Figure 1. Molecular threading apparatus.

(A) Device for stretching and positioning DNA molecules extracted at a liquid-air interface. A set of three 3-axis micro-positioners are used for coarse alignment of a DNA-binding tip, a target substrate, and the droplet containing a DNA suspension. Horizontal and vertical cameras are used to monitor the process (vertical camera not shown). (B) Illustration of the work area for “spider” threading. The droplet is immobilized between two low-wetting surfaces and a piezo-controlled tip is then moved between the surface of the suspension and the adjacent substrate. (C) Molecular threading at a liquid-air interface. (i) Needle tip penetrates into DNA suspension, binding to one or more strands (collectively called a “thread”). (ii) Needle tip extracts from the suspension parallel to substrate surface. The restoring force of the meniscus places the bound thread in tension. (iii) Needle tip is brought into direct contact with the target surface, transferring the strand to the substrate and the needle. (iv) A lateral translation of the needle after each extraction permits the creation of an array of linearized DNA. (D) Images of the needle, droplet, and substrate, taken under magnification, and corresponding to the illustrations in (C).