Surface Enhanced Raman Spectroscopy Substrates Research Articles

Core-satellite nanocomposites via PEI-induced self-assembly for enhanced SERS sensing of thiram and ciprofloxacin

Developing sensitive, reliable, and robust surface-enhanced Raman spectroscopy (SERS) substrates relies heavily on fabricating a substantial number of hot spots. In this study, we present a straightforward method for creating Ag@PEI/Ag core-satellite nanocomposites. Large Ag nanospheres serve as the cores, and smaller Ag nanoparticles are electrostatically assembled around them through the introduction of polyethyleneimine (PEI). This assembly process generates numerous hot spots not only between two Ag satellites but also between the inner Ag core and Ag satellites, thanks to the sub-nm PEI interlayer. The nanocomposites exhibit great potential for SERS analysis, enabling effective sensing of various organic pollutants, such as thiram and ciprofloxacin, using a portable Raman spectrometer. Notably, these nanocomposites obtain an exceptional detection limit of as low as 10−8 M for them, which falls below the safety level set by the United States Environmental Protection Agency. Additionally, the substrates demonstrate excellent uniformity, reproducibility and storing stability. Consequently, the Ag@PEI/Ag core-satellite nanocomposites hold great promise as efficient SERS platforms for reliable and highly sensitive monitoring of food safety and environmental analysis.

Exploring the potential of branched submicron channels-based structures in ultra-thin Ag films for SERS molecular sensing

Noble metal-based nanostructures are actively studied due to their promising prospects for fabricating efficient substrates for Surface Enhanced Raman Spectroscopy (SERS)-based molecular sensing. In this work, we report the gross potential of SERS substrates based on branched submicron channels in ultra-thin Ag films. These films were fabricated by magnetron sputtering and then annealed in high vacuum conditions to induce branched channels growth by thermal dewetting. Different sets of nominally equal samples were tested during a determined period of time, using confocal Raman spectroscopy and methylene blue (MB) as Raman-active molecule, to assess their performance for SERS in ambient aging conditions. Micro-Raman intensity mapping studies demonstrated the emergence of “hot spots” enhancing the Raman signal in the branched submicron channels. A good mass sensitivity and fast spectral acquisition were achieved using these nanostructures, observing an exceptional spectral resolution and identifying all main vibrational states of MB in a few seconds for samples with a MB surface mass density of about 2 ng/mm2. A good spectral resolution was achieved even using shorter measurement times from 1.00 to 0.05 s, suggesting the potential for fast SERS determinations. Samples showed good reproducibility in the Raman spectral response during the tested period, demonstrating the marginal impact of the aging effects on the Raman signal enhancement and ensuring a time-stable SERS performance in the short term. Our results show that the proposed nanostructures are promising candidates for the development of substrates with competitive-sensitivity, time-stability, and fast SERS response, representing a simple and attractive alternative for efficient SERS-based molecular sensing.

Paper-based substrates for surface-enhanced Raman spectroscopy sensing.

Surface-enhanced Raman scattering (SERS) has been recognized as one of the most sensitive analytical methods by adsorbing the target of interest onto a plasmonic surface. Growing attention has been directed towards the fabrication of various substrates to broaden SERS applications. Among these, flexible SERS substrates, particularly paper-based ones, have gained popularity due to their easy-to-use features by full contact with the sample surface. Herein, we reviewed the latest advancements in flexible SERS substrates, with a focus on paper-based substrates. Firstly, it begins by introducing various methods for preparing paper-based substrates and highlights their advantages through several illustrative examples. Subsequently, we demonstrated the booming applications of these paper-based SERS substrates in abiotic and biological matrix detection, with particular emphasis on their potential application in clinical diagnosis. Finally, the prospects and challenges of paper-based SERS substrates in broader applications are discussed.

A rapid localization and analysis method for isoquinoline alkaloids with fluorescence in Coptis chinensis Franch. By fabricating the nano-silver sol as a substrate for surface-enhanced Raman spectroscopy

BackgroundThe quality of traditional Chinese medicines (TCMs) directly impacts their clinical efficacy and drug safety, making standardization a critical component of modern TCMs. Surface-enhanced Raman spectroscopy (SERS) is an effective physical detection method with speed, sensitivity, and suitability for large sample analyses. In this study, a SERS analysis method was developed using a nano-silver sol as the matrix to address the interference of fluorescence components in TCMs and overcome the limitations of traditional detection methods. ResultsThe higher sensitivity and efficiency of SERS was used, enabling detection of a single sample within 30 s. Coptis chinensis Franch. (CCF) was chosen as the model medicine, the nano-silver sol was used as the matrix, and CCF’s fourteen main fluorescent alkaloids were tested as index components. Typical signal peaks of the main components in CCF corresponded to the bending deformation of the nitrogen-containing ring plane outer ring system, methoxy stretching vibration, and isoquinoline ring deformation vibration. Through SERS detection of different parts, the distribution content of the main active components in the cortex of CCF was found to be lower than that in the xylem and phloem. Additionally, rapid quality control analyses indicated that among the nine batches of original medicinal materials purchased from Emei and Guangxi, the main active ingredient showed a higher content. SignificanceA SERS-based method for the rapid localization and analysis of multiple components of TCMs was established. The findings highlight the potential of SERS as a valuable tool for the analysis and quality control of TCMs, especially for fluorescent components.

Femtosecond laser-generated dome structures on Si substrate for surface-enhanced Raman spectroscopy

We exploit the impact of light diffraction on the morphology of silicon substrates when they are surface-structured in liquid environments using femtosecond laser pulses. This is done with the aim of applying these substrates in surface-enhanced Raman spectroscopy (SERS). Our findings demonstrate the successful creation of dome-like structures when ablating silicon substrates, while immersed in water, ethanol, and n-heptane, with a diffracted laser beam. We find that the process of creating dome-like structures is more efficient when using heptane and ethanol, and this efficiency increases as the number of line-by-line laser scans across the sample is increased. The laser ablation of Si surface in air results in forming ripples only, and the increase of scan number does not lead to domes formation. The SERS experiments on Rhodamine 6G (R6G) deposited on the laser-structured silicon substrates coated with silver nanoparticles (AgNPs) show significant enhancement of the Raman signal. Notably, the enhancement observed on surfaces featuring domed structures surpassed that seen on surfaces with ripple patterns. When evaluating R6G at a concentration of 10−9 mol/L, the presence of domes resulted in a Raman signal that was over threefold stronger.

Two-dimensional silver nanonetwork on Ag4Ti5O12 film as highly efficient SERS substrate

Surface Enhanced Raman Spectroscopy (SERS) is a powerful technique to study and detect single molecules adsorbed onto a surface. In this work, molar concentrations were varied over three consecutive orders of magnitude (10-3 M, 10-6 M, 10-9 M) of Methylene Blue (MB) to study SERS on different thicknesses of silver (6, 8, 10, 12 nm) coated on Ag4Ti5O12 deposited onto glass substrates as the base material. The Ag4Ti5O12 thin films were prepared by a unique ion-exchange method where Li4Ti5O12 thin films were initially deposited by the sol–gel method followed by the exchange of Li+ ion with Ag+ ion. The varied thicknesses of thermally deposited Ag-thin films were grown with unaltered Ag+ ions nucleation sites atop the Ag4Ti5O12 layer to create the two-dimensional (2D) nanonetwork. The structure and morphology of the as-prepared thin-film samples were characterized using X-ray diffraction, Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM) techniques. The SERS enhancement factor (EF), calculated using Raman spectroscopy, showed the systematic changes in the Raman signal enhancement as a function of Ag-thickness. The 10 nm thick as-deposited Ag sample showed the highest signal enhancement in Raman spectra than the other Ag thickness films. The successive signal enhancement was obtained due to forming the critical nuclei size of Ag on top of Ag4Ti5O12, which was further bolstered with film surface roughness and surface energy measurements. The as-prepared Ag-10 nm sample showed the lowest film roughness of ∼2.07 nm, in tune with the maximum enhancement factor (EF). We believe this work could open wide opportunities for developing efficient SERS substrates with sensing capabilities for ultra-low analyte concentration coupled with low cost and high enhancement factors.

Photoactive Au@MoS2 Micromotors for Dynamic Surface-Enhanced Raman Spectroscopy Sensing.

Photophoretic Au@MoS2 micromotors are used as smart mobile substrates for dynamic surface-enhanced Raman spectroscopy (SERS) sensing. The photophoretic capabilities and swarming-like propulsion of the micromotors allow for their schooling and accumulation in the measuring spot, increasing the density of SERS-active gold nanoparticles for Raman mapping and, simultaneously, the preconcentration of the target analyte. The generation of "hot-microflake spots" directly in the Raman irradiation point results in a 15-18-fold enhancement in the detection of crystal violet without the requirement for additional external sources for propulsion. Moreover, the reproducible collective micromotor motion does not depend on the exact position of the laser spot concerning individual micromotors, which greatly simplifies the experimental setup, avoiding the requirements of sophisticated equipment. The strategy was further applied for the detection of malachite green and paraquat with a good signal enhancement. The new on-the-move-based SERS strategy holds great promise for on-site detection with portable instrumentation in a myriad of environmental monitoring and clinical applications.

Triangular Au nanoparticle arrays based on flexible materials as temperature-sensitive SERS substrates

In this study, PS microspheres were used as masks to obtain tip-connected triangular Au nanoparticle arrays on the surface of Cu films by thermal evaporation. Then transferred to flexible polydimethylsiloxane (PDMS), triangular Au nanoparticle arrays (Au NPAs/PDMS) were obtained by increasing the temperature using concentrated stress to cause fracture at the junction. The prepared Au NPAs/PDMS was used as an active substrate for surface-enhanced Raman spectroscopy (SERS), and the Raman signal of probe molecule rhodamine 6G (R6G) was collected while the substrate was heated. Due to the thermal expansion of PDMS, the gap of Au NPAs/PDMS changes with increasing temperature, enabling dynamic SERS detection. When the temperature reaches 64 °C, the substrate achieves the optimal Raman enhancement with a low RSD value of 5.8 % and a detection limit of 10−8 M for R6G. Furthermore, we modified the substrate hydrophobic, and finally obtained a low concentration of 10−10 M, with an enhancement factor of 3.5 × 108, to achieve highly sensitive SERS signal detection. In addition, due to the high optical transmittance and flexibility, the PDMS can be well-fitted to the surface of the object, indicating the potential of the fabricated substrates for in-situ detection.

Two-Dimensional Amorphous Titanium Dioxide/Silver (TiO2/Ag) Nanosheets as a Surface-Enhanced Raman Spectroscopy Substrate for Highly Sensitive Detection.

For the purpose of investigating the chemical enhancement of amorphous semiconductors as well as increasing the sensitivity of the surface-enhanced Raman spectroscopy (SERS) substrate, titanium dioxide (TiO2) precursors were calcined at different temperatures to generate crystallized TiO2 (c-TiO2) and amorphous TiO2 (a-TiO2) nanosheets, respectively. Afterward, a two-dimensional (2D) a-TiO2/Ag nanosheet SERS substrate was successfully fabricated using electrostatic interaction between a-TiO2 and Ag nanoparticles. In order to demonstrate a greater SERS sensitivity on a-TiO2/Ag compared to either c-TiO2 or Ag nanoparticles alone, the SERS probe molecules rhodamine 6G (R6G) and malachite green (MG) were utilized. Based on the results of SERS detections for probe molecules and contaminants, it demonstrates that a-TiO2/Ag nanosheets produce highly sensitive and repeatable Raman signals. The detectable concentration limits for R6G and MG were found to be 10-11 M and 10-10 M, respectively. And it has been determined that the system exhibits an enhancement factor (EF) of up to 1 × 108. The limit of detection for 4-mercaptobenzoic acid and alizarin red can both reach 1 × 10-8. Furthermore, a finite-difference time-domain simulation is performed in order to evaluate the magnetic field strength generated by Ag nanoparticles. As a result of the simulation, it is evident that the actual EF is smaller than the calculated one, leading support to the view that a-TiO2 nanosheets have a beneficial effect on the chemical enhancement of SERS.

AgTNP@TiO2@Ag core-satellite composites for sensitive sensing and in situ monitoring photodegradation of organic dyes by portable Raman spectrometer

The development of sensitive, reliable, and robust substrates for surface-enhanced Raman spectroscopy (SERS) heavily relies on the creation of numerous hot spots. In this study, we propose a simple approach to fabricate core-satellite composites composed of AgTNP@TiO2@Ag, where Ag triangular nanoplates (AgTNPs) act as the cores, TiO2 serves as the interlayer, and Ag nanoparticles are deposited around them to form Ag satellites. By adjusting the amount of AgNO3, we precisely control the coverage of Ag nanoparticles on AgTNP@TiO2@Ag, thus fine-tuning their SERS sensitivity. Various characterization techniques were employed to examine their composition, morphology, and crystal structure. Thanks to the abundant hot spots created by the Ag satellites, these composites exhibit significantly enhanced SERS sensitivity and they demonstrate the capability to detect methylene blue (MB) at a concentration of 10−10 M by portable Raman spectrometer. Moreover, the AgTNP@TiO2@Ag composites effectively enable in situ SERS monitoring of the photodegradation reaction of MB. Overall, the novel AgTNP@TiO2@Ag composites prepared in this study exhibit high SERS sensitivity and excellent photocatalytic performance, making them highly valuable for environmental detection and ecological restoration purposes.

Optimization of physical vapor deposition process for low background nanoimprinted SERS substrate in quantitative melamine analysis

Uniformity, sensitivity, reproducibility, and cost are the critical parameters of practical surface-enhanced-Raman-spectroscopy (SERS) substrates. Herein, we proposed a High-Aspect-Ratio-Nano-Pillar-Array (HARNPA) substrate deposited silver by physical vapor deposition (PVD) methods (e.g. E-beam evaporation, sputtering, and a two-stage intermittent sputtering) to fabricate high-performance SERS substrates. The substrate by the E-beam evaporation has a significant SERS effect, but the Raman background induced by the exposure of the polymer HARNPA limits the analyte choice. The substrate by the sputtering method has better step coverage of silver but a lower enhancement factor. Therefore, we proposed a process of two-stage intermittent sputtering to solve these limitations. In addition, we define a factor called the signal-to-background peak ratio (S/B peak ratio) to evaluate the influence of the Raman background from the SERS substrate. Finally, we accomplished a SERS substrate with an S/B peak ratio of 3.48 by intermittent sputtering, which has the best linearity (R2 = 0.97) of the melamine concentration curve and the lowest detection limit (LoD = 5.6 × 10-7 M) that meets the regulatory requirements for melamine detection (3.96 × 10-6 M). The benefits of our SERS substrates are easy fabrication, high sensitivity (EF = 1.44 × 107), high reproducibility (CV = 8.4 %), and excellent uniformity (CV = 7 % in 4″ area), which are beneficial for mass production in the future.

Metal–Organic Frameworks–Based Surface–Enhanced Raman Scattering Substrates for Gas Sensing

Gas sensing holds great significance in environment monitoring, real–time security alerts and clinical diagnosis, which require sensing technology to distinguish various target molecules with extreme sensitivity and selectivity. Surface–enhanced Raman spectroscopy (SERS) has great potential in gas sensing for its single molecule sensitivity and fingerprint specificity. However, different from molecule sensing in solutions, SERS detection of gas often suffers from low sensitivity as gas molecules usually display a low Raman cross–section and poor affinity on traditional noble metal nanoparticle (NMNP)–based substrates. Therefore, much effort has been made to solve these problems. Fortunately, the appearance of metal–organic frameworks (MOFs) has shed new light on this direction. Due to the unique functional characteristics of MOFs, such as controllable pore size/shape, structural diversity and large specific surface area, SERS substrates based on MOFs can achieve high sensitivity, excellent selectivity and good stability. Although several reviews on MOF–based SERS substrates have been reported, few focus on gas sensing, which is a great challenge. Here, we mainly review the latest research progress on SERS substrates based on different MOFs. Sensitive and active SERS substrates can be prepared according to the unique advantages of MOFs with different metal centers. Then, we focus on composite SERS substrates based on different MOFs and NMNPs and summarize the application of composite SERS substrates in gas sensing. Finally, the future difficulties and potential possibilities of SERS substrates based on MOFs and NMNPs for gas sensing are discussed.

Application of high sensitive silver nanocubes SERS substrate for detection of metribuzin

Metribuzin, which is a triazinone herbicide, is extensively used in agricultural activities in order to control the spread of broad leaved weeds and grasses. This herbicide is treated as a hazardous chemical, since it multiplies the contamination in the ecosystem by infiltrating to groundwater and soil layers. Thus, detection of Metribuzin in even low concentrations is of vital importance. To date, analytical methods such as High Performance Liquid Chromatography (HPLC), reversed-phase thin-layer chromatography (RP-TLC) with UV absorption detection, Gas chromatography, and Mass spectrometry were utilized in order to detect Metribuzin. At this point, Surface Enhanced Raman Spectroscopy (SERS), while being not as analytical as the methods discussed above, emerges as a significant alternative, since it requires almost no consumables, requires a very short time for analysis and it allows on site analysis. In this study Ag nanocubes were synthesized as a SERS substrate and They were utilized for detection of Metribuzin at concentrations from 10−3 to 10−10 M. Reproducibility, sensitivity and chemical stability tests exhibited that Ag nanocubes were excellent candidates of SERS substrates by allowing detection at ultra- low concentrations up to 10−10 M.

Designing of a functional paper-tip substrate for sensitive surface-enhanced Raman spectroscopy (SERS) detection

A simple and flexible fabrication method of paper SERS substrate was developed by nanoparticles (NPs) droplet self-assembly at the paper tip with a temperature gradient (PTTG). We turned the drawback of the coffee ring effect into an effective way of preparing paper SERS substrate. When the NPs droplets were continuously dripped onto the PTTG, NPs were densely and uniformly distributed at the paper-tip front based on the combination of gravity and the coffee ring effect, which could achieve 91.2-fold improvement of SERS performance compared to a flat filter paper. Meanwhile, the analytes could also be enriched at the paper-tip front, which could achieve 9.3-fold signal enhancement compared to the paper-tip tail. Thus, the PTTG realized an excellent signal amplification for SERS detection. The paper-tip SERS substrate combined with a portable Raman spectrometer yielded an excellent analytical enhancement factor of 1.15 × 105 with the detection limit of 10 nM Rhodamine 6G (R6G). The whole fabrication procedure was completed within 2 h, and the paper-tip substrate showed a satisfactory substrate-to-substrate reproducibility with a relative standard deviation (RSD) of 5.13% (n = 10). It was successfully applied for quantitatively detecting real samples of oxytetracycline and malachite green with recoveries of 83.84–105.25% (n = 3). Meanwhile, we further evaluated the SERS performance of the PTTG using a laboratory-based Raman spectrometer, and it could realize the detection as low as 10 pM R6G. The proposed paper-tip substrate would offer a promising potential application for the on-site SERS analysis of food safety and environmental health.

Superhydrophobic Surface Modification of Polymer Microneedles Enables Fabrication of Multimodal Surface-Enhanced Raman Spectroscopy and Mass Spectrometry Substrates for Synthetic Drug Detection in Blood Plasma.

Microneedles are widely used substrates for various chemical and biological sensing applications utilizing surface-enhanced Raman spectroscopy (SERS), which is indeed a highly sensitive and specific analytical approach. This article reports the fabrication of a nanoparticle (NP)-decorated microneedle substrate that is both a SERS substrate and a substrate-supported electrospray ionization (ssESI) mass spectrometry (MS) sample ionization platform. Polymeric ligand-functionalized gold nanorods (Au NRs) are adsorbed onto superhydrophobic surface-modified polydimethylsiloxane (PDMS) microneedles through the control of various interfacial interactions. We show that the chain length of the polymer ligands dictates the NR adsorption process. Importantly, assembling Au NRs onto the micrometer-diameter needle tips allows the formation of highly concentrated electromagnetic hot spots, which provide the SERS enhancement factor as high as 1.0 × 106. The micrometer-sized area of the microneedle top and high electromagnetic field enhancement of our system can be loosely compared with tip-enhanced Raman spectroscopy, where the apex of a plasmonic NP-functionalized sharp probe produces high-intensity plasmonic hot spots. Utilizing our NR-decorated microneedle substrates, the synthetic drugs fentanyl and alprazolam are analyzed with a subpicomolar limit of detection. Further analysis of drug-molecule interactions on the NR surface utilizing the Langmuir adsorption model suggests that the higher polarizability of fentanyl allows for a stronger interaction with hydrophilic polymer layers on the NR surface. We further demonstrate the translational aspect of the microneedle substrate for both SERS- and ssESI-MS-based detection of these two potent drugs in 10 drug-of-abuse (DOA) patient plasma samples with minimal preanalysis sample preparation steps. Chemometric analysis for the SERS-based detection shows a very good classification between fentanyl, alprazolam, or a mixture thereof in our selected 10 samples. Most importantly, ssESI-MS analysis also successfully identifies fentanyl or alprazolam in these same 10 DOA plasma samples. We believe that our multimodal detection approach presented herein is a highly versatile detection technology that can be applicable to the detection of any analyte type without performing any complicated sample preparation.

Preparation of 3D nano silver trees/sea urchin-like gold and SERS detection of uric acid

In this paper, 3D nano-silver trees/sea urchin-like gold Surface Enhanced Raman Spectroscopy (SERS) substrates were prepared by chemical reduction method, characterized by SEM, EDS, UV–Vis and XRD et.al, and the preparation process was optimized using Rhodamine B (RB) as the Raman signal molecule. The SERS characteristics of Uric Acid on this substrate were investigated and the results showed that the SERS substrate had a Raman enhancement factor of 1.9 × 107 for RB, and also had a significant Raman enhancement effect on Uric Acid. The SERS intensity (ISERS) at 1400 cm−1 showed a good linear relationship with the logarithm value of uric acid concentration (log C) between the range of 5 × 10−4 M to 1 × 10−7 M. The linear fitting equation was ISERS = 890 (log C) + 8066 (R2 = 0.983), and the LOD = 2.8 × 10−8 M. The spiked test was performed in human serum with recoveries ranging from 82.86% to 125.13% and RSD (n = 3) < 3.5%.

Tuning LSPR of Thermal Spike-Induced Shape-Engineered Au Nanoparticles Embedded in Si3N4 Thin-Film Matrix for SERS Applications.

While gold nanoparticles (Au NPs) are widely used as surface-enhanced Raman spectroscopy (SERS) substrates, their agglomeration and dynamic movement under laser irradiation result in the major drawback in SERS applications, viz., the repeatability of SERS signals. We tune the optical and structural properties of size- and shape-modified Au NPs embedded in a thin silicon nitride (Si3N4) matrix by intense electronic excitation with swift heavy ion (SHI) irradiation with the aim of overcoming this classical SERS disadvantage. We demonstrate the shape evolution of a single layer of Au NPs inserted between amorphous Si3N4 thin films under fluences of 120 MeV Au9+ ions ranging between 1 × 1011 and 1 × 1013 ions cm-2. This shape modification results in the gradual blue shift of the localized surface plasmon resonance (LSPR) dip until 1 × 1012 ions/cm2 and then a sudden diminishment at 1 × 1013 ions/cm2. Finite domain time difference (FDTD) simulations further justify our experimental optical spectra. The dynamical NP aggregation and dissolution, in addition to NP elongation and deformation at different fluences, are noted from 2D grazing incidence small-angle X-ray scattering (GISAXS) profiles, as well as cross-sectional transmission electron microscopy (X-TEM). The systematic shape evolution of metal NPs embedded in the insulating matrix is shown to be due to thermal spike-induced localized melting and a localized pressure hike upon SHI irradiation. Utilizing this specific control over the characteristics of Au NPs, viz., shape, size, interparticle gap, and corresponding optical response via SHI irradiation, we demonstrate their applications as very stable SERS substrates, where the separation between NPs and analyte does not alter under laser illumination. Thus, these irradiated SERS active substrates with controlled NP size and gap provide the optimal conditions for creating localized electromagnetic hotspots that amplify the SERS signals, which do not alter with time or laser exposure. We found that the film irradiated with 1 × 1011 exhibits the highest SERS intensity due to its optimal NP size distribution and shape. Thus, not only our study provides a SERS substrate for stable and repeatable signals but also the understanding depicted here opens new research avenues in designing SERS substrates, photovoltaics, optoelectronic devices, etc. with ion beam irradiation.

Detection and quantification of antiviral drug tenofovir using silver nanoparticles and surface enhanced Raman spectroscopy (SERS) with spatially resolved hotspot selection

This study introduces a convenient and ultra-sensitive method of detection and quantification of the antiviral drug, tenofovir (TFV), by surface-enhanced Raman spectroscopy (SERS). Novel spatially resolved instrumentation for spectral acquisition and subsequent statistical analysis for hot spot selection was developed for convenient quantification of TFV in an aqueous matrix. Methods of statistical analysis include the use of partial least squares (PLS) regression vector analysis and spectral ranking by quality indices computed using CHAOS theory. Hydroxylamine-reduced Ag colloidal nanoparticles evaporated to dryness on an aluminum well-plate were used as the SERS substrate. To our knowledge, quantification of TFV down to 25 ng/mL by SERS, comprising clinically relevant concentrations, has not been previously reported. Furthermore, in this work we propose a novel method of quantification of aqueous TFV standards by SERS using statistical treatment of data by PLS and CHAOS theory. Based on these data, we propose future studies to develop a method of TFV detection and quantification in biological samples, beneficial to clinicians for rapid assessment of drug adherence during the treatment and prevention of viral diseases.

Atomic layer deposition assisted fabrication of insertable silver dendrites-based SERS substrates with high adhesion

Considerable efforts have been dedicated to the development of low-cost and highly sensitive surface-enhanced Raman spectroscopy (SERS) substrates, which have found applications in numerous fields. However, the critical factors of adhesion and stability have been insufficiently addressed. Such as Ag dendrites (Ag D) have been recognized for their cost-effectiveness and superior efficiency as SERS substrates, nonetheless, the issue of weak adhesion to the substrate has remained a challenge. Herein, a novel strategy to fabricate a Planar Ag dendrites-based SERS substrate with high adhesion is reported, that employs a combination of atomic layer deposition, roll milling, and chemical etching. The resulting Planar Ag dendrites show excellent adhesion, with a surface stripping force 18 times greater than that of pristine Ag dendrites, allowing for prolonged ultrasonic cleaning. Moreover, the substrate can be used as an insertable SERS sensor to obtain spectral information inside apples due to its excellent adhesion. The proposed design achieves high SERS sensitivity, with a limit of detection of 10-9 M and an analytical enhancement factor of 1.5 × 108 for R6G. Overall, this work provides a valuable reference for improving the adhesion of noble metal nanostructures on supporting substrates, offering a reliable SERS substrate for practical applications.

Enhanced phase transfer of Ag-nanospheres using amine-containing amphiphiles for sensitive chemical detection in nonaqueous environments

Effective phase transfer of Ag-nanospheres (AgNSs) was achieved through molecular interactions, rendering them interfacially compatible with various organic chemicals. This transfer was confirmed by distinct color changes and scanning electron microscope images, and the transferred AgNSs were employed as substrates for surface-enhanced Raman spectroscopy (SERS), enabling the sensitive detection of rhodamine 6G molecules dispersed in nonaqueous solutions. Notably, this detection capability extended to concentrations as low as 1 × 10−14 M. These findings underscore the potential of phase transferred AgNSs as versatile SERS substrates for sensitive chemical sensing in nonaqueous environments.