Tunable optical tweezers for wavelength-dependent measurements

Invariant correlated optical fields driven by multiplicative noise

We describe the evolution of a linear transmittance when it is perturbed with multiplicative noise; the evolution is approximated through an ensemble of random transmittances that are used to generate diffraction fields. The randomness induces a competition mechanism between noise and transmittance, and it is identified through the self-correlation function. We show that the geometry of the self-correlation function is a single peak preserved in the diffraction field that can be matched with localization-like effects. To corroborate the theoretical predictions, we perform an experiment using a linear grating where the noise is approximated by a stochastic Markov chain. Experimental results are shown.

Optical Fiber Tweezers: A Versatile Tool for Optical Trapping and Manipulation

Optical trapping is widely used in different areas, ranging from biomedical applications, to physics and material sciences. In recent years, optical fiber tweezers have attracted significant attention in the field of optical trapping due to their flexible manipulation, compact structure, and easy fabrication. As a versatile tool for optical trapping and manipulation, optical fiber tweezers can be used to trap, manipulate, arrange, and assemble tiny objects. Here, we review the optical fiber tweezers-based trapping and manipulation, including dual fiber tweezers for trapping and manipulation, single fiber tweezers for trapping and single cell analysis, optical fiber tweezers for cell assembly, structured optical fiber for enhanced trapping and manipulation, subwavelength optical fiber wire for evanescent fields-based trapping and delivery, and photothermal trapping, assembly, and manipulation.

Remotely controlled fusion of selected vesicles and living cells: a key issue review

Remote control over fusion of single cells and vesicles has a great potential in biological and chemical research allowing both transfer of genetic material between cells and transfer of molecular content between vesicles. Membrane fusion is a critical process in biology that facilitates molecular transport and mixing of cellular cytoplasms with potential formation of hybrid cells. Cells precisely regulate internal membrane fusions with the aid of specialized fusion complexes that physically provide the energy necessary for mediating fusion. Physical factors like membrane curvature, tension and temperature, affect biological membrane fusion by lowering the associated energy barrier. This has inspired the development of physical approaches to harness the fusion process at a single cell level by using remotely controlled electromagnetic fields to trigger membrane fusion. Here, we critically review various approaches, based on lasers or electric pulses, to control fusion between individual cells or between individual lipid vesicles and discuss their potential and limitations for present and future applications within biochemistry, biology and soft matter.

Optical manipulation of individual strongly absorbing platinum nanoparticles

Nanostructures with exceptional absorption in the near infrared (NIR) regime are receiving significant attention due to their ability to promote controlled local heating in biological material upon irradiation. Also, such nano-structures have numerous applications in nano-electronics and for bio-exploration. Therefore, significant effort is being put into controlling and understanding plasmonic nanostructures. However, essentially all focus has been on NIR resonant gold nanoparticles and remarkably little attention has been given to nanoparticles of other materials that may have superior properties. Here, we demonstrate optical control and manipulation of individual strongly absorbing platinum nanoparticles in three dimensions using a single focused continuous wave NIR laser beam. Also, we quantify how the platinum nanoparticles interact with light and compare to similarly sized absorbing gold nanoparticles, both massive gold and gold nanoshells. By finite element modeling, we find the scattering and absorption cross sections and the polarizability of all particles. The trapping experiments allow for direct measurements of the interaction between the nanoparticles and NIR light which compares well to the theoretical predictions. In the NIR, platinum nanoparticles are stronger absorbers than similarly sized massive gold nanoparticles and scatter similarly. Compared to NIR resonant gold nanoshells, platinum nanoparticles absorb less, however, they also scatter significantly less, thus leading to more stable optical trapping. These results pave the way for nano-manipulation and positioning of platinum nanoparticles and for using these for to enhance spectroscopic signals, for localized heating, and for manipulation of biological systems.

Optofluidic tunable manipulation of microparticles by integrating graded-index fiber taper with a microcavity

We propose and demonstrate optofluidic tunable manipulation of polystyrene microparticles based on the combination of a graded-index fiber (GIF) taper and a microcavity. The tunability on the manipulation length is experimentally explored by changing the balance between the optical force and the microfluidic flow force, as well as by tuning the focus of light emitting from the GIF taper via adjusting the length of an air microcavity. By optimizing the geometric shape of the GIF taper, as well as the flow rate and laser power, a manipulation length of 177 μm is achieved, more than 4 times longer than the state-of-the-art optical fiber tweezers. This method has advantages of high flexibility, ease of fabrication and use, integration with microfluidics and has the potential for optofluidic sensing applications.

Quantitative analysis of temperature dependent acoustic trapping characteristics by using concentric annular type dual element ultrasonic transducer

This paper presents the temperature dependence of lateral acoustic trapping capability by probing the speed of sound in individual lipid droplets at a given temperature of water and measuring its corresponding displacement, a value for quantitatively evaluating a spring-like behavior of the acoustic trap with certain strength. A 20/40 MHz dual element LiNbO3 ultrasonic transducer is fabricated to simultaneously perform both transverse trapping and sound speed measurement for each droplet over a discrete temperature range from 20°C to 30°C. Time of flight method is employed for pulse tracking that determines the arrival time of an echo reflected back from either a trapped droplet or a mylar film. The estimated speeds of sound in water and droplets are 1484.8 m/s and 1431.6 m/s at 20°C, while 1506.0 m/s and 1400.6 m/s at 30°C, respectively. As the temperature rises, the sound speed in droplets decreases at an average rate of 3.1 m/s/°C, and the speed in water increases at 2.1 m/s/°C. The average displacement varies from 150.0 μm to 179.0 μm with an increasing rate of 2.9 μm/°C, and its standard deviation is obtained between 1.0 μm and 2.0 μm over the same temperature range. Reduced sound speed as a function of rising temperature results in increased displacement, indicating that the trapping strength is adjustable by regulating ambient temperature in water as well as by changing transducer excitation parameters. Therefore, the results suggest that the temperature dependence of this trapping technique can be exploited for developing a remote manipulation tool of micron-sized particles in a thermally fluctuating environment. It is also shown that any deviated trapping strength caused by thermal disturbance near the trap can be restored to its desired level by compensating either temperature difference or trapping system condition.

Gold nanorod assisted intracellular optical manipulation of silica microspheres

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.