Spatial Heterogeneity of Sulfate in Tap Water across China: Insights from a Rapid and Reliable Surface-Enhanced Raman Spectroscopy Analysis.

Thesynthesis of three-dimensional silver nanopopcorns (Ag NPCs) onto a flexible polycarbonate membrane (PCM) for the detection of nitrofurazone (NFZ) on the fish surface by surface-enhanced Raman spectroscopy (SERS)is presented. The proposed flexible Ag-NPCs/PCM SERS substrate exhibits significant Raman signal intensity enhancement with the measured enhancement factor of 2.36 × 106. This is primarily attributed to the hotspots created on Ag NPCs, including numerous nanoscale protrusions and internal crevices distributed across the surface of Ag NPCs. The detection of NFZ by this flexible SERS substrate demonstrates a low limit of detection (LOD) of 3.7 × 10-9M and uniform and reproducible Raman signal intensities with a relative standard deviation below 8.34%. It also exhibits excellent stability, retaining 70% of its efficacy even after 10days of storage. Notably, the practical detection of NFZ in tap water, honey water, and fish surfaces achieves LOD values of 1.35 × 10-8M, 5.76 × 10-7M, and 3.61 × 10-8M,respectively, which highlights its effectiveness across different sample types. The developed Ag-NPCs/PCM SERS substrate presents promising potential for sensitive SERS detection of toxic substances in real-world samples.

Facile fabrication of silver nanoparticle decorated α-Fe2O3 nanoflakes as ultrasensitive surface-enhanced Raman spectroscopy substrates

Preface to the special issue dedicated to Professor Richard P. Van Duyne (1945–2019)

In this work, TiO2 nanotube arrays were fabricated on Ti meshes via anodic oxidation and decorated with Ag nanoparticles by a photodeposition process. Then the surface-enhanced Raman scattering (SERS) effect of the as-prepared samples for trace thiram was directly investigated in a thiram aqueous solution. The stability and selectivity of our substrates were also explored. In addition, for practical purposes, we further studied the SERS of trace thiram in tap water using the as-prepared sample as a SERS substrate. At last, the surface-enhanced mechanism was discussed preliminarily. It can be found that the Ag-nanoparticle-decorated TiO2 nanotube array on a Ti mesh is an ultrasensitive SERS substrate for trace thiram in water. The detection limits are up to 1 × 10–9 mol L–1 in deionized water and 1 × 10–7 mol L–1 in tap water, respectively. Moreover, this substrate possesses dramatic signal uniformity [relative standard deviation <6% (spot-to-spot)], excellent reproducibility [relative standard deviation <...

One-pot synthesis of silver nanoparticle-coated fiberglass as a reusable and flexible SERS substrate of malachite green

A surface-enhanced Raman spectroscopy (SERS) substrate consisting of Au nanoparticles supported on twice-oxidized graphene oxide (ro-GO) for the determination of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was prepared. The Raman shift at △v = 779, 993, and 1203cm-1 was collected on the excitation condition of λ = 785nm for the qualitative identification of 2,3,7,8-TCDD in milk. Thepeak at △v = 1203cm-1 was selected as the characteristic peak for quantitation. The quantitation calculation was realized in the concentration range 10 to 100ngmL-1 with a limit of detection of3.24ngmL-1 in milk samples. The average recoveries of 2,3,7,8-TCDD in milk were 60.6-68.6% with relative standard deviations less than 6.4%. The long-term stability of the substrates was approximately 180days at 4°C. Further, theSERS method for the determination of 2,3,7,8-TCDD in milk samples based on the optimized hybrid SERS substrate and corresponding pre-treatment procedure is proposed. Graphical abstract Schematic representation of surface-enhanced Raman spectroscopy (SERS) determination of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) in milk samples by Au nanoparticles supported on twice-oxidized graphene oxide (ro-GO/AuNP) as a substrate.

Micro- and nanopatterning is crucial for advanced photonic, electronic, and sensing devices. Yet achieving large-area periodic nanostructures with a 75 nm half-pitch on low-cost laboratory systems remains difficult, because conventional near-ultraviolet laser interference lithography (LIL) suffers from Gaussian-beam non-uniformity and a narrow exposure latitude. Here, we report a cost-effective deep-ultraviolet (DUV) dual-beam LIL system based on a 266 nm laser and diffractive flat-top beam shaping, enabling large-area patterning of periodical nanostructures. At this wavelength, a moderate half-angle can be chosen to preserve a large beam-overlap region while still delivering 150 nm period (75 nm half-pitch) structures. By independently tuning the incident angle and beam uniformity, we pattern one-dimensional (1D) gratings and two-dimensional (2D) arrays over a Ø 1.0 cm field with critical-dimension variation < 5 nm (1σ), smooth edges, and near-vertical sidewalls. As a proof of concept, we transfer a 2D pattern into Si to create non-metal-coated nanodot arrays that serve as surface-enhanced Raman spectroscopy (SERS) substrates. The arrays deliver an average enhancement factor of ~1.12 × 104 with 11% intensity relative standard deviation (RSD) over 65 sampling points, a performance near the upper limit of all-dielectric SERS substrates. The proposed method overcomes the uneven hotspot distribution and complex fabrication procedures in conventional SERS substrates, enabling reliable and large-area chemical sensing. Compared to electron-beam lithography, the flat-top DUV-LIL approach offers orders-of-magnitude higher throughput at a fraction of the cost, while its centimeter-scale uniformity can be scaled to full wafers with larger beam-shaping optics. These attributes position the method as a versatile and economical route to large-area photonic metasurfaces and sensing devices.

Exhaled breath analysis offers noninvasive, early lung cancer detection via volatile organic compound (VOC) biomarkers, surpassing blood-based methods. Surface-enhanced Raman spectroscopy (SERS) is ideal for this purpose, combining molecular fingerprint specificity with single-molecule sensitivity. However, conventional SERS substrates face a fundamental limitation: while porous materials such as metal-organic frameworks effectively adsorb VOCs through their subnanometer pores (0.5-2 nm), their nonmetallic composition and confined pore architecture (orders of magnitude smaller than Raman excitation wavelengths) severely restrict plasmonic enhancement. In contrast, ordered plasmonic arrays deliver strong signal amplification but lack sufficient porosity for efficient VOCs adsorption. Here, we develop semiopen ordered Ag@Au nanotube arrays fabricated through nanoimprint lithography and ion beam etching-induced sidewall growth, which simultaneously function as optical resonators and molecular traps, enabling multimodal plasmonic coupling (localized surface plasmon resonance, surface plasmon resonance, and periodic lattice resonance) for superior light-matter interactions. The substrate's performance is further enhanced through Ag nanoparticle decoration for hotspot amplification and 4-aminothiophenol (4-ATP) functionalization for selective aldehyde capture via Schiff base reaction. The resulting SERS substrate shows strong visible absorption (86.5%), excellent benzaldehyde sensitivity (limit of detection: 10 ppb), and long-term stability (relative standard deviation = 4.9%, >50 days), offering a practical platform for breath-based lung cancer diagnostics.

In this work, an "off" to "on" surface-enhanced Raman spectroscopy (SERS) platform was constructed for ultrasensitive detection of microRNA (miRNA) by using a magnetic SERS substrate (Co@C/PEI/Ag) and padlock probe-based exponential rolling circle amplification (P-ERCA) strategy. Herein, miRNA 155 could act as primers to initiate rolling circle amplification (RCA) for producing a long repeat sequence, and then the obtained DNA would be cleaved into two kinds of single-stranded DNAs in the presence of nickase. One of the DNAs can be a new primer to initiate new cycle reactions for obtaining large numbers of the other one (trigger DNA), consequently leading to an exponential amplification. On the other hand, the hairpin DNA (H1), with a Raman label (Cy5) at one end, would form a hairpin structure to make the Cy5 closer to the SERS substrates, which could produce a strong SERS signal ("on" status). Then placeholder DNA (P2) partly hybridized with H1 to open the hairpin structure making Cy5 far away from substrates with a decreased signal ("off" status). Next, the obtained trigger DNA can complement with P2 to make the Raman label reclosed to the SERS substrates with a strong SERS signal ("on" status). From this principle, the strategy could achieve the change from "off" to "on" status. This SERS strategy exhibited a wide linear range of 100 aM to 100 pM with a low detection limit of 70.2 aM, which indicated the proposed SERS platform has potential application value for ultrasensitive bioassay of miRNA.

Discovery of new surface-enhanced Raman spectroscopy (SERS) substrates consisting of inexpensive and earth-abundant elements is an unmet need for the advancement of future analysis techniques for the ultrasensitive detection and quantification of chemical and biological analytes. Nanostructures (NSs) of noble metals such as Au, Ag, and Cu are the benchmarks for the preparation of highly efficient SERS substrates because of their unique localized surface plasmon resonance (LSPR) properties. Non-noble-metal SERS substrates, e.g., metal chalcogenide semiconductors and transition metal oxides, have been prepared to mitigate the cost; however, their low sensitivity restricts widespread applications. In this article, we report for the first time that the structure of oxygen-deficient, LSPR-active, nonstoichiometric tungsten oxide (i.e., WO3-x) NSs can control the SERS enhancement factor (EF). SERS substrates prepared with colloidally synthesized WO3-x nanowires, nanorods, and nanoplatelets display SERS EF of 2.5 × 106, 3.1 × 107, and 5.5 × 107, respectively, using rhodamine 6G (R6G) molecules as Raman probes. Our experimentally acquired SERS data and spectroscopically determined electronic band structure of LSPR-active WO3-x NSs, and time-domain density functional theory (TDDFT)-based calculations support a dual enhancement scheme involving a strong plasmonic effect controlled electromagnetic field and their oxygen vacancy-induced chemical enhancement mechanisms, respectively. To demonstrate the practical utility of our WO3-x NCs, we are able to detect aromatic nitro-explosives (tetryl, TNT, and DNT) with a very low limit of detection (LOD, 10-9 M). Importantly, machine learning-driven chemometric analysis for SERS-based detection shows excellent classification between these three explosives. Finally, three nonaromatic, nitro-explosives, HMX, RDX, and PETN are also successfully detected utilizing our LSPR-active, WO3-x-based SERS substrates. To the best of our knowledge, this is the first example where LSPR-active, non-noble-metal NSs are used for the detection of both aromatic and aliphatic nitro-explosives. Taken together, our work represents the advancement of the fabrication of non-noble-metal-based SERS substrates, which can be widely employed for the low-cost detection of analytes across forensic science, chemistry, and biomedical fields.

In-situ galvanic replacement reaction assisted preparation of porous Cu-Au composites as highly sensitive SERS substrates.

Innovative Synthesis of Adhesive-Assisted and Recyclable Fe3O4@PD-Ag Photomagnetic Nanocomposites as SERS probes for Ultrasensitive Thiram Detection on Fruit Peels

Surface-enhanced Raman spectroscopy (SERS) is a powerful technique for discrimination of bimolecules in complex systems. However, its practical applications face challenges such as complicated manufacturing procedures and limited scalability of SERS substrates, as well as poor reproducibility during detection which compromises the reliability of SERS-based analysis. In this study, we developed a convenient method for simultaneous fabrication of massive SERS substrates with an internal standard to eliminate the substrate-to-substrate differences. We first synthesized Au@CN@Au nanoparticles (NPs) which contain embedded internal standard molecules with a single characteristic peak in the Raman-silent region, and then deposited the NPs on 6 mm glass wafers in a 96-well plate simply by centrifugation for 3 min. The one-time obtained 96 SERS substrates have excellent intrasubstrate uniformity and intersubstrate repeatability for SERS detection by using the internal standard (relative standard deviation = 10.47%), and were able to detect both charged and neutral molecules (crystal violet and triphenylphosphine) at a concentration of 10-9 M. Importantly, cells can be directly cultured on glass wafers in the 96-well plate, enabling real time monitoring of the secretes and metabolism change in response to external stimulation. We found that the release of nucleic acids, amino acids and lipids by MDA-MB-231 cells significantly increased under hypoxic conditions. Overall, our approach enables fast and large-scale production of Au@CN@Au NPs-coated glass wafers as SERS substrates, which are homogeneous and highly sensitive for monitoring trace changes of biomolecules.

Near infrared and colorimetric fluorescence sensor for ultra-selective detection of Cu2+ level with applications in diverse water samples, brain tumor cell and flow injection analysis

We describe a patterned surface-enhanced Raman spectroscopy (SERS) substrate with the ability to pre-concentrate target molecules. A surface-adsorbed nanosphere monolayer can serve two different functions. First, it can be made into a SERS platform when covered by silver. Alternatively, it can be fashioned into a superhydrophobic surface when coated with a hydrophobic molecular species such as decyltrimethoxy silane (DCTMS). Thus, if silver is patterned onto a latter type of substrate, a SERS spot surrounded by a superhydrophobic surface can be prepared. When an aqueous sample is placed on it and allowed to dry, target molecules in the sample become pre-concentrated. We demonstrate the utility of the patterned SERS substrate by evaluating the effects of inhibitors to acetylcholinesterase (AChE). AChE is a popular target for drugs and pesticides because it plays a critical role in nerve signal transduction. We monitored the enzymatic activity of AChE through the SERS spectrum of thiocholine (TC), the end product from acetylthiocholine (ATC). Inhibitory effects of paraoxon and carbaryl on AChE were evaluated from the TC peak intensity. We show that the patterned SERS substrate can reduce both the necessary volumes and concentrations of the enzyme and substrate by a few orders of magnitude in comparison to a non-patterned SERS substrate and the conventional colorimetric method.