Single molecule manipulation techniques measurements

The techniques involved are single-molecule spectroscopy including optical (fluorescence) methods and single-molecule mechanical manipulation including scanning probe techniques (e.g., force measurements). 

Using a combination of manipulation techniques together with tunneling spectroscopy measurements, a number of chemical reactions have been induced on single molecules leading to the synthesis of new chemical products [39,47,48]. 

In summary of this section, it can be said that experimental manipulations and conductance measurements on single molecules are still a big scientific challenge, and a lot of the progress that has been recently made has been achieved for particular substrate/molecule systems and can not be easily transferred to other surface materials or types of molecules. The STM is certainly the most versatile instrument for manipulations and measurements on the nanoscale but it is not very suitable for an integration into nano-electronic devices. New techniques such as mechanically controlled break-junctions will have to be further developed for this purpose in the future. 

Finally, plans to build any type of polymer sequencing platform around the methods discussed here will involve ion current manipulation of analytes. Indeed, ion current measurements make an excellent analytical tool by themselves and have already been applied to single-molecule DNA sequencing. There is much yet to be done in integrating electronic and ionic techniques, a topic for a future review. 

STM measurements on molecular junctions in solution have been realized by groups in Miami [66], Lyngby [34] and Liverpool [33, 67]. Performing the STM experiments in a liquid environment provides a way to combine well-established electrochemical techniques with in situ electronic STM characterization of a single or a small number of molecules. One particular advantage of this approach is the option to use an electrochemical reference electrode as a third electrode (gate) in the setup in addition to the tip and substrate electrodes (source and drain). Such a setup closely resembles a (three-terminal) transistor setup, as the third electrode can be used to manipulate the transmission properties of the junction molecules by applying a potential between the substrate and the reference electrode. 

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