Magnetic Nanoparticles and microNMR for Diagnostic Applications

Integrated microHall magnetometer to measure the magnetic properties of nanoparticles

Magnetic nanoparticles (MNPs) are widely used in biomedical and clinical applications, including medical imaging, therapeutics, and biological sample processing. Rapid characterization of MNPs, notably their magnetic moments, should facilitate optimization of particle synthesis and accelerate assay development. Here, we report a compact and low-cost magnetometer for fast, on-site MNP characterization. Termed integrated microHall magnetometer (iHM), our device was fabricated using standard semiconductor processes: an array of Hall sensors, transistor switches, and amplifiers were integrated into a single chip, thus improving the detection sensitivity and facilitating chip operation. By applying the iHM, we demonstrate versatile magnetic assays. We measured the magnetic susceptibility and moments of MNPs using small sample amounts (∼10 pL), identified different MNP compositions in mixtures, and detected MNP-labeled single cells.

Giant Magnetoresistive Biosensor Array for Detecting Magnetorelaxation

In this paper, a time-domain magnetorelaxometry biosensing scheme is presented using giant magnetoresistive (GMR) sensors to measure the fast relaxation response of superparamagnetic magnetic nanoparticles (MNPs) in a pulsed magnetic field. The system consists of an 8 × 10 GMR sensor array, a Helmholtz coil, an electromagnet driver, and an integrator-based analog front-end needed to capture the fast relaxation dynamics of MNPs. A custom designed electromagnet driver and Helmholtz coil improve the switch-off speed to >5 Oe/μs, limiting the dead zone time to <10 μs, and thus enables the system to monitor fast relaxation processes of 30 nm MNPs. A magnetic correlated double sampling technique is proposed to reduce sensor-to-sensor variation by 99.98% while also reducing temperature drift, circuit offset, and nonlinearity below the noise level. An optimum integration time is calculated and experimentally verified to maximize the SNR. Experiments with dried MNPs have shown successful relaxation detection, and immunoassay experiments have demonstrated their binding kinetics.

Iron oxide nanoclusters for T 1 magnetic resonance imaging of non-human primates

Iron-oxide-based contrast agents for magnetic resonance imaging (MRI) had been clinically approved in the United States and Europe, yet most of these nanoparticle products were discontinued owing to failures to meet rigorous clinical requirements. Significant advances have been made in the synthesis of magnetic nanoparticles and their biomedical applications, but several major challenges remain for their clinical translation, in particular large-scale and reproducible synthesis, systematic toxicity assessment, and their preclinical evaluation in MRI of large animals. Here, we report the results of a toxicity study of iron oxide nanoclusters of uniform size in large animal models, including beagle dogs and the more clinically relevant macaques. We also show that iron oxide nanoclusters can be used as T ₁ MRI contrast agents for high-resolution magnetic resonance angiography in beagle dogs and macaques, and that dynamic MRI enables the detection of cerebral ischaemia in these large animals. Iron oxide nanoclusters show clinical potential as next-generation MRI contrast agents.

Nanotechnology-Enhanced No-Wash Biosensors for in Vitro Diagnostics of Cancer

In vitro biosensors have been an integral component for early diagnosis of cancer in the clinic. Among them, no-wash biosensors, which only depend on the simple mixing of the signal generating probes and the sample solution without additional washing and separation steps, have been found to be particularly attractive. The outstanding advantages of facile, convenient, and rapid response of no-wash biosensors are especially suitable for point-of-care testing (POCT). One fast-growing field of no-wash biosensor design involves the usage of nanomaterials as signal amplification carriers or direct signal generating elements. The analytical capacity of no-wash biosensors with respect to sensitivity or limit of detection, specificity, stability, and multiplexing detection capacity is largely improved because of their large surface area, excellent optical, electrical, catalytic, and magnetic properties. This review provides a comprehensive overview of various nanomaterial-enhanced no-wash biosensing technologies and focuses on the analysis of the underlying mechanism of these technologies applied for the early detection of cancer biomarkers ranging from small molecules to proteins, and even whole cancerous cells. Representative examples are selected to demonstrate the proof-of-concept with promising applications for in vitro diagnostics of cancer. Finally, a brief discussion of common unresolved issues and a perspective outlook on the field are provided.

Artificial local magnetic field inhomogeneity enhances T2 relaxivity

Clustering of magnetic nanoparticles (MNPs) is perhaps the most effective, yet intriguing strategy to enhance T₂ relaxivity in magnetic resonance imaging (MRI). However, the underlying mechanism is still not fully understood and the attempts to generalize the classic outersphere theory from single particles to clusters have been found to be inadequate. Here we show that clustering of MNPs enhances local field inhomogeneity due to reduced field symmetry, which can be further elevated by artificially involving iron oxide NPs with heterogeneous geometries in terms of size and shape. The r₂ values of iron oxide clusters and Landau–Lifshitz–Gilbert simulations confirmed our hypothesis, indicating that solving magnetic field inhomogeneity may become a powerful way to build correlation between magnetization and T₂ relaxivity of MNPs, especially magnetic clusters. This study provides a simple yet distinct mechanism to interpret T₂ relaxivity of MNPs, which is crucial to the design of high-performance MRI contrast agents.

The signal detected in magnetic resonance imaging comes from the relaxation of proton nuclear magnetization. Here, Zhou et al. introduce magnetic field inhomogeneity as a parameter to design iron oxide nanoparticle clusters to enhance the relaxation rate of nearby protons, thereby increasing image contrast.

Toward biotechnology in space: High-throughput instruments for in situ biological research beyond Earth

Space biotechnology is a nascent field aimed at applying tools of modern biology to advance our goals in space exploration. These advances rely on our ability to exploit in situ high throughput techniques for amplification and sequencing DNA, and measuring levels of RNA transcripts, proteins and metabolites in a cell. These techniques, collectively known as "omics" techniques have already revolutionized terrestrial biology. A number of on-going efforts are aimed at developing instruments to carry out "omics" research in space, in particular on board the International Space Station and small satellites. For space applications these instruments require substantial and creative reengineering that includes automation, miniaturization and ensuring that the device is resistant to conditions in space and works independently of the direction of the gravity vector. Different paths taken to meet these requirements for different "omics" instruments are the subjects of this review. The advantages and disadvantages of these instruments and technological solutions and their level of readiness for deployment in space are discussed. Considering that effects of space environments on terrestrial organisms appear to be global, it is argued that high throughput instruments are essential to advance (1) biomedical and physiological studies to control and reduce space-related stressors on living systems, (2) application of biology to life support and in situ resource utilization, (3) planetary protection, and (4) basic research about the limits on life in space. It is also argued that carrying out measurements in situ provides considerable advantages over the traditional space biology paradigm that relies on post-flight data analysis.

Smart materials on the way to theranostic nanorobots: Molecular machines and nanomotors, advanced biosensors, and intelligent vehicles for drug delivery

BACKGROUND

Theranostics, a fusion of two key parts of modern medicine - diagnostics and therapy of the organism's disorders, promises to bring the efficacy of medical treatment to a fundamentally new level and to become the basis of personalized medicine. Extrapolating today's progress in the field of smart materials to the long-run prospect, we can imagine future intelligent agents capable of performing complex analysis of different physiological factors inside the living organism and implementing a built-in program thereby triggering a series of therapeutic actions. These agents, by analogy with their macroscopic counterparts, can be called nanorobots. It is quite obscure what these devices are going to look like but they will be more or less based on today's achievements in nanobiotechnology.

SCOPE OF REVIEW

The present Review is an attempt to systematize highly diverse nanomaterials, which may potentially serve as modules for theranostic nanorobotics, e.g., nanomotors, sensing units, and payload carriers.

MAJOR CONCLUSIONS

Biocomputing-based sensing, externally actuated or chemically "fueled" autonomous movement, swarm inter-agent communication behavior are just a few inspiring examples that nanobiotechnology can offer today for construction of truly intelligent drug delivery systems.

GENERAL SIGNIFICANCE

The progress of smart nanomaterials toward fully autonomous drug delivery nanorobots is an exciting prospect for disease treatment. Synergistic combination of the available approaches and their further development may produce intelligent drugs of unmatched functionality.

Multifunctional Magnetic Particles for Combined Circulating Tumor Cells Isolation and Cellular Metabolism Detection

We for the first time demonstrate multi-functional magnetic particles based rare cell isolation combined with the downstream laser desorption/ionization mass spectrometry (LDI-MS) to measure the metabolism of enriched circulating tumor cells (CTCs). The characterization of CTCs metabolism plays a significant role in understanding the tumor microenvironment, through exploring the diverse cellular process. However, characterizing cell metabolism is still challenging due to the low detection sensitivity, high sample complexity, and tedious preparation procedures, particularly for rare cells analysis in clinical study. Here we conjugate ferric oxide magnetic particles with anti-EpCAM on the surface for specific, efficient enrichment of CTCs from PBS and whole blood with cells concentration of 6-100 cells per mL. Moreover, these hydrophilic particles as matrix enable sensitive and selective LDI-MS detection of small metabolites (MW<500 Da) in complex bio-mixtures and can be further coupled with isotopic quantification to monitor selected molecules metabolism of ~50 CTCs. Our unique approach couples the immunomagnetic separation of CTCs and LDI-MS based metabolic analysis, which represents a key step forward for downstream metabolites analysis of rare cells to investigate the biological features of CTCs and their cellular responses in both pathological and physiological phenomena.

Homogeneous Biosensing Based on Magnetic Particle Labels

The growing availability of biomarker panels for molecular diagnostics is leading to an increasing need for fast and sensitive biosensing technologies that are applicable to point-of-care testing. In that regard, homogeneous measurement principles are especially relevant as they usually do not require extensive sample preparation procedures, thus reducing the total analysis time and maximizing ease-of-use. In this review, we focus on homogeneous biosensors for the in vitro detection of biomarkers. Within this broad range of biosensors, we concentrate on methods that apply magnetic particle labels. The advantage of such methods lies in the added possibility to manipulate the particle labels by applied magnetic fields, which can be exploited, for example, to decrease incubation times or to enhance the signal-to-noise-ratio of the measurement signal by applying frequency-selective detection. In our review, we discriminate the corresponding methods based on the nature of the acquired measurement signal, which can either be based on magnetic or optical detection. The underlying measurement principles of the different techniques are discussed, and biosensing examples for all techniques are reported, thereby demonstrating the broad applicability of homogeneous in vitro biosensing based on magnetic particle label actuation.

Extracellular vesicle isolation and characterization: toward clinical application

Two broad categories of extracellular vesicles (EVs), exosomes and shed microvesicles (sMVs), which differ in size distribution as well as protein and RNA profiles, have been described. EVs are known to play key roles in cell-cell communication, acting proximally as well as systemically. This Review discusses the nature of EV subtypes, strategies for isolating EVs from both cell-culture media and body fluids, and procedures for quantifying EVs. We also discuss proteins selectively enriched in exosomes and sMVs that have the potential for use as markers to discriminate between EV subtypes, as well as various applications of EVs in clinical diagnosis.

Folic acid-targeted iron oxide nanoparticles as contrast agents for magnetic resonance imaging of human ovarian cancer

BACKGROUND

Improved methods for the early and specific detection of ovarian cancer are needed.

METHODS

In this experimental study, we used folic acid (FA)-targeted iron oxide (Fe3O4) nanoparticles (NPs) as a T2-negative contrast agent for magnetic resonance (MR) imaging to accurately detect ovarian cancer tissues in an intraperitoneal xenograft tumor model. Human serous ovarian cell line (Skov-3), with overexpressed FA receptors, was chosen as the targeted tumor cell mode. For in vivo experiments, the cells were injected intraperitoneally into nude mice to produce intraabdominal ovarian cancers. FA-targeted and non-targeted Fe3O4 NPs were prepared.

RESULTS

FA-targeted Fe3O4 NPs with a mean size of 9.2 ± 1.7 nm have a negligible cytotoxicity to human serous ovarian cell line (Skov-3). Importantly, the results of cellular uptake suggested that FA-targeted Fe3O4 NPs have a targeting specificity to Skov-3 cells overexpressing FA receptors. FA-targeted Fe3O4 NPs could be specifically localized by magnetic resonance (MR) imaging to the intraperitoneal human ovarian carcinoma tissues, as documented by a statistically significant difference (p = 0.002, n = 3) in T2 signal intensities of xenograft tumor tissues when injected with FA-targeted and non-targeted Fe3O4 NPs at 4 h post-injection.

CONCLUSION

FA-targeted Fe3O4 NPs appear to be promising agents for the detection of human ovarian carcinoma by MR imaging, and possibly also for the hyperthermal treatment of the tumors.

The use of magnetic nanoparticles in cancer theranostics: Toward handheld diagnostic devices

Magnetic nanoparticles are frequently used in a wide range of biomedical applications. In the first part of this review the most commonly used preparation and surface coating approaches of MNPs are briefly summarized including multifunctional hybrid particles. The second part gives a detailed overview of the use of MNPs in "traditional" biomedical applications related to cancer theranostics, like magnetic resonance imaging, drug delivery, hyperthermia and also their applicability in the next generation of point of care devices based on micro nuclear magnetic resonance and surface enhanced Raman spectroscopic detection technology that all can be routinely applied in everyday clinical practice.

Assaying Carcinoembryonic Antigens by Normalized Saturation Magnetization

Biofunctionalized magnetic nanoparticles (BMNs) that provide unique advantages have been extensively used to develop immunoassay methods. However, these developed magnetic methods have been used only for specific immunoassays and not in studies of magnetic characteristics of materials. In this study, a common vibration sample magnetometer (VSM) was used for the measurement of the hysteresis loop for different carcinoembryonic antigens (CEA) concentrations (Φ CEA) based on the synthesized BMNs with anti-CEA coating. Additionally, magnetic parameters such as magnetization (M), remanent magnetization (M R), saturation magnetization (M S), and normalized parameters (ΔM R/M R and ΔM S/M S) were studied. Here, ΔM R and ΔM s were defined as the difference between any Φ CEA and zero Φ CEA. The parameters M, ΔM R, and ΔM S increased with Φ CEA, and ΔM S showed the largest increase. Magnetic clusters produced by the conjugation of the BMNs to CEAs showed a ΔM S greater than that of BMNs. Furthermore, the relationship between ΔM S/M S and Φ CEA could be described by a characteristic logistic function, which was appropriate for assaying the amount of CEAs. This analytic ΔM S/M S and the BMNs used in general magnetic immunoassays can be used for upgrading the functions of the VSM and for studying the magnetic characteristics of materials.

Nanotechnology and regenerative therapeutics in plastic surgery: The next frontier

The rapid ascent of nanotechnology and regenerative therapeutics as applied to medicine and surgery has seen an exponential rise in the scale of research generated in this field. This is evidenced not only by the sheer volume of papers dedicated to nanotechnology but also in a large number of new journals dedicated to nanotechnology and regenerative therapeutics specifically to medicine and surgery. Aspects of nanotechnology that have already brought benefits to these areas include advanced drug delivery platforms, molecular imaging and materials engineering for surgical implants. Particular areas of interest include nerve regeneration, burns and wound care, artificial skin with nanoelectronic sensors and head and neck surgery. This study presents a review of nanotechnology and regenerative therapeutics, with focus on its applications and implications in plastic surgery.

Exosomes serve as tumour markers for personalized diagnostics owing to their important role in cancer metastasis

Exosomes, membrane vesicles of 40–100 nm in diameter, are derived from endosomes in various cells. The bioactive molecules specifically packed into exosomes can be horizontally transferred into recipient cells changing their biological properties, by which tumour cells continuously modify their surrounding microenvironment and distant target cells favouring cancer metastasis. It has been suspected for a long time that exosomes participate in the whole process of tumour metastasis. Although there is much unknown and many controversies in the role of cancer exosome, the major contribution of tumour-associated exosomes to different steps of cancer metastasis are demonstrated in this review. Mainly because these exosomes are easily accessible and capable of representing their parental cells, exosomes draw much attention as a promising biomarker for tumour screening, diagnosis and prognosis. Currently, researchers have found numerous biomarkers in exosomes with great potential to be utilized in personalized medicine. In this article, we summarize the roles of biomarkers, which are validated by clinical samples. Even though many conundrums remain, such as exosome extraction, large multicentre validation of biomarkers and data interpretation, exosomes are certain to be used in clinical practice in the near future as the field rapidly expands.

Exosomes and Their Role in the Life Cycle and Pathogenesis of RNA Viruses

Exosomes are membrane-enclosed vesicles actively released into the extracellular space, whose content reflect the physiological/pathological state of the cells they originate from. These vesicles participate in cell-to-cell communication and transfer of biologically active proteins, lipids, and RNAs. Their role in viral infections is just beginning to be appreciated. RNA viruses are an important class of pathogens and affect millions of people worldwide. Recent studies on Human Immunodeficiency Virus (HIV), Hepatitis C Virus (HCV), human T-cell lymphotropic virus (HTLV), and Dengue Virus (DENV) have demonstrated that exosomes released from infected cells harbor and deliver many regulatory factors including viral RNA and proteins, viral and cellular miRNA, and other host functional genetic elements to neighboring cells, helping to establish productive infections and modulating cellular responses. Exosomes can either spread or limit an infection depending on the type of pathogen and target cells, and can be exploited as candidates for development of antiviral or vaccine treatments. This review summarizes recent progress made in understanding the role of exosomes in RNA virus infections with an emphasis on their potential contribution to pathogenesis.

Selection of HBsAg-Specific DNA Aptamers Based on Carboxylated Magnetic Nanoparticles and Their Application in the Rapid and Simple Detection of Hepatitis B Virus Infection

Aptamers are short single-stranded DNA or RNA oligonucleotides and can be selected from synthetic combinatorial libraries in vitro. They have a high binding affinity and specificity for their targets. Agarose gels, nitrocellulose membranes, and adsorptive microplates are often used as carriers to immobilize targets in the SELEX (systematic evolution of ligands by exponential enrichment) process, but the subsequent separation step is tedious and time-consuming. Therefore, we used magnetic nanoparticles (MNPs) as carriers to immobilize the target, hepatitis B surface antigen (HBsAg), which is convenient for fast magnetic separation. In this study, we first selected DNA aptamers against HBsAg by immobilizing HBsAg on the surface of carboxylated MNPs. The ssDNA library of each selection round was prepared by asymmetric PCR amplification for the next selection round. To obtain aptamer sequences, the final selected products were purified by gel electrophoresis, then cloned, and sequenced. DNA aptamers that specifically bind to HBsAg were successfully obtained after 13 selection rounds. The selected aptamers were used to construct a chemiluminescence aptasensor based on magnetic separation and immunoassay to detect HBsAg from pure protein or actual serum samples. There was a linear relationship between HBsAg concentration and chemiluminescent intensity in the range of 1-200 ng/mL. The aptasensor worked well even in the presence of interfering substances and was highly specific in the detection of HBsAg in serum samples, with a detection limit 0.1 ng/mL lower than the 0.5 ng/mL limit of an ELISA in use at the hospital. This aptasensor can contribute to better detection of hepatitis B virus infection.

Toward routine detection of extracellular vesicles in clinical samples

The majority, if not all, of human cell types secrete extracellular vesicles (EVs) into their environment, at least partly as a means of intercellular communication. These secreted vesicles can be detected in most bodily fluids including blood, urine, and saliva. The number of secreted vesicles and their composition is altered in various pathological conditions, raising opportunities to exploit EVs as diagnostic and/or prognostic biomarkers. For this to become a reality, it is important to reach consensus regarding the standardization of protocols for sample collection, EV isolation, handling, and storage for valid comparison and interpretation of measurements. Depending on the information required, there are several detection options including EV number and size distribution, molecular surface markers, procoagulation activity, and RNA content. For these purposes, different techniques are currently utilized or under development. This review discusses the techniques that have the potential to become standard EV detection methods in a clinical diagnostic setting. In addition to the accuracy of the detection technique, other factors such as high-throughput, cost-effectiveness, time consumption, and required operator skill are important to consider. A combination of increasing fundamental knowledge, technological progress, standardization of sample collection, and processing protocols is required for EVs to become reliable predictors of altered physiology or development of disease suitable for routine clinical diagnostics. Cancer and (cardio)vascular disorders are examples of pathologies where EV detection may be applied in the near future for diagnosis and/or prognosis.

Using bio-functionalized magnetic nanoparticles and dynamic nuclear magnetic resonance to characterize the time-dependent spin-spin relaxation time for sensitive bio-detection

In this work, we report the use of bio-functionalized magnetic nanoparticles (BMNs) and dynamic magnetic resonance (DMR) to characterize the time-dependent spin-spin relaxation time for sensitive bio-detection. The biomarkers are the human C-reactive protein (CRP) while the BMNs are the anti-CRP bound onto dextran-coated Fe₃O₄ particles labeled as Fe₃O₄-antiCRP. It was found the time-dependent spin-spin relaxation time, T₂, of protons decreases as time evolves. Additionally, the ΔT₂ of of protons in BMNs increases as the concentration of CRP increases. We attribute these to the formation of the magnetic clusters that deteriorate the field homogeneity of nearby protons. A sensitivity better than 0.1 μg/mL for assaying CRP is achieved, which is much higher than that required by the clinical criteria (0.5 mg/dL). The present MR-detection platform shows promise for further use in detecting tumors, viruses, and proteins.

A reusable aptamer-based evanescent wave all-fiber biosensor for highly sensitive detection of Ochratoxin A

Although aptamer-based biosensors have attracted ever-increasing attentions and found potential applications in a wide range of areas, they usually adopted the assay protocol of immobilizing DNA probe (e.g., aptamer, aptamer-complementary oligonucleotides) on a solid sensing surface, making it critical and challengeable to keep the integration of nucleic acid surface during the regeneration and the restoration to its original DNA probe form after repeated uses. In order to address the issue, we report a novel aptamer-based biosensing strategy based on an evanescent wave all-fiber (EWA) platform. In a simple target capturing step using aptamer-functionalized magnetic microbeads, signal probes conjugated with streptavidin are released and further detected by a EWA biosensor via a facial dethiobiotin-streptavidin recognition. Apart from the inherent advantages of aptamer-based evanescent wave biosensors (e.g. target versatility, sensitivity, selectivity and portability), the proposed strategy exhibits a high stability and remarkable reusability over other aptasensors. Under the optimized conditions, the typical calibration curve obtained for Ochratoxin A has a detection limit of 3nM with a linear response ranging from 6nM to 500nM. The dethiobiotin-streptavidin sensing surface instead of the traditional nucleic acid one can be reused for over 300 times without losing sensitivity.

Magnetic sensing technology for molecular analyses

Magnetic biosensors, based on nanomaterials and miniature electronics, have emerged as a powerful diagnostic platform. Benefiting from the inherently negligible magnetic background of biological objects, magnetic detection is highly selective even in complex biological media. The sensing thus requires minimal sample purification and yet achieves a high signal-to-background contrast. Moreover, magnetic sensors are also well-suited for miniaturization to match the size of biological targets, which enables sensitive detection of rare cells and small amounts of molecular markers. We herein summarize recent advances in magnetic sensing technologies, with an emphasis on clinical applications in point-of-care settings. Key components of sensors, including magnetic nanomaterials, labeling strategies and magnetometry, are reviewed.

Current methods for the isolation of extracellular vesicles

Extracellular vesicles (EVs), including microvesicles and exosomes, are nano- to micron-sized vesicles, which may deliver bioactive cargos that include lipids, growth factors and their receptors, proteases, signaling molecules, as well as mRNA and non-coding RNA, released from the cell of origin, to target cells. EVs are released by all cell types and likely induced by mechanisms involved in oncogenic transformation, environmental stimulation, cellular activation, oxidative stress, or death. Ongoing studies investigate the molecular mechanisms and mediators of EVs-based intercellular communication at physiological and oncogenic conditions with the hope of using this information as a possible source for explaining physiological processes in addition to using them as therapeutic targets and disease biomarkers in a variety of diseases. A major limitation in this evolving discipline is the hardship and the lack of standardization for already challenging techniques to isolate EVs. Technical advances have been accomplished in the field of isolation with improving knowledge and emerging novel technologies, including ultracentrifugation, microfluidics, magnetic beads and filtration-based isolation methods. In this review, we will discuss the latest advances in methods of isolation methods and production of clinical grade EVs as well as their advantages and disadvantages, and the justification for their support and the challenges that they encounter.

SpyLigase peptide-peptide ligation polymerizes affibodies to enhance magnetic cancer cell capture

Individual proteins can now often be modified with atomic precision, but there are still major obstacles to connecting proteins into larger assemblies. To direct protein assembly, ideally, peptide tags would be used, providing the minimal perturbation to protein function. However, binding to peptides is generally weak, so assemblies are unstable over time and disassemble with force or harsh conditions. We have recently developed an irreversible protein-peptide interaction (SpyTag/SpyCatcher), based on a protein domain from Streptococcus pyogenes, that locks itself together via spontaneous isopeptide bond formation. Here we develop irreversible peptide-peptide interaction, through redesign of this domain and genetic dissection into three parts: a protein domain termed SpyLigase, which now ligates two peptide tags to each other. All components expressed efficiently in Escherichia coli and peptide tags were reactive at the N terminus, at the C terminus, or at internal sites. Peptide-peptide ligation enabled covalent and site-specific polymerization of affibodies or antibodies against the tumor markers epidermal growth factor receptor (EGFR) and HER2. Magnetic capture of circulating tumor cells (CTCs) is one of the most promising approaches to improve cancer prognosis and management, but CTC capture is limited by inefficient recovery of cells expressing low levels of tumor antigen. SpyLigase-assembled protein polymers made possible the isolation of cancerous cells expressing lower levels of tumor antigen and should have general application in enhancing molecular capture.

Magnetic nanosensors optimized for rapid and reversible self-assembly

Magnetic nanoparticle-based sensors for MRI have been accelerated to a timescale of seconds using densely-functionalized particles of small size. Parameters that increase response rates also result in large nuclear magnetic relaxation rate and light scattering changes, allowing signals to be detected almost immediately after changes in calcium concentration.

Microchip-based detection of magnetically labeled cancer biomarkers

Micro-magnetic sensing and actuation have emerged as powerful tools for the diagnosis and monitoring of cancer. These technologies can be miniaturized and integrated onto compact, microfluidic platforms, enabling molecular diagnostics to be performed in practical clinical settings. Molecular targets tagged with magnetic nanoparticles can be detected with high sensitivity directly in unprocessed clinical samples (e.g. blood, sputum) due to the inherently negligible magnetic susceptibility of biological material. As a result, magnetic microchip-based diagnostics have been applied with great success to the isolation and detection of rare cells and the measurement of sparse soluble proteins. In this paper, we review recent advances in microchip-based detection of magnetically labeled biomarkers and their translation to clinical applications in cancer.

Magic-angle spinning solid-state multinuclear NMR on low-field instrumentation

Mobile and cost-effective NMR spectroscopy exploiting low-field permanent magnets is a field of tremendous development with obvious applications for arrayed large scale analysis, field work, and industrial screening. So far such demonstrations have concentrated on relaxation measurements and lately high-resolution liquid-state NMR applications. With high-resolution solid-state NMR spectroscopy being increasingly important in a broad variety of applications, we here introduce low-field magic-angle spinning (MAS) solid-state multinuclear NMR based on a commercial ACT 0.45 T 62 mm bore Halbach magnet along with a homebuilt FPGA digital NMR console, amplifiers, and a modified standard 45 mm wide MAS probe for 7 mm rotors. To illustrate the performance of the instrument and address cases where the low magnetic field may offer complementarity to high-field NMR experiments, we demonstrate applications for (23)Na MAS NMR with enhanced second-order quadrupolar coupling effects and (31)P MAS NMR where reduced influence from chemical shift anisotropy at low field may facilitate determination of heteronuclear dipole-dipole couplings.

Molecular sensing with magnetic nanoparticles using magnetic spectroscopy of nanoparticle Brownian motion

Functionalized magnetic nanoparticles (mNPs) have shown promise in biosensing and other biomedical applications. Here we use functionalized mNPs to develop a highly sensitive, versatile sensing strategy required in practical biological assays and potentially in vivo analysis. We demonstrate a new sensing scheme based on magnetic spectroscopy of nanoparticle Brownian motion (MSB) to quantitatively detect molecular targets. MSB uses the harmonics of oscillating mNPs as a metric for the freedom of rotational motion, thus reflecting the bound state of the mNP. The harmonics can be detected in vivo from nanogram quantities of iron within 5s. Using a streptavidin-biotin binding system, we show that the detection limit of the current MSB technique is lower than 150 pM (0.075 pmole), which is much more sensitive than previously reported techniques based on mNP detection. Using mNPs conjugated with two anti-thrombin DNA aptamers, we show that thrombin can be detected with high sensitivity (4 nM or 2 pmole). A DNA-DNA interaction was also investigated. The results demonstrated that sequence selective DNA detection can be achieved with 100 pM (0.05 pmole) sensitivity. The results of using MSB to sense these interactions, show that the MSB based sensing technique can achieve rapid measurement (within 10s), and is suitable for detecting and quantifying a wide range of biomarkers or analytes. It has the potential to be applied in variety of biomedical applications or diagnostic analyses.

Quaternized magnetic nanoparticles-fluorescent polymer system for detection and identification of bacteria

Nanomaterial-based 'chemical nose' sensor with sufficient sensing specificity is a useful analytical tool for the detection of toxicologically important substances in complicated biological systems. A sensor array containing three quaternized magnetic nanoparticles (q-MNPs)-fluorescent polymer systems has been designed to identify and quantify bacteria. The bacterial cell membranes disrupt the q-MNP-fluorescent polymer, generating unique fluorescence response array. The response intensity of the array is dependent on the level of displacement determined by the relative q-MNP-fluorescent polymer binding strength and bacteria cells-MNP interaction. These characteristic responses show a highly repeatable bacteria cells and can be differentiated by linear discriminant analysis (LDA). Based on the array response matrix from LDA, our approach has been used to measure bacteria with an accuracy of 87.5% for 10(7) cfu mL(-1) within 20 min. Combined with UV-vis measurement, the method can be successfully performed to identify and detect eight different pathogen samples with an accuracy of 96.8%. The measurement system has a potential for further applications and provides a facile and simple method for the rapid analysis of protein, DNA, and pathogens.

Molecular characterization of scant lung tumor cells using iron-oxide nanoparticles and micro-nuclear magnetic resonance

Advances in nanotechnology and microfluidics are enabling the analysis of small amounts of human cells. We tested whether recently developed micro-nuclear magnetic resonance (μNMR) technology could be leveraged for diagnosing pulmonary malignancy using fine needle aspirate (FNA) of primary lesions and/or peripheral blood samples. We enrolled a cohort of 35 patients referred for CT biopsy of primary pulmonary nodules, liver or adrenal masses and concurrently obtained FNA and peripheral blood samples. FNA sampling yielded sufficient material for μNMR analysis in 91% of cases and had a sensitivity and specificity of 91.6% and 100% respectively. Interestingly, among blood samples with positive circulating tumor cells (CTC), μNMR analysis of each patient's peripheral blood led to similar diagnosis (malignant vs benign) and differential diagnosis (lung malignancy subtype) in 100% and 90% (18/20) of samples, respectively. μNMR appears to be a valuable, non-invasive adjunct in the diagnosis of lung cancer.

FROM THE CLINICAL EDITOR

The authors of this study established that recently developed micro-nuclear magnetic resonance (μNMR) technology can be leveraged for diagnosing pulmonary malignancy using fine needle aspirate (FNA) of primary lesions and/or peripheral blood samples derived from 35 patients, suggesting practical clinical applicability of this technique.

Multifunctional superparamagnetic iron oxide nanoparticles: design, synthesis and biomedical photonic applications

Superparamagnetic iron oxide nanoparticles (SPIONs) have shown great promise in biomedical applications. In this review, we summarize the recent advances in the design and fabrication of core-shell and hetero-structured SPIONs and further outline some exciting developments and progresses of these multifunctional SPIONs for diagnosis, multimodality imaging, therapy, and biophotonics.

Multimodal iron oxide nanoparticles for hybrid biomedical imaging

Iron oxide core nanoparticles are attractive imaging agents because their material properties allow the tuning of pharmacokinetics as well as the attachment of multiple moieties to their surface. In addition to affinity ligands, these include fluorochromes and radioisotopes for detection with optical and nuclear imaging. As the iron oxide core can be detected by MRI, options for combining imaging modalities are manifold. Already, preclinical imaging strategies have combined noninvasive imaging with higher resolution techniques, such as intravital microscopy, to gain unprecedented insight into steady-state biology and disease. Going forward, hybrid iron oxide nanoparticles will help to merge modalities, creating a synergy that will enable imaging in basic research and, potentially, also in the clinic.

Superparamagnetic nanoparticle clusters for cancer theranostics combining magnetic resonance imaging and hyperthermia treatment

Superparamagnetic nanoparticles (SPIONs) could enable cancer theranostics if magnetic resonance imaging (MRI) and magnetic hyperthermia treatment (MHT) were combined. However, the particle size of SPIONs is smaller than the pores of fenestrated capillaries in normal tissues because superparamagnetism is expressed only at a particle size <10 nm. Therefore, SPIONs leak from the capillaries of normal tissues, resulting in low accumulation in tumors. Furthermore, MHT studies have been conducted in an impractical way: direct injection of magnetic materials into tumor and application of hazardous alternating current (AC) magnetic fields. To accomplish effective enhancement of MRI contrast agents in tumors and inhibition of tumor growth by MHT with intravenous injection and a safe AC magnetic field, we clustered SPIONs not only to prevent their leakage from fenestrated capillaries in normal tissues, but also for increasing their relaxivity and the specific absorption rate. We modified the clusters with folic acid (FA) and polyethylene glycol (PEG) to promote their accumulation in tumors. SPION clustering and cluster modification with FA and PEG were achieved simultaneously via the thiol-ene click reaction. Twenty-four hours after intravenous injection of FA- and PEG-modified SPION nanoclusters (FA-PEG-SPION NCs), they accumulated locally in cancer (not necrotic) tissues within the tumor and enhanced the MRI contrast. Furthermore, 24 h after intravenous injection of the NCs, the mice were placed in an AC magnetic field with H = 8 kA/m and f = 230 kHz (Hf = 1.8×10⁹ A/m∙s) for 20 min. The tumors of the mice underwent local heating by application of an AC magnetic field. The temperature of the tumor was higher than the surrounding tissues by ≈6°C at 20 min after treatment. Thirty-five days after treatment, the tumor volume of treated mice was one-tenth that of the control mice. Furthermore, the treated mice were alive after 12 weeks; control mice died up to 8 weeks after treatment.

Comparison of select cancer biomarkers in human circulating and bulk tumor cells using magnetic nanoparticles and a miniaturized micro-NMR system

Circulating tumor cells (CTC) harvested from peripheral blood have received significant interest as sources for serial sampling to gauge treatment efficacy. Nanotechnology and microfluidic based approaches are emerging to facilitate such analyses. While of considerable clinical importance, there is little information on how similar or different CTCs are from their shedding bulk tumors. In this clinical study, paired tumor fine needle aspirate and peripheral blood samples were obtained from cancer patients during image-guided biopsy. Using targeted magnetic nanoparticles and a point-of-care micro-NMR system, we compared selected biomarkers (EpCAM, EGFR, HER-2 and vimentin) in both CTC and fine needle biopsies of solid epithelial cancers. We show a weak correlation between each paired sample, suggesting that use of CTC as "liquid biopsies" and proxies to metastatic solid lesions could be misleading.

FROM THE CLINICAL EDITOR

In this clinical study, paired tumor fine needle aspirate and peripheral blood samples were obtained from patients with solid epithelial cancers during image-guided biopsy. Using targeted magnetic nanoparticles and a point-of-care micro-NMR system, the authors compared selected biomarkers in both circulating tumor cells (CTC) and fine needle biopsies, demonstrating a weak correlation between each paired sample, suggesting that use of CTC could be misleading in this context.

Radiofrequency microcoils for magnetic resonance imaging and spectroscopy

Small radiofrequency coils, often termed "microcoils", have found extensive use in many areas of magnetic resonance. Their advantageous properties include a very high intrinsic sensitivity, a high (several MHz) excitation and reception bandwidth, the fact that large arrays can fit within the homogeneous volume of the static magnetic field, and the very high resonance frequencies (several GHz) that can be achieved. This review concentrates on recent developments in the construction of single and multiple RF microcoil systems, and new types of experiments that can be performed using such assemblies.

Nanotheranostics for personalized medicine

Nanotheranostics, the integration of diagnostic and therapeutic function in one system using the benefits of nanotechnology, is extremely attractive for personalized medicine. Because treating cancer is not a one-size-fits-all scenario, it requires therapy to be adapted to the patient's specific biomolecules. Personalized and precision medicine (PM) does just that. It identifies biomarkers to gain an understanding of the diagnosis and in turn treating the specific disorder based on the precise diagnosis. By predominantly utilizing the unique properties of nanoparticles to achieve biomarker identification and drug delivery, nanotheranostics can be applied to noninvasively discover and target image biomarkers and further deliver treatment based on the biomarker distribution. This is a large and hopeful role theranostics must fill. However, as described in this expert opinion, current nanotechnology-based theranostics systems engineered for PM applications are not yet sufficient. PM is an ever-growing field that will be a driving force for future discoveries in biomedicine, especially cancer theranostics. In this article, the authors dissect the requirements for successful nanotheranostics-based PM.

Multicolor upconversion nanoparticles for protein conjugation

We describe the preparation of monodisperse, lanthanide-doped hexagonal-phase NaYF₄ upconverting luminescent nanoparticles for protein conjugation. Their core was coated with a silica shell which then was modified with a poly(ethylene glycol) spacer and N-hydroxysuccinimide ester groups. The nanoparticles were characterized by transmission electron microscopy, Raman spectroscopy, X-ray diffraction, and dynamic light scattering. The N-hydroxysuccinimide ester functionalization renders them highly reactive towards amine nucleophiles (e.g., proteins). We show that such particles can be conjugated to proteins. The protein-reactive UCLNPs and their conjugates to streptavidin and bovine serum albumin display multicolor emissions upon 980-nm continuous wave laser excitation. Surface plasmon resonance studies were carried out to prove bioconjugation and to compare the affinity of the particles for proteins immobilized on a thin gold film.