Diversified Design and Application of Upconversion Nanoparticle Composites | Photo: Alfa Chemistry
In recent years, the design and application of multifunctional nanocomposites have attracted extensive research interest from scientists. Combining two or more materials through a specific route to construct a new type of material not only overcomes the limitations of a single component itself, but also exhibits dual or multifunctional properties. Rare earth ion-doped upconversion nanoparticles (UCNPs) are favored by researchers in various fields due to their unique physical and chemical properties. UCNPs are combined with other functional materials to achieve synergistic effects, and the resulting nanocomposites show great application potential in biomedicine, anti-counterfeiting and photocatalysis.
Upconversion luminescence is the luminescence process of absorbing two or more low-energy photons and radiating one high-energy photon, which is, converting long-wave radiation into short-wave radiation. It is an anti-Stokes luminescence.
Rare earth-doped UCNPs have the advantages of:
narrow emission band
long fluorescence lifetime
low toxicity
large anti-Stokes shift
adjustable luminescence color
no spontaneous fluorescence of biological tissues
no photobleaching and flickering, etc.
show great application potential in biomedicine, three-dimensional stereoscopic display, anti-counterfeiting technology and solar spectrum conversion.
Construction Strategies of Upconversion Nanoparticles -based Nanocomposites
At present, many strategies have been developed to integrate UCNPs and other functional materials into a nanosystem. The research on the construction strategies and synthesis methods of UCNPs nanocomposites mainly includes self-assembly (electrostatic adsorption, specific recognition and covalent bonding), in situ growth and epitaxial growth.
Self-assembly is the most commonly used method for constructing UCNPs-based nanocomposites. It usually requires the preparation of various monomer components in advance, and then self-assembles to form a nanosystem through electrostatic adsorption, specific recognition or covalent bonding.
In situ growth usually requires polymer modification with special functional groups to form UCNPs to form precursors, which are used as nucleation and growth centers to induce other nanodots to further grow on their surface to form a core-satellite structure. Epitaxial growth first synthesizes monodisperse core nanocrystals, and then introduces shell precursors to achieve orderly growth of core-shell structures by regulating composition, relative arrangement, exposed crystal faces and interfaces. Usually, some strict requirements need to be met, such as matching of crystal structure and lattice parameters, similar reaction temperature and synthesis conditions, etc.
Applications of Upconversion Nanoparticles-based Nanocomposites
With the increasing interest in research on UCNPs-based nanocomposites, it has been widely used in some emerging fields.
Bioimaging is an important biological analysis and diagnostic tool. Common imaging techniques include optical imaging, magnetic resonance imaging (MRI), computed tomography X-ray scanning imaging (CT), single photon emission computed tomography (SPECT) and photoacoustic imaging (PAI). Although molecular probes have been used for imaging for many years, the imaging contrast provided by traditional molecular probes is insufficient and can usually only be used in a single imaging mode. UCNPs have good chemical and optical stability and good biocompatibility, and near-infrared excitation light can effectively avoid the interference of biological background fluorescence and achieve high signal-to-noise ratio biological imaging. At the same time, the combination of UCNPs with other nanofunctional materials as multimodal bioimaging probes has also been widely studied, and its imaging performance has been verified in cell and small animal models.
How to achieve effective treatment of cancer has always been a difficult problem and research hotspot in the medical field. Due to the complexity and diversity of the tumor environment, single-mode treatment cannot completely eradicate malignant tumors. The combination of multiple treatment methods can overcome the limitations of a single treatment method and achieve synergistic and effective cancer treatment. This article focuses on the application potential of UCNPs-based nanocomposites in various treatment systems, including chemotherapy, photothermal therapy, photodynamic therapy, radiation therapy, chemodynamic therapy, gas therapy, immunotherapy, and synergistic treatment of various treatment methods. The combination of multiple treatment methods can overcome the weaknesses and limitations of a single treatment method, thereby effectively inhibiting tumor growth, recurrence and metastasis.
Counterfeit and shoddy currency, drugs and valuables are increasingly damaging the market economy, causing immeasurable losses to consumers and copyright owners. Rare earth-doped UCNPs are ideal anti-counterfeiting materials in the field of fluorescent anti-counterfeiting due to their rich intermediate energy levels and distinguishable spectral characteristics. However, traditional single-light source excitation and single-mode fluorescence greatly limit their application. By combining UCNPs with other luminescent materials to develop new nanocomposites, specific fluorescence signals can be emitted over a wide spectral range to achieve multi-color dual-mode fluorescence anti-counterfeiting and information storage.
The development of photocatalysts with broad-spectrum absorption characteristics (ultraviolet to near-infrared light region) to achieve the effective use of solar energy in various fields (such as photocatalytic hydrogen production, elimination of environmental pollutants, antibacterial, etc.) has always been a hot topic of research. UCNPs can absorb near-infrared light and convert it into ultraviolet/visible light. Therefore, the nanocomposite constructed by combining UCNPs and semiconductor materials can be excited by near-infrared light to generate photogenerated electrons (e⁻) and holes (h⁺), thereby making full use of sunlight and improving photocatalytic efficiency.