Nanodot Arrays Research Articles

Nanoplasmonic immunosensor for the detection of SCG2, a candidate serum biomarker for the early diagnosis of neurodevelopmental disorder

The neural circuits of the infant brain are rapidly established near 6 months of age, but neurodevelopmental disorders can be diagnosed only at the age of 2–3 years using existing diagnostic methods. Early diagnosis is very important to alleviate life-long disability in patients through appropriate early intervention, and it is imperative to develop new diagnostic methods for early detection of neurodevelopmental disorders. We examined the serum level of secretogranin II (SCG2) in pediatric patients to evaluate its potential role as a biomarker for neurodevelopmental disorders. A plasmonic immunosensor performing an enzyme-linked immunosorbent assay (ELISA) on a gold nanodot array was developed to detect SCG2 in small volumes of serum. This nanoplasmonic immunosensor combined with tyramide signal amplification was highly sensitive to detect SCG2 in only 5 μL serum samples. The analysis using the nanoplasmonic immunosensor revealed higher serum SCG2 levels in pediatric patients with developmental delay than in the control group. Overexpression or knockdown of SCG2 in hippocampal neurons significantly attenuated dendritic arborization and synaptic formation. These results suggest that dysregulated SCG2 expression impairs neural development. In conclusion, we developed a highly sensitive nanoplasmonic immunosensor to detect serum SCG2, a candidate biomarker for the early diagnosis of neurodevelopmental disorders.

Si-Based Infrared Detector Using Organic Nano-Dot Array

Silicon-based infrared photodetector is proposed using an organic nano-dot array covered with an Au thin film. The nano-dots were self-assembled structures composed of crystalline CuPc and PTCDA organic semiconductors, and they enhanced the absorption of the incident infrared light. The annealing process at the CuPc and PTCDA deposition formed these semiconductor materials to be a nano-dot array shape. The Au-coated nano-dots presented broadband reflectance decrease in the near- to mid-infrared region. The Arrhenius plot investigation revealed that the proposed photodetector had 0.4-0.43 eV activation energy, a sub-Si-bandgap energy barrier. The photodetection experiments in the near-infrared region presented the proposed photodetector discriminated on and off of 2.07- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> -long super continuum light. In addition, band-pass filtered emission from a black body cavity with a wavelength of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.05~\mu \text{m}$ </tex-math></inline-formula> could be measured. Since the derivation of the activation energy and the cut-off wavelength showed a good agreement, the organic semiconductor generated a carrier at the photodetection. A possible detection mechanism was thus attributed to carrier excitations at an interface between organic semiconductors, CuPc and PTCDA. The proposed structure contributes to fabricate mid-infrared silicon-based photodetectors with high light absorption performance.

Magneto-electric coupled ordered PMN-PT/NiFe2O4 composite nanostructures

In this work, a well-ordered array of multiferroic magnetoelectric (ME) dot-like nanostructures of Pb(Mg1/3Nb2/3)O3]0.65–[PbTiO3]0.35 (PMN-PT)/NiFe2O4 is explored for high density and low power consuming memory devices. Ordered arrays of ferromagnetic NiFe2O4 nanodots underneath a ferroelectric PMN-PT layer were fabricated using silicon nitride based stencil masks and pulsed laser deposition techniques. The piezo-response and magnetic force microscopy (PFM) measurements reveal coexistence of magnetic and ferroelectric domains in PMN-PT/NiFe2O4 films at room temperature. The ferroelectric polarization can be switched with the electrically biased PFM tip. The ME coupling is evident in the PMN-PT/NiFe2O4 films, which is attributed to the transfer of the elastic strain from PMN-PT to NiFe2O4. The PMN-PT/NiFe2O4 nanodot films exhibit enhanced ME coupling coefficient (α) as compared to continuous bilayer PMN-PT/NiFe2O4 films, owing to the superior strain transfer efficiency in nanodot heterostructures. The nanodot films demonstrate electric-field controlled nonvolatile switching of α, which can be used to store binary information in memory devices, holding all the advantages of ferroelectric random access memory but overcoming the major disadvantage of destructive reading of polarization. The results reveal a versatile approach for fabrication of well-ordered nanodot arrays for low power consuming, high-density ME device applications.

Features in the Resonance Behavior of Magnetization in Arrays of Triangular and Square Nanodots

Collective modes of the gyrotropic motion of a magnetic vortex core in ordered arrays of triangular and square ferromagnetic film nanodots have been theoretically investigated. The dispersion relations have been derived. The dipole–dipole interaction of the magnetic moments of the magnetic vortex cores of elements has been taken into account in the approximation of a small shift from the equilibrium position. It is shown that the effective rigidity of the magnetic subsystem of triangular elements is noticeably higher than that of the subsystem of square elements of the same linear sizes. The potential application of the polygonal film nanodisks as nanoscalpels for noninvasive tumor cell surgery is discussed

Nanoarchitecturing Carbon Nanodot Arrays on Zeolitic Imidazolate Framework-Derived Cobalt-Nitrogen-Doped Carbon Nanoflakes toward Oxygen Reduction Electrocatalysts.

Two-dimensional (2D) nanoporous heterostructured composites formed by uniformly coating individual monolayers with porous layers introduce unparalleled opportunities to improve and optimize the electrochemical performances of 2D materials. Here, an all-porous carbon heterostructure composed of 2D microporous carbon nanoflakes uniformly decorated with carbon nanodots has been developed. Interestingly, resol-F127 micelles self-assemble on the surface of zeolitic imidazolate framework (ZIF) nanoflakes in the form of a nanodot array, yielding a heterostructure. Hydrothermal treatment followed by carbonization under a nitrogen atmosphere causes conversion of the nanodot-nanoflake assembly into a carbon-based material composed of hollow carbon nanodots (CNDs) and microporous carbon nanoflakes (CNFs), that is, a CND@CNF composite. The combination of 2D microporous carbon nanoflakes with carbon hollow nanodots enhances exposure of the active sites and improves mass transfer in all directions (including through the nanoflakes). The use of cobalt (Co)-containing ZIF leads to the synthesis of a Co-Nx-doped CND@CNF composite, which exhibits oxygen reduction reaction electrocatalytic activity and long-term stability superior even to commercial Pt/C catalysts. This architecture-engineering strategy has been used to design and synthesize 2D heterostructures possessing high electrocatalytic efficiency and will be useful for future developments in important electrochemical energy storage and conversion applications.

Nanograting-Enhanced Optical Fibers for Visible and Infrared Light Collection at Large Input Angles

The efficient incoupling of light into particular fibers at large angles is essential for a multitude of applications; however, this is difficult to achieve with commonly used fibers due to low numerical aperture. Here, we demonstrate that commonly used optical fibers functionalized with arrays of metallic nanodots show substantially improved large-angle light-collection performances at multiple wavelengths. In particular, we show that at visible wavelengths, higher diffraction orders contribute significantly to the light-coupling efficiency, independent of the incident polarization, with a dominant excitation of the fundamental mode. The experimental observation is confirmed by an analytical model, which directly suggests further improvement in incoupling efficiency through the use of powerful nanostructures such as metasurface or dielectric gratings. Therefore, our concept paves the way for high-performance fiber-based optical devices and is particularly relevant within the context of endoscopic-type applications in life science and light collection within quantum technology.

Biocompatible Nanotransfer Printing Based on Water Bridge Formation in Hyaluronic Acid and Its Application to Smart Contact Lenses.

Many conventional micropatterning and nanopatterning techniques employ toxic chemicals, rendering them nonbiocompatible and unsuited for biodevice production. Herein the formation of water bridges on the surface of hyaluronic acid (HA) films is exploited to develop a transfer-based nanopatterning method applicable to diverse structures and materials. The HA film surface, made deformable via water bridge generation, is brought into contact with a functional material and subjected to thermal treatment, which results in film shrinkage, allowing a robust pattern transfer. The proposed biocompatible method, which avoids the use of extra chemicals, enables the transfer of nanoscale, microscale, and thin-film structures as well as functional materials such as metals and metal oxides. A nanopatterned HA film is transferred onto a moisture-containing contact lens to fabricate smart contact lenses with unique optical characteristics of rationally designed optical nanopatterns. These lenses demonstrated binocular parallax-induced stereoscopy via nanoline array polarization and acted as cutoff filters, with nanodot arrays, capable of treating Irlen syndrome.

Directly visualizing the crossover from incoherent to coherent phonons in two-dimensional periodic MoS2/MoSe2 arrayed heterostructure

Recently, massive efforts have been done on controlling thermal transport via coherent phonons in the various periodic nanostructures. However, the intrinsic lattice difference between the constituent materials inevitably generates the disorder at the interfaces, thus limiting the opportunity of directly observing the coherent phonon transport. Here, we investigate the controllability and visualization of the coherent phonon transport in a periodic MoS2/MoSe2 arrayed heterostructure with minimum lattice mismatching using non-equilibrium molecular dynamics simulation. It is found that the coherent phonon transport can be destroyed and rebuilt through adjusting the density of MoSe2 nanodot arrays. The phonon localization induced by the destruction of correlation is visualized based on the spatial energy distribution and anharmonic analysis. Furthermore, the eigen vector diagrams provide a distinct visualization of the localized phonon modes. Besides, the correlation of phonon can be rebuilt by reducing the period length, which is verified by the enhanced group velocities extracted from phonon dispersion curves. Interestingly, the crossover from incoherent to coherent phonon transport is directly observed by the spatial energy distributions and the spectral phonon transmission coefficients. Finally, the size and temperature dependence of thermal conductivity are also discussed. This study of the phonon coherence and its visualizing manipulation on thermal conductivity will be beneficial to fine heat control and management in the real applications.

Nonvolatile switching of magnetostrictive nanodot from single-domain to vortex states by voltage at room temperature

We report the voltage regulation of electrodeposited elliptical magnetostrictive Ni nanodot arrays from single-domain to nonvolatile vortex state at room temperature. On the piezoelectric substrate, isolated elliptical Ni nanodots are fabricated between a pair of square electrodes, with the long axis parallel to the joint line of the electrodes. By applying a voltage to the surface electrodes pair, local stress is generated to induce the magnetization of the nanodots from single-domain to vortex state. The magnetization state of the nanodots is characterized by a magnetic force microscope. Even after the voltage is removed or applying another voltage, the nanodots maintain a stable vortex magnetization state, which shows that the vortex state after regulation is nonvolatile. These results are of great significance for the study of the low-energy-consumption regulation of the nano-dimensional magnetic material and vortex state-based nonvolatile memory.

Facile fabrication of ordered discontinuous nanotopography on photosensitive substrates for enhanced neuronal differentiation

Controlling the development and morphology of neurons is important for basic neuroscience research as well as for applications in nerve regeneration and neural interfaces. Various studies have shown that nanoscale topographies can promote the development of neuronal cells and the differentiation of neural stem cells; however, the fabrication of these nanotopographical features often involves expensive and sophisticated techniques. Here, we employ nanosphere lens lithography combined with UV-LED technology to create nanopatterns on an SU-8 photoresist. We develop a facile method to create a reusable polystyrene nanosphere (PS-NS) lens array by the spontaneous formation of a hexagonal close-packed array of PS-NSs at a water–air interface and its subsequent transfer to a polydimethylsiloxane carrier film without using any special equipment. We show that this simple technique can create ordered arrays of nanodots on an SU-8 film, the dimensions of which can be controlled by the size of the PS-NSs. When used as a substrate for the neuronal differentiation of pheochromocytoma (PC12) cells, the nanopatterned SU-8 films exhibit enhanced differentiation parameters with respect to conventional tissue culture plastic as compared with their flat counterparts. The method proposed here can greatly facilitate the nanopatterning of various photosensitive substrates for the development of implants for nerve regeneration and neural interfacing.

Comparative study of anodization of small-scale and wafer-scale aluminum films on a silicon substrate and controlling pores shape for practical applications

• Anodization of small and wafer scales of pure Al and impure Al films were compared. • Suitable anodizing current density was determined to avoid the PAA burns. • Effect of starting Al thicknesses on the electrochemical response was discussed. • Anodizing strategy was proposed to form multibranched pores from a single pore with smaller pore sizes. • Anodization of annealed Al film could be used to form ordered arrays of alumina nanodots. Porous anodic alumina (PAA), comprising arranged pores in hexagonal cells obtained by anodizing aluminum (Al), has been studied and is usually used as a template for synthesizing one-dimensional nanostructure. However, there is growing interest in more effective applications with tunable pores and more complex structures with reasonable cost. For example, the branching and interconnected pores are obtained in multiple bifurcations under certain anodizing conditions. From manufacturing perspectives, large-area anodization on special substrates, such as Si, is extremely significant and required. Herein, we present a robust analysis of the different types of branched and modulated pores in the PAA templates; the newly developed methodology and the morphological evolution of each type are discussed. The proposed anodizing strategies help reduce anodizing time and result in smaller pore sizes than those obtained by the traditional methods. Therefore, they be effectively implemented for separation science technology. Furthermore, the work was extended to anodize a full Al wafer (200 mm in diameter) on a Si wafer without lithography or pretemplating. Additionally, the required anodizing conditions to prevent PAA from burning were followed. The opportunities for this PAA template to serve as generic templates for potential applications will be explored and discussed. The anodization of annealed Al/SiO 2 films can be used to create highly hexagonal ordered arrays of alumina nanodots between alumina and SiO 2 substrate, which were observed when the anodized sample was cleaved. Therefore, the obtained results could help, from manufacturing perspectives, modulate pores and a large area of the PAA on special substrates, such as Si, for many technological applications.

Multilayer regular hexagonal prism barium ferrite nanodot arrays on a substrate based on an AAO mask

Herein, the multilayer regular hexagonal barium ferrite nanodot arrays have been prepared by pulsed laser deposition through a porous anodic alumina template. The BaM nanodot arrays displayed a c-axis oriented crystal with a multilayer regular hexagonal structure, and the degree of orientation was improved by the post-annealing. Furthermore, the hysteresis loops showed the annealed nanodot arrays have a high squareness ratio of 0.65 along the easy magnetization direction. The first-order reversal curve diagram confirmed that the nanodots have a small interactive field between the particles. Consequently, this effective approach is potentially applied in self-biased microwave devices.

Straightforward Patterning of Functional Polymers by Sequential Nanosecond Pulsed Laser Irradiation.

Laser-based methods have demonstrated to be effective in the fabrication of surface micro- and nanostructures, which have a wide range of applications, such as cell culture, sensors or controlled wettability. One laser-based technique used for micro- and nanostructuring of surfaces is the formation of laser-induced periodic surface structures (LIPSS). LIPSS are formed upon repetitive irradiation at fluences well below the ablation threshold and in particular, linear structures are formed in the case of irradiation with linearly polarized laser beams. In this work, we report on the simple fabrication of a library of ordered nanostructures in a polymer surface by repeated irradiation using a nanosecond pulsed laser operating in the UV and visible region in order to obtain nanoscale-controlled functionality. By using a combination of pulses at different wavelengths and sequential irradiation with different polarization orientations, it is possible to obtain different geometries of nanostructures, in particular linear gratings, grids and arrays of nanodots. We use this experimental approach to nanostructure the semiconductor polymer poly(3-hexylthiophene) (P3HT) and the ferroelectric copolymer poly[(vinylidenefluoride-co-trifluoroethylene] (P(VDF-TrFE)) since nanogratings in semiconductor polymers, such as P3HT and nanodots, in ferroelectric systems are viewed as systems with potential applications in organic photovoltaics or non-volatile memories.

Effects of native oxidation on Ti/TiO2 nanodot arrays and their plasmonic properties compared to Au nanodot arrays

Unlike for noble metals, localized surface plasmon resonance (LSPR) of metallic nanodot array (NDA), which forms a surface oxide layer, has not been fully explored. We have investigated the surface oxide layers, LSPR, and surface-enhanced Raman scattering (SERS) of Au and Ti/TiO2 NDAs with similar shapes. Au NDA and Ti/TiO2 NDA with 80 ± 5 nm diameters were fabricated on indium tin oxide glass substrates using anodic aluminum oxide masks. The native oxide surface layer of Au NDA was very thin, whereas the Ti/TiO2 NDA’s surface was identified as TiO2 due to its inherent oxide layer. XPS depth profiling confirmed that the Ti metal’s surface transformed into a native oxide layer of TiO2 on Ti metal. The SERS signal of the Au NDA was approximately 104 times higher than that of the Ti/TiO2 NDA. The Au NDA’s LSPR had a strong peak centered at 659 nm, while the Ti/TiO2 NDA’s LSPR had a broad peak centered at ~420 nm. The Ti/TiO2 NDA’s LSPR was weak because the native surface layer dampened the LSPR but was clearly observed in the visible light region. These results suggested that Ti/TiO2 NDA has the potential for use as a visible light-responsive photocatalyst in solar energy systems.

Charge-offset stability of single-electron devices based on single-layered Fe nanodot array

In metal-based single-electron devices (SEDs), charge-offset drift has been observed, which is a time-dependent instability caused by charge noise. This instability is an issue in the application of new information processing devices, such as neural network devices, quantum computing devices (charge sensing), and reservoir computing devices. Therefore, the charge-offset drift in metal-based SEDs needs to be suppressed. However, the charge-offset stability of metal-based SEDs has not been investigated in depth, except in the case of Al and Al2O3 SEDs. In this work, Fe-based SEDs formed by single-layer Fe nanodot arrays embedded in MgF2 were studied with regard to their charge-offset stability. Using devices that produce simple current oscillations, the charge-offset drift (ΔQ0) of Fe-based SEDs was evaluated by focusing on peak shifts of the simple current oscillation over time, despite the use of a multi-dot system. This drift (ΔQ0 ≈ 0.3e) was shown to be much lower than in SEDs with Al-dots and Al2O3 tunnel junctions. Notably, the charge-offset drift in the metal-based SEDs was suppressed using the Fe–MgF2 system. The excellent stability of these devices was attributed to the material properties of the Fe–MgF2 system. Finally, as the Fe nanodot array contained numerous dots, the effect of satellite dots acting as traps on the charge-offset instability was discussed. The findings of this study will be important in future applications of metal-based SEDs in new information processing devices.

Nanotopography as Artificial Microenvironment for Accurate Visualization of Metastasis Development via Simulation of ECM Dynamics.

Metastatic progression is mediated by complex interactions between deregulated extracellular matrix (ECM) and cancer cells and remains a major challenge in cancer management. To investigate the role of ECM dynamics in promoting metastasis development, we developed an artificial microenvironment (AME) platform comprised of nanodot arrays of increasing diameter. Cells cultured on the platform showed increasing signs of mesenchymal-like cell transition as AME diameter increased, suggesting accurate simulation of ECM-mediated gene regulation. Gene expression was analyzed to determine genes significant to transition, which were then used to select appropriate small molecule drugs for time course treatments. Our results suggest that the platform can identify critical target genes as well as possible drug candidates. Overall, the AME platform allows for the study of intricate ECM-induced gene expression trends across metastasis development that would otherwise be difficult to visualize in vivo and may open new avenues toward successful personalized cancer management.

Micromagnetic Simulations of Fe and Ni Nanodot Arrays Surrounded by Magnetic or Non-Magnetic Matrices.

Combining clusters of magnetic materials with a matrix of other magnetic materials is very interesting for basic research because new, possibly technologically applicable magnetic properties or magnetization reversal processes may be found. Here we report on different arrays combining iron and nickel, for example, by surrounding circular nanodots of one material with a matrix of the other or by combining iron and nickel nanodots in air. Micromagnetic simulations were performed using the OOMMF (Object Oriented MicroMagnetic Framework). Our results show that magnetization reversal processes are strongly influenced by neighboring nanodots and the magnetic matrix by which the nanodots are surrounded, respectively, which becomes macroscopically visible by several steps along the slopes of the hysteresis loops. Such material combinations allow for preparing quaternary memory systems, and are thus highly relevant for applications in data storage and processing.

Label-free sensing of virus-like particles below the sub-diffraction limit by wide-field photon state parametric imaging of a gold nanodot array.

A parallel four-quadrant sensing method utilizing a specially designed gold nanodot array is created for sensing virus-like particles with a sub-diffraction limit size (∼100 nm) in a wide-field image. Direct label-free sensing of viruses using multiple four-quadrant sensing channels in parallel in a wide-field view enables the possibility of high-throughput onsite screening of viruses.

Fabrication of a Plasmonic Nanoantenna Array Using Metal Deposition on Polymer Nanoimprinted Nanodots for an Enhanced Fluorescence Substrate.

A simple and cost-effective method is proposed herein for a plasmonic nanoantenna array (PNAA) for the fabrication of metal-enhanced fluorescence (MEF) substrates in which fluorophores interact with the enhanced electromagnetic field generated by a localized surface plasmon to provide a higher fluorescence signal. The PNAA is fabricated by the deposition of a silver (Ag) layer on an ultraviolet (UV) nanoimprinted nanodot array with a pitch of 400 nm, diameter of 200 nm, and height of 100 nm. During deposition, raised Ag nanodisks and a lower Ag layer are, respectively, formed on the top and bottom of the imprinted nanodot array, and the gap between these Ag layers acts as a plasmonic nanoantenna. Since the thickness of the gap within the PNAA is influenced by the thickness of Ag deposition, the effects of the latter upon the geometrical properties of the fabricated PNAA are examined, and the electromagnetic field intensity distributions of PNAAs with various Ag thicknesses are simulated. Finally, the fluorescence enhancement factor (FEF) of the fabricated PNAA MEF substrate is measured using spotted Cy5-conjugated streptavidin to indicate a maximum enhancement factor of ~22× for the PNAA with an Ag layer thickness of 75 nm. The experimental results are shown to match the simulated results.

Localized surface plasmon resonance and structural characteristics of Ti nanodot arrays covered with an amorphous TiO2 native oxide layer

Localized surface plasmon resonance (LSPR) of Ti nanodot arrays (NDA) has not been studied much due to the surface oxide layer. In this study, we report the LSPR of titania on titanium (TOT) NDA fabricated on an indium tin oxide (ITO) glass using an anodic aluminum oxide layer with through-holes as a shadow mask. After depositing a 50 nm thick Ti layer, the TOT NDA was revealed on the ITO glass by dissolving the mask. The surface of TOT NDA was identified as TiO2 due to surface oxidation. Using XPS depth profiling, a chemical shift from the surface to interior showed a change of 4.6 eV, which corresponded to the difference in the binding energy between the TiO2 and Ti metal at the Ti 2p core level. Thus, the TOT NDA indicated that the Ti metal core was covered with a TiO2 layer. The LSPR of the TOT NDA with an 80 nm diameter was clearly observed at ~420 nm in the visible range, demonstrating the potential application of TOT NDA as a visible light-responsive photocatalyst.