"Elastic" property of mesoporous silica shell: for dynamic surface enhanced Raman scattering ability monitoring of growing noble metal nanostructures via a simplified spatially confined growth method

Template-directed growth of Ag nanostructures: soft templates versus hard templates

Hard template-directed growth methods present a compelling route for the synthesis of Ag nanostructures with precise size control. Meanwhile, soft template methods are effective and flexible for the synthesis of Ag nanostructures with various morphologies. However, the role of the soft template is ambiguous and obviously neglected in hard template-directed growth processes due to the strong confinement effect of the hard template, limiting the diversity of Ag nanostructures that can be obtained. Herein, we design Au nanoframes with deformable head structures as a hard template while using cetyltrimethylammonium chloride as a soft template, to direct the growth of Ag atoms on Au nanobipyramid seeds. When using the Au nanoframes with a closed head, the longitudinal growth of the Ag atoms is clearly limited by the hard template, leading to the formation of thick Ag nanorods with a five-fold twinned structure. The soft template starts to influence the growth process when the head structure of the Au nanoframes becomes hollow. In particular, the confinement effect of the hard template can be completely broken by selectively strengthening the role of the soft template, promoting the production of slender Ag nanorods similar to the results obtained in the absence of the hard template. Our results indicate that the morphology of the Ag nanostructures depends on the competition between the qualitatively confined energies of the hard and soft templates during the template-directed growth process. Moreover, this confined growth mechanism is also verified by the successful construction of various Ag nanostructures. The understanding of the collaborative competition mechanism between the soft and hard templates presents a great opportunity to construct novel Ag nanostructures through a template-directed method.

Dimensional Design for Surface-Enhanced Raman Spectroscopy

Surface-enhanced Raman spectroscopy (SERS) is a vibrational spectroscopy technique that enables specific identification of target analytes with sensitivity down to the single-molecule level by harnessing metal nanoparticles and nanostructures. Excitation of localized surface plasmon resonance of a nanostructured surface and the associated huge local electric field enhancement lie at the heart of SERS, and things will become better if strong chemical enhancement is also available simultaneously. Thus, the precise control of surface characteristics of enhancing substrates plays a key role in broadening the scope of SERS for scientific purposes and developing SERS into a routine analytical tool. In this review, the development of SERS substrates is outlined with some milestones in the nearly half-century history of SERS. In particular, these substrates are classified into zero-dimensional, one-dimensional, two-dimensional, and three-dimensional substrates according to their geometric dimension. We show that, in each category of SERS substrates, design upon the geometric and composite configuration can be made to achieve an optimized enhancement factor for the Raman signal. We also show that the temporal dimension can be incorporated into SERS by applying femtosecond pulse laser technology, so that the SERS technique can be used not only to identify the chemical structure of molecules but also to uncover the ultrafast dynamics of molecular structural changes. By adopting SERS substrates with the power of four-dimensional spatiotemporal control and design, the ultimate goal of probing the single-molecule chemical structural changes in the femtosecond time scale, watching the chemical reactions in four dimensions, and visualizing the elementary reaction steps in chemistry might be realized in the near future.

Structural Control over Bimetallic Core-Shell Nanorods for Surface-Enhanced Raman Spectroscopy

Bimetallic nanorods are important colloidal nanoparticles for optical applications, sensing, and light-enhanced catalysis due to their versatile plasmonic properties. However, tuning the plasmonic resonances is challenging as it requires a simultaneous control over the particle shape, shell thickness, and morphology. Here, we show that we have full control over these parameters by performing metal overgrowth on gold nanorods within a mesoporous silica shell, resulting in Au-Ag, Au-Pd, and Au-Pt core-shell nanorods with precisely tunable plasmonic properties. The metal shell thickness was regulated via the precursor concentration and reaction time in the metal overgrowth. Control over the shell morphology was achieved via a thermal annealing, enabling a transition from rough nonepitaxial to smooth epitaxial Pd shells while retaining the anisotropic rod shape. The core-shell synthesis was successfully scaled up from micro- to milligrams, by controlling the kinetics of the metal overgrowth via the pH. By carefully tuning the structure, we optimized the plasmonic properties of the bimetallic core-shell nanorods for surface-enhanced Raman spectroscopy. The Raman signal was the most strongly enhanced by the Au core-Ag shell nanorods, which we explain using finite-difference time-domain calculations.

Enantioselective SERS sensing of pseudoephedrine in blood plasma biomatrix by hierarchical mesoporous Au films coated with a homochiral MOF

Here, we present a new family of hierarchical porous hybrid materials as an innovative tool for ultrasensitive and selective sensing of enantiomeric drugs in complex biosamples via chiral surface-enhanced Raman spectroscopy (SERS). Hierarchical porous hybrid films were prepared by the combination of mesoporous plasmonic Au films and microporous homochiral metal-organic frameworks (HMOFs). The proposed hierarchical porous substrates enable extremely low limit of detection values (10^-12 M) for pseudoephedrine in undiluted blood plasma due to dual enhancement mechanisms (physical enhancement by the mesoporous Au nanostructures and chemical enhancement by HMOF), chemical recognition by HMOF, and a discriminant function for bio-samples containing large biomolecules, such as blood components. We demonstrate the effect of each component (mesoporous Au and microporous AlaZnCl (HMOF)) on the analytical performance for sensing. The growth of AlaZnCl leads to an increase in the SERS signal (by around 17 times), while the use of mesoporous Au leads to an increase in the signal (by up to 40%). In the presence of a complex biomatrix (blood serum or plasma), the hybrid hierarchical porous substrate provides control over the transport of the molecules inside the pores and prevents blood protein infiltration, provoking competition with existing plasmonic materials at the limit of detection and enantioselectivity in the presence of a multicomponent biomatrix.

Mesoporous Nanostructures Encapsulated with Metallic Nanodots for Smart SERS Sensing

In virtue of uniform mesopores and core-shell nanoarchitectures, metallic nanodot-encapsulated hollow mesoporous nanostructures have shown promising potential in various applications. However, their fabrication with versatile tunability of the encapsulated metallic content has been a challenge. Herein, we have prepared metallic nanodot-encapsulated hollow mesoporous silica nanoparticles (M-HMSNPs) with adjustable inner metallic components. The sacrificial template of polystyrene (PS) nanoparticles precoated with metals (Au/Ag/Pt) is fully wrapped with mesoporous silica (mSiO₂). The metallic nanodots are formed during the template removal process by calcination. The type and content of the encapsulated nanodots can be readily and precisely controlled by the initially deposited metallic layers. We demonstrate the application of the gold (Au) nanodot-loaded HMSNPs (denoted Au-HMSNPs) as smart surface-enhanced Raman spectroscopy (SERS) probes, which can screen between big molecules and small analytes. With the aid of a Raman reporter, the SERS probe can successfully quantify H₂O₂, which is used to distinguish cancer cells in vitro. Further integrated with enzymes, the SERS chips of specificity are prepared and used to detect corresponding substrates of glucose and uric acid, responsively. Besides SERS sensing, the current strategy can inspire future development of many other M-HMSNPs for various applications such as catalysis, energy storage, theranostics, etc.

An Expanded Surface-Enhanced Raman Scattering Tags Library by Combinatorial Encapsulation of Reporter Molecules in Metal Nanoshells

Raman-encoded gold nanoparticles (NPs) have been widely employed as photostable multifunctional probes for sensing, bioimaging, multiplex diagnostics, and surface-enhanced Raman scattering (SERS)-guided tumor therapy. We report a strategy toward obtaining a particularly large library of Au nanocapsules encoded with Raman codes defined by the combination of different thiol-free Raman reporters, encapsulated at defined molar ratios. The fabrication of SERS tags with tailored size and predefined codes is based on the in situ incorporation of Raman reporter molecules inside Au nanocapsules during their formation via galvanic replacement coupled to seeded growth on Ag NPs. The hole-free closed-shell structure of the nanocapsules is confirmed by electron tomography. The unusually wide encoding possibilities of the obtained SERS tags are investigated by means of either wavenumber-based encoding or Raman frequency combined with signal intensity, leading to an outstanding performance as exemplified by 26 and 54 different codes, respectively. We additionally demonstrate that encoded nanocapsules can be readily bioconjugated with antibodies for applications such as SERS-based targeted cell imaging and phenotyping.

Optimizing the SERS Performance of 3D Substrates through Tunable 3D Plasmonic Coupling toward Label-Free Liver Cancer Cell Classification

Three-dimensional (3D) plasmonic nanostructures are emerging as excellent surface-enhanced Raman spectroscopy (SERS) substrates for chemical and biomedical applications. However, the correlation of 3D (including both in-plane and out-of-plane) plasmonic coupling with the SERS properties to deepen the understanding of 3D SERS substrates remains a challenge. Here, we perform correlation studies of 3D plasmonic coupling and SERS properties of the 3D hierarchical SERS substrates by tuning the multiscale structural elements. The effects of zero-dimensional (0D; the size of the building blocks), one-dimensional (1D; the thickness of the 3D substrates), and two-dimensional (2D; the composition of individual monolayers) structural elements on 3D plasmonic coupling are studied by performing UV-vis-near-infrared (NIR) spectroscopy and measuring SERS performance. It shows that both the extinction spectra and SERS enhancement are tuned at the 3D structural level. It is demonstrated that the plasmonic resonance wavelength (PRW) stemming from the 3D plasmonic coupling correlates with the SERS averaged surface enhancement factor (ASEF) and is improved by more than tenfold at the optimum 3D nanostructure. The optimized substrate is used to quantitatively analyze two small biological molecules. Moreover, as a proof-of-concept study, the substrate is first applied to differentiate between living liver normal and cancer cells with a high prediction accuracy through the spectral features of the cell membranes and the metabolites secreted outside the cells. We expect that the tuning of plasmonic coupling at the 3D level can open up new routes to design high-performance SERS substrates for wide applications.

Gold Nanorod Array-Bridged Internal-Standard SERS Tags: From Ultrasensitivity to Multifunctionality

Bimetallic gold core-silver shell (Au@Ag) surface-enhanced Raman scattering (SERS) tags draw broad interest in the fields of biological and environmental analysis. In reported tags, silver coating tended to smooth the surface and merge the original hotspot of Au cores, which was disadvantageous to signal enhancement from the aspect of surface topography. Herein, we developed gold nanorod (AuNR)-bridged Au@Ag SERS tags with uniform three-dimensional (3D) topography for the first time. This unique structure was achieved by selecting waxberry-like Au nanoparticles (NPs) as cores, which were capped by vertically oriented AuNR arrays. Upon selective surface blocking with thiol-ligands, Ag NPs were controlled to anisotropically grow on the tips of the AuNRs, producing high-density homo- (Ag-Ag) and hetero- (Au-Ag) hotspots in a single NP. The 3D hotspots rendered this NP extraordinary SERS enhancement ability (an analytical enhancement factor of 3.4 × 10⁶) 30 times higher than the counterpart with a smooth surface, realizing signal detection from a single NP. More importantly, multiplexing signals ("blank" or multiplex "internal standard") can be achieved by simply changing thiol-ligands, as exemplified in the synthesis of NPs with 8 signatures. Furthermore, the multifunctionality has been demonstrated in living cell/in vivo imaging, photothermal therapy, and SERS substrates for ratiometric quantitative analysis, relying on the inherent internal standard signal. The prepared Au@Ag NPs have great potential as standard tools in many SERS-related fields.

Are plasmonic optical biosensors ready for use in point-of-need applications?

Plasmonics has drawn significant attention in the area of biosensors for decades due to the unique optical properties of plasmonic resonant nanostructures. While the sensitivity and specificity of molecular detection relies significantly on the resonance conditions, significant attention has been dedicated to the design, fabrication, and optimization of plasmonic substrates. The adequate choice of materials, structures, and functionality goes hand in hand with a fundamental understanding of plasmonics to enable the development of practical biosensors that can be deployed in real life situations. Here we provide a brief review of plasmonic biosensors detailing most recent developments and applications. Besides metals, novel plasmonic materials such as graphene are highlighted. Sensors based on Surface Plasmon Resonance (SPR), Localized Surface Plasmon Resonance (LSPR), and Surface Enhanced Raman Spectroscopy (SERS) are presented and classified based on their materials and structure. In addition, most recent applications to environment monitoring, health diagnosis, and food safety are presented. Potential problems related to the implementation in such applications are discussed and an outlook is presented.

Study of Chemical Enhancement Mechanism in Non-plasmonic Surface Enhanced Raman Spectroscopy (SERS)

Surface enhanced Raman spectroscopy (SERS) has been intensively investigated during the past decades for its enormous electromagnetic field enhancement near the nanoscale metallic surfaces. Chemical enhancement of SERS, however, remains rather elusive despite intensive research efforts, mainly due to the relatively complex enhancing factors and inconsistent experimental results. To study details of chemical enhancement mechanism, we prepared various low dimensional semiconductor substrates such as ZnO and GaN that were fabricated via metal organic chemical vapor deposition process. We used three kinds of molecules (4-MPY, 4-MBA, 4-ATP) as analytes to measure SERS spectra under non-plasmonic conditions to understand charge transfer mechanisms between a substrate and analyte molecules leading to chemical enhancement. We observed that there is a preferential route for charge transfer responsible for chemical enhancement, that is, there exists a dominant enhancement process in non-plasmonic SERS. To further confirm our idea of charge transfer mechanism, we used a combination of 2-dimensional transition metal dichalcogenide substrates and analyte molecules. We also observed significant enhancement of Raman signal from molecules adsorbed on 2-dimensional transition metal dichalcogenide surface that is completely consistent with our previous results. We also discuss crucial factors for increasing enhancement factors for chemical enhancement without involving plasmonic resonance.

Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy

In 2010, Tian et al. reported the development of a new, relatively sensitive method of the chemical analysis of various surfaces, including buried interfaces (for example the surfaces of solid samples in a high-pressure gas or a liquid), which makes it possible to analyze various biological samples in situ. They called their method shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). SHINERS spectroscopy is a type of surface-enhanced Raman spectroscopy (SERS) in which an increase in the efficiency of the Raman scattering is induced by plasmonic nanoparticles acting as electromagnetic resonators that locally significantly enhance the electric field of the incident electromagnetic radiation. In the case of SHINERS measurements, the plasmonic nanoparticles are covered by a very thin transparent protective layer (formed, for example, from various oxides such as SiO2, MnO2, TiO2, or organic polymers) that does not significantly damp surface electromagnetic enhancement, but does separate the nanoparticles from direct contact with the probed material and keeps them from agglomerating. Preventing direct contact between the metal plasmonic structures and the analyzed samples is especially important when biological samples are investigated, because direct interaction between the metal nanoparticles and various biological molecules (e.g., peptides) may lead to a change in the structure of those biomolecules. In this mini-review, the state of the art of SHINERS spectroscopy is briefly described.

Reproducible mesoporous silica-coated gold@silver nanoprobes for the bright colorimetric sensing of ascorbic acid

Herein, a colorimetric approach for the detection of ascorbic acid (AA) was developed by controlling the surface chemistry of silica-coated gold nanorod@silver nanoparticles (AuNR@Ag@mSiO₂).

Fabrication of tubular braid reinforced PMIA nanofiber membrane with mussel-inspired Ag nanoparticles and its superior performance for the reduction of 4-nitrophenol

A novel tubular braid reinforced (TBR) PMIA/CA-PEI/Ag nanofiber membrane for application in dynamic catalysis was introduced in this study. The preparation method of the TBR PMIA/CA-PEI/Ag nanofiber membrane was facile and efficient. The TBR PMIA/CA-PEI/Ag nanofiber membrane was characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and thermal gravimetric analysis (TGA). The mechanical properties were evaluated by a universal material testing machine. The tensile strength of TBR nanofiber membrane exceeded 500 MPa, whereas that of the nanofiber membrane without reinforcement was merely 10 MPa. Besides, the compressive strength of the TBR nanofiber membrane was also reinforced, which indicated that the TBR nanofiber membrane could withstand a higher operating pressure. The reduction of 4-NP to 4-AP was selected as the model reaction to evaluate the catalytic property of TBR PMIA/CA-PEI/Ag nanofiber membrane. The apparent rate constant of dynamic catalysis was 34.58 times higher than that of static catalysis. After 10 cycles, the conversion of 4-NP was still higher than 95.3%. This indicated that the TBR PMIA/CA-PEI/Ag nanofiber membrane had superior stability and recyclability. Besides, the TBR PMIA/CA-PEI/Ag nanofiber membrane also showed superior catalytic performance when it was used for catalyzing other environmental pollutants.

Lipid Bilayer-Enabled Synthesis of Waxberry-like Core-Fluidic Satellite Nanoparticles: Toward Ultrasensitive Surface-Enhanced Raman Scattering Tags for Bioimaging

Herein, we presented waxberry-like core-satellite (C-S) nanoparticles (NPs) prepared by an in situ growth of satellite gold NPs on spherical phospholipid bilayer-coated gold cores. The fluidic lipid bilayer cross-linker was reported for the first time, which imparted several novel morphological and optical properties to the C-S NPs. First, it regulated the anisotropic growth of the satellite NPs into vertically oriented nanorods on the core NP surface. Thus, an interesting waxberry-like nanostructure could be obtained, which was different from the conventional raspberry-like C-S structures decorated with spherical satellite NPs. Second, the satellite NPs were "soft-landed" on the lipid bilayer and could move on the core NP surface under certain conditions. The movement induced tunable plasmonic features in the C-S NPs. Furthermore, the fluidic lipid bilayer was capable of not only holding an abundance of reporter molecules but also delivering them to the hotspots at the junctions between the core and satellite NPs, which made the C-S NPs an excellent candidate for preparing ultrasensitive surface-enhanced Raman scattering (SERS) tags. The bioimaging capabilities of the C-S NP-based SERS tags were successfully demonstrated in living cells and mice. The developed SERS tags hold great potential for bioanalysis and medical diagnostics.

In solution SERS sensing using mesoporous silica-coated gold nanorods

Mesoporous silica-coated gold nanorods (AuNR@MS) act as a colloidally stable Raman sensing platform with a built-in analyte size cutoff. Herein, these core-shell plasmonic nanostructures were presented with a range of thiolated Raman-active molecules to probe the limits of this platform for SERS sensing. The experimental results show generally, that the transport of molecules through the mesopores is highly dependent on the size of the molecule and specifically, that AuNR@MS with pores of ∼4 nm diameter are able to sense analytes with molecular dimensions smaller than 1.5 nm. This sensing platform will likely find broad use, performing well even in complex media based on the high colloidal stability imbued by the mesoporous silica shell.

Rational Design of Yolk-Shell CuO/Silicalite-1@mSiO2 Composites for a High-Performance Nonenzymatic Glucose Biosensor

In this study, an interface coassembly strategy is employed to rationally synthesize a yolk-shell CuO/silicalite-1@void@mSiO₂ composite consisting of silicalite-1 supported CuO nanoparticles confined in the hollow space of mesoporous silica, and the obtained composite materials were used as a novel nonenzymatic biosensor for highly sensitive and selective detecting glucose with excellent anti-interference ability. The synthesis of CuO/silicalite-1@mSiO₂ includes four steps: coating silicalite-1 particles with resorcinol-formaldehyde polymer (RF), immobilization of copper species, interface deposition of a mesoporous silica layer, and final calcination in air to decompose RF and form CuO nanoparticles. The unique hierarchical porous structure with mesopores and micropores is beneficial to selectively enrich glucose for fast oxidation into gluconic acid. Besides, the mesopores in the silica shell can effectively inhibit the large interfering substances or biomacromolecules diffusing into the void as well as the loss of CuO nanoparticles. The hollow chamber inside serves as a nanoreactor for glucose oxidation catalyzed by the active CuO nanoparticles, which are spatially accessible for glucose molecules. The nonenzymatic glucose biosensors based on CuO/silicalite-1@mSiO₂ materials show excellent electrocatalytic sensing performance with a wide linear range (5-500 μM), high sensitivity (5.5 μA·mM^-1·cm^-2), low detection limit (0.17 μM), and high selectivity against interfering species. Furthermore, the unique sensors even display a good capability in the determination of glucose in real blood serum samples.

A CO2-tunable plasmonic nanosensor based on the interfacial assembly of gold nanoparticles on diblock copolymers grafted from gold surfaces

A general stepwise strategy for the fabrication of CO₂-tunable plasmonic nanosensors was described for the first time, based on gold surface functionalization by CO₂-responsive poly(N,N-diethylaminoethyl methacrylate) (PDEAEMA) brushes via a surface-initiated atom transfer radical polymerization (SI-ATRP) method, then the extremity of PDEAEMA was functionalized by linking the polyacrylamide (PAAm) brushes via ATRP, where they were assembled with gold nanoparticles (AuNPs) efficiently by altering the deposition time. The swelling–shrinking states of the PDEAEMA brushes can be tuned just by passing CO₂ and N₂ through a solution alternately. The unique plasmonic surface-enhanced Raman scattering (SERS) sensing properties of these stimulable substrates were investigated using 4-mercaptophenol (4MPh) as a molecular probe. When alternating CO₂ and N₂ bubbling in the water solution, the reversible switching of the SERS signals was complete. By in situ contact-mode atomic force microscopy, the thickness of the polymer layer was observed to be 26 nm in CO₂ saturated water, and after N₂ bubbling to remove CO₂ it decreased to 15 nm, causing the AuNPs to move near to the gold surface. Meanwhile, the distance between the nearby AuNPs becomes smaller, and the surface coverage (φ) of the AuNPs increased from 27% to 35%. The reported CO₂-responsive plasmonic nanosensor provided a dynamic SERS platform, with reversible regulation for electromagnetic coupling between the AuNPs and the gold surface, and between nearby AuNPs.

A CO₂-tunable plasmonic nanosensor: just by passing CO₂ and N₂ through a water solution alternately, the swelling–shrinking states of PDEAEMA brushes can be tuned, and reversible switching of SERS signals can be obtained.

Ag–Au bimetallic nanocomposites stabilized with organic–inorganic hybrid microgels: synthesis and their regulated optical and catalytic properties

Ag–Au bimetallic nanocomposites stabilized with organic–inorganic hybrid microgels allowed the mass transfer of reactants to be controlled by temperature modulation.

Bimetallic gold core–silver shell nanorod performance for surface enhanced Raman spectroscopy

Plasmonic gold nanorods (AuNRs) coated with four different thickness silver shells (AuNR\Ags) were synthesized and tested for their efficiency in Surface Enhanced Raman Scattering (SERS) signal enhancement for biomedical applications.

Reporter-Embedded SERS Tags from Gold Nanorod Seeds: Selective Immobilization of Reporter Molecules at the Tip of Nanorods

Reporter-embedded (RE) tags are a new generation of sensitive, stable surface enhanced Raman scattering (SERS) tags with Raman reporters embedded between gold nanoparticle (NP) cores and gold (or silver) shells. Most of the reported RE tags have been designed using Au nanospheres as a seed material. Herein, we investigated the synthesis and SERS properties of AuNR/reporter/Ag tags by using gold nanorod (AuNR) seeds with anisotropic physical and optical features. Several highlighted points were discovered, including the following: (1) The cetyltrimethylammonium bromide (CTAB) layer induced the coexistence of chemically and physically adsorbed Raman reporters on AuNR. Conventional washing of the AuNR-reporter complex with water results in the formation of an "internal-external" mixed tag. To obtain a "pure" RE structure, an additional extraction step involving a CTAB solution was essential. (2) The anisotropic distribution of CTAB on AuNR resulted in the preference of the Raman reporters to adsorb to the hotspot at the AuNR tip, which made it a perfect match for improving the SERS signal of the tag. (3) An anisotropic silver coating occurred with the shell thickness on the AuNR side growing much faster than the shell thickness at the tip. This feature ensured that the tag grew to a suitable size with enough silver for SERS enhancement without shadowing the effective Raman reporters at the tip too much. (4) RE tags showed better in vitro and in vivo signal stabilities compared with their external labeling counterparts. Moreover, a novel pH-sensitive SERS peak test was proposed by using 4-mercaptobenzoic acid as the Raman reporter to verify thin coverage by a silver layer. We believe this tag can be broadly applied for molecular detection and bioimaging, and the proposed preparation and structure verification methods can provide universal guidance in the design of novel RE tags.

Template-Engaged Solid-State Synthesis of Barium Magnesium Silicate Yolk@Shell Particles and Their High Photoluminescence Efficiency

This study presents a new synthetic method for fabricating yolk@shell-structured barium magnesium silicate (BMS) particles through a template-engaged solid-state reaction. First, as the core template, (BaMg)CO3 spherical particles were prepared based on the coprecipitation of Ba(2+) and Mg(2+) . These core particles were then uniformly shelled with silica (SiO2 ) by using CTAB as the structure-directing template to form (BaMg)CO3 @SiO2 particles with a core@shell structure. The (BaMg)CO3 @SiO2 particles were then converted to yolk@shell barium magnesium silicate (BMS) particles by an interfacial solid-state reaction between the (BaMg)CO3 (core) and the SiO2 (shell) at 750 °C. During this interfacial solid-state reaction, Kirkendall diffusion contributed to the formation of yolk@shell BMS particles. Thus, the synthetic temperature for the (BaMg)SiO4 :Eu(3+) phosphor is significantly reduced from 1200 °C with the conventional method to 750 °C with the proposed method. In addition, the photoluminescence intensity of the yolk@shell (BaMg)SiO4 :Eu(3+) phosphor was found to be 9.8 times higher than that of the conventional (BaMg)SiO4 :Eu(3+) phosphor. The higher absorption of excitation light by the structure of the yolk@shell phosphor is induced by multiple light-reflection and -scattering events in the interstitial void between the yolk and the shell. When preparing the yolk@shell (BaMg)SiO4 :Eu(3+) phosphor, a hydrogen environment for the solid-state reaction results in higher photoluminescence efficiency than nitrogen and air environments. The proposed synthetic method can be easily extended to the synthesis of other yolk@shell multicomponent metal silicates.

Phospholipid Encapsulated AuNR@Ag/Au Nanosphere SERS Tags with Environmental Stimulus Responsive Signal Property

Surface-enhanced Raman scattering (SERS) tags draw much attention due to the ultrasensitivity and multiplex labeling capability. Recently, a new kind of SERS tags was rationally designed by encapsulating metal nanoparticles with phospholipid bilayers, showing great potential in theranostics. The lipid bilayer coating confers biocompatibility and versatility to changing surface chemistry of the tag; however, its "soft" feature may influence SERS signal stability, which is rarely investigated. Herein, we prepared phospholipid-coated AuNR@Ag/Au nanosphere SERS tags by using three different kinds of Raman reporters, i.e., thio-containing 4-nitrothiophenol (NT), nitrogen-containing hydrophobic chromophore cyanine 7 monoacid (Cy7), and alkyl chain-chromophore conjugate 1,1'-dioctadecyl-3,3,3',3'-tetramethylindodicarbocyanine (DiD). It was found that signal responses were different upon additional stimulation which the tags may encounter in theranostic applications including the presence of detergent Triton X-100, lipid membrane, and photothermal treatment. Living-cell imaging also showed signal changing distinction. The different SERS signal performances were attributed to the different Raman reporter releasing behaviors from the tags. This work revealed that Raman reporter structure determined signal stability of lipid-coated SERS tags, providing guidance for the design of stimulus responsive tags. Moreover, it also implied the potential of SERS technique for real time drug release study of lipid based nanomedicine.

Hydrothermal synthesis of Ag@MSiO2@Ag three core-shell nanoparticles and their sensitive and stable SERS properties

An Ag@MSiO2@Ag three core-shell architecture was synthesized by a facial hydrothermal method. The features of the sample were characterized by SEM, TEM, and AFM images, EDS analyses and absorption spectra. This novel nanostructure exhibited excellent SERS properties due to the formation of hot spots around the inner and outer Ag NPs, which were identified by theoretical calculations. A detection limit of the analyte molecule was obtained as low as 10(-11) M by using this SERS nanostructure. Moreover, the homogeneity of SERS signals from the three core-shell nanostructure was checked by Raman mapping. Our studies show that the unique Ag@MSiO2@Ag three core-shell nanostructure has significant potential to realize a SERS substrate with both sensitivity and stability, which are important in SERS-based immunoassay.

Rational assembly of a biointerfaced core@shell nanocomplex towards selective and highly efficient synergistic photothermal/photodynamic therapy

To optimize synergistic cancer therapy, we rationally assemble an inorganic-organic nanocomplex using a folate-modified lipid bilayer spread on photosensitizer-entrapped mesoporous silica nanoparticle (MSN) coated gold nanorods (AuNRs). In this hybrid bioconjugate, the large specific surface area and pore size of AuNR@MSN guarantee a high loading capacity of small photosensitive molecules. The modification with selective mixed liposomes on the surface of AuNR@MSN enables faster cellular internalization and enhancement of endocytosis. Under one-time NIR two-photon illumination, AuNR-mediated hyperthermia can kill cancer cells directly. Meanwhile, the loaded photosensitizer, hypocrellin B, generates two kinds of reactive oxygen species (ROS) to induce cell apoptosis. Remarkably, hyperthermia can improve the yield of ROS. After intravenous injection of this bioconjugate into female BALB/c nude mice followed by laser irradiation (808 nm, 1.3 W cm(-2), 6 min), the tumor growth is suppressed completely. The tumors are not recurrent within the observation time (19 days), and the normal or main organs are not obviously pathological. Thus, such a simplified and selective cancer treatment, combining photothermal and photodynamic therapy in a synergistic manner, provides outstanding efficiency in vivo. This nanocomplex with well-defined core@shell nanostructures integrated with a two-photon technique holds great promise to improve cancer phototherapy with a high efficiency in the clinic.

Universal chitosan-assisted synthesis of Ag-including heterostructured nanocrystals for label-free in situ SERS monitoring

A universal chitosan-assisted method was developed to synthesize various Ag-including heterostructured nanocrystals, in which chelation probably plays a vital role. The as-prepared Ag/Pd heterostructured nanocrystals show outstanding properties when used as bifunctional nanocomposites in label-free in situ SERS monitoring of Pd-catalyzed reaction.

An inorganic capping strategy for the seeded growth of versatile bimetallic nanostructures

Metal nanostructures have attracted great attention in various fields due to their tunable properties through precisely tailored sizes, compositions and structures. Using mesoporous silica (mSiO2) as the inorganic capping agent and encapsulated Pt nanoparticles as the seeds, we developed a robust seeded growth method to prepare uniform bimetallic nanoparticles encapsulated in mesoporous silica shells (PtM@mSiO2, M = Pd, Rh, Ni and Cu). Unexpectedly, we found that the inorganic silica shell is able to accommodate an eight-fold volume increase in the metallic core by reducing its thickness. The bimetallic nanoparticles encapsulated in mesoporous silica shells showed enhanced catalytic properties and thermal stabilities compared with those prepared with organic capping agents. This inorganic capping strategy could find a broad application in the synthesis of versatile bimetallic nanostructures with exceptional structural control and enhanced catalytic properties.

Facilely synthesized polydopamine encapsulated surface-enhanced Raman scattering (SERS) probes for multiplex tumor associated cell surface antigen detection using SERS imaging

A novel SERS probes fabrication were studies and used for multiplex tumor associated cell surface antigens detection using SERS imaging.

Surface-enhanced Raman scattering on a silver film-modified Au nanoparticle-decorated SiO2 mask array

SERS of R6G absorbed on this developed array exhibits a higher intensity by ca. 30-fold, as compared with that of R6G absorbed on the Au NP-based array without the modification of Ag films.