Single-Molecule Detection in Analytical Chemistry

Chemical analysis conventionally entails two tasks. The first, qualitative analysis, deals with the identification of an unknown substance, typically in a complex environment. Inevitably, some sort of separation technique, be it chromatographic, electrophoretic, or immunological, is employed when analyzing biological substances. The second, quantitative analysis, deals with the determination of the amount of analyte present. Inevitably, some sort of spectroscopic, electrochemical, or mass spectroscopic method is employed to determine the amount of substance present in the sample following the qualitative analysis step. 

This chapter considers the quantitative aspects of single-molecule detection in solution by laser-induced fluorescence. We will describe the combination of single molecule detection with capillary electrophoresis as the ultimate analytical procedure. Other methods of single molecule detection, such as electrochemical detection, are not considered [1, 2]. 

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S. Bhat, J. Herrmann, P. Armishaw, P. Corbisier, and K. R. Emslie, Single molecule detection in nanofluidic digital array enables accmate measurement of DNA copy number, Analytical and Bioanalytical Chemistry, vol. 394, no. 2, pp. 457-467, May 2009. 

The first aspect of laser applications in analytical chemistry is the sensitive detection of small concentrations of impurity atoms or molecules. With the laser-spectroscopic techniques discussed in Chap. 1, detection limits down into the parts-per-billion (ppb) range can be achieved for molecules, which corresponds to a relative concentration of 10 . Atomic species and some favorable molecules can even be traced in concentrations within the parts-per-trillion (ppt) (=10 ) range. Recently single molecule detection in solids, solutions, and gases has become possible. 

New Frontiers in Ultrasensitive Bioanalysis Advanced Analytical Chemistry Applications in Nanobiotechnology, Single Molecule Detection, and Single Cell Analysis. 

In the past, there has been surprisingly little concern regarding the possibility of fast energy migration amongst the chromophores of supramolecular assemblies but Muller and Stock have now reported on this subject and have formulated an expression for the temporal dependence of the distribution of the excited states of structurally identical chromophores in bichromophoric compounds. Dovinchi and Chen have reviewed recent advances in photophysical processes of single and isolated molecules with particular reference to applications in analytical chemistry and to the combination of single molecule detection with capillary electrophoresis. 

Haab, B.B. and Mathies, R.A., Single-molecule detection of DNA separations in microfabricated capillary electrophoresis chips employing focused molecular streams. Analytical Chemistry, 71,5137-5145,1999. 

Nie, S.M., Chiu, D.T., and Zare, R.N. (1995) Real-time detection of single-molecules in solution by confocal fluorescence microscopy. Analytical Chemistry, 61, 2849-2857. 

Moerner, WE and Kador, L, Finding a single molecule in a haystack—optical-detection and spectroscopy of single absorbers in so]ids. Analytical Chemistry 61 (1989) A1217-A1223. 

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