Metal Surface Plasmon Resonance Research Articles

Surface plasmon resonance effect cooperated with Z-scheme heterostructure for enhancing photocatalytic nitrogen reduction to ammonia

The photocatalytic efficiency can be improved by constructing a Z-scheme heterojunction, but hindered by the only half utilization efficiency of photogenerated carriers. Thus, a novel material, UiO-66-NH2@TAPB-BTCA-COP-Ag (U6N@COP-Ag), with surface plasmon resonance (SPR) effect synergistic Z-scheme heterostructure has been prepared by depositing Ag nanoparticles (Ag NPs) on TAPB-BTCA-COP (COP)-coated UiO-66-NH2. The deposited Ag NPs expand the range of light absorption and introduce more photogenerated electrons in the composite. The SPR effect of noble metal compensates for the limited utilization of the Z-scheme heterojunction photogenerated carriers and the increased density of semiconductor carriers at the reducing end, which is more conducive to the redox reaction of the catalyst. Without sacrificial agents, U6N@COP-Ag shows great photocatalytic nitrogen reduction conversion efficiency with the rate of NH4+ in ammonia water at 167.63μmol g-1h−1, which is 6.6 and 2.8 times that of the original UiO-66-NH2 and COP, respectively. In-situ XPS and Kelvin probe technology verify that UiO-66-NH2 and Ag nanoparticles provide more photogenerated electrons to COP. The cleavage and conversion of N2 to NH4+ on U6N@COP-Ag was confirmed by the enhancement of NH bonds and NH4+ characteristic absorption peaks in the in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS). This work presents a great method to improve the Z-scheme heterojunction photogenerated carrier utilization and the density of semiconductor carriers at the reducing end by the noble metal SPR effect, which is more conducive to enhance the redox reaction of the catalyst.

Enhanced photocatalysis-Fenton degradation of levofloxacin by Fe doped BiOCl microspheres with rich surface oxygen vacancies: The accelerated redox cycle of ≡Fe(III)/≡Fe(II)

The photocatalysis-Fenton process was considered as an effective water treatment method due to its superior efficiency and technical feasibility, but its application was limited by ≡Fe(III)/≡Fe(II). Herein, Fe doped BiOCl hierarchical microspheres with rich surface oxygen vacancies (Fe/BiOCl OVs) were synthesized to modulate the interface structure for efficient photocatalysis-Fenton degradation of levofloxacin (LEV). The systematic characterization analysis confirmed the existence of strong interfacial interactions, which facilitated the activation of H2O2 and the degradation of LEV. The synergism of metal deposition, OVs and surface plasmon resonance (SPR) effect of Bi contributed to the enhanced light absorption ability and suppressed carriers recombination. The LEV degradation efficiency reached 99.0% after 60-min photocatalysis-Fenton reaction. The interfacial charge transfer theory demonstrated that the presence of oxygen vacancies accelerated the redox cycle of ≡Fe(III)/≡Fe(II), which promoted the H2O2 activation to produce ·OH. The ·OH and e- played important roles during the photocatalysis-Fenton degradation of LEV, while ·O2–, 1O2 and h+ also contributed in LEV degradation. Based on density-functional theory (DFT) calculations and LC-MS analysis, four degradation pathways of LEV were proposed. The photocatalysis-Fenton degradation process of Fe/BiOCl OVs effectively reduced the toxicity of LEV, which ultimately mitigated the harmful effects of antibiotics on the environment.

Selective Photocatalytic CO2 Reduction Through Plasmonic Z‐Scheme Ag‐Bi2O3‐ZnO Heterostructures

AbstractCombination of plasmonic noble metal with semiconductors offers a promising and potential solar energy harvesting and conversion route. Herein, plasmonic Z‐scheme Ag‐Bi2O3‐ZnO (AgBZ) heterostructure is designed and synthesized via solution combustion and photo‐deposition method. Metallic Ag nanoparticles (NPs) were deposited over Bi2O3‐ZnO heterostructure; thus, they exhibit strong visible light absorption owing to surface plasmon resonance (SPR). The photocatalytic efficiency of the synthesized catalysts is investigated by the photocatalytic CO2 reduction to fuels under simulated solar light irradiation. The present system has shown an outstanding photocatalytic CO2 reduction and excellent selectivity of CO. The evolved rate of CO fuel, the amount of CO produced per unit time, over optimized Ag‐Bi2O3‐ZnO (3AgBZ) heterostructures was (96.74 μmol g−1/h) which was approximately 12 times larger than that of Bi2O3‐ZnO (0AgBZ) and 49‐fold than the quantity of evolved CO fuels over pure ZnO photocatalyst. The percentage of evolved CO to CH4 fuels over optimized Ag‐Bi2O3‐ZnO (3AgBZ) heterostructures was about 50 : 1compared to that of 2 : 3 over Bi2O3‐ZnO (0AgBZ). The great improvement and the high selectivity would be ascribed to the synergistic effect of metallic surface plasmon resonance and the Z‐scheme charges transfer system. This work would open a window to construct a single photocatalyst with different charge separation systems and excellent CO2 reduction selectivity. Finally, the mechanism for the enhanced photocatalytic performance by the synergistic effect was described and discussed.

Sodium-based no-core fiber surface plasmon resonance sensor with high sensitivity and narrow FWHM

Since fiber-optic sensors using noble metal-excited surface plasmon resonance (SPR) effects have encountered bottlenecks in improving performance, we propose a fiber-optic sensor using sodium in combination with a no-core fiber (NCF) to measure both refractive index (RI) and temperature. We deposited sodium thin films on the surface of NCF optical fibers and protected them with polymethyl methacrylate (PMMA) or polydimethylsiloxane (PDMS) for RI sensing or temperature sensing. We performed computational simulations and performance analyses of the sensors using the finite element method, and the results show that the sodium-based SPR sensors have higher sensitivity, wider detection range, and narrower full width at half-maximum (FWHM) than the noble metal SPR sensors. SPR sensors with different sodium film thicknesses have different sensing characteristics, so we can get optical fiber sensors with more flexible transmission characteristics, which helps us arrange sensors more conveniently in practical applications. The simulation and numerical results show that when the sensor is used to measure RI, the average sensitivity of the sensor can reach 7977 nm RIU−1, the maximum sensitivity can reach 23100 nm RIU−1, the narrowest FWHM is 14.23 nm, and the maximum figure of merit (FOM) is 719.42 RIU−1 under different thicknesses of sodium film. The corresponding RI ranges from 1.32 to 1.41. When the temperature measurement range is 0 °C ∼ 100 °C, the average sensitivity can reach 7.86 nm °C−1, the maximum temperature sensitivity can reach 21.1 nm °C−1, and the narrowest FWHM is 17.84 nm. In summary, the proposed sodium-based SPR sensor has flexible and high-performance sensing characteristics, and our research work provides more powerful theoretical support for the application of sodium-based plasma devices.

Synergetic surface enhancement of quantum dots-based electrochemiluminescence with photonic crystal light scattering and metal surface plasmon resonance for sensitive bioanalysis

Noble metal nanostructures and photonic crystals (PhCs) have been widely investigated as substrates for constructing surface enhanced electrochemiluminescence (SE-ECL) biosensors. However, their applications are hindered by the limited enhancement intensity of surface plasmon resonance (SPR) and an incomplete mechanism for the photonic enhancement effect. Hence, developing a novel SE-ECL strategy with better signal enhanced capability and enriching our understanding of the intrinsic mechanisms for efficient bioanalysis is extremely urgent.Here, a synergistic SE-ECL strategy was developed for the sensitive determination of prostate specific antigen (PSA) protein. The randomly arranged polystyrene (r-PS) spheres and PS PhC arrays were applied to enhance the ECL emission of cadmium sulfide quantum dots (CdS QDs) and the results suggested that the PhC arrays displayed superior intensity (0.22) than the r-PS interface (0.10). Au nanoparticles (NPs) were introduced onto the two kinds of surfaces and further boosted the ECL intensity. According to the ECL measurements, Au NPs modified at the r-PS surface exhibited only a slight increase (0.13), while the PhC arrays showed approximately 5-fold enhancement (0.92), benefiting from the synergistic enhancement. The finite-difference time-domain (FDTD) simulation indicated that the ECL enhancement was ascribed to the coupled electromagnetic (EM) field at the surfaces of PS PhCs and Au NPs. The SE-ECL could achieve a detection range from 1 pg/mL to 1 μg/mL with a detection limit of 0.41 pg/mL (S/N = 3).This study provides the first combination of PhC arrays and metal surface plasmon nanostructure for the synergetic enhancement of SE-ECL systems. It opens a new avenue for the rational design of advanced ECL biosensors and shows great perspective for clinical diagnosis.

Deciphering Interactions Involved in Immobilized Metal Ion Affinity Chromatography and Surface Plasmon Resonance for Validating the Analogy between Both Technologies

Various peptides can be obtained through protein enzymatic hydrolysis. Immobilized metal ion affinity chromatography (IMAC) is one of the methods which can be used to separate metal chelating peptides (MCPs) in a hydrolysate mixture. In this context, this work aims to understand deeply the interactions in IMAC and surface plasmon resonance (SPR) in order to validate experimentally the analogy between both technologies and to be further able to perform IMAC modeling in the next work using peptide sorption isotherm parameters obtained from SPR. Indeed, chromatography modeling can be used to predict separation of MCPs in IMAC and the knowledge of peptide sorption isotherm obtained from SPR is a crucial step. For this purpose, 22 peptides were selected and investigated in IMAC using HisTrap X-Ni2+ and HiFliQ NTA-Ni2+ columns and were also studied in SPR as well. Results showed that peptides with histidine residues had good affinity to Ni2+, while the high positive charge of peptides was responsible of ionic interactions. Further, most of the peptides with good retention time in IMAC showed a good affinity in SPR as well, which validated experimentally the SPR-IMAC analogy.

Theoretical Design of Near-Infrared Tunable Surface Plasmon Resonance Biosensors Based on Gate-Controlled Graphene Plasmons

A tunable near-infrared surface plasmon resonance (SPR) biosensor based on gate-controlled graphene plasmons is numerically investigated by using the finite element method (FEM) and the transfer matrix method (TMM). The novel properties of chemical potential sensing make the proposed sensor promising in the application of ultra-sensitive and highly specific biosensing technology. The sensitivity of chemical potential sensing in wavelength interrogation mode can be calculated to be 1.5, 1.89, 2.29, 3.21, 3.73 and 4.68 nm/meV, respectively, at the resonance wavelengths of 1100, 1200, 1310, 1550, 1700 and 1900 nm. The figure of merit (FOM) achieves 129.3, 101.1, 84.5, 67.7, 69.5 and 59.7 eV−1, respectively, at these resonance wavelengths. The sensitivity of chemical potential sensing in gate voltage interrogation mode also can be calculated to be 156.9822, 143.6147, 131.0779, 111.0351, 101.3415 and 90.6038 mV/meV, respectively, at the incident wavelengths of 1100, 1200, 1310, 1550, 1700 and 1900 nm. The FOM achieves 135.6, 103.0, 88.9, 62.2, 66.6 and 61.5 eV−1, respectively, at these incident wavelengths. Theoretical estimates suggest that the limit of detection (LOD) of the sensor’s DNA sensing can reach the level of femtomolar or even attomolar, comparable to and even lower than that of 2D nanomaterial-enhanced metal SPR sensors with AuNPs as a sensitivity enhancement strategy. The feasibility of preparation and operation of this new concept SPR biosensor is also analyzed and discussed.

Photo‐Mediated Cascade Growth of Ag Nanocrystals in Flow Reactors for High‐Performance Flexible Transparent Electrodes

AbstractPhoto‐mediated synthesis wielding localized surface plasmon resonance (LSPR) of nanoscale metal is widely applied to sculpt silver (Ag) nanocrystals with controllable dimensions and morphologies. However, this photo‐mediated strategy remains underutilized owing to low efficiency and inferior quality in conventional batch reactors. Here, the effective synthesis of Ag nanocrystals is demonstrated via flow reactors and elucidates the photo‐mediated anisotropic growth mechanism. The investigation reveals that the intersection between excitation wavelengths and LSPR of Ag nanocrystals is a prerequisite for their growth. The final morphology is highly correlated with excitation wavelengths, which modulate the redox potential (reaction barrier) of Ag nanocrystals featuring distinct defective structures. Thus, by utilizing tandem‐connected flow reactors, size‐controllable Ag nanoplates can be yielded in a highly efficient cascade growth manner. In addition, composite conductive ink (submicron/nano‐Ag particles) is employed to create high‐performance flexible transparent electrodes. A sixfold conductivity enhancement especially under low sintering temperature (<80 °C), along with superior transmittance (over 90%), and distinguished cyclic durability (negligible resistance change over 1000 cycles) are achieved simultaneously. The study not only establishes comprehensive insights into the acquisition of well‐defined Ag nanocrystals in flow reactors but also ushers in enormous feasibility toward high‐performance and cost‐effective flexible electronics.

Insight into the synergistic effect of metal surface plasmon resonance and clay loading to boost the antibiotics degradation of Bentonite/BiOBr/bismuth

Insight into the synergistic effect of metal surface plasmon resonance and clay loading to boost the antibiotics degradation of Bentonite/BiOBr/bismuth

Visible light driven hydrogen generation and pollutant degradation with Au loaded 2D/2D heterojunctional nanocomposite of MoS2 and g-C3N4

The growing energy crises and accumulating organics in water have caused significant threats to the economy and environment in the current time. To minimize the impact of these problem, here we established a 2D/2D interaction between MoS2 and g-C3N4 through simple hydrothermal and calcination processes and was further loaded with Au nanoparticles. The visible light driven photocatalysis was arrived by splitting water and degrading hazardous pollutant in wastewater. The large surface to surface interaction exceedingly increased the charge transfer and separation for highly speedy photocatalysis. About 220 μmol H2 was available from 2Au/9MS/CN nanocomposite in 1 h which was 24.44 times higher than the amount available from bare g-C3N4. Further, all the photocatalysts delivered acceptable eradication activity for 2-chlorphenol and 68% pollutant was removed in 1 h. The highly accelerated photocatalysis with 2Au/9MS/CN nanocomposite is related to the extended visible light purchasing due to the surface plasmon resonance of the Au metal and enhanced charge separation arrived from the well-established 2D/2D heterojunction. We hope that this work will attract major attention of the researchers towards the preparation of dimension-matched 2D/2D heterojunctional nanocomposites for energy production and eradication of organics from water.

Biofilm growth monitoring using guided wave ultralong-range Surface Plasmon Resonance: A proof of concept

Unwelcomed biofilms are problematic in food industries, surgical devices, marine applications, and wastewater treatment plants, essentially everywhere where there is moisture. Very recently, label-free advanced sensors such as localized and extended surface plasmon resonance (SPR) have been explored as tools for monitoring biofilm formation. However, conventional noble metal SPR substrates suffer from low penetration depth (100–300 nm) into the dielectric medium above the surface, preventing the reliable detection of large entities of single or multi-layered cell assemblies like biofilms which can grow up to a few micrometers or more. In this study, we propose using a plasmonic insulator-metal-insulator (IMI) structure (SiO2–Ag–SiO2) with a higher penetration depth based on a diverging beam single wavelength format of Kretschmann configuration in a portable SPR device. An SPR line detection algorithm for locating the reflectance minimum of the device helps to view changes in refractive index and accumulation of the biofilm in real-time down to 10−7 RIU precision. The optimized IMI structure exhibits strong penetration dependence on wavelength and incidence angle. Within the plasmonic resonance, different angles penetrate different depths, showing a maximum near the critical angle. At the wavelength of 635 nm, a high penetration depth of more than 4 μm was obtained. Compared to a thin gold film substrate, for which the penetration depth is only ∼200 nm, the IMI substrate provides more reliable results. The average thickness of the biofilm after 24 h of growth was found to be between 6 and 7 μm with ∼63% live cell volume, as estimated from confocal microscopic images using an image processing tool. To explain this saturation thickness, a graded index biofilm structure is proposed in which the refractive index decreases with the distance from the interface. Furthermore, when plasma-assisted degeneration of biofilms was studied in a semi-real-time format, there was almost no effect on the IMI substrate compared to the gold substrate. The growth rate over the SiO2 surface was higher than on gold, possibly due to differences between surface charge effects. On the gold, the excited plasmon generates an oscillating cloud of electrons, while for the SiO2 case, this does not happen. This methodology can be utilized to detect and characterize biofilms with better signal reliability with respect to concentration and size dependence.

Enhanced interfacial charge transfer and photothermal effect via in-situ construction of atom co-sharing Bi plasmonic/Bi4O5Br2 nanosheet heterojunction towards improved full-spectrum photocatalysis

Constructing a plasmonic heterojunction photocatalyst is a prospective approach to improve full-spectrum photocatalytic performance. However, low interfacial charge transfer efficiency due to lattice mismatch severely limits its photocatalytic performance. Herein, a Bi atom co-sharing Bi/Bi4O5Br2 plasmonic heterojunctions were fabricated via in-situ reduction. Experimental characterizations and theoretical calculations demonstrate that the co-sharing Bi atom enables intimate contact in the heterointerface, significantly promoting interfacial charge transfer and separation. In addition, Bi metal's surface plasmon resonance effect extends the photoresponse to the near-infrared region and enhances the photothermal performances, significantly improving solar energy's utilization efficiency. By these prominent features, the optimized Bi/Bi4O5Br2 heterojunctions show that the photocatalytic degradation ratio of BPA reaches 100 % within 40 min under full-spectrum irradiation, which is about three times higher than that of Bi4O5Br2. Moreover, the photocatalytic efficiency was significantly increased by 7.5 times with the increase in temperature under NIR light irradiation due to the photothermal effect. This work offers new insights into the rational design of low-cost, highly efficient, and stable Bi-based plasmonic heterojunction photocatalysts for full solar spectrum utilization by integrating plasmonic nanostructures and photothermal effect.

Probe type TFBG-excited SPR fiber sensor for simultaneous measurement of multiple ocean parameters assisted by CFBG.

The tilted fiber Bragg grating(TFBG), chirped fiber Bragg grating(CFBG), Vernier effect and metal surface plasmon resonance(SPR) effect are effectively combined to form a probe type fiber sensor for simultaneous measurement of seawater salinity, temperature and depth(STD). The SPR effect excited by the TFBG is achieved by covering a gold layer around the TFBG, which is used to measure the refractive index (RI) of seawater. The core mode of TFBG is used to detect the change of seawater temperature and the measurement of TFBG reflection spectrum is realized by inscribing a CFBG after the TFBG, which makes the sensor have a probe type design and more beneficial to practical applications. The fusion of quartz micro-spheres on the end face of the sensing fiber and the parallel connection of an Fabry Perot(F-P) interference cavity enables the use of Vernier effect to detect the depth of the ocean. Femtosecond laser line-by-line method is used to the inscribing of TFBG, which allows the grating parameters to be changed flexibly depending on the desired spectrum. The experimental results show that the temperature sensitivity is 10.82pm/°C, the salinity sensitivity is 0.122nm/g/Kg, the depth sensitivity is 116.85 pm/m and the depth can be tested to 1000 m or even deeper.

Tunable Bi-bridge S-scheme Bi2S3/BiOBr heterojunction with oxygen vacancy and SPR effect for efficient photocatalytic reduction of Cr(VI) and industrial electroplating wastewater treatment

Surface plasmon resonance (SPR), oxygen vacancy modification and the construction of S-scheme heterostructure are important strategies to enhance visible-light absorption and improve photocatalytic performance. Here, a Bi-bridge S-scheme Bi2S3/BiOBr heterojunction (Bi2S3/Bi/BiOBr) with oxygen vacancies and SPR effect of Bi metal was prepared by one-pot solvothermal method for Cr(VI) reduction. The 3:10 Bi2S3/Bi/BiOBr exhibited superior visible-light photocatalytic reduction performance with 95.82 % Cr(VI) removal efficiency. Additionally, the 3:10 Bi2S3/Bi/BiOBr showed high stability and good anti-interference ability, and can effectively remove Cr(VI) from industrial electroplating wastewater with 97 % of Cr(VI) removal efficiency and residual Cr(VI) concentration of 0.304 mg/L, meeting the industrial effluent standard, which made it potentially attractive for real wastewater treatment. The enhanced photocatalytic performance of Bi2S3/Bi/BiOBr heterojunction was attributed to Bi metal SPR effect and the role of Bi as e-bridge, the presence of oxygen vacancies, the formation of internal electric field and S-scheme charge transfer, which were confirmed by various experimental results and density functional theory (DFT) calculations. This work provided theoretical and experimental reference for the construction of stable S-scheme heterojunctions with high catalytic activity and anti-interference, and a reliable solution for Cr(VI) removal from electroplating wastewater.

Plasma Ag-loaded bandgap variational Zn1-xMgxO-enhanced charge separation for photoelectrochemical water oxidation of CuWO4 photoanodes

The recombination of photogenerated carriers and sluggish surface oxidation kinetics severely inhibited the development of copper tungstate (CuWO4) photoanode photoelectrochemical (PEC) water oxidation. Herein, the Zn1-xMgxO-modified CuWO4 photoanode ameliorated the vital matter of easy recombination of electron-hole pairs, where the transformation of the heterojunction type (type I to type II) between Zn1-xMgxO and CuWO4 played a crucial role in the extraction of carriers. Further, the effective charge separation was obtained utilizing the local surface plasmon resonance (LSPR) of plasma metal (Ag), which facilitated the PEC water oxidation reaction. Besides, the surface states trapped/stored holes and reduced charge transfer resistance, thus facilitating charge transfer. The overlap of the fillable surface states with filled redox coupled states ensured the enhancement of the water oxidation kinetics, which further promoted the charge transfer. As a result, the optimized CuWO4/Zn0.7Mg0.3O/Ag photoanode showed significant advancement in photocurrent density (1.71 mA/cm2 at 1.23 V vs. RHE), electrochemical impedance and stability. This work emphasized the interfacial structure modulation of two strategies that potentially provide more ideas and options for the design of other efficient photoanodes.

Large-area metal surface plasmon–polymer coupled nanocomposite thin film at air–liquid interface for low voltage operated high-performance photodetector

Coupling of metal surface plasmon resonance (SPR) with organic molecules and successive fabrication of large-area films is an effective approach for enhancing photogenerated excitons while retaining their optical thickness. In this regard, we present the facile synthesis of a silver nanoparticle (Ag NP) SPR–polymer coupled large-area nanocomposite thin film (8 ± 0.5-cm-diameter circular film) at the air–liquid interface and the fabrication of a high-performance visible-region photodetector (PD). The formation of nanocomposite films was investigated via multiple techniques, which revealed the formation of an SPR/organic molecule unified system. The photoresponse of the nanocomposite film was examined by fabricating a sandwich-structure ITO/PQT-12-Ag NP/Al Schottky device PD and measuring the photocurrent; responsivity R(λ), which was 9.624 × 104, 3.384 × 104, and 2.372 × 104 mA/W; external quantum efficiency, which was 19.03 × 103, 8.92 × 103, and 5.54 × 103; and detectivity (D), which was 1.06 × 1013, 3.70 × 1012, and 2.60 × 1012 Jones, at a bias voltage of −1.5 V for 627-nm (red), 470-nm (blue), and 530-nm (green) light, respectively. The high performance of the PDs in the visible region was discussed according to the spectral, KPFM, morphological, and energy band diagram results.

Z-scheme Au@TiO2/Bi2WO6 heterojunction as efficient visible-light photocatalyst for degradation of antibiotics

Semiconductor photocatalysis can be regarded as one of effective strategies to overcome the great challenges encountered with conventional technologies for environmental remediation. In this research, Z-scheme heterostructure composed of core–shell Au@TiO2 nanoparticles and flower-like Bi2WO6 nanosheets has been successfully prepared through the reverse micelle sol–gel method followed by a hydrothermal process. The structural characteristics, chemical compositions and photoelectrochemical properties of this ternary composite photocatalyst (Au@TiO2/Bi2WO6) were further investigated in detail. Benefitted from the synergy of the heterojunction construction and metallic surface plasmon resonance effect, the Au@TiO2/Bi2WO6 with an optimal mass ratio of Au@TiO2 to Bi2WO6 exhibited the significantly enhanced photocatalytic activity for degradation of antibiotics under visible-light irradiation, in which the degradation efficiency of sulfamethoxazole (SMX) and tetracycline hydrochloride (TC) could be up to 96.9% and 95.0% within 75 min, respectively. The reaction rate constant for SMX and TC degradation was calculated to be around 0.0425 min−1 and 0.0314 min−1, which has 7.2 times and 1.9 times enhancement compared with single Bi2WO6, respectively. In addition, the cyclic stability and photocatalytic mechanism of Au@TiO2/Bi2WO6 were further verified. Our primary results provide a feasible strategy to develop core–shell heterostructured photocatalysts with superior performance for the efficient removal of low-concentration antibiotics in water.

Direct Z-scheme In2S3/Bi2S3 heterojunction-based photoelectrochemical aptasensor for detecting oxytetracycline in water

The threats of the discharge of antibiotics to the environment and ecology cannot be ignored. Accurate detection of the antibiotic concentration in the matrix is important to determine the contamination status. In this work, we proposed an In2S3/Bi2S3 heterojunction-based photoelectrochemical (PEC) sensor to detect antibiotics in water. The Z-scheme heterostructure promoted the separation of photo-generated carriers and achieved a stronger light response. Gold nanoparticles electrodeposited on the heterojunction surface as anchoring points slightly increased the photocurrent due to its metallic properties and surface plasmon resonance effect. Oxytetracycline (OTC), a broad-spectrum antibiotic was used as the target to test the performance of PEC sensor. Specific junction aptamer was used as the probe to recognize OTC to avoid the interference of complex components in matrix. The composition of In2S3/Bi2S3 heterojunction and the measurement conditions were optimized before the detection of OTC. The presence of OTC resulted in the increase in steric hindrance and the decrease in photocurrent. The PEC aptasensor showed a linear detection range of 0.04–10 nM and a calculated detection limit of 0.007 nM for OTC. In addition, the PEC aptasensor could distinguish OTC from other antibiotics and exhibited a stable light response under 20 continuous on-off irradiations. The practicability of the PEC aptasensor was verified by detecting OTC in river water. The proposed Z-scheme In2S3/Bi2S3 heterojunction-based PEC aptasensor can offer analysis applications for other antibiotics in water by substituting the corresponding aptamer.

Dispersion Management for Hyperbolic-Metamaterials Based Surface Plasmon Resonance Sensor Towards Extremely High Sensitivity

Extremely high sensitivity is the long-time pursing goal for surface plasmon resonance (SPR) sensors, which means the capability to detect analytes with lower concentrations or interactions for smaller biomolecules. It was suggested that a flat dispersion for the plasmon material enables to enhance the sensitivity dramatically. However, the regulation ability of inherent dispersion in natural materials is limited. With the appearance of hyperbolic metamaterials (HMMs), the management of the plasmon materials dispersion becomes possible. In this paper, the HMMs with metal/dielectric multilayer structure are proposed to construct the SPR sensors. Through numerical simulations and theoretical analysis, we find that the flat dispersion in the HMM structure could significantly benefit the sensitivity improvement for HMM-SPR sensors. As a result, the proposed HMM-SPR sensor obtains an ultrahigh sensitivity of 34.00 μm/RIU in the experiment, which is one order higher in magnitude than that of the conventional monolayer metallic SPR sensors. Thus, this research shows insight into understanding the dependence of the HMM-SPR sensitivity on dispersion management and provides a practical methodology to develop extremely high-sensitivity SPR sensors based on artificial plasmon materials.

Non-noble metal plasmonic enhanced photoelectrochemical sensing of chlorpyrifos based on 1D TiO2-x/3D nitrogen-doped graphene hydrogel heterostructure.

Low-cost and resource-rich non-noble metal plasmonic materials have attracted tremendous attention as potential substitutes for plasmonic noble metals. Herein, 3D nitrogen-doped graphene hydrogels (NGH) decorated with Ti3+ self-doped 1D rod-shaped titanium dioxide nanorods (TiO2-x NR), 10-25nm in size, were prepared by a facile one-step method. It was found that the as-fabricated TiO2-x NR/NGH showed a synergistic effect, displaying enhanced photoelectrochemical (PEC) activity by controlling the nanoscale architecture and improving the electronic properties, while also producing abundant oxygen vacancies, which extended the light harvesting and suppressed the recombination of electron-hole pairs induced by the non-noble metal surface plasmon resonance (SPR) effect. In particular, the transient-state photocurrent intensity of the TiO2-x NR/NGH composites was 5.1 times as high as that of pure TiO2. Therefore, the TiO2-x NR/NGH composites could serve as a substrate material for PEC sensing, providing a good basis for selective and sensitive detection of chlorpyrifos. Under optimal conditions, the constructed PEC sensor was found to have several advantages including a broad linear range (0.05ng/mL-0.5μg/mL), low detection limit (0.017ng/mL), and considerable stability, demonstrating that the sensor may offer a promising route in the field of environmental analysis.