Contents: (Small 24/2013)

Hundreds of years after the little boy saved his city with urine, X. Chen and coworkers now use urine to detect deleterious ions in a colorimetric assay. As reported on page 4104, the synergetic effect of uric acid and creatinine decorated on gold nanoparticles is the reason for the selective binding of mercury ions, leading to the aggregation of nanoparticles and thereby causing a visual color change. This work inspires the development of the "turning trash into treasure" strategy and the exploitation of natural products in exploring nanotechnology.