Hydrogen-Bonding Recognition-Induced Color Change of Gold Nanoparticles for Visual Detection of Melamine in Raw Milk and Infant Formula

Hydrogen-Bonding Recognition-Induced Color Change of Gold Nanoparticles for Visual Detection of Melamine in Raw Milk and Infant Formul

Nanoparticulate X‑ray Computed Tomography Contrast Agents: From Design Validation to in Vivo Applications

X-ray computed tomography (CT) is one of the most powerful noninvasive diagnostic imaging techniques in modern medicine. Nevertheless, the iodinated molecules used as CT contrast agents in the clinic have relatively short circulation times in vivo, which significantly restrict the applications of this technique in target-specific imaging and angiography. In addition, the use of these agents can present adverse. For example, an adult patient typically receives approximately 70 mL of iodinated agent (350 mg I/mL) because of iodine’s low contrast efficacy. Rapid renal clearance of such a large dose of these agents may lead to serious adverse effects. Furthermore, some patients are hypersensitive to iodine.Therefore, biomedical researchers have invested tremendous efforts to address these issues. Over the past decade, advances in nanoscience have created new paradigms for imaging. The unique properties of nanomaterials, such as their prolonged circulating half-life, passive accumulation at the tumor sites, facile surface modification, and integration of multiple diverse functions into a single particle, make them advantageous for in vivo applications. However, research on the utilization of nanomaterials for CT imaging has lagged far behind their applications for other imaging techniques such as MRI and fluorescence imaging because of the challenges in the preparation of cost-effective nanoparticulate CT contrast agents with excellent biocompatibility, high contrast efficacy, long in vivo circulation time, and long-term colloidal stability in physiological environments.This Account reviews our recent work on the design and in vivo applications of nanoparticulate CT contrast agents. By optimizing the contrast elements in the nanoparticles according to the fundamental principles of X-ray imaging and by employing the surface engineering approaches that we and others have developed, we have synthesized several nanoparticulate CT contrast agents with excellent imaging performance. For example, a novel Yb-based nanoparticulate agent provides enhanced contrast efficacy compared to currently available CT contrast agents under normal operating conditions. To deal with special situations, we integrated both Ba and Yb with great differential in K-edge value into a single particle to yield the first example of binary contrast agents. This agent displays much higher contrast than iodinated agents at different voltages and is highly suited to diagnostic imaging of various patients. Because of their prolonged in vivo circulation time and extremely low toxicity, these agents can be used for angiography

Silver Nanoplates with Special Shapes: Controlled Synthesis and Their Surface Plasmon Resonance and Surface-Enhanced Raman Scattering Properties

Shape-controlled synthesis of metal nanostructures has opened many new possibilities to design ideal building blocks for future nanodevices. In this work, new types of monodisperse silver nanoplates with complex shapes, namely, a disklike shape and flowerlike shapes, were controllably synthesized in high yield by reducing [Ag(NH3)2]+ with ascorbic acid in the presence of silver seed at room temperature. Unlike previous methods for synthesizing the silver nanoplates in the presence of cetyltrimethylammonium bromide (CTAB) micelles, the use of the precursor [Ag(NH3)2]+, other than Ag+, provides a flexible strategy to control the procession of the reduction reaction in a mild way. These silver nanoplates with shapes of disk and flower were shown to possess surface plasmon resonance (SPR) that directly relates to their geometric shapes. As a result of their high anisotropy in shape, the flowerlike silver nanoplates exhibit excellent surface-enhanced Raman scattering (SERS) enhancement ability relative to spherical silver nanoparticles and the disklike silver nanoplates. We believe that with the efficient synthesis and excellent SERS enhancement ability, these novel flowerlike silver nanoplates may find potential applications for biological sensing and labeling systems

Tailor-Made Charge-Conversional Nanocomposite for pH-Responsive Drug Delivery and Cell Imaging

Imaging labels, therapeutic drugs, as well as many other agents can all be integrated into one nanoplatform to allow for molecular imaging and therapy. With this in mind, herein we report the first example of a tailor-made charge-conversional nanocomposite composed of mesoporous γ-AlO­(OH) and upconversion nanoparticles (UCNPs) via a simple and versatile method, and the obtained nanocomposite could be performed as a drug delivery carrier and applied for cell imaging. The nanocomposite (UCNPs-Al) was found to be able to efficiently transport DOX, a typical chemotherapeutic anticancer drug, into the cancer cell and release DOX from UCNPs-Al triggering by the mildly acidic environment. In vitro cell cytotoxicity assay verified that DOX-loaded nanocomposites (UCNPs-Al-DOX) exhibited greater cytotoxicity with respect to free DOX at the same concentrations, because of the increase in cell uptake of anti-cancer drug delivery vehicles mediated by the charge-conversional property. Moreover, the UCL emission from UCNPs and the red fluorescence of DOX allow the nanocomposite to track and monitor the drug delivery system simultaneously. These findings have opened up new insights into designing and producing the highly versatile multifunctional nanoparticles for simultaneous imaging and therapeutic applications

In situ Controllable Growth of Prussian Blue Nanocubes on Reduced Graphene Oxide: Facile Synthesis and Their Application as Enhanced Nanoelectrocatalyst for H₂O₂ Reduction

As a single-atom-thick carbon material with high surface area and conductivity, graphene provides an ideal platform for designing composite nanomaterials for high-performance electrocatalytic or electrochemical devices. Herein, we demonstrated a facile strategy for controllably growing high-quality Prussian blue nanocubes on the surface of reduced graphene oxide (PBNCs/rGO), which represents a new type of graphene/transition metal complex heterostructure. The merit of this method is that the composite nanomaterials could be produced directly from GO in an in situ wet-chemical reaction, where the reduction of GO and the deposition of PBNCs occurred simultaneously. The obtained composite nanomaterials were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Raman spectroscopy, and electrochemical techniques. It was found that uniform PBNCs with controlled size and good dispersion were directly grown on the surface of graphene nanosheets. Moreover, we also investigated the performance of PBNCs/rGO nanocomposites as amperometric sensor toward reduction of H2O2. Such a sensor showed a rapid and highly sensitive response to H2O2 with a low detection limit (45 nM), which might find promising applications in developing a new type of enzymeless biosensor

Template-Free Synthesis of Renewable Macroporous Carbon via Yeast Cells for High-Performance Supercapacitor Electrode Materials

The urgent need for sustainable development has forced material scientists to explore novel materials for next-generation energy storage devices through a green and facile strategy. In this context, yeast, which is a large group of single cell fungi widely distributed in nature environments, will be an ideal candidate for developing effective electrode materials with fascinating structures for high-performance supercapacitors. With this in mind, herein, we present the first example of creating three-dimensional (3D) interpenetrating macroporous carbon materials via a template-free method, using the green, renewable, and widespread yeast cells as the precursors. Remarkably, when the as-prepared materials are used as the electrode materials for supercapacitors, they exhibit outstanding performance with high specific capacitance of 330 F g^–1 at a current density of 1 A g^–1, and good stability, even after 1000 charge/discharge cycles. The approach developed in this work provides a new view of making full use of sustainable resources endowed by nature, opening the avenue to designing and producing robust materials with great promising applications in high-performance energy-storage devices

Oriented Attachment-Based Assembly of Dendritic Silver Nanostructures at Room Temperature

How particles aggregate into an interesting dendritic structure has been the object of research for many years because of its importance in understanding physical processes involved and in designing novel materials. In this work, we for the first time describe an oriented attachment-based assembly mechanism for formation of different types of dendritic silver nanostructures at room temperature. It is found that the concentration of both AgNO3 and p-aminoazobenzene (PA) molecules has a significant effect on the formation and growth of these novel nanostructures. Characterization by transmission electron microscopy (TEM) clearly shows that the dendritic silver nanostructures can be obtained through the preferential oriented growth along a crystallographically special direction. Interestingly, we observe that the oriented attachment at room temperature can also take place between relatively large single-crystalline silver particles with a diameter range from 20 to 60 nm, which may provide a new possibility for the design of novel metal nanostructures by using large metal nanoparticles as building blocks at room temperature. Moreover, a surface-enhanced Raman scattering (SERS) technique is used to investigate the role of PA molecules during the growth of the dendritic silver nanostructures

Functionalizing Metal Nanostructured Film with Graphene Oxide for Ultrasensitive Detection of Aromatic Molecules by Surface-Enhanced Raman Spectroscopy

Surface-enhanced Raman spectroscopy (SERS) as a powerful analytical tool has gained extensive attention. Despite of many efforts in the design of SERS substrates, it remains a grand challenge for creating a general substrate that can detect diverse target analytes. Herein, we report our attempt to address this issue by constructing a novel metal-graphene oxide nanostructured film as SERS substrate. Taking advantages of the high affinity of graphene oxide (GO) toward aromatic molecules and the SERS property of nanostructured metal, this structure exhibits great potential for diverse aromatic molecules sensing, which is demonstrated by using crystal violet (CV) with positive charge, amaranth with negative charge, and neutral phosphorus triphenyl (PPh3) as model molecules

Dual-Emission Fluorescent Silica Nanoparticle-Based Probe for Ultrasensitive Detection of Cu²⁺

An effective dual-emission fluorescent silica nanoparticle-based probe has been constructed for rapid and ultrasensitive detection of Cu2+. In this nanoprobe, a dye-doped silica core served as a reference signal, thus providing a built-in correction for environmental effects. A response dye was covalently grafted on the surface of the silica nanoparticles through a chelating reagent for Cu2+. The fluorescence of the response dye could be selectively quenched in the presence of Cu2+, accompanied by a visual orange-to-green color switch of the nanoprobe. The nanoprobe provided an effective platform for reliable detection of Cu2+ with a detection limit as low as 10 nM, which is nearly 2 × 103 times lower than the maximum level (∼20 μM) of Cu2+ in drinking water permitted by the U.S. Environmental Protection Agency (EPA). The high sensitivity was attributed to the strong chelation of Cu2+ with polyethyleneimine (PEI) and a signal amplification effect. The nanoprobe constructed by this method was very stable, enabling the rapid detection of Cu2+ in real water samples. Good linear correlations were obtained over the concentration range from 1 × 10−7 to 8 × 10−7 (R2 = 0.99) with recoveries of 103.8−99.14% and 95.5−95.14% for industrial wastewater and lake water, respectively. Additionally, the long-wavelength emission of the response dye can avoid the interference of the autofluorescence of the biosystems, which facilitated their applications in monitoring Cu2+ in cells. Furthermore, the nanoprobe showed a good reversibility; the fluorescence can be switched “off” and “on” by an addition of Cu2+ and EDTA, respectively

Engineering Natural Materials as Surface-Enhanced Raman Spectroscopy Substrates for In situ Molecular Sensing

Surface-enhanced Raman spectroscopy (SERS) is a powerful analytical tool. However, its applications for in situ detection of target molecules presented on diverse material surfaces have been hindered by difficulties in rapid fabricating SERS-active substrates on the surfaces of these materials through a simple, low-cost, and portable approach. Here, we demonstrate our attempt to address this issue by developing a facile and versatile method capable of in situ generating silver nanoparticle film (SNF) on the surfaces of both artificial and natural materials in a simple, cheap, practical, and disposable manner. Taking advantage of the high SERS enhancement ability of the prepared SNF, the proposed strategy can be used for in situ inspecting herbicide and pesticide residues on vegetables, as well as the abuse of antiseptic in aquaculture industry. Therefore, it opens new avenues for advancing the application prospects of SERS technique in the fields of food safety, drug security, as well as environment monitoring