Ultrasensitive detection enabled by nonlinear magnetization of nanomagnetic labels

New technologies and reagents in lateral flow assay (LFA) designs for enhancing accuracy and sensitivity

Lateral flow assays (LFAs) are a popular method for quick and affordable diagnostic testing because they are easy to use, portable, and user-friendly. However, LFA design has always faced challenges regarding sensitivity, accuracy, and complexity of the operation. By integrating new technologies and reagents, the sensitivity and accuracy of LFAs can be improved while minimizing the complexity and potential for false positives. Surface enhanced Raman spectroscopy (SERS), photoacoustic techniques, fluorescence resonance energy transfer (FRET), and the integration of smartphones and thermal readers can improve LFA accuracy and sensitivity. To ensure reliable and accurate results, careful assay design and validation, appropriate controls, and optimization of assay conditions are necessary. Continued innovation in LFA technology is crucial to improving the reliability and accuracy of rapid diagnostic testing and expanding its applications to various areas, such as food testing, water quality monitoring, and environmental testing.

Fluorescent Magnetic Nanoparticles for Bioimaging through Biomimetic Surface Modification

Nanostructured materials and systems find various applications in biomedical fields. Hybrid organo-inorganic nanomaterials are intensively studied in a wide range of areas, from visualization to drug delivery or tissue engineering. One of the recent trends in material science is biomimetic approaches toward the synthesis or modification of functional nanosystems. Here, we describe an approach toward multifunctional nanomaterials through the biomimetic polymerization of dopamine derivatives. Magnetite nanoparticles were modified with a combination of dopamine conjugates to give multifunctional magneto-fluorescent nanocomposites in one synthetic step. The obtained material showed excellent biocompatibility at concentrations up to 200 μg/mL and an in vivo biodistribution profile typical for nanosized formulations. The synthesized systems were conjugated with antibodies against HER2 to improve their selectivity toward HER2-positive cancer cells. The produced material can be used for dual magneto-optical in vivo studies or targeted drug delivery. The applied synthetic strategy can be used for the creation of various multifunctional hybrid nanomaterials in mild conditions.

Express high-sensitive detection of ochratoxin A in food by a lateral flow immunoassay based on magnetic biolabels

We present an easy-to-use lateral flow immunoassay for rapid, precise and sensitive quantification of one of the most hazardous mycotoxins - ochratoxin A (OTA), which is widely present in food and agricultural commodities. The achieved limit of detection during the 20-min OTA registration is 11 pg/mL. The assay provides accurate results in both low- and high-concentration ranges. That is due to the extraordinary steepness of the linear calibration plot: 5-order dynamic range of concentrations causes almost a 1000-fold change in the signal obtained by electronic detection of magnetic biolabels using their non-linear magnetization. High specificity, repeatability, and reproducibility of the assay have been verified, including measuring OTA in real samples of contaminated corn flour. The developed assay is a promising analytical tool for food and feed safety control; it may become an express, convenient and high-precision alternative to the traditional sophisticated laboratory techniques based on liquid chromatography.

Pharmacokinetics of magnetic iron oxide nanoparticles for medical applications

Magnetic iron oxide nanoparticles (MNPs) have been under intense investigation for at least the last five decades as they show enormous potential for many biomedical applications, such as biomolecule separation, MRI imaging and hyperthermia. Moreover, a large area of research on these nanostructures is concerned with their use as carriers of drugs, nucleic acids, peptides and other biologically active compounds, often leading to the development of targeted therapies. The uniqueness of MNPs is due to their nanometric size and unique magnetic properties. In addition, iron ions, which, along with oxygen, are a part of the MNPs, belong to the trace elements in the body. Therefore, after digesting MNPs in lysosomes, iron ions are incorporated into the natural circulation of this element in the body, which reduces the risk of excessive storage of nanoparticles. Still, one of the key issues for the therapeutic applications of magnetic nanoparticles is their pharmacokinetics which is reflected in the circulation time of MNPs in the bloodstream. These characteristics depend on many factors, such as the size and charge of MNPs, the nature of the polymers and any molecules attached to their surface, and other. Since the pharmacokinetics depends on the resultant of the physicochemical properties of nanoparticles, research should be carried out individually for all the nanostructures designed. Almost every year there are new reports on the results of studies on the pharmacokinetics of specific magnetic nanoparticles, thus it is very important to follow the achievements on this matter. This paper reviews the latest findings in this field. The mechanism of action of the mononuclear phagocytic system and the half-lives of a wide range of nanostructures are presented. Moreover, factors affecting clearance such as hydrodynamic and core size, core morphology and coatings molecules, surface charge and technical aspects have been described.

Magnetic nanoparticles and magnetic particle spectroscopy-based bioassays: a 15 year recap

Magnetic nanoparticles (MNPs) have unique physical and chemical properties, such as high surface area to volume ratio and size-related magnetism, which are completely different from their bulk materials. Benefiting from the facile synthesis and chemical modification strategies, MNPs have been widely studied for applications in nanomedicine. Herein, we firstly summarized the designs of MNPs from the perspectives of materials and physicochemical properties tailored for biomedical applications. Magnetic particle spectroscopy (MPS), first reported in 2006, has flourished as an independent platform for many biological and biomedical applications. It has been extensively reported as a versatile platform for a variety of bioassays along with the artificially designed MNPs, where the MNPs serve as magnetic nanoprobes to specifically probe target analytes from fluid samples. In this review, the mechanisms and theories of different MPS platforms realizing volumetric- and surface-based bioassays are discussed. Some representative works of MPS platforms for applications such as disease diagnosis, food safety and plant pathology monitoring, drug screening, thrombus maturity assessments are reviewed. At the end of this review, we commented on the rapid growth and booming of MPS-based bioassays in its first 15 years. We also prospected opportunities and challenges that portable MPS devices face in the rapidly growing demand for fast, inexpensive, and easy-to-use biometric techniques.

Ferrofluids and bio-ferrofluids: looking back and stepping forward

Ferrofluids investigated along for about five decades are ultrastable colloidal suspensions of magnetic nanoparticles, which manifest simultaneously fluid and magnetic properties. Their magnetically controllable and tunable feature proved to be from the beginning an extremely fertile ground for a wide range of engineering applications. More recently, biocompatible ferrofluids attracted huge interest and produced a considerable increase of the applicative potential in nanomedicine, biotechnology and environmental protection. This paper offers a brief overview of the most relevant early results and a comprehensive description of recent achievements in ferrofluid synthesis, advanced characterization, as well as the governing equations of ferrohydrodynamics, the most important interfacial phenomena and the flow properties. Finally, it provides an overview of recent advances in tunable and adaptive multifunctional materials derived from ferrofluids and a detailed presentation of the recent progress of applications in the field of sensors and actuators, ferrofluid-driven assembly and manipulation, droplet technology, including droplet generation and control, mechanical actuation, liquid computing and robotics.

An Overview for the Nanoparticles-Based Quantitative Lateral Flow Assay

The development of the lateral flow assay (LFA) has received much attention in both academia and industry because of their broad applications to food safety, environmental monitoring, clinical diagnosis, and so forth. The user friendliness, low cost, and easy operation are the most attractive advantages of the LFA. In recent years, quantitative detection has become another focus of LFA development. Here, the most recent studies of quantitative LFAs are reviewed. First, the principles and corresponding formats of quantitative LFAs are introduced. In the biomaterial and nanomaterial sections, the detection, capture, and signal amplification biomolecules and the optical, fluorescent, luminescent, and magnetic labels used in LFAs are described. The invention of dedicated strip readers has drawn further interest in exploiting the better performance of LFAs. Therefore, next, the development of dedicated reader devices is described and the usefulness and specifications of these devices for LFAs are discussed. Finally, the applications of LFAs in the detection of metal ions, biotoxins, pathogenic microorganisms, veterinary drugs, and pesticides in the fields of food safety and environmental health and the detection of nucleic acids, biomarkers, and viruses in clinical analyses are summarized.

Magnetic Nanoparticles in Medicine: Progress, Problems, and Advances

The review presents an analysis of the current state of research related to the design, development, and practical application of methods for biomedical radioelectronics and nanomedicine, including the use of magnetic nanoparticles. The important role of rational scientific physical approaches and experimental methods in the design of efficient and safe magnetic nanoparticle-based agents for therapy, controlled targeted drug delivery, and diagnostics, including spatial imaging, is emphasized. Examples of successful practical application of magnetic nanoparticles in medicine based on these methods are given, and an analysis of the main problems and prospects of this area of science is conducted.

Magnetofection In Vivo by Nanomagnetic Carriers Systemically Administered into the Bloodstream

Nanoparticle-based technologies are rapidly expanding into many areas of biomedicine and molecular science. The unique ability of magnetic nanoparticles to respond to the magnetic field makes them especially attractive for a number of in vivo applications including magnetofection. The magnetofection principle consists of the accumulation and retention of magnetic nanoparticles carrying nucleic acids in the area of magnetic field application. The method is highly promising as a clinically efficient tool for gene delivery in vivo. However, the data on in vivo magnetofection are often only descriptive or poorly studied, insufficiently systematized, and sometimes even contradictory. Therefore, the aim of the review was to systematize and analyze the data that influence the in vivo magnetofection processes after the systemic injection of magnetic nanostructures. The main emphasis is placed on the structure and coating of the nanomagnetic vectors. The present problems and future trends of the method development are also considered.

Development of an in-line magnetometer for flow chemistry and its demonstration for magnetic nanoparticle synthesis

Despite the wide usage of magnetic nanoparticles, it remains challenging to synthesise particles with properties that exploit each application's full potential. Time consuming experimental procedures and particle analysis hinder process development, which is commonly constrained to a handful of experiments without considering particle formation kinetics, reproducibility and scalability. Flow reactors are known for their potential of large-scale production and high-throughput screening of process parameters. These advantages, however, have not been utilised for magnetic nanoparticle synthesis where particle characterisation is performed, with a few exceptions, post-synthesis. To overcome this bottleneck, we developed a highly sensitive magnetometer for flow reactors to characterise magnetic nanoparticles in solution in-line and in real-time using alternating current susceptometry. This flow magnetometer enriches the flow-chemistry toolbox by facilitating continuous quality control and high-throughput screening of magnetic nanoparticle syntheses. The sensitivity required to monitor magnetic nanoparticle syntheses at the typically low concentrations (<100 mM of Fe) was achieved by comparing the signals induced in the sample and reference cell, each of which contained near-identical pairs of induction and pick-up coils. The reference cell was filled only with air, whereas the sample cell was a flow cell allowing sample solution to pass through. Balancing the flow and reference cell impedance with a newly developed electronic circuit was pivotal for the magnetometer's sensitivity. To showcase its potential, the flow magnetometer was used to monitor two iron oxide nanoparticle syntheses with well-known particle formation kinetics, i.e., co-precipitation syntheses with sodium carbonate and sodium hydroxide as base, which have been previously studied via synchrotron X-ray diffraction. The flow magnetometer facilitated batch (on-line) and flow (in-line) synthesis monitoring, providing new insights into the particle formation kinetics as well as, effect of temperature and pH. The compact lab-scale flow device presented here, opens up new possibilities for magnetic nanoparticle synthesis and manufacturing, including 1) early stage reaction characterisation 2) process monitoring and control and 3) high-throughput screening in combination with flow reactors.

Magnetic Particle Spectroscopy with One-Stage Lock-In Implementation for Magnetic Bioassays with Improved Sensitivities

In recent years, magnetic particle spectroscopy (MPS) has become a highly sensitive and versatile sensing technique for quantitative bioassays. It relies on the dynamic magnetic responses of magnetic nanoparticles (MNPs) for the detection of target analytes in the liquid phase. There are many research studies reporting the application of MPS for detecting a variety of analytes including viruses, toxins, nucleic acids, and so forth. Herein, we report a modified version of the MPS platform with the addition of a one-stage lock-in design to remove the feedthrough signals induced by external driving magnetic fields, thus capturing only MNP responses for improved system sensitivity. This one-stage lock-in MPS system is able to detect as low as 781 ng multi-core Nanomag50 iron oxide MNPs (micromod Partikeltechnologie GmbH) and 78 ng single-core SHB30 iron oxide MNPs (Ocean NanoTech). We first demonstrated the performance of this MPS system for bioassay-related applications. Using the SARS-CoV-2 spike protein as a model, we have achieved a detection limit of 125 nM (equal to 5 pmole) for detecting spike protein molecules in the liquid phase. In addition, using a streptavidin-biotin binding system as a proof-of-concept, we show that these single-core SHB30 MNPs can be used for Brownian relaxation-based bioassays while the multi-core Nanomag50 cannot be used. The effects of MNP amount on the concentration-dependent response profiles for detecting streptavidin were also investigated. Results show that by using a lower concentration/ amount of MNPs, concentration-response curves shift to a lower concentration/amount of target analytes. This lower concentration-response indicates the possibility of improved bioassay sensitivities by using lower amounts of MNPs.

Long-Term Fate of Magnetic Particles in Mice: A Comprehensive Study

Safe application of nanoparticles in medicine requires full understanding of their pharmacokinetics including catabolism in the organism. However, information about nanoparticle degradation is still scanty due to difficulty of long-term measurements by invasive techniques. Here, we describe a magnetic spectral approach for in vivo monitoring of magnetic particle (MP) degradation. The method noninvasiveness has allowed performing of a broad comprehensive study of the 1-year fate of 17 types of iron oxide particles. We show a long-lasting influence of five parameters on the MP degradation half-life: dose, hydrodynamic size, ζ-potential, surface coating, and internal architecture. We observed a slowdown in MP biotransformation with an increase of the injected dose and faster degradation of the particles of a small hydrodynamic size. A comparison of six types of 100 nm particles coated by different hydrophilic polymer shells has shown that the slowest (t_1/2 = 38 ± 6 days) and the fastest (t_1/2 = 15 ± 4 days) degradations were achieved with a polyethylene glycol and polyglucuronic acid coatings, respectively. The most significant influence on the MP degradation was due to the internal architecture of the particles as the coverage of magnetic cores with a solid 39 nm polystyrene layer slowed down the half-life of the core-shell MPs from 48 days to more than 1 year. The revealed deeper insights into the particle degradation in vivo may facilitate rational design of nano- and microparticles with predictable long-term fate in vivo.

Nanobiosensing based on optically selected antibodies and superparamagnetic labels for rapid and highly sensitive quantification of polyvalent hepatitis B surface antigen

Hepatitis B surface antigen (HBsAg) is the most clinically relevant serological marker of hepatitis B virus (HBV) infection. Its detection in blood is extremely important for identification of asymptomatic individuals or chronic HBV carriers, screening blood donors, and early seroconversion. Rapid point-of-care HBsAg tests are predominantly qualitative, and their analytical sensitivity does not meet the requirements of regulatory agencies. We present a highly sensitive lateral flow assay based on superparamagnetic nanoparticles for rapid quantification (within 30 min) of polyvalent HBsAg in serum. The demonstrated limit of detection (LOD) of 80 pg mL^-1 in human serum is better than both the FDA recommendations for HBsAg assays (which is 0.5 ng mL^-1) and the sensitivity of traditional laboratory-based methods such as enzyme linked immunosorbent assays. Along with the attractive LOD at lower concentrations and the wide linear dynamic range of more than 2.5 orders, the assay features rapidity, user-friendliness, on-site operation and effective performance in the complex biological medium. These are due to the combination of the immunochromatographic approach with a highly sensitive electronic registration of superparamagnetic nanolabels over the entire volume of a 3D test structure by their non-linear magnetization and selection of optimal antibodies by original optical label-free methods. The developed cost-efficient bioanalytical technology can be used in many socially important fields such as out-of-lab screening and diagnosis of HBV infection at a point-of-demand, especially in hard-to-reach or sparsely populated areas, as well as highly endemic regions.

The Potential Application of Magnetic Nanoparticles for Liver Fibrosis Theranostics

Liver fibrosis is a major cause of morbidity and mortality worldwide due to chronic liver damage and leading to cirrhosis, liver cancer, and liver failure. To date, there is no effective and specific therapy for patients with hepatic fibrosis. As a result of their various advantages such as biocompatibility, imaging contrast ability, improved tissue penetration, and superparamagnetic properties, magnetic nanoparticles have a great potential for diagnosis and therapy in various liver diseases including fibrosis. In this review, we focus on the molecular mechanisms and important factors for hepatic fibrosis and on potential magnetic nanoparticles-based therapeutics. New strategies for the diagnosis of liver fibrosis are also discussed, with a summary of the challenges and perspectives in the translational application of magnetic nanoparticles from bench to bedside.

Nonviral Locally Injected Magnetic Vectors for In Vivo Gene Delivery: A Review of Studies on Magnetofection

Magnetic nanoparticles have been widely used in nanobiomedicine for diagnostics and the treatment of diseases, and as carriers for various drugs. The unique magnetic properties of "magnetic" drugs allow their delivery in a targeted tumor or tissue upon application of a magnetic field. The approach of combining magnetic drug targeting and gene delivery is called magnetofection, and it is very promising. This method is simple and efficient for the delivery of genetic material to cells using magnetic nanoparticles controlled by an external magnetic field. However, magnetofection in vivo has been studied insufficiently both for local and systemic routes of magnetic vector injection, and the relevant data available in the literature are often merely descriptive and contradictory. In this review, we collected and systematized the data on the efficiency of the local injections of magnetic nanoparticles that carry genetic information upon application of external magnetic fields. We also investigated the efficiency of magnetofection in vivo, depending on the structure and coverage of magnetic vectors. The perspectives of the development of the method were also considered.

Rapid and Easy-to-Use Method for Accurate Characterization of Target Binding and Kinetics of Magnetic Particle Bioconjugates for Biosensing

The ever-increasing use of magnetic particle bioconjugates (MPB) in biosensors calls for methods of comprehensive characterization of their interaction with targets. Label-free optical sensors commonly used for studying inter-molecular interactions have limited potential for MPB because of their large size and multi-component non-transparent structure. We present an easy-to-use method that requires only three 20-min express measurements to determine the key parameters for selection of optimal MPB for a biosensor: kinetic and equilibrium characteristics, and a fraction of biomolecules on the MPB surface that are capable of active targeting. The method also provides a prognostic dependence of MPB targeting efficiency upon interaction duration and sample volume. These features are possible due to joining a magnetic lateral flow assay, a highly sensitive sensor for MPB detection by the magnetic particle quantification technique, and a novel mathematical model that explicitly describes the MPB-target interactions and does not comprise parameters to be fitted additionally. The method was demonstrated by experiments on MPB targeting of cardiac troponin I and staphylococcal enterotoxin B. The validation by an independent label-free technique of spectral-correlation interferometry showed good correlation between the results obtained by both methods. The presented method can be applied to other targets for faster development and selection of MPB for affinity sensors, analytical technologies, and realization of novel concepts of MPB-based biosensing in vivo.

Fast processes of nanoparticle blood clearance: Comprehensive study

Blood circulation is the key parameter that determines the in vivo efficiency of nanoagents. Despite clinical success of the stealth liposomal agents with their inert and shielded surfaces, a great number of non-stealth nanomaterials is being developed due to their potential of enhanced functionality. By harnessing surface phenomena, such agents can offer advanced control over drug release through intricately designed nanopores, catalysis-propelled motion, computer-like analysis of several disease markers for precise target identification, etc. However, investigation of pharmacokinetic behavior of these agents becomes a great challenge due to ultra-short circulation (usually around several minutes) and impossibility to use the invasive blood-sampling techniques. Accordingly, the data on circulation of such agents has been scarce and irregular. Here, we demonstrate high-throughput capabilities of the developed magnetic particle quantification technique for nanoparticle circulation measurements and present a comprehensive investigation of factors that affect blood circulation of the non-stealth nanoparticles. Namely, we studied the following 9 factors: particle size, zeta-potential, coating, injection dose, repetitive administration, induction of anesthesia, mice strain, absence/presence of tumors, tumor size. Our fundamental findings demonstrate potential ways to extend the half-life of the agents in blood thereby giving them a better chance of achieving their goal in the organism. The study will be valuable for design of the next generation nanomaterials with advanced biomedical functionality.

Enhancement of the blood-circulation time and performance of nanomedicines via the forced clearance of erythrocytes

The rapid elimination of nanoparticles from the bloodstream by the mononuclear phagocyte system limits the activity of many nanoparticle formulations. Here, we show that inducing a slight and transient depletion of erythrocytes in mice (~5% decrease in haematocrit) by administrating a low dose (1.25 mg kg^-1) of allogeneic anti-erythrocyte antibodies increases the circulation half-life of a range of short-circulating and long-circulating nanoparticle formulations by up to 32-fold. Treatment of the animals with anti-erythrocyte antibodies significantly improved the targeting of CD4⁺ cells in vivo with fluorescent anti-CD4-antibody-conjugated nanoparticles, the magnetically guided delivery of ferrofluid nanoparticles to subcutaneous tumour allografts and xenografts, and the treatment of subcutaneous tumour allografts with magnetically guided liposomes loaded with doxorubicin and magnetite or with clinically approved 'stealthy' doxorubicin liposomes. The transient and partial blocking of the mononuclear phagocyte system may enhance the performance of a wide variety of nanoparticle drugs.

Upscale Design, Process Development, and Economic Analysis of Industrial Plants for Nanomagnetic Particle Production for Environmental and Biomedical Use

Very few economical and process engineering studies have been made concerning the scale-up and implementation of nanomagnetic particle manufacturing into a full-scale plant, and determination of its viability. In this work we describe such a study for two types of industrial plants, one for manufacturing magnetic particles for applications in the environmental area, and the other for manufacturing nanomagnetic particles for applications in the biotechnology area; the two different applications are compared. The following methodology was followed: establish the manufacturing process for each application; determine the market demand of the product (magnetic nanoparticles) for both applications; determine the production capacity of each plant; engineer all the manufacturing process, determining all the process units and performing all the mass and energy balances for both plants; scale-up the main equipment; and determine the global economic impact and profitability. At the end both plants are found to be technologically and economically viable, the characteristics of the final products being, however, quite different, as well as the process engineering, economic analysis, and scale-up.

Hematite Nanoparticles from Unexpected Reaction of Ferrihydrite with Concentrated Acids for Biomedical Applications

The development of synthetic ways to fabricate nanosized materials with a well-defined shape, narrow-sized distribution, and high stability is of great importance to a rapidly developing area of nanotechnology. Here, we report an unusual reaction between amorphous two-line ferrihydrite and concentrated sulfuric or other mineral and organic acids. Instead of the expected dissolution, we observed the formation of new narrow-distributed brick-red nanoparticles (NPs) of hematite. Different acids produce similar nanoparticles according to scanning (SEM) and transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), infrared spectroscopy (FTIR), and energy-dispersive X-ray spectroscopy (EDX). The reaction demonstrates new possibilities for the synthesis of acid-resistant iron oxide nanoparticles and shows a novel pathway for the reaction of iron hydroxide with concentrated acids. The biomedical potential of the fabricated nanoparticles is demonstrated by the functionalization of the particles with polymers, fluorescent labels, and antibodies. Three different applications are demonstrated: i) specific targeting of the red blood cells, e.g., for red blood cell (RBC)-hitchhiking; ii) cancer cell targeting in vitro; iii) infrared ex vivo bioimaging. This novel synthesis route may be useful for the development of iron oxide materials for such specificity-demanding applications such as nanosensors, imaging, and therapy.

Nanomagnetic lateral flow assay for high-precision quantification of diagnostically relevant concentrations of serum TSH

Thyroid stimulating hormone (TSH) is the first-line marker for initial evaluation of the thyroid gland function. We present a lateral flow immunoassay based on superparamagnetic nanolabels for rapid (<25 min) quantitative determination of TSH at a point of care. The demonstrated limit of detection (LOD) of 0.017 μIU/mL in human serum is on the level of third-generation TSH laboratory tests. The wide linear dynamic range of more than 3 orders covers the whole range of clinically relevant TSH concentrations for confident quantitative diagnostics of the gland function from hyper- to hypothyroidism, and different states in-between. The attractive values of LOD and linear dynamic range are due to counting of the superparamagnetic nanolabels over the whole reaction volume by their non-linear magnetization at two frequencies of an alternating magnetic field and detecting the response at combinatorial frequencies. The developed cost-efficient and user-friendly immunoassay can be used for express in vitro diagnostics and long-term quantitative monitoring of thyroid dysfunctions, especially in distant regions, developing countries, and sparsely populated areas.

Magnetic Particle Spectroscopy for Detection of Influenza A Virus Subtype H1N1

Magnetic nanoparticles (MNPs) with proper surface functionalization have been extensively applied as labels for magnetic immunoassays, carriers for controlled drug/gene delivery, tracers and contrasts for magnetic imaging, etc. Here, we introduce a new biosensing scheme based on magnetic particle spectroscopy (MPS) and the self-assembly of MNPs to quantitatively detect H1N1 nucleoprotein molecules. MPS monitors the harmonics of oscillating MNPs as a metric for the freedom of rotational process, thus indicating the bound states of MNPs. These harmonics can be readily collected from nanogram quantities of iron oxide nanoparticles within 10 s. The H1N1 nucleoprotein molecule hosts multiple different epitopes that forms binding sites for many IgG polyclonal antibodies. Anchoring IgG polyclonal antibodies onto MNPs triggers the cross-linking between MNPs and H1N1 nucleoprotein molecules, thereby forming MNP self-assemblies. Using MPS and the self-assembly of MNPs, we were able to detect as low as 44 nM (4.4 pmole) H1N1 nucleoprotein. In addition, the morphologies and the hydrodynamic sizes of the MNP self-assemblies are characterized to verify the MPS results. Different MNP self-assembly models such as classical cluster, open ring tetramer, and chain model as well as multimers (from dimer to pentamer) are proposed in this paper. Herein, we claim the feasibility of using MPS and the self-assembly of MNPs as a new biosensing scheme for detecting ultralow concentrations of target biomolecules, which can be employed as rapid, sensitive, and wash-free magnetic immunoassays.

Ultrasensitive Magnetic Field Sensors for Biomedical Applications

The development of magnetic field sensors for biomedical applications primarily focuses on equivalent magnetic noise reduction or overall design improvement in order to make them smaller and cheaper while keeping the required values of a limit of detection. One of the cutting-edge topics today is the use of magnetic field sensors for applications such as magnetocardiography, magnetotomography, magnetomyography, magnetoneurography, or their application in point-of-care devices. This introductory review focuses on modern magnetic field sensors suitable for biomedicine applications from a physical point of view and provides an overview of recent studies in this field. Types of magnetic field sensors include direct current superconducting quantum interference devices, search coil, fluxgate, magnetoelectric, giant magneto-impedance, anisotropic/giant/tunneling magnetoresistance, optically pumped, cavity optomechanical, Hall effect, magnetoelastic, spin wave interferometry, and those based on the behavior of nitrogen-vacancy centers in the atomic lattice of diamond.

Antibody-directed metal-organic framework nanoparticles for targeted drug delivery

Nanosized metal-organic frameworks (nMOFs) have shown great promise as high-capacity carriers for a variety of applications. For biomedicine, numerous nMOFs have been proposed that can transport virtually any molecular drug, can finely tune their payload release profile, etc. However, perspectives of their applications for the targeted drug delivery remain relatively unclear. So far, only a few works have reported specific cell targeting by nMOFs exclusively through small ligands such as folic acid or RGD peptides. Here we show feasibility of targeted drug delivery to specific cancer cells in vitro with nMOFs functionalized with such universal tool as an antibody. We demonstrate ca. 120 nm magnetic core/MOFs shell nanoagents loaded with doxorubicin/daunorubicin and coupled with an antibody though a hydrophilic carbohydrate interface. We show that carboxymethyl-dextran coating of nMOFs allows extensive loading of the drug molecules (up to 15.7 mg/g), offers their sustained release in physiological media and preserves antibody specificity. Reliable performance of the agents is illustrated with trastuzumab-guided selective targeting and killing of HER2/neu-positive breast cancer cells in vitro. The approach expands the scope of nMOF applications and can serve as a platform for the development of potent theranostic nanoagents. STATEMENT OF SIGNIFICANCE: The unique combination of exceptional drug capacity and controlled release, biodegradability and low toxicity makes nanosized metal-organic frameworks (nMOFs) nearly ideal drug vehicles for various biomedical applications. Unfortunately, the prospective of nMOF applications for the targeted drug delivery is still unclear since only a few examples have been reported for nMOF cell targeting, exclusively for small ligands. In this work, we fill the important gap and demonstrate nanoagent that can specifically kill target cancer cells via drug delivery based on recognition of HER2/neu cell surface receptors by such universal and specific tool as antibodies. The proposed approach is universal and can be adapted for specific biomedical tasks using antibodies of any specificity and nMOFs of a various composition.

Recent advances in high-sensitivity detection methods for paper-based lateral-flow assay

Paper-based lateral-flow assays (LFAs) have achieved considerable commercial success and continue to have a significant impact on medical diagnostics and environmental monitoring. Conventional LFAs are typically performed by examining the color changes in the test bands by naked eye. However, for critical biochemical markers that are present in extremely small amounts in the clinical specimens, this readout method is not quantitative, and does not provide sufficient sensitivity or suitable detection limit for a reliable assay. Diverse technologies for high-sensitivity LFA detection have been developed and commercialization efforts are underway. In this review, we aim to provide a critical and objective overview of the recent progress in high-sensitivity LFA detection technologies, which involve the exploitation of the physical and chemical responses of transducing particles. The features and biomedical applications of the technologies, along with future prospects and challenges, are also discussed.

PCB-Based Magnetometer as a Platform for Quantification of Lateral-Flow Assays

This work presents a proof-of-concept demonstration of a novel inductive transducer, the femtoMag, that can be integrated with a lateral-flow assay (LFA) to provide detection and quantification of molecular biomarkers. The femtoMag transducer is manufactured using a low-cost printed circuit board (PCB) technology and can be controlled by relatively inexpensive electronics. It allows rapid high-precision quantification of the number (or amount) of superparamagnetic nanoparticle reporters along the length of an LFA test strip. It has a detection limit of 10-10 emu, which is equivalent to detecting 4 ng of superparamagnetic iron oxide (Fe3O4) nanoparticles. The femtoMag was used to quantify the hCG pregnancy hormone by quantifying the number of 200 nm magnetic reporters (superparamagnetic Fe3O4 nanoparticles embedded into a polymer matrix) immuno-captured within the test line of the LFA strip. A sensitivity of 100 pg/mL has been demonstrated. Upon further design and control electronics improvements, the sensitivity is projected to be better than 10 pg/mL. Analysis suggests that an average of 109 hCG molecules are needed to specifically bind 107 nanoparticles in the test line. The ratio of the number of hCG molecules in the sample to the number of reporters in the test line increases monotonically from 20 to 500 as the hCG concentration increases from 0.1 ng/mL to 10 ng/mL. The low-cost easy-to-use femtoMag platform offers high-sensitivity/high-precision target analyte quantification and promises to bring state-of-the-art medical diagnostic tests to the point of care.

Magnetic-Assisted Treatment of Liver Fibrosis

Chronic liver injury can be induced by viruses, toxins, cellular activation, and metabolic dysregulation and can lead to liver fibrosis. Hepatic fibrosis still remains a major burden on the global health systems. Nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) are considered the main cause of liver fibrosis. Hepatic stellate cells are key targets in antifibrotic treatment, but selective engagement of these cells is an unresolved issue. Current strategies for antifibrotic drugs, which are at the critical stage 3 clinical trials, target metabolic regulation, immune cell activation, and cell death. Here, we report on the critical factors for liver fibrosis, and on prospective novel drugs, which might soon enter the market. Apart from the current clinical trials, novel perspectives for anti-fibrotic treatment may arise from magnetic particles and controlled magnetic forces in various different fields. Magnetic-assisted techniques can, for instance, enable cell engineering and cell therapy to fight cancer, might enable to control the shape or orientation of single cells or tissues mechanically. Furthermore, magnetic forces may improve localized drug delivery mediated by magnetism-induced conformational changes, and they may also enhance non-invasive imaging applications.

Optical response of magnetically actuated biocompatible membranes

Biocompatible suspended magneto-elastic membranes were prepared. They consist of PDMS (polydimethylsiloxane) films, with embedded arrays of micrometric magnetic pillars made with lithography techniques. For visible light wavelengths, our membranes constitute magnetically tunable optical diffraction gratings, in transmission and reflection. The optical response has been quantitatively correlated with membrane structure and deformation, through optical and magneto-mechanical models. In contrast to the case of planar membranes, the diffraction patterns measured in reflection and transmission vary very differently upon magnetic field application. Indeed, the reflected beam is largely affected by the membrane bending, whereas the transmitted beam remains almost unchanged. In reflection, even weak membrane deformation can produce significant changes of the diffraction patterns. This field-controlled optical response may be used in adaptive optical applications, photonic devices, and for biological applications.

Magnetometry based method for investigation of nanoparticle clearance from circulation in a liver perfusion model

Nanoparticles (NPs) are among the most promising agents for advanced theranostics. However, their functioning in vivo is severely inhibited by the mononuclear phagocyte system (MPS), which rapidly removes all foreign entities from blood circulation. Little is known about the sequestration mechanisms and the ways to counteract them. New methods are highly demanded for investigation with high scrutiny of each aspect of NP clearance from blood. For example, while liver macrophages capture the majority of the administered particles, reliable investigation of this process in absence of other MPS components is hard to implement in vivo. Here, we demonstrate a novel method for real-time investigation hepatic uptake of NPs in an isolated perfused liver based on an extremely accurate magnetometric registration technique. The signal is obtained solely from the magnetic NPs without any 'background' from blood or tissues, which is a significant advantage over other techniques, e.g. optical ones. We illustrate the method capacity by investigation of behavior of different particles and show good correlation with in vivo studies. We also demonstrate notable suitability of the method for studying the NP clearance from the flow in the user-defined mediums, e.g. those containing specific serum components. Finally, the method was applied to reveal an interesting effect of short-term decrease of liver macrophage activity after the first interaction with small amounts of NPs. The developed perfusion model based on the high-performance magnetometry can be used for finding new mechanisms of NP sequestration and for development of novel 'stealth' nanoagents.

Nanoparticle-based drug delivery via RBC-hitchhiking for the inhibition of lung metastases growth

Delivery of particle-based theranostic agents via their transportation on the surfaces of red blood cells, commonly referred to as RBC-hitchhiking, has historically been developed as a promising strategy for increasing the extremely poor blood circulation lifetime, primarily, of the large-sized sub-micron agents. Here, we show for the first time that RBC-hitchhiking can be extremely efficient for nanoparticle delivery and tumor treatment even in those cases when no circulation prolongation is observed. Specifically, we demonstrate that RBC-hitchhiking of certain small 100 nm particles, unlike that of the conventional sub-micron ones, can boost the delivery of non-targeted particles to lungs up to a record high value of 120-fold (and up to 40% of the injected dose). To achieve this remarkable result, we screened sub-200 nm nanoparticles of different sizes, polymer coatings and ζ-potentials and identified particles with the optimal RBC adsorption/desorption behavior. Furthermore, we demonstrated that such RBC-mediated rerouting of particles to lungs can be used to fight pulmonary metastases of aggressive melanoma B16-F1. Our findings could change the general paradigm of drug delivery for cancer treatment with RBC-hitchhiking. It is not the blood circulation lifetime that is the key factor for nanoparticle efficiency, but rather the complexation of nanoparticles with the RBC. The demonstrated technology could become a valuable tool for development of new strategies based on small nanoparticles for the treatment of aggressive and small-cell types of cancer as well as other lung diseases.

Data on characterization and validation of assays for ultrasensitive quantitative detection of small molecules: Determination of free thyroxine with magnetic and interferometric methods

The presented data refer to optimization and quantitative characterization of a rapid lateral flow assay based on high-affinity bifunctional ligand and magnetic nanolabels, which was developed for detection of small molecules of thyroid hormones. The results were obtained by several techniques, including the magnetic particle quantification method, spectral-correlation interferometry and spectral-phase interferometry, dynamic light scattering, enzyme linked immunosorbent assay. The long-term stability of "antibody - magnetic nanoparticle" conjugates is shown. The assay specificity is confirmed, and verification of successful combination of magnetic particles and antibodies is demonstrated. The kinetic and equilibrium dissociation constants are determined for interactions between thyroxine and monoclonal antibodies. The obtained data could be used for design of other platforms for detection of small molecules.