REVIEW Lanthanide-doped up-converting nanoparticles: Merits and challenges (original) (raw)
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Upconversion nanoparticles in biological labeling, imaging, and therapy
Analyst, 2010
Upconversion refers to non-linear optical processes that convert two or more low-energy pump photons to a higher-energy output photon. After being recognized in the mid-1960s, upconversion has attracted significant research interest for its applications in optical devices such as infrared quantum counter detectors and compact solid-state lasers. Over the past decade, upconversion has become more prominent in biological sciences as the preparation of high-quality lanthanide-doped nanoparticles has become increasingly routine. Owing to their small physical dimensions and biocompatibility, upconversion nanoparticles can be easily coupled to proteins or other biological macromolecular systems and used in a variety of assay formats ranging from bio-detection to cancer therapy. In addition, intense visible emission from these nanoparticles under near-infrared excitation, which is less harmful to biological samples and has greater sample penetration depths than conventional ultraviolet excitation, enhances their prospects as luminescent stains in bio-imaging. In this article, we review recent developments in optical biolabeling and bio-imaging involving upconversion nanoparticles, simultaneously bringing to the forefront the desirable characteristics, strengths and weaknesses of these luminescent nanomaterials.
Materials, 2022
Upconverting luminescent nanoparticles (UCNPs) are “new generation fluorophores” with an evolving landscape of applications in diverse industries, especially life sciences and healthcare. The anti-Stokes emission accompanied by long luminescence lifetimes, multiple absorptions, emission bands, and good photostability, enables background-free and multiplexed detection in deep tissues for enhanced imaging contrast. Their properties such as high color purity, high resistance to photobleaching, less photodamage to biological samples, attractive physical and chemical stability, and low toxicity are affected by the chemical composition; nanoparticle crystal structure, size, shape and the route; reagents; and procedure used in their synthesis. A wide range of hosts and lanthanide ion (Ln3+) types have been used to control the luminescent properties of nanosystems. By modification of these properties, the performance of UCNPs can be designed for anticipated end-use applications such as phot...
2018
Lanthanide ion doped upconversion nanoparticles (UCNPs) that can convert low-energy infrared photons into high-energy visible and ultraviolet photons, are becoming highly sought-after for advanced biomedical and biophotonics applications. Their unique luminescent properties enable UCNPs to be applied for diagnosis, including biolabeling, biosensing, bioimaging and multiple imaging modality, as well as therapeutic treatments including photothermal and photodynamic therapy, bio-reductive chemotherapy and drug delivery. For the employment of the inorganic nanomaterials into biological environment, it is critical to bridge the gap in between nanoparticles and biomolecules via surface modifications and subsequent functionalisation. This work reviews the various ways to surface modify and functionalise UCNPs so as to impart different functional molecular groups to the UCNPs surfaces for a board range of applications in biomedical areas. We discussed commonly used base functionalities, inc...
Upconversion nanoparticles: synthesis, surface modification and biological applications
Nanomedicine: Nanotechnology, Biology and Medicine, 2011
New generation fluorophores, also termed upconversion nanoparticles (UCNPs), have the ability to convert near infrared radiations with lower energy into visible radiations with higher energy via a non-linear optical process. Recently, these UCNPs have evolved as alternative fluorescent labels to traditional fluorophores, showing great potential for imaging and biodetection assays in both in vitro and in vivo applications. UCNPs exhibit unique luminescent properties, including high penetration depth into tissues, low background signals, large Stokes shifts, sharp emission bands, and high resistance to photo-bleaching, making UCNPs an attractive alternative source for overcoming current limitations in traditional fluorescent probes. In this review, we discuss the recent progress in the synthesis and surface modification of rare earth doped UCNPs with a specific focus on their biological applications.
Breakthroughs in medicine and bioimaging with up-conversion nanoparticles
International Journal of Nanomedicine, 2019
Nanomedicine is a medical application of biochemistry incorporated with materials chemistry at the scale of nanometer for the purpose of diagnosis, prevention, and treatment. New models and approaches are typically associated with nanomedicine for precise multifunctional diagnostic systems at molecular level. Hence, employing nanoparticles (NPs) has unveiled new opportunities for efficient therapies and remedy of difficult-to-cure diseases. Among all types of inorganic NPs, lanthanide-doped up-conversion nanoparticles (UCNPs) have shown excellent potential for biomedical applications, especially for multimodal bioimaging including fluorescence and electron microscopy. Association of these visualization techniques plus the capability for transporting biomaterials and drugs make them superior agents in the field of nanomedicine. Accordingly, in this review, we firstly presented a fundamental understanding of physical and optical properties of UCNPs and secondly, we illustrated some of the prominent associations with bioimaging, theranostics, cancer therapy, and optogenetics.
Biomimetic Surface Engineering of Lanthanide-Doped Upconversion Nanoparticles as Versatile Bioprobes
Angewandte Chemie International Edition, 2012
A general and versatile biomimetic approach to synthesize water dispersible and functionalizable upconverting nanoparticles (UCNPs) for selective imaging of live cancer cells is reported. The approach involves coating the surface of UCNPs with a monolayer of phospholipids containing different functional groups, allowing for conjugation of many molecules for a wide range of applications in fields such as bioinspired nanoassembly, biosensing, and bio-medicine.
Nanomaterials, 2014
Lanthanide-doped upconversion-luminescent nanoparticles (UCNPs), which can be excited by near-infrared (NIR) laser irradiation to emit multiplex light, have been proven to be very useful for in vitro and in vivo molecular imaging studies. In comparison with the conventionally used down-conversion fluorescence imaging strategies, the NIR light excited luminescence of UCNPs displays high photostability, low cytotoxicity, little background auto-fluorescence, which allows for deep tissue penetration, making them attractive as contrast agents for biomedical imaging applications. In this review, we will mainly focus on the latest development of a new type of lanthanide-doped UCNP material and its main applications for in vitro and in vivo molecular imaging and we will also discuss the challenges and future perspectives.
Advances in highly doped upconversion nanoparticles
Nature communications, 2018
Lanthanide-doped upconversion nanoparticles (UCNPs) are capable of converting near-infra-red excitation into visible and ultraviolet emission. Their unique optical properties have advanced a broad range of applications, such as fluorescent microscopy, deep-tissue bioimaging, nanomedicine, optogenetics, security labelling and volumetric display. However, the constraint of concentration quenching on upconversion luminescence has hampered the nanoscience community to develop bright UCNPs with a large number of dopants. This review surveys recent advances in developing highly doped UCNPs, highlights the strategies that bypass the concentration quenching effect, and discusses new optical properties as well as emerging applications enabled by these nanoparticles.
Recent Advancements in Ln‐Ion‐Based Upconverting Nanomaterials and Their Biological Applications
Particle & Particle Systems Characterization, 2019
render them particularly useful in many biological applications including multimodal in vivo biological imaging, [4,7] biodetection, [8,9] clinical diagnosis, [10] and drug/gene delivery (Figure 1). [4] UCNPs enable the conversion of NIR photons of low-energy into visible or ultraviolet (UV) photons of high-energy via photon upconversion process. [11] The concept of photon upconversion is developed from anti-Stokes emission process generated by upconverting luminescent materials. In conventional host luminescent nanomaterials, anti-Stokes emission is generated through simultaneous twophoton absorption (STPA) and second harmonic generation (SHG). [12-15] These photon absorption processes need an ultrashort pulse laser (e.g., femtosecond pulse laser) with extremely high exciting power-density (10 6-10 9 W cm −2) to produce large numbers of excitation photons and, the use of such a pulse laser is very expensive. [1,16,17] Another drawback is the use of noncentrosymmetric molecular structure with a weak D-π-A configuration (D: donor, A: acceptor) that results in low twophoton absorption (TPA) capacity. [12,15] Many efforts have been made to enhance the TPA capacity by optimizing the atomic or molecular structure, which includes conformation rigidity, strong π-conjugation, and incorporation of electron donors and acceptor atoms on a π-conjugated structure. [18] However, the excitation power-density is still high to produce sufficient photons essential for the process. The most popular and attractive alternative for the generation of anti-Stokes emission is an upconversion emission process induced by doping of trivalent transition metals such as rare-earth (RE) trivalent lanthanide ions (Ln 3+) on the host luminescent material. [19-21] Unlike STPA and SHG processes, it is a nonlinear anti-Stokes emission process in which a sequential, rather than simultaneous, absorption of two or more low-energy photons (longer wavelength) occurs leading to the emission of high-energy photons (short wavelength). [22-25] The fundamental concept of upconversion was first proposed by the physicist N. Bloembergen in 1959. His idea was to construct a solid-state IR counter device capable of counting IR photons through their interaction with a solid inorganic matrix (upconverting materials). [26] Later in the mid-1960s, the process of upconversion was first discovered by Auzel, [22] and rapidly became popular for the emission of large anti-Stokes shifts (up to 500 nm), sharp emission bandwidths (10-20 nm full-width Upconversion nanoparticles (UCNPs) convert low-energy infrared (IR) or near-infrared (NIR) photons into high-energy emission radiation ranging from ultraviolet to visible through a photon upconversion process. In comparison to conventional fluorophores, such as organic dyes or semiconductor quantum dots, lanthanide-ion-doped UCNPs exhibit high photostability, no photoblinking, no photobleaching, low cytotoxicity, sharp emission lines, and long luminescent lifetimes. Additionally, the use of IR or NIR for excitation in such UCNPs reduces the autofluorescence background and enables deeper penetration into biological samples due to reduced light scattering with negligible damage to the samples. Because of these attributes, UCNPs have found numerous potential applications in biological and medicinal fields as novel fluorescent materials. Different upconversion mechanisms commonly observed in UCNPs, various methods that are used in their synthesis, and surface modification processes are discussed. Recent applications of Ln-UCNPs in the biological and medicinal fields, including in vivo and in vitro biological imaging, multimodal imaging, photodynamic therapy, drug delivery, and antibacterial activity, are also presented.