Surface Plasmon Resonance Response Research Articles

Optofluidic SERS based on Ag nanocubes with high sensitivity for detecting a prevalent water pollutant.

To enhance the integration and practical applicability of the Raman detection system, silver nanocubes (Ag NCs) were synthesized using a polyol method. A liquid-liquid interface approach was employed to transfer a monolayer of Ag NCs "film" onto a SiO2 substrate, resulting in the fabrication of a highly sensitive and uniform surface-enhanced Raman scattering (SERS) substrate denoted as "Ag NCs@SiO2." The electromagnetic field distribution of various dimers on the Ag NCs@SiO2 was analyzed using finite difference time domain (FDTD) software. The results reveal that the electromagnetic enhancement effect is most pronounced in cube-cube dimers, indicating that Ag NCs exhibit superior localized surface plasmon resonance (LSPR) response due to their well-defined geometric regularity and sharp geometric angles. For Rhodamine 6G (R6G) probe molecules, the Ag NCs@SiO2 shows ultrahigh sensitivity, with a limit of detection (LOD) of 10-12 mol/L, and the enhancement factor (EF) can reach 1.4 × 1010. The relative standard deviation (RSD) at the main characteristic peaks is below 10%, demonstrating good consistency in substrate performance. In addition, the Ag NCs@SiO2 modified with hexanethiol exhibits high sensitivity, uniformity, and repeatability in detecting for pyrene, with the LOD of 10-8 mol/L and a minimum RSD of 6.09% at the main characteristic peak, and effective recognition capabilities for pyrene and anthracene in mixed solutions. Finally, chemisorption and physisorption strategies were prepared in optofluidic channels and experimentally compared, enabling real-time detection of the pyrene solution. This method can achieve a rapid detection and precise differentiation of polycyclic aromatic hydrocarbons in a water pollutant.

Oxidative and Colloidal Kinetics of Size‐Controlled Copper Structures through Surface Plasmon‐Regulated Examinations for Broadband Absorbance

AbstractOut of all the candidate plasmonic metals, copper has noteworthy optical characteristics and is also economically favourable for use. However, the stability of plasmonic copper nanomaterials against the loss of the plasmonic property is a setback. The present work is on the synthesis of oxidation‐stable copper micro/nanoparticles (CuMps/NPs) at ambient conditions with chosen precursors, antioxidizing agents, polymeric capping agents and chelating ligands. The Surface Plasmon Resonance (SPR) response of the synthesized Cu structures and their morphological analyses are studied. XRD data revealed changes in crystal structure such as crystallite sizes, lattice distortions and dislocation densities as a result of variations in the synthesis conditions. We present from these analyses micro/nanostructures of oxidation‐stable plasmonic Cu. The validation of the aggregation and oxidation stabilities of the different synthesized samples make them a worthy choice for multiple plasmonic applications, along with showing the synthesis protocols as viable approaches for achieving such structures with a markedly increased shelf life.

Transmission electron microscopy reveals clusters of Au–Ag nanoparticles formed in TiO2 thin film, with enhanced plasmonic response

This work reports on the influence of nanoparticle (NP) size distribution and the chemical nature of gold (Au) and/or silver (Ag) NPs in the localized surface plasmon resonance (LSPR) responses. The NPs were produced embedded in a titanium dioxide (TiO2) thin film, deposited by reactive magnetron sputtering technique followed by in-vacuum thermal treatment at 400 °C. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) gave quantitative key information in terms of both the size and distribution of the noble metal NPs. The average Feret diameter was 17 nm (σ = 8) and 55 nm (σ = 28) for Au/TiO2 and Ag/TiO2 films, respectively, while the Au–Ag/TiO2 film showed intermediate values, with an average size of 22 nm (σ = 9). HAAD-STEM, complemented by EDX chemical mapping, revealed an unusual formation of cluster structures containing local distributions of bimetallic (alloyed) Au–Ag NPs. The synergetic characteristics and properties of such bimetallic Au–Ag NPs resulted in an outstanding LSPR sensitivity compared to the monometallic counterparts. Furthermore, the analysis of the average nearest neighbor distances (about one order of magnitude lower than counterparts) suggests the existence of plasmonic hotspots relevant to be explored in sensing and surface-enhanced spectroscopies.

Study of cell and drug interactions based on dual-mode detection using SPR and fluorescence imaging

The investigation of the interactions between cells and drugs forms a crucial aspect of biological and clinical medical studies. Generally, single-cell or local-cellular studies require a microscopic imaging system with high magnifications, which suffers from low detection throughputs and poor time responses. The study presented in this paper combined SPR and fluorescence to achieve cell localization, real-time monitoring of cell images and quantitative analysis of drugs. In order to obtain more comprehensive, accurate and real-time data, a dual-mode system based on surface plasmon resonance (SPR) and fluorescence was constructed based on a 4× magnification lens. This enables simultaneous studies of an entire cell and a specific region of the cell membrane. An adaptive adjustment algorithm was established for distorted SPR images, achieving temporal and spatial matching of the dual-mode detection. The combination of SPR and fluorescence not only achieved micro-detection but also complemented the qualitative or quantitative limitations of SPR or fluorescence method alone. In system characterization, the response signal of SPR was noticed to increase with the increasing concentration of EGF in stimulated cells. It indicated that this platform could be employed for quantitative detection of the cell membrane region. Upon addition of EGF, a peak in the SPR curve was observed, and the cells in the corresponding SPR image turned whiter. This indicated that the platform can simultaneously monitor the SPR response signal and image changes. The response time of fluorescence in EGF testing was several seconds earlier than SPR, revealing that signal transduction first occurred in the whole cell and then propagated to the cell membrane region. The inhibitory ability of Gefitinib on cells was verified in a fast and real-time manner within 20 min. The results indicated that the detection limit of this method was 20 IU/mL for EGF and 10 µg/mL for Gefitinib. In conclusion, this study demonstrates the advantages of SPR and fluorescence dual-mode techniques in the analysis of cell-drug interactions, as well as their strong potential in drug screening.

Piezo inkjet formation of Ag nanoparticles from microdots arrays for surface plasmonic resonance

The study aims to explore a novel approach for fabricating plasmonic nanostructures to enhance the optical properties and performance of various optoelectronic devices. The research begins by employing a piezo-inkjet printing technique to deposit drops containing Ag nanoparticles (NPs) onto a glass substrate at a predefined equidistance, with the goal of obtaining arrays of Ag microdots (Ag-µdots) on the glass substrate. This process is followed by a thermal annealing treatment. The printing parameters are first optimized to achieve uniform deposition of different sizes of Ag-µdots arrays by controlling the number of Ag ink drops. Subsequently, the printed arrays undergo thermal annealing at various temperatures in air for 60 min, enabling precise and uniform control over nanoparticle formation. The printed Ag nanoparticles are characterized using field emission scanning electron microscopy and atomic force microscopy to analyze their morphological features, ensuring their suitability for plasmonic applications. UV–Vis spectrophotometry is employed to investigate the enhanced surface-plasmonic-resonance properties of the printed AgNPs. Measurements confirm that the equidistant arrays of AgNPs obtained from annealing Ag microdots exhibit enhanced light-matter interaction, leading to a surface plasmon resonance response dependent on the Ag NPs’ specific surface area. These enhanced surface plasmonic resonances open avenues for developing cutting-edge optoelectronic devices that leverage the benefits of plasmonic nanostructures, thereby enabling new opportunities for future technological developments across various fields.

Thermo-sensitive PLGA-PEG-PLGA hydrogel for sustained release of EGF to inhibit cervical cancer recurrence

Overexpression of epidermal growth factor receptor (EGFR) in cancer is a key cause of recurrence of cervical cancer (CC). Although the EGF-EGFR pathway has been studied for decades, preventing tumor growth and recurrence caused by peripheral EGF remains a great challenge. In this work, a strategy is proposed to reduce the stimulation of high concentration EGF on tumor growth by using a thermo-sensitive hydrogel. The hydrogel is a triblock copolymer composed of polyethylene glycol (PEG) and poly (lactide glycolide) (PLGA). Based on the excellent temperature sensitivity, carrier capacity, swelling property and biocompatibility, the hydrogel can absorb the liquid around the tumor by injection and release EGF continuously at low concentration. The inhibitory effect of hydrogel on tumor growth is fully confirmed by an implanted tumor mouse model with human cervical cancer cell lines (HeLa) using triple-immunodeficient NCG mice. Compared with free EGF, the EGF-loaded hydrogel can hardly induce surface plasmon resonance (SPR) response, which proves that hydrogel can effectively weaken cytoskeleton rearrangement and inhibit cell migration by continuously releasing low concentration EGF. In addition, the EGF-loaded hydrogel can reduce cell proliferation by delaying the progress of cell cycle progression. Taken together, the hydrogel can effectively protect tumor microenvironment from the stimulation of high concentration EGF, delay cancer cellular processes and tumor growth, and thus providing an approach for inhibiting tumor recurrence of CC.

Tyndall-effect-amplified colorimetric detection of trypsin based on the analyte-regulated formation of Au nanoparticle network with no visual change in surface plasmon resonance response

The classical colorimetric assays with Au nanoparticles (AuNPs) are not suitable for analytical systems where the analyte could not induce a red-to-blue color change related to their surface plasmon resonance (SPR). To respond this challenge, herein this study utilizes Tyndall effect (TE) of AuNPs as amplified colorimetric signaling to design a universal visual assay for sensitive detection of trypsin (model analyte). The AuNPs are modified with biotinylated peptides. In the absence of trypsin, streptavidin binds biotin on these probes to form a network-like complex consisting of repeated units of “AuNP-biotin-streptavidin-biotin-AuNP” resulting in a mixture that shows an intense TE response as well a SPR-related red color. Upon trypsin incubation, however, the analyte can cleave the peptide chain to inhibit the streptavidin-mediated production of network-like complex; the resultant red reaction solution containing free AuNP probes would display a weak TE signal. The reduction degree in the TE positively relies on the trypsin level in sample. The results demonstrate that this new equipment-free method only requires a laser pointer pen (for the TE creation) and a smartphone (for portable TE imaging readout) to linearly detect trypsin in a concentration range of 3.9–1000 nM, with an estimated limit of ∼0.63 nM (3σ). The satisfactory recovery of trypsin in actual human serum samples is between 94.93–102.21 %. Such TE-enhanced strategy may significantly expand theoretical scope of widely used AuNP-based visual assays and their applications in various resources-limited settings like point-of-care testing of trypsin for medical diagnosis.

Detection of backside coupled propagating surface plasmon resonance on the sidewall of a wafer

We proposed a surface plasmon resonance (SPR) sensor structure that utilized a glass wafer with a diffraction grating and an n-type silicon piece bonded near the SPR coupling site. This configuration enabled surface plasmon excitation from the back of the substrate without the unwanted interaction between the excitation light and the sample, and electrical detection of the SPR response by a 0.7-eV Schottky barrier at the Au/n-Si interface formed on the sidewall of the silicon piece was achieved. Experimental evaluation of the surface plasmon coupling performance was conducted, showing clear peaks in the photocurrent for various wavelengths in the NIR-II window, ranging from 1100 to 1300 nm. The device’s ability to detect propagating surface plasmons as a photocurrent was confirmed; the results indicated a consistent trend with theoretical and numerical calculations. Since the device was composed of a glass substrate, the use of wavelengths shorter than the near-infrared wavelength was possible, including visible wavelengths where the optical absorption by water is negligible. Thus, our proposed sensor provides a compact and efficient solution for SPR sensing in aqueous solutions.

Real-Time Imaging of Plasmonic Concentric Circular Gratings Fabricated by Lens-Axicon Laser Interference Lithography.

Concentric circular gratings are diffractive optical elements useful for polarization-independent applications in photonics and plasmonics. They are usually fabricated using a low-throughput and expensive electron beam lithography technique. In this paper, concentric circular gratings with selectable pitch values were successfully manufactured on thin films of azobenzene molecular glass using a novel laser interference lithography technique utilizing Bessel beams generated by a combined lens-axicon configuration. This innovative approach offers enhanced scalability and a simplified manufacturing process on larger surface areas compared to the previously reported techniques. Furthermore, the plasmonic characteristics of these concentric circular gratings were investigated using conventional spectrometric techniques after transferring the nanostructured patterns from azobenzene to transparent gold/epoxy thin films. In addition, the real-time imaging of surface plasmon resonance colors transmitted from the concentric circular gratings was obtained using a 45-megapixel digital camera. The results demonstrated a strong correlation between the real-time photographic technique and the spectroscopy measurements, validating the efficacy and accuracy of this approach for the colorimetric studying of surface plasmon resonance responses in thin film photonics.

Polymer Doping as a Novel Approach to Improve the Performance of Plasmonic Plastic Optical Fibers Sensors

In this work, Fe2O3 was investigated as a doping agent for poly(methyl methacrylate) (PMMA) in order to enhance the plasmonic effect in sensors based on D-shaped plastic optical fibers (POFs). The doping procedure consists of immerging a premanufactured POF sensor chip in an iron (III) solution, avoiding repolymerization and its related disadvantages. After treatment, a sputtering process was used to deposit a gold nanofilm on the doped PMMA in order to obtain the surface plasmon resonance (SPR). More specifically, the doping procedure increases the refractive index of the POF’s PMMA in contact with the gold nanofilm, improving the SPR phenomena. The doping of the PMMA was characterized by different analyses in order to determine the effectiveness of the doping procedure. Moreover, experimental results obtained by exploiting different water–glycerin solutions have been used to test the different SPR responses. The achieved bulk sensitivities confirmed the improvement of the plasmonic phenomenon with respect to a similar sensor configuration based on a not-doped PMMA SPR-POF chip. Finally, doped and non-doped SPR-POF platforms were functionalized with a molecularly imprinted polymer (MIP), specific for the bovine serum albumin (BSA) detection, to obtain dose-response curves. These experimental results confirmed an increase in binding sensitivity for the doped PMMA sensor. Therefore, a lower limit of detection (LOD), equal to 0.04 μM, has been obtained in the case of the doped PMMA sensor when compared to the one calculated for the not-doped sensor configuration equal to about 0.09 μM.

A Novel SPR Immunosensor Based on Dual Signal Amplification Strategy for Detection of SARS-CoV-2 Nucleocapsid Protein

Since the global outbreak of coronavirus disease 2019 (COVID-19), it has spread rapidly around the world. The nucleocapsid (N) protein is one of the most abundant SARS-CoV-2 proteins. Therefore, a sensitive and effective detection method for SARS-CoV-2 N protein is the focus of research. Here, we developed a surface plasmon resonance (SPR) biosensor based on the dual signal-amplification strategy of Au@Ag@Au nanoparticles (NPs) and graphene oxide (GO). Additionally, a sandwich immunoassay was utilized to sensitively and efficiently detect SARS-CoV-2 N protein. On the one hand, Au@Ag@Au NPs have a high refractive index and the capability to electromagnetically couple with the plasma waves propagating on the surface of gold film, which are harnessed for amplifying the SPR response signal. On the other hand, GO, which has the large specific surface area and the abundant oxygen-containing functional groups, could provide unique light absorption bands that can enhance plasmonic coupling to further amplify the SPR response signal. The proposed biosensor could efficiently detect SARS-CoV-2 N protein for 15 min and the detection limit for SARS-CoV-2 N protein was 0.083 ng/mL, with a linear range of 0.1 ng/mL~1000 ng/mL. This novel method can meet the analytical requirements of artificial saliva simulated samples, and the developed biosensor had a good anti-interference capability.

Performance Enhancement of an Ag–Au Bimetallic SPR Sensor: A Theoretical and Experimental Study

Ag-Au bimetallic surface plasmon resonance (SPR) sensors operating in the Kretschmann configuration were investigated by numerical modelling and experiment. While Ag-based sensors have good sensitivity, they suffer from poor stability, and the addition of an Au capping layer offers improved chemical resistance and reliable analyte bonding via thiol-gold interactions. Sensors were evaluated with an Ag-Au combined thickness of 50 nm but different thickness ratios, and SPR reflectivity curves were obtained for 632.8 nm wavelength light incident over a range of angles. Numerical modelling using the transfer matrix method showed the SPR response improving as Au thickness decreased, giving the best results for 45 nm of Ag and 5 nm of Au. Experimental characterisation of fabricated Ag-Au bimetallic sensors was carried out with a custom SPR testbed. Performance parameters, including minimum reflectivity, FWHM, stability, and sensitivity were measured and the results were compared to those of single-layer Ag and Au sensors. A 5 nm Au coating was unable to preserve stable bimetallic sensor performance; however, increasing the Au thickness to 10 nm was sufficient to protect the Ag sensing layer, allowing only a small variation in the minimum reflectivity and FWHM when exposed to analytes for multiple hours. The sensitivity of the single-layer Ag, bimetallic Ag-Au, and Au sensors was measured as 3041%/Refractive Index Unit (RIU), 1817%/RIU, and 1229%/RIU, respectively. The sensitivity of the thickness-optimized bimetallic layer was ~1.5× that of the single-layer Au sensor.

Fully Aqueous Self-Assembly of a Gold-Nanoparticle-Based Pathogen Sensor.

Surface plasmon resonance (SPR) is a very sensitive measure of biomolecular interactions but is generally too expensive for routine analysis of clinical samples. Here we demonstrate the simplified formation of virus-detecting gold nanoparticle (AuNP) assemblies on glass using only aqueous buffers at room temperature. The AuNP assembled on silanized glass and displayed a distinctive absorbance peak due to the localized SPR (LSPR) response of the AuNPs. Next, assembly of a protein engineering scaffold was followed using LSPR and a sensitive neutron reflectometry approach, which measured the formation and structure of the biological layer on the spherical AuNP. Finally, the assembly and function of an artificial flu sensor layer consisting of an in vitro-selected single-chain antibody (scFv)-membrane protein fusion was followed using the LSPR response of AuNPs within glass capillaries. In vitro selection avoids the need for separate animal-derived antibodies and allows for the rapid production of low-cost sensor proteins. This work demonstrates a simple approach to forming oriented arrays of protein sensors on nanostructured surfaces that uses (i) an easily assembled AuNP silane layer, (ii) self-assembly of an oriented protein layer on AuNPs, and (iii) simple highly specific artificial receptor proteins.

Do conformational changes contribute to the surface plasmon resonance signal?

Surface plasmon resonance (SPR)-based biosensors are widely used instruments for characterizing molecular interactions. In theory the SPR signal depends only on mass changes for interacting molecules of same chemical nature. Whether conformational changes of interacting molecules also contribute to the SPR signal is still a subject of lively debates. Works have been published claiming that conformational changes were detected but all factors contributing to the SPR signal were not carefully considered, in addition to often using no or improper controls. In the present work we used a very well-characterized oligonucleotide, the thrombin-binding DNA aptamer (TBA), which upon binding of potassium ions folds into a two G-tetrad antiparallel G-quadruplex structure. All terms contributing to the maximal expected SPR response, Rmax, in particular the refractive index increment, RII, of both partners and the fraction of immobilized TBA target available, ca, were experimentally assessed. The resulting Rmax was then compared to the maximal experimental SPR response for potassium ions binding to TBA using appropriate controls. Regardless how the RIIs were measured, by SPR or refractometry, and how much TBA available for interacting with potassium ions was considered, the theoretical and the experimental SPR responses never matched, the former being always lower than the latter. Using a straightforward experimental model system and by thoroughly taking into account all contributing factors we therefore conclude that conformational changes can indeed contribute to the measured SPR signal.

Surface Plasmon Resonance Sensor Based on Core-Shell Fe3O4@SiO2@Au Nanoparticles Amplification Effect for Detection of T-2 Toxin

In this paper, a core-shell based on the Fe3O4@SiO2@Au nanoparticle amplification technique for a surface plasmon resonance (SPR) sensor is proposed. Fe3O4@SiO2@AuNPs were used not only to amplify SPR signals, but also to rapidly separate and enrich T-2 toxin via an external magnetic field. We detected T-2 toxin using the direct competition method in order to evaluate the amplification effect of Fe3O4@SiO2@AuNPs. A T-2 toxin-protein conjugate (T2-OVA) immobilized on the surface of 3-mercaptopropionic acid-modified sensing film competed with T-2 toxin to combine with the T-2 toxin antibody-Fe3O4@SiO2@AuNPs conjugates (mAb-Fe3O4@SiO2@AuNPs) as signal amplification elements. With the decrease in T-2 toxin concentration, the SPR signal gradually increased. In other words, the SPR response was inversely proportional to T-2 toxin. The results showed that there was a good linear relationship in the range of 1 ng/mL~100 ng/mL, and the limit of detection was 0.57 ng/mL. This work also provides a new possibility to improve the sensitivity of SPR biosensors in the detection of small molecules and in disease diagnosis.

Development of a multi-functional SPR sensing system using a square glass rod with two gold-deposited adjacent faces.

A multi-functional sensing system based on surface plasmon resonance (SPR) phenomenon using a square glass rod with two gold-deposited adjacent faces was developed in this work. This sensor system consists of a unpolarized light-emitting diode, a gold-deposited square glass rod, a polarizing beam splitter, and two photodiodes. The SPR responses of two adjacent faces are independently and simultaneously measured with a polarizing beam splitter and two PDs. The response property of the gold-deposited face was confirmed using methanol solutions of ethylene glycol. The response curve of the sensor of the 45nm gold-deposited face was compared with the theoretical curve calculated using multi-layer Fresnel equations. It was confirmed that the experimental curve is similar to the theoretical one. An evaluation was carried out on the square glass rod, which has an unmodified face and Teflon AF2400 coated gold-deposited face as multi-functional sensor. It was confirmed that this sensor can simultaneously measure the ethanol concentration in the glucose mix solution and refractive index of the sample from the calibration curve. Since this sensor can measure multiple components simultaneously, expected applications to various fields include medical diagnosis, food analysis, and environmental monitoring.

Voltage-modulated surface plasmon resonance biosensors integrated with gold nanohole arrays.

Surface plasmon resonance (SPR) has emerged as one of the most efficient and attractive techniques for optical sensors in biological applications. The traditional approach of an EC (electrochemical)-SPR biosensor to generate SPR is by adopting a prism underneath the sensing substrate, and an angular scan is performed to characterize the reflectivity of target analytes. In this paper, we designed and investigated a novel optical biosensor based on a hybrid plasmonic and electrochemical phenomenon. The SPR was generated from a thin layer of gold nanohole array on a glass substrate. Using C-Reactive Protein (CRP) as the target analyte, we tested our device for different concentrations and observed the optical response under various voltage bias conditions. We observed that SPR response is concentration-dependent and can be modulated by varying DC voltages or AC bias frequencies. For CRP concentrations ranging from 1 to 1000 µg/mL, at the applied voltage of -600 mV, we obtained a limit of detection for this device of 16.5 ng/mL at the resonance peak wavelength of 690 nm. The phenomenon is due to spatial re-distribution of electron concentration at the metal-solution interface. The results suggest that CRP concentration can be determined from the SPR peak wavelength shift by scanning the voltages. The proposed new sensor structure is permissible for various future optoelectronic integration for plasmonic and electrochemical sensing.

ArsenazoIII functionalized gold nanoparticles: SPR based optical sensor for determination of uranyl ions (UO22+) in groundwater

Surface plasmon resonance (SPR) based spectrophotometric determination of UO22+ was carried out by arsenazoIII functionalized gold nanoparticles (AZ-AuNPs) based miniaturized detection assay in ground water samples. AZ-AuNPs were synthesized, characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR) and dynamic light scattering (DLS) techniques; AZ-AuNPs were of uniform size (∼10nm), dispersed, highly stable and negative charge surface. The addition of analyte (UO22+) into the detection assay led to UO22+-arsenazoIII complex formation and subsequent release of uncapped gold nanoparticules in solution. Agglomeration based SPR response of gold nanoparticles resulted in visual and spectrophotometric change in the detection assay. The UV-vis spectroscopic investigations showed changes in AZ-AuNPs characteristic absorption peak and an additional peak correspond to UO22+-arsenazoIII complex. Ratio of A650nm/A535nm was used to quantify the concentration of UO22+ in environmental samples. The method showed a linear response from 50−300 ppb (R2> 0.95) for UO22+ with the detection limit of 0.081 µM for ground water samples of total dissolve solids concentration of ∼1000 ppm.

Plasmon‐Assisted Self‐Encrypted All‐Optical Memory

AbstractAll‐optical responsive nanomaterials, which can rapidly switch between two stable states, have been regarded as the next‐generation memories due to their potential to realize binary information storage and implement on‐chip, integrated photonic neuromorphic systems. Rare earth oxides are preeminent candidates owing to their extraordinary luminescent stability and narrow optical transitions. However, due to the lack of simple and effective optical switches, it is difficult to realize all‐optical data storage, encoding, and retrieval by pure rare earth‐doped luminescent nanoparticles. Here, a rapid and high‐contrast of 104 luminescent switching of Y2O3:Eu3+ nanoparticle between the enhancement and quenching states is achieved by employing the strong light confinement and ultrafast thermal response of localized surface plasmon resonance. A self‐encrypted all‐optical memory is presented with optical information writing, encryption, reading, and re‐writing, and a high‐sensitivity synaptic response of emitters to frequency and light intensity flux, which can be harnessed to encrypt information flows and promote convenient and high‐security information encryption. Such a convenient and secure plasmonic thermally assisted self‐encrypting luminescent switch paves the way for constructing high‐performance stimuli‐responsive rare earth oxide crystals on demand and expanding their applications in various data encryption, anti‐counterfeiting, and rewritable colouration devices.

Sensitive detection of organophosphorus pesticides based on the localized surface plasmon resonance and fluorescence dual-signal readout

In this work, a dual-signal visual biosensor was designed for organophosphorus pesticides (OPs) detection using DNA functionalized Ag/Au bimetallic nanoparticles (Ag/Au NPs) as multifunctional nanoprobe. The dual-signal detection strategy was based on the inhibition of enzyme-induced H2O2 generation by OPs in the detection solution containing acetylcholinesterase (AChE), choline oxidase (CHO), acetylcholine (ACh) and nanoprobe. H2O2 produced by enzyme-catalyzed reaction could trigger the etching of Ag and dissociation of carboxyfluorescein (FAM)-labeled aptamer from the nanoprobe, resulting in significant localized surface plasmon resonance (LPRR) and fluorescence (FL) signal responses. In the presence of OPs, AChE activity was inhibited to disrupt the enzymatic generation of H2O2, which allowed to simultaneous quantitative measure OPs through the LSPR peak shifts and FL intensity variations of the nanoprobe. The LSPR/FL dual-signal biosensor showed great selectivity and sensitivity for OPs detection. In addition, two distinct colour changes were visually observed to match the LSPR/FL spectra signal responses, which was a feasible means for visual analysis of OPs. Consequently, the work provided a dual-signal visual biosensor via the combination of multifunctional nanoprobe, and had significant potential to monitor pesticide residue with high anti-interference capability and detection accuracy.