Improved SERS Performance from Au Nanopillar Arrays by Abridging the Pillar Tip Spacing by Ag Sputtering

Their properties are usually dependent on morphologies and sizes, and hence the fabrication of controllable uniform micro/nanostructured arrays on a large-scale becomes more important. Conventional methods for obtaining periodical nanostructured arrays are lithographic techniques including laser lithography, [ 26,27 ] electron-beam lithography, [28][29][30] X-ray lithography, [ 31 ] atomic force microscope lithography, [ 32 ] scanning tunneling microscopy technology, [ 33 ] and so on. However, these techniques can not be afforded to most laboratories because of their high processing costs and lower production effi ciency. [ 34 ] In recent decades, with fast development of colloidal science and self-assembly technology, large-scaled monolayer colloidal crystals can be fabricated using highly monodispersed colloidal spheres. [ 35 ] Based on this achievement, another alternative method, colloidal lithography, has been well developed to fabricate multiform periodic micro/nanostructured arrays (i.e., nanoparticle arrays, nanobowl arrays, nanoring arrays, and nanopillar arrays) using these monolayer colloidal crystals as templates or masks [36][37][38][39] by chemical routes including solution-dipping strategy, wet chemical etching, and electrochemical deposition. [40][41][42][43] Such periodic micro/nanostructured array fi lms generally have special rough surfaces, which can be used as SERS-active substrates for detection and identification of organic molecules with trace concentrations. Although chemical routes based on colloidal templates possess advantages of the simple operation, low processing costs, it is still quite diffi cult to achieve micro/nanostructured arrays with very uniform morphology on large-scale by above routes. If these micro/ nanostructured arrays are applied as active substrates in SERS detection, the intensity of SERS spectra in different areas on the sample will fl uctuate in a large range, leading to the failure in practical applications. Whereas other parallel routes, based on physical process method, such as sputtering deposition, pulsed laser deposition, thermal evaporation deposition, atomic layer deposition, and so on, combining with monolayer colloidal crystals template can well resolve these problems. [ 44 ] SERS enhancement activities are mainly dependent on chemical enhancement or local electromagnetic fi eld enhancement at nanoscaled protrusions and cavities. For the latter case, the Periodic hexagonal spherical nanoparticle arrays are fabricated by a sacrificial colloidal monolayer template route by chemical deposition and further physical deposition. The regular network-structured arrays are fi rst templated by colloidal monolayers and then they are changed to novel periodic spherical nanoparticle arrays by further sputtering deposition due to multiple direction deposition and shadow effect between adjacent nanoparticles. The nanogaps between two adjacent spherical nanoparticles can be well tuned by controlling deposition time. Such periodic nanoparticle arrays with gold coatings ...

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“…[45][46][47] Therefore, tuning the nanogap value properly to enhance plasmonic coupling is more meaningful to SERS examination.…”

Section: Introductionmentioning

confidence: 99%

Spherical Nanoparticle Arrays with Tunable Nanogaps and Their Hydrophobicity Enhanced Rapid SERS Detection by Localized Concentration of Droplet Evaporation

Zhang

Zhou

Liu

et al. 2015

Adv Materials Inter

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“…Various NP arrays using e-beam lithography 32 , anodized aluminum oxide templates 33,35 , nanoimprinting 34 , oxygen-plasma-stripping-of-photoresist technique 36 , ion milling 37 , interference lithography 38,40 , and coating of multi-walled carbon nanotubes 39 have been reported. Recently, we have developed a new method to fabricate wafer scale Ag-capped Si nanopillar (Ag NP) SERS substrates utilizing maskless lithography.…”

Section: Introductionmentioning

confidence: 99%

Wafer-Scale Leaning Silver Nanopillars for Molecular Detection at Ultra-Low Concentrations

Rindzevicius

Schmidt

et al. 2015

J. Phys. Chem. C

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Wafer-scale surface-enhanced Raman scattering (SERS) substrates fabricated using maskless lithography are important for scalable production targets. Large-area, leaning silver-capped silicon nanopillar (Ag NP) structures suitable for SERS molecular detection at extremely low analyte concentrations are investigated. Theoretical results show that isolated Ag NPs essentially support two localized surface plasmon (LSP) modes. The most prominent LSP resonance is observed in the near-infrared region (~800 nm) and can be tuned by changing the diameter of the silicon nanopillars (Si NPs). The corresponding electric field distribution maps indicate that the maximum E-field enhancement is found at the Ag cavity, i.e. the bottom part of the Ag cap. We argue that the plasmon coupling between the resonant Ag cap cavities contributes most to the enhancement of the Raman signal. We experimentally evaluate these findings and show that by exposing Si NPs to an O 2 -plasma the average Ag NP cluster size, and thus the overall inter-pillar coupling, can be systematically reduced. We show that deposition of Cr adhesion layers on Si NPs (>3 nm) introduce plasmon coupling loss to the Ag NP LSP cavity mode that significantly reduces the SERS intensity. Results also show that short exposures to the O 2 -plasma and the use of 1-3 nm Cr adhesion layers are advantageous for reducing the signal background noise from Ag NPs. In addition, influence of the Ag NP height and Ag metal thickness on SERS intensities is investigated and optimal fabrication process parameters are evaluated. Finally, the SERS spectrum from 100 pM of trans-1,2-bis (4-pyridyl) ethylene (BPE) is recorded showing distinct characteristic Raman vibrational modes. The calculated enhancement factor is of the order of 10 8 , and the SERS signal intensity exhibits a standard deviation of around 14% (660 data points) across a 5x5 mm 2 surface area.

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“…Figure 10b shows a large-scale flexible film of Ag-NPs decorated polyacrylonitrile (PAN) nanohump array pattern, which was able to detect methyl parathion (the pesticide residual) by swabbing the peel of apples. 197 Recently the ordered porous anodic aluminum oxide (AAO) membranes and the polystyrene sphere assemblies were used as templates to create highly ordered three-dimensional (3D) silver nanorod (NR) array 74,77 and the Ag-NR bundle array (Figure 10c). 85 The 3D hierarchical structure not only generates more "hot spots" without increasing the footprint, but also creates stronger localized EM field.…”

Section: -180mentioning

confidence: 99%

“…To achieve signal uniformity and reproducibility, large-area ordered nanostructures are desirable. Periodic nanostructure arrays on solid substrates have been developed using self-assembly, [63][64][65][66][67][68][69] electrodeposition, [70][71][72][73] template-assisted fabrication, [74][75][76][77][78][79][80][81][82][83][84][85][86][87][88][89] lithography, 70,[90][91][92][93][94][95] and skeletonassisted methods. [96][97][98][99][100][101][102][103][104][105] Resonance with excitation light.-When LSPR band is overlapped the wavelength of the excitation light, that is, the plasmon is in resonance with the excitation light, it can enhance SERS activity.…”

mentioning

confidence: 99%

Review—Surface-Enhanced Raman Scattering Sensors for Food Safety and Environmental Monitoring

Tang

Zhu

Meng

et al. 2018

J. Electrochem. Soc.

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153

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This article gives a review of surface-enhanced Raman scattering (SERS) sensors for food safety and environmental pollution monitoring. It introduces the basic concepts of SERS substrates, SERS enhancement factors and mechanisms, SERS probes/labels, molecular recognition elements as well as optofluidic SERS devices (SERS sensors integrated with microfluidics). This article places an emphasis on the design strategies of various SERS sensors by utilizing fingerprinting SERS spectra or by using SERS probes. It highlights the applications of SERS sensors in detection of heavy metals (such as Hg 2+ , Pb 2+ , Cd 2+ and As 3+ ), inorganic anions (nitrite, nitrate, perchlorate and fluoride), toxic small molecules (polycyclic aromatic hydrocarbon, polychlorinated biphenyls, herbicides, pesticides, antibiotics and food additives), as well as pathogens (bacteria and viruses Food safety and environment pollution are among great challenges in the human society. There are some common pollutants in the environment and food, such as heavy metals, nitrites, phosphates, pesticides, herbicides, antibiotics, hormone, pathogens and other additives. Some pollutants initially are released into the environment, and then accumulate in the food chain, and enter human bodies. Uptake of pollutants by human poses a threat to human health to different extents. 1,2Hence it is essential to monitor pollutants in the environment and food. Currently pollutants are typically measured with various laboratorybased techniques, such as atomic absorption spectroscopy, atomic fluorescence spectrometry, X-ray fluorescence spectrum, inductively coupled plasma and ion-coupled plasma-mass spectroscopy, mass spectrometry, chromatography, capillary electrophoresis, analytical profile index (API), polymerase chain reaction (PCR), and enzymelinked immunosorbent assay (ELISA).3-7 Although these techniques have high sensitivity and accuracy, they rely on expensive instruments and require professional to treat samples and operate instruments in centralized laboratories. Additionally, analysis generally takes several hours to days. For example, 0.024 ppb of Hg 2+ and 0.023 ppb of As 3+ in drinking water can be detected using atomic absorption spectroscopy with a two-step electrothermal atomizer and hydride generation atomic fluorescence spectrometry, respectively. 8,9 However, they need multiple sample preconcentration processing and expensive instruments. PCR can improve the number of the target while ELISA can produce amplified recognition signal, which could both improve the detection sensitivity to pathogens. For example, oligonucleotide microarray with combination of CdSe/ZnS quantum dots as fluorescent labels shown high specificity and sensitivity of 10 colony forming units (CFU)/mL. 10 However, the complicated procedures are very time-consuming, and the method is also vulnerable to contamination. These laboratory-based techniques cannot meet the critical need of rapid on-site measurement of pollutants. Therefore, it is essential to develop portable sensors f...

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Improved SERS Performance from Au Nanopillar Arrays by Abridging the Pillar Tip Spacing by Ag Sputtering

Cited by 222 publications

References 25 publications

Spherical Nanoparticle Arrays with Tunable Nanogaps and Their Hydrophobicity Enhanced Rapid SERS Detection by Localized Concentration of Droplet Evaporation

Spherical Nanoparticle Arrays with Tunable Nanogaps and Their Hydrophobicity Enhanced Rapid SERS Detection by Localized Concentration of Droplet Evaporation

Wafer-Scale Leaning Silver Nanopillars for Molecular Detection at Ultra-Low Concentrations

Review—Surface-Enhanced Raman Scattering Sensors for Food Safety and Environmental Monitoring

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