Size distribution and mapping analyses of Ag and Au nanoparticles (NPs) have been made using an ICP-MS combined with laser ablation sampling technique (LA-ICP-MS). With the femtosecond laser (Ti:S laser) ablation system, the measured size distribution was modified to be smaller, whereas this disintegration could be reduced when the nanosecond laser (ArF Excimer laser) ablation was employed. This suggests that both the size and position of the NPs can be defined by the nanosecond LA-ICP-MS technique. More importantly, based on the peak-height analyses (PHA) of the measured signal intensity profiles, the present form of the analytes, whether particulate or ionic form, could be defined. This is very important to investigate the transport of the NPs within biological samples. To demonstrate the unique feature of the technique, imaging analyses of Ag and Au NPs, together with distribution analysis of the ionic form, were conducted on onion cells, prepared through dosing experiments of the Ag and Au NPs. There were clear differences in both the increasing rates of the numbers of NPs and the concentration range of the ionic form between the Ag and Au. The data obtained here demonstrate clearly that the LA-ICP-MS technique can become a major analytical tool to obtain both the size distribution and position of NPs from tissue samples.

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This study aimed to evaluate the effects of phosphoproteins on bacterial mineralization. Dental calculus formation is attributed to bacterial mineralization in the oral cavity; however, the influence of phosphoproteins (which are abundant in saliva) is not clear. The model bacterium Escherichia coli was suspended in a calcification solution containing casein as a model phosphoprotein. To evaluate mineralization independent of bacterial metabolism, bacteria killed by heat treatment at 70°C were compared with viable bacteria. After incubation at 37°C for 24 h, the mode of calcification was observed using electron microscopy and energy dispersive x‐ray spectroscopy. Solutions without casein produced precipitation in solution, which was identical to that in experiments without bacteria. In contrast, calcification solutions with 200 ppm casein only produced calcium phosphate deposition intracellularly. Without heat treatment, intracellular calcification rarely occurred, even when casein was added. Thus, phosphoproteins promoted intracellular calcification of dead bacteria; this is similar to the calcification of insoluble matrices, such as collagen fibrils, promoted by acidic polymers. We concluded that intracellular calcification is caused by the collagen fibril‐like behavior of dead bacteria. The promotion of intracellular calcification of dead bacteria by phosphoproteins suggested a basic principle of dental calculus formation.