Improved nm displacement detector for microscopic beads at frequencies below 10 Hz

A modular differential interference contrast microscope combined with laser interferometry has been designed and constructed to detect nm-scale displacements of microscopic beads with a root mean square noise less than 0.4 nm. The unique feature of our system lies in its capability of preserving the nm-scale detection sensitivity down to a low-frequency region of a few Hz. The modularized design ensures the system is accessible to further modifications as frequently required by various biological experiments such as employing multiple laser traps to manipulate rod-shaped samples.