Journal: Science Advances

Article Title: Feedback-tracking microrheology in living cells

doi: 10.1126/sciadv.1700318

Figure Lengend Snippet: ( A ) Optical trap–based AMR setup with 3D feedback controls. A probe particle in a cell is trapped and oscillated by the drive laser (pink). QPD signals from the probe laser (cyan) are fed into PID controllers, which regulate piezo stage motion in x and y directions such that the trapped probe particle is maintained near the optical trap center. The bright-field image of the probe is simultaneously projected onto a charge-coupled device (CCD) camera [green thick line; light-emitting diode (LED) light source is omitted]. The image is analyzed on a personal computer (PC) to adjust the z position of the objective lens through a z direction piezo scanner. ( B ) Schematics for bead displacements and laser positions. Positions of fixed probe laser (830 nm, cyan) and acousto-optic deflector (AOD)–steered drive laser (1064 nm, pink) are shown by solid and dashed vertical lines, respectively. The drive laser is drawn displaced to the right of the probe laser. The pale particle indicates the probe starting position.

Article Snippet: Angular intensity shifts of the probe laser light due to the displacement of the probe particle were detected with a QPD (SPOT9D, OSI Optoelectronics AS).

Techniques:

Journal: Science Advances

Article Title: Feedback-tracking microrheology in living cells

doi: 10.1126/sciadv.1700318

Figure Lengend Snippet: ( A ) Diagram of signal flow in PMR under feedback control. A FB is the apparent response function in the time domain that relates (thermal) fluctuating force ζ( t ′) and total probe displacement u ( t ) under feedback. u QPD and u stage are correlated via the PID controller. A is the response function of the optically trapped probe in the absence of feedback. k t u stage represents the reduction of the optical trapping force due to feedback. ( B ) Power spectral densities (PSDs) of displacement fluctuations of the probe embedded in entangled actin solution (1 mg/ml) measured with PMR. Open triangles and the dashed curve show PSDs directly measured with and without feedback, respectively. Open circles and the solid curve show 〈| ũ (ω)| 2 〉 no trap calculated from 〈| ũ (ω)| 2 〉 FB using and PSDs calculated from 〈| ũ (ω)| 2 〉 trap using the conventional PMR method, respectively.

Article Snippet: Angular intensity shifts of the probe laser light due to the displacement of the probe particle were detected with a QPD (SPOT9D, OSI Optoelectronics AS).

Techniques: Control

Journal: Science Advances

Article Title: Feedback-tracking microrheology in living cells

doi: 10.1126/sciadv.1700318

Figure Lengend Snippet: ( A ) QPD and control signals for piezo stage as output by PID controller were recorded and calibrated to obtain displacements u QPD (green) and u stage (blue), respectively. Total displacement u (t) (red) was obtained by summing these quantities. ( B ) The displacement PSD measured using QPD with conventional PMR (black curve) agrees with that obtained under feedback by summing u QPD and u stage .

Article Snippet: Angular intensity shifts of the probe laser light due to the displacement of the probe particle were detected with a QPD (SPOT9D, OSI Optoelectronics AS).

Techniques: Control