The paper by Eiger and Rigler describes a method for detecting and identifying single molecules in solution using fluorescence correlation spectroscopy (FCS). This technique combines FCS with devices for trapping single molecules in an electric field, enabling fast screening of large mutant spectra in molecular evolution studies. The method's sensitivity allows for monitoring concentrations down to \(10^{-15}\) M without amplification, making it valuable for molecular diagnostics and evolutionary biotechnology. The authors detail the principles of FCS, including the use of small volume elements and high quantum flux to detect single molecules. They also discuss the application of FCS in tracing single molecules, screening large numbers of molecules, and its potential in DNA and RNA sequencing. The method's ability to detect rare structures and activities, as well as its sensitivity in molecular diagnostics, is highlighted, along with its implications for evolutionary optimization.The paper by Eiger and Rigler describes a method for detecting and identifying single molecules in solution using fluorescence correlation spectroscopy (FCS). This technique combines FCS with devices for trapping single molecules in an electric field, enabling fast screening of large mutant spectra in molecular evolution studies. The method's sensitivity allows for monitoring concentrations down to \(10^{-15}\) M without amplification, making it valuable for molecular diagnostics and evolutionary biotechnology. The authors detail the principles of FCS, including the use of small volume elements and high quantum flux to detect single molecules. They also discuss the application of FCS in tracing single molecules, screening large numbers of molecules, and its potential in DNA and RNA sequencing. The method's ability to detect rare structures and activities, as well as its sensitivity in molecular diagnostics, is highlighted, along with its implications for evolutionary optimization.