I recommend Chinese chalk. We found it at one of the Korean stores in the barrio. The sign said "Kills Ants," so the kids wanted to try it. I was pretty sure it was bogus, but what did we have to lose?
My wife is one of those crazy old ladies that thinks it is her mission on earth to save and feed all of the alley cats that show up at our house. Anyway, she puts the food out on the patio, and the black ants make a bee line for it.
We bought a couple of sticks of this Chinese chalk just to give it a try. The label said "Follow instruction carefully," but that was the only English on the thing. Everything else was in Chinese.
When we got home, I put out the cat food and then I drew a large circle around it with the chalk. Sure enough, within a matter of minutes, the black ants appeared. They crossed the circle of death and died. When I saw that, I went and washed my hands very carefully. I am not sure what is in that chalk, but it sure works.
Now when I use it, I put my hand into a plastic bag and use it like a glove. Then I throw the bag away when done with it.
Rufus