Optical micro manipulation of live cells has been extensively used to study a wide range of cellular phenomena with relevance in basic research or in diagnostics. The approaches span from manipulation of many cells for high throughput measurement or sorting, to more elaborated studies of intracellular events on trapped single cells when coupled with modern imaging techniques. In case of direct cell trapping the damaging effects of light-cell interaction must be minimized, for instance with the choice of proper laser wavelength. Microbeads have already been used for trapping cells indirectly thereby reducing the irradiation damage and increasing trapping efficiency with their high refractive index contrast. We show here that such intermediate objects can be tailor-made for indirect cell trapping to further increase cell-to-focal spot distance while maintaining their free and fast maneuverability. Carefully designed structures were produced with two-photon polymerization with shapes optimized for effective manipulation and cell attachment. Functionalization of the microstructures is also presented that enables cell attachment to them within a few seconds with strength much higher that the optical forces. Fast cell actuation in 6 degrees of freedom is demonstrated with the outlook to possible applications in cell imaging.
We demonstrate the use of microfabricated supporting structures for maneuvering and supporting polystyrene microspheres for use as magnifying lenses in imaging applications. The supporting structure isolates the trapping light from the magnifier, hence avoiding direct radiation to the sample being observed which could be damaging, especially for biological specimens. Using an optical trapping setup, we demonstrate the actuation of a microsphere not held by optical traps, and show the possibility of imaging through such microspheres.
Robotics can use optics feedback in vision-based control of intelligent robotic guidance systems. With light’s miniscule momentum, shrinking robots down to the microscale regime creates opportunities for exploiting optical forces and torques in microrobotic actuation and control. Indeed, the literature on optical trapping and micromanipulation attests to the possibilities for optical microrobotics. This work presents an optical microrobotics perspective on the optical microfabrication and micromanipulation work that we performed. We designed different three-dimensional microstructures and fabricated them by two-photon polymerization. These microstructures were then handled using our biophotonics workstation (BWS) for proof-of-principle demonstrations of optical actuation, akin to 6DOF actuation of robotic micromanipulators. Furthermore, we also show an example of dynamic behavior of the trapped microstructure that can be achieved when using static traps in the BWS. This can be generalized, in the future, towards a structural shaping optimization strategy for optimally controlling microstructures to complement approaches based on lightshaping. We also show that light channeled to microfabricated, free-standing waveguides can be used not only to redirect light for targeted delivery of optical energy but can also for targeted delivery of optical force, which can serve to further extend the manipulation arms in optical robotics. Moreover, light deflection with waveguide also creates a recoil force on the waveguide, which can be exploited for controlling the optical force.
We demonstrate a system for constructing reconfigurable microstructures using multiple, real-time configurable
counterpropagating-beam traps. We optically assemble geometrically complementary microstructures with complex
three-dimensional (3D) topologies produced by two-photon polymerization. This demonstrates utilization of
controllable 3D optical traps for building hierarchical structures from microfabricated building blocks. Optical
microassembly with translational and tip-tilt control in 3D achieved by dynamic multiple CB traps can potentially
facilitate the construction of functional microdevices and may also lead to the future realization of optically actuated
micromachines. Fabricating morphologically complex microstructures and then optically manipulating these archetypal
building blocks can also be used to construct reconfigurable microenvironments that can aid in understanding cellular
Coupling of optical data-processing devices with microelectronics, telecocommunication and sensory functions, is
among the biggest challenges in molecular electronics. Intensive research is going on to find suitable nonlinear optical
materials that could meet the demanding requirements of optoelectronic applications, especially regarding high
sensitivity and stability. In addition to inorganic and organic crystals, biological molecules have also been considered
for use in integrated optics, among which the bacterial chromoprotein, <i>bacteriorhodopsin</i> (bR) generated the most
interest. bR undergoes enormous absorption and concomitant refractive index changes upon initiation of a cyclic
series of photoreactions by a burst of actinic light. This effect can be exploited to create highly versatile all-optical
logical elements. We demonstrate the potential of this approach by investigating the static and dynamic response of
several basic elements of integrated optical devices. Our results show that, due to its relatively high refractive index
changes, bR can be used as an active nonlinear optical material to produce a variety of integrated optical switching and
The emerging field of micro fluidics is challenged with a desire to pump, move and mix minute amounts of fluid. Such micro devices are operated by means of light matter interaction, namely they can be driven through utilizing birefringence and the polarization of the light as well as the reflection and refraction of light. The latter one enables micro motors to be operated in a tangential setup where the rotors are on axis with an optical waveguide. This has the advantage that the complexity of driving such a device in a lab on a chip configuration is reduced by delivering the driving light by means of a waveguide or fiber optics. In this publication we study a micro motor being driven by a fiber optically delivered light beam. We present experimentally and theoretically how light is getting diffracted when in interaction with the rotors of a turning micro motor. By utilizing the two photon signal from a fluorescein dye being excited by a pulsed femtosecond Laser which was used to drive the motor. Additionally the rotation rate is investigated in dependence of the light field parameters.
Electro-osmosis is an efficient means to move fluid in microfluidic channels. The flow is driven by the interaction of the electrical double layer at the channel wall with an electric field along the channel. The flow can be controlled by modifying the electrical &muparameters, either the charge of the channel wall or the electric field. If the surface chagre or the surface rsistance of the channel wall is sensitive to light, the flow can be modulated by light. We have demonstrated this effect by using photoconductive surfaces. The resistance change due to the illumination changes the electric field above the photoconductive layer and consequently changing the rate of fluid flow. By using channels where upon a photoresistive CdS surface a linear PDMS channel was placed, flow rate changes of an order of magnitude were achieved. This gives serious possibilities for optical control of flow. We further developed the method by building channel structures of more complicated patterns, e.g. Y-junctions. By appropriate illumination of the arms the flow direction could be selected between the arms optically. This unit is the basis of more complex flow patterns, it demonstrates the feasibility of optical control of such devices.
Photopolymerisation by computer controlled scanning of a focused laser beam is a powerful method to build structures of arbitrary complexity with submicrometer resolution. The procedure has already proven effective to produce complex structures that can be manipulated in optical tweezers. These micromechanical systems consist of static and moving parts and are expected to be building blocks of highly capable microfluidic systems. To enhance the efficiency of structure building, we developed single shot photopolymerisation. Instead of complicated multidimensional scanning the whole structure is generated simultaneously with special diffractive patterns. We experimented with fixed diffractive optical elements, kinoforms, and Spatial Light Modulators (SLMs). By using kinoforms, cross shaped structures were produced in single shots as an illustration. These propellers were produced about an order of magnitude faster than by simple scanning, and can be rotated by optical tweezer. The complexity of the structure depends on the quality of the kinoform and the available laser power. With the concerted movement of the appropriately chosen basic pattern and the sample, the building of more complicated structures can also be greatly accelerated due to the parallel nature of the polymerisation. The possibilities of photopolymerisation using SLM were also explored: the added flexibility using the programmable device is demonstrated.
Electro-osmotic pumping is an efficient way to move fluids in microfluidic systems. It is driven by the interaction of the Debye layer formed in the vicinity of the charged channel wall with a tangential electric field. The key parameters that determine the flow properties are the zeta potential of the surface and the electric field that drives the flow. Consequently, the flow can be controlled by appropriately modifying these parameters. Controlling the charge on the channel wall makes it possible to modify fluid flow. Likewise, the electric field close to the surface can be modified by changing the conductivity of the surface. The surface charge of appropriate materials can be changed by light illumination: the application of this phenomenon offers the possibility to optically control flow parameters. We have tested this possibility with several light sensitive surfaces. In the class of materials that change their charge upon illumination TiO<sub>2</sub>, a well known photoactive material was investigated. Experiments were also performed with the protein bacteriorhodopsin, known to change its surface charge following the release of protons into the solvent upon illumination. CdS was tested as the photoconductive material to modify the electric field by light. Linear microfluidic channels were prepared by soft lithography: a PDMS mold was placed upon a planar glass surface so that a rectangular cross section channel was formed upon the glass. The photosensitive materials covered the bottom glass surface.
The experiments show that the flow can be readily modulated by illumination. The results demonstrate that it is possible to dynamically control microfluidic flow, opening up the prospect to create optically controlled complex microfluidic networks.
We have shown earlier that photopolymerization offers a relatively simple method to produce microscopic particles of arbitrary shape that are practical to expand the possibilities of optical manipulation. Propeller shaped micrometer sized rotors are rotated in optical tweezers, while flat objects are oriented in traps formed by linearly polarized light. Such elements and the possibilities opened up by their use would find numerous applications in lab-on-a-chip devices. We have extended these methods by developing new elements for applications. We have built microscopic wheels ad gears that have a central flat component so that its rotational position can be controlled by linearly polarized light. These rotors are rotated by rotating the polarisation of the light. Such gears can be used as actuators of more complex micromechanical devices (pumps, valves,) also built by photopolymerization in a single process. Important component of such devices are gears rotating on fixed axes, readily built by the method. An alternative way of optically actuating rotating devices by light is the illumination of cogwheel shaped rotors from a tangential direction. The advantage of this latter approach is that the whole system (i.e. the rotors on axes and optical waveguides that carry the actuating as well as possibly the sensing light) can be built as an integrated system in a single process. Such devices would not need optical tweezers and thus bulky microscopes for actuation, significantly reducing the complexity of eventual lab-on-a-chip devices. Operational examples will be demonstrated and the properties of the different approaches will be compared.
We describe a novel method by which it is possible to apply and measure torque directly on particles grabbed in optical tweezers. It can be used to orient particles of micron size or even on single molecules, biopolymers by the use of test particles.
The procedure is based on the observation that flat objects are oriented in an optical trap formed by linearly polarized light. The orienting torque originates from the anisotropic scattering of polarized light by the trapped particle. The phenomenon is characterized in detail, the physics is analysed.
A tool is developed that exploits this effect to manuipulate biological macromolecules. Microscopic particles are produced by photopolymerisation that exploit this orientation effect and by which the torque is applied upon the biological object. In our system the applied torque can be turned on and off, it is controlled independently of the grabbing force of the tweezers during the manipulation process.
The capabilities of the method are demonstrated. The method has great promise for application on DNA, DNA-protein complexes, actin filaments and other biopolymers.