Distance-dependent magnetic resonance tuning as a versatile MRI sensing platform for biological targets

Cu(II)-induced magnetic resonance tuning and enhanced magnetic relaxation switching immunosensor for sensitive detection of chlorpyrifos and Salmonella

Magnetic relaxation switching (MRS) biosensors have been recognized as useful analytical tools for a range of targets; however, traditional MRS biosensors are limited by the "prozone effect", resulting in a narrow linear range and low sensitivity. Herein, we proposed a paramagnetic Cu2+-induced magnetic resonance tuning (MRET) strategy, based on which Cu2+ ions and magnetic nanoparticles (MNPs) were adopted to construct a Cu-MNP-mediated MRS (Cu-M-MRS) immunosensor with Cu2+ ions acting as a quencher and MNPs as an enhancer. An Fe3O4@polydopamine-secondary antibody conjugate was prepared and used to correlate the amount of Cu2+ ions to the target concentration through an immunoassay. Based on the immunoreaction, the Cu-M-MRS immunosensor enabled the sensitive detection of chlorpyrifos (0.05 ng/mL, a 77-fold enhancement in sensitivity compared with the traditional MRS immunosensor) and Salmonella (50 CFU/mL). The proposed MRET strategy effectively improved the sensitivity and accuracy of the MRS immunosensor, offering a promising and versatile platform for food safety detection.

A novel magnetic resonance tuning-magnetic relaxation switching sensor based on Gd-MOF/USPIO assembly for sensitive and convenient aflatoxin B1 detection

Aflatoxin B1 (AFB1) can accumulate in different organs or tissues and seriously harm humans. Traditional magnetic relaxation switching (MRS) sensors have relatively low sensitivity, but are complex to use. Rapid small-trace molecule analysis in complex samples is challenging. In this study, we used a gadolinium-based metal-organic framework (Gd-MOF) and ultra-small superparamagnetic iron oxide (USPIO) assembly to develop a magnetic resonance tuning-magnetic relaxation switching (MRET-MRS) sensor to improve conventional MRS sensor sensitivity and simplify operational steps in complex samples. Importantly, the local magnetic field generated by USPIO interfered with Gd-MOF electron spin fluctuation and directly affected dipole-dipole interactions between Gd electrons and water molecules, thus rendering relaxation signal changes more sensitive. The sensitivity (0.54 pg mL-1) was 833 times more sensitive than that of a conventional MRS sensor (0.45 ng mL-1). Finally, a convenient one-step detection approach can be achieved by mixing antigen/antibody functionalized Gd-MOF/USPIO and target samples.

DNA-Mediated Magnetic-Dimer Assembly for Fault-Free Ultra-High-Field Magnetic Resonance Imaging of Tumors

Ultra-high-field (UHF) magnetic resonance imaging (MRI) stands as a pivotal cornerstone in biomedical imaging, yet the challenge of false imaging persists, constraining its full potential. Despite the development of dual-mode contrast agents improving conventional MRI, their effectiveness in UHF remains suboptimal due to the high magnetic moment, resulting in diminished T1 relaxivity and excessively enhanced T2 relaxivity. Herein, we report a DNA-mediated magnetic-dimer assembly (DMA) of iron oxide nanoparticles that harnesses UHF-tailored nanomagnetism for fault-free UHF-MRI. DMA exhibits a dually enhanced longitudinal relaxivity of 4.42 mM-1·s-1 and transverse relaxivity of 26.23 mM-1·s-1 at 9 T, demonstrating a typical T1-T2 dual-mode UHF-MRI contrast agent. Importantly, DMA leverages T1-T2 dual-modality image fusion to achieve artifact-free breast cancer visualization, effectively filtering interference from hundred-micrometer-level false-positive signals with unprecedented precision. The UHF-tailored T1-T2 dual-mode DMA contrast agents hold promise for elevating the accuracy of MR imaging in disease diagnosis.

Furin-Catalyzed Enhanced Magnetic Resonance Imaging Probe for Differential Diagnosis of Malignant Breast Cancers

Molecular magnetic resonance imaging (mMRI) of biomarkers is essential for accurate cancer detection in precision medicine. However, the current clinically used contrast agents provide structural magnetic resonance imaging (sMRI) information only and rarely provide mMRI information. Here, a tumor-specific furin-catalyzed nanoprobe (NP) was reported for differential diagnosis of malignant breast cancers (BCs) in vivo. This NP with a compact structure of Fe3O4@Gd-DOTA NPs (FFG NPs) contains an "always-on" T2-weighted MR signal provided by the magnetic Fe3O4 core and a furin-catalyzed enhanced T1-weighted MR signal provided by the Gd-DOTA moiety. The FFG NPs were found to produce an activated T1 signal in the presence of furin catalysis and an "always-on" T2 signal, providing mMRI and sMRI information simultaneously. Ratiometric mMRI:sMRI intensity can be used for differential diagnosis of malignant BCs MDA-MB-231 and MCF-7, where the furin levels relatively differ. The proposed probe not only provides structural imaging but also enables real-time molecular differential visualization of BC through enzymatic activities of cancer tissues.

Emerging Trends in Magnetic Resonance Fingerprinting for Quantitative Biomedical Imaging Applications: A Review

Magnetic resonance imaging (MRI) stands as a vital medical imaging technique, renowned for its ability to offer high-resolution images of the human body with remarkable soft-tissue contrast. This enables healthcare professionals to gain valuable insights into various aspects of the human body, including morphology, structural integrity, and physiological processes. Quantitative imaging provides compositional measurements of the human body, but, currently, either it takes a long scan time or is limited to low spatial resolutions. Undersampled k-space data acquisitions have significantly helped to reduce MRI scan time, while compressed sensing (CS) and deep learning (DL) reconstructions have mitigated the associated undersampling artifacts. Alternatively, magnetic resonance fingerprinting (MRF) provides an efficient and versatile framework to acquire and quantify multiple tissue properties simultaneously from a single fast MRI scan. The MRF framework involves four key aspects: (1) pulse sequence design; (2) rapid (undersampled) data acquisition; (3) encoding of tissue properties in MR signal evolutions or fingerprints; and (4) simultaneous recovery of multiple quantitative spatial maps. This paper provides an extensive literature review of the MRF framework, addressing the trends associated with these four key aspects. There are specific challenges in MRF for all ranges of magnetic field strengths and all body parts, which can present opportunities for further investigation. We aim to review the best practices in each key aspect of MRF, as well as for different applications, such as cardiac, brain, and musculoskeletal imaging, among others. A comprehensive review of these applications will enable us to assess future trends and their implications for the translation of MRF into these biomedical imaging applications.

Azo Reductase Activated Magnetic Resonance Tuning Probe with "Switch-On" Property for Specific and Sensitive Tumor Imaging in Vivo

Cancer remains a threat to human health. However, if tumors can be detected in the early stage, then the effectiveness of cancer treatment could be significantly improved. Therefore, it is worthwhile to develop more sensitive and accurate cancer diagnostic methods. Herein, we demonstrated an azo reductase (AzoR)-activated magnetic resonance tuning (MRET) probe with a "switch-on" property for specific and sensitive tumor imaging in vivo. Specifically, Gd-labeled DNA1 (DNA1-Gd) and cyclodextrin-coated magnetic nanoparticles (MNP-CD) were employed as enhancer and quencher of MRET, respectively, while DNA2, an azobenzene (Azo) group-modified aptamer (AS1411), served as a linker between enhancer and quencher to construct the MRET probe of MNP@DNA(1-2)-Gd. In tumor tissues with high-level AzoR, the T1-weighted magnetic resonance signal of the MRET probe could be restored by intelligently regulating the switch from "OFF" to "ON" after activation with AzoR, thus accurately indicating the location of the tumor accurately. Moreover, the tumor with a 4 times smaller size than that of the normal tumor model could be imaged based on the proposed MRET probe. The as-proposed MRET-based magnetic resonance imaging strategy not only achieves tumor imaging accurately but also shows promise for early diagnosis of tumors, which might improve patients' survival rates and provide an opportunity for image-guided biomedical applications in the future.

Molecular imaging of tumour-associated pathological biomarkers with smart nanoprobe: From "Seeing" to "Measuring"

Although the extraordinary progress has been made in molecular biology, the prevention of cancer remains arduous. Most solid tumours exhibit both spatial and temporal heterogeneity, which is difficult to be mimicked in vitro. Additionally, the complex biochemical and immune features of tumour microenvironment significantly affect the tumour development. Molecular imaging aims at the exploitation of tumour-associated molecules as specific targets of customized molecular probe, thereby generating image contrast of tumour markers, and offering opportunities to non-invasively evaluate the pathological characteristics of tumours in vivo. Particularly, there are no "standard markers" as control in clinical imaging diagnosis of individuals, so the tumour pathological characteristics-responsive nanoprobe-based quantitative molecular imaging, which is able to visualize and determine the accurate content values of heterogeneous distribution of pathological molecules in solid tumours, can provide criteria for cancer diagnosis. In this context, a variety of "smart" quantitative molecular imaging nanoprobes have been designed, in order to provide feasible approaches to quantitatively visualize the tumour-associated pathological molecules in vivo. This review summarizes the recent achievements in the designs of these nanoprobes, and highlights the state-of-the-art technologies in quantitative imaging of tumour-associated pathological molecules.

Dual-Responsive Turn-On T1 Imaging-Guided Mild Photothermia for Precise Apoptotic Cancer Therapy

Apoptosis has gained increasing attention in cancer therapy as an intrinsic signaling pathway, which leads to minimal leakage of waste products from a dying cell to neighboring normal cells. Among various stimuli to trigger apoptosis, mild hyperthermia is attractive but confronts limitations of non-specific heating and acquired resistance from elevated expression of heat shock proteins. Here, a dual-stimulation activated turn-on T1 imaging-based nanoparticulate system (DAS) is developed for mild photothermia (≈43 °C)-mediated precise apoptotic cancer therapy. In the DAS, a superparamagnetic quencher (ferroferric oxide nanoparticles, Fe3 O4 NPs) and a paramagnetic enhancer (Gd-DOTA complexes) are connected via the N6-methyladenine (m6 A)-caged, Zn2+ -dependent DNAzyme molecular device. The substrate strand of the DNAzyme contains one segment of Gd-DOTA complex-labeled sequence and another one of HSP70 antisense oligonucleotide. When the DAS is taken up by cancer cells, overexpressed fat mass and obesity-associated protein (FTO) specifically demethylates the m6 A group, thereby activating DNAzymes to cleave the substrate strand and simultaneously releasing Gd-DOTA complex-labeled oligonucleotides. The restored T1 signal from the liberated Gd-DOTA complexes lights up the tumor to guide the location and time of deploying 808 nm laser irradiation. Afterward, locally generated mild photothermia works in concert with HSP70 antisense oligonucleotides to promote apoptosis of tumor cells. This highly integrated design provides an alternative strategy for mild hyperthermia-mediated precise apoptotic cancer therapy.

Nanoprobe-based molecular imaging for tumor stratification

The responses of patients to tumor therapies vary due to tumor heterogeneity. Tumor stratification has been attracting increasing attention for accurately distinguishing between responders to treatment and non-responders. Nanoprobes with unique physical and chemical properties have great potential for patient stratification. This review begins by describing the features and design principles of nanoprobes that can visualize specific cell types and biomarkers and release inflammatory factors during or before tumor treatment. Then, we focus on the recent advancements in using nanoprobes to stratify various therapeutic modalities, including chemotherapy, radiotherapy (RT), photothermal therapy (PTT), photodynamic therapy (PDT), chemodynamic therapy (CDT), ferroptosis, and immunotherapy. The main challenges and perspectives of nanoprobes in cancer stratification are also discussed to facilitate probe development and clinical applications.

Large-scale in situ self-assembly and doping engineering of zinc ferrite nanoclusters for high performance bioimaging

Iron oxide nanomaterials has good biocompatibility and safety, and has been used as contrast agents for magnetic resonance imaging (MRI). However, its clinical usefulness is hampered by its difficult preparation on large scale, its rapid clearance in vivo and low target tissue enrichment efficiency. Here, we report the synthesis of water-soluble, biocompatible, superparamagnetic non-stoichiometric zinc ferrite nanoclusters (nZFNCs) of approximately 50 g in a single batch using a one-pot synthesis technique. nZFNCs is a secondary cluster structure with a size of about 40 nm composed of zinc-doped iron oxide nanoparticles with a size of about 6 nm. The surface of nZFNCS is endowed with a large number of carboxyl groups as active sites. By simply controlling the synthesis process and adjusting the proportion of metal precursors, the amount of zinc doping can be controlled, while maintaining the same size to ensure similar pharmacokinetics. Compared with undoped, the magnetic responsiveness and relaxation efficiency of nZFNCs are significantly improved, and the transverse relaxation efficiency (r2) can reach 425.5 mM-1 s-1 (doping amount x = 0.25), which is 7 times higher than that of commercial Resovist and 10 times higher than that of Feridex. In vivo imaging results also further confirmed the excellent contrast enhancement performance of the nanoclusters, which can achieve high contrast for more than 2 h in the liver. The advantage of this platform over comparable systems is that the contrast enhancement features are derived from simple techniques that do not require complex physical and chemical methods.

Plasmon Resonance Energy Transfer Nanoruler for Pinpointing Molecular Distance and Interaction on the Living Cell Membrane

Developing novel strategies to measure nanoscale distance and molecular interaction on a living cell membrane is of great significance but challenging. Here we develop a model of a linker-free plasmon resonance energy transfer, termed "PRET nanoruler", which is composed of a single-sized nanogold-antibody conjugates donor (G26@antiCD71) and a fluorophore-labeled XQ-2d aptamer receptor (XQ-2d-Cy3), that produces a separation distance (r) dependent energy transfer (ηPRET). Both the theoretical finite element simulation and experiments evidence the observable PRET between single G26NPs and XQ-2d-Cy3. Regardless of the size of ηPRET, we could confirm r is less than 5 nm, the separation of two binding sites is in the range of 13.0-18.0 nm. There is a competitive binding of Tf and XQ-2d-Cy3 on CD71 receptors. PRET nanoruler realizes the estimation of the nanoscale separation distance, and determines the molecular interaction and competitive binding. It is an alternative tool for observing nanoscale single molecular events in the future.

Designing Smart Iron Oxide Nanoparticles for MR Imaging of Tumors

Iron oxide nanoparticles (IONPs) possess unique magnetism and good biocompatibility, and they have been widely applied as contrast agents (CAs) for magnetic resonance imaging (MRI). Traditional CAs typically show a fixed enhanced signal, thus exhibiting the limitations of low sensitivity and a lack of specificity. Nowadays, the progress of stimulus-responsive IONPs allows alteration of the relaxation signal in response to internal stimuli of the tumor, or external stimuli, thus providing an opportunity to overcome those limitations. This review summarizes the current status of smart IONPs as tumor imaging MRI CAs that exhibit responsiveness to endogenous stimuli, such as pH, hypoxia, glutathione, and enzymes, or exogenous stimuli, such as magnets, light, and so on. We discuss the challenges and future opportunities for IONPs as MRI CAs and comprehensively illustrate the applications of these stimuli-responsive IONPs. This review will help provide guidance for designing IONPs as MRI CAs and further promote the reasonable design of magnetic nanoparticles and achieve early and accurate tumor detection.

Enzyme-Triggered Transforming of Assembly Peptide-Modified Magnetic Resonance-Tuned Probe for Highly Sensitive Imaging of Bacterial Infection In Vivo

Confirming bacterial infection at an early stage and distinguishing between sterile inflammation and bacterial infection is still highly needed for efficient treatment. Here, in situ highly sensitive magnetic resonance imaging (MRI) bacterial infection in vivo based on a peptide-modified magnetic resonance tuning (MRET) probe (MPD-1) that responds to matrix metallopeptidase 2 (MMP-2) highly expressed in bacteria-infected microenvironments is achieved. MPD-1 is an assembly of magnetic nanoparticle (MNP) bearing with gadolinium ion (Gd3+ ) modified MMP-2-cleavable self-assembled peptide (P1 ) and bacteria-targeting peptide (P), and it shows T2 -weighted signal due to the assemble of MNP and MRET ON phenomenon between MNP assembly and Gd3+ . Once MPD-1 accumulates at the bacterially infected site, P1 included in MPD-1 is cleaved explicitly by MMP-2, which triggers the T2 contrast agent of MPD-1 to disassemble into the monomer of MNP, leading the recovery of T1 -weighted signal. Simultaneously, Gd3+ detaches from MNP, further enhancing the T1 -weighted signal due to MRET OFF. The sensitive MRI of Staphylococcus aureus (low to 104 CFU) at the myositis site and accurate differentiation between sterile inflammation and bacterial infection based on the proposed MPD-1 probe suggests that this novel probe would be a promising candidate for efficiently detecting bacterial infection in vivo.

A pH-responsive magnetic resonance tuning probe for precise imaging of bacterial infection in vivo

Accurate and sensitive detection of bacteria is essential for treating bacterial infections. Herein, a pH-responsive magnetic resonance tuning (MRET) probe, whose T₁-weighted signal is activated in the bacteria-infected acid microenvironment, is developed for in situ accurately magnetic resonance imaging (MRI) of bacterial infection in vivo. The MRET probe (MDVG-1) is an assembly of paramagnetic enhancer (gadolinium-modified i-motif DNA₃, abbreviated as Gd-DNA₃-Gd) and the precursor of superparamagnetic quencher (DNA and vancomycin-modified magnetic nanoparticle, abbreviated as MDV). The T₁-weighted signal of Gd-DNA₃-Gd is quenched once the formation of MDVG-1 (MRET ON). Interestingly, the MDVG-1 probe was disassembled into the monomers of Gd-DNA₃-Gd and MDV under the bacteria-infected acid microenvironment, resulting significantly enhanced T₁-weighted signal at the infected site (MRET OFF). The pH-responsive MRET probe-based enhanced MRI signal and bacteria targeting significantly improve the distinction between bacterial infectious tissues and sterile inflamed tissues, which provides a promising approach for accurately detecting bacterial infection in vivo. STATEMENT OF SIGNIFICANCE: : Detecting pathogenic bacteria in vivo based on magnetic resonance imaging (MRI) strategy has been exploring recently. Although various bacterial-targeted MRI probes have been developed to image bacteria in vivo, the MRI signal of these MRI probes is always "on", which inevitably generates nonspecific background MRI signals, affecting the accuracy of MRI to a certain extent. In the current study, based on the magnetic resonance tuning (MRET) phenomenon, we present a pH-responsive MRET probe (MDVG-1) with T₂-weighted imaging to T₁-weighted imaging switchable properties to achieve in situ precise imaging of bacterial infection in vivo.

Shape programmable T1-T2 dual-mode MRI nanoprobes for cancer theranostics

The shape effect is an important parameter in the design of novel nanomaterials. Engineering the shape of nanomaterials is an effective strategy for optimizing their bioactive performance. Nanomaterials with a unique shape are beneficial to blood circulation, tumor targeting, cell uptake, and even improved magnetism properties. Therefore, magnetic resonance imaging (MRI) nanoprobes with different shapes have been extensively focused on in recent years. Different from other multimodal imaging techniques, dual-mode MRI can provide imaging simultaneously by a single instrument, which can avoid differences in penetration depth, and the spatial and temporal resolution of multiple imaging devices, and ensure the accurate matching of spatial and temporal imaging parameters for the precise diagnosis of early tumors. This review summarizes the latest developments of nanomaterials with various shapes for T₁-T₂ dual-mode MRI, and highlights the mechanism of how shape intelligently affects nanomaterials' longitudinal or transverse relaxation, namely sphere, hollow, core-shell, cube, cluster, flower, dumbbell, rod, sheet, and bipyramid shapes. In addition, the combination of T₁-T₂ dual-mode MRI nanoprobes and advanced therapeutic strategies, as well as possible challenges from basic research to clinical transformation, are also systematically discussed. Therefore, this review will help others quickly understand the basic information on dual-mode MRI nanoprobes and gather thought-provoking ideas to advance the subfield of cancer nanomedicine.

Dual Anticancer and Antibacterial Properties of Silica-Based Theranostic Nanomaterials Functionalized with Coumarin343, Folic Acid and a Cytotoxic Organotin(IV) Metallodrug

Five different silica nanoparticles functionalized with vitamin B12, a derivative of coumarin found in green plants and a minimum content of an organotin(IV) fragment (1-MSN-Sn, 2-MSN-Sn, 2-SBA-Sn, 2-FSPm-Sn and 2-FSPs-Sn), were identified as excellent anticancer agents against triple negative breast cancer, one of the most diagnosed and aggressive cancerous tumors, with very poor prognosis. Notably, compound 2-MSN-Sn shows selectivity for cancer cells and excellent luminescent properties detectable by imaging techniques once internalized. The same compound is also able to interact with and nearly eradicate biofilms of Staphylococcus aureus, the most common bacteria isolated from chronic wounds and burns, whose treatment is a clinical challenge. 2-MSN-Sn is efficiently internalized by bacteria in a biofilm state and destroys the latter through reactive oxygen species (ROS) generation. Its internalization by bacteria was also efficiently monitored by fluorescence imaging. Since silica nanoparticles are particularly suitable for oral or topical administration, and considering both its anticancer and antibacterial activity, 2-MSN-Sn represents a new dual-condition theranostic agent, based primarily on natural products or their derivatives and with only a minimum amount of a novel metallodrug.

A Telomerase-Activated Magnetic Resonance Imaging Probe for Consecutively Monitoring Tumor Growth Kinetics and In Situ Screening Inhibitors

Telomerase has long been considered as a biomarker for cancer diagnosis and a therapeutic target for drug discovery. Detecting telomerase activity in vivo could provide more direct information of tumor progression and response to drug treatment, which, however, is hampered by the lack of an effective probe that can generate an output signal without a tissue penetration depth limit. In this study, using the principle of distance-dependent magnetic resonance tuning, we constructed a telomerase-activated magnetic resonance imaging probe (TAMP) by connecting superparamagnetic ferroferric oxide nanoparticles (SPFONs) and paramagnetic Gd-DOTA (Gd(III) 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) complexes via telomerase-responsive DNA motifs. Upon telomerase-catalyzed extension of the primer in TAMP, Gd-DOTA-conjugated oligonucleotides can be liberated from the surface of SPFONs through a DNA strand displacement reaction, restoring the T₁ signal of the Gd-DOTA for a direct readout of the telomerase activity. Here we show that, by tracking telomerase activity, this probe provides consistent monitoring of tumor growth kinetics during progression and in response to drug treatment and enables in situ screening of telomerase inhibitors in whole-animal models. This study provides an alternative toolkit for cancer diagnosis, treatment response assessment, and anticancer drug screening.

Nanoprobe Based on Biominerals in Protein Corona for Dual-Modality MR Imaging and Therapy of Tumors

Various functional nanomaterials have been fabricated as diagnostic and therapeutic nanomedicines; however, the nanoparticles closely interact with proteins when immersed in biological fluids, forming a "protein corona" that critically alters the biological identity of nanomedicine. Here, we developed a robust strategy to construct theranostic nanoprobes based on protein-corona-coated Fe₃O₄ nanoparticles and biomineralization in the corona. Water-soluble carboxylic Fe₃O₄ nanoparticles were prepared by treating oleate-capped Fe₃O₄ nanoparticles with Lemieux-von Rudloff reagent. Bovine serum albumin (BSA) was used as a model protein to form a corona on the surface of Fe₃O₄ nanoparticles, endowing the Fe₃O₄ nanoparticles with biocompatibility and nonimmunogenicity. The protein corona also provides a template for biomimetic mineralization of Fe³⁺ with tannic acid (TA) to construct Fe₃O₄@BSA-TAFe^III nanoprobes. The TA-Fe(III) biominerals can not only act as photothermal therapy agents but also interact with unsaturated transferrin in plasma to form a "hybrid" corona, enabling the nanoprobes to target tumor cells through the mediation of transferrin receptors, which commonly overexpress on tumor cell membranes. Once taken in by tumor cells, the protonation of phenol hydroxyl groups in acidic lysosomes would lead to the release of Fe³⁺, inducing tumor cell death through a ferroptosis/apoptosis hybrid pathway. In addition, the released Fe³⁺ can boost the T₁-weighted MR imaging performance, and the Fe₃O₄ nanoparticles serve as T₂-weighted MR imaging contrast agents. It is thus believed that the current nanoprobes can realize the enhanced dual-modality MR imaging and combined therapy of tumors through controlling the protein corona and biomineralization.

PDGFB-targeted functional MRI nanoswitch for activatable T1-T2 dual-modal ultra-sensitive diagnosis of cancer

As one of the most significant imaging modalities currently available, magnetic resonance imaging (MRI) has been extensively utilized for clinically accurate cancer diagnosis. However, low signal-to-noise ratio (SNR) and low specificity for tumors continue to pose significant challenges. Inspired by the distance-dependent magnetic resonance tuning (MRET) phenomenon, the tumor microenvironment (TME)-activated off-on T₁-T₂ dual-mode MRI nanoswitch is presented in the current study to realize the sensitive early diagnosis of tumors. The tumor-specific nanoswitch is designed and manufactured on the basis of PDGFB-conjugating ferroferric oxide coated by Mn-doped silica (PDGFB-FMS), which can be degraded under the high-concentration GSH and low pH in TME to activate the T₁-T₂ dual-mode MRI signals. The tumor-specific off-on dual-mode MRI nanoswitch can significantly improve the SNR and is used successfully for the accurate diagnosis of early-stage tumors, particularly for orthotopic prostate cancer. In addition, the systemic delivery of the nanoswitch did not cause blood or tissue damage, and it can be excreted out of the body in a timely manner, demonstrating excellent biosafety. Overall, the strategy is a significant step in the direction of designing off-on dual-mode MRI nanoprobes to improve imaging accuracy, which opens up new avenues for the development of new MRI probes.

A pH-responsive T1-T2 dual-modal MRI contrast agent for cancer imaging

Magnetic resonance imaging (MRI) is a non-invasive imaging technology to diagnose health conditions, showing the weakness of low sensitivity. Herein, we synthesize a contrast agent, SPIO@SiO₂@MnO₂, which shows decreased T₁ and T₂ contrast intensity in normal physiological conditions. In the acid environment of tumor or inflamed tissue, the manganese dioxide (MnO₂) layer decomposes into magnetically active Mn²⁺ (T₁-weighted), and the T₁ and T₂ signals are sequentially recovered. In addition, both constrast quenching-activation degrees of T₁ and T₂ images can be accurately regulated by the silicon dioxide (SiO₂) intermediate layer between superparamagnetic iron oxide (SPIO) and MnO₂. Through the "dual-contrast enhanced subtraction" imaging processing technique, the contrast sensitivity of this MRI contrast agent is enhanced to a 12.3-time difference between diseased and normal tissue. Consequently, SPIO@SiO₂@MnO₂ is successfully applied to trace the tiny liver metastases of approximately 0.5 mm and monitor tissue inflammation.

Shield-activated two-way imaging nanomaterials for enhanced cancer theranostics

Smart nanomaterials with stimuli-responsive imaging enhancement have been widely developed to meet the requirements of accurate cancer diagnosis. However, these imaging nanoenhancers tend to be always on during circulation, which significantly increases the background signal when assessing the imaging performance. To improve unfavorable signal-to-noise ratios, an effective way is to shield the noise signal of these nanoprobes in non-targeted areas. Fortunately, there is a natural mutual shielding effect between some imaging nanomaterials, which provides the possibility of designing engineered nanomaterials with imaging quenching between two different components at the beginning. Once in the tumor microenvironment, the two components will present activated dual-mode imaging ability because of their separation, designated as two-way imaging tuning. This review highlights the design and mechanism of a series of engineered nanomaterials with two-way imaging tuning and their latest applications in the fields of cancer magnetic resonance imaging, fluorescence imaging, and their combination. The challenges and future directions for the improvement of these engineered nanomaterials towards clinical transformation are also discussed. This review aims to introduce the special constraint relationships of imaging components and provide scientists with simpler and more efficient nanoplatform construction ideas, promoting the development of engineered nanomaterials with two-way imaging tuning in cancer theranostics.

Analysing the effects of metallic biomaterial design and imaging sequences on MRI interpretation challenges due to image artefacts

Biometals cause signal loss and susceptibility artefacts in the surrounding tissue, resulting in deterioration in magnetic resonance (MR) images. This metal-artefact effect may lead to interpretation challenges for MR images. Therefore, artefact reduction is required to obtain higher-quality images. This paper aims to analyse the impact of imaging sequence and metallic biomaterial design on MR image artefacts. In this respect, implant specimens were designed in thin, thick, and pointed forms and manufactured using 316LVM, 316L, CoCr-alloy, and Ti-alloy, which are commonly utilized materials in the biomaterials field. Specimens were placed in a phantom that simulates average human anatomy separately and scanned in a 1.5 T MRI under four imaging conditions: "Axial-T₁-Gradient-Echo (GRE)", "Sagittal-T₁-GRE", "Axial-T₂-Spin-Echo (SE)" and "Sagittal-T₂-SE". Images were analysed regarding image artefact amount. The lower magnetic susceptibility of Ti-alloy specimens caused 84.76% less deterioration than 316LVM specimens in the MR images with the mean image artefact-to-specimen size ratio. Thinner implant designs provided better performance regarding the metal artefact by reducing the artefact-to-specimen size ratio. T₂SE decreased the image artefact by 44.7% for 316LVM and 54.6% for Ti-Alloy specimens and provided better image quality than T₁GRE for clinical interpretation. This study reveals that image artefacts directly depend on material content, implant volume, geometry, and imaging sequence selection. The minor artefact effect of T₂SE provides more accurate MR images than T₁GRE regarding the interpretation of the images of the patients with biometals. The higher magnetic susceptibility of biometals causes more deterioration of the images.

Tailoring Materials for Epilepsy Imaging: From Biomarkers to Imaging Probes

Excising epileptic foci (EF) is the most efficient approach for treating drug-resistant epilepsy (DRE). However, owing to the vast heterogeneity of epilepsies, EF in one-third of patients cannot be accurately located, even after exhausting all current diagnostic strategies. Therefore, identifying biomarkers that truly represent the status of epilepsy and fabricating probes with high targeting specificity are prerequisites for identifying the "concealed" EF. However, no systematic summary of this topic has been published. Herein, the potential biomarkers of EF are first summarized and classified into three categories: functional, molecular, and structural aberrances during epileptogenesis, a procedure of nonepileptic brain biasing toward epileptic tissue. The materials used to fabricate these imaging probes and their performance in defining the EF in preclinical and clinical studies are highlighted. Finally, perspectives for developing the next generation of probes and their challenges in clinical translation are discussed. In general, this review can be helpful in guiding the development of imaging probes defining EF with improved accuracy and holds promise for increasing the number of DRE patients who are eligible for surgical intervention.

Hofmeister Effect-Based T1-T2 Dual-Mode MRI and Enhanced Synergistic Therapy of Tumor

The imaging resolution of magnetic resonance imaging (MRI) is influenced by many factors. The development of more effective MRI contrast agents (CAs) is significant for early tumor detection and radical treatment, albeit challenging. In this work, the Hofmeister effect of Fe2O3 nanoparticles within the tumor microenvironment was confirmed for the first time. Based on this discovery, we designed a nanocomposite (FePN) by loading Fe2O3 nanoparticles on black phosphorus nanosheets. After reacting with glutathione, the FePN will undergo two stages in the tumor microenvironment, resulting in the robust enhancement of r1 and r2 based on the Hofmeister effect in the commonly used magnetic field (3.0 T). The glutathione-activated MRI signal of FePN was higher than most of the activatable MRI CAs, enabling a more robust visualization of tumors. Furthermore, benefiting from the long circulation time of FePN in the blood and retention time in tumors, the synergistic therapy of FePN exhibited an outstanding inhibition toward tumors. The FePN with good biosafety and biocompatibility will not only pave a new way for designing a common magnetic field-tailored T1-T2 dual-mode MRI CA but also offer a novel pattern for the accurate clinical diagnosis and therapy of tumors.

Matrix Metalloproteinases: From Molecular Mechanisms to Physiology, Pathophysiology, and Pharmacology

The first matrix metalloproteinase (MMP) was discovered in 1962 from the tail of a tadpole by its ability to degrade collagen. As their name suggests, matrix metalloproteinases are proteases capable of remodeling the extracellular matrix. More recently, MMPs have been demonstrated to play numerous additional biologic roles in cell signaling, immune regulation, and transcriptional control, all of which are unrelated to the degradation of the extracellular matrix. In this review, we will present milestones and major discoveries of MMP research, including various clinical trials for the use of MMP inhibitors. We will discuss the reasons behind the failures of most MMP inhibitors for the treatment of cancer and inflammatory diseases. There are still misconceptions about the pathophysiological roles of MMPs and the best strategies to inhibit their detrimental functions. This review aims to discuss MMPs in preclinical models and human pathologies. We will discuss new biochemical tools to track their proteolytic activity in vivo and ex vivo, in addition to future pharmacological alternatives to inhibit their detrimental functions in diseases. SIGNIFICANCE STATEMENT: Matrix metalloproteinases (MMPs) have been implicated in most inflammatory, autoimmune, cancers, and pathogen-mediated diseases. Initially overlooked, MMP contributions can be both beneficial and detrimental in disease progression and resolution. Thousands of MMP substrates have been suggested, and a few hundred have been validated. After more than 60 years of MMP research, there remain intriguing enigmas to solve regarding their biological functions in diseases.

Emerging nanobiotechnology-encoded relaxation tuning establishes new MRI modes to localize, monitor and predict diseases

Magnetic resonance imaging (MRI) is one of the most important techniques in the diagnosis of many diseases including cancers, where contrast agents (CAs) are usually necessary to improve its precision and sensitivity. Previous MRI CAs are confined to the signal-to-noise ratio (SNR) elevation of lesions for precisely localizing lesions. As nanobiotechnology advances, some new MRI CAs or nanobiotechnology-enabled MRI modes have been established to vary the longitudinal or transverse relaxation of CAs, which are harnessed to detect lesion targets, monitor disease evolution, predict or evaluate curative effect, etc. These distinct cases provide unexpected insights into the correlation of the design principles of these nanobiotechnologies and corresponding MRI CAs with their potential applications. In this review, first, we briefly present the principles, classifications and applications of conventional MRI CAs, and then elucidate the recent advances in relaxation tuning via the development of various nanobiotechnologies with emphasis on the design strategies of nanobiotechnology and the corresponding MRI CAs to target the tumor microenvironment (TME) and biological targets or activities in tumors or other diseases. In addition, we exemplified the advantages of these strategies in disease theranostics and explored their potential application fields. Finally, we analyzed the present limitations, potential solutions and future development direction of MRI after its combination with nanobiotechnology.

Contrast Agents for Hepatocellular Carcinoma Imaging: Value and Progression

Hepatocellular carcinoma (HCC) has the third-highest incidence in cancers and has become one of the leading threats to cancer death. With the research on the etiological reasons for cirrhosis and HCC, early diagnosis has been placed great hope to form a favorable prognosis. Non-invasive medical imaging, including the associated contrast media (CM)-based enhancement scan, is taking charge of early diagnosis as mainstream. Meanwhile, it is notable that various CM with different advantages are playing an important role in the different imaging modalities, or even combined modalities. For both physicians and radiologists, it is necessary to know more about the proper imaging approach, along with the characteristic CM, for HCC diagnosis and treatment. Therefore, a summarized navigating map of CM commonly used in the clinic, along with ongoing work of agent research and potential seeded agents in the future, could be a needed practicable aid for HCC diagnosis and prognosis.

Recent advances in engineering iron oxide nanoparticles for effective magnetic resonance imaging

Iron oxide nanoparticle (IONP) with unique magnetic property and high biocompatibility have been widely used as magnetic resonance imaging (MRI) contrast agent (CA) for long time. However, a review which comprehensively summarizes the recent development of IONP as traditional T₂ CA and its new application for different modality of MRI, such as T₁ imaging, simultaneous T₂/T₁ or MRI/other imaging modality, and as environment responsive CA is rare. This review starts with an investigation of direction on the development of high-performance MRI CA in both T₂ and T₁ modal based on quantum mechanical outer sphere and Solomon–Bloembergen–Morgan (SBM) theory. Recent rational attempts to increase the MRI contrast of IONP by adjusting the key parameters, including magnetization, size, effective radius, inhomogeneity of surrounding generated magnetic field, crystal phase, coordination number of water, electronic relaxation time, and surface modification are summarized. Besides the strategies to improve r₂ or r₁ values, strategies to increase the in vivo contrast efficiency of IONP have been reviewed from three different aspects, those are introducing second imaging modality to increase the imaging accuracy, endowing IONP with environment response capacity to elevate the signal difference between lesion and normal tissue, and optimizing the interface structure to improve the accumulation amount of IONP in lesion. This detailed review provides a deep understanding of recent researches on the development of high-performance IONP based MRI CAs. It is hoped to trigger deep thinking for design of next generation MRI CAs for early and accurate diagnosis.

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T₂ contrast capacity of iron oxide nanoparticles (IONPs) could be improved based on quantum mechanical outer sphere theory.

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IONPs could be expand to be used as effective T₁ CAs by improving q value, extending τ_s, and optimizing interface structure.

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Environment responsive MRI CAs have been developed to improve the diagnosis accuracy.

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Introducing other imaging contrast moiety into IONPs could increase the contrast efficiency.

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Optimizing in vivo behavior of IONPs have been proved to enlarge the signal difference between normal tissue and lesion.

Biological interactions of ferromagnetic iron oxide-carbon nanohybrids with alveolar epithelial cells

Iron oxide nanoparticles (IONPs) have been largely investigated in a plethora of biological fields for their interesting physical-chemical properties, which make them suitable for application in cancer therapy, neuroscience, and imaging. Several encouraging results have been reported in these contexts. However, the possible toxic effects of some IONP formulations can limit their applicability. In this work, IONPs were synthesized with a carbon shell (IONP@C), providing enhanced stability both as colloidal dispersion and in the biological environment. We conducted a careful multiparametric evaluation of IONP@C biological interactions in vitro, providing them with an in vivo-like biological identity. Our hybrid nanoformulation showed no cytotoxic effects on a widely employed model of alveolar epithelial cells for a variety of concentrations and exposure times. The IONP@C were efficiently internalized and TEM analysis allowed the protective role of the carbon shell against intracellular degradation to be assessed. Intracellular redistribution of the IONP@C from the lysosomes to the lamellar bodies was also observed after 72 hours.

Fluorinated Ionic Liquid Based Multicolor 19 F MRI Nanoprobes for In Vivo Sensing of Multiple Biological Targets

Multicolor imaging, which maps the distribution of different targets, is important for in vivo molecular imaging and clinical diagnosis. Fluorine 19 magnetic resonance imaging (¹⁹ F MRI) is a promising technique because of unique insights without endogenous background or tissue penetration limit. Thus multicolor ¹⁹ F MRI probes, which can sense a wide variety of molecular species, are expected to help elucidate the biomolecular networks in complex biological systems. Here, a versatile model of activatable probes based on fluorinated ionic liquids (ILs) for multicolor ¹⁹ F MRI is reported. Three types of ILs at different chemical shifts are loaded in nanocarriers and sealed by three stimuli-sensitive copolymers, leading to "off" ¹⁹ F signals. The coating polymers specifically respond to their environmental stimuli, then degrade to release the loaded ILs, causing ¹⁹ F signals recovery. The nanoprobes are utilized for non-invasive detection of tumor hallmarks, which are distinguished by their individual colors in one living mouse, without interference between each other. This multicolor imaging strategy, which adopts modular construction of various ILs and stimuli-responsive polymers, will allow more comprehensive sensing of multiple biological targets, thus, opening a new realm in mechanistic understanding of complex pathophysiologic processes in vivo.

When imaging meets size-transformable nanosystems

Imaging techniques, including magnetic, optical, acoustic and nuclear imaging, are gaining popularity as a research tool and clinical diagnostics. The advent of imaging agents-incorporated nanosystems (NSs), with sufficient contrast and high resolution, facilitates better monitoring of disease progression, targeted delivery and therapeutic process. Of note, the size of NSs remarkably affects imaging performance, while both large and small NSs enjoy respective features and superiority for imaging aspect, including penetration depth, signal-to-background ratio and spatiotemporal resolution. In this review, after a systematic summary of the basic knowledge of imaging techniques and its relation with size-tunable strategies, we further provide insights into the opportunities and challenges facing size-transformable NSs of the future for bio-imaging application and clinical translation.

Click Chemistry-Mediated Particle Counting Sensing via Cu(II)-Polyglutamic Acid Coordination Chemistry and Enzymatic Reaction

An electrical resistance-based particle counter (ERPC) with simple operation and high resolution has proved to be a promising biosensing toolkit, whereas amplification-free ERPC biosensors are incapable of analyzing trace small molecules due to their relatively low sensitivity. In this work, click chemistry-mediated particle counting sensing of small-molecule hazards in food samples with high sensitivity was developed. In this strategy, unbound alkyne-functionalized polystyrene microspheres were collected by magnetic separation from the copper-ion-mediated click reaction between alkyne-functionalized polystyrene microspheres and azido-functionalized magnetic beads, which could be used as signal probes for the readout. This click chemistry-mediated ERPC biosensor converts the detection of targets to the quantification of copper ions or ascorbic acid by performing competitive immunoassay-based coordination chemistry and enzymatic reaction, respectively. The sensitivity of the ERPC biosensor has been improved by an order of magnitude due to the signal amplification effects of click chemistry, coordination adsorption, and enzyme catalysis. Furthermore, because of the efficient separation and enrichment of immunomagnetic beads and the robustness of click chemistry, the interference from food matrixes and immunoassay is effectively reduced, and thus, our strategy is exceedingly suitable for detecting trace targets in complex samples.

In situ ratiometric SERS imaging of intracellular protease activity for subtype discrimination of human breast cancer

Accurate discrimination between different cells at the molecular level is of fundamental importance for disease diagnosis. Endogenous proteases are such molecular candidates for cancer cell subtype study. But in situ probing their activity in live cells remains challenging for surface-enhanced Raman scattering (SERS). Here, we present a sensitive ratio-type SERS nanoprobe for imaging of matrix metalloproteinase-2 (MMP-2) in different cancer cells subtypes. The nanoprobe contained three components: a plasmon-active gold nanoparticle as the SERS enhancing matrix, Raman dye rhodamine B (Rh B)-labelled substrate peptides as the specific MMP-2 recognizer, and 2-naphthalenethiol (2-NT) as the internal standard. MMP-2-responsive cleavage of peptides from the nanoprobe surface results in decrease or even disappearance of SERS emission of Rh B, which was ratioed over the emission of 2-NT for the quantification of MMP-2 activity. Both in-tube assay and in-cell imaging results show that the MMP-responsive nanoprobe can work and serve to differentiate the normal breast cells from the tumorous ones, to differentiate two breast cancer cell subtypes with a different degree of malignancy. We believe that this SERS nanoprobe could find a wide application in the fields of tumor biology and accurate disease diagnosis.

Nuclease activity: an exploitable biomarker in bacterial infections

INTRODUCTION

In the increasingly challenging field of clinical microbiology, diagnosis is a cornerstone whose accuracy and timing are crucial for the successful management, therapy, and outcome of infectious diseases. Currently employed biomarkers of infectious diseases define the scope and limitations of diagnostic techniques. As such, expanding the biomarker catalog is crucial to address unmet needs and bring about novel diagnostic functionalities and applications.

AREAS COVERED

This review describes the extracellular nucleases of 15 relevant bacterial pathogens and discusses the potential use of nuclease activity as a diagnostic biomarker. Articles were searched for in PubMed using terms: "nuclease", "bacteria", "nuclease activity" or "biomarker". For overview sections, original and review articles between 2000 and 2019 were searched for using terms: "infections", "diagnosis", "bacterial", "burden", "challenges". Informative articles were selected.

EXPERT OPINION

Using the catalytic activity of nucleases offers new possibilities compared to established biomarkers. Nucleic acid activatable reporters in combination with different transduction platforms and delivery methods can be used to detect disease-associated nuclease activity patterns in vitro and in vivo for prognostic and diagnostic applications. Even when these patterns are not obvious or of unknown etiology, screening platforms could be used to identify new disease reporters.

Transition metal ion-doped ferrites nanoparticles for bioimaging and cancer therapy

Magnetic nanoparticles (MNPs) have been extensively researched and implemented in biomedicine for more than half a century due to their non-invasive nature, ease of temporal and spatial manipulation, and considerable biocompatibility. However, the complex magnetic behaviour of MNPs is influenced by several parameters (e.g., particle size, shape, composition, core-shell structure, etc.), among which the amount of transition metal doping plays an important factor. For this reason, the doping of ferrite with transition metals has been used as an effective strategy to precisely tailor MNPs to achieve satisfactory performance in biomedical applications. In this review, we first introduced the main properties of coordinated MNPs (including magnetic moment and saturated magnetisation) and provide a comprehensive overview of the mechanistic studies related to the doping of transition metal ions into ferrite to precisely modulate its magnetic properties. We also highlighted the potential mechanisms and recent advances in transition metal ion-doped MNPs (TMNPs) for bioimaging (magnetic resonance imaging and magnetic particle imaging) and tumour therapy (e.g., magneto-mechanical killing, magnetothermal therapy, and drug delivery). Finally, we summarised the current challenges and future trends of TMNPs in the biomedical field based on the latest advances by researchers.

Activatable MRI probes for the specific detection of bacteria

Activatable fluorescent probes have been successfully used as molecular tools for biomedical research in the last decades. Fluorescent probes allow the detection of molecular events, providing an extraordinary platform for protein and cellular research. Nevertheless, most of the fluorescent probes reported are susceptible to interferences from endogenous fluorescence (background signal) and limited tissue penetration is expected. These drawbacks prevent the use of fluorescent tracers in the clinical setting. To overcome the limitation of fluorescent probes, we and others have developed activatable magnetic resonance probes. Herein, we report for the first time, an oligonucleotide-based probe with the capability to detect bacteria using magnetic resonance imaging (MRI). The activatable MRI probe consists of a specific oligonucleotide that targets micrococcal nuclease (MN), a nuclease derived from Staphylococcus aureus. The oligonucleotide is flanked by a superparamagnetic iron oxide nanoparticle (SPION) at one end, and by a dendron functionalized with several gadolinium complexes as enhancers, at the other end. Therefore, only upon recognition of the MRI probe by the specific bacteria is the probe activated and the MRI signal can be detected. This approach may be widely applied to detect bacterial infections or other human conditions with the potential to be translated into the clinic as an activatable contrast agent.

Multifunctional superparamagnetic nanoparticles with a fluorescent silica shell for the in vitro study of bio-nano interactions at the subcellular scale

Despite the high level of interest in bio-nano interactions, detailed intracellular mechanisms that govern nanoscale recognition and signalling still need to be unravelled. Magnetic nanoparticles (NPs) are valuable tools for elucidating complex intracellular bio-nano interactions. Using magnetic NPs, it is possible to isolate cell compartments that the particles interact with during intracellular trafficking. Studies at the subcellular scale rely heavily on optical microscopy; therefore, combining the advantages of magnetic recovery with excellent imaging properties to allow intracellular NP tracking is of utmost interest for the nanoscience field. However, it is a challenge to prepare highly magnetic NPs with a suitable fluorescence for the fluorescence imaging techniques typically used for biological studies. Here we present the synthesis of biocompatible multifunctional superparamagnetic multicore NPs with a bright fluorescent silica shell. The incorporation of an organic fluorophore in the silica surrounding the magnetic multicore was optimised to enable the particles to be tracked with the most common imaging techniques. To prevent dye loss resulting from silica dissolution in biological environments, which would reduce the time that the particles could be tracked, we added a thin dense encapsulating silica layer to the NPs which is highly stable in biological media. The synthesised multifunctional nanoparticles were evaluated in cell uptake experiments in which their intracellular location could be clearly identified using fluorescence imaging microscopy, even after 3 days. The magnetic properties of the iron oxide core enabled both efficient recovery of the NPs from the intracellular environment and the extraction of cell compartments involved in their intracellular trafficking. Thus, the NPs reported here provide a promising tool for the study of the processes regulating bio-nano interactions.

Dynamic nanoassemblies for imaging and therapy of neurological disorders

The past decades have witnessed an increased incidence of neurological disorders (NDs) such as Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, ischemic stroke, and epilepsy, which significantly lower patients' life quality and increase the economic and social burden. Recently, nanomedicines composed of imaging and/or therapeutic agents have been explored to diagnose and/or treat NDs due to their enhanced bioavailability, blood-brain barrier (BBB) permeability, and targeting capacity. Intriguingly, dynamic nanoassemblies self-assembled from functional nanoparticles to simultaneously interfere with multiple pathogenic substances and pathological changes, have been regarded as one of the foremost candidates to improve the diagnostic and therapeutic efficacy of NDs. To help readers better understand this emerging field, in this review, the pathogenic mechanism of different types of NDs is briefly introduced, then the functional nanoparticles used as building blocks in the construction of dynamic nanoassemblies for NDs theranostics are summarized. Furthermore, dynamic nanoassemblies that can actively cross the BBB to target brain lesions, sensitively and efficiently diagnose or treat NDs, and effectively promote neuroregeneration are highlighted. Finally, we conclude with our perspectives on the future development in this field.

Engineering of magnetic nanoparticles as magnetic particle imaging tracers

Magnetic particle imaging (MPI) has recently emerged as a promising non-invasive imaging technique because of its signal linearly propotional to the tracer mass, ability to generate positive contrast, low tissue background, unlimited tissue penetration depth, and lack of ionizing radiation. The sensitivity and resolution of MPI are highly dependent on the properties of magnetic nanoparticles (MNPs), and extensive research efforts have been focused on the design and synthesis of tracers. This review examines parameters that dictate the performance of MNPs, including size, shape, composition, surface property, crystallinity, the surrounding environment, and aggregation state to provide guidance for engineering MPI tracers with better performance. Finally, we discuss applications of MPI imaging and its challenges and perspectives in clinical translation.

Microenvironment-tailored nanoassemblies for the diagnosis and therapy of neurodegenerative diseases

Neurodegenerative disorder is an illness involving neural dysfunction/death attributed to complex pathological processes, which eventually lead to the mortality of the host. It is generally recognized through features such as mitochondrial dysfunction, protein aggregation, oxidative stress, metal ions dyshomeostasis, membrane potential change, neuroinflammation and neurotransmitter impairment. The aforementioned neuronal dysregulations result in the formation of a complex neurodegenerative microenvironment (NME), and may interact with each other, hindering the performance of therapeutics for neurodegenerative disease (ND). Recently, smart nanoassemblies prepared from functional nanoparticles, which possess the ability to interfere with different NME factors, have shown great promise to enhance the diagnostic and therapeutic efficacy of NDs. Herein, this review highlights the recent advances of stimuli-responsive nanoassemblies that can effectively combat the NME for the management of ND. The first section outlined the NME properties and their interrelations that are exploitable for nanoscale targeting. The discussion is then extended to the controlled assembly of functional nanoparticles for the construction of stimuli-responsive nanoassemblies. Further, the applications of stimuli-responsive nanoassemblies for the enhanced diagnosis and therapy of ND are introduced. Finally, perspectives on the future development of NME-tailored nanomedicines are given.

A Microfluidic Chip-Based MRS Immunosensor for Biomarker Detection via Enzyme-Mediated Nanoparticle Assembly

Conventional immunoassay methods have their common defects, such as tedious processing steps and inadequate sensitivity, in detecting whole blood. To overcome the above problems, we report a microfluidic chip-based magnetic relaxation switching (MRS) immunosensor via enzyme-mediated nanoparticles to simplify operation and amplify the signal in detecting whole blood samples. In the silver mirror reaction with catalase (CAT) as the catalyst, H2O2 can effectively control the production of Ag NPs. The amount of Ag NPs formed further affects the degree of aggregation of magnetic nanoparticles (MNPS), which gives rise to the changes of transverse relaxation time (T2). Both sample addition and reagent reaction are carried out in the microfluidic chip, thereby saving time and reagent consumption. We also successfully apply the sensor to detect alpha-fetoprotein (AFP) in real samples with a satisfied limit of detection (LOD = 0.56 ng/ml), which is superior to the conventional ELISA.

Chemical Transformations of Anisotropic Platelets and Spherical Nanocrystals

ConspectusInorganic nanocrystal design has been continuously evolving with a better understanding of the chemical reaction mechanisms between chemical stimuli and nanocrystals. Under certain conditions, molecular compounds can be effective as chemical stimuli to induce transformative reactions of nanocrystals toward new materials that would differ in geometric shape, composition, and crystallographic structure. To explore such evolutionary processes, two-dimensional (2D) layered transition-metal chalcogenide (TMC) nanostructures are an interesting structural platform because they not only exhibit unique transformation pathways due to their structural anisotropy but also present new opportunities for improved material properties for potential applications such as catalysis and energy conversion and storage. The high surface area/volume ratio, interlayer van der Waals (vdW) spacing, and different coordination states between the unsaturated edges and the fully saturated basal planes of the chalcogens are characteristic of 2D layered TMC nanostructures, which subsequently lead to anisotropic chemical processes during chemical transformations, such as regioselective reactions at the interfacial boundaries in the pathways for either porous or solid heteronanostructures. In this Account, we first discuss the chemical reactivity of 2D layered TMC nanostructures. By categorizing the external stimuli in terms of chemical principles, such as Lewis acid-base chemistry, a desirable regioselective chemical reaction can occur with controlled reactivity. In association with the knowledge obtained from the nanoscale chemical reactivity of 2D layered nanocrystals, similar efforts in other important morphologies such as 1D and isotropic 0D nanocrystals are introduced. For instance, for 1D and 0D metal oxide nanocrystals, the effects of molecular stimuli on the atomic-level changes in the crystal lattice are demonstrated, eventually leading to a variety of shape transformations.

The Tumor Proteolytic Landscape: A Challenging Frontier in Cancer Diagnosis and Therapy

In recent decades, dysregulation of proteases and atypical proteolysis have become increasingly recognized as important hallmarks of cancer, driving community-wide efforts to explore the proteolytic landscape of oncologic disease. With more than 100 proteases currently associated with different aspects of cancer development and progression, there is a clear impetus to harness their potential in the context of oncology. Advances in the protease field have yielded technologies enabling sensitive protease detection in various settings, paving the way towards diagnostic profiling of disease-related protease activity patterns. Methods including activity-based probes and substrates, antibodies, and various nanosystems that generate reporter signals, i.e., for PET or MRI, after interaction with the target protease have shown potential for clinical translation. Nevertheless, these technologies are costly, not easily multiplexed, and require advanced imaging technologies. While the current clinical applications of protease-responsive technologies in oncologic settings are still limited, emerging technologies and protease sensors are poised to enable comprehensive exploration of the tumor proteolytic landscape as a diagnostic and therapeutic frontier. This review aims to give an overview of the most relevant classes of proteases as indicators for tumor diagnosis, current approaches to detect and monitor their activity in vivo, and associated therapeutic applications.