Muhammad Umar

Biocompatible, optically transparent, patterned, and flexible electrodes and radio-frequency antennas prepared from silk protein and silver nanowire networks

Biological polymers offer new opportunities for flexible electronics, which are necessary for applications in soft and biological systems, because of their bio- and eco-friendly material traits. However, integrating an arbitrarily patterned electrode, the backbone of electronic devices, is still challenging when transparency of the electrode is required. Here, we report the fabrication of patterned silver nanowire (AgNW) networks buried at the surface of a silk fibroin film, which are suitable for bioelectronic applications that require biocompatibility, flexibility, high conductivity, and optical transparency. The AgNW-buried silk film exhibits excellent low sheet resistance of ∼15 Ω sq.−1 and high optical transparency of over 80%, along with smoothness of the surface. A light-emitting diode (LED) chip is successfully integrated on the patterned electrodes and can be stably turned on and off. Furthermore, we can produce a transparent resistor and a radio-frequency (RF) antenna on the silk film, and use them together as a food sensor that responds to the decreased conductivity caused by rancidity of spoiled food.

Silk protein as a new optically transparent adhesion layer for an ultra-smooth sub-10 nm gold layer

Ultra-thin and ultra-smooth gold (Au) films are appealing for photonic applications including surface plasmon resonances and transparent contacts. However, poor adhesion at the Au-dielectric interface prohibits the formation of a mechanically stable, ultra-thin, and ultra-smooth Au film. A conventional solution is to use a metallic adhesion layer, such as titanium and chromium, however such layers cause the optical properties of pure Au to deteriorate. Here we report the use of silk protein to enhance the adhesion at the Au-dielectric interface, thus obtaining ultra-smooth sub-10 nm Au films. The Au films that were deposited onto the silk layer exhibited superior surface roughness to those deposited on SiO2, Si, and poly(methyl methacrylate), along with improved adhesion, electrical conductivity, and optical transparency. Additionally, we confirm that a metal-insulator-metal optical resonator can be successfully generated using a silk insulating layer without the use of a metallic adhesion layer.

Single transverse mode protein laser

Here, we report a single transverse mode distributed feedback (DFB) protein laser. The gain medium that is composed of enhanced green fluorescent protein in a silk fibroin matrix yields a waveguiding gain layer on a DFB resonator. The thin TiO2 layer on the quartz grating improves optical feedback due to the increased effective refractive index. The protein laser shows a single transverse mode lasing at the wavelength of 520 nm with the threshold level of 92.1 μJ/ mm2.

A single mode distributed feedback laser for arbitrary gain morphology

We report a reusable photonic structure using the 25 nm thin and discrete titanium dioxide (TİO2) layer deposited on one dimensional (1D) quartz grating to induce single mode lasing from variety of states of gain medium. Optically thick solid and liquid gains were used to reveal single mode lasing with reliable performance. The simulation showed that the DFB mode was obtained by the thin TiO2 layer and could be tuned by changing the superstrate refractive index.

An optically transparent, flexible, patterned and conductive silk biopolymer film (Conference Presentation)

Transparent, flexible, and conducting films are of great interest for wearable electronics. For better biotic/abiotic interface, the films to integrate the electronics components requires the patterned surface conductors with optical transparency, smoothness, good electrical conductivity, along with the biofriendly traits of films. We focus on silk fibroin, a natural biopolymer extracted from the Bombyx mori cocoons, for this bioelectronics applications. Here we report an optically transparent, flexible, and patterned surface conductor on a silk film by burying a silver nanowires (AgNW) network below the surface of the silk film. The conducting silk film reveals high optical transparency of ~80% and the excellent electronic conductivity of ~15 Ω/sq, along with smooth surface. The integration of light emitting diode (LED) chip on the patterned electrodes confirms that the current can flow through the transparent and patterned electrodes on the silk film, and this result shows an application for integration of functional electronic/opto-electronic devices. Additionally, we fabricate a transparent and flexible radio frequency (RF) antenna and resistor on a silk film and apply these as a food sensor by monitoring the increasing resistance by the flow of gases from the spoiled food.