A New Single 808 nm NIR Light‐Induced Imaging‐Guided Multifunctional Cancer Therapy Platform

The NIR light‐induced imaging‐guided cancer therapy is a promising route in the targeting cancer therapy field. However, up to now, the existing single‐modality light‐induced imaging effects are not enough to meet the higher diagnosis requirement. Thus, the multifunctional cancer therapy platform with multimode light‐induced imaging effects is highly desirable. In this work, captopril stabilized‐Au nanoclusters Au₂₅(Capt)₁₈?(Au₂₅) are assembled into the mesoporous silica shell coating outside of Nd³⁺‐sensitized upconversion nanoparticles (UCNPs) for the first time. The newly formed Au₂₅ shell exhibits considerable photothermal effects, bringing about the photothermal imaging and photoacoustic imaging properties, which couple with the upconversion luminescence imaging. More importantly, the three light‐induced imaging effects can be simultaneously achieved by exciting with a single NIR light (808 nm), which is also the triggering factor for the photothermal and photodynamic cancer therapy. Besides, the nanoparticles can also present the magnetic resonance and computer tomography imaging effects due to the Gd³⁺ and Yb³⁺ ions in the UCNPs. Furthermore, due to the photodynamic and the photothermal effects, the nanoparticles possess efficient in vivo tumor growth inhibition under the single irradiation of 808 nm light. The multifunctional cancer therapy platform with multimode imaging effects realizes a true sense of light‐induced imaging‐guided cancer therapy.     

The Active‐Core/Active‐Shell Approach: A Strategy to Enhance the Upconversion Luminescence in Lanthanide‐Doped Nanoparticles

Nanoparticles of NaGdF₄ doped with trivalent erbium (Er³⁺) and ytterbium (Yb³⁺) are prepared by a modified thermal decomposition synthesis from trifluoroacetate precursors in 1‐octadecene and oleic acid. The nanoparticles emit visible upconverted luminescence on excitation with near‐infrared light. To minimize quenching of this luminescence by surface defects and surface‐associated ligands, the nanoparticles are coated with a shell of NaGdF₄. The intensity of the upconversion luminescence is compared for nanoparticles that were coated with an undoped shell (inert shell) and similar particles coated with a Yb³⁺‐doped shell (active shell). Luminescence is also measured for nanoparticles lacking the shell (core only), and doped with Yb³⁺ at levels corresponding to the doped and undoped core/shell materials respectively. Upconversion luminescence was more intense for the core/shell materials than for the uncoated nanoparticles, and is greatest for the materials having the “active” doped shell. Increasing the Yb³⁺ concentration in the “core‐only” nanoparticles decreases the upconversion luminescence intensity. The processes responsible for the upconversion are presented and the potential advantages of “active‐core”/“active‐shell” nanoparticles are discussed.     

An O2 Self‐Supplementing and Reactive‐Oxygen‐Species‐Circulating Amplified Nanoplatform via H2O/H2O2 Splitting for Tumor Imaging and Photodynamic Therapy

Conventional photodynamic therapy (PDT) has limited applications in clinical cancer therapy due to the insufficient O₂ supply, inefficient reactive oxygen species (ROS) generation, and low penetration depth of light. In this work, a multifunctional nanoplatform, upconversion nanoparticles (UCNPs)@TiO₂@MnO₂ core/shell/sheet nanocomposites (UTMs), is designed and constructed to overcome these drawbacks by generating O₂ in situ, amplifying the content of singlet oxygen (¹O₂) and hydroxyl radical (?OH) via water‐splitting, and utilizing 980 nm near‐infrared (NIR) light to increase penetration depth. Once UTMs are accumulated at tumor site, intracellular H₂O₂ is catalyzed by MnO₂ nanosheets to generate O₂ for improving oxygen‐dependent PDT. Simultaneously, with the decomposition of MnO₂ nanosheets and 980 nm NIR irradiation, UCNPs can efficiently convert NIR to ultraviolet light to activate TiO₂ and generate toxic ROS for deep tumor therapy. In addition, UCNPs and decomposed Mn²⁺ can be used for further upconversion luminescence and magnetic resonance imaging in tumor site. Both in vitro and in vivo experiments demonstrate that this nanoplatform can significantly improve PDT efficiency with tumor imaging capability, which will find great potential in the fight against tumor.     

Highly Emissive Nd3+‐Sensitized Multilayered Upconversion Nanoparticles for Efficient 795 nm Operated Photodynamic Therapy

Photodynamic therapy (PDT) is a noninvasive and site‐specific therapeutic technique for the clinical treatment of various of superficial diseases. In order to tuning the operation wavelength and improve the tissue penetration of PDT, rare‐earth doped upconversion nanoparticles (UCNPs) with strong anti‐stokes emission are introduced in PDT recently. However, the conventional Yb³⁺‐sensitized UCNPs are excited at 980 nm which is overlapped with the absorption of water, thus resulting in strong overheating effect. Herein, a convenient but effective design to obtain highly emissive 795 nm excited Nd³⁺‐sensitized UCNPs (NaYF₄:Yb,Er@NaYF₄:Yb_0.1Nd_0.4@NaYF₄) is reported, which provides about six times enhanced upconversion luminescence, comparing with traditional UCNPs (NaYF₄:Yb,Er@NaYF₄). A colloidal stable and non‐leaking PDT nanoplatform is fabricated later through a highly PEGylated mesoporous silica layer with covalently linked photosensitizer (Rose Bengal derivative). With as‐prepared Nd³⁺‐sensitized UCNPs, the nanoplatform can produce singlet oxygen more effective than traditional UCNPs. Significant higher penetration depth and lower overheating are demonstrated as well. All these features make as‐prepared nanocomposites excellent platform for PDT treatment. In addition, the nanoplatform with uniform size, high surface area, and excellent colloidal stability can be extended for other biomedical applications, such as imaging probes, biosensors, and drug delivery vehicles.     

Imaging‐Guided pH‐Sensitive Photodynamic Therapy Using Charge Reversible Upconversion Nanoparticles under Near‐Infrared Light

Photodynamic therapy (PDT) based on upconversion nanoparticles (UCNPs) can effectively destroy cancer cells under tissue‐penetrating near‐infrared light (NIR) light. Herein, we synthesize manganese (Mn²⁺)‐doped UCNPs with strong red light emission at ca. 660 nm under 980 nm NIR excitation to activate Chlorin e6 (Ce6), producing singlet oxygen (¹O₂) to kill cancer cells. A layer‐by‐layer (LbL) self‐assembly strategy is employed to load multiple layers of Ce6 conjugated polymers onto UCNPs via electrostatic interactions. UCNPs with two layers of Ce6 loading (UCNP@2xCe6) are found to be optimal in terms of Ce6 loading and ¹O₂ generation. By further coating UCNP@2xCe6 with an outer layer of charge‐reversible polymer containing dimethylmaleic acid (DMMA) groups and polyethylene glycol (PEG) chains, we obtain a UCNP@2xCe6‐DMMA‐PEG nanocomplex, the surface of which is negatively charged and PEG coated under pH 7.4; this could be converted to have a positively charged naked surface at pH 6.8, significantly enhancing cell internalization of nanoparticles and increasing in vitro NIR‐induced PDT efficacy. We then utilize the intrinsic optical and paramagnetic properties of Mn²⁺‐doped UCNPs for in vivo dual modal imaging, and uncover an enhanced retention of UCNP@2xCe6‐DMMA‐PEG inside the tumor after intratumoral injection, owing to the slightly acidic tumor microenvironment. Consequently, a significantly improved in vivo PDT therapeutic effect is achieved using our charge‐reversible UCNP@2xCe6‐DMMA‐PEG nanoparticles. Finally, we further demonstrate the remarkably enhanced tumor‐homing of these pH‐responsive charge‐switchable nanoparticles in comparison to a control counterpart without pH sensitivity after systemic intravenous injection. Our results suggest that UCNPs with finely designed surface coatings could serve as smart pH‐responsive PDT agents promising in cancer theranostics.     

Plasmon‐Enhanced Blue Upconversion Luminescence by Indium Nanocrystals

Numerous endeavors have been undertaken to gain enhanced upconversion luminescence via surface plasmon resonance (SPR) generated by specially designed nanostructures of noble metals (e.g., Au, Ag). However, the SPR response of these metals is usually weak in the ultraviolet (UV) region because of their intrinsic electronic configurations; thus, only green and red upconversion emissions can undergo significant plasmonic enhancement yet without selectivity, while an efficient approach to selectively enhancing the blue upconversion luminescence has been lacking. Herein, by integrating the pronounced UV SPR of silica‐coated indium nanocrystals (InNCs) with blue‐emission upconversion nanoparticles (UCNPs) of NaYbF₄:Tm, an up to tenfold selective luminescence enhancement at 450 nm is obtained upon 980 nm laser excitation. Precise manipulation of the silica shell thickness suggests an optimal working distance of 3 nm between InNCs and UCNPs. This study has, for the first time, realized selective blue upconversion luminescence enhancement by using an inexpensive, non‐noble metal material, which will not only enrich the fundamental investigations of SPR‐enhanced upconversion emission, but also widen the applications of blue light‐emitting nanomaterials, for example, in therapeutics.     

Controlling Red Color–Based Multicolor Upconversion through Selective Photon Blocking

Photon upconversion multiplexing has attracted increasing interest in recent years; however, realizing the red color–based multicolor‐tunable output in upconversion nanoparticles (UCNPs) at a fixed composition remains a huge challenge. Here, a novel and versatile approach to fine‐control upconversion luminescence (UCL) colors from UCNPs through selectively confining specific excitation energy by the photon blocking effect is reported. Four types of dual‐color switchable UCNPs capable of emitting red‐blue and red‐green emissions are successfully designed following this strategy, and their UCL performance shows a multiwavelength (808/980/1550 nm) excitable feature that is well sustained in a wide range of excitation power density. The use of the photon blocking effect further enables the dynamically switchable red‐green‐blue UCL with 808/980 nm excitations. These findings provide a general method to achieve multicolor‐tunable UCL at a single nanoparticle level. Moreover, the UCNPs with red‐based multicolor emissions in this work enriches the upconversion system and should have potential applications in display, anti‐counterfeiting, and bioimaging.     

Plasmonic Dual‐Enhancement and Precise Color Tuning of Gold Nanorod@SiO2 Coupled Core–Shell–Shell Upconversion Nanocrystals

The last decade has witnessed the remarkable research progress of lanthanide‐doped upconversion nanocrystals (UCNCs) at the forefront of promising applications. However, the future development and application of UCNCs are constrained greatly by their underlying shortcomings such as significant nonradiative processes, low quantum efficiency, and single emission colors. Here a hybrid plasmonic upconversion nanostructure consisting of a GNR@SiO₂ coupled with NaGdF₄:Yb³⁺,Nd³⁺@NaGdF₄:Yb³⁺,Er³⁺@NaGdF₄ core–shell–shell UCNCs is rationally designed and fabricated, which exhibits strongly enhanced UC fluorescence (up to 20 folds) and flexibly tunable UC colors. The experimental findings show that controlling the SiO₂ spacer thickness enables readily manipulating the intensity ratio of the Er³⁺ red, green, and blue emissions, thereby allowing us to achieve the emission color tuning from pale yellow to green upon excitation at 808 nm. Electrodynamic simulations reveal that the tunable UC colors are due to the interplay of plasmon‐mediated simultaneous excitation and emission enhancements in the Er³⁺ green emission yet only excitation enhancement in the blue and red emissions. The results not only provide an upfront experimental design for constructing hybrid plasmonic UC nanostructures with high efficiency and color tunability, but also deepen the understanding of the interaction mechanism between the Er³⁺ emissions and plasmon resonances in such complex hybrid nanostructure.     

Single Ho3+‐Doped Upconversion Nanoparticles for High‐Performance T2‐Weighted Brain Tumor Diagnosis and MR/UCL/CT Multimodal Imaging

Multimodal bio‐imaging has attracted great attention for early and accurate diagnosis of tumors, which, however, suffers from the intractable issues such as complicated multi‐step syntheses for composite nanostructures and interferences among different modalities like fluorescence quenching by MRI contrast agents (e.g., magnetic iron oxide NPs). Herein, the first example of T₂‐weighted MR imaging of Ho³⁺‐doped upconversion nanoparticles (UCNPs) is presented, which, very attractively, could also be simultaneously used for upconversion luminesence (UCL) and CT imaging, thus enabling high performance multi‐modal MRI/UCL/CT imagings in single UCNPs. The new finding of T₂‐MRI contrast enhancement by integrated sensitizer (Yb³⁺) and activator (Ho³⁺) in UCNPs favors accurate MR diagnosis of brain tumor and provides a new strategy for acquiring T₂‐MRI/optical imaging without fluorescence quenching. Unlike other multi‐phased composite nanostructures for multimodality imaging, this Ho³⁺‐doped UCNPs are featured with simplicity of synthesis and highly efficient multimodal MRI/UCL/CT imaging without fluorescence quenching, thus simplify nanostructure and probe preparation and enable win–win multimodality imaging.     

Solution‐Processable Near‐Infrared–Responsive Composite of Perovskite Nanowires and Photon‐Upconversion Nanoparticles

Organolead halide perovskites (OHPs) have shown unprecedented potentials in optoelectronics. However, the inherent large bandgap has restrained its working wavelength within 280–800 nm, while light at other regions, e.g., near‐infrared (NIR), may cause drastic thermal heating effect that goes against the duration of OHP devices, if not properly exploited. Herein, a solution processable and large‐scale synthesis of multifunctional OHP composites containing lanthanide‐doped upconversion nanoparticles (UCNPs) is reported. Upon NIR illumination, the upconverted photons from UCNPs at 520–550 nm can be efficiently absorbed by closely surrounded OHP nanowires (NWs) and photocurrent is subsequently generated. The narrow full width at half maximum of the absorption of rare earth ions (Yb³⁺ and Er³⁺) has ensured high‐selective NIR response. Lifetime characterizations have suggested that Förster resonance energy transfer with an efficiency of 28.5% should be responsible for the direct energy transfer from UCNPs to OHP NWs. The fabricated proof‐of‐concept device has showcased perfect response to NIR light at 980 and 1532 nm, which has paved new avenues for applications of such composites in remote control, distance measurement, and stealth materials.     

Tumor Microenvironment‐Responsive Mesoporous MnO2‐Coated Upconversion Nanoplatform for Self‐Enhanced Tumor Theranostics

The insufficient blood flow and oxygen supply in solid tumor cause hypoxia, which leads to low sensitivity of tumorous cells and thus causing poor treatment outcome. Here, mesoporous manganese dioxide (mMnO₂) with ultrasensitive biodegradability in a tumor microenvironment (TME) is grown on upconversion photodynamic nanoparticles for not only TME‐enhanced bioimaging and drug release, but also for relieving tumor hypoxia, thereby markedly improving photodynamic therapy (PDT). In this nanoplatform, mesoporous silica coated upconversion nanoparticles (UCNPs@mSiO₂) with covalently loaded chlorin e6 are obtained as near‐infrared light mediated PDT agents, and then a mMnO₂ shell is grown via a facile ultrasonic way. Because of its unique mesoporous structure, the obtained nanoplatform postmodified with polyethylene glycol can load the chemotherapeutic drug of doxorubicin (DOX). When used for antitumor application, the mMnO₂ degrades rapidly within the TME, releasing Mn²⁺ ions, which couple with trimodal (upconversion luminescence, computed tomography (CT), and magnetic resonance imaging) imaging of UCNPs to perform a self‐enhanced imaging. Significantly, the degradation of mMnO₂ shell brings an efficient DOX release, and relieve tumor hypoxia by simultaneously inducing decomposition of tumor endogenous H₂O₂ and reduction of glutathione, thus achieving a highly potent chemo‐photodynamic therapy.     

Positive and Negative Lattice Shielding Effects Co‐existing in Gd (III) Ion Doped Bifunctional Upconversion Nanoprobes

Gadolinium (Gd) doped upconversion nanoparticles (UCNPs) have been well documented as T₁‐MR and fluorescent imaging agents. However, the performance of Gd³⁺ ions located differently in the crystal lattice still remains debatable. Here, a well‐designed model was built based on a seed‐mediated growth technique to systematically probe the longitudinal relaxivity of Gd³⁺ ions within the crystal lattice and at the surface of UCNPs. We found, for the first time, a nearly 100% loss of relaxivity of Gd³⁺ ions buried deeply within crystal lattices (> 4 nm), which we named a “negative lattice shielding effect” (n‐LSE) as compared to the “positive lattice shielding effect” (p‐LSE) for the enhanced upconversion fluorescent intensity. As‐observed n‐LSE was further found to be shell thickness dependent. By suppressing the n‐LSE as far as possible, we optimized the UCNPs' structure design and achieved the highest r₁ value (6.18 mM^?1s^?1 per Gd³⁺ ion) among previously reported counterparts. The potential bimodal imaging application both in vitro and in vivo of as‐designed nano‐probes was also demonstrated. This study clears the debate over the role of bulk and surface Gd³⁺ ions in MRI contrast imaging and paves the way for modulation of other Gd‐doped nanostructures for highly efficient T₁‐MR and upconversion fluorescent bimodal imaging.     

Remarkable NIR Enhancement of Multifunctional Nanoprobes for In Vivo Trimodal Bioimaging and Upconversion Optical/T2‐Weighted MRI‐Guided Small Tumor Diagnosis

Effective nanoprobes and contrast agents are urgently sought for early‐stage cancer diagnosis. Upconversion nanoparticles (UCNPs) are considerable alternatives for bioimaging, cancer diagnosis, and therapy. Yb³⁺/Tm³⁺ co‐doping brings both emission and excitation wavelengths into the near‐infrared (NIR) region, which is known as “optical transmission window” and ideally suitable for bioimaging. Here, NIR emission intensity is remarkably enhanced by 113 times with the increase of Yb³⁺ concentration from 20% to 98% in polyethylene glycol (PEG) modified NaYF₄:Yb³⁺/Tm³⁺ UCNPs. PEG‐UCNPs‐5 (98% Yb³⁺) can act as excellent nanoprobes and contrast agents for trimodal upconversion (UC) optical/CT/T₂‐weighted magnetic resonance imaging (MRI). In addition, the enhanced detection of lung in vivo long‐lasting tracking, as well as possible clearance mechanism and excretion routes of PEG‐UCNPs‐5 have been demonstrated. More significantly, a small tumor down to 4 mm is detected in vivo via intravenous injection of these nanoprobes under both UC optical and T₂‐weighted MRI modalities. PEG‐UCNPs‐5 can emerge as bioprobes for multi‐modal bioimaging, disease diagnosis, and therapy, especially the early‐stage tumor diagnosis.     

Electrochromic Switch Devices Mixing Small‐ and Large‐Sized Upconverting Nanocrystals

The hasty progress in smart, portable, flexible, and transparent integrated electronics and optoelectronics is currently one of the driving forces in nanoscience and nanotechnology. A promising approach is the combination of transparent conducting electrode materials (e.g., silver nanowires, AgNWs) and upconverting nanoparticles (UCNPs). Here, electrochromic devices based on transparent nanocomposite films of poly(methyl methacrylate) and AgNWs covered by UCNPs of different sizes and compositions are developed. By combining the electrical control of the heat dissipation in AgNW networks with size‐dependent thermal properties of UCNPs, tunable electrochromic transparent devices covering a broad range of the chromatic diagrams are fabricated. As illustrative examples, devices mixing large‐sized (>70 nm) β‐NaYF₄:Yb,Ln and small‐sized (<15 nm) NaGdF₄:Yb,Ln@NaYF₄ core@shell UCNPs (Ln = Tm, Er, Ce/Ho) are presented, permitting to monitor the temperature‐dependent emission of the particles by the intensity ratio of the Er^{3+ 2}H_11/2 and ⁴S_3/2 → ⁴I_15/2 emission lines, while externally controlling the current flow in the AgNW network. Moreover, by defining a new thermometric parameter involving the intensity ratio of transitions of large‐ and small‐sized UCNPs, a relative thermal sensitivity of 5.88% K^?1 (at 339 K) is obtained, a sixfold improvement over the values reported so far.     

Multifunctional Up‐Converting Nanocomposites with Smart Polymer Brushes Gated Mesopores for Cell Imaging and Thermo/pH Dual‐Responsive Drug Controlled Release

Multifunctional nanocarriers based on the up‐conversion luminescent nanoparticles of NaYF₄:Yb³⁺/Er³⁺ core (UCNPs) and thermo/pH‐coupling sensitive polymer poly[(N‐isopropylacrylamide)‐co‐(methacrylic acid)] (P(NIPAm‐co‐MAA)) gated mesoporous silica shell are reported for cancer theranostics, including fluorescence imaging, and for controlled drug release for therapy. The as‐synthesized hybrid nanospheres UCNPs@mSiO₂‐P(NIPAm‐co‐MAA) show bright green up‐conversion fluorescence under 980 nm laser excitation and the thermo/pH‐sensitive polymer is active as a “valve” to moderate the diffusion of the embedded drugs in‐and‐out of the pore channels of the silica container. The anticancer drug doxorubicin hydrochloride (DOX) can be absorbed into UCNPs@mSiO₂‐P(NIPAm‐co‐MAA) nanospheres and the composite drug delivery system (DDS) shows a low level of leakage at low temperature/high pH values but significantly enhanced release at higher temperature/lower pH values, exhibiting an apparent thermo/pH controlled “on‐off” drug release pattern. The as‐prepared UCNPs@mSiO₂‐P(NIPAm‐co‐MAA) hybrid nanospheres can be used as bioimaging agents and biomonitors to track the extent of drug release. The reported multifunctional nanocarriers represent a novel and versatile class of platform for simultaneous imaging and stimuli‐responsive controlled drug delivery.     

Cover Picture: Synthesis of Gadolinium‐Labeled Shell‐Crosslinked Nanoparticles for Magnetic Resonance Imaging Applications (Adv. Funct. Mater. 8/2005)

Robust, amphiphilic core–shell nanoparticles that are selectively labeled with gadolinium in the hydrophilic and water‐swollen shell layer are depicted in the cover picture. These well‐defined nanostructured materials exhibit high relaxivity, a large loading capacity, and are based upon a biocompatible platform for ultimate function in magnetic resonance imaging (MRI) applications, as reported by Wooley and co‐workers on p. 1248. Shell‐crosslinked knedel‐like nanoparticles (SCKs; “knedel” is a Polish term for dumplings) were derivatized with gadolinium chelates and studied as robust magnetic‐resonance‐imaging‐active structures with hydrodynamic diameters of 40 ± 3 nm. SCKs possessing an amphiphilic core–shell morphology were produced from the aqueous assembly of diblock copolymers of poly‐(acrylic acid) (PAA) and poly(methyl acrylate) (PMA), PAA₅₂–b–PMA₁₂₈, and subsequent covalent crosslinking by amidation upon reaction with 2,2′‐(ethylenedioxy)bis(ethylamine) throughout the shell layer. The properties of these materials, including non‐toxicity towards mammalian cells, non‐immunogenicity within mice, and capability for polyvalent targeting, make them ideal candidates for utilization within biological systems. The synthesis of SCKs derivatized with Gd^III and designed for potential use as a unique nanometer‐scale contrast agent for MRI applications is described herein. Utilization of an amino‐functionalized diethylenetriaminepentaacetic acid–Gd analogue allowed for direct covalent conjugation throughout the hydrophilic shell layer of the SCKs and served to increase the rotational correlation lifetime of the Gd. In addition, the highly hydrated nature of the shell layer in which the Gd was located allowed for rapid water exchange; thus, the resulting material demonstrated large ionic relaxivities (39 s^–1 mM^–1) in an applied magnetic field of 0.47 T at 40 °C and, as a result of the large loading capacity of the material, also demonstrated high molecular relaxivities (20 000 s^–1 mM^–1).     

Synthesis of Gadolinium‐Labeled Shell‐Crosslinked Nanoparticles for Magnetic Resonance Imaging Applications

Shell‐crosslinked knedel‐like nanoparticles (SCKs; “knedel” is a Polish term for dumplings) were derivatized with gadolinium chelates and studied as robust magnetic‐resonance‐imaging‐active structures with hydrodynamic diameters of 40 ± 3 nm. SCKs possessing an amphiphilic core–shell morphology were produced from the aqueous assembly of diblock copolymers of poly‐(acrylic acid) (PAA) and poly(methyl acrylate) (PMA), PAA₅₂–b–PMA₁₂₈, and subsequent covalent crosslinking by amidation upon reaction with 2,2′‐(ethylenedioxy)bis(ethylamine) throughout the shell layer. The properties of these materials, including non‐toxicity towards mammalian cells, non‐immunogenicity within mice, and capability for polyvalent targeting, make them ideal candidates for utilization within biological systems. The synthesis of SCKs derivatized with Gd^III and designed for potential use as a unique nanometer‐scale contrast agent for MRI applications is described herein. Utilization of an amino‐functionalized diethylenetriaminepentaacetic acid–Gd analogue allowed for direct covalent conjugation throughout the hydrophilic shell layer of the SCKs and served to increase the rotational correlation lifetime of the Gd. In addition, the highly hydrated nature of the shell layer in which the Gd was located allowed for rapid water exchange; thus, the resulting material demonstrated large ionic relaxivities (39 s^–1 mM^–1) in an applied magnetic field of 0.47 T at 40 °C and, as a result of the large loading capacity of the material, also demonstrated high molecular relaxivities (20 000 s^–1 mM^–1).     

Atomic‐Level Passivation of Individual Upconversion Nanocrystal for Single Particle Microscopic Imaging

Lanthanide‐doped upconversion nanoparticles (UCNPs) have significant applications for single‐molecule probes and high‐resolution display. However, one of their major hurdles is the weak luminescence, and this remains a grand challenge to achieve at the single‐particle level. Here, 484‐fold luminescence enhancement in LuF₃:Yb³⁺, Er³⁺ rhombic flake UCNPs is achieved, thanks to the Yb³⁺‐mediated local photothermal effect, and their original morphology, size, and good dispersibility are well preserved. These data show that the surface atomic structure of UCNPs as well as transfer from amorphous to ordered crystal structure is modulated by making use of the local photothermal conversion that is generated by the directional absorption of 980 nm light by Yb³⁺ ions. The confocal luminescence images obtained by super‐resolution stimulated emission depletion also show the great enhancement of individual LuF₃:Yb³⁺, Er³⁺ nanoparticles; the high signal‐to‐noise ratio images indicate that the laser treatment technology opens the door for single particle imaging and practical application.     

One‐Step Fabrication of Multifunctional Core‐Shell Fibres by Co‐Electrospinning

In the present study, multifunctional core‐shell fibre mats were designed by co‐electrospinning. These core‐shell fibre mats have three different functionalities: 1) they are magnetic, 2) they change their optical properties with the pH of the media, and 3) they are sensitive to O₂. The shell is formed by a fluorescent pH‐sensitive co‐polymer which was previously synthesised and characterized by our research group. The core is a suspension formed by magnetic nanoparticles in a solution made up by a lipophilic indicator dye (oxygen indicator; PtOEP) and, poly‐methyl methacrylate, in THF. The magnetic nanoparticles were prepared by encapsulation of magnetite within a cross‐linked polymeric matrix (MMA‐co‐EDMA). To our knowledge, this is the first time that three functionalities (magnetic properties, sensitivity to pH, and response to O₂ concentration) were successful conjugated on the same micro‐ or nano‐material via a facile one‐step process with high yield and cost effectiveness. The morphology of the well‐organized core‐shell fibres were characterized by high resolution scanning electron microcopy (HRSEM), transmission electron microcopy (TEM), and confocal laser microscopy. The luminescent properties of core‐shell fibre mats were analysed and successfully used for simultaneously monitoring pH (from 6 to 8) and O₂, showing complete reversibility, high sensitivity (i.e., K_sv = 7.07 bar^?1 for determining O₂ in aqueous media), high magnetic susceptibility, and short response times.     

Novel Au–SiO2–WO3 Core–Shell Composite Nanoparticles for Surface‐Enhanced Raman Spectroscopy with Potential Application in Cancer Cell Imaging

With the rapid development of nanotechnology during the last decades, the ability to detect and control individual objects at the nanoscale has enabled us to deal with complex biomedical challenges. In cancer imaging, novel nanoparticles (NPs) offer promising potential to identify single cancer cells and precisely label larger areas of cancer tissues. Herein, a new class of size tunable core–shell composite (Au–SiO₂–WO₃) nanoparticles is reported. These nanoparticles display an easily improvable ≈10³ surface‐enhanced Raman scattering (SERS) enhancement factor with a double Au shell for dried samples over Si wafers and several orders of magnitude for liquid samples. WO₃ core nanoparticles measuring 20–50 nm in diameter are sheathed by an intermediate 10–60 nm silica layer, produced by following the Stöber‐based process and Turkevich method, followed by a 5–20 nm thick Au outer shell. By attaching 4‐mercaptobenzoic acid (4‐MBA) molecules as Raman reporters to the Au, high‐resolution Raman maps that pinpoint the nanoparticles' location are obtained. The preliminary results confirm their advantageous SERS properties for single‐molecule detection, significant cell viability after 24 h and in vitro cell imaging using coherent anti‐stokes Raman scattering. The long‐term objective is to measure SERS nanoparticles in vivo using near‐infrared light.