Fabrication of functional silver nanobowl arrays via sphere lithography

Highly sensitive and simultaneous detection of ctDNAs related to non-small cell lung cancer in serum using a catalytic hairpin assembly strategy in a SERS microfluidic chip

Circulating tumor DNA (ctDNA) is an ideal biomarker for cancer diagnosis based on liquid biopsy, so there is an urgent need for developing an efficient, rapid, and ultrasensitive detection method to meet clinical needs. In this paper, a novel surface-enhanced Raman scattering (SERS) microfluidic chip combined with a catalytic hairpin assembly (CHA) was proposed to detect two non-small cell lung cancer (NSCLC)-related ctDNA (TP53 and PIK3CA-Q546K) simultaneously. The chip consists of six channels for parallel detection. In the reaction region, the CHA reaction between HP₁ of the SERS probe and HP₂ of the capture substrate was triggered by ctDNAs to form HP₁-HP₂ duplexes. As the reaction proceeds, more and more SERS probes are captured on the substrate. The gathered reaction products continuously form a lot of hot spots, which greatly enhance the SERS signal. This reaction was completed within 5 minutes. Through this method, the detection limits of TP53 and PIK3CA-Q546K in human serum were as low as 2.26 aM and 2.34 aM, respectively. The microfluidic chip also exhibited high specificity, reproducibility and stability. The clinical feasibility of the SERS microfluidic chip was verified by analyzing the serum samples of healthy subjects and NSCLC patients. The reliability of the experimental results was verified by the qRT-PCR test. The constructed SERS-based analytical micro-platform has great potential in dynamic monitoring of cancer staging and could be used as a clinical tool for early cancer screening.

Bowl-Shaped Polydopamine Nanocapsules: Control of Morphology via Template-Free Synthesis

Synthesis of hollow polydopamine bowl-shaped nanoparticles (nanobowls), as small as 80 nm in diameter, via a one-pot template-free rapid method is reported. Addition of dopamine to a solution of 0.606 mg/mL tris(hydroxymethyl)aminomethane in an ethanol/water mixed solvent resulted in the formation of hollow spherical nanocapsules within 2 h. At longer reaction times, the formation of conventional solid nanospheres dominated the reaction. The wall thickness of the nanocapsules increased with increasing dopamine concentration in the reaction medium. Wall thickness was also influenced by oxygen availability during the reaction. Nanocapsules with thin walls were prone to collapse. When dried, over 90% of the nanocapsules with wall thickness on the order of 11 nm collapsed. Also, the degree of collapse of individual nanoparticles changed from complete to partial to no collapse as the wall thickness was increased. Varying the ethanol content affected the cavity size and overall dimension of the nanocapsules produced but did not result in a significant change to the wall thickness. A mechanism describing the formation of the nanocapsules and their subsequent collapse into nanobowls is presented. The shape-tunable nanobowls prepared through this green, rapid, and affordable method are expected to have applications in the biomedical, electrochemical, and catalytic fields.

Effective plasmon coupling in conical cavities for sensitive surface enhanced Raman scattering with quantitative analysis ability

Conical silver nanocavity arrays are fabricated by directly depositing Ag on porous alumina templates with V-shaped nanopores. By controlling the thickness of deposited Ag, complete and cracked cavity arrays are constructed respectively. The cracked cavity arrays with the cavity wall consisting of Ag nanoparticles are demonstrated to exhibit higher surface enhanced Raman scattering (SERS) activity than the complete one. Numerical simulation reveals that an effective coupling of the cavity modes with the surface plasmons of Ag nanoparticles (NPs) generates a significantly enhanced local electric field on the cavity wall responsible for the high SERS activity. The optimized cavity array presents an enhancement factor (EF) of ∼7.4 × 106 and an excellent uniformity with a relative standard deviation (RSD) as small as ∼5% for rhodamine 6G (R6G) molecules. Moreover, a good linear correlation between the logarithmic Raman intensity and the molecular concentration endows the array with quantitative analysis ability. These cavity arrays therefore are of great potential for qualitative and quantitative chemical and biomedical analysis with high sensitivity and reproducibility.

Gold surface plasmon crystal structure based-on polystyrene template for biosensor application

In this communication, we assembled ordered polystyrene (PS) microsphere array as a template with the drop-coating method, and the oxygen plasma was used to etch the template to adjust the spacing between the PS microspheres. Nano-triangular gold array and silver nano-pyramid array were obtained by ion beam sputtering to deposit precious metal gold and silver. We observed the surface morphology of Au and Au/Ag composite films by scanning electron microscope and characterized the films by X-ray diffraction and ultraviolet/visible light spectrophotometer. The results show that the etching time of oxygen plasma has an obvious effect in adjusting the spacing between PSs and has a significant effect on the morphology of Au structure.

Trapping analyte molecules in hotspots with modified free-standing silver bowtie nanostructures for SERS detection

A free-standing silver bowtie nanostructure with supporting bridge is fabricated to trap analyte molecules in hotspots for SERS detection.

Simple SERS substrates: powerful, portable, and full of potential

Surface enhanced Raman spectroscopy (SERS) is a powerful spectroscopic technique capable of detecting trace amounts of chemicals and identifying them based on their unique vibrational characteristics. While there are many complex methods for fabricating SERS substrates, there has been a recent shift towards the development of simple, low cost fabrication methods that can be performed in most labs or even in the field. The potential of SERS for widespread use will likely be realized only with development of cheaper, simpler methods. In this Perspective article we briefly review several of the more popular methods for SERS substrate fabrication, discuss the characteristics of simple SERS substrates, and examine several methods for producing simple SERS substrates. We highlight potential applications and future directions for simple SERS substrates, focusing on highly SERS active three-dimensional nanostructures fabricated by inkjet and screen printing and galvanic displacement for portable SERS analysis - an area that we believe has exciting potential for future research and commercialization.

Fabrication of antireflective compound eyes by imprinting

In this article, we demonstrate a simple and cost-effective approach to fabricate antireflective polymer coatings. The antireflective surfaces have 3D structures that mimick moth compound eyes. The fabrication is easily performed via a one-step imprinting process. The 3D arrays exhibit better antireflective performance than 2D arrays over most wavelengths from 400 to 2400 nm. The reflectivity of the 3D arrays is lower than 5.7% over the all of the wavelengths, and the minimum reflectivity is 0.27% at a wavelength of around 1000 nm.

Fabrication and functionalization of periodically aligned metallic nanocup arrays using colloidal lithography with a sinusoidally wrinkled substrate

We propose a general strategy for fabricating ultrasmall attoliter-sized (10(-18) L) one-dimensional (1D) aligned nanocup arrays embedded in poly(dimethylsiloxane) (PDMS) films based on a combination of colloidal soft-lithography and wrinkle processing. The nanocup consists of a metallic shell (silver-single or double-layer silver/gold type) with a thickness of several tens of nanometers and whose diameter was ca. 500 nm and cavity depth was ca. 250 nm. First, monodisperse polystyrene (PS) colloids (d = 500 nm) were arranged onto a sinusoidally wrinkled PDMS substrate. Then, the colloid particle arrays were transferred onto another flat PDMS substrate, and a metal film was vacuum deposited over the array to form a nanostructured surface consisting of half-shell metal-coated colloid particle arrays. After the metal-coated PS array was gently transferred onto another soft PDMS substrate prepared by nonthermal curing, the attached films were thermally cured. After that, both films were carefully separated to selectively transfer the metal-coated PS particle arrays, since the metallic shell on the PS surface can adhere to the soft PDMS. Finally, the PS colloids were removed by plasma etching, leaving behind the 1D hemispherical metallic shells, called here the "metallic nanocup array structure". This structure was evaluated by performing atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy measurements. We further demonstrate chemical modification of the inner nanocup surface through construction of a self-assembled monolayer, and we also fill them with nanomaterials (silica nanoparticles) to demonstrate their application to size-selecting devices. The obtained metallic nanocup arrays could be components in a new class of chemical and/or biological nanoreactors with small reaction vessels, surface-enhanced Raman scattering (SERS)-based sensors, and size separators for nanoparticles.

Fabrication of nanowire network AAO and its application in SERS

In this paper, nanowire network anodized aluminum oxide (AAO) was fabricated by just adding a simple film-eroding process after the production of porous AAO. After depositing 50 nm of Au onto the surface, nanowire network AAO can be used as ultrasensitive and high reproducibility surface-enhanced Raman scattering (SERS) substrate. The average Raman enhancement factor of the nanowire network AAO SERS substrate can reach 5.93 × 106, which is about 14% larger than that of commercial Klarite® substrates. Simultaneously, the relative standard deviations in the SERS intensities are limited to approximately 7%. All of the results indicate that our large-area low-cost high-performance nanowire structure AAO SERS substrates have a great advantage in chemical/biological sensing applications.

Large-area high-performance SERS substrates with deep controllable sub-10-nm gap structure fabricated by depositing Au film on the cicada wing

Noble metal nanogap structure supports strong surface-enhanced Raman scattering (SERS) which can be used to detect single molecules. However, the lack of reproducible fabrication techniques with nanometer-level control over the gap size has limited practical applications. In this letter, by depositing the Au film onto the cicada wing, we engineer the ordered array of nanopillar structures on the wing to form large-area high-performance SERS substrates. Through the control of the thickness of the Au film deposited onto the cicada wing, the gap sizes between neighboring nanopillars are fine defined. SERS substrates with sub-10-nm gap sizes are obtained, which have the highest average Raman enhancement factor (EF) larger than 2 × 108, about 40 times as large as that of commercial Klarite® substrates. The cicada wings used as templates are natural and environment-friendly. The depositing method is low cost and high throughput so that our large-area high-performance SERS substrates have great advantage for chemical/biological sensing applications.

Hydrogen peroxide biosensor based on microperoxidase-11 immobilized in a silica cavity array electrode

Hydrogen peroxide biosensor based on the silica cavity array modified indium-doped tin oxide (ITO) electrode was constructed. An array of silica microcavities was fabricated by electrodeposition using the assembled polystyrene particles as template. Due to the resistance gradient of the silica cavity structure, the silica cavity exhibits a confinement effect on the electrochemical reactions, making the electrode function as an array of "soft" microelectrodes. The covalently immobilized microperoxidase-11(MP-11) inside these SiO2 cavities can keep its physiological activities, the electron transfer between the MP-11 and electrode was investigated through electrochemical method. The cyclic voltammetric curve shows a quasi-reversible electrochemical redox behavior with a pair of well-defined redox peaks, the cathodic and anodic peaks are located at -0.26 and -0.15V. Furthermore, the modified electrode exhibits high electrocatalytic activity toward the reduction of hydrogen peroxide and also shows good analytical performance for the amperometric detection of H2O2 with a linear range from 2×10(-6) to 6×10(-4)M. The good reproducibility and long-term stability of this novel electrode not only offer an opportunity for the detection of H2O2 in low concentration, but also provide a platform to construct various biosensors based on many other enzymes.

Recent progress on surface pattern fabrications based on monolayer colloidal crystal templates and related applications

This review summarizes the recent progress toward the fabrication of surface patterns depending on the monolayer colloidal crystal templates. Based on the structural differences of the acquired surface patterns, various synthesis routes are introduced in detail. The diverse device applications of the synthesized surface patterns are also summarized, including sensors, energy-related devices, field emissions, wettability control, and so on. Future research should focus on surface patterns composed of multiple-layered structures and hybrid materials, and the widening of their application explorations.

Simple strategy to improve surface-enhanced Raman scattering based on electrochemically prepared roughened silver substrates

We develop an easy and effective pathway to improve surface-enhanced Raman scattering (SERS) effects of probe molecules of Rhodamine 6G (R6G) adsorbed on electrochemically prepared roughened Ag substrates. In general SERS studies, SERS-active metal substrates are first prepared. Then probe molecules are adsorbed on them to evaluate the relative SERS effects. In this study, we employ electrochemical oxidation-reduction cycle (ORC) treatments in 0.1 M KCl solutions containing probe molecules of 2 x 10(-5) M R6G to prepare R6G-adsorbed SERS-active Ag substrates for one step. Encouragingly, based on this strategy, the SERS intensity of adsorbed R6G can be increased by 1 order of magnitude, as compared with that of R6G adsorbed on a roughened Ag substrate beforehand, which was generally shown in the literature. Moreover, this improved SERS effect based on this strategy is also effective for 2 x 10(-9) M probe molecules, which is at a level of single molecule detection based on Ag colloids. It is also effective for probe molecules of ClO(4)(-) with low Raman cross section and for other electrochemically prepared SERS-active substrates of Au. Further analyses indicate that the increase in SERS activity in this new method is most likely due to the incorporation of more chloride ions into the substrate.