Sensitive Detection and Quantification of Oxygenated Compounds in Complex Samples Using GC-Combustion-MS.

This work introduces a new element-selective gas chromatography detector for the accurate quantification of traces of volatile oxygen-containing compounds in complex samples without the need for specific standards. The key to this approach is the use of oxygen highly enriched in 18O as the oxidizing gas in a combustion unit (800 °C) that allows us to directly and unambiguously detect the natural oxygen present in the GC-separated compounds through its incorporation into the volatile species formed after their combustion and their subsequent degradation to 16O in the ion source. The unspecific signal due to the low 16O abundance in the oxidizing gas could be compensated by measuring the m/z 12 that comes as well from the CO2 degradation. Equimolarity was proved with several O-containing compounds with different sizes and functionalities. A detection limit of 28 pg of injected O was achieved, which is the lowest ever reported for any GC detector, which barely worsened to 55 and 214 pg of O when the oxygenate partially or completely coeluted with a very abundant matrix compound. Validation was attained by the analysis of a SRM to obtain accurate (99-103%) and precise (1-4% RSD) results. Robustness was tested after spiking a hydrotreated diesel with 10 O-compounds at the ppm level, which could be discriminated from the matrix crowd and quantified (mean recovery of 102 ± 9%) with a single generic standard. Finally, it was also successfully applied to easily spot and quantify the 33 oxygenates naturally present in a complex wood bio-oil sample.

An in-depth physicochemical investigation of drug-loaded core-shell UiO66 nanoMOFs.

Nanosized UiO66 are among the most studied MOF materials. They have been extensively applied in various areas, such as catalysis, gas absorption, electrochemistry, chemical sensing, and biomedical applications. However, the preparation of stable nano-sized UiO66 for drug delivery applications is challenging because of the high tendency of UiO66 to aggregate during storage. To address this issue, we coated UiO66 with oligomers made of crosslinked cyclodextrins. The coated UiO66 exhibited a good stability upon storage for more than three weeks, even for low quantities of coating materials. The resulting core-shell UiO66 were characterized using a set of complementary methods including microscopies, spectroscopies, X-ray diffraction, and thermogravimetric investigations. Size distribution was assessed by orthogonal methods. Cisplatin was loaded in the core-shell nanoparticles, followed by an in-depth analysis by asymmetric flow field-flow fractionation (AF4) hyphenated with inductively coupled plasma-mass spectrometry (ICP-MS). This method combines the extremely high elemental selectivity and ultratrace detection limits of mass spectrometry with the capacity of AF4 to differentiate the diverse populations present in the sample. Free cisplatin and UiO66-associated cisplatin could be well separated by AF4. AF4-ICP-MS/MS analysis provided the exact drug loading, without the need of separating the nanoparticles from their suspension media. These data suggest the potential of AF4-ICP-MS/MS in the optimization of drug delivery systems.

A plasmonic MNAzyme signal amplification strategy for quantification of miRNA-4739 breast cancer biomarker.

A major challenge in the 21st century is the development of point-of-care diagnostic tools capable to detect and quantify disease biomarkers in a straightforward, affordable, sensitive, and specific manner. The remarkable plasmonic properties of gold nanoparticles (AuNPs) have promoted their use for development of simple methodologies for nucleic acid detection in combination with a variety of oligonucleotides amplification techniques. Here, assemblies of AuNPs with Multicomponent Nucleic Acid enzymes (MNAzymes) has been successfully used in the design of a highly sensitive and simple bioassay for rapid spectroscopic detection and quantification of miRNA-4739 in blood samples. The miRNA selected is a doxorubicin chemoresistant biomarker in breast cancer which overexpression promotes the proliferation, progression, and survival of cancer cells. In this work, two alternatives experimental designs, based on use of MNAzymes and AuNPs, have been optimized and applied for sensitive miRNA-4739 quantification: one based on a traditional direct measurement of wavelength shift and a second non-conventional simple approach based on isolation and measurement of free nanoparticles absorbance. Improvement in sensitivity and, higher measurement accuracy and precision were achieved with the second approach. The developed bioassay provides a detection limit as low as 7 pmolL-1 for miRNA-4739 quantification and performed satisfactory selectivity and well practical applicability by analysis of the miRNA-4739 in blood, demonstrating that the proposed strategy is a promising and suitable spectroscopic method for breast cancer diagnosis thought liquid biopsy of circulating tumoral cells.

Potential of GC-Combustion-MS as a Powerful and Versatile Nitrogen-Selective Detector in Gas Chromatography.

Here, we show the potential and applicability of the novel GC-combustion-MS approach as a nitrogen-selective GC detector. Operating requirements to achieve reproducible and compound-independent formation of volatile NO species as a selective N-signal during the combustion step are described. Specifically, high temperatures (≥1000 °C) and post-column O2 flows (0.4 mL min-1 of 0.3% O2 in He) turned out to be necessary when using a vertical oven without makeup flow (prototype #1). In contrast, the use of a horizontal oven with 1.7 mL min-1 He as an additional makeup flow (prototype #2) required milder conditions (850 °C and 0.2 mL min-1). A detection limit of 0.02 pg of N injected was achieved, which is by far the lowest ever reported for any GC detector. Equimolarity, linearity, and peak shape were also adequate. Validation of the approach was performed by the analysis of a certified reference material obtaining accurate (2% error) and precise (2% RSD) results. Robustness was tested with the analysis of two complex samples with different matrices (diesel and biomass pyrolysis oil) and N concentration levels. Total N determined after the integration of the whole chromatograms (524 ± 22 and 11,140 ± 330 µg N g-1, respectively) was in good agreement with the reference values (497 ± 10 and 11,000 ± 1200 µg N g-1, respectively). In contrast, GC-NCD results were lower for the diesel sample (394 ± 42 µg N g-1). Quantitative values for the individual and families of N species identified in the real samples by parallel GC-MS and additional GC × GC-MS analyses were also obtained using a single generic internal standard.

Relative and Transport Efficiency-Independent Approach for the Determination of Nanoparticle Size Using Single-Particle ICP-MS.

Herein, we introduce the first relative single-particle inductively coupled plasma mass spectrometry (spICP-MS) approach where size calibration is carried out using the target NP itself measured under different instrumental conditions without external dependence on the complex and prone-to-error determination of transport efficiency or mass flux calibrations, in contrast to most spICP-MS approaches. The simple approach proposed allows determining gold nanoparticle (AuNP) sizes, with errors ranging from 0.3 to 3.1% (corroborated by HR-TEM). It has been demonstrated that the changes observed in the single-particle histograms obtained for a suspension of AuNPs under different sensitivity conditions (n = 5) are directly and exclusively related to the mass (size) of the target AuNP itself. Interestingly, the relative nature of the approach shows that once the ICP-MS system has been calibrated with a generic NP standard, it is no longer necessary to repeat the calibration for the size determination of different unimetallic NPs carried out along time (at least 8 months), independently of their size (16-73 nm) and even nature (AuNP or AgNP). Additionally, neither the NP surface functionalization with biomolecules nor protein corona formation led to significant changes (relative errors slightly increased 1.3- to 1.5-fold, up to 7%) in the NP size determination, in contrast to conventional spICP-MS approaches where relative errors increased 2- to 8-fold, up to 32%. This feature could be especially valuable for the analysis of NPs in real samples without the need of matrix-matched calibration.

Certification of protein biomarker standards using element MS and generic standards: Application to human cytokines.

The availability of protein standards and methods for their characterization, quantification, and purity assessment are currently a bottleneck in absolute quantitative proteomics. In this work, we introduce an absolute quantitative analytical strategy based on ICP-MS sulfur detection that uses sulfate as generic standard to quantify and certify the mass purity of protein standards. The methodology combines capillary chromatographic separation with parallel detection with ICP-MS and ESI-MS to determine proteoforms concentration and identity, respectively. The workability of the methodology was demonstrated using recombinant human cytokine standards IP-10 and Flt3L (2 batches), which are relevant biomarkers for carcinoma or inflammatory diseases. Every key factor (transport efficiency, column recovery, signal stability and internal standard suitability) was taken into account and certified BSA standard was used as quality control for validation purposes. Protein quantification values and resulting mass purity certification of IP-10 and one batch of Flt3L were very high (100 and 86%, respectively). Lower mass purity obtained for another batch of Flt3L (<70%) concurred with the finding of significant proteoforms resulted from oxidation processes as observed by parallel ESI-MS.

AF4-UV/VIS-MALS-ICPMS/MS for the characterization of the different nanoparticulated species present in oligonucleotide-gold nanoparticle conjugates.

In-depth characterization of functionalized nanomaterials is still a remaining challenge in nanobioanalytical chemistry. In this work, we propose the online coupling of Asymmetric Flow Field-Flow Fractionation (AF4) with UV/Vis, Multiangle Light Scattering (MALS) and Inductively Coupled Plasma-Tandem Mass Spectrometry (ICP-MS/MS) detectors to carry out, in less than 10 min and directly in the functionalization reaction mixture, the complete characterization of gold nanoparticles (AuNPs) functionalized with oligonucleotides and surface-modified with polyethylene glycol (PEG). AF4 separation provided full separation of the bioconjugates from the original AuNPs while P/Au and S/Au ICP-MS/MS ratios in the bioconjugate fractographic peaks could be used to compute the corresponding stoichiometries, oligonucleotide/AuNP and PEG/AuNPs. MALS detection clearly showed the coexistence of two distinct nanoparticulated populations in the bioconjugation mixture, which were demonstrated to be different not only in size but in functionality as well. The major bioconjugate population showed lower hydrodynamic ratios (18 nm) with higher and steadier oligonucleotides/AuNPs (92) and PEG/AuNPs (2350) stoichiometries, in comparison to the minor abundant population (54 nm, 51 and 1877, respectively). Moreover, the ratio between the absorbance signals measured at 520 nm and 650 nm reflects a lower AuNP aggregation in the major (10.5) than in the minor (4.5) population. Results obtained prove the benefits of a detailed characterization to find out if subsequent purification of functionalized AuNP-oligonucleotides is required to design more efficiently their final bioanalytical application.

Absolute quantification of proteins using element mass spectrometry and generic standards.

Elemental mass spectrometry is a powerful analytical technique widely established in inorganic analysis. However, despite its quantitative capabilities, it is not yet fully integrated or considered in Life Sciences fields like proteomics. Whereas it is true that ICP-MS has suffered from several instrumental and analytical limitations that have hindered its applicability in protein analysis, significant developments during the last decades have turned ICP-MS into an interesting and, in our opinion, a powerful tool to consider for accurate protein quantification without recourse to specific protein standards. Herein we will try to discuss how these traditional limitations in ICP-MS have been overcome, what further improvements are yet necessary (some of which are shared with MS-based proteomics platforms) and enlighten some of the already existing and potential applications of ICP-MS in absolute quantitative proteomics. SIGNIFICANCE: ICP-MS has the potential to become a complementary tool to help molecular mass spectrometry cope with existing limitations, especially those related to standardization and accuracy, in the absolute proteomics field. It can provide absolute quantification of diverse proteoforms using a single generic compound containing sulfur and/or another target element (e.g., phosphorous). Moreover, its applications in quantitative proteomics are no longer limited to protein standards certification or quantification of simple or purified mixtures. Interestingly, absolute quantification of proteins using ICP-MS is favored when carried out at the intact level, making it very compatible with top-down proteomics approaches. Recent instrumental and methodological advances enable synergic combination of ICP-MS with stablished LC-MS proteomics methodologies, setting the basis for its implementation in quantitative proteomics workflows.

Signal amplification strategies for clinical biomarker quantification using elemental mass spectrometry.

The current trends in modern medicine towards early diagnosis, or even prognosis, of different diseases have brought about the need for the corresponding biomarker detection at ever lower levels in really complex matrices. To do so, it is necessary to use proper extremely sensitive detection techniques such as elemental mass spectrometry. However, target labelling with metals for subsequent sensitive ICP-MS detection falls short nowadays even if resorting to inorganic nanoparticles containing a high number of detectable elements. Thus, new amplification strategies are being proposed to face this analytical challenge that will be critically discussed in this paper. Fundamentals of different novel strategies developed to achieve signal amplification and sensitive elemental mass spectrometry detection are here discussed. Some representative examples of relevant clinical applications are highlighted, along with future prospects and challenges.

Combined Molecular and Elemental Mass Spectrometry Approaches for Absolute Quantification of Proteomes: Application to the Venomics Characterization of the Two Species of Desert Black Cobras, Walterinnesia aegyptia and Walterinnesia morgani.

We report a novel hybrid, molecular and elemental mass spectrometry (MS) setup for the absolute quantification of snake venom proteomes shown here for two desert black cobra species within the genus Walterinnesia, Walterinnesia aegyptia and Walterinnesia morgani. The experimental design includes the decomplexation of the venom samples by reverse-phase chromatography independently coupled to four mass spectrometry systems: the combined bottom-up and top-down molecular MS for protein identification and a parallel reverse-phase microbore high-performance liquid chromatograph (RP-µHPLC) on-line to inductively coupled plasma (ICP-MS/MS) elemental mass spectrometry and electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-QToF MS). This allows to continuously record the absolute sulfur concentration throughout the chromatogram and assign it to the parent venom proteins separated in the RP-µHPLC-ESI-QToF parallel run via mass profiling. The results provide a locus-resolved and quantitative insight into the three desert black cobra venom proteome samples. They also validate the units of measure of our snake venomics strategy for the relative quantification of snake venom proteomes as % of total venom peptide bonds as a proxy for the % by weight of the venom toxins/toxin families. In a more general context, our work may pave the way for broader applications of hybrid elemental/molecular MS setups in diverse areas of proteomics.

Assessment of the Potential and Limitations of Elemental Mass Spectrometry in Life Sciences for Absolute Quantification of Biomolecules Using Generic Standards.

Inductively coupled plasma-mass spectrometry (ICP-MS) has been widely used in Life Sciences for the absolute quantification of biomolecules without specific standards, assuming the same response for generic compounds including complex biomolecules. However, contradictory results have been published on this regard. We present the first critical statistical comparison of the ICP-MS response factors obtained for 14 different relevant S-containing biomolecules (three peptides, four proteins, one amino acid, two cofactors, three polyethylene glycol (PEG) derivatives, and sulfate standard), covering a wide range of hydrophobicities and molecular sizes. Two regular flow nebulizers and a total consumption nebulizer (TCN) were tested. ICP-MS response factors were determined though calibration curves, and isotope dilution analysis was used to normalize the results. No statistical differences have been found for low-molecular-weight biocompounds, PEGs, and nonhydrophobic peptides using any of the nebulizers tested. Interestingly, while statistical differences were still found negligible (96-104%) for the proteins and hydrophobic peptide using the TCN, significantly lower response factors (87-40%) were obtained using regular flow nebulizers. Such differential behavior seems to be related mostly to hydrophobicity and partially to the molecular weight. Findings were validated using IDA in intact and digested bovine serum albumin solutions using the TCN (98 and 100%, respectively) and the concentric nebulizer (73 and 97%, respectively). Additionally, in the case of a phosphoprotein, results were corroborated using the P trace in parallel to the S trace used along the manuscript. This work seems to suggest that ICP-MS operated with regular nebulizers can offer absolute quantification using generic standards for most biomolecules except proteins and hydrophobic peptides.

Quantitative multiplexed elemental (C, H, N and S) detection in complex mixtures using gas chromatography.

We present a novel and single detection approach that enables sensitive, accurate and compound-independent quantification of N, S and H in the individual compounds present in complex samples. Integration of the whole chromatographic profile gives the total content of the elements. Simultaneous universal detection is also achieved using the C profile.

Capabilities of asymmetrical flow field - Flow fractionation on-line coupled to different detectors for characterization of water-stabilized quantum dots bioconjugated to biomolecules.

The asymmetric flow field-flow fractionation (AF4) coupled on-line with elemental (inductively coupled plasma-mass spectrometry, ICP-MS) and molecular (fluorescence and UV) detection has been investigated as a powerful tool for the characterization of bioinorganic nano-conjugates. In this study, we described methods for the characterization of biotin-antibody complexes bioconjugated with streptavidin quantum dots (QDs-SA-b-Ab). Operating parameters of AF4 separation technique were optimized and two procedures are proposed using a channel thickness of 350 µm and 500 µm. The use of a 500 µm spacer allowed to achieve an efficient AF4 separation of the QDs-SA-b-Ab complexes from the excess of individual species used in the bioconjugation that was required for a proper characterization of the bioconjugates. Optimization of the AF4 allowed a separation resolution good enough to isolate the QDs-SA-b-Ab bioconjugates from the free excess of b-Ab and QD-SA. The efficiency of the bioconjugation process could be then calculated, obtaining a value of 86% for a 1 QDs-SA: 5 b-Ab bioconjugation ratio. In addition, sample recovery around 90% was achieved.

Anion-Specific Sulfur Isotope Analysis by Liquid Chromatography Coupled to Multicollector ICPMS.

An accurate method has been developed to measure, in a single analytical run, δ34S in sulfite, sulfate and thiosulfate in water samples by liquid chromatography combined with multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). The method is based on the anionic exchange separation of sulfur species prior to their online isotope ratio determination by MC-ICPMS. Mass bias correction was accomplished by a novel approach based on the addition of an internal sulfur-containing standard to the sample. This innovative approach was compared to the sample-standard bracketing procedure. On-column isotopic fractionation was observed and therefore corrected by external calibration. Isotopic ratios were calculated by linear regression slope (LRS), an advantageous method for transient signals, leading to a combined uncertainty of δ34S below 0.25‰ and a reproducibility below 0.5‰ for the injection of 1 µg of S. The method was successfully applied to the measurement of δ34S in synthetic solutions and environmental water samples. Matrix effects leading to δ34S overestimation were observed for sulfate in some samples with high sodium/sulfate mass ratios. The developed analytical procedure simplifies the δ34S analysis of liquid environmental samples since preparation steps are no longer required and allows the analysis of several sulfur-containing species in a single run.

Simple and rapid electrochemical quantification of water-stabilized HgSe nanoparticles of great concern in environmental studies.

The sensitive monitoring of mercury (II) selenide nanoparticles (HgSe NPs) is of great potential relevance in environmental studies, since such NPs are believed to be the ultimate metabolic product of the lifesaving mechanism pathway of Hg detoxification in biological systems. In this context, we take advantage of using gold-nanostructured screen-printed carbon electrodes (SPCE-Au) for the rapid, simple and sensitive electrochemical quantification of engineered water-stable HgSe NPs, as an advantageous alternative to conventional elemental analysis techniques. HgSe NPs are first treated in an optimized oxidative/acidic medium for Hg2+ release, followed by sensitive electrochemical detection by anodic stripping voltammetry (ASV). To the best of our knowledge, this is the first time that water-stable HgSe NPs are quantified using electrochemical techniques. The low limit of detection achieved (3.86 × 107 HgSe NPs/mL) together with the excellent repeatability (RSD: 3%), reproducibility (RSD: 5%) and trueness (relative error: 10%), the good performance in real sea water samples (recoveries of the analytical signal higher than 90%) and the simplicity/low cost of analysis make our method an ideal candidate for HgSe NPs monitoring in future environmental studies.

GC-ICP-MS/MS Instrumental Setup for Total and Speciation Sulfur Analysis in Gasolines using Generic Standards.

Quantitative characterization of sulfur-containing petroleum derivatives is mainly limited by the large number of potential targets present and the matrix effects suffered due to the high-carbon-containing matrices. Herein we describe the instrumental modifications required in a commercial GC-ICP-MS/MS instrument, and their corresponding optimization, for turning it into a compound-independent quantitative technique for both total and speciation sulfur analysis in gasolines. Additionally, carbon-derived matrix effects were made negligible for direct and fast total S analysis, making the use of relatively complex isotope-dilution strategies not necessary anymore. An absolute detection limit of 0.3 pg of S was achieved, which is, to the best of our knowledge, more than 1 order of magnitude below the ones reported for other sulfur GC selective detectors. The precision was below 3% RSD. Total analysis was performed by flow-injection analysis through a transfer line and external calibration, whereas speciation analysis was carried out by chromatographic separation and internal standardization. In both cases, simple generic standards were used, which enabled us to get rid of specific S-containing standards, which were sometimes not available or unstable. The proposed method was successfully applied to total and speciation sulfur analysis of a commercial gasoline sample and validated with a certified-reference-material (ERM-EF213) gasoline. The approach has proved to be simple, fast, robust, and convenient for implementation in routine laboratories, as demonstrated by the successive analyses of 50 gasoline samples in 3 h without any instrumental drift.

A reflection on the role of ICP-MS in proteomics: Update and future perspective.

Mass spectrometry is the technique of reference for the identification and quantification of proteins. Whereas ESI and MALDI ionization sources are inherently not quantitative being highly influenced by the chemical nature of the analyte and the matrix, ICP-MS uses a hard ionization source that destroys proteins into its atoms and measures the elemental signal, which is independent of its chemical environment. As a consequence, ICP-MS turns up as an excellent technique for the screening, mapping and quantification of peptides and proteins in a sample through elemental detection (any element but C, H, N, or O) once they have been previously separated by chromatography. In this time, great efforts have been put in developing instrumentation and new methodologies that enable a better, more efficient, and more useful analysis of proteins with ICP-MS. Moreover, quantitative capabilities but lack of molecular information of ICP has led to a synergic relationship both with identifying capabilities of ESI-MS, or the use of protein-specific antibodies carrying an elemental label. JOURNAL SIGNIFICANCE: We are delighted to participate in this special issue and have the chance to congratulate Journal of Proteomics for its 10th Anniversary, and wish for many further successful anniversaries. During this last decade, Journal of Proteomics has been a clear promotor of works integrating ICP-MS for proteomics analysis. In fact, already in 2009, a review was published by invitation of the editor in chief focused on the established and potential role of ICP-MS in different areas of the proteomics analysis at the time: "The emerging role of ICP-MS in proteomics" [1]. Even though ICP-MS is not fully known or acknowledged in the proteomics world yet, its impact was significant as demonstrated by the really high interest in such publication (over 150 citations). Since then, several excellent papers relating to ICP-MS applications in proteomics have been published in this journal. Following the trend, we expect through this personal view of the current standing of ICP-MS in proteomics to enlighten the readers of Journal of Proteomics with a vision of the full present and future potential of ICP-MS in proteomics.

Functionalized phosphorescent nanoparticles in (bio)chemical sensing and imaging - A review.

Inorganic nanoparticles are a fascinating class of materials which promise great potential in numerous fields, including optical (bio)sensing. Many different kinds of such nanoparticles have been widely used for fluorescent sensing and imaging due to the different merits of fluorescent nanoparticles compared to molecular fluorophores. Progress made in the rational design of nanomaterials also allowed the synthesis of hybrid phosphorescent nanoparticles, that finds growing applications in sensing due to the combination of the interesting size- and shape-dependent properties of nanomaterials with a phosphorescence-type emission. In this review, we intend to highlight some of progress made in this active research area and update the database of various phosphorescent nanoparticles-based sensors on the basis of different sensing targets of interest in environmental, industrial and biomedical areas. Following an introduction and a discussion of merits of the synergy between nanomaterials and phosphorescence detection as compared to molecular luminophores the article assesses the kinds and specific features of nanomaterials often used in phosphorescence sensing. Specific examples on the use of phosphorescence nanoparticles in chemical sensing and bioimaging are given next. A final section intends to provide an overview of the prospects of such type of nanomaterials in the design of future devices for analytical chemistry.

Enhanced Universal Quantification of Biomolecules Using Element MS and Generic Standards: Application to Intact Protein and Phosphoprotein Determination.

Tools that provide absolute quantification of biomolecules, particularly of proteins and their post-translational modifications, without needing suitable specific standards, are urgently demanded nowadays. To this end, we have significantly improved the recently introduced strategy based on CH4 addition to the plasma for absolute quantification of biomolecules using HPLC-ICP-MS. Addition of CO2 has been optimized and finally selected as a safer, more efficient quantitative strategy that is able to provide constant (<6% error) signal response factor for the six elements assayed (S, P, As, Se, Br, I) under compromised conditions. In the particular case of absolute protein quantification, accuracy and precision attainable for S-based absolute determination of intact proteins using internal and external S-generic standards were compared. Potential for real sample analysis was demonstrated by the high-sensitivity analysis of toxins present in snake venoms. Finally, multielemental speciation capabilities of the approach have been also demonstrated through P and S simultaneous analysis in phosphoproteomics. Simultaneous accurate determination of both absolute protein amount and corresponding phosphorylation degree for intact ß-casein, and even impurity traces of κ and α-s1 isoforms present, has been successfully achieved using a simple mixture of inorganic P and S standards. The lowest detection limits (<1 fmol protein) ever published for S- and P-based intact protein quantification with ICP-MS are reported.

Controlling Ligand Surface Density on Streptavidin-Magnetic Particles by a Simple, Rapid, and Reliable Chemiluminescent Test.

The use of functionalized magnetic particles is increasing because they simplify the analytical process and yield promising results in a wide range of applications. Particularly, streptavidin-coated magnetic beads offer the possibility of rapid and very efficient grafting of biomolecules. Unfortunately, current methods to monitor and compute this grafting process are cumbersome and scarce. We describe herein a simple, rapid, and reliable chemiluminescent assay we have developed to check the grafting rate of functionalized magnetic beads. The power of the assay also relies on its ability to predict the amount of ligands required to obtain a precise grafting rate. In addition, results were correlated with a more general parameter in material functionalization characterization like surface ligand density. Finally, the assay was validated for a wide variety of biotinylated biomolecule sizes, ranging from small molecules (around 200 Da) to antibodies (around 150 kDa). This approach will allow a precise quantification and prediction of the functionalization of magnetic particles that is of enormous importance for quality control in many applications.