Fig. 2.

Single-cell force measurement revealed that the RCA-aptamer binds target cells more effectively than Unit-aptamers. (A) Representative images of individual CCRF-CEM cells held in a piezo-controlled micropipette that were brought (Left) into direct contact with an optically trapped Unit-aptamer coated bead or (Right) at a 1-μm distance from an RCA-aptamer coated bead. RCA-aptamers formed stronger bonds to the target cell than the maximum trap force (>40 pN and a force loading rate of ∼58 pN/s) as evidenced by the micropipette/cell pulling the bead out of the optical trap, whereas the Unit-aptamer system was unable to achieve this. Images were obtained with 40× oil immersion objective. (B) RCA-aptamer beads exhibited a much higher frequency of binding to target cells (100% for direct contact and 100% for 1-µm distance) than Unit-aptamer beads (29% for direct contact and 0% for a 1-µm distance).