To investigate the possibility of recovering fluorescence by complementary base pairing, we measured the fluorescence emission of a mixture of DFNS-20@DA and FAM-ssDNA, before and after addition of a complementary ssDNA (cDNA). As shown in Fig. , the fluorescence of FAM-ssDNA (200 nM) was quenched by DFNS-20@DA (arrow a in Fig. ). After addition of the cDNA (200 nM), nearly 50% of the fluorescence was recovered (arrow b in Fig. ), indicating that hybridized dsDNA formed and detached from DFNS-20@DA. When the uncoated DFNS-20 was tested under the same condition, the nanosilica was not able to quench the fluorescence from FAM-ssDNA (Fig. ). These results demonstrate the high sensitivity and specificity of the DFNS@DA-based "turn-on" fluorescence sensor.