What can be added to fuel that would create a problem for the plane?
Would water added to the fuel create a problem?
Part of the pre-flight check is to take a device that looks like a test tube with a probe and drain some fuel from your fuel tanks. If there is water contamination, the water will be at the bottom of the tube. You also check to see if the color of the fuel is correct for the octane level required by your engine. Different octane grades are dyed different colors. You should also be looking for particulate contamination.
A classic way to spoil gasoline is to add sugar. It would not be hard to dump some sugar into the fuel tank in such a manner that it doesn't migrate down to the inspection drain port. Once underway, the motion of the aircraft would mix the sugar with the fuel and allow sucking it into the engine. Hopefully, you would notice that by the time you reach the end of the taxiway and do your full power runup of the engine before attempting a takeoff roll.
I'm sure a competent petro-chemical engineer could devise a means to taint fuel that would have a delayed action. That would put you in the air with bad fuel. That is exactly why a good pilot is always looking for somewhere satisfactory to land in case of an engine failure.