Biorecognition and detection of antigens from Mycobacterium tuberculosis using a sandwich ELISA associated with magnetic nanoparticles

Tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB), is one of the 10 leading causes of death worldwide, especially in low-income areas. A rapid, low-cost diagnostic assay for TB with high sensitivity and specificity is not currently available. Bio-functionalized magnetic nanoparticles (MNPs) which are able to efficiently detect and concentrate biomolecules from complex biological samples, allows improving the diagnostic immunoassays. In this way, a proof-of-concept of MNP-based sandwich immunoassay was developed to detect various MTB protein antigens. The superficial and secretory antigenic proteins considered in this research were: CFP10, ESAT6, MTC28, MPT64, 38 kDa protein, Ag85B, and MoeX. The proteins were cloned and expressed in an E. coli system. Polyclonal antibodies (ab) against the recombinant antigens were elicited in rabbits and mice. Antibodies were immobilized on the surface of amine-silanized nanoparticles (MNP@Si). The functionalized MNP@Si@ab were tested in a colorimetric sandwich enzyme-linked immunosorbent assay (sELISA-MNP@Si@ab) to recognize the selected antigens in sputum samples. The selected MTB antigens were successfully detected in sputum from TB patients in a shorter time (~ 4 h) using the sELISA-MNP@Si@ab, compared to the conventional sELISA (~15 h) standardized in home. Moreover, the sELISA-MNP@Si@ab showed the higher sensitivity in the real biological samples from infected patients.

Detection of ricin activity and structure by using novel galactose-terminated magnetic bead extraction coupled with mass spectrometric detection

Ricin is a toxic protein derived from the castor bean plant (Ricinus communis) and has potential for bioterrorism or criminal use. Therefore, sensitive and rapid analytical methods are needed for its confirmatory detection in environmental samples. Our laboratory previously reported on the development of a confirmatory method to detect ricin involving antibody capture of ricin followed by mass spectrometric detection of ricin’s enzymatic activity and of tryptic fragments unique to ricin. Here, we describe a novel ricin capture method of magnetic beads coated with 4-aminophenyl-1-thiol-β-galactopyranoside, using ricin’s lectin characteristics. The assay has been adapted for use on a simple, benchtop MALDI-TOF MS mass spectrometer common in clinical microbiology laboratories. Validation of the novel assay includes establishment of a limit of detection, and an examination of assay selectivity. The limit of detection of the enzymatic activity method is 8 ng/mL and 500 ng/mL for the confirmatory tryptic fragment assay. The assay is highly selective with no cross-reactivity from near neighbors and highly specific with a panel of 19 cultivars all testing positive. Additionally, there were no interferences found during testing of a panel of white powders. This allows for a confirmatory detection method for ricin in laboratories lacking expensive, sophisticated mass spectrometers.

Functional magnetic nanoparticle-based affinity probe for MALDI mass spectrometric detection of ricin B

The use of lactosylated Fe₃O₄ magnetic nanoparticles (MNP@LAC) has been explored as affinity probes against ricin B based on galactose-ricin B binding interactions. Lactose was bound onto the surface of aminated MNPs through the Maillard reaction. The enrichment of ricin B took ~1 h by incubating MNP@LAC with samples under shaking at room temperature, followed by magnetic isolation. The resultant MNP@LAC-ricin B conjugates were characterized by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The limit of detection toward ricin B was ~3 nM by using the developed method. It was possible to detect the peptides derived from the tryptic digest of trace ricin B (~0.39 nM) enriched by the MNP@LAC probes followed by tryptic digestion and MALDI-MS analysis. The feasibility of using the developed method for detection of ricin B from complex white corn starch samples spiked with trace ricin B was demonstrated.

Gold-Speckled SPION@SiO2 Nanoparticles Decorated with Thiocarbohydrates for ASGPR1 Targeting: Towards HCC Dual Mode Imaging Potential Applications

Efforts are made to perform an early and accurate detection of hepatocellular carcinoma (HCC) by simultaneous exploiting multiple clinically non-invasive imaging modalities. Original nanostructures derived from the combination of different inorganic domains can be used as efficient contrast agents in multimodal imaging. Superparamagnetic iron oxide nanoparticles (SPIONs) and Au nanoparticles (NPs) possess well-established contrasting features in magnetic resonance imaging (MRI) and X-ray computed tomography (CT), respectively. HCC can be targeted by using specific carbohydrates able to recognize asialoglycoprotein receptor 1 (ASGPR1) overexpressed in hepatocytes. Here, two different thiocarbohydrate ligands were purposely designed and alternatively conjugated to the surface of Au-speckled silica-coated SPIONs NPs, to achieve two original nanostructures that could be potentially used for dual mode targeted imaging of HCC. The results indicated that the two thiocarbohydrate decorated nanostructures possess convenient plasmonic/superparamagnetic properties, well-controlled size and morphology and good selectivity for targeting ASGPR1 receptor.

Synthesis, characterization and bio-functionalization of magnetic nanoparticles to improve the diagnosis of tuberculosis

Mycobacterium tuberculosis is the cause of one of the diseases with the highest mortality and morbidity rate in the Americas and in the world. In developing countries, the diagnosis of tuberculosis (TB) is based on baciloscopy and bacteriological cultures. The first method has a low sensitivity, and the second can take several weeks to reach a confirmatory diagnosis. The lack of a rapid diagnosis compromises the efforts to control this disease and favors the transmission of tuberculosis to the susceptible population. In this work, we present the synthesis, amine-silanization, characterization and bio-functionalization of magnetic nanoparticles (MNPs) to develop a sandwich ELISA to detect and concentrate antigens from M. tuberculosis. For this purpose, a recombinant mycobacterial heat shock protein Hsp16.3, which contributes to the persistence of TB, was cloned and expressed in the E. coli system. Polyclonal antibodies anti-Hsp16.3 were produced in a rabbit and in mice. Magnetic nanoparticles were synthesized by co-precipitation, amine-functionalized and characterized by several physical-chemical methods. The XRD, Mossbauer spectroscopy, zeta potential, TEM, and FTIR all proved the successful preparation of the MNPs showing a diffraction crystal diameter of 10.48 ± 2.56 nm, superficial net charge of [Formula: see text]: +23.57 ± 2.87 mV, characteristic patterns of magnetite and a structure similar to a sphere. Additionally, it showed a magnetization saturation of 37.06 emu.g-1. For the functionalization of nanoparticle surfaces with anti-Hsp16.3, the active ester method was used for bond formation, and parameters such as time of incubation, coupling agents ratio (EDC/NHS) and concentration as well as surface saturation level of amine-silanized MNPs (MNP@Si@NH2) were standardized. Finally, bio-functionalized MNPs were used to detect, fix and concentrate the recombinant antigen Hsp16.3 from M. tuberculosis in a sandwich ELISA-MNP assay.

Rapid and sensitive identification of ricin in environmental samples based on lactamyl agarose beads using LC-MS/MS (MRM)

Ricin, a plant-derived toxin extracted from the seeds of Ricinus communis (castor bean plant), is one of the most toxic proteins known. Ricin's high toxicity, widespread availability, and ease of its extraction make it a potential agent for bioterrorist attacks. Most ricin detection methods are based on immunoassays. These methods may suffer from low efficiency in matrices containing interfering substances, or from false positive results due to antibody cross reactivity, with highly homologous proteins. In this study, we have developed a simple, rapid, sensitive, and selective mass spectrometry assay, for the identification of ricin in complex environmental samples. This assay involves three main stages: (a) Ricin affinity capture by commercial lactamyl-agarose (LA) beads. (b) Tryptic digestion. (c) LC-MS/MS (MRM) analysis of tryptic fragments. The assay was validated using 60 diverse environmental samples such as soil, asphalt, and vegetation, taken from various geographic regions. The assay's selectivity was established in the presence of high concentrations of competing lectin interferences. Based on our findings, we have defined strict criteria for unambiguous identification of ricin. Our novel method, which combines affinity capture beads followed by MRM-based analysis, enabled the identification of 1 ppb ricin spiked into complex environmental matrices. This methodology has the potential to be extended for the identification of ricin in body fluids from individuals exposed (deliberately or accidentally) to the toxin, contaminated food or for the detection of the entire family of RIP-II toxins, by applying multiplex format.

Using lactosylated cysteine functionalized gold nanoparticles as colorimetric sensing probes for rapid detection of the ricin B chain

A new colorimetric method that can be used to rapidly detect toxic ricin is demonstrated. Lactosylated cysteine-functionalized gold nanoparticles (Au@LACY NPs) were prepared by a one-pot reaction and employed as optical probes for determination of ricin B chain. It is found that the Au@LACY NPs undergo aggregation in the presence of ricin B chain. This leads to surface plasmon coupling effects of the particles and a color change from red to blue, with absorption maxima at 519 and 670 nm, respectively. The feasibility of using the current approach for quantitative analysis of ricin B chain is also demonstrated. The calibration plot is generated by plotting the ratio of the absorbance at the wavelength of 634 to 518 nm versus the concentration of the ricin B chain. The spectrophotometric method has a ~29 pM (~ 0.91 ng·mL^-1) detection limit, and the sample with the concentration of ~ 400 pM (~ 13 ng·mL^-1) can be detected visually. Graphical abstractSchematic representation of using lactosylated cysteine capped gold nanoparticles (Au@LACY NPs) as colorimetric probes for the ricin B chain through surface plasmon coupling effects. Sample solution turns from red to blue in the presence of ricin B chain.

Porous MnFe2O4@SiO2 magnetic glycopolymer: A multivalent nanostructure for efficient removal of bacteria from aqueous solution

The focuses of this research is to prepare an efficient magnetic glycopolymer for bacteria removal from aqueous solution. To perform this idea; porous MnFe₂O₄@SiO₂ was functionalized with glucose and or maltose as an anchors to adhere onto bacteria cell surface. Aminopropyltriethoxysilane was employed to link the saccharides on magnetic nanoparticle surface. The hybrid materials were characterized with XRD, VSM, FT-IR, FESEM, TEM, zeta potential measurement and elemental mapping. Microscopic image showed that MnFe₂O₄ is in cluster form composed from tiny nanoparticles. After saccharide functionalization hybrid composite generate hyper-crosslinked porous structure as a result of polysilicate formation due to hydrolysis of silica source. Escherichia coli and bacillus subtilis were selected as sample pathogens to evaluate the bacteria capturing ability of the magnetic glycopolymer. At the optimum conditions (pH = 6, time of 20 min, dosage of 15 mg) removal efficiency was more than 99% using both saccharide.

Exonuclease III-assisted graphene oxide amplified fluorescence anisotropy strategy for ricin detection

Graphene oxide (GO) is an excellent fluorescence anisotropy (FA) amplifier. However, in the conventional GO amplified FA strategy, one target can only induce the FA change of one fluorophore on probe, which limits the detection sensitivity. Herein, we developed an exonuclease III (Exo III) aided GO amplified FA strategy by using aptamer as an recognition element and ricin B-chain as a proof-of-concept target. The aptamer was hybridized with a blocker sequence and linked onto the surface of magnetic beads (MBs). Upon the addition of ricin B-chain, blocker was released from the surface of MBs and hybridized with the dye-modified probe DNA on the surface of GO through the toehold-mediated strand exchange reaction. The formed blocker-probe DNA duplex triggered the Exo III-assisted cyclic signal amplification by repeating the hybridization and digestion of probe DNA, liberating the fluorophore with several nucleotides (low FA value). Thus, ricin B-chain could be sensitively detected by the significantly decreased FA. The linear range was from 1.0μg/mL to 13.3μg/mL and the limit of detection (LOD) was 400ng/mL. This method improved the sensitivity of FA assay and it could be generalized to any kind of target detection based on the use of an appropriate aptamer.

A facile label-free colorimetric aptasensor for ricin based on the peroxidase-like activity of gold nanoparticles

A facile colorimetric aptasensor for ricin based on the peroxidase-like activity of gold nanoparticles was demonstrated for the first time.

Highly sensitive and rapid visual detection of ricin using unmodified gold nanoparticle probes

A sensitive aptamer-based colorimetric biosensor for the detection of ricin using unmodified gold nanoparticles as probe was developed.

A single DNA aptamer functions as a biosensor for ricin

The use of microorganisms or toxins as weapons of death and fear is not a novel concept; however, the modes by which these agents of bioterrorism are deployed are increasingly clever and insidious. One mechanism by which biothreats are readily disseminated is through a nation's food supply. Ricin, a toxin derived from the castor bean plant, displays a strong thermostability and remains active at acidic and alkaline pHs. Therefore, the CDC has assigned ricin as a category B reagent since it may be easily amendable as a deliberate food biocontaminate. Current tools for ricin detection utilize enzymatic activity, immunointeractions and presence of castor bean DNA. Many of these tools are confounded by complex food matrices, display a limited dynamic range of detection and/or lack specificity. Aptamers, short RNA and single stranded DNA sequences, have increased affinity to their selected receptors, experience little cross-reactivity to other homologous compounds and are currently being sought after as biosensors for bacterial contaminants in food. This paper describes the selection and characterization of a single, dominant aptamer, designated as SSRA1, against the B-chain of ricin. SSRA1 displays one folding conformation that is stable across 4-63 °C (ΔG = -5.05). SSRA1 is able to concentrate at least 30 ng mL(-1) of ricin B chain from several liquid food matrices and outcompetes a currently available ELISA kit and ricin aptamer. Furthermore, we show detection of 25 ng mL(-1) of intact ricin A-B complex using SSRA1 combined with surface enhanced Raman scattering technique. Thus, SSRA1 would serve well as pre-analytical tool for processing of ricin from liquid foods to aid current diagnostics as well as a sensor for direct ricin detection.