Combined optical micromanipulation and interferometric topography (COMMIT).

Mohammad Sarshar,Bahman Anvari,Thompson Lu

doi:10.1364/boe.7.001365

Abstract

Optical tweezers have emerged as a prominent light-based tool for pico-Newton (pN) force microscopy in mechanobiological studies. However, the efficacy of optical tweezers are limited in applications where concurrent metrology of the nano-sized structures under interrogation is essential to the quantitative analysis of its mechanical properties and various mechanotransduction events. We have developed an all-optical platform delivering pN force resolution in parallel with nano-scale structural imaging of the biological sample by combining optical tweezers with interferometric quantitative phase microscopy. These capabilities allow real-time micromanipulation and label-free measurement of sample's nanostructures and nanomechanical responses, opening avenues to a wide range of new research possibilities and applications in biology.

Highlights

Optical tweezers (OTs) continue to remain a desired, and in many cases, the only nondestructive tool in biophysical studies that involve force measurements on the cellular, subcellular, and molecular scales [1,2,3,4]
The efficacy of optical tweezers are limited in applications where concurrent metrology of the nano-sized structures under interrogation is essential to the quantitative analysis of its mechanical properties and various mechanotransduction events
While the lateral resolution of the quantitative phase image is diffraction limited, parallel to the direction of light propagation, quantitative phase microscopy (QPM) reported the size of the sub-diffraction structures within ± 7.2 nm of the corresponding features measured using atomic force microscopy (AFM)

Summary

Introduction

Optical tweezers (OTs) continue to remain a desired, and in many cases, the only nondestructive tool in biophysical studies that involve force measurements on the cellular, subcellular, and molecular scales [1,2,3,4]. Scanning probe SRM techniques such as atomic force microscopy (AFM) [12], tip-enhanced near-field optical microscopy [13], and the recent method of scanning optically trapped spheres for surface imaging [14] are not suitable for concurrent micromanipulation and wide-filed imaging of the sample. We report on a platform that for the first time combines stiffness-calibrated OTs with an interferometric QPM technique based on Zernike’s phase contrast and Gabor’s holography [20] This combined optical micromanipulation and interferometric topography (COMMIT) platform allows simultaneous measurements of pN level forces with nm scale spatial resolution associated with the object under interrogation. Low coherence illumination and common-path interferometry allow for speckle-free imaging [20] at high phase stability [21]

COMMIT platform

Validation of interferometric QPM

Cell culture and tether formation

Results and discussion

Conclusions