Most expensive substance
Who
Designer Carbon Materials
Where
United Kingdom (Oxford)
When

In December 2015, Designer Carbon Materials (UK) sold 200 micrograms of nitrogen-atom-based endohedral fullerenes for £22,000 ($32,611) in Oxford, UK. At this price, a gram would have cost £110 m ($163 m). The substance can be used in tiny atomic clocks.

This is distinct from the most valuable substance at 400,000 times this price, the estimated value of antimatter.