We have developed a cantilevered probe chip called the Nano Fountain Probe (NFP) which can be mounted on commercial AFM equipment for the delivery of liquid solutions of chemical or biological molecules. The ultimate goal of this project is to develop a robust microsystem platform for the mass production of nanoscale devices, sensors and structures using chemicals, biomolecules, nanoparticles, nanotubes, and nanowires. Microfluidic transport of various molecular inks to AFM tips, with high throughput, is of main interest since fluid is a very effective medium for direct delivery of molecules, which self-assemble on substrates with very specific nanoscale architectures.

NFP chips on a wafer, Cantilevers and Apertured tip of an NFP

Each NFP chip makes use of two separate reservoirs, each connected via microfluidic channels to six cantilevers. At the end of each cantilever is a ring-shaped apertured tip consisting of a shell surrounding a core tip. The solution in the reservoir is driven by capillary action to the dispensing tips, forming an air-liquid interface at the aperture. Molecules from the interface diffuse along the core tip to the substrate. NFPs are fabricated on the wafer-scale using standard surface micromachining processes allowing for batch fabrication of numerous chips.

Our current efforts include:

1. establishing a protocol for the deposition of biomolecules and nanoparticles through self assembly or electrically driven deposition, and
2. computer modeling of fluidic transport and the transport of organic and/or inorganic molecules from probe tips to the substrate.

Direct Patterning of DNA

The NFP was employed for the direct deposition of hexanethiol-modified oligonucleotides on a gold substrate. After passivation of the unpatterned areas, the DNA spots were hybridized with complementary DNA-functionalized gold nanoparticles demonstrating that the patterned DNA maintained its biological activity. Features 200-300 nm in diameter were routinely achieved. Successful delivery of the biomolecules could be verified via AFM, optical dark-field imaging and scanning electron microscopy (SEM).

Schematic of experimental procedure for DNA patterning: (a) molecular ink feeding, (b) direct patterning of a Au surface with alkanethiol-modified oligonucleotides, (c) passivation of the unpatterned areas with C6 thiol to avoid unspecific binding, (d) hybridization of the linker and probe DNA strands. C) height profile of the same array, acquired in tapping mode operation. D) and E) SEM image of dot array and single dot, respectively. Multiple Au nanoparticles are visible in E).

Direct Deposition of Nanoparticles

Gold nanoparticles 10 and 15 nm in diameter were directly delivered by the NFP. The particles were immobilized via electrostatic interactions to silicon dioxide surfaced modified to be positively charged. Nanometer-scale dot and line features were fabricated. The same fountain probe can be used continuously to deposit the particles for over 40 minutes, with repeatable results. It is anticipated that the NFP will be able to construct conductive nanowires and other metal structures in the future.

Personnel

• H.D. Espinosa (PI)
• Owen Loh (Graduate Student)
• Jee Rim (Postdoc)

Collaborators

• D. Ho (Biomedical and Mechanical Engineering, NU)
• C. Mirkin (Chemistry, NU)
• I. Szleifer (Biomedical Engineering, NU)
• S. O'Brien (SEAS, Columbia University)
• P. Kohli (Chemistry, SIU)

Selected Publications

• K.-H. Kim, R.G. Sanedrin, A.M. Ho, S.W. Lee, N. Moldovan, C.A. Mirkin, H.D. Espinosa, "Direct Delivery and Submicrometer Patterning of DNA by a Nanofountain Probe," Advanced Materials, Vol. 20, No. 2, p. 330-334, 2008.

• B. Wu, A. Ho, N. Moldovan, H.D. Espinosa, "Direct Deposition and Assembly of Gold Colloidal Particles Using a Nanofountain Probe," Langmuir, Vol. 23, No. 17, p. 9120-9123, 2007.

• A. Ho, H.D. Espinosa, "Scanning Probes for the Life Sciences," Applied Scanning Probe Methods 8: Scanning Probe Microscopy Techniques, Edited by B. Bhushan, H. Fuchs, and T. Masahiko, Springer-Verlag, Heidelberg, 2008.

• N. Moldovan, K-H. Kim, and H.D. Espinosa. "Multi-Ink Linear Array of Nanofountain Probes." Journal of Micromechanics and Microengineering, Vol. 16, No. 10, p. 1935-1942, 2006.

• H.D. Espinosa, K.-H. Kim, and N. Moldovan, "Microcantilever-based Nanodevices in the Life Sciences." Nanotechnologies for the Life Sciences series, Vol.4: Nanodevices for the Life sciences. Edited by Challa S.S.R. Kumar. Willey-VCH Publishers, 2006.

• H.D. Espinosa, N. Moldovan, K.-H. Kim, "Novel AFM Nano Probes." Applied Scanning Probe Methods, Vol. 5: Scanning Probe Microscopy Techniques. Edited by B. Bhushan, H. Fuchs, and S. Kawata. Springer-Verlag, Heidelberg, to be published in 2007.

• N. Moldovan, K.-H. Kim, and H.D. Espinosa, "Design and Fabrication of a Novel Microfluidic Nanoprobe" JMEMS, 15 (2006) 204-213.

• K.-H. Kim, N. Moldovan, C. Ke, H.D. Espinosa, X. Xiao, J.A. Carlisle, and O. Auciello. "Novel Ultrananocrystalline Diamond Probes for High- Resolution Low-Wear Nanolithographic Techniques," Small, Vol. 1, No. 8-9, pp. 866-874, 2005.

• K.-H. Kim, N. Moldovan, and H.D. Espinosa. "A Nanofountain Probe with Sub-100 nm Molecular Writing Resolution," Small, Vol. 1, No. 6, pp. 632-635, 2005.

• K.-H. Kim, N. Moldovan, C. Ke and H. D. Espinosa. "A Novel AFM Chip for Fountain Pen Nanolithography - Design and Microfabrication," Materials Research Society Symposium Proceedings, Vol. 782, 2003, and Fall MRS Meeting, A5.56.1, 2004.

Patents

• H.D. Espinosa, and N.A. Moldovan, "Scanning Nanodispensing Device Using Cantilevers with Microchannels and Nanotips- Design and Fabrication." NU Disclosure No. 25075 (US patent application filed on 2006).

• H.D. Espinosa, N.A. Moldovan and K.-H. Kim, "Scanning Nanodispensing Device Using Cantilevers with Microchannels and Nanotips- Design and Fabrication." NU Disclosure No. 23014 (US patent application USSN 60/455,898, filed on March 19, 2003).