a) Fluorescence intensity of A549 cells measured after incubation with Ap1 or Ap2 at a series of concentrations (e.g., 0–400 × 10−9 M). b) Comparisons of flow cytometry results of A549 cells after incubation with different aptamer solutions containing: (i) Ap1 200 × 10−9 M, Ap1 400 × 10−9 M, or Ap1 200 × 10−9 M plus Ap2 200 × 10−9 M; (ii) Ap2 200 × 10−9 M, Ap2 400 × 10−9 M, or Ap1 200 × 10−9 M plus Ap2 200 × 10−9 M. c) The capture efficiency of A549 cells of SiNS with different aptamer densities, which were achieved by mixing a scramble DNA sequence Rc and aptamer Ap1 at various proportions during surface modification.