The study of non-equilibrium systems has led to several mathematically rigorous and general results on the statistics of entropy production in non-equilibrium systems. These results are generally known under the name of 'fluctuation theorems' and include the Gallavotti-Cohen theorem or the Jarzynski equality. My research focuses on performing experiments in which such results can be tested in real physical systems. I am interested in assessing their range of validity but even more interested in exploiting them to develop new measurement techniques. I will present some recent experiments, in which focused laser beams (optical tweezers) are used to perform thermodynamic transformations on single DNA molecules. As a first example I will show how to use fluctuation theorems to measure the free energy change across the transformation. As a second example I will discuss how, in specific cases, fluctuation theorems can be used to measure the full entropy production in a nano-scale system starting from a partial measurement through what we call an 'inference' procedure. This last example provides a new and general application of fluctuation theorems which we are only beginning to explore.