All work performed under the support of the National Institute of Standards and Technology. Certain commercial equipment, instruments, or materials are identified to foster understanding of this protocol. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.

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The authors declare no competing financial interest.

משגר פיזואלקטריים נועד כדי למטב את הביצועים הדינמיים של PZT שנבחר. בחירה נכונה של חומרי PZT וניהול של תנודות קוליות הן השלבים העיקריים להניב בניסוי מוצלח. יש PZTs מאפיינים שונים בהתאם לסוג של מתמר (בתפזורת או מוערם) וחומרי רכיב (קשים או רכים). PZT סוג בתפזורת עשוי מחומר פיזוא...

Ashkin דיווח על האצה הלכידה של microparticles ידי לחץ קרינה בשנת 1970. 1 הישג הרומן שלו לקדם את הפיתוח של טכניקות השמנה אופטיות ככלי עיקרי ללימודי פיסיקה בסיסיים וביופיסיקה. 2, 3, 4, 5 עד כה, היישום של השמנה אופטית, והוא מתמקד בעיקר סביבות נוזליות, ו נעשה שימוש כדי ללמוד מגוון רחב מאוד של מערכות, מהתנהגות קולואידים אל התכונות המכאניות של ביומולקולות יחידה. 6, 7, 8 יישום של השמנה אופטית כדי סביבות דמויות גז, לעומת זאת, דורש פתרון כמה בעיות טכניות חדשות. לאחרונה, השמנה אופטית באוויר / ואקום בשנים אחרונות חלה עלייה ב מחקר בסיסי. מאז לוי אופטיtation פוטנציאל מספק בידוד כמעט-מלא של מערכה מהסביבה, החלקיק לרחף אופטי הופך מעבדה אידיאלית לחקר ארצות קרקע הקוואנטים חפצים קטן, 4 גלי כבידה בתדירות גבוהה מדידה, 9 וחיפוש תשלום חלקי. 10 יתר על כן, הצמיגות הנמוכה של אוויר / ואקום מאפשרת להשתמש אינרציה כדי למדוד את המהירות הרגעית של חלקיק בראוני 11 וכדי ליצור תנועה בליסטית על פני טווח רחב של תנועה מעבר למשטר ליניארי באביב דמוי. 12 לכן, מידע טכני מפורט ופרקטיקות מלכודות אופטיות סביבות דמויות גז הפכו יותר חשובים לקהילת המחקר הרחבה. ניסיוני בטכניקות חדשות נדרשות לטעון ננו / microparticles לתוך מלכודות אופטיות סביבות דמויות גז. מתמר פיזואלקטריים (PZT), מכשיר הממיר אלקטרונic אנרגיה לאנרגיה mechano-אקוסטי, נעשה שימוש כדי לספק חלקיקים קטנים לתוך מלכודות אופטי באוויר / ואקום 5, 12 מאז ההפגנה הראשונה של ריחוף אופטי. 1 מאז, טכניקות טעינת מספר הוצעו על מנת לטעון חלקיקים קטנים באמצעות אירוסולים נדיפים שנוצרו על ידי nebulizer מסחרי 13 או מחולל גל אקוסטי. 14 לאווירוסולים צפו עם תכלילים מוצקים (חלקיקים) לעבור באופן אקראי ליד מיקוד לכודים במקרה. לאחר אירוסול לכוד, הממס מתאדה החוצה החלקיק נשאר במלכודת האופטית. עם זאת, שיטות אלה אינן מתאימים היטב לזהות חלקיקים הרצוי מתוך מדגם, לטעון חלקיק נבחר כדי לעקוב אחר השינויים שלה אם שוחררו מן המלכודת. פרוטוקול זה מיועד לספק פרטים למתרגלים חדשים על טעינת מלכודת אופטית סלקטיבי באוויר, כולל הניסויהתקנה אל, ייצור של בעל PZT מתחם מדגם, טעינת מלכודת, ורכישת נתונים הקשורים לניתוח תנועת חלקיקים בשני התחומים התדירים ההרכבה וזמן. פרוטוקולים על השמנה בתקשורת נוזלית גם פורסמו. 15, 16 ההתקנה ניסיון הכוללת מפותחת על מיקרוסקופ אופטי מסחרי הפוך. איור 1 מציג תרשים סכמטי של ההתקנה נהגה להציג את הצעדים של טעינת המלכודת אופטית סלקטיבי: לשחרר את microparticles נח, הרמת החלקיק נבחר עם הקרן הממוקדת, מדידת התנועה שלה, ומעמיד אותו על המצע שוב. ראשית, בשלבי translational (רוחבי ואנכי) משמשים להביא microparticle שנבחר על מצע מוקד ליזר השמנה (ננומטר אורך הגל 1064) התמקד על ידי עדשה אובייקטיבית (קרובת אינפרא אדום תקנה מטרה למרחקים ארוכה-עבודה: NA 0.4, הגדלה 20X, עובד דistance 20 מ&quot;מ) דרך מצע שקוף. לאחר מכן, משגר חשמלי (PZT טעון מראש טבעת מהסוג מכאני) מייצר ויברציות קולי לשבור את ההידבקות בין microparticles ואת מצע. לפיכך, כל חלקיק משוחררים ניתן להרים ידי מלכודת לייזר שיפוע חד קרן ממוקדת על החלקיק שנבחרו. לאחר החלקיק הוא לכוד, זה מתורגם במרכז המתחם מדגם המכיל שני לוחות מוליכים מקבילים עבור עירור אלקטרוסטטי. לבסוף, רכישת נתונים (DAQ) מערכת זמנית מתעדת את תנועת החלקיקים, שנתפסה על ידי גלאי אור תאים ברבע (QPD), ואת השדה החשמלי מיושם. לאחר סיום המדידה, החלקיק מושם מבוקר על גבי המצע כך שהוא יכול להיות לכוד שוב באופן הפיך. תהליך הכולל זה ניתן לחזור מאות פעמים ללא איבוד חלקיקים כדי למדוד שינויים כגון חשמול קשר המתרחשים על פני מחזורי שמנה מספר. עיין f לאחרונה המאמר שלנואו פרטים. 12

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optical trap loading of dielectric microparticles in air

We demonstrate a method to trap a selected dielectric microparticle in air using radiation pressure from a single-beam gradient optical trap. Randomly scattered dielectric microparticles adhered to a glass substrate are momentarily detached using ultrasonic vibrations generated by a piezoelectric transducer (PZT). Then, the optical beam focused on a selected particle lifts it up to the optical trap while the vibrationally excited microparticles fall back to the substrate. A particle may be trapped at the nominal focus of the trapping beam or at a position above the focus (referred to here as the levitation position) where gravity provides the restoring force. After the measurement, the trapped particle can be placed at a desired position on the substrate in a controlled manner. 
In this protocol, an experimental procedure for selective optical trap loading in air is outlined. First, the experimental setup is briefly introduced. Second, the design and fabrication of a PZT holder and a sample enclosure are illustrated in detail. The optical trap loading of a selected microparticle is then demonstrated with step-by-step instructions including sample preparation, launching into the trap, and use of electrostatic force to excite particle motion in the trap and measure charge. Finally, we present recorded particle trajectories of Brownian and ballistic motions of a trapped microparticle in air. These trajectories can be used to measure stiffness or to verify optical alignment through time domain and frequency domain analysis. Selective trap loading enables optical tweezers to track a particle and its changes over repeated trap loadings in a reversible manner, thereby enabling studies of particle-surface interaction.

משגר PZT נועד באמצעות חבילת תוכנות CAD. כאן, אנו משתמשים מבנה כריך פשוט עבור הטעינה המוקדמת (א PZT הדק עם שתי צלחות), כפי שמוצג באיור 2 בעל PZT ואת מתחם המדגם יכול להיות מפוברק ממגוון חומרים ושיטות. להדגמה מהירה, אנו בוחרים הדפסת 3D עם תרמופלסטיים כפי...

Watch this Scientific Journal Video about Optical Trap Loading of Dielectric Microparticles In Air at JoVE.com

Optical Trap Loading of Dielectric Microparticles In Air

A protocol for launching and stably trapping selected dielectric microparticles in air is presented.

טוען מלכודת אופטית של דיאלקטרי microparticles באוויר

We demonstrate a method to trap a selected dielectric microparticle in air using radiation pressure from a single-beam gradient optical trap. Randomly ...

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9.0K Views.  National Institute of Standards and Technology. A protocol for launching and stably trapping selected dielectric microparticles in air is presented.

Video: Optical Trap Loading of Dielectric Microparticles In Air

A Microfluidic-based Hydrodynamic Trap for Single Particles

The ability to confine and manipulate single particles in free solution is a key enabling technology for fundamental and applied science. Methods for particle trapping based on optical, magnetic, electrokinetic, and acoustic techniques have led to major advancements in physics and biology ranging from the molecular to cellular level. In this article, we introduce a new microfluidic-based technique for particle trapping and manipulation based solely on hydrodynamic fluid flow. Using this method, we demonstrate trapping of micro- and nano-scale particles in aqueous solutions for long time scales. The hydrodynamic trap consists of an integrated microfluidic device with a cross-slot channel geometry where two opposing laminar streams converge, thereby generating a planar extensional flow with a fluid stagnation point (zero-velocity point). In this device, particles are confined at the trap center by active control of the flow field to maintain particle position at the fluid stagnation point. In this manner, particles are effectively trapped in free solution using a feedback control algorithm implemented with a custom-built LabVIEW code. The control algorithm consists of image acquisition for a particle in the microfluidic device, followed by particle tracking, determination of particle centroid position, and active adjustment of fluid flow by regulating the pressure applied to an on-chip pneumatic valve using a pressure regulator. In this way, the on-chip dynamic metering valve functions to regulate the relative flow rates in the outlet channels, thereby enabling fine-scale control of stagnation point position and particle trapping. The microfluidic-based hydrodynamic trap exhibits several advantages as a method for particle trapping. Hydrodynamic trapping is possible for any arbitrary particle without specific requirements on the physical or chemical properties of the trapped object. In addition, hydrodynamic trapping enables confinement of a "single" target object in concentrated or crowded particle suspensions, which is difficult using alternative force field-based trapping methods. The hydrodynamic trap is user-friendly, straightforward to implement and may be added to existing microfluidic devices to facilitate trapping and long-time analysis of particles. Overall, the hydrodynamic trap is a new platform for confinement, micromanipulation, and observation of particles without surface immobilization and eliminates the need for potentially perturbative optical, magnetic, and electric fields in the free-solution trapping of small particles.

In this article, we present a microfluidic-based method for particle confinement based on hydrodynamic flow. We demonstrate stable particle trapping at a fluid stagnation point using a feedback control mechanism, thereby enabling confinement and micromanipulation of arbitrary particles in an integrated microdevice.

Microfluidic מבוססי הידרודינמית מלכודת חלקיקים יחיד

The ability to confine and manipulate single particles in free solution is a key enabling technology for fundamental and applied science.  Methods for ...

Bioengineering

Optical Trapping of Nanoparticles

Optical trapping is a technique for immobilizing and manipulating small objects in a gentle way using light, and it has been widely applied in trapping and manipulating small biological particles. Ashkin and co-workers first demonstrated optical tweezers using a single focused beam1. The single beam trap can be described accurately using the perturbative gradient force formulation in the case of small Rayleigh regime particles1. In the perturbative regime, the optical power required for trapping a particle scales as the inverse fourth power of the particle size. High optical powers can damage dielectric particles and cause heating. For instance, trapped latex spheres of 109 nm in diameter were destroyed by a 15 mW beam in 25 sec1, which has serious implications for biological matter2,3.
A self-induced back-action (SIBA) optical trapping was proposed to trap 50 nm polystyrene spheres in the non-perturbative regime4. In a non-perturbative regime, even a small particle with little permittivity contrast to the background can influence significantly the ambient electromagnetic field and induce a large optical force. As a particle enters an illuminated aperture, light transmission increases dramatically because of dielectric loading. If the particle attempts to leave the aperture, decreased transmission causes a change in momentum outwards from the hole and, by Newton's Third Law, results in a force on the particle inwards into the hole, trapping the particle. The light transmission can be monitored; hence, the trap can become a sensor. The SIBA trapping technique can be further improved by using a double-nanohole structure.
The double-nanohole structure has been shown to give a strong local field enhancement5,6. Between the two sharp tips of the double-nanohole, a small particle can cause a large change in optical transmission, thereby inducing a large optical force. As a result, smaller nanoparticles can be trapped, such as 12 nm silicate spheres7 and 3.4 nm hydrodynamic radius bovine serum albumin proteins8. In this work, the experimental configuration used for nanoparticle trapping is outlined. First, we detail the assembly of the trapping setup which is based on a Thorlabs Optical Tweezer Kit. Next, we explain the nanofabrication procedure of the double-nanohole in a metal film, the fabrication of the microfluidic chamber and the sample preparation. Finally, we detail the data acquisition procedure and provide typical results for trapping 20 nm polystyrene nanospheres.

The following setup approach details low power optical trapping of dielectric nanoparticles using a double-nanohole in metal film.

לכידה אופטית של חלקיקים

Optical trapping is a technique for immobilizing and manipulating small objects in a gentle way using light, and it has been widely applied in trapping ...

Utilization of Plasmonic and Photonic Crystal Nanostructures for Enhanced Micro- and Nanoparticle Manipulation

A method to manipulate the position and orientation of submicron particles nondestructively would be an incredibly useful tool for basic biological research. Perhaps the most widely used physical force to achieve noninvasive manipulation of small particles has been dielectrophoresis(DEP).1 However, DEP on its own lacks the versatility and precision that are desired when manipulating cells since it is traditionally done with stationary electrodes. Optical tweezers, which utilize a three dimensional electromagnetic field gradient to exert forces on small particles, achieve this desired versatility and precision.2 However, a major drawback of this approach is the high radiation intensity required to achieve the necessary force to trap a particle which can damage biological samples.3 A solution that allows trapping and sorting with lower optical intensities are optoelectronic tweezers (OET) but OET's have limitations with fine manipulation of small particles; being DEP-based technology also puts constraint on the property of the solution.4,5
This video article will describe two methods that decrease the intensity of the radiation needed for optical manipulation of living cells and also describe a method for orientation control. The first method is plasmonic tweezers which use a random gold nanoparticle (AuNP) array as a substrate for the sample as shown in Figure 1. The AuNP array converts the incident photons into localized surface plasmons (LSP) which consist of resonant dipole moments that radiate and generate a patterned radiation field with a large gradient in the cell solution. Initial work on surface plasmon enhanced trapping by Righini et al and our own modeling have shown the fields generated by the plasmonic substrate reduce the initial intensity required by enhancing the gradient field that traps the particle.6,7,8 The plasmonic approach allows for fine orientation control of ellipsoidal particles and cells with low optical intensities because of more efficient optical energy conversion into mechanical energy and a dipole-dependent radiation field. These fields are shown in figure 2 and the low trapping intensities are detailed in figures 4 and 5. The main problems with plasmonic tweezers are that the LSP's generate a considerable amount of heat and the trapping is only two dimensional. This heat generates convective flows and thermophoresis which can be powerful enough to expel submicron particles from the trap.9,10 The second approach that we will describe is utilizing periodic dielectric nanostructures to scatter incident light very efficiently into diffraction modes, as shown in figure 6.11 Ideally, one would make this structure out of a dielectric material to avoid the same heating problems experienced with the plasmonic tweezers but in our approach an aluminum-coated diffraction grating is used as a one-dimensional periodic dielectric nanostructure. Although it is not a semiconductor, it did not experience significant heating and effectively trapped small particles with low trapping intensities, as shown in figure 7. Alignment of particles with the grating substrate conceptually validates the proposition that a 2-D photonic crystal could allow precise rotation of non-spherical micron sized particles.10 The efficiencies of these optical traps are increased due to the enhanced fields produced by the nanostructures described in this paper.

Plasmonic tweezers and photonic crystal nanostructures are shown to produce useful enhancements in the efficiency and orientation control of optically trapping micro- and nano-particles.

ניצול של ננו גבישים פוטוניים Plasmonic ו מניפולציה מיקרו ו Nanoparticle משופרת

A method to manipulate the position and orientation of submicron particles nondestructively would be an incredibly useful tool for basic biological ...

Fabrication and Operation of a Nano-Optical Conveyor Belt

The technique of using focused laser beams to trap and exert forces on small particles has enabled many pivotal discoveries in the nanoscale biological and physical sciences over the past few decades. The progress made in this field invites further study of even smaller systems and at a larger scale, with tools that could be distributed more easily and made more widely available. Unfortunately, the fundamental laws of diffraction limit the minimum size of the focal spot of a laser beam, which makes particles smaller than a half-wavelength in diameter hard to trap and generally prevents an operator from discriminating between particles which are closer together than one half-wavelength. This precludes the optical manipulation of many closely-spaced nanoparticles and&#160;limits the&#160;resolution of optical-mechanical systems. Furthermore, manipulation using focused beams requires beam-forming or steering optics, which can be very bulky and expensive. To address these limitations in the system scalability of conventional optical trapping our lab has devised an alternative technique which utilizes near-field optics to move particles across a chip. Instead of focusing laser beams in the far-field, the optical near field of plasmonic resonators produces the necessary local optical intensity enhancement to overcome the restrictions of diffraction and manipulate particles at higher resolution. Closely-spaced resonators produce strong optical traps which can be addressed to mediate the hand-off of particles from one to the next in a conveyor-belt-like fashion. Here, we describe how to design and produce a conveyor belt using a gold surface patterned with plasmonic C-shaped resonators and how to operate it with polarized laser light to achieve super-resolution nanoparticle manipulation and transport. The nano-optical conveyor belt chip can be produced using lithography techniques and easily packaged and distributed.

The scalability and resolution of conventional optical manipulation techniques are limited by diffraction. We circumvent the diffraction limit and describe a method of optically transporting nanoparticles across a chip using a gold surface patterned with a path of closely spaced C-shaped plasmonic resonators.

ייצור ותפעול של מסוע ננו-אופטי

The technique of using focused laser beams to trap and exert forces on small particles has enabled many pivotal discoveries in the nanoscale biological ...

Plasmonic Trapping and Release of Nanoparticles in a Monitoring Environment

Plasmonic tweezers use surface plasmon polaritons to confine polarizable nanoscale objects. Among the various designs of plasmonic tweezers, only a few can observe immobilized particles. Moreover, a limited number of studies have experimentally measured the exertable forces on the particles. The designs can be classified as the protruding nanodisk type or the suppressed nanohole type. For the latter, microscopic observation is extremely challenging. In this paper, a new plasmonic tweezer system is introduced to monitor particles, both in directions parallel and orthogonal to the symmetric axis of a plasmonic nanohole structure. This feature enables us to observe the movement of each particle near the rim of the nanohole. Furthermore, we can quantitatively estimate the maximal trapping forces using a new fluidic channel.

A microchip fabrication process that incorporates plasmonic tweezers is presented here. The microchip enables the imaging of a trapped particle to measure maximal trapping forces.

השמנת Plasmonic ושחרור של חלקיקים בסביבת ניטור

Plasmonic tweezers use surface plasmon polaritons to confine polarizable nanoscale objects. Among the various designs of plasmonic tweezers, only a few ...

Experimental Methods for Trapping Ions Using Microfabricated Surface Ion Traps

Ions trapped in a quadrupole Paul trap have been considered one of the strong physical candidates to implement quantum information processing. This is due to their long coherence time and their capability to manipulate and detect individual quantum bits (qubits). In more recent years, microfabricated surface ion traps have received more attention for large-scale integrated qubit platforms. This paper presents a microfabrication methodology for ion traps using micro-electro-mechanical system (MEMS) technology, including the fabrication method for a 14 &#181;m-thick dielectric layer and metal overhang structures atop the dielectric layer. In addition, an experimental procedure for trapping ytterbium (Yb) ions of isotope 174 (174Yb+) using 369.5 nm, 399 nm, and 935 nm diode lasers is described. These methodologies and procedures involve many scientific and engineering disciplines, and this paper first presents the detailed experimental procedures. The methods discussed in this paper can easily be extended to the trapping of Yb ions of isotope 171 (171Yb+) and to the manipulation of qubits.

This paper presents a microfabrication methodology for surface ion traps, as well as a detailed experimental procedure for trapping ytterbium ions in a room-temperature environment.

שיטות נסיוניות שמחייב יונים באמצעות Microfabricated על פני השטח מלכודות יונים

Ions trapped in a quadrupole Paul trap have been considered one of the strong physical candidates to implement quantum information processing. This is due ...

Use of Dual Optical Tweezers and Microfluidics for Single-Molecule Studies

Visual biochemistry is a powerful technique for observing the stochastic properties of single enzymes or enzyme complexes that are obscured in the averaging that takes place in bulk-phase studies. To achieve visualization, dual optical tweezers, where one trap is fixed and the other is mobile, are focused into one channel of a multi-stream microfluidic chamber positioned on the stage of an inverted fluorescence microscope. The optical tweezers trap single molecules of fluorescently labeled DNA and fluid flow through the chamber and past the trapped beads, stretches the DNA to B-form (under minimal force, i.e., 0 pN) with the nucleic acid being observed as a white string against a black background. DNA molecules are moved from one stream to the next, by translating the stage perpendicular to the flow to enable the initiation of reactions in a controlled manner. To achieve success, microfluidic devices with optically clear channels are mated to glass syringes held in place in a syringe pump. Optimal results use connectors permanently bonded to the flow cell, tubing that is mechanically rigid and chemically resistant, and which is connected to switching valves that eliminate bubbles that prohibit laminar flow.

Visual, single-molecule biochemistry studied through microfluidic chambers is greatly facilitated using glass barrel, gas-tight syringes, stable connections of tubing to flow cells, and elimination of bubbles by placing switching valves between the syringes and tubing. The protocol describes dual optical traps that enable visualization of DNA transactions and intermolecular interactions.

שימוש בפינצטה אופטית כפולה ומיקרופלואידיקה למחקרי מולקולות בודדות

Visual biochemistry is a powerful technique for observing the stochastic properties of single enzymes or enzyme complexes that are obscured in the ...

Biochemistry

Trapping of Micro Particles in Nanoplasmonic Optical Lattice

The plasmonic optical tweezer has been developed to overcome the diffraction limits of the conventional far field optical tweezer. Plasmonic optical lattice consists of an array of nanostructures, which exhibit a variety of trapping and transport behaviors. We report the experimental procedures to trap micro-particles in a simple square nanoplasmonic optical lattice. We also describe the optical setup and the nanofabrication of a nanoplasmonic array. The optical potential is created by illuminating an array of gold nanodiscs with a Gaussian beam of 980 nm wavelength, and exciting plasmon resonance. The motion of particles is monitored by fluorescence imaging. A scheme to suppress photothermal convection is also described to increase usable optical power for optimal trapping. Suppression of convection is achieved by cooling the sample to a low temperature, and utilizing the near-zero thermal expansion coefficient of a water medium. Both single particle transport and multiple particle trapping are reported here.

We describe a procedure to optically trap micro-particles in nanoplasmonic optical lattice.

השמנה של חלקיקי מיקרו סריג אופטי Nanoplasmonic

The plasmonic optical tweezer has been developed to overcome the diffraction limits of the conventional far field optical tweezer. Plasmonic optical ...

Direct Force Measurements of Subcellular Mechanics in Confinement using Optical Tweezers

During the development of a multicellular organism, a single fertilized cell divides and gives rise to multiple tissues with diverse functions. Tissue morphogenesis goes in hand with molecular and structural changes at the single cell level that result in variations of subcellular mechanical properties. As a consequence, even within the same cell, different organelles and compartments resist differently to mechanical stresses; and mechanotransduction pathways can actively regulate their mechanical properties. The ability of a cell to adapt to the microenvironment of the tissue niche thus is in part due to the ability to sense and respond to mechanical stresses. We recently proposed a new mechanosensation paradigm in which nuclear deformation and positioning enables a cell to gauge the physical 3D environment and endows the cell with a sense of proprioception to decode changes in cell shape. In this article, we describe a new method to measure the forces and material properties that shape the cell nucleus inside living cells, exemplified on adherent cells and mechanically confined cells. The measurements can be performed non-invasively with optical traps inside cells, and the forces are directly accessible through calibration-free detection of light momentum. This allows measuring the mechanics of the nucleus independently from cell surface deformations and allowing dissection of exteroceptive and interoceptive mechanotransduction pathways. Importantly, the trapping experiment can be combined with optical microscopy to investigate the cellular response and subcellular dynamics using fluorescence imaging of the cytoskeleton, calcium ions, or nuclear morphology. The presented method is straightforward to apply, compatible with commercial solutions for force measurements, and can easily be extended to investigate the mechanics of other subcellular compartments, e.g., mitochondria, stress-fibers, and endosomes.

Here, we present a protocol to investigate the intracellular mechanical properties of isolated embryonic zebrafish cells in three-dimensional confinement with direct force measurement by an optical trap.

מדידות כוח ישירות של מכניקה תת-תאית בכליאה באמצעות פינצטה אופטית

During the development of a multicellular organism, a single fertilized cell divides and gives rise to multiple tissues with diverse functions. Tissue ...

Developmental Biology

Optical Trapping of Plasmonic Nanoparticles for In Situ Surface-Enhanced Raman Spectroscopy Characterizations

Surface-enhanced Raman spectroscopy (SERS) enables the ultrasensitive detection of analyte molecules in various applications due to the enhanced electric field of metallic nanostructures. Salt-induced silver nanoparticle aggregation is the most popular method for generating SERS-active substrates; however, it is limited by poor reproducibility, stability, and biocompatibility. The present protocol integrates optical manipulation and SERS detection to develop an efficient analytical platform to address this. A 1064 nm trapping laser and a 532 nm Raman probe laser are combined in a microscope to assemble silver nanoparticles, which generate plasmonic hotspots for in situ SERS measurements in aqueous environments. Without aggregating agents, this dynamic plasmonic silver nanoparticle assembly enables an approximately 50-fold enhancement of the analyte molecule signal. Moreover, it provides spatial and temporal control to form the SERS-active assembly in as low as 0.05 nM analyte-coated silver nanoparticle solution, which minimizes the potential perturbation for in vivo analysis. Hence, this optical trapping-integrated SERS platform holds great potential for efficient, reproducible, and stable molecular analyses in liquids, especially in aqueous physiological environments.