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Ratiometric quantification for competitive immunoassay based on internal standard element detection utilizing inductively coupled plasma mass spectrometry (ICP-MS) as multiplex readout has been demonstrated. The Beta-2-microglobulin (β2-MG) associated with clinical diseases was detected by Y-labeled capture antibody used as internal standard probes and Sm-labeled antigen used as report probes via antigen-antibody reaction. The ratiometric quantification was achieved by taking the signal ratio of Sm/Y. The ratiometric method could compensate for the particle loss and suppress the signal fluctuation, which improved the precision of the quantitative result. Under the optimized conditions, the calibration curves for β2-MG antigen was linear in the range of 0.25–8.0 μg/mL with a detection limit of 0.17 μg/mL (3σ, n = 11). The recoveries of 96.5%–132% were obtained for serum samples spiked with different concentration standards, and the relative standard deviation (RSD) was less than 10%. The β2-MG results in serum samples obtained by the proposed method correlated well with those obtained by time-resolved fluorescence immunoassay (r = 0.947). This proposed method provides a simpler labeling strategy for ratiometric quantification of immunoassay.

ICP-MS-based multiplex immunoassays have the advantages of low sample consumption and minimized repetitions of tedious procedures. However, this technique is seldom used in clinical tests because of the complicated matrix effect in clinical samples and the discrimination effect to the target proteins. In this work, we developed an ICP-MS-based magnetic immunoassay by using magnetic beads as highly efficient affinity probes and optimizing the magnetic immunoassay parameters. We applied this method to the simultaneous determination of three crucial gynecological tumor biomarkers that are vital in the prognosis and monitoring of the recurrence of breast cancer and ovarian cancer. The measurable ranges of HER-2, HE4 and CA15-3 were 12–1000 ng mL−1, 8–2000 pmol L−1 and 5–200 U mL−1, with detection limits (3σ) of 3.94 ng mL−1, 2.59 pmol L−1 and 1.62 U mL−1, respectively. The relative standard deviations (RSDs) were 2.61% for HER-2 at 15 ng mL−1, 4.90% for HE4 at 25 pmol L−1 and 6.68% for CA15-3 at 10 U mL−1, indicating good accuracy of the method. The spiking test indicated that the present method had a low matrix effect. Under optimized conditions, the simultaneous detection of HER-2, HE4, and CA15-3 in clinical serum samples was performed and the values correlated well with those obtained by the time resolved fluorescence immunoassay (r2 = 0.9568 for HER-2, 0.9485 for HE4, 0.9133 for CA15-3). The present work shows that the ICP-MS-based magnetic immunoassay meets the requirements for the quantification of three crucial gynecological tumor biomarkers in real clinical tests.

Introduction Element-tagged immunoassay coupled with inductively coupled plasma-mass spectrometry (ICP-MS) detection has the potential to revolutionize immunoassay analysis in clinical detection; however, a systematic evaluation with the standard guidelines of the assay is needed to ensure its performance meets the requirements of the clinical laboratory. Methods Carcinoembryonic antigen (CEA) was chosen for analysis using the proposed method. A systematic evaluation of the proposed assay was carried out according to the Clinical and Laboratory Standards Institute (CLSI). The 469 clinical samples were analyzed using the new method and compared with the electrochemiluminescent immunoassay (ECLIA) method. Results The measurement range of the assay was 1–900 ng/mL, with a detection limit of 0.83 ng/mL. The inter-assay and intra-assay imprecision were 4.67% and 5.38% with high concentration samples, and 9.27% and 17.64% with low concentration samples, respectively. The cross-reactivity (%) for different antigens was less than 0.05%, and the recovery was between 94% and 108%. Percentage deviation of all the dilutions was less than 12.5% during linearity estimation. The interference bias caused by different substances was less than 10%. The reference interval of the assay was 0–4.442 ng/mL. Comparison with the commercial ECLIA method for clinical sample detection, the proposed method showed a correlation of 0.9878 and no significant differences between the methods were observed (p = 0.6666). Conclusions The ICP-MS based immunoassay was successfully developed, and the analytical performance of the assay met the requirements of the CLSI, which fully proved the clinical transferability and application of the new method.

Multiplex biomolecular analysis with inductively coupled plasma mass spectrometry (ICP-MS) becomes increasingly important in clinical diagnosis and single cell analysis. However, the sensitivity of ICP-MS-based immunoassay is only comparable or lower than those of fluorescence methods at the present stage. Therefore, designing elemental tags with a large number of metal atoms is necessary to achieve high-sensitive detection. In this work, we proposed a new strategy to build up elemental tag loading with hundreds of rare earth ions by coupling alkyne-DNA chains with rare earth element (REE)-DOTA complexes a click chemistry reaction. There are about 2 orders of magnitude improvement in sensitivity compared with single metal-ion tags. DNA chains with multialkynyl groups were facilely prepared by PCR synthesis. Moreover, the DNA-based elemental tags own excellent water-solubility and biocompatibility. The tags would be potentially applied to mass cytometry and clinical diagnosis.

Intermediates in the gas-phase reaction of diatomic [TaO]+ with CH4 to generate ethane and ethylene have been explored using ICP-MS/MS complemented by high-level quantum chemical calculations. [TaOH]+, [TaOCH2]+, [TaOC2H6]+and [TaOC2H4]+ were identified and the formation pathways of them were discussed, revealing the mechanistic scenario for this oxidative coupling of methane to the C2 hydrocarbons process.

Background: Element-tagged immunoassay coupled with inductively coupled plasma mass spectrometry (ICP-MS) detection has the potential to revolutionize immunoassay analysis for multiplex detection. However, a further study referring to the standard evaluation and clinical sample verification is needed to ensure its reliability for simultaneous analysis in clinical laboratories. Methods: Carcinoembryonic antigen (CEA) and &alpha, fetoprotein (AFP) were chosen for the duplex immunoassay. The performance of the assay was evaluated according to guidelines from the Clinical and Laboratory Standards Institute (CLSI). Moreover, reference intervals (RIs) of CEA and AFP were established. At last, 329 clinical samples were analyzed by the proposed method and results were compared with those obtained with electrochemiluminescent immunoassay (ECLIA) method. Results: The measurement range of the assay was 2&ndash, 940 ng/mL for CEA and 1.5&ndash, 1000 ng/mL for AFP, with a detection limit of 0.94 ng/mL and 0.34 ng/mL, respectively. The inter-assay and intra-assay imprecision were all less than 6.58% and 10.62%, respectively. The RI of CEA and AFP was 0&ndash, 3.84 ng/mL and 0&ndash, 9.94 ng/mL, respectively. Regarding to clinical sample detection, no significant difference was observed between the proposed duplex assay and the ECLIA method. Conclusions: The ICP-MS-based duplex immunoassay was successfully developed and the analytical performance fully proved clinical applicability. Well, this could be different with other analytes.

Inductively Coupled Plasma Mass Spectrometry (ICP-MS) based immunoassay method has been proposed in multiple immunoassays but has not been used in competitive and sandwich formats immunoassay simultaneously. The two immunoassays were usually conducted separately in clinical field depending on the size and the amount of binding sites of targets. We proposed an immunoassay method based on magnetic beads and ICP-MS detection that could be suitable for both small and large molecules. The functionalized magnetic beads were added to capture the immune complex after immune reaction. In this way, thyrotropin and free thyroid hormone can be captured, separated and then detected according to the elemental tags by ICP-MS simultaneously. The new method was evaluated by comparing the results with time resolved fluorescence immunoassays (TRFIA). The dynamic ranges of TSH and FT4 were 0.16-105 mU/L and 3.5-65 pmol/L, respectively. The limits of detections were 0.06 mU/L for TSH and 1.59 pmol/L for FT4. And the relative standard deviations (RSD) of TSH and FT4 were 4.64% at 2.5 mU/L and 1.87% at 5.85 pmol/L. This immunoassay method enables the determination of small and large biomolecules simultaneously via competitive and sandwich immunoassay formats.

Methylmercury (CH3Hg) is one of the most widespread toxic contaminants. Although the formation of CH3Hg in aqueous environments has been widely investigated, little information is available on direct anthropogenic or natural emissions of CH3Hg to the atmosphere. In this work, ICP-MS/MS was chosen as a tool to study abiotic methylation of inorganic mercury reacting with VOCs in a gas environment for the first time. We found that the gaseous Hg+ ions were transformed to the more toxic CH3Hg+ ions instantaneously when colliding with some VOCs. Several VOCs, e.g., methyl iodide (CH3I), methylbenzene, acetic acid and ethyl acetate, exhibited good methylation of Hg+ ions with productivities of 1.77%, 1.28%, 1.35% and 1.18%, respectively. Four isotope peaks of CH3199Hg (M = 214), CH3200Hg (M = 215), CH3201Hg (M = 216) and CH3202Hg (M = 217) were identified when Hg+ ions collided with CH3I, and the methyl group in CH3Hg+ was validated by the source of CD3I, indicating that CH3Hg+ ions were formed. This study reveals that the abiotic methylation of Hg+ ions could occur when in contact with the VOCs in the atmosphere, leading to secondary environmental pollution.

The development of material science increasingly calls for rapid characterization methods with low limits of detection and high spatial resolution. Here we report a depth profile analysis method for thin layer coatings by combining low temperature plasma (LTP) probe with inductively coupled plasma mass spectrometry (ICP-MS). The LTP probe with diameter of several tens of micrometers served as a tool for mass removal, which is generated by the discharge in a quartz capillary at ambient condition. The sample material is ablated by the LTP probe and converted into an aerosol, and transported by a carrier gas flow to the ICP-MS, where the decomposed and ionized aerosol particles are analyzed with high sensitivity. Scanning electron microscope (SEM) micrographs reveal that the trace after ablation by the LTP probe is a hole with a diameter less than 10 microm. A lateral resolution of approximately 200 microm has been achieved by analyzing an electron component with interval metal stripes. Depth profiling of a 100 nm single layer sample and a multiple layer sample (100 nm Al/250 nm SiO(2)/100 nm Au/50 nm Cr) on a silicon substrate have been successfully performed at ambient condition. The present method offers unique advantages in terms of high spatial resolution, fast analysis speed and ease of implementation. It might be considered a complementary technique to existing depth profiling methods such as GD-MS/OES, AES, and SIMS. In addition, the simple-to-fabricate LTP probe is easily coupled to various other elemental analysis tools for thin layer or direct solid sample analysis in micro area.

A highly sensitive immunoassay is proposed based on time-resolved inductively coupled plasma mass spectrometry with nanoparticles as tags to antibody. Instead of using traditional integral mode detection, the transient signals induced by the flash of ions in the plasma torch from the ionization of nanoparticles tagged on antibody were recorded in a time-resolved mode. Since, under certain conditions, the frequency of transient signals is directly correlated to the concentration of nanoparticle tags, the concentration of nanoparticle-tagged antibodies can be quantified by the frequency of transient signals. With the present instrument setup, gold nanoparticle (Au-NP) tags, as small as about 15 nm in diameter, can be detected. This protocol is evaluated for a competitive immunoassay and the linear range for -fetoprotein is 0.016 – 6.8 g/L (between 20 and 80% inhibition). The limit of quantification is 0.016 g/L (20% inhibition, IC20) with a relative standard deviation of 4.2% (20% inhibition, 4 replicates) for -fetoprotein. The present strategy provides a sensitive readout method for nanoparticle tags, which is quite promising for numerous applications in immunoassay, DNA hybridization, and other biological analyses. (J Am Soc Mass Spectrom 2009, 20, 1096 –1103) © 2009 American Society for Mass Spectrometry

Background: An inductively coupled plasma mass spectrometry (ICP-MS)-based immunoassay has been proposed independently by Baranov et al. (Anal Chem 2002;74:1629–36) and our group, but the applicability of this method for multianalyte analysis in clinical samples has not been fully illustrated. We developed a dual-label immunoassay method for the simultaneous determination of α-fetoprotein (AFP) and free β-human chorionic gonadotropin (hCGβ) in human serum.Methods: Monoclonal antibodies immobilized on microtiter plates captured AFP and hCGβ, which were detected by use of Eu3+-labeled anti-AFP and Sm3+-labeled anti-hCGβ monoclonal antibodies. Eu3+ and Sm3+ were dissociated from the immunocomplex with HNO3 solution (10 mL/L) and delivered by peristaltic pump to the ICP mass spectrometer.Results: The measurable ranges of AFP and hCGβ were 4.6–500 and 5.0–170 μg/L, respectively, with detection limits of 1.2 and 1.7 μg/L (3 SD above mean of zero calibrator), respectively. The intraassay imprecision (CV) for AFP was 8.3%, 4.0%, and 2.7% at 16.3, 86, and 354 μg/L, respectively, and the interassay CV was 10%, 5.7%, and 3.5%. For hCGβ, the intraassay CV was 5.4%, 6.4%, and 3.1%, respectively, at 10.5, 45.2, and 105 μg/L, and the interassay CV was 7.2%, 8.0%, and 3.7%. Comparison with IRMAs for AFP and hCGβ yielded correlation coefficients (r2) of 0.97 and 0.95.Conclusions: Two proteins can be measured simultaneously by immunoassays using two rare earth elemental tags (Eu3+ and Sm3+) and ICP-MS detection. The multielement capability and the multiple potential elemental labels make ICP-MS attractive for multianalyte immunoassays. Implementation of ICP-MS-linked immunoassays may be relatively straightforward because the labeling and immunoreaction procedures have been well developed for clinical time-resolved immunofluorometric assays.

A multiplex DNA assay based on nanoparticle (NP) tags detection utilizing single particle mode inductively coupled plasma mass spectrometry (SP-ICP-MS) as ultrasensitive readout has been demonstrated in the article. Three DNA targets associated with clinical diseases (HIV, HAV, and HBV) down to 1 pM were detected by DNA probes labeled with AuNPs, AgNPs, and PtNPs via DNA sandwich assay. Single nucleotide polymorphisms in genes can also be effectively discriminated. Since our method is unaffected by the sample matrix, it is well-suited for diagnostic applications. Moreover, with the high sensitivity of SP-ICP-MS and the variety of NPs detectable by SP-ICP-MS, high-throughput DNA assay could be achieved without signal amplification or chain reaction amplification.

This paper describes the study of atomization of nanoparticles by inductively coupled plasma mass spectrometry (ICPMS) and developes a novel nonisotopic immunoassay by coupling sandwich-type immunoreaction to ICPMS. The goat-anti-rabbit immunoglobulin G (IgG) labeled with colloidal gold nanoparticles served as an analyte in ICPMS for the indirect measurement of rabbit-anti-human IgG. Matrix effect studies showed the gold signal was not sensitive to the organic matrix. A relatively good correlation (r2 = 0.9528) between the proposed method and enzyme-linked immunosorbent assay has been obtained. The method may have significant potential as an important ICPMS-based nonisotopic immnoassay method for the simultaneous determination of biologic analytes of interest by labeling different kinds of inorganic nanoparticles.

The novel coupling method based on the hyphenation of immunoreaction with ICP-MS was developed and applied to the determination of thyroid-stimulating hormone (TSH) in human serum. In this system, TSH was firstly captured by anti-TSH monoclonal antibodies immobilized on a solid support. Biotinylated anti-TSH monoclonal antibodies and Eu3+-labelled streptavidin were then added to form the complex, captured antibody–TSH–biotinylated anti-TSH antibody–Eu3+-labelled streptavidin. After unbound reactants were washed away, Eu3+ bound to the complex was extracted by 1% HNO3 and measured by ICP-MS. The Eu signal was directly proportional to the serum TSH concentration. The limit of detection was 0.5 mIU L−1 and the assay was linear up to 170 mIU L−1. The within-run (n = 6) and between-run (n = 6) relative standard deviations (RSD) for low, medium and high concentration standards did not exceed 10%. The TSH results obtained by this procedure correlated well with those obtained by radioimmunoassay (r2 = 0.9639).

A hyphenated technique for the determination of As III , As V , arsenobetaine (AsB), arsenocholine (AsC), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) has been developed by coupling an anion-exchange column to an inductively coupled plasma mass spectrometer, using an in-house developed thermospray nebulizer (TN) as an interface. Optimisation of the chromatographic conditions led to baseline separation of the signals from the six aforementioned compounds in approximately 10 min, using isocratic elution. Application of the TN offered a ten-fold improvement in sensitivity in comparison with the standard pneumatic nebulizer. To prevent clogging of the torch and to slow down deposit formation on the sampling cone, use was made of a second HPLC pump and a switching valve, allowing rinsing with HNO 3 between two measurements. Detection limits were also improved and were in the range 0.04–0.12 µg l -1 as arsenic. Finally, the technique developed was used for the analysis of several mineral waters and urine samples. The improved sensitivity was also obtained for real samples. In the mineral waters analysed only As V could be detected. In the ten-fold diluted urine samples, all aforementioned arsenic compounds were present, except for AsC, which could not be detected.

A sensitive sandwich type immunoassay has been proposed with the detection by inductively coupled plasma mass spectrometry (ICP-MS) in a single particle mode (time resolved analysis). The signal induced by the flash of ions ( 197 Au + ) due to the ionization of single Au-nanoparticle (Au-NP) label in the plasma torch can be measured by the mass spectrometer. The frequency of the transient signals is proportional to the concentration of Au-NPs labels. Characteristics of the signals obtained from Au-NPs of 20, 45 and 80 nm in diameters were discussed. The analytical figures for the determination of Au-labeled IgG using ICP-MS in conventional integral mode and single particle mode were compared in detail. Rabbit-anti-human IgG was used as a model analyte in the sandwich immunoassay. A detection limit (3 σ ) of 0.1 ng mL −1 was obtained for rabbit-anti-human IgG after immunoreactions, with a linear range of 0.3–10 ng mL −1 and a RSD of 8.1% (2.0 ng mL −1 ). Finally, the proposed method was successfully applied to spiked rabbit-anti-human IgG samples and rabbit-anti-human serum samples. The method resulted to be a highly sensitive ICP-MS based sandwich type immunoassay.

A sandwich-type immunoassay linked with inductively coupled plasma mass spectrometry (ICP-MS) has been developed for the detection of anti-erythropoietin antibodies (anti-EPO Abs). Recombinant human erythropoietin (rhEPO) was immobilized on the solid phase to capture anti-rhEPO Abs specifically. After the immunoreactions with Au-labeled goat-anti-rabbit IgG, a diluted HNO(3) (2%) was used to dissociate Au nanoparticles which was then introduced to the ICP-MS for measurements. Under the optimized conditions, the calibration graph for anti-EPO Abs was linear in the range of 35.6-500 ng mL(-1) with a detection limit of 10.7 ng mL(-1) (3sigma, n=9). The relative standard deviation (R.S.D.) for three replicate measurements of 30.9 ng mL(-1) of anti-EPO Abs was 8.43%. The recoveries of anti-EPO Abs in sera at the spiking level of 50, 100, 150, 200 and 400 ng mL(-1) were 99.2%, 101.5%, 95.0%, 94.0% and 102.9%, respectively. For the real sample analysis, 26 samples from healthy people and 53 samples from patients with rhEPO treatments were studied. One sample from patients showed significantly higher anti-EPO Abs from other samples, indicating a possibility of immune response of this patient.

Inductively coupled plasma mass spectrometry (ICPMS) has been successfully used for the detection of element-tagged biomolecules with the advantage of multielement capability. However, this technique cannot be used for microarray detection due to the necessity to dissolve the elemental tags before introducing them to the plasma source. Here, we report the detection of multiple proteins on each spot of the immuno-microarray by laser ablation ICPMS. alpha-Fetoprotein IgG (AFP), carcinoembryonic antigen (CEA), and human IgG, as model proteins, have been detected on the basis of sandwich-type immunoreactions on a microarray with Sm3+-labeled AFP antibody, Eu3+-labeled CEA antibody, and Au-labeled goat-anti-human IgG (GAH) as labeled antibodies. The detection limits were 0.20, 0.14, and 0.012 ng mL-1 (3sigma) with the RSD of 5.7%, 2.6%, and 2.3% at the concentration of 1.0 ng mL-1 for AFP, CEA, and human IgG, respectively. The present detection method permits detecting multiple analytes from each spot of microarray with a spatial resolution at micrometer range, which can alleviate the stress to fabricate high-density arrays. Furthermore, the substrate materials and immobilized proteins do not interfere with the detection. The present technique provides a new strategy for readout of microarray.

Three common Chinese edible seaweeds, one brown (Laminaria japonica) and two red (Porphyra crispata and Eucheuma denticulatum), were examined for their total arsenic content. The As species were extracted with yields of 76.4, 69.8 and 25.0%, respectively. Anion-exchange and cation-exchange high-performance liquid chromatography (HPLC) in combination with inductively coupled plasma mass spectrometry (ICP-MS) were used for the separation of the different arsenic species in two of the three seaweed extracts (Laminaria and Porphyra). The main arsenic species in the algal extracts are arseno sugars, although it has been shown that the Laminaria seaweed contains significant amounts of dimethylarsinic acid (DMA). HPLC was coupled with electrospray mass spectrometry (ES-MS) for structural confirmation of the arsenic species. The mass spectrometer settings for the arseno sugars were optimised using standards. The conclusions drawn on the basis of HPLC-ICP-MS were confirmed by the HPLC-ES-MS data. The HPLC-ES-MS method is capable of determining both arseno sugars and DMA in the seaweeds. The unknown compounds seen in the HPLC-ICP-MS chromatogram of Laminaria could not be ascribed to trimethylarsenic oxide or tetramethylarsonium ion.

Real-time and in-situ monitoring of ongoing chemical reactions by mass spectrometry was achieved by simply directing the low-temperature plasma (LTP) to the surface of the reaction system for analyte desorption and ionization without any sample pretreatment.