Optical fibers are widely used in biomedical applications for sensing, imaging, and therapies. Unlike existing solid-state optical fibers, soft polymer and hydrogel fibers offer physical and chemical properties well suited for functionalization with biomolecules and long-term implantation in the body. Here, hydrogel optical fibers are fabricated with glucose-sensitive moieties and the swelling-induced sensing is demonstrated. The core of the fiber is made of poly(acrylamide-co-poly(ethylene glycol) diacrylate) (p(AM-co-PEGDA)) hydrogel functionalized with phenylboronic acid. The complexation of the phenylboronic acid and cis diols of glucose molecules lowers the apparent pKa of the hydrogel network and increases the concentration of the boronate anions that enhances the Donnan osmotic pressure to swell and change the physical size of the hydrogel optical fiber. This mechanism is reversible through ester group dynamic covalent binding of the phenylboronic acid with glucose molecules. Dynamic changes in the effective RI of the hydrogel optical fiber are measured through light propagation loss. The sensor sensitivity to glucose concentration is 1.2 mmol L−1 over a physiological range of 1–12 mmol L−1. The biocompatible hydrogel optical fibers may be subcutaneously implanted for continuous monitoring of interstitial glucose concentrations.

Recently, there has been a drive to design and develop fully tunable metamaterials for applications ranging from new classes of sensors to superlenses among others. Although advances have been made, tuning and modulating the optical properties in real time remains a challenge. We report on the first realization of a reversible electrotunable liquid mirror based on voltage-controlled self-assembly/disassembly of 16 nm plasmonic nanoparticles at the interface between two immiscible electrolyte solutions. We show that optical properties such as reflectivity and spectral position of the absorption band can be varied in situ within ±0.5 V. This observed effect is in excellent agreement with theoretical calculations corresponding to the change in average interparticle spacing. This electrochemical fully tunable nanoplasmonic platform can be switched from a highly reflective 'mirror' to a transmissive 'window' and back again. This study opens a route towards realization of such platforms in future micro/nanoscale electrochemical cells, enabling the creation of tunable plasmonic metamaterials.

This work presents an original approach to create holograms based on the optical scattering of plasmonic nanoparticles. By analogy to the diffraction produced by the scattering of atoms in X-ray crystallography, we show that plasmonic nanoparticles can produce a wave-front reconstruction when they are sampled on a diffractive plane. By applying this method, all of the scattering characteristics of the nanoparticles are transferred to the reconstructed field. Hence, we demonstrate that a narrow-band reconstruction can be achieved for direct white light illumination on an array of plasmonic nanoparticles. Furthermore, multicolor capabilities are shown with minimal cross-talk by multiplexing different plasmonic nanoparticles at subwavelength distances. The holograms were fabricated from a single subwavelength thin film of silver and demonstrate that the total amount of binary information stored in the plane can exceed the limits of diffraction and that this wavelength modulation can be detected optically in the far field.holography | nanotechnology | optics M etallic nanoparticles have been used for centuries to create vibrant colors in works of art. The Lycurgus cup (fourth century), for example, uses metallic nanoparticles to produce a dichroic effect. The nanoparticles are positioned randomly, and the optical characteristics can be approximated using its effective refractive index. Their spectra response depends on the size, shape, and material of the nanoparticles (1). This phenomenon is analogous to the electronic resonance of an antenna in the visible region of the electromagnetic spectrum. In photonics, behavior of this kind is attributed to the interaction of the electric component of light and free electron oscillations in the materials, commonly referred to as surface plasmon resonance (SPR). Although this phenomenon has always fascinated scientists, only over recent years has it been possible to accurately manipulate these structures on the nanoscale due to improved fabrication techniques. In this work, we show a novel approach to produce narrow-band diffraction and holography based on plasmonic enhanced optical scattering of nanostructures. The diffraction produced by the scattering of atoms has been widely studied in X-ray crystallography. We apply a similar concept with 2D arrays of scattering nanoparticles to produce diffraction for visible light. Furthermore, we designed and fabricated a directbeam hologram that produces a narrow-band image when directly observed in reflection. We also achieved colorful holography by placing two independent plasmonic nanostructures in a subwavelength distance to diffract two colors simultaneously. In contrast with dielectric multiplexing of nansutructures, we show that metallic nanoparticles can be uncoupled because of their plasmonic properties. This feature allows them to carry independent wavelength information without cross-talk.In the traditional concept of holography, the fringes that produce diffraction are larger than half the wavelength. For instance, accor...

We prove theoretically and experimentally the concept of polarization holography by producing visible diffraction through radiation emitted by plasmonic nanoantennas. We show a methodology to selectively activate the nanoantenna emission by controlling the orientation of the electric field of a beam. Additionally, we demonstrate that it is possible to superpose two independent transverse nanoantennas in the same plane without producing interference in their radiated field. Hence, we introduce an alternative view to the traditional concept of holography where fringes (or diffractive units) are band-limited to half the wavelength.

Dynamic photonic structures can be tuned by changing the periodic structure and/or the index of refraction. [ 1 ] These dynamic photonic structures allow optically responsive capability to control the properties of light and act as optical transducers to sense external stimuli. [ 2 ] Tunable optical systems operating in the visible and near-infrared region offer great promise for designing adaptive optical materials, telecommunication devices and sensors. Such sensors have been prepared by various methods, including microfabrication, self-assembly or a combination of both. [ 3 ] However, achieving the attributes of a narrow-band response with a high-tunability range to construct off-axis optical sensors still remains a signifi cant challenge.We recently developed an optical sensing platform [ 4 ] based on Denisyuk refl ection holography [ 5 ] and in situ size reduction of metallic nanoparticles in polymers through laser ablation, where an intense laser pulse produces Bragg gratings in a fraction of the time, cost and complexity compared to silver-halide chemistry-based fabrication techniques. [ 6 ] This technique allows the fabrication of holographic sensors that display improved versatility and scalability. The platform utilizes an effi cient approach to produce off-axis chemical-stimuli responsive holographic sensors with a large, reversible narrow-band tunability, using metallic nanoparticles that can be organized in densityconcentrated 3D regions.The present work employs a hologram fabricated by laser ablation comprising of a functionalized hydrophilic host polymer. The optical characteristics of the system were investigated by analyzing the distribution of the mean diameter of Ag 0 nanoparticles, effective refractive indices of ablated and non-ablated polymer-nanoparticle regions, along with angular-resolved measurements. Furthermore, the system was characterized through computational modeling and diffraction simulations. The putative clinical utility of the sensor for the quantifi cation of pH was demonstrated with large wavelength shifts in the entire visible spectrum.Our sensor employs a simultaneous lateral and vertical periodic diffraction grating of silver nanoparticles dispersed within a poly (hydroxyethyl methacrylate)-based (pHEMA) matrix with a dry thickness of approximately 10 µm. The diffracted light is spectrally concentrated at a specifi c narrowband color due to the vertically-ordered periodicity. We use 6 ns-pulsed laser (λ = 532 nm, 240 mJ) standing waves to order the density of silver nanoparticles (mean diameter of 13 ± 9 nm) into regions with a periodicity of approximately half of the wavelength distributed throughout the cross section of the polymer matrix (see Supporting Information). The fabrication of the holographic sensors begins with UV-initiated free radical polymerization of the pHEMA-based hydrogel on an O 2 -plasma-treated poly (methyl methacrylate) (PMMA) substrate ( Figure 1 (a)). Subsequently, Ag + ions are perfused into the pHEMA polymer matrix (Figure 1 (b)), and reduc...