Pan, R. et al. Proc. Natl. Acad. Sci. USA 113, 11436–11440 (2016).

Methods for analyzing small molecules and proteins at the single-cell level are crucial for understanding cellular heterogeneity. Pan et al. describe a 'nanokit' for probing single cells. The nanokit consists of a nanometer-sized capillary with a ring electrode at the tip. This nanocapillary, which is filled with components from traditional assay kits, is stuck into cells to introduce femtoliters of assay solution. The extent of assay kit reactions are then read out by coulometry, rather than fluorescence. The researchers demonstrated the utility of the device by examining the abundance of glucose, as a representative small molecule, and the activity of the protein sphingomyelase, as a representative enzyme, at the single-cell level. This nanokit should facilitate single-cell analysis of many important biological targets.