Daniel Andrén

Gold Nanorod Rotary Motors Driven by Resonant Light Scattering.

Efficient and robust artificial nanomotors could provide a variety of exciting possibilities for applications in physics, biology and chemistry, including nanoelectromechanical systems, biochemical sensing, and drug delivery. However, the application of current man-made nanomotors is limited by their sophisticated fabrication techniques, low mechanical output power and severe environmental requirements, making their performance far below that of natural biomotors. Here we show that single-crystal gold nanorods can be rotated extremely fast in aqueous solutions through optical torques dominated by plasmonic resonant scattering of circularly polarized laser light with power as low as a few mW. The nanorods are trapped in 2D against a glass surface, and their rotational dynamics is highly dependent on their surface plasmon resonance properties. They can be kept continuously rotating for hours with limited photothermal side effects and they can be applied for detection of molecular binding with high sensitivity. Because of their biocompatibility, mechanical and thermal stability, and record rotation speeds reaching up to 42 kHz (2.5 million revolutions per minute), these rotary nanomotors could advance technologies to meet a wide range of future nanomechanical and biomedical needs in fields such as nanorobotics, nanosurgery, DNA manipulation and nano/microfluidic flow control.

Brownian fluctuations of an optically rotated nanorod

Gold nanorods can be optically trapped in aqueous solution and forced to rotate at kilohertz rates by circularly polarized laser light. This enables detailed investigations of local environmental p ...

Probing Photothermal Effects on Optically Trapped Gold Nanorods by Simultaneous Plasmon Spectroscopy and Brownian Dynamics Analysis

Plasmonic gold nanorods are prime candidates for a variety of biomedical, spectroscopy, data storage, and sensing applications. It was recently shown that gold nanorods optically trapped by a focused circularly polarized laser beam can function as extremely efficient nanoscopic rotary motors. The system holds promise for applications ranging from nanofluidic flow control and nanorobotics to biomolecular actuation and analysis. However, to fully exploit this potential, one needs to be able to control and understand heating effects associated with laser trapping. We investigated photothermal heating of individual rotating gold nanorods by simultaneously probing their localized surface plasmon resonance spectrum and rotational Brownian dynamics over extended periods of time. The data reveal an extremely slow nanoparticle reshaping process, involving migration of the order of a few hundred atoms per minute, for moderate laser powers and a trapping wavelength close to plasmon resonance. The plasmon spectroscopy and Brownian analysis allows for separate temperature estimates based on the refractive index and the viscosity of the water surrounding a trapped nanorod. We show that both measurements yield similar effective temperatures, which correspond to the actual temperature at a distance of the order 10-15 nm from the particle surface. Our results shed light on photothermal processes on the nanoscale and will be useful in evaluating the applicability and performance of nanorod motors and optically heated nanoparticles for a variety of applications.

A Frequency Selective Surface Based Focal Plane Receiver for the OLIMPO Balloon-Borne Telescope

We describe here a focal plane array of Cold-Electron Bolometer (CEB) detectors integrated in a frequency selective surface (FSS) for the 350 GHz detection band of the OLIMPO balloon-borne telescope. In our architecture, the two-terminal CEB has been integrated in the periodic unit cell of the FSS structure and is impedance matched to the embedding impedance seen by it and provides a resonant interaction with the incident submillimeter radiation. The detector array has been designed to operate in background noise limited condition for incident powers of 20 pW to 80 pW, making it possible to use the same pixel in both photometric and spectrometric configurations. We present high-frequency and dc simulations of our system, together with fabrication details. The frequency response of the FSS array, optical response measurements with hot/cold load in front of optical window, and with variable-temperature blackbody source inside cryostat are presented. A comparison of the optical response to the CEB model and estimations of noise equivalent power (NEP) is also presented.

Optically controlled stochastic jumps of individual gold nanorod rotary motors

Brownian microparticles diffusing in optical potential-energy landscapes constitute a generic test bed for nonequilibrium statistical thermodynamics and have been used to emulate a wide variety of physical systems, ranging from Josephson junctions to Carnot engines. Here we demonstrate that it is possible to scale down this approach to nanometric length scales by constructing a tilted washboard potential for the rotation of plasmonic gold nanorods. The potential depth and tilt can be precisely adjusted by modulating the light polarization. This allo`ws for a gradual transition from continuous rotation to discrete stochastic jumps, which are found to follow Kramers dynamics in excellent agreement with stochastic simulations. The results widen the possibilities for fundamental experiments in statistical physics and provide insights into how to construct light-driven nanomachines and multifunctional sensing elements.

Construction and Operation of a Light-driven Gold Nanorod Rotary Motor System

The possibility to generate and measure rotation and torque at the nanoscale is of fundamental interest to the study and application of biological and artificial nanomotors and may provide new routes towards single cell analysis, studies of non-equilibrium thermodynamics, and mechanical actuation of nanoscale systems. A facile way to drive rotation is to use focused circularly polarized laser light in optical tweezers. Using this approach, metallic nanoparticles can be operated as highly efficient scattering-driven rotary motors spinning at unprecedented rotation frequencies in water. In this protocol, we outline the construction and operation of circularly-polarized optical tweezers for nanoparticle rotation and describe the instrumentation needed for recording the Brownian dynamics and Rayleigh scattering of the trapped particle. The rotational motion and the scattering spectra provides independent information on the properties of the nanoparticle and its immediate environment. The experimental platform has proven useful as a nanoscopic gauge of viscosity and local temperature, for tracking morphological changes of nanorods and molecular coatings, and as a transducer and probe of photothermal and thermodynamic processes.

High index dielectric metasurfaces and colloidal solutions: from fabrication to application

High index dielectric nanoparticles and meta-materials have been proposed for many different applications, including light harvesting, sensing and metalenses. However, widespread utilization in practice also requires large-scale fabrication methods able to produce homogeneous structures with engineered optical properties in a cost effective manner. Here, it is presented a facile fabrication method for silicon nanoparticles which is scalable to 4-inch wafers and can produce a wide range of nanoparticle shapes on demand. We also show that the fabricated nanoparticles can be detached from their support using a simple substrate removal technique and then transferred to colloidal suspension. We will finally discuss some uses of the fabricated systems. For the metasurfaces, we will demonstrate complete absorption due to far field interference effects. For the nanoparticles colloids we will show the possibility of realizing an intrinsically chiral structure composed of a low-loss dielectric resonator and we will study optical trapping phenomena for different particle sizes and shapes.