Gold nanorod assisted intracellular optical manipulation of silica microspheres P. Haro-González,1 P. Rodríguez Sevilla,1 F. Sanz-Rodríguez,1,2 E. Martín Rodríguez,1,3 Nicoleta Bogdan,3 J.A. Capobianco,3 K. Dholakia4 and D. Jaque1,* 1
Fluorescence Imaging Group, Departamento de Física de Materiales, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049, Madrid, Spain 2 Departamento de Biología, Facultad de Ciencias. Campus de Cantoblanco. Universidad Autónoma de Madrid. Madrid 28049, Spain 3 Department of Chemistry and Biochemistry, Center for NanoScience Research, Concordia University, 7141 Sherbrooke Street, Montreal, QC, Canada, H4B 1R6. 4 School of Physics & Astronomy, University of St. Andrews, St Andrews KY16 9SS, UK * [email protected]
Abstract: We report on the improvement of the infrared optical trapping efficiency of dielectric microspheres by the controlled adhesion of gold nanorods to their surface. When trapping wavelength was equal to the surface plasmon resonance wavelength of the gold nanorods (808 nm), a 7 times improvement in the optical force acting on the microspheres was obtained. Such a gold nanorod assisted enhancement of the optical trapping efficiency enabled the intracellular manipulation of the decorated dielectric microsphere by using a low power (22 mW) infrared optical trap. ©2014 Optical Society of America OCIS codes: (110.6820) Thermal imaging; (240.6680) Surface plasmons; (350.4855) Optical tweezers or optical manipulation; (160.3900) Metals; (160.6030) Silica.
References and links 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
12. 13. 14. 15.
Y. Liu and J. Hu, “Ultrasonic trapping of small particles by a vibrating rod,” IEEE Trans. Ultrason. Ferroelectr. Freq. Control 56(4), 798–805 (2008). M. Q. Li, “Scanning probe microscopy (STM/AFM) and applications in biology,” Applied Physics a Materials Science and Processing. 68(2), 255–258 (1999). K. Dholakia, P. Reece, and M. Gu, “Optical micromanipulation,” Chem. Soc. Rev. 37(1), 42–55 (2008). A. Ashkin, J. M. Dziedzic, and T. Yamane, “Optical trapping and manipulation of single cells using infrared laser beams,” Nature 330(6150), 769–771 (1987). D. J. Stevenson, F. Gunn-Moore, and K. Dholakia, “Light forces the pace: optical manipulation for biophotonics,” J. Biomed. Opt. 15(4), 041503 (2010). K. C. Neuman and A. Nagy, “Single-molecule force spectroscopy: optical tweezers, magnetic tweezers and atomic force microscopy,” Nat. Methods 5(6), 491–505 (2008). A. Ashkin, J. M. Dziedzic, J. E. Bjorkholm, and S. Chu, “Observation of a single-beam gradient force optical trap for dielectric particles,” Opt. Lett. 11(5), 288–290 (1986). A. Ashkin and J. M. Dziedzic, “Optical Trapping and Manipulation of Viruses and Bacteria,” Science 235(4795), 1517–1520 (1987). W. H. Wright, G. J. Sonek, Y. Tadir, and M. W. Berns, “Laser trapping in cell biology,” IEEE J. Quantum Electron. 26(12), 2148–2157 (1990). L. Sacconi, I. M. Tolić-Nørrelykke, C. Stringari, R. Antolini, and F. S. Pavone, “Optical micromanipulations inside yeast cells,” Appl. Opt. 44(11), 2001–2007 (2005). P. Haro-González, W. T. Ramsay, L. Martinez Maestro, B. del Rosal, K. Santacruz-Gomez, M. C. Iglesias-de la Cruz, F. Sanz-Rodríguez, J. Y. Chooi, P. Rodriguez Sevilla, M. Bettinelli, D. Choudhury, A. K. Kar, J. G. Solé, D. Jaque, and L. Paterson, “Quantum dot-based thermal spectroscopy and imaging of optically trapped microspheres and single cells,” Small 9(12), 2162–2170 (2013). K. C. Neuman, E. H. Chadd, G. F. Liou, K. Bergman, and S. M. Block, “Characterization of photodamage to Escherichia coli in optical traps,” Biophys. J. 77(5), 2856–2863 (1999). G. Leitz, E. Fällman, S. Tuck, and O. Axner, “Stress response in Caenorhabditis elegans caused by optical tweezers: Wavelength, power, and time dependence,” Biophys. J. 82(4), 2224–2231 (2002). H. Liang, K. T. Vu, P. Krishnan, T. C. Trang, D. Shin, S. Kimel, and M. W. Berns, “Wavelength dependence of cell cloning efficiency after optical trapping,” Biophys. J. 70(3), 1529–1533 (1996). Z. P. Cai and H. Y. Xu, “Point temperature sensor based on green upconversion emission in an Er: ZBLALiP microsphere,” Sens. Actuators A Phys. 108(1-3), 187–192 (2003).
#213777 - $15.00 USD Received 10 Jun 2014; revised 26 Jul 2014; accepted 28 Jul 2014; published 8 Aug 2014 (C) 2014 OSA 11 August 2014 | Vol. 22, No. 16 | DOI:10.1364/OE.22.01914119735 | OPTICS EXPRESS 19735
16. C.-H. Dong, L. He, Y.-F. Xiao, V. R. Gaddam, S. K. Ozdemir, Z.-F. Han, G.-C. Guo, and L. Yang, “Fabrication of high-Q polydimethylsiloxane optical microspheres for thermal sensing,” Appl. Phys. Lett. 94(23), 231119 (2009). 17. I. Tsagkatakis, S. Peper, and E. Bakker, “Spatial and spectral imaging of single micrometer-sized solvent cast fluorescent plasticized poly(vinyl chloride) sensing particles,” Anal. Chem. 73(2), 315–320 (2001). 18. S. Peper, I. Tsagkatakis, and E. Bakker, “Cross-linked dodecyl acrylate microspheres: novel matrices for plasticizer-free optical ion sensing,” Anal. Chim. Acta 442(1), 25–33 (2001). 19. A. Salinas-Castillo, M. Camprubí-Robles, and R. Mallavia, “Synthesis of a new fluorescent conjugated polymer microsphere for chemical sensing in aqueous media,” Chem. Commun. (Camb.) 46(8), 1263–1265 (2010). 20. A. Ashkin, “Forces of a single-beam gradient laser trap on a dielectric sphere in the ray optics regime,” Biophys. J. 61(2), 569–582 (1992). 21. A. Ashkin, “History of optical trapping and manipulation of small-neutral particle, atoms, and molecules,” Ieee J Sel Top Quant 6(6), 841–856 (2000). 22. A. Ashkin, “Optical trapping and manipulation of neutral particles using lasers,” Proc. Natl. Acad. Sci. U.S.A. 94(10), 4853–4860 (1997). 23. W. H. Wright, G. J. Sonek, and M. W. Berns, “Parametric study of the forces on microspheres held by optical tweezers,” Appl. Opt. 33(9), 1735–1748 (1994). 24. A. V. Kachynski, A. N. Kuzmin, H. E. Pudavar, D. S. Kaputa, A. N. Cartwright, and P. N. Prasad, “Measurement of optical trapping forces by use of the two-photon-excited fluorescence of microspheres,” Opt. Lett. 28(23), 2288–2290 (2003). 25. C. Ying-chun and W. Chien-ming, “To study the effect of paclitaxel on the cytoplasmic viscosity of murine macrophage immune cell RAW 264.7 using self-developed optical tweezers system,” Jpn. J. Appl. Phys. 51(12R), 127001 (2012). 26. A. Jonáš and P. Zemánek, “Light at work: The use of optical forces for particle manipulation, sorting, and analysis,” Electrophoresis 29(24), 4813–4851 (2008). 27. E. Hutter and J. H. Fendler, “Exploitation of localized surface plasmon resonance,” Adv. Mater. 16(19), 1685– 1706 (2004). 28. P. V. Ruijgrok, N. R. Verhart, P. Zijlstra, A. L. Tchebotareva, and M. Orrit, “Brownian Fluctuations and Heating of an Optically Aligned Gold Nanorod,” Phys. Rev. Lett. 107(3), 037401 (2011). 29. K. C. Toussaint, Jr., M. Liu, M. Pelton, J. Pesic, M. J. Guffey, P. Guyot-Sionnest, and N. F. Scherer, “Plasmon resonance-based optical trapping of single and multiple Au nanoparticles,” Opt. Express 15(19), 12017–12029 (2007). 30. B. Hester, G. K. Campbell, C. López-Mariscal, C. L. Filgueira, R. Huschka, N. J. Halas, and K. Helmerson, “Tunable optical tweezers for wavelength-dependent measurements,” Rev. Sci. Instrum. 83(4), 043114 (2012). 31. Y. Seol, A. E. Carpenter, and T. T. Perkins, “Gold nanoparticles: enhanced optical trapping and sensitivity coupled with significant heating,” Opt. Lett. 31(16), 2429–2431 (2006). 32. K. Svoboda and S. M. Block, “Optical trapping of metallic Rayleigh particles,” Opt. Lett. 19(13), 930–932 (1994). 33. J. Burgin, S. Si, M.-H. Delville, and J.-P. Delville, “Enhancing optofluidic actuation of micro-objects by tagging with plasmonic nanoparticles,” Opt. Express 22(9), 10139–10150 (2014). 34. S. Y. Kim, J. D. Taylor, H. D. Ladouceur, S. J. Hart, and A. Terray, “Radiation pressure efficiency measurements of nanoparticle coated microspheres,” Appl. Phys. Lett. 103(23), 234101 (2013). 35. I. Pastoriza-Santos, D. Gomez, J. Perez-Juste, L. M. Liz-Marzan, and P. Mulvaney, “Optical properties of metal nanoparticle coated silica spheres: a simple effective medium approach,” Phys. Chem. Chem. Phys. 6, 5056– 5060 (2004). 36. A. S. Zelenina, R. Quidant, G. Badenes, and M. Nieto-Vesperinas, “Tunable optical sorting and manipulation of nanoparticles via plasmon excitation,” Opt. Lett. 31(13), 2054–2056 (2006). 37. J. Perez-Juste, I. Pastoriza-Santos, L. M. Liz-Marzan, and P. Mulvaney, “Gold nanorods: Synthesis, characterization and applications,” Coord. Chem. Rev. 249(17-18), 1870–1901 (2005). 38. S. Link, M. B. Mohamed, and M. A. El-Sayed, “Simulation of the optical absorption spectra of gold nanorods as a function of their aspect ratio and the effect of the medium dielectric constant,” J. Phys. Chem. B 103(16), 3073–3077 (1999). 39. C. Selhuber-Unkel, I. Zins, O. Schubert, C. Sönnichsen, and L. B. Oddershede, “Quantitative optical trapping of single gold nanorods,” Nano Lett. 8(9), 2998–3003 (2008). 40. L. M. Maestro, P. Haro-Gonzalez, J. G. Coello, and D. Jaque, “Absorption efficiency of gold nanorods determined by quantum dot fluorescence thermometry,” Appl. Phys. Lett. 100(20), 201110 (2012). 41. T. Mosmann, “Rapid colorimetric assay for cellular growth and survival: Application to proliferation and cytotoxicity assays,” J. Immunol. Methods 65(1-2), 55–63 (1983). 42. A. S. Urban, S. Carretero-Palacios, A. A. Lutich, T. Lohmüller, J. Feldmann, and F. Jäckel, “Optical trapping and manipulation of plasmonic nanoparticles: fundamentals, applications, and perspectives,” Nanoscale 6(9), 4458–4474 (2014). 43. M. Gu, H. C. Bao, X. S. Gan, N. Stokes, and J. Z. Wu, “Tweezing and manipulating micro- and nanoparticles by optical nonlinear endoscopy,” Light-Science & Applications 3(1), e126 (2014). 44. S. Tehranian, F. Giovane, J. Blum, Y. L. Xu, and B. A. S. Gustafson, “Photophoresis of micrometer-sized particles in the free-molecular regime,” Int. J. Heat Mass Transfer 44(9), 1649–1657 (2001).
#213777 - $15.00 USD Received 10 Jun 2014; revised 26 Jul 2014; accepted 28 Jul 2014; published 8 Aug 2014 (C) 2014 OSA 11 August 2014 | Vol. 22, No. 16 | DOI:10.1364/OE.22.01914119735 | OPTICS EXPRESS 19736
1. Introduction Manipulation and trapping of nano-objects are of great interest in biology, biotechnology and medicine. The trapping and manipulation of individual cells or particles in suspension with submicrometer, or nanometer, accuracy is an essential requirement in single cell studies, high resolution single particle sensing and, also, in the emerging field of single cell proteomics. There are several methods for efficient manipulation of single cells or microparticles, including ultrasonic trapping, atomic force microscopy (AFM) and optical trapping (OT) [1– 6]. Within this group of methods, OT is of particular interest since it allows both force measurement and particle manipulation in absence of physical contact thus minimizing any perturbations to the cell or particle under investigation [6]. OT is the common term used to describe trapping of individual particles at the focus of a single tightly focused beam due to the simultaneous presence of scattering and gradient forces. OT was first demonstrated by Ashkin et al. [4, 7] who trapped water dispersed dielectric nano and micro spheres by using a single 514 nm focused laser beam. Ashkin and associates also proposed and demonstrated the potential use of optical traps for biological applications [4, 7, 8]. Since these pioneering studies, various biological objects, including viruses, bacteria, and single cells have been trapped successfully, using the single-beam configuration and a great variety of laser sources (with different trapping wavelength, λ) [9, 10]. From these studies, it was determined that near infrared (700 nm < λ < 1070nm) laser traps had the lowest detrimental effect on cell viability, compared to using lasers sources in the visible region [11]. This feature of nearinfrared optical traps has been explained in the past in terms of the reduction in the laserinduced thermal loading (water does not absorb to a significant extent in the 700-980 nm range) and also by the fact that certain wavelengths in the infrared do not promote harmful intracellular reactions [11–14]. Recent results have concluded that almost damage-free single cell manipulation can be achieved by using trapping wavelengths close to 800 nm [11]. This opens the door for damage-free intracellular manipulation of sensing microparticles for intracellular dynamical studies. Among the different sensing microparticles, microspheres (µSp) are of special relevance as they have been demonstrated to be capable of a wide range of both chemical and thermal sensing with very high accuracy [15–19]. Whilst manipulation and trapping in standard liquid environment is straightforward, intracellular manipulation of a dielectric, transparent µ-Sp by OT is far more challenging, due to the inhomogeneity and large viscosity of the intracellular medium. Intracellular optical manipulation would be only possible provided that the optical force would overcome the drag force acting on the particle due to the medium viscosity. Therefore, the larger intracellular viscosity would lead to large drag forces in such a way that the optical forces required for intracellular manipulation to be larger than those required in a low viscosity medium. The principle relationship between optical trapping force and power acting on a µ-Sp is given by [20]; F = QPn1 / c
(1)
where Q is a dimensionless efficiency parameter, n1, is the refractive index of the surrounding medium, P is the trapping laser power, and c is the speed of light in free space [3, 20–22]. For typical values of n1 (1.33), P (tens of mW), and Q (ranging from 10−2 to 10−3, for silica microspheres) [23, 24], F is usually of the order of few hundreds of fN. The viscosity of the intracellular medium has been estimated to be as large as 137.05 Pa·s for 1µm sized bead Murine Macrophage [25]. Note that intracellular optical manipulation would be only possible provided that the optical force would overcome the drag force acting on the particle due to the medium viscosity. Therefore, the larger intracellular viscosity particle manipulation would make the optical forces required for intracellular manipulation to be larger than those required in a low viscosity medium at moderate/low laser powers [23, 26]. To increase trapping forces, one can potentially increase P, n1 or Q. The refractive index of the surrounding medium n1, in experiments dealing with intracellular manipulation, is that of the cytoplasm and, generally, it cannot be modified without adversely affecting the cell. Increasing the trapping power may be impractical since it may lead to absorption by the medium, causing significant heating and
#213777 - $15.00 USD Received 10 Jun 2014; revised 26 Jul 2014; accepted 28 Jul 2014; published 8 Aug 2014 (C) 2014 OSA 11 August 2014 | Vol. 22, No. 16 | DOI:10.1364/OE.22.01914119735 | OPTICS EXPRESS 19737
subsequent thermal damage [11]. In addition, when dealing with intracellular optical manipulation the laser power should also be maintained below the membrane ablation threshold in order to avoid undesired photoporation and thermal loading [11]. The last term, Q, has the greatest influence on the performance of the trap and determines whether the µ-Sp is trapped or not. The resultant efficiency is determined by a range of diverse parameters such as the numerical aperture of the optics, spot size, wavelength, polarization, aberrations and beam profile, which have an effect on the optical force. The efficiency parameter, Q, also takes into account the optical properties of the µ-Sp, and the size, shape, surface reflectivity and relative refractive index with respect to the surrounding medium. In the case of a silica microsphere (diameter 1 µm) the value Q is close to 0.006 [23]. Intracellular manipulation requires the challenging task of achieving an appropriate enhancement of this parameter. A possible approach to increase OT forces on silica microspheres is to combine them with metallic nanoparticles. Under appropriate optical excitation, metal nanoparticles display resonances, the so-termed Surface Plasmonic Resonances (SPRs). These correspond to the collective motion of surface charges. Such a collective motion is only induced for certain excitations wavelengths, denoted by λSPR, whose spectral location depends on the size and shape of the metallic nanoparticle [27]. When a metallic nanoparticle is optically excited at λSPR, a strong field enhancement is produced, accompanied by the appearance of a large electronic polarizability and a marked variation in the refractive index of nanoparticle [28– 30]. These effects make the trapping efficiency of a Rayleigh metallic particle (diameter d
Fluorescence Imaging Group, Departamento de Física de Materiales, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049, Madrid, Spain 2 Departamento de Biología, Facultad de Ciencias. Campus de Cantoblanco. Universidad Autónoma de Madrid. Madrid 28049, Spain 3 Department of Chemistry and Biochemistry, Center for NanoScience Research, Concordia University, 7141 Sherbrooke Street, Montreal, QC, Canada, H4B 1R6. 4 School of Physics & Astronomy, University of St. Andrews, St Andrews KY16 9SS, UK * [email protected]
Abstract: We report on the improvement of the infrared optical trapping efficiency of dielectric microspheres by the controlled adhesion of gold nanorods to their surface. When trapping wavelength was equal to the surface plasmon resonance wavelength of the gold nanorods (808 nm), a 7 times improvement in the optical force acting on the microspheres was obtained. Such a gold nanorod assisted enhancement of the optical trapping efficiency enabled the intracellular manipulation of the decorated dielectric microsphere by using a low power (22 mW) infrared optical trap. ©2014 Optical Society of America OCIS codes: (110.6820) Thermal imaging; (240.6680) Surface plasmons; (350.4855) Optical tweezers or optical manipulation; (160.3900) Metals; (160.6030) Silica.
References and links 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
12. 13. 14. 15.
Y. Liu and J. Hu, “Ultrasonic trapping of small particles by a vibrating rod,” IEEE Trans. Ultrason. Ferroelectr. Freq. Control 56(4), 798–805 (2008). M. Q. Li, “Scanning probe microscopy (STM/AFM) and applications in biology,” Applied Physics a Materials Science and Processing. 68(2), 255–258 (1999). K. Dholakia, P. Reece, and M. Gu, “Optical micromanipulation,” Chem. Soc. Rev. 37(1), 42–55 (2008). A. Ashkin, J. M. Dziedzic, and T. Yamane, “Optical trapping and manipulation of single cells using infrared laser beams,” Nature 330(6150), 769–771 (1987). D. J. Stevenson, F. Gunn-Moore, and K. Dholakia, “Light forces the pace: optical manipulation for biophotonics,” J. Biomed. Opt. 15(4), 041503 (2010). K. C. Neuman and A. Nagy, “Single-molecule force spectroscopy: optical tweezers, magnetic tweezers and atomic force microscopy,” Nat. Methods 5(6), 491–505 (2008). A. Ashkin, J. M. Dziedzic, J. E. Bjorkholm, and S. Chu, “Observation of a single-beam gradient force optical trap for dielectric particles,” Opt. Lett. 11(5), 288–290 (1986). A. Ashkin and J. M. Dziedzic, “Optical Trapping and Manipulation of Viruses and Bacteria,” Science 235(4795), 1517–1520 (1987). W. H. Wright, G. J. Sonek, Y. Tadir, and M. W. Berns, “Laser trapping in cell biology,” IEEE J. Quantum Electron. 26(12), 2148–2157 (1990). L. Sacconi, I. M. Tolić-Nørrelykke, C. Stringari, R. Antolini, and F. S. Pavone, “Optical micromanipulations inside yeast cells,” Appl. Opt. 44(11), 2001–2007 (2005). P. Haro-González, W. T. Ramsay, L. Martinez Maestro, B. del Rosal, K. Santacruz-Gomez, M. C. Iglesias-de la Cruz, F. Sanz-Rodríguez, J. Y. Chooi, P. Rodriguez Sevilla, M. Bettinelli, D. Choudhury, A. K. Kar, J. G. Solé, D. Jaque, and L. Paterson, “Quantum dot-based thermal spectroscopy and imaging of optically trapped microspheres and single cells,” Small 9(12), 2162–2170 (2013). K. C. Neuman, E. H. Chadd, G. F. Liou, K. Bergman, and S. M. Block, “Characterization of photodamage to Escherichia coli in optical traps,” Biophys. J. 77(5), 2856–2863 (1999). G. Leitz, E. Fällman, S. Tuck, and O. Axner, “Stress response in Caenorhabditis elegans caused by optical tweezers: Wavelength, power, and time dependence,” Biophys. J. 82(4), 2224–2231 (2002). H. Liang, K. T. Vu, P. Krishnan, T. C. Trang, D. Shin, S. Kimel, and M. W. Berns, “Wavelength dependence of cell cloning efficiency after optical trapping,” Biophys. J. 70(3), 1529–1533 (1996). Z. P. Cai and H. Y. Xu, “Point temperature sensor based on green upconversion emission in an Er: ZBLALiP microsphere,” Sens. Actuators A Phys. 108(1-3), 187–192 (2003).
#213777 - $15.00 USD Received 10 Jun 2014; revised 26 Jul 2014; accepted 28 Jul 2014; published 8 Aug 2014 (C) 2014 OSA 11 August 2014 | Vol. 22, No. 16 | DOI:10.1364/OE.22.01914119735 | OPTICS EXPRESS 19735
16. C.-H. Dong, L. He, Y.-F. Xiao, V. R. Gaddam, S. K. Ozdemir, Z.-F. Han, G.-C. Guo, and L. Yang, “Fabrication of high-Q polydimethylsiloxane optical microspheres for thermal sensing,” Appl. Phys. Lett. 94(23), 231119 (2009). 17. I. Tsagkatakis, S. Peper, and E. Bakker, “Spatial and spectral imaging of single micrometer-sized solvent cast fluorescent plasticized poly(vinyl chloride) sensing particles,” Anal. Chem. 73(2), 315–320 (2001). 18. S. Peper, I. Tsagkatakis, and E. Bakker, “Cross-linked dodecyl acrylate microspheres: novel matrices for plasticizer-free optical ion sensing,” Anal. Chim. Acta 442(1), 25–33 (2001). 19. A. Salinas-Castillo, M. Camprubí-Robles, and R. Mallavia, “Synthesis of a new fluorescent conjugated polymer microsphere for chemical sensing in aqueous media,” Chem. Commun. (Camb.) 46(8), 1263–1265 (2010). 20. A. Ashkin, “Forces of a single-beam gradient laser trap on a dielectric sphere in the ray optics regime,” Biophys. J. 61(2), 569–582 (1992). 21. A. Ashkin, “History of optical trapping and manipulation of small-neutral particle, atoms, and molecules,” Ieee J Sel Top Quant 6(6), 841–856 (2000). 22. A. Ashkin, “Optical trapping and manipulation of neutral particles using lasers,” Proc. Natl. Acad. Sci. U.S.A. 94(10), 4853–4860 (1997). 23. W. H. Wright, G. J. Sonek, and M. W. Berns, “Parametric study of the forces on microspheres held by optical tweezers,” Appl. Opt. 33(9), 1735–1748 (1994). 24. A. V. Kachynski, A. N. Kuzmin, H. E. Pudavar, D. S. Kaputa, A. N. Cartwright, and P. N. Prasad, “Measurement of optical trapping forces by use of the two-photon-excited fluorescence of microspheres,” Opt. Lett. 28(23), 2288–2290 (2003). 25. C. Ying-chun and W. Chien-ming, “To study the effect of paclitaxel on the cytoplasmic viscosity of murine macrophage immune cell RAW 264.7 using self-developed optical tweezers system,” Jpn. J. Appl. Phys. 51(12R), 127001 (2012). 26. A. Jonáš and P. Zemánek, “Light at work: The use of optical forces for particle manipulation, sorting, and analysis,” Electrophoresis 29(24), 4813–4851 (2008). 27. E. Hutter and J. H. Fendler, “Exploitation of localized surface plasmon resonance,” Adv. Mater. 16(19), 1685– 1706 (2004). 28. P. V. Ruijgrok, N. R. Verhart, P. Zijlstra, A. L. Tchebotareva, and M. Orrit, “Brownian Fluctuations and Heating of an Optically Aligned Gold Nanorod,” Phys. Rev. Lett. 107(3), 037401 (2011). 29. K. C. Toussaint, Jr., M. Liu, M. Pelton, J. Pesic, M. J. Guffey, P. Guyot-Sionnest, and N. F. Scherer, “Plasmon resonance-based optical trapping of single and multiple Au nanoparticles,” Opt. Express 15(19), 12017–12029 (2007). 30. B. Hester, G. K. Campbell, C. López-Mariscal, C. L. Filgueira, R. Huschka, N. J. Halas, and K. Helmerson, “Tunable optical tweezers for wavelength-dependent measurements,” Rev. Sci. Instrum. 83(4), 043114 (2012). 31. Y. Seol, A. E. Carpenter, and T. T. Perkins, “Gold nanoparticles: enhanced optical trapping and sensitivity coupled with significant heating,” Opt. Lett. 31(16), 2429–2431 (2006). 32. K. Svoboda and S. M. Block, “Optical trapping of metallic Rayleigh particles,” Opt. Lett. 19(13), 930–932 (1994). 33. J. Burgin, S. Si, M.-H. Delville, and J.-P. Delville, “Enhancing optofluidic actuation of micro-objects by tagging with plasmonic nanoparticles,” Opt. Express 22(9), 10139–10150 (2014). 34. S. Y. Kim, J. D. Taylor, H. D. Ladouceur, S. J. Hart, and A. Terray, “Radiation pressure efficiency measurements of nanoparticle coated microspheres,” Appl. Phys. Lett. 103(23), 234101 (2013). 35. I. Pastoriza-Santos, D. Gomez, J. Perez-Juste, L. M. Liz-Marzan, and P. Mulvaney, “Optical properties of metal nanoparticle coated silica spheres: a simple effective medium approach,” Phys. Chem. Chem. Phys. 6, 5056– 5060 (2004). 36. A. S. Zelenina, R. Quidant, G. Badenes, and M. Nieto-Vesperinas, “Tunable optical sorting and manipulation of nanoparticles via plasmon excitation,” Opt. Lett. 31(13), 2054–2056 (2006). 37. J. Perez-Juste, I. Pastoriza-Santos, L. M. Liz-Marzan, and P. Mulvaney, “Gold nanorods: Synthesis, characterization and applications,” Coord. Chem. Rev. 249(17-18), 1870–1901 (2005). 38. S. Link, M. B. Mohamed, and M. A. El-Sayed, “Simulation of the optical absorption spectra of gold nanorods as a function of their aspect ratio and the effect of the medium dielectric constant,” J. Phys. Chem. B 103(16), 3073–3077 (1999). 39. C. Selhuber-Unkel, I. Zins, O. Schubert, C. Sönnichsen, and L. B. Oddershede, “Quantitative optical trapping of single gold nanorods,” Nano Lett. 8(9), 2998–3003 (2008). 40. L. M. Maestro, P. Haro-Gonzalez, J. G. Coello, and D. Jaque, “Absorption efficiency of gold nanorods determined by quantum dot fluorescence thermometry,” Appl. Phys. Lett. 100(20), 201110 (2012). 41. T. Mosmann, “Rapid colorimetric assay for cellular growth and survival: Application to proliferation and cytotoxicity assays,” J. Immunol. Methods 65(1-2), 55–63 (1983). 42. A. S. Urban, S. Carretero-Palacios, A. A. Lutich, T. Lohmüller, J. Feldmann, and F. Jäckel, “Optical trapping and manipulation of plasmonic nanoparticles: fundamentals, applications, and perspectives,” Nanoscale 6(9), 4458–4474 (2014). 43. M. Gu, H. C. Bao, X. S. Gan, N. Stokes, and J. Z. Wu, “Tweezing and manipulating micro- and nanoparticles by optical nonlinear endoscopy,” Light-Science & Applications 3(1), e126 (2014). 44. S. Tehranian, F. Giovane, J. Blum, Y. L. Xu, and B. A. S. Gustafson, “Photophoresis of micrometer-sized particles in the free-molecular regime,” Int. J. Heat Mass Transfer 44(9), 1649–1657 (2001).
#213777 - $15.00 USD Received 10 Jun 2014; revised 26 Jul 2014; accepted 28 Jul 2014; published 8 Aug 2014 (C) 2014 OSA 11 August 2014 | Vol. 22, No. 16 | DOI:10.1364/OE.22.01914119735 | OPTICS EXPRESS 19736
1. Introduction Manipulation and trapping of nano-objects are of great interest in biology, biotechnology and medicine. The trapping and manipulation of individual cells or particles in suspension with submicrometer, or nanometer, accuracy is an essential requirement in single cell studies, high resolution single particle sensing and, also, in the emerging field of single cell proteomics. There are several methods for efficient manipulation of single cells or microparticles, including ultrasonic trapping, atomic force microscopy (AFM) and optical trapping (OT) [1– 6]. Within this group of methods, OT is of particular interest since it allows both force measurement and particle manipulation in absence of physical contact thus minimizing any perturbations to the cell or particle under investigation [6]. OT is the common term used to describe trapping of individual particles at the focus of a single tightly focused beam due to the simultaneous presence of scattering and gradient forces. OT was first demonstrated by Ashkin et al. [4, 7] who trapped water dispersed dielectric nano and micro spheres by using a single 514 nm focused laser beam. Ashkin and associates also proposed and demonstrated the potential use of optical traps for biological applications [4, 7, 8]. Since these pioneering studies, various biological objects, including viruses, bacteria, and single cells have been trapped successfully, using the single-beam configuration and a great variety of laser sources (with different trapping wavelength, λ) [9, 10]. From these studies, it was determined that near infrared (700 nm < λ < 1070nm) laser traps had the lowest detrimental effect on cell viability, compared to using lasers sources in the visible region [11]. This feature of nearinfrared optical traps has been explained in the past in terms of the reduction in the laserinduced thermal loading (water does not absorb to a significant extent in the 700-980 nm range) and also by the fact that certain wavelengths in the infrared do not promote harmful intracellular reactions [11–14]. Recent results have concluded that almost damage-free single cell manipulation can be achieved by using trapping wavelengths close to 800 nm [11]. This opens the door for damage-free intracellular manipulation of sensing microparticles for intracellular dynamical studies. Among the different sensing microparticles, microspheres (µSp) are of special relevance as they have been demonstrated to be capable of a wide range of both chemical and thermal sensing with very high accuracy [15–19]. Whilst manipulation and trapping in standard liquid environment is straightforward, intracellular manipulation of a dielectric, transparent µ-Sp by OT is far more challenging, due to the inhomogeneity and large viscosity of the intracellular medium. Intracellular optical manipulation would be only possible provided that the optical force would overcome the drag force acting on the particle due to the medium viscosity. Therefore, the larger intracellular viscosity would lead to large drag forces in such a way that the optical forces required for intracellular manipulation to be larger than those required in a low viscosity medium. The principle relationship between optical trapping force and power acting on a µ-Sp is given by [20]; F = QPn1 / c
(1)
where Q is a dimensionless efficiency parameter, n1, is the refractive index of the surrounding medium, P is the trapping laser power, and c is the speed of light in free space [3, 20–22]. For typical values of n1 (1.33), P (tens of mW), and Q (ranging from 10−2 to 10−3, for silica microspheres) [23, 24], F is usually of the order of few hundreds of fN. The viscosity of the intracellular medium has been estimated to be as large as 137.05 Pa·s for 1µm sized bead Murine Macrophage [25]. Note that intracellular optical manipulation would be only possible provided that the optical force would overcome the drag force acting on the particle due to the medium viscosity. Therefore, the larger intracellular viscosity particle manipulation would make the optical forces required for intracellular manipulation to be larger than those required in a low viscosity medium at moderate/low laser powers [23, 26]. To increase trapping forces, one can potentially increase P, n1 or Q. The refractive index of the surrounding medium n1, in experiments dealing with intracellular manipulation, is that of the cytoplasm and, generally, it cannot be modified without adversely affecting the cell. Increasing the trapping power may be impractical since it may lead to absorption by the medium, causing significant heating and
#213777 - $15.00 USD Received 10 Jun 2014; revised 26 Jul 2014; accepted 28 Jul 2014; published 8 Aug 2014 (C) 2014 OSA 11 August 2014 | Vol. 22, No. 16 | DOI:10.1364/OE.22.01914119735 | OPTICS EXPRESS 19737
subsequent thermal damage [11]. In addition, when dealing with intracellular optical manipulation the laser power should also be maintained below the membrane ablation threshold in order to avoid undesired photoporation and thermal loading [11]. The last term, Q, has the greatest influence on the performance of the trap and determines whether the µ-Sp is trapped or not. The resultant efficiency is determined by a range of diverse parameters such as the numerical aperture of the optics, spot size, wavelength, polarization, aberrations and beam profile, which have an effect on the optical force. The efficiency parameter, Q, also takes into account the optical properties of the µ-Sp, and the size, shape, surface reflectivity and relative refractive index with respect to the surrounding medium. In the case of a silica microsphere (diameter 1 µm) the value Q is close to 0.006 [23]. Intracellular manipulation requires the challenging task of achieving an appropriate enhancement of this parameter. A possible approach to increase OT forces on silica microspheres is to combine them with metallic nanoparticles. Under appropriate optical excitation, metal nanoparticles display resonances, the so-termed Surface Plasmonic Resonances (SPRs). These correspond to the collective motion of surface charges. Such a collective motion is only induced for certain excitations wavelengths, denoted by λSPR, whose spectral location depends on the size and shape of the metallic nanoparticle [27]. When a metallic nanoparticle is optically excited at λSPR, a strong field enhancement is produced, accompanied by the appearance of a large electronic polarizability and a marked variation in the refractive index of nanoparticle [28– 30]. These effects make the trapping efficiency of a Rayleigh metallic particle (diameter d
