2D Film-Like Magnetic SERS Tag with Enhanced Capture and Detection Abilities for Immunochromatographic Diagnosis of Multiple Bacteria.

Here, a multiplex surface-enhanced Raman scattering (SERS)-immunochromatography (ICA) platform is presented using a graphene oxide (GO)-based film-like magnetic tag (GFe-DAu-D/M) that effectively captures and detects multiple bacteria in complex specimens. The 2D GFe-DAu-D/M tag with universal bacterial capture ability is fabricated through the layer-by-layer assembly of one layer of small Fe3O4 nanoparticles (NPs) and two layers of 30 nm AuNPs with a 0.5 nm built-in nanogap on monolayer GO nanosheets followed by co-modification with 4-mercaptophenylboronic acid (MPBA) and 5,5'-dithiobis-(2-nitrobenzoic acid).The GFe-DAu-D/M enabled the rapid enrichment of multiple bacteria by MPBA and quantitative analysis of target bacteria on test lines by specific antibodies, thus achieving multiple signal amplification of magnetic enrichment effect and multilayer dense hotspots and eliminating matrix interference in real-world applications. The developed technology can directly and simultaneously diagnose three major pathogens (Staphylococcus aureus, Pseudomonas aeruginosa, and Salmonella typhimurium) with detection limits down to the level of 10 cells mL-1. The good performance of the proposed method in the detection of real urinary tract infection specimens is also demonstrated, suggesting the great potential of the GFe-DAu-D/M-ICA platform for the highly sensitive monitoring of bacterial infections or contamination.

Introduction of a multilayered fluorescent nanofilm into lateral flow immunoassay for ultrasensitive detection of Salmonella typhimurium in food samples.

Fast and sensitive identification of foodborne bacteria in complex samples is the key to the prevention and control of microbial infections. Herein, an ultrasensitive lateral flow assay (LFIA) based on multilayered fluorescent nanofilm (GO/DQD)-guided signal amplification was developed for the rapid and quantitative determination of Salmonella typhimurium (S. typhi). The film-like GO/DQD was prepared through the electrostatic mediated layer-by-layer assembly of numerous carboxylated CdSe/ZnS quantum dots (QDs) onto an ultrathin graphene oxide (GO) nanosheet, which possessed advantages including higher QD loading, larger surface areas, superior luminescence, and better stability, than traditional spherical nanomaterials. The antibody-modified GO/DQD can effectively attach onto a target bacterial cell to form a GO/DQD-bacteria immunocomplex containing almost ten thousand QDs, thus greatly improving the detection sensitivity of LFIA. The constructed GO/DQD-LFIA biosensor achieved the rapid and sensitive detection of S. typhi in 14 min with detection limits of as low as 9 cells/mL. Moreover, compared with traditional LFIA techniques for bacteria detection, the proposed assay exhibited excellent stability and accuracy in real food samples and enormously improved sensitivity (2-3 orders of magnitude), demonstrating its great potential in the field of rapid diagnosis.

Molybdenum disulfide-loaded multilayer AuNPs with colorimetric-SERS dual-signal enhancement activities for flexible immunochromatographic diagnosis of monkeypox virus.

The sudden outbreak of monkeypox in 2022 suggests the importance of developing a rapid but sensitive virus detection technology. Herein, we report a colorimetric/surface-enhanced Raman scattering (SERS) dual-signal co-enhanced immunochromatographic assay (ICA) for the flexible, ultrasensitive, and accurate detection of monkeypox virus (MPXV) in various complex samples. A thickness-controlled polyethyleneimine interlayer (1 nm) is coated onto two-dimensional molybdenum disulfide (MoS2) nanosheet to enable the electrostatic adsorption of two layers of dense 30 nm AuNPs, which not only improves colorimetric ability but also creates numerous efficient SERS hotspots. Moreover, the SERS activity of film-like dual-signal tag (MoS2@Au-Au) is drastically enhanced by combining the chemical enhancement effect of MoS2 sheets and the electromagnetic enhancement effect of Au-Au hotspots. The introduction of MoS2@Au-Au greatly broadens the application range of existing ICA methods, in which the colorimetric signal supports the quick identification of the target virus and the SERS signal allows the quantitative detection of MPXV with detection limits of as low as 0.2 and 0.002 ng/mL. Given its rapid detection ability (< 20 min), high accuracy in real samples (RSD < 9.89 %), and superior sensitivity than traditional AuNP-based colorimetric ICA (> 500 times), the proposed assay has great potential for field application.

Ultrasensitive and multiplex detection of four pathogenic bacteria on a bi-channel lateral flow immunoassay strip with three-dimensional membrane-like SERS nanostickers.

A lateral flow immunoassay (LFA) technique for sensitive and multiplexed on-site detection of bacteria remains a challenge. Here, we develop a bi-channel surface-enhanced Raman scattering (SERS)-based LFA by using three-dimensional membrane-like SERS tags as nanostickers (named GO@Au/Ag) for direct and ultrasensitive analysis of multiple pathogens in a single test. The grafting of numerous Ag satellites onto nanosticker significantly increased the relative surface area for bacteria binding and generated efficient SERS hotspots over large area to improve the sensing sensitivity. Antibody-labeled GO@Au/Ag nanostickers can rapidly stick onto the target bacteria and generate superior SERS signals and fluidity on the paper strip, thus conquering the adverse effect of bacteria size and improving the multiplex analysis ability of LFA. The integration of two different Raman reporter molecules into nanostickers allows simultaneous detection of four pathogens on two test lines, which significantly simplifies the reading process of SERS signals. The proposed biosensor can quantitatively detect four different bacteria in real clinical samples with low detection limit (9 cells mL-1 level), short assay time (20 min), high accuracy and excellent stability, indicating its great application potential for on-site detection of pathogens.

Ultrasensitive multichannel immunochromatographic assay for rapid detection of foodborne bacteria based on two-dimensional film-like SERS labels.

Rapid and sensitive detection of multiple foodborne bacteria without DNA amplification is still challenging. Here, we proposed an immunochromatographic assay (ICA) with multiplex analysis ability and high sensitivity for direct detection of bacteria in real food samples, based on an improved surface-enhanced Raman scattering (SERS) sensing strategy. Multifunctional Au shell-coated graphene oxide nanosheets (GO@Au) were fabricated and for the first time introduced into the ICA system as a two-dimensional film-like SERS label, which possessed huge surface area, excellent stability, and superior SERS activity. Different from the conventional spherical nanotags, the antibody-conjugated GO@Au nanosheet effectively and rapidly adhered to bacterial cells, improved the dispersibility of bacteria-nanolabel complexes on the ICA strips, and provided numerous stable hotspots for SERS signal enhancement. The combination of GO@Au labels and the ICA system achieved the multiplex and ultrasensitive determination of three major foodborne pathogens, namely, Staphylococcus aureus, Escherichia coli O157:H7, and Salmonella typhimurium, in a single test, with low detection limits (8, 10, and 10 cells/mL) and short detection time (20 min). The proposed biosensor demonstrated high stability and good accuracy in various food samples and is thus a promising tool for the rapid identification of bacteria.

Magnetic SERS Strip for Sensitive and Simultaneous Detection of Respiratory Viruses.

Rapid and early diagnosis of respiratory viruses is key to preventing infections from spreading and guiding treatments. Here, we developed a sensitive and quantitative surface-enhanced Raman scattering-based lateral flow immunoassay (SERS-based LFIA) strip for simultaneous detection of influenza A H1N1 virus and human adenovirus (HAdV) by using Fe3O4@Ag nanoparticles as magnetic SERS nanotags. The new type of Fe3O4@Ag magnetic tags, which were conjugated with dual-layer Raman dye molecules and target virus-capture antibodies, performs the following functions: specific recognition and magnetic enrichment of target viruses in the solution and SERS detection of the viruses on the strip. Based on this strategy, the magnetic SERS strip can directly be used for real biological samples without any sample pretreatment steps. The limits of detection for H1N1 and HAdV were 50 and 10 pfu/mL, respectively, which were 2000 times more sensitive than those from the standard colloidal gold strip method. Moreover, the proposed strip is easy to operate, rapid, stable, and can achieve high throughput and is thus a potential tool for early detection of virus infection.

Dual-SERS biosensor for one-step detection of microRNAs in exosome and residual plasma of blood samples for diagnosing pancreatic cancer.

MicroRNAs have been proved to be the biomarker for early detection of pancreatic cancer and the precisely quantitation of the MicroRNA-10b in the blood samples even can distinguish pancreatic cancer from chronic pancreatitis (CP) and normal controls (NC). In this study, we developed a DSN-assisted dual-SERS biosensor for microRNA-10b in exosome and residual plasma of blood samples detection based on the Fe3O4 @Ag-DNA-Au@Ag@DTNB (SERS tag) conjugates. In presence of target microRNA, it can hybridized with the complementary DNA probes. DSN enzyme was then added to selectively cleaves the DNA probe of the DNA/microRNA duplex, SERS tags can be released from the Fe3O4@Ag and SERS intensity quenching can be triggered, the released microRNA can enter the cycle to decluster other DNA and SERS tags. Due to the dual-SERS enhancement of the Fe3O4@Ag-SERS tag conjugates and the recycling signal amplification, a detection limit of 1 aM with single-base recognition can be performed by one step. The target microRNA in plasma-derived exosome and residual supernatant plasma of blood samples from pancreatic ductal adenocarcinoma (PDAC), chronic pancreatitis (CP) and normal controls (NC) were directly quantified and significant SERS signal distinction can be found among them. The precise quantitation, one-step and one-pot operation can ensure this assay a promising future for point-of-care cancer diagnosis technology.

Optimization of a hybrid plasmonic configuration: particle on a corrugated film and its SERS application.

Hybrid SERS configurations, which combine manufactured metallic chips with nanoparticles, have emerged as powerful and promising SERS substrates because they not only provide cost-effective and high-yield manufacture, but also demonstrate excellent sensitivity and outstanding reproducibility. Herein, a plasmonic hybrid structure, a particle on an Au film over nanoparticles (particle-AuFON) configuration, was studied for SERS application. In a previous study, we constructed a hybrid substrate by grafting Au@Ag core-shell NPs onto the AuFON structure. In this study, the hybrid substrate is designed and simulated to optimize electromagnetic enhancement while also affording exceptional uniformity, repeatability and stability, which are essential factors in SERS applications. This hybrid substrate provides good SERS performance with a detection limit of 1 × 10-10 M, which is 100-fold improvement compared to AuFON substrate or Au@Ag NPs. The excellent signal enhancement originates from the hotspot improvement and densification, as visualized by the FDTD calculations. Additional hotspots were created at the gaps between the Au@Ag NPs and the AuFON, thus improving the density of hotspots. Moreover, the intensity of the hotspots was improved due to EM coupling between the original hotspots and additional hotspots. To validate the feasibility of this hybrid substrate in SERS-based detection, melamine was detected as an example. The detection limit was 10 nM, which was much lower than the maximum limit of melamine in infant formula (1 ppm) legislated by the governments of both the United States and China. A calibration curve was plotted between the SERS intensity and melamine concentration with a correlation coefficient of 0.98. This hybrid SERS substrate shows great potential in SERS-based sensing and imaging, as it provides high sensitivity and outstanding reproducibility with a simple fabrication procedure, facilitating the cost-effective and high-yield manufacture of SERS substrates.

Investigating the Relationship Between Eye Movement and Brain Wave Activity Using Video Games: Pilot Study.

BACKGROUND: All eye movements are related in one way or another to our mental processes with lateral eye movements being associated with the different hemispheres of the brain. Eye movement techniques form the basis of eye movement desensitization and reprocessing therapy, wherein forced eye movements activate neurological pathways to treat the subject. OBJECTIVE: The objective of our study was to examine the relationship between players' eye movements and their brain wave activities using a video game. METHODS: We used similar eye movement techniques in the form of a video game called Lifeguard that could potentially stimulate different eye movement mode and create a more engaging experience for the user. By designing an experiment, we further explored the differences in electroencephalogram spectral power activity for the alpha, beta, theta, delta, and gamma frequency bands in Lifeguard and Tetris. RESULTS: The game based on eye movement technologies resulted in decreased delta power and increased beta power, but significant difference between 2 games was not found. CONCLUSIONS: The applied uses of this research could mean that eye movement desensitization and reprocessing can be conducted in a more fun and engaging way through the use of gaming technology.

Hotspots engineering by grafting Au@Ag core-shell nanoparticles on the Au film over slightly etched nanoparticles substrate for on-site paraquat sensing.

Paraquat (PQ) pollutions are ultra-toxic to human beings and hard to be decomposed in the environment, thus requiring an on-site detection strategy. Herein, we developed a robust and rapid PQ sensing strategy based on the surface-enhanced Raman scattering (SERS) technique. A hybrid SERS substrate was prepared by grafting the Au@Ag core-shell nanoparticles (NPs) on the Au film over slightly etched nanoparticles (Au FOSEN). Hotspots were engineered at the junctions as indicated by the finite difference time domain calculation. SERS performance of the hybrid substrate was explored using p-ATP as the Raman probe. The hybrid substrate gives higher enhancement factor comparing to either the Au FOSEN substrate or the Au@Ag core-shell NPs, and exhibits excellent reproducibility, homogeneity and stability. The proposed SERS substrates were prepared in batches for the practical PQ sensing. The total analysis time for a single sample, including the pre-treatment and measurement, was less than 5min with a PQ detection limit of 10nM. Peak intensities of the SERS signal were plotted as a function of the PQ concentrations to calibrate the sensitivity by fitting the Hill's equation. The plotted calibration curve showed a good log-log linearity with the coefficient of determination of 0.98. The selectivity of the sensing proposal was based on the "finger print" Raman spectra of the analyte. The proposed substrate exhibited good recovery when it applied to real water samples, including lab tap water, bottled water, and commercially obtained apple juice and grape juice. This SERS-based PQ detection method is simple, rapid, sensitive and selective, which shows great potential in pesticide residue and additives abuse monitoring.

Silver nanopartical over AuFON substrate for enhanced raman readout and their application in pesticide monitoring.

Surface-enhanced Raman detection of thiram is demonstrated by using Ag-nanoparticles (Ag NPs) on Au film over nanosphere (AuFON) substrate as the hybrid substrate. The SERS signal of the Ag NPs attached to solid supports is studied. The close coupling together of thousands of Ag NPs on AuFON leads to the generation of hot spots for SERS. The Ag NPs on AuFON can be applied to detect rhodamine-6G (R6G) with the detection limitation of 10-11 M and the pesticide thiram in acetone with a detection limit of as low as 0.24 ppm, which is much lower than the maximal residue limit (MRL) of 7 ppm in fruit prescribed by the U.S. Environmental Protection Agency (EPA). The hybrid substrates are shown to be highly sensitive for the detection of thriam, which produce highly enhanced Raman signals with good uniformity and reproducibility due to having plenty of hot spots on its surface.

Ultra-sensitive, high-throughput detection of infectious diarrheal diseases by portable chemiluminescence imaging.

This paper describes a rapid, ultra-sensitive, and high-throughput pathogenic DNA identification strategy for infectious diarrheal diseases diagnosis. This strategy is based on specific DNA hybridization and horseradish-peroxidase-catalyzed chemiluminescence (CL) detection. Probe DNA strands are covalently immobilized on the aldehyde-group-modified slide and hybridized with biotin-modified target DNA strands. Horseradish-peroxidase (HRP) is then combined with the target DNA via a biotin-streptavidin linkage. The subsequently added mixture of luminol and hydrogen peroxide is catalyzed by HRP and radiates photons. The photons are collected and read out by a portable imager. The specific detection of target DNA strands was realized at a detection limitation of about 0.75 nM. This strategy facilitates quantitative detection, as indicated by the fact that the CL signals were consistent well with a linear function. This method was applied to identify a myriad of real diarrheal pathogens samples, including Enterohemorrhagic Escherichia coli (EHEC), Vibrio cholerae (VBC), Shigella (SHLA), and Salmonella (SMLA). Triple-assay of six gene sequences from these pathogens was realized, which facilitates accurate, high-throughput identification of diarrheal pathogens. This CL assay strategy is appropriate for application in disease diagnosis and prevention.

Diversification of nanostructure morphology by modifying angle-resolved heterogeneous shadow mask.

This article presents a facile and generally applicable methodology for the morphology diversification of two-dimensional (2D) nanostructure arrays by modifying angle-resolved heterogeneous shadow mask (AR-HSM). Colloid spheres are used to prepare scalable well-organized monolayer film by self-assembly method and then etched in oxygen plasma to reduce size. Subsequently, the heterogeneous layer is generated by tilted metal deposition technique, then utilized as shadow mask in the substrate etching process, and finally removed by wet etching technique. As a result, the controllable fabrication of a series of complex morphologies, ranging from the crescent structure to the hoof-like structure and the stripes with apexes, is realized. The morphology of the nanostructure array is depend on the profile of the heterogeneous shadow mask (HSM) which is correlated to the incidence angle of the metal vapor. Therefore, a theoretical model is built for the prediction and design of the nanostructure morphology. This AR-HSM aided approach provides a novel and accessible route for the diversification of nanostructure morphology; and can be readily extended to other functional substrates which may be applied in photovoltaic devices or bio-chemical sensors.