Fluorescein as a model molecular calculator with reset capability

The evolution of molecules capable of performing boolean operations1,2,3,4 has gone a long way since the inception of the first molecular AND5 logic gate, followed by other logic functions, such as XOR6 and INHIBIT7, and has reached the stage where these tiny processors execute arithmetic calculations8,9,10,11,12,13,14,15. Molecular logic gates that process a variety of chemical inputs can now be loaded with arrays of logic functions16, enabling even a single molecular species to execute distinct algebraic operations: addition and subtraction12. However, unlike electronic or optical signals, the accumulation of chemical inputs prevents chemical arithmetic systems8,9,10,11,12 from resetting. Consequently, a set of solutions is required to complete even the simplest arithmetic cycle. It has been suggested that these limitations can be overcome by washing off the input signals from solid supports8,9. An alternative approach, which does not require solvent exchange or incorporation of bulk surfaces, is to reset the arithmetic system chemically. Ultimately, this is how some biological systems regenerate. Here we report a highly efficient and exceptionally simple molecular arithmetic system based on a plain fluorescein dye, capable of performing a full scale of elementary addition and subtraction algebraic operations. This system can be reset following each separate arithmetic step. The ability to selectively eradicate chemical inputs brings us closer to the realization of chemical computation.