Infrared nanoscopy of structured SAMs

A challenging scientific task is the label-free and non-invasive investigation of molecules with a nanometer scale resolution. Due to the significant absorption lines in the infrared region - the so-called fingerprint region - a combination of apertureless near-field scanning optical microscopy with unique infrared laser spectroscopy provides a powerful method for spectroscopic characterization of self-assembled monolayers (SAMs) at the nanoscale. First experiments were performed on organic microstructured monolayers of octadecanethiol and biotinylated alkylthiol using a tunable CO-Laser as radiation source in the characteristic amide I region around 1700 cm-1. With our scanning near-field infrared microscopy (SNIM) we were able to record the frequency dependence of a single monolayer with a lateral resolution of 90 x 90 nm2 corresponding to /60 which is well below the Abbe limit. The detection limit for biotinylated alkylthiol was estimated to be 5x10-20 mol corresponding to 27 attogram.