Multicolor tuning of lanthanide-doped nanoparticles by single wavelength excitation

Molecular and supramolecular switches on mesoporous silica nanoparticles

This review summarizes the recent advances of molecular and supramolecular switches installed on mesoporous silica nanoparticles.

Upconversion luminescence enhancement of Yb3+, Nd3+ sensitized NaYF4 core–shell nanocrystals on Ag grating films

The UCL enhancement of NaYF₄:Yb³⁺,Tm³⁺@NaYF₄:Yb³⁺,Nd³⁺ core–shell NCs resulting from Ag grating structures provides a novel insight for improving UCL.

Energy transfer in lanthanide upconversion studies for extended optical applications

In this review, the various energy transfer pathways involved in lanthanide-related upconversion emissions are comprehensively discussed.

Intrinsic [VO4]3− emission of cesium vanadate Cs5V3O10

Luminescence in Cs₅V₃O₁₀ increases below 150 K and decreases above 150 K. Unusual blue-shift is observed. This is understood by relaxation processes of emitting ³T₁ and ³T₂ states including thermal feeding by lower ³T₁ state to higher-energy ³T₂ state.

Time-resolved luminescent biosensing based on inorganic lanthanide-doped nanoprobes

In this feature article, we review the latest advancements in lanthanide-doped luminescent nanocrystals as time-resolved luminescent nano-bioprobes, from their fundamental optical properties to their potential applications for ultrasensitive biodetection and high-resolution bioimaging.

Stimuli responsive upconversion luminescence nanomaterials and films for various applications

This review highlights recent advances in upconversion luminescence materials in response to various stimuli for a broad spectrum of applications.

Enhancing the dual magnetic and optical properties of co-doped cerium oxide nanostructures

Iron and europium co-doped cerium oxide nanoparticles exhibits interesting optical and magnetic properties.

Upconversion nanoparticles: a versatile solution to multiscale biological imaging

Lanthanide-doped photon upconverting nanomaterials are emerging as a new class of imaging contrast agents, providing numerous unprecedented possibilities in the realm of biomedical imaging. Because of their ability to convert long-wavelength near-infrared excitation radiation into shorter-wavelength emissions, these nanomaterials are able to produce assets of low imaging background, large anti-Stokes shift, as well as high optical penetration depth of light for deep tissue optical imaging or light-activated drug release and therapy. The aim of this review is to line up some issues associated with conventional fluorescent probes, and to address the recent advances of upconverting nanoparticles (UCNPs) as a solution to multiscale biological imaging applications.

Polypeptide-functionalized NaYF4:Yb(3+),Er(3+) nanoparticles: red-emission biomarkers for high quality bioimaging using a 915 nm laser

We prepared poly-L-aspartic acid (PASP) functionalized NaYF4:Yb(3+),Er(3+) upconversion nanoparticles (UCNP-PASP). These nanoparticles can give red upconversion emission under excitation at 915 nm, whose wavelength of emission and excitation is located in the optical window of biological tissue. Dynamic laser scatting and zeta potentials of UCNP-PASP were used to study their stabilities in different aqueous solution. To understand the mechanism of the red emission of UCNP-PASP, photoluminescence spectra of samples were recorded before and after modification with PASP, poly acrylic acid (PAA), and poly(ether imide) (PEI) ligands under excitation at 915 and 980 nm, respectively. The cytotoxicity of the UCNP-PASP was also examined on a A549 cell and KB cell by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) assay. Moreover, the PASP-functionalized UCNP was employed as a potential biomarker for in vitro and in vivo experiments of upconversion luminescence imaging.

Ultrasmall biomolecule-anchored hybrid GdVO4 nanophosphors as a metabolizable multimodal bioimaging contrast agent

Multimodal molecular imaging has recently attracted much attention on disease diagnostics by taking advantage of individual imaging modalities. Herein, we have demonstrated a new paradigm for multimodal bioimaging based on amino acids-anchored ultrasmall lanthanide-doped GdVO4 nanoprobes. On the merit of special metal-cation complexation and abundant functional groups, these amino acids-anchored nanoprobes showed high colloidal stability and excellent dispersibility. Additionally, due to typical paramagnetic behaviour, high X-ray mass absorption coefficient and strong fluorescence, these nanoprobes would provide a unique opportunity to develop multifunctional probes for MRI, CT and luminescence imaging. More importantly, the small size and biomolecular coatings endow the nanoprobes with effective metabolisability and high biocompatibility. With the superior stability, high biocompatibility, effective metabolisability and excellent contrast performance, amino acids-capped GdVO4:Eu(3+) nanocastings are a promising candidate as multimodal contrast agents and would bring more opportunities for biological and medical applications with further modifications.

Magnetically engineered semiconductor quantum dots as multimodal imaging probes

Light-emitting semiconductor quantum dots (QDs) combined with magnetic resonance imaging contrast agents within a single nanoparticle platform are considered to perform as multimodal imaging probes in biomedical research and related clinical applications. The principles of their rational design are outlined and contemporary synthetic strategies are reviewed (heterocrystalline growth; co-encapsulation or assembly of preformed QDs and magnetic nanoparticles; conjugation of magnetic chelates onto QDs; and doping of QDs with transition metal ions), identifying the strengths and weaknesses of different approaches. Some of the opportunities and benefits that arise through in vivo imaging using these dual-mode probes are highlighted where tumor location and delineation is demonstrated in both MRI and fluorescence modality. Work on the toxicological assessments of QD/magnetic nanoparticles is also reviewed, along with progress in reducing their toxicological side effects for eventual clinical use. The review concludes with an outlook for future biomedical imaging and the identification of key challenges in reaching clinical applications.

Phospholipid-modified upconversion nanoprobe for ratiometric fluorescence detection and imaging of phospholipase D in cell lysate and in living cells

Phospholipase D (PLD) is a critical component of intracellular signal transduction and has been implicated in many important biological processes. It has been observed that there are abnormalities in PLD expression in many human cancers, and PLD is thus recognized as a potential diagnostic biomarker as well as a target for drug discovery. We report for the first time a phospholipid-modified nanoprobe for ratiometric upconversion fluorescence (UCF) sensing and bioimaging of PLD activity. The nanoprobe can be synthesized by a facile one-step self-assembly of a phospholipid monolayer composed of poly(ethylene glycol) (PEG)ylated phospholipid and rhodamine B-labeled phospholipid on the surface of upconversion nanoparticles (UCNPs) NaYF4: 20%Yb, 2%Er. The fluorescence resonance energy transfer (FRET) process from the UCF emission at 540 nm of the UCNPs to the absorbance of the rhodamine B occurs in the nanoprobe. The PLD-mediated hydrolysis of the phosphodiester bond makes rhodamine B apart from the UCNP surface, leading to the inhibition of FRET. Using the unaffected UCF emission at 655 nm as an internal standard, the nanoprobe can be used for ratiometric UCF detection of PLD activity with high sensitivity and selectivity. The PLD activity in cell lysates is also determined by the nanoprobe, confirming that PLD activity in a breast cancer cell is at least 7-fold higher than in normal cell. Moreover, the nanoprobe has been successfully applied to monitoring PLD activity in living cells by UCF bioimaging. The results reveal that the nanoprobe provides a simple, sensitive, and robust platform for point-of-care diagnostics and drug screening in biomedical applications.

Ultrasensitive nanosensors based on upconversion nanoparticles for selective hypoxia imaging in vivo upon near-infrared excitation

Hypoxia is a distinct feature of malignant solid tumors, which is a possible causative factor for the serious resistance to chemo- and radiotherapy or the development of invasion and metastasis. The exploration of nanosensors with the capabilities like the accurate diagnosis of hypoxic level will be helpful to estimate the malignant degree of tumor and subsequently implement more effective personalized treatment. Here, we report the design and synthesis of nanosensors that can selectively and reversibly detect the level of hypoxia both in vitro and in vivo. The designed nanosensor is composed of two main moieties: oxygen indicator [Ru(dpp)3](2+)Cl2 for detection of hypoxia and upconversion nanoparticles for offering the excitation light of [Ru(dpp)3](2+)Cl2 by upconversion process under 980 nm exposure. The results show that the nanosensors can reversibly become quenched or luminescent under hyperoxic or hypoxic conditions, respectively. Compared with free [Ru(dpp)3](2+)Cl2, the designed nanosensors exhibit enhanced sensitivity for the detection of oxygen in hypoxic regions. More attractively, the nanosensors can image hypoxic regions with high penetration depth because the absorption and emission wavelength are within the NIR and far-red region, respectively. Most importantly, nanosensors display a high selectivity for detection of relevant oxygen changes in cells and zebrafish.

Controllable multicolor output, white luminescence and cathodoluminescence properties of high quality NaCeF4:Ln3+ (Ln3+ = Eu3+, Dy3+, Tb3+) nanorods

Tunable multicolor and white emissions of hexagonal phase lanthanides (Ln³⁺, Ln³⁺ = Eu³⁺, Dy³⁺, Tb³⁺) doped NaCeF₄ nanorods with uniform morphology and monodispersity were synthesized via a hydrothermal method.

Visible Discrimination of Broadband Infrared Light by Dye-Enhanced Upconversion in Lanthanide-Doped Nanocrystals

Optical upconversion of near infrared light to visible light is an attractive way to capture the optical energy or optical information contained in low-energy photons that is otherwise lost to the human eye or to certain photodetectors and solar cells. Until the recent application of broadband absorbing optical antennas, upconversion efficiency in lanthanide-doped nanocrystals was limited by the weak, narrow atomic absorption of a handful of sensitizer elements. In this work, we extend the role of the optical antenna to provide false-color, visible discrimination between bands of infrared radiation. By pairing different optical antenna dyes to specific nanoparticle compositions, unique visible emission is associated with different bands of infrared excitation. In one material set, the peak emission was increased 10-fold, and the width of the spectral response was increased more than 10-fold.

Construction of Au@NaYF4:Yb3+,Er3+/Ho3+ bifunctional hybrid nanocomposites with upconversion luminescence and photothermal properties

The Au@NaYF₄:Yb³⁺,Er³⁺/Ho³⁺ bifunctional hybrid nanocomposites are constructed by a facile solution route, they simultaneously take advantage of both upconversion luminescence of NaYF₄:Yb³⁺,Er³⁺/Ho³⁺ nanocrystals and photothermal transduction property of AuNPs.