Magnetic Field-Modulated Plasmonic Scattering of Hybrid Nanorods for FFT-Weighted OCT Imaging in NIR-II

Abstract

We report a method for fast Fourier transform (FFT)-weighted optical coherence tomography (OCT) in the second biological tissue transparency window by actively modulating the plasmonic scattering of Fe3O4@Au hybrid nanorods using magnetic fields. Instead of tracking the nanoparticles’ lateral displacement in conventional magnetomotive OCT imaging, we monitor the nanorod rotation and optical signal changes under an alternating magnetic field in real time. The coherent rotation of the nanorods with the field produces periodic OCT signals, and the FFT is then used to convert the periodic OCT signals in the time domain to a single peak in the frequency domain. This allows automatic screening of nanorod signals from the random biological noises and reconstruction of FFT-weighted images using a computer program based on a time-sequence image set. Compared with conventional magnetomotive OCT, the FFT-weighted imaging technique creates enhanced OCT images with dB-scale contrast over an order of magnitude higher than the original images.

Seeded Growth of Plasmonic Nanostructures in Deformable Polymer Confinement

“…Extensive overgrowth of Au on the seeds produces core–shell structures (i) that display magnetically tunable scattering properties under the irradiation of polarized light (ii). Reprinted with permission from ref . Copyright 2022 American Chemical Society.…”

“…28,29 Recently, we demonstrated the use of Fe 3 O 4 @Au NRs as active contrast agents for optical coherence tomographic (OCT) imaging, generating strong scattering signals by magnetically switching on their longitudinal resonance mode (Figure 6e). 28 In another effort, we have shown that the strong absorption associated with their longitudinal mode can lead to local heating, producing ultrasound signals for photoacoustic imaging when a pulsed laser is used as the light source. 29 In both cases, the imaging modalities can be enhanced or deactivated by controlling the nanorod orientation using magnetic fields, allowing effective minimization of background noises through simple pixel subtraction.…”

“…An advantageous feature of plasmonic nanostructures is their shape-dependent resonance, which allows for anisotropic behaviors in both absorption and scattering due to spatially differentiated photon-electron interactions. , In brief, the light-nanostructure interaction can be described by the Mie-Gans theory, in which the absorption-affecting depolarization factor alter with the aspect ratio of the plasmonic nanostructure . It enables convenient control over the plasmonic resonant frequency of the nanostructures over a broad range by simply controlling their shapes through chemical synthesis. − Further, by controlling their orientation collectively, e.g., through magnetic alignment of anisotropic nanorods hybridized with magnetic materials, one can create novel functional components that display orientation-dependent color contrast for applications in flexible displays and bioimaging, − or enable programmability in photothermal actuators that can be controlled by tunning the orientation or polarization of the light excitation. , Therefore, this shape dependence, coupled with the development of processes to enable uniform and robust synthesis and effective orientational alignment of the anisotropic plasmonic nanostructures, significant broadens their potential applications.…”

Smart Nanostructured Materials for SARS-CoV-2 and Variants Prevention, Biosensing and Vaccination

“…Taking nanorods for example, depending on the relative orientation of the nanorods to the polarization of the light, their LSPR has longitudinal and transverse modes [ 115 , 116 ]. These interesting optical properties have been used for developing high-performance mechanochromic and thermochromic sensors [ 116 , 117 ] or smart imaging contrast agents in photoacoustic imaging and optical coherence imaging [ 118 , 119 ]. The resonant frequency of plasmonic nanostructures is also highly susceptible to surrounding environments.…”

Magnetic assembly of stimuli-responsive chiral superstructures

“…Moreover, integrating optical materials into magnetic nanorods through surface coating or attachment techniques allows the magnetic manipulation of their optical characteristics. [11][12][13] This approach opens doors to developing stimuli-responsive chiroptical materials, incorporating responsive mechanisms that pave the way for practical applications in chiral sensing, optical display and information encryption. This paper reviews our recent progress in the field of magnetic field-induced chiral superstructures, highlighting their dynamic assembly, and the vast potential of these structures in practical applications.…”