Wafer Testing

A QA engineer must isolate exactly one poisoned wafer from a batch of 1000 wafers. The chemical test strip turns blue if exposed to the poison, but it takes exactly 24 hours to develop. The engineer has exactly 24 hours to determine the culprit. Assuming samples from multiple wafers can be combined onto a single test strip without diluting the effect, what is the absolute minimum number of test strips required to guarantee finding the poisoned wafer?