MAC mode

Magnetic AC atomic force microscopy (MAC Mode AFM) has proved to be a powerful surface analysis technique to investigate the interfacial and conformational properties of biological samples softly bound to the electrode surface and can be used as an important tool to characterize DNA-electrochemical biosensor surfaces [25,27],... 

Fig. 20.1. MAC Mode AFM three-dimensional images in air of (A) clean HOPG electrode (B) thin-film dsDNA-biosensor surface, prepared onto HOPG by 3 min free adsorption from 60 pg/mL dsDNA in pH 4.5 0.1 M acetate buffer (C) multi-layer film dsDNA biosensor, prepared onto HOPG by evaporation of three consecutive drops each containing 5pL of 50 pg/mL dsDNA in pH 4.5 0.1 M acetate buffer (D) thick-film dsDNA biosensor, prepared onto HOPG by evaporation from 37.5mg/mL dsDNA in pH 4.5 0.1M acetate buffer. With permission from Refs. [28,29].

MAC Mode AFM 415 Magnesium 114, e5 Magnetic beads 454, 484, 590, el80, e228... 

Better control of the cantilever oscillation in liquid environment can be achieved when the cantilever is oscillated directly by an external force. This idea was implemented by the so-called Magnetic-Alternative-Current Mode (MAC Mode) [194]. A magnetic cantilever is driven by an external magnetic field which is generated by a solenoid placed beneath the sample. The direct excitation of the cantilever avoids unwanted resonance s from the cantilever holder, the fluid body, and the sample itself. Furthermore, the improved signal-to-noise ratio allows smaller oscillation amplitudes and set point ratios Asp/Af closer to 1. Both factors result in a significant reduction in the energy deposited into the sample,... 

Fig. 41. Two independent measurements of force spectra of the MAC mode SFM at OMCTS-graphite interface. The amplitude of oscillation of the magnetic cantilever driven by an external magnetic field oscillates in both approaching (solid line) and retracting (dotted line) curves in the region of a few nanometers away from the surface due to ordered layers of OM-CTS molecules at the interface. The period of oscillation 8.2 A reflects the dimension ol OMCTS molecules along the direction perpendicular to the layers, a Driving frequency 500 Hz, scan rate 2.8 nm/s. b 200 Hz and 1.6 nm/s. The arrows on the plots correspond to repulsive-force maxima. Reproduced from [183]...

Figure 57. The MAC mode AFM images of Ti02 nanoporous films (a) before and (b) after the coating with Zn(4-TRpPyP) prepared from ethanol solution.

A critical issue in the development of an electrochemical DNA-biosensor is the sensor material and the degree of surface coverage. MAC Mode AFM images were used to characterize different procedures for immobilising nanoscale double-stranded DNA (ds-DNA) surface nanofilms on carbon electrodes, Rg. 6.1. 

Figure 3. Schematic representation of the MAC Mode scanning for< microscope with a liquid cell. A cantilever, coated with a magnetic material, is driven by an alternating magnetic field of a solenoid placed under the sample.

Figure 4. In-situ observation of poly(2-vinyI-N-benzyipyridinium bromide) brushes by the MAC mode SFM as adsorbed on mica from a salt-free aqueous solution at a concentration of 0.01 mg/ml.

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