基于锥形光纤光镊的细胞操控与神经调控 下载: 1034次封底文章
Optical trapping is widely used in various fields ranging from biomedical applications to physics and material sciences. Recently, tapered optical fiber tweezers (TOFTs) have attracted significant attention in the optical trapping field owing to their flexible manipulation, compact structure, and ease of fabrication. As a non-invasive technique, TOFTs can be used to directly manipulate cells in multiple dimensions in different bio-microenvironments. In addition, infrared light waves penetrate biological tissues well, which enhances the performance of TOFTs technology in the biology and medicine fields. Here, we review TOFT-based trapping and manipulation at the single-, multi-, and sub-cellular levels, as well as the latest developments in neuron regulation.
Since Arthur Ashkin used two focused and counter-propagating beams to trap particles in 1970, optical forces have been widely used to manipulate and trap particles using laser beams. In 1986, Ashkin et al. discovered that a single tightly focused laser beam could achieve stable particle trapping. Subsequently, they named the optical-trapping technique as “optical tweezers,” which we now refer to as conventional optical tweezers (COTs). Over the years that followed, Ashkin et al. conducted numerous studies using a single focused laser beam for capturing particles ranging from tens of nanometers to tens of microns, including viruses and bacteria. Optical trapping and manipulation using COTs has undergone substantial progress regarding its methodologies and applications over the span of nearly 50 years. These techniques involve manipulating various samples, including dielectric particles, biological cells, and biomolecules. Nonetheless, focusing light via COTs requires a high-numerical-aperture (NA) objective along with diverse optical components for beam steering and expansion. Owing to its bulky structure, this framework remains deficient in control and manipulation flexibility.
Alternatively, holographic optical tweezers (HOTs) were created in 1998 to allow the manipulation of multiple particles using complex-structured light fields. This technology uses computer-generated holograms through spatial light modulators to achieve multiple traps, thereby providing enhanced control and manipulation capabilities. However, trapping particles at the nanometer scale using HOTs remains challenging because of the diffraction limit. Surface-plasmon-based optical tweezers (SPOTs) were developed in the late 2000s to trap and manipulate nanoscale particles, including single molecules that are only a few nanometers in size. However, owing to their ability to trap nanoscale particles, the carefully designed and elaborated nanostructures necessary for SPOTs limit their flexibility. Techniques, such as COTs, HOTs, and SPOT, involve complex devices and components with inflexible control. Therefore, it is critical to develop simple and flexible manipulation tools. The advancements in optical fiber tweezers (OFTs) has made them versatile candidates for the optical trapping and manipulation of different samples. The simple structure of OFTs, consisting solely of optical fibers, provides them with exceptional advantages in terms of manipulation flexibility. OFTs can be easily inserted into thick samples and turbid media, significantly extending sample applicability. In addition, OFTs offer a low-cost solution because of their simple fabrication procedures. They can be integrated into small devices, such as optofluidic channels and chips, paving the way for a scaled-down approach. OFTs were first demonstrated in 1993 by employing two aligned single-mode fibers for optical trapping. Although tiny particles and cells can be directly captured and manipulated using the optical scattering force generated by two fibers, they also result in limited manipulation flexibility. A single optical fiber can also be used for particle trapping and manipulation. Single tapered optical fiber tweezers (TOFTs) were introduced in 1997 and have significantly improved the flexibility of optical manipulation. The end of a single fiber used for focusing the light beam is similar to that used in COTs after being drawn into a lenticular shape, which creates a stronger gradient force on the particle and facilitates optical trapping.
In conclusion, this review highlights recent advancements in tapered optical fiber based tweezers for optical trapping and manipulation. Despite the significant progress, TOFTs still face numerous challenges. One of the major issues is the direct contact of the fiber end surface with the sample, which leads to mechanical damage. Thus, it is necessary to develop of non-contact and damage-free trapping techniques. Another critical area of concern is the stable trapping and manipulation of nanometer-sized samples that surpass the diffraction limits. TOFTs encounter difficulties in trapping individual biomolecules, which is of great importance for single-molecule analysis. Furthermore, optical trapping of cells and biological structures for biosensing in vivo is an upcoming trend; however, inserting fibers into living samples may cause mechanical damage. Hence, the construction of biocompatible TOFTs is crucial to maintain their application potential. Biophotonic waveguides composed of living cells enable the manufacturing of biocompatible optical fibers, making trapping, manipulation, sensing, and diagnostics feasible in vivo. On the other hand, TOFTs technology is constantly experiencing new breakthroughs owing to its combination with new technologies like artificial intelligence (AI) and spectral analysis, as well as new applications like neuromodulation and precision medicine.
1 引言
“光学操控”——依托于“光镊”这一工具——起源于20世纪。早在1970年,“光镊之父”Ashkin[1]就在贝尔实验室使用两束反向传播的激光束来捕获粒子。此后,Ashkin及其同事[2]在进行光力研究时发现,利用单束高度聚焦的激光所产生的光梯度力和散射力,可以实现对微粒的稳定捕获。因而,他们将光捕获技术命名为“光镊”,该技术也被称为传统光镊(COTs)。在随后的几年中,Ashkin及其同事[3-4]进行了一系列的相关研究,利用单个聚焦光束不仅实现了从几十纳米到几十微米尺寸粒子的捕获,还实现了对病毒和细菌的捕获。经过近50年的发展,利用传统光镊进行光学捕获和操控在方法及应用方面都取得了巨大进展,操控样品的范围从不同的介质颗粒拓展到生物细胞和生物分子[5-8]。然而,传统光镊技术必须依靠高数值孔径(NA)的物镜对激光束进行聚焦,用于激光扩束和转向的各类光学元件是必不可少的。这种庞大的结构使得传统光镊技术缺乏可操作性和灵活性。1998年,全息光镊(HOTs)被开发出来[9],该技术通过空间光调制器实现计算机生成的全息图,从而利用复杂的结构光场对多个光阱进行控制。全息光镊技术极大地提高了光镊的可控程度,因而被广泛应用于多个粒子的捕获和操控[10-13]。然而,由于衍射极限的限制,全息光镊难以在纳米尺度上对粒子进行稳定捕获。21世纪后期,基于表面等离激元的光镊技术(SPOTs)问世[14-15],该技术可以实现对纳米粒子的稳定捕获,甚至可以对几纳米尺度的单分子进行操控[16-17]。基于表面等离激元的光镊虽然具有捕获纳米级粒子的能力,但需要精心设计和制作纳米结构,操控灵活性有限。总的来说,传统光镊、全息光镊以及基于表面等离激元的光镊虽然在原理、结构等方面存在差异,但都需要一些灵活性较差的复杂设备和组件。因此,寻求一种简单且灵活的操控工具十分重要。
光纤光镊(OFTs)的发展使其成为光学捕获和样品操控的有力候选者[18-19]。光纤光镊仅需要两根光纤即可实现样品操控,结构简单,因此在操作灵活性方面具有非凡的优势。光纤可以直接插入厚样品和浑浊介质中,大大增加了该技术的适用性。由于制造工艺简单,光纤光镊使光学操控成为一种低成本的技术。此外,光纤光镊还可以方便地集成到小型设备中,例如光流控通道和芯片等[20]。光纤光镊首次出现于1993年,研究人员使用两根对齐的单模光纤进行了光学捕获[21]。这种结构虽然可以利用光散射力直接捕获和操控微小的粒子和细胞,但需要使用两根光纤,操控灵活性受限[22]。事实上,使用单根锥形光纤(TFPs)便可实现对粒子的捕获和操控。1997年,采用单根锥形光纤进行光学操控的方法被首次报道[23]。这种基于锥形光纤的光镊技术大大提高了光操控的灵活性。单根光纤的末端被拉成类似透镜的形状(锥形)后,出射激光就会在粒子上产生更强的梯度力,使光学捕获更容易实现[24-28]。目前,锥形光纤已被广泛应用于单细胞、多细胞、亚细胞操控与分析以及神经调控研究中。锥形光纤光镊(TOFTs)的工作原理可以细分为两类:光热效应和光力。前者通过激光在粒子周围介质中产生热梯度和声梯度进行捕获[29],而后者则依靠沿着光传播方向的散射力和沿着光强梯度方向的梯度力的协同作用进行捕获[30]。在这篇综述中,笔者将聚焦锥形光纤光镊技术,总结它在单细胞分析、多细胞组装、亚细胞水平操控方面的研究现状,并进一步关注其在神经细胞调控上的最新进展(如
图 1. 利用锥形光纤进行细胞光学操控与神经调控的概览图。(a)单细胞捕获与分析;(b)多细胞组装;(c)亚细胞水平操控;(d)神经细胞调控
Fig. 1. An overview of cell manipulation and neuromodulation using tapered optical fibers. (a) Single-cell trapping and analysis;(b) multi-cellular assembly; (c) sub-cellular manipulation; (d) neuromodulation
2 锥形光纤光镊介绍
2.1 传统光镊的基本原理
粒子位于激光束的焦点附近时,照射到介质粒子上的入射光发生散射产生动量转移,从而在粒子上产生光力作用。由此产生的光学力一般由散射力和梯度力这两个分量组成。在瑞利散射条件下,即入射激光的波长远大于捕获粒子尺寸时,可以将粒子作为电偶极子处理,从而计算光力[30]。此时,对于半径为a的粒子来说,光散射力的计算公式为
其中,
式中:
其中,
然而,在许多情况下,被捕获粒子的尺寸与激光的波长相当。在这种情况下,电偶极子方法是无效的。对于光力的计算,需要应用更复杂的电磁理论。幸运的是,基于电磁理论的数值模拟和计算方法,如有限元法和有限时域差分法,可以应对各种情况下的光力计算。通过计算与时间无关的麦克斯韦应力张量沿粒子外表面的总积分,可以得到施加在粒子上的总光力(
式中:
式中:
2.2 锥形光纤光镊的原理
一般来说,光纤光镊仅需一根锥形光纤即可实现光捕获和操控,且结构简单,易于制作。
图 2. 锥形光纤光镊的光捕获原理[31-32]。(a)利用锥形光纤光镊进行光捕获和操控的示意图[31];(b)光纤尖端附近的光强分布[32];(c)~(d)锥形光纤光镊施加在粒子上的光力的计算结果[31]:(c)沿光轴方向的光力(Fx)随DA的变化;(d)DA=4.5 μm处的横向光力(Fy)分布
Fig. 2. Optical trapping principle of tapered optical fiber tweezers (TOFTs)[31-32]。(a) Schematic of optical trapping and manipulation using TOFTs[31]; (b) light intensity distribution near the fiber tip[32]; (c)-(d) calculated optical force exerted on particles by TOFTs[31]: (c) variation of optical force in axial direction (Fx) with DA; (d) transverse optical force (Fy) distribution at DA=4.5 μm
2.3 锥形光纤光镊与传统光镊
对于锥形光纤光镊,只有具备光聚焦的光纤末端才能产生足够的光梯度力,进而实现对粒子的捕获,这与传统的光镊机制相同。只不过传统的光镊依靠高数值孔径(NA)的物镜实现强聚焦,从而产生足够的光梯度力将粒子捕获在焦点附近。对于锥形光纤光镊,激光被光纤的端面聚焦,产生的光梯度力也可以捕获粒子。锥形光纤光镊的捕获能力在很大程度上取决于光纤末端的形状,因为光纤末端的形状直接影响了光纤末端的光聚焦情况。对于具有平坦端面的光纤,其出射光难以被聚焦,无法捕获粒子,相反,粒子还会被光散射力推开。只有具有抛物面或凸面的锥形光纤才能将激光进行高度聚焦,从而产生光梯度力,捕获粒子。光纤尖端的聚焦效果越强,产生的光梯度力就越大。这种高度聚焦的光可为粒子捕获提供强大的光梯度力。与传统的光镊相比,锥形光纤光镊的捕获效率毫不逊色。实际上,已有计算表明:对于直径为10 μm的聚苯乙烯颗粒,锥形光纤光镊的捕获效率接近传统光镊的2倍[31]。因而,锥形光纤光镊也可以用于捕获尺寸从几百纳米到几十微米的粒子和细胞。
图 3. 利用锥形光纤光镊实现颗粒、细胞、细菌的捕获[31,34-36]。(a)锥形光纤光镊用于捕获不同大小的颗粒和细胞:(a1)直径为0.7 μm的二氧化硅微球[31];(a2)大肠杆菌[31];(a3)酵母细胞[34];(a4)中国仓鼠卵巢细胞[35];(b)锥形光纤光镊对大肠杆菌的非接触光捕获[36]
Fig. 3. Trapping particles, cells, and bacterium by TOFTs. (a) TOFTs for trapping particles and cells of different sizes: (a1) silica microspheres with a diameter of 0.7 μm[31]; (a2) E.coli[31]; (a3) yeast cells[34]; (a4) Chinese hamster ovary cell[35]; (b) non-contact optical trapping of E.coli by TOFTs[36]
传统光镊系统依赖用于光聚焦的高数值孔径物镜,以及用于激光扩束和转向的光学元件。而锥形光纤光镊易于制造,结构简单,除了结构紧凑外,在操作灵活性上也更具优势,仅需简单地移动光纤,就可以灵活地操控被捕获的粒子。
图 4. 通过锥形光纤光镊灵活地操控粒子和细菌。(a)使用锥形光纤光镊将粒子排列成六边形图案[31]:锥形光纤完成捕获后,粒子被拾取并被放置到指定位置;(b)~(c)在流动环境中灵活操控大肠杆菌[37],其中黄色箭头表示光纤移动方向,蓝色箭头表示流动方向
Fig. 4. Flexible manipulation of trapped particles and bacteria by TOFTs. (a) Arrangement of six particles into a hexagon[31]: the particles are picked up and placed into the designated position after trapping by flexible movement of the fiber (yellow arrow indicated); (b)-(c) flexible manipulation of a trapped E.coli bacterium in flowing environment[37], where the yellow solid arrows indicate the fiber movement direction and the blue arrows indicate the flowing direction
表 1. 锥形光纤光镊(TOFTs)与传统光镊(COTs)的对比
Table 1. Comparison of TOFTs and COTs
|
3 锥形光纤光镊在单细胞分析上的应用
3.1 单细胞标记
当粒子位于激光束焦点附近时,锥形光纤光镊除了可以捕获各种各样的粒子和细胞外,还被广泛用于细胞捕获后的单细胞标记和分析。例如,锥形光纤光镊通过同时捕获单个细菌和上转换纳米粒子(UCNP)来标记单个细菌,如
图 5. 锥形光纤光镊实现单细胞标记和分析[39]。(a)~(b)细菌被捕获和标记的示意图和实验图像;(c)不同大小被标记细菌的实时反射光信号
Fig. 5. TOFTs for single-cell labeling and analysis[39]. (a)-(b) Schematic and experimental images of bacterial trapping and labeling;(c) real-time reflected optical signal from labeled single bacteria with different sizes
3.2 单细胞能量分析
除了可以根据光信号对单个细菌进行分析外,借助锥形光纤光镊还可以对活细菌进行能量分析。锥形光纤光镊在溶液中捕获单个细菌后,通过分析运动细菌在光势阱中的动力学特征,就可以分析其能量[36]。
图 6. 通过单个细菌的非接触式光捕获对运动细菌进行能量分析[36]。(a)大肠杆菌被光捕获并挣扎的光学显微镜图像;(b)非接触捕获过程中的细菌动力学示意图
Fig. 6. Dynamic analysis of motile bacteria via non-contact optical trapping of single bacterium[36]. (a) Optical microscopy images showing capture and struggle of E.coli; (b) schematic of the bacterium dynamics in the non-contact trapping
4 锥形光纤光镊在多细胞组装上的应用
4.1 多细胞组装
除了捕获和操控单个细胞外,锥形光纤光镊还可以用于多细胞组装,这对于研究细胞间的相互作用和联系是非常重要的。此外,将随机分布的细胞组装成规则形状的结构或阵列,在组织工程[40]、药物输送和靶向治疗[41-42]等生物医学和生物光子学领域发挥着重要作用。
Tam等[43]利用多根光纤形成的密集光阱来捕获和平行排列微球。但是,这种方法过于繁琐。事实上,仅用一根锥形光纤即可实现上述功能,完成对大量微球的捕获和排列。
图 7. 锥形光纤光镊实现多细胞组装[44]。(a)锥形光纤光镊对粒子和细胞进行光学组装的示意图;(b)一维粒子链的显微图像;(c)二维粒子阵列的显微图像;(d)酵母细胞链的显微图像
Fig. 7. Realizing multicellular assembly by TOFTs[44]. (a) Schematic of optical assembly of particles and cells via TOFTs; (b) microscopic images of one-dimensional (1D) patterned particle chains; (c) microscopic images of two-dimensional (2D) particle arrays; (d) microscopic images of yeast cell chains
上述方法利用光散射力和光梯度力共同进行多细胞组装,事实上,通过延伸的光梯度力方法即可实现对多个细胞的组装[45]。一般来说,当细胞被锥形光纤的光梯度力捕获后,光可以继续在细胞内传播,并在细胞表面重新聚焦,如
图 8. 生物光波导和生物纳米长矛组装。(a)通过延伸光梯度力进行生物光波导组装[45]:(a1)光学组装和生物光波导的形成示意图;(a2)锥形光纤光镊捕获不同数量大肠杆菌时的能量密度分布;(a3)形成的不同长度的生物光波导的图像;(b)通过拓展光梯度力组装生物纳米长矛[46]:(b1)组装好的生物纳米长矛示意图;(b2)由酵母和嗜酸乳杆菌细胞组装而成的生物纳米长矛的光学图像
Fig. 8. Biological optical waveguides (bio-WGs) and bio-nanospear assembly. (a) Bio-WGs assembly via extended optical gradient force[45]: (a1) schematic of optical assembly and bio-WGs formation; (a2) distribution of energy density of TOFTs capturing different numbers of E. coli; (a3) images of formed bio-WGs with different lengths; (b) bio-nanospear assembly via extended optical gradient force[46]: (b1) schematic illustration of assembled bio-nanospear; (b2) optical image of bio-nanospear assembled from a yeast and L. acidophilus cells
4.2 多细胞收集与分选
锥形光纤光镊不仅可以进行多细胞的组装,还可以进行多细胞的分离和筛选。例如,将锥形光纤集成到T型微流控通道中组成紧凑且小型化的光流控芯片,可以实现选择性捕获细胞和细菌[48]。显然,锥形光纤光镊的光捕获能力因其自身结构、激光波长、样品尺寸、形状、折射率等不同而存在一定差异。这种差异性为锥形光纤光镊实现选择性捕获提供了可能。实验结果表明,锥形光纤光镊可以在捕获和组装大肠杆菌细胞的同时,只对红细胞(RBCs)存在排斥作用,从而对两种细胞的捕获能力存在显著差异,如
图 9. 锥形光纤光镊实现多细胞的收集和分选[48]。(a)示意图展示大肠杆菌、红细胞在锥形光纤尖端的不同光响应行为;(b)选择性捕获:(b1)激光关闭时,大肠杆菌和红细胞在通道1中混合在一起;(b2)~(b4)激光开启后,大肠杆菌被吸引,红细胞被释放
Fig. 9. Muli-cell collection and sorting by TOFTs[48]. (a) Schematic showing different light response behaviors of E. coli and red blood cells (RBCs) in tapered fiber tip; (b) selective capture: (b1) E. coli and RBCs are mixed together in channel 1 when the laser is turned off; (b2)-(b4) E. coli is attracted and the RBCs are released when the laser is turned on
5 锥形光纤光镊在亚细胞层面生物操控上的应用
5.1 细胞微手术
锥形光纤光镊的尖端尺寸极小,仅有几百纳米,能够将激光高度局域地传送到目标微区,因而在三维操控中表现出了极高的精度和灵活性。该技术有望在高精度、高选择性、亚细胞水平的生物目标操控方面发挥巨大作用[4,49]。而将锥形光纤技术与热等离子体结合,可以进一步实现对单细胞的原位、高精度微手术以及细胞内细胞器的操控[50]。
图 10. 单细胞微手术及修复的原理[50]。(a)通过局域等离激元诱导的光热效应进行膜穿孔和修复的示意图;(b)利用锥形光纤光镊在细胞膜上进行微手术(b1,b2)和修复(b3,b4);(c)从细胞膜上的微孔中对微丝进行光学提取和操控;(d)锥形光纤光镊捕获和释放线粒体样细胞器,随着激光关闭,被困的细胞器被释放
Fig. 10. Principle of single-cell microsurgery and repair[50]. (a) Schematic of thermoplasmonics-based membrane perforation and repair; (b) single-cell microsurgery (b1, b2) and repair (b3, b4) via TOFTs; (c) optical extraction and manipulation of microfilaments from the micropore in cell membrane; (d) TOFTs trap and release a mitochondria-like organelle, and the trapped organelle is released as the laser is turned off
5.2 细胞器操控
以上研究利用锥形光纤光镊产生的光热效应来实现对细胞膜的微手术及修复,而锥形光纤光镊本身又可以依靠光力对细胞器进行捕获和灵活操控,因而其可以在对细胞进行微手术后进一步实现对单细胞的活检[50]。
图 11. 锥形光纤光镊对叶绿体的操控[51]。(a)锥形光纤光镊进行植物细胞内叶绿体链组装的示意图;(b)叶绿体链的形成过程;
Fig. 11. TOFTs manipulating chloroplast[51]. (a) Schematic of TOFTs for chloroplast chain assembly in plant cells; (b) formation process of chloroplast chains; (c) TOFTs for two-dimensional assembly of chloroplasts
6 锥形光纤光镊在神经调控上的应用
6.1 神经元引导
神经元的轴突生长锥向其突触伙伴神经元的可控引导是形成神经元回路的基本过程。虽然在过去的几十年中研究人员已经探索了许多用于轴突引导的技术,但它们要么是侵入性的,要么是不可控的,而具有高空间和时间分辨率的技术又通常受到低引导效率的限制。最近,光镊技术在神经元调控上的研究引起了越来越多的关注。目前,传统光镊技术已被证明可以增强和引导神经元的生长[53-54],比如将光镊技术用作“神经元信标”,实现对皮质原代神经元的高效可控引导[52]。
图 12. 锥形光纤光镊技术对神经元的引导[35,52]。(a)排斥性轴突引导的神经元信标示意图[52];(b)激光辅助引导的大鼠皮质神经元[52];(c)使用锥形光纤光镊操纵神经元生长锥[35];(d)利用锥形光纤光镊改造成的“激光剪刀”在神经元突起上进行纳米手术[35]
Fig. 12. Neuron guidance of TOFTs[35,52]. (a) Illustration of the neuronal beacon for repulsive axonal guidance[52]; (b) laser assisted navigation of RCNs[52]; (c) modulation of neuronal growth cones using TOFTs[35]; (d) nanosurgery on neuronal protrusions using TOFTs-based “laser scissors”[35]
6.2 神经元刺激
锥形光纤还可以与光声转换器进行集成,实现对神经元的高精度光声刺激。早期,研究人员将基于光纤的光声传感器与增强现实图像技术相结合,用于亚毫米肿瘤定位及可视化手术引导,帮助外科医生准确、快速地切除肿瘤[55]。此后,这种小型化光纤光声转换器被拓展应用到神经元的光声刺激研究中[56-57]。研究人员在光纤尖端利用光声效应产生的全向超声波,实现了对小鼠体外神经元的亚毫米精度调控和活体大脑刺激[56]。这一应用,开辟了光声技术在神经调控领域研究的新途径。为了进一步提高神经刺激的空间分辨率,研究人员缩小了光声转换器的尺寸(如
图 13. TFOE进行高精度的神经元光声刺激[57]。(a)TFOE进行神经元刺激的示意图;(b)TFOE的制作步骤:多层CNT/PDMS混合物作为涂层材料浇铸在金属网上,然后采用穿孔法将涂层材料涂覆在锥形光纤表面;(c)激光照射时长为50 ms和1 ms时,TFOE刺激下神经元内钙离子分布的荧光图像
Fig. 13. TFOE for high-precision optoacoustic stimulation[57]. (a) Schematic of TFOE enabling single-neuron stimulation; (b) manufacturing steps of TFOE: multiwall CNT/PDMS mixture as coating material was casted on a metal mesh followed by a punch-through method to coat the tapered fiber; (c) fluorescence images and calcium traces stimulated by TFOE with a laser duration of 50 ms and 1 ms
7 结束语
本文从锥形光纤的结构及原理出发,介绍了锥形光纤光镊在不同细胞层次上进行光捕获和操控的最新发展,重点阐述了其在单细胞捕获与分析、多细胞组装、亚细胞层面操控及神经细胞调控领域的关键进展。锥形光纤光镊由于具有易于制造、尺寸紧凑和操作灵活等优点,在不久的将来将为亚细胞层面精准分析、高精度神经调控等生物光子学研究及应用提供新的可能性。
尽管锥形光纤光镊取得了很大进展,但在技术上仍存在许多挑战和机遇。首先,样品和光纤端面之间的直接接触可能会对样品造成机械损伤。因此,有必要发展基于锥形光纤的非接触、无损伤光捕获技术。其次,在使用锥形光纤稳定捕获和灵活操作纳米级尺寸生物样品时,如何克服衍射极限仍然是一个巨大挑战。特别地,单个生物分子的稳定捕获非常困难,但其对于单分子分析来说又非常重要。最后,细胞和生物结构的光捕获和操纵,以及随后的体内生物传感是未来几年的新趋势。然而,当将锥形光纤插入活体样本后,锥形光纤可能会引起组织的机械损伤。因此,构建具有生物相容性的锥形光纤光镊具有重要意义。通过活体细菌或细胞在体内组装的活体生物光子波导为生物相容性光纤的形成提供了新的可能性[45-46]。使用这种光纤有望在体内实现对生物样本的捕获、操控、传感和诊断。
此外,锥形光纤光镊与新技术、新应用结合方面的技术也在不断地迸发出新活力。比如,将人工智能(AI)技术与锥形光纤光镊技术结合,可以实现对生物信号的快速分析和高效识别。一个典型的应用是利用锥形光纤光镊捕获微生物,借助人工智能技术对其拉曼光谱进行采集和分析,从而实现对致病性微生物感染的高效、准确诊断[58]。在神经调控领域,随着神经研究深入到亚细胞层面,传统的声学、电学等手段由于固有的限制,越来越难以胜任这一领域的前沿研究。而锥形光纤光镊本身具有高空间分辨率和高抗干扰能力,可以有效地解决当前神经调控精度不够的难题,有望在神经光子学、光遗传学等神经调控领域发挥重要作用[59]。在精准医疗领域,利用锥形光纤光镊实现对活细胞内单个细胞器(特别是病变细胞)的精确捕获、光谱分析、形态操控和直接手术,将为单细胞器水平的治病机制研究提供无限可能[60]。此外,锥形光纤光镊由于具有紧凑和小型化的结构特点,可以很容易地插入深处的毛细血管中,作为一种微创工具来操纵体内的微马达,从而为靶向药物输送、显微外科手术等生物医学应用提供新的技术手段[50]。
[1] Ashkin A. Acceleration and trapping of particles by radiation pressure[J]. Physical Review Letters, 1970, 24(4): 156-159.
[2] Ashkin A, Dziedzic J M, Bjorkholm J E, et al. Observation of a single-beam gradient force optical trap for dielectric particles[J]. Optics Letters, 1986, 11(5): 288-290.
[3] Ashkin A, Dziedzic J M. Optical trapping and manipulation of viruses and bacteria[J]. Science, 1987, 235(4795): 1517-1520.
[4] Xin H B, Li Y C, Liu Y C, et al. Optical forces: from fundamental to biological applications[J]. Advanced Materials, 2020, 32(37): 2001994.
[5] Xin H B, Zhao N, Wang Y N, et al. Optically controlled living micromotors for the manipulation and disruption of biological targets[J]. Nano Letters, 2020, 20(10): 7177-7185.
[6] Choudhary D, Mossa A, Jadhav M, et al. Bio-molecular applications of recent developments in optical tweezers[J]. Biomolecules, 2019, 9(1): 23.
[7] 荣升, 刘洪双, 钟莹, 等. 基于光力捕获金纳米立方体的拉曼光谱增强[J]. 光学学报, 2021, 41(17): 1730003.
[8] 张聿全, 张硕硕, 闵长俊, 等. 飞秒光镊技术研究与应用进展[J]. 中国激光, 2021, 48(19): 1918001.
[9] Dufresne E R, Grier D G. Optical tweezer arrays and optical substrates created with diffractive optics[J]. Review of Scientific Instruments, 1998, 69(5): 1974-1977.
[10] Strasser F, Barnett S M, Ritsch-Marte M, et al. Generally applicable holographic torque measurement for optically trapped particles[J]. Physical Review Letters, 2022, 128(21): 213604.
[11] Li C Y, Zheng B, Li J T, et al. Holographic optical tweezers and boosting upconversion luminescent resonance energy transfer combined clustered regularly interspaced short palindromic repeats (CRISPR)/Cas12a biosensors[J]. ACS Nano, 2021, 15(5): 8142-8154.
[12] Chapin S C, Germain V, Dufresne E R. Automated trapping, assembly, and sorting with holographic optical tweezers[J]. Optics Express, 2006, 14(26): 13095-13100.
[13] Sun B, Roichman Y, Grier D G. Theory of holographic optical trapping[J]. Optics Express, 2008, 16(20): 15765-15776.
[14] Quidant R, Girard C. Surface-plasmon-based optical manipulation[J]. Laser & Photonics Reviews, 2008, 2(1/2): 47-57.
[15] Righini M, Volpe G, Girard C, et al. Surface plasmon optical tweezers: tunable optical manipulation in the femtonewton range[J]. Physical Review Letters, 2008, 100(18): 186804.
[16] Ren Y T, Chen Q, He M J, et al. Plasmonic optical tweezers for particle manipulation: principles, methods, and applications[J]. ACS Nano, 2021, 15(4): 6105-6128.
[17] Zhang Y Q, Min C J, Dou X J, et al. Plasmonic tweezers: for nanoscale optical trapping and beyond[J]. Light: Science & Applications, 2021, 10(1): 1-41.
[18] Fuh M R S, Burgess L W, Hirschfeld T, et al. Single fibre optic fluorescence pH probe[J]. Analyst, 1987, 112(8): 1159-1163.
[19] Hu Z H, Wang J, Liang J W. Manipulation and arrangement of biological and dielectric particles by a lensed fiber probe[J]. Optics Express, 2004, 12(17): 4123-4128.
[20] Ribeiro R S R, Soppera O, Oliva A G, et al. New trends on optical fiber tweezers[J]. Journal of Lightwave Technology, 2015, 33(16): 3394-3405.
[21] Constable A, Kim J, Mervis J, et al. Demonstration of a fiber-optical light-force trap[J]. Optics Letters, 1993, 18(21): 1867-1869.
[22] Jensen-McMullin C, Lee H P, Lyons E R. Demonstration of trapping, motion control, sensing and fluorescence detection of polystyrene beads in a multi-fiber optical trap[J]. Optics Express, 2005, 13(7): 2634-2642.
[23] Taguchi K, Ueno H, Hiramatsu T, et al. Optical trapping of dielectric particle and biological cell using optical fibre[J]. Electronics Letters, 1997, 33(5): 413-414.
[24] Wu H, Jiang C L, Ren A N, et al. Single-fiber optical tweezers for particle trapping and axial reciprocating motion using dual wavelength and dual mode[J]. Optics Communications, 2022, 517: 128333.
[25] Taguchi K, Ueno H, Ikeda M. Rotational manipulation of a yeast cell using optical fibres[J]. Electronics Letters, 1997, 33(14): 1249-1250.
[26] Taguchi K, Atsuta K, Nakata T, et al. Levitation of a microscopic object using plural optical fibers[J]. Optics Communications, 2000, 176(1/2/3): 43-47.
[27] 申泽, 成煜, 邓洪昌, 等. 鸟喙形环形芯光纤光镊粒子捕获受力分析[J]. 光学学报, 2021, 41(18): 1808001.
[28] 陈朋, 党雨婷, 钟慧, 等. 基于LP01和LP11模式共存的单光纤光镊实现生物细胞多路捕获和操纵[J]. 光学学报, 2023, 43(4): 0406004.
[29] Zharov V P, Kurten R C, Bauman J. Photothermal tweezers[J]. Procceedings of SPIE, 2003, 4960: 134-141.
[31] Xin H B, Xu R, Li B J. Optical trapping, driving and arrangement of particles using a tapered fibre probe[J]. Scientific Reports, 2012, 2(1): 1-8.
[32] Liu Z H, Guo C K, Yang J, et al. Tapered fiber optical tweezers for microscopic particle trapping: fabrication and application[J]. Optics Express, 2006, 14(25): 12510-12516.
[33] Grier D G. A revolution in optical manipulation[J]. Nature, 2003, 424(6950): 810-816.
[34] Yuan L B, Liu Z H, Yang J, et al. Twin-core fiber optical tweezers[J]. Optics Express, 2008, 16(7): 4559-4566.
[35] Mohanty S K, Mohanty K, Berns M W. Manipulation of mammalian cells using a single-fiber optical microbeam[J]. Journal of Biomedical Optics, 2008, 13(5): 054049.
[36] Xin H B, Liu Q Y, Li B J. Non-contact fiber-optical trapping of motile bacteria: dynamics observation and energy estimation[J]. Scientific Reports, 2014, 4(1): 1-8.
[37] Xin H B, Li Y Y, Li L S, et al. Optofluidic manipulation of Escherichia coli in a microfluidic channel using an abruptly tapered optical fiber[J]. Applied Physics Letters, 2013, 103(3): 033703.
[38] Mestres P, Berthelot J, Spasenović M, et al. Cooling and manipulation of a levitated nanoparticle with an optical fiber trap[J]. Applied Physics Letters, 2015, 107(15): 151102.
[39] Xin H B, Li Y C, Xu D K, et al. Single upconversion nanoparticle-bacterium cotrapping for single-bacterium labeling and analysis[J]. Small, 2017, 13(14): 1603418.
[40] Derby B. Printing and prototyping of tissues and scaffolds[J]. Science, 2012, 338(6109): 921-926.
[41] Saltzman W M, Olbricht W L. Building drug delivery into tissue engineering design[J]. Nature Reviews Drug Discovery, 2002, 1(3): 177-186.
[42] Chen Z L, Li Y, Liu W W, et al. Patterning mammalian cells for modeling three types of naturally occurring cell-cell interactions[J]. Angewandte Chemie International Edition, 2009, 48(44): 8303-8305.
[43] Tam J M, Biran I, Walt D R. An imaging fiber-based optical tweezer array for microparticle array assembly[J]. Applied Physics Letters, 2004, 84(21): 4289-4291.
[44] Xin H B, Xu R, Li B J. Optical formation and manipulation of particle and cell patterns using a tapered optical fiber[J]. Laser & Photonics Reviews, 2013, 7(5): 801-809.
[45] Xin H B, Li Y Y, Liu X S, et al. Escherichia coli-based biophotonic waveguides[J]. Nano Letters, 2013, 13(7): 3408-3413.
[46] Li Y C, Xin H B, Zhang Y, et al. Living nanospear for near-field optical probing[J]. ACS Nano, 2018, 12(11): 10703-10711.
[47] Li Y C, Liu X S, Yang X G, et al. Enhancing upconversion fluorescence with a natural bio-microlens[J]. ACS Nano, 2017, 11(11): 10672-10680.
[48] Liu S J, Li Z B, Weng Z, et al. Miniaturized optical fiber tweezers for cell separation by optical force[J]. Optics Letters, 2019, 44(7): 1868-1871.
[49] Liu S F, Lin L H, Sun H B. Opto-thermophoretic manipulation[J]. ACS Nano, 2021, 15(4): 5925-5943.
[50] Zhao X T, Shi Y, Pan T, et al. In situ single-cell surgery and intracellular organelle manipulation via thermoplasmonics combined optical trapping[J]. Nano Letters, 2022, 22(1): 402-410.
[51] Li Y C, Xin H B, Liu X S, et al. Non-contact intracellular binding of chloroplasts in vivo[J]. Scientific Reports, 2015, 5(1): 1-9.
[52] Black B, Mondal A, Kim Y, et al. Neuronal beacon[J]. Optics Letters, 2013, 38(13): 2174-2176.
[53] Carnegie D J, Stevenson D J, Mazilu M, et al. Guided neuronal growth using optical line traps[J]. Optics Express, 2008, 16(14): 10507-10517.
[54] Ehrlicher A, Betz T, Stuhrmann B, et al. Guiding neuronal growth with light[J]. Proceedings of the National Academy of Sciences of the United States of America, 2002, 99(25): 16024-16028.
[55] Lan L, Xia Y, Li R, et al. A fiber optoacoustic guide with augmented reality for precision breast-conserving surgery[J]. Light: Science & Applications, 2018, 7(1): 1-11.
[56] Jiang Y, Lee H J, Lan L, et al. Optoacoustic brain stimulation at submillimeter spatial precision[J]. Nature Communications, 2020, 11(1): 1-9.
[57] Shi L L, Jiang Y, Fernandez F R, et al. Non-genetic photoacoustic stimulation of single neurons by a tapered fiber optoacoustic emitter[J]. Light: Science & Applications, 2021, 10(1): 1-13.
[58] Lin C H, Li X F, Wu T L, et al. Optofluidic identification of single microorganisms using fiber-optical-tweezer-based Raman spectroscopy with artificial neural network[J]. BMEMat, 2023, 1(1): e12007.
[59] Guo J H, Wu Y, Gong Z Y, et al. Photonic nanojet-mediated optogenetics[J]. Advanced Science, 2022, 9(12): e2104140.
[60] Nadappuram B P, Cadinu P, Barik A, et al. Nanoscale tweezers for single-cell biopsies[J]. Nature Nanotechnology, 2019, 14(1): 80-88.
Article Outline
肖雨晴, 史阳, 李宝军, 辛洪宝. 基于锥形光纤光镊的细胞操控与神经调控[J]. 中国激光, 2023, 50(15): 1507302. Yuqing Xiao, Yang Shi, Baojun Li, Hongbao Xin. Cell Manipulation and Neuron Regulation Based on Tapered Optical Fiber Tweezers[J]. Chinese Journal of Lasers, 2023, 50(15): 1507302.