Optical manipulation and characterization of nonspherical nanoparticles

Project leaders

Maria Donato, Pavel Zemanek

Agreement

REPUBBLICA CECA - CAS (ex AVCR) - Czech Academy of Sciences

Call

CNR-CAS (ex AVCR) 2016-2018

Department

Chemical sciences and materials technology

Thematic area

Chemical sciences and materials technology

Status of the project

New

Research proposal

Light can exert forces and torques on matter due to the exchange of both linear and angular momentum. By tightly focusing a laser beam to a high-intensity spot micro and nanoparticles can be trapped by realizing the so-called optical tweezers. In the last years, the development of optical tweezers stimulated the exploitation of optical forces and torques in several research areas such as biophysics, nanotechnology, complex fluids, microrheology, and microfluidics. Here, in contrast to previous methods of manipulation of nanoparticles in liquids using the force exerted by laser light [1] we will focus also on orientation of nanoobjects, their self-arrangement to organized spatial structures in liquids [2] and, as a point of novelty, also in air or vacuum. The key feature is that we will deal with non-spherical particles that can be oriented with the help of beam polarization or shape [3-5]. To this aim, we will use nonspherical nanoparticles having different dimensionality, such as carbon nanotubes, silicon nanowires (both 1D) and silver nanoplatelets (2D) [6-8], and structured laser beams [9]. Beam properties will be changed by means of holographic techniques. The role of the particle different size, shape and composition in their optical arrangement and manipulation will be studied. We will also exploit the plasmonic enhancement [10] of optical forces on metal nanoparticles to control their aggregation on surfaces. Such controlled deposition of plasmonic particles will foster ultrasensitive surface-enhanced Raman spectroscopy (SERS) characterization of molecular species.
Our project aims to have a broad impact as self-assembly and alignment of nanoparticles into structures plays a key role in bottom-up nanotechnologies. Here, we propose an approach that uses laser beams to localize nanoparticles, manipulate them and form structures. Investigation of various methods leading to reproducible results is the first logical step to apply such approach in practical applications. Identification of robust methods and deep understanding of the underlying processes pave the way to practical applications in nanotechnologies and high-resolution spectroscopy.
In particular our research will span along the following milestones:
1.Nanoparticles of different dimensionality and composition will be obtained by means of both physical and chemical processes.
2. A single beam optical trap will be used to characterize the properties of the nanoparticle from the analysis of its Brownian dynamics and Raman spectrum.
3. Holographic single beam and dual beam optical traps will be used to trap particles and align them. Holographic technique uses spatial light modulators to modify the beam properties in a real time without mechanical touching the system. Dual beam setup will be used for optical trapping in air or vacuum.
4. Dark-field illumination will be used to observe the particles at the CCD camera, quadrant photodiodes will detect the Brownian dynamics of the particles. Spectrometer with CCD camera will be used to detect the Raman spectra in the optical trap and on substrate prepared by optical force deposition.
5. Rayleigh approximation for smaller particles and T-matrix approach for larger and more complex ones will be used for theoretical calculations of forces acting upon trapped nanoparticles.
Both groups involved in this proposal belong to the forefront and long-term players in the area of optical trapping and manipulation with atoms, nanoparticles, and microparticles. The Messina group has long term experience with manufacturing and characterization of nanoparticles in optical traps, Raman spectroscopy, and exact calculations of optical forces in the T-matrix framework. The Brno group has long-term experiences in the optical trapping of various particles, shaping the beam properties, especially in the dual-beam geometry, and theoretical simulation of optical forces acting upon particles of various shapes illuminated with structured laser beams. More in detail, the Messina team will provide nanoparticles of different shape, dimensionality and composition that will be characterized in single-beam optical traps using both force measurements and Raman tweezers. Moreover, it will also perform the controlled deposition of metal nanostructures on surfaces for surface-enhanced Raman spectroscopy (SERS). The Brno group will perform experiments in the holographic dual-beam setup and provide theoretical simulation of nanoparticles behaviour.

References:

[1] Maragò, et al. Nature Nanotech. 8, 807-819 (2013)
[2] Dholakia & Zemanek. Rev. Mod. Phys. 82, 1767-1791 (2010)
[3] Trojek et al., J. Opt. Soc. Am. A 29, 1224 (2012)
[4] Brzobohaty et al, Sci Rep 5, 8106 (2015)
[5] Brzobohaty et al., Opt. Express 23, 8179 (2015)
[6] Maragò et al., Nano Letters 8, 3211-3216 (2008)
[7] Irrera et al., Nano Letters 11, 4879-4884 (2011)
[8] Messina et al. Optics Express 23, 8720-8730 (2015)
[9] Dholakia and Cizmar, Nature Photon. 5, 335 (2011)
[10] Messina et al., ACS Nano 5 905, (2011)

Research goals

In this project we will focus on nanoparticles of nonspherical shape with the aim to reach their arrangement and especially orientation in space using laser beams with tailored intensity and polarization profiles. The goal of the project is proof-of-the-principle of methods providing characterization of nanoparticles together with their spatial arrangement and orientation. Specific objectives are summarized as follows:

1. Deeper experimental and theoretical understanding of trapping and alignment of a single nanoparticle and several nanoparticles of different shapes and compositions in a single beam and dual beam laser trap.

2. Pioneering experiments with nanoparticles optically confined in an underdamped trap in air or vacuum.

3. Characterization of nanostructures by Brownian dynamics and spectroscopic measurements, controlled optical forces deposition/aggregation of plasmonic particles (gold nanorods, silver platelets) for high-resolution (SERS) spectroscopy.

Last update: 03/08/2025