Rapidly evolving fields of biomedical, energy, and (opto)electronic devices bring forward the need for deformable conductors with constantly rising benchmarks for mechanical properties and electronic conductivity. The search for conductors with improved strength and strain have inspired the multiple studies of nanocomposites and amorphous metals. However, finding conductors that defy the boundaries of classical materials and exhibit simultaneously high strength, toughness, and fast charge transport while enabling their scalable production, remains a difficult materials engineering challenge. Here, composites made from aramid nanofibers (ANFs) and gold nanoparticles (Au NPs) that offer a new toolset for engineering high strength flexible conductors are described. ANFs are derived from Kevlar macrofibers and retain their strong mechanical properties and temperature resilience. Au NPs are infiltrated into a porous, free-standing aramid matrix, becoming aligned on ANFs, which reduces the charge percolation threshold and facilitates charge transport. Further thermal annealing at 300 °C results in the Au-ANF composites with an electrical conductivity of 1.25 × 10 4 S cm −1 combined with a tensile strength of 96 MPa, a Young's modulus of 5.29 GPa, and a toughness of 1.3 MJ m −3 . These para meters exceed those of most of the composite materials, and are comparable to those of amorphous metals but have no volume limitations. The plasmonic optical frequencies characteristic for constituent NPs are present in the composites with ANFs enabling plasmon-based optoelectronic applications.

Abstract

Broadband plasmonic absorbers are essential components for photovoltaic, photothermal, and light-emitting devices. They are often made by lithographic processes that impart out-of-plane surface features with subwavelength dimensions to metallic films. However, lithographic subwavelength patterning of inexpensive plasmonic ceramics, such as TiN, is challenging because of high-temperature processing and the chemical robustness of these materials. In this work, we show that layer-by-layer assembly (LbL) of TiN plasmonic nanoparticles with polyelectrolytes results in spontaneous formation of out-of-plane topography with subwavelength dimensions. The columnar morphology of these corrugated coatings and their plasmonic functionality results in broadband absorption capabilities exemplified by 90% of the light from the ultraviolet to infrared parts of the spectrum being absorbed. The method is applicable to large, flexible, and conformal surfaces with complex geometry. It is also fast, scalable, and environmentally friendly. LBL processing of TiN nanoparticles demonstrates the possibility of replacement of lithographic patterning with stochastic self-assembly processes in manufacturing of photonic metasurfaces.

A stronger coupling can be achieved if a molecule is placed into a small resonant Fabry-Perot cavity or to a vicinity of a nanostructure supporting surface plasmon (SP) resonance. The time evolution of the two coupled oscillators, e.g., a cavity and a molecule, can be described as a linear superposition of their normal hybrid modes. [4] The even (odd) oscillation mode has the higher (lower) frequency, ω ± = ω 0 ± Δ, and corresponds to the upper (lower) branch of the dispersion curve. (Here Δ is the coupling frequency and the frequencies of uncoupled oscillators ω 0 are assumed to be the same.) If Δ exceeds all relaxation rates in the system, the dispersion curve features the avoided crossing and the well-resolved energy gap known as the normal mode splitting or the Rabi splitting [4,5] (Figure 1a,b). This criterion does not require the coupling to be large, [3,4] e.g., ≈5 meV, [6] as long as all relaxation processes of importance are sufficiently slow. This is often the case of single quantum emitters coupled to cavities. [7,8] We also propose in Figure 1c,d a model to explain this splitting behavior, which shall be discussed in detail shortly.On the other hand, as the splitting energy 2Δ is getting comparable to ω 0 , one enters the so-called ultrastrong coupling regime. [9] This is the case of large ensembles of dye molecules coupled to plasmonic nanostructures and resonant cavities, which routinely leads to the normal mode splitting (proportional to the square root of the molecular number density / N V ) [4] of the order of 1 eV. [10] Such a large change in the eigenvalues of the hybrid modes paves the way to unprecedented control of electrical conductivity, [11] excitation transport, [12] surface potential, [13] and rates of chemical reactions. [9] Early research of the strong coupling was focused on quantum wells in resonant Bragg cavities. [5] In more recent years, this phenomenon has been studied at low and high (room) temperatures in multiple quantum and classical systems, including quantum dots, [7] single molecules, [8] and large molecular ensembles [14,15] interacting with localized and propagating SPs, [15,16] and cavities. [8,9,17] In spite of large-scale theoretical and experimental efforts, some fundamental aspects of the strong coupling remain to be unexplored. One of them is the debated applicability of the quantum mechanical model to large ensembles of molecules, which may be possible if the latter act as one "giant atom," [4] providing for coherent spontaneous emission, [18,19] and energy oscillations. [20] This fundamental question and the intriguing Strong coupling of excitons in macroscopic ensembles of quantum emitters and cavities (or surface plasmons) can lead to dramatic change of the optical properties and modification of the dispersion curves, characterized by the normal mode splitting of the order of 1 eV. Such gigantic alteration of the hybrid energy states enables scores of unparalleled physical phenomena and functionalities, ranging from enhancement of electrical conductivity to co...

We discovered that several types of steroid hormones quench the fluorescence of quantum dots (QDs) at close proximity. Inspired by the finding, we developed a new type of biosensor for the sensitive detection of cortisol via direct fluorescence quenching of functionalized QD probes directly induced by the capture of target cortisol without additional reporter reagents. The detection selectivity was provided by cortisol-selective aptamers or anticortisol antibodies conjugated on the QD surfaces. With the magnetic nanoparticle labeling, the new sensing method enabled rapid cortisol sensing at physiologically relevant concentrations and yielded the detection limit of ∼1 nM for aptamer-based sensors and ∼100 pM for antibody-based sensors. We also evaluated the new detection method using saliva samples with an optimized sample preparation process under the assistance of magnetic manipulation. The result showed a satisfying recovery rate for spiked saliva tests. The facile sensing technology offers an appealing approach for the detection of steroid hormones in point-of-care settings.