Discoveries in Liquids

Grantees at Drexel University have demonstrated that light emitted from a new form of plasma (non‑thermal corona discharge) in liquid permits analysis of the elemental composition of solutions within nanoseconds from volumes that are 10-100 times smaller than a single mammalian cell. This new chemical spectroscopy technique not only enables analysis from tiny volumes, but provides spectra of better quality than conventional emission spectroscopy. The analysis can be performed remotely, without connecting a wire to the probe, by using carbon nanotubes (tiny tubes with the diameter 1,000 times smaller than human hair) dispersed in liquid.

The newly demonstrated nanoscale probes open a new era in chemical, environmental and biological sensing and detection. They may replace large and expensive instruments, which are used for elemental analysis or measurements of metals in solutions with simple, portable and very inexpensive tools. Nanoscale corona discharge can also find applications in forensics, patterning and functionalization of surfaces in manufacturing of sensors and electronic devices and in tools for cellular surgery.

Figure 1. The schematic shows corona discharge in liquid generated around the tip of a nanoscale probe and nanotubes dispersed in liquid and placed between two electrodes. A typical optical emission spectrum is shown in the middle. The photograph shows a picture of a corona discharge around a tungsten electrode with a 100 nm tip placed in blood plasma.

Figure 2. Colored scanning electron microscope images of a nanotube-tipped cellular probe. The probe was assembled by inserting a magnetic nanotube into a tip of a conventional glass pipette.

Figure 3. Time resolved spectra with 25 ns resolution of 10 millimolar aqueous solution of potassium chloride (KCl). Spectral range shows simultaneous acquisition of three peaks: two due to potassium (766.5, 769.9) and a single peak due to oxygen (around 777.4).