Where does nanotechnology belong in the map of science?

It is commonplace to read that nanoscience and nanotechnology are highly multidisciplinary, and that the convergence of nanotechnology, biotechnology, information technology and cognitive sciences (NBIC) will lead to big changes in many aspects of our lives and modern society1,2. Understanding the multidisciplinary nature of nanoscience and nanotechnology, and their relationships with other areas of research, is therefore important for science policy, funding, research management and effective knowledge transfer. A number of researchers have used bibliometric techniques to explore this multidisciplinary nature. For example, an analysis of the Science Citation Index (SCI; a database containing information on about 6,650 journals in most fields of science3) that used phrases and citations to search for topical structures in the nanoliterature showed that nanotechnology (as defined in refs 4 and 5) encompassed a range of diverse applications4,5. A study of a large government-funded nanotechnology project in Japan that examined publication patterns, and also looked at the extent of knowledge transfer between technology and science, concluded that the project had been notably interdisciplinary6. In May 2008, Grodal and Thoma presented another study at the National Bureau of Economic Research conference on ‘Emerging Industries: Nanotechnology and NanoIndicators’ that tracked the migration of detailed concepts through large datasets of publications (using SCI), patents (from the US Patent and Trade Office) and press releases (Lexis-Nexis). They found that the cross-pollination of knowledge between nanotechnology and biotechnology had instigated the rapid emergence of a new field called nanobiotechnology (S. Grodal & G. Thoma, personal communication). However, a different study of patent data concluded that much of the apparent convergence of nanotechnology and biotechnology to give nanobiotechnology was due to the use of common instrumentation, rather than true interdisciplinarity7. Furthermore, a project that used SCI subject categories to examine 600 nanotechnology papers published in 2002 and 2003 concluded that “under the umbrella of ‘nano’, classical disciplinary patterns have continued or reproduced themselves without much interaction between them”8. Here we explore the cross-disciplinary nature of research in nanoscience and nanotechnology with a combination of metrics and maps. Previously we had developed a Boolean search strategy to retrieve the abstracts of nanoscience and nanotechnology papers from the SCI (see Methods and ref. 9), profiled this nanoliterature in terms of its interactions with the other fields of research it engaged, studied its evolution over time, and explored modes of interchange of research knowledge in the nanoliterature10. In this paper we use our Boolean approach to extract the abstracts of nanotechnology papers published in the period January–July 2008 (a total of 30,762 papers, hereafter called nanopapers or the nanoliterature), and then ask two questions: how broadly does this nanoliterature engage with the rest of the literature; and to what extent does the nanoliterature integrate knowledge from multiple disciplines? To address the first question, we use the 175 subject categories in the SCI as Materials Engineering Agricultural Infectious diseases Ecological