Ultrasensitive Magnetic Particle-Based Immunosupported Liquid Membrane Assay

Extraction, Enrichment, and in situ Electrochemical Detection on Lab-on-a-Disc: Monitoring the Production of a Bacterial Secondary Metabolite

Development of microsystems, which enable "sample-to-answer" detection from real samples, is often challenging. We present the first integration of supported liquid membrane extraction combined with electrochemical detection on a centrifugal fluidic platform. The developed lab-on-a-disc (LoD) system enabled the separation, enrichment, and subsequent electrochemical detection of the target analyte from a complex sample mixture. As a case study, we quantified the amount of a dietary supplement and pharmaceutical precursor, p-coumaric acid, from bacterial growth media at different time points during production. The assay, extraction, and detection, performed on the LoD device, proved to be a low cost and environmentally friendly approach, requiring only a few tens of microliters of organic solvent and enabled detection in a 3 μL volume. In addition, the data obtained from the centrifugal platform showed a good correlation with data obtained from the high performance liquid chromatography analysis.

Affinity enrichment for mass spectrometry: improving the yield of low abundance biomarkers

INTRODUCTION

Mass spectrometry (MS) is the premier tool for discovering novel disease-associated protein biomarkers. Unfortunately, when applied to complex body fluid samples, MS has poor sensitivity for the detection of low abundance biomarkers (≪10 ng/mL), derived directly from the diseased tissue cells or pathogens. Areas covered: Herein we discuss the strengths and drawbacks of technologies used to concentrate low abundance analytes in body fluids, with the aim to improve the effective sensitivity for MS discovery. Solvent removal by dry-down or dialysis, and immune-depletion of high abundance serum or plasma proteins, is shown to have disadvantages compared to positive selection of the candidate biomarkers by affinity enrichment. A theoretical analysis of affinity enrichment reveals that the yield for low abundance biomarkers is a direct function of the binding affinity (Association/Dissociation rates) used for biomarker capture. In addition, a high affinity capture pre processing step can effectively dissociate the candidate biomarker from partitioning with high abundance proteins such as albumin. Expert commentary: Properly designed high affinity capture materials can enrich the yield of low abundance (0.1-10 picograms/mL) candidate biomarkers for MS detection. Affinity capture and concentration, as an upfront step in sample preparation for MS, combined with MS advances in software and hardware that improve the resolution of the chromatographic separation can yield a transformative new class of low abundance biomarkers predicting disease risk or disease latency.

Synthesis of magnetic Fe3O4/polyamine hybrid microsphere using O/W/O Pickering emulsion droplet as the polymerization micro-reactor

An O/W/O emulsion containing Fe₃O₄NPs and PEI was obtained using SM-CaCO₃NPs as the stabilizer. In a droplet-to-droplet reaction mode, a magnetic polyamine microsphere was achieved by crosslinking PEI in the emulsion droplet with glutaraldehyde.

Surface plasmon resonance sensor based on magnetic molecularly imprinted polymers amplification for pesticide recognition

We reported here a method to enhance detection sensitivity in surface plasmon resonance (SPR) spectroscopy integrated with a surface molecular imprinting recognition system and employing magnetic molecular imprinting polymer nanoparticles for amplifying SPR response. The proposed magnetic molecular imprinting polymer was designed by self-polymerization of dopamine on the Fe3O4 NPs surface in weak base aqueous solution in the presence of template chlorpyrifos (CPF). The imprinted Fe3O4@polydopamine nanoparticles (Fe3O4@PDA NPs) were characterized by Fourier transform infrared spectroscopy, UV-vis absorption spectroscopy, and transmission electron microscopy. The biosensor showed a good linear relationship between the SPR angle shift and the chlorpyrifos concentration over a range from 0.001 to 10 μM with a detection limit of 0.76 nM. A significant increase in sensitivity was therefore afforded through the use of imprinted Fe3O4@PDA NPs as an amplifier, and meanwhile, the imprinted Fe3O4@PDA NPs had an excellent recognition capacity to chlorpyrifos over other pesticides. The excellent sensitivity and selectivity and high stability of the designed biosensor make this magnetic imprinted Fe3O4@PDA NP an attractive recognition element for various SPR sensors for detecting pesticide residuals and other environmentally deleterious chemicals.

Modeling of mass transfer limitation in biomolecular assays

Many biomolecular assays involve the capture of an analyte by ligands that are attached or immobilized upon a solid surface. Often the binding kinetics of the ligand and analyte are fast enough that the capture step is limited by diffusion or mass transfer of the analyte from the bulk fluid phase onto the surface. In this contribution, after a brief survey of various mathematical models for mass transfer-limited analyte capture, we analyze one model problem. The model involves the capture of analytes by suspended solid spherical beads on whose surface many ligands are attached. The rate of association of the ligand and analyte molecules is taken to be high enough that the overall rate of the capture process is limited by diffusion. Two distinct limits are examined analytically. In early times, when the analytes near a bead are being captured and the depletion layers in the neighborhood of the individual beads are nonoverlapping, the problem is modeled as a diffusion/surface reaction problem about a single bead, and analytical results are obtained that describe the amount of analyte captured as a function of time. At later times, when the depletion layers from neighboring beads begin to overlap, the problem is modeled by means of generalized Taylor dispersion or macrotransport theory. In each case, scaling laws are derived that characterize the capture efficiency as a function of number density, volume fraction, and radius of beads.

Sensitive Aflatoxin B1 Determination Using a Magnetic Particles-Based Enzyme-Linked Immunosorbent Assay

A magnetic particle-based enzyme-liked immunosorbent assay (mp-ELISA) has been developed as new an alternative immunoassay for Aflatoxin B1 determination. The method is based on conventional competitive ELISA whereby the anti-Aflatoxin B1 antibody is immobilized on the magnetic particles' surface. The influence of the antibody type as well as antibody immobilization on the magnetic beads surface was investigated in detail. Also, optimum values for the general parameters of the method (e.g. tracer concentration, type of antibody, and incubation time) were established. Finally, a sensitive immunoassay method (mp-ELISA) was performed for Aflatoxin B1 determination at ppt level (LOD = 1 ppt Aflatoxin B1).

Magnetic Control of an Electrochemical Microfluidic Device with an Arrayed Immunosensor for Simultaneous Multiple Immunoassays

Background: Methods based on magnetic bead probes have been developed for immunoassay, but most involve complicated labeling or stripping procedures and are unsuitable for routine use.

Methods: We synthesized magnet core/shell NiFe2O4/SiO2 nanoparticles and fabricated an electrochemical magnetic controlled microfluidic device for the detection of 4 tumor markers. The immunoassay system consisted of 5 working electrodes and an Ag/AgCl reference electrode integrated on a glass substrate. Each working electrode contained a different antibody immobilized on the NiFe2O4/SiO2 nanoparticle surface and was capable of measuring a specific tumor marker using noncompetitive electrochemical immunoassay.

Results: Under optimal conditions, the multiplex immunoassay enabled the simultaneous detection of 4 tumor markers. The sensor detection limit was <0.5 μg/L (or <0.5 kunits/L) for most analytes. Intra- and interassay imprecisions (CVs) were <4.5% and 8.7% for analyte concentrations >5 μg/L (or >5 kunits/L), respectively. No nonspecific adsorption was observed during a series of procedures to detect target proteins, and electrochemical cross-talk (CV) between neighboring sites was <10%.

Conclusion: This immunoassay system offers promise for label-free, rapid, simple, cost-effective analysis of biological samples. Importantly, the chip-based immunosensor could be suitable for use in the mass production of miniaturized lab-on-a-chip devices and open new opportunities for protein diagnostics and biosecurity.

Quantification of oligonucleotide modifications of small unilamellar lipid vesicles

We present a new method for quantification of the coupling efficiency between amphiphilic oligonucleotides and suspended small unilamellar lipid vesicles (SUVs). The method employs a supported (phospho)lipid bilayer (SLB)-modified sensor template, which upon exposure to a mixture of SUVs and amphiphilic DNA reacts neither with free SUVs nor with DNA-modified SUVs, but with free DNA only. Using calibration curves obtained by recording the concentration dependence of the initial binding rate of free amphiphilic DNA (in the absence of SUVs), it is demonstrated how concentration determinations of both free and bound DNA in the two-component mixture (amphiphilic DNA and lipid vesicles) can be obtained. The calibration curves and the binding analysis were obtained using a quartz crystal microbalance with dissipation (QCM-D) monitoring. The binding efficiency of DNA coupled to SUVs (Ø approximately 50 nm) with two cholesterol moieties revealed that the bivalent coupling is essentially 100% in the range of approximately 1 to approximately 35 oligonucleotides per vesicle, whereas reversible coupling was confirmed in the case of monovalent coupling. Coupling of DNA via two cholesterol moieties was obtained by prehybridization of two single-stranded DNA strands modified with single cholesterol moieties in their 3' and 5' ends, respectively, and the monovalent coupling was obtained using single-stranded DNA. In the latter case, the analysis of the amount of free DNA at different DNA-SUV ratios also allowed for a determination of the maximum number of available binding sites on the SUVs, shown to be in good agreement with data obtained for DNA coupling on planar surfaces. With the only requirement that the SLB-modified sensor template react with one of the components in the two-component mixture only, as verified through fingerprint analysis of frequency, f, and energy dissipation, D, QCM-D measurements, it is emphasized that the method is generic and offers a fast and reliable method for evaluations of biomolecular modifications of any type of colloidal nanoparticles.

Evaluation of progesterone content in saliva using magnetic particle-based immuno supported liquid membrane assay (m-ISLMA)

Progesterone in saliva was monitored using a new method called magnetic particle-based immuno supported liquid membrane assay (m-ISLMA) in a sequential injection (SI) setup, allowing automatic sample cleanup, analyte enrichment, and detection in a single analysis unit. Progesterone (Ag) diffuses from a continuous flowing sample - the donor - into a supported organic liquid membrane (SLM), based on analyte partitioning (solubility) between the aqueous donor and the organic phase. The Ag is re-extracted from the SLM into a second stagnant aqueous acceptor, containing antibodies (Ab) immobilized on magnetic beads, held at the bottom of the acceptor by a magnet. Due to the formation of strong Ag-Ab-bead complexes and a large excess of Ab-beads, the Ag is accumulated and selectively enriched in the acceptor. The extracted progesterone was quantified by injecting into the acceptor a horseradish peroxidase (HRP) labeled analyte tracer, the substrate (luminol, H(2)O(2), and p-iodophenol), and finally detection of the generated chemiluminescence by a photomultiplier tube. After optimization of experimental parameters (e.g., sample flow rate, extraction time, type of organic solvent and antibody-bead concentration in the acceptor), a detection limit of 8.50+/-0.17 fgL(-1) and a dynamic range between 35 fgL(-1) and 10 pgL(-1) was reached. The progesterone level of saliva for three subjects (women in different period of ovarian cycle) was investigated, and the corresponding progesterone concentrations detected with m-ISLMA coincided well with the expected values.