AFM Biosensors

AFM biosensors Biosensors using scaiming force microscope Cantilever biosensors Force-based biosensors Force biosensors... 

AFM biosensors have been used by researchers to measure binding or rupture forces between biological molecules. However, they have a few drawbacks, for example, the nonideal geometry of AFM can produce artifacts the result of measurement is affected by many factors, and in order to obtain good results, very strict experimental conditions are required. Improvements of the AFM biosensors are being studied. 

The FABS, whose working principle was very similar to that of the AFM biosensor, was a cantilever-based immunosensor [7]. However, its configuration was much simpler than that of the AFM. Rather than using a piezoceramic translator to pull on intermolecular bonds, it used magnetic particles, which eliminated the need to manually position a tip and sample next to each other with picometer precision and stability. The cantilever-beam force transducer was the only element of the AFM retained by the FABS. 

The first studies using AFM as a detection tool for intra-or intermolecular force can only measure discrete force. As the techniques for tip and sample preparation improve, single molecular interaction force detection will become the focus of AFM biosensors. 

AFM biosensors have been used by researchers to measure binding or rupture forces between biological molecules. 

The analysis of biomolecules by AFM is sometimes [3] referred to as surface biology, as opposed to the so-called test-tube biology, because the immobilisation of oligonucleotides on sohd surfaces is central to the design, fabrication and operation of DNA-based microdevices, such as biosensors, DNA micro- and nanoarrays, microPCR and lab-on-a-chip devices. As the analysed biomolecules are in close contact and very often in intimate interaction with the surface, sample preparation for the AFM analysis of surface-immobihsed biomolecules is both critical and dehcate. The biomolecules need to be firmly anchored on the substrate, which has to have a sufficiently minimal or easily discriminated topography [1]. The Kleinschmidt method [6] for the DNA... 

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].

Determination of the optimal experimental conditions for the atomic force microscopy (AFM) characterization of the surface morphology of a DNA electrochemical biosensor obtained using different immobilization procedures of calf-thymus double-stranded DNA (dsDNA) on a highly oriented pyrolytic graphite (HOPG) electrode surface. 

Biosensors based on cantilever action were briefly mentioned above. Nanosized cantilevers have been first used in AFM. Here, intermolecular forces between the cantilever and a smface are detected by monitoring the motion of the cantilever tip. In the case of biosensor applications, they are... 

Figure 9. AFM images of TPSP-ZnO before (A)and after(B)GOD loading.(C) Cyclic voltammograms ofTPSP-ZnO/Nafion (a), GOD/Nafion (b)GOD/spherical ZnO/ Nafion (c) and GOD/TPSP-ZnO/Nalion (d) modified in 0.1M pH 7.0 PB at 0.1 Vs" ( Reprinted from Biosensors and Bioelectronics, 24, Z. Dai, G. Shao, J. Hong, J. Bao, J. Shen, Immobilization and direct electrochemistry of glucose oxidase on a tetragonal pyramid-shaped porous ZnO nanostructure for a glucose biosensor, 1288,1289, Copyrights (2009) with permission fom Elsevier.

Reprinted from Biosensors and bioelectronics, 17(6-7), Henke L, Nagy N, Krull UJ, An AFM determination of the effects on surface roughness caused by cleaning of fused silica and glass substrates in the process of optical biosensor preparation, 547-551, 2002, with permission from Elsevier. 

The AFM analysis showed that the collapsed film has broken up into islands due to mechanical handling. However, the large parts are perfect in structure. This information is useful when such LB films are to be used for the electronics industry or biosensors. 

Biosensors using atomic force microscopes (AFMs) are devices which employ an atomic force microscope for biological recognition events. The principle of biosensors using atomic force microscopy is mainly based on the mass-sensitive detection of binding events that change the deflection of a cantilever whose surface is modified with immobilized bioreceptors. 

Biosensors Using Atomic Force Microscopes, Fig. 1 (a) Basic components and working principle of AFM. A sharp tip fixed at the end of a fiexible cantilever is raster scanned over the surface of a sample. As the tip interacts with the surface, the cantilever deflects, and its deflections are monitored by a laser and a photodiode and then used to reconstruct the topography of the sample, (b) A schematic diagram of AFM as a biosensor in detecting... 

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