Standardizing Nanomaterials
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It is now time for the nanomaterials community to consolidate and to agree on methods of characterization and minimum levels of analysis of materials. These methods and analyses may need to be updated as Peck and Gale did in their review, but systematic procedures and protocols recognized and demanded by research journals would create well-defined benchmarks for the field. A further benefit of prescribed characterization methods and reporting of properties is a dramatic reduction in the duplication of known synthetic steps in manuscripts. Many manuscripts reproduce well-understood procedures as part of the research outcomes, whereas they are really part of the everyday workload of the chemist. Many figures and outcomes from research could readily be relegated to Supporting Information sections, as is common in organic chemistry, where absorption spectra, nuclear magnetic resonance (NMR) spectra, X-ray data, and infrared (IR) spectra are routinely carried out but are subsumed into the SI for the interested reader.
ne of the greatest challenges in materials science is determining how best to characterize the increasing numbers of complex structures and materials being created by chemists, physicists, and engineers. Without agreed upon methods of characterization, both reproducibility and quality control are rendered impossible, and the impact of the entire field is endangered by the inability to replicate data, syntheses, and properties. Where these properties are to be applied, in catalysis, energy conversion, photonics, sensors, and elsewhere, or modeled and understood with theory and simulation, having standards of characterization would enable better connections between laboratories and between synthesis, understanding, and application. While the incredible diversity of materials that can be created by molecular synthesis is one of the most appealing aspects of the field, this panorama of possibilities also poses challenges. The field of organic chemistry has long had highly established methods for characterizing new chemical compounds, and refining those processes and protocols has been going on for close to a century. Conversely, the global fascination with nanoscale materials has not been accompanied by the same degree of rigor, and the nanomaterials community has been much slower to standardize characterization procedures and requirements. In an update on methods for organic compound characterization in 1952, Peck and Gale pointed out that “The accepted requirements for full characterization of an organic compound include establishment of purity of sample, determination, of physical properties, determination of elementary composition, functional groups, and empirical formula, and elucidation of structural formula and spatial relationships.”1 This thought was written well over half a century ago, but few papers on nanoscale materials today would meet these ideal requirements.
A further benefit of prescribed characterization methods and reporting of properties is a dramatic reduction in the duplication of known synthetic steps in manuscripts. A further consequence of this lack of rigor has been the use of “chemicals as supplied”. This route has actually slowed down research in some cases since it has turned out that impurities in solvents such as trioctylphosphine oxide (TOPO) or surfactants such as cetrimonium bromide (CTAB) had significant and dominating effects on the outcomes of chemical reactions.2 Poor characterization and lack of purification meant that it took considerable time for these problems to be recognized. Inorganic chemists tended to focus on characterization of the inorganic materials under investigation with the result that organic chemical effects were often not recognized. The American Chemical Society (ACS) publishes the broadest range of chemistry research across the globe. Many ACS journals publish manuscripts on complex materials. It is appropriate to consider creating a prescribed or expected set of characterization requirements for publication that takes into account the nature of modern chemical research into complex nanomaterials and the wide range of new tools available for characterization such as scanning probe and electron microscopy. Having authors put more basic characterization into Supporting Information would allow them to focus on the novelty of their research. Thereby, we may define suitable benchmarks for publication within the ACS journals. Due to the larger variety of nanomaterials, there is not one single characterization method for all materials. Often, for the
It is now time for the nanomaterials community to consolidate and to agree on methods of characterization and minimum levels of analysis of materials. One reason for this situation is that nanoscale materials are often fabricated or synthesized in different ways, sometimes by biologists, sometimes by physicists or engineers, and of course also by chemists. Each group has preferred processes and methods. Different dimensions, compositions, and structural hierarchies are involved, and materials may be amorphous, composite, or polycrystalline. Another issue is that nanoscale materials may be formed as thin films, dry powders, or solutiondispersed materials. Common characterization methods are neither obvious nor applicable to all different classes of nanomaterials. We note that protein chemists faced with the analogous difficulties of characterization recognized and agreed on the need for the arduous process of protein crystallization in order to carry out X-ray diffraction of protein structures. © 2016 American Chemical Society
Published: November 22, 2016 9763
DOI: 10.1021/acsnano.6b07629 ACS Nano 2016, 10, 9763−9764
Editorial
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characterization of certain properties, several similar or methodologies exist that give similar or related information. Concerning structural properties of nanomaterials, transmission electron microscopy (TEM), scanning electron microscopy (SEM), scanning tunnelling microscopy (STM), atomic force microscopy (AFM), electron diffraction pattern, X-ray diffraction (XRD), NMR, Fourier-transformed IR spectroscopy (FTIR), thermal gravimetry analysis (TGA), quartz crystal microbalance (QCM), inductively coupled plasma mass spectrometry (ICP-MS), elemental analysis, etc. are standard techniques. For nanomaterials dispersed in solvent, colloidal properties should also be investigated, in the solvent in which the nanomaterials will be applied. Typical characterization methods include dynamic light scattering (DLS), fluorescence correlation spectroscopy (FCS), titration against salt and pH, absorption spectroscopy, column chromatography, gel electrophoresis, etc. Where the sizes of the nanomaterials in solvent are bigger than the structural sizes, agglomeration has most likely occurred. Notably, there is also not only one “size” for nanomaterials, but different methods will lead to different “types” of sizes.3 For fluorescent nanomaterials, optical characterization should be performed, such as ultraviolet/ visible absorption spectra, fluorescence spectra, determination of quantum yield, etc. The nature of the respective study will largely determine which are the best characterization techniques to apply. However, using standard characterization is a good way to benchmark “new” nanomaterials against existing ones.
Editorial
REFERENCES
(1) Peck, R. L.; Gale, P. H. Characterization of Organic Compounds. Anal. Chem. 1952, 24, 116−120. (2) Leonov, A. P.; Zheng, J.; Clogston, J. D.; Stern, S. T.; Patri, A. K.; Wei, A. Detoxification of Gold Nanorods by Treatment with Polystyrenesulfonate. ACS Nano 2008, 2, 2481−2488. (3) Sperling, R. A.; Liedl, T.; Duhr, S.; Kudera, S.; Zanella, M.; Lin, C.-A. J.; Chang, W. H.; Braun, D.; Parak, W. J. Size Determination of (Bio-) Conjugated Water-Soluble Colloidal Nanoparticles: A Comparison of Different Techniques. J. Phys. Chem. C 2007, 111, 11552−11559.
Paul Mulvaney, Associate Editor
Wolfgang J. Parak, Associate Editor
Frank Caruso, Associate Editor, Chemistry of Materials
Paul S. Weiss, Editor-in-Chief
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AUTHOR INFORMATION
ORCID
Paul Mulvaney: 0000-0002-8007-3247 Wolfgang J. Parak: 0000-0003-1672-6650 Frank Caruso: 0000-0002-0197-497X Paul S. Weiss: 0000-0001-5527-6248 Notes
Views expressed in this editorial are those of the authors and not necessarily the views of the ACS. 9764
DOI: 10.1021/acsnano.6b07629 ACS Nano 2016, 10, 9763−9764
