Exploring quantitative cellular bioimaging and assessment of CdSe/ZnS quantum dots cellular uptake in single cells, using ns-LA-ICP-SFMS.

Quantitative bioimaging of Quantum Dots (QDs) uptake in single cells by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a challenging task due to the high sensitivity and high spatial resolution required, and to the lack of matrix-matched reference materials. In this work, high spatially resolved quantitative bioimaging of CdSe/ZnS QDs uptake in single HT22 mouse hippocampal neuronal cells and in single HeLa human cervical carcinoma cells is novelty investigated combining: (a) the use of a ns-LA-ICP-Sector Field (SF)MS unit with mono-elemental fast and sensitive single pulse response for 114Cd+; and (b) the spatially resolved analysis of dried pL-droplets from a solution with a known concentration of these QDs to obtain a response factor that allows quantification of elemental bioimages. Single cells and dried pL-droplets are morphologically characterized by Atomic Force Microscopy (AFM) to determine their volume and thickness distribution. Moreover, operating conditions (e.g. spot size, energy per laser pulse, etc.) are optimized to completely ablate the cells and pL droplets at high spatial resolution. Constant operating conditions for the analysis of the single cells and calibrating samples is employed to reduce potential fractionation effects related to mass load effects in the ICP. A number concentration of CdSe/ZnS QDs between 3.5 104 and 48 104 is estimated to be uptaken by several selected single HT22 and HeLa cells, after being incubated in the presence of a QDs suspension added to a standard cell culture medium. Mono-elemental bioimaging at subcellular resolution seems to show a higher number concentration of the CdSe/ZnS QDs in the cytosol around the cell nucleus.

A novel gas sampling introduction interface for fast analysis of volatile organic compounds using radiofrequency pulsed glow discharge time of flight mass spectrometry.

An improved gas sample introduction interface is developed and characterized for gas chromatography coupling and for direct injection of volatile organic compounds (VOCs), in a pulsed glow discharge (pulsed-GD) ion source coupled to a time of flight mass spectrometer (TOFMS) that is typically used for direct solid analysis. The novel interface allows the introduction of the analytes in the flowing afterglow region of the GD (a few mm away from the negative glow region) to reduce plasma quenching effects. Analyte ion signals are acquired in the temporal afterglow region, where low fragmentation of the molecular species is produced, providing useful qualitative and quantitative molecular information (e.g. molecular ion). Analytical capabilities of the pulsed-GD ion source with the novel gas sampling interface provides improved performance compared to previous designs. In particular, limits of detection for the analysis of VOCs in air were below (better) that legally established limits according to Directive 2008/50/EC of the European Parliament.

Pulsed rf-GD-TOFMS for depth profile analysis of ultrathin layers using the analyte prepeak region.

Direct solid analysis of ultrathin layers is investigated using pulsed radiofrequency (rf) glow discharge (GD) time-of-flight mass spectrometry (TOFMS). In particular, previous studies have always integrated the detected ion signals in the afterglow region of the rf-GD pulse, which is known to be the most sensitive one. Nevertheless, the analytical capabilities of other pulse time regions have not been evaluated in detail. Therefore, in this work, we investigate the analyte prepeak region, which is the pulse region where the analyte ions peak after the initial sputtering process of each GD pulse, aiming at obtaining improved depth profile analysis with high depth resolution and with minimum polyatomic spectral interferences. To perform these studies, challenging ultrathin Si-Co bilayers deposited on a Si substrate were investigated. The thickness of the external Si layer was 30 nm for all the samples, whilst the internal Co layer thicknesses were 30, 10, 5, 2 and 1 nm, respectively. It should be remarked that the top layer and the substrate have the same matrix composition (Si > 99.99%). Therefore, the selected samples are suitable to evaluate the response of the Si ion signal in the presence of an ultrathin Co layer as well as the possible oxygen contaminations or its reactions. Additionally, these samples have been evaluated using time-of-flight secondary ion mass spectrometry, and the results compare well to those obtained by our pulsed rf-GD time-of-flight mass spectrometry results.

Polymer screening by radiofrequency glow discharge time-of-flight mass spectrometry.

The aim of this work is to optimise and evaluate radiofrequency glow discharge (RF GD) time-of-flight mass spectrometry (TOFMS) for identification of organic polymers. For this purpose, different polymers including poly[methylmethacrylate], poly[styrene], polyethylene terephthalate-co-isophthalate and poly[alpha-methylstyrene] have been deposited on silicon wafers and the RF GD-TOFMS capabilities for qualitative identification of these polymeric layers by molecular depth profiling have been investigated. Although some molecular information using the RF continuous mode is available, the pulsed mode offers a greater analytical potential to characterise such organic coatings. Some formed polyatomic ions have proved to be useful to identify the different polymer layers, confirming that layers having similar elemental composition but different polymer structure could be also differentiated and identified.

Direct chemical in-depth profile analysis and thickness quantification of nanometer multilayers using pulsed-rf-GD-TOFMS.

Nanometer depth resolution is investigated using an innovative pulsed-radiofrequency glow discharge time-of-flight mass spectrometer (pulsed-rf-GD-TOFMS). A series of ultra-thin (in nanometers approximately) Al/Nb bilayers, deposited on Si wafers by dc-magnetron sputtering, is analyzed. An Al layer is first deposited on the Si substrate with controlled and different values of the layer thickness, t(Al). Samples with t(Al) = 50, 20, 5, 2, and 1 nm have been prepared. Then, a Nb layer is deposited on top of the Al one, with a thickness t(Nb) = 50 nm that is kept constant along the whole series. Qualitative depth profiles of those layered sandwich-type samples are determined using our pulsed-rf-GD-TOFMS set-up, which demonstrated to be able to detect and measure ultra-thin layers (even of 1 nm). Moreover, Gaussian fitting of the internal Al layer depth profile is used here to obtain a calibration curve, allowing thickness estimation of such nanometer layers. In addition, the useful yield (estimation of the number of detected ions per sputtered atom) of the employed pulsed-rf-GD-TOFMS system is evaluated for Al at the selected operating conditions, which are optimized for the in-depth profile analysis with high depth resolution.

Spectroscopic evaluation of a compact magnetically boosted radiofrequency glow discharge for time-of-flight mass spectrometry.

A compact magnetically boosted radiofrequency glow discharge (GD) has been designed, constructed and its analytical potential evaluated by its coupling to a mass spectrometer (MS). Simple modifications to the original source configuration permitted the insertion of permanent magnets. Small cylindrical Nd-Fe-B magnets (diameter = 4 mm, h = 10 mm) were placed in an in-house-modified GD holder disc that allows easy and fast exchange of the magnets. The different processes taking place within the GD plasma under the influence of a magnetic field, such as sputtering, ionisation processes and ion transport into the MS, were studied using different GD operating conditions. Changes to the ionisation and ion transport efficiency caused by the magnetic field were studied using an rf-GD-TOFMS setup. A magnetic field of 60-75 gauss (G) was found not to affect the sputtering rates but to enhance the analyte ion signal intensities while decreasing the Ar species ion signals. Moreover, magnetic fields in this range were shown not to modify the crater shapes, enabling the fast and sensitive high depth resolved analysis of relatively thick coated samples (micrometre) by using the designed compact magnetically boosted rf-GD-TOFMS.

Capabilities of femtosecond laser ablation inductively coupled plasma mass spectrometry for depth profiling of thin metal coatings.

The capabilities of ultraviolet femtosecond laser ablation inductively coupled plasma mass spectrometry (UV-fs-LA-ICPMS) for depth profile analysis of thin metal coatings were evaluated. A standard sample consisting of a single Cr thin layer of 500 nm +/- 5% on a Ni substrate was used. A fast washout was obtained by a high-efficiency aerosol dispersion ablation cell (V approximately 1 cm3), which allowed single-shot analysis with increased depth resolution. Laser ablation was performed in helium at atmospheric pressure conditions. A laser repetition rate of 1 Hz and low laser fluence (<0.5 J/cm2) were used. Very low ablation rates (<10 nm/pulse) were determined by atomic force microscopy (AFM). Information about the crater geometry and morphology was investigated using scanning electron microscopy and AFM. The depth resolution, calculated via the maximum slope of the tangent in the layer interface region, was smaller than 300 nm. Our data indicate that UV-fs-LA-ICPMS represents a powerful combination of high lateral and depth resolution for the analysis of thin metal coatings. Moreover, an overall ion yield, defined as the ratio of detected ions and ablated atoms, of approximately 5 x 10-5 was estimated for the chromium layer under the operating conditions chosen. The absolute amount of ablated material per laser pulse was approximately 1 pg, which corresponds to a detection limit of 180 microg/g.