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Elastic organic single crystals with light-emitting and multifaceted bending properties are extremely rare. They have potential application in optical materials and have attracted the extensive attention of researchers. In this paper, we reported a structurally simple barbituric derivative DBDT , which was easily crystallized and gained long needle-like crystals (centimeter-scale) in DCM/CH 3 OH (v/v=2/8). Upon applying or removing the mechanical force, both the (100) and (040) faces of the needle-like crystal showed reversible bending behaviour, showing the nature of multi-faceted bending. The average hardness ( H ) and elastic modulus ( E ) were 0.28 ± 0.01 GPa and 4.56 ± 0.03 GPa for the (040) plane, respectively. Through the analysis of the single crystal data, it could be seen that the van der waals (C-H···π and C-H···C), H-bond (C-H···O) and π···π interactions between molecules were responsible for the generation of the crystal elasticity. Interestingly, elastic crystals exhibited optical waveguide characteristics in straight or bent state. The optical loss coefficients measured at 627 nm were 0.7 dBmm -1 (straight state) and 0.9 dBmm -1 (bent state), while the optical loss coefficient (α) were 1.5 dBmm -1 (straight state) and 1.8 dBmm -1 (bent state) at 567 nm. Notably, the elastic organic molecular crystal based on barbituric derivative could be used as the candidate for flexible optical devices.

Challenges in studying the structures and functions of cell membrane proteins lie in their lipophilicity, which makes them hard to be stabilized, crystallized, and expressed by E. coli. Herein, we propose an evanescent field excited surface-enhanced Raman scattering (EF-SERS) strategy for label-free analysis of membrane proteins in situ. Extracted cell membranes tightly wrapped the metal nanoparticles by an extruder, which ensures the SERS signals of the membrane proteins precisely benefit from the localized surface plasmons (LSPs). The leaky mode of a waveguide was employed to improve the plasmon excitation coupling. Thus, the LSPs and waveguide modes together enable the achievement of high-quality SERS profiles of membrane proteins. By spectral analysis, the structural changes of membrane proteins can be deeply understood at the molecular level. This method has broader applicability in establishing the Ramanomics of membrane proteins and unraveling the exact changes of membrane proteins during physiological processes.

We propose a bimetallic waveguide-coupled surface plasmon resonance (WCSPR) configuration to enhance Raman scattering with an evanescent field excited using surface plasmons. The WCSPR configuratio...

Highly reliable detection, imaging, and monitoring of reactive oxygen species (ROS) at subcellular organelles are critical for understanding the biological roles of ROS and learning the pathogenesis of some diseases. In this study, we presented an interference-free surface-enhanced Raman scattering (SERS)-active nanoprobe for the intracellular ROS detection. This nanoprobe was designed as an Au core-Ag shell nanoparticle (Au@Ag NPs) with a SERS reporter (4-mercaptobenzonitrile) resided in the inner of the core-shell. Intracellular ROS is able to etch the Ag shell and dramatically decreases the SERS intensity of the SERS reporters. It is worth mentioning that the Raman band of the reporter we used in this study locate in the cellular Raman-silent region (1800–2800 cm−1), which eliminates interference possibility from cellular molecules. The shell can also further protect the reporters from the interference of mediums. We detected ROS at subcellular organelle level, e.g. mitochondria, by modifying the surface of the nanoprobes with a mitochondria-targeting peptide. And for the first time, the SERS-based monitoring of ROS at mitochondria during the photothermal therapy process was validated and the profiles of the ROS distribution were disclosed by SERS mapping.

Piezochromic luminescence behaviours of 9, 10-distyrylanthracene (DSA) derivatives with different substituents based on their single crystal structures were investigated under hydrostatic pressure via a diamond anvil cell (DAC), compared with the anisotropic force produced from grinding. Upon grinding, three single crystals show identifiable blue-shifts in fluorescent spectra because of the disturbance for ordered crystal structure to amorphous state, but nearly sightless color changes. The high-pressure fluorescent experiments applied by DAC reveal three DSA crystals all show large red-shifts. High pressure absorption spectra display that a new charge transfer state appears when -CH3 or -2CN is introduced to DSA and all of them show obvious red-shifts. Once the pressure was relieved gradually to the ambient pressure, the fluorescence and absorption spectra both entirely recovered, indicating this geometric change is reversible in a certain pressure region, which is further confirmed by Raman spectra. The relationships between molecular structures and spectroscopic behaviours were further discussed by their single crystal data. This work provides deep insights into the relationship between molecular structure and photo-physical properties of practical mechanochromic luminescent materials, and is significant in the potential applications of pressure transducers.

Metal nanostructures with the configurations of narrow gaps or sharp tips attract plenty of researchers due to their superior performances in plasmonic sensing and surface-enhanced spectroscopy. Too many attempts were devoted for manufacturing elaborate structures to achieve controllable and better performance. However, the excitation and emission ways for these nanostructures which can more feasibly tune the plasmonic features of these nanostructures are lack of study. In this work, we demonstrate a strategy to obtain the considerable signal amplification by efficiently exciting a nanohemisphere array with dozens of nanometers’ gap and a non-sharp nanocone array with different waveguide modes under two polarizations of light in the evanescent field. For the gap-type structure, the TE light is preferred. The enhancement is attributed from the dipolar resonance of nanohemisphere. The best enhancement is achieved on the tip-type nanocone array due to the lightning rod effect under TM polarized light, which allows for the lowest detectable concentration for the Raman signal of 4-mercapto-benzoic acid reaching to 1.0 × 10−10 M. The waveguide-coupled antenna array has great potential for label-free sensing and detections of macromolecules and biomolecules.

A surface-enhanced Raman scattering (SERS)-microfluidic droplet platform for the rapid, ultrasensitive and simultaneous detection of vascular endothelial growth factor (VEGF) and interleukin-8 (IL-8) secreted by a single cell is presented. The high-throughput water-in-oil droplets containing an individual cell along with four kinds of immune-particles (antibody-conjugated silver nanoparticles or magnetic beads, AgNPs@Ab1 and MNs@Ab2) in each were achieved by a cross-typed microfluidic chip, and then they were captured by a collection channel array for SERS measurements. In the appearance of cytokines secreted by one cell, AgNPs@Ab1 can be linked onto the surface of MNs@Ab2 through the immune-recognition to form an immune-sandwich, which makes the “turn on” SERS signal of the Raman reporters previously laid on the surface of MNs due to the adjacent AgNPs. Furthermore, the second SERS signal amplification is from the magnetic field-induced spontaneous collection effect, which brings 75 times enhancement for...

A simple and highly sensitive Raman approach for detecting alkaline phosphatase (ALP) is developed on the basis of the conversion of fosfosal to salicylic acid via an ALP-catalyzed reaction. This method can be used for the clinical detection of ALP in serum.

Realizing fexible and tunable emission conversion in organic solid-state luminescent materials is always fascinating. Herein, we successfully achieved fexible photochemical conversion under pressure and temperature on two types of 4-methyl-2-(5-[4-dimethylaminophenyl]-1H-pyrazole-3-yl)phenol (4MPP) single crystals with distinct aggregation form and geometry showing as green (GC) and blue-violet (BVC). These conversions were studied in detail by fluoresence and Raman spectroscopies, followed with Hirshfeld surface analysis, and this study provides a significant material system for understanding the mechanisms of structural conversion between normal emission (E*) and excited state intramolecular proton transfer (ESIPT, K*) comprehensively under pressure and temperature. Owing to having a proton transferred tautomer, BVC exhibits remarkable changes in its emission feature with pressure increasing to 4.79 GPa, along with the blue-shift and fluorescence enhancement according to a conversion from E* to K*. This compression-induced conversion is proved to be caused by the contraction of the intermolecular distances, the increase of molecular planarization degree, and the enhanced O–H⋯N intramolecular interaction, along with the reduced distance of H⋯N and the elongation of the bond length of O–H. Differently, GC shows rapidly weakened fluorescence and slight blue-shift at a relatively lower pressure (1.01 GPa) based on its more restricted structure. Moreover, GC can realize an excited state transition from K* to E* when lowering its temperature. BVC experiences an abrupt phase transformation to GC at a high temperature of 190 °C. This work discloses the photo-physical properties and stimuli-responsive behaviours of two 4MPP polymorphs, which provides deep insight into the relationship between molecular structure and photoluminescent nature, especially in the crystals with the ESIPT property.

Monitoring externalization of phosphatidylserine (PS) and gaining insights into molecular events of cell membrane damage are significant for programmed cell death studies. Herein, by encapsulating zeolitic imidazole frameworks-8 with plasmonic gold nanoparticles to form micron-nano composites and using them as a single-particle surface-enhanced Raman spectroscopy (SERS) substrate, we succeeded in real-time discriminating and monitoring the externalization of PS on cell membranes during electrostimulus-induced apoptosis. The micron-nano composite probe provides rich "hot spots" and robust anchoring capacity for cell membranes, achieving the capture and label-free single-particle SERS detection of the externalized PS. By this method, the dynamic PS externalization process differences between cancerous cells and normal cells were clearly revealed of which the cell membrane damage of cancerous cells was more serious than that of normal cells. This method is versatile and robust for monitoring the externalization of PS and uncovering related cell membrane damage mechanisms. This work also broadens the application of metal-organic framework materials for advanced biomedical applications.

High-efficiency induction of bone marrow mesenchymal stem cells (BMSCs) to osteogenic differentiation in vitro can help solve a series of bone diseases such as bone injury, fracture repair, and osteoporosis. In order to explore the optimal conditions for different chemical inducers to promote BMSCs differentiation and the possible differentiation mechanisms, we developed a smart nanoprobe that can achieve in situ alkaline phosphatase (ALP) activity detection during osteogenic differentiation in cells. The smart nanoprobe (Au@BCIP) was designed as the surface decoration of gold nanoparticles (AuNPs) with 5-bromo-4-chloro-3-indolyl phosphate (BCIP). The nanoprobe was co-cultured with differentiated BMSCs at different stages to monitor ALP activity based on an ALP-catalyzed hydrolysis reaction with BCIP as a substrate. The product can be quickly oxidized by dissolved oxygen to obtain a Raman-active species (5,5'-dibromo-4,4'-dichloro-1

The expression levels of glycans on the surfaces of cancer and normal cells show different, however, this difference is not noticeable enough to distinguish them directly. So, herein, based on the targeted molecular recognition of the glycans on cell surfaces by 4-mercaptophenyl boronic acid (MPBA), a novel surface-enhanced Raman scattering (SERS) nanoprobe (glucose-MPBA@AgNPs) was prepared by inducing controllable assembly of MPBA decorated Ag nanoparticles (MPBA@AgNPs) in a certain level via the bridge of glucose to amplify such a limited difference in SERS measurements. On the basis of the aggregation-induced 3D SERS hot spot effect, this multi-particle nanoprobe possesses over 10 times stronger SERS enhancement ability than the individual MPBA@AgNPs. As the different sialic acid (SA) expression on the surfaces of cancer and normal cells led to the different accumulation of glucose-MPBA@AgNPs, the results we obtained (mean intensities recorded from five cells) indicate the SA amounts on two kinds of cells can provide 5-7 times signal contrast grade in SERS band intensities (P < 0.001). Compared with the monodispersed nanoprobe, our developed nanoprobe amplifies the SA expression difference on cell surfaces and supports high sensitivity for cancer cell recognition, which might be useful in providing highly effective recognition of the edges of tumor tissues in clinic field.

The technique of solid phase micro-extraction (SPME) is an important method for sample pretreatment in analytical chemistry, especially for the analysis in micro-systems. Surface enhanced Raman scattering (SERS) is an ultra-sensitive and fast detection technique. Both are particularly important in qualitative analysis of trace amount of substance. In this study, combining the magnetic nanoparticles with magnetic SPME device, we develop a high efficient new pretreatment method named as disperse magnetic solid phase micro-extraction (Dis-MSPME). In comparison to the traditional SPME, the proposed Dis-MSPME realizes solid phase micro-extraction from dispersive system, which improved the extraction efficiency largely. Conjunction the advantages both of Dis-MSPME and SERS is proposed as Dis-MSPME-SERS as a new detection method, which realize enrichment, magnetic separation and detection all-in-one. Making it a simpler, more efficient and sensitive approach in identifying the illegal additives. Sildenafil citrate (SC) in 500 μL health wine as an example of illegal additive was successfully detected in a LOD of 1.0 × 10−8 M. Moreover, comparative study on the extract efficient of Dis-MSPME-SERS with SPME-SERS shows it takes only 10 min to detect sildenafil citrate in the health wine, from enrichment to detection by Dis-MSPME-SERS.

A series of two-component co-crystals driven by IN interactions based on the bipyridine (BIPY) chromophore with one among three different co-former building blocks, iodopentafluorobenzene (IPFB), 1,4-diiodotetrafluorobenzene (DITFB) and 1,3,5-trifluoro-2,4,6-triiodobenzene (IFB), were prepared and analysed via infared spectroscopy and single-crystal X-ray diffraction. By comparing the IN distances in the co-crystal structures, we found that the higher the -F ratio in the building blocks the closer the contact of the IN bond, enhancing the intermolecular interactions in these co-crystals as well. That is, the positive electrostatic potential on the iodine atom(s) in the co-formers was enhanced by the presence of strong electron-withdrawing groups. The distinct spectroscopic behaviours (fluorescence and Raman spectra) among the two-component BIPY co-crystal systems in response to hydrostatic pressure were also investigated. Interestingly, the fluorescence of BIPY-DITFB presented intriguing abnormal evolution from dark to bright, suggesting a new charge transfer state due to the decreased intermolecular distance and the enhanced IN interactions. Theoretical simulations by Materials Studio also showed the shortened IN distance and the increased angle of C-IN, evidencing the enhanced IN interactions. In contrast, BIPY-IFB showed only slightly enhanced fluorescence intensity at 550 nm consistent with BIPY-DITFB. Once the pressure was relieved, both the Raman and fluorescence spectra for BIPY co-crystal systems entirely self-recovered. Remarkable emission enhancement in a solid-state co-crystal has been rarely reported in previous publications and in fact, this study paves a unique way for designing and developing novel stimuli-responsive photo-functional materials.

Continuous tunable photoemission of a novel co-crystal (9-acetylanthracene-tetrafluoroterephthalonitrile, 9ACA-TFP) depending on intermolecular charge transfer (CT) is achieved in situ under high pressure via a diamond anvil cell. Compared with other methods for tuning the emission of organic co-crystals based on organic synthesis or doped organic co-crystals, this pressure-based tuning method is simple and effective. The high-pressure data show that this organic co-crystal (9ACA-TFP) exhibits continuous redshifts in its emission bands (from 490 to 620 nm) with the pressure increasing, and its colour and emission bands can recover to their initial state once the pressure is completely released. Raman and ultraviolet-visible absorption spectra with pressure were also measured. All Raman vibrational bands move to higher wavenumbers and exhibit decreased intensities with pressure, proving that the shortened bond lengths and donor–acceptor–donor (D–A–D) interplanar distance result in stronger intermolecular interactions. The in situ absorption spectra of the 9ACA-TFP co-crystal show a 134 nm redshift from 0 to 7.22 GPa, indicating that high pressure enhances the intermolecular CT transition between D and A. The co-crystal materials show on/off switching of photoemission upon cycling compression and decompression. This study is of sigificance in determining the intermolecular CT interaction –photoemission property relation of organic co-crystals.

Velocity map imaging (VMI) spectrometry is widely used to measure the momentum distribution of charged particles with the kinetic energy of a few tens of electronVolts. With the progress of femtosecond laser and X-ray free-electron laser, it becomes increasingly important to extend the electron kinetic energy to 1 keV. Here, we report on a recently built composite VMI spectrometer at the Shanghai soft X-ray free-electron laser, which can measure ion images and high-energy electron images simultaneously. In the SIMION simulation, we extended the electron kinetic energy to 1 keV with a resolution &lt, 2% while measuring the ions with the kinetic energy of 20 eV. The experimental performance is tested by measuring Ar 2p photoelectron spectra at Shanghai Synchrotron Radiation Facility, and O+ kinetic energy spectrum from dissociative ionization of O2 by 800 nm femtosecond laser. We reached a resolution of 1.5% at the electron kinetic energy of 500 eV. When the electron arm is set for 100 eV, a resolution of 4% is reached at the ion kinetic energy of 5.6 eV. This composite VMI spectrometer will support the experiment, such as X-ray multi-photon excitation/ionization, Auger electrons emission, attosecond streaking.

Sialoglycan expression is critical for assessing various diseases progression. Especially, its abnormal levels are commonly believed to be associated with tumor and metastatic cancer types. While, complicated structures, multiple types and dynamic distributions make it challenging for in situ investigating sialoglycans at the physiological status. Herein, we developed a 4-mercaptophenylboronic acid (MPBA)-based surface-enhanced Raman scattering (SERS) nanosensor to in situ study sialoglycan levels and dynamic expression processes of different cell types based on molecular recognition between phenylboronic acid and sialoglycans at physiological condition. This nanosensor is designed by the MPBA decorated silver nanoparticle (AgNP), which is unique and multifunctional because of its three-in-one role involving the Raman signal enhancer (AgNP), the sensing reporter of MPBA and the target receptor based on the recognition of phenylboronic acid and sialoglycans. When this nanosensor binds to sialoglycans, the molecular vibrational modes of MPBA will change, which can be traced by ultrasensitive SERS technique. The superiority of this study is that we built the relation between the spectral changes of MPBA (relative intensities) in molecular recognition with the sialoglycan dynamic expression of cells. We believe that our SERS strategy could be further extended to explore crucial physiological processes and significant biological system that glycans are involved in.

The effects of the high pressure on two single crystals, pyrene and N,N-diphenyl-4-(pyren-1-yl)aniline (TPA-Py), were studied by in situ fluorescent and Raman spectroscopies. During the compression, the pyrene with one structureless excimer emission band showed a continuous bathochromic-shift. In contrast, with the pressure increasing to 10.36 GPa, TPA-Py previously dominated with the hybridized local and charge transfer (HLCT) excited state gradually exhibited a new band at longer wavelengths, which is assigned to a new excited state species with the intramolecular charge transfer (ICT) state, caused by the pressure-induced changes on its molecular configuration. Accompanied by the spectral changes, a sequential color variation from blue to cyan was observed, giving a change to yellow and then red. The significant broadening of the full-width half-maximum (FWHM) of the TPA-Py is observed due to the enhanced dipole-dipole interaction and the existence of pressure gradient. Both pyrene and TPA-Py showed the delayed recovery of the luminescence in the compression-decompression cycle, which results from the poor reversibility of electronic structure caused by the compression-induced piezochromic effect. Furthermore, the evolutions of the Raman spectra of pyrene and TPA-Py indicated that the pressure-induced reversible transformation is caused by the molecular conformational change. This study is a deeper understanding of the structure-property relation of the HLCT species and will be a helpful reference for the regulation of photoluminescence in these intramolecular electron donor-acceptor crystal materials.

Abnormal cellular biothiol levels are related to many abnormal physiological processes, including cancer, multidrug resistance and Alzheimer's disease, etc. In this study, the nano-aggregates of the background-free surface-enhanced Raman scattering (SERS) tags were constructed and developed for the intracellular biothiol detection via a target-triggered disaggregation process. The plasmonic nano-tags were prepared by coating gold nanoparticles with a Raman reporter (4-mercaptobenzonitrile, MBN), which exhibits a single strong peak in the cellular Raman silent region (1800−2800 cm−1) that can eliminate the background interference of cells. Interestingly, this reporter is also the host ligand for guest mercury ions. The coordination of mercury/cyano group induce the formation of the pre-aggregates of nano-tags and the formed nano-aggregates allowing strong SERS signals of reporters. Intracellular biothiols show higher affinity to mercury ions than the SERS tags do, which can break the hot spot geometry and redisperse tags by taking away mercury ions from nano-aggregates, which dramatically decreases the SERS signals of reporters previously laid on gold nanoparticles. The developed SERS “turn off” method was used for biothiol detections in normal, cancer, drug-resistant cells, and biothiol dynamics during chemotherapy. The results demonstrate that the drug-resistant cells (MCF-ADR) lie in a higher biothiol level than cancer cells (MCF-7 and HepG2), and the normal cells (LO2) give a lower biothiol concentration compared with cancer cells. Moreover, most cancer cells are more sensitive to doxorubicin compared with the normal ones. This study provides an important strategy in learning the cellular processes that are highly associated with intracellular biothiol level.

When an electron is resonantly excited from a core orbital to a Rydberg one in a molecule, complex multi-time-scale multi-step processes are triggered. By using a high-resolution energy-resolved coincidence between Auger electron and ions, we identified the sequences of processes following the spectator Auger decays induced by K-shell excitation in O-2. The first step of the spectator Auger decay can end up to a few metastable O-2(+) states which autoionize into stable O-2(2+). However, the majority of O-2(+) states are dissociative. They evolve into several dissociation limits with complex crossings between potential-energy curves. After the molecular dissociation is finished, the generated fragments can further decay either by fluorescence emission or by autoionization. Interestingly, some electrons are always emitted after molecular dissociation.

We describe a simple and universal method for trypsin determination with the surface-enhanced Raman scattering (SERS) technique. This trypsin assay was carried out on a SERS sensing chip made by immobilizing an unlabeled double charged peptide on an Ag vapour-deposited film, while a Raman probe (4-mercaptobenzoic acid) was fixed together above the Ag film as the signal reporter. This designed peptide contains a specific amino acid (arginine) as the substrate domain of trypsin in the middle and two oppositely charged segments at two ends. When trypsin catalyzes the hydrolysis reaction of peptide at the location of arginine in a buffer solution, the segment that contains the negatively charged amino chain will leave from the Ag film. The remaining sequence makes positive charges on the Ag film surface increase, enabling the assembly of the citrate-stabilized Ag nanoparticles (negative charges) on the chip via an electrostatic interaction for the purpose of signal amplification. As a result, SERS signals of 4-mercaptobenzoic acid sharply increase due to the formation of the hotspot-like particle-on-a-film configuration, by which the concentration and activity of trypsin can be determined indirectly. Owing to the strong electromagnetic field enhancement in the gap region, the detection limit of trypsin down to 1.0 nM (the ratio of signal to noise of 3) can be reached. The specificity of this method can also be guaranteed due to the enzyme/substrate specific identification. The method can be extended to other enzyme-catalyzed systems and become a universal approach for other proteases.

A facile, highly sensitive “turn on” surface-enhanced Raman scattering (SERS) nanosensor for the detection of glucose has been developed based on the aggregation of 4-mercaptophenylboronic acid (4-MPBA)-decorated silver nanoparticles in specific bonding to glucose, which can be used for the clinical detection of glucose in urine.

Gap-type metallic nanostructures are widely used in catalytic reactions, sensors, and photonics because the hotspot effect on these nanostructures supports giant local electromagnetic field enhancement. To achieve hotspots, researchers devote themselves to reducing gap distances, even to 1 nm. However, current techniques to fabricate such narrow gaps in large areas are still challenging. Herein, a new coupling way to boost the sub-10 nm plasmonic nanogap array is developed, based on the plasmon-triggered optical waveguide resonance via near-field coupling. This effect leads to an amplified local electromagnetic field within the gap regions equivalent to narrower gaps, which is evidenced experimentally by the surface-enhanced Raman scattering intensity of probed molecules located in the gap and the finite-difference time-domain numerical simulation results. This study provides a universal strategy to promote the performance of the existing hotspot configurations without changing their geometries.

International audience; We show that electron and ion spectroscopy reveals the details of the oligomer formation in Ar clusters exposed to an x-ray free electron laser (XFEL) pulse, i.e., chemical dynamics triggered by x rays. With guidance from a dedicated molecular dynamics simulation tool, we find that van der Waals bonding, the oligomer formation mechanism, and charge transfer among the cluster constituents significantly affect ionization dynamics induced by an XFEL pulse of moderate fluence. Our results clearly demonstrate that XFEL pulses can be used not only to “damage and destroy” molecular assemblies but also to modify and transform their molecular structure. The accuracy of the predictions obtained makes it possible to apply the cluster spectroscopy, in connection with the respective simulations, for estimation of the XFEL pulse fluence in the fluence regime below single-atom multiple-photon absorption, which is hardly accessible with other diagnostic tools.

The photoinduced charge transfer (CT) phenomenon of a metal–organic complex, Ag ion-coordinated tetrafluorotetracyano-p-quinodimethane (AgTCNQF4), produced by a solution reaction of immersing an Ag deposited film into TCNQF4 acetonitrile solution, was studied by the resonance Raman spectroscopy. The produced AgTCNQF4 formed abundant crystalline microrods over the slide. The analysis of Raman results shows that the photoinduced CT in the AgTCNQF4 microrods possesses a light energy threshold that the excitation wavelengths should be shorter than 514 nm. And the complete degree of CT reaction from TCNQF4− to TCNQF42− accelerates with the irradiation energy increasing. A divalent metal–organic complex (Ag2TCNQF4) is produced as a result of the photoinduced electron transition of AgTCNQF4. The conductive-atomic force microscope characterization of the AgTCNQF4 microrods proves that this metal–organic complex possesses the reversible electrical bistable switching property. This study is of significance in deeper understanding the electrical and optical properties of such kinds of metal–organic CT complexes and promoting the promising application potential based on the light and electric dual control devices. Copyright © 2015 John Wiley & Sons, Ltd.

In the studies of surface-enhanced Raman scattering (SERS), it is considered to be a key point to couple the surface plasmons of metallic nanomaterials and structures to resonate, which can assist higher SERS signal enhancement. This paper is to explore a strategy for plasmon resonating based on the leaky mode resonance (LMR) of a polyimide (PI) optical waveguide (OWG), for the purpose of achieving the highly sensitive evanescent field-excited SERS. PI was chosen to build the waveguide layer due to its merits of exhibiting small extinction coefficients in the natural light frequency, low cost, high flexibility, easy fabrication, and almost no Raman spectral interference. The OWG configuration guarantees a high harvesting efficiency for the incident light. Ag nanoparticles were assembled on top of the OWG layer as plasmonic antennas to provide a large scattering cross section based on the coupling of the LMR and metal plasmon resonance (MPR), which supports highly efficient SERS radiation and being conduci...

A surface-enhanced Raman scattering(SERS) optical fiber sensor was prepared by the laser-induced deposition of Ag nanoparticle membrane on a silica optical fiber tip, which was applied to the real time SERS spectral monitoring on the biorecognition of biotin/avidin. The bioidentification of biotin/avidin was carried out through a indirect method, in which the bioidentification is based on the SERS response signal of a labeled dye(Atto610) after its fluorescence has been quenched totally by the deposited Ag nanoparticle membrane. By SERS monitoring the bioidentification process of biotin/avidin, it has been found that this recognition process is finished in 40 min. The lowest detection concentration of biotin is 1.0×10−7 mg/mL. This research is promising in the application of immunoassays on line and in vivo.

The pH value of subcellular organelles in living cells is a significant parameter in the physiological activities of cells. Its abnormal fluctuations are commonly believed to be associated with cancers and other diseases. Herein, a series of surface-enhanced Raman scattering (SERS) nanosensors with high sensitivity and targeting function was prepared for the quantification and monitoring of pH values in mitochondria, nucleus, and lysosome. The nanosensors were composed of gold nanorods (AuNRs) functionalized with a pH-responsive molecule (4-mercaptopyridine, MPy) and peptides that could specifically deliver the AuNRs to the targeting subcellular organelles. The localization of our prepared nanoprobes in specific organelles was confirmed by super-high resolution fluorescence imaging and bio-transmission electron microscopy (TEM) methods. By the targeting ability, the pH values of the specific organelles can be determined by monitoring the vibrational spectral changes of MPy with different pH values. Compared to the cases of reported lysosome and cytoplasm SERS pH sensors, more accurate pH values of mitochondria and nucleus, which could be two additional intracellular tracers for subcellular microenvironments, were disclosed by this SERS approach, further improving the accuracy of discrimination of related diseases. Our sensitive SERS strategy can also be employed to explore crucial physiological and biological processes that are related to subcellular pH fluctuations.

A new strategy named integrated plasmon-enhanced Raman scattering (iPERS) spectroscopy that features a configuration of evanescent field excitation and inverted collection is presented, which well unites the local field enhancement and far field emission, couples localized and propagating surface plasmons, integrates the SERS substrates and Raman spectrometers via a self-designed aplanatic solid immersion lens. A metallic nanoparticle-on-a film (NOF) system was adopted in this configuration because it improves the amplification of the incidence light field in near field by 10 orders of magnitude due to the simultaneous excitation of quadrupolar and dipolar resonance modes. This iPERS allows for higher excitation efficiency to probed molecules and full collection of the directional-radiation Raman scattering signal in an inverted way, which exhibits a practical possibility to monitor plasmonic photocatalytic reactions in nanoscale and a bright future on interfacial reaction studies.

The luminescence and structural changes of 4, 4′-bipyridine in the crystal and powder forms under the effect of high pressure applied by a diamond anvil cell has been investigated through the fluorescence and Raman spectroscopies. In its single crystal structure, the 4, 4′-bipyridine molecules are paralleled arranged with the identifiable C H⋯N and π⋯π interactions among molecules. However, in the powder form, these intermolecular interactions nearly diminish. The 4, 4′-bipyridine crystal shows the obvious bathochromic-shifting of the emission band, which is different from the powder sample that displays a fixed luminescent band during compression. Additionally, the Raman bands of them both show shifts to higher wavenumbers as different degrees. The detailed peak assignments are performed based on the theoretical calculation through B3LYP method. Comparisons in spectral behaviors between the crystal and powder under compression show the crystal form exhibits a superior mechanochromic performance relative to the powder one, because the intermolecular interactions in the crystal form play dominating roles and they can be easily tuned along with pressure in such a highly ordered structure compared to the powder form. The relation investigation between property and supramolecular interactions not only makes deeper understanding in the mechanochromic mechanisms of 4, 4′-bipyridine, but also gives a helpful reference for the molecular designs of coordination polymers and co-crystals with 4, 4′-bipyridine involved.

The aim of this study was to find the differences and relationships between normal, atypical ductal hyperplasia (ADH), ductal carcinoma in situ (DCIS), and invasive ductal carcinoma (IDC) lesions of the breast based on biochemical characteristics determined by Raman spectroscopy (RS). After collecting 39 frozen sections from patients who underwent surgical resection or mammotome biopsy, nine normal tissues, seven ADH, eight DCIS, and 15 IDC lesions were detected using confocal RS. We then used leave-one-out cross-validation (LOOCV) and radial basis function (RBF) to build a support vector machine (SVM) diagnosis model. Pronounced mean Raman spectra differences were observed between normal tissues, ADH, DCIS, and IDC tissues. Most noticeable was the increased protein and reduced lipid levels of ADH tissues compared to normal tissues. The major spectra differences in ADH, DCIS, and IDC spectrograms were evidenced by a red shift with a broad peak of CH2 (1301 cm−1), the intensity of the stretching vibration peak of carotenoids (1526 cm−1), a relatively strong band of amide-I (1656 cm−1), and the nuclear (882 cm−1) acid peak. Atypical ductal hyperplasia tissues had the largest constituent variations between subjects. During the disease progression, IDC tissues have smaller inter-subject constituent variations than DCIS and ADH tissues. The overall accuracy of SVM model is 74.39%. The sensitivities of normal tissue, ADH, DCIS, and IDC are 62.5%, 50%, 90%, and 66.7%, respectively. The specificities of normal tissue, ADH, DCIS, and IDC are 100%, 100%, 66.7%, and 89.06%, respectively. Atypical ductal hyperplasia shows significant differences and the relationship between normal tissue and malignant disease. Further study to explain the biochemical relationships between these differences will shed more light into a better understanding of the mechanism by which ADH converts to DCIS and to IDC.

A highly sensitive and recyclable surface-enhanced Raman scattering (SERS) chip sensor is designed for the determination of silver ions. It is based on the specific reversible binding between silver ions and glucose oxidase (GOD). The sensing chip is made by layer-by-layer assembling GOD on a metal nanoparticle-assembled, SERS-active chip with a positive charged polyelectrolyte as a linker. Iso-alloxazine, a chromophore in flavin adenine dinucleotide (FAD) in GOD, coordinates with silver ions, which causes significant variation in SERS spectra of GOD. The reaction shows high sensitivity and selectivity for silver ions with the detection limit of 1.0×10-10M. Most significantly, the bonded Ag(I) in GOD can be reduced to Ag(0) by sodium borohydride and the GOD structure can be recovered then. Thus, the chip sensor is recyclable. Merits of using GOD as a novel SERS probe toward Ag+ are embodied in not only a simplified sensor structure based on its dual role of Ag+ accepter and SERS signal reporter, but also a nontoxic label to biological systems, indicating that it is promising for tracing Ag+ in vivo.

Raman spectroscopy has been widely used as an important clinical tool for real-time in vivo cancer diagnosis. Raman information can be obtained from whole organisms and tissues, at the cellular level and at the biomolecular level. The aim of this paper is to review the newest developments of Raman spectroscopy in the field of breast cancer diagnosis and treatment. Raman spectroscopy can distinguish malignant tissues from noncancerous/normal tissues and can assess tumor margins or sentinel lymph nodes during an operation. At the cellular level, Raman spectra can be used to monitor the intracellular processes occurring in blood circulation. At the biomolecular level, surface-enhanced Raman spectroscopy techniques may help detect the biomarker on the tumor surface as well as evaluate the efficacy of anticancer drugs. Furthermore, Raman images reveal an inhomogeneous distribution of different compounds, especially proteins, lipids, microcalcifications, and their metabolic products, in cancerous breast tissues. Information about these compounds may further our understanding of the mechanisms of breast cancer.

We propose a highly sensitive and selective surface-enhanced Raman scattering (SERS) method for determining lead ions based on a DNAzyme-linked plasmonic nanomachine. A metallic nanoparticle-on-a-film structure was built through a rigid double-stranded bridge linker composed of a DNAzyme and its substrate. This DNAzyme could be activated by lead ions and catalyze a fracture action of the substrate. Thus, the double chain structure of DNA would turn into a flexible single strand, making the metal nanoparticles that connected to the terminal of DNAzyme fall to the surface of the metal film. Hereby, a narrow gap close to 2 nm generated between metal nanoparticles and the metal film, exhibiting a similar effect of a "hot spot" and remarkably enhancing the signal of randomly dispersed Raman-active molecules on the surface of metal film. By measuring the improvement of SERS intensity of the Raman-active molecules, we realized the lowest detection concentration of Pb(2+) ions to 1.0 nM. This SERS analytical method is highly selective and can be extended universally to other targets via the accurate programming of corresponding DNA sequences.

The characteristics of type II microcalcifications in fibroadenoma (FB), atypical ductal hyperplasia (ADH), and ductal carcinoma in situ (DCIS) breast tissues has been analyzed by the fingerprint features of Raman spectroscopy. Fresh breast tissues were first handled to frozen sections and then they were measured by normal Raman spectroscopy. Due to inherently low sensitivity of Raman scattering, Au@SiO2 shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) technique was utilized. A total number of 71 Raman spectra and 70 SHINERS spectra were obtained from the microcalcifications in benign and premalignant breast tissues. Principal component analysis (PCA) was used to distinguish the type II microcalcifications between these tissues. This is the first time to detect type II microcalcifications in premalignant (ADH and DCIS) breast tissue frozen sections, and also the first time SHINERS has been utilized for breast cancer detection. Conclusions demonstrated in this paper confirm that SHINERS has great potentials to be applied to the identification of breast lesions as an auxiliary method to mammography in the early diagnosis of breast cancer.

In this study, a hybrid structure of inversely truncated pyramid-shaped diamond nanopits infilled with gold nanoparticle (Au NP) has been fabricated from a Au film coated single crystal diamond by oxygen plasma etching. Surface enhanced Raman scattering (SERS) performances based on the Au-NP/diamond-pit, using 4-Mercaptopyridine as the probe molecule, show that the hybrid structure could realize a larger SERS enhancement factor compared to the conventional isolated Au NPs. This is attributed to the increased concentration of incident light field on the Au NPs due to the special geometric feature, and the coupling of localized surface plasmon resonance from Au NPs. Taking into account the unique properties of diamond, the diamond-related hybrid structure could be used as a kind of high performance SERS substrate.

A measurement of antigen–antibody binding in the porous anodic alumina (PAA) waveguide layer via waveguide-assisted surface-enhanced Raman spectroscopy (SERS) was demonstrated. The highest SERS signals of dye-labeled antibody molecules were recorded under the waveguide resonance modes, where most of the light is confined in the waveguide layer to generate localized surface plasmon resonance of Ag nanoparticles under the evanescent field, resulting in an enhanced electromagnetic field. It is a useful configuration for biosensing. Results showed that the PAA waveguide is advantageous in sensing biomolecules with high sensitivity. We performed the SERS detection of immune-recognition with a concentration as low as 0.1 ng/ml level through this method.

To fabricate a new surface-enhanced Raman scattering (SERS)-active optical fiber sensor, the design and preparation of SERS-active sensing layer is one of important topics. In this study, we fabricated a highly sensitive three-dimensional (3D) SERS-active sensing layer on the optical fiber terminal via in situ polymerizing a porous polymer material on a flat optical fiber terminal through thermal-induced process, following with the photochemical silver nanoparticles growth. The polymerized polymer formed a 3D porous structure with the pore size of 0.29–0.81 μm, which were afterward decorated with abundant silver nanoparticles with the size of about 100 nm, allowing for higher SERS enhancement. This SERS-active optical fiber sensor was applied for the determination of 4-mercaptopyridine, crystal violet and maleic acid The enhancement factor of this SERS sensing layer can be reached as about 108. The optical fiber sensor with high sensitive SERS-active porous polymer is expected for online analysis and environment detection. Keywords: Optical fiber sensor, 3D SERS substrate, Porous polymer, Laser-induced growth, Ag nanoparticles

We report a method for fabricating a highly sensitive, microfluidic surface-enhanced Raman scattering (SERS) chip with highly ordered Ag nanodot arrays as the enhancement substrate for the detection of multiplexed low-concentration analytes. The microfluidic SERS chip features a highly-ordered Ag nanodot array on quartz slides fabricated by depositing Ag with an ultrathin anodic aluminium oxide (AAO) film as template and a channel-patterned polydimethylsiloxane (PDMS) cover on top, allowing a tremendous enhancement of electromagnetic field in the proximity of the chip surface because of the localized surface plasmon resonance (LSPR) of the Ag nanodots. Via the utilization of a self-built SERS microspectrometer with an inverted configuration, the multiplexed SERS signals of low concentration adenine and thiram can be readily detected with a detection limit down to 5.0 × 10−7 M. This detection system that we developed is flexible and has potential for real commercialization.

Ag2–TCNQF4 (TCNQF4 = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) was synthesized for the first time via a photo-induced charge transfer of the precursor of semiconductor Ag–TCNQF4 using Au nanoparticles (AuNPs) as a catalyst. We first prepared the one-dimensional Ag–TCNQF4 crystal wires on a solid-supported substrate via a solution process. Then, Ag–TCNQF4 was reacted with KAuCl4via the galvanic replacement reaction to form a metal–semiconductor complex, AuNPs decorated Ag–TCNQF4 (AuNPs@Ag–TCNQF4). The resulting Ag–TCNQF4 crystal wires and AuNPs@Ag–TCNQF4 complex were characterized by scanning electron microscopy (SEM), X-ray diffraction, ultraviolet-visible (UV-vis) and X-ray photoelectron spectroscopies. Under the plasmon-enhanced catalysis of AuNPs, a laser-induced charge transfer process occurred on Ag–TCNQF4, altering it to Ag2–TCNQF4. Time-resolved in situ Raman spectra were recorded to monitor the photo-induced charge transfer process. The Raman data show that this photo-induced charge transfer process is laser wavelength-dependant, power-dependant and irradiation time-dependant. It is also affected by the loading of AuNPs. The SEM images, UV-vis and infrared spectra of the AuNPs@Ag–TCNQF4 before and after laser irradiation further prove that the charge transfer product is Ag2–TCNQF4. The mechanism of the plasmon-enhanced catalysis of photo-induced charge transfer from TCNQF4− to TCNQF42− is suggested, which provides a good model to study the charge transfer process in metal–semiconductor systems. In addition, this material has significance for applications in memory storage and photoelectric devices.

We employed an electrospinning method to prepare metal nanoparticle (NP) doped polymer nanofiber mats, which can be easily cut to size and fixed on slides or in microfluidic channels for surface-enhanced Raman scattering (SERS) measurements. Metal NPs embedded in the composite nanofibers maintained their intrinsic shape and monodispersity, as well as their enhancement ability. In addition, they can be re-suspended in aqueous solution to recover a colloidal solution with persistent SERS activity. The SERS chips made from the metal NP-doped polymer nanofiber mats displayed high detection sensitivity and reproducibility. The microfluidic chips decorated with several metal NP-doped polymer nanofiber mats possess multi-SPR properties and can be widely used for different analytes. These composite polymer mats can be easily stored and transported, and also possess potential for use as antibacterial filters and paint for medical purposes.

Two polymorphs of 9,10-bis(phenylethynyl)anthracene (OC and RC) were obtained and they were characterized by multi spectroscopies including X-ray diffraction, absorption, fluorescence and Raman. The single-crystal structure analysis shows that RC has richer intermolecular interactions (C–H … π and C–H⋯H–C) than OC, which accounts for different spectroscopic behaviors of RC from OC in high pressure studies. Under mechanical grinding, two polymorphs have similar spectral changes in their fluorescence as significant enhancement and slight blue-shifts of the shoulder emission bands at lower wavelength, except that RC shows more sensitive to grinding than OC. During the compression process applied by diamond anvil cell (DAC), OC and RC both demonstrate remarkable red-shifts with increasing pressure, while RC shows a smaller shifting rate than OC. These spectral phenomena reveal that the richer intermolecular interactions in RC can be easily destroyed upon grinding. This work provides the in-depth insight into the mechanism of mechanochromism and the structure-property relation, and proves again that the intermolecular interactions play the key role in modulating the photo-physical properties.

Recent developments on the technologies and equipments of surface plasmon-enhanced Raman scattering (SERS) based on the propagating surface plasmons (PSPs) are introduced in this review. It involves three aspects: (1) The principle and the configuration of PSPs-enhanced Raman spectroscopy are stated. The technology of the PSPs-based SERS in the evanescent field, the combination of SERS and SPR sensing, and the long-range SP-enhanced Raman scattering are included. (2) SERS based on the PSPs-LSPs co-enhancement for ultra-sensitive detection is introduced. Under the configuration of the PSPs-excited SERS in the evanescent field, the addition of metal nanoparticles resulted in the resonance of localized surface plasmons (LSPs), which can further enhance the local electric field. Applications of the SPR-SERS spectroscopy for monitoring the recognition system of biomolecules are referred, which indicate that the sensitivities of SERS and SPR are both greatly improved. Besides, SERS on periodical metallic substrates due to the PSPs and LSPs co-excitation is achieved. (3) The directional SERS technology based on PSPs is shown. High SERS exciting and collecting efficiency could be achieved via the directional SERS technology.

We design an ultrasensitive surface-enhanced Raman scattering (SERS) substrate based on waveguide-enhanced surface plasmons (SPs). An optical waveguide was exploited to concentrate and restrict the electromagnetic (EM) energy of the incident light, and Ag nanoparticles that were assembled on the waveguide surface were used to enhance the EM field further by means of SP resonance. The enhancement factor (EF) of the incident EM field can reach 103 on the two sides of nanoparticles, and a 108–1012 EF of SERS is expected. This waveguide-assisted isolated nanoparticle substrate can reach a comparable SERS enhancement capability to that of gap-type SERS hot spots. In addition, this SERS substrate is applicable to the SERS detection of large molecules (biomacromolecules etc.), which cannot be placed in traditional gap-type hot spots.

We have first time demonstrated the construction of a plasmonic gold dimer model for bioassays based on immune recognition with surface-enhanced Raman scattering (SERS). To induce a strong plasmonic coupling effect, a dimer of gold nanoparticles (NPs) with a Raman label located between adjacent NPs is assembled through specific recognition in biological systems. One promising application for this model is the provision of a new type of in situ self-calibrated and reliable SERS platform where biotinylated molecules can selectively be trapped by streptavidin and placed in the gap enhanced plasmonic field, which may enable the development of powerful, biospecific recognition-based SERS assays. The capabilities of the dimeric constructions for analytical applications were demonstrated through the use of the SERS technique to detect biotin at very low concentrations. Additionally, the spatial SERS radiation for the gold dimer assembled on the silicon slide was simulated using the finite-difference time-domain method; this simulation demonstrated the distribution of the electric field as well as the utility of the proposed system, thereby introducing potential uses of bio-specific recognition as well as opportunities for the construction of plasmonically coupled nanostructures and bioassay applications. Copyright © 2013 John Wiley & Sons, Ltd.

Close-packed Ag pyramidal arrays have been fabricated by using inverted pyramidal pits on Si as a template and used to generate plentiful and homogeneous surface-enhanced Raman scattering (SERS) hot sites. The sharp nanotip and the four edges of the Ag pyramid result in strong electromagnetic field enhancement with an average enhancement factor (EF) of 2.84 × 107. Moreover, the features of the close-packed Ag pyramidal array can be well controlled, which allows SERS substrates with good reproducibility to be obtained. The relative standard deviation (RSD) was lower than 8.78% both across a single substrate and different batches of substrates.

A supramolecular recognition and oriented assembly system was developed on chip for the highly selective surface-enhanced Raman scattering (SERS) detection of thrombin by means of the aptamer-based SERS tag method. A 15-base thrombin-binding aptamer (TBA15) with a thiol end was first immobilized on an Ag nanoprism array by the S-Ag bond. This aptamer has high binding affinity with thrombin when it folds into a G-quadruplex structure. After the recognition between the aptamer and thrombin, a bridge is built between the SERS tag (4-mercaptobenzoic acid marked Ag nanoparticle) and the fixed thrombin based on the activation of the carboxylic group of 4-mercaptobenzoic acid. Thus, the quantitative detection of thrombin can be achieved based on the SERS intensity of the immobilized SERS tags. The obvious advantages of this sensing method are as follows: (1) remarkable SERS enhancement due to the high electric field coupling effect via the gap structure formation, which improves the sensitivity of the SERS detection and the limit of detection of this method arrives in 1.6 × 10-11 M, (2) high selectivity based on the specific aptamer recognition toward thrombin, which can be extended to other enzymes easily by changing a proper sequence, (3) high repeatability of SERS signals according to a highly ordered structure, and (4) highly efficient oriented assembly of a sandwich structure over an Ag nanoprism array. The proposed method is expected to be a practical implement in medical diagnosis. Graphical Abstract Illustration of the aptamer-based SERS sensor for thrombin detection.

A multifunctional magnetic graphene surface-enhanced Raman scattering (SERS) substrate was fabricated successfully by the layer-by-layer assembly of silver and graphene oxide (GO) nanoparticles (NPs) on the magnetic ferroferric oxide particles (Fe3O4@GO@Ag). This ternary particle possesses magnetic properties, SERS activity, and adsorption ability simultaneously. Owing to the multifunction of this Fe3O4@GO@Ag ternary complex, we put forward a new method called a surface magnetic solid-phase extraction (SMSPE) technique, for the SERS detections of pesticide residues on the fruit peels. SMSPE integrates many sample pretreatment procedures, such as surface extraction, separation sample, and detection, all-in-one. So this method shows great superiority in simplicity, rapidity, and high efficiency above other standard methods. The whole detection process can be finished within 20 min including the sample pretreatment and SERS detection. Owing to the high density of Ag NPs, the detection sensitivity is high enough that the lowest detectable concentrations are 0.48 and 40 ng/cm(2) for thiram and thiabendazole, which are much lower than the maximal residue limits in fruit prescribed by the U.S. Environmental Protection Agency. This multifunctional ternary particle and its corresponding analytical method have been proven to be applicable for practical samples and also valuable for other surface analysis.

We reported a highly efficient and low-cost way to synthesize silver nanosphere dimers on a poly(dimethylsiloxane) (PDMS) sheet by using a stepwise upright assembly method for the “hot spots” study of surface-enhanced Raman scattering (SERS). The first silver nanoparticle (NP) layer is almost entirely embedded in PDMS, and the second-layered silver NPs directionally position the tops of the embedded particles. The analysis of the localized electric field distributions of the silver nanosphere dimer presents that the strongest electric field coupling appears at the gap of two nanospheres when the incident angle is about 45° and its intensity achieves 400 times enhancement. The SERS enhancement activity on this novel substrate was determined, and the results showed that SERS intensities on nanodimers were much stronger than those on the silver NP monolayer due to the electromagnetic field coupling of upright NP-NP. By using this novel SERS substrate, the lowest detection concentration for 4-mercaptopyridine...