Luminescent Nanocrystals for Nonenzymatic Glucose Concentration Determination

Fluorophore-Probed Curdlan Polysaccharide Chemosensor: "Turn-On" Oligosaccharide Sensing in Aqueous Media

The ability to sense saccharides in aqueous media has attracted much attention in multidisciplinary sciences because the detection of ultrahigh concentrations of sugar chains associated with serious diseases could lead to further health promotion. However, there are notable challenges. In this study, a rhodamine-modified Curdlan (Rhod-Cur) chemosensor was synthesized that exhibited distinctive fluorescence "turn-on" responses. Rhod-Cur exhibited simultaneous sensitive and selective sensing of clinically useful acarbose with a good limit of detection (5 μM) from among those of the saccharides examined. The (chir)optical properties of Rhod-Cur were elucidated using UV/vis, fluorescence, excitation, and circular dichroism spectroscopies; lifetime measurements and morphological studies using atomic force and confocal laser scanning microscopy and dynamic light scattering techniques revealed that the fluorescence "turn-on" behavior originates from globule-to-coaggregation conversion upon insertion of the oligosaccharides in the dynamic Cur backbone.

Nanocrystals for Deep-Tissue In Vivo Luminescence Imaging in the Near-Infrared Region

In vivo imaging technologies have emerged as a powerful tool for both fundamental research and clinical practice. In particular, luminescence imaging in the tissue-transparent near-infrared (NIR, 700-1700 nm) region offers tremendous potential for visualizing biological architectures and pathophysiological events in living subjects with deep tissue penetration and high imaging contrast owing to the reduced light-tissue interactions of absorption, scattering, and autofluorescence. The distinctive quantum effects of nanocrystals have been harnessed to achieve exceptional photophysical properties, establishing them as a promising category of luminescent probes. In this comprehensive review, the interactions between light and biological tissues, as well as the advantages of NIR light for in vivo luminescence imaging, are initially elaborated. Subsequently, we focus on achieving deep tissue penetration and improved imaging contrast by optimizing the performance of nanocrystal fluorophores. The ingenious design strategies of NIR nanocrystal probes are discussed, along with their respective biomedical applications in versatile in vivo luminescence imaging modalities. Finally, thought-provoking reflections on the challenges and prospects for future clinical translation of nanocrystal-based in vivo luminescence imaging in the NIR region are wisely provided.

Physiochemical characterization of highly biocompatible, and colloidal LaF3:Yb/Er upconversion nanoparticles

Highly colloidal upconversion nanoparticles (UCNPs) were synthesized at low temperatures by the thermal decomposition process. The structure, morphology, crystallinity, surface chemistry, and optical properties were systematically optimized and studied through various spectroscopic techniques. X-ray diffraction (XRD) patterns have shown the formation of single-phase, highly purified, well-crystalline, hexagonal LaF₃ NPs, while the TEM micrographs show small, irregular sizes, spherically shaped, and aggregated polycrystalline UCNPs with an average crystalline size of about 8-15 nm. The Negative Zeta Potential value exhibits good biocompatibility of the UCNPs, which supports the idea that surface-anchored hydroxyl groups facilitate the stabilization of the NPs in aqueous media, as well as enhance biomolecules' tagging efficiency. The absorption spectrum, Zeta Potential, and hydrodynamic size that were measured in aqueous media illustrate excellent dispersibility, colloidal stability, biocompatibility, and cytotoxicity character of the UCNPs. Zeta potential and MTT assay studies illustrated high biocompatibility, it could be due to the surface-anchored hydroxyl groups. The nanoproduct demonstrates an excellent UC luminescence spectrum (i.e., prominent green emission ⁴S_3/2 → ⁴I/_15/2) upon irradiation by the 980-nm laser diode. TEM micrographs, further, revealed that this optically active material with aqueous sensitivities, porous crystal structure, and excellent UCNPs, could be a favorable candidate for potential photonics-based bio-related applications.

Dual-Signal Luminescent Detection of Dopamine by a Single Type of Lanthanide-Doped Nanoparticles

Detection of dopamine, an important neurotransmitter, is vital for understanding its roles in mammals and disease diagnosis. However, commonly available methods for dopamine detection typically rely on a single signal readout, which can be susceptible to interference by internal or external factors. Here, we report a dual-signal detection of dopamine based on label-free luminescent NaGdF₄:Tb nanoparticles. In the presence of dopamine, the NaGdF₄:Tb nanoparticles exhibit luminescence quenching under the excitation of 272 nm, while they give enhanced luminescence under 297 nm excitation, realizing both turn off and turn on detection of dopamine. The nanoparticle-based dual-signal sensors exhibit high sensitivity, with a detection limit of ∼30 nM, and good selectivity, which offers the possibility to identify potential interferents in the samples. We further demonstrate that the dual-signal response results from different energy-transfer processes within the nanoparticles under the excitation of different light. The new strategy demonstrated here should pave the way for the development of multiresponse nanosensors based on lanthanide-doped luminescent nanomaterials.

A luminescent lanthanide coordination polymer based on energy transfer from metal to metal for hydrogen peroxide detection

A bimetal lanthanide coordination polymer nanoparticle (ATP-Ce/Tb-Tris CPNs) with good biocompatibility was synthesized in Tris-HCl buffer using adenosine triphosphate (ATP) molecules as the bridge ligands. The large absorption cross section and suitable emission energy of Ce³⁺ matching to the adsorption energy of Tb³⁺(⁴f_n) results in the efficient energy transfer from Ce³⁺ to Tb³⁺, thus the synthesized ATP-Ce/Tb-Tris CPNs exhibit the characteristic green emission of Tb³⁺. Such energy transfer from metal to metal in fluorescent lanthanide coordination polymer nanoparticles (Ln-CPNs) has been demonstrated. It is found that the oxidation of Ce³⁺ in ATP-Ce/Tb-Tris CNPs to Ce⁴⁺ would interrupt the energy transfer from Ce³⁺ to Tb³⁺, leading to fluorescence quenching of Tb³⁺. On the basis of this quenching mechanism, ATP-Ce/Tb-Tris CPNs has been successfully used to detect reactive oxygen H₂O₂ with detection limit as low as 2nM. If glucose oxidase is present in the system, glucose can be determined using the ATP-Ce/Tb-Tris CNPs nanosensor.

DNA base pair resolution measurements using resonance energy transfer efficiency in lanthanide doped nanoparticles

Lanthanide-doped nanoparticles are of considerable interest for biodetection and bioimaging techniques thanks to their unique chemical and optical properties. As a sensitive luminescence material, they can be used as (bio) probes in Förster Resonance Energy Transfer (FRET) where trivalent lanthanide ions (La3+) act as energy donors. In this paper we present an efficient method to transfer ultrasmall (ca. 8 nm) NaYF4 nanoparticles dispersed in organic solvent to an aqueous solution via oxidation of the oleic acid ligand. Nanoparticles were then functionalized with single strand DNA oligomers (ssDNA) by inducing covalent bonds between surface carboxylic groups and a 5' amine modified-ssDNA. Hybridization with the 5' fluorophore (Cy5) modified complementary ssDNA strand demonstrated the specificity of binding and allowed the fine control over the distance between Eu3+ ions doped nanoparticle and the fluorophore by varying the number of the dsDNA base pairs. First, our results confirmed nonradiative resonance energy transfer and demonstrate the dependence of its efficiency on the distance between the donor (Eu3+) and the acceptor (Cy5) with sensitivity at a nanometre scale.

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.

The intersection of CMOS microsystems and upconversion nanoparticles for luminescence bioimaging and bioassays

Organic fluorophores and quantum dots are ubiquitous as contrast agents for bio-imaging and as labels in bioassays to enable the detection of biological targets and processes. Upconversion nanoparticles (UCNPs) offer a different set of opportunities as labels in bioassays and for bioimaging. UCNPs are excited at near-infrared (NIR) wavelengths where biological molecules are optically transparent, and their luminesce in the visible and ultraviolet (UV) wavelength range is suitable for detection using complementary metal-oxide-semiconductor (CMOS) technology. These nanoparticles provide multiple sharp emission bands, long lifetimes, tunable emission, high photostability, and low cytotoxicity, which render them particularly useful for bio-imaging applications and multiplexed bioassays. This paper surveys several key concepts surrounding upconversion nanoparticles and the systems that detect and process the corresponding luminescence signals. The principle of photon upconversion, tuning of emission wavelengths, UCNP bioassays, and UCNP time-resolved techniques are described. Electronic readout systems for signal detection and processing suitable for UCNP luminescence using CMOS technology are discussed. This includes recent progress in miniaturized detectors, integrated spectral sensing, and high-precision time-domain circuits. Emphasis is placed on the physical attributes of UCNPs that map strongly to the technical features that CMOS devices excel in delivering, exploring the interoperability between the two technologies.

Lanthanide upconversion nanoparticles and applications in bioassays and bioimaging: a review

Through the process of photon upconversion, trivalent lanthanide doped nanocrystals convert long-wavelength excitation radiation in the infrared or near infrared region to higher energy emission radiation from ultraviolet to infrared. Such materials offer potential for numerous advantages in analytical applications in comparison to molecular fluorophores and quantum dots. The use of IR radiation as an excitation source reduces autofluorescence and scattering of excitation radiation, which leads to a reduction of background in optical experiments. The upconverting nanocrystals offer excellent photostability and are composed of materials that are not particularly toxic to biological organisms. Excitation at long wavelengths also minimizes damage to biological materials. In this review, the different mechanisms responsible for the upconversion process, and methods that are used to synthesize and decorate upconverting nanoparticles are presented to indicate how absorption and emission can be tuned. Examples of recent applications of upconverting nanoparticles in bioassays for the detection of proteins, nucleic acids, metabolites and metal ions offer indications of analytical advantages in the development of methods of analysis. Examples include multi-color and multi-modal imaging, and the use of upconverting nanoparticles in theranostics.

Lanthanide-doped luminescent nano-bioprobes: from fundamentals to biodetection

Trivalent lanthanide (Ln(3+))-doped luminescent inorganic nanoparticles (NPs), characterized by long-lived luminescence, large Stokes and/or anti-Stokes shifts, narrow emission bands and high photochemical stability, are considered to be promising candidates as luminescent bioprobes in biomedicine and biotechnology. In this feature article, we provide a brief overview of the most recent advances in Ln(3+)-doped luminescent inorganic NPs as sensors, which covers from their chemical and physical fundamentals to biodetection, such as controlled synthesis methodology, surface modification chemistry, optical physics, and their promising applications in diverse bioassays, with an emphasis on heterogeneous and homogeneous in vitro biodetection. Finally, some of the most important emerging trends and future efforts toward this active research field are also proposed.

Amine-functionalized lanthanide-doped zirconia nanoparticles: optical spectroscopy, time-resolved fluorescence resonance energy transfer biodetection, and targeted imaging

Ultrasmall inorganic oxide nanoparticles doped with trivalent lanthanide ions (Ln(3+)), a new and huge family of luminescent bioprobes, remain nearly untouched. Currently it is a challenge to synthesize biocompatible ultrasmall oxide bioprobes. Herein, we report a new inorganic oxide bioprobe based on sub-5 nm amine-functionalized tetragonal ZrO(2)-Ln(3+) nanoparticles synthesized via a facile solvothermal method and ligand exchange. By utilizing the long-lived luminescence of Ln(3+), we demonstrate its application as a sensitive time-resolved fluorescence resonance energy transfer (FRET) bioprobe to detect avidin with a record-low detection limit of 3.0 nM. The oxide nanoparticles also exhibit specific recognition of cancer cells overexpressed with urokinase plasminogen activator receptor (uPAR, an important marker of tumor biology and metastasis) and thus may have great potentials in targeted bioimaging.

Lanthanide-doped nanocrystals: synthesis, optical-magnetic properties, and applications

Because of the potential applications of lanthanide-doped nanocrystals in display devices, optical communication, solid-state lasers, catalysis, and biological labeling, the controlled synthesis of these new nanomaterials has sparked considerable interest. Nanosized phosphorescent or optoelectronic devices usually exhibit novel properties, depending on their structures, shapes, and sizes, such as tunable wavelengths, rapid responses, and high efficiencies. Thus, the development of facile synthetic methods towards high-quality lanthanide-doped nanocrystals with uniform size and shape appears to be of key importance both for the exploration of their materials properties and for potential applications. This Account focuses on the recent development in our laboratory of the synthesis and applications of lanthanide-doped nanocrystals. Since 2005, when we proposed a general strategy for nanocrystal synthesis via a liquid-solid-solution process, a range of monodisperse and colloidal lanthanide-doped fluoride, oxide, hydroxide, orthovanadate, thiooxide, borate, and phosphate nanocrystals have been successfully prepared. By rationally tuning the reaction conditions, we have readily synthesized nanostructures, such as hollow microspheres, nanorods, nanowires, hexagonal nanoplates, and nanobelts. By adjusting the different colloidal nanocrystal mixtures, we fabricated unique binary nanostructures with novel dual-mode luminescence properties through a facile ultrasonic method. By tridoping with lanthanide ions that had different electronic structures, we successfully achieved β-NaYF(4) nanorods that were paramagnetic with tuned upconversion luminescence. We have also used NaYF(4):Yb(3+)/Er(3+) conbined with magnetite nanoparticles as a sensitive detection system for DNA: NaYF(4):Yb(3+)/Er(3+) and Fe(3)O(4) nanoparticles were modified with two different DNA sequences. Then, the modified NaYF(4):Yb(3+)/Er(3+) nanoparticles were conjugated to the modified Fe(3)O(4) nanoparticles. These binary nanoparticles can be hybridized with a third DNA (target DNA) molecule and separated with the assistance of a magnetic field. In addition, a novel fluorescence resonance energy transfer (FRET) method for nonenzymatic glucose determination has been developed by using the glucose-modified LaF(3):Ce(3+)/Tb(3+) nanocrystals. By using bioconjugated NaYF(4):Yb(3+)/Er(3+) nanoparticles as the energy donor and bioconjugated gold nanoparticles as the energy acceptor, we successfully developed a simple and sensitive fluorescence resonance energy transfer (FRET) biosensor for avidin. Meanwhile, we also carried out preliminary studies to investigate possible applications of lanthanide-doped nanocrystals in catalysis and in dye-sensitized solar cells.

Terbium (III) chelate complexes as fluorescence energy transfer donor in the determination of formaldehyde in aqueous solutions

The sensitized fluorescence intensity of the terbium (III) ion can be notably enhanced in the presence of sodium hexametaphosphate (SHMP). Based on this, water-soluble Tb-SHMP chelate complexes were synthesized in aqueous solutions, and characterized by spectrofluorometry. 6-Mercapto-5-triazole[4,3-b]-S-tetrazine was generated by the quantitative reaction of HCHO with 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole under alkaline conditions at room temperature. The spectral overlap between the emission of Tb-SHMP chelate complexes and absorption of 6-mercapto-5-triazole[4,3-b]-S-tetrazine meets the prerequisite for fluorescence energy transfer. Based on this, a novel efficient fluorescence energy transfer system between Tb-SHMP chelate complexes as donor and 6-mercapto-5-triazole[4,3-b]-S-tetrazine as acceptor was developed for the determination of HCHO in aqueous solutions. Under the optimal experimental conditions, this method is capable of detecting HCHO concentrations from 2.06×10(-5) to 6.18×10(-3) mg mL(-1) and the limit of detection was 7.11×10(-6) mg mL(-1). Compared with other general methods for the determination of HCHO, the proposed method improved the sensitivity and selectivity. Moreover, the proposed method was successfully applied to the determination of HCHO in water samples.

Oligosaccharide sensing with chromophore-modified curdlan in aqueous media

A newly synthesized chromophore-modified curdlan functions as a saccharide chemosensor in aqueous solution, enabling us to discriminate tetrasaccharide acarbose from 24 mono-, di-, tri-, and tetrasaccharides.

Novel luminescent nanoparticles for DNA detection

Highly luminescent LaF(3):Ce(3+)/Tb(3+) nanocrystals were successfully prepared and surface functionalized via Layer-by-Layer technology. These as-prepared nanocrystals are highly resistant to photobleaching and pretty dispersible in aqueous solution. Due to the efficient luminescence quenching of the nanocrystals by nucleic acids, a facile fluorescence quenching method was developed for the detection of trace amount of nucleic acids. Under optimal conditions, the fluorescence intensity was proportional to the DNA concentration over the range of 0.60-25.0microgmL(-1) for calf thymus DNA (ct-DNA) and 0.60-30.0microgmL(-1) for herring sperm DNA (hs-DNA), respectively. The corresponding detection limit is 0.21microgmL(-1) for ct-DNA and 0.31microgmL(-1) for hs-DNA, respectively. The results indicated that the reported method is simple and rapid with wide linear range. Also, the recovery and relative standard deviation of this method are reasonable and satisfactory.

Carbohydrate recognition by boronolectins, small molecules, and lectins

Carbohydrates are known to mediate a large number of biological and pathological events. Small and macromolecules capable of carbohydrate recognition have great potentials as research tools, diagnostics, vectors for targeted delivery of therapeutic and imaging agents, and therapeutic agents. However, this potential is far from being realized. One key issue is the difficulty in the development of "binders" capable of specific recognition of carbohydrates of biological relevance. This review discusses systematically the general approaches that are available in developing carbohydrate sensors and "binders/receptors," and their applications. The focus is on discoveries during the last 5 years.

Luminescent rare earth nanomaterials for bioprobe applications

Inorganic fluorescent nanoparticles (NPs) have initiated an extensive upsurge in biological application research. Just as quantum dots are regarded as a vigorous reinforcement of the organic dye family, rare earth (RE) fluorescent NPs, as another phosphors branch, also possess unique optical characteristics. The advantages of RE NPs in photostability and colorimetric purity make them suitable for bioprobe applications. Since the preparation technologies have been well developed, it is favourable to prompt the research in the interdisciplinary field of biology and material sciences. Herein, we summarize the synthesis and performance, together with bioprobe applications of RE oxide, sulfoxide, vanadate, phosphate, fluoride, and sodium RE fluoride nanomaterials. The prospects of these promising materials as applied in the biological field is described to draw readers' attention and to attract more research interest.

Monodisperse nanocrystals: general synthesis, assembly, and their applications

This article summarizes the recent advances in the synthesis, assembly and applications of monodisperse nanocrystals, which may be suggestive for the designed synthesis and assemblies of target nanocrystals according to practical requirements.