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...

Antibiotics cure infections by influencing bacterial growth or viability. Antibiotics can be divided to two groups on the basis of their effect on microbial cells through two main mechanisms, which are either bactericidal or bacteriostatic. Bactericidal antibiotics kill the bacteria and bacteriostatic antibiotics suppress the growth of bacteria (keep them in the stationary phase of growth). One of many factors to predict a favorable clinical outcome of the potential action of antimicrobial chemicals may be provided using in vitro bactericidal/bacteriostatic data (e.g., minimum inhibitory concentrations-MICs). Consequently, MICs are used in clinical situations mainly to confirm resistance, and to determine the in vitro activities of new antimicrobials. We report on the combination of data obtained from MICs with information on microorganisms' "fingerprint" (e.g., DNA/RNA, and proteins) provided by Raman spectroscopy. Thus, we could follow mechanisms of the bacteriostatic versus bactericidal action simply by detecting the Raman bands corresponding to DNA. The Raman spectra of Staphylococcus epidermidis treated with clindamycin (a bacteriostatic agent) indeed show little effect on DNA which is in contrast OPEN ACESSMolecules 2013, 18 13189 with the action of ciprofloxacin (a bactericidal agent), where the Raman spectra show a decrease in strength of the signal assigned to DNA, suggesting DNA fragmentation.

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Advanced optical instruments can serve for analysis and manipulation of individual living cells and their internal structures. We have used Raman microspectroscopic analysis for assessment of β-carotene concentration in algal lipid bodies (LBs) in vivo. Some algae contain β-carotene in high amounts in their LBs, including strains which are considered useful in biotechnology for lipid and pigment production. We have devised a simple method to measure the concentration of β-carotene in a mixture of algal storage lipids from the ratio of their Raman vibrations. This finding may allow fast acquisition of β-carotene concentration valuable, e.g., for Raman microspectroscopy assisted cell sorting for selection of the overproducing strains. Furthermore, we demonstrate that β-carotene concentration can be proportional to LB volume and light intensity during the cultivation. We combine optical manipulation and analysis on a microfluidic platform in order to achieve fast, effective, and non-invasive sorting based on the spectroscopic features of the individual living cells. The resultant apparatus could find its use in demanding biotechnological applications such as selection of rare natural mutants or artificially modified cells resulting from genetic manipulations.

We present a unique technique for optical sorting of heterogeneous suspensions of microparticles, which does not require the flow of the immersion medium. The method employs the size-dependent response of suspended dielectric particles to the optical field of three intersecting beams that form a fringelike interference pattern. We experimentally demonstrate sorting of a polydisperse suspension of polystyrene beads of diameters 1, 2, and 5.2μm and living yeast cells.

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