A magnetically assisted surface-enhanced Raman scattering (SERS) biosensor for single-cell detection of S. aureus on the basis of aptamer recognition is reported for the first time. The biosensor ...consists of two basic elements including a SERS substrate (Ag-coated magnetic nanoparticles, AgMNPs) and a novel SERS tag (AuNR-DTNB@Ag-DTNB core-shell plasmonic NPs or DTNB-labeled inside-and-outside plasmonic NPs, DioPNPs). Uniform, monodisperse, and superparamagnetic AgMNPs with favorable SERS activity and magnetic responsiveness are synthesized by using polymer polyethylenimine. AgMNPs use magnetic enrichment instead of repeated centrifugation to prevent sample sedimentation. DioPNPs are designed and synthesized as a novel SERS tag. The Raman signal of DioPNPs is 10 times stronger than that of the commonly used SERS tag AuNR-DTNB because of the double-layer DTNB and the LSPR position adjustment to match the given laser excitation wavelength. Consequently, a strong SERS enhancement is achieved. Under the optimized aptamer density and linker length, capture by aptamer-modified AgMNPs can achieve favorable bacteria arrest (up to 75%). With the conventional Raman spectroscopy, the limit of detection (LOD) is 10 cells/mL for S. aureus detection, and a good linear relationship is also observed between the SERS intensity at Raman peak 1331 cm(-1) and the logarithm of bacteria concentrations ranging from 10(1) to 10(5) cells/mL. With the help of the newly developed SERS mapping technique, single-cell detection of S. aureus is easily achieved.
Oblique angle deposition (OAD) is a simple, low cost, effective, and maskless nanofabrication process. It can offer a reliable method for the mass fabrication of uniform metal nanorods which can be ...used as the surface-enhanced Raman scattering (SERS) substrate with an excellent enhancing performance. Up to now, Ag nanorods SERS substrates have been extensively studied. However, Ag is chemically active and easy to oxidize under atmospheric conditions. Comparatively, Au is chemically stable and has better biocompatibility than Ag. In this paper, we in detail, studied the electromechanical (EM) field distribution simulation, fabrication, and application of Au nanorods (AuNRs) on trace detection of methamphetamine. According to the finite-difference time-domain (FDTD) calculation results, the maximum EM intensity can be obtained with the length of AuNRs to be 800 nm and the tilting angle of AuNRs to be 71° respectively. The aligned Au nanorod array substrate was fabricated by the OAD process. The two key process parameters, deposition angle, and deposition rate were optimized by experiments, which were 86° and 2 Å/s, respectively. Using 1,2-bis (4-pyridyl) ethylene (BPE) as the probe molecule, the limit of detection (LOD) was characterized to be 10
M. The AuNRs were also used to detect methamphetamine. The LOD can be down to M (i.e., 14.92 pg/ml), which meet the requirements of the on-site rapid detection of the methamphetamine in human urine (500 ng/ml).
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.
•A robust and on-site PQ sensing strategy was developed based on a hybrid SERS substrate.•Hotspots of the hybrid substrate were engineered by grafting the Au@Ag core-shell nanoparticles on the Au FOSEN substrate.•The hybrid substrate gives higher enhancement factor comparing to either the Au FOSEN substrate or the Au@Ag core-shell NPs.•The hybrid substrate exhibits excellent reproducibility, homogeneity and stability.•PQ detection limit is 10nM with a good calibration line by fitting the Hill's equation.
This review describes recent advances in the use of magnetic-plasmonic particles (MPPs) for bacteria detection by Surface-Enhanced Raman Scattering (SERS). Pathogenic bacteria pollution has always ...been a major threat to human health and safety. SERS spectroscopy has emerged as a powerful and promising technique for sensitive and selective detection of pathogen bacteria. MPPs are considered as a versatile SERS platform for their excellent plasmonic properties and good magnetic responsiveness. Improved preparation method and typical characterization technique of MPPs are introduced, focusing on the thin and continuous metallic shell covering process. Consequently, the SERS-based sensing methods for bacteria identification were discussed, including the label-free and label-based methods. Finally, an overview of the current state of the field and our perspective on future development directions are given.
► Self-assembly, spin-coating, polystyrene nanosphere, colloidal-crystal films, physical mask.
Monolayer and bilayer colloidal-crystal films are used as physical mask in nanosphere lithography (NSL). ...So far, spin-coating experiments have mainly been designed to form nanosphere monolayer with one given size or obtain small areas of polystyrene (PS) nanosphere monolayer which limited the application of these films used as physical masks. The development of NSL required more study focused on the preparation of colloidal-crystal films with large-scale, high ordering degree and nanospheres of different diameters. In this study, PS nanospheres were self-assembled to form monolayer and bilayer colloidal-crystal films by employing spin-coating technology. Based on our experiments, we have built an experiment system of PS nanospheres of certain size ranging from 200nm to 1300nm. To give an instance, we have chosen PS nanospheres of four diameters (223nm, 347nm, 509nm, 1300nm) to fabricate colloidal-crystal films by adjusting the spin speed and acceleration, and we have investigated the relationship between the monolayer coverage areas and spin parameters by designing different spin speed and acceleration for 509nm nanosphere. Results revealed that monolayer and bilayer films of PS nanospheres with four different diameters were prepared successfully and the single structure where PS nanospheres were in hexagonal close-packed (HCP) order dominated the surface morphologies of both monolayer and bilayer colloidal-crystal films. For 509nm PS nanosphere, as the spin speed and acceleration increasing, the monolayer coverage areas increase firstly then decrease and at spin speed 1750rpm and acceleration 600rpm/s, the areas reaches the biggest.
In this research, a method was developed for fabricating Au-Au nanorod array substrates through the deposition of large-area Au nanostructures on an Au nanorod array using a galvanic cell reaction. ...The incorporation of a granular structure enhanced both the number and intensity of surface-enhanced Raman scattering (SERS) hot spots on the substrate, thereby elevating the SERS performance beyond that of substrates composed solely of an Au nanorod. Calculations using the finite difference time domain method confirmed the generation of a strong electromagnetic field around the nanoparticles. Motivated by the electromotive force, Au ions in the chloroauric acid solution were reduced to form nanostructures on the nanorod array. The size and distribution density of these granular nanostructures could be modulated by varying the reaction time and the concentration of chloroauric acid. The resulting Au-Au nanorod array substrate exhibited an active, uniform, and reproducible SERS effect. With 1,2-bis(4-pyridyl)ethylene as the probe molecule, the detection sensitivity of the Au-Au nanorod array substrate was enhanced to 10
M, improving by five orders of magnitude over the substrate consisting only of an Au nanorod array. For a practical application, this substrate was utilized for the detection of pesticides, including thiram, thiabendazole, carbendazim, and phosmet, within the concentration range of 10
to 5 × 10
M. An analytical model combining a random forest and a one-dimensional convolutional neural network, referring to the important variable-one-dimensional convolutional neural network model, was developed for the precise identification of thiram. This approach demonstrated significant potential for biochemical sensing and rapid on-site identification.
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 0.75nM. 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.
•An ultra-sensitive and high-specific DNA detection method was developed for infectious diarrheal diseases diagnosis.•This method is high-throughput based on the microarrays that covalently immobilized on the slide.•The CL signals were consistent well with a linear function, facilitating the quantitative detection.•Multiplex PCR product was used in the diagnosis to save the time and cost.•A portable and cost-effective chemiluminescence imager was developed for point-of-care diagnosis.
It is reported in the published literature that the resonant frequency of a silicon micromachined gyroscope decreases linearly with increasing temperature. However, when the axial force is ...considerable, the resonant frequency might increase as the temperature increases. The axial force is mainly induced by thermal stress due to the mismatch between the thermal expansion coefficients of the structure and substrate. In this paper, two types of micromachined suspended vibratory gyroscopes with slanted beams were proposed to evaluate the effect of the axial force. One type was suspended with a clamped-free (C-F) beam and the other one was suspended with a clamped-clamped (C-C) beam. Their drive modes are the bending of the slanted beam, and their sense modes are the torsion of the slanted beam. The relationships between the resonant frequencies of the two types were developed. The prototypes were packaged by vacuum under 0.1 mbar and an analytical solution for the axial force effect on the resonant frequency was obtained. The temperature dependent performances of the operated mode responses of the micromachined gyroscopes were measured. The experimental values of the temperature coefficients of resonant frequencies (TCF) due to axial force were 101.5 ppm/°C for the drive mode and 21.6 ppm/°C for the sense mode. The axial force has a great influence on the modal frequency of the micromachined gyroscopes suspended with a C-C beam, especially for the flexure mode. The quality factors of the operated modes decreased with increasing temperature, and changed drastically when the micromachined gyroscopes worked at higher temperatures.
The vibration characteristic analysis method for a quartz microgyroscope based on the admittance circle is reported in this paper. Admittance theory is introduced and the admittance circle principle ...is analysed to study the vibration characteristics of the quartz microgyroscope. The prototype gyroscope was fabricated by micro-electromechanical systems (MEMS) technology. The admittance and phase diagram of the work mode were obtained by vibration mode test systems. Then the admittance circle of the work mode was drawn, and the parameter identification of the transfer function between the voltage and current was completed to analyse the vibration characteristics. Therefore, the vibration characteristic analysis method based on the admittance circle can be used to build the transfer function of the quartz microgyroscope, which is helpful for the design of a high performance quartz microgyroscope.
Structure optimization and simulation analysis of the quartz micromachined gyroscope are reported in this paper. The relationships between the structure parameters and the frequencies of work mode ...were analysed by finite element analysis. The structure parameters of the quartz micromachined gyroscope were optimized to reduce the difference between the frequencies of the drive mode and the sense mode. The simulation results were proved by testing the prototype gyroscope, which was fabricated by micro-electromechanical systems (MEMS) technology. Therefore, the frequencies of the drive mode and the sense mode can match each other by the structure optimization and simulation analysis of the quartz micromachined gyroscope, which is helpful in the design of the high sensitivity quartz micromachined gyroscope.
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