Magnetic immunoassay

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Magnetic immunoassay (MIA) is a type of diagnostic immunoassay using magnetic beads as labels in lieu of conventional enzymes (ELISA), radioisotopes (RIA) or fluorescent moieties (fluorescent immunoassays) [1] to detect a specified analyte. MIA involves the specific binding of an antibody to its antigen, where a magnetic label is conjugated to one element of the pair. The presence of magnetic beads is then detected by a magnetic reader (magnetometer) which measures the magnetic field change induced by the beads. The signal measured by the magnetometer is proportional to the analyte (virus, toxin, bacteria, cardiac marker, etc.) concentration in the initial sample.

Contents

Magnetic labels

Magnetic beads are made of nanometric-sized iron oxide particles encapsulated or glued together with polymers. These magnetic beads range from 35 nm up to 4.5 μm. The component magnetic nanoparticles range from 5 to 50 nm and exhibit a unique quality referred to as superparamagnetism in the presence of an externally applied magnetic field. [2] First discovered by Frenchman Louis Néel, Nobel Physics Prize winner in 1970, this superparamagnetic quality has already been used for medical application in Magnetic Resonance Imaging (MRI) and in biological separations, but not yet for labeling in commercial diagnostic applications. Magnetic labels exhibit several features very well adapted for such applications:[ citation needed ]

Detection

Magnetic Immunoassay (MIA) is able to detect select molecules or pathogens through the use of a magnetically tagged antibody. Functioning in a way similar to that of an ELISA or Western Blot, a two-antibody binding process is used to determine concentrations of analytes. MIA uses antibodies that are coating a magnetic bead. These anti-bodies directly bind to the desired pathogen or molecule and the magnetic signal given off the bound beads is read using a magnetometer. The largest benefit this technology provides for immunostaining is that it can be conducted in a liquid medium, where methods such as ELISA or Western Blotting require a stationary medium for the desired target to bind to before the secondary antibody (such as HRP [Horse Radish Peroxidase]) is able to be applied. Since MIA can be conducted in a liquid medium a more accurate measurement of desired molecules can be performed in the model system. Since no isolation must occur to achieve quantifiable results users can monitor activity within a system. Getting a better idea of the behavior of their target. [ citation needed ]

The manners in which this detection can occur are very numerous. The most basic form of detection is to run a sample through a gravity column that contains a polyethylene matrix with the secondary anti-body. The target compound binds to the antibody contained in the matrix, and any residual substances are washed out using a chosen buffer. The magnetic antibodies are then passed through the same column and after an incubation period, any unbound antibodies are washed out using the same method as before. The reading obtained from the magnetic beads bound to the target which is captured by the antibodies on the membrane is used to quantify the target compound in solution.[ citation needed ]

Also, because it is so similar in methodology to ELISA or Western Blot the experiments for MIA can be adapted to use the same detection if the researcher wants to quantify their data in a similar manner.

Magnetometers

A simple instrument can detect the presence and measure the total magnetic signal of a sample, however, the challenge of developing an effective MIA is to separate naturally occurring magnetic background (noise) from the weak magnetically labeled target (signal). Various approaches and devices have been employed to achieve a meaningful signal-to-noise ratio (SNR) for bio-sensing applications:[ citation needed ]

But improving SNR often requires a complex instrument to provide repeated scanning and extrapolation through data processing, or precise alignment of target and sensor of miniature and matching size. Beyond this requirement, MIA that exploits the non-linear magnetic properties of magnetic labels[ citation needed ] can effectively use the intrinsic ability of a magnetic field to pass through plastic, water, nitrocellulose, and other materials, thus allowing for true volumetric measurements in various immunoassay formats. Unlike conventional methods that measure the susceptibility of superparamagnetic materials, a MIA-based on non-linear magnetization eliminates the impact of linear dia- or paramagnetic materials such as sample matrix, consumable plastics and/or nitrocellulose. Although the intrinsic magnetism of these materials is very weak, with typical susceptibility values of –10−5 (dia) or +10−3 (para), when one is investigating very small quantities of superparamagnetic materials, such as nanograms per test, the background signal generated by ancillary materials cannot be ignored. In MIA based on non-linear magnetic properties of magnetic labels the beads are exposed to an alternating magnetic field at two frequencies, f1 and f2. In the presence of non-linear materials such as superparamagnetic labels, a signal can be recorded at combinatorial frequencies, for example, at f = f1 ± 2×f2. This signal is exactly proportional to the amount of magnetic material inside the reading coil.

This technology makes magnetic immunoassay possible in a variety of formats such as:

It was also described for in vivo applications [4] and for multiparametric testing.

Uses

MIA is a versatile technique that can be used for a wide variety of practices.

Currently it has been used to detect viruses in plants to catch pathogens that would normally devastate crops such as Grapevine fanleaf virus , [5] [ full citation needed ] and Potato virus X . Its adaptations now include portable devices that allow the user to gather sensitive data in the field. [6] [ full citation needed ]

MIA can also be used to monitor therapeutic drugs. A case report of a 53-year-old [7] [ full citation needed ] kidney transplant patient details how the doctors were able to alter the quantities of the therapeutic drug.

Related Research Articles

<span class="mw-page-title-main">Magnetometer</span> Device that measures magnetism

A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, one that measures the direction of an ambient magnetic field, in this case, the Earth's magnetic field. Other magnetometers measure the magnetic dipole moment of a magnetic material such as a ferromagnet, for example by recording the effect of this magnetic dipole on the induced current in a coil.

<span class="mw-page-title-main">ELISA</span> Method to detect an antigen using an antibody and enzyme

The enzyme-linked immunosorbent assay (ELISA) is a commonly used analytical biochemistry assay, first described by Eva Engvall and Peter Perlmann in 1971. The assay is a solid-phase type of enzyme immunoassay (EIA) to detect the presence of a ligand in a liquid sample using antibodies directed against the protein to be measured. ELISA has been used as a diagnostic tool in medicine, plant pathology, and biotechnology, as well as a quality control check in various industries.

A biosensor is an analytical device, used for the detection of a chemical substance, that combines a biological component with a physicochemical detector. The sensitive biological element, e.g. tissue, microorganisms, organelles, cell receptors, enzymes, antibodies, nucleic acids, etc., is a biologically derived material or biomimetic component that interacts with, binds with, or recognizes the analyte under study. The biologically sensitive elements can also be created by biological engineering. The transducer or the detector element, which transforms one signal into another one, works in a physicochemical way: optical, piezoelectric, electrochemical, electrochemiluminescence etc., resulting from the interaction of the analyte with the biological element, to easily measure and quantify. The biosensor reader device connects with the associated electronics or signal processors that are primarily responsible for the display of the results in a user-friendly way. This sometimes accounts for the most expensive part of the sensor device, however it is possible to generate a user friendly display that includes transducer and sensitive element. The readers are usually custom-designed and manufactured to suit the different working principles of biosensors.

<span class="mw-page-title-main">Biochip</span> Substrates performing biochemical reactions

In molecular biology, biochips are engineered substrates that can host large numbers of simultaneous biochemical reactions. One of the goals of biochip technology is to efficiently screen large numbers of biological analytes, with potential applications ranging from disease diagnosis to detection of bioterrorism agents. For example, digital microfluidic biochips are under investigation for applications in biomedical fields. In a digital microfluidic biochip, a group of (adjacent) cells in the microfluidic array can be configured to work as storage, functional operations, as well as for transporting fluid droplets dynamically.

<span class="mw-page-title-main">Radioimmunoassay</span> Immunoassay that uses radiolabeled molecules

A radioimmunoassay (RIA) is an immunoassay that uses radiolabeled molecules in a stepwise formation of immune complexes. A RIA is a very sensitive in vitro assay technique used to measure concentrations of substances, usually measuring antigen concentrations by use of antibodies.

<span class="mw-page-title-main">Immunoassay</span> Biochemical test for a protein or other molecule using an antibody

An immunoassay (IA) is a biochemical test that measures the presence or concentration of a macromolecule or a small molecule in a solution through the use of an antibody (usually) or an antigen (sometimes). The molecule detected by the immunoassay is often referred to as an "analyte" and is in many cases a protein, although it may be other kinds of molecules, of different sizes and types, as long as the proper antibodies that have the required properties for the assay are developed. Analytes in biological liquids such as serum or urine are frequently measured using immunoassays for medical and research purposes.

Immunoprecipitation (IP) is the technique of precipitating a protein antigen out of solution using an antibody that specifically binds to that particular protein. This process can be used to isolate and concentrate a particular protein from a sample containing many thousands of different proteins. Immunoprecipitation requires that the antibody be coupled to a solid substrate at some point in the procedure.

<span class="mw-page-title-main">Surface plasmon resonance</span> Physical phenomenon of electron resonance

Surface plasmon resonance (SPR) is a phenomenon that occurs where electrons in a thin metal sheet become excited by light that is directed to the sheet with a particular angle of incidence, and then travel parallel to the sheet. Assuming a constant light source wavelength and that the metal sheet is thin, the angle of incidence that triggers SPR is related to the refractive index of the material and even a small change in the refractive index will cause SPR to not be observed. This makes SPR a possible technique for detecting particular substances (analytes) and SPR biosensors have been developed to detect various important biomarkers.

Heterophile antibodies are antibodies induced by external antigens.

<span class="mw-page-title-main">Antibody microarray</span>

An antibody microarray is a specific form of protein microarray. In this technology, a collection of captured antibodies are spotted and fixed on a solid surface such as glass, plastic, membrane, or silicon chip, and the interaction between the antibody and its target antigen is detected. Antibody microarrays are often used for detecting protein expression from various biofluids including serum, plasma and cell or tissue lysates. Antibody arrays may be used for both basic research and medical and diagnostic applications.

The planar Hall sensor is a type of magnetic sensor based on the planar Hall effect of ferromagnetic materials. It measures the change in anisotropic magnetoresistance caused by an external magnetic field in the Hall geometry. As opposed to an ordinary Hall sensor, which measures field components perpendicular to the sensor plane, the planar Hall sensor responds to magnetic field components in the sensor plane. Generally speaking, for ferromagnetic materials, the resistance is larger when the current flows along the direction of magnetization than when it flows perpendicular to the magnetization vector. This creates an asymmetric electric field perpendicular to the current, which depends on the magnetization state of the sensor. Exactly controlling the magnetization state is the key to the operation of the planar Hall sensor. From fabrication the magnetization is confined to one certain direction in zero applied field, and the application of a field perpendicular to this direction changes the magnetization state in such a way that the electronic readout is linear with respect to the magnitude of the applied field. This is true for applied fields smaller than a fourth of the intrinsic effective anisotropy field.

<span class="mw-page-title-main">Lateral flow test</span> Immunochromatographic testing devices

A lateral flow test (LFT), is an assay also known as a lateral flow device (LFD), lateral flow immunochromatographic assay, or rapid test. It is a simple device intended to detect the presence of a target substance in a liquid sample without the need for specialized and costly equipment. LFTs are widely used in medical diagnostics in the home, at the point of care, and in the laboratory. For instance, the home pregnancy test is an LFT that detects a specific hormone. These tests are simple and economical and generally show results in around five to thirty minutes. Many lab-based applications increase the sensitivity of simple LFTs by employing additional dedicated equipment. Because the target substance is often a biological antigen, many lateral flow tests are rapid antigen tests.

Magnetic nanoparticles are a class of nanoparticle that can be manipulated using magnetic fields. Such particles commonly consist of two components, a magnetic material, often iron, nickel and cobalt, and a chemical component that has functionality. While nanoparticles are smaller than 1 micrometer in diameter, the larger microbeads are 0.5–500 micrometer in diameter. Magnetic nanoparticle clusters that are composed of a number of individual magnetic nanoparticles are known as magnetic nanobeads with a diameter of 50–200 nanometers. Magnetic nanoparticle clusters are a basis for their further magnetic assembly into magnetic nanochains. The magnetic nanoparticles have been the focus of much research recently because they possess attractive properties which could see potential use in catalysis including nanomaterial-based catalysts, biomedicine and tissue specific targeting, magnetically tunable colloidal photonic crystals, microfluidics, magnetic resonance imaging, magnetic particle imaging, data storage, environmental remediation, nanofluids, optical filters, defect sensor, magnetic cooling and cation sensors.

In the biological sciences, a multiplex assay is a type of immunoassay that uses magnetic beads to simultaneously measure multiple analytes in a single experiment. A multiplex assay is a derivative of an ELISA using beads for binding the capture antibody. Multiplex assays are still more common in research than in clinical settings.

A reverse phase protein lysate microarray (RPMA) is a protein microarray designed as a dot-blot platform that allows measurement of protein expression levels in a large number of biological samples simultaneously in a quantitative manner when high-quality antibodies are available.

<span class="mw-page-title-main">Centrifugal micro-fluidic biochip</span>

The centrifugal micro-fluidic biochip or centrifugal micro-fluidic biodisk is a type of lab-on-a-chip technology, also known as lab-on-a-disc, that can be used to integrate processes such as separating, mixing, reaction and detecting molecules of nano-size in a single piece of platform, including a compact disk or DVD. This type of micro-fluidic biochip is based upon the principle of microfluidics; to take advantage of noninertial pumping for lab-on-a-chip devices using noninertial valves and switches under centrifugal force and Coriolis effect to distribute fluids about the disks in a highly parallel order.

<span class="mw-page-title-main">Surround optical-fiber immunoassay</span>

Surround optical-fiber immunoassay (SOFIA) is an ultrasensitive, in vitro diagnostic platform incorporating a surround optical-fiber assembly that captures fluorescence emissions from an entire sample. The technology's defining characteristics are its extremely high limit of detection, sensitivity, and dynamic range. SOFIA's sensitivity is measured at the attogram level (10−18 g), making it about one billion times more sensitive than conventional diagnostic techniques. Based on its enhanced dynamic range, SOFIA is able to discriminate levels of analyte in a sample over 10 orders of magnitude, facilitating accurate titering.

Flow-through tests or immunoconcentration assays are a type of diagnostic assay that allows users to test for the presence of a biomarker, usually a specific antibody, in a sample such as blood. They are a type of point of care test, a test designed to be used by a healthcare provider at patient contact. Point of care tests often allow for rapid detection of a specific biomarker without specialized lab equipment and training; this aids in diagnosis and allows therapeutic action to be initiated more quickly. Flow-through tests began development in the early 1980s and were the first type of immunostrip to be developed, although lateral flow tests have subsequently become the dominant immunostrip point of care device.

Mass spectrometric immunoassay (MSIA) is a rapid method is used to detect and/ or quantify antigens and or antibody analytes. This method uses an analyte affinity isolation to extract targeted molecules and internal standards from biological fluid in preparation for matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS). This method allows for "top down" and "bottom up" analysis. This sensitive method allows for a new and improved process for detecting multiple antigens and antibodies in a single assay. This assay is also capable of distinguishing mass shifted forms of the same molecule via a panantibody, as well as distinguish point mutations in proteins. Each specific form is detected uniquely based on their characteristic molecular mass. MSIA has dual specificity because of the antibody-antigen reaction coupled with the power of a mass spectrometer.

Stable isotope standards and capture by anti-peptide antibodies (SISCAPA) is a mass spectrometry method for measuring the amount of a protein in a biological sample.

References

  1. ↑ Zanut, A.; Fiorani, A.; Canola, S.; Saito, T.; Ziebart, N.; Rapino, S.; Rebeccani, S.; Barbon, A.; Irie, T.; Josel, H.; Negri, F.; Marcaccio, M.; Windfuhr, M.; Imai, K.; Valenti, G.; Paolucci, F. (2020). "Insights into the mechanism of coreactant electrochemiluminescence facilitating enhanced bioanalytical performance". Nat. Commun. 11 (1): 2668. Bibcode:2020NatCo..11.2668Z. doi:10.1038/s41467-020-16476-2. PMC   7260178 . PMID   32472057.
  2. ↑ Sullivan, Mark V; Stockburn, William J; Hawes, Philippa C; Mercer, Tim; Reddy, Subrayal M (26 February 2021). "Green synthesis as a simple and rapid route to protein modified magnetic nanoparticles for use in the development of a fluorometric molecularly imprinted polymer-based assay for detection of myoglobin". Nanotechnology. 32 (9): 095502. doi: 10.1088/1361-6528/abce2d . PMC   8314874 . PMID   33242844.
  3. ↑ Rife, J.C.; Miller, M.M.; Sheehan, P.E.; Tamanaha, C.R.; Tondra, M.; Whitman, L.J. (2003). "Design and performance of GMR sensors for the detection of magnetic microbeads in biosensors". Sensors and Actuators A: Physical. Elsevier BV. 107 (3): 209–218. doi:10.1016/s0924-4247(03)00380-7. ISSN   0924-4247.[ verification needed ]
  4. ↑ Nikitin, M. P.; Torno, M.; Chen, H.; Rosengart, A.; Nikitin, P. I. (2008). "Quantitative real-time in vivo detection of magnetic nanoparticles by their nonlinear magnetization". Journal of Applied Physics. AIP Publishing. 103 (7): 07A304. Bibcode:2008JAP...103gA304N. doi:10.1063/1.2830947. ISSN   0021-8979.[ verification needed ]
  5. ↑ "Yang et al". 2008.{{cite journal}}: Cite journal requires |journal= (help)
  6. ↑ "Rettcher et al". 2015.{{cite journal}}: Cite journal requires |journal= (help)
  7. ↑ "McMilin et al". 2013.{{cite journal}}: Cite journal requires |journal= (help)
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