Research in the materials and surfaces subgroup in the Rotello Group focuses on the development and manufacturing of functional patterned substrates for nanoelectronics, biosensing, and security applications. By using techniques such as nanoimprint lithography and inkjet printing along with our extensive knowledge of functionalized nanoparticles, we can create low cost materials that are compatible with roll to roll manufacturing. We also are interested in supramolecular assemblies and their impact in photovoltaic applications.

  • Inkjet Printing
  • Inkjet printing is a low cost mature roll-to-roll manufacturing technique for creating microscale patterns on surfaces. The Rotello Group has recently deposited functionalized gold nanoparticles (AuNPs) onto conductive surfaces for anti-counterfeiting applications using inkjet printing. This “mass barcode” can be detect the AuNPs by laser desorption ionization mass spectrometry imaging – a method to determine the spatial distribution of particles based on their mass. By incorporating ligands of varying alkyl chain length that alters the overall mass into the nanoparticle, the area can be selectively scanned for a particular mass. By combining the different nanoparticles onto a surface using inkjet printing enables a complex signature that can be visualized only when all the nanoparticles are scanned.

    General scheme for nanoparticle security printing using inkjet printing. To prove that this system works, we printed two different patterns on one surface using AuNPs with differing ligands. A) shows the visualized response searching for the mass of gold, b) is the image searching the surface for one of the printed AuNP, and c) shows the surface searching for the second.

    The Rotello Group is also developing low cost inkjet printed bacterial test strips for recreational and drinking water using nanoparticles. By using the multiple inherent channels of the printer along with chemically modifying the surface of the particle, colorimetric determination of the overall concentration of bacteria can be obtained.

    Schematic design of a new bacteria sensing test strip for drinking water via inkjet printing.

  • Nanoimprint Lithography (NIL)
  • Nanoimprint lithography (NIL) has emerged as particularly promising technique for printing features on surfaces on the order of 50nm. In our research, we have used NIL to deposit a wide range of nanoparticles and polymers onto surfaces to create functional surfaces and devices. Recently, we have demonstrated that ionically functionalized AuNPs can be thermally imprinted using NIL to form stable shapes and surface patterns. These particle films are amorphous, providing enhanced processability and imprintability. Significantly, these films retain the electronic properties of the nanoparticles, allowing direct fabrication of light modulated devices.

    Functionalized AuNPs not only show the ability to be imprinted into stable features, but can also be used for applications such as light modulated devices.

    For tissue engineering and biomedical applications, we have reported the use of NIL and AuNPs to create biocompatible surfaces. The topology provided by AuNP-based surfaces provides enhanced cell viability and adhesion relative to planar surfaces. These surfaces could then be patterned via NIL to generate scaffolds that provide essentially complete control over the cellular alignment.

    Biocompatible surfaces are generated to provide protein nonfouling patterns, offering direct communication to the cells for controlling cell adhesion and proliferation.

  • Supramolecular Assemblies
  • The organization of nanoparticles into assembled and ordered structures is critical for optoelectronics, photovoltaics, and catalysis. For many years, we have investigated the use of supramolecular interactions such as flavin/diaminopyridine (DAP) to drive assembly of polymers and nanoparticles. In one recent work, we have shown that recognition-mediated self-assembly between ZnSe quantum dots (QDs) and a complementary polymer featuring DAP and flavin moieties is possible in solution and solid states. The assembly process was based upon three point hydrogen bonding between the moieties attached to the QDs and the DAP moieties of the polymer. Importantly, similar properties were extended to the solid state as thin films of QDs–polymer nanocomposite also displayed significant fluorescence resonance energy transfer (FRET). This methodology of producing self-assembled structures both in solution and solid state provides a powerful tool for the creation of highly structured multifunctional materials and devices.

    The Rotello Group has demonstrated fluorescence resonance energy transfer facilitated by recognition mediated assembly of quantum dots and a tailor-made fluorescent polymer.

    Selected References:

    1) Creran, B.; Yan, B.; Moyano, D. F.; Gilbert, M. M.; Vachet, R. W.; Rotello, V. M. “Laser Desorption Ionization Mass Spectrometric Imaging of Mass Barcoded Gold Nanoparticles for Security Applications” Chem. Commun. 2012, 48, 4543-4545.
    2) Yu, X.; Pham, J. T.; Subramani, C.; Creran, B.; Yeh, Y.-C.; Du, K.; Patra, D.; Miranda, O. R.; Crosby, A. J.; Rotello, V. M. “Direct Patterning of Engineered Ionic Gold Nanoparticles via Nanoimprint Lithography” Adv. Mater. 2012, 24, 6330-6334.
    3) Subramani, C.; Saha, K.; Creran, B.; Bajaj, A.; Moyano, D. F.; Wang, H.; Rotello, V. M. “Cell Alignment using Patterned Biocompatible Gold Nanoparticle Templates” Small 2012, 8, 1209-1213.
    4) Nandwana, V.; Fitzpatrick, B.; Liu, Q.; Solntsev, K.; Yu, X.; Tonga, G. Y.; Eymur, S.; Tonga, M.; Cooke, G.; Rotello, V. M. “Fluorescence Resonance Energy Transfer in Recognition-mediated Polymer-quantum Dot Assemblies” Polym. Chem. 2012, 3, 3072-3076.