Implementing Biological Logic Gates Using Fluorescence Lifetime Imaging

There is a paradigm shift in modern medicine from general to personalized treatments. One approach toward this personalized medicine is biological logic gates, which are able to identify and possibly even treat underlying conditions by inherently reacting to patient-specific biological stimuli. Here, we describe recent research in which we explored biologically relevant logic gates using gold nanoparticles (GNPs) conjugated to fluorophores and tracing the results remotely by time-domain fluorescence lifetime imaging microscopy (FLIM).

GNPs have a well-known effect on nearby fluorophores in terms of their fluorescence intensity (FI) as well as fluorescence lifetime (FLT). We have designed a few bio-switch systems in which the FLIM-detected fluorescence varies after biologically relevant stimulation. Some of our tools include Oregon Green which can be activated by either calcium ions or pH, peptide chains cleavable by the enzymes trypsin and caspase 3, and the polymer polyacrylic acid which varies in size based on surrounding pH. After conjugating GNPs to chosen fluorophores, we have successfully demonstrated the logic gates of NOT, AND, OR, NAND, NOR, and XOR by imaging different stages of activation. These logic gates have been demonstrated both in solutions as well as within cultured cells, thereby possibly opening the door for nanoparticulate in vivo smart detection.

While these initial probes are mainly tools for intelligent detection systems, they lay the foundation for logic gates functioning in conjunction so as to lead to a form of ­in vivo biological computing, where the system would be able to release proper treatment options in specific situations without external influence.