Scanning Imaging of Magnetic Nanoparticles for Quantitative Molecular Imaging

Force-Encoding DNA Nanomachines for Simultaneous and Direct Detection of Multiple Pathogenic Bacteria in Blood

Pathogen detection is growing in importance in the early stages of bacterial infection and treatment due to the significant morbidity and mortality associated with bloodstream infections. Although various diagnostic approaches for pathogen detection have been proposed, most of them are time-consuming, with insufficient sensitivity and limited specificity and multiplexing capability for clinical use. Here, we report a force-encoding DNA nanomachine for simultaneous and high-throughput detection of multiple pathogens in blood through force-induced remnant magnetization spectroscopy (FIRMS). The force-encoding DNA nanomachines coupled with DNA walkers enable analytical sensitivity down to a single bacterium via a cascade signal amplification strategy. More importantly, it allows for rapid and specific profiling of various pathogens directly in blood samples, without being affected by factors such as light color and solution properties. We expect that this magnetic sensing platform holds great promise for various applications in biomedical research and clinical diagnostics.

Highly Sensitive and Quantitative Magnetic Nanoparticle-Based Lateral Flow Immunoassay with an Atomic Magnetometer

Lateral flow immunoassay (LFIA) is a simple point-of-care method for detecting various analytes. However, the lack of test result precision and poor quantification are the main bottlenecks of LFIA. Although magnetic nanoparticles (MNPs) have gained prominence as potent labels in LIFA, the quantitative detection method for trace biomarkers remains to be improved. Here, we propose a promising real-time biosensing platform based on a highly sensitive atomic magnetometer to fulfill the quantitative detection of MNP-based lateral flow immunochromatographic assays. The strategy entails obtaining the residual flux density component spectrum by continuously and linearly scanning the trace MNP label and then resolving the magnetization and quantity from the spectrum. Moreover, we exploit the theoretical model of the magnetic dipole to verify the method's reliability. Regarding carcinoembryonic antigen detection, the atomic magnetometer exhibits a low detection limit of ∼0.01 ng mL-1 with a 100-fold enhancement factor compared to optical detection methods and a more straightforward mechanism than other magnetic detection approaches. Together, these results provide valuable insight for the potential application of atomic magnetometer quantum measurement techniques in intelligent diagnosis and treatment.

Force-Coded Strategy for the Simultaneous Detection of Multiple Tumor-Related Proteins

Multiplexed simultaneous detection of various cancer markers is required for accurate diagnosis and treatment of early cancer. In this work, we present a force-coded strategy for the simultaneous detection of tumor-related proteins with tunable dynamic range via magnetic sensing. The multiplexing capability of this method is achieved by designing DNA devices that can recognize different biomarkers and code them with different binding forces measured by the force-induced remnant magnetization spectroscopy, which is not influenced by the color of the light and the solution. Moreover, the force-coded assay with high sensitivity and adjustable detection range is robust, which could be used for practical biological applications such as magnetic sensing, handheld miniaturized systems, and potential in vivo diagnosis.

Nanoprobe-based force spectroscopy as a versatile platform for probing the mechanical adhesion of bacteria

The first stage of biofilm-associated infections is commonly caused by initial adhesion of bacteria to intravascular tubes, catheters and other medical devices. The overuse of antibiotics to treat these infections has led to the spread of antibiotic resistance, which has made infections difficult to eradicate. It is crucial to develop advanced strategies to inhibit biofilm formation, avoiding the emergence of antibiotic resistance. Previously, it has been reported that substrate stiffness plays an important role in the initial attachment of bacteria. However, the mechanism of how the stiffness modulates the initial adhesion of bacteria remains unclear. Here, we developed magnetic nanoprobe-based force-induced remnant magnetization spectroscopy (FIRMS) as a new platform to measure the adhesion force of bacteria. Through examining the initial adhesion force and the adhesive protein, fibronectin-binding protein (FnBP), of Staphylococcus aureus (S. aureus), we found that the increase of the substrate stiffness promoted the expression of FnBP, thus enhancing the initial adhesion force of bacteria. Following the formation of initial adhesion, the substrates with soft stiffness delayed the biofilm formation, whereas those with moderate stiffness showed preferential promotion of the biofilm formation. We expect this versatile platform to be beneficial to the study of adhesion behaviors of bacteria that sheds light on the design of new medical materials to treat microbial infections.

Nanoparticle-Regulated Semiartificial Magnetotactic Bacteria with Tunable Magnetic Moment and Magnetic Sensitivity

Micro-/nanomotors are widely used in micro-/nanoprocessing, cargo transportation, and other microscale tasks because of their ability to move independently. Many biological hybrid motors based on bacteria have been developed. Magnetotactic bacteria (MTB) have been employed as motors in biological systems because of their good biocompatibility and magnetotactic motion in magnetic fields. However, the magnetotaxis of MTB is difficult to control due to the lack of effective methods. Herein, a strategy that enables control over the motion of MTB is presented. By depositing synthetic Fe₃ O₄ magnetic nanoparticles on the surface of MTB, semiartificial magnetotactic bacteria (SAMTB) are produced. The overall magnetic properties of SAMTB, including saturation magnetization, residual magnetization, and blocking temperature, are regulated in a multivariate and multilevel fashion, thus regulating the magnetic sensitivity of SAMTB. This strategy provides a feasible method to manoeuvre MTB for applications in complex fluid environments, such as magnetic drug release systems and real-time tracking systems. Furthermore, this concept and methodology provide a paradigm for controlling the mobility of micro-/nanomotors based on natural small organisms.

Insulin-like growth factor type I selectively binds to G-quadruplex structures

BACKGROUND

G-quadruplex has been viewed as a promising therapeutic target in oncology due to its potentially important roles in physiological and pathological processes. Emerging evidence suggests that the biological functions of G-quadruplexes are closely related to the binding of some proteins. Insulin-like growth factor type I (IGF-1), as a significant modulator of cell growth and development, may serve as a quadruplex-binding protein.

METHODS

The binding affinity and selectivity of IGF-1 to different DNA motifs in solution were measured by using fluorescence spectroscopy, Surface Plasmon Resonance (SPR), and force-induced remnant magnetization (FIRM). The effects of IGF-1 on the formation and stability of G-quadruplex structures were evaluated by circular dichroism (CD) and melting fluorescence resonance energy transfer (FRET) spectroscopy. The influence of quadruplex-specific ligands on the binding of G-quadruplexes with IGF-1 was determined by FIRM.

RESULTS

IGF-1 shows a binding specificity for G-quadruplex structures, especially the G-quadruplex structure with a parallel topology. The quadruplex-specific ligands TMPyP4 and PDS (Pyridostatin) can inhibit the interaction between G-quadruplexes and proteins.

CONCLUSIONS

IGF-1 is demonstrated to selectively bind with G-quadruplex structures. The use of quadruplex-interactive ligands could modulate the binding of IGF-1 to G-quadruplexes.

GENERAL SIGNIFICANCE

This study provides us with a new perspective to understand the possible physiological relationship between IGF-1 and G-quadruplexes and also conveys a strategy to regulate the interaction between G-quadruplex DNA and proteins.

Applications of optically detected MRI for enhanced contrast and penetration in metal

We report quantitative measurements using optically detected magnetic resonance imaging (MRI) for enhanced pH contrast and flow inside porous metals. Using a gadolinium chelate as the pH contrast agent, we show the response is 0.6s(-1) mM(-1) per pH unit at the ambient magnetic field for the pH range 6-8.5. A stopped flow scheme was used to directly measure T(1) relaxation time to determine the relaxivity. Flow profiles and images were obtained for a series of porous metals with different average pore sizes. The signal amplitudes and spatial distributions were compared. A clogged region in one of the samples was revealed using optically detected MRI but not optical imaging or scanning electron microscopy. These applications will significantly broaden the impact of optically detected MRI in chemical imaging and materials research.

Note: Detection of a single cobalt microparticle with a microfabricated atomic magnetometer

We present magnetic detection of a single, 2 μm diameter cobalt microparticle using an atomic magnetometer based on a microfabricated vapor cell. These results represent an improvement by a factor of 10(5) in terms of the detected magnetic moment over previous work using atomic magnetometers to detect magnetic microparticles. The improved sensitivity is due largely to the use of small vapor cells. In an optimized setup, we predict detection limits of 0.17 μm(3).