Single-Atom Gd Nanoprobes for Self-Confirmative MRI with Robust Stability.

Gadolinium (Gd)-based complexes are extensively utilized as contrast agents (CAs) in magnetic resonance imaging (MRI), yet, suffer from potential safety concerns and poor tumor targeting. Herein, as a mimic of Gd complex, single-atom Gd nanoprobes with r1 and r2 values of 34.2 and 80.1 mM-1 s-1 (far higher than that of commercial Gd CAs) at 3 T are constructed, which possessed T1 /T2 dual-mode MRI with excellent stability and good tumor targeting ability. Specifically, single-atom Gd is anchored on nitrogen-doped carbon matrix (Gd-Nx C) through spatial-confinement method, which is further subjected to controllable chemical etching to afford fully etched bowl-shape Gd-Nx C (feGd-Nx C) with hydrophilic properties and defined coordination structure, similar to commercial Gd complex. Such nanostructures not only maximized the Gd3+ site exposure, but also are suitable for self-confirmative diagnosis through one probe with dual-mode MRI. Moreover, the strong electron localization and interaction between Gd and N atoms afforded feGd-Nx C excellent kinetic inertness and thermal stability (no significant Gd3+ leaching is observed even incubated with Cu2+ and Zn2+ for two months), providing a creative design protocol for MRI CAs.

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.

Dual-Channel Recognition of Human Serum Albumin and Glutathione by Fluorescent Probes with Site-Dependent Responsive Features.

Design of chemical probes with high specificity and responses are particularly intriguing. In this work, a fluorescent probe (M-OH-SO3) with dual-channel spectral responses toward human serum albumin (HSA) is presented. By employing dinitrobenzenesulfonate as a recognition site as well as a fluorescence quencher, probe M-OH-SO3 displayed weak fluorescence, which, nevertheless, exhibits extensive yellow (575 nm) and red (660 nm) fluorescence emissions toward HSA under excitations at 400 and 500 nm, respectively. Interestingly, M-OH-SO3 displayed the best performance toward HSA with distinctly higher selectivity than that of its counterparts M-SO3, M-H-SO3, and M-F-SO3, which were prepared simply by modulating the functional group at the ortho position of the dicyanoisophorone core. Molecular docking results revealed that M-OH-SO3 possesses the lowest binding energy among the tested derivatives and accordingly the strongest binding affinity. Probe M-OH-SO3 showed a good linear relationship toward HSA in a range of 0.5-18 µM with a limit of detection of 35 nM. Cell imaging results demonstrated that probe M-OH-SO3 could visualize the variation HSA levels in hepatocarcinoma cells. In addition, probe M-OH-SO3 could also be employed for the recognition of glutathione through the cleavage of the dinitrobenzenesulfonate group along with an enhancement of emission at 575 nm. The site-dependent properties inspired a novel paradigm for design of fluorescent probes with optimized selectivity and responses.

Stepwise-Enhanced Tumor Targeting of Near-Infrared Emissive Au Nanoclusters with High Quantum Yields and Long-Term Stability.

We developed an in situ coordination-driven spatially confined strategy for preparing near-infrared emissive gold nanoclusters encapsulated by fluorinated polymers (AuNCs@PF, λmax = 810 nm) with good stability and high quantum yields (27.7%), far higher than those previously reported for NIR AuNCs (>800 nm). Based on the stepwise enhancements including long blood circulation-induced passive tumor targeting, fluoro-enhanced tumor permeation, and tumor microenvironment (weak acid)-induced aggregation retention in cells, these AuNCs demonstrated bright and stable NIR fluorescence imaging ability in tumors. Additionally, the AuNCs@PF were capable of fluorine magnetic resonance imaging and computed tomographic imaging. The multimodal imaging of tumor-bearing mice clearly implied the potential of AuNCs@PF in biomedical fields.

Coordination-Driven Self-Assembly of Iron Oxide Nanoparticles for Tumor Microenvironment-Responsive Magnetic Resonance Imaging.

Accurate diagnosis of diseases located in deep tissues is always challenging. The "always-on" probe often leads to false-positive signals due to nonspecific interaction of nanoprobes. Thus, stimuli-responsive nanoprobes are highly desirable, which, however, require complicated surface modification so as to achieve trigger-induced signal changes. Here pH-triggered switchable magnetic resonance imaging (MRI) nanoprobes were constructed by coordination-driven self-assembly of monodispersed iron oxide nanoparticles (MIONPs) with simple amino acid derivatives, which displayed typical T2-weighted MRI features, yet, were turned into T1-weighted MRI under slightly acidic conditions at the tumor site. The dynamic assembly and disassembly properties of MIONPs afford T2/T1 switchable contrast imaging, enabling selective "turn-on" signals at the tumor site with high specificity.

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.

Selective Ligand Sensitization of Lanthanide Nanoparticles for Multilevel Information Encryption with Excellent Durability.

Durable and multilevel information encryption technology has been of great importance in recent decades. Here, an inkjet printer-adaptable invisible ink was prepared with lanthanide nanoparticles, and optical decoding of information could only be achieved when specific ligand dipicolinic acid was utilized in the presence of UV illumination. In addition, the proposed protocols displayed long shelf life (>one year) and excellent durability even at harsh conditions such as in the presence of strong acids (1 M HCl) and alkalis (1 M NaOH). Meanwhile, such invisible inks could be further employed on a soft matrix via screen-printing, holding great potential for practical applications.

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

Tumor microenvironment turn-on nanoprobes that could specifically detect the occurrence of diseases possess great potential in early diagnosis. Here, a GSH activated nanoprobe was designed for fluorescence and 19F magnetic resonance (MR) dual-modal turn-on imaging of tumors. Specifically, fluorescence AgInS2 quantum dots (QDs for fluorescence imaging) were co-encapsulated with perfluoro-15-crown-5-ether (P19FCE for19F MRI) by amphiphilic polymers and further coated with in situ formed manganese dioxide (MnO2) nanoshells, which served as efficient fluorescence and 19F MR quenchers due to energy transfer and paramagnetic relaxation effects, respectively. The over-expressed GSH in tumors would decompose the MnO2 nanoshells, resulting in remarkable enhancement of both fluorescence and 19F MRI signals of the nanoprobes, accordingly lighting up the tumor site.

19F MRI Nanoprobes for the Turn-On Detection of Phospholipase A2 with a Low Background.

The highly sensitive detection and imaging of enzymatic activities in vivo could provide effective information about biological functions for monitoring the process of disease and evaluating the effect of therapy. 19F magnetic resonance imaging (MRI) has attracted wide interest because of its deep tissue imaging capability and negligible endogenous background interference, which are suitable for the visualization of enzymatic activities in vivo, but the fabrication of this probe faces challenges. Here, we report nanoprobes with turn-on 19F MRI for sensing the activity of phospholipase A2 (PLA2). These nanoprobes are composed of Gd3+-exchanged NaYF4:Yb3+/Er3+ upconversion luminescent nanoparticles grafted with perfluoro-15-crown-5-ether (PFCE) as the hydrophobic core with a phospholipid shell in which the 19F MRI signal of PFCE is obviously quenched by adjacent Gd3+. The shielded 19F MRI signal of these nanoprobes is then turned on by the nanoprobe dissolution stemming from phospholipid hydrolysis by PLA2 and increases linearly along with the increment of PLA2 in the range of 5.0-200 U/L. Apart from the in vitro detection of PLA2 by 19F NMR, these nanoprobes show great potential for both the in vivo 19F MRI sensing of PLA2 and activity screening of PLA2 inhibitors with a high signal-to-noise ratio and a high penetration depth.

Solvent Tailored Strategy for Synthesis of Ultrasmall Ag2S Quantum Dots with Near-Infrared-II Luminescence.

Highly luminescent semiconductor with ultrasmall size is always desirable for biomedical applications. Here, we developed a novel solvent-directing strategy to prepare ultrasmall monodispersed Ag2S quantum dots (QDs) with strong luminescence in the second near infrared (NIR-II) range (1000∼1400 nm). The particle size and luminescence of these Ag2S QDs could be desirably tuned by adjusting the solvents of the system. With further surface modification, the hydrophilic Ag2S QDs could be successfully utilised for cancerous cells imaging, indicating great potentials in biomedical fields.

Fluorine Grafted Cu7S4-Au Heterodimers for Multimodal Imaging Guided Photothermal Therapy with High Penetration Depth.

We report the multifunctional nanocomposites (NCs) consisting of 19F-moieties grafted Cu7S4-Au nanoparticles (NPs) for negligible background 19F-magnetic resonance imaging (19F-MRI) and computed tomography (CT) imaging guided photothermal therapy. The localized surface plasmon resonance (LSPR) absorption can be reasonably tuned to the in vivo transparent window (800-900 nm) by coupling Au (<10 nm, LSPR ∼530 nm) with Cu7S4 (<15 nm, LSPR ∼1500 nm) into Cu7S4-Au heterodimers. The in vivo photothermal tests show that Cu7S4-Au show deeper light penetration with 808 nm irradiation, better photothermal efficacy, and less damage to normal tissues than Cu7S4 with 1500 nm irradiation. Moreover, compared to traditional 1H-MRI, the 19F-MRI based on these NCs demonstrates much better sensitivity due to the negligible background. This work offers a promising strategy for multimodal imaging guided photothermal therapy of deep tissue with good efficacy.

Full-Range pH Stable Au-Clusters in Nanogel for Confinement-Enhanced Emission and Improved Sulfide Sensing in Living Cells.

The sensitive and selective detection of hydrogen sulfide is of great importance due to its crucial role in pathological and physiological processes. Herein, we report a novel fluorescent platform, AuNCs@GC, for selective detection of hydrogen sulfide in living cells by impregnating the Au nanoclusters (AuNCs) into a biocompatible cationic polymer matrix, glycol-chitosan (GC) nanogel. The confinement effect significantly increased the emissive Au(I) units, resulting in a 6-fold enhancement of quantum yield (from 6.38% to 36.42%). In addition, the prepared positively charged AuNCs@GC nanogel exhibits excellent selectivity and improved sensitivity to aqueous sulfides. Moreover, the as-fabricated AuNCs@GC showed very good biocompatibility and super fluorescence stability across the full pH range and good salt tolerance, which demonstrated excellent adaptability toward intracellular sulfide imaging.

Plasmon-Enhanced Photoelectrical Hydrogen Evolution on Monolayer MoS2 Decorated Cu1.75 S-Au Nanocrystals.

Hydrogen production from water splitting through an efficient photoelectrochemical route requires photoinduced electron transfer from light harvesters to efficient electrocatalysts. Here, the plasmon-enhanced photoelectrical nanocatalysts (NCs) have been successfully developed by coating a monolayer MoS2 on the Cu1.75 S-Au hetero-nanoparticle for hydrogen evolution reaction (HER). The plasmonic NCs dramatically improve the HER, leading to 29.5-fold increase of current under 650 nm excitation (1.0 W cm-2 ). These NCs generate an exceptionally high current density of 200 mA cm-2 at overpotential of 182.8 mV with a Tafel slope of 39 mV per decade and excellent stability, which is better than or comparable to the Pt-free catalysts with carbon rod as counter electrode. The enhanced HER performance can be attributed to the significantly improved broad light absorption (400-3000 nm), more efficient charge separation and abundant active edge sites of monolayer MoS2 . The studies may provide a facile strategy for the fabrication of efficient plasmon-enhanced photoelectrical NCs for HER.

A Fluorescent Chemodosimeter for Live-Cell Monitoring of Aqueous Sulfides.

Aqueous sulfides are emerging signaling agents implicated in various pathological and physiological processes. The development of sensitive and selective methods for the sensing of these sulfides is therefore very important. Herein, we report that the as-synthesized 1-oxo-1H-phenalene-2,3-dicarbonitrile (OPD) compound provides promising fluorescent properties and unique reactive properties toward aqueous sulfides. It was found that OPD showed high selectivity and sensitivity toward Na2S over thiols and other inorganic sulfur compounds through a sulfide involved reaction which was confirmed by high-resolution mass spectroscopy (HRMS) and nuclear magnetic resonance (NMR) results. The fluorescence intensity increases linearly with sulfide concentration in the range of 1.0-30 µM with a limit of detection of 52 nM. This novel fluorescent probe was further exploited for the fluorescence imaging sensing of aqueous sulfide in HeLa cells.

Ultrasmall Organic Nanoparticles with Aggregation-Induced Emission and Enhanced Quantum Yield for Fluorescence Cell Imaging.

The use of fluorescence probes for biomedical imaging has attracted significant attention over recent years owing to their high resolution at cellular level. The probes are available in many formats including small particle size based imaging agents which are considered to be promising candidates, due to their excellent stabilities. Yet, concerns over the potential cytotoxicity effects of inorganic luminescent particles have led to questions about their suitability for imaging applications. Exploration of alternatives inspired us to use organic fluorophores with aggregation-induced emission (AIE), prepared by functionalizing the amine group on tetraphenylethene with 3,5-bis(trifluoromethyl)phenyl isocyanate. The as-synthesized novel AIE fluorophore (TPE-F) display enhanced quantum yield and longer lifetime as compared with its counterparts (4,4',4″,4‴-(ethene-1,1,2,2-tetrayl)tetraaniline, TPE-AM). Furthermore, the TPE-F was encapsulated into small-size organic nanoparticles (NPs; dynamic light scattering size, ∼10 nm) with polysuccinimide (PSI). The biocompatibility, excellent stability, bright fluorescence, and selective cell targeting of these NPs enable the as-prepared TPE-F NPs to be suitable for specific fluorescence cell imaging.

Ultrasmall Cu7 S4 @MoS2 Hetero-Nanoframes with Abundant Active Edge Sites for Ultrahigh-Performance Hydrogen Evolution.

Increasing the active edge sites of molybdenum disulfide (MoS2 ) is an efficient strategy to improve the overall activity of MoS2 for the hydrogen-evolution reaction (HER). Herein, we report a strategy to synthesize the ultrasmall donut-shaped Cu7 S4 @MoS2 hetero-nanoframes with abundant active MoS2 edge sites as alternatives to platinum (Pt) as efficient HER electrocatalysts. These nanoframes demonstrate an ultrahigh activity with 200 mA cm(-2) current density at only 206 mV overpotential using a carbon-rod counter electrode. The finding may provide guidelines for the design and synthesis of efficient and non-precious chalcogenide nanoframe catalysts.

Polyaniline-based photothermal paper sensor for sensitive and selective detection of 2,4,6-trinitrotoluene.

We report for the first time a photothermal paper sensor for the selective and sensitive detection of 2,4,6-trinitrotoluene (TNT) down to 14 ng/cm(2). In the presence of TNT, a Meisenheimer complex was formed by means of a charge transfer process from an electron-rich group in polyaniline (PANI) to an electron-deficient nitro group in TNT, which resulted in the near-infrared absorption around 800 nm. Upon irradiation with an 808 nm diode laser, the photothermal effect of the PANI/TNT complex caused the temperature increase, and the temperature difference (ΔT) was proportional to the TNT concentration, while the temperature increase was hardly observed for other nitroaromatics including 2,4-dinitrotoluene (DNT), 2,4,6-trinitrophenol (TNP), and nitrobenzene (NB), affording high selectivity toward TNT. All the tests can be conducted both in solution and on paper. Therefore, the proposed photothermal strategy not only offers a fast and convenient protocol for selective detection of TNT but also indicates great potential in practical applications, especially for airport/railway security inspection and prevention of terrorist attacks.

Fluorescent nanosensors via photoinduced polymerization of hydrophobic inorganic quantum dots for the sensitive and selective detection of nitroaromatics.

We developed an efficient one-pot strategy for the preparation of hydrophilic amine-functionalized nanocomposites by using hydrophobic fluorescence quantum dots ZnS:Mn(2+)@allyl mercaptan (QDs@AM) as building blocks through novel light-induced in situ polymerization. The average size of as-prepared hydrophilic nanocomposites was ∼50 nm, which could be further tuned by varying the concentrations of the monomers. Importantly, these nanocomposites were further utilized for the facile, highly sensitive, and selective detection of nitroaromatics. The linear ranges for 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrophenol (TNP) lie in 0.01-0.5 µg/mL and 0.05-8.0 µg/mL, respectively, barely interfered with by other nitroaromatics such as 2,4-dinitrotoluene (DNT) and nitrobenzene (NB). Moreover, the novel surface modification method developed here offered a general strategy for fabricating hydrophobic nanocomposites with hydrophilic properties and indicated various potential applications including sensing and imaging.

Highly Efficient Photothermal Semiconductor Nanocomposites for Photothermal Imaging of Latent Fingerprints.

Optical imaging of latent fingerprints (LFPs) has been widely used in forensic science and for antiterrorist applications, but it suffers from interference from autofluorescence and the substrates background color. Cu7S4 nanoparticles (NPs), with excellent photothermal properties, were synthesized using a new strategy and then fabricated into amphiphilic nanocomposites (NCs) via polymerization of allyl mercaptan coated on Cu7S4 NPs to offer good affinities toward LFPs. Here, we develop a facile and versatile photothermal LFP imaging method based on the high photothermal conversion efficiency (52.92%, 808 nm) of Cu7S4 NCs, indicating its effectiveness for imaging LFPs left on different substrates (with various background colors), which will be extremely useful for crime scene investigations. Furthermore, by fabricating Cu7S4-CdSe@ZnS NCs, a fluorescent-photothermal dual-mode imaging strategy was used to detect trinitrotoluene (TNT) in LFPs while still maintaining a complete photothermal image of LFP.

Cu7 S4 Nanosuperlattices with Greatly Enhanced Photothermal Efficiency.

According to the simulation, the self-assembly of Cu7 S4 nanocrystals would enhance the photothermal conversion efficiency (PCE) because of the localized surface plasmon resonance effects, which is highly desirable for photothermal therapy (PTT). A new strategy to synthesize Cu7 S4 nanosuperlattices with greatly enhanced PCE up to 65.7% under irradiation of 808 nm near infrared light is reported here. By tuning the surface properties of Cu7 S4 nanocrystals during the synthesis via thermolysis of a new single precursor, dispersed nanoparticles (NPs), rod-like alignments, and nanosuperlattices are obtained, respectively. To explore their PTT applications, these hydrophobic nanostructures are transferred into water by coating with home-made amphiphilic polymer while maintaining their original structures. Under identical conditions, the PCE are 48.62% and 56.32% for dispersed NPs and rod-like alignments, respectively. As expected, when the nanoparticles are self-assembled into nanosuperlattices, the PCE is greatly enhanced up to 65.7%. This strong PCE, along with their excellent photothermal stability and good biocompatibility, renders these nanosuperlattices good candidates as PTT agents. In vitro photothermal ablation performances have undoubtedly proved the excellent PCE of our Cu7 S4 nanosuperlattices. This research offers a versatile and effective solution to get PTT agents with high photothermal efficiency.