To systematically study the GNPs-enhanced PL enhancement from GaAs with the DNA bridge, we explored series of different complementary DNA molecules ranging from 5 to 30 bases in length (see Fig. 1 for the DNA sequences). Each DNA duplex was attached onto GaAs and then adsorbed the GNPs (step 1 in Fig. 1). The effect of GNPs on the PL properties of GaAs was studied (Fig. 3A). As can be seen, the PL emissions at ∼875 nm became more intense, and the PL emission intensities were dependent on the DNAlength between GNPs and GaAs. The stronger PL emission was observed when the shorter DNA was used relative to longer oligomers. Next, we used the simple model reported by Clegg et al. to evaluatethe separation distance between the GaAs and the GNPs 0005 and 0095. As described by Hagermanet al., the duplex DNA with less than 100 base pairs can be modeled as a rigidrod-like molecule [6]. Thus, the length of duplex DNA is increased in 0.32 nm with the addition of each DNA base pair. 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).