Geometric gradients within ordered micro/nanostructures exhibit unique wetting properties. Well-defined and ordered microsphere arrays with geometric gradient (OMAGG) are successfully fabricated through combining colloidal lithography and inclined reactive ion etching (RIE). During the inclined RIE, the graded etching rates in vertical direction of etcher chamber are the key to generating a geometric gradient. The OMAGG can be used as an effective mask for the preparation of micro/nanostructure arrays with geometric gradient by selective RIE. Through this strategy, a well-defined wettability "library" with graded silicon cone arrays is fabricated, and the possibility of screening one desired "book" from the designated wettability "library" is demonstrated. Meanwhile, the silicon cone arrays with geometric gradient (SCAGG) can be applied to control the wetting behavior of water after being modified by hydrophilic or hydrophobic chemical groups. Based on this result, a temperature-responsive wetting substrate is fabricated by modifying poly n-isopropyl acrylamide (PNIPAM) on the SCAGG. These wettability gradients have great potential in tissue engineering, microfluidic devices, and integrated sensors.
Optical biosensors, especially those based on plasmonic structures, have emerged recently as a potential tool for disease diagnostics. Plasmonic biosensors have demonstrated impressive benefits for the label‐free detection of trace biomarkers in human serum. However, widespread applications of these technologies are hindered because of their insufficient sensitivity, their relatively complex chemical immobilization processes, and the use of prism couplers. Accordingly, a sandwiched plasmon ruler (SW‐PR) based on a Au nanohole array with ultrahigh sensitivity arising from the plasmonic coupling effect is developed. Highly confined surface charges caused by Bloch wave surface plasmon polarizations substantially increase the coupling efficiency. This platform exhibits thickness sensitivity as high as 61 nm nm−1 and can detect at least 200 000‐fold lower analyte concentrations than a nanowell sensing platform with the same wavelength shift. Additionally, the sandwiched plasmonic biosensor allows precise and label‐free testing of clinical biomarkers, namely C‐reactive protein and procalcitonin, in patient serum samples without requiring a sophisticated prism coupler, extra antibodies, or a chemical immobilization technique. This study yields new insight into the structural design of plasmon rulers and will open exciting avenues for disease diagnosis and therapy follow‐up at the point‐of‐care.
We show morphology-patterned stripes modified by thermal-responsive polymer for smartly guiding flow motion of fluid in chips. With a two-step modification process, we fabricated PNIPAAm-modified Si stripes on silicon slides, which were employed as substrates for fluid manipulation in microchannels. When the system temperature switches between above and below the lower critical solution temperature (LCST) of PNIPAAm, the wettability of the substrates also switches between strong anisotropy and weak anisotropy, which resulted in anisotropic (even unidirectional) flow and isotropic flow behavior of liquid in microchannels. The thermal-responsive flow motion of fluid in the chip is influenced by the applied pressure, the thickness of PNIPAAm, and dimension of the microchannels. Moreover, we measured the feasible applied pressure scopes under different structure factors. Because of the excellent reversibility and quick switching speed, the chip could be used as a thermal-responsive microvalve. Through tuning the system temperature and adding the assistant gas, we realized successive "valve" function. We believe that the practical and simple chip could be widely utilized in medical detection, immunodetection, protein analysis, and cell cultures.
We present an effective approach for fabricating graded plasmonic arrays based on ordered micro-/nanostructures with a geometric gradient. Ag nanowell arrays with graded geometric parameters were fabricated and systematically investigated. The order of the graded plasmonic arrays is generated by colloidal lithography, while the geometric gradient is the result of inclined reactive ion etching. The surface plasmon resonance (SPR) peaks were measured at different positions, which move gradually along the Ag nanowell arrays with a geometric gradient. Such micro-/nanostructure arrays with graded and integrated SPR peaks can work as a fine plasmonic "library" (FPL), and the spectral range can be controlled using a "coarse adjustment knob" (lattice constant) and a "fine adjustment knob" (pore diameter). Additionally, the spectral resolution of the FPL is high, which benefits from the high value of the full height/full width at half-maximum and the small step size of the wavelength shift (0.5 nm). Meanwhile, the FPL could be effectively applied as a well-defined model to verify the plasmonic enhancement in surface enhanced Raman scattering. As the FPL is an integrated optical material with graded individual SPR peaks, it can not only be a theoretical model for fundamental research, but also has great potential in high-throughput screening of optical materials, multiplex sensors, etc.
In this article, we report the morphology modulation of gold nanoparticle (NP) arrays by polymer-assisted thermal treatment. Simultaneously, localized surface plasmon resonance (LSPR) UV–vis extinction (absorption plus scattering) of gold NP arrays was monitored and analyzed. First, through horizontal lifting, gold NP monolayers were transferred from a water/hexane interface to glass slides. After thin polymer films were spin-coated on the gold NP monolayers, thermal treatment was carried out, which results in apparent color changes in the obtained samples. The color changes could be attributed to the shift of the surface plasmon band (SPB), along with increasing gold NP size and interparticle distance. We found that different polymers show different effects on the modulation of gold NPs’ morphology, accompanied by different shifts of the SPB. Polymers with relatively lower glass transition temperatures (T g), such as poly(methyl methacrylate), promoted gold NPs to merge into spheres, while polymers with relatively higher T g, such as polyphenylene sulfone resins, inhibited the fusion of gold NPs, which collapsed as a whole slice. We believe that the difference should be attributed to the polymer chain’s ability to move during heating. Therefore, the temperature of thermal treatment and the T g of the polymer play critical roles in the merging process of gold NPs. Moreover, through combining colloidal lithography technology, patterned gold NP monolayers have been fabricated. The current strategy is simple and facile to control the morphology of gold NP arrays, as well as to control their optical properties.
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