Magnetic Tunability via Control of Crystallinity and Size in Polycrystalline Iron Oxide Nanoparticles.

Iron oxide nanoparticles (IONPs) are widely used for biomedical applications due to their unique magnetic properties and biocompatibility. However, the controlled synthesis of IONPs with tunable particle sizes and crystallite/grain sizes to achieve desired magnetic functionalities across single-domain and multi-domain size ranges remains an important challenge. Here, a facile synthetic method is used to produce iron oxide nanospheres (IONSs) with controllable size and crystallinity for magnetic tunability. First, highly crystalline Fe3O4 IONSs (crystallite sizes above 24 nm) having an average diameter of 50 to 400 nm are synthesized with enhanced ferrimagnetic properties. The magnetic properties of these highly crystalline IONSs are comparable to those of their nanocube counterparts, which typically possess superior magnetic properties. Second, the crystallite size can be widely tuned from 37 to 10 nm while maintaining the overall particle diameter, thereby allowing precise manipulation from the ferrimagnetic to the superparamagnetic state. In addition, demonstrations of reaction scale-up and the proposed growth mechanism of the IONSs are presented. This study highlights the pivotal role of crystal size in controlling the magnetic properties of IONSs and offers a viable means to produce IONSs with magnetic properties desirable for wider applications in sensors, electronics, energy, environmental remediation, and biomedicine.

A review of rapid food safety testing: using lateral flow assay platform to detect foodborne pathogens.

The detrimental impact of foodborne pathogens on human health makes food safety a major concern at all levels of production. Conventional methods to detect foodborne pathogens, such as live culture, high-performance liquid chromatography, and molecular techniques, are relatively tedious, time-consuming, laborious, and expensive, which hinders their use for on-site applications. Recurrent outbreaks of foodborne illness have heightened the demand for rapid and simple technologies for detection of foodborne pathogens. Recently, Lateral flow assays (LFA) have drawn attention because of their ability to detect pathogens rapidly, cheaply, and on-site. Here, we reviewed the latest developments in LFAs to detect various foodborne pathogens in food samples, giving special attention to how reporters and labels have improved LFA performance. We also discussed different approaches to improve LFA sensitivity and specificity. Most importantly, due to the lack of studies on LFAs for the detection of viral foodborne pathogens in food samples, we summarized our recent research on developing LFAs for the detection of viral foodborne pathogens. Finally, we highlighted the main challenges for further development of LFA platforms. In summary, with continuing improvements, LFAs may soon offer excellent performance at point-of-care that is competitive with laboratory techniques while retaining a rapid format.

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.

Specific Detection of Proteins Using Exceptionally Responsive Magnetic Particles.

Sensitivity and specificity are among the most important parameters for viable sensor technologies based on magnetic nanoparticles. In this work, we describe synthetic routes and analytical approaches to improve both aspects. Magnetic iron oxide particles having diameters of 120, 440, and 700 nm were synthesized, and their surfaces were specifically functionalized. The larger particles showed significantly stronger magnetic signals and responses when compared to commercially available magnetic particles (Dynabeads). A force-based detection method was used to distinguish specifically bound particles (via protein interactions) and nonspecifically bound ones (e.g., via physisorption). In addition, an exchange platform, denoted as exchange-induced remnant magnetization (EXIRM), was developed and utilized to detect label-free proteins specifically. Using EXIRM, the 700 nm magnetic particles showed a 7-fold increase in detection sensitivity when compared to the markedly larger commercially available Dynabeads; furthermore, EXIRM exhibited high specificity, even in a 100-fold increase of nontargeted protein. More generally, particle size effects, reaction times, and dynamic ranges are evaluated and discussed herein.

Ultrasensitive Magnetic Nanoparticle Detector for Biosensor Applications.

Ta/Ru/Co/Ru/Co/Cu/Co/Ni80Fe20/Ta spin-valve giant magnetoresistive (GMR) multilayers were deposited using UHV magnetron sputtering and optimized to achieve a 13% GMR ratio before patterning. The GMR multilayer was patterned into 12 sensor arrays using a combination of e-beam and optical lithographies. Arrays were constructed with 400 nm × 400 nm and 400 nm × 200 nm sensors for the detection of reporter nanoparticles. Nanoparticle detection was based on measuring the shift in high-to-low resistance switching field of the GMR sensors in the presence of magnetic particle(s). Due to shape anisotropy and the corresponding demag field, the resistance state switching fields were significantly larger and the switching field distribution significantly broader in the 400 nm × 200 nm sensors as compared to the 400 nm × 400 nm sensors. Thus, sensor arrays with 400 nm × 400 nm dimensions were used for the demonstration of particle detection. Detection of a single 225 nm Fe3O4 magnetic nanoparticle and a small number (~10) of 100 nm nanoparticles was demonstrated. With appropriate functionalization for biomolecular recognition, submicron GMR sensor arrays can serve as the basis of ultrasensitive chemical and biological sensors.

Enzymatic conversion of magnetic nanoparticles to a non-magnetic precipitate: a new approach to magnetic sensing.

Magnetic sensing utilizes the detection of biomolecule-conjugated magnetic nanoparticles (MNPs). Our new strategy offers a novel approach to magnetic sensing where in situ conversion produces a "loss of signal" in the sensing device. This report demonstrates the enzymatic conversion of Fe3O4 MNPs to a non-magnetic precipitate via reduction by l-ascorbic acid generated by the action of alkaline phosphatase.

Enzymatic synthesis of magnetic nanoparticles.

We report the first in vitro enzymatic synthesis of paramagnetic and antiferromagnetic nanoparticles toward magnetic ELISA reporting. With our procedure, alkaline phosphatase catalyzes the dephosphorylation of l-ascorbic-2-phosphate, which then serves as a reducing agent for salts of iron, gadolinium, and holmium, forming magnetic precipitates of Fe45±14Gd5±2O50±15 and Fe42±4Ho6±4O52±5. The nanoparticles were found to be paramagnetic at 300 K and antiferromagnetic under 25 K. Although weakly magnetic at 300 K, the room-temperature magnetization of the nanoparticles found here is considerably greater than that of analogous chemically-synthesized LnxFeyOz (Ln = Gd, Ho) samples reported previously. At 5 K, the nanoparticles showed a significantly higher saturation magnetization of 45 and 30 emu/g for Fe45±14Gd5±2O50±15 and Fe42±4Ho6±4O52±5, respectively. Our approach of enzymatically synthesizing magnetic labels reduces the cost and avoids diffusional mass-transfer limitations associated with pre-synthesized magnetic reporter particles, while retaining the advantages of magnetic sensing.

Development of Pinhole-Free Amorphous Aluminum Oxide Protective Layers for Biomedical Device Applications.

This paper describes synthesis of ultrathin pinhole-free insulating aluminum oxide layers for electronic device protection in corrosive liquid environments, such as phosphate buffered saline (PBS) or clinical fluids, to enable emerging biomedical applications such as biomolecular sensors. A pinhole-free 25-nm thick amorphous aluminum oxide layer has been achieved using ultra-high vacuum DC magnetron reactive sputtering of aluminum in oxygen/argon plasma followed by oxygen plasma post-processing. Deposition parameters were optimized to achieve the best corrosion protection of lithographically defined device structures. Electrochemical deposition of copper through the aluminum oxide layers was used to detect the presence (or absence) of pinholes. FTIR, XPS, and spectroscopic ellipsometry were used to characterize the material properties of the protective layers. Electrical resistance of the copper device structures protected by the aluminum oxide layers and exposed to a PBS solution was used as a metric to evaluate the long-term stability of these device structures.

Tuning the magnetic properties of nanoparticles.

The tremendous interest in magnetic nanoparticles (MNPs) is reflected in published research that ranges from novel methods of synthesis of unique nanoparticle shapes and composite structures to a large number of MNP characterization techniques, and finally to their use in many biomedical and nanotechnology-based applications. The knowledge gained from this vast body of research can be made more useful if we organize the associated results to correlate key magnetic properties with the parameters that influence them. Tuning these properties of MNPs will allow us to tailor nanoparticles for specific applications, thus increasing their effectiveness. The complex magnetic behavior exhibited by MNPs is governed by many factors; these factors can either improve or adversely affect the desired magnetic properties. In this report, we have outlined a matrix of parameters that can be varied to tune the magnetic properties of nanoparticles. For practical utility, this review focuses on the effect of size, shape, composition, and shell-core structure on saturation magnetization, coercivity, blocking temperature, and relaxation time.

Seroprevalence of hepatitis E virus (HEV) among male craft and manual workers in Qatar (2020-2021).

Background: The rapid growth of Qatar in the last two decades has attracted a large influx of immigrant craft and manual workers (CMWs) seeking employment in jobs associated with food handling, domestic service, and construction. Nearly 60 % of Qatar's population are expatriates CMWs, including many from hyperendemic countries for HEV. Thus, estimating the seroprevalence of HEV in Qatar and understanding its epidemiology is essential for public health efforts to control HEV transmission in Qatar. Methods: Blood samples from 2670 CMWs were collected between 2020 and 2021. All samples were tested for HEV-IgG antibodies. Positive HEV-IgG samples were tested for HEV-IgM antibodies, and those positives were also tested for viral antigens using an HEV-Ag ELISA kit and HEV-RNA by RT-PCR to confirm current HEV infections. Results: The seroprevalence of HEV-IgG was 27.3 % (729/2670; 95 % CI: 25.6-29.0). Of those HEV-IgG positive, 8.23 % (60/729; 95 % CI: 6.30-10.5) were HEV-IgM positive. Of the IgM-positive samples, 2 were HEV-RNA positive (3.39 %; 95 % CI: 0.40-11.7), and 1 was HEV-Ag positive (1.69 %; 95 % CI: 0.04-9.09). In addition, HEV-IgG seroprevalence was associated with age and nationality, with the highest seroprevalence in participants from Egypt (IgG 60.0 %; IgM 5.56 %), Pakistan (IgG 59.0 %; IgM 2.24 %), Nepal (IgG 29.3 %; IgM 2.70 %), Bangladesh (IgG 27.8 %; IgM 2.45 %), and India (IgG 23.9 %; IgM 2.43 %). Conclusion: In this study, we showed that the seroprevalence of HEV among CMWs was slightly higher than what was previously reported among the urban population in Qatar (2013-2016).

Piezoelectricity across 2D Phase Boundaries.

Piezoelectricity in low-dimensional materials and metal-semiconductor junctions has attracted recent attention. Herein, a 2D in-plane metal-semiconductor junction made of multilayer 2H and 1T' phases of molybdenum(IV) telluride (MoTe2 ) is investigated. Strong piezoelectric response is observed using piezoresponse force microscopy at the 2H-1T' junction, despite that the multilayers of each individual phase are weakly piezoelectric. The experimental results and density functional theory calculations suggest that the amplified piezoelectric response observed at the junction is due to the charge transfer across the semiconducting and metallic junctions resulting in the formation of dipoles and excess charge density, allowing the engineering of piezoelectric response in atomically thin materials.

Recombinant expression, characterization, and quantification in human cancer cell lines of the Anaplastic Large-Cell Lymphoma-characteristic NPM-ALK fusion protein.

Systemic anaplastic large cell lymphoma (ALCL) is an aggressive T-cell lymphoma most commonly seen in children and young adults. The majority of pediatric ALCLs are associated with the t(2;5)(p23;q35) translocation which fuses the Anaplastic Lymphoma Kinase (ALK) gene with the Nucleophosmin (NPM) gene. The NPM-ALK fusion protein is a constitutively-active tyrosine kinase, and plays a major role in tumor pathogenesis. In an effort to advance novel diagnostic approaches and the understanding of the function of this fusion protein in cancer cells, we expressed in E. coli, purified and characterized human NPM-ALK fusion protein to be used as a standard for estimating expression levels in cultured human ALCL cells, a key tool in ALCL pathobiology research. We estimated that NPM-ALK fusion protein is expressed at substantial levels in both Karpas 299 and SU-DHL-1 cells (ca. 4-6 million molecules or 0.5-0.7 pg protein per cell; based on our in-house developed NPM-ALK ELISA; LOD of 40 pM) as compared to the ubiquitous ß-actin protein (ca. 64 million molecules or 4.5 pg per lymphocyte). We also compared NPM-ALK/ ß-actin ratios determined by ELISA to those independently determined by two-dimensional electrophoresis and showed that the two methods are in good agreement.

2D Electrets of Ultrathin MoO2 with Apparent Piezoelectricity.

Since graphene, a variety of 2D materials have been fabricated in a quest for a tantalizing combination of properties and desired physiochemical behavior. 2D materials that are piezoelectric, i.e., that allow for a facile conversion of electrical energy into mechanical and vice versa, offer applications for sensors, actuators, energy harvesting, stretchable and flexible electronics, and energy storage, among others. Unfortunately, materials must satisfy stringent symmetry requirements to be classified as piezoelectric. Here, 2D ultrathin single-crystal molybdenum oxide (MoO2 ) flakes that exhibit unexpected piezoelectric-like response are fabricated, as MoO2 is centrosymmetric and should not exhibit intrinsic piezoelectricity. However, it is demonstrated that the apparent piezoelectricity in 2D MoO2 emerges from an electret-like behavior induced by the trapping and stabilization of charges around defects in the material. Arguably, the material represents the first 2D electret material and suggests a route to artificially engineer piezoelectricity in 2D crystals. Specifically, it is found that the maximum out-of-plane piezoresponse is 0.56 pm V-1 , which is as strong as that observed in conventional 2D piezoelectric materials. The charges are found to be highly stable at room temperature with a trapping energy barrier of ≈2 eV.

Correction: Enhancement of lateral flow assay performance by electromagnetic relocation of reporter particles.

[This corrects the article DOI: 10.1371/journal.pone.0186782.].

Gold nanoparticle effects in polymerase chain reaction: favoring of smaller products by polymerase adsorption.

Gold nanoparticles were recently reported to reduce the formation of nonspecific products in polymerase chain reaction (PCR) at remarkably low temperatures, with hypothesized mechanisms including adsorption of DNA and heat-transfer enhancement. In contrast to these reports, we report that gold nanoparticles do not enhance the specificity of PCR but rather suppress the amplification of longer products while favoring amplification of shorter products, independent of specificity. Gold nanoparticles bearing a self-assembled monolayer of hexadecanethiol did not affect PCR, suggesting that surface interactions play an essential role. This role was further confirmed by experiments in which a similar effect on PCR was observed for the same total surface area of particles over a 100-fold range of per-particle surface area. The effect was seen with Taq and Tfl polymerases but not with Vent polymerase, and the effects of nanoparticles can be reversed by increasing the polymerase concentration or by adding bovine serum albumin (BSA). Transient high-temperature nanoparticle pre-exposure of PCR mix containing polymerase but not template or primers, followed by nanoparticle removal, modified subsequent nanoparticle-free PCR. Interaction between polymerase and gold nanoparticles was confirmed by changes in nanoparticle absorption spectrum and electrophoretic mobility in the presence of polymerase. Taken together, these results suggest that the nanoparticles nonspecifically adsorb polymerase, thus effectively reducing polymerase concentration.

Facile synthesis, assembly, and immobilization of ordered arrays of monodisperse magnetic nanoparticles on silicon substrates.

This paper outlines the preparation of monodisperse MnFe(2)O(4) nanoparticles modified with omega-alkenyl moieties in a one-pot reaction, requiring no ligand-exchange step, followed by deposition of the resulting surfactant-coated nanoparticles onto a hydrogen-terminated silicon (111) wafer and covalent anchoring to the surface via UV-initiated bonding, creating a stable two-dimensional array of monodisperse magnetic nanoparticles.

Enhancement of lateral flow assay performance by electromagnetic relocation of reporter particles.

Lateral flow assays (LFAs) are a widely-used point-of care diagnostic format, but suffer from limited analytical sensitivity, especially when read by eye. It has recently been reported that LFA performance can be improved by using magnetic reporter particles and an external magnetic field applied at the test line. The mechanism of sensitivity/performance enhancement was suggested to be concentration/retardation of reporter particles at the test line. Here we demonstrate an additional mechanism of particle relocation where reporter particles from the lower depths of the translucent LFA strip relocate to more-visible locations nearer to the top surface, producing a more visible signal. With a magnetic field we observed an improvement in sensitivity of human chorionic gonadotropin (hCG) detection from 1.25 ng/mL to 0.31 ng/mL. We also observed an increase of the color intensity per particle in test lines when the magnetic field was present.

Physics of perpendicular recording with a patterned soft underlayer.

In this paper, it is argued that perpendicular recording in the most popular current form--with the use of a continuous soft underlayer (SUL)--may not be the most optimal way to maximize the achievable areal density. As a possible solution, patterning of SUL is discussed. The purpose of patterning of a SUL is to effectively move the image head closer to the recording media, as compared to the real recording head, and thus increase the net recording field and the field gradient across the thickness of the media. Various patterning configurations and combinations with recording layers are comparatively studied. It is illustrated that with a patterned SUL, the recording and sensitivity fields, responsible for writing and reading information, respectively, could be not only increased by several factors but also localized across the entire thickness of the recording media.

Near-infrared-responsive, superparamagnetic Au@Co nanochains.

This manuscript describes a new type of nanomaterial, namely superparamagnetic Au@Co nanochains with optical extinctions in the near infrared (NIR). The Au@Co nanochains were synthesized via a one-pot galvanic replacement route involving a redox-transmetalation process in aqueous medium, where Au salt was reduced to form Au shells on Co seed templates, affording hollow Au@Co nanochains. The Au shells serve not only as a protective coating for the Co nanochain cores, but also to give rise to the optical properties of these unique nanostructures. Importantly, these bifunctional, magneto-optical Au@Co nanochains combine the advantages of nanophotonics (extinction at ca. 900 nm) and nanomagnetism (superparamagnetism) and provide a potentially useful new nanoarchitecture for biomedical or catalytic applications that can benefit from both activation by light and manipulation using an external magnetic field.

Magnetic Sensing Potential of Fe3O4 Nanocubes Exceeds That of Fe3O4 Nanospheres.

This paper highlights the relation between the shape of iron oxide (Fe3O4) particles and their magnetic sensing ability. We synthesized Fe3O4 nanocubes and nanospheres having tunable sizes via solvothermal and thermal decomposition synthesis reactions, respectively, to obtain samples in which the volumes and body diagonals/diameters were equivalent. Vibrating sample magnetometry (VSM) data showed that the saturation magnetization (Ms) and coercivity of 100-225 nm cubic magnetic nanoparticles (MNPs) were, respectively, 1.4-3.0 and 1.1-8.4 times those of spherical MNPs on a same-volume and same-body diagonal/diameter basis. The Curie temperature for the cubic Fe3O4 MNPs for each size was also higher than that of the corresponding spherical MNPs; furthermore, the cubic Fe3O4 MNPs were more crystalline than the corresponding spherical MNPs. For applications relying on both higher contact area and enhanced magnetic properties, higher-Ms Fe3O4 nanocubes offer distinct advantages over Fe3O4 nanospheres of the same-volume or same-body diagonal/diameter. We evaluated the sensing potential of our synthesized MNPs using giant magnetoresistive (GMR) sensing and force-induced remnant magnetization spectroscopy (FIRMS). Preliminary data obtained by GMR sensing confirmed that the nanocubes exhibited a distinct sensitivity advantage over the nanospheres. Similarly, FIRMS data showed that when subjected to the same force at the same initial concentration, a greater number of nanocubes remained bound to the sensor surface because of higher surface contact area. Because greater binding and higher Ms translate to stronger signal and better analytical sensitivity, nanocubes are an attractive alternative to nanospheres in sensing applications.