Name: optical trap loading of dielectric microparticles in air
Uploaded: 2017-02-05T13:00:00
Description: Watch this Scientific Journal Video about Optical Trap Loading of Dielectric Microparticles In Air at JoVE.com

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.

Achtung: Bitte lesen Sie alle relevanten Sicherheitsprogramme vor dem Experiment. Alle experimentellen Verfahren in diesem Protokoll beschrieben werden, in Übereinstimmung mit dem NIST LASER Sicherheitsprogramm sowie andere einschlägigen Bestimmungen durchgeführt. Bitte achten Sie darauf, die richtige persönliche Schutzausrüstung (PSA), wie Laserschutzbrille für die spezifische Wellenlänge und Leistung ausgelegt zu wählen und zu tragen. trocken Nano- / Mikropartikel Handhabung können zusätzliche Atemschutz erf...

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Der piezoelektrische Abschuß soll die dynamische Leistung eines ausgewählten PZT zu optimieren. Die richtige Auswahl von PZT-Materialien und das Management von Ultraschallschwingungen sind die wichtigsten Schritte, um ein erfolgreiches Experiment zu erhalten. PZTs haben unterschiedliche Eigenschaften in Abhängigkeit von der Art des Wandlers (bulk oder gestapelt) und Komponentenmaterialien (hart oder weich). Eine Masse Typ PZT aus einem harten piezoelektrischen Material wird aus den folgenden Gründen ausgewählt. Ers...

Ashkins berichtet die Beschleunigung und das Einfangen von Mikroteilchen durch Strahlungsdruck im Jahr 1970 1 Sein Roman Erfolg förderte die Entwicklung von optischen Trapping Techniken als primäres Werkzeug für die Grundlagenforschung der Physik und Biophysik. 2, 3, 4, 5 Bisher wurde die Anwendung von optischen Einfangen konzentrierte sich hauptsächlich auf flüssigen Umgebungen, und einen sehr weiten Bereich von Systemen zu untersuchen, von dem Verhalten von Kolloiden zu den mechanischen Eigenschaften von einzelnen Biomolekülen verwendet. 6, 7, 8 Anwendung von optischen Fallen zu gasförmigen Medien, erfordert jedoch einige neue technische Probleme zu lösen. Vor kurzem optische Fallen in Luft / Vakuum zunehmend wurde in der Grundlagenforschung eingesetzt. Da optische levitation bietet potenziell nahezu vollständige Isolierung eines Systems aus der Umgebung, die optisch levitierten Partikel für das Studium der Quantengrundzustände in kleinen Objekten, 4 Messung Hochfrequenz Gravitationswellen, 9 und der Suche nach fraktionierte Ladung ein ideales Labor wird. Außerdem 10 ermöglicht die niedrige Viskosität von Luft / Vakuum eine Trägheit zu verwenden , um die momentane Geschwindigkeit eines Brownsche Teilchen 11 zu messen und zu ballistischen Bewegung über einen weiten Bereich von Bewegung über die linearen federartigen Regelung zu schaffen. 12 Daher detaillierte technische Informationen und Verfahren für optische Fallen in gasförmigen Medien haben wertvoller für den breiteren Forschungsgemeinschaft geworden. Neue experimentelle Techniken sind erforderlich, Nano- / Mikropartikel in optischen Fallen in gasförmigen Medien zu laden. Ein piezoelektrischer Wandler (PZT), eine Einrichtung, die Strom umwandeltic Energie in mechanisch-akustischen Energie, verwendet worden , um kleine Partikel in optischen Fallen in Luft / Vakuum - 5, 12 , da die erste Demonstration der optischen Schwebe zu liefern. 1 Seitdem haben mehrere Ladetechniken vorgeschlagen worden , kleinere Teilchen unter Verwendung von flüchtigen Aerosolen durch einen kommerziellen Vernebler 13 oder einen akustischen Wellengenerator erzeugt zu laden. 14 Die schwimmenden Aerosole mit festen Einschlüsse (Partikel) zufällig in der Nähe des Fokus passieren und durch Zufall gefangen. Nachdem das Aerosol eingefangen wird, verdampft das Lösungsmittel und das Teilchen verbleibt in der optischen Falle. Jedoch sind diese Verfahren nicht gut geeignet, um die gewünschten Partikel aus einer Probe zu identifizieren, um eine ausgewählte Partikel laden und seine Veränderungen zu verfolgen, wenn von der Falle freigegeben. Dieses Protokoll soll Details neue Praktizierende auf selektiven optischen Falle Laden in Luft zu versorgen, einschließlich des Experimentesal-Setup, die Herstellung einer PZT Halter und Probengehäuse, Trap-Laden, und die Datenerfassung mit der Analyse der Partikelbewegung zugeordnet ist sowohl in der Frequenz- und Zeitbereich. Protokolle für die in flüssigen Medien Trapping wurden ebenfalls veröffentlicht. 15, 16 Die gesamte Versuchsaufbau ist auf einem kommerziellen invertierten optischen Mikroskop entwickelt. Figur 1 zeigt eine schematische Darstellung der Einrichtung verwendeten Schritte der selektiven optischen Falle Laden zu demonstrieren: Die Ruhe Mikroteilchen befreien, die gewählte Teilchen mit dem fokussierten Strahl Anheben Messen seiner Bewegung, und sie auf dem Substrat wieder setzt. Zuerst Translationsstufen (quer und vertikal) werden verwendet, um eine ausgewählte Mikropartikel auf dem Substrat zu dem Fokus eines Trapping-Laser (Wellenlänge 1064 nm) durch eine Objektivlinse (near-infrared korrigiert Langarbeitsabstand Ziel fokussiert zu bringen: NA 0,4 ist, Vergrößerung 20X, Arbeits distance 20 mm) durch das transparente Substrat. Dann wird eine piezoelektrische Werfer (ein mechanisch vorgeladene Ring-PZT) erzeugt Ultraschallvibrationen, die Haftung zwischen Mikroteilchen und einem Substrat zu brechen. Somit kann jeder befreite Partikel vom Einzelstrahl Gradient Laser trap auf dem ausgewählten Partikel konzentriert angehoben werden. Sobald das Teilchen eingefangen ist, wird es in der Mitte des Proben Gehäuse zur elektrostatischen Anregung mit zwei Platten parallel leitende übersetzt. Schließlich zeichnet eine Datenerfassung (DAQ) System gleichzeitig die Partikelbewegung, erfasst durch einen Quadranten-Photodetektor Zelle (QPD) und dem angelegten elektrischen Feld. Nach Beendigung der Messung wird die Partikel steuerbar auf das Substrat gelegt, so daß es wieder in einer reversiblen Art und Weise eingefangen werden kann. Dieser Gesamtprozess kann mehrere hundert Mal ohne Partikelverlust wiederholt werden, um Änderungen zu messen, wie Kontaktelektrisierung mehrere Fang Zyklen auftreten über. Bitte beachten Sie unsere aktuellen Artikel foder Details. 12

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			<td style="width:216px;">562-XYZ</td>
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			<td style="width:216px;">06463B-AB</td>
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			<td style="width:216px;">P1&#8722;1064PM-FC-5</td>
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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.

Die PZT-Launcher ist so konzipiert, eine CAD-Software-Paket. Hier verwenden wir eine einfache Sandwich - Struktur für die Vorbelastung (a PZT eingespannt mit zwei Platten), wie in Abbildung 2. Die PZT Halter und das Probengehäuse gezeigt , kann aus einer Vielzahl von Materialien und Verfahren hergestellt werden. Für eine schnelle Demonstration, wählen wir den 3D - Druck mit thermoplastischen wie in 2d dargestellt ist . Basierend auf den vorgefertigte...

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.

Optische Trap-Laden von Dielectric Mikroteilchen in der Luft

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

The goal of this video protocol is to demonstrate how a piezoelectric launcher is constructed and used to overcome particle adhesion and ease particle release from the substrate to achieve micro particle levitation in air. The advantage of launching from a surface is that the particle may be selected based on size, shape, optical properties, or orientation. This last can be useful for trapping asymmetric particles.Repeated trapping and landing of particle can provide a new tool to study questions in surface chemistry, such as charged transfer during the particle's repeat interaction. Returning the particle to the surface also allows subsequent measurements of the same particle by other methods, such as scanning electron microscopy, and also allows repeated cycles of trapping and landing. First, 3D print a rectangular frame in a holder for piezoelectric transducer.Fit the narrow sides of the frame with indium tin oxide coated glass, and the wide sides and top with conventional glass to construct the transparent sample enclosure. Next, pour a small portion of 20 micrometer diameter dielectric micro particles onto a glass slide. Immediately return the container to a desiccator.Using a glass capillary tube, pick up some of the micro particles from the slide. Scatter the particles onto a cover slip by gently tapping the capillary tube. Use a microscope to verify the quantity and distribution of dispersed micro particles on the substrate.Next, begin piezo-launcher assembly by applying insulating film to an aluminum plate. Center a ring type piezoelectric transducer on the plate, ensuring that is separated from the plate by the insulating film. Place the micro particle dispersed cover slip on the transducer, and snap a copper ring into the 3D printed holder.Secure the transducer in place on the plate with the 3D printed holder and two M6 screws. Lightly glue the sample enclosure onto the holder with instant adhesive. Mount the completed launcher assembly on an XYZ translational stage of an inverted optical microscope.Connect the piezoelectric transducer leads to the voltage amplifier, and the amplifier to the function generator, ensuring that all connections are secure and properly grounded. Connect the amplifier monitoring output port to an oscilloscope to monitor the transducer-driving voltage signal. Configure the function generator to send a continuous square wave of zero to one volts to the amplifier.Set the amplifier gain to 200 volts per volt. Set up the microscope to image the micro particles in real time. Then manually scan the modulation frequency of the driving signal from 0 to 150 kilohertz while monitoring the micro particle motion.The piezoelectric assembly is designed to apply mechanical pre-load to the transducer, to amplify the resonance amplitude and reduce failure. Frequencies can help to determine the resonance frequency of transducer by monitoring the particle on the surface. The frequency at which micro particle motion is maximized with no adhered particles is the launcher resonance frequency.Repeat the scan as needed at lower voltages to precisely determine the resonance frequency. Set the wave form to generate a voltage signal at the resonance frequency with a 600 volt amplitude. Configure the function generator for a square wave with 10 to 20 cycles in burst mode.Check that the particles are released after each pulse. If the particles are not released, increase the amplitude or number of cycles. Remove the laser lined filter from the microscope, to locate the focus of the trapping beam on the CCD.Optimize the focus by adjusting the vertical position of the motorized focusing block. Replace the filter, and translate the sample so a selected particle is at the trapping laser focus position. Focus on the particle to image the particle center.Actuate the piezoelectric launcher with several voltage pulses to launch the particle, adjusting the power supply of the electro object modulator as needed. When the particle blurs slightly and begins Brownian motion, trapping has occurred. The focus of trapping beam is critical for successful trap loading.Placing the pin focus few micron below the sample plane helps to increase the trapping efficiency. If the particle only moves slightly and remains in focus on the substrate, increase the trapping power. If the particle flies away to a new location on the surface, decrease the power.Once the particle is successfully loaded, move the objective lens up to translate the levitated particle about one millimeter above the glass cover slip to avoid surface interactions. Then reduce the optical power to move the levitated particle into the more stable nominal trapping position. Move the launcher so the transducer-holder is centered on the optical axis.Move the objective lens to vertically translate the particle higher into the sample enclosure. To begin the measurements, adjust the condenser and focusing lens until the power spectrum density plots of the X and Y channels are well matched. Then connect a high voltage source to the sample enclosure.To measure the trap properties and particle charge, apply an electrostatic field to generate ballistic motion of the particle. Record the step excitation signal in the induced particle trajectory. Average the data for multiple periods as needed to reduce the effects of Brownian motion.After performing the measurement, move the objective lens down to position the particle onto the center of the glass cover slip, to keep it separate from the other particles. The piezoelectric launcher assembly consists of a transparent enclosure to protect the levitated particle from air currents, and a piezoelectric transducer that vibrates the substrate to release the particle. The enclosure bottom is open so that the substrate can be placed directly on the transducer.The micro particles can either be trapped in the levitation position above focus or in the trapping position near focus where optical forces stabilize the particle in all directions. In the levitation position, gravity counteracts the upward radiation pressure so optical forces only stabilize the particle transversely. For small displacements, such as Brownian motion, the optical force can be treated as a linear spring.The resonance frequency can be determined from the power spectral density plot. The trap's stiffness and optical force in the linear regime can then be calculated from the resonance frequency, known mass, and measured displacement. Forces over wider ranges of displacement can be determined from the induced ballistic motion in the applied electric field.Analysis of ballistic displacement by the transient response method gives the resonance frequency, damping, and steady state displacement. Non-linear forces can be determined with the parametric force method. This approach levitating microparticles enables precision measurements using particles selected for size, shape, or material properties, and also allows subsequent measurements on the same particles.Using this method, launching and landing a particle can be repeated over hundred of cycles. This will also allow sensitive studies of particle surface interaction, such as contact electrification with single electron sensitivity.

Research

JoVE Journal

Engineering

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