Role of the external NH2 linker on the conformation of surface immobilized single strand DNA probes and their SERS detection

- Comparison of SERS spectra of DNA polybase probes immobilized on Ag nanoparticles.
- Highlighting the conformation of immobilized DNA probes molecules.
- The external amino linker has a preponderant role for extended and oriented probes.
- Extended and oriented probes are presumed to be more suited for DNA hybridization.

The conformation and topological properties of DNA single strand probe molecules attached on solid surfaces are important, notably for the performances of devices such as biosensors. Commonly, the DNA probes are tethered to the surface using external linkers such as NH2. In this study, the role and influence of this amino-linker on the immobilization way and conformation of DNA probes on Ag nanoparticle surface is emphasized using Surface Enhanced Raman Spectroscopy (SERS). We compare the SERS spectra and their reproducibility in the case of two groups of DNA polybase probes which are polyA, polyC, polyT, and polyG. In the first group, the polybases exhibit an external NH2 functional linker while in the second group the polybases are NH2-free. The results show that the reproducibility of SERS spectra is enhanced in the case of the first group. It leads us to propose two models of polybase conformation on Ag surface according to the presence or the absence of the external NH2 linker. In the presence of the NH2 external linker, the latter would act as a major anchoring point. As a result, the polybases are much ordered with a less random orientation than in the case of NH2-free polybases. Consequently, in view of further in situ hybridization for biosensing applications, it is strongly recommended to use NH2 linker functionalized DNA probes.