Detection of Femtomolar Amyloid-ß Peptides for Early-Stage Identification of Alzheimer's Amyloid-ß Aggregation with Functionalized Gold Nanoparticles.

Progressive amyloid-ß (Aß) fibrillar aggregates have long been considered as the pathogenesis of Alzheimer's disease (AD). Biocompatible and stable cysteine-Aß peptide-conjugated gold nanoparticles (Cys-Aß@AuNP) are demonstrated as suitable materials for detecting subfemtomolar Aß peptides in human plasma. Incubation with Aß peptides causes the Cys-Aß@AuNP to aggregate and changes its absorption spectra. The spectral change is especially apparent and noticeable when detecting subfemtomolar Aß peptides, and the aggregates contain only two or three AuNPs. Cys-Aß@AuNP can also be used to identify early-stage Aß oligomerization, which is not possible using the conventional method, in which the fluorescence of thioflavin-T is measured. The ability to detect Aß oligomerization can facilitate therapeutics for AD. In addition, the binding of Aß peptides by Cys-Aß@AuNP in combination with centrifugation redirects the conventional Aß aggregation pathway and can effectively inhibit the formation of toxic Aß oligomers or fibrils. Therefore, the proposed Cys-Aß@AuNP can also be used to develop effective therapeutic agents to inhibit Aß aggregation. The results obtained in this study are expected to open revolutionary ways to both detect and inhibit Aß aggregation at an early stage.

Nonlinear two-photon pumped vortex lasing based on quasi-bound states in the continuum from perovskite metasurface.

The experimental observation of nonlinear two-photon pumped vortex lasing from perovskite metasurfaces is demonstrated. The vortex lasing beam is based on symmetry-protected quasi-bound states in the continuum (QBICs). The topological charge is estimated to be +1 according to the simulation result. The quality factor and lasing threshold are around 1100 and 4.28 mJ/cm2, respectively. Theoretical analysis reveals that the QBIC mode originates from the magnetic dipole mode. The lasing wavelength can be experimentally designed within a broad spectral range by changing the diameter and periodicity of the metasurface. The finite array size effect of QBIC can affect the quality factor of the lasing and be used to modulate the lasing. Results shown in this study can lead to more complex vortex beam lasing from a single chip and previously unidentified ways to obtain ultrafast modulation of the QBIC lasing via the finite array size effect.

Molecular Chirality Detection with Periodic Arrays of Three-Dimensional Twisted Metamaterials.

Rapid detection of the handiness of chiral molecules is an important topic for pharmaceutical industries because chiral drugs with opposing handiness sometimes exhibit unwanted side effects. In this research, a rapid optical method is proposed to determine the handiness of the chiral drug "Thalidomide". The platform is a large array of three-dimensional (3D) twisted metamaterials fabricated with a novel method by combining nanospherical-lens lithography (NLL) and hole-mask lithography (HML). The fabrication is high-throughput and the twisted metamaterials cover a large area. Strong circular dichroism (CD) response is observed in the near-infrared (NIR) region, which enables the chiral detection to be performed by a low-cost and portable spectroscope system. The proposed nanofabrication method significantly improves the capabilities of NLL and HML, which can be quickly adapted to fabricate various periodic 3D metamaterials. In addition, the results of this research pave the road for the rapid penetration of nanophotonics into the pharmaceutical industries.

A Polarization-Actuated Plasmonic Circulator.

A circulator for surface plasmon polaritons (SPPs) based on a plasmonic two-wire transmission-line (TWTL) structure is experimentally realized. A TWTL offers two distinct plasmon modes that can be independently excited, solely determined by the polarization of the laser field. Through controlled superposition of the two modes, TWTLs are exploited to enable polarization-actuated plasmonic circulators. In the first demonstration, the coupling antennas to the plasmonic circulator are designed to circulate SPPs sensitive to linearly polarized excitation. In the second design, the circulator reacts to the spin angular momenta carried by circularly polarized laser excitations. In both cases, the SPP circulation directions are directly controlled by the laser polarization, and the number of ports is easily expandable. Experimentally, a wide optical operational bandwidth of ∼100 nm is achieved. The results show a major step toward the realization of multifunctioning photonic nanocircuitry.

Polarization-Selecting III-Nitride Elliptical Nanorod Light-Emitting Diodes Fabricated with Nanospherical-Lens Lithography.

Current-injected elliptical nanorod light-emitting diodes (LEDs) are demonstrated to emit polarized light with a bottom-emitting configuration. The polarization ratio of the electroluminescence reaches 3.17 when the length of the minor axis for the elliptical nanorods is as small as 150 nm. Electromagnetic simulation confirms the occurrence of the polarization selectivity especially when the length of the minor axis is down to 150 nm. Light with different polarization travels at different speeds in these asymmetric elliptical nanorods. Only one polarization experiences destructive interference between the light directly from the source and the reflected light by the top metal interface. A thin light-blocking layer is incorporated to increase the polarization selectivity. It is also not recommended to infill the gap with SiO2 since the polarization selectivity will be reduced. The proposed nanorod LEDs are fabricated using top-down nanofabrication approaches by combining nanospherical-lens lithography and two-step etch processes, which are both fully compatible with current semiconductor manufacturing processes. Results in this study will help to develop a chip-level polarization-selecting LED, which will be very useful for applications that require polarized light. It is especially beneficial for applications that are not suitable for using an external polarizer or require polarized light at the individual chip level.

Top Illuminated Hysteresis-Free Perovskite Solar Cells Incorporating Microcavity Structures on Metal Electrodes: A Combined Experimental and Theoretical Approach.

Further technological development of perovskite solar cells (PSCs) will require improvements in power conversion efficiency and stability, while maintaining low material costs and simple fabrication. In this Research Article, we describe top-illuminated ITO-free, stable PSCs featuring microcavity structures, wherein metal layers on both sides on the active layers exerted light interference effects in the active layer, potentially increasing the light path length inside the active layer. The optical constants (refractive index and extinction coefficient) of each layer in the PSC devices were measured, while the optical field intensity distribution was simulated using the transfer matrix method. The photocurrent densities of perovskite layers of various thicknesses were also simulated; these results mimic our experimental values exceptionally well. To modify the cavity electrode surface, we deposited a few nanometers of ultrathin MoO3 (2, 4, and 6 nm) in between the Ag and poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) layers provide hydrophobicity to the Ag surface and elevate the work function of Ag to match that of the hole transport layer. We achieved a power conversion efficiency (PCE) of 13.54% without hysteresis in the device containing a 4 nm-thick layer of MoO3. In addition, we fabricated these devices on various cavity electrodes (Al, Ag, Au, Cu); those prepared using Cu and Au anodes displayed improved device stability of up to 72 days. Furthermore, we prepared flexible PSCs having a PCE of 12.81% after incorporating the microcavity structures onto poly(ethylene terephthalate) as the substrate. These flexible solar cells displayed excellent stability against bending deformation, maintaining greater than 94% stability after 1000 bending cycles and greater than 85% after 2500 bending cycles performed with a bending radius of 5 mm.

Large-Scale Nanofabrication of Designed Nanostructures Using Angled Nanospherical-Lens Lithography for Surface Enhanced Infrared Absorption Spectroscopy.

Nanophotonics has been a focused research discipline for the past decade and has resulted in many novel concepts that promise to change human life. However, the actual penetration of this research into real products is severely limited mostly due to the slow development of economic nanofabrication. In this study, we have demonstrated a versatile and low-cost nanofabrication method referred to as "angled nanospherical-lens lithography (A-NLL)", which is able to produce large-scale and periodic nanopatterns. The nanopatterns designed within a two-dimensional polar chart can be carefully fabricated on the substrate. The fabricated patterns easily cover an area larger than 1 cm2, which is beneficial as platforms for surface enhanced infrared absorption (SEIRA) where an expensive and bulky IR microscope is not required. We believe that the proposed A-NLL method is ideal for industrialization of future nanophotonic applications.

NiOx Electrode Interlayer and CH3 NH2 /CH3 NH3 PbBr3 Interface Treatment to Markedly Advance Hybrid Perovskite-Based Light-Emitting Diodes.

The performance of hybrid perovskite-based light-emitting diodes (LEDs) is markedly enhanced by the application of a NiOx electrode interlayer and moderate methylamine treatment. A hybrid perovskite-based LED exhibits a peak luminous efficiency of 15.9 cd A-1 biased at 8.5 V, 407.65 mA cm-2 , and 65 300 cd m-2 , showing a distinctive impact for future applications.

Nickel oxide electrode interlayer in CH3 NH3 PbI3 perovskite/PCBM planar-heterojunction hybrid solar cells.

This study successfully demonstrates the application of inorganic p-type nickel oxide (NiOx ) as electrode interlayer for the fabrication of NiOx /CH3 NH3 PbI3 perovskite/PCBM PHJ hybrid solar cells with a respectable solar-to-electrical PCE of 7.8%. The better energy level alignment and improved wetting of the NiOx electrode interlayer significantly enhance the overall photovoltaic performance.

High-throughput nanofabrication of infra-red and chiral metamaterials using nanospherical-lens lithography.

Various infra-red and planar chiral metamaterials were fabricated using the modified Nanospherical-Lens Lithography. By replacing the light source with a hand-held ultraviolet lamp, its asymmetric light emission pattern produces the elliptical-shaped photoresist holes after passing through the spheres. The long axis of the ellipse is parallel to the lamp direction. The fabricated ellipse arrays exhibit localized surface plasmon resonance in mid-infra-red and are ideal platforms for surface enhanced infra-red absorption (SEIRA). We also demonstrate a way to design and fabricate complicated patterns by tuning parameters in each exposure step. This method is both high-throughput and low-cost, which is a powerful tool for future infra-red metamaterials applications.

Lighting up ultraviolet fluorescence from chicken albumen through plasmon resonance energy transfer of gold nanoparticles.

Au nanoparticles (AuNPs), which easily aggregate in organic thin film, are observed to well-disperse in chicken albumen thin films. The incorporated AuNPs is distributed uniformly inside the thin film and is as dense as 650 (particles/µm(3)). In addition, enhanced ultraviolet (UV) fluorescence centered at 350 nm is observed from the AuNPs-containing chicken albumen thin film. The enhancement is proposed to be originated from the plasmon resonance energy transfer (PRET) from the d-band absorption of AuNPs to the chicken albumen protein. The enhanced fluorescence is further verified by the shorter fluorescence lifetime from the time-resolved fluorescence spectra. These results indicate that d-band transition of AuNPs can be used to interface with other UV-emitting biomolecules. Results in this study demonstrate that AuNPs exhibit future potentials in applications for both the organic thin-film technology and nano-biotechnology.

A large-scale sub-100 nm Au nanodisk array fabricated using nanospherical-lens lithography: a low-cost localized surface plasmon resonance sensor.

Large-scale Au nanodisk arrays are successfully fabricated using nanospherical-lens lithography (NLL). By incorporating both rotational oblique-angle deposition and oxygen plasma treatment, the improved NLL is capable of fabricating Au nanodisks with diameters as small as 75 nm that cover an area larger than 1 cm(2). The fabricated nanodisk arrays are investigated as sensitive localized surface plasmon resonance (LSPR) sensors. The extinction spectra of the Au nanodisk arrays reveal a narrower LSPR peak when the diameter becomes smaller. The shape imperfection severely limits the minimum obtainable linewidth, especially when the nanodisk diameter is smaller than 200 nm. The imperfection is found to be improved by thermal annealing at high temperatures. The maximum theoretically predicted and experimentally obtained figure-of-merit for Au nanodisk arrays whose periodicities are 500 nm are around 15 and 9, respectively. Further optimization of the periodicity and thickness of the nanodisks will further improve their sensitivity and lead to more novel applications.

Negatively charged gold nanoparticles inhibit Alzheimer's amyloid-ß fibrillization, induce fibril dissociation, and mitigate neurotoxicity.

Amyloids are pathogenic hallmarks in many neurodegenerative diseases such as amyloid-ß (Aß) fibrils in Alzheimer's disease (AD). Here, the effect of gold nanoparticles (AuNPs) on amyloids is examined using Aß as a model system. It is found that bare AuNPs inhibited Aß fibrillization to form fragmented fibrils and spherical oligomers. Adding bare AuNPs to preformed Aß fibrils results in ragged species where AuNPs bind preferentially to fibrils. Similar results are demonstrated with carboxyl- but not amine-conjugated AuNPs. Co-incubation of negatively charged AuNPs with Aß relieved Aß toxicity to neuroblastoma. Overall, it is demonstrated that AuNPs possessing negative surface potential serve as nano-chaperones to inhibit and redirect Aß fibrillization, which could contribute to applications for AD.

Observation of absorption-dominated bonding dark plasmon mode from metal-insulator-metal nanodisk arrays fabricated by nanospherical-lens lithography.

Plasmon hybridization modes are observed in the extinction spectra of a metal-insulator-metal (MIM) nanodisk array fabricated using nanospherical-lens lithography. Two distinct hybridization modes are observed in this vertically aligned configuration. Theoretical simulation indicates that the bonding mode located at a lower energy level exhibits an antiphase charge distribution and corresponds to the dark plasmon mode. This is vastly different compared to antibonding dark plasmon mode observed in the conventional dimer configuration. The observed mode is tunable over a wide spectral range simply by varying the insulator thickness and the diameters of the MIM nanodisks. Absorption is the dominating extinction process for the dark plasmon, while scattering dominates the bright plasmon mode. The ability to experimentally measure and tune dark plasmon modes using a MIM configuration should catalyze more novel studies that take full advantages of the absorption-dominated dark plasmon mode.

Surface potential variations on a silicon nanowire transistor in biomolecular modification and detection.

Using a silicon nanowire field-effect transistor (SiNW-FET) for biomolecule detections, we selected 3-(mercaptopropyl)trimethoxysilane (MPTMS), N-[6-(biotinamido)hexyl]-3(')-(2(')-pyridyldithio) propionamide (biotin-HPDP), and avidin, respectively, as the designated linker, receptor, and target molecules as a study model, where the biotin molecules were modified on the SiNW-FET to act as a receptor for avidin. We applied high-resolution scanning Kelvin probe force microscopy (KPFM) to detect the modified/bound biomolecules by measuring the induced change of the surface potential (ΔΦ(s)) on the SiNW-FET under ambient conditions. After biotin-immobilization and avidin-binding, the ΔΦ(s) on the SiNW-FET characterized by KPFM was demonstrated to correlate to the conductance change inside the SiNW-FET acquired in aqueous solution. The ΔΦ(s) values on the SiNW-FET caused by the same biotin-immobilization and avidin-binding were also measured from drain current versus gate voltage curves (I(d)-V(g)) in both aqueous condition and dried state. For comparison, we also study the ΔΦ(s) values on a Si wafer caused by the same biotin-immobilization and avidin-binding through KPFM and ζ potential measurements. This study has demonstrated that the surface potential measurement on a SiNW-FET by KPFM can be applied as a diagnostic tool that complements the electrical detection with a SiNW-FET sensor. Although the KPFM experiments were carried out under ambient conditions, the measured surface properties of a SiNW-FET are qualitatively valid compared with those obtained by other biosensory techniques performed in liquid environment.

Folding stability of amyloid-beta 40 monomer is an important determinant of the nucleation kinetics in fibrillization.

Amyloid formation is initiated by protein misfolding, followed by self-association to ultimately form amyloid fibrils. The discovery of toxic prefibrillar oligomers in many amyloidosis underscores the importance of understanding the folding mechanism prior to such aggregation. Here, we investigated the folding properties of the natively unfolded amyloid-ß (Aß) peptide and the familial variants (A21G, E22Q, E22G, E22K, and D23N) in Alzheimer's disease (AD). In combinations of native electrophoresis, analytical ultracentrifugation, fluorescence emission, and far-UV circular dichroism, we showed that all Aß40 variants are predominantly monomeric with similar residual secondary structures, but distinct hydrophobic-exposed protein surfaces. Guanidine hydrochloride (GdnHCl) denaturation in the absence and presence of trifluoroethanol (TFE) showed that Aß variants adopt an apparent 2-state equilibrium model with different stabilities, in which wild type is less stable than A21G but more stable than D23N and E22 mutants. By correlating the folding stability with the nucleation phase in fibrillization, we found the more stable the variant, the slower the nucleation, except for D23N. Besides, the unfolding of Aß conformation leads to reduced formation of mature fibrils, but an increase in nonfibrillar, amorphous type of aggregates. Overall, we demonstrated that folding stability of Aß is an important determinant of the nucleation kinetics.

Influence of surface plasmon resonance on the emission intermittency of photoluminescence from gold nano-sea-urchins.

The effect of surface plasmon resonance (SPR) on the blinking emission of photoluminescence from noble metal nanostructures still requires further investigation in quantum mechanics and limits their applications. We investigate one photon luminescent emission intermittency of noble metal nanostructures with differently sized sea-urchin-shaped nanoparticles, known as nano-sea-urchins (NSUs). The probability of the "on" process in one photon luminescent emission intermittency of NSUs increases due to the strong electric field of SPR. This mechanism is explained by the reaction potential threshold model we propose here. Furthermore, the ameliorated photoluminescence of NSUs is strong enough to excite waterweed bioluminescence and can act as an in vivo bio-light emitting device, which has potential applications in cytotoxicity, bio-imaging and bio-labeling.