One of the winning images of the 2014 Nano Today Cover Competition. Look out for more cover competition winners, here on Materials Today.

The new issue of Nano Today (Volume 9, Issue 5) is out now. Click here to read the articles.

FE-SEM image of MnSO4 salt micro-bowls

The synthesis of inorganic materials with complex patterns will have significant implications in separation, catalysis and biomedicine [1]. Inorganic biominerals are known to display stunning structural patterns at different length scales, defying their rigid geometric symmetry [2–4]. Mimicking such complex forms in inorganic synthesis is still a challenging task, though the guiding principles involved in the formation of many biological minerals are more understood now than ever before. Nevertheless, some progress has been made in generating inorganic structures with complex forms and patterns by mimicking the biological design principles [5]. Synergistic synthesis, transcriptive synthesis, metamorphic reconstruction and microphase separation mechanisms are usually identified with inorganic morphosynthesis [1, 6]. For example, the synergistic assembly of organic and inorganic molecules has been the basis for the formation of zeolites and meso-structured materials [7]. To take the complexity to higher levels, vesicle-based synthesis, in which nature masters the art of patterning skeletons at multiple length-scales in a spatio–temporal process, has been used to create mesoscale inorganic structures of different shapes and patterns [8]. Assembly of inorganic nanoparticles into mesoscale structures was possible by template directed or surfactant/polymer mediated self-assembly process [9–11]. Similarly, individual components of micrometer and millimeter sizes have also been tailored to self-assemble (mesoscale self-assembly) into complex 3-D structures through capillary, electrostatic, optical, gravitational or magnetic interactions [11]. However, the great challenge in making individual components of different shapes other than spherical and plate like forms limit this strategy in microfabrication [12].

The cover image on volume 9, Issue 5 of Nano Today shows mesoscale MnSO4 salt micro-bowls produced through a thermolysis route [13]. This field emission-scanning electron microscope (FE-SEM) image shows an array of Manganous Sulfate (MnSO4.H2O) salt micro-bowls formed from the controlled calcination of MnSO4-polyvinylpyrrolidone composite film at 550 °C for 5h with a heating rate of 1 °C min-1. Since the decomposition temperature of the MnSO4 salt is around 850 °C, MnSO4 salt doesn’t undergo any change at 550 °C, except for the loss of water of crystallization from the precursor, MnSO4.H2O. Calcination also removes the polymer, polyvinylpyrrolidone with spontaneous formation of ordered, mesoscale structures made up of inorganic salt micro-bowls. These tiny bowls are generating a lot of interest due to their unique application as ‘containers’ to hold ultra-low volumes. Arrays of these ultra-low volume containers are applied in molecular biology [14] for screening and the bio-sensing of proteins and DNA. The spontaneously formed salt micro-bowls through this simple synthesis were water-soluble and were also used as a soluble template to obtain gold bowls.

The material was synthesized at Nanomaterials and Catalysis Laboratory, Chemistry and Physics of Materials Unit, Jawaharlal Nehru Center for Advanced Scientific Research, India.


  1.  S. Mann, G. A. Ozin, Nature, 1996, 382, 313.
  2.  G.A.Ozin, Acc. Chem. Res., 1997, 30, 17.
  3.  S.Mann, Angew. Chem., Int. Ed., 2000, 39, 3392.
  4.  C. Sanchez, H. Arribart, M. G. Guille, Nat. Mater., 2005, 4, 277.
  5.  S. Mann, Biomineralization: Principles and Concepts in Bioinorganic Materials Chemistry, Oxford University Press, Oxford, 2001.
  6.  H. Yang, N. Coombs, G. A. Ozin, Nature, 1997, 386, 692.
  7.  C. T. Kresge, M. Leonowicz, W. J. Roth, J. C. Vartuli and J. C. Beck, Nature, 1992, 359, 710.
  8.  E. Dujardin, S. Mann, Adv. Eng. Mater., 2002, 4, 461.
  9.  M. Li, H. Schnablegger S. Mann, Nature, 1999, 402, 393.
  10.  H. Cölfen, S. H. Yu, MRS Bull., 2005, 30, 727.
  11.  M. Boncheva, G. M. Whitesides, MRS Bull., 2005, 30, 736.
  12.  G. M. Whitesides, M. Boncheva, Proc. Natl. Acad. Sci. U. S. A., 2002, 99, 4769.
  13. K. S. Krishna, B. V. V. S. P. Kumar, M. Eswaramoorthy, RSC Adv., 2012, 2, 5947–5949.
  14. Y. Rondelez, G. Tresset, K. V. Tabata, H. Arata, H. Fujita, S. Takeuchi, H. Noji, Nat. Biotechnol., 2005, 23, 361.