Fig. 4. (A) TEM image shows TPS ruler made using partial sequence of A9 aptamer where two nanoparticles are separated by thiolated 12 bp ds-RNA. (B) TEM image shows A9 aptamer attached gold nanoparticles are bound on PSMA positive LNCaP cells, when 100 cancer cells were added. It also shows that due to the presence of PSMA in LNCaP cells, most of the dsRNA is dehybridized. (C) Plot shows how the normalized TPS intensity (Inano-antenna2ω/Imonomer2ω) varies in the presence of different numbers of cells. Our result clearly shows that A9 aptamer based TPS ruler can be used for screening of PSMA (+) cancer cells selectively even at a concentration of 5 cells per mL.