DOCSLIB.ORG

Optical Trapping and Coherent Anti-Stokes Raman Scattering (CARS) Spectroscopy of Submicron-Size Particles James W

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Optical Trapping and Coherent Anti-Stokes Raman Scattering (CARS) Spectroscopy of Submicron-Size Particles James W 858 IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 11, NO. 4, JULY/AUGUST 2005 Optical Trapping and Coherent Anti-Stokes Raman Scattering (CARS) Spectroscopy of Submicron-Size Particles James W. Chan, Heiko Winhold, Stephen M. Lane, and Thomas Huser Abstract—Optical trapping combined with coherent anti-Stokes (∼ 10−30 cm2) that limit its practical use for imaging applica- Raman scattering (CARS) spectroscopy is demonstrated for the tions. The orders of magnitude higher signals in CARS mi- first time as a new technique for the chemical analysis of individ- croscopy allow for rapid CARS imaging approaching video rate ual particles over an extended period of time with high temporal resolution. Single submicron-size particles suspended in aqueous speed over long time periods, which enables monitoring of rapid media are optically trapped and immobilized using two tightly dynamic processes [5], [6] that are otherwise not feasible with focused collinear laser beams from two pulsed Ti:Sapphire laser conventional fluorescence or Raman microscopy. sources. The particles can remain stably trapped at the focus for In the CARS technique, two laser beams at two different many tens of minutes. The same lasers generate a CARS vibra- frequencies (ω , the pump frequency and ω , the Stokes fre- tional signal from the molecular bonds in the trapped particle when p s the laser frequencies are tuned to a vibrational mode of interest, quency) are tightly focused into the sample to generate a co- providing chemical information about the sample. The technique herent anti-Stokes signal at frequency 2ωp − ωs . Strong reso- is characterized using single polystyrene beads and unilamellar nant CARS signals are generated when the frequency differ- phospholipid vesicles as test samples and can be extended to the ence ωp − ωs matches a Raman-active molecular vibration in study of living biological samples. This novel method could poten- the sample, which induces collective oscillations of the molec- tially be used to monitor rapid dynamics of biological processes in single particles on short time scales that cannot be achieved by ular bonds. Because CARS is a nonlinear multiphoton pro- using other vibrational spectroscopy techniques. cess, the signal is only generated within the focal volume, providing high spatial resolution akin to other multiphoton Index Terms—Biophotonics, coherent anti-Stokes Raman scat- tering (CARS), laser tweezers, Raman spectroscopy. techniques, such as two-photon fluorescence and second har- monic generation. A CARS image is generated by rapid scan- ning of the laser focus over the entire biological sample. An I. INTRODUCTION additional benefit of CARS microscopy is that sample aut- OHERENT anti-Stokes Raman scattering (CARS) mi- ofluorescence does not usually interfere with the CARS sig- C croscopy has been developed recently [1]–[4] as a tech- nal, which is located at wavelengths shorter than the excitation nique capable of high spatial resolution for the chemical imag- wavelengths. ing of live biological samples without the need for intrusive The long-term CARS analysis of submicron-size biological labeling with fluorescent probes. Contrast in CARS imaging particles suspended in aqueous media is difficult, if not impos- is generated from vibrational signals of Raman active molec- sible, due to the constant Brownian motion of the particle in ular vibrations in the sample itself. Consequently, a major and out of the laser focus. Optical tweezers [7]–[11] have been benefit of CARS imaging is that the signal, unlike the sig- shown to be able to immobilize a particle in solution such that nal from fluorescent probes, does not photobleach, enabling it remains within the focal volume of the focused laser beam, long-term imaging of a living sample as it undergoes biolog- essentially “trapping” the particle indefinitely. This trapping is ical processes. The coherent nature of the nonlinear CARS enabled by photons from the laser beam imparting their mo- process results in vibrational signals that are much stronger mentum to the particle, which results in transverse and axial than spontaneous Raman signals. Spontaneous Raman spec- forces that are balanced near the laser focus. Several more re- troscopy is known for its relatively low scattering cross-sections cent studies [12]–[18] have already demonstrated the ability to combine optical trapping with spontaneous Raman spectroscopy using continuous wave (CW) laser sources, which allows for the Manuscript received December 17, 2004; revised June 15, 2005. This work chemical analysis of biological specimens and their dynamics. was supported by the National Science Foundation (NSF). The Center for Bio- However, this laser tweezers Raman spectroscopy (LTRS) tech- photonics, an NSF Science and Technology Center, is managed by the University of California, Davis, under Cooperative Agreement No. PHY 0120999. Work at nique still suffers from the inability to acquire spectra rapidly LLNL was performed under the auspices of the U.S. Department of Energy by enough to monitor fast dynamics. Typically, spectra have to the University of California, Lawrence Livermore National Laboratory, under be acquired over periods of many seconds to minutes, thus al- Contract No. W-7405-Eng-48. The authors are with Lawrence Livermore National Laboratory, Livermore, lowing only slow, long-term dynamics (e.g., apoptosis) to be CA 94550 USA, and also with the NSF Center for Biophotonics Science studied. CARS signals, in contrast, being that much stronger and Technology, University of California-Davis, Sacramento, CA 95817 USA than spontaneous Raman signals, would enable monitoring of (e-mail: [email protected]; [email protected]; [email protected]; huser1@ llnl.gov). fast dynamics with higher temporal resolution and maintaining Digital Object Identifier 10.1109/JSTQE.2005.857381 of chemical specificity. 1077-260X/$20.00 © 2005 IEEE CHAN et al.: OPTICAL TRAPPING AND (CARS) SPECTROSCOPY OF SUBMICRON-SIZE PARTICLES 859 spectrometer (Ocean Optics, Dunedin, FL) with a resolution of roughly 1 nm. The parallel-polarized beams are expanded with a telescope assembly to approximately 5 mm and sent into an inverted optical microscope (Axiovert 200, Zeiss) equipped with a dichroic mirror and a 100 ×, 1.3 NA oil immersion objective (Plan-NEOFLUAR, Zeiss, Germany). CARS signals generated at the laser focus are epi-detected and sent through a 100-µm confocal pinhole and a short pass filter for rejection of the excitation light. The CARS signal is detected with either an avalanche photodiode or a grating spectrometer equipped with a liquid nitrogen cooled 1340 × 100 pixel charge-coupled device (CCD) camera (Roper Scientific, Trenton, NJ). The system is also equipped with a separate 30-mW He-Ne laser at 633 nm that is capable of trapping single particles and functions as an excitation laser for acquiring spontaneous Raman spectra. In addition, a pulse picker (NEOS Technologies, Melbourne, Fig. 1. Schematic of the Raman and CARS confocal detection system. Two FL) can be added right after both beams are combined by the pulsed Ti:Sapphire laser beams are collinearly combined into an inverted mi- croscope. Detection of the spectral signals is achieved using a standard confocal dichroic reflector to reduce the repetition rate of each laser geometry, an avalanche photodiode, and spectrometer. A CW He-Ne laser is beam down to 200 kHz. This reduces the average power of also implemented for spontaneous Raman measurements, and a pulse picker is the beams and minimizes photodamage to samples, while used to reduce the repetition rate of the Ti:Sapphire beams. maintaining high peak powers for CARS signal generation. Optical trapping with pulsed laser systems has not been as B. Preparation of Unilamellar Vesicles widely demonstrated as with CW lasers but has been gaining 1,2-Dimyristoyl-sn-glycero-3-phosphocholine (DMPC) is considerable attention due to the ability to study a trapped purchased in powder form from Avanti Polar Lipids, Alabaster, particle by nonlinear spectroscopic methods that require intense AL. Liposomes are prepared using standard techniques [23]. short laser pulses. Modeling studies [19] have predicted the Briefly, a DMPC/chloroform solution is dried under nitrogen for feasibility of ultrashort-pulsed laser tweezers, and experimental several minutes, placed under vacuum overnight to remove trace studies have demonstrated the combination of trapping with quantities of chloroform, and hydrated above its lipid transition SHG [20], [21] and two-photon fluorescence [22]. In this temperature. Unilamellar vesicles are prepared through extru- paper, we demonstrate the combination of optical trapping with sion of the multilamellar vesicle solution using a mini-extruder CARS spectroscopy using two pulsed laser sources at different (Avanti Polar Lipids). Approximately 1 mL of the hydrated lipid wavelengths that are overlapped both spatially and temporally. suspension is extruded several times at its phase transition tem- This technique makes it possible to rapidly obtain chemical perature using polycarbonate membranes (Avanti Polar Lipids) information from submicron-size particles in their natural with a 0.4-µm pore size to yield a concentrated solution of environment. The trapping parameters and CARS signal are 0.4-µm diameter unilamellar vesicles. This solution is then di- demonstrated and fully characterized for polystyrene bead and luted several times to a point where single vesicles can be ob- unilamellar vesicle samples. served and trapped
Load more

Recommended publications
  • Quantitative Force Measurements with Optical Tweezers: the JPK Nanotracker™
    Quantitative force measurements with optical tweezers: The JPK NanoTracker™ Introduction to optical tweezers manipulate biomolecules and cells, but also to directly and accurately measure the minute forces (on the order of Optical tweezers methodology has developed from proof-of- fractions of picoNewtons) involved. Most often, the principle experiments to an established quantitative biomolecules of interest are not trapped themselves technique in fields ranging from (bio)physics through cell directly, but manipulated through functionalized biology. As the name suggests, optical tweezers are a microspheres. means to manipulate objects with light. With this technique, The correct physical description of optical trapping depends microscopically small objects can be held and manipulated. on the size of the trapped object. One speaks of the ‘ray- At the same time, the forces exerted on the trapped objects optics’ regime when the object’s dimension d is much larger can be accurately measured. The basic physical principle than the wavelength of the trapping light: d>>λ. In this case, underlying optical tweezers is the radiation pressure diffraction effects can be neglected and the trapping forces exerted by light when colliding with matter. For macroscopic of the light can be understood in terms of ray optics. The objects, the radiation pressure exerted by typical light regime where d<<λ is called the Rayleigh regime. In this sources is orders of magnitude too small to have any case, the trapped particles can be treated as point dipoles, measurable effect: we do not feel the light power of the sun as the electromagnetic field is constant on the scale of the pushing us away.
    [Show full text]
  • A Quantum Origin of Life?
    June 26, 2008 11:1 World Scientific Book - 9in x 6in quantum Chapter 1 A Quantum Origin of Life? Paul C. W. Davies The origin of life is one of the great unsolved problems of science. In the nineteenth century, many scientists believed that life was some sort of magic matter. The continued use of the term “organic chemistry” is a hangover from that era. The assumption that there is a chemical recipe for life led to the hope that, if only we knew the details, we could mix up the right stuff in a test tube and make life in the lab. Most research on biogenesis has followed that tradition, by assuming chemistry was a bridge—albeit a long one—from matter to life. Elucidat- ing the chemical pathway has been a tantalizing goal, spurred on by the famous Miller-Urey experiment of 1952, in which amino acids were made by sparking electricity through a mixture of water and common gases [Miller (1953)]. But this concept turned out to be something of a blind alley, and further progress with pre-biotic chemical synthesis has been frustratingly slow. In 1944, Erwin Schr¨odinger published his famous lectures under the ti- tle What is Life? [Schr¨odinger (1944)] and ushered in the age of molecular biology. Sch¨odinger argued that the stable transmission of genetic infor- mation from generation to generation in discrete bits implied a quantum mechanical process, although he was unaware of the role of or the specifics of genetic encoding. The other founders of quantum mechanics, including Niels Bohr, Werner Heisenberg and Eugene Wigner shared Schr¨odinger’s belief that quantum physics was the key to understanding the phenomenon Received May 9, 2007 3 QUANTUM ASPECTS OF LIFE © Imperial College Press http://www.worldscibooks.com/physics/p581.html June 26, 2008 11:1 World Scientific Book - 9in x 6in quantum 4 Quantum Aspects of Life of life.
    [Show full text]
  • Depth-Resolved Measurement of Optical Radiation-Pressure Forces with Optical Coherence Tomography
    Vol. 26, No. 3 | 5 Feb 2018 | OPTICS EXPRESS 2410 Depth-resolved measurement of optical radiation-pressure forces with optical coherence tomography NICHALUK LEARTPRAPUN, RISHYASHRING R. IYER, AND STEVEN G. ADIE* Meinig School of Biomedical Engineering, Cornell University, Ithaca, NY 14853, USA *[email protected] Abstract: A weakly focused laser beam can exert sufficient radiation pressure to manipulate microscopic particles over a large depth range. However, depth-resolved continuous measurement of radiation-pressure force profiles over an extended range about the focal plane has not been demonstrated despite decades of research on optical manipulation. Here, we present a method for continuous measurement of axial radiation-pressure forces from a weakly focused beam on polystyrene micro-beads suspended in viscous fluids over a depth range of 400 μm, based on real-time monitoring of particle dynamics using optical coherence tomography (OCT). Measurements of radiation-pressure forces as a function of beam power, wavelength, bead size, and refractive index are consistent with theoretical trends. However, our continuous measurements also reveal localized depth-dependent features in the radiation- pressure force profiles that deviate from theoretical predictions based on an aberration-free Gaussian beam. The combination of long-range radiation pressure and OCT offers a new mode of quantitative optical manipulation and detection with extended spatial coverage. This may find applications in the characterization of optical tractor beams, or volumetric optical manipulation and interrogation of beads in viscoelastic media. © 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement OCIS codes: (110.4500) Optical coherence tomography; (350.4855) Optical tweezers or optical manipulation.
    [Show full text]
  • Optical Micromachines for Biological Studies
    micromachines Review Optical Micromachines for Biological Studies Philippa-Kate Andrew 1 , Martin A. K. Williams 2,3 and Ebubekir Avci 1,3,* 1 Department of Mechanical and Electrical Engineering, Massey University, Palmerston North 4410, New Zealand; [email protected] 2 School of Fundamental Sciences, Massey University, Palmerston North 4410, New Zealand; [email protected] 3 MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington 6140, New Zealand * Correspondence: [email protected] Received: 21 January 2020; Accepted: 9 February 2020; Published: 13 February 2020 Abstract: Optical tweezers have been used for biological studies since shortly after their inception. However, over the years research has suggested that the intense laser light used to create optical traps may damage the specimens being studied. This review aims to provide a brief overview of optical tweezers and the possible mechanisms for damage, and more importantly examines the role of optical micromachines as tools for biological studies. This review covers the achievements to date in the field of optical micromachines: improvements in the ability to produce micromachines, including multi-body microrobots; and design considerations for both optical microrobots and the optical trapping set-up used for controlling them are all discussed. The review focuses especially on the role of micromachines in biological research, and explores some of the potential that the technology has in this area. Keywords: optical tweezers; multi-component micromanipulators; radiation damage; life sciences; optical microrobots 1. Introduction Improvements in tools for the visualisation of objects at the micro- and nano- scale have given researchers the ability to investigate materials and processes previously out of reach.
    [Show full text]
  • Pulsed Optical Tweezers for Levitation and Manipulation of Stuck Biological
    2005 Conference on Lasers & Electro-Optics (CLEO) CFN3 Pulsed optical tweezers for levitation and manipulation of stuck biological particles Amol Ashok Ambardekar and Yong-qing Li Department ofPhysics, East Carolina University, Greenville, North Carolina 27858 acube3(1!yahoo. covm,livrnail.ecu. ec/ Abstract: We report on optical levitation and manipulation of microscopic particles that are stuck on a glass surface with a pulsed optical tweezers. Both the stuck dielectric beads and biological cells are demonstrated to be levitated. ©2005 Optical Society of America OCIS codes: (170.4520) Optical confinement and manipulation; (140.7010) Trapping Optical tweezers has become a powerful tool for capturing and manipulation of micron-sized particles, typically by using continuous-wave (cw) lasers [1, 2]. It has been routinely applied to manipulate living cells, bacteria, viruses, chromosomes and other organelles [3, 4], To reduce the photodamage to the trapped particles, the average power of the trapping lasers is usually limited to below hundreds of mW and near-infrared (NIR) or infrared lasers were used for trapping [3, 6]. The trapping force generated by the cw optical tweezers is typically in the order of 10-12 N [4, 5]. This weak force is efficient to confine micro-particles suspended in liquids, but not sufficient to levitate the particles that are stuck on the glass surface, where it has to overcome the binding force. Therefore, the stuck particles cannot be manipulated with the optical tweezers that only employs cw lasers. In this paper, we describe a pulsed optical tweezers that employs a pulsed laser for levitation of the stuck particles and a low-power cw laser for successive trapping and manipulation.
    [Show full text]
  • Tip-Enhanced Laser Ablation Sample Transfer for Mass Spectrometry
    Louisiana State University LSU Digital Commons LSU Doctoral Dissertations Graduate School 2016 Tip-Enhanced Laser Ablation Sample Transfer for Mass Spectrometry Chinthaka Aravinda Seneviratne Louisiana State University and Agricultural and Mechanical College, [email protected] Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_dissertations Part of the Chemistry Commons Recommended Citation Seneviratne, Chinthaka Aravinda, "Tip-Enhanced Laser Ablation Sample Transfer for Mass Spectrometry" (2016). LSU Doctoral Dissertations. 2355. https://digitalcommons.lsu.edu/gradschool_dissertations/2355 This Dissertation is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Doctoral Dissertations by an authorized graduate school editor of LSU Digital Commons. For more information, please [email protected]. TIP-ENHANCED LASER ABLATION SAMPLE TRANSFER FOR MASS SPECTROMETRY A Dissertation Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Doctor of Philosophy in The Department of Chemistry by Chinthaka Aravinda Seneviratne M.S., Bucknell University, 2011 B.Sc., University of Kelaniya, 2008 May 2016 This dissertation is dedicated with love to my parents, Hector and Dayani Seneviratne my wife Sameera Herath and my little buddy Julian !. ii ACKNOWLEDGEMENTS First and foremost, I give glory to God. Without God’s blessings, none of this would have been possible. It is a great pleasure to offer my unbounding appreciation for all who have supported and guided me over the course my doctoral studies to the completion of this dissertation. I would like to thank my doctoral mentor, Dr.
    [Show full text]
  • Nobel Prize in Physics – 2018
    GENERAL ARTICLE Nobel Prize in Physics – 2018 Debabrata Goswami On Tuesday, 02 October 2018, Arthur Ashkin of the United States, who pioneered a way of using light to manipulate phys- ical objects, shared the first half of the 2018 Nobel Prize in Physics. The second half was divided equally between Gerard´ Mourou of France and Donna Strickland of Canada for their method of generating high-intensity, ultra-short optical pulses. With this announcement, Donna Strickland, who was awarded the Nobel for her work as a PhD student with Gerard´ Mourou, Debabrata Goswami is a became the third woman to have ever won the Physics Nobel Senior Professor at Indian Prize, and the 96-year-old Arthur Ashkin who was awarded Institute of Technology Kanpur, and holds the for his work on optical tweezers and their application to bi- endowed Prof. S Sampath ological systems, became the oldest Nobel Prize winner. Ac- Chair Professorship of cording to Nobel.org, the practical applications leading to the Chemistry. His research work Prize in 2018 are tools made of light that have revolutionised spans across frontiers of interdisciplinary research laser physics – a discipline which in turn is represented by with femtosecond lasers that generations of advancements and not just a single example of have been recognised brilliant work. globally, the latest being the 2018 Galileo Galilei Award of It is easy to take lasers for granted; more so in 2018, as they are the International Commission a near-ubiquitous symbol of technological acumen. Light may be of Optics. As a part of his doctoral thesis at Princeton, a wave, but producing coherent (in-phase), monochromatic (of a Prof.
    [Show full text]
  • Frontiers in Optics 2010/Laser Science XXVI
    Frontiers in Optics 2010/Laser Science XXVI FiO/LS 2010 wrapped up in Rochester after a week of cutting- edge optics and photonics research presentations, powerful networking opportunities, quality educational programming and an exhibit hall featuring leading companies in the field. Headlining the popular Plenary Session and Awards Ceremony were Alain Aspect, speaking on quantum optics; Steven Block, who discussed single molecule biophysics; and award winners Joseph Eberly, Henry Kapteyn and Margaret Murnane. Led by general co-chairs Karl Koch of Corning Inc. and Lukas Novotny of the University of Rochester, FiO/LS 2010 showcased the highest quality optics and photonics research—in many cases merging multiple disciplines, including chemistry, biology, quantum mechanics and materials science, to name a few. This year, highlighted research included using LEDs to treat skin cancer, examining energy trends of communications equipment, quantum encryption over longer distances, and improvements to biological and chemical sensors. Select recorded sessions are now available to all OSA members. Members should log in and go to “Recorded Programs” to view available presentations. FiO 2010 also drew together leading laser scientists for one final celebration of LaserFest – the 50th anniversary of the first laser. In honor of the anniversary, the conference’s Industrial Physics Forum brought together speakers to discuss Applications in Laser Technology in areas like biomedicine, environmental technology and metrology. Other special events included the Arthur Ashkin Symposium, commemorating Ashkin's contributions to the understanding and use of light pressure forces on the 40th anniversary of his seminal paper “Acceleration and trapping of particles by radiation pressure,” and the Symposium on Optical Communications, where speakers reviewed the history and physics of optical fiber communication systems, in honor of 2009 Nobel Prize Winner and “Father of Fiber Optics” Charles Kao.
    [Show full text]
  • Informacja Dla PRAC IPPT
    IPPT Reports on Fundamental Technological Research 2/2016 Krzysztof Zembrzycki, Sylwia Pawłowska Paweł Nakielski, Filippo Pierini DEVELOPMENT OF A HYBRID ATOMIC FORCE MICROSCOPE AND OPTICAL TWEEZERS APPARATUS Institute of Fundamental Technological Research Polish Academy of Sciences Warsaw 2016 IPPT Reports on Fundamental Technological Research ISSN 2299-3657 ISBN 978-83-89687-99-9 Editorial Board/Kolegium Redakcyjne: Wojciech Nasalski (Editor-in-Chief/Redaktor Naczelny), Paweł Dłużewski, Zbigniew Kotulski, Wiera Oliferuk, Jerzy Rojek, Zygmunt Szymański, Yuriy Tasinkevych Reviewer/Recenzent: Jan Masajada Received on 8th April 2016 Copyright © 2016 by IPPT-PAN Institute of Fundamental Technological Research Polish Academy of Sciences Instytut Podstawowych Problemów Techniki Polskiej Akademii Nauk (IPPT-PAN) Pawińskiego 5B, PL 02-106 Warsaw, Poland Printed by/Druk: Drukarnia Braci Grodzickich, Piaseczno, ul. Geodetów 47A Acknowledgements This work was supported by NCN grant no. 2011/03/B/ST8/05481. Research subject carried out with the use of CePT infrastructure financed by the European Union – the European Regional Development Fund within the Operational Program “Innovative Economy” for 2007–2013. The authors gratefully acknowledge NT-MDT for technical support. In addition, we would like to thank IOP Publishing to provide us with the permission to reproduce part of the paper: “Atomic force microscopy combined with optical tweezers (AFM/OT)” [1]. Development of a hybrid Atomic Force Microscope and Optical Tweezers apparatus Krzysztof Zembrzycki, Sylwia Pawłowska Paweł Nakielski, Filippo Pierini Institute of Fundamental Technological Research Polish Academy of Sciences Abstract The role of mechanical properties is essential to understand molecular, biological materials and nanostructures dynamics and interaction processes. Atomic force mi- croscopy (AFM), due to its sensitivity is the most commonly used method of direct force evaluation.
    [Show full text]
  • Integration of Confocal Laser Scanning Microscopy (CLSM) with the JPK Nanotracker™ 2
    Integration of Confocal Laser Scanning Microscopy (CLSM) with the JPK NanoTracker™ 2 This technical note describes the combination of optical that plane is selectively collected by photodetectors. Light manipulation and measurements with JPK’s emitted from other sample layers than the focal plane is NanoTracker™ and simultaneous confocal imaging. As screened using an adjustable pinhole. As a result, only will be discussed below, the unique optical design of the light coming from a small (confocal) volume is analyzed NanoTracker™ 2 allows undisturbed high quality while background signals from other parts of the sample confocal imaging and eliminates unwanted interactions are largely reduced. Besides the ability to image different between the trapping and scanning lasers. planes in the sample, this approach results in a high signal-to-noise ratio and superior spatial resolution Introduction compared to conventional fluorescence microscopy. For Optical manipulation as well as the related measurement more detailed information on confocal imaging of forces and displacements has become a frequently techniques and their biological applications, we used tool in a broad range of disciplines from material recommend the book by James Pawley [6]. sciences to biophysics and biology. Dielectric objects (typically spherical polystyrene or silica beads in the micrometer range) are optically trapped in a tightly focused laser beam and serve as handles for precise manipulations on the nanometer scale down to the single molecule level. With the NanoTracker™ 2, the simultaneous high resolution measurement of piconewton forces and nanometer displacements within the trap becomes available. Many biological applications require the combination of optical manipulation with advanced imaging techniques like differential interference contrast (DIC) and fluorescence microscopy.
    [Show full text]
  • Optical Tweezers with Enhanced Efficiency Based on Laser-Structured Substrates
    Optical tweezers with enhanced efficiency based on laser-structured substrates D. G. Kotsifaki1 , M. Kandyla2, I. Zergioti1, M. Makropoulou1, E. Chatzitheodoridis3, A. A. Serafetinides1,a) 1Physics Department, National Technical University of Athens, Heroon Polytechniou 9, 15780 Athens, Greece 2Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vasileos Constantinou Avenue, 11635 Athens, Greece 3School of Mining and Metallurgical Engineering, National Technical University of Athens, 15780 Athens, Greece a) Electronic mail: [email protected] 1 ABSTRACT We present an optical nanotrapping setup that exhibits enhanced efficiency, based on localized plasmonic fields around sharp metallic features. The substrates consist of laser- structured silicon wafers with quasi-ordered microspikes on the surface, coated with a thin silver layer. The resulting optical traps show orders of magnitude enhancement of the trapping force and the effective quality factor. 2 Conventional optical tweezers, initially proposed by Ashkin1, are widely employed for trapping micro- and nanometer-size particles, from micro-colloids and droplets2,3 to living cells4,5, in a microfluidic environment. This technique is based on radiation pressure forces, and stable trapping is achieved when the gradient of the electromagnetic field intensity (gradient force) dominates scattering forces and Brownian motion1. However, in the case of nanometer-size particles, the magnitude of the gradient force decreases. Additionally, damping of the trapped particles decreases rapidly due to a decline in viscous drag6. The above mentioned effects work against stable trapping. Therefore, optical trapping of nanometric particles requires more sophisticated optical techniques7. Alternative methods based on evanescent fields are used for optical nanotrapping, such as scattering by sub- wavelength particles8,9 or confinement of light in a metallic tip10.
    [Show full text]
  • Dual Wavelength Optical Tweezers for Confocal Raman Spectroscopy
    Optics Communications 245 (2005) 465–470 www.elsevier.com/locate/optcom Dual wavelength optical tweezers for confocal Raman spectroscopy C.M. Creely a, G.P. Singh a, D. Petrov a,b,* a ICFO – Institut de Cie`ncies Foto`niques, c/Jordi Girona 29, 08034, Barcelona, Spain b ICREA – Institucio´ Catalana de Recerca i Estudis Avanc¸at, Barcelona, Spain Received 16 September 2004; received in revised form 5 October 2004; accepted 6 October 2004 Abstract We describe the use of dual optical tweezers to manipulate micron-size particles in and out of the focus of a confocal Raman microscope. One of the beams excites the Raman spectrum while the second tweezers improves the sensitivity of the technique and also allows for the manipulation of the environment of the trapped objects. We concentrated on optimising the alignment of both trapping and Raman excitation beams and on the background subtraction method. Even at the low trapping/excitation powers used a single living cell could be trapped and monitored for over 2 h without incurring damage. Ó 2004 Elsevier B.V. All rights reserved. PACS: 87.80.Cc; 87.64.Je; 87.64.Tt Keywords: Optical tweezers; Raman spectroscopy; Microspectroscopy Optical tweezers utilise the force of radiation perform spectroscopy on a single object of micron pressure to trap and manipulate micron and sub- size. A greater signal to noise ratio from the micron sized particles whose refractive index dif- trapped object can be achieved when background fers from that of the environment [1,2]. Since signals from the cover slip and immersion oil are 1984 radiation forces have been used to perform minimised by manipulating the particle inside a spectroscopy on trapped particles, aerosols and sample holder.
    [Show full text]