During hair coloring a number of disulfide bonds in cystine are oxidized (1) to create cysteic acid, forming binding sites for metal ions such as Ca(2+ )and Cu(2+ )from tap water (2). The increased uptake of these metals can have a detrimental impact on fiber properties-for example, reducing shine and causing a poor wet and dry feel (3). In addition, the increased uptake of copper can also contribute to further fiber damage during subsequent coloring due to its ability to take part in metal-induced radical chemistry (4). It is important to know where in the fibers these metals are located in order to either effectively remove these metals or control their chemistry. Nanoscale secondary ion mass spectrometry (NanoSIMS) has been used to locate the calcium and copper within hair that has been treated with a colorant and washed multiple times in tap water containing these ions. Untreated hair is used as a baseline standard material. Images with up to 50-nm spatial resolution of the preferential locations of calcium uptake were obtained, showing a high concentration of calcium in the cuticle region of colored hair, specifically in the sulfur-rich regions (A-layer and exocuticle).

Certain plants known as ‘metal hyperaccumulators’ can accumulate exceptional concentrations of elements such as zinc, manganese, nickel, cobalt, copper, selenium, cadmium or arsenic in their above ground tissue. In members of the genus Alyssum, nickel concentrations can reach values as high as 3% of leaf dry biomass. These plants must possess very effective mechanisms for the transport, chelation and sequestration of such elements within their tissues to avoid the toxic effects of free metal ions. Evidence from a number of different techniques suggests that nickel is concentrated primarily in the outermost, epidermal tissue of leaves of Alyssum hyperaccumulators, but there is currently no consensus on the principal sites of nickel sequestration. In this study, high resolution secondary ion mass spectrometry (NanoSIMS) analysis has been performed on longitudinal sections of Alyssum lesbiacum leaves. Elemental maps were obtained which revealed the high concentrations of nickel in the peripheral regions of the large unicellular stellate leaf hairs (trichomes) and in the epidermal cell layer. Electron probe microanalysis (EPMA) was used to provide independent confirmation of elemental distribution in the specimens, but the superior spatial resolution and high chemical sensitivity of the NanoSIMS technique provided a more detailed image of elemental distribution in these biological specimens at the cellular level.

In order to achieve reliable and reproducible analysis of biological materials by SIMS, it is critical both that the chosen specimen preparation method does not modify substantially the in vivo chemistry that is the focus of the study and that any chemical information obtained can be calibrated accurately by selection of appropriate standards. In Oxford, we have been working with our new Cameca NanoSIMS50 on two very distinct classes of biological materials; the first where the sample preparation problems are relatively undemanding – human hair – but calibration for trace metal analysis is a critical issue and, the second, marine coccoliths and hyperaccumulator plants where reliable specimen preparation by rapid freezing and controlled drying to preserve the distribution of diffusible species is the first and most demanding requirement, but worthwhile experiments on tracking key elements can still be undertaken even when it is clear that some redistribution of the most diffusible ions has occurred.