Adv. Biophys., Vol. 32, pp. 17-29 (1996) FLUORESCENCE PHOTOBLEACHING IN DNA SEQUENCING BENJAMIN CHU Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400, U.S.A. Improvements in DNA sequencing technology are clearly needed in order to achieve the many specific goals of the Human Genome Project (1). More importantly, DNA sequencing is a fundamental tool, like digital computing, for which one could always expect further improve- ments to satisfy future potential applications (2). For example, the study of gene variation, which is of central importance in molecular biology and medicine, should create unlimited demands for DNA- sequence data. There are conventional and unconventional approaches to im- proving DNA sequencing methodologies (3). Unconventional ap- proaches can be very radical and truly test the limits of human ingenu- ity. At this time, one should only consider those new ideas and possi- bilities with an open mind. For examples, the relatively new technique of matrix-assisted laser desorption and ionization (MALDI) has been successful in the mass analysis of some proteins (4) or other homopoly- mers and mixed sequence oligomers (5). If progress continues as is hoped, separation of Sanger mixtures by mass spectral based DNA sequencing (6-10) may be performed in seconds (3). Another promising new approach is sequencing by hybridization (SBH) (I l-24), including possible preparation of large combinatorial arrays by means of photolithography and microfabrication (15-17). SBH could be made practical in the future with anticipated improve- 17