Abstract
Chemical force microscopy analyzes the interactions between various chemical/biochemical moieties in situ. In this work we examined force-distance curves and lateral force to measure the interaction between modified AFM tips and differently functionalized molecular monolayers. Especially for the measurements in gas phase, we investigated the effect of humidity on the analysis of force-distance curves and the images in lateral force mode. Flat chemical patterns composed of different functional groups were made through micro-contact printing and lateral force mode provided more resolved analysis of the chemical patterns. From the images of 1-octadecanethiol/11-mercapto-1-undecanoic acid patterns, the amine group functionalized tip brought out higher contrast of the patterns than an intact silicon nitride tip owing to the additional chemical interaction between carboxyl and amine groups. For more complex chemical interactions, relative chemical affinities toward specific peptides were assessed on the pattern of 1-octadecanethiol/phenyl-terminated alkanethiol. The lateral image of chemical force microscopy reflected specific preference of a peptide to phenyl group as well as the hydrophobic interaction.
Highlights
Chemical force microscopy (CFM), derived from atomic force microscopy (AFM), works under atmospheric or aqueous environments with high spatial resolution and force sensitivity
To analyze the delicate affinity between molecules, two modes of scanning were evaluated in parallel: force-distance curve and lateral force mode
Lateral forces on each chemical zone were ranked in the order ODT > Phenyl terminated alkanethiol (PTA) > bare Au both with a random peptide and with benzene-specific peptide consistently, which can be explained with the hydrophobic alanine and valine at the outer ends of the two peptides
Summary
Chemical force microscopy (CFM), derived from atomic force microscopy (AFM), works under atmospheric or aqueous environments with high spatial resolution and force sensitivity. Measurements of chemical forces in the gas phase are important for evaluating specific molecules recognizing certain gas targets Those measurements are applicable to an increasing number of scientific studies reporting various types of recognizing molecules such as oligonucleotides, oligopeptides, and protein receptors that interact selectively toward gaseous organic molecules [8,9,10,11,12]. Comparison of interactions between receptors and target in the gas phase is still challenging due to weak binding between the molecules These specific interactions have been analyzed by Fourier transform infrared spectroscopy (FTIR) and AFM [13,14]. We integrated a gas control system (Supplementary Information, Figure S1) and measured force-distant curves and lateral force to evaluate the interaction between chemically-modified AFM tips and differently functionalized organic molecular monolayers, as shown in Scheme 1. The schematic presentation of the strategy for fabricating a mixed organic pattern and analysis by AFM. (a) Preparation of gold ball tip modification using thiolated peptide. (b) Chemical was printed on a bare gold surface and the second stamp was printed the surface sequentially. (c) The chemical pattern was analyzed by AFM
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
