Magnetic sensitive optical tweezers and particle manipulation method

Abstract

The invention relates to the technical field of particle manipulation, in particular to magnetic sensitive optical tweezers and a particle manipulation method. The optical tweezers comprise an excitation source module, a magnetic field excitation and particle capture module and a substrate; the excitation source module generates angular polarized light, the magnetic field is radially polarized, the electric field is tangentially polarized, and the cross section is axisymmetric; in the magnetic field excitation and particle capture module, a gold column serves as the center, an air ring is nested outside the gold column, a gold ring is nested outside the air ring, the gold column and the gold ring are made of metal materials, the air ring is of a hollow structure, and the module is integrated on a silicon dioxide substrate. Angular polarized light covers the outer surface of the gold column and the inner surface of the gold ring to excite loop current, a longitudinal magnetic field component (magnetic focusing) and a hollow tubular light beam (optical potential well) are generated, and micron-sized particle capture, magnetic screening and magnetic conductivity measurement are achieved. The optical tweezers break through the limitation of capturing distance, magnetic field dependence, structural complexity and wavelength adaptability of the existing optical tweezers, and an efficient and universal scheme is provided.

Description

Technical Field

[0001] The present invention relates to the technical field of particle manipulation, in particular to a magnetically sensitive optical tweezers and a particle manipulation method. Background Art

[0002] Optical tweezers, a non-contact particle manipulation technology based on laser beams, can achieve precise capture and manipulation of micron- to nanometer-sized particles by leveraging the synergistic effect of scattering force and gradient force, demonstrating important application value in biomedicine, nanotechnology and other fields.

[0003] As research deepens, new manipulation technologies based on metasurfaces and magnetic fields have gradually become a hot topic: metasurface optical tweezers capture particles by constructing a quasi-bound state in a continuum (quasi-BIC) structure and utilizing the optical field hotspots between metasurface units. However, they rely on evanescent wave effects and are limited to the near-field range of hundreds of nanometers, making it impossible to manipulate particles over longer distances. Magnetic tweezers, on the other hand, position tiny particles using the magnetic force generated by the magnetic field gradient by designing microstructures and applying an external magnetic field. However, this system relies on specific magnetic field conditions, and the processing of micro-nanostructures is complex, limiting its ease of operation and the expansion of its application scenarios.

[0004] In summary, the existing optical tweezers technology has the following problems:

[0005] First, the near-field limitations of metasurface optical tweezers: the capture mechanism based on evanescent waves results in an extremely short action distance (only hundreds of nanometers), which makes it difficult to meet the needs of long-distance particle capture, limiting its application in complex environments (such as long-range manipulation in fluid environments).

[0006] Second, the complexity and dependence of the magnetic tweezers system: Traditional magnetic tweezers rely on the application of external magnetic fields and the processing of complex micro-nano structures, which not only increases the cost of system design and preparation, but may also introduce interference factors such as magnetic field inhomogeneity, affecting the control accuracy and stability.

[0007] Therefore, existing optical tweezers and magnetic tweezers technologies mostly rely on a single physical field (light or magnetism), and lack a universal solution that can achieve particle manipulation at micron-level distances without the need for complex structures or external magnetic field assistance. In particular, the functional manipulation needs in interdisciplinary fields such as magnetic particle screening and material magnetic permeability measurement have not yet been effectively met. Summary of the Invention

[0008] Therefore, the technical problem to be solved by the present invention is to overcome the problems of the existing optical tweezers, such as limited capture distance, requirement of external magnetic field and complex structure.

[0009] To solve the above technical problems, the present invention provides a magnetically sensitive optical tweezers and particle manipulation method. By introducing a magnetic field component, without the aid of an external magnetic field or complex micro-nanostructure, the magnetically sensitive optical tweezers can be used to screen magnetic particles, measure the magnetic permeability of materials, and capture particles at micrometer-level distances. Specifically, the optical tweezers include: an excitation source module, a magnetic field excitation and particle capture module, and a substrate; wherein,

[0010] The excitation source module is used to generate angularly polarized light;

[0011] The magnetic field excitation and particle capture module includes: a first unit, a second unit and a third unit, with the first unit as the center, the second unit nested around the first unit, and the third unit nested around the second unit; the first unit and the third unit are both made of metal materials, and the second unit is an air ring structure;

[0012] The magnetic field excitation and particle capture unit is integrally mounted on the substrate;

[0013] The angularly polarized light covers the outer surface of the first unit and the inner surface of the third unit to excite a loop current.

[0014] In one embodiment of the present invention, the first unit and the third unit have the same thickness and are both made of gold.

[0015] In one embodiment of the present invention, the substrate is made of silicon dioxide.

[0016] In one embodiment of the present invention, the radius of the angularly polarized light is set to 1 μm, and the third unit is a ring structure with an outer diameter of 4.14 μm.

[0017] In one embodiment of the present invention, the second unit is a ring structure with an inner diameter of 417 nm and an outer diameter of 997 nm.

[0018] In one embodiment of the present invention, the first unit is a cylindrical structure with a radius of 417 nm.

[0019] Based on the same inventive concept, the present invention also provides a particle manipulation method, which uses the optical tweezers to capture particles. The particle manipulation method includes the following steps:

[0020] generating angularly polarized light, wherein the magnetic field of the angularly polarized light is radially polarized, the electric field is tangentially polarized, and the distribution is axisymmetric in the cross section;

[0021] The angularly polarized light is vertically incident on the magnetic field excitation and particle capture unit, and a loop current is excited by the first unit and the third unit, generating a longitudinal magnetic field component on the propagation axis. Through the phase control of the second unit, a hollow tubular light beam is formed, and an optical potential well is formed in the light intensity peak area at its tube wall, thereby realizing the capture and magnetic screening of micron-sized particles.

[0022] In one embodiment of the present invention, the particle manipulation method further includes a magnetic particle screening step: using the magnetic field component on the propagation axis to apply a gradient force to the magnetic particles to move them toward the propagation axis, thereby separating the magnetic particles from the non-magnetic particles.

[0023] In one embodiment of the present invention, the particle manipulation method further includes an adjustment step for adapting to angularly polarized light of different wavelengths: by adjusting the sizes of the first unit, the second unit, and the third unit, the intensity of the magnetic field component on the propagation axis is enhanced to adapt to angularly polarized light of different wavelengths;

[0024] The size adjustment principle still follows the condition: the radius of the angularly polarized light is greater than or equal to the outer diameter of the second unit and less than or equal to the outer diameter of the third unit.

[0025] In one embodiment of the present invention, the optical loss of the substrate is lower than a preset threshold and does not interfere with the interaction between light and the first unit and the third unit.

[0026] The above technical solution of the present invention has the following advantages over the prior art:

[0027] First, by designing a nested micro-nanostructure of "gold pillar-air ring-gold ring", and utilizing the special polarization characteristics of angularly polarized light, a loop current is excited in the gold ring, and the "magnetic focusing" longitudinal magnetic field component and the "hollow tube"-shaped optical potential well are simultaneously realized, breaking through the limitations of traditional optical tweezers' near-field capture at the hundred-nanometer level, and extending the particle capture distance to the micron level.

[0028] Second, magnetic particle screening and material permeability measurement can be achieved through the built-in magnetic field component without the need for an external magnetic field.

[0029] Third, the structure consists of only three simple nested structures, and the materials used are gold and silicon dioxide, which have low processing difficulty and low cost.

[0030] Fourth, by adjusting the size parameters of each layer, it can adapt to angular polarized light of any wavelength and has wide wavelength adaptability, providing an efficient, universal and easy-to-implement solution for particle manipulation and magnetic analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0032] Figure 1 1 is a schematic structural diagram of a magnetically sensitive optical tweezers provided in an embodiment of the present invention;

[0033] Figure 2 is a flow chart of a particle manipulation method provided in an embodiment of the present invention;

[0034] Figure 3 When the wavelength of the incident light is 500nm, Figure 1 A magnetically sensitive optical tweezers provided in the XOZ plane magnetic field Z component intensity (H Z )distributed;

[0035] Figure 4 When the wavelength of the incident light is 500nm, Figure 1 The total intensity distribution of the magnetic and electric field components of a magnetically sensitive optical tweezers designed in the XOZ plane, where (a) is the intensity distribution of the magnetic field component and (b) is the intensity distribution of the electric field component.

[0036] Description of the accompanying drawings in the specification: 1. Excitation source module; 2. Magnetic field excitation and particle capture module; 21. First unit; 22. Second unit; 23. Third unit; 3. Substrate. DETAILED DESCRIPTION

[0037] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0038] Example 1:

[0039] like Figure 1 As shown, the present invention provides a magnetically sensitive optical tweezers and particle manipulation method. By introducing a magnetic field component, without the aid of an external magnetic field or complex micro-nanostructure, the magnetically sensitive optical tweezers can be used to screen magnetic particles, measure the magnetic permeability of materials, and capture particles at micrometer-level distances. Specifically, the optical tweezers include: an excitation source module 1, a magnetic field excitation and particle capture module 2, and a substrate 3; wherein,

[0040] The excitation source module 1 is used to generate angularly polarized light;

[0041] The magnetic field excitation and particle capture module 2 includes: a first unit 21, a second unit 22 and a third unit 23, with the first unit 21 as the center, the second unit 22 nested around the first unit 21, and the third unit 23 nested around the second unit 22; the first unit 21 and the third unit 23 are both made of metal materials, and the second unit 22 is an air ring structure;

[0042] The magnetic field excitation and particle capture unit 2 is integrated and mounted on the substrate 3;

[0043] The angularly polarized light covers the outer surface of the first unit 21 and the inner surface of the third unit 23 to excite a loop current.

[0044] Furthermore, in this embodiment, in order to ensure that the angularly polarized light can completely hit the micro-nano structure, the radius of the angularly polarized light is set to 1 μm, and the radius of the outermost ring of the magnetic field excitation and particle capture unit 2 is set to 4.14 μm.

[0045] In order to generate a stronger circular current in the magnetic field excitation and particle capture unit 2 to better enhance the effect of the independent magnetic field on the propagation axis, the thickness of the first unit 21 and the third unit 23 are equal, the constituent materials of the first unit 21 and the third unit 23 are preferably gold, and the constituent material of the substrate 3 is silicon dioxide.

[0046] When the incident wavelength of the azimuthally polarized light is selected to be 500 nm, in order to achieve both the ability of the optical tweezers to capture particles and the intensity of the magnetic field component on the propagation axis to be relatively strong, the thickness of the magnetic field excitation and particle capture unit 2 is 115 nm, and the dimensions are:

[0047] The first unit 21 is a cylindrical structure with a radius of 417 nm; the second unit 22 is a ring structure with an inner diameter of 417 nm and an outer diameter of 997 nm; the third unit 23 is a ring structure with an outer diameter of 4.14 μm.

[0048] Example 2:

[0049] Based on the same inventive concept as that of the first embodiment, the present invention also provides a particle manipulation method, which uses the optical tweezers described in the first embodiment to capture particles. Figure 2 As shown, the particle manipulation method includes the following steps:

[0050] Generate angularly polarized light, which is a special type of vector polarized light with radial magnetic field and tangential electric field, i.e., tangential to the circumference of the beam and axially symmetrical in cross section;

[0051] The angularly polarized light is vertically incident on the magnetic field excitation and particle capture unit, and a loop current is excited through the first unit 21 and the third unit 23, generating a longitudinal magnetic field component on the propagation axis. Through the phase control of the second unit 22, a hollow tubular light beam is formed, and an optical potential well is formed in the light intensity peak area at its tube wall, thereby realizing the capture and magnetic screening of micron-sized particles.

[0052] Specifically, the angularly polarized light is vertically incident on the magnetic field excitation and particle capture unit 2, and a set of rapidly oscillating closed loop currents are excited in the gold ring (third unit 23) through interaction with the gold column (first unit 21) and the gold ring (third unit 23); at the same time, the light propagation phase is regulated by the geometric size of the air ring (second unit 22), and a longitudinal polarized magnetic field component (H) is induced on the propagation axis. Z ), creating a "magnetic focusing" effect similar to controllable focal length.

[0053] The polarization state of the angularly polarized light is axially symmetrically distributed on the beam cross section. The characteristics of radial polarization of the magnetic field and tangential polarization of the electric field result in the following effects on the propagation axis after focusing:

[0054] The polarization characteristics excite the loop current in the gold ring, generating a longitudinal polarized magnetic field component (H) along the propagation axis. Z ); Since the electric field satisfies the symmetry constraint on the propagation axis and disappears (singularity effect), the light beam presents a hollow ring distribution. After the phase is controlled by the air ring (the second unit 22), it propagates in the form of a hollow tube. The light intensity at the tube wall is significantly enhanced, forming an optical potential well.

[0055] At the wall of the hollow tube, the light intensity peak area uses gradient force to bind the particles to a position deviating from the central axis, achieving capture; at the same time, the longitudinal magnetic field component on the propagation axis exerts a magnetic field gradient force on the magnetic particles, causing them to migrate near the axis, thereby simultaneously realizing the magnetic sensitivity functions of magnetic particle screening and material magnetic permeability measurement.

[0056] For magnetic particles, they will move towards the area with high magnetic field intensity (near the propagation axis) under the action of the magnetic field gradient force, forming a synergistic effect with the gradient force of the optical potential well: the optical potential well binds the particles to the tube wall, and the magnetic field gradient force further shortens the distance between the magnetic particles and the propagation axis, enhancing the capture stability.

[0057] For non-magnetic particles, they are only affected by the optical potential well, and the capture position is closer to the outside of the tube wall, thereby achieving the screening of magnetic particles and non-magnetic particles.

[0058] Furthermore, in this embodiment, the particle manipulation method also includes a magnetic particle screening step: using the magnetic field component on the propagation axis to apply a gradient force to the magnetic particles to make them move toward the vicinity of the propagation axis, thereby separating the magnetic particles from the non-magnetic particles.

[0059] Furthermore, in this embodiment, the particle manipulation method further includes an adjustment step for adapting to angularly polarized light of different wavelengths: by adjusting the sizes of the first unit 21, the second unit 22, and the third unit 23, the intensity of the magnetic field component on the propagation axis after emission is selectively enhanced to adapt to angularly polarized light of different wavelengths, thereby producing a "magnetic focusing" effect similar to controllable focal length;

[0060] Among them, the size adjustment principle still follows the condition: the radius of the angularly polarized light is greater than or equal to the outer diameter of the second unit and less than or equal to the outer diameter of the third unit, ensuring that the angularly polarized light can cover the outer surface of the gold column (first unit 21) and the inner surface of the gold ring (third unit 23) to stimulate the loop current.

[0061] Furthermore, in this embodiment, the optical loss of the substrate is lower than a preset threshold and does not interfere with the interaction between light and the first unit 21 and the third unit 23 .

[0062] In order to verify the simultaneous existence of the above two phenomena, the following experiment is conducted, setting the wavelength of the incident light to 500nm. Figure 3 The magnetic field Z component intensity (H) of the magnetically sensitive optical tweezers provided in this application in the XOZ plane Z ) distribution, the x-axis is the radial distance (unit: μm), the z-axis is the propagation direction distance (unit: μm), wherein the thickness of the third unit 23 (gold ring micro-nano structure) is 115nm. It can be seen that: near the propagation axis (x=y=0nm), the H Z The intensity shows a peak concentration, forming a "magnetic focusing" phenomenon, indicating that the magnetic field component is enhanced along the optical axis.

[0063] See also Figure 4 As shown in (a) and (b), the intensity distribution results of the total components of the magnetic and electric fields of the magnetically sensitive optical tweezers provided by this application on the XOZ plane show that: in the annular region deviating from the central axis (the wall of the "hollow tube"), the light intensity is significantly enhanced, forming an optical potential well, which can confine the particles to the position of the tube wall (the peak light intensity area); combined with Figure 3 The magnetic focusing effect of the distribution realizes the capture and magnetic screening of particles.

[0064] In summary, the magnetically sensitive optical tweezers provided by the present invention can extend the particle capture distance to the micron level, compared to near-field optical tweezers with a capture distance of hundreds of nanometers; compared to magnetic tweezers with an external magnetic field, the designed magnetically sensitive optical tweezers inherently have an additional "magnetic focusing" magnetic field component, so magnetic particles can be detected without applying external magnetic field conditions; because the magnetically sensitive optical tweezers have a simple structure, consisting of only three nested structures: a gold column, an air ring, and a gold ring, the actual processing process is relatively simple; and because their electromagnetic properties do not change regardless of the wavelength of angularly polarized light, in theory, the designed magnetically sensitive optical tweezers only need to change the structural size parameters corresponding to different wavelengths to be applicable to any wavelength.

[0065] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A magnetically sensitive optical tweezers, characterized in that include: An excitation source module, used for generating angularly polarized light; The magnetic field excitation and particle capture module includes: a first unit, a second unit, and a third unit, with the first unit as the center, the second unit nested around the first unit, and the third unit nested around the second unit; the first unit and the third unit are both made of metal materials, and the second unit is an air ring structure; and a substrate on which the magnetic field excitation and particle capture unit is integrally mounted; The angularly polarized light covers the outer surface of the first unit and the inner surface of the third unit to excite a loop current.

2. The magnetically sensitive optical tweezers according to claim 1, characterized in that The first unit and the third unit have the same thickness and are both made of gold.

3. The magnetically sensitive optical tweezers according to claim 1, characterized in that The substrate is made of silicon dioxide.

4. The magnetically sensitive optical tweezers according to claim 1, characterized in that When the incident wavelength of the angularly polarized light is 500 nm, the radius of the angularly polarized light is set to 1 μm, and the third unit is a ring structure with an outer diameter of 4.14 μm.

5. The magnetically sensitive optical tweezers according to claim 4, characterized in that The second unit is a ring structure with an inner diameter of 417 nm and an outer diameter of 997 nm.

6. The magnetically sensitive optical tweezers according to claim 5, characterized in that The first unit is a cylindrical structure with a radius of 417 nm.

7. A particle manipulation method, characterized in that: The method for capturing microparticles using the optical tweezers according to any one of claims 1 to 6 comprises the following steps: generating angularly polarized light, wherein the magnetic field of the angularly polarized light is radially polarized, the electric field is tangentially polarized, and the distribution is axisymmetric in the cross section; The angularly polarized light is vertically incident on the magnetic field excitation and particle capture unit, and a loop current is excited by the first unit and the third unit, generating a longitudinal magnetic field component on the propagation axis. Through the phase control of the second unit, a hollow tubular light beam is formed, and an optical potential well is formed in the light intensity peak area at its tube wall, thereby realizing the capture and magnetic screening of micron-sized particles.

8. The particle manipulation method according to claim 7, characterized in that: The particle manipulation method also includes a magnetic particle screening step: using the magnetic field component on the propagation axis to apply a gradient force to the magnetic particles, causing them to move toward the propagation axis, thereby separating the magnetic particles from the non-magnetic particles.

9. The particle manipulation method according to claim 7, characterized in that: The particle manipulation method further includes an adjustment step for adapting to angularly polarized light of different wavelengths: by adjusting the sizes of the first unit, the second unit, and the third unit, the intensity of the magnetic field component on the propagation axis is enhanced to adapt to angularly polarized light of different wavelengths; The size adjustment principle still follows the condition: the radius of the angularly polarized light is greater than or equal to the outer diameter of the second unit and less than or equal to the outer diameter of the third unit.

10. The particle manipulation method according to claim 7, characterized in that: The optical loss of the substrate is lower than a preset threshold and does not interfere with the interaction between light and the first unit and the third unit.

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