Nanoscopy

The development of novel DNA sequencing methods is still one of the ongoing challenges in various fields of research to address the demand for sequence information. However, many of these techniques rely on some kind of labelling or amplification steps. Here we investigate the intrinsic properties of tip-enhanced Raman scattering (TERS) towards the development of a novel label-free direct sequencing method. It is known that TERS allows the acquisition of spectral information with high lateral resolution and single molecule sensitivity. In the presented experiments single stranded adenine and uracil homopolymers were immobilized on different kinds of substrates (mica and gold nanoplates, respectively) and TERS experiments were conducted, which demonstrate the reproducibility of the technique. To elucidate the signal contributions of the specific nucleobases TERS spectra were collected on single stranded calf thymus DNA with arbitrary sequence. The results show that while the Raman signals with respect to the four nucleobases differ remarkably, specific markers can be determined for each respective base. The combination of sensitivity and reproducibility shows that crucial demands for a sequencing procedure are met.