Certification of New Selenium-Enriched Yeast and Supplement Reference Materials for Selenomethionine Using Two Independent Measurement Strategies.

Selenium-enriched yeast possesses the unique ability of transforming chemical selenium, such as sodium selenite, into a biologically active form, which mitigates its toxic effects on the human body. The transformation product of this process, selenomethionine, can be safely and effectively absorbed and utilized by the human body; hence, it has been spiked into a selenium-enriched supplement. This study employs two distinct measurement strategies to determine the selenomethionine content in two candidate reference materials, a selenium-enriched yeast powder and supplement, using both organic and inorganic mass spectrometry. The concentrations of selenomethionine in the selenium-enriched yeast were determined using HPLC-ICP-MS and HPLC- ESI-MS/MS, with mass fractions measured at 718 mg SeMet kg-1 and 715 mg SeMet kg-1, respectively. Notably, both methods yielded consistent results for the selenium supplement, with a selenomethionine mass fraction of 59 mg SeMet kg-1. Ultimately, the certified values of these candidate reference materials were determined as 716 mg kg-1 and 59 mg SeMet kg-1 with expanded uncertainties of 36 mg SeMet kg-1 (k = 2) and 5 mg SeMet kg-1 (k = 2), respectively. The development of these candidate reference materials serves as a valuable reference for diverse methods aiming to determine the value of organic selenium speciation in complex food substrates.

An improved calibrated mass spectrometry for absolute copper isotope-ratio measurement using two strategies for mass bias correction factor.

Modern advances in multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) have greatly promoted the investigation of copper isotopes in various research fields. To meet the demand, an improved calibrated mass spectrometry for the absolute determination of copper isotopic composition was developed in this study. The method has made progress in the investigation of instrumental mass bias correction factor for copper isotopic analysis using MC-ICPMS through employing two independent strategies. One is the conventional mathematical iterative method based on the MC-ICPMS measurement data; the other one is direct calculation using the absolute copper isotopic compositions in isotopically enriched 63Cu and 65Cu materials by developing a TE-TIMS method. The results of Kiter = 0.95563(16)k = 1 and KTE = 0.95551(17)k = 1 were consistent in their standard uncertainties, demonstrated the first cross-validation of these two strategies. Thereafter, the proposed calibrated mass spectrometry were applied to re-measure the copper isotope amount ratios in three isotopic reference materials, resulted in RNIST SRM 97665/63 = 0.44547(16)k = 2, RERM®-AE63365/63 = 0.44549(16)k = 2, and RERM®-AE64765/63 = 0.44557(16)k = 2, respectively. These expended uncertainties were only one third or one fifth of the stated uncertainties in their certificates. Furthermore, the absolute copper isotopic compositions in four natural-abundance samples and a new copper isotopic reference material GBW04624 were determined, given an average atomic weight of copper as Ar(Cu) = 63.5456(4)k = 2. The δ65Cu values of GBW04624 relative to NIST SRM 976, ERM®-AE633 and ERM®-AE647 were also applied by implementing the C-SSBIN calibration model. This provides an additional independently certified and SI-traceable copper isotopic reference material, in support of various scientific researches.

Accurate Determination of Trace Molybdenum in Drinking Water by Isotope Dilution Inductively Coupled Plasma Mass Spectrometry.

A method for accurate and precise determination of trace molybdenum in drinking water by isotope dilution inductively coupled plasma mass spectrometry was developed, given the concentrations of Mo in drinking-water samples from Chaoyang and Changping districts of Beijing (China) as 1.017 ± 0.008 and 1.033 ± 0.007 µg kg-1 (k = 2), respectively. Special care was taken for the validation of the proposed ID-ICPMS method using CRM 7203-a, a certified reference material for elemental analysis of tap water.

Investigation of the crucial factors affecting accurate measurement of strontium isotope ratios by total evaporation thermal ionization mass spectrometry.

RATIONALE: An absolute method that does not require calibration is very important in several areas of isotope analysis due to the shortage of suitable certified reference materials (CRMs). As total evaporation thermal ionization mass spectrometry (TE-TIMS) theoretically overcomes mass fractionation through integrating the ion currents till the sample on the filament is completely exhausted, it could be an absolute method that does not require the use of CRMs for calibration. However, the lack of reliable method verification and reasonable uncertainty evaluation restricts its extensive application, and these effects need to be quantitatively evaluated. METHODS: A series of different amounts of strontium reference material SRM987 was deposited on both single and triple tantalum filament sources, and analyzed by TE-TIMS. The work function of the tantalum filament loaded with the sample was measured by ultraviolet photoelectron spectroscopy. In order to evaluate the change in ion transmission efficiency, we terminated the total evaporation process manually after running for a certain period of time, and recorded the ion beam intensity before and after this operation. RESULTS: The TE results obtained with the triple filament source agreed well with the reference values of SRM987, while the TE results obtained with the single filament source changed significantly with the amount of sample loading. The crucial effect factors on TE-TIMS, including ionization temperature fluctuation, variation of ion transmission efficiency and ion loss before data acquisition, were quantitatively assessed. These factors were used to correct the single filament TE results and the measurement uncertainty was quantitatively evaluated. CONCLUSIONS: The reliability of strontium isotopic ratio measurement with triple filament TE-TIMS was verified. The mathematical model for correction of each crucial effect factor was successfully established, thus providing a feasible way for the correction of single filament TE-TIMS results.

On-off-on luminescent pyrophosphate probe based on the use of Mn-doped ZnS quantum dots and using Eu(III) as a mediator.

A selective phosphorescent on-off-on probe with long decay lifetime has been designed for the detection of pyrophosphate ions (PPi). The detection scheme is based on the use of europium(III)-modulated Mn(II)-doped ZnS quantum dots capped with N-acetyl-L-cysteine. Both the aggregation of quantum dots and electron transfer induced by Eu(III) ions cause phosphorescence to be quenched ("off" state). Phosphorescence is, however, restored on addition of PPi to the system ("on" state). The effect is attributed to the removal of Eu(III) from the carboxy groups on the surface of the quantum dots owing to the stronger interaction between PPi and Eu(III). A linear relationship exists between phosphorescence intensity (best measured at excitation/emission wavelengths of 316/594 nm) and PPi concentration in the 400 nM to 6000 nM with a detection limit of 145 nM. An additional attractive feature is provided by the long-lived phosphorescence (1920 µs) of the quantum dots. It can be used to eliminate interference by short-lived fluorescence in biological samples by performing time resolved measurements. The probe was applied to the determination of PPi in spiked in urine samples and gave recoveries in the range from 98 to 105% with RSDs of <2.0%. Graphical abstract Schematic of a long-lived phosphorescent on-off-on probe for the sensitive and selective detection of pyrophosphate ions (PPi). It is based on the use of Eu(III)-modulated Mn(II)-doped ZnS quantum dots (QDs). Phosphorescence is quenched of QDs after the addition of Eu3+but restored after the addition of PPi.

Dispersion-aggregation-dispersion colorimetric detection for mercury ions based on an assembly of gold nanoparticles and carbon nanodots.

Mercury is a common heavy metal element in natural systems and is highly toxic to the human body. Herein, a novel colorimetric detection of Hg2+ ions is proposed based on the aggregation of gold nanoparticles (AuNPs) induced by carbon quantum dots (CDs) with the assistance of glutathione (GSH). In this sensing system, the AuNP/CDs composite forms through Au-N bonds. Simultaneously, the color of the solution turns from wine red to blue. The well-dispersed AuNPs can be restored after the addition of GSH, because GSH competes with CDs to bind onto the surface of AuNPs and protect AuNPs from aggregation. In the presence of Hg2+ ions, GSH can chelate with Hg2+ to form a complex, which subsequently enables CDs to facilitate the aggregation of the AuNPs again. Therefore, according to the red-to-blue color change, a colorimetric sensor is established for the sensitive and selective detection of Hg2+ with a detection limit of 7.5 nM. Moreover, this sensor is successfully used to detect Hg2+ spiked in environmental water. This very simple and cost-effective strategy will promote the development of a colorimetric sensor for the determination of other metal ions in biological and environmental fields.

Accurate Determination of the Absolute Isotopic Composition and Atomic Weight of Molybdenum by Multiple Collector Inductively Coupled Plasma Mass Spectrometry with a Fully Calibrated Strategy.

A fully calibrated strategy has been investigated for the first time for the accurate determination of absolute isotopic composition and atomic weight of molybdenum using multiple-collector inductively coupled plasma mass spectrometry. The correction for instrumental mass bias was performed using synthetic isotope mixtures, which were gravimetrically prepared with all of the seven high-purity and isotopically enriched molybdenum isotope materials together. Six natural molybdenum materials, including molybdenum standard solution NIST SRM 3134, were accurately measured and yielded the absolute isotopic composition (in atom %, k = 1) of 92Mo-14.690(18), 94Mo-9.173(6), 95Mo-15.865(5), 96Mo-16.666(3), 97Mo-9.588(4), 98Mo-24.307(16), and 100Mo-9.711(13). These isotopic data enable an atomic weight Ar(Mo) of 95.9466(34) (k = 2) to be calculated, which is slightly lower than the current standard atomic weight 95.95(1) and with a much improved uncertainty. The associated uncertainties were evaluated according to the Guide to Expression of Uncertainty in Measurement of ISO/BIPM and Monte Carlo simulation to ensure that all sources of uncertainty were fully accounted for. A particular characteristic of the proposed new approach is that mass bias correction factor K for each isotope ratio of molybdenum can be achieved via fully experimental determination without using the traditional semiempirical correction mathematical models. In addition, the relationship between mass of isotope and bias per mass unit ß was investigated based on the thorough measurement data.

Aggregation-Induced Emission Luminogen-Embedded Silica Nanoparticles Containing DNA Aptamers for Targeted Cell Imaging.

Conventional fluorophores usually undergo aggregation-caused quenching (ACQ), which limits the loading amount of these fluorophores in nanoparticles for bright fluorescence imaging. On the contrary, fluorophores with aggregation-induced emission (AIE) characteristics are strongly fluorescent in their aggregate states and have been an ideal platform for developing highly fluorescent nanomaterials, such as fluorescent silica nanoparticles (FSNPs). In this work, AIE luminogens based on salicylaldehyde hydrazones were embedded in silica nanoparticles through a facile noncovalent approach, which afforded AIE-FSNPs emitting much brighter fluorescence than that of some commercial fluorescein-doped silica and polystyrene nanoparticles. These AIE-FSNPs displaying multiple fluorescence colors were fabricated by a general method, and they underwent much less fluorescence variation due to environmental pH changes compared with fluorescein-hybridized FSNPs. In addition, a DNA aptamer specific to nucleolin was functionalized on the surface of AIE-FSNPs for targeted cell imaging. Fluorescent microscopy and flow cytometry studies both revealed highly selective fluorescence staining of MCF-7 (a cancer cell line with nucleolin overexpression) over MCF-10A (normal) cells by the aptamer-functionalized AIE-FSNPs. The fluorescence imaging in different color channels was achieved using AIE-FSNPs containing each of the AIE luminogens, as well as photoactivatable fluorescent imaging of target cells by the caged AIE fluorophore.

A label-free and sensitive fluorescent method for the detection of uracil-DNA glycosylase activity.

The activity of uracil-DNA glycosylase (UDG), an enzyme in the base excision repair, is detected at a high sensitivity by a DNA substrate containing only one uracil through a label-free fluorescent approach, which is also successfully applied for the measurement of UDG inhibitors.

A facile, sensitive and selective fluorescent probe for heparin based on aggregation-induced emission.

A facile, rapidly responsive fluorescence turn-on probe for heparin with high selectivity and sensitivity was reported in this paper. The probe could aggregate on the negatively charged heparin template through electrostatic interactions and then display intense fluorescence due to its aggregation-induced emission (AIE) characteristics. Under optimal condition, the probe showed high selectivity to heparin over chondroitin sulfate(ChS), hyaluronic acid (HA), dextran (DeX) and other substances, with a linear range of 0.2-14 µg/mL, and a detection limit of 57.6 ng/mL. In diluted serum, it also showed good performance.

A ratiometric fluorescent probe for hydrophobic proteins in aqueous solution based on aggregation-induced emission.

A novel fluorescent probe 1 is reported here with ratiometric response to hydrophobic proteins (casein) or proteins with hydrophobic pockets (BSA, HSA) through hydrophobic interaction. Probe 1 underwent deprotonation in aqueous solution at pH 7.4 and emitted blue fluorescence at 436 nm. Upon the addition of BSA, HSA or casein, the aggregation-induced emission fluorescence of 1 at 518 nm was turned on. The fluorescence intensity ratio, I518/I436 was linearly related to the concentrations of these proteins. The detection limits for BSA, HSA and casein based on IUPAC (CDL = 3Sb m(-1)) were 16.2 µg mL(-1), 10.5 µg mL(-1) and 5.7 µg mL(-1), respectively.

Label-free catalytic and molecular beacon containing an abasic site for sensitive fluorescent detection of small inorganic and organic molecules.

In this work, two methods with complementary features, catalytic and molecular beacon (CAMB) and label-free fluorescent sensors using an abasic site, have been combined into new label-free CAMB sensors that possess advantages of each method. The label-free method using a dSpacer-containing molecular beacon makes CAMB more cost-effective and less interfering with the catalytic activity, while CAMB allows the label-free method to use true catalytic turnovers for signal amplifications, resulting in a new label-free CAMB sensor for Pb(2+) ion, with a detection limit of 3.8 nM while maintaining the same selectivity. Furthermore, by using CAMB to overcome the label-free method's limitation of requiring excess enzyme strands, a new label-free CAMB sensor using aptazyme is also designed to detect adenosine down to 1.4 µM, with excellent selectivity over other nucleosides.

Fluorescence turn-on detection of protamine based on aggregation-induced emission enhancement characteristics of 4-(6'-carboxyl)hexyloxysalicylaldehyde azine.

A novel fluorescence turn-on method for sensitive and selective detection of protamine was developed based on aggregation-induced emission enhancement (AIEE) characteristics of 4-(6'-carboxyl)hexyloxysalicylaldehyde azine (CHSA) induced by electrostatic interaction between protamine and CHSA(-). Under optimal conditions described, a large Stokes shift of approximately 198 nm could be observed, and the fluorescence enhancement at 538 nm was linearly related to the concentration of protamine in the range of 0.6-18 microg mL(-1) with the relative correlation coefficient of R(2) = 0.9996 (n = 11) and a detection limit as low as 43 ng mL(-1). The relative standard deviation (R.S.D.) was 2.0% (n = 5). The proposed method was successfully utilized in quantifying protamine in diluted horse serum. In addition, due to the special electrostatic association between protamine and heparin, CHSA could also be employed as a probe to study the interaction between them.