Recent Advances in Molecular Imprinting for Proteins on Magnetic Microspheres

The separation of proteins in biological samples plays an essential role in the development of disease detection, drug discovery, and biological analysis. Protein imprinted polymers (PIPs) serve as a tool to capture target proteins specifically and selectively from complex media for separation purposes. Whereas conventional molecularly imprinted polymer is time-consuming in terms of incubation studies and solvent removal, magnetic particles are introduced using their magnetic properties for sedimentation and separation, resulting in saving extraction and centrifugation steps. Magnetic protein imprinted polymers (MPIPs), which combine molecularly imprinting materials with magnetic properties, have emerged as a new area of research hotspot. This review provides an overview of MPIPs for proteins, including synthesis, preparation strategies, and applications. Moreover, it also looks forward to the future directions for research in this emerging field.

Construction of Magnetic Core-Large Mesoporous Satellite Immunosensor for Long-Lasting Chemiluminescence and Highly Sensitive Tumor Marker Determination

Chemiluminescence immunoassay exhibits high sensitivity and signal-to-noise ratio, thus attracting great attention in the early diagnosis and dynamic monitoring of diseases. However, the collection of conventional flash-type chemiluminescence signal (<5 s) relies heavily on automatic sampling and reading instrument. Herein, a novel core-satellite multifunctional chemiluminescence immunosensor is designed for the efficient enrichment and highly sensitive determination of cancer biomarker carcinoembryonic antigen (CEA) with enhanced and long-lasting output signal that can be conveniently recorded by a simple microplate plate reading instrument. Anti-CEA monoclonal antibody 2 (Ab2) modified Fe3 O4 @SiO2 microspheres (Fe3 O4 @SiO2 -Ab2, 370 nm in diameter) are synthesized as the core for selectively capturing and enriching target CEA in solution, and anti-human CEA monoclonal antibody 1 (Ab1) and horseradish peroxidase (HRP) co-immobilized dendritic large-mesoporous silica nanospheres (MSNs-HRP/Ab1, 80 nm in diameter, pore size: 17 nm) are synthesized as the satellite for efficient immunological recognition and signal amplification. The as-designed core-satellite magnetic chemiluminescence immunosensors exhibit a broad linear range of 0.01-20 ng mL-1 and a low detection limit of 3.0 pg mL-1 for the convenient, highly specific, and sensitive determination of CEA in human serum. Such core-satellite chemiluminescence immunosensors are expected to act as a powerful tool for in vitro detection of various biomarkers, overcome the defect of conventional chemiluminescence relying heavily on expensive and bulky automatic instruments and popularize chemiluminescence analysis to primary medical institutions and remote areas.

Characterization of Modified Mechanically Activated Cassava Starch Magnetic Porous Microspheres and Its Adsorption for Cd(II) Ions

The magnetic polymer microsphere is a promising adsorbent due to its high adsorption efficiency and good regeneration ability from wastewater. Cassava starch magnetic porous microspheres (AAM-MSMPMs) were synthesized by graft copolymerization in inverse emulsion. Mechanically activated cassava starch (MS) was used to graft skeletons, vinyl monomers [acrylic acid (AA) and acrylamide (AM)] as copolymerized unsaturated monomers, methyl methacrylate (MMA) as the dispersing agent, and polyethylene glycol/methanol (PEG2000/MeOH) as the porogen. It was found that the AAM-MSMPM adsorbent is superparamagnetic, the saturation magnetization is 14.9 emu·g^-1, and it can be rapidly and directionally separated from Cd(II) ions in aqueous solution. The FTIR indicated that the carboxyl and hydroxyl groups were grafted into MS. The AAM-MSMPM had good speroidization and a uniform size. After the porogen was added, the particle size of the AAM-MSMPM decreased from 19.00 to 7.00 nm, and the specific surface area increased from 7.00 to 35.00 m²·g^-1. The pore volume increased from 0.03 to 0.13 cm³·g^-1. The AAM-MSMPM exhibited a large specific surface area and provided more adsorption active sites for Cd(II) ions. The maximum adsorption capacity of the AAM-MSMPM for Cd(II) ions was 210.68 mg·g^-1, i.e., 81.02% higher than that without porogen. Additionally, the Cd(II) ion adsorption process on the AAM-MSMPM can be described by Langmuir isothermal and pseudo-second-order kinetic models. A chemical reaction dominated the Cd(II) ion adsorption process on the AAM-MSMPM, and chemisorption was the rate-controlling step during the Cd(II) ion adsorption process. The AAM-MSMPM still had excellent stability after five consecutive reuses.

One-step Photocatalytic Synthesis of Fe3O4@Polydiallyl Isophthalate Magnetic Microspheres for Magnetocaloric Tumor Ablation and Its Potential for Tracing on MRI and CT

Allyl monomers that were previously considered to be difficult to polymerize are applied, and Fe₃O₄@polydiallyl isophthalate (Fe₃O₄@PDAIP) magnetic were synthesized by one-step photopolymerization. The skeleton of the microspheres is made of diallyl isophthalate (DAIP). We obtained the microspheres using the photo-click technique in a soft template with Nano-Fe₃O₄ evenly disseminated in hydrophobic DAIP by cation-π and polar interaction. The obtained Fe₃O₄@PDAIP magnetic microspheres can achieve tumor cell necrosis temperatures (41-52 ℃) in an alternating magnetic field due to their inherent magnetic response. The results of in vitro CT and MR imaging indicate that the microspheres might be monitored accurately in vivo. Then the structural characteristics of the microspheres were confirmed by morphological analysis and physicochemical property analysis. Experiments in vitro and in vivo revealed that the microspheres had an anti-tumor effect and their biocompatibility satisfies the standards. The stability experiment proves that the microspheres have the potential for long-term effectiveness in vivo. It demonstrates the promise of Fe₃O₄@PDAIP magnetic microspheres in clinical applications.

Competitive Ratiometric Aptasensing with Core-Internal Standard-Shell Structure Based on Surface-Enhanced Raman Scattering

Reproducibility and stability are important indicators for the evaluation of quantitative sensing methods based on surface-enhanced Raman scattering (SERS) technology. Developing a SERS substrate with self-calibration capabilities is vital for effectively quantifying targets. In this work, a competitive ratiometric SERS aptasensor was developed. 4-Aminothiophenol as an internal standard (IS) was embedded in the substrate followed by gradually loading with the aptamer and methylene blue functionalizing of the complementary sequences of the aptamer (MB-cDNA). Recognition and binding of the target to the aptamer resulted in the shedding of MB-cDNA after magnetic separation reducing the SERS signal of MB, allowing for the ratiometric determination of the target based on the constant intensity from the IS. For the selective detection of okadaic acid (OA), a good negative correlation was achieved between the SERS ratiometric intensity and OA concentration in the range of 0.5-100 ng/mL. The magnetic separation strategy effectively simplifies the production steps of the aptasensor, and the ratiometric strategy effectively improved the reproducibility and stability of the OA sensing. This ratiometric aptasensor has been successfully employed to detect OA in food and environmental samples and is expected to be extended to detect other targets.

A New Method for Abrin Detection Based on the Interaction between Target Molecules and Fluorescently Labeled Aptamers on Magnetic Microspheres

A quantitative structure-activity relationship (QSAR) model for the structure and affinity of abrin aptamers was established. A higher affinity abrin aptamer based on the established QSAR model was screened by site-directed mutagenesis. The fluorescence quenching effect between magnetic microspheres and fluorescent molecules was studied for the first time. A new method for abrin detection based on the interaction between target molecules and fluorescently labeled aptamers on magnetic microspheres was developed, with the detection limit of 5 ng mL^-1. This method can overcome the influence of complex environmental interferents in abrin detection and can meet the analysis requirements for simulated samples such as water, soil, and food.

Mono-Sized Anion-Exchange Magnetic Microspheres for Protein Adsorption

In this study, mono-sized anion-exchange microspheres with polyglycidylmethacrylate were engineered and processed to introduce magnetic granules by penetration-deposition approaches. The obtained magnetic microspheres showed a uniform particle diameter of 1.235 μm in average and a good spherical shape with a saturation magnetic intensity of 12.48 emu/g by VSM and 12% magnetite content by TGA. The magnetic microspheres showed no cytotoxicity when the concentration was below 10 μg/mg. The magnetic microspheres possess respective adsorption capacity for three proteins including Bovine albumin, Hemoglobin from bovine blood, and Cytochrome C. These magnetic microspheres are also potential biomaterials as targeting medicine carriers or protein separation carriers at low concentration.

High-Density Anisotropy Magnetism Enhanced Microwave Absorption Performance in Ti3C2Tx MXene@Ni Microspheres

Two-dimensional materials, especially the newly emerging MXene, have attracted numerous interests in the fields of energy conversion/storage and electromagnetic shielding/absorption. However, the inherently inevitable aggregation and absence of magnetic loss of MXene considerably limit its electromagnetic absorption application. The introduction of magnetic component and favorable structural engineering are the alternatives to improve the microwave absorption (MA) performance. Herein, we report a spheroidization strategy to assemble double-shell MXene@Ni microspheres, where the commonly lamellar MXene are reshaped into three-dimensional microspheres that provide the substrate for oriented growth of Ni nanospikes. Whereas this structural feature offers massive accessible active surfaces that effectively promote the dielectric loss ability, the introduction of magnetic Ni nanospikes enables the additional magnetic loss capacity. Benefiting from these merits, the synthesized 3D MXene@Ni microspheres exhibit superior MA performance with the minimum reflection loss value of -59.6 dB at an ultrathin thickness (∼1.5 mm) and effective absorption bandwidth of 4.48 GHz. Moreover, the electron holography results reveal that the high-density anisotropy magnetism plays an important role in the improvement of MA performance, which provides an insight for the design of MXene-based materials as high-efficient microwave absorbers.

Magnetic Agarose Microspheres/Hyaluronic Acid Hydrogel as a Trackable Bulking Agent for Vesicoureteral Reflux Treatment

Vesicoureteral reflux (VUR) is one of the most common congenital anomalies in the kidney and the urinary tract. Endoscopic subureteral injection of a bulking agent has become popular in VUR treatment due to its high success rates, few complications, and a straightforward procedure. In this study, a novel magnetic bulking agent was prepared by embedding Fe₃O₄ magnetic nanoparticles in cross-linked agarose microspheres with diameters of 80–250 μm and dispersing the magnetic microspheres in a hyaluronic acid hydrogel. The bulking agent has good biocompatibility and biosecurity validated by the tests of cytotoxicity, in vitro genotoxicity, animal irritation, skin sensitization, acute systemic toxicity, and pathological analysis after the injection of the bulking agent extract solution into healthy mice as well as injection of the bulking agent into VUR rabbits. The VUR rabbits were created by incising the roof of the intravesical ureter to enlarge the ureteral orifice. The success rate of the bulking agent in treating VUR rabbits using a subureteral transurethral injection technique was 67% (4/6) or 80% (4/5, excluding the unfinished rabbit), and no migrated particles were found in the organs of the rabbits. The transverse relaxation rate of the bulking agent was 104 mM⁻¹s⁻¹. After injection, the bulking agent was long-term trackable through magnetic resonance imaging that can help clinicians to inspect the VUR treatment effect. For the first time, this study demonstrates that the bulking agent with a long-term stable tracer is promising for endoscopic VUR treatment.

Establishment of time-resolved fluoroimmunoassay of IgG4 based on magnetic microspheres

BACKGROUND

The abnormal increase in serum IgG4 level is an important clinical symptom of IgG4-related disease (IgG4-RD), and the detection of serum IgG4 level is a powerful tool for the diagnosis of IgG4-RD. This study was conducted to establish a simple and rapid immunoassay for the determination of human serum IgG4 levels.

METHODS

Based on the competition method, a novel immunoassay was established for the determination of human serum IgG4 using a combination of time-resolved fluoroimmunoassay (TRFIA) and magnetic microspheres. IgG4 was coupled with magnetic microspheres and competed with IgG4 in the samples to bind the Eu3+ -labeled anti-IgG4 antibody. The immunocomplex was separated and washed in a magnetic field, and the fluorescence counts were measured according to the number of dissociated europium ions.

RESULTS

The analytical sensitivity of IgG4-TRFIA based on magnetic microspheres was 0.006 g/L, and the detection range was 0.006-20 g/L under optimal conditions. The precision, recovery, and specificity of this immunoassay were demonstrated to be acceptable. The clinical application of IgG4-TRFIA based on magnetic microspheres was evaluated and compared with that of immunonephelometry. The results showed that the two detection methods had a good correlation, with a correlation coefficient of .9871.

CONCLUSION

IgG4-TRFIA based on magnetic microspheres has the advantages of high sensitivity, wide detection range, and short analysis time and has the potential to become a useful tool for the diagnosis of IgG4-RD.

Immobilization of GH78 α-L-Rhamnosidase from Thermotoga petrophilea with High-Temperature-Resistant Magnetic Particles Fe3O4-SiO2-NH2-Cellu-ZIF8 and Its Application in the Production of Prunin Form Naringin

To efficiently recycle GH78 thermostable rhamnosidase (TpeRha) and easily separate it from the reaction mixture and furtherly improve the enzyme properties, the magnetic particle Fe₃O₄-SiO₂-NH₂-Cellu-ZIF8 (FSNcZ8) was prepared by modifying Fe₃O₄-NH₂ with tetraethyl silicate (TEOS), microcrystalline cellulose and zinc nitrate hexahydrate. FSNcZ8 displayed better magnetic stability and higher-temperature stability than unmodified Fe₃O₄-NH₂ (FN), and it was used to adsorb and immobilize TpeRha from Thermotoga petrophilea 13995. As for properties, FSNcZ8-TpeRha showed optimal reaction temperature and pH of 90°C and 5.0, while its highest activity approached 714 U/g. In addition, FSNcZ8-TpeRha had better higher-temperature stability than FN. After incubation at 80°C for 3 h, the residual enzyme activities of FSNcZ8-TpeRha, FN-TpeRha and free enzyme were 93.5%, 63.32%, and 62.77%, respectively. The organic solvent tolerance and the monosaccharides tolerance of FSNcZ8-TpeRha, compared with free TpeRha, were greatly improved. Using naringin (1 mmol/l) as the substrate, the optimal conversion conditions were as follows: FSNcZ8-TpeRha concentration was 6 U/ml; induction temperature was 80°C; the pH was 5.5; induction time was 30 min, and the yield of products was the same as free enzyme. After repeating the reaction 10 times, the conversion of naringin remained above 80%, showing great improvement of the catalytic efficiency and repeated utilization of the immobilized α-L-rhamnosidase.

Preparation and Microwave Absorption Properties of C@Fe3O4 Magnetic Composite Microspheres

In this work, C@Fe₃O₄ magnetic microspheres were designed and prepared by a novel strategy, and the microwave absorption properties of the materials were investigated. Four kinds of monodisperse P(MAA/St) microspheres with different carboxyl content were synthesized via facile dispersion polymerization. The Fe₃O₄ nanoparticles were grown on the surface of P(MAA/St) to obtain P(MAA/St)@Fe₃O₄ microspheres. Using P(MAA/St)@Fe₃O₄ as the precursors, after vacuum carbonization, C@Fe₃O₄ were obtained. It was observed that the carboxyl content on the microspheres’ surface increased with the increasing of MAA, which made the magnetic content and maximum specific saturation magnetization of P(MAA/St)@Fe₃O₄ and C@Fe₃O₄ increase. The obtained four kinds of C@Fe₃O₄ microspheres had a particle size range of 4–6 μm. The microwave absorption properties indicated that the magnetic content made a difference to the microwave absorption properties of C@Fe₃O₄ magnetic microspheres. The microwave absorption properties of materials were determined by controlling dielectric loss, magnetic loss and impedance matching. C@Fe₃O₄ microspheres exhibited excellent microwave absorption properties. The maximum reflection loss could reach −45.6 dB at 12.8 GHz with 3 mm in thickness. The effective bandwidth was 5.9 GHz with RL < −10 dB. Therefore, C@Fe₃O₄ microspheres were lightweight and efficient microwave absorption materials.

Nonsacrificial Self-Template Synthesis of Colloidal Magnetic Yolk-Shell Mesoporous Organosilicas for Efficient Oil/Water Interface Catalysis

Using interfacial reaction systems for biphasic catalytic reactions is attracting more and more attention due to their simple reaction process and low environmental pollution. Yolk-shell structured materials have broad applications in biomedicine, catalysis, and environmental remediation owing to their open channels and large space for guest molecules. Conventional methods to obtain yolk-shell mesoporous materials rely on costly and complex hard-template strategies. In this study, a mild and convenient nonsacrificial self-template strategy is developed to construct yolk-shell magnetic periodic mesoporous organosilica (YS-mPMO) particles by using the unique swelling-deswelling property of low-crosslinking density resorcinol formaldehyde (RF). The obtained YS-mPMO microspheres possess an amphiphilic outer shell, high surface area (393 m² g^-1 ), uniform mesopores (2.58 nm), a tunable middle hollow space (50-156 nm), and high superparamagnetism (34.4-37.1 emu g^-1 ). By tuning the synthesis conditions, heterojunction structured yolk-shell Fe₃ O₄ @RF@void@PMO particles with different morphologies can be produced. Owing to the amphipathy of PMO framworks, the YS-mPMO particles show great emulsion stabilization ability and recyclability under a magnetic field. YS-mPMO microspheres with immobilized Au nanoparticles (≈3 nm) act as both solid emulsifier for dispersing styrene (St) in water and interface catalysts for selective conversion of St into styrene oxide with a high selectivity of 86%, and yields of over 97%.

Cetylpyridinium chloride functionalized silica-coated magnetite microspheres for the solid-phase extraction and pre-concentration of ochratoxin A from environmental water samples with high-performance liquid chromatographic analysis

A new method based on cetylpyridinium chloride coated ferroferric oxide/silica magnetic microspheres as an efficient solid-phase adsorbent was developed for the extraction and enrichment of ochratoxin A. The determination of ochratoxin A was obtained by high-performance liquid chromatography with fluorescence detection. In the presence of cetylpyridinium chloride, the adsorption capacity of ferroferric oxide/silica microspheres was 5.95 mg/g for ochratoxin A. The experimental parameters were optimized, including the amounts of ferroferric oxide/silica microspheres (20 mg) and cetylpyridinium chloride (0.18 mL, 0.5 mg/mL), pH value of media (9), ultrasonic time (5 min), elution solvent and volume [2(1 + 1) mL (washed twice, 1 mL each time) 1% acetic acid acetonitrile]. Under optimal experiment conditions, ochratoxin A had good linearity in the range of 2.5-250.0 ng/L in water samples with correlation coefficient of the calibration curve 0.9995. The limit of detection for ochratoxin A was 0.83 ng/L, and the recoveries were 89.8-96.8% with the relative standard deviation of 1.5-3.5% in environmental water samples. Furthermore, ferroferric oxide/silica microspheres show excellent reusability during extraction procedures for no less than six times.

Magnetic poly(2-hydroxyethyl methacrylate) microspheres for affinity purification of monospecific anti-p46 kDa/Myo1C antibodies for early diagnosis of multiple sclerosis patients

The aim of the present study is to develop new magnetic polymer microspheres with functional groups available for easy protein and antibody binding. Monodisperse macroporous poly(2-hydroxyethyl methacrylate) (PHEMA-COOH) microspheres ~4 µm in diameter and containing ∼1 mmol COOH/g were synthesized by multistep swelling polymerization of 2-hydroxyethyl methacrylate (HEMA), ethylene dimethacrylate (EDMA), and 2-[(methoxycarbonyl)methoxy]ethyl methacrylate (MCMEMA), which was followed by MCMEMA hydrolysis. The microspheres were rendered magnetic by precipitation of iron oxide inside the pores, which made them easily separable in a magnetic field. Properties of the resulting magnetic poly(2-hydroxyethyl methacrylate) (mgt.PHEMA) particles with COOH functionality were examined by scanning and transmission electron microscopy (SEM and TEM), static volumetric adsorption of helium and nitrogen, mercury porosimetry, Fourier transform infrared (FTIR) and atomic absorption spectroscopy (AAS), and elemental analysis. Mgt.PHEMA microspheres were coupled with p46/Myo1C protein purified from blood serum of multiple sclerosis (MS) patients, which enabled easy isolation of monospecific anti-p46/Myo1C immunoglobulin G (IgG) antibodies from crude antibody preparations of mouse blood serum. High efficiency of this approach was confirmed by SDS/PAGE, Western blot, and dot blot analyses. The newly developed mgt.PHEMA microspheres conjugated with a potential disease biomarker, p46/Myo1C protein, are thus a promising tool for affinity purification of antibodies, which can improve diagnosis and treatment of MS patients.

xMAP Technology: Applications in Detection of Pathogens

xMAP technology is applicable for high-throughput, multiplex and simultaneous detection of different analytes within a single complex sample. xMAP multiplex assays are currently available in various nucleic acid and immunoassay formats, enabling simultaneous detection and typing of pathogenic viruses, bacteria, parasites and fungi and also antigen or antibody interception. As an open architecture platform, the xMAP technology is beneficial to end users and therefore it is used in various pharmaceutical, clinical and research laboratories. The main aim of this review is to summarize the latest findings and applications in the field of pathogen detection using microsphere-based multiplex assays.

A generic magnetic microsphere platform with "clickable" ligands for purification and immobilization of targeted proteins

While much effort has been made to prepare magnetic microspheres (MMs) with surface moieties that bind to affinity tags or fusion partners of interest in the recombinant proteins, it remains a challenge to develop a generic platform that is capable of incorporating a variety of capture ligands by a simple chemistry. Herein, we developed core-shell structured magnetic microspheres with a high magnetic susceptibility and a low nonspecific protein adsorption. Surface functionalization of these MMs with azide groups facilitates covalent attachment of alkynylated ligands on their surfaces by "click" chemistry and creates a versatile platform for selective purification and immobilization of recombinant proteins carrying corresponding affinity tags. The general applicability of the approach was demonstrated in incorporating four widely used affinity ligands with different reactive groups (-CHO, -SH, -COOH, and -NH2) onto the MMs platform for purification and immobilization of targeted proteins. The azide-functionalized MMs would be applicable for a variety of ligands and substrates that are amenable to alkynylation modification.

Facile synthesis of guanidyl-functionalized magnetic polymer microspheres for tunable and specific capture of global phosphopeptides or only multiphosphopeptides

The highly selective and efficient capture of heterogeneous types of phosphopeptides is critical for comprehensive and in-depth phosphoproteome analysis, but it still remains a challenge since the lack of affinity material with large binding capacity and controllable specificity. Here, a new affinity material was prepared to improve the enrichment capacity and endue the tunable specificity by introducing guanidyl onto poly(glycidyl methacrylate) (PGMA) modified Fe3O4 microsphere (denoted as Fe3O4@PGMA-Guanidyl). The thick polymer shell endows the composite microsphere with large amount of guanidyl and is beneficial to enhancing the affinity interaction between phosphopeptides and the material. Interestingly, the Fe3O4@PGMA-Guanidyl possesses tunable enriching ability for global phosphopeptides or only multiphosphopeptides through simple regulation of buffer composition. The composite has large enrichment capacity (200 mg g(-1)), extremely high detection sensitivity (0.5 fmol), high enrichment recovery (91.30%), great specificity, and rapid magnetic separation. Moreover, the result of the application to capture of phosphopeptides from tryptic digest of nonfat milk has demonstrated the great potential of Fe3O4@PGMA-Guanidyl in detection and identification of low-abundance phosphopeptides of interest in biological sample.

Detection of Mycobacterium tuberculosis based on H37R(v) binding peptides using surface functionalized magnetic microspheres coupled with quantum dots – a nano detection method for Mycobacterium tuberculosis

Despite suffering from the major disadvantage of low sensitivity, microscopy of direct smear with the Ziehl–Neelsen stain is still broadly used for detection of acid-fast bacilli and diagnosis of tuberculosis. Here, we present a unique detection method of Mycobacterium tuberculosis (MTB) using surface functionalized magnetic microspheres (MMSs) coupled with quantum dots (QDs), conjugated with various antibodies and phage display-derived peptides. The principle is based upon the conformation of the sandwich complex composed of bacterial cells, MMSs, and QDs. The complex system is tagged with QDs for providing the fluorescent signal as part of the detection while magnetic separation is achieved by MMSs. The peptide ligand H8 derived from the phage display library Ph.D.-7 is developed for MTB cells. Using the combinations of MMS-polyclonal antibody+QD-H8 and MMS-H8+QD-H8, a strong signal of 10³ colony forming units (CFU)/mL H₃₇R_v was obtained with improved specificity. MS-H8+QD-H8 combination was further optimized by adjusting the concentrations of MMSs, QDs, and incubation time for the maximum detection signal. The limit of detection for MTB was found to reach 10³ CFU/mL even for the sputum matrices. Positive sputum samples could be distinguished from control. Thus, this novel method is shown to improve the detection limit and specificity of MTB from the sputum samples, and to reduce the testing time for accurate diagnosis of tuberculosis, which needs further confirmation of more clinical samples.

Rapid Characterization of Magnetic Moment of Cells for Magnetic Separation

NCI-H1650 lung cancer cell lines labeled with magnetic nanoparticles via the Epithelial Cell Adhesion Molecule (EpCAM) antigen were previously shown to be captured at high efficiencies by a microfabricated magnetic sifter. If fine control and optimization of the magnetic separation process is to be achieved, it is vital to be able to characterize the labeled cells' magnetic moment rapidly. We have thus adapted a rapid prototyping method to obtain the saturation magnetic moment of these cells. This method utilizes a cross-correlation algorithm to analyze the cells' motion in a simple fluidic channel to obtain their magnetophoretic velocity, and is effective even when the magnetic moments of cells are small. This rapid characterization is proven useful in optimizing our microfabricated magnetic sifter procedures for magnetic cell capture.

Effect of Magnetic Field Gradient on Effectiveness of the Magnetic Sifter for Cell Purification

In our experiments with NCI-H1650 lung cancer cell lines labeled with magnetic nanoparticles via the Epithelial Cell Adhesion Molecule (EpCAM) antigen, we demonstrate capture efficiencies above 90% even at sample flow rates of 5 ml/h through our microfabricated magnetic sifter. We also improve the elution efficiencies from between 50% and 60% to close to 90% via optimization of the permanent magnet size and position used to magnetize the sifter. We then explain our observations via the use of finite element software for magnetic field and field gradient distributions, and a particle tracing algorithm, illustrating the impact of magnetic field gradients on the performance of the magnetic sifter. The high capture and elution efficiencies observed here is especially significant for magnetic separation of biologically interesting but rare moieties such as cancer stem cells for downstream analysis.

Studies in the use of magnetic microspheres for immunoaffinity extraction of paralytic shellfish poisoning toxins from shellfish

Paralytic shellfish poisoning (PSP) is a potentially fatal human health condition caused by the consumption of shellfish containing high levels of PSP toxins. Toxin extraction from shellfish and from algal cultures for use as standards and analysis by alternative analytical monitoring methods to the mouse bioassay is extensive and laborious. This study investigated whether a selected MAb antibody could be coupled to a novel form of magnetic microsphere (hollow glass magnetic microspheres, brand name Ferrospheres-N) and whether these coated microspheres could be utilized in the extraction of low concentrations of the PSP toxin, STX, from potential extraction buffers and spiked mussel extracts. The feasibility of utilizing a mass of 25 mg of Ferrospheres-N, as a simple extraction procedure for STX from spiked sodium acetate buffer, spiked PBS buffer and spiked mussel extracts was determined. The effects of a range of toxin concentrations (20-300 ng/mL), incubation times and temperature on the capability of the immuno-capture of the STX from the spiked mussel extracts were investigated. Finally, the coated microspheres were tested to determine their efficiency at extracting PSP toxins from naturally contaminated mussel samples. Toxin recovery after each experiment was determined by HPLC analysis. This study on using a highly novel immunoaffinity based extraction procedure, using STX as a model, has indicated that it could be a convenient alternative to conventional extraction procedures used in toxin purification prior to sample analysis.

Amperometric hydrogen peroxide biosensor based on immobilization of hemoglobin on a glassy carbon electrode modified with fe(3)o(4)/chitosan core-shell microspheres

Novel magnetic Fe₃O₄/chitosan (CS) microspheres were prepared using magnetic Fe₃O₄ nanoparticles and the natural macromolecule chitosan. Then, using an easy and effective hemoglobin (Hb) immobilization method, an innovative biosensor with a Fe₃O₄/CS-Hb-Fe₃O₄/CS “sandwich” configuration was constructed. This biosensor had a fast (less than 10 s) response to H₂O₂ and excellent linear relationships were obtained in the concentration range of 5.0 × 10⁻⁵ to 1.8 × 10⁻³ M and 1.8 × 10⁻³ to 6.8 × 10⁻³ M with a detection limit of 4.0 × 10⁻⁶ M (s/n = 3) under the optimum conditions. The apparent Michaelis-Menten constant K_m was 0.29 mM and it showed the excellent biological activity of the fixed Hb. Moreover, the biosensor had long-time stability and good reproducibility. The method was used to determine H₂O₂ concentration in real samples.

Design, fabrication and demonstration of a magnetophoresis chamber with 25 output fractions

Our goal is to develop an instrument for parallel and multiplexed bioassay using magnetic labels. Toward this end we are developing a multi-outlet magnetophoresis instrument incorporating a fluidic flow chamber placed inside a magnetic field gradient. Magnetic microparticles are sorted by their magnetic moment for eventual use as biological labels based on magnetic signature.In this paper we concentrate on developments in our flow chamber fabrication methods that have allowed us to scale the number of sorting channels from 8 to 25. We present data for instrument performance and reproducibility of sorting.