Pitch-rotational manipulation of single cells and particles using single-beam thermo-optical tweezers

Abstract

3D pitch rotation of microparticles and cells assumes importance in a wide variety of applications in biology, physics, chemistry and medicine. Applications such as cell imaging and injection benefit from pitch-rotational manipulation. Generation of such motion in single beam optical tweezers has remained elusive due to complicacies of generating high enough ellipticity perpendicular to the direction of propagation. Further, trapping an extended object at two locations can only generate partial pitch motion by moving one of the foci in the axial direction. Here, we use hexagonal-shaped upconverting particles and single cells trapped close to a goldcoated glass cover slip in a sample chamber to generate complete 360 degree and continuous pitch motion even with a single optical tweezers beam. The tweezers beam passing through the gold surface is partially absorbed and generates a hot-spot to produce circulatory convective flows in the vicinity which rotates the objects. The rotation rate can be controlled by the intensity of the laser light and the thickness of the gold layer. Thus such a simple configuration can turn the particle in the pitch sense. The circulatory flows in this technique have a diameter of about 5 µm which is smaller than those reported using acousto-fluidic techniques.

Controlled orientation and sustained rotation of biological samples in a sono-optical microfluidic device

“…In this case apparently the induced fluid flow leads to the sustained rotation of the particle via viscous drag, at least indirectly: it could be that the drag torque in combination with the acoustic viscous torque overcomes the acoustic radiation torque acting to lock the particle in a fixed orientation. This effect of inducing a particle rotation by a flow is similar to what happens in 'thermo-optical tweezers', 71 which utilize the convective flow induced by heating the fluid by light absorption at gold-coated cover slips to rotate the single cells around a transverse axis. However, in our case, the flow is not induced by convection due to laser heating, because it is strongly reduced if we keep the laser on but switch off the acoustic field.…”

Programmable motion control and trajectory manipulation of microparticles through tri-directional symmetrical acoustic tweezers

“…For magnetic tweezers, the manipulated samples need a pre-treatment of magnetization, 22 which significantly limits the applications of tweezers in biochemistry. Optical tweezers use high-intensity lasers for capturing and moving objects, 23 and they may scorch the cells and reduce the survivability of the cells in biological applications. 24 Acoustic tweezers utilize surface acoustic waves (SAWs) to manipulate the microfluids and inside microparticles, 25 contactless transportation and noninvasive injuries can be achieved.…”

Simultaneous optical trapping and magnetic micromanipulation of ferromagnetic iron-doped upconversion microparticles in six degrees of freedom

“…We show that Fe-doped upconverting NaYF 4 :Yb,Er particles (Fe-NYF) have ferromagnetic features and yet the refractive index is well conducive for optical tweezers measurements (the lattice NaYF 4 has a refractive index of 1.55) , even for particles as large as 5 µm, with large saturation magnetisation of 1 Am 2 /kg . The upconverting NaYF 4 :Yb,Er (NYF) non-magnetic particles have been routinely used with optical tweezers [26][27][28] but, for the first time, the magnetic properties of these NYF through co-doping with Fe are being explored. We show that this co-doped particle can be held in optical tweezers while the magnetic field could be used to turn the particle in all the three degrees of freedom, namely, yaw [29][30][31][32] , pitch 27,[33][34][35] and roll, in the nomenclature of the airlines.…”

“…The upconverting NaYF 4 :Yb,Er (NYF) non-magnetic particles have been routinely used with optical tweezers [26][27][28] but, for the first time, the magnetic properties of these NYF through co-doping with Fe are being explored. We show that this co-doped particle can be held in optical tweezers while the magnetic field could be used to turn the particle in all the three degrees of freedom, namely, yaw [29][30][31][32] , pitch 27,[33][34][35] and roll, in the nomenclature of the airlines.…”