By exploiting the intense fluorescence and scattering signals generated by surface-anchored metal nanostructures, chemists at the Indian Institute of Technology, Madras, have developed optical methods capable of selectively detecting less than 1 zeptomole (10−21 mol) of 2,4,6-trinitrotoluene (TNT) (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201203810). The method, which can also selectively detect similarly low levels of mercury in the presence of Pb, Ni, Cd, and other metal ions, may lead to rapid detection tools for a variety of hazardous substances. Thalappil Pradeep, Ammu Mathew, and P. R. Sajanlal synthesized 15-atom Ag clusters embedded in bovine serum albumin and supported the clusters on silica-coated Au microstructures. The microstructures are flower-shaped and measure roughly 4 µm from edge to edge. The team showed that the intense red luminescence observed via microscopy when the particles are irradiated is rapidly quenched in the presence of low levels of TNT but not other common organic explosives. They demonstrated that tagging the structures with a green-fluorescing dye and then exposing the particles to TNT switches off the red, enabling the otherwise-buried green light to be detected. The team further showed that the Ag and Au microstructures stimulate surface-enhanced Raman scattering, thereby providing a complementary way to detect TNT at the zeptomole level.