Height measurement of dsDNA and antibodies adsorbed on solid substrates in air by vibrating mode scanning polarization force microscopy

Abstract

Articles you may be interested inStudy of substrate-directed ordering of long double-stranded DNA molecules on bare highly oriented pyrolytic graphite surface based on atomic force microscopy relocation imaging A method of height measurement based on vibrating mode scanning polarization force microscopy is developed and applied to soft molecules such as dsDNA and antibodies. In the experiment, a bias voltage is applied to a conductive atomic force microscopy ͑AFM͒ tip to maintain it farther from the surface during imaging in vibrating mode. By changing amplitude setpoint (A sp ) the tip can be lowered from the top of a molecule to the substrate, and the displacement of the tip in the z direction (D Z ) approximates the true height of this molecule. This method is first applied to rigid colloidal gold particles and then to dsDNA and antibodies. The measured heights of gold particles are consistent with those in normal tapping mode AFM ͑TM-AFM͒. However, the measured heights of dsDNA molecules and antibodies CA125 are much larger than the results in TM-AFM. We deduce that tip pressure might have caused large deformation on soft biomolecules when imaging is performed in TM-AFM.

Measuring radial Young’s modulus of DNA by tapping mode AFM

“…A few instrumentations have been applied in the measurement of DNA elasticity [4,5] , and atomic force microscopy (AFM) is one of the most commonly used techniques. AFM has advantages in high-resolution imaging and ultra-sensitive force measurement [6][7][8] .…”

Height measurement of DNA molecules with lift mode AFM

“…Newly cleaved mica was stuck to a spinning disc and 10 flL Milli-Q water, 10 flL Ni(N0 3 h (analytical grade) solution (l mmollL) and water was dropped to the rotating mica to rinse the remaining salt.…”

Analysis of vibrating mode scanning polarization force microscope

“…It seems also reasonable to deduce that a large part of sample deformation is caused by tip pressure. 1,2 VSPFM combines the features of SPFM and TMAFM. It a)…”

“…1 It can be considered as the improvement of the two microscopes. Nowadays, the dynamic operation of atomic force microscope (AFM), namely TMAFM, has been widely used in nanometer-scale imaging of soft materials.…”

“…1 The applied bias voltage causes polarization interactions between tip and sample. Polarization forces are long range in nature and adjusting the bias voltage can control the magnitude of polarization forces.…”