Consequently, we can assume that the separation between GaAs and GNPs can be tuned easily by changing the dsDNA length. If taking no account of the size of the GNPs, Au–S distance and GaAs-S distance, the separation between GaAs and GNPs was systematically varied by changing the number of base pairs. Fig. 3B presents the enhanced PL emission at ∼875 nm of the different GaAs substrates as functions of thedifferent length of DNAs between GNPs and GaAs. An approximately 20-fold enhancement in the PL intensity compared to untreated GaAs was measured for 5 bp DNA used, corresponding to a distance of ∼2 nm between the GNPs and the GaAs. While only a lower PL enhancement (8 fold) for 30 bp of DNA used,which means a ∼10 nm distance. And, no obvious fluorescence signal was obtained from pure GNPs (data not shown here).