Accessible Superchiral Near-Fields Driven by Tailored Electric and Magnetic Resonances in All-Dielectric Nanostructures

Detection and differentiation of enantiomers in small quantities are crucially important in many scientific fields, including biology, chemistry, and pharmacy. Chiral molecules manifest their handedness in their interaction with the chiral state of light (e.g., circularly polarized light), which is commonly leveraged in circular dichroism (CD) spectroscopy. However, compared to the linear refractive index molecular chirality is extremely weak, resulting in low detection efficiencies. Recently, it has been shown that these weak chiroptical signals can be enhanced by increasing the optical chirality of the electromagnetic fields interacting with chiral samples. Here, we show numerically and analytically that dielectric structures can provide an optimum chiral sensing platform by offering uniform superchiral near-fields. To illustrate this, we first study a simple dielectric dimer and show that circularly polarized light can induce parallel and out of phase electric and magnetic fields, which are spectrally and spatially overlapped, and therefore produce superchiral fields at the midpoint of the dimer. This behavior is in contrast to, for example, a plasmonic dimer, where the optical chirality is limited by the electric dipolar field, which is not completely out of phase with the incident magnetic field. With the insights gained from this analysis, next we develop an approach for overlapping electric and magnetic fields in a single particle, based on Kerker effect. In particular, we introduce a Kerker-inspired metasurface consisting of holey dielectric disks, which offers uniform and accessible superchiral near-fields with CD signal enhancements of nearly 24 times.

Enhanced Circular Dichroism and Chiral Sensing with Bound States in the Continuum

Hatice Altug, Yasaman Jahani, Andreas Tittl

We reveal that optical chirality at the nanoscale can be boosted dramatically by bound states in the continuum (BIC). We predict the enhancement of chiroptical signals from nanostructures supporting quasi-BICs in mid-IR with a record-high efficiency. (C) 2019 The Author(s)

IEEE2019

Optimized electrochemical breakdown etching using temporal voltage variation for formation of nanopores in a silicon membrane

Miao Zhang

Dielectric breakdown etching is a well-known method of making nanopores on thin (similar to 50 nm) dielectric membranes. However, voltage driven translocation of biomolecules through such nanopores becomes extremely fast. For improved detection, for instance by the current blockage, a high-aspect-ratio nanopore could be beneficial for slowing down the translocation. High-aspect-ratio nanopore on silicon fabrication requires a well-controlled process and is dependent on specific crystal orientation, dopant type and resistivity of substrate. Therefore, an optimized method of processing high-aspect-ratio nanopores is necessary considering the advantage of a silicon membrane being able to be integrated with standard CMOS processing. Here, we present an optimized fabrication method for mass-producing a single and an array of nanopores on a thick (2 mu m) silicon device layer based on a silicon-on-insulator (SOI) wafer. A method of temporal voltage variation is exploited to optimize the etching parameters for the nanopore formation during electrochemical breakdown etching, diameters of nanopores around 12 nm have been achieved. Besides, the correlation between the parameters of etching and nanopore diameter is deduced. The processed high-aspect-ratio nanopore enables applications in single-molecule sensing such as DNA, exosomes, viruses, and protein markers. The developed process is inexpensive, fast and can be batch fabricated.

ELSEVIER SCIENCE SA2021

Nanoscale Magnetometry with Single Fluorescent Nanodiamonds Manipulated in an Anti-Brownian Electrokinetic Trap

Metin Kayci

Studies on single-molecule spectroscopy and nanoscale detection have been remarkably driven by an interest to reveal quantum and conformational states of single particles, the intra-molecular dynamics and their response to physical observables hidden by ensemble level measurements. A straightforward practice used in enhancing the signal from single particles is either to immobilize them on an engineered substrate or to embed them in a solid matrix. Given that the biophysical properties of the host environment introduce new perturbations and the particles will not behave as in their native environment, such approaches are inefficient to reflect the real dynamics. Therefore, recent advances in the field of single-molecule have led to a renewed interest in novel trapping methods, increased efforts into the development of promising tools for extended investigation, and the manipulation of solution-phase bio-molecules in real time. Despite the variety of successful passive trapping techniques, precise manipulation through non-perturbative forces is a big challenge for nano-sized particles. Such techniques either exert high power to the sample or compel special operating conditions disturbing the native environment. Therefore, an active trapping scheme guiding non-perturbative forces can break the trade-off between the particle size and the excreted power. This dissertation presents the development of an active trapping set-up using non-perturbative electrokinetic feedback and demonstrates its performance on nano-sized single particles for aims in biophysics. The essential theme is the engineering aspect of the technique, including the feedback configurations for various fluidic devices, the corresponding particle tracking schemes and the integration of the trapping platform to an integrated circuit pattern for advanced manipulation aims. The second theme is on specialized single fluorescence nanodiamonds (FNDs) as scanning magnetometer in fluidics. The implemented active trapping tool is employed for the manipulation of a rotationally free single FND to detect the localized magnetic field through an optically detected magnetic resonance (ODMR) spectrum. While the laser beam used in particle tracking can serve in optical excitation, an external radio frequency (RF) source is not sufficient to achieve microwave manipulation. Therefore, an RF antenna is designed to transmit the microwave signal to the proximity of the trapping chamber for electron spin resonance (ESR) spectroscopy. A nanostage positioning controller introduces scanning ability to the sample plane, in relative position of the trapped particle, in order to map the distribution of the detected fields over a fluidic volume. As FNDs are also sensitive to many other physical quantities, nanoscale single particle trapping and diamond photonics linkages are realized in this work, which provide an outstanding alternative for detection and imaging in complex fluidic environments that are closed to AFM-like physically supported probes.

EPFL2016

Nanoscale Magnetometry with Single Fluorescent Nanodiamonds Manipulated in an Anti-Brownian Electrokinetic Trap

Metin Kayci

EPFL2016