This review is focused on recent developments of surface-enhanced Raman scattering (SERS) applications in Analytical Chemistry. The work covers advances in the fabrication methods of SERS substrates, ...including nanoparticles immobilization techniques and advanced nanopatterning with metallic features. Recent insights in quantitative and sampling methods for SERS implementation and the development of new SERS-based approaches for both qualitative and quantitative analysis are discussed. The advent of methods for pre-concentration and new approaches for single-molecule SERS quantification, such as the digital SERS procedure, has provided additional improvements in the analytical figures-of-merit for analysis and assays based on SERS. The use of metal nanostructures as SERS detection elements integrated in devices, such as microfluidic systems and optical fibers, provided new tools for SERS applications that expand beyond the laboratory environment, bringing new opportunities for real-time field tests and process monitoring based on SERS. Finally, selected examples of SERS applications in analytical and bioanalytical chemistry are discussed.
The breadth of this work reflects the vast diversity of subjects and approaches that are inherent to the SERS field. The state of the field indicates the potential for a variety of new SERS-based methods and technologies that can be routinely applied in analytical laboratories.
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•This review covers recent advances of SERS applications in analytical chemistry.•Progresses in substrate development are discussed.•New types of devices that use SERS as a detection platform have been introduced.•SERS for bioanalytical applications is the area with most activity in the field.•New SERS quantification techniques are now available.
This work reviews different types of substrates used for surface-enhanced Raman scattering (SERS) that have been developed in the last 10 years. The different techniques of self-assembly to ...immobilize metallic nanoparticles on solid support are covered. An overview of SERS platforms developed using nanolithography methods, including electron-beam (e-beam) lithography and focused ion beam (FIB) milling are also included, together with several examples of template-based methodologies to generate metallic nano-patterns. The potential of SERS to impact several aspects of analytical chemistry is demonstrated by selected examples of applications in electrochemistry, biosensing, environmental analysis, and remote sensing. This review shows that highly enhancing SERS substrates with a high degree of reliability and reproducibility can now be fabricated at relative low cost, indicating that SERS may finally realize its full potential as a very sensitive tool for routine analytical applications.
Further progress in the applications of self-assembled nanostructures critically depends on developing a fundamental understanding of the relation between the properties of nanoparticle ensembles and ...their time-dependent structural characteristics. Following dynamic generation of hot-spots in the self-assembled chains of gold nanorods, we established a direct correlation between ensemble-averaged surface-enhanced Raman scattering and extinction properties of the chains. Experimental results were supported with comprehensive finite-difference time-domain simulations. The established relationship between the structure of nanorod ensembles and their optical properties provides the basis for creating dynamic, solution-based, plasmonic platforms that can be utilized in applications ranging from sensing to nanoelectronics.
This work presents the construction and optimization of nanoparticles-modified optical fiber tip (NPs-MOFT) devices for remote sensing by surface-enhanced Raman scattering (SERS). Silver ...nanoparticles (Ag-NPs) were self-assembled on optical fiber tips through a “layer-by-layer” procedure. It is shown that the SERS performance is at optimum when 5 “layers” of 50
nm Ag-NPs were deposited on the optical fiber tip. Using the optimized Ag-NPs-MOFT device, it was possible to detect 200
nM of the R6G dye in remote sensing mode (backscattering through the fiber). It was also possible to detect dye molecules with different structures and charges at the micro-molar concentration level, including anions, cations and neutral species. It can be envisioned that the Ag-NPs-MOFT device reported in this work can be further developed for SERS-based remote biosensing.
Schistosomiasis is a neglected tropical disease of a significant public health impact. The water rat Nectomys squamipes is one of the most important non-human hosts in the schistosomiasis mansoni ...transmission in Brazil, being considered a wild reservoir. Cellular mechanisms that contribute to the physiological adaptation of this rodent to the Schistosoma mansoni parasite are poorly understood. Here we identified, for the first time, that a hepatic steatosis, a condition characterized by excessive lipid accumulation with formation of lipid droplets (LDs) within hepatocytes, occurs in response to the natural S. mansoni infection of N. squamipes, captured in an endemic region. Significant increases of LD area in the hepatic tissue and LD numbers/hepatocyte, detected by quantitative histopathological and ultrastructural analyses, were paralleled by increased serum profile (total cholesterol and triglycerides) in infected compared to uninfected animals. Raman spectroscopy showed high content of polyunsaturated fatty acids (PUFAs) in the liver of both groups. MALDI-TOFF mass spectroscopy revealed an amplified pool of omega-6 PUFA arachidonic acid in the liver of infected animals. Assessment of liver functional activity by the levels of hepatic transaminases (ALT and AST) did not detect any alteration during the natural infection. In summary, this work demonstrates that the natural infection of the wild reservoir N. squamipes with S. mansoni elicits hepatic steatosis in the absence of liver functional harm and that accumulation of lipids, markedly PUFAs, coexists with low occurrence of inflammatory granulomatous processes, suggesting that lipid stores may be acting as a protective mechanism for dealing with the infection.
Raman microspectroscopy is a powerful analytical technique in cultural heritage. However, results are often compromised by luminescence interference and poor sensitivity. Surface‐enhanced Raman ...spectroscopy (SERS) is an alternative that can enhance the Raman signal and quench luminescence, but the interaction of an analyte and metal substrate produces altered Raman spectra. Shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) is a promising modification of SERS that encases the metal nanoparticles in ultrathin inert shells. As a consequence, it is reported that SHINERS spectra can be directly compared with normal Raman spectra, but this is not always the case, as discussed in this work. SHINERS, SERS, and normal Raman spectra were obtained from alizarin. The resulting spectra showed that the SHINERS data are comparable with the normal Raman spectrum of alizarin adsorbed in silica, not that of isolated alizarin. The structure of alizarin adsorbed in silica is discussed. Luminescence quenching observed in the SHINERS spectra can be attributed both to LSPR of the metallic nanoparticle cores and to alizarin–silica shell chemisorption. Both silica‐encapsulated silver and gold nanoparticles were considered, and it is shown that SHINERS spectra are dependent on the interaction of alizarin with silica, rather than the specific metal core within, in contrast to our observations of Ag and Au SERS nanoparticles. The metal agnostic quality of SHINERS is a potential advantage for the collection and comparison of reference data. Additionally, SHINERS systems result in quite stable spectra in pHs ranging from, at least, 6.0 to 9.3. Future research directions for SHINERS in cultural heritage are also discussed.
The resulting SHINERS spectra are comparable with normal Raman spectrum of alizarin adsorbed in silica, not that of isolated alizarin. Both Ag@SiO2 and Au@SiO2 were considered, and their spectra are dependent on the interaction of alizarin with silica, rather than the specific metal core within. Such metal agnostic quality is a potential advantage for the collection and comparison of reference data, and SHINERS systems also result in stable spectra in pHs ranging from, at least, 6.0 to 9.3, for alizarin.
Biosensors presenting high sensitivity for the detection of biomolecules are very promising for diseases diagnosis. Nowadays, there is a need for the development of biosensors with fast, trustworthy ...diagnosis and mostly with low cost, mainly for applications in developing countries. Label-free plasmonic biosensors are good candidates to reach out all these characteristics due to the possibility of spectral tunability, fast sensor response, real-time detection, strong enhancement of the local electric field and excellent adaptability to assemble different nanobiotechnology architectures. In this paper, two different configurations for LSPR based biosensor were developed by using solution-phase gold nanorods (S–P-AuNRs) and AuNRs-chip. The LSPR sensitivities were evaluated by monitoring shifts in the longitudinal plasmon band with changes in the refractive index of the medium surrounding the nanoparticles. AuNRs-chip presented higher sensitivity of 297 nm RIU−1 (refractive index unit) against 196 nm RIU−1 for S–P-AuNRs. Figure of merit (FOM) for AuNRs-chip and S–P-AuNRs were 3.0 and 2.2 RIU−1, respectively. This result was assigned to the coupling of the lower energy longitudinal LSPR mode of propagation for AuNRs-chip among nearby nanoparticles in the film. In addition, an improvement of at least 18% in sensitivity was obtained comparing to others AuNRs based assay with similar aspect ratio. FOM is more appropriate to compare different approaches, in this case, the proposed biosensor reached improvements of at least 114%, presenting higher values even when compared to AuNRs of higher aspect ratio. As a proof of concept, AuNRs surface was chemically modified using mercaptoundecanoic acid followed activation with ethylcarbodiimide and N-hidroxysuccinimide to allow the interaction between Bovine Serum Albumin (BSA) antibody and correspondent antigen. Both configurations studied resulted in efficient plasmonic biosensors, presenting high sensitivity for changes in the refractive index and for surface binding with anti-BSA.
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•Biosensors based on Au nanorods suitable for two different approaches were developed.•The sensitivity and figure-of-merit for LSPR are at least 18% and 114% superior to that reported before.•Both substrates were submitted to proof-of-concept experiments for biosensing of anti-BSA performing satisfactorily.•This study presents a step toward optimization of Au anisotropic nanoparticles LSPR biosensors.•This biosensor presents a simple methodology and short time of analysis.
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•Development of biosensors based on Au nanorods and surface-enhanced fluorescence.•Biosensing based on sandwich immunoassays for monitoring the molecular recognition.•Highly positive ...response for anti-BSA detection using antigen–antibody interaction.•Conversion of spectroscopic data into a digital protocol, simplifying data analysis.•Contributing for advancing SEF and AuNRs as an efficient biosensors platforms.
Gold nanoparticles (AuNPs) are attractive structures for biosensing, most due to different properties at nanoscale and biocompatibility. Localized surface plasmon resonance (LSPR) is one of these properties; LSPR enable the electromagnetic field enhancement closer to metallic surface, which allows surface-enhanced spectroscopies, like surface enhanced fluorescence (SEF). In this study, an immuno-biosensor based on gold nanorods (AuNRs) and SEF was constructed for simple and fast analysis to detect albumin antibody (anti-BSA) using antigen–antibody (anti-BSA/BSA) interaction as the biorecognition model. AuNRs were presented in two distinct configurations, in suspension (S-AuNRs) and adsorbed on glass slides (AuNRs-chip), and the detection was performed through an extrinsic method, wherein the SEF signal of a reporter molecule (IR-820 cyanine-type dye) was monitored. The analyte detection was evidenced by SEF mapping, where the average signal in the presence of anti-BSA was three times more intense than for the assay in the absence of analyte. A digital protocol was proposed to simplify the spectroscopic data analysis and reduce the intensity variability; in this protocol the number of positive events in the presence of anti-BSA is much larger (around two times) compared to the absence of analyte. The AuNRs based SEF immuno-biosensor allowed an efficient and simple analysis with specific biorecognition and may contribute as an efficient spectroscopy platform for immuno-biosensing.
This work reports on a new application of CuNPs-containing tellurite glasses as surface-enhanced Raman scattering (SERS) substrate for detection of the molecular probe 2,2′-bipyridine (bpy) at low ...concentrations. First, the structural features of the glasses were analyzed by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and Raman spectroscopy. The glassy nature of the samples was elucidated. Afterwards, the glasses were submitted to heat treatment, resulting in a glass-ceramic, and UV–visible spectroscopy revealed a red-shift in the localized surface plasmon resonance (LSPR) band of CuNPs. The glass-ceramic showed better SERS results in comparison to the glass and glass-metal composite, indicating an efficient enhancement mechanism to be investigated. Furthermore, SERS spectra of bpy solutions suggest the effectiveness of CuNPs-containing tellurite glasses as SERS substrate. This work contributes to the development of simple approach in obtaining an efficient SERS substrate.
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•Copper nanoparticles-containing tellurite glasses applied as SERS substrate for bpy detection.•The glassy nature of the samples was elucidated.•The glass-ceramic showed a red-shift in the LSPR band of CuNP.•The glass-ceramic showed better SERS results.
Green synthesis is an ecological technique for the production of well characterized metallic nanoparticles using plants. This study investigated the synthesis of silver nanoparticles (AgNPs) using a
...seed extract as a reducing agent.
The formation of AgNPs was identified by instrumental analysis, including ultraviolet-visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) of the AgNPs, and surface-enhanced Raman scattering (SERS) spectra of rhodamine-6G (R6G). We studied the physicochemical characterization of AgNPs, evaluated them as an antifungal agent against
,
and
, and estimated their minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) values. Lastly, this study evaluated the cytotoxicity of the AgNPs in murine L929 fibroblasts cells using an MTT assay.
The UV-Vis spectroscopy, SERS, SEM and XRD results confirmed the rapid formation of spheroidal 30-50 nm AgNPs. The MIC and MFC values indicated the antifungal potential of AgNPs against most of the fungi studied and high cell viability in murine L929 fibroblasts. In addition, this study demonstrated that
seed extracts may be used for the green synthesis of AgNPs at room temperature for the treatment of candidiasis.
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