arXiv subjects

Theodore Anyika

Publications and source records attributed to Theodore Anyika.

5 recordsLinked to original sources

arXiv2026

Experimental Investigation of Surface Passivation Chemistries for Optical Nanotweezers

Nanotweezers are actively investigated as a powerful means to reversibly trap and characterize nanoparticles with profound biological and environmental importance. To ensure that these particles can be reversibly trapped and released, surface passivation is essential. To mitigate the issue of fouling, we investigated the antifouling properties of poly(sodium styrene sulphate) (PSS) synthesized using the Atom Transfer Radical Polymerization (ATRP) technique on our previously reported gold-based Interferometric Electrohydrodynamic Tweezers (IET) device. Fluorescence and interferometric scattering (ISCAT) imaging were used to record trapping performance and study the antifouling properties of our passivated nanotweezer device. The results show that PSS exhibits superior anti-fouling performance against polystyrene nanoparticles when compared to 11-mercaptoundecanoic acid (MUA). By comparing the antifouling properties of PSS and zwitterionic poly(methacryloyloxyethyl phosphorylcholine) (PMPC) in preventing extracellular vesicle adhesion, we found that both exhibited similar performance. Overall, the ATRP technique is broadly applicable across nanotweezer substrates with appropriately chosen initiators.

physics.optics↗

arXiv2025

Engineering thermal emission with enhanced emissivity and quality factor using bound states in the continuum and electromagnetically-induced absorption

Metal-based thermal metasurfaces exhibit stable spectral characteristics under temperature fluctuations, in contrast to more traditional gray- and near black-bodies, as well as some dielectric metasurfaces, whose emission spectra shift with changing temperatures. However, they often suffer from limited quality (Q) factors due to significant non-radiative ohmic losses. In this study, we address the challenge of achieving high emissivity and Q-factors in metal-based thermal emitters. By leveraging the coupling between a magnetic dipole resonance and two bound-state-in-continuum (BIC) resonances to achieve electromagnetically induced absorption (EIA) in an asymmetric metallic ring structure, we design a metal-based thermal metasurface with a near-unity emissivity (0.96) and a Q factor as high as 320 per simulations. Experimental validation yields an emissivity of 0.82 and a Q factor of 202, representing an approximately five-fold improvement in the experimentally measured Q factor compared to the state-of-the-art metal-based thermal metasurfaces. Our work offers a promising approach for developing efficient, narrow-band, directional thermal emitters with stable emission spectra across a wide temperature range.

physics.optics↗

arXiv2024

Rapid Trapping and Label-free Characterization of Single Nanoscale Extracellular Vesicles and Nanoparticles in Solution

Achieving high-throughput, comprehensive analysis of single nanoparticles to determine their size, shape, and composition is essential for understanding particle heterogeneity with applications ranging from drug delivery to environmental monitoring. Existing techniques are hindered by low throughput, lengthy trapping times, irreversible particle adsorption, or limited characterization capabilities. Here, we introduce Interferometric Electrohydrodynamic Tweezers (IET), an integrated platform that rapidly traps single nanoparticles in parallel within three seconds. IET enables label-free characterization of particle size and shape via interferometric imaging and identifies molecular composition through Raman spectroscopy, all without the need for fluorescent labeling. We demonstrate the platform's capabilities by trapping and imaging colloidal polymer beads, nanoscale extracellular vesicles (EVs), and newly discovered extracellular nanoparticles known as supermeres. By monitoring their interferometric contrast images while trapped, we accurately determine the sizes of EVs and supermeres. Our IET represents a powerful optofluidics platform for comprehensive characterization of nanoscale objects, opening new avenues in nanomedicine, environmental monitoring, and beyond.

physics.optics↗

arXiv2023

Optically assisted diffusophoretic tweezers using resonant plasmonic bowtie nano-antennas

Plasmonic antennas, leveraging localized surface plasmon resonance (LSPR), hold significant promise for efficiently trapping nanoscale particles at low power levels. However, their effectiveness is hindered by photothermal effects in metallic nanoparticles, leading to repulsive thermophoretic forces. To address this limitation, we propose a novel hybrid approach that combines depletion attraction and photothermal effects inherent in plasmonic structures, capitalizing on thermally induced concentration gradients. Through the thermophoretic depletion of polyethylene glycol (PEG) molecules around plasmonic hotspots, we create sharp concentration gradients, enabling precise localization of nanoscopic particles through a synergistic effect with diffusophoretic forces. In our experiments, we successfully demonstrate the trapping and dynamic 2D manipulation of 100 nm polystyrene beads, showcasing the platform's potential for colloidal assembly at the nanoscale. Remarkably, this method maintains highly stable trapping performance even at an incredibly low 2.5 mW laser power, rendering it particularly appealing for applications involving biological species. Our study introduces a promising avenue for the precise and efficient manipulation of sub-nanoscale particles, with wide-ranging implications in nanotechnology, biophysics, and nanomedicine. This research opens up new opportunities for advancing nanoscale particle studies and applications, ushering in a new era of nanoscale manipulation techniques.

physics.optics↗

arXiv2023

Mirror-enhanced plasmonic nanoaperture for ultrahigh optical force generation with minimal heat generation

Double Nanohole Plasmonic Tweezers (DNH) have revolutionized particle trapping capabilities, enabling trapping of nanoscale particles well beyond the diffraction limit. This advancement allows for the low-power trapping of extremely small particles, such as 20 nm nanoparticles and individual proteins. However, to mitigate the potentially amplified effects of plasmonic heating at resonance illumination, DNH plasmonic tweezers are typically operated under off-resonance conditions.Consequently, this results in a decrease in optical forces and electric field enhancement within the plasmonic hotspot, which is undesirable for applications that require enhanced light-matter interaction like Surface Enhanced Raman Spectroscopy (SERS). In this study, we present a novel design for DNH plasmonic tweezers that addresses these limitations and provides significantly higher field enhancements. By introducing a reflector layer, on-resonance illumination can be achieved while significantly reducing plasmonic heating.This reflector layer facilitates efficient dissipation of heat both in-plane and axially. Furthermore, the integration of a reflector layer enables a redistribution of hotspots via Maxwell's boundary conditions for metals, creating more accessible hotspots optimal for applications that require enhanced light-matter interaction. We also demonstrate low-power trapping of small extracellular vesicles using our novel design, thereby opening possibilities for applications such as SERS and single photon emission that require intense light-matter interaction.

physics.optics↗