My research project combines two major topics, i.e., (1) synthesis and functionalization of nanoparticles and (2) use of β-cylcodextrin (CD) self-assembled monolayers (SAM) on gold and silicon oxide substrates as molecular printboard to chemically-direct nanoparticles assembly on substrate via supramolecular interactions. Supramolecular chemistry is particularly attractive as it possesses controllable molecular recognition abilities with the possibility for correction.1
The synthesis and functionalization of nanoparticles involve the design and controlled synthesis of nanoparticles with special surface functional groups that are spaced sufficiently for addressing of ordered nanoparticles. As shown in Figure 1, CD-functionalized gold, silica and poly(styrene-co-acrylic acid) and ferrocenyl-functionalized silica nanoparticles were prepared.2,3,4,5 The CD-functionalized nanoparticles can be were assembled onto CD SAMs, by using adamantyl- or ferrocenyl-functionalized dendrimers as a noncovalent supramolecular glue,6 whereas the ferrocenyl-functionalized nanoparticles can be directly adsorbed onto molecular printboards via host-guest recognition.
Figure 1. Various CD-functionalized nanoparticles and ferrocenyl-functionalized nanoparticle.
To compare the packing order and density of the nanoparticle lattices as a result of different binding affinities between the nanoparticles and the surfaces. The formation of particle monolayers by convective assembly on native oxide surfaces, with additional electrostatic interactions, and with supramolecular host-guest interactions were studied in-situ.4
Particle lattices on native oxide surfaces formed the best hexagonal close packed (hcp) order, and could be easily desorbed by reducing the temperature to below dew point. The electrostatically modified assembly resulted in densely packed, but disordered particle lattices. The specificity and selectivity of the supramolecular assembly process were optimized using ferrocenyl-functionalized dendrimers of low generation and by the introduction of competitive interaction by native b-CD molecules during the assembly. The fine-tuned supramolecularly formed particle lattices were nearly hcp packed. The supramolecularly formed lattices of particles were strongly attached to the surfaces and could not be removed by condensation.
Figure 2. SEM micrographs of the assembled particles formed by via pure convective assembly (A), with additional electrostatic interactions (B), with supramolecular interactions (C) and fine-tuned supramolecular interactions (D).
The chemically directed assembly of functionalized nanoparticles on desired patterned substrate is anticipated to construct an ordered array of chemically, optically and geometrically tunable nanostructured building blocks. These ordered nanostructured building blocks are potentially useful in development of novel technologies, such as optical data processing, molecular electronics, quantum computing, etc.
1. Reinhoudt, D. N.; Crego-Calama, M. Science 2002, 295, 2403.
2. Crespo-Biel, O.; Dordi, B.; Reinhoudt, D. N.; Huskens, J. J. Am. Chem. Soc. 2005, 127, 7594.
3. Mahalingam, V.; Onclin, S.; Peter, M.; Ravoo, B. J.; Huskens, J.; Reinhoudt, D. N. Langmuir 2004, 20, 11756.
4. Ling, X. Y.; Malaquin, L.; Reinhoudt, D. N.; Wolf, H.; Huskens, J. Langmuir 2007, 23, 9990.
5. Ling, X. Y.; Reinhoudt, D. N.; Huskens, J. Langmuir 2006, 22, 8777.
6. Nijhuis, C. A.; Huskens, J.; Reinhoudt, D. N. J. Am. Chem. Soc. 2004, 126, 12266.