Nanoparticle manipulation using plasmonic optical tweezers based on particle sizes and refractive indices

Nanoparticle manipulation based on chiral plasmon effects

Chiral plasmonic structures have garnered increasing attention owing to their distinctive chiroptical response. Localized surface plasmon resonance can significantly enhance the circular dichroism and local electromagnetic field of chiral plasmonic structures, resulting in enhanced electromagnetic forces acting on surrounding nanoparticles. Moreover, the circular dichroism response of chiral structures provides an effective means for macroscopic adjustment of microscopic electromagnetic fields. However, chiral plasmon effects are naturally related to angular momentum, and particle control studies of chirality usually focus on angular momentum. This paper proposes a particle manipulation method utilizing chiral light-matter interactions. Through optimization of the optical response of the chiral structure, the direction of electromagnetic forces exerted on surrounding polystyrene particles reverses upon a change in the incident light's handedness. According to this characteristic, the movement direction control of polystyrene particles with a diameter of 100 nm was achieved. By altering the handedness of a single circularly polarized light, more than 94% high-precision particle manipulation was achieved, reducing the complexity of particle manipulation. This microfluidic method has significant implications for advancing microfluidic research and chiral applications.

Simultaneous Reconstruction of Multiple Time-Varying Thermal Properties Based on Translucent Materials

In the realm of high-tech materials and energy applications, accurately measuring the transient heat flow at media boundaries and the internal thermal conductivity of materials in harsh heat exchange environments poses a significant challenge when using conventional direct measurement methods. Consequently, the study of photothermal parameter reconstruction in translucent media, which relies on indirect measurement techniques, has crucial practical value. Current research on reconstructing photothermal properties within participating media typically focuses on single-objective or time-invariant properties. There is a pressing need to develop effective methods for the simultaneous reconstruction of time-varying thermal flow fields and internal thermal conductivity at the boundaries of participating media. This paper introduces a computational model based on the numerical simulation theory of internal heat transfer systems in participating media, stochastic particle swarm optimization algorithms, and Kalman filter technology. The model aims to enable the simultaneous reconstruction of various thermal parameters within the target medium. Our results demonstrate that under varying levels of measurement noise, the inversion results for different target parameters exhibit slight oscillations around the true values, leading to a reduction in reconstruction accuracy. However, overall, the model demonstrates robustness and accuracy in ideal conditions, validating its effectiveness.

Tunable plasmonic tweezers based on graphene nano-taper for nano-bio-particles manipulation: numerical study

We take advantage of graphene nano-taper plasmons to design tunable plasmonic tweezers for neuroblastoma extracellular vesicles manipulation. It consists of Si/SiO₂/Graphene stack topped by a microfluidic chamber. Using plasmons of isosceles-triangle-shaped graphene nano-taper with a resonance frequency of 6.25 THz, the proposed device can efficiently trap the nanoparticles. The plasmons of graphene nano-taper generate a large field intensity in the deep sub-wavelength area around the vertices of the triangle. We show that by engineering the dimensions of the graphene nano-taper and an appropriate choice of its Fermi energy, the desired near-field gradient force for trapping can be generated under relatively low-intensity illumination of the THz source when the nanoparticles are placed near the front vertex of the nano-taper. Our results show that the designed system with graphene nano-taper of L = 1200 nm length and W = 600 nm base size and THz source intensity of I = 2 mW/µm², can trap polystyrene nanoparticles with diameters of D = 140, 73, and 54 nm, and with trap stiffnesses of k_y = 9.9 fN/nm, k_y = 23.77 fN/nm, and k_y = 35.51 fN/nm at Fermi energies of E_f = 0.4, 0.5, and 0.6 eV, respectively. It is well known that the plasmonic tweezer as a high-precision and non-contact means of control has potential applications in biology. Our investigations demonstrate that the proposed tweezing device with L = 1200 nm, W = 600 nm, and E_f = 0.6 eV can be utilized to manipulate the nano-bio-specimens. So that, at the given source intensity, it can trap the neuroblastoma extracellular vesicles, which are released by neuroblastoma cells and play an important role in modulating the function of neuroblastoma cells and other cell populations, as small as 88 nm at the front tip of isosceles-triangle-shaped graphene nano-taper. The trap stiffness for the given neuroblastoma extracellular vesicle is obtained as k_y = 17.92 fN/nm.

Evaluations of nanoparticle capture and transport methods in dielectric bowtie core capillaries

We propose a flexibly tunable and low-loss optical burette with an all-dielectric bowtie core capillary structure, where nanoparticle arrays can be transported bidirectionally with incident light from one end. Multiple hot spots, acting as optical traps, are periodically distributed at the center of the bowtie cores along the propagation direction because of the mode interference effect of guided lights. By adjusting the beam waist position, the hot spots continuously move across the entire capillary length; thus, trapped nanoparticles also transfer with the hot spots. The bidirectional transfer can be realized simply by changing the beam waist in the forward or backward direction. We confirmed that nanosized polystyrene spheres can be bidirectionally moved along a capillary length of ≈ 20 µm. Furthermore, the magnitude of the optical force can be adjusted using the incident angle and beam waist width, whereas the trapping period can be adjusted using the incident wavelength. These results were evaluated using the finite-difference time-domain method. We believe that this new approach can be extensively used in the field of biochemical and life sciences because of the properties of an all-dielectric structure, bidirectional transportation, and single incident light.

Acoustic tweezers using bisymmetric coherent surface acoustic waves for dynamic and reconfigurable manipulation of particle multimers

HYPOTHESIS

The accurate and dynamic manipulation of multiple micro-sized objects has always been a technical challenge in areas of colloid assembly, tissue engineering, and organ regeneration. The hypothesis of this paper is the precise modulation and parallel manipulation of morphology of individual and multiple colloidal multimers can be achieved by customizing acoustic field.

EXPERIMENTS

Herein, we present a colloidal multimer manipulation method by using acoustic tweezers with bisymmetric coherent surface acoustic waves (SAWs), which enables contactless morphology modulation of individual colloidal multimers and patterning arrays by regulating the shape of acoustic field to specific desired distributions with high accuracy. Rapid switching of multimer patterning arrays, morphology modulation of individual multimers, and controllable rotation can be achieved by regulating coherent wave vector configurations and phase relations in real time.

FINDINGS

To demonstrate the capabilities of this technology, we have firstly achieved eleven patterns of deterministic morphology switching for single hexamer and precise switching between three array modes. In addition, the assembly of multimers with three kinds of specific widths and controllable rotation of single multimers and arrays were demonstrated from 0 to 22.4 rpm (tetramers). Therefore, this technique enables reversible assembly and dynamic manipulation of particles and/or cells in colloid synthesis applications.