Dynamic Nuclear Polarization (DNP) enhanced NMR spectroscopy has gained tremendous interest in recent years. At least that is what we, the scientist in this research area, like to think. However, is it true? One way to find out is to look at the number of research papers published in the area. I love data mining and below is the result of my latest analysis.
Although DNP was known from the early days of magnetic resonance, it took a long time for the methodology to find its way into the scientific repertoire. This is mainly due to the increased technical difficulties to develop the required double-resonance instrumentation, with frequencies that are almost three orders of magnitude apart.
In the 1960s and 1970s low-field (0.35 T, 9 GHz e-, 14 MHz 1H) solution and solid-state DNP spectroscopy was successfully used to study molecular motions. However, microwave technology could not keep up with the rapid pace at which NMR spectroscopy was moving to higher magnetic field strengths. As a consequence interest in DNP spectroscopy remained low until the early 1990s.
This changed dramatically in 1993 with the introduction of the gyrotron as a reliable, high-frequency, high-power microwave source by Griffin and Temkin et al. Also with the increased interest in high-field Electron Paramagnetic Resonance (EPR) spectroscopy, more microwave and THz components becoming available, and the introduction of the dissolution-DNP experiment by Ardenkær-Larsan et al. in 2003.
Today, commercial equipment for DNP-NMR spectroscopy is available at NMR frequencies between 300 and 800 MHz (1H NMR), and the interest in DNP, as seen in the number of articles published in the area, has increased exponentially. So far 2015 has seen the most publications in the area, let’s see if this trend will continue.
Note: This analysis is done using Google Scholar searching for the keywords “Dynamic Nuclear Polarization” and “Dynamic Nuclear Polarisation” excluding patents. All raw data are available upon request. Earlier studies using Scopus (Elsevier) have shown similar trends.