ATTRACTIVE ATOMIC FORCE MICROSCOPY FOR DNA SEQUENCING

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Atomic force microscopy (AFM) views non-conducting surfaces at atomic resolution by measuring deflection of a lever with an atomically sharp tip. The small forces (10-13 to 10-8Newtons), and deflections (of the order of Angstroms) are measured using a tunneling tip. The inter-atomic forces measured have a repulsive and an attractive region. The conventional AFM arrangement, with the tunneling tip behind the atomic force tip, can only measure the repulsive branch. To observe the attractive branch with 0.1 nm resolution the tunneling tip must be on the specimen side of the atomic force tip. This novel rearrangement is the essence of this proposal. This mode of operation would produce a smaller specimen tip force, greater specimen-to-tip working distance (approximately 0.5 nm, rather than approximately 0.3 nm) and less movement of the specimen. Any specimen-to-substrate adhesion will decrease specimen-tip interaction, freeing the tip. (In the repulsive mode the opposite occurs, increasing specimen motion). Reduced force on the specimen is important in imaging biological molecules. This could be of relevance in sequencing the human genome by direct, physical observation - a task which will be possible if 0.1 nm resolution can be obtained on DNA.