The first time people order espresso, they are usually surprised at the dainty dimensions of the porcelain cup in which it is served. But those cups are huge compared with the ones created by researchers at Jawaharlal Nehru Center for Advanced Scientific Research in India. The microscopic metal mugs are so diminutive that their capacity is measured in femtoliters. Although the cups are less than ideal for a caffeine fix, researchers led by G.U. Kulkarni say that the supershrunk containers have a variety of biological applications. They can be functionalized easily to create the right environment for living cells used for single-cell studies. The cuplike structures (see figure) were created by the laser ablation of metals in a vacuum, which produced molten metal droplets. A hydraulic jump driven solely by surface tension was the underlying mechanism in their formation. The femtoliter cups can be made from virtually any metal. The researchers made them from aluminum, gold, copper, cadmium, indium, niobium, tin and zinc. They also used a variety of flat substrates, including glass and silicon. To demonstrate the effectiveness and strength of the containers, the scientists filled them with fluorescent biomarkers and metal nanoparticles. The capacity of the cups was between 0.2 and 10 fl. Although tinier containers have been made — including some with a zeptoliter capacity, or about a million times smaller — the research team believes that its manufacturing method is simpler and, importantly, produces metal cups. Their results were published in the Nov. 23 issue of The Journal of Physical Chemistry B. The investigators said that a shortcoming of their method was that it gave them little control over the size of the cups. A metal injection system designed to deliver uniform droplets should provide greater control over size.