Localized Surface Plasma Resonance Research Articles

Au@Pt nanoparticles-based signal-enhanced lateral flow immunoassay for ultrasensitive naked-eye detection of SARS-CoV-2.

With SARS-CoV-2 N protein as a model target, a signal-enhanced LFIA based on Au@Pt nanoparticles (NPs) as labelsis proposed. This Au@Pt NPs combined the distinguished localized surface plasma resonance (LSPR) effect of Au NPs and the ultrahigh peroxidase-like catalytic activity of Pt NPs. Au@Pt NPs could trigger substrate chromogenic reaction, generating acolor signal orders of magnitude darker than their intrinsic color. In the detection, after the coloration of the strips, 3,3',5,5'-tetramethylbenzidine (TMB) and H2O2 were added, and adark blue chelate (OxTMB) was produced soon, enhancing the band color significantly. After the signal amplification, the naked-eye detection limit for N protein reached 40pg/mL. The detection sensitivity enhanced more than 1000 times than that without signal amplification. Compared with mainstream LFIA requiring complex readout instruments, theAu@Pt-based LFIA achieved a comparable sensitivity usingnaked eyesdetection. This point is crucial, especially for unprofessional users or low-resource areas. Hence, this signal-enhanced LFIA may serve as a sensitive, cost-effective, and user-friendly detection method. It can shorten the testing window period and help identify early infections.

Broadband Solar Absorber and Thermal Emitter Based on Single-Layer Molybdenum Disulfide.

In recent years, solar energy has become popular because of its clean and renewable properties. Meanwhile, two-dimensional materials have become a new favorite in scientific research due to their unique physicochemical properties. Among them, monolayer molybdenum disulfide (MoS2), as an outstanding representative of transition metal sulfides, is a hot research topic after graphene. Therefore, we have conducted an in-depth theoretical study and design simulation using the finite-difference method in time domain (FDTD) for a solar absorber based on the two-dimensional material MoS2. In this paper, a broadband solar absorber and thermal emitter based on a single layer of molybdenum disulfide is designed. It is shown that the broadband absorption of the absorber is mainly due to the propagating plasma resonance on the metal surface of the patterned layer and the localized surface plasma resonance excited in the adjacent patterned air cavity. The research results show that the designed structure boasts an exceptional broadband performance, achieving an ultra-wide spectral range spanning 2040 nm, with an overall absorption efficiency exceeding 90%. Notably, it maintains an average absorption rate of 94.61% across its spectrum, and in a narrow bandwidth centered at 303 nm, it demonstrates a near-unity absorption rate, surpassing 99%, underscoring its remarkable absorptive capabilities. The weighted average absorption rate of the whole wavelength range (280 nm-2500 nm) at AM1.5 is above 95.03%, and even at the extreme temperature of up to 1500 K, its heat radiation efficiency is high. Furthermore, the solar absorber in question exhibits polarization insensitivity, ensuring its performance is not influenced by the orientation of incident light. These advantages can enable our absorber to be widely used in solar thermal photovoltaics and other fields and provide new ideas for broadband absorbers based on two-dimensional materials.

Ultrafast dynamics and mechanism of structure formation in titanium nitride upon femtosecond laser irradiation for plasmonic enhanced photothermal effect

Femtosecond laser has great potential in controlling the surface structure of titanium nitride (TiN) to promote plasmonic photothermal effect. Studying the mechanism of femtosecond laser irradiation on the surface and inside of the TiN benefits the photothermal microdevices. Ultrafast dynamics of electrons and lattices of TiN films with different thicknesses were first studied through pump-probe technique, which found that the electron density is easier to reach the maximum on the surface than the electrons in deep-layers. High-frequency ripple was formed by tiny nucleation resulted from weak eruption of surface material on the thin TiN film, and low-frequency ripple was emerged through large nucleation of material clusters simultaneously on the thick TiN film. The blue shift and intensity changes of Raman peak on 200 nm TiN film indicate the heterogeneous structure changed from TiN to TiN0.26 after laser processing, and the vacancy occupies causes the lattice vibration weakened. The 200 nm TiN film after processing shows enhanced local surface plasma resonance absorption effect, which induced the reflectivity is reduced by 30 %, and the light and thermal conversion efficiency increased by 80 %. These results proved the promising utilization of TiN in biological and medical applications, energy collection and thermal auxiliary magnetic records.

Advanced bionic inverted coral solar evaporator: Enhancing sustainable water utilization with efficient and salt-resistant evaporation

Interfacial solar-driven steam generation technology shows great potential in addressing desalination and wastewater purification. However, there is a lack of advanced evaporators with high evaporation efficiency and salt tolerance, which is an obstacle to its widespread application. Drawing inspiration from marine coral structures, we develop a bionic inverted coral-type 3D solar evaporator with an array structure using structural engineering design. The microscopically porous vertical channel structure within the overall skeleton enhances the longitudinal reflux of salt ions and water evaporation, while macroscopic gaps in the bionic coral branching facilitate lateral advection–diffusion of salt ions. Numerical simulations confirm that this bionic coral structure design improves the diffusion rate of concentrated brine. Due to the localized surface plasma resonance and the Marangoni effect, the evaporator achieves remarkable water evaporation performance (evaporation rate: 2.72 kg m−2h−1, energy efficiency: 95.8 %) and operates reliably even under 20 % brine concentration (evaporation rate: 2.65 kg m−2h−1) without significant salt crystallization. Furthermore, it exhibits good wettability and robust mechanical properties, capable of withstanding a wide range of temperatures. The efficient and salt-resistant evaporation makes it valuable for applications including desalination, various wastewater treatments, and agricultural irrigation, thereby promoting the sustainable utilization of water resources.

2D ordered porous VO2-based composite film with enhanced thermochromism performance and high stability for smart windows

Thermochromic vanadium dioxide (VO2) can autonomously adjust near-infrared light transmittance in response to the external temperature changes, offering a significant reduction in building energy consumption when applied it in smart window. However, it is a big challenge for simultaneous optimization of visible light transmittance, solar modulation ability, and stability in VO2. To address such a big challenge, this study successfully prepared a 2D ordered porous VO2@Zn3V3O8 composite film. The as-obtained film exhibits exceptional optical performance with a visible light transmittance (Tlum) of 62.75 % and the solar modulation ability (ΔTsol) of 10.62 %, based on the anti-reflective effects of porous structure and the localized surface plasma resonance (LSPR) absorption of independently distributed VO2 nanoparticles. In addition, the composite structural film showcases excellent environmental durability that 80 % of ΔTsol could be retained after 30 days aging under the conditions of 50 % humidity and 100 °C. This work propels the practical application of VO2 smart windows and offers valuable insights for the design of composite structures.

High performance CH3NH3PbI3 perovskite photodetector functionalized by T-Ag plasmonic nanostructure

Photodetectors with ultrathin thickness and high efficiency are increasingly needed in the developing of wearable devices. However, the very limited active layer thickness has seriously restricted the photoelectric conversion efficiency. Here, the optical nanostructure fabricated with the assistance of self-assembly polystyrene mask layer has been integrated to increase the light absorption capacity by simultaneously utilizing the local surface plasma resonance, gap plasma, and the microcavity resonance effect. With the incorporation of triangular silver (T-Ag) nanostructure, the photogenerated current and response speed have significantly enhanced 481.25% and 26.30%, respectively. This strategy provides a viable way to design high-efficiency ultra-thin photodetectors.

Near-infrared responsive gold nanorods for highly sensitive colorimetric and photothermal lateral flow immuno-detection of SARS-CoV-2.

The highly infectious characteristics of coronavirus disease 2019 (COVID-19), which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), highlight the necessity of sensitive and rapid nucleocapsid (N) protein-based antigen testing for early triage and epidemic management. In this study, a colorimetric and photothermal dual-mode lateral flow immunoassay (LFIA) platform for the rapid and sensitive detection of the SARS-CoV-2 N protein was developed based on gold nanorods (GNRs), which possessed tunable local surface plasma resonance (LSPR) absorption peaks from UV-visible to near-infrared (NIR). The LSPR peak was adjusted to match the NIR emission laser 808 nm by controlling the length-to-diameter ratio, which could maximize the photothermal conversion efficiency and achieve photothermal detection signal amplification. Qualitative detection of SARS-CoV-2 N protein was achieved by observing the strip color, and the limit of detection was 2 ng mL-1, while that for photothermal detection was 0.096 ng mL-1. Artificial saliva samples spiked with the N protein were analyzed with the recoveries ranging from 84.38% to 107.72%. The intra-assay and inter-assay coefficients of variation were 6.76% and 10.39%, respectively. We further evaluated the reliability of this platform by detecting 40 clinical samples collected from nasal swabs, and the results matched well with that of nucleic acid detection (87.5%). This method shows great promise in early disease diagnosis and screening.

Resonance-Assisted Surface-Enhanced Raman Spectroscopy Amplification on Hierarchical Rose-Shaped MoS2/Au Nanocomposites.

Surface-enhanced Raman spectroscopy (SERS) has emerged as a highly sensitive trace detection technique in recent decades, yet its exceptional performance remains elusive in semiconductor materials due to the intricate and ambiguous nature of the SERS mechanism. Herein, we have synthesized MoS2 nanoflowers (NFs) decorated with Au nanoparticles (NPs) by hydrothermal and redox methods to explore the size-dependence SERS effect. This strategy enhances the interactions between the substrate and molecules, resulting in exceptional uniformity and reproducibility. Compared to the unadorned Au nanoparticles (NPs), the decoration of Au NPs induces an n-type effect on MoS2, resulting in a significant enhancement of the SERS effect. This augmentation empowers MoS2 to achieve a low limit of detection concentration of 2.1 × 10-9 M for crystal violet (CV) molecules and the enhancement factor (EF) is about 8.52 × 106. The time-stability for a duration of 20 days was carried out, revealing that the Raman intensity of CV on the MoS2/Au-6 substrate only exhibited a reduction of 24.36% after undergoing aging for 20 days. The proposed mechanism for SERS primarily stems from the synergistic interplay among the resonance of CV molecules, local surface plasma resonance (LSPR) of Au NPs, and the dual-step charge transfer enhancement. This research offers comprehensive insights into SERS enhancement and provides guidance for the molecular design of highly sensitive SERS systems.

Daylight-driven catalytic removal of pyridine over Ag-embedded ZnO porous nanosheets

Structure of heterogeneous photocatalyst with adequate coupling interface has an important effect on energy transfer and photoinduced electron-hole pairs separation. In this work, Ag-embedded ZnO heterogeneous porous nanosheets (PNSs) have been synthesized by thermal pyrolyzing of Ag2CO3-modified Zn5(CO3)2(OH)6 nanosheets at 400 °C. Photoelectron spectra and X-ray diffraction measurements demonstrate that there exists an adequate coupling between Ag and ZnO phase. Ag-embedded ZnO PNSs, in contrast to bare ZnO PNSs, performs 6-fold enhancement in natural-daylight-driven degradation of pyridine which requires participation of ·OH radicals. This result demonstrates that the adequate coupling interface between Ag and ZnO for Ag-embedded ZnO PNSs promotes an energy transfer from local surface plasma resonance of Ag nanoparticles to bound excitons in ZnO region, activating them to dissociate into free photoinduced carriers. In addition, external control experiments indicate that the best photocatalytic degradation is obtained in the 7–10 pH range of 10 mg/L pyridine solution in presence of 0.5 g/L photocatalyst dosage. The optimal Ag-embedded ZnO PNSs under outdoor daylight irradiation also performs an efficiently photocatalytic degradability for pyridine present in ground water. Our work provides a new approach to fabricate ZnO-based photocatalyst with efficient energy transfer for treating stubborn organics present in polluted water.

SnO2 tetragonal nanonails with enhanced optical and photoelectric performances via localized surface plasmon resonance effect of Au nanoparticles

Enhanced optical and photoelectric characteristics of semiconductors via Localized Surface Plasma Resonance (LSPR) effect strategy has drawn extensive attentions and researches in the fields of semiconductor industry. Specially, Au/SnO2 tetragonal nanonails (TNs) Schottky heterojunctions have been innovatively synthesized by modified CVD and hydrothermal methods. Au/SnO2 TNs Schottky heterojunction fabricated at the volume ratio of 0.5/45 HAuCl4/Water (0.5 Au/SO) exhibits the remarkable photocurrent density about of 52.8 μA cm−2 at 0.5 V vs. Ag/AgCl, which is about of 1.5 and 1.2 times than that of SO-550 (36.4 μA cm−2) and 0.7 Au/SO (44.8 μA cm−2) photoelectrodes, respectively. Optical absorption properties of all Au/SnO2 TNs Schottky heterojunctions have obviously improved in ultraviolet–visible regions due to the strong LSPR effect of Au nanoparticles (NPs). Au NPs also act as photosensitizers, which can generate more high-energy active electrons by LSPR excitation and then inject into CB of SnO2 TNs photoelectrode. This process can effectively enhance separation and transportation efficiencies of photogenerated charge carriers, further improving photoelectric performances of Au/SnO2 TNs Schottky heterojunctions. This work can provide novel strategies to synthesize one-dimensional metallic oxide photoelectrodes and Schottky heterojunctions, and further laying the foundation for exploring the interface/surface novel effects of heterojunctions at the applications of catalysis, sensors or detection fields.

Preparation of LSPR enhanced Z-scheme Pd/WO3@SnO2 for photocatalytic decomposition of organic compounds under simulated sunlight

The decoration of semiconductor photocatalysts with metal nanoparticles (NPs) is an efficient strategy for improving their performance via localized-surface-plasma-resonance (LSPR). For this study, a LSPR enhanced Z-scheme Pd/WO3@SnO2 photocatalyst was synthesized, which revealed excellent photocatalytic performance and reusability against Rhodamine B (RhB) with degradation rate of 100 % after 1 h under simulated sunlight. The reaction rate constants (k) of the Pd/WO3@SnO2 were ∼4.9, 3.5, and 2.1 times higher than those of the WO3, SnO2, and WO3@SnO2, respectively. In this Z-scheme-structure, the transfer efficacy of photogenerated electrons was significantly promoted due to integrated electric-field between the SnO2 and WO3, which was supported by experimental results and theoretical calculations. The deposited Pd nanoparticles served as an electron-transfer-bridge, as well as a LSPR excitation source, which played significant role in the degradation of RhB. The photodecomposition pathway of RhB was explored, and the toxicities of the intermediates were evaluated. Moreover, tetracycline (TC), chlortetracycline-hydrochloride (CTC), doxycycline-hydrate (DOX), and oxytetracycline (OTC) were tested as common antibiotic models to verify the effectiveness of the catalysts. The degradation efficiencies for TC, CTC, DOX, and OTC over Pd/WO3@SnO2 attained 90.98 %, 96.33 %, 75.37 %, and 50.90 %, respectively, under simulated sunlight, which confirmed its strong potential for the removal of recent pollutants. Experiments and electron paramagnetic resonance (EPR) tests indicated that •O2– served as the major active species in the photocatalysis process, while •OH and h+ played secondary roles. Finally, an LSPR enhanced direct Z-scheme mechanism was proposed. This study provides a rational design strategy for the development of more efficient Z-scheme photocatalysts that exploit the LSPR-effect for photodecomposition of organic pollutant compounds.

Plasmonic Cu2-xSe Mediated Colorimetric/Photothermal Dual-Readout Detection of Glutathione.

Plasmonic nanomaterials have attracted great attention in the field of catalysis and sensing for their outstanding electrical and optical properties. Here, a representative type of nonstoichiometric Cu2-xSe nanoparticles with typical near-infrared (NIR) localized surface plasma resonance (LSPR) properties originating from their copper deficiency was applied to catalyze the oxidation of colorless TMB into their blue product in the presence of H2O2, indicating they had good peroxidase-like activity. However, glutathione (GSH) inhibited the catalytic oxidation of TMB, as it can consume the reactive oxygen species. Meanwhile, it can induce the reduction of Cu(II) in Cu2-xSe, resulting in a decrease in the degree of copper deficiency, which can lead to a reduction in the LSPR. Therefore, the catalytic ability and photothermal responses of Cu2-xSe were decreased. Thus, in our work, a colorimetric/photothermal dual-readout array was developed for the detection of GSH. The linear calibration for GSH concentration was in the range of 1-50 μM with the LOD as 0.13 μM and 50-800 μM with the LOD as 39.27 μM. To evaluate the practicability of the assay, tomatoes and cucumbers were selected as real samples, and good recoveries indicated that the developed assay had great potential in real applications.

Fine-tuning of plasmonics by Au@AuY/Au core–shell nanoparticle monolayer for enhancement of third-order nonlinearity

The manipulation of plasmonics on noble metal nanoparticles (NPs) is of great interest in developing nonlinear photonic devices, such as all-optical switches and frequency combs. An Au@AuY-core/Au-shell nanoparticle (Au@AuY/Au NP) monolayer is proposed for the fine-tuning of plasmonics and enhanced third-order nonlinearity. Based on the different thermodynamic mechanisms of Au and Y ions, the compact Au@AuY/Au core–shell architectures are designed and surface-modified in fused silica (SiO2) with enhanced free electron density, mobility, and quantum size effect. The flexible modulation of plasmonics is realized, resulting in significant absorption enhancement (165% for interband absorption and 38% for free electron absorption, respectively) and fine-tuning of the localized surface plasma resonance (LSPR) band. In addition, the physical mechanism is investigated by density functional theory (DFT) and Mie theory, which reveals a transition from size-independence to size-dependence of LSPR owing to the synergistic effect of multiple physical factors such as free electron density and mobility. With the above advantages, the third-order nonlinearity is enhanced by 4.4 times compared with traditional Au NPs. It indicates the significant potential of Au@AuY/Au core–shell NP monolayer in the performance improvement of nonlinear photonic devices.

Nitrogen deficient porous C3N4 on carbon cloth as photoanode with enhanced photoelectrocatalytic activity in hydrogen production

Photoelectrochemical water splitting is an effective way to convert solar energy into hydrogen energy. In this manuscript, Pt-loaded nitrogen-deficient C3N4 was firmly grown on carbon cloth as a photoanode for efficiently photoelectrocatalytic (PEC) water splitting to produce hydrogen. The PEC activity of C3N4 was increased from 0 (C3N4 powder) to 2.45 mmol/h/m2. The performance was further improved to 13.49 mmol/h/m2 after the loading of Pt nanoparticles. The significant improvement in PEC performance can be summarized as the following points: (a) Carbon cloth as substrate enhanced the conductivity of C3N4 and further facilitated photogenerated charges' transfer, (b) enhanced optical absorption and emerged more active edges due to nitrogen defects and porous structures, (c) improved charge transfer and separation efficiency and increased specific surface area at nitrogen-deficient active sites, (d) Pt nanoparticles with local surface plasma resonance (LSPR) effect absorbed more optical electrons and enhanced the rate of electron transport. Therefore, Pt-NCN-CC exhibited great potentials as a photoanode for highly efficient hydrogen production.

Ag quantum dots decorated ultrathin g-C3N4 nanosheets for boosting degradation of pharmaceutical contaminants: Insight from interfacial electric field induced by local surface plasma resonance

The design of photocatalysts that can generate local surface plasmon resonance effect (LSPR) is expected to be an effective strategy for improving photocatalytic activity. However, the photocatalytic mechanism of interfacial electric field induced by quantum dot plasma is still unclear. Herein, different amount of Ag quantum dots was loaded on ultrathin carbon nitride sheets (Ag/UCN) to construct Schottky junction. The 1:1 Ag/UCN Schottky junction exhibits excellent photocatalytic activity in ofloxacin degradation with 95.2% removal, and is highly stable during four consecutive photocatalytic cycles. Ag/UCN can also effectively mineralize ofloxacin with 65.8% TOC removal, and NH4+, F− and NO3− were detected in the degradation solution of ofloxacin. Moreover, Ag/UCN shows high antibacterial activity and is effective in pharmaceutical wastewater treatment. The enhanced visible-light absorption of Ag/UCN nanocomposites is attributed to the LSPR effect of Ag quantum dots. Finite difference time domain (FDTD) simulations, density functional theory (DFT) calculations and surface potential confirm that the interfacial electric field drives the photogenerated carriers to cross the Schottky barrier, thus effectively accelerating the electron transfer rate at Ag/UCN interface. The photocatalytic mechanism of the interfacial electric field induced by LSPR effect was also revealed, which provides a new insight for design of LSPR-promoted photocatalyst with interfacial electric field induced by quantum dots.

Controllable Preparation of Gold Nanocrystals with Different Porous Structures for SERS Sensing.

Porous Au nanocrystals (Au NCs) have been widely used in catalysis, sensing, and biomedicine due to their excellent localized surface plasma resonance effect and a large number of active sites exposed by three-dimensional internal channels. Here, we developed a ligand-induced one-step method for the controllable preparation of mesoporous, microporous, and hierarchical porous Au NCs with internal 3D connecting channels. At 25 °C, using glutathione (GTH) as both a ligand and reducing agent combined with the Au precursor to form GTH-Au(I), and under the action of the reducing agent ascorbic acid, the Au precursor is reduced in situ to form a dandelion-like microporous structure assembled by Au rods. When cetyltrimethylammonium bromide (C16TAB) and GTH are used as ligands, mesoporous Au NCs formed. When increasing the reaction temperature to 80 °C, hierarchical porous Au NCs with both microporous and mesoporous structures will be synthesized. We systematically explored the effect of reaction parameters on porous Au NCs and proposed possible reaction mechanisms. Furthermore, we compared the SERS-enhancing effect of Au NCs with three different pore structures. With hierarchical porous Au NCs as the SERS base, the detection limit for rhodamine 6G (R6G) reached 10-10 M.

Drastic performance enhancement of photoluminescence and water electrolysis by local-magnetic-field-assisted LSPR of Ag NPs and NCs

A novel method is presented for drastically improving the local surface plasma resonance (LSPR) effect of noble metal nanoparticles (NPs) and nanoclusters (NCs). This is realized by magnetizing particles comprising a ferrimagnetic core and a noble metal nanoshell. In this study, we prepared Fe3O4 @SiO2 @Ag composite particles. Ag NPs and NCs had the size of 10–15 nm and 2–3 nm, respectively. The photoluminescence (PL) intensities of ZnO and YAG:Ce substrates coated with the magnetic composite particles increased by 160 % and 50 %, respectively, after magnetization under a magnetic field of 18 mT compared to the unmagnetized state. The activity of Ni-foam-based-Fe3O4 @SiO2 @Ag working electrode for water electrolysis was also significantly improved after magnetization. The increasing rate of current density after magnetization was 226 mA∙cm−2/0.1 V, which is higher than 158 mA∙cm−2/0.1 V before the magnetization. The mechanism for drastic performance enhancement of PL and water electrolysis postulates that after magnetization, the remanence of the ferrimagnetic Fe3O4 core provides a local magnetic field to strengthen the local electric field in the confined area of Ag NPs/NCs. It was confirmed by the higher intensity of peaks in Raman spectroscopy and contributed to the enhancement of LSPR effect. This efficient and practical approach to magnetization-induced LSPR improvement has potential application prospects in LSPR-related fields.

Conformation of neurofilament heavy chain effect on neurofilament-neurofilament association and bundling.

Mammalian neurofilaments (NFs) are composed of Heavy (NF-H), Medium (NF-M), and Light (NF-L) subunits, named according to their molecular mass, along with α-internexin or peripherin (in central or peripheral nervous systems, respectively). Phosphorylated NF subunits assemble linearly, with C-terminal regions extending from the filament “backbone.” Phosphorylation of C-terminal “side arms” of NF-H promotes NF-NF interactions, providing stability to axons. Transport of NFs from the perikaryon into the axon and NF-NF interactions are dependent upon regulation of multiple kinases. The complete sequence of phosphorylation events does not occur until NFs have entered the axon. Sidearm phosphorylation fosters lateral extension away from the NF backbone. By contrast, sidearm conformation prior to phosphorylation remains unresolved. Scrutiny of the NF-H side-arm sequence revealed 4 proline-proline (PP) motifs; these motifs allow tremendous rotation of their peptide chains from a closed, folded-back hairpin (cis) to a fully extended, linear confirmation (trans). Notably, one PP motif is located within each of the consensus sequences for the NF kinases. We hypothesize that phosphorylation-induced alterations in the configuration of these PP motifs are critical for NF transport, NF-NF association within axons. Mutated NFs constructs with changed PP motifs were expressed (with or without PP motifs /Phosphorylated or unphosphorylated) and incubated with NFs medium chain then trapped using a his-tag column to demonstrate bundling. Our initial data were inconclusive. A different experimental approach, such as Localized Surface Plasma Resonance (LSPR) is necessary to analyze the role of PP motifs in NFs association. We predict that constructs lacking PP motifs will present lower association affinity to NF-M (even when phosphorylated. Understanding the mechanisms that allow NF-NF associations within neurites will help guide targeted treatments for NF-based neurodegenerative disorders.

High performance amorphous Ga<sub>2</sub>O<sub>3</sub> thin film solar blind ultraviolet photodetectors decorated with Al nanoparticles

Gallium oxide (Ga<sub>2</sub>O<sub>3</sub>) as a wide bandgap semiconductor material has attracted much attention in the field of solar blind ultraviolet photodetection recently. Localized surface plasmon resonance is considered an effective way to improve the performance of optoelectronic devices by decorating the materials with metal particles. Al nanoparticle is a potential candidate for ultraviolet photodetectors because its suitable resonance wavelength is located in the ultraviolet wavelength range. In this work, the preparation temperature of the Ga<sub>2</sub>O<sub>3</sub> thin film is reduced by ultraviolet photo-annealing, and the amorphous Ga<sub>2</sub>O<sub>3</sub> thin film is prepared by using the solution method. In addition, aluminum (Al) nanoparticles are used to decorate the surface of Ga<sub>2</sub>O<sub>3</sub> thin film through thermal evaporation of aluminum film and then annealing, which improves the optoelectrical performance in the solar-blind wavelength spectrum. The X-ray diffraction (XRD) is employed to demonstrate the amorphous Ga<sub>2</sub>O<sub>3</sub> thin film. The surface roughness and the diameters of Al nanoparticles are analyzed by atomic force microscope (AFM). When the thickness of the deposited Al layer is about 3–5 nm, Al particles with the diameters in a range of 2–3 nm can be obtained. When the thickness of the deposited Al layer is more than 7 nm, Al nanoparticles turn into the particles with non-identical diameters and distribute in the form of agglomeration. Transmittance spectrum and absorption spectrum are employed to characterize the optical properties. The bandgaps of different samples are obtained, and the results are consistent with the theoretical ones. The Ga<sub>2</sub>O<sub>3</sub> thin film shows excellent optoelectrical performance and solar blind rejection ratio. Under 254 nm illumination, the maximum photo-to-dark current ratio is 2.55×10<sup>4</sup>, and the rejection ratio of <i>I</i><sub>254 nm</sub>/<i>I</i><sub>365 nm</sub> is 2.2×10<sup>4</sup>. The best responsivity and detectivity of prepared samples are 0.771 A/W and 1.13×10<sup>11</sup> Jones, which are about 34 times and 36 times higher than those without Al decoration. The improvement is attributed to the scattering effect of surface Al nanoparticles for illumination, which enhances the Ga<sub>2</sub>O<sub>3</sub> thin film absorption of solar blind ultraviolet light. Meanwhile, owing to the localized surface plasma resonance, the local electromagnetic fields generated near the Al nanoparticles promote the transfer of carriers in the film. Furthermore, the point about how the Al nanoparticles decorated on the surface of Ga<sub>2</sub>O<sub>3</sub> thin film influence the time response is also discussed in this work. As a result, the introduction of defect states will lead to an increase of fall time due to the Al deposition. In this work, the effect of Al nanoparticles decoration on the optoelectrical performance of amorphous Ga<sub>2</sub>O<sub>3</sub> thin film solar blind ultraviolet photodetectors is studied based on a simple preparation, which provides a possible pathway for developing the flexible solar blind electronic devices in the future.

Fabrication of a high-performance photoelectrochemical aptamer sensor based on Er-MOF nanoballs functionalized with ionic liquid and gold nanoparticles for aflatoxin B1 detection

One of the most dangerous mycotoxins is Aflatoxin B1 (AFB1) that is commonly found in food. Thus, AFB1 has been considered as a serious food safety concern. Herein, using Er-MOF nanoballs assembled with gold nanoparticles (AuNPs) as photoactive elements, a photoelectrochemical aptasensor with high analytical performance was developed for sensing AFB1. Er-MOFs nanoballs were prepared by using ionic liquid as a ligand and Er3+ as a metal center through a solvothermal method. Chloroauric acid was reduced in-situ onto Er-MOF nanoballs to form Er-MOF@AuNPs nanocomposites. AuNPs can effectively enhance the photocurrent of Er-MOF nanoballs attributed to their excellent conductivity and local surface plasma resonance effect. In addition, they can provide active sites for immobilizing more biorecognition elements that can further enhance the sensing performance. Through self-assembling reaction, thiol-functionalized hairpin DNA (hDNA) was immobilized onto an Er-MOF@AuNPs-based interface to construct a photoelectrochemical biosensing platform. As the AFB1 aptamers labeled with gold nanoparticles (AuNPs-Apt) were selectively recognized, the photocurrent response can be further amplified. Due to the high affinity of AFB1 and its aptamer (Apt), when Apt is reacted with AFB1, it causes AuNPs-Apt detaching from the PEC aptasensing interface, and thus a reduced photocurrent response is generated. Under optimized conditions, the changes of photocurrent before and after recognition of AFB1 exhibits a linear response from 0.005 to 10.0 ng mL−1. In addition, the limit of detection obtained was 19.6 fg mL−1. This PEC aptasensor provides relatively high selectivity, reproducibility and accuracy in the determination of AFB1 in real corn samples.