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We demonstrate a simple, cost-effective method to enhance the photoluminescence intensity of monolayer MoS2. A hexagonal symmetric Au metasurface, made by polystyrene nanosphere lithography and metal coating, is developed to enhance the photoluminescence intensity of monolayer MoS2. By using nanospheres of different sizes, the localized surface plasmon resonances of the Au metasurfaces can be effectively tuned. By transferring monolayer MoS2 onto the Au metasurface, the photoluminescence signal of the monolayer MoS2 can be significantly enhanced up to 12-fold over a square-centimeter area. The simple, large-area, cost-effective fabrication technique could pave a new way for plasmon-enhanced light-mater interactions of atomically thin two-dimensional materials.

Highly efficient plasmon-driven catalysis and excellent surface-enhanced Raman spectroscopy (SERS) performance are proportional to the square of the local electromagnetic field (hot spot). However, a proven way to realize the enhancement in intensity and density of “hot spot” still needs to be investigated. Here, we report on multilayered Ag nanoparticle (Ag NP)/graphene coupled to an underlying Cu film system (MAgNP-CuF) which can be used as an effective SERS substrates realizing ultra-sensitive detection for toxic molecules and in situ monitoring the plasmon-driven reaction for p-nitrothiophenol (PNTP) to p,p′-dimercaptobenzene (DMAB) conversion. The mechanism of ultra-sensitive SERS response and catalytic reaction is investigated via Ag NP/graphene layer-dependent experiments combined with theoretical simulations. The research found that the intensity and density of “hot spot” can be effectively manipulated by the number of plasmonic layers, and the bottom Cu film could also reflect the scattered and excitation beam and would further enhance the Raman signals. Moreover, the MAgNP-CuF exhibits outstanding performance in stability and reproducibility. We believe that this concept of multilayered plasmonic structures would be widely used not only in the field of SERS but also in the wider research in photocatalysis.

Layered transition metal dichalcogenides with excellent nonlinear absorption properties have shown remarkable performance in acting as ultrafast photonics devices. In our work, palladium diselenide (PdSe2) nanosheets with competitive advantages of wide tunable bandgap, unique puckered pentagonal structure and excellent air stability are prepared by the liquid-phase exfoliation method. Its ultrafast absorption performance was verified by demonstrating conventional and dissipative soliton operations within Er-doped fiber lasers. The minimum pulse width of the conventional soliton was 1.19 ps. Meanwhile, dissipative soliton with a 46.67 mW output power, 35.37 nm spectrum width, 14.92 ps pulse width and 2.86 nJ pulse energy was also generated successfully. Our enhanced experiment results present the excellent absorption performance of PdSe2 and highlight the capacity of PdSe2 in acting as ultrafast photonics devices.

Two-dimensional layered monoelemental materials (Xenes) with excellent optoelectronic properties have various property-related applications, such as energy, biomedicine, and optoelectronic devices. Xenes also show excellent performance in acting as saturable absorbers (SAs) for obtaining ultrafast laser operations. Few-layer tellurene as a typical Xenens exhibits distinct optoelectronic properties and promising practical application potential, and its nonlinear optical absorption characteristics and related ultrafast modulation applications have been investigated preliminarily. However, tellurene-based SAs to demonstrate large-energy mode-locked operations, which have special applications in industrial and scientific research areas, are seldom studied. In this work, we focus on the preparation of tellurene-based SAs and explore its applications in demonstrating large-energy mode-locked operations [dissipative soliton (DS) and noise-like pulses (NLP)]. For DS operation, the maximum average output power, pulse width, and largest pulse energy are 23.61 mW, 5.87 ps, and 1.94 nJ, respectively. NLP operation with a recorded average output power of 106.6 mW and a pulse energy of 8.76 nJ is also generated, which shows significant enhancement in comparison to previously reported Xenes-based works. Our contribution reveals the great potential and capacity of tellurene-based SAs in obtaining large-energy pulse operations and further promotes the explorative investigation of Xenes-based optoelectronic devices.

In this work, we theoretically present a reconfigurable plasmonic chiral metasurface based on a sandwiched metal–insulator–metal structure, which can strongly, spin-selectively absorb circularly polarized light. Through finite-difference time-domain simulation, the absorption of left- or right-handed circularly polarized light can reach nearly 100% at the resonant position, and the magnitude of the circular dichroism can be 80%, which is larger than most of the previously reported value. This strong chiroptical effect originates from plasmonic resonances induced by the incident circularly polarized light. Furthermore, the proposed plasmonic chiral metasurface is able to be reconfigurable by either changing its intrinsic or extrinsic chirality, which can be numerically confirmed by the change of the sign and magnitude of the CD. Such a reconfigurable plasmonic chiral metasurface could find many potential applications in chirality detection/sensing, polarimetric imaging, spin–orbit communications, etc.

An efficient electrospun aligned surface enhanced Raman scattering (SERS) and maize-like substrate of polyvinyl alcohol (PVA) composite and Ag colloid nanofibers decorated with thermal evaporated Ag nanoparticles (AgNPs) has been developed by taking advantage of electrostatic interactions. The synergistic effects of the evaporated AgNPs (niblets) and the Ag colloid in PVA (corncob) could arouse strong electromagnetic field between the lateral and vertical nanogaps which has been demonstrated by experiment and finite-different time-domain (FDTD) simulation. In this experiment, the aligned nanofibers possesses an excellent sensitivity by detection of crystal violet (CV) and malachite green (MG) molecule at low concentration. Moreover, the proposed flexible SERS sensor was measured with outstanding uniformity and reproducibility. We also carried out in-situ electrospinning on a curved surface to detect the mixture of Sudan I, CV and MG molecule, which demonstrates that flexible SERS sensor, has enormous potential in accurate and in-situ detection on the complex geometric structure.

This study investigated the third-order nonlinear optical properties of amorphous silicon carbide (SiC) films prepared via magnetron sputtering at room temperature (RT) and annealed at 200 °C–800 °C. The third-order optical nonlinearity was investigated by Z-scan measurement at a wavelength of 1064 nm and a pulse duration of 25 ps. The self-defocusing behaviour was observed in a large nonlinear refractive index n2 ∼10−14 m2/W, which was five orders of magnitude larger than the value of SiC crystals. By fitting the open-aperture data of the Z-scan, we determined the two- and three-photon absorption in the SiC films prepared at RT and in the annealed samples, respectively. The different nonlinear absorption behaviour was probably ascribed to the intermediate states between the conduction and valence bands.

As the major energy molecule of cells, adenosine triphosphate (ATP) regulates various biological processes and has been found to be closely related to many diseases. Therefore, ATP detection in trace amounts is very useful for understanding various biological processes, studying cellular events such as proliferation and apoptosis, and estimating contaminated degree of food and medical instrument. To date, the trace sensing ATP at picomolar level in biological systems is still a major challenge. Because of unique electrical and structural properties, graphene has attracted much attention in biosensing applications. Here, a sensitive and selective graphene foam field-effect transistor (GF-FET) biosensor for ATP detection is demonstrated. The lowest detection limit of the biosensors for analyzing ATP is down to 0.5 pM, which is one or several orders lower than the reported results. Moreover, the GF-FET biosensor show a good linear current response to ATP concentrations in a broad range from 0.5 pM to 50 μM. The GF-FET sensor surface can be regenerated for many times and used for up to weeks without significant loss of functionality. Based on this sensing platform, label-free measurements of ATP concentrations in human serum as well as in cell lysate are demonstrated. The work may provide a novel platform to study ATP release and energy-regulated biological processes, suggesting a promising future for biosensing applications.

Hyperbolic metamaterials (HMMs), supporting surface plasmon polaritons (SPPs), and highly confined bulk plasmon polaritons (BPPs) possess promising potential for application as surface-enhanced Raman scattering (SERS) substrates. In the present study, a composite SERS substrate based on a multilayer HMM and gold-nanoparticle (Au-NP) layer was fabricated. A strong electromagnetic field was generated at the nanogaps of the Au NPs under the coupling between localized surface plasmon resonance (LSPR) and a BPP. Additionally, a simulation of the composite structure was assessed using COMSOL, the results complied with those achieved through experiments: the SERS performance was enhanced, while the enhancing rate was downregulated, with the extension of the HMM periods. Furthermore, this structure exhibited high detection performance. During the experiments, rhodamine 6G (R6G) and malachite green (MG) acted as the probe molecules, and the limits of detection of the SERS substrate reached 10−10 and 10−8 M for R6G and MG, respectively. Moreover, the composite structure demonstrated prominent reproducibility and stability. The mentioned promising results reveal that the composite structure could have extensive applications, such as in biosensors and food safety inspection.

The weak plasmonic coupling intensity in an aluminum (Al) nanostructure has limited potential applications in excellent low-cost surface-enhanced Raman scattering (SERS) substrates and light harvesting. In this report, we aim to elevate the plasmonic coupling intensity by fabricating an Al nanoparticle (NP)−film system. In the system, the Al NP are fabricated directly on different Al film layers, and the nanoscale-thick alumina interlayer obtained between neighboring Al films acts as natural dielectric gaps. Interestingly, as the number of Al film layers increase, the plasmonic couplings generated between the Al NP and Al film increase as well. It is demonstrated that the confined gap plasmon modes stimulated in the nanoscale-thick alumina region between the adjacent Al films contribute significantly to elevating the plasmonic coupling intensity. The finite-difference time-domain (FDTD) method is used to carry out the simulations and verifies this result.

Indium Tin Oxide nanowire arrays (ITO-NWAs), as epsilon-near-zero (ENZ) materials, exhibit a fast response time and a low saturable absorption intensity, which make them promising photoelectric materials. In this study, ITO-NWAs were successfully fabricated using a chemical vapor deposition (CVD) method, and the saturable absorption properties of this material were characterized in the near-infrared region. Further, passively Q-switched all-solid-state lasers were realized at wavelengths of 1.0, 1.3, and 2.0 µm using the as-prepared saturable absorber (SA). To the best of our knowledge, we present the first application of ITO-NWAs in all-solid-state lasers. The results reveal that ITO-NWAs may be applied as an SA while developing Q-switched lasers and that they exhibit a broad application prospect as broadband saturable absorption materials.

It is widely accepted that resonant cavity system represents the effective laser utilization due to the back and forth reflection and the electric field energy storage. Here, a three-dimensional (3D) hybrid MoS2/AgNPs/inverted pyramid polymethyl methacrylate (iPPMMA) resonant cavity system as a flexible surface enhanced Raman scattering (SERS) sensor was investigated in experiment and theory. The obtained resonant cavity between MoS2, iPPMMA and the plasmonic silver nanoparticles offers the tremendous local near-field enhancements, which is manifested using the finite-difference time-domain (FDTD) theoretical simulation. Additionally, by virtue of the lower light absorption, the iPPMMA gains the advantage over pyramid Si (PSi) in term of enhancing local electric field. The synergistic effects of MoS2, iPPMMA and AgNPs can generate the 3D dense hot spots and extremely contribute to the excellent ultrasensitivity, stablity, reproducibility and recyclability of the proposed flexible SERS sensor. Moreover, the fabricated MoS2/AgNPs/iPPMMA hybrid structure was housed at the end of the optical fiber to remotely detect the toxic mixtures solution, which demonstrates our flexible SERS sensor has enormous potential to be applied in food safety field.

Hot spots generated from the ultra-small nanogaps will tremendously contribute to the strong electromagnetic field. Therefore, the establishment and design of nanogaps are extremely significant. Here, a hierarchical structure, AgNPs/bilayer graphene/Au nanonet, was proposed to form the dense three-dimensional (3D) hot spots and demonstrated in experiment and theory. Numerous nanometer gaps in the complex Au nanonet structure (∼8.67 nm) and in AgNPs/Au nanonet isolated by bilayer graphene (0.64 nm) were achieved, which is much beneficial for the obtainment of the hot spots. Based on this surface enhanced Raman scattering (SERS) substrate, an excellent SERS activity (EF ∼ 9.1 × 109), high sensitivity (10−13 and 10−12 M respective for Rhodamine 6G (R6G) and crystal violet (CV)), and SERS signals homogeneity, outstanding reproducibility (maximum intensity deviation from substrate to substrate ∼10.43%) were obtained, which can be attributed to the abundant lateral and vertical hot spots introduced by the hierarchical structure. Moreover, the proposed SERS substrate was used to sensitively detect the harmful malachite green (MG), which exhibits a great prospect as a potential SERS sensor in food safety field and biochemical molecules.

The sensitivity of the evanescent wave absorption sensor is always a hot topic which has been attracted researchers' discussion. It is still a challenge for developing the effective sensor to sensitively detect some biochemical molecules solution in a simple and low-cost way. In this paper, an evanescent wave absorption (EWA) sensor has been presented based on the U-bent multimode fiber coated with tungsten disulfide (WS2) film and in-situ growth of gold nanoparticles (AuNPs) for the detection of ethanol solution and sodium chloride (NaCl) solution. Benefitted from the effective light coupling produced between U-bent probe and AuNPs, we attained the optimal size of the AuNPs by changing the reaction time between WS2 and tetrachloroauric acid (HAuCl4). With the AuNPs/WS2@U-bent optical fiber, we discussed the behaviors of EWA sensor, such as sensitivity, reproducibility, fast response-recovery time and stability. The sensitivity (△A/△C) of the proposed AuNPs/WS2@U-bent optical fiber EWA sensor is 0.65 for the detection of the ethanol solution. Besides, the AuNPs/WS2@U-bent optical fiber EWA sensor exhibits high sensitivity in detection of the sodium chloride (NaCl), which can reach 1.5 when the proposed sensor was immersed into NaCl solution. Our work demonstrates that the U-bent optical fiber EWA sensor may have promising applications in testing the solution of concentration.

Recently, biological materials have attracted more and more attentions on preparing the surface-enhanced Raman spectroscopy (SERS) substrate with the conspicuous SERS performance. Herein, we demonstrate a simply facile and inexpensive approach to fabricate a novel natural SERS substrate based on graphene oxide-Ag nanoparticles-Mytilus coruscus (GO-AgNPs-M.c.). The surface-enhanced resonance Raman spectroscopy (SERRS) signals of the Rhodamine 6G (R6G) on the GO-AgNPs-M.c. hybrids exhibit the much better SERRS performances in terms of the sensitivity, the signal reproducibility and the antioxidant stability than that on the AgNPs-M.c. one. The well electric field enhancement contribution is likewise confirmed in theory via the COMSOL software. Moreover, the successful detection of trace malachite green (MG) and methylene blue (MB) indicates the well feasibility for multi-molecules detection on the GO-AgNPs-M.c. hybrids. Thus, this inexpensive and high-efficiency natural SERS substrate have great potential for the considerable biochemical SERS applications and broaden the way for preparing multiple SERS platforms derived from other natural materials.

Dark solitons, which have good stability, long transmission distance and strong anti-interference ability. By using a coprecipitation method, the high quality indium tin oxide (ITO) were prepared with an average diameter of 34.1 nm. We used a typical Z-scan scheme involving a balanced twin-detector measurement system to investigated nonlinear optical properties of the ITO nanoparticles. The saturation intensity and modulation depths are 13.21 MW/cm2 and 0.48%, respectively. In an erbium-doped fiber (EDF) lasers, we using the ITO nanoparticles as saturable absorber (SA), and the formation of dark soliton is experimentally demonstrated. The generated dark solitons are centered at the wavelength of 1561.1 nm with a repetition rate of 22.06 MHz. Besides, the pulse width and pulse-to-pulse interval of the dark solitons is ∼1.33ns and 45.11 ns, respectively. These results indicate that the ITO nanoparticles is a promising nanomaterial for ultrafast photonics.

Hot spots have been considered as a dominant role in surface enhancement Raman scattering (SERS). Its generation cannot be separated from the ultra-small nanogaps, which will tremendously contribute to the strong electromagnetic field. We propose a AgNPs/graphene@AuNPs system with three-dimensional hot spots and tunable nanometer gap by changing the layer of graphene with a simple and facile method. The excellent SERS behaviors of the proposed AgNPs/graphene@AuNPs substrate are demonstrated experimentally using rhodamine 6G (R6G) and crystal violet (CV) as probe molecules and theoretically using commercial COMSOL software. The excellent SERS behaviors can be attributed to the electromagnetic mechanism (EM) in all three dimensions introduced by the lateral nanogaps (AgNP-AgNP) and the vertical nanogaps (AgNP-AuNPs), and the chemical enhancement mechanism (CM) induced by the graphene film. For practical application, the prepared sensitive AgNPs/graphene@AuNPs SERS substrate was used to detect Malachite green (MG) in sea water, which provides a bran-new avenue for the detection of biological and chemical molecule.

The methods of chemical vapor deposition (CVD) and seed-mediated growth were used to obtain graphene and gold nanorods (GNRs), respectively. We fabricate graphene @ gold nanorods (G@GNRs) nanocomposites by successively using dropping and transferring methods Through SEM, Raman spectra and TEM analysis, the number of graphene layers is 6–7. The diameter of gold nanorods (GNRs) is about 10 nm and the average aspect ratio is 6.5. In addition, we systematically investigate their nonlinear optical responses by using open-aperture Z-scan technique. In contrast with graphene and GNRs, the G@GNRs nanocomposites exhibit excellent nonlinear optical response with a modulation depth of about 51% and a saturable intensity of about 6.23 GW/cm2. The results suggest that the G@GNRs nanocomposites could potentially be used as an optical modulator in pulsed laser generation.

We propose a liquid-crystal-based reconfigurable chiral metasurface absorber and numerically investigate its chiro-optical properties. The chiral metasurface absorber consists of a metal-insulator-metal structure with the substrate, which can strongly absorb a circularly polarized wave of one spin state and reflects that of the opposite spin, resulting a strong circular dichroism (CD). A birefringent liquid crystal (LC) is exploited to serve as the insulator layer in the metal-insulator-metal structure. We could then vary the circular state of the incident light by controlling the alignment of the LC molecules, hence inversing the CD. The simulation results show that the CD will change the sign as the LC molecules are realigned from 0° to 90°. The absorption efficiency for the specific circularly polarized wave is larger than 80% and the CD is nearly 70%. The simple and compact design of our proposed chiral metasurface absorber is especially favorable for integration, and such a reconfigurable chiral absorber could find many potential applications in biological detection/sensing, polarimetric imaging, and optical communications.

Graphene has attracted much attention in biosensing applications for its unique properties. Because of one-atom layer structure, every atom of graphene is exposed to the environment, making the electronic properties of graphene are very sensitive to charged analytes. Therefore, graphene is an ideal material for transistors in high-performance sensors. Chemical vapor deposition (CVD) method has been demonstrated the most successful method for fabricating large area graphene. However, the conventional CVD methods can only grow graphene on metallic substrate and the graphene has to be transferred to the insulating substrate for further device fabrication. The transfer process creates wrinkles, cracks, or tears on the graphene, which severely degrade electrical properties of graphene. These factors severely degrade the sensing performance of graphene. Here, we directly fabricated graphene on sapphire substrate by high temperature CVD without the use of metal catalysts. The sapphire-based graphene was patterned and make into a DNA biosensor in the configuration of field-effect transistor. The sensors show high performance and achieve the DNA detection sensitivity as low as 100 fM (10 −13 M), which is at least 10 times lower than prior transferred CVD G-FET DNA sensors. The use of the sapphire-based G-FETs suggests a promising future for biosensing applications.

Surface-enhanced Raman scattering (SERS) substrates based on Hyperbolic metamaterials (HMM) have received tremendous attention due to the presence of confined optical modes, i.e., the surface plasmon polaritons (SPP) and bulk plasmon polaritons (BPP). In the present study, a multilayer HMM SERS substrate was fabricated, comprising a monolayer of silver nanoparticles (Ag NPs) and Au-Al2O3 films. Our study demonstrates that the Ag NPs layer excited SPP and BPP, and the localized surface plasmon (LSP) resonance of the Ag NPs layer coupled with BPP, creating a strong electromagnetic field at the interparticle gaps of the Ag NPs. Interestingly, increasing the multilayer stacking of HMM will strengthen the SERS activity until a certain threshold. On the top of HMM, the interparticle gaps of the Ag NPs were adjusted to enhance the SERS characteristics and the maximum EF appeared at the gap of 10 nm. Performing theoretical simulations as well as experiments, the ultra-sensitivity, good reproducibility, reusability, and high enhancement factor of the proposed SERS substrate were assessed. Lastly, the ultralow limits of detection for melamine in milk were 10−7 M, satisfying the needs for successful implementation in the food safety field.

We theoretically demonstrate a low threshold and widely tunable spaser based on a plasmonic nanostructure consisting of two sets of disk-rings (TSDR). The TSDR nanostructure supports two dark surface plasmons (SPs), which are excited simultaneously by two bright SPs at Fano dips. The two dark SPs support lower effective mode volume, higher quality factor and higher Purcell factors. When the dark SPs serve as the pumping and lasing mode of a spaser, the spaser has a lower lasing threshold, a higher pump absorption efficiency and a lower threshold absorbed pump power than the spaser based on a bright SP. In addition, the lasing and pumping wavelengths of the spaser proposed in this article can each be tuned over a very wide wavelength range. Our results should be significant for the development of spasers.

Flexible substrate consisted of PMMA-supported monolayer graphene with sandwiched Ag-nanoflowers (G/AgNFs/PMMA) for ultrasensitive, reproducible, and stable surface-enhanced Raman scattering (SERS) detection is reported. Graphene templated micro-current-assisted chemical reduction method was employed to support AgNFs growth, and uniform-distribution AgNFs with all directions nanotips can generate tremendous enhancement factor and intensive hotspots. The minimum detectable concentration (i.e., detection limit) for rhodamine 6G (R6G) in-situ detection by covering this as-synthesized G/AgNFs/PMMA flexible substrate can be as low as 10−14M. Moreover, graphene can effectively stabilize the SERS signals and protect AgNFs from oxidation, endowing this flexible substrate a long-term stability with maximum intensity deviation lower than 10%, for the quantitative measurements from spot-to-spot or substrate-to-substrate. In order to trial its practical applications with various real-world surfaces, the in-situ SERS detection of phenylalanine@apple, adenosine aqueous solution and methylene-blue@fish was performed by covering this G/AgNFs/PMMA flexible substrate. Clear Raman peaks can be obtained for all the selected samples with concentration of 10−10M and, importantly, good linear relationship between Raman intensity and molecular concentration indicates the potential application of the G/AgNFs/PMMA flexible substrate in quantitative determination. Thus, this high-efficiency and low-cost flexible SERS substrate may provide a new way for the molecular trace-detection in food security and environmental protection.

The three-dimensional (3D) MoS 2 decorated with Au nanoparticles (Au NPs) hybrids (3D MoS 2 -Au NPs) for surface-enhanced Raman scattering (SERS) sensing was demonstrated in this paper. SEM, Raman spectroscopy, TEM, SAED, EDX and XRD were performed to characterize 3D MoS 2 -Au NPs hybrids. Rhodamine 6G (R6G), fluorescein and gallic acid molecules were used as the probe for the SERS detection of the 3D MoS 2 -Au NPs hybrids. In addition, we modeled the enhancement of the electric field of MoS 2 -Au NPs hybrids using Finite-difference time-domain (FDTD) analysis, which can further give assistance to the mechanism understanding of the SERS activity.

The report presents conventional soliton operation in an anomalous-dispersion fiber laser with a novel WS 2 saturable absorber (SA) based on fluorine mica (FM) substrate. Compared to organic host material such as polymer composite, FM has higher softening temperature, heat dissipation and laser damage threshold. In this work, the modulation depth (MD) and non-saturable loss (NL) of WS 2 /FM SA are measured to be 3.1% and 15%, respectively. By employing the SA, a stable conventional soliton mode-locked fiber laser is achieved. The repetition rate is 8.2 MHz and the pulse duration is 830 fs. The fiber laser works in mode locking operation for at least ten days and no damage of the SA is observed. The results indicate that WS 2 /FM material is an ideal SA for Er-doped fiber (EDF) lasers.

We report a simple method to fabricate Ag2O@Ag core-shell nanostructure employed as SERS (surface enhanced Raman scattering) active substrate. The Ag2O shell was fabricated via the oxidation of AgNPs with the assist of laser irradiation in atmosphere. In this way, the prepared Ag2O@Ag hybrid system possesses ultrasensitivity, homogeneity, reproducibility and chemical stability by virtue of ultra-thin inner shell. The minimum detectable concentration of R6G was presented as low as 10−11 M. The enhancement factor of Ag2O@Ag core-shell nanostructure using R6G as probe molecules was found to be as high as 6 × 107. Furthermore, the flexible Ag2O@Ag/PMMA SERS substrate were first presented and the SERRS (surface enhanced resonance Raman scattering) spectra of the R6G on this substrate were investigated. The characteristic peaks of R6G with concentration from 10−5–10−11 M can be also easily observed by detecting from both sides of the flexible substrate. A good linear response between SERRS intensity and R6G concentration from 10−5 to 10−11 M was obtained. For practical application, the Ag2O@Ag/PMMA hybrids flexible SERS substrate was used for real-time and in-situ detection of chlorpyrifos with 10−7 M on cucumber and apple peels. These results are exactly consistent with the DFT simulation on chlorpyrifos pesticide and confirm that the Ag2O@Ag/PMMA hybrids flexible SERS substrate is highly promising for food safety field in the future.

In our work, few layers graphene oxide (GO) were directly synthesized on Ag nanoparticles (AgNPs) by spin-coating method to fabricate a GO-AgNPs hybrid structure on a pyramidal silicon (PSi) substrate for surface-enhanced Raman scattering (SERS). The GO-AgNPs-PSi substrate showed excellent Raman enhancement effect, the minimum detected concentration for Rhodamine 6G (R6G) can reach 10 −12 M, which is one order of magnitude lower than the AgNPs-PSi substrate and two order of magnitude lower than the GO-AgNPs-flat-Si substrate. The linear fit calibration curve with error bars is presented and the value of R 2 of 612 and 773 cm −1 can reach 0.986 and 0.980, respectively. The excellent linear response between the Raman intensity and R6G concentrations prove that the prepared GO-AgNPs-PSi substrates can serve as good SERS substrate for molecule detection. The maximum deviations of SERS intensities from 20 positions of the GO-AgNPs-PSi substrate are less than 8%, revealing the high homogeneity of the SERS substrate. The excellent homogeneity of the enhanced Raman signals can be attributed to well-separated pyramid arrays of PSi, the uniform morphology of AgNPs and multi-functions of GO layer. Besides, the uniform GO film can effectively protect AgNPs from oxidation and endow the hybrid system a good stability and long lifetime. This GO-AgNPs-PSi substrate may provide a new way toward practical applications for the ultrasensitive and label-free SERS detection in areas of medicine, food safety and biotechnology.

Compared to conventional chemical sensors, this paper presented a chemical sensor system with broad selectivity for a variety of molecules without any surface modification. The system consisted of an unmodified graphene foam as sensing element, an electrical resistance time domain detection system and a Support Vector Machine (SVM) identification system. The chemical sensor adopted 3D graphene foam to increase the reaction area and improve the sensitivity for detecting target molecules. The electrical resistance time domain detection system was constructed to record the graphene resistance curve in real time with different molecules. Based on the diverse shapes of the electrical resistance curves, SVM was used to extract features of each resistance curve and discriminate the corresponding molecules via pattern recognition of each resistance curve without any graphene modification. As validation experiments, six kinds of chemical molecules (chloroform, acetone, ether, toluene, ethyl benzene and methanol) have been tested. The discrimination accuracy for each molecule could be above 98% which showed a broad selectivity for a variety of molecules. Furthermore, through theoretical calculation with the first principle, we concluded that different band structures of the graphene caused by different molecules were the mechanism for the graphene chemical sensor system to discriminate chemical molecules with selectivity. This work may present a new strategy for research and application for graphene chemical sensors.

By combining the excellent surface-enhanced Raman scattering (SERS) activity of Ag nanoparticles (AgNPs), the well-separated pyramid arrays of the pyramidal silicon (PSi) and unique physical/chemical properties of molybdenum disulfide (MoS2), the MoS2@AgNPs@PSi substrate shows high performance in terms of sensitivity, uniformity, reproducibility and stability. By using rhodamine 6G (R6G) as probe molecule, the SERS results indicate that the MoS2@AgNPs@PSi substrate is superior to the AgNPs@PSi, AgA@PSi (the second annealing of the AgNPs@PSi) and the MoS2@AgNPs@flat-Si substrate. The MoS2@AgNPs@PSi substrate also shows the reasonable linear response between the Raman intensity and R6G concentration. The maximum deviations of SERS intensities from 20 positions on a same MoS2@AgNPs@PSi substrate and 10 MoS2@AgNPs@PSi substrates in different batches are less than 7.6% and 9%, respectively, revealing the excellent uniformity and reproducibility of the substrate. Besides, the SERS substrate has a good stability, the Raman intensity of the MoS2@AgNPs@PSi substrate only drop by 15% in a month. The corresponding experimental and theoretical results suggest that our proposed MoS2@AgNPs@PSi substrate is expected to offer a new and practical way to accelerate the development of label-free SERS detection.

We proposed a high sensitivity and a high resolution surface plasmon resonance sensor composed of graphene–WS2 hybrid nanostructure and Au–Ag bimetallic-layers film. The bimetallic-layer configuration uses the high sensitivity of gold and the narrow full width at half maximum (FWHM) of silver to improve the sensor's sensitivity and resolution respectively. Graphene and WS2 serve as an effective light absorption medium. Once they cover the bimetallic-layer, the sensitivity can be further improved significantly. Graphene–WS2–Au–Ag model shows a higher sensitivity and higher resolution than that of the conventional sensing scheme where pure Au thin film is used. In our paper, we mainly use Fresnel equations and the transfer matrix method (TMM) to study the reflectivity and sensitivity as well as the full width at half maximum (FWHM) of the SPR sensor.

Stretchable sensors are essential and important for the new-type stretchable intelligent electronic devices. Three-dimensional (3D) graphene foams are attractive to increase the sensitivity and stretchability, benefiting from a high specific surface area and mechanical strength. Herein, 3D graphene/nickel particles (Gr–NiP) peasecod foams, which were fabricated using CVD and stamp-transfer processes, are proposed and used for stretchable sensor applications. The existing nickel particles, covered by graphene layers, are useful for the formation of 3D nanostructures and separated from each other for stretchable applications. A stretchability (e) of such Gr–NiP foams of up to 80% can be achieved. A low limit of detection (

In this work, we demonstrated facile and low-cost fabrication of highly sensitive SERS substrates via replacement reaction by immersing Cu foils into a AgNO 3 solution. Different morphologies of Ag nanostructures were observed on the substrate surface by controlling the reaction time. The growth mechanism of Ag nanostructures on the Cu substrates was also analyzed based on the nanostructure evolution. The Ag-Cu substrates showed optimum SERS enhancement at certain reaction time, and the minimum detected concentration of Rhodamine 6G is as low as 10 −13 M. The easy and low-cost fabrication makes the Ag-Cu SERS substrates promising for rapid, sensitive detection of targeted analytes, such as biomolecules, pollutants, and explosives in the environment.

We demonstrate graphene oxide (GO)-decorated Ag dendritic nanostructures on a copper substrate for surface enhanced Raman scattering (SERS) applications. The Ag dendrites (AgD) were synthesized through a facile and low-cost galvanic replacement reaction of Ag nitrate solution and copper foils. The AgD/Cu was further decorated with GO by a dip-coating method. The GO-decorated AgD exhibited a much higher SERS activity in terms of sensitivity, signal-to-noise ratio and stability compared with non-decorated AgD, indicating that the GO/AgD/Cu substrates could be potentially useful for highly sensitive molecule detecting applications.

In this study, a double-end pumped high-power passively mode-locked erbium-doped fiber laser (EDFL) was realized by employing a few-layered In2Se3 flakes as a saturable absorber (SA). Herein, the uniform large-scale In2Se3 flakes were synthesized by the physical vapor deposition (PVD) method. The PVD-In2Se3 SA exhibited a remarkable damage threshold of higher than 24 mJ/cm2. Meanwhile, the PVD-In2Se3 SA had a modulation depth and saturable intensity of 18.75% and 6.8 MW/cm2, respectively. Based on the In2Se3 SA, the stable bright pulses emitting at 1559.4 nm with an average output power/pulse energy/pulse duration of 122.4 mW/5.8 nJ/14.4 ns were obtained successfully. To our knowledge, 122.4 mW was the new major breakthrough of mode-locked Er-doped fiber lasers. In addition, this is the first demonstration of the dark-bright pulse pair generation based on In2Se3 SA. The maximum average output power of the dark-bright pulse reached 121.2 mW, which also showed significant enhancement in comparison with previous works. Our excellent experiment results fully prove the superiority of our experimental design scheme and indicate that the PVD-In2Se3 could operate as a promising highly-nonlinear photonic material for a high-power fiber laser.

We demonstrate the generation of versatile mode-locked operations in an Er-doped fiber laser with an indium tin oxide (ITO) saturable absorber (SA). As an epsilon-near-zero material, ITO has been only used to fashion a mode-locked fiber laser as an ITO nanoparticle-polyvinyl alcohol SA. However, this type of SA cannot work at high power or ensure that the SA materials can be transmitted by the light. Thus, we covered the end face of a fiber with a uniform ITO film using the radio frequency magnetron sputtering technology to fabricate a novel ITO SA. Using this new type of SA, single-wavelength pulses, dual-wavelength pulses, and triple-wavelength multi-pulses were achieved easily. The pulse durations of these mode-locked operations were 1.67, 6.91, and 1 ns, respectively. At the dual-wavelength mode-locked state, the fiber laser could achieve an output power of 2.91 mW and a pulse energy of 1.48 nJ. This study reveals that such a proposed film-type ITO SA has excellent nonlinear absorption properties, which can promote the application of ITO film for ultrafast photonics.

In recent years, biomaterials have increasingly attracted attention on surface-enhanced Raman spectroscopy (SERS) due to their well Raman performance while metal particles are combined with biological substrates. Therefore, we propose an environmentally friendly substrate based on silver-plated cicada wings with seamless graphene layer (Gr-AgNPs-C.w.), which can be prepared with a simple and inexpensive method. Compared with AgNPs-C.w., Gr-AgNPs-C.w. hybrids show better SERS performance with high sensitivity, good uniformity and good stability with R6G detection. The minimum detected concentration can reach 10-15 M, and the value of R2 can reach 0.996, respectively. Theoretical simulation demonstrates the situation of electromagnetic field through COMSOL software. In addition, due to the affinity of graphene for biomolecules, we can successfully detect the DNA biomolecules through a simple process. Therefore, this cheap and efficient natural SERS substrate has great potential for a considerable number of biochemical SERS applications and can broaden the way in which multiple SERS platforms derived from other natural materials are prepared.

A D-shape plastic optical fiber (D-POF) surface plasmon resonance (SPR) biosensor based on the graphene/Au film (G/Au) was proposed and experimentally demonstrated for detection of DNA hybridization process. To improve the detection performance of SPR sensors, the Physical Vapor Deposition (PVD) method was used to evaporate the Au film directly onto the graphene grown on copper foil, and the Au film acted as a role of traditional Polymethyl Methacrylate (PMMA). The process made graphene and Au film form seamless contact. Next, the G/Au was transferred onto the D-shape fiber together. We explored the G/Au SPR sensor by using the finite element method (FEM) and obtained the optimum materials thickness to form configuration. Compared to other plastic optical fiber experiments, the proposed sensor’s sensitivity was improved effectively and calculated as 1227 nm/RIU in a range of glucose solution. Meanwhile, our proposed sensor successfully distinguishes hybridization and single nucleotide polymorphisms (SNP) by observing the resonance wavelength change. It also exhibits a satisfactory linear response (R2 = 0.996) to the target DNA liquids with respective concentrations of 0.1nM to1µM, which shows this method’s wide potential in medical diagnostics.

Herein, a magnetic graphene field-effect transistor biosensor was prepared through the transfer of a chemical vapor deposition graphene film onto a glass substrate to produce a sensing film and conductive channel. By fixing 1-pyrenebutanoic acid succinimidyl ester onto graphene film as an anchor, a probe aptamer was immobilized on the graphene film in order to capture magnetically labeled complementary single-stranded DNA. Our experiments showed that, within a periodic magnetic field, the biosensor impedance exhibited a periodic oscillation, the amplitude of which was correlated to the complementary DNA concentration. Based on this principle, the magnetic graphene field-effect transistor was utilized to detect single-stranded DNA with detection limition of 1 pM. The results were rationalized using a model wherein the magnetic force causes the DNA strand to bend, thereby resulting in magnetic nanobeads/DNA modulation of the double conductive layer of graphene transistors. Furthermore, since a periodic magnetic field could be introduced to produce a periodic impedance changes of MGFETs, sampling integration could be used to improve the signal-to-noise ratio efficiently by increasing the number of periods of the external magnetic field. Therefore, a novel biosensor for DNA detection with high sensitivity has been presented in this work. Based on the detection principle, this system may also be a potential tool for detecting other bio-molecules, cells, etc.

Surface-enhanced Raman spectroscopy (SERS) has become an ultrasensitive technique in trace molecule detection through its unique vibrational fingerprint. However, development of a SERS platform with large enhancement factor, superior stability, and excellent reproducibility is still a grand challenge for practical applications. Recently, two-dimensional (2D) materials play an intriguing role for SERS through the use of their unique structures and properties. This review summarizes the recent progress of 2D materials-based SERS that could be complements to plasmonic SERS substrates. Based on the symmetry of the lattice structure, isotropic and anisotropic 2D materials for SERS are introduced. Particularly, various methods to improve the SERS performance are described. The sensitivity, limit of detection, and stability are discussed for 2D materials-based heterostructures as SERS platforms, including van der Waals and hybrid heterostructures. Furthermore, the applications of 2D materials-based SERS substrates in niche areas, including local strain probing, remote/in-situ chemical analysis, and fine structure characterization are summarized.

Surface enhanced Raman scattering (SERS), as a molecular-specific spectroscopy method using plasmonic nanostructures to significantly enhance Raman spectroscopy, has broad application prospects in various fileds. In our work, the Ag/CuO nanowires (NWs)/pyramidal PDMS multiscale structure were rationally fabricated as a multi-dimensional plasmon coupling SERS substrate with molecular enrichment effect. CuO NWs were grown in the pyramid cavity by alkaline etching and formed micro-nano multiscale strucure. The Ag film was decorated on the nano-micro multiscale structure by physical vapor deposition method, endowing the SERS activity. The subwavelength-size Ag/CuO NWs can also provide a rough enough surface to separate the droplets from the air, reduce the surface energy, and achieve a hydrophobic effect. To demonstrate the SERS activity, the proposed multiscale micro-nano structure has been successfully applied to sensitively detect Rhodamine 6G (R6G) at low concentration. Interestingly, we also demonstrate that the Ag/CuO NWs/pyramidal PDMS multiscale structure has excellent molecular adsorption for practical application detection. We successfully achieve the detection for the mixture of R6G, Crystal Violet (CV) and Congo Red (CR) molecule under turbid and different PH environment, which demonstrates its great potential for in-situ detection of chemical dye molecules in complex environments.

In the present study, a nanoparticle-multilayer metal film substrate was presented with silver nanoparticles (Ag NPs) assembled on a multilayer gold (Au) film by employing alumina (Al2O3) as a spacer. The SERS performance of the proposed structures was determined. It was suggested that the SERS effect was improved with the increase in the number of layers, which was saturated at four layers. The SERS performance of the structures resulted from the mutual coupling of multiple plasmon modes [localized surface plasmons (LSPs), surface plasmon polaritons (SPPs), as well as bulk plasmon polaritons (BPPs)] generated by the Ag NP-multilayer Au film structure. Furthermore, the electric field distribution of the hybrid system was studied with COMSOL Multiphysics software, which changed in almost consistency with the experimentally achieved results. For this substrate, the limit of detection (LOD) was down to 10−13 M for the rhodamine 6G (R6G), and the proposed SERS substrate was exhibited prominently quantitatively detected capability and high reproducibility. Moreover, a highly sensitive detection was conducted on toluidine blue (TB) molecules. As revealed from the present study, the Ag NP-multilayer Au film structure can act as a dependable SERS substrate for its sensitive molecular sensing applications in the medical field.

In the present study, an optical fiber surface plasmon resonance (SPR) biosensor was developed for measuring time- and concentration-dependent DNA hybridization kinetics. Its design complies with a 3D Au / Al 2 O 3 multilayer composite hyperbolic metamaterial (HMM), a graphene film, and a D-shaped plastic optical fiber. According to the numerical simulation and the experimental demonstration, the SPR peak of the designed biosensor can be effectively altered in the range of visible to near-infrared by varying the HMM structure. The sensitivity of the appliance was shown to achieve a value of up to 4461 nm/RIU, allowing its applicability for bulk refractive index sensing. Furthermore, a biosensor designed in this work displayed high-resolution capability (ranging from 10 pM to 100 nM), good linearity, and high repeatability along with a detection limit down to 10 pM, thus suggesting a vast potential for medical diagnostics and clinical applications.

We synthesized large-area single-crystal graphene sheets to use them in biosensors based on field-effect transistors (FET) for quantitative analysis of interaction kinetics and affinity between the imatinib drug and its target protein kinase Abl1. The G-FET biosensor showed an excellent performance and recognized imatinib at as low as 15.5 fM. The biosensor also showed a linear response to the logarithm of imatinib concentration in the 0.1 pM-10 μM range. This graphene-based FET biosensor (G-FET) was also applied to quantify Abl1 Y253 F mutation and Abl1 dependency on Mg2+ to bind to imatinib in real-time. Results demonstrated in this work clearly showed that the novel G-FET biosensors are very promising to analyze interactions between proteins and low molecular weight drugs.

An evanescent wave absorption (EWA) sensor based tapered plastic optical fiber (TPOF) coated with monolayer graphene film for ethanol molecules detection is demonstrated in this study. The continuous and monolayer graphene films were grown on a Cu foil by using chemical vapor deposition (CVD) technology. Polymethyl methacrylate (PMMA) was used as the carrier to support the transfer of graphene from Cu foil to the skinless tapered optical fiber core. The accuracy of the TPOF sensor with graphene (G-TPOF sensor) is much higher than that without graphene (TPOF sensor), which can be attributed to the molecules enriched on the surface of graphene. The absorbance (A) and the concentrations of ethanol solution show an excellent proportional relationship in a range of 0–100%. The dynamic response of the G-TPOF sensor has shown strong reversibility, repeatability and stability at room temperature. The response time and recovery time of the G-TPOF sensor for different concentrations are all less than 30 s. Beyond that, we selected the Chinese liquor as the analyte, and the results are consistent with the concentration-list obtained in the experiment.

Here we designed a new kind of SERS substrate referred to as a MoS 2 -coated Cu nanopaticles (MoS 2 @CuNPs) substrate for R6G detection. The Cu nanoparticles wrapped by a thin MoS 2 film were directly synthesized on flat quartz by two annealing process in a mixture of argon and hydrogen. Signals from a MoS 2 @CuNPs SERS substrate were also demonstrated to have interesting advantages over pure CuNPs SERS, in terms of the excellent linear relationship between Raman intensity and analyte concentration, strongly background fluorescence quenching and being more stable against photo-induced damage and oxidation. The minimum detectable concentrations of R6G on MoS 2 @CuNPs hybrids can be as low as 10 −9 M which is one order lower than that on the pure CuNPs substrates. This synthetic approach is facile, scalable and applicable to the MoS 2 film compound with other metals such as Ag, Au etc.

The C 1s X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy for three C56 fullerene isomers and their chlorinated derivatives have been theoretically simulated by means of density functional theory (DFT). Compared with XPS, the NEXAFS spectra present remarkable dependence on the structures of all the studied molecules and thus can be used to identify the three C56 isomers and chlorinated species. The spectra of the chlorinated species present significant variations compared with the pristine fullerenes. The spectral components of carbon atoms of different local environment have been investigated as well. The spectra of carbons saturated by chlorine atoms exhibit a shift toward higher energies compared with the others.

An evanescent wave absorption (EWA) sensor based on tapered multimode fiber (TMMF) coated with monolayer graphene film for the detection of double-stranded DNA (DS-DNA) is investigated in this work. The TMMF is a silica multimode fiber (nominally at 62.5 μm), which was tapered to symmetric taper with waist diameters of ~30 μm and total length of ~3 mm. Monolayer graphene film was grown on a copper foil via chemical vapor deposition (CVD) technology and transferred onto skinless tapered fiber core via dry transfer technology. All the components of the sensor are coupled together by fusion splicer in order to eliminate the external disturbance. DS-DNA is created by the assembly of two relatively complemented oligonucleotides. The measurements are obtained by using a spectrometer in the optical wavelength range of 400–900 nm. With the increase of DS-DNA concentration, the output light intensity (OPLI) arisen an obvious attenuation. Importantly, the absorbance (A) and the DS-DNA concentrations shown a reasonable linear variation in a wide range of 5–400 μM. Through a series of comparison, the accuracy of TMMF sensor with graphene (G-TMMF) is much better than that without graphene (TMMF), which can be attributed to the molecular enrichment of graphene by π–π stacking.

A facile fabrication of high-quality and large-area tungsten disulfide (WS2) layers is demonstrated using a thermal decomposition of tetrathiotungstates ((NH4)2WS4) with two annealing process. During synthesis, the first annealing step is utilized to achieve lateral epitaxial growth of the WS2 and create seamless and large-area WS2 film. The second annealing step can offer an S-rich and high temperature condition, which is beneficial for the high quality of the WS2 film. Scanning electron microscopy, Raman spectroscopy and atomic force microscopy confirm the presence of large-area and high-quality WS2 film. The crucial role of the S, H2 and the effect of the temperature during the experiment are also investigated. Furthermore, the potential application of the prepared WS2 as a substrate for Raman enhancement is first discussed using R6G molecules as probe molecule.

We numerically study second harmonic generation from plasmonic nanotubes of air-core and ultrathin gold shell using classical nonlocal hydrodynamic model of free electron. We demonstrate that the nonlocal effect of gold significantly affects the linear optical response and second harmonic generation in such ultrathin nanotubes with shell down to a few nanometers or subnanometer scale, comparing with the conventional local Drude model of gold. We specially emphasize second harmonic generation from the nanotube structures of dipole plasmon resonance at fundamental wavelength and dipole/quadrupole resonance at second harmonic wavelength. Our results indicate that, the output of second harmonic generation is dominantly enhanced by the dipole plasmon resonance at fundamental wavelength via the strong local electric field and also can be significantly enhanced by dipole- and quadrupole-resonant scattering at second harmonic wavelength. The nonlinear sources of second harmonic generation in ultrathin gold nanotubes, including nonlinear Coulomb interaction, convective term, Lorentz force, and nonlinear pressure are studied separately, and the dominant contributions from convective term and nonlinear Coulomb term are reported.

Se seed layers were used to synthesize the high-quality graphene–Bi2Se3 nanoplates hybrid Dirac materials via chemical vapor deposition (CVD) method. The morphology, crystallization and structural properties of the hybrid Dirac materials were characterized by SEM, EDS, Raman, XRD, AFM and HRTEM. The measurement results verify that the Se seed layer on the graphene surface can effectively saturate the surface dangling bonds of the graphene, which not only impel the uniform Bi2Se3 nanoplates growing along the horizontal direction but also can supply enough Se atoms to fill the Se vacancies. We also demonstrate the Se seed layer can effectively avoid the interaction of Bi2Se3 and the graphene. Further experiments testify the different Se seed layer on the graphene surface can be used to control the density of the Bi2Se3 nanoplates.