ICP-MS Signal Research Articles

Heteromultivalent DNA Enhances the Assembly Yield of Hybrid Nanoparticles and Facilitates Dynamic Disassembly for Bioanalysis Using ICP-MS.

To obtain enhanced physical and biological properties, various nanoparticles are typically assembled into hybrid nanoparticles through the binding of multiple homologous DNA strands to their complementary counterparts, commonly referred to as homomultivalent assembly. However, the poor binding affinity and limited controllability of homomultivalent disassembly restrict the assembly yield and dynamic functionality of the hybrid nanoparticles. To achieve a higher binding affinity and flexible assembly choice, we utilized the paired heteromultivalency DNA to construct hybrid nanoparticles and demonstrate their excellent assembly characteristics and dynamic applications. Specifically, through heteromultivalency, DNA-functionalized magnetic beads (MBs) and gold nanoparticles (AuNPs) were efficiently assembled. By utilizing ICP-MS, the assembly efficiency of AuNPs on MBs was directly monitored, enabling quantitative analysis and optimization of heteromultivalent binding events. As a result, the enhanced assembly yield is primarily attributed to the fact that heteromultivalency allows for the maximization of effective DNA probes on the surface of nanoparticles, eliminating steric hindrance interference. Subsequently, with external oligonucleotides as triggers, it was revealed that the disassembly mechanism of hybrid nanoparticles was initiated, which was based on an increased local concentration rather than toehold-mediated displacement of paired heteromultivalency DNA probes. Capitalizing on these features, an output platform was then established based on ICP-MS signals that several Boolean operations and analytical applications can be achieved by simply modifying the design sequences. The findings provide new insights into DNA biointerface interaction, with potential applications to complex logic operations and the construction of large DNA nanostructures.

The single-crystal diamond trap (SCDT): a new method to determine the composition of high-P\u2013T fluids

In view of recently reported discrepancies in mineral solubility results obtained with the classical diamond trap method, an alternative approach to quantify the composition of high P–T fluids was developed. In this approach the high P–T fluids are trapped in laser-drilled holes within single-crystal diamond plates and subsequently analyzed by LA–ICP–MS using the same pit size as the one that was used to drill the holes, which allows more rigorous testing of the data reproducibility than in the case of the classical diamond trap, where the fluid resides in a large, open network. To reduce the spikiness of the LA–ICP–MS signals and minimize element fractionation, the aqueous solution within the holes was allowed to evaporate, and the solid residue was melted to a glass. Because this results in the partial loss of the internal standard elements that are usually used for quantifying the LA–ICP–MS signals we developed a new quantification procedure that works without any internal standard in the fluid but instead uses the carbon signal produced by the epoxy that was filled into the holes after melting the precipitates. The new method was first tested on holes filled with epoxy resins doped with known amounts of chemicals, then on holes filled with known amounts of minerals that were subsequently melted, and finally on real high P–T mineral solubility experiments at 1.0 GPa and 700–900 °C in the quartz–H2O and olivine–enstatite–H2O systems, for which reliable reference data exist. In all 15 experiments the measured concentrations agree within 1–21% (avg. 13%) with the reference values. In contrast, four mineral solubility experiments that were performed at identical conditions with the classical diamond trap method returned concentrations that deviated by 7–56% (avg. 28%) from the reference value. Furthermore, a strong fractionation effect that has been observed during the ablation of albite + H2O in a classical diamond trap is efficiently prevented in our single-crystal diamond trap (SCDT) approach. On the downside, we observe significant mobility of alkalies during the melting step in our approach.

Influence of sample surface topography on laser ablation process

In this work we discuss how sample surface topography can significantly influence the laser ablation (LA) process and, in turn, the analytical response of the LA Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) method. Six different surface topographies were prepared on a certified aluminium alloy sample BAM 311 and SRM NIST 610 to investigate the phenomenon. All the samples were repetitively measured by LA-ICP-MS using a spot by spot analysis. The effect of laser fluence in the range of 1–13 J/cm2 was studied. For majority of measured isotopes, the ICP-MS signal was amplified with roughening of the sample surface. A stronger effect was observed on the Al alloy sample, where the more than sixty-time enhancement was achieved in comparison to the polished surface of the sample. Since the effect of surface topography is different for each analyte, it can be stated that surface properties affect not only the ICP-MS response, but also elemental fractionation in LA. The presented results show that different surface topographies may lead to misleading data interpretation because even when applying ablation preshots, the signal of individual elements changes. The utmost care must be taken when preparing the surface for single shot analysis or chemical mapping. On the other hand, by roughening the sample surface, it is possible to significantly increase the sensitivity of the method for individual analytes and supress a matrix effect.

The ICPMS signal as a Poisson process: a review of basic concepts

The random distribution of count numbers is defined by the binomial selection of ions en route through the interface and ion channel and by fluctuations of the ion contents sampled from the ICP.

Click Chemistry Mediated Eu-Tagging: Activity-Based Specific Quantification and Simultaneous Activity Evaluation of CYP3A4 Using 153Eu Species-Unspecific Isotope Dilution Inductively Coupled Plasma Mass Spectrometry

P450 3A4 (CYP3A4) is one of the most important isoforms in the human cytochrome P450 superfamily. It was used as an example in this proof-of-concept study in order to demonstrate an activity-based labeling and then click chemistry (CC) mediated element-tagging strategy for simultaneously specific quantification and activity measurement of an enzyme using species-unspecific isotope dilution inductively coupled plasma mass spectrometry (SUID ICPMS). A dual functional hexynylated 17α-ethynylestradiol activity-based probe was synthesized for specifically labeling CYP3A4 and then CC-mediated Eu-tagging with an azido-DOTA-Eu complex for CYP3A4 quantification and activity measurement in human liver microsome and serum samples using (153)Eu SUID ICPMS. The LOD (3σ) of CYP3A4 reached 20.3 fmol when monitoring (151/153)Eu ICPMS signals, in addition to the merits of specificity and simultaneous activity measurement achieved. We believe that this activity-based CC-mediated element-tagging strategy will liberate more potential advantages of ICPMS in bioanalysis.

Non-denaturating isoelectric focusing gel electrophoresis for uranium–protein complexes quantitative analysis with LA-ICP MS

A non-denaturating isoelectric focusing (ND-IEF) gel electrophoresis protocol has been developed to study and identify uranium (U)-protein complexes with laser ablation-inductively coupled plasma mass spectrometry (LA-ICP MS) and electrospray ionization mass spectrometry (ESI-MS). The ND-IEF-LA-ICP MS methodology set-up was initiated using in vitro U-protein complex standards (i.e., U-bovine serum albumin and U-transferrin) allowing the assessment of U recovery to 64.4 ± 0.4 %. This methodology enabled the quantification of U-protein complexes at 9.03 ± 0.23, 15.27 ± 0.36, and 177.31 ± 25.51 nmol U L(-1) in digestive gland cytosols of the crayfish, Procambarus clarkii, exposed respectively to 0, 0.12, and 2.5 μmol of waterborne depleted U L(-1) during 10 days. ND-IEF-LA-ICP MS limit of detection was 19.3 pmol U L(-1). Elemental ICP MS signals obtained both in ND-IEF electropherograms and in size exclusion chromatograms of in vivo U-protein complexes revealed interactions between U- and Fe- and Cu-proteins. Moreover, three proteins (hemocyanin, pseudohemocyanin-2, and arginine kinase) out of 42 were identified as potential uranium targets in waterborne-exposed crayfish cytosols by microbore reversed phase chromatography coupled to molecular mass spectrometry (µRPC-ESI-MS/MS) after ND-IEF separation.

Tungsten carbide precursors as an example for influence of a binder on the particle formation in the nanosecond laser ablation of powdered materials

A study of LA-ICP-MS analysis of pressed powdered tungsten carbide precursors was performed to show the advantages and problems of nanosecond laser ablation of matrix-unified samples. Five samples with different compositions were pressed into pellets both with silver powder as a binder serving to keep the matrix unified, and without any binder. The laser ablation was performed by nanosecond Nd:YAG laser working at 213 nm. The particle formation during ablation of both sets of pellets was studied using an optical aerosol spectrometer allowing the measurement of particle concentration in two size ranges (10-250 nm and 0.25-17 microm) and particle size distribution in the range of 0.25-17 microm. Additionally, the structure of the laser-generated particles was studied after their collection on a filter using a scanning electron microscope (SEM) and the particle chemical composition was determined by an energy dispersive X-ray spectroscope (EDS). The matrix effect was proved to be reduced using the same silver powdered binder for pellet preparation in the case of the laser ablation of powdered materials. The LA-ICP-MS signal dependence on the element content present in the material showed an improved correlation for Co, Ti, Ta and Nb of the matrix-unified samples compared to the non-matrix-unified pellets. In the case of W, the ICP-MS signal of matrix-unified pellets was influenced by the changes in the particle formation.

A new ICP–TOFMS. Measurement and readout of mass spectra with 30 μs time resolution, applied to in-torch LA–ICP–MS

In-torch LA-ICP-MS was implemented into an in-house-built ICP-TOFMS system. The fast data acquisition capabilities of the new configuration allowed simultaneous multi-element measurement and readout of in-torch LA-ICP-MS signals with 30 micros time resolution. The measurements confirmed previously observed fine structures of in-torch generated signals and provided new insights in the dynamic processes in the plasma on a microsecond time scale. The new setup is described in detail and first figures of merit are given.

Determination of absolute transport efficiencies of Be, Cd, In, Pb and Bi for electrothermal vaporization sample introduction into an inductively coupled plasma using an in-line electrostatic precipitator

A novel laboratory-constructed electrostatic precipitator for the determination of analyte transport efficiencies from a tube furnace electrothermal vaporization (ETV) sample introduction system is described. This simple experimental set up captures the analyte electrostatically using a negative corona discharge. The absolute transport efficiencies using experimental conditions typical of those applied to real analysis by ETV–ICP-MS were determined for Be, Cd, In, Pb and Bi to be 26±3, 39±8, 35±1, 50±11 and 35±1%, respectively. Pd and NaCl were evaluated as ‘carriers’ and were found to only marginally increase analyte transport for the elements investigated. Pd enhanced efficiencies 20–50% for all but Bi, which decreased by 17%. The NaCl produced transport enhancements of 10–50% for all five analytes. However, uncertainties in the measurements made several of the individual improvements statistically insignificant. The mean precipitator collection efficiency of the aerosol leaving the ETV for the five elements studied was found to be greater than 90% and was determined using the ICP-MS signal with the in-line precipitator's voltage either on or off. While 30 ETV firings were used for a single efficiency determination, reasonable precision could be obtained with approximately 10 firings while still employing reasonable analyte masses, i.e. approximately 20 ng. The transport results are in good agreement with previous studies using similar ETV design and analyte masses.

Ion chromatographic separation of sulfur-containing inorganic anions with an ICP–MS as element-specific detector

An inductively coupled plasma mass spectrometer (ICP–MS) was used as element-specific detector for sulfide, sulfite, sulfate, and thiosulfate after their chromatographic separation on a Dionex IonPac ® AS12A analytical column. The sulfur-containing anions were detected as 32S 16O + at m/z=48 with the ICP–MS operated with cool and normal plasma conditions, both tuned for the production of high oxide ratios. Three different mobile phases [(NH 4) 2CO 3, Na 2CO 3, and NaOH] were tested. The ICP–MS signal at m/z=48 for the sulfur-containing anions was obtained only with NaOH based eluents and application of a membrane suppressor for removal of sodium. The detection limits ( S/N=3, calculated on elemental basis) at optimal chromatographic conditions for sulfide, sulfite, sulfate, and thiosulfate were 35 μg l −1, 200 μg l −1, 130 μg l −1, and 270 μg l −1, respectively. A lower detection limit for sulfide was found to be a result of a higher absolute sulfur amount input into the plasma due to the release of the dissolved H 2S from the aerosol droplets into the gas phase. Severe signal suppression for sulfide with cool plasma and shortening of the sulfide retention with normal plasma were observed in the case of highly saline samples. Both effects were confirmed to be caused by chloride anions.