Fluorescence detection of single molecules applicable to small volume assays

In this chapter we give an overview of optical detection of single molecules with respect to possible application to high throughput screening of substance libraries. We restrict ourselves to single molecule detection (SMD) because the field of ultrasensitive detection is too broad to be covered by a single chapter; thus we will concentrate on the ultimate detection limit In the future SMD will be the method of choice because of the ultimate small amount of analyte needed in connection with extremely high speed screening of vast libraries. Besides the topic of high-speed DNA sequencing (see below), the high sensitivity received attention also in the context of combinatorial chemistry (Eigen, 1984; Pluckthun,1991; Eigen, 1994; Xiang, 1995) and molecular computation (Adleman, 1994; Lipton, 1995). The basic idea of combinatorial chemistry is to synthesize large arrays of slightly different molecules, followed by screening and selection of molecules with desired properties. In the case of molecular computation, a random chemical synthesis is used to find solutions of numerically difficult problems; again, a fast and ultrasensitive screening method is needed to extract the result of the “computation”.

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