Since fluorescent PET sensors are based on rather small (ca. 1 nm) molecules, they can enter living cells and remain undetected by the cell machinery for reasonable periods of time. During their residence, these molecules act as little James Bonds and gives us a window into the private lives of protons, for instance \cite{probescom}.
Fluorescent PET sensors switch their emission signal rather sharply upon encountering the target species, e.g. from ‘off’ to ‘on’. Such switching of signals is similar to those seen inside computers and we recognized this connection between disciplines in 1993 \cite{de_Silva_1993}. The field of molecular logic-based computation arose as a result \cite{de_Silva_1993,Ling2015}. Over 610 laboratories have joined this field (Figure \ref{816506}). Many logic gate arrays of varying degrees of small-scale integration have now been constructed. Some of these have been operated within small spaces, some of which are alive. Since these small spaces are not usually accessible by semiconductor logic devices, they are virgin territory for exploration by intelligent molecular devices \cite{Ling2015}. Even certain aspects of human behaviour can be emulated by molecular logic-based computation already . More progress along these lines can be expected \cite{Ling2015a,Ling2015b,Ling2015c}.