Intratumoral Glutathione Activatable Nanoprobes for Fluorescence and 19F Magnetic Resonance Turn-On Imaging

pH-Responsive magnetic nanocarriers for chelator-free bimodal (MRI/SPECT-CT) image-guided chemo-hyperthermia therapy in human breast carcinoma

Although chemotherapy with magnetic nanocarriers has witnessed significant advancement in the field of cancer treatment, multimodal diagnosis and combinatorial therapy using a single nanoplatform will have much better efficacy in achieving superior results. Herein, we constructed a smart theranostic system by combining pH-sensitive tartaric acid-stabilized Fe3O4 magnetic nanocarriers (TMNCs) with SPECT imaging and a chemotherapeutic agent for image-guided chemo-hyperthermia therapy. The carboxyl-enriched exteriors of TMNCs provided sites for the conjugation of a chemotherapeutic drug (doxorubicin hydrochloride, DOX) and radiolabeling (141Ce). The usage of 145.4 keV gamma rays made this platform an ideal choice for in vivo SPECT-CT imaging, showing the retention of the nanoformulation in the tumor site even after 28 days. Further, TMNCs showed a very high transverse relaxation rate (r2) of 171 mM-1 s-1, which is higher than that of clinically approved magnetic resonance imaging (MRI) contrast agents such as ferumoxtran (65 mM-1 s-1) and ferumoxides (120 mM-1 s-1). Further, the developed drug-loaded hybrid platform showed significantly higher cytotoxicity towards breast cancer cells, which was augmented by in vitro magnetic hyperthermia. Bright-field microscopy and cell cycle analysis suggested that cell death occurred through induction of G2-M arrest and subsequent apoptosis. These findings clearly suggest the potential of the developed hybrid nanoplatform for image-guided combination therapy.

Nanoprobe Based on Novel NIR-II Quinolinium Cyanine for Multimodal Imaging

NIR-II imaging has the advantages of high sensitivity, spatiotemporal resolution, and high penetration depth, thereby serving as a potential alternative to conventional imaging methods. Herein, a novel NIR-II dye IR-1010 (λex/λem = 1010/1058 nm) is reported with high quantum yield (3.08%) and good stability, by incorporating p-methoxyphenyl groups into a quinolinium cyanine dye. Then a multifunctional nanoprobe, termed IUFP NPs, is developed by the incorporation of upconversion (UC) nanoparticles (NPs), perfluoro-15-crown-5-ether (PFCE), and IR-1010, to display the novel performance of multimodal imaging. Under the single-wavelength excitation (980 nm), IUFP NPs simultaneously emit the NIR-II fluorescence of IR-1010 and visible UC luminescence of UCNPs, and thus realize the UC imaging for cells, and NIR-II fluorescence/photoacoustic/19F magnetic resonance imaging for blood vessels, lymph nodes and tumor in mice. This work affords a novel approach to NIR-II dyes and a general strategy for the design of multimodal imaging probes.

Design of a high-performance NIR-II nanoprobe by steric regulation for in vivo vasculature and tumor imaging

A novel NIR-II nanoprobe was developed through regulating the steric effect of an A-DA'D-A dye. The probe features the properties of strong fluorescence, high stability, and a large Stokes shift, thereby serving as a remarkable contrast agent for the fluorescence imaging of hindlimb vasculature and tumors in live mice.

Fluorinated 1,7-DO2A-Based Iron(II) Complexes as Sensitive 19F MRI Molecular Probes for Visualizing Renal Dysfunction in Living Mice

Kidney diseases have become an important global health concern due to their high incidence, inefficient diagnosis, and poor prognosis. Devising direct methods, especially imaging means, to assess renal function is the key for better understanding the mechanisms of various kidney diseases and subsequent development of effective treatment. Herein, we developed a fluorinated ferrous chelate-based sensitive probe, 1,7-DO2A-Fe(II)-F18 (Probe 1), for 19F magnetic resonance imaging (MRI). This highly fluorinated probe (containing 18 chemically equivalent 19F atoms with a fluorine content at 35 wt %) achieves a 15-time enhancement in signal intensity compared with the fluorine-containing ligand alone due to the appropriately regulated 19F relaxation times by the ferrous ion, which significantly increases imaging sensitivity and reduces acquisition time. Owing to its high aqueous solubility, biostability, and biocompatibility, this probe could be rapidly cleared by kidneys, which provides a means for monitoring renal dysfunction via 19F MRI. With this probe, we accomplish in vivo imaging of the impaired renal dysfunction caused by various kidney diseases including acute kidney injury, unilateral ureteral obstruction, and renal fibrosis at different stages. Our study illustrates the promising potential of Probe 1 for in vivo real-time visualization of kidney dysfunction, which is beneficial for the study, diagnosis, and even stratification of different kidney diseases. Furthermore, the design strategy of our probe is inspiring for the development of more high-performance 19F MRI probes for monitoring various biological processes.

Building in biologically appropriate multifunctionality in aqueous copper indium selenide-based quantum dots

Advanced nanoplatforms equipped with different functional moieties for theranostics hold appealing promise for reshaping precision medicine. The reliable construction of an individual nanomaterial with intrinsic near-infrared (NIR) photofunction and magnetic domains is much desired but largely unexplored in a direct aqueous synthesis system. Herein, we develop an aqueous phase synthetic strategy for Mn2+ doping of ZnS shell grown on Zn-Cu-In-Se core quantum dots (ZCISe@ZnS:Mn QDs), providing the optimal NIR fluorescence quantum efficiency of up to 18.9% and meanwhile efficiently introducing paramagnetic domains. The relaxometric properties of the water-soluble Mn-doped QDs make them desirable for both the longitudinal and transverse (T1 and T2) magnetic resonance (MR) contrast enhancement due to the shell lattice-doped Mn2+ ions with slow tumbling rates and favoured spin-proton dipolar interactions with surrounding water molecules. Surprisingly, the incorporation of Mn2+ ions into the shell is found to significantly enhance the production of reactive oxygen species (ROS) by combining both the chemodynamic and photodynamic processes upon NIR light irradiation, showing great potential for efficient photo-assisted ablation of cancer cells. Furthermore, a broad-spectrum excitation range beneficial for bright NIR fluorescence imaging of breast cancer has been proven and offers high flexibility in the choice of incident light sources. Multiparametric MR imaging of the brain has also been successfully demonstrated in vivo.

A trade-off between ligand coating and crystallinity of Gd-doped ultrasmall CeO2 for improving relaxivity

A Gd-doped ultrasmall CeO₂ contrast agent was prepared with high longitudinal relaxivity (r₁ = 10.1 mM^-1 s^-1, 7.0 T) through rationally regulating the crystallinity and surface coatings, providing a new paradigm for optimizing MRI performance. Moreover, responsive photoacoustic imaging (PAI) was established via tumor microenvironment-triggered oxidation, affording dual-modal imaging.

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.

Imaging strategies for monitoring the immune response

Real-time monitoring of the immune response can be used to evaluate the immune status of the body and to distinguish immune responders and non-responders, so as to better guide immunotherapy. Through direct labelling of immune cells and imaging specific biomarkers of different cells, the activation status of immune cells and immunosuppressive status of tumor cells can be visualized. The immunotherapeutic regimen can then be adjusted accordingly in a timely manner to improve the efficacy of immunotherapy. In this review, various imaging methods, immune-related imaging probes, current challenges and opportunities are summarized and discussed.

Fluorescent/magnetic nano-aggregation via electrostatic force between modified quantum dot and iron oxide nanoparticles for bimodal imaging of U87MG tumor cells

Imaging technology based on novel nanomaterials is burgeoning as a potential tool for exploring various physiological processes. We herein report a fluorescent and magnetic nanoprobe (QMNP-RGD) for bimodal imaging of in vitro tumor cells. The preparation of this multifunctional nanomaterial is divided into three steps. First, commercial quantum dots (QDs) with high fluorescence intensity are covalently modified with an RGD peptide, which can facilitate the tumor cell uptake by α_vβ₃ integrin-induced active recognition. Superparamagnetic iron oxide (SPIO) nanoparticles (NPs) are then capped using a cationic polysaccharide to improve stability. Integration is finally achieved by convenient electrostatic binding. We successfully demonstrated that QMNP-RGD can be efficiently delivered into U87MG cells and used for fluorescence/magnetic resonance (MR) bimodal imaging. Other multimodal probes may be able to be designed for imaging based on this strategy of electrostatic binding.

Micro-/nano-fluidic devices and in vivo fluorescence imaging based on quantum dots for cytologic diagnosis

Semiconductor quantum dots (QDs) possess attractive merits over traditional organic dyes, such as tunable emission, narrow emission spectra and good resistance against optical bleaching, and play a vital role in biosensing and bioimaging for cytologic diagnoses. Microfluidic technology is a potentially useful strategy, as it provides a rapid platform for tracing of disease markers. In vivo fluorescence imaging (FI) based on QDs has become popular for the analysis of complex biological processes. We herein report the applications of multifunctional fluorescent QDs as sensitive probes for diagnoses on cancer medicine and stem cell therapy via microfluidic chips and in vivo imaging.

Versatile Photoelectrochemical Biosensing for Hg2+ and Aflatoxin B1 Based on Enhanced Photocurrent of AgInS2 Quantum Dot-DNA Nanowires Sensitizing NPC-ZnO Nanopolyhedra

Eliminating false positives or negatives in analysis has been a challenge. Herein, a phenomenon of polarity-switching photocurrent of AgInS₂ quantum dot (QD)-DNA nanowires reversing nitrogen-doped porous carbon-ZnO (NPC-ZnO) nanopolyhedra was found for the first time, and a versatile photoelectrochemical (PEC) biosensor with a reversed signal was innovatively proposed for dual-target detection. NPC-ZnO is a photoactive material with excellent PEC properties, while AgInS₂ QDs as a photosensitive material match NPC-ZnO in the energy level, which not only promotes the transfer of photogenerated carriers but also switches the direction of PEC current. Furthermore, in order to prevent spontaneous agglomeration of AgInS₂ (AIS) QDs and improve its utilization rate, a new multiple-branched DNA nanowire was specially designed to assemble AgInS₂ QDs for constructing amplified signal probes, which not only greatly increased the load of AgInS₂ QDs but also further enhanced the photoelectric signal. When the target Hg²⁺-induced cyclic amplification process generated abundant RDNA, the DNA nanowire signal probe with plenty of QDs was linked to the NPC-ZnO/electrode by RDNA, generating greatly amplified polarity-reversed photocurrent for signal "ON" detection of Hg²⁺. After specific binding of the target (aflatoxin B1, AFB1) to its aptamer, the signal probes of AIS QD-DNA nanowires were released, realizing signal "OFF" assay of AFB1. Thus, the proposed new PEC biosensor provides a versatile method for detection of dual targets and also effectively avoids both false positive and negative phenomena in the assay process, which has great practical application potential in both environmental and food analysis.

ATP-Triggered Intracellular In Situ Aggregation of a Gold-Nanoparticle-Equipped Triple-Helix Molecular Switch for Fluorescence Imaging and Photothermal Tumor Therapy

Isotropic gold nanoparticles (AuNPs) can generate a plasma-plasma interaction when aggregating and can also produce ideal photothermal effects. Some studies have designed ATP-responsive nanodrug delivery systems by taking advantage of the differences between internal and external ATP in tumor cells, but few studies have focused on the photothermal effects of ATP-induced AuNP aggregation in tumors. Here, a triple-helix probe (THP) molecular switch and MUC1 aptamer-functionalized AuNPs were constructed for fluorescence imaging analysis and photothermal therapy (PTT). The MUC1 aptamer guides THP-AuNP targeting in tumor cells, followed by the high concentration of ATP inducing structural changes in triple-helix probes and causing the intracellular aggregation of AuNPs, which cannot escape from the tumor site, enabling tumor imaging while performing PTT. Therefore, the designed THP-AuNPs have promising applications in fluorescence imaging and PTT.

In Situ Fabrication of Nanoprobes for 19F Magnetic Resonance and Photoacoustic Imaging-Guided Tumor Therapy

It is challenging to fabricate multimodal imaging nanoprobes with high penetration depth and long blood circulation. Herein, we present multifunctional fluorinated nanoprobes (CFPP NPs) containing in situ formed copper chalcogenide nanoparticles for ¹⁹F magnetic resonance imaging (MRI) and photoacoustic imaging (PAI). The formed hydrophilic copper chalcogenide nanoassemblies demonstrated easy excretion stemming from facile disassembly, enhanced photothermal ability, and novel localized surface plasmon resonance (LSPR) absorption (centered at 1064 nm) in the "biological transparent" region. Both ¹⁹F MRI and PAI render these CFPP NPs suitable for multimodal imaging with high penetration depth and low background. Moreover, the chemo-photothermal synergistic therapy results suggest great potential in multimodal nanoprobes for imaging-guided tumor therapy applications.

Acid-Triggered H2O2 Self-Supplying Nanoplatform for 19F-MRI with Enhanced Chemo-Chemodynamic Therapy

The real-time tracking and efficacy evaluation of therapeutic nanoplatforms especially in deep-tissues is of great importance but faces challenges. Meanwhile, chemodynamic therapy (CDT), relying on Fenton reaction by converting H₂O₂ into toxic hydroxyl radicals (•OH), has drawn wide interests in the fabrication of nanozymes for tumor therapy, while endogenous H₂O₂ is usually insufficient for effective CDT. Here, we report the pH-responsive multifunctional nanoplatforms consisting of copper peroxide (CP) nanoparticles, paclitaxel (PTX) and perfluoro-15-crown-5-ether (PFCE), for ¹⁹F magnetic resonance imaging guided and enhanced chemo-chemodynamic synergetic therapy with self-supplied H₂O₂ stemmed from the decomposition of CP nanoparticles under acid conditions in tumor. The decomposition of CP nanoparticles further promotes the release of PTX for enhanced chemotherapy. Both in vitro and in vivo results indicate that the efficient generation of •OH and drug release effectively inhibits tumor growth. Furthermore, ¹⁹F MRI signal can clearly track the fate of nanoplatforms in tumor and guide tumor treatment. This work provides a promising strategy for the rational design and construction of multifunctional nanoplatforms for imaging-guided synergistic therapy of deep seated tumor.

19 F MRI Probes for Multimodal Imaging*

Magnetic resonance imaging (MRI) is one of the most powerful imaging tools today, capable of displaying superior soft-tissue contrast. This review discusses developments in the field of ¹⁹ F MRI multimodal probes in combination with optical fluorescence imaging (OFI), ¹ H MRI, chemical exchange saturation transfer (CEST) MRI, ultrasonography (USG), X-ray computed tomography (CT), single photon emission tomography (SPECT), positron emission tomography (PET), and photoacoustic imaging (PAI). In each case, multimodal ¹⁹ F MRI probes compensate for the deficiency of individual techniques and offer improved sensitivity or accuracy of detection over unimodal counterparts. Strategies for designing ¹⁹ F MRI multimodal probes are described with respect to their structure, physicochemical properties, biocompatibility, and the quality of images.

19F-Grafted Fluorescent Carbonized Polymer Dots for Dual-Mode Imaging

Dual-modal imaging systems could provide complementary information by taking advantage of each imaging modality. Herein, a fluorescence and ¹⁹F magnetic resonance imaging nanoprobe was developed through preparation of ¹⁹F-grafted fluorescent carbonized polymer dots (FCPDs). Both fluorescence and ¹⁹F nuclear magnetic resonance intensities of these FCPDs can be modulated by controlling the carbonization processes. The strong yellow fluorescence renders these FCPDs capable of cell fluorescence imaging. The in vitro and in vivo assessments demonstrated that the as-prepared FCPDs were suitable for ¹⁹F magnetic resonance imaging (¹⁹F MRI), which would provide great potential for biological imaging and early diagnosis applications. Moreover, this fabrication strategy offers a new protocol for ¹⁹F MRI nanoprobe design.

19F-nanoparticles: Platform for in vivo delivery of fluorinated biomaterials for 19F-MRI

Fluorine-19 (¹⁹F) magnetic resonance imaging (MRI) features one of the most investigated and innovative techniques for quantitative and unambiguous cell tracking, providing information for both localization and number of cells. Because of the relative insensitivity of the MRI technique, a high number of magnetically equivalent fluorine atoms are required to gain detectable signals. However, an increased amount of ¹⁹F nuclei induces low solubility in aqueous solutions, making fluorine-based probes not suitable for in vivo imaging applications. In this context, nanoparticle-based platforms play a crucial role, since nanoparticles may carry a high payload of ¹⁹F-based contrast agents into the relevant cells or tissues, increase the imaging agents biocompatibility, and provide a highly versatile platform. In this review, we present an overview of the ¹⁹F-based nanoprobes for sensitive ¹⁹F-MRI, focusing on the main nanotechnologies employed to date, such as fluorine and theranostic nanovectors, including their design and applications.

Aggregation-induced emission luminogen@manganese dioxide core-shell nanomaterial-based paper analytical device for equipment-free and visual detection of organophosphorus pesticide

Organophosphorus pesticide (OP) residues have gathered considerable attention because of their significant threat to society development and healthy life. Developing a sensitive and practical OPs sensor is highly urgent, whereas remains a huge challenge. To this end, we fabricated a high-performance fluorescence paper analytical device (PAD) for apparatus-free and visual sensing of OPs based on aggregation-induced emission (AIE) luminogen's bright emission in aggregated state, unique response of MnO₂ to thiol compounds, and difference of MnO₂ and Mn²⁺ in quenching fluorescence. AIE nanoparticles PTDNPs-0.10 and MnO₂ respectively acted as core and shell to prepare PTDNPs@MnO₂, which possessed high stability and were dripped on cellulose paper's surface to fabricate AIE-PAD. The sensing mechanism is that OPs-treated acetylcholinesterase (AChE) prevents the formation of thiocholine, thereby minimizing the reduction of MnO₂ into Mn²⁺ and changing the output signal. As a result, equipment-free and visual sensing of OPs was acquired with limit of detection of 1.60 ng/mL. This work justifies the feasibility of applying core-shell material to develop high-performance sensor and substituting complex/expensive solution-phase sensor with PAD, providing a new avenue to bring OPs analysis out of the lab and into the world.