Invited Paper SS2-TuA8
Scanning Near Field Infrared Microsocopy (SNIM) – Combining Topographical and Chemical Mapping of Bio Materials

Tuesday, October 21, 2008, 4:00 pm, Room 209

We have set-up a scanning near field microscope (SNIM) in Bochum. As radiation source serves an Infrared Opto Parametric Oscillator (IR-OPO) and a CO laser. This allows us to cover the chemically important frequency range of the amide bands and the C-H and O-H stretching region. In 2007 our group has reported chemical imaging of microstructure self-assembled monolayers (SAMs) with nanometre resolution¹ using SNIM. This study demonstrated the extreme sensitivity of SNIM which even allowed recording the IR spectrum of a single monolayer of a specific absorbing functional group (biotin). Our measurements were carried out on a microcontact printed line pattern of a monomolecular film of biotinylated alkylthiolates. Whereas in conventional IR microscopy, about 1 μm thick layers of protein sample are required in order to record a full IR spectrum, here the IR fingerprint spectrum of approximately 30 000 biotin molecules in a 90 nm by 90nm patch of 3.7 nm height were detected. Biotin can also be considered as a model system for more complex protein systems. Further applications include the use for label-free analysis of biochips on the nano-scale. The possibility of simultaneously accessing topographic and spectroscopic information from biological nanostructures could be the basis for a new generation of nanodevices e.g. for medical diagnostics. As a proof-of-principle we demonstrate the feasibility of detecting hybridization reactions in nanostructured DNA-patches. For the DNA nanofabrication process we use nanografting which is a scanning probe microscopy based lithography technique. The nanografted single stranded nano structures can be clearly detected within the double stranded self assembled monolayers due to their distinct IR frequency response. Moreover, even nanografted double stranded nanostructures can be imaged since they have a higher packing density, yielding increased IR absorption in the corresponding amide band. This work is carried out in cooperation with the group of L. Casalis and G. Scoles at ELETTRA.

¹ I. Kopf, J.-S. Samson, G. Wollny, Ch. Grunwald, E. Bründermann, and M. Havenith, Chemical imaging of microstructured self-assembled monolayers (SAMs) with subwavelength resolution, J. Phys. Chem. C, 111 (23), 8166-8171 (2007).