Optical sorting and detection of submicrometer objects in a motional standing wave

Abstract

An extended interference pattern close to surface may result in both a transmissive or evanescent surface fields for large area manipulation of trapped particles. The affinity of differing particle sizes to a moving standing wave light pattern allows us to hold and deliver them in a bi-directional manner and importantly demonstrate experimentally particle sorting in the sub-micron region. This is performed without the need of fluid flow (static sorting). Theoretical calculations experimentally confirm that certain sizes of colloidal particles thermally hop more easily between neighboring traps. A new generic method is also presented for particle position detection in an extended periodic light pattern and applied to characterization of optical traps and particle behavior.PACS numbers: 42.50.Vk; 82.70.Dd Optical trapping and guiding of micron and sub-micron size objects have been a key topic of numerous studies in the last three decades in the realm of mesoscale science [1]. A recent drive in the field is the ability to interact with large scale ensembles of particles in two-dimensions (2D) and ultimately in three-dimensions (3D): interferometric patterns may help achieve this. Light fields at or near total internal reflection may assist allowing one to organize upwards of 1000 particles adjacent to a surface [2,3]. Recent work has shown the experimental demonstration of optical separation using an extended optical lattice or holographic methods in the presence of a laminar flow [4,5] and it has been followed by theoretical analyses [6]. In these studies the particles are not trapped per se but rather their differing affinity to a periodic light pattern were exploited. This sensitivity is very high and potentially offers a new non-invasive method for optical separation or sorting. Thus it would be a key advance to show how we may separate sub-micrometer objects in the absence of a flow and potentially over a large area, facilitating greater throughput. The near field optical trapping has shown the ability to potentially organise particles over areas of mm 2 and offers a potential test area for sorting over a large region [2,3,7]. Tuning the incident angle from below to above the critical angle results in a transition between propagating and evanescent light fields. This geometry for such optical organization[8] is eminently suitable for sorting, even if a small part of the incident focused beam is below the critical angle and thus forms propagating field. Ultimately we are creating light field patterning in 2D over an extended region.In this letter we present an interferometric system that provides confinement and two-directional controllable delivery of particles of sub-micrometer sizes. Our system * Electronic address: zemanek@isibrno.cz is employed in a geometry that both permits evanescent wave confinement as well as confinement just above the surface (by judicious choice of incident angle): this choice of geometry in all instances allows extension of the data presented here to a large area and concomitan...

Optical tweezers for single cells

“…Zemanek et al (2004) described using a three-beam interference light field to locate big particles in intensity minimum but small particles in intensity maximum. A size-selective optical-moving pattern is a more productive way to enhance separation, such as a vibrating fringe pattern (Ricardez-Vargas et al 2006), a moving periodic light pattern (Cizmar et al 2006) and time-dependent optical potential energy landscape (Libal et al 2006;Smith et al 2007). …”

Speckle optical tweezers: micromanipulation with random light fields

“…Although a carefully engineered periodic potential or array of traps optimized for a given application can perform better than a speckle field, this technique expands the set of tools that researchers and engineers can adopt to perform optical manipulation tasks. As it is the case for alternative optofluidic devices based on periodic optical potentials or holographic optical tweezers [3,[7][8][9][10][11][12][13][14][15][16][17]32,33], our approach can also be scaled to achieve the high throughput or sensitivity needed in microfluidics by increasing the flow speed and laser power. In fact, the required optical intensities are comparable to those reported in similar studies where the force field was generated either with holographic optical traps or with periodic potentials [3,[7][8][9][10][11][12][13][14][15][16][17]32,33].…”

“…As it is the case for alternative optofluidic devices based on periodic optical potentials or holographic optical tweezers [3,[7][8][9][10][11][12][13][14][15][16][17]32,33], our approach can also be scaled to achieve the high throughput or sensitivity needed in microfluidics by increasing the flow speed and laser power. In fact, the required optical intensities are comparable to those reported in similar studies where the force field was generated either with holographic optical traps or with periodic potentials [3,[7][8][9][10][11][12][13][14][15][16][17]32,33]. Our technique, beyond demonstrating that random potentials are a valid alternative to more regular potentials for the purpose of optical manipulation, offers some additional advantages to current optical manipulation techniques [3,[7][8][9][10][11][12][13][14][15][16][17]32,33], such as intrinsic robustness to noise and aberrations from the optics and the environment.…”

“…They have, therefore, gained increasing importance as tools in microbiology and biophysics both for fundamental studies [6] and for more advanced applications such as optical sorting and optical delivery [3,7,8]. In particular, the development of techniques based on reconfigurable spatially extended patterns of light, such as multiple traps [3,[9][10][11][12] or periodic potentials [13][14][15][16][17], offers the promise of high throughput optical methods to be applied both in static and moving fluids. Also, particles' delivery, trapping and manipulation over extended areas was demonstrated near a surface employing the evanescent fields associated, for example, to surface plasmons [18] or to optical waveguides [19].…”

Standing wave-mediated molecular reorientation and spontaneous formation of tunable, concentric defect arrays in liquid crystal cells

“…1,2 The De Broglie standing wave explains the origin of matter formation, that is, it stabilizes electronic orbitals and generates an electronic bandgap in matter. Electromagnetic standing waves also cause various fundamental phenomena, for example, particle trapping, 3 tuning electron density profiles 1 and lasing. Mechanical standing waves are involved in the heat capacity and superconductivity of matter on the nanoscale and can be observed in massive, wobbly bridges on the macroscale.…”