Analytical Platform with Selectable Assay Parameters Based on Three Functions of Magnetic Nanoparticles: Demonstration of Highly Sensitive Rapid Quantitation of Staphylococcal Enterotoxin B in Food

A comprehensive review on the detection of Staphylococcus aureus enterotoxins in food samples

Staphylococcal enterotoxins (SEs), the major virulence factors of Staphylococcus aureus, cause a wide range of food poisoning and seriously threaten human health by infiltrating the food supply chain at different phases of manufacture, processes, distribution, and market. The significant prevalence of Staphylococcus aureus calls for efficient, fast, and sensitive methods for the early detection of SEs. Here, we provide a comprehensive review of the hazards of SEs in contaminated food, the characteristic and worldwide regulations of SEs, and various detection methods for SEs with extensive comparison and discussion of benefits and drawbacks, mainly including biological detection, genetic detection, and mass spectrometry detection and biosensors. We highlight the biosensors for the screening purpose of SEs, which are classified according to different recognition elements such as antibodies, aptamers, molecularly imprinted polymers, T-cell receptors, and transducers such as optical, electrochemical, and piezoelectric biosensors. We analyzed challenges of biosensors for the monitoring of SEs and conclude the trends for the development of novel biosensors should pay attention to improve samples pretreatment efficiency, employ innovative nanomaterials, and develop portable instruments. This review provides new information and insightful commentary, important to the development and innovation of further detection methods for SEs in food samples.

Magnetic and Fluorescent Dual-Labeled Genetically Encoded Targeted Nanoparticles for Malignant Glioma Cell Tracking and Drug Delivery

Human glioblastoma multiforme (GBM) is a primary malignant brain tumor, a radically incurable disease characterized by rapid growth resistance to classical therapies, with a median patient survival of about 15 months. For decades, a plethora of approaches have been developed to make GBM therapy more precise and improve the diagnosis of this pathology. Targeted delivery mediated by the use of various molecules (monoclonal antibodies, ligands to overexpressed tumor receptors) is one of the promising methods to achieve this goal. Here we present a novel genetically encoded nanoscale dual-labeled system based on Quasibacillus thermotolerans (Qt) encapsulins exploiting biologically inspired designs with iron-containing nanoparticles as a cargo, conjugated with human fluorescent labeled transferrin (Tf) acting as a vector. It is known that the expression of transferrin receptors (TfR) in glioma cells is significantly higher compared to non-tumor cells, which enables the targeting of the resulting nanocarrier. The selectivity of binding of the obtained nanosystem to glioma cells was studied by qualitative and quantitative assessment of the accumulation of intracellular iron, as well as by magnetic particle quantification method and laser scanning confocal microscopy. Used approaches unambiguously demonstrated that transferrin-conjugated encapsulins were captured by glioma cells much more efficiently than by benign cells. The resulting bioinspired nanoplatform can be supplemented with a chemotherapeutic drug or genotherapeutic agent and used for targeted delivery of a therapeutic agent to malignant glioma cells. Additionally, the observed cell-assisted biosynthesis of magnetic nanoparticles could be an attractive way to achieve a narrow size distribution of particles for various applications.

Magnetic nanoprobe-enabled lateral flow assays: recent advances

In recent years, magnetic nanoparticle sensor technologies have attracted considerable interest in the point-of-care-testing (POCT) field, especially in lateral flow immunoassays (LFIAs). Although the visual signal of magnetic nanoparticles is reduced during an inspection, it can be compensated for by magnetic induction, and detection results can be quantified by magnetic sensors. Sensors that use magnetic nanoparticles (MNPs) as markers can overcome the high background noise of complex samples. In this study, MNP signal detection strategies are described from the perspectives of magnetoresistance, magnetic flux, frequency mixing technology, and magnetic permeability, and the principles and development of each technology are introduced in detail. Typical applications of magnetic nanoparticle sensor technologies are introduced. By describing the advantages and limitations of different sensing strategies, we highlight the development and improvement directions of different sensing strategies. In general, the future development of magnetic nanoparticle sensor technologies will be toward intelligent, convenient, and mobile high-performance detection equipment.

Comparative Study of Nanoparticle Blood Circulation after Forced Clearance of Own Erythrocytes (Mononuclear Phagocyte System-Cytoblockade) or Administration of Cytotoxic Doxorubicin- or Clodronate-Loaded Liposomes

Recent developments in the field of nanomedicine have introduced a wide variety of nanomaterials that are capable of recognizing and killing tumor cells with increased specificity. A major limitation preventing the widespread introduction of nanomaterials into the clinical setting is their fast clearance from the bloodstream via the mononuclear phagocyte system (MPS). One of the most promising methods used to overcome this limitation is the MPS-cytoblockade, which forces the MPS to intensify the clearance of erythrocytes by injecting allogeneic anti-erythrocyte antibodies and, thus, significantly prolongs the circulation of nanoagents in the blood. However, on the way to the clinical application of this approach, the question arises whether the induced suppression of macrophage phagocytosis via the MPS-cytoblockade could pose health risks. Here, we show that highly cytotoxic doxorubicin- or clodronate-loaded liposomes, which are widely used for cancer therapy and biomedical research, induce a similar increase in the nanoparticle blood circulation half-life in mice as the MPS-cytoblockade, which only gently and temporarily saturates the macrophages with the organism's own erythrocytes. This result suggests that from the point of view of in vivo macrophage suppression, the MPS-cytoblockade should be less detrimental than the liposomal anti-cancer drugs that are already approved for clinical application while allowing for the substantial improvement in the nanoagent effectiveness.

Development of a Gold Nanoparticle-Linked Immunosorbent Assay of Staphylococcal Enterotoxin B Detection with Extremely High Sensitivity by Determination of Gold Atom Content Using Graphite Furnace Atomic Absorption Spectrometry

Highly sensitive staphylococcal enterotoxin B (SEB) assay is of great importance for the prevention of toxic diseases caused by SEB. In this study, we present a gold nanoparticle (AuNP)-linked immunosorbent assay (ALISA) for detecting SEB in a sandwich format using a pair of SEB specific monoclonal antibodies (mAbs) performed in microplates. First, the detection mAb was labeled with AuNPs of different particle sizes (15, 40 and 60 nm). Then the sandwich immunosorbent assay for SEB detection was performed routinely in a microplate except for using AuNPs-labeled detection mAb. Next, the AuNPs adsorbed on the microplate were dissolved with aqua regia and the content of gold atoms was determined by graphite furnace atomic absorption spectrometry (GFAAS). Finally, a standard curve was drawn of the gold atomic content against the corresponding SEB concentration. The detection time of ALISA was about 2.5 h. AuNPs at 60 nm showed the highest sensitivity with an actual measured limit of detection (LOD) of 0.125 pg/mL and a dynamic range of 0.125-32 pg/mL. AuNPs at 40 nm had an actual measured LOD of 0.5 pg/mL and a dynamic range of 0.5 to 128 pg/mL. AuNPs at 15 nm had an actual measured LOD of 5 pg/mL, with a dynamic range of 5-1280 pg/mL. With detection mAb labeled with AuNPs at 60 nm, ALISA's intra- and interassay coefficient variations (CV) at three concentrations (2, 8, and 20 pg/mL) were all lower than 12% and the average recovery level was ranged from 92.7% to 95.0%, indicating a high precision and accuracy of the ALISA method. Moreover, the ALISA method could be successfully applied to the detection of various food, environmental, and biological samples. Therefore, the successful establishment of the ALISA method for SEB detection might provide a powerful tool for food hygiene supervision, environmental management, and anti-terrorism procedures and this method might achieve detection and high-throughput analysis automatically in the near future, even though GFAAS testing remains costly at present.

Magnetic Particle Spectroscopy for Point-of-Care: A Review on Recent Advances

Since its first report in 2006, magnetic particle spectroscopy (MPS)-based biosensors have flourished over the past decade. Currently, MPS are used for a wide range of applications, such as disease diagnosis, foodborne pathogen detection, etc. In this work, different MPS platforms, such as dual-frequency and mono-frequency driving field designs, were reviewed. MPS combined with multi-functional magnetic nanoparticles (MNPs) have been extensively reported as a versatile platform for the detection of a long list of biomarkers. The surface-functionalized MNPs serve as nanoprobes that specifically bind and label target analytes from liquid samples. Herein, an analysis of the theories and mechanisms that underlie different MPS platforms, which enable the implementation of bioassays based on either volume or surface, was carried out. Furthermore, this review draws attention to some significant MPS platform applications in the biomedical and biological fields. In recent years, different kinds of MPS point-of-care (POC) devices have been reported independently by several groups in the world. Due to the high detection sensitivity, simple assay procedures and low cost per run, the MPS POC devices are expected to become more widespread in the future. In addition, the growth of telemedicine and remote monitoring has created a greater demand for POC devices, as patients are able to receive health assessments and obtain results from the comfort of their own homes. At the end of this review, we comment on the opportunities and challenges for POC devices as well as MPS devices regarding the intensely growing demand for rapid, affordable, high-sensitivity and user-friendly devices.

A novel ultrasensitive and fast aptamer biosensor of SEB based on AuNPs-assisted metal-enhanced fluorescence

A fluorescent biosensor strategy was developed in combination with immunomagnetic separation for rapid and sensitive detection of staphylococcal enterotoxin B (SEB). Magnetic nanoparticles (MNPs) modified with aptamer of SEB could capture the SEB. Then the gold nanoparticles (AuNPs) fluorescent probe was added and a "sandwich structure" was formed between AuNPs, SEB and MNPs. The MNPs-SEB-AuNPs structure could be separated with an additional magnetic field, which resulted the lower signals of AuNPs fluorescent probe. In optimal conditions, the current method displayed a broad quantitative range from 100 to 10⁷ fg/mL and the limit of detection was 3.43 fg/mL. The recovery of SEB-spiked milk samples ranged from 92.00 to 119.00 %, which revealed that the developed method had great accuracy. Furthermore, the method was fast and economical for ultrasensitive detection. Therefore, the fluorescent biosensor based on MNPs-AuNPs is promising for the detection of other environmental and food pollutants.

Five-Minute Magnetic Nanoparticle Spectroscopy-Based Bioassay for Ultrafast Detection of SARS-CoV-2 Spike Protein

In this work, we report a 5-min magnetic particle spectroscopy (MPS)-based bioassay strategy. In our approach, surface-functionalized magnetic nanoparticles are incubated with target analytes at 37 °C with agitation for 3 min, and the MPS reading is then taken at the fifth minute. We prove the feasibility of 5 min ultrafast detection of SARS-CoV-2 spike protein with a detection limit below 5 nM (0.2 pmol). Our proposed 5-min bioassay strategy may be applied to reduce the assay time for other liquid-phase, volumetric biosensors such as NMR, quantum dots, fluorescent biosensors, etc.

Influence of magnetic nanoparticle biotransformation on contrasting efficiency and iron metabolism

Magnetic nanoparticles are widely used in biomedicine for MRI imaging and anemia treatment. The aging of these nanomaterials in vivo may lead to gradual diminishing of their contrast properties and inducing toxicity. Here, we describe observation of the full lifecycle of 40-nm magnetic particles from their injection to the complete degradation in vivo and associated impact on the organism. We found that in 2 h the nanoparticles were eliminated from the bloodstream, but their initial biodistribution changed over time. In 1 week, a major part of the nanoparticles was transferred to the liver and spleen, where they degraded with a half-life of 21 days. MRI and a magnetic spectral approach revealed preservation of contrast in these organs for more than 1 month. The particle degradation led to the increased number of red blood cells and blood hemoglobin level due to released iron without causing any toxicity in tissues. We also observed an increase in gene expression level of Fe-associated proteins such as transferrin, DMT1, and ferroportin in the liver in response to the iron particle degradation. A deeper understanding of the organism response to the particle degradation can bring new directions to the field of MRI contrast agent design.

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.

Highly Sensitive Nanomagnetic Quantification of Extracellular Vesicles by Immunochromatographic Strips: A Tool for Liquid Biopsy

Extracellular vesicles (EVs) are promising agents for liquid biopsy-a non-invasive approach for the diagnosis of cancer and evaluation of therapy response. However, EV potential is limited by the lack of sufficiently sensitive, time-, and cost-efficient methods for their registration. This research aimed at developing a highly sensitive and easy-to-use immunochromatographic tool based on magnetic nanoparticles for EV quantification. The tool is demonstrated by detection of EVs isolated from cell culture supernatants and various body fluids using characteristic biomarkers, CD9 and CD81, and a tumor-associated marker-epithelial cell adhesion molecules. The detection limit of 3.7 × 105 EV/µL is one to two orders better than the most sensitive traditional lateral flow system and commercial ELISA kits. The detection specificity is ensured by an isotype control line on the test strip. The tool's advantages are due to the spatial quantification of EV-bound magnetic nanolabels within the strip volume by an original electronic technique. The inexpensive tool, promising for liquid biopsy in daily clinical routines, can be extended to other relevant biomarkers.

Multiplex Label-Free Kinetic Characterization of Antibodies for Rapid Sensitive Cardiac Troponin I Detection Based on Functionalized Magnetic Nanotags

Express and highly sensitive immunoassays for the quantitative registration of cardiac troponin I (cTnI) are in high demand for early point-of-care differential diagnosis of acute myocardial infarction. The selection of antibodies that feature rapid and tight binding with antigens is crucial for immunoassay rate and sensitivity. A method is presented for the selection of the most promising clones for advanced immunoassays via simultaneous characterization of interaction kinetics of different monoclonal antibodies (mAb) using a direct label-free method of multiplex spectral correlation interferometry. mAb-cTnI interactions were real-time registered on an epoxy-modified microarray glass sensor chip that did not require activation. The covalent immobilization of mAb microdots on its surface provided versatility, convenience, and virtually unlimited multiplexing potential. The kinetics of tracer antibody interaction with the “cTnI—capture antibody” complex was characterized. Algorithms are shown for excluding mutual competition of the tracer/capture antibodies and selecting the optimal pairs for different assay formats. Using the selected mAbs, a lateral flow assay was developed for rapid quantitative cTnI determination based on electronic detection of functionalized magnetic nanoparticles applied as labels (detection limit—0.08 ng/mL, dynamic range > 3 orders). The method can be extended to other molecular biomarkers for high-throughput screening of mAbs and rational development of immunoassays.

"Lighting-up" methylene blue-embedded zirconium based organic framework triggered by Al3+ for advancing the sensitivity of E. coli O157:H7 analysis in dual-signal lateral flow immunochromatographic assay

The sensitive detection of foodborne pathogens is of great significance for ensuring food safety and quality. Herein, on the basis of methylene blue-embedded zirconium based organic framework (UIO@MB) as the remarkable capture carrier and signal indicator, with the Al³⁺-assisted the fluorescent signal response, we developed a label-free and dual-signal lateral flow immunochromatographic assay (LDLFIA) for sensitive detection of Escherichia coli (E. coli) O157:H7. The UIO@MB sensing carrier without monoclonal antibodies (mAbs) was manufactured, which adhered to bacteria to form the UIO@MB-E. coli O157:H7 conjugate, resulting in visible blue band. Then the fluorescent response of the OH-rich UIO@MB was excited by introducing Al³⁺, arising from capturing of Al³⁺ by -OH through coordination and electrostatic affinity, thus generating a green fluorescent band. Impressively, a smartphone-based portable reading system was developed that can reflect the test results of UIO@MB-LDLFIA immediately. Under optimum conditions, UIO@MB-LDLFIA can complete colorimetric and fluorescent mode detection within 90 min, with a detection sensitivity of 10³ CFU/mL, which were 100 times lower than traditional gold nanoparticles-based LFIA and polymerase chain reaction (PCR). Moreover, the feasibility of the method was further evaluated by the determination of E. coli O157: H7 in drinking water and cabbage with average recoveries of 85.1-123.0%.

A centrifugal microfluidic chip for point-of-care testing of staphylococcal enterotoxin B in complex matrices

Staphylococcal enterotoxin B (SEB) is a typical biological toxin that causes food poisoning. Currently reported SEB detection methods have the drawbacks of sophisticated sample preparation and being time-consuming and labor-intensive. Herein, we propose a strategy based on an immune sandwich structure operating on a centrifugal microfluidic chip for point-of-care testing (POCT) of SEB. The fluorescent microparticle-labeled primary antibody (CM-EUs-Ab₁), capture antibody (CAb), and goat anti-mouse IgG antibody (SAb) were modified on the bond area, T-area, and C-area, respectively. When SEB was added, it first reacted with the CM-EUs-Ab₁ through the specific recognition between SEB and the Ab₁. Then, under capillarity, the conjugates of SEB and the CM-EUs-Ab₁ were captured by the CAb when they flowed to the T-area, and the remaining CM-EUs-Ab₁ bound with the SAb in the C-area. Finally, this chip was put into a dry fluorescence detection analyzer for centrifugation and on-site detection of SEB. The fluorescence intensity ratio of the T-area to the C-area was positively correlated with the concentration of SEB. The resulting linear range was 0.1-250 ng mL^-1, and the limit of detection (3σ/k) was 68 pg mL^-1. This POCT platform only needs 20 μL of sample and can realize the full process of detection within 12 min. This chip also exhibits good stability for 35 days. Additionally, the proposed method has been successfully utilized for the detection of SEB in urine, milk, and juice without any pre-treatment of the samples. Thus, this platform is expected to be applied to food safety testing and clinical diagnosis.

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.

Synthesis and application of 0D/2D nanocomposite for the nanomolar level detection of antiandrogen drug

In this work, Sr@FeNi-S nanostructures were synthesized through chemical approach. The as synthesized nanostructures were explored for the fabrication of a nanocomposite based potentiometric flutamide (FLU) sensor. A conducting graphene...

Applications of Pristine and Functionalized Carbon Nanotubes, Graphene, and Graphene Nanoribbons in Biomedicine

This review is dedicated to a comprehensive description of the latest achievements in the chemical functionalization routes and applications of carbon nanomaterials (CNMs), such as carbon nanotubes, graphene, and graphene nanoribbons. The review starts from the description of noncovalent and covalent exohedral modification approaches, as well as an endohedral functionalization method. After that, the methods to improve the functionalities of CNMs are highlighted. These methods include the functionalization for improving the hydrophilicity, biocompatibility, blood circulation time and tumor accumulation, and the cellular uptake and selectivity. The main part of this review includes the description of the applications of functionalized CNMs in bioimaging, drug delivery, and biosensors. Then, the toxicity studies of CNMs are highlighted. Finally, the further directions of the development of the field are presented.

Applications of Filled Single-Walled Carbon Nanotubes: Progress, Challenges, and Perspectives

Single-walled carbon nanotubes (SWCNTs), which possess electrical and thermal conductivity, mechanical strength, and flexibility, and are ultra-light weight, are an outstanding material for applications in nanoelectronics, photovoltaics, thermoelectric power generation, light emission, electrochemical energy storage, catalysis, sensors, spintronics, magnetic recording, and biomedicine. Applications of SWCNTs require nanotube samples with precisely controlled and customized electronic properties. The filling of SWCNTs is a promising approach in the fine-tuning of their electronic properties because a large variety of substances with appropriate physical and chemical properties can be introduced inside SWCNTs. The encapsulation of electron donor or acceptor substances inside SWCNTs opens the way for the Fermi-level engineering of SWCNTs for specific applications. This paper reviews the recent progress in applications of filled SWCNTs and highlights challenges that exist in the field.

Copper nanocluster composites for analytical (bio)-sensing and imaging: a review

As an ideal substitute for traditional organic fluorescent dyes or up-conversion nanomaterials, copper nanoclusters (CuNCs) have developed rapidly and have been involved in exciting achievements in versatile applications. The emergence of novel CuNCs composites improves the poor stability and fluorescence intensity of CuNCs. With this in mind, great efforts have been made to develop a wide variety of CuNCs composites, and impressive progress has been made in the past few years. In this review, we systematically summarize absorption, fluorescence, electrochemiluminescence, and catalytic properties and focus on the multiple factors that affect the fluorescence properties of CuNCs. The fluorescence properties of CuNCs are discussed from the point of view of core size, surface ligands, self-assembly, metal defects, pH, solvent, ions, metal doping, and confinement effect. Especially, we illustrate the research progress and representative applications of CuNCs composites in bio-related fields, which have received considerable interests in the past years. Additionally, the sensing mechanism of CuNCs composites is highlighted. Finally, we summarize current challenges and look forward to the future development of CuNCs composites. Schematic diagram of the categories, possible sensing mechanisms, and bio-related applications of copper nanoclusters composites.

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.

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.

A Portable Magnetic Particle Spectrometer for Future Rapid and Wash-Free Bioassays

Nowadays, there is an increasing demand for more accessible routine diagnostics for patients with respect to high accuracy, ease of use, and low cost. However, the quantitative and high accuracy bioassays in large hospitals and laboratories usually require trained technicians and equipment that is both bulky and expensive. In addition, the multistep bioassays and long turnaround time could severely affect the disease surveillance and control especially in pandemics such as influenza and COVID-19. In view of this, a portable, quantitative bioassay device will be valuable in regions with scarce medical resources and help relieve burden on local healthcare systems. Herein, we introduce the MagiCoil diagnostic device, an inexpensive, portable, quantitative, and rapid bioassay platform based on the magnetic particle spectrometer (MPS) technique. MPS detects the dynamic magnetic responses of magnetic nanoparticles (MNPs) and uses the harmonics from oscillating MNPs as metrics for sensitive and quantitative bioassays. This device does not require trained technicians to operate and employs a fully automatic, one-step, and wash-free assay with a user friendly smartphone interface. Using a streptavidin-biotin binding system as a model, we show that the detection limit of the current portable device for streptavidin is 64 nM (equal to 5.12 pmole). In addition, this MPS technique is very versatile and allows for the detection of different diseases just by changing the surface modifications on MNPs. Although MPS-based bioassays show high sensitivities as reported in many literatures, at the current stage, this portable device faces insufficient sensitivity and needs further improvements. It is foreseen that this kind of portable device can transform the multistep, laboratory-based bioassays to one-step field testing in nonclinical settings such as schools, homes, offices, etc.

An innovative prussian blue nanocubes decomposition-assisted signal amplification strategy suitable for competitive lateral flow immunoassay to sensitively detect aflatoxin B1

A prussian blue nanocubes decomposition-assisted signal amplification strategy for competitive lateral flow immunoassay (PBNCD-SALFIA) was innovatively proposed to analyze aflatoxin B₁ (AFB₁) in foodstuffs. The signal was amplified on account of the PBNCs can degrade and fade under alkaline condition, which could weak the color of the test- and control-lines, thereby improving the sensitivity of the sensor. The strategy was technically-simple, just using NaOH as an amplifier can realize signal amplification in the competition assay. Under optimized conditions, the enhanced strip exhibited excellent specificity and sensitivity in AFB₁ monitoring with a detection limit of 23 pg/mL, which was approximately 4- and 8-folds lower than those of PBNCs-LFIA (90 pg/mL) and conventional gold nanoparticles-LFIA (175 pg/mL), respectively. Taking the advantage of the color-fading, this platform revealing the lowest detectable concentration of 0.184, 0.368 and 0.184 μg/kg for AFB₁ in corn, peanut and pumpkin seed within 58 min, separately, showing reliable results.

Magnetic-Nanosensor-Based Virus and Pathogen Detection Strategies before and during COVID-19

The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19), is a threat to the global healthcare system and economic security. As of July 2020, no specific drugs or vaccines are yet available for COVID-19; a fast and accurate diagnosis for SARS-CoV-2 is essential in slowing the spread of COVID-19 and for efficient implementation of control and containment strategies. Magnetic nanosensing is an emerging topic representing the frontiers of current biosensing and magnetic areas. The past decade has seen rapid growth in applying magnetic tools for biological and biomedical applications. Recent advances in magnetic nanomaterials and nanotechnologies have transformed current diagnostic methods to nanoscale and pushed the detection limit to early-stage disease diagnosis. Herein, this review covers the literature of magnetic nanosensors for virus and pathogen detection before COVID-19. We review popular magnetic nanosensing techniques including magnetoresistance, magnetic particle spectroscopy, and nuclear magnetic resonance. Magnetic point-of-care diagnostic kits are also reviewed aiming at developing plug-and-play diagnostics to manage the SARS-CoV-2 outbreak as well as preventing future epidemics. In addition, other platforms that use magnetic nanomaterials as auxiliary tools for enhanced pathogen and virus detection are also covered. The goal of this review is to inform the researchers of diagnostic and surveillance platforms for SARS-CoV-2 and their performances.

Metal-polydopamine framework based lateral flow assay for high sensitive detection of tetracycline in food samples

Gold nanoparticles (AuNPs)-based lateral flow assay (LFA) enables a rapid detection of tetracycline (TET) in food samples but suffers from low sensitivity. Herein, metal-polydopamine framework (MPF), as a label, was employed to load monoclonal antibodies (mAbs) directly as the probe in LFA for highly sensitive sensing of TET. Combining zeolitic imidazolate framework (ZIF-67) and polydopamine (PDA), a stable MPF with large size, well water-dispersible, excellent affinity and optical properties was prepared through a versatile layer-by-layer assembly (LLA) strategy. Under optimized conditions, the biosensor (MPF-LFA) exhibited a great linear relationship in the range of 0.09-6 ng/mL and a detection limit of 0.045 ng/mL for TET detection, which was over 66-fold more sensitive than traditional AuNPs based LFA. Furthermore, the MPF-LFA was successfully applied to the screening of TET in fish, chicken, milk and shrimp samples with satisfied recoveries from 91% to 114%.

Data on characterization of glass biochips and validation of the label-free biosensor for detection of autoantibodies in human serum

The data represent in-depth characterization of a novel method for highly sensitive simultaneous measuring in human serum of both critical parameters of autoantibodies: concentration and native kinetics. The latter refers to autoantibody interaction with free, not immobilized, antigen. The method and related biosensors are based on the spectral-correlation and spectral-phase interferometry. The data cover: multi-factor optimization and quantitative characterization of the developed affordable single-used biochips, including X-ray photoelectron spectroscopy (XPS) control of chemical modifications of the surface during fabrication; antibody screening; optimization and verification of protocols for label-free biosensing in human serum; mathematical model for fitting experimental data and calculation of kinetic constants of interaction of autoantibodies with free antigen; comprehensive verification of the method specificity; correlation between the data obtained with the developed biosensor and with enzyme linked immunosorbent assay (ELISA); comparison of analytical characteristics of the developed biosensor with the most advanced label-based methods. The data importance is confirmed by a companion paper (DOI 10.1016/j.bios.2020.112187), which shows that the combination of mentioned autoantibody parameters is promising for more accurate criteria for early diagnostics and efficient therapy of autoimmune disorders. The obtained data can be used in development of a wide range of biosensors, both label-free and based on various labels.

Application of Zero-Dimensional Nanomaterials in Biosensing

Zero-dimensional (0D) nanomaterials, including graphene quantum dots (GQDs), carbon quantum dots (CQDs), fullerenes, inorganic quantum dots (QDs), magnetic nanoparticles (MNPs), noble metal nanoparticles, upconversion nanoparticles (UCNPs) and polymer dots (Pdots), have attracted extensive research interest in the field of biosensing in recent years. Benefiting from the ultra-small size, quantum confinement effect, excellent physical and chemical properties and good biocompatibility, 0D nanomaterials have shown great potential in ion detection, biomolecular recognition, disease diagnosis and pathogen detection. Here we first introduce the structures and properties of different 0D nanomaterials. On this basis, recent progress and application examples of 0D nanomaterials in the field of biosensing are discussed. In the last part, we summarize the research status of 0D nanomaterials in the field of biosensing and anticipate the development prospects and future challenges in this field.

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.

Nanoparticle Beacons: Supersensitive Smart Materials with On/Off-Switchable Affinity to Biomedical Targets

Smart materials that can switch between different states under the influence of chemical triggers are highly demanded in biomedicine, where specific responsiveness to biomarkers is imperative for precise diagnostics and therapy. Superior selectivity of drug delivery to malignant cells may be achieved with the nanoagents that stay "inert" until "activation" by the characteristic profile of microenvironment cues (e.g., tumor metabolites, angiogenesis factors, microRNA/DNA, etc.). However, despite a wide variety and functional complexity of smart material designs, their real-life applications are hindered by very limited sensitivity to inputs. Here, we present ultrasensitive smart nanoagents with input-dependent On/Off switchable affinity to a biomedical target based on a combination of gold nanoparticles with low-energy polymer structures. In the proposed method, a nanoparticle-based agent is surface coated with a custom designed flexible polymer chain, which has an input-switchable structure that regulates accessibility of the terminal receptor for target binding. Implementation of the concept with a DNA-model of such polymer has yielded nanoagents that have input-dependent cell-targeting capabilities and responsiveness to as little as 30 fM of DNA input in 15 min lateral flow assay. Thus, we show that surface phenomena can augment nanoagents with capability for switchable affinity without compromising the sensitivity to inputs. The proposed approach is promising for development of next-generation theranostic agents and ultrasensitive nanosensors for point-of-care diagnostics.

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.