Single molecule spectroscopic measurements

Arguably the first single molecule spectroscopic measurement was made by Rotman in the 1960s [4] in which a single enzyme was detected indirectly through its reaction products. However, Hirschfeld [5,6] was probably the first to make direct measurements with single molecule sensitivity when he demonstrated the detection of an individual antibody molecule, albeit labelled with 100 fluorophores One can argue that his is not the seminal work but... 

The studies of well defined systems consists of spectroscopic studies of individual molecules and measurements of the rate of catalytic reactions on single crystal surfaces, as well as structure and reactivity of well-defined catalyst models. 

Fluorescence resonance energy transfer (FRET) is a spectroscopic means of obtaining distance information over a range up to 80 A in solution. It is based on the dipolar coupling between the electronic transition moments of a donor and acceptor fluorophore attached at known positions on the RNA species of interest. It can be applied in ensembles of molecules, either by steady-state fluorescence or by lifetime measurements, but it is also very appropriate for single-molecule studies. In addition to the provision of distance information, recent studies have emphasized the orientation dependence of energy transfer. 

During the past five decades, spectroscopy has moved out from the laboratories of physicists and theoretical chemists into every area of analysis and chemical research. Applications vary from routine, single data point measurements for control of plant streams to structural analysis of complex molecules and conformational analysis of polymers. Enhancement of the sensitivity of all spectroscopic methods has been achieved through computer-assisted data handling. It is possible to find structural differences in polymers under different degrees of stress and to analyze for very low levels of chemical structures at surfaces and interfaces. For difficult structure determinations, data from several spectroscopic disciplines may be combined and require months or years of research. 

---