Oligonucleotides are small pieces of DNA or RNA with a specific sequence. This sequence results in a unique 3D structure which determines their function, but better methods are needed to study this structure. Oligonucleotides occur naturally and are essential in all life forms, but can also be made synthetically. They play a role in e.g. gene regulation, but also in the defence against bacterial and viral infections, and are therefore interesting targets for therapeutic purposes. Synthetic oligonucleotides called aptamers, which can interact with specific molecules, are now also considered for sensor applications. There is a rapidly growing need for efficient and fast methods for the characterization of oligonucleotide sequence, modifications, interactions and 3D structure. I propose an approach, which is now well-established for proteins but new for oligonucleotides, that can specify some of these characteristics and will lead to a better understanding of the sequence-structure-function relationship of DNA/RNA. In addition, understanding these structural properties will result in the ability to better design synthetic oligonucleotides in the future. By gaining insights in the structure and function of oligonucleotides, it becomes possible to use them in various applications such as sensors, for targeted drug delivery and the development of new antibody-like drugs which will result in better and more targeted treatment of diseases.