Jinliang Liu

Cysteine modified rare-earth up-converting nanoparticles for in vitro and in vivo bioimaging

Cysteine, as a small organic molecule and amino acid, is a basic building block for proteins and has special physiological functions in vivo. Cysteine has strong affinity for cells, which can be taken advantage for various applications. A new and facile surface modification method has been developed for rare-earth doped upconversion nanoparticles (UCNs) using cysteine. Compared with unmodified samples, the water-solubility and biocompatibility of the cysteine modified NaYF4:Yb,Er and NaYF4:Yb,Tm UCNs (termed as UCN-Er-Cys and UCN-Tm-Cys, respectively) have been significantly improved, while their particle size and emission properties did not change substantially. Due to the low cytotoxicity as revealed by methyl thiazolyl tetrazolium assay, the cysteine modified UCNs were successfully applied to imaging of Hela cells in vitro and nude mouse in vivo. Most significant is that the method offers the advantages of ease of synthesis and handling as well as potentially low cost for biomedical emerging applications.

Nile Red Derivative-Modified Nanostructure for Upconversion Luminescence Sensing and Intracellular Detection of Fe3+ and MR Imaging

Iron ion (Fe(3+)) which is the physiologically most abundant and versatile transition metal in biological systems, has been closely related to many certain cancers, metabolism, and dysfunction of organs, such as the liver, heart, and pancreas. In this Research Article, a novel Nile red derivative (NRD) fluorescent probe was synthesized and, in conjunction with polymer-modified core-shell upconversion nanoparticles (UCNPs), demonstrated in the detection of Fe(3+) ion with high sensitivity and selectivity. The core-shell UCNPs were surface modified using a synthesized PEGylated amphiphilic polymer (C18PMH-mPEG), and the resulting mPEG modified core-shell UCNPs (mPEG-UCNPs) show good water solubility. The overall Fe(3+)-responsive upconversion luminescence nanostructure was fabricated by linking the NRD to the mPEG-UCNPs, denoted as mPEG-UCNPs-NRD. In the nanostructure, the core-shell UCNPs, NaYF4:Yb,Er,Tm@NaGdF4, serve as the energy donor while the Fe(3+)-responsive NRD as the energy acceptor, which leads to efficient luminescence resonance energy transfer (LRET). The mPEG-UCNPs-NRD nanostructure shows high selectivity and sensitivity for detecting Fe(3+) in water. In addition, benefited from the good biocompatibility, the nanostructure was successfully applied for detecting Fe(3+) in living cells based on upconversion luminescence (UCL) from the UCNPs. Furthermore, the doped Gd(3+) ion in the UCNPs endows the mPEG-UCNPs-NRD nanostructure with effective T1 signal enhancement, making it a potential magnetic resonance imaging (MRI) contrast agent. This work demonstrates a simple yet powerful strategy to combine metal ion sensing with multimodal bioimaging based on upconversion luminescence for biomedical applications.

Visible and near-infrared luminescent mesoporous titania microspheres functionalized with lanthanide complexes: microstructure and luminescence with visible excitation

A new type of monodisperse mesoporous titania microspheres possessing visible (Eu3+, Sm3+) and near-infrared (Sm3+, Yb3+, Nd3+) luminescence were synthesized with covalent linking to Ln(dbm)3bpdc complexes (Ln = Eu, Sm, Yb, Nd, dbm = dibenzoylmethanate, bpdc = 2,2′-bipyridine-4,4′-dicarboxylic acid). These lanthanide complex-functionalized titania microspheres can be excited with visible light to extend the practical application in lighting devices and biomedical analysis. The materials were characterized using Fourier-transform infrared (FT-IR) spectroscopy, wide-angle X-ray powder diffraction (WAXD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), nitrogen adsorption/desorption, diffuse reflectance (DR) spectroscopy, fluorescence spectroscopy, and thermogravimetric analysis. The results show that the microsphere morphology composed of single anatase crystallites and mesoporous structure is retained after linking to the lanthanide complexes. To the best of our knowledge, this is the first successful attempt to graft lanthanide complexes onto mesoporous anatase titania microspheres with high crystallinity. The novel combination of lanthanide complexes with NIR luminescence under visible light excitation and mesoporous titania microspheres with high thermal and chemical stabilities as well as anatase crystallinity affords potential applications in the fields of energy conversion, photocatalysis, and biomaterials.

Direct formation of mesoporous upconverting core-shell nanoparticles for bioimaging of living cells

AbstractWe have developed a one-step method for the synthesis of mesoporous upconverting nanoparticles (MUCNs) of the type NaYF4:Yb,Er@mSiO2 in ammoniacal ethanol/water solution. The mesoporous silica is directly encapsulating the hydrophobic upconversion nanoparticles (UCNs) due to the presence of the template CTAB. Intense green emission (between 520 and 560 nm) and weaker red emission (between 630 and 670 nm) is observed upon 980-nm laser excitation. The MUCNs display low cytotoxicity (as revealed by an MTT test) and were successfully applied to label and image human nasopharyngeal epidermal carcinoma (KB) cells. FigureA facile one-step method was proposed for direct formation of core-shell mesoporous silica coated upconverting nanoparticles (MUCNs), NaYF4:Yb,Er@mSiO2, in an ammonia and ethanol aqueous solution and the obtained MUCNs were successfully applied to bioimaging of living cells.

A new fluorescent rhodamine B derivative as an “off–on” chemosensor for Cu2+ with high selectivity and sensitivity

A novel fluorescent chemosensor containing two rhodamine B moieties per molecule was synthesized and characterized as an “off–on” fluorescent probe for the detection of copper ions (Cu2+). The crystal structure of the chemosensor was confirmed by X-ray analysis and the recognition mechanism of detecting Cu2+ was proposed with absorption and fluorescence characterization. The chemosensor showed high selectivity and sensitivity and good repetition in sensing Cu2+, and the detection limit is as low as 38.00 nM. In addition, the chemosensor displayed low cytotoxicity as revealed by methyl thiazolyl tetrazolium (MTT) assays and was successfully applied to fluorescence test paper and living cell imaging for detecting Cu2+. Therefore, based on its environmental friendliness and good biocompatibility, the results offered the advantages including the detection of Cu2+ in the environment and bioimaging of intracellular Cu2+.

Rhodamine-modified upconversion nanoprobe for distinguishing Cu2+ from Hg2+ and live cell imaging

It is greatly important to seek a fast and sensitive method for the detection of Cu2+ ions because of their vital role in the human body. Fluorescent probes, especially the rhodamine derivatives, have been considered as promising candidates for detection of Cu2+ ions due to their attractive features. However, one problem frequently encountered in rhodamine-based fluorescent probes is that some of them could not distinguish Cu2+ from Hg2+ and these drawbacks limit their application in biological samples. In this paper, a rhodamine B derivative (RBH) was grafted to mesoporous silica coated upconversion nanoparticles (CS-UCNP) to fabricate a new organic–inorganic hybrid nanoprobe. On addition of Cu2+ ions, an emission band at about 580 nm appeared while the intensity of the green emission at about 545 nm of the nanoprobe decreased upon excitation of a 980 nm laser, implying that a luminescence resonance energy transfer (LRET) happened from the CS-UCNP to the RBH–Cu2+ complex. The obtained LRET nanoprobe could detect Cu2+ exclusively even in the presence of Hg2+ with a detection limit of 0.82 μM in absolute ethanol solution. Most importantly, this nanoprobe can be used for monitoring subcellular distribution of Cu2+ in living cells based on upconversion luminescence and downconversion fluorescence.

Luminescent nanoprobes based on upconversion nanoparticles and single-walled carbon nanohorns or graphene oxide for detection of Pb2+ ion

Two kinds of luminescent nanoprobes were developed for Pb2+ detection based on luminescence resonance energy transfer (LRET) by using sodium citrate functionalized upconversion nanoparticles (Cit-UCNPs) as the energy donor and single-walled carbon nanohorns (SWCNHs) or graphene oxide (GO) as the energy acceptor. A Pb2+ aptamer 5′-NH2-(CH2)6-GGGTGGGTGGGTGGGT-3′ (denoted as pDNA) sequence was assembled with Cit-UCNPs to form the Cit-UCNPs–pDNA. By using the SWCNHs (or GO) as matrix, the final Cit-UCNPs–pDNA–SWCNHs (or Cit-UCNPs–pDNA–GO) nanoprobe can be obtained, in which the LRET process happened and the upconversion luminescence of the probe was quenched. With the addition of Pb2+, a stable G-quadruplex–Pb2+ complex was formed, which results in the separation between Cit-UCNPs–pDNA nanoparticles and SWCNHs (or GO) and the recovery of the upconversion luminescence. The two turn-on luminescence probes could detect Pb2+ ions from amongst other ions with high sensitivity and selectivity in aqueous solution. To the best of our knowledge, a nanoprobe for the detection of Pb2+ ions based on LRET between UCNPs and SWCNHs (or GO) has not been reported in the literature to date. This work demonstrates a simple yet powerful sensing strategy, which may open up potential perspectives for environmental monitoring applications.

Lanthanide complex-functionalized polyhedral oligomeric silsesquioxane with multicolor emission covered from 450 nm to 1700 nm

A new 2,2′-bipyridine-4,4′-dicarboxylic acid-functionalized polyhedral oligomeric silsesquioxane (named as bpdc-POSS) was successfully synthesized. Subsequently, six new Ln-bpdc-POSS (Ln = Eu, Tb, Sm, Nd, Yb, Er) hybrid materials covalently linked with lanthanide complexes were prepared, based on the bpdc-POSS material acting as a matrix. The Ln-bpdc-POSS hybrid materials retain the structure of POSS and size distribution approximately 50 nm, and display visible as well as near-infrared luminescence (covered from 450 to 1700 nm wavelength region) under UV/visible light excitation. The Ln-bpdc-POSS materials (Ln = Eu, Tb, Sm, Er, Nd, Yb) were characterized by using wide-angle X-ray powder diffraction, Fourier-transform infrared (FT-IR) spectroscopy, high-resolution transmission electron microscopy (HRTEM), fluorescent spectroscopy and thermogravimetric analysis. The method offers advantages including the ease of synthesis and handling, as well as extending the use of POSS and expanding the field of luminescent inorganic–organic hybrid materials based on lanthanides.

New nanoplatforms based on upconversion nanoparticles and single-walled carbon nanohorns for sensitive detection of acute promyelocytic leukemia

A new luminescence “Turn-On” nanoplatform based on luminescence resonance energy transfer (LRET) from sodium citrate functionalized upconversion nanoparticles (Cit-UCNPs, energy donor) to single-walled carbon nanohorns (SWCNHs, energy acceptor) was prepared for sensitive detection of acute promyelocytic leukemia (APL). In the presence of the target DNA, a PML/RARα fusion gene of APL, the π–π stacking interaction between the energy donor Cit-UCNPs and energy acceptor SWCNHs weakened and their distance enlarged. Therefore, the luminescence of Cit-UCNPs would be recovered (turn on) due to the inhibition of the LRET process. Based on this fact, a sensitive method was developed for the fluorescence turn on detection of ALP with a detection limit as low as 0.28 nM. To the best of our knowledge, this is the first time that upconversion nanoparticles and single-walled carbon nanohorns were used as a donor–acceptor pair to detect PML/RARα fusion gene sequences through a LRET process.

Light modulation (vis-NIR region) based on lanthanide complex-functionalized carbon dots

A new kind of carbon dots with an average diameter of approximately 3–5 nm were synthesized using L-lysine. Subsequently, a series of lanthanide complex-functionalized carbon dots were designed and synthesized, denoted as Ln-CDs (Ln = Eu, Sm, Er, Yb, Nd). In addition, by changing the ratio of Eu complexes and carbon dots, four kinds of Eu complex-functionalized carbon dots were also obtained (Eu-CDs-1, Eu-CDs-2, Eu-CDs-3, Eu-CDs-4). The derived nanomaterials were characterized by Fourier-transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and fluorescence spectroscopy. Upon visible-light excitation, these lanthanide complex-functionalized carbon dots show multicolor visible (Eu; with red, orange, grey and blue colors, respectively) and near-infrared (Sm, Er, Nd, Yb) luminescence (emission covered from 400 nm to 1700 nm spectral region).