Credit: © 2007 Wiley

Some of the most widely studied nanomaterials are those made from carbon — namely fullerenes, graphene, nanotubes and nanofibres. A more recent addition to this particular family, however, are carbon nanoparticles (CNPs) — small-diameter clusters that have interesting photoluminescence properties.

A lack of methods to prepare and isolate CNPs has hampered their study to date, but Chengde Mao and co-workers1 from Purdue University in the US have now discovered that candle soot is a rich source of these materials. Soot collected on glass plates held over smouldering candles was boiled in nitric acid and the resulting black suspension centrifuged to give a light brown liquid that fluoresced yellow when exposed to ultraviolet light. Fluorescent CNPs were separated from this solution with a technique called polyacrylamide gel electrophoresis. This method — normally used to purify biomolecules — separates materials based on a combination of their size and charge as they pass through a crosslinked polymer under the influence of an electric field.

Different fractions of CNPs taken from the gel were shown to fluoresce with different peak-emission wavelengths, ranging from the red–orange region of the visible spectrum through to violet. Although much is left to be discovered regarding the exact nature of the CNPs isolated by Mao and co-workers, these materials may have a promising future in biosensing and related applications.