Recently, the development of single-molecule spectroscopic imaging has enabled local chemical polarity sensing at single-molecule level, which has been masked in the ensemble averages of bulk measurements. However, such a single-molecule polarity sensing method (i.e. Nile red) often yields out of the expected values from solvatochromism since the specific intermolecular forces between dye and solvent molecules in a given system may introduce a further shift of the dye spectrum, thereby limiting the precise determination of the chemical properties of individual molecules. Herein, we developed a new single-molecule sensing approach to probe the nature of the local hydrogen bonding with surrounding molecules at the single-molecule level by employing single-molecule spectroscopic imaging and a Nile blue dye as a single-molecule sensor. By separately probing each non-specific and specific interactions between a Nile blue molecule and surrounding molecules, we could clearly differentiate their hydrogen-bonding characteristics at the single-molecule level, even for the solvent mixtures. We believe that our new chemical sensing approach can enable the examination of various local chemical environments surrounding single molecules of interest that are inaccessible by conventional sensing methods.

Development of nanoscale hydrogen-bonding sensing method using single-molecule spectroscopic imaging

ACS Spring 2022

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