A synthetic circuit chains a biosensor promoter to a logic module
and an actuator gene, so the cell only makes a therapeutic protein
when the right combination of molecular inputs is present.
dP/dt = gain · Logic(A, B) − decay · P
AND: A·B OR: A+B−A·B NOT: 1−A TOGGLE: bistable latch
- AND gate fires only when both sensors detect their ligand — used for tumour-specific targeting (two markers must both be present).
- OR gate fires on either input — broader safety net.
- NOT gate (a repressor) fires only when input A is absent — a kill-switch topology.
- Toggle switch — two mutually-repressing genes: input A latches it ON, input B latches it OFF, and it holds state until pushed again — real bistable memory used in cell-state recording.
- Gain / decay — translation rate vs. protein turnover set how fast output rises and how sharply it falls once the gate closes.