The enthusiasm for research on lanthanide‐doped upconversion nanoparticles is driven by both a fundamental interest in the optical properties of lanthanides embedded in different host lattices and ...their promise for broad applications ranging from biological imaging to photodynamic therapy. Despite the considerable progress made in the past decade, the field of upconversion nanoparticles has been hindered by significant experimental challenges associated with low upconversion conversion efficiencies. Recent experimental and theoretical studies on upconversion nanoparticles have, however, led to the development of several effective approaches to enhancing upconversion luminescence, which could have profound implications for a range of applications. Herein we present the underlying principles of controlling energy transfer through lanthanide doping, overview the major advances and key challenging issues in improving upconversion luminescence, and consider the likely directions of future research in the field.
Lighten up: Light trapping by upconversion nanoparticles often suffers from low conversion efficiency because of the small absorption cross‐section and surface quenching effects of the nanoparticles. To this end, effective strategies have been developed to enhance upconversion luminescence, thus paving the way for new biological approaches and inexpensive energy conversion methods.
A new type of core–shell upconversion nanoparticles which can be effectively excited at 795 nm has been designed and synthesized through spatially confined doping of neodymium (Nd3+) ions. The use of ...Nd3+ ions as sensitizers facilitates the energy transfer and photon upconversion of a series of lanthanide activators (Er3+, Tm3+, and Ho3+) at a biocompatible excitation wavelength (795 nm) and also significantly minimizes the overheating problem associated with conventional 980 nm excitation. Importantly, the core–shell design enabled high-concentration doping of Nd3+ (∼20 mol %) in the shell layer and thus markedly enhanced the upconversion emission from the activators, providing highly attractive luminescent biomarkers for bioimaging without autofluorescence and concern of overheating.
We report a novel design, based on a combination of lanthanide-doped upconversion nanoparticles and manganese dioxide nanosheets, for rapid, selective detection of glutathione in aqueous solutions ...and living cells. In this approach, manganese dioxide (MnO2) nanosheets formed on the surface of nanoparticles serve as an efficient quencher for upconverted luminescence. The luminescence can be turned on by introducing glutathione that reduces MnO2 into Mn2+. The ability to monitor the glutathione concentration intracellularly may enable rational design of a convenient platform for targeted drug and gene delivery.
Lanthanide-doped upconversion nanoparticles have received growing attention in the development of low-background, highly sensitive and selective sensors. Here, we report a water probe based on ...ligand-free NaYF4:Yb/Er nanoparticles, utilizing their intrinsically nonlinear upconversion process. The water molecule sensing was realized by monitoring the upconversion emission quenching, which is mainly attributed to efficient energy transfer between upconversion nanoparticles and water molecules as well as water-absorption-induced excitation energy attenuation. The nonlinear upconversion process, together with power function relationship between upconversion emission intensity and excitation power density, offers a sensitive detection of water content down to 0.008 vol % (80 ppm) in an organic solvent. As an added benefit, we show that noncontact detection of water can be achieved just by using water attenuation effect. Moreover, these upconversion nanoparticle based recyclable probes should be particularly suitable for real-time and long-term water monitoring, due to their superior chemical and physical stability. These results could provide insights into the design of upconversion nanoparticle based sensors.
The discovery of the DNA-mediated assembly of gold nanoparticles was a great moment in the history of science; this understanding and chemical control enabled the rational design of functional ...nanomaterials as novel probes in biodetection. In contrast with conventional probes such as organic dyes, gold nanoparticles exhibit high photostability and unique size-dependent optical properties. Because of their high extinction coefficients and strong distance dependent optical properties, these nanoparticles have emerged over the past decade as a promising platform for rapid, highly sensitive colorimetric assays that allow for the visual detection of low concentrations of metal ions, small molecules, and biomacromolecules. These discoveries have deepened our knowledge of biological phenomena and facilitated the development of many new diagnostic and therapeutic tools. Despite these many advances and continued research efforts, current nanoparticle-based colorimetric detection systems still suffer from several drawbacks, such as limited sensitivity and selectivity. This Account describes the recent development of colorimetric assays based on protein enzyme-assisted gold nanoparticle amplification. The benefits of such detection systems include significantly improved detection sensitivity and selectivity. First, we discuss the general design of enzyme-modified nanoparticle systems in colorimetric assays. We show that a quantitative understanding of the unique properties of different enzymes is paramount for effective biological assays. We then examine the assays for nucleic acid detection based on different types of enzymes, including endonucleases, ligases, and polymerases. For each of these assays, we identify the underlying principles that contribute to the enhanced detection capability of nanoparticle systems and illustrate them with selected examples. Furthermore, we demonstrate that the combination of gold nanoparticles and specific enzymes can probe enzyme dynamics and function with high specificity, offering substantial advantages in both sensitivity and specificity over conventional detection methods. The screening of nuclease, methyltransferase, protease, and kinase activities can be colorimetrically performed in a straightforward manner. Finally, we discuss examples of colorimetric assays for metal ions and small molecules that constitute important advances toward visual monitoring of enzyme catalytic functions and gene expression. Although these enzyme-assisted assay methods hold great promise for myriad applications in biomedicine and bioimaging, the application of the described techniques in vivo faces formidable challenges. In addition, researchers do not fully understand the interactions of gold nanoparticles with enzyme molecules. This understanding will require the development of new techniques to probe enzyme substrate dynamics at the particle interface with higher spatial resolution and chemical specificity.
Two-dimensional (2D) metal-organic framework (MOF) nanosheets have been recently regarded as the model electrocatalysts due to their porous structure, fast mass and ion transfer through the ...thickness, and large portion of exposed active metal centers. Combining them with electrically conductive 2D nanosheets is anticipated to achieve further improved performance in electrocatalysis. In this work, we in situ hybridized 2D cobalt 1,4-benzenedicarboxylate (CoBDC) with Ti3C2Tx (the MXene phase) nanosheets via an interdiffusion reaction-assisted process. The resulting hybrid material was applied in the oxygen evolution reaction and achieved a current density of 10 mA cm-2 at a potential of 1.64 V vs reversible hydrogen electrode and a Tafel slope of 48.2 mV dec-1 in 0.1 M KOH. These results outperform those obtained by the standard IrO2-based catalyst and are comparable with or even better than those achieved by the previously reported state-of-the-art transition-metal-based catalysts. While the CoBDC layer provided the highly porous structure and large active surface area, the electrically conductive and hydrophilic Ti3C2Tx nanosheets enabled the rapid charge and ion transfer across the well-defined Ti3C2Tx-CoBDC interface and facilitated the access of aqueous electrolyte to the catalytically active CoBDC surfaces. The hybrid nanosheets were further fabricated into an air cathode for a rechargeable zinc-air battery, which was successfully used to power a light-emitting diode. We believe that the in situ hybridization of MXenes and 2D MOFs with interface control will provide more opportunities for their use in energy-based applications.
Materials that exhibit X-ray-excited luminescence have great potential in radiation detection, security inspection, biomedical applications and X-ray astronomy1–5. However, high-performance materials ...are almost exclusively limited to ceramic scintillators, which are typically prepared under high temperatures6. Herein we report metal-free organic phosphors based on a molecular design that supports efficient triplet exciton harvesting to enhance radioluminescence. These organic scintillators exhibit a detection limit of 33 nGy s–1, which is 167 times lower than the standard dosage for X-ray medical examination and we demonstrate their potential application in X-ray radiography. These findings provide a fundamental design principle and new route for the creation of promising alternatives to incumbent inorganic scintillators. Furthermore, they offer new opportunities for development of flexible, stretchable X-ray detectors and imagers for non-destructive radiography testing and medical imaging.Organic, metal-free materials that act as efficient X-ray scintillators could bring new opportunities for X-ray imaging.
•Platinum nanoenzyme was anchored on BP NSs to ameliorate tumor hypoxia.•Ce6 was covalently linked to BP/Pt NSs to provide enhanced ROS production in the tumor.•Oxygen self-supplied photodynamic and ...photothermal synergistic therapy was performed towards 4T1 tumor ablation.
Tumor hypoxia can cause undesirable barriers for many therapeutic interventions, especially for oxygen-dependent photodynamic therapy (PDT). To ameliorate hypoxia and enhance the cancer therapeutic efficacy, herein, catalase-like platinum (Pt) nanoparticles (NPs) were designed as nanoenzyme to anchor onto the surface of black phosphorus nanosheets (BP NSs), followed by Ce6 conjugation and subsequent PEGylation to obtain BP/Pt-Ce6@PEG NSs. As-prepared BP/Pt-Ce6@PEG NSs could decompose endogenous H2O2 into O2in situ to relieve tumor hypoxia, affording enhanced reactive oxygen species (ROS) production. In vitro cytotoxicity studies demonstrated the best therapeutic effect of BP/Pt-Ce6@PEG NSs in comparison to that of BP/Pt NSs or Ce6 alone. In vivo experiments on the 4T1 tumor xenograft mouse model showed that BP/Pt-Ce6@PEG NSs could efficiently alleviate tumor hypoxia and eliminate tumor cells, presenting excellent oxygen self-supplied photodynamic and photothermal synergistic therapy therapeutic efficacy. These results highlight that platinum nanoenzyme functionalization is promising to raise the intratumoral oxygen level to surmount tumor hypoxia for efficient tumor treatment.
Brownian motion is one of the most fascinating phenomena in nature. Its conceptual implications have a profound impact in almost every field of science and even economics, from dissipative processes ...in thermodynamic systems, gene therapy in biomedical research, artificial motors and galaxy formation to the behaviour of stock prices. However, despite extensive experimental investigations, the basic microscopic knowledge of prototypical systems such as colloidal particles in a fluid is still far from being complete. This is particularly the case for the measurement of the particles' instantaneous velocities, elusive due to the rapid random movements on extremely short timescales. Here, we report the measurement of the instantaneous ballistic velocity of Brownian nanocrystals suspended in both aqueous and organic solvents. To achieve this, we develop a technique based on upconversion nanothermometry. We find that the population of excited electronic states in NaYF
:Yb/Er nanocrystals at thermal equilibrium can be used for temperature mapping of the nanofluid with great thermal sensitivity (1.15% K
at 296 K) and a high spatial resolution (<1 μm). A distinct correlation between the heat flux in the nanofluid and the temporal evolution of Er
emission allows us to measure the instantaneous velocity of nanocrystals with different sizes and shapes.
Developing efficient carbon-based metal-free electrocatalysts can bridge the gap between laboratory studies and practical applications of CO
2
reduction. However, along with the ambiguous ...understanding of the active sites in carbon-based electrocatalysts, carbon-based electrocatalysts with high selectivity and satisfactory stability for electroreduction of CO
2
remain rare. Here, using the nitrogen rich silk cocoon as a precursor, carbon-based electrocatalysts with intrinsic defects can be prepared for efficient and long-term electroreduction of CO
2
by a simple two-step carbonization. The obtained electrocatalyst can catalyze CO
2
reduction to CO with a Faradaic efficiency of ~ 89% and maintain good selectivity for about 10 days. Particularly, our experimental studies suggest that in-plane defects are the main active sites on which the rate-determining step for CO
2
reduction should be the direct electron transfer to CO
2
but not the proton-coupled electron transfer. Further theoretical calculations consistently demonstrate that the intrinsic defects in carbon matrix, particularly the pentagon-containing defects, act as main active sites to accelerate the direct electron transfer for CO
2
reduction. In addition, our synthetic approach can convert egg white into efficient catalysts for CO
2
electroreduction. These findings, providing new insights into the biomass-derived catalysts, should pave the way for fabricating efficient and stable carbon-based electrocatalysts with catalytically active defects by using naturally abundant precursors.
