Particle directional and fixed-point transport system and method based on asymmetric astigmatism light field regulation and control

Abstract

The invention discloses a particle directional and fixed-point transport system and method based on asymmetric astigmatism light field regulation and control, and belongs to the technical field of optical micro-control. The system comprises a laser, a cylindrical lens, a first plano-convex lens, a second plano-convex lens, a first reflector, a second reflector and a microscope objective. The cylindrical lens is controlled in an off-axis mode to enable a light beam to be incident vertically in an off-axis mode, and light intensity deviation perpendicular to the optical tweezer line direction is formed on the focal plane of the cylindrical lens. And converting the offset into light intensity gradient distribution along the optical tweezers line direction by using a reflector group, and generating the asymmetric linear optical tweezers after focusing by a microscope objective. The light field generates a directional net scattering force to drive the particles to move unidirectionally along the optical tweezers line direction while maintaining stable capture of the particles. Active modulation devices such as an acousto-optic deflector and a spatial light modulator are not needed, particle directional transportation can be achieved only through cooperative regulation and control of optical elements, and the device has the advantages of being simple in structure, low in cost and high in light field stability and is suitable for biomedical microoperation and particle control in a micro-fluidic chip.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical micro-manipulation, and particularly to a micro-particle directional and fixed-point transport system and method based on asymmetric astigmatic light field regulation, which utilizes asymmetric linear optical tweezers to achieve stable capture and directional driving of micro-particles. BACKGROUND

[0002] Optical tweezers technology utilizes the optical gradient force potential well generated by a highly focused laser beam to achieve non-contact capture and manipulation of micro-nano particles. The piconewton-level acting force is suitable for precise operation of biological cells, colloidal particles and other objects. Since Ashkin first realized a single-beam three-dimensional optical trap in 1986, the technology has been widely used in the fields of biomedicine (such as cell sorting), physics (such as colloidal dynamics) and micro-nano manufacturing. Traditional optical tweezers rely on a symmetric light field formed by focusing a Gaussian beam through a high numerical aperture objective lens, and the center of its gradient force potential well is symmetrical, which can only achieve fixed-point capture of micro-particles. To achieve directional transport, mechanical scanning or complex external field modulation is required, resulting in delayed system response and insufficient stability.

[0003] To break through the limitations of single-point capture, researchers have developed various directional manipulation strategies. A cylindrical lens is used to convert a Gaussian beam into a linearly focused spot, which can simultaneously capture multiple micro-particles arranged in one dimension. However, the symmetrical light intensity distribution leads to a balance of the gradient force, and the micro-particles are in a random diffusion state in the line, which cannot achieve directional driving. Phase modulation through a spatial light modulator (SLM) to generate a multi-focus array or an asymmetric light field can achieve complex path manipulation. However, the SLM is expensive, has low diffraction efficiency (usually <80%), and the focal spot uniformity generated by the iterative algorithm is poor, resulting in fluctuations in the capture force. Tapered or parabolic fiber probes can simplify the system structure, but their strong focusing effect limits the micro-particles to the vicinity of the port (usually <20 μm), and long-distance transport requires reliance on fluid resistance or photothermal effects, which can easily cause damage to biological samples.

[0004] Based on the experimental verification of micro-particle transport by asymmetric scanning line optical tweezers, the transverse scattering force component can drive the micro-particles to move along the scanning line, but high-speed scanning (kHz level) is required to maintain the stability of the force field, resulting in low energy utilization. An acousto-optic deflector (AOD) can dynamically regulate the intensity distribution of the linear optical tweezers to generate an asymmetric scattering force component. However, the response bandwidth of the AOD limits the transport speed, and the system complexity increases significantly when manipulating multiple particles. The deformable linear optical tweezers technology adjusts the light field configuration by rotating the cylindrical lens, which can achieve capture and rotation of micro-particles, but still cannot achieve one-way linear transport. SUMMARY

[0005] This invention provides a particle-oriented and targeted transport system and method based on asymmetric astigmatic field modulation, aiming to provide a solution that eliminates the need for active modulators. This system generates asymmetric linear optical tweezers solely through the coordinated modulation of optical elements, achieving directional particle transport.

[0006] A particle-oriented and point-to-point transport system and method based on asymmetric astigmatic field modulation, characterized in that, as Figure 1 As shown, it includes: a Gaussian beam (1), a cylindrical lens (2), a first plano-convex lens (3), a first reflecting mirror (4), a second plano-convex lens (5), a second reflecting mirror (6), and a microscope objective (7).

[0007] The system operates by including the following steps:

[0008] 1. Astigmatic optical tweezers modulation: The Gaussian beam output from the laser is shaped into a linear laser beam by a cylindrical lens, and then passes sequentially through a first plano-convex lens, a first reflecting mirror, a second plano-convex lens, a second reflecting mirror, and a microscope objective to finally generate linear optical tweezers.

[0009] 2. Off-axis adjustment: Adjust the displacement ∆y of the cylindrical lens along its sagittal plane so that the laser beam is incident perpendicularly to the cylindrical lens off-axis. After being converged by the cylindrical lens, the intensity distribution along the focal line in the direction perpendicular to the optical tweezers line is shifted.

[0010] 3. Optical path conversion: By adjusting the reflector group, the light intensity convergence shift perpendicular to the optical tweezers line direction caused by off-axis incident light is converted into a light intensity convergence shift along the optical tweezers line direction.

[0011] 4. Asymmetric linear optical tweezers capture and drive: After the microscope objective is focused, it forms an asymmetric linear optical tweezer with a significant intensity gradient. This light field gradient generates a net scattering force component that drives the directional motion of particles. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the optical structure of the particle-oriented and point-to-point transport system and method based on asymmetric astigmatic light field modulation described in this invention.

[0013] Figure 2 This is a simulation diagram of the back focal line light field distribution of the off-axis incident cylindrical lens described in this invention.

[0014] Figure 3 This is a simulation diagram of the asymmetric linear optical tweezers light field distribution formed by the off-axis incident cylindrical lens of the present invention after passing through the reflecting mirror group and the microscope objective.

[0015] Figure 4 The optical field distribution map of the asymmetric linear optical tweezers, acquired by a CCD camera, is shown in the optical particle directional transport system constructed according to the present invention.

[0016] Figure 5 This diagram illustrates the transport positions at different times when two 10µm polystyrene microspheres are captured and transported along the optical tweezers line (downward) using an asymmetric linear optical tweezers system constructed according to the present invention.

[0017] Explanation of reference numerals in the attached figures: 1-Gaussian beam, 2-cylindrical lens, 3-first plano-convex lens, 4-first reflecting mirror, 5-second plano-convex lens, 6-second reflecting mirror, 7-microscope objective. Detailed Implementation

[0018] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0019] (I) Astigmatic optical tweezers modulation stage: First, a basic linear optical tweezers system is built. The Gaussian beam is shaped into a linear laser beam by a cylindrical lens, and then collimated and expanded by a first plano-convex lens and a second plano-convex lens in sequence. The first and second reflecting mirrors are adjusted so that the beam enters the entrance pupil of the microscope objective vertically, and finally forms symmetrical linear optical tweezers on the focal plane of the objective.

[0020] (II) Off-axis manipulation and optical path conversion stage: Based on the system built in the first stage, the cylindrical lens is moved along the sagittal plane of the cylindrical lens, so that the laser beam enters the cylindrical lens at a preset off-axis distance (the specific off-axis distance is determined according to the actual application requirements). The optical field distribution of the beam after off-axis incident on the cylindrical lens on its focal plane is as follows. Figure 2 As shown in the simulation, the peak light intensity shifts to the left from the center position in the direction perpendicular to the optical tweezers line. The first reflecting mirror is adjusted to compensate for the overall beam shift caused by off-axis incident light, ensuring the beam remains perpendicular to the second plano-convex lens. After adjustment by the second reflecting mirror, the original intensity convergence shift perpendicular to the optical tweezers line is converted into a shift along the optical tweezers line. The beam is finally converged by the microscope objective, forming a peak at the focal plane as shown in the simulation. Figure 3 The simulation image shows an asymmetric linear optical tweezer with an intensity gradient.

[0021] (III) Asymmetric linear optical tweezers capture and drive stage: The system is built according to the above method. Figure 4 The experiment demonstrates an asymmetric linear optical tweezers generated by the experimental system, with its light intensity distribution captured by a CCD camera. This optical tweezers was used to capture and directionally transport polystyrene microspheres with a particle size of 10 μm. Figure 5 The images show screenshots of the positions of two polystyrene microspheres at different times during their transport along an asymmetric linear optical tweezers direction (downward) (sourced from experimental video frames).

[0022] This invention pioneers an "off-axis-reflector" offset conversion mechanism. By using a non-coplanar layout of the reflector group, the light intensity convergence offset generated by off-axis incident light perpendicular to the optical tweezers line is converted into a light intensity convergence offset along the optical tweezers line. No active device is required, making it suitable for live cell delivery.

Claims

1. A particle-oriented and point-to-point transport system and method based on asymmetric astigmatic field modulation, characterized in that: A cylindrical lens is used to modulate the astigmatism of a laser beam, which is then focused by an objective lens to form a linear optical tweezer. The cylindrical lens is then translated so that the laser beam is incident off-axis in the sagittal plane of the cylindrical lens, thereby controlling the spatial distribution of the astigmatic light after focusing by the objective lens and generating a linear optical tweezer with asymmetric intensity distribution characteristics. The optical gradient force generated by this asymmetric optical field can capture multiple particles and drive the particles to be transported in a directional and fixed-point manner along the trajectory of the linear optical tweezer.

2. The particle-oriented and point-to-point transport system and method based on asymmetric astigmatic field modulation as described in claim 1, characterized in that, The system comprises, arranged sequentially along the optical path: A laser generates a Gaussian beam (1); a cylindrical lens (2) is used to perform astigmatic modulation and intensity shift modulation on the Gaussian beam; a beam expanding system, which includes a first plano-convex lens (3), a first reflecting mirror (4), a second plano-convex lens (5), and a second reflecting mirror (6) arranged sequentially along the optical path, is used to expand the astigmatic beam modulated by the cylindrical lens and adjust the optical path; a microscope objective (7) is used to collect and focus the modulated astigmatic beam to form the linear optical tweezers; Specifically, the position of the center of the cylindrical lens relative to the incident position of the Gaussian beam on the cylindrical lens is adjusted so that the incident end of the laser beam is offset along the perpendicular axis of the cylindrical lens; after being modulated by the cylindrical lens, the Gaussian beam converges at the focal plane of the cylindrical lens to generate linear astigmatism, the intensity of which is shifted in the direction perpendicular to the line; the first mirror, the second mirror, and the microscope objective are used to convert the shift of the intensity of the linear astigmatism in the direction perpendicular to the line into a shift of the intensity of the linear optical tweezers in the direction of the line, thereby forming the asymmetric linear optical tweezers.

3. The particle-oriented and point-to-point transport system and method based on asymmetric astigmatic field modulation as described in claim 1, characterized in that, The offset of the cylindrical lens controls the position of the strongest optical trapping force on the linear optical tweezers, the weakest and strongest optical trapping forces on the linear optical tweezers control the entry and exit of the particles, and the rotation angle of the cylindrical lens controls the transport direction of the particles.

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