Immuno-based sample preparation for trace analysis

Oriented immobilization of nanobodies using SpyCatcher/SpyTag significantly enhances the capacity of affinity chromatography

The use of nanobodies (Nbs) in affinity chromatography for biomacromolecule purification is gaining popularity. However, high-performance Nb-based affinity resins are not readily available, mainly due to the lack of suitable immobilization methods. In this study, we explored an autocatalytic coupling strategy based on the SpyCatcher/SpyTag chemistry to achieve oriented immobilization of Nb ligands. To facilitate this approach, a variant cSpyCatcher003 (cSC003) was coupled onto agarose microspheres, providing a specific attachment site for SpyTagged nanobody ligands. The cSC003 easily purified from Escherichia coli through a two-step procedure, exhibits exceptional alkali resistance and structural recovery capability, highlighting its robustness as a linker in the coupling strategy. To validate the effectiveness of cSC003-derivatized support, we employed VHSA, a nanobody against human serum albumin (HSA), as the model ligand. Notably, the immobilization of SpyTagged VHSA onto the cSC003-derivatized support was achieved with a coupling efficiency of 90 %, significantly higher than that of traditional thiol-based coupling method. This improvement directly correlated to the preservation of the native conformation of nanobodies during the coupling process. In addition, the Spy-immobilized resin demonstrated better performance in the binding capacity, with a 3-fold improvement in capture efficiency, underscoring the advantages of the Spy immobilization strategy for oriented immobilization of VHSA ligands. Moreover, online purification and immobilization of SpyTagged VHSA from crude bacterial lysate was achieved using the cSC003-derivatized support. The resulting resin exhibited high binding specificity towards HSA, yielding a purity above 95 % directly from human serum, and maintained good stability throughout multiple purification cycles. These findings highlight the potential of the Spy immobilization strategy for developing Nb-based affinity chromatographic materials, with significant implications for biopharmaceutical downstream processes.

Evaluation of Antibiotics Residues in Milk and Meat Using Different Analytical Methods

Veterinary drugs are pharmacologically and biologically active chemical agents. At present, veterinary drugs are extensively used to prevent and treat animal diseases, to promote animal growth, and to improve the conversion rate of feed. However, the use of veterinary drugs in food-producing animals may leave residues of the parent compounds and/or their metabolites in food products resulting in harmful effects on humans. To ensure food safety, sensitive and effective analytical methods have been developing rapidly. This review describes sample extraction and cleanup methods, and different analytical techniques are used for the determination of veterinary drug residues in milk and meat. Sample extraction methods, such as solvent extraction, liquid-liquid extraction, and cleanup methods such as dispersive solid-phase extraction and immunoaffinity chromatography, were summarized. Different types of analytical methods such as microbial, immunological, biosensor, thin layer chromatography, high-performance liquid chromatography, and liquid chromatography-tandem mass spectrometry were discussed for the analysis of veterinary drug residues in animal-derived foods. Liquid chromatography-tandem mass spectrometry is the most widely used analytical technique for the determination of antibiotic drug residues. This is due to the powerful separation of LC and accurate identification of MS, and LC-MS/MS is more popular in the analysis of veterinary drug residues.

Solid-phase immunoextraction followed by liquid chromatography-tandem mass spectrometry for the selective determination of thyroxine in human serum

In this work, an analytical method based on solid-phase extraction (SPE) followed by liquid chromatography-tandem mass spectrometry analysis (LC-MS/MS) has been developed for the selective determination of thyroxine (T4) in human serum. For this purpose, two immunosorbents (ISs) specific to T4 were synthesized by grafting two different T4-specific monoclonal antibodies on a cyanogen bromide (CNBr)-activated-Sepharose® 4B solid support. The grafting yields obtained from the immobilization of each antibody on the CNBr-activated-Sepharose® 4B were over 90%, demonstrating that most of the antibodies were covalently bound to the solid support. The SPE procedure was optimized by studying the retention capability and selectivity of the two ISs in pure media fortified with T4. Under the optimized conditions, high elution efficiencies were achieved in the elution fraction for both specific ISs (i.e., 85%), whereas low ones were obtained in the control ISs (ca. 2%), showing the selectivity of the specific ISs. The ISs were also characterized by studying extraction and synthesis repeatability (RSD <8%), and capacity (104 ng of T4 per 35 mg of ISs, i.e., 3 μg g^-1). Finally, the methodology was applied to a pooled human serum sample in order to study its analytical utility and accuracy. Relative recovery (RR) values between 81 and 107% were obtained, showing no matrix effects during the global methodology. Furthermore, the need to perform the immunoextraction was evidenced by comparing the LC-MS scan chromatograms and RR values with and without applying the immunoextraction procedure on a serum sample submitted to protein precipitation. This works exploits, for the first time, the use of an IS on the selective determination of T4 in human serum samples.

Rabbit IgG-imprinted nanoMIPs by solid phase synthesis: the effect of cross-linkers on their affinity and selectivity

Solid phase synthesis (SPS) of molecularly imprinted nanopolymers (nanoMIPs) represents an innovative method to prepare nanomaterials with tailor-made molecular recognition properties towards peptides and proteins. The synthesis of nanoMIPs by SPS usually involves a pre-polymerization formulation, where the cross-linker is invariably N,N'-methylen-bis-acrylamide (BIS). To date, the effect of cross-linkers on the binding properties of nanoMIPs prepared using cross-linkers other than BIS has never been reported. In this work, in order to investigate the effect of different cross-linkers in protein-imprinted nanoMIPs prepared by SPS, alongside BIS we considered other similar cross-linkers: N,N'-ethylene dimethacrylamide (EDAM), N,O-bis-methacryloylethanolamine (NOBE), ethylene glycol dimethacrilate (EDMA) and glycerol dimethacrylate (GDMA), replacing BIS with them in pre-polymerization mixtures. The synthetized nanoMIPs were homogeneous, with a polydispersity index of 0.24-0.30 and a mean diameter of 129-169 nm in water. The binding properties of the nanoMIPs were measured via equilibrium partition experiments with the template, rabbit IgG (RIgG), and the selectivity was evaluated with respect to bovine IgG (BIgG), bovine serum albumin (BSA) and hen egg lysozyme (LZM). The experimental results show that all the cross-linkers, with the exception of EDMA, endowed nanoMIPs with high binding affinities for the template (BIS: 16.0 × 10⁶ mol^-1 L, EDAM: 8.8 × 10⁶ mol^-1 L, NOBE: 15.8 × 10⁶ mol^-1 L, and GDMA: 12.8 × 10⁶ mol^-1 L), medium to high imprinting factors (BIS: 12.3, EDAM: 5.5, NOBE: 7.2, and GDMA: 11.6) and good selectivity towards other proteins but markedly dependent on the structure of the cross-linker, confirming the importance of the latter in the SPS of imprinted nanopolymers.

Analytical Extraction Methods and Sorbents' Development for Simultaneous Determination of Organophosphorus Pesticides' Residues in Food and Water Samples: A Review

Extensive use of organophosphorus pesticides in agriculture leads to adverse effects to the environment and human health. Sample preparation is compulsory to enrich target analytes prior to detection as they often exist at trace levels and this step is critical as it determines the concentration of pollutants present in samples. The selection of a suitable extraction method is of great importance. The analytical performance of the extraction methods is influenced by the selection of sorbents as sorbents play a vital role in the sensitivity and selectivity of an analytical method. To date, numerous sorbent materials have been developed to cater to the needs of selective and sensitive pesticides' detection. Comprehensive details pertaining to extraction methods, developed sorbents, and analytical performance are provided. This review intended to provide a general overview on different extraction techniques and sorbents that have been developed in the last 10 years for organophosphorus pesticides' determinations in food and water samples.

Use of a Branched Linker for Enhanced Biosensing Properties in IgG Detection from Mixed Chinese Hamster Ovary Cell Cultures

Tris(2-aminoethyl)-amine (TREN), a branched amine, was coupled to planar surfaces of alkanethiol self-assembled monolayers (SAMs) to increase the grafting density of IgG-binding peptide (HWRGWV or HWRGWVG) on gold surfaces. One of the three primary amine pendant groups of TREN anchors onto the SAM, while the other two are available for grafting with the C-termini of the peptide. The ellipsometric peptide density on the SAM-branched amine was 1.24 molecules nm^-2. The surfaces carrying the peptides were investigated via surface plasmon resonance (SPR) to quantify the adsorption of IgG and showed maximum binding capacity, Q_m of 4.45 mg m^-2, and dissociation constant, K_d of 8.7 × 10^-7 M. Real-time dynamic adsorption data was used to determine adsorption rate constants, k_a values, and the values were dependent on IgG concentration. IgG binding from complex mixtures of Chinese hamster ovary supernatant (CHO) was investigated and regeneration studies were carried out. Compared to the unbranched amine-based surfaces, the branched amines increased the overall sensitivity and selectivity for IgG adsorption from complex mixtures. Regeneration of the branched amine-based surfaces was achieved with 0.1 M NaOH, with less than 10% decline in peptide activity after 12 cycles of regeneration-binding.

Fucosyl monosialoganglioside: Quantitative analysis of specific potential biomarkers of lung cancer in biological matrices using immunocapture extraction/tandem mass spectrometry

RATIONALE

Certain lung cancer patients express elevated Fucosyl Monosialoganglioside (Fuc-GM1) in circulation compared to control groups. Several sensitive methods involving characterization of Fuc-GM1 have been reported. However, a highly specific and sensitive method for quantifying multiple potential Fuc-GM1 biomarkers present in various biological matrices has not been reported to date.

METHODS

Individual Fuc-GM1 analogs in a commercially obtained standard mixture were characterized using HPLC/UV/MS and high-resolution mass spectrometry (HRMS). Proprietary antibodies, mAb1 and mAb2, were used to selectively capture and pre-concentrate the soluble and drug-bound forms of Fuc-GM1 molecules present in human serum and whole blood, eliminating the background matrix components. Immunocapture extraction (ICE) followed by HPLC/MS/MS was used to quantify specific Fuc-GM1 analogs in biological matrices.

RESULTS

The concentration of individual Fuc-GM1 analogs in the standard mixture was estimated to be 7-34%, using HPLC/UV/MS. Using the standard mixture spiked into the biological matrices (100 μL), the lower limit of quantification (LLOQ) of each analog was 0.2-0.4 ng/mL with a dynamic range of up to 200 ng/mL. The applicability of the ICE-HPLC/MS/MS method was demonstrated by detecting endogenous Fuc-GM1 analogs present in rat blood and in several lung cancer cell lines.

CONCLUSIONS

This highly specific and sensitive HPLC/MS/MS method for quantifying individual potential Fuc-GM1 biomarkers in serum and whole blood can play a critical role in patient stratification strategies and during drug treatment. This method can be employed for monitoring both free (soluble) form and antibody drug-bound Fuc-GM1.

A novel aptamer-based online magnetic solid phase extraction method for the selective determination of 8-hydroxy-2'-deoxyguanosine in human urine

In this work, an innovative magnetic aptamer adsorbent (Fe₃O₄-aptamer MNPs) was synthesized for the selective extraction of 8-hydroxy-2'-deoxyguanosine (8-OHdG). Amino-functionalized-Fe₃O₄ was crosslinked with 8-OHdG aptamer by glutaraldehyde and fixed into a steel stainless tube as the sorbent of magnetic solid phase extraction (MSPE). After selective extraction by the aptamer adsorbent, the adsorbed 8-OHdG was desorbed dynamically and online analyzed by high performance liquid chromatography-mass spectrometry (HPLC-MS). The synthesized sorbent presented outstanding features, including specific selectivity, high enrichment capacity, stability and biocompatibility. Moreover, this proposed MSPE-HPLC-MS can achieve adsorption and desorption operation integration, greatly simplify the analysis process and reduce human errors. When compared with offline MSPE, a sensitivity enhancement of 800 times was obtained for the online method. Some experimental parameters such as the amount of the sorbent, sample flow rate and sample volume, were optimized systematically. Under the optimal conditions, low limit of detection (0.01 ng mL^-1, S/N = 3), limit of quantity (0.03 ng mL^-1, S/N = 10) and wide linear range with a satisfactory correlation coefficient (R² ≥ 0.9992) were obtained. And the recoveries of 8-OHdG in the urine samples varied from 82% to 116%. All these results revealed that the method is simple, rapid, selective, sensitive and automated, and it could be expected to become a potential approach for the selective determination of trace 8-OHdG in complex urinary samples.

Highly-sensitive detection of eight typical fluoroquinolone antibiotics by capillary electrophoresis-mass spectroscopy coupled with immunoaffinity extraction

An off-line procedure, immunoaffinity extraction (IAE), followed by capillary electrophoresis-mass spectroscopy (CE-MS) has been developed for the simultaneous determination of eight typical FQs in environmental water samples.

Immunoaffinity chromatography combined with tandem mass spectrometry: A new tool for the selective capture and analysis of brassinosteroid plant hormones

Brassinosteroids (BRs) are plant-specific steroid hormones that play essential roles in the regulation of many important physiological processes in plant life. Their extremely low concentrations (~pmoles/g FW) in plant tissue and huge differences in polarity of individual members within the BR family hamper their detection and quantification. To address this problem, an immunoaffinity sorbent with broad specificity and high capacity for different BR metabolites containing a monoclonal antibody (mAb) against a BR spacer (20S)-2α,3α-dihydroxy-7-oxa-7α-homo-5α-pregnane-6-one-20 carboxylic acid (BR4812) was used for the rapid and highly selective isolation of endogenous BRs containing a 2α,3α-diol in ring A from minute plant samples. This enrichment procedure was successfully applied as a sample preparation method prior to quantitative analysis of BRs in real plant tissues by ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Use of immunoaffinity chromatography (IAC) increased the sensitivity of the UHPLC-MS/MS analysis owing to improvements in the BR signal-to-noise ratio (S/N) and matrix factor (MF). Although MF values of BRs analyzed in classical samples ranged from 8.9% to 47.4%, MF values for the IAC purified samples reached 44.5-96.6%. Thus, the developed IAC-UHPLC-MS/MS approach was shown to be a simple, robust, effective and extremely fast procedure requiring minute amounts of plant samples suitable for the quantitative profiling of many BR metabolites, helping to overcome the major problems associated with their determination in very complex plant matrices.

Filter Plate-Based Screening of MIP SPE Materials for Capture of the Biomarker Pro-Gastrin-Releasing Peptide

Affinity-based solid-phase extraction (SPE) is an attractive low-cost sample preparation strategy for biomarker analysis. Molecularly imprinted polymers (MIPs) as affinity sorbents offer unique opportunities for affinity SPE, due to their low manufacturing cost and high robustness. A limitation is the prediction of their affinity; therefore, screening of analyte recovery and specificity within a large range of SPE conditions is important in order to ensure high-sensitivity detection and assay reproducibility. Here, a µ-SPE method for screening of the MIP-SPE materials using a commercial 384-well filter plate is presented. The method allows for rapid and automated screening using 10-30 µL of packed SPE sorbent per well and sample volumes in the range of 10-70 µL. This enables screening of many different SPE sorbents while simultaneously identifying optimal SPE conditions. In addition, the 384-well format also facilitates detection with a multitude of analytical platforms. Performance of the µ-MIP-SPE method was investigated using a series of MIPs designed to capture pro-gastrin-releasing peptide (ProGRP). Fractions coming from sample load, cartridge wash, and elution were collected and analyzed using mass spectrometry (MS). The top-performing MIPs were identified, together with proper SPE conditions.

Site-selective orientated immobilization of antibodies and conjugates for immunodiagnostics development

Immobilized antibody systems are the key to develop efficient diagnostics and separations tools. In the last decade, developments in the field of biomolecular engineering and crosslinker chemistry have greatly influenced the development of this field. With all these new approaches at our disposal, several new immobilization methods have been created to address the main challenges associated with immobilized antibodies. Few of these challenges that we have discussed in this review are mainly associated to the site-specific immobilization, appropriate orientation, and activity retention. We have discussed the effect of antibody immobilization approaches on the parameters on the performance of an immunoassay.

Microscale magnetic microparticle-based immunopurification of cytokinins from Arabidopsis root apex

Cytokinins (CKs) are pivotal plant hormones that have crucial roles in plant growth and development. However, their isolation and quantification are usually challenging because of their extremely low levels in plant tissues (pmol g^-1 fresh weight). We have developed a simple microscale magnetic immunoaffinity-based method for selective one-step isolation of CKs from very small amounts of plant tissue (less than 0.1 mg fresh weight). The capacity of the immunosorbent and the effect of the complex plant matrix on the yield of the rapid one-step purification were tested using a wide range of CK concentrations. The total recovery range of the new microscale isolation procedure was found to be 30-80% depending on individual CKs. Immunoaffinity extraction using group-specific monoclonal CK antibodies immobilized onto magnetic microparticles was combined with a highly sensitive ultrafast mass spectrometry-based method with a detection limit close to one attomole. This combined approach allowed metabolic profiling of a wide range of naturally occurring CKs (bases, ribosides and N⁹ -glucosides) in 1.0-mm sections of the Arabidopsis thaliana root meristematic zone. The magnetic immunoaffinity separation method was shown to be a simple and extremely fast procedure requiring minimal amounts of plant tissue.

Automated Enrichment of Sulfanilamide in Milk Matrices by Utilization of Aptamer-Linked Magnetic Particles

The present work demonstrates the first automated enrichment approach for antibiotics in milk using specific DNA aptamers. First, aptamers toward the antibiotic sulfanilamide were selected and characterized regarding their dissociation constants and specificity toward relevant antibiotics via fluorescence assay and LC-MS/MS detection. The performed enrichment was automated using the KingFisherDuo and compared to a manual approach. Verifying the functionality, trapping was realized in different milk matrices: (i) 0.3% fat milk, (ii) 1.5% fat milk, (iii) 3.5% fat milk, and (iv) 0.3% fat cocoa milk drink. Enrichment factors up to 8-fold could be achieved. Furthermore, it could be shown that novel implementation of a magnetic separator increases the reproducibility and reduces the hands-on time from approximately half a day to 30 min.

Preparation and characterization of chitosan microparticles for immunoaffinity extraction and determination of enrofloxacin

The use of chitosan microparticles as chromatographic support has received much attention. In this study, the effects of process parameters, namely, chitosan molecular weight, chitosan concentration, molar ratio of amino group to aldehyde group, volume ratio of water to oil phase and stirring speed on the size and size distribution of chitosan microparticles and their application for immunoaffinity extraction were extensively investigated. Size distribution analysis indicated that the average diameter of the microparticles was 124μm with Span value of 1.1. The obtained microparticles exhibited low non-specific adsorption and kept stable in the pH range 4.0-10.0. Immunoaffinity chromatography (IAC) column was prepared by coupling antibody against enrofloxacin (ENR) with chitosan microparticles. Further characterization indicated that the binding capacity of the column was 4392ng ENR/mL gel and the variation of ENR extraction efficiency among columns was less than 5.2%. When challenged with ENR-fortified bovine milk samples, recoveries of ENR by immunoaffinity extraction were found to be in the range of 85.9% to 101.9%, demonstrated the feasibility of the prepared IAC columns for sample clean-up in ENR residue determination.

Selective tools for the solid-phase extraction of Ochratoxin A from various complex samples: immunosorbents, oligosorbents, and molecularly imprinted polymers

The evolution of instrumentation in terms of separation and detection has allowed a real improvement of the sensitivity and the analysis time. However, the analysis of ultra-traces of toxins such as ochratoxin A (OTA) from complex samples (foodstuffs, biological fluids…) still requires a step of purification and of preconcentration before chromatographic determination. In this context, extraction sorbents leading to a molecular recognition mechanism appear as powerful tools for the selective extraction of OTA and of its structural analogs in order to obtain more reliable and sensitive quantitative analyses of these compounds in complex media. Indeed, immunosorbents and oligosorbents that are based on the use of immobilized antibodies and of aptamers, respectively, and that are specific to OTA allow its selective clean-up from complex samples with high enrichment factors. Similar molecular recognition mechanisms can also be obtained by developing molecularly imprinted polymers, the synthesis of which leads to the formation of cavities that are specific to OTA, thus mimicking the recognition site of the biomolecules. Therefore, the principle, the advantages, the limits of these different types of extraction tools, and their complementary behaviors will be presented. The introduction of these selective tools in miniaturized devices will also be discussed.

2,4-D and IAA Amino Acid Conjugates Show Distinct Metabolism in Arabidopsis

The herbicide 2,4-D exhibits an auxinic activity and therefore can be used as a synthetic and traceable analog to study auxin-related responses. Here we identified that not only exogenous 2,4-D but also its amide-linked metabolite 2,4-D-Glu displayed an inhibitory effect on plant growth via the TIR1/AFB auxin-mediated signaling pathway. To further investigate 2,4-D metabolite conversion, identity and activity, we have developed a novel purification procedure based on the combination of ion exchange and immuno-specific sorbents combined with a sensitive liquid chromatography-mass spectrometry method. In 2,4-D treated samples, 2,4-D-Glu and 2,4-D-Asp were detected at 100-fold lower concentrations compared to 2,4-D levels, showing that 2,4-D can be metabolized in the plant. Moreover, 2,4-D-Asp and 2,4-D-Glu were identified as reversible forms of 2,4-D homeostasis that can be converted to free 2,4-D. This work paves the way to new studies of auxin action in plant development.

Application of immunoaffinity purification technology as the pretreatment technology for traditional Chinese medicine: Its application to analysis of hesperidin and narirutin in traditional Chinese medicine preparations containing Citri reticulatae Pericarpium

In the present study, the feasibility of immunoaffinity chromatography (IAC) as a purification technology for the analysis of bioactive components in Traditional Chinese Medicine (TCM) was evaluated. IAC was used to analyze hesperidin (HP) and narirutin (NR) in TCM preparations containing Citri reticulatae Pericarpium (CRP, Chenpi in Chinese). An IAC column for the specific extraction and enrichment of HP and NR from TCM preparations containing CRP was developed and characterized. After HP reacted with carbonyl diimidazole and coupled to protein, it was used to immune mice for the generation of antibody. Through cell fusion, cloning and screening, monoclonal antibody was obtained. The IAC column was constructed by covalently coupling specific monoclonal antibody against HP and NR to CNBr-activated Sepharose 4B and packed into a common solid phase extraction cartridge. The extraction conditions including loading, washing and eluting, as well as flow rate for the extraction of HP and NR were optimized. Under optimal conditions, the maximum capacity, extraction recovery rate and stability of IAC column was also characterized. Results revealed that the maximum capacity of IAC column for HP and NR was approximately 16μg and the relative binding capacity per 1mL of the column volume was 27μg. The extraction recovery rate of IAC column for HP and NR at three spiked levels was in the range of 94.05-109.15%. After the repeated application for 5 times, no significant loss of specific recognition was observed. Using high performance liquid chromatography (HPLC) as an effective analytic tool, HP and NR could be successfully separated via IAC column without the inference from impurities, suggesting that the extraction of HP and NR using the prepared IAC column is feasible. The application of IAC can solve the problem of quantitative analysis due to severe interference or low content. Furthermore, pretreatment methods in different matrixes can be unified. The IAC purification procedure can be used as an alternative effective analytical method for the pretreatment of bioactive components in TCM.

Development and characteristics of polymer monoliths for advanced LC bioscreening applications: A review

Biomedical research advances over the past two decades in bioseparation science and engineering have led to the development of new adsorbent systems called monoliths, mostly as stationary supports for liquid chromatography (LC) applications. They are acknowledged to offer better mass transfer hydrodynamics than their particulate counterparts. Also, their architectural and morphological traits can be tailored in situ to meet the hydrodynamic size of molecules which include proteins, pDNA, cells and viral targets. This has enabled their development for a plethora of enhanced bioscreening applications including biosensing, biomolecular purification, concentration and separation, achieved through the introduction of specific functional moieties or ligands (such as triethylamine, N,N-dimethyl-N-dodecylamine, antibodies, enzymes and aptamers) into the molecular architecture of monoliths. Notwithstanding, the application of monoliths presents major material and bioprocess challenges. The relationship between in-process polymerisation characteristics and the physicochemical properties of monolith is critical to optimise chromatographic performance. There is also a need to develop theoretical models for non-invasive analyses and predictions. This review article therefore discusses in-process analytical conditions, functionalisation chemistries and ligands relevant to establish the characteristics of monoliths in order to facilitate a wide range of enhanced bioscreening applications. It gives emphasis to the development of functional polymethacrylate monoliths for microfluidic and preparative scale bio-applications.

Ultrasensitive quantitative LC–MS/MS of an inhibitor of apoptosis protein's antagonist in plasma using protein target affinity extraction

Background: A target protein-based affinity extraction LC–MS/MS method was developed to enable plasma level determination following ultralow dosing (0.1–3 µg/kg) of an inhibitor of apoptosis proteins molecule. Methodology & results: Affinity extraction (AE) utilizing immobilized target protein BIR2/BIR3 was used to selectively capture the inhibitor of apoptosis proteins molecule from dog plasma and enable removal of background matrix components. Pretreatment of plasma samples using protein precipitation was found to provide an additional sensitivity gain. A LLOQ of 7.8 pM was achieved by combining protein precipitation with AE. The method was used to support an ultralow dose dog toxicity study. Conclusion: AE-LC–MS/MS, utilizing target protein, is a highly sensitive methodology for small molecule quantification with potential for broader applicability.

Miniaturized DNA aptamer-based monolithic sorbent for selective extraction of a target analyte coupled on-line to nanoLC

A complete characterization of a novel target-specific DNA aptamer-based miniaturized solid phase extraction (SPE)-sorbent coupled on-line to nanoLC is presented. A miniaturized oligosorbent (mOS) was prepared via the in situ sol-gel synthesis of a hybrid organic-inorganic monolith in 100 μm i.d. capillary columns using tetraethoxysilane and 3-aminopropyltriethoxysilane as precursors, followed by covalent binding of a 5'-amino-modified DNA aptamer with a C12 spacer arm specific for a molecule of small molecular weight. Ochratoxin A (OTA), one of the most abundant naturally occurring mycotoxins, was chosen as model analyte to demonstrate the principle of such an approach. The mOS was coupled on-line to RP-nanoLC-LIF. Selective extraction of OTA on several mOSs was demonstrated with an average extraction recovery above 80 % when percolating spiked binding buffer and a low recovery on control monoliths grafted with a non-specific aptamer. Reproducibility of mOSs preparation was highlighted by comparing extraction yields. Otherwise, the mOSs demonstrated no cross-reactivity towards an OTA structural analogue, i.e., ochratoxin B. Due to the high specific surface area of the hybrid silica-based monolith, the coverage density of DNA aptamers covalently immobilized in the capillaries was very high and reached 6.27 nmol μL(-1), thus leading to a capacity above 5 ng of OTA. This miniaturized device was then applied to the selective extraction of OTA from beer samples. It revealed to be effective in isolating OTA from this complex matrix, thus improving the reliability of its analysis at the trace level.

Aptamer-based-sorbents for sample treatment--a review

To improve selectivity during sample pretreatment, various selective tools inducing a molecular recognition mechanism during the extraction procedure have been developed, such as sorbents constituted of immobilized antibodies, i.e., immunosorbents, or molecularly imprinted polymers. More recently, as an alternative to both previous approaches, aptamers immobilized onto a solid support, i.e., oligosorbents, were proposed. Thanks to the high affinity and high selectivity of the interaction that some aptamers offer toward some target analytes, they also provide powerful techniques that make selective extraction and the concentration of a target analyte from liquid matrices in one step or sample purification of extracts from solid matrices possible. This review describes the development and the properties of these oligosorbents developed for different types of targets-pharmaceuticals, mycotoxins, proteins, cells, etc. After describing the immobilization procedures, we discuss different parameters characterizing the potential of aptamer-based supports as extraction sorbents. Close relations exist between extraction recoveries and the affinity and amounts of aptamers immobilized on the extraction device. In addition, analyte-aptamer interactions may be affected by matrix components and by additives in the samples. This may also lower extraction recoveries and affect the stability and the possible reusability of the aptamer-based sorbent. All these points are discussed and illustrated. Numerous examples of applications of these sorbents to the treatment of complex samples such as food samples, environmental samples, and biological fluids are also reported. Their association with analytical devices, from conventional to miniaturized analytical systems, is also discussed.

Immunoaffinity clean-up of mycotoxins with organic solvent-free elution

A novel immunoaffinity (IA) clean-up procedure for the isolation of mycotoxins from maize extracts is described. Commonly, mycotoxins are eluted with organic solvents from IA columns after isolation. The new procedure uses water at 70 °C as alternative. The resulting eluate is suitable for direct and complete injection onto a reversed-phase liquid-chromatography column. Evaporation, reconstitution or dilution are not required. The procedure has been tested for a variety of mycotoxins, including deoxynivalenol (DON) zearalenone, T-2 and HT-2 toxins, aflatoxins and ochratoxin A in an array of different matrices. The example of DON in maize is discussed in more detail and evaluated for repeatability (5%, n=10) and recovery (95%, n=10).

In-situ immuno-gold nanoparticle network ELISA biosensors for pathogen detection

Food poisoning microorganisms that contaminate food products and compromise food safety and security have been considered a major health threat and a serious concern for food producers and processors. Developing sensor technologies that are rapid for sensitive and selective detection and quantification of pathogens is a high priority for scientists in academia, state and federal research institutes, and industries. In this work we propose an in-situ immuno-AuNP network-based ELISA biosensor integrated with a sample concentration step based on immuno-magnetic separation to detect pathogenic microorganisms with high sensitivity. The sensor system was optimized by the specific formation of immuno-AuNP network onto the antigenic site present at the outer membrane surface of bacteria and the analytical concept was validated by a microtiter immunoassay. The in-situ network biosensor was able to detect pathogens at extremely low numbers: 3 cells/mL of Escherichia coli O157:H7 and Salmonella typhimurium in buffer and 3 CFU/mL of E. coli O157:H7 and 15CFU/mL of S. typhimurium in real sample conditions within 2h of inoculation. The ability to monitor target bacteria with improved analytical sensitivity compared to the current techniques presents a unique opportunity for routine monitoring to improve the safety of foods.