanorods, the electroluminescence (EL) peak intensity for the SP-enhanced LED was greatly enhanced by 380% and 220% at an injection current density of 1 and 20A/cm(2), respectively. Our results show that the increased EL intensity is mainly attributed to the improved internal quantum efficiency of LED due to the SP coupling between Ag nanorods and MQWs.

Defect-induced color-tunable monolithic GaN-based light-emitting diodes

We have demonstrated defect-induced color-tunable monolithic GaN-based vertical light-emitting diodes (VLEDs). With Ag nanorod arrays embedded in p-GaN, large numbers of Ga vacancies (VGa) were produced during the thermal bonding process in VLED fabrication. VGa-related donor–acceptor pair (DAP) transitions in p-GaN resulted in red emission in photoluminescence (PL) measurements as well as a broad electroluminescence (EL) emission spectrum extending from green to red. In combination with high-emission-efficiency blue InGaN/GaN multiple quantum wells (MQWs), the emission color of VLEDs can be changed from red to white by increasing the injection current.

Impact of filling ratio on subwavelength optical imaging using metallic nanolens of different geometries.

A nanolens based on a metallic nanorod has been considered as a prospective candidate for transporting subwavelength information. Such a lens is tuned to a particular frequency by tailoring the length of the nanorod. In this paper, we have investigated the impact of filling ratio on the subwavelength imaging capabilities of such a lens. Through full-wave electromagnetic simulation, we have demonstrated that the imaging performance of a silver (Ag) nanorod array depends not only on the length and periodicity but also on the filling ratio or the radius of the nanorod. We have studied this impact for nanorods having different cross-sectional shapes such as cylindrical and triangular and examined their performances for various filling ratios.

Deposition of Ta2O5 upon silver nanorods as an ultra-thin light absorber

We report the plasmon-assisted absorption enhancement of an ultra-thin light absorber composed of an Ag nanorod array with Ta2O5 deposited upon each rod. A significant increase in the absorptance efficiency of the plasmonic Ta2O5-capped Ag nanorod array was experimentally observed both in s- and p-polarization states. The causes of the enhanced local electric field intensity were systematically investigated using three-dimensional finite difference time domain. The simulations show that the maximum E-field intensities measured at the end surface of the Ta2O5-capped Ag rod are higher than those obtained from the bare Ag nanorod.