Tosyl-activated Magnetic Beads Research Articles

Use of uncoated magnetic beads to capture Mycobacterium smegmatis and Mycobacterium avium paratuberculosis prior detection by mycobacteriophage D29 and real-time-PCR

Uncoated tosyl-activated magnetic beads were evaluated to capture Mycobacterium smegmatis and Mycobacterium avium subspecies paratuberculosis (MAP) from spiked feces, milk, and urine. Centrifugation and uncoated magnetic beads recovered more than 99% and 93%, respectively, of 1.68 × 107 CFU/mL, 1.68 × 106 CFU/mL and 1.68 × 105 CFU/mL M. smegmatis cells resuspended in phosphate buffer saline. The use of magnetic beads was more efficient to concentrate cells from 1.68 × 104 CFU/mL of M. smegmatis than centrifugation. Likewise, the F57-qPCR detection of MAP cells was different whether they were recovered by beads or centrifugation; cycle threshold (Ct) was lower (p < 0.05) for the detection of MAP cells recovered by beads than centrifugation, indicative of greater recovery. Magnetic separation of MAP cells from milk, urine, and feces specimens was demonstrated by detection of F57 and IS900 sequences. Beads captured no less than 109 CFU/mL from feces and no less than 104 CFU/mL from milk and urine suspensions. In another detection strategy, M. smegmatis coupled to magnetic beads were infected by mycobacteriophage D29. Plaque forming units were observed after 24 h of incubation from urine samples containing 2 × 105 and 2 × 103 CFU/mL M. smegmatis. The results of this study provide a promising tool for diagnosis of tuberculosis and Johne's disease.

Enrichment of circulating tumor DNA from cell-free DNA of hematopoietic origin.

e13534 Background: In liquid biopsy, circulating tumor DNA (ctDNA) is more fragmented than background cell free DNA, peaking at 147bp (equivalent to a mono-nucleosome) instead of 165bp (nucleosome with an additional 20bp of linker DNA). Isolation of these shorter cell free DNA fragments from longer, extracted cell-free DNA improves detection of ctDNA as demonstrated by enrichment of tumor specific mutations. Nuclease protection of the additional 20bp of linker DNA, conferred by bound linker proteins such as Histone 1, would account for the 165bp peak in host background DNA. We hypothesised that extracting intact nucleosomes with linker DNA using a novel, H1 antigen based, immunocapture approach would enrich the ctDNA fraction in the remaining nucleosomes. Methods: We expressed H1.0 protein in E. coli and following extraction, purification and chemically immobilised it to tosyl-activated magnetic beads. The beads were first used to immunodeplete mono-nucleosomes from HeLa cell digests and the level of immunocaptured nucleosomes was determined by immunoassay targeting intact nucleosomes. The level of nucleosome levels determined before and after depletion was further determined by ELISA targeting H3.1 containing intact nucleosomes. DNA was extracted from the H1 immunocaptured “long” nucleosomes and size profiles compared with the remaining nucleosomes in the supernatant by BioAnalyzer. Then, the method was applied to clinical plasma samples and the size distribution of NGS Libraries (Illumina system) prepared from five colorectal cancer and three healthy samples, their immune depleted supernatants and the immunocaptured nucleosomes were then compared. Enrichment of specific genomic regions was also evaluated. Results: We observed relative enrichment of nucleosomes with short DNA in supernatants following H1 immuno-depletion of the cancer samples as evidenced by a change in size distribution by Bioanalyzer and NGS-sequencing. We also observed potential enrichment of TSS is the H1 immunocaptured nucleosomes consistent with linker DNA positioning of TF binding sites. Conclusions: Histone 1.0 has the highest affinity of H1 mammalian isoforms and successfully immunodepleted plasma samples containing cell free circulating nucleosomes with DNA longer that 147bp. Immobilized H1.0 effectively formed a pseudo-chromatosome by binding to free linker DNA or displacing endogenous H1 and other linker associated proteins. H1 antigen based immuno-depletion offers a simple way to enrich tumour derived nucleosomes and thus cell free DNA.

3D printed UV/VIS detection systems constructed from transparent filaments and immobilised enzymes

Transparent materials for fused filament fabrication printers are widely available and may be useful for constructing 3D printed devices with applications in UV/VIS spectroscopy. In this study, colourless polylactic acid, HD Glass and T-Glase were evaluated as construction materials for biochemical sensors, which contain immobilised enzymes, for analysis by UV/VIS spectrophotometry. Experiments were conducted on both the native 3D print and after coating with XTC-3D®, a transparent epoxy resin used to improve optical transparency of 3D prints. A combination of HD Glass or T-Glase with XTC-3D®, gave the highest transparency, probably due to the similar refractive indices of these materials. Individual enzymes were immobilised within the 3D prints by coupling the enzymes to tosyl-activated magnetic beads and attracted to the print surface by magnets embedded in the 3D print. A transparent 3D printed device was demonstrated using enzymatic assays of lactose and glucose. This device can be configured to contain up to three separate reaction chambers and features a separate colorimetric analysis chamber. Further studies showed that enzyme assays performed in these 3D printed devices are reproducible, accurate and of comparable sensitivity to the same assays performed in polystyrene cuvettes.

Development of a sandwich ELIME assay exploiting different antibody combinations as sensing strategy for an early detection of Campylobacter

Campylobacter is an important cause of acute bacterial disease in human worldwide. Within the genus Campylobacter, C. jejuni and C. coli are the two species responsible for over 95% of human infections. The purpose of this work is the development of an Enzyme-Linked-Immuno-Magnetic-Electrochemical (ELIME) assay for a simple and rapid detection of both Campylobacter species. Tosyl-activated magnetic beads (MBs), supporting a sandwich immunological complex, were coupled to a strip of 8-magnetized screen-printed electrodes, as electrochemical transducing element. With the aim to simultaneously detect C. jejuni and C. coli, four anti-campylobacter antibodies were screened in ELISA paying the attention to the selection of both culture medium and cell treatment (whole campylobacter cells inactivated with NaN3 and heat killed cells) for a suitable antigen-antibody interaction. Six combinations of the selected anti-campylobacter antibodies, unconjugated and conjugated with Horseradish Peroxidase (HRP) or Alkaline Phosphatase (AP), were exploited as sensing strategy to set-up the ELIME assay. The antibody pair, consisting of a goat polyclonal antibody anti-campylobacter (coated on the surface of MBs) and the same antibody conjugated with AP (to label the captured cells), was selected given the best response for both Campylobacter species and the lowest detection limit (9 × 103 CFU/mL for C. jejuni and 2 × 104 CFU/mL for C. coli). The selectivity of the ELIME assay was proved by analyzing other C. jejuni strains and non target microorganisms attaining promising results.

Highly Specific Bacteriophage-Affinity Strategy for Rapid Separation and Sensitive Detection of Viable Pseudomonas aeruginosa.

A virulent bacteriophage highly specific to Pseudomonas aeruginosa (P. aeruginosa) was isolated from hospital sewage using a lambda bacteriophage isolation protocol. The bacteriophage, named as PAP1, was used to functionalize tosyl-activated magnetic beads to establish a bacteriophage-affinity strategy for separation and detection of viable P. aeruginosa. Recognition of the target bacteria by tail fibers and baseplate of the bacteriophage led to capture of P. aeruginosa onto the magnetic beads. After a replication cycle of about 100 min, the progenies lysed the target bacteria and released the intracellular adenosine triphosphate. Subsequently, firefly luciferase-adenosine triphosphate bioluminescence system was used to quantitate the amount of P. aeruginosa. This bacteriophage-affinity strategy for viable P. aeruginosa detection showed a linear range of 6.0 × 102 to 3.0 × 105 CFU mL-1, with a detection limit of 2.0 × 102 CFU mL-1. The whole process for separation and detection could be completed after bacteria capture, bacteriophage replication, and bacteria lysis within 2 h. Since the isolated bacteriophage recognized the target bacteria with very high specificity, the proposed strategy did not show any signal response to all of the tested interfering bacteria. Furthermore, it excluded the interference from inactivated P. aeruginosa because the bacteriophage could replicate only in viable cells. The proposed strategy had been applied for detection of P. aeruginosa in glucose injection, human urine, and rat plasma. In the further work, this facile bacteriophage-affinity strategy could be extended for detection of other pathogens by utilizing virulent bacteriophage specific to other targets.

ELISA microplate: a viable immunocapture platform over magnetic beads for immunoaffinity-LC-MS/MS quantitation of protein therapeutics?

Evaluate the performance of ELISA microplates versus commonly used magnetic beads for biological sample cleanup and/or enrichment in immunoaffinity-LC-MS/MS to reduce tedious beads washing procedures and a relatively high assay cost. ELISA microplates were used as immunicapture platform and compared with magnetic beads for sample cleanup for LC-MS/MS quantitation of protein therapeutics. One unmodified and two surface-activated microplates provided comparable linear ranges and sensitivities for a therapeutic protein (mass 78 kDa) using a human serum sample of 100 µl with 1:1 dilution compared with Tosylactivated magnetic beads using 200 µl of human serum without sample dilution. The assays' precision and accuracy were all within acceptable ranges. No nonspecific binding or other selectivity issues were observed. The results suggested an ELISA microplate could be a viable immunocapture platform for immunoaffinity-LC-MS/MS quantitation of protein therapeutics.

Delineating monoclonal antibody specificity by mass spectrometry.

The inoculation of animals with complex biological samples is aiming at the discovery of novel disease biomarkers, present in the biological specimens, as well as the production of rare reagents that will facilitate the ultra-sensitive analysis of the biomolecules' native form. In the present study, we initially propose a general workflow concerning the handling of biological samples, as well as the monoclonal antibody production. Furthermore, we established protocols for the reliable and reproducible identification of antibody specificity using various immuno-affinity purification techniques coupled to mass spectrometry. Our data suggest that processed biological fluids can be used for the production of mAbs targeting proteins of varying abundance, and that various immuno-MS protocols can offer great capabilities for the mAb characterization procedure.

On-chip magneto-immunoassay for Alzheimer's biomarker electrochemical detection by using quantum dots as labels

Electrochemical detection of cadmium-selenide/zinc-sulfide (CdSe@ZnS) quantum dots (QDs) as labeling carriers in an assay for apolipoprotein E (ApoE) detection has been evaluated. The immunocomplex was performed by using tosylactivated magnetic beads as preconcentration platform into a flexible hybrid polydimethylsiloxane (PDMS)-polycarbonate (PC) microfluidic chip with integrated screen printed electrodes (SPE). All the immunoassay was performed in chip and in flow mode. The sensitive electrochemical detection was obtained by square wave anodic stripping voltammetry. ApoE was evaluated for its potential as biomarker for Alzheimer's disease detection, achieving a limit of detection (LOD) of ~12.5ngmL−1 with a linear range from 10 to 200ngmL−1 and high accuracy for diluted human plasma.

Amyloid-β42 Interacts Mainly with Insoluble Prion Protein in the Alzheimer Brain

The prion protein (PrP) is best known for its association with prion diseases. However, a controversial new role for PrP in Alzheimer disease (AD) has recently emerged. In vitro studies and mouse models of AD suggest that PrP may be involved in AD pathogenesis through a highly specific interaction with amyloid-β (Aβ42) oligomers. Immobilized recombinant human PrP (huPrP) also exhibited high affinity and specificity for Aβ42 oligomers. Here we report the novel finding that aggregated forms of huPrP and Aβ42 are co-purified from AD brain extracts. Moreover, an anti-PrP antibody and an agent that specifically binds to insoluble PrP (iPrP) co-precipitate insoluble Aβ from human AD brain. Finally, using peptide membrane arrays of 99 13-mer peptides that span the entire sequence of mature huPrP, two distinct types of Aβ binding sites on huPrP are identified in vitro. One specifically binds to Aβ42 and the other binds to both Aβ42 and Aβ40. Notably, Aβ42-specific binding sites are localized predominantly in the octapeptide repeat region, whereas sites that bind both Aβ40 and Aβ42 are mainly in the extreme N-terminal or C-terminal domains of PrP. Our study suggests that iPrP is the major PrP species that interacts with insoluble Aβ42 in vivo. Although this work indicated the interaction of Aβ42 with huPrP in the AD brain, the pathophysiological relevance of the iPrP/Aβ42 interaction remains to be established.

Single-stranded DNA aptamers specific for antibiotics tetracyclines

Tetracyclines (TCs) are a group of antibiotics comprising of a common tetracycline (TET) nucleus with variable X 1 and X 2 positions on 5 and 6 carbon atoms, such as oxytetracycline (OTC) and doxycycline (DOX). In this study, the tetracycline group specific (TGS) ssDNA aptamers were identified by modified SELEX method by employing tosylactivated magnetic beads (TMB) coated with OTC, TET, and DOX, respectively, as targets and counter targets. Twenty TGS-aptamers were selected, of which seven aptamers, designated as T7, T15, T19, T20, T22, T23, and T24, showed high affinity to the basic TET backbone ( K d = 63–483 nM). The specificity of these TGS-aptamers to structural analogues followed the order in which the TCs was employed during SELEX process (OTC > TET > DOX) except aptamer T22, which was highly specific to TET than OTC or DOX. Aptamers that were specific to one target molecule but fail to bind the other structurally related TCs were eliminated during counter selection steps. Three aptamers, T7, T19, and T23 contained palindromic consensus sequence motif GGTGTGG. The remaining TGS-aptamers showed many consensus sequences that are truncated forms of this palindrome forming mirror image or inverted sequences. For example, GTGG or its inverted form, GGTG motif was found in all TGS-aptamers. A consensus sequence motif TGTGCT or its truncated terminal T-residue was found in most TGS-aptamers, which is predicted to be essential for high affinity and group specificity. These TGS-aptamers have potential applications such as target drug delivery, and detection of TCs in pharmaceutical preparations and contaminated food products.

Electrochemical magneto immunosensing of antibiotic residues in milk

A novel electrochemical immunosensing strategy for the detection of sulfonamide antibiotics in milk based on magnetic beads is presented. Among the different strategies for immobilizing the class-specific anti-sulfonamide antibody to the magnetic beads – such as those based on the use of Protein A or carboxylate modified magnetic beads – ,the best strategy was found to be the covalent bonding on tosyl-activated magnetic beads. The immunological reaction for the detection of sulfonamide antibiotics performed on the magnetic bead is based on a direct competitive assay using a tracer with HRP peroxidase for the enzymatic labelling. After the immunochemical reactions, the modified magnetic beads can be easily captured by a magneto sensor made of graphite–epoxy composite (m-GEC), which is also used as the transducer for the electrochemical immunosensing. The electrochemical detection is thus achieved through a suitable substrate for the enzyme HRP and an electrochemical mediator. The electrochemical approach is also compared with a novel magneto-ELISA with optical detection. The performance of the electrochemical immunosensing strategy based on magnetic beads was successfully evaluated using spiked milk samples, and the detection limit was found to be 1.44 μg L −1 (5.92 nmol L −1) for raw full cream milk. This strategy offers great promise for rapid, simple, cost-effective and on-site analysis of biological, food and environmental samples.

Insoluble Aggregates and Protease-resistant Conformers of Prion Protein in Uninfected Human Brains

Aggregated prion protein (PrPSc), which is detergent-insoluble and partially proteinase K (PK)-resistant, constitutes the major component of infectious prions that cause a group of transmissible spongiform encephalopathies in animals and humans. PrPSc derives from a detergent-soluble and PK-sensitive cellular prion protein (PrPC) through an alpha-helix to beta-sheet transition. This transition confers on the PrPSc molecule unique physicochemical and biological properties, including insolubility in nondenaturing detergents, an enhanced tendency to form aggregates, resistance to PK digestion, and infectivity, which together are regarded as the basis for distinguishing PrPSc from PrPC. Here we demonstrate, using sedimentation and size exclusion chromatography, that small amounts of detergent-insoluble PrP aggregates are present in uninfected human brains. Moreover, PK-resistant PrP core fragments are detectable following PK treatment. This is the first study that provides experimental evidence supporting the hypothesis that there might be silent prions lying dormant in normal human brains.

Electrochemical Magnetoimmunosensing Strategy for the Detection of Pesticides Residues

A novel electrochemical immunosensing strategy for the detection of atrazine based on magnetic beads is presented. Different coupling strategies for the modification of the magnetic beads with the specific anti-atrazine antibody have been developed. The immunological reaction for the detection of atrazine performed on the magnetic bead is based on a direct competitive assay using a peroxidase (HRP) tracer as the enzymatic label. After the immunochemical reactions, the modified magnetic beads can be easily captured by a magnetosensor made of graphite-epoxy composite, which is also used as the transducer for the electrochemical immunosensing. The electrochemical detection is thus achieved through a suitable substrate and mediator for the enzyme HRP. The electrochemical approach is also compared with a novel magneto-ELISA based on optical detection. The performance of the electrochemical immunosensing strategy based on magnetic beads was successfully evaluated using spiked real orange juice samples. The detection limit for atrazine using the competitive electrochemical magnetoimmunosensing strategy with anti-atrazine-specific antibody covalent coupled with tosyl-activated magnetic beads was found to be 6 x 10(-3) microg L(-1) (0.027 nmol L(-1)). This strategy offers great promise for rapid, simple, cost-effective, and on-site analysis of biological, food, and environmental samples.

Cholesterol-independent Interactions with CD47 Enhance αvβ3 Avidity

Expression in OV10 cells of either wild-type CD47 or its extracellular IgV domain linked to a glycosylphosphatidylinositol anchor-(IgV-GPI) enhanced ligand-induced alpha(v)beta(3) activation as detected by the binding of LIBS1 and LIBS6 mAbs. The amplitude of LIBS binding was greater with both CD47 and IgV-GPI expression, indicating an increase in the population of "activable" integrin molecules. Expression of either CD47 species also increased alpha(v)beta(3)-mediated adhesion to vitronectin, and to surfaces coated with the anti-beta(3) antibody AP3, because of enhanced clustering of alpha(v)beta(3) as confirmed by chemical cross-linking. Cholesterol depletion with methyl-beta-cyclodextrin did not prevent the increase in anti-LIBS binding, but reduced cell adhesion to vitronectin and AP3. However, cells expressing CD47 were partially insulated against this disruption, and IgV-GPI was even more effective. Both CD47 and IgV-GPI were found in cholesterol-rich rafts prepared in the absence of detergent, but only CD47 could recruit alpha(v)beta(3) and its associated signaling molecules to these domains. Thus CD47-alpha(v)beta(3) complexes in cholesterol-rich raft domains appear to engage in G(i)-dependent signaling whereas CD47-alpha(v)beta(3) interactions that lead to integrin clustering are also detergent resistant, but are insensitive to cholesterol depletion and do not require the transmembrane region of CD47.

Use of magnetic beads in selection and detection of biotoxin aptamers by electrochemiluminescence and enzymatic methods.

Systematic evolution of ligands by exponential enrichment (SELEX) was used to develop DNA ligands (aptamers) to cholera whole toxin and staphylococcal enterotoxin B (SEB). Affinity selection of aptamers was accomplished by conjugating the biotoxins to tosyl-activated magnetic beads. The use of magnetic beads reduces the volumes needed to perform aptamer selection, thus obviating alcohol precipitation and allowing direct PCR amplification from the bead surface. Following five rounds of SELEX, 5'-biotinylated aptamers were bound to streptavidin-coated magnetic beads and used for the detection of ruthenium trisbypyridine [Ru(bpy)3(2+)]-labeled cholera toxin and SEB by an electrochemiluminescence methodology. A comparison of control (double-stranded) aptamer binding was made with aptamers that were heat denatured at 96 degrees C (single-stranded) and allowed to cool (conform) in the presence of biotoxin-conjugated magnetic beads. Results suggest that control aptamers performed equally well when compared to heat-denatured DNA aptamers in the cholera toxin electrochemiluminescence assay and a colorimetric microplate assay employing peroxidase-labeled cholera toxin and 5'-amino terminated aptamers conjugated to N-oxysuccinimide-activated microtiter wells. Interestingly, however, in the SEB electrochemiluminescence assay, double-stranded aptamers exceeded the performance of single-stranded aptamers. The detection limits of all aptamer assays were in the low nanogram to low picogram ranges.