Optical conductivity-based ultrasensitive mid-infrared biosensing on a hybrid metasurface

Optical devices are highly attractive for biosensing as they can not only enable quantitative measurements of analytes but also provide information on molecular structures.Unfortunately,typical refractive index-based optical sensors do not have sufficient sensitivity to probe the binding of low-molecular-weight analytes.Non-optical devices such as field-effect transistors can be more sensitive but do not offer some of the significant features of optical devices,particularly molecular fingerprinting.We present optical conductivity-based mid-infrared(mid-IR)biosensors that allow for sensitive and quantitative measurements of low-molecular-weight analytes as well as the enhancement of spectral fingerprints.The sensors employ a hybrid metasurface consisting of monolayer graphene and metallic nano-antennas and combine individual advantages of plasmonic,electronic and spectroscopic approaches.First,the hybrid metasurface sensors can optically detect target molecule-induced carrier doping to graphene,allowing highly sensitive detection of low-molecular-weight analytes despite their small sizes.Second,the resonance shifts caused by changes in graphene optical conductivity is a well-defined function of graphene carrier density,thereby allowing for quantification of the binding of molecules.Third,the sensor performance is highly stable and consistent thanks to its insensitivity to graphene carrier mobility degradation.Finally,the sensors can also act as substrates for surfaceenhanced infrared spectroscopy.We demonstrated the measurement of monolayers of sub-nanometer-sized molecules or particles and affinity binding-based quantitative detection of glucose down to 200 pM(36 pg/mL).We also demonstrated enhanced fingerprinting of minute quantities of glucose and polymer molecules.

Electrically focus-tuneable ultrathin lens for high-resolution square subpixels

Owing to the tremendous demands for high-resolution pixel-scale thin lenses in displays,we developed a graphenebased ultrathin square subpixel lens(USSL)capable of electrically tuneable focusing(ETF)with a performance competitive with that of a typical mechanical refractive lens.The fringe field due to a voltage bias in the graphene proves that our ETF-USSL can focus light onto a single point regardless of the wavelength of the visible light—by controlling the carriers at the Dirac point using radially patterned graphene layers,the focal length of the planar structure can be adjusted without changing the curvature or position of the lens.A high focusing efficiency of over 60% at a visible wavelength of 405 nm was achieved with a lens thickness of <13 nm,and a change of 19.42% in the focal length with a 9% increase in transmission was exhibited under a driving voltage.This design is first presented as an ETF-USSL that can be controlled in pixel units of flat panel displays for visible light.It can be easily applied as an add-on to high resolution,slim displays and provides a new direction for the application of multifunctional autostereoscopic displays.

Growth of Serpentine Carbon Nanotubes on Quartz Substrates and Their Electrical Properties

A simple method for high-yield,chemical vapor deposition(CVD)synthesis of serpentine carbon nanotubes,employing quartz substrates and a molecular cluster catalyst,is described.The growth mechanism is analyzed by controlled addition of nanoscale barriers,and by mechanical analysis of the curved sections.The serpentine structures are used to study the electrical transport properties of parallel arrays of identical nanotubes,which show three-terminal conductance that scales linearly with the number of nanotube segments.