Trapping-Assisted Sensing of Particles and Proteins Using On-Chip Optical Microcavities

An improved ability to sense particles and biological molecules is crucial for continued progress in applications ranging from medical diagnostics to environmental monitoring to basic research. Impressive electronic and photonic devices have been developed to this end. However, several drawbacks exist. The sensing of molecules is almost exclusively performed <i>via</i> their binding to a functionalized device surface. This means that the devices are seldom reusable, that their functionalization needs to be decided before use, and that they face the diffusion bottleneck. The latter challenge also applies to particle detection using photonic devices. Here, we demonstrate particle sensing using optical forces to trap and align them on waveguide-coupled silicon microcavities. A second probe laser detects the trapped particles by measuring the microcavity resonance shift. We also apply this platform to quantitatively sense green fluorescent proteins by detecting the size distribution of clusters of antibody-coated particles bound by the proteins

Media 2: Light field moment imaging

Originally published in Optics Letters on 01 August 2013 (ol-38-15-2666

Media 3: Light field moment imaging

Originally published in Optics Letters on 01 August 2013 (ol-38-15-2666

Media 1: High throughput multichannel fluorescence microscopy with microlens arrays

Originally published in Optics Express on 28 July 2014 (oe-22-15-18101

Media 4: Light field moment imaging

Originally published in Optics Letters on 01 August 2013 (ol-38-15-2666

Media 1: Light field moment imaging

Originally published in Optics Letters on 01 August 2013 (ol-38-15-2666

Media 1: An integrated microparticle sorting system based on near-field optical forces and a structural perturbation

Originally published in Optics Express on 13 February 2012 (oe-20-4-3367

Direct Observation of Beamed Raman Scattering

Appropriately designed surface plasmon nanostructures enable the emission patterns of surface-enhanced Raman scattering to be modified to facilitate efficient collection, an effect sometimes termed “beamed Raman scattering”. Here, we demonstrate the direct and unambiguous observation of this phenomenon by separating the Raman emission pattern from the luminescent background using energy momentum spectroscopy. We observe beamed Raman scattering from two types of optical antennas: the first are Yagi–Uda optical antennas, and the second are optical dimer antennas formed above a plasmonic substrate consisting of a gold film integrated with a one-dimensional array of gold stripes. For both antenna types, the emission patterns from different Raman lines are simultaneously measured. For the second antenna type, the emission patterns show signatures stemming from the bandstructure of the plasmonic substrate

Direct Particle Tracking Observation and Brownian Dynamics Simulations of a Single Nanoparticle Optically Trapped by a Plasmonic Nanoaperture

Optical trapping using plasmonic nanoapertures has proven to be an effective means for the contactless manipulation of nanometer-sized particles under low optical intensities. These particles have included polystyrene and silica nanospheres, proteins, coated quantum dots and magnetic nanoparticles. Here we employ fluorescence microscopy to directly observe the optical trapping process, tracking the position of a polystyrene nanosphere (20 nm diameter) trapped in water by a double nanohole (DNH) aperture in a gold film. We show that position distribution in the plane of the film has an elliptical shape. Comprehensive simulations are performed to gain insight into the trapping process, including of the distributions of the electric field, temperature, fluid velocity, optical force, and potential energy. These simulations are combined with stochastic Brownian diffusion to directly model the dynamics of the trapping process, that is, particle trajectories. We anticipate that the combination of direct particle tracking experiments with Brownian motion simulations will be valuable tool for the better understanding of fundamental mechanisms underlying nanostructure-based trapping. It could thus be helpful in the development of the future novel optical trapping devices

Harnessing the Interplay between Photonic Resonances and Carrier Extraction for Narrowband Germanium Nanowire Photodetectors Spanning the Visible to Infrared

At visible wavelengths, photodetection in three channels (red, green, and blue) enables color imaging. Yet the spectra of most materials provide richer information than just color, and therefore considerable interest exists for imaging with multiple spectral bands across the visible to infrared. This endeavor requires narrowband photodetection, which is generally achieved by combining broadband photodetectors with filters or spectrometers, but with added bulk and cost. Here we report, for the first time to our knowledge, vertical germanium nanowires as narrowband photodetectors. Our devices exhibit spectral response peaks that are as narrow as 40 nm and can be shifted from visible (∼600 nm) to infrared (∼1600 nm) wavelengths by appropriate design. The spectral selectivity arises from the nanowires acting as waveguides and, surprisingly, is enhanced by radial narrowing of the carrier collection region due to surface recombination. The incorporation of germanium into integrated circuits in a high-yield and cost-effective manner is well-established, making our approach promising for many detection applications