Torque detection using Brownian fluctuations
Giovanni Volpe & Dmitri Petrov
Physical Review Letters 97(21), 210603 (2006)
We report the statistical analysis of the movement of a submicron particle confined in a harmonic potential in the presence of a torque. The absolute value of the torque can be found from the auto- and cross-correlation functions of the particle’s coordinates. We experimentally prove this analysis by detecting the torque produced onto an optically trapped particle by an optical beam with orbital angular momentum.
We report the first experimental observation of momentum transfer from a surface plasmon to a single dielectric sphere. Using a photonic force microscope, we measure the plasmon radiation forces on different polystyrene beads as a function of their distance from the metal surface. We show that the force magnitude at resonance is strongly enhanced compared to a nonresonant illumination. Measurements performed as a function of the probe particle size indicate that optical manipulation by plasmon fields has a strong potential for optical sorting.
Dynamics of a growing cell in an optical trap
Giovanni Volpe, Gajendra Pratap Singh & Dmitri Petrov
Applied Physics Letters 88(23), 231106 (2006)
We analyze the forward scattered light from a single optically trapped cellduring its growth. We show that the cell continues adjusting itself to the applied optical force because of the growth processes, and hence it keeps changing its orientation in the trap. We point out the importance of taking this variation into account in the interpretation of spectroscopic data. This method can also be used as a means for cell identification and cell sorting.
The lag phase and G1 phase of a single yeast cell monitored by Raman microspectroscopy
Gajendra P. Singh, Giovanni Volpe, Caitriona M. Creely, Helga Grötsch, Isabel M. Geli & Dmitri Petrov
Journal of Raman Spectroscopy 37(8), 858—864 (2006)
We optically trapped a single yeast cell for up to 3 h and monitored the changes in the Raman spectra during the lag phase of its growth and the G1 phase of its cell cycle. A non‐budding cell (corresponding either to the G0 or G1 phase) was chosen for each experiment. During the lag phase, the cell synthesises new proteins and lipids and the observed behaviour of the peaks corresponding to these constituents as well as those of RNA served as a sensitive indicator of the adaptation of the cell to its changed environment. Temporal behaviour of the Raman peaks observed was different in the lag phase as compared to the late lag phase. Two different laser wavelengths were applied to study the effect of long‐term optical trapping on the living cells. Yeast cells killed either by boiling or by a chemical protocol were also trapped for a long time in a single beam optical trap to understand the effect of optical trapping on the behaviour of observed Raman peaks. The changes observed in the Raman spectra of a trapped yeast cell in the late G1 phase or the beginning of S phase corresponded to the growth of a bud.
Raman imaging of floating cells
Caitriona M. Creely, Giovanni Volpe, Gajendra P. Singh, Marta Soler & Dmitri Petrov
Optics Express 13(16), 6105–6110 (2005)
Raman imaging can yield spatially resolved biochemical information from living cells. To date there have been no Raman images published of cells in suspension because of the problem of immobilising them suitably to acquire space-resolved spectra. In this paper in order to overcome this problem the use of holographic optical tweezers is proposed and implemented, and data is shown for spatially resolved Raman spectroscopy of a live cell in suspension.
Real-time detection of hyperosmotic stress response in optically trapped single yeast cells using Raman microspectroscopy
Gajendra P. Singh, Caitriona M. Creely, Giovanni Volpe, Helga Grötsch & Dmitri Petrov
Analytical Chemistry 77(8), 2564–2568 (2005)
Living cells survive environmentally stressful conditions by initiating a stress response. We monitored changes in the Raman spectra of optically trapped Saccharomyces cerevisiae yeast cell under normal, heat-treated, and hyperosmotic stress conditions. It is shown that when glucose was used to exert hyperosmotic stress, two chemical substancesglycerol and ethanolcan be monitored in real time in a single cell.
Generation of cylindrical vector beams with few-mode fibers excited by Laguerre–Gaussian beams
Giovanni Volpe & Dmitri Petrov
Optics Communications 237(1), 89–95 (2004)
We propose a novel method to efficiently produce light beams with radial, azimuthal, and hybrid polarization, through a few-mode fiber excited by a Laguerre–Gaussian beam. With different input polarization we can selectively excite different combinations of modes from the LP11 group. We propose to show how to transform the output beam into a cylindrical vector beam in free-space through various polarization transformations.