Critical evaluation of fast and highly resolved elemental distribution in single cells using LA-ICP-SFMS

The analytical potential of a nanosecond laser ablation inductively coupled plasma mass spectrometer (nsLA- ICP-SFMS) system, equipped with an ultra-fast wash-out ablation chamber, is critically investigated for fast and highly spatially resolved (similar to mu m) qualitative elemental distribution within single cells. Initially, a low surface roughness (< 10 nm) thin In-SnO2 layer (total coating thickness similar to 200 nm) deposited on glass is employed to investigate the size, morphology and overlapping of laser-induced craters obtained at different laser repetition rates, making use of Atomic Force Microscopy (AFM). Conical craters with a surface diameter of about 2 mm and depths of about 100 nm were measured after a single laser shot. Furthermore, the influence of the sampling distance (i. e. distance between the sample surface and the inner sniffer of the ablation chamber) on the LA-ICP-MS ion signal wash-out time is evaluated. A significant decrease of the transient Sn-120(+) ion signal is noticed after slight variations (similar to 200 mm) around the optimum sampling position. Ultra-fast wash-outs (< 10 ms) are achieved reducing the aerosol mixing from consecutive laser shots even when operating the laser at high repetition rates (25-100 Hz). Fast and highly spatially resolved images of elemental distribution within mouse embryonic fibroblast cells (NIH/3T3 fibroblast cells) and human cervical carcinoma cells (HeLa cells), incubated with gold nanoparticles (Au NPs) and Cd-based quantum dots (QDs), respectively, are determined at the optimized operating conditions. Elemental distribution of Au and Cd in single cells is achieved using a high scanning speed (50 mm s(-1)) and high repetition rate (100 Hz). The results obtained for the distribution of fluorescent Cd-based QDs within the HeLa cells are in good agreement with those obtained by confocal microscopy. The size, morphology and overlapping of laser-induced craters in the fixed cells are also investigated using AFM, observing conical craters with a surface diameter of about 2.5 mm and depths of about 800 nm after a single laser shot.