Ultra-sensitive and specific detection of pathogenic nucleic acids using composite-excited hyperfine plasma spectroscopy combs sensitized by Au nanoarrays functionalized with 2D Ta2C-MXene.

Accurate and rapid screening techniques on a population scale are crucial for preventing and managing epidemics like COVID-19. The standard gold test for nucleic acids in pathogenic infections is primarily the reverse transcription polymerase chain reaction (RT-PCR). However, this method is not suitable for widespread screening due to its reliance on large-scale equipment and time-consuming extraction and amplification processes. Here, we developed a collaborative system that combines high-load hybridization probes targeting N and OFR1a with Au NPs@Ta2C-M modified gold-coated tilted fiber Bragg grating (TFBG) sensors to enable direct nucleic acid detection. Multiple activation sites of SARS-CoV-2 were saturable modified on the surface of a homogeneous arrayed AuNPs@Ta2C-M/Au structure based on a segmental modification approach. The combination of hybrid probe synergy and composite polarisation response in the excitation structure results in highly specific hybridization analysis and excellent signal transduction of trace target sequences. The system demonstrates excellent trace specificity, with a limit of detection of 0.2 pg/mL, and achieves a rapid response time of 1.5 min for clinical samples without amplification. The results showed high agreement with the RT-PCR test (Kappa index = 1). And the gradient-based detection of 10-in-1 mixed samples exhibits high-intensity interference immunity and excellent trace identification. Therefore, the proposed synergistic detection platform has a good tendency to curb the global spread of epidemics such as COVID-19.

Ultra-sensitive specific detection of nucleic acids in pathogenic infections by Ta2C-MXene sensitization-based ultrafine plasmon spectroscopy combs.

Accurate and rapid population-scale screening techniques based on SARS-CoV-2 RNA are essential in preventing and controlling the COVID-19 epidemic. However, the sensitivity and specificity of the assay signal are challenged by the problems of target dilution and sample contamination inherent in high-volume pooled testing. Here, we reported a collaborative system of high-loaded hybrid probes targeting N and OFR1a coupling with the novel Ta2C-M/Au/TFBG biosensor, providing high-intensity vector signals for detecting SARS-CoV-2. The method relies on a segmental modification approach to saturable modify multiple activation sites of SARS-CoV-2 on the high-performance Ta2C-M surface. The coupling of multi-site synergy with composite excited TFBG results in excellent signal transduction, detection limits (0.2 pg/mL), and hybridization efficiency. Without relying on amplification, the collaborative system achieved specific differentiation of 30 clinical samples in an average diagnostic time of 1.8 min. In addition, for the first time, a kinetic determination of dilution mixed samples was achieved and showed a high-intensity carrier signal and fantastic stability. Therefore, it can be used as a collaborative, integrated tool to play a massive role in the screening, prevention, and control of COVID-19 and other epidemics.

SERS Sensing Using Graphene-Covered Silver Nanoparticles and Metamaterials for the Detection of Thiram in Soil.

Multilayer hyperbolic metamaterial (HMM)-based SERS substrates have received special consideration because they accommodate various propagation modes such as surface plasmonic polaritons (SPP). However, the SPP modes are difficult to generate in HMM due to their weak electric field enhancement. In this article, we designed novel SERS substrates consisting of graphene-covered AgNPs and HMM. The graphene-covered AgNPs work as an external coupling structure for hyperbolic metamaterials due to this structure exhibiting significant plasmonic effects as well as unique optical features. The localized surface plasmonic resonance (LSPR) of the graphene-covered AgNPs excited the SPP and thus formed a strong hot spot zone in the nanogap area of the graphene. The Raman experiment was performed using rhodamine 6G (R6G) and crystal violet (CV), which showed high stability and a maximum enhancement factor of 2.12 × 108. The COMSOL simulation further clarified that enhanced SERS performance was due to the presence of monolayer graphene and provided an atomically flat surface for organic molecules in a more controllable manner. Interestingly, the proposed SERS structure carries out quantitative detection of thiram in soil and can satisfy the basic environmental need for pesticide residue in the soil.

Plasmonic optical fiber gratings based on few-layer Ta2C MXenes for refractive index sensing.

Tilted fiber Bragg grating (TFBG) is a widespread approach for developing refractive index (RI) sensors. The unique optoelectronic properties exhibited by MXene are expected to enhance the performance of TFBG-SPR sensors. In this study, a Ta2C coating appropriate for sensing was obtained by optimizing the photo-deposition time, which addressed the challenge of preparing large areas of MXene. The uniform coating of the few-layer Ta2C increases the wavelength sensitivity and FOM of the sensor to 229.5 nm/RIU and 2228.15 respectively. This significant enhancement was attributed to an ordered MXene phase of the grown Ta2C. The energy band theory verified the metallic nature of the Ta2C and the amplification effect on the RI response. Finite element analysis demonstrated that the stronger absorption band of Ta2C facilitated the generation of surface plasmon polariton. Based on the above benefits, the sensor detected melamine in milk with a detection limit of 7.9 × 10-9M. The TFBG/Au/Ta2C sensor is a promising approach for biochemical analysis and trace detection.

Composite substrate of graphene/Ag nanoparticles coupled with a multilayer film for surface-enhanced Raman scattering biosensing.

In this paper, we designed a surface-enhanced Raman scattering (SERS) substrate for graphene/Ag nanoparticles (Ag NPs) bonded multilayer film (MLF) using the hybrid nanostructures composed of graphene and plasmonic metal components with significant plasmonic electrical effects and unique optical characteristics. This paper achieved the advantages of efficient utilization of electromagnetic field and reduction of fluorescence background based on the electromagnetic enhancement activity of Ag NPs and unique physical/chemical properties of graphene with zero gap structures. Au/Al2O3 was stacked periodically to construct MLF. As indicated by the electric field intensity at the Au/Al2O3 interface of the respective layer, bulk plasmon polariton (BPP) in the MLF was excited and coupled with localized surface plasmon (LSP) in the Ag NPs, which enhanced the electromagnetic field on the top-layer of SERS substrate. To measure the performance of the SERS substrate, rhodamine 6G (R6G) and malachite green (MG) were used as the probe molecules, with the detection limits of 10-11 M and 10-8 M, respectively. The SERS substrate had high sensitivity and uniformity, which indicated that it has a broad application prospect in the field of molecular detection.

LSPR optical fiber sensor based on 3D gold nanoparticles with monolayer graphene as a spacer.

Localized surface plasmon resonance (LSPR) optical fiber biosensing is an advanced and powerful label-free technique which gets great attention for its high sensitivity to refractive index change in surroundings. However, the pursuit of a higher sensitivity is still challenging and should be further investigated. In this paper, based on a monolayer graphene/gold nanoparticles (Grm/Au NPs) three-dimensional (3D) hybrid structure, we fabricated a D-shaped plastic optical fiber (D-POF) LSPR sensor using a facile two-step method. The coupling enhancement of the resonance of this multilayer structure was extremely excited by the surface plasmon property of the stacked Au NPs/Grm layer. We found that the number of plasmonic structure layers was of high importance to the performance of the sensor. Moreover, the optimal electromagnetic field enhancement effect was found in three-layer plasmonic structure. Besides, the n*(Grm/Au NPs)/D-POF sensor exhibited outstanding performance in sensitivity (2160 nm/RIU), linearity (linear fitting coefficient R2 = 0.996) and reproducibility. Moreover, the sensor successfully detected the concentration of glucose, achieving a sensitivity of 1317.61 nm/RIU, which suggested a promising prospect for the application in medicine and biotechnology.

Surface-enhanced Raman scattering by the composite structure of Ag NP-multilayer Au films separated by Al2O3.

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

Composite Structure Based on Gold-Nanoparticle Layer and HMM for Surface-Enhanced Raman Spectroscopy Analysis.

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