SERSitive substrates in publications

Jagannath Rathod, Sree Satya Bharati Moram, Byram Chandu, Paweł Albrycht and Venugopal Rao Soma
We present a simple, fast, and single-step approach for fabricating hybrid semiconductor-metal nanoentities through liquid-assisted ultrafast (∼50 fs, 1 kHz, 800 nm) laser ablation. Femtosecond (fs) ablation of Germanium (Ge) substrate was executed in (i) distilled water (ii) silver nitrate (AgNO3—3, 5, 10 mM) (iii) Chloroauric acid (HAuCl4—3, 5, 10 mM), yielding the formation of pure Ge, hybrid Ge-silver (Ag), Ge-gold (Au) nanostructures (NSs) and nanoparticles (NPs). The morphological features and corresponding elemental compositions of Ge, Ge-Ag, and Ge-Au NSs/NPs have been conscientiously studied using different characterization techniques. Most importantly, the deposition of Ag/Au NPs on the Ge substrate and their size variation were thoroughly investigated by changing the precursor concentration. By increasing the precursor concentration (from 3 mM to 10 mM), the deposited Au NPs and Ag NPs’ size on the Ge nanostructured surface was increased from ∼46 nm to ∼100 nm and from ∼43 nm to ∼70 nm, respectively. Subsequently, the as-fabricated hybrid (Ge-Au/Ge-Ag) NSs were effectively utilized to detect diverse hazardous molecules (e.g. picric acid and thiram) via the technique of surface-enhanced Raman scattering (SERS). Our findings revealed that the hybrid SERS substrates achieved at 5 mM precursor concentration of Ag (denoted as Ge-5Ag) and Au (denoted as Ge-5Au) had demonstrated superior sensitivity with the enhancement factors of ∼2.5 × 104, 1.38 × 104 (for PA), and ∼9.7 × 105 and 9.2 × 104 (for thiram), respectively. Interestingly, the Ge-5Ag substrate has exhibited ∼10.5 times higher SERS signals than the Ge-5Au substrate.
Keywords: SERS, SERS Substrates, Raman, New methods, SERS Substrates production
Lee Chin-Heng, Tsai Chun-Hung, Lin Ding-Zheng
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.
Keywords: Surface plasmon resonance, Surface lattice resonance, Capillarity-assisted particle assembly, Surface-enhanced Raman scattering spectroscopy, Silver nanoparticles, Molecule detection
Haipeng Li, Elodie Dumont, Roman Slipets Thomas Thersleff, Anja Boisen, Georgios A. Sotiriou
Pesticide residues in food products cause human health concerns through food contamination, thereby necessitating their rapid and facile detection. Although surface-enhanced Raman scattering (SERS) technique can rapidly and reliably detect pesticide residues, its application in food safety diagnostics is restricted by its high expense, low scalability, and low reproducibility of the necessary sensors. Herein, we present a low-cost, large-scale, and highly reproducible nanofabrication route for SERS nano-sensors, based on the thermophoresis-assisted direct deposition of plasmonic core–shell structured Ag-SiO2 nanoparticles produced in the gas phase, on temperature-controlled inexpensive glass substrates. The high-performance SERS substrates were fabricated at a laboratory production rate of 100 samples/hour, demonstrating the scalability and cost-effectiveness of our aerosol manufacturing strategy. Our highly sensitive SERS substrates rapidly and quantitatively detected pesticide residues in fresh orange, indicating their practical applicability for food safety diagnostics.
Keywords: Pesticide residueFast and quantitative detection, Surface-enhance Raman scattering (SERS), Low-cost and large-scale substrate fabrication, Uniformity and reproducibility
Nadzeya Khinevich, Mindaugas Juodėnas, Asta Tamulevičienė, Tomas Tamulevičius, Martynas Talaikis, Gediminas Niaura, Sigitas Tamulevičius
Routine single-molecule analysis using surface-enhanced Raman scattering (SERS) is still out of reach using conventional substrates based on corrugated metallic surfaces. Tailoring the substrate to a specific excitation wavelength is an effective way to improve the SERS enhancement factor. Here, we present a comprehensive theoretical and experimental study of wavelength-tailored SERS substrates with improved sensitivity, exploiting the surface lattice resonance (SLR) in a plasmonic lattice comprised of assembled Ag nanoparticles. We tuned the SLR close to 532 nm and evaluated its effect on SERS. We found that SLR-based substrates had 10 times overall higher sensitivity and 100 times higher sensitivity at the target wavelength compared to non-tuned counterparts. Furthermore, we compared monomer and tetramer unit cell cases and found that the combined effect of tuned SLR and hot spots further improves the enhancement factor more than 400 times over a substrate with a random layer of nanoparticles.
Keywords: Surface plasmon resonance, Surface lattice resonance, Capillarity-assisted particle assembly, Surface-enhanced Raman scattering spectroscopy, Silver nanoparticles, Molecule detection
Chiara Olla, Antonio Cappai, Stefania Porcu, Luigi Stagi, Marzia Fantauzzi, Maria Francesca Casula, Francesca Mocci, Riccardo Corpino, Daniele Chiriu, Pier Carlo Ricci and Carlo Maria Carbonaro
The differences between bare carbon dots (CDs) and nitrogen-doped CDs synthesized from citric acid as a precursor are investigated, aiming at understanding the mechanisms of emission and the role of the doping atoms in shaping the optical properties. Despite their appealing emissive features, the origin of the peculiar excitation-dependent luminescence in doped CDs is still debated and intensively being examined. This study focuses on the identification of intrinsic and extrinsic emissive centers by using a multi-technique experimental approach and computational chemistry simulations. As compared to bare CDs, nitrogen doping causes the decrease in the relative content of O-containing functional groups and the formation of both N-related molecular and surface centers that enhance the quantum yield of the material. The optical analysis suggests that the main emission in undoped nanoparticles comes from low-efficient blue centers bonded to the carbogenic core, eventually with surface-attached carbonyl groups, the contribution in the green range being possibly related to larger aromatic domains. On the other hand, the emission features of N-doped CDs are mainly due to the presence of N-related molecules, with the computed absorption transitions calling for imidic rings fused to the carbogenic core as the potential structures for the emission in the green range.
Keywords: carbon dots; nitrogen doping; fluorescent nanomaterials; optical spectroscopy; computational chemistry
H. Takei, N. Saito, T. Okamoto, K. Watanabe, M. Westphal, R. Tomioka and A. Gölzhäuser
We have developed a SERS stamp that can be pressed directly onto a solid surface for characterization of surface-adsorbed target molecules. The stamp was fabricated by transfer of a dense monolayer of SiO2 nanospheres from a glass surface onto a piece of adhesive tape and subsequent evaporation of silver. The performance of the resulting SERS stamps was evaluated by their exposure to methyl mercaptan vapor, and immersion in rhodamine 6G and ferbam solutions. It was found that beside the nanosphere diameter and metal deposition thickness, the extent of burial of the nanospheres into the adhesive tape, dictated by the pressure during the nanosphere transfer process, had a significant effect. We carried out FDTD calculations of the near field. Models are based on morphological information obtained from helium ion microscopy, which can provide high-resolution images of poor electrical conductors such as our SERS stamp. While one of our main eventual goals is detection of pesticides on agricultural produce, we have begun to take a careful step by testing our SERS stamp on better characterized surfaces such as a porous gel surface, having been immersed in fungicides such as ferbam. We also present our preliminary results with ferbam on oranges. It is expected that our well-characterized SERS stamp will play a role in shedding light on the poorly studied transfer process of target molecules onto a SERS surface as well as serving as a new SERS platform.
Keywords: SERS, SERS Substrates, Raman, New methods, SERS Substrates production
Mateusz Czerwiński, Ruben del Olmo Martinez and Marta Michalska-Domańska
The formation of nanostructured anodic titanium oxide (ATO) layers was explored on pure titanium by conventional anodizing under two different operating conditions to form nanotube and nanopore morphologies. The ATO layers were successfully developed and showed optimal structural integrity after the annealing process conducted in the air atmosphere at 450 °C. The ATO nanopore film was thinner (1.2 +/− 0.3 μm) than the ATO nanotube layer (3.3 +/− 0.6 μm). Differences in internal pore diameter were also noticeable, i.e., 88 +/− 9 nm and 64 +/− 7 nm for ATO nanopore and nanotube morphology, respectively. The silver deposition on ATO was successfully carried out on both ATO morphologies by silver electrodeposition and Ag colloid deposition. The most homogeneous silver deposit was prepared by Ag electrodeposition on the ATO nanopores. Therefore, these samples were selected as potential surface-enhanced Raman spectroscopy (SERS) substrate, and evaluation using pyridine (aq.) as a testing analyte was conducted. The results revealed that the most intense SERS signal was registered for nanopore ATO/Ag substrate obtained by electrodeposition of silver on ATO by 2.5 min at 1 V from 0.05M AgNO3 (aq.) (analytical enhancement factor, AEF ~5.3 × 104) and 0.025 M AgNO3 (aq.) (AEF ~2.7 × 102). The current findings reveal a low-complexity and inexpensive synthesis of efficient SERS substrates, which allows modification of the substrate morphology by selecting the parameters of the synthesis process.
Keywords: titanium anodization; anodic titanium oxide (ATO); silver nanoparticles; silver electrodeposition; colloidal silver deposition; surface-enhanced Raman spectroscopy (SERS)
M. Rahmani, P. Taugeron, A. Rousseau, N. Delorme, L. Douillard, L. Duponchel & J.-F. Bardeau
Surface enhanced Raman spectroscopy (SERS) is a powerful non-invasive technique to detect and identify molecule traces. The accurate identification of molecules is based on the detection of distinctive vibrational modes characteristic of a molecule adsorbed onto the surface. We investigated the detection performances of three commercial SERS substrates: nanostructured Au supports from Hamamatsu, Premium Ag–Au supports from SERSitive, and RAM–SERS–Au from Ocean Insight, which were tested with solutions of thiophenol (C6H6S) at 10–6 M and 10–8 M concentration. SERS measurements were performed systematically with 633 and 785 nm excitation wavelengths and Raman mappings were recorded randomly on the surfaces. The spectral quality (baseline intensity and signal-to-noise ratio), the thermal stability under laser illumination, and the Raman intensity distribution of the Hamamatsu substrate and our own fabricated gold substrate were discussed for the detection of 10–8 M thiophenol molecules. The detection of crystal violet (CV), a toxic dye, is demonstrated at 5.10–9 M.
Keywords: SERS, Commercial substrates, Nanorough surface, Trace detection, Raman analysis
Jagannath Rathod, Sree Satya Bharati Moram, Byram Chandu, Paweł Henryk Albrycht and VENUGOPAL RAO SOMA
We present a simple, fast, and single-step approach for fabricating hybrid semiconductor-metal nanoentities through liquid-assisted ultrafast (~50 fs, 1 kHz, 800 nm) laser ablation. Femtosecond (fs) ablation of Germanium (Ge) substrate was executed in (i) distilled water (DW) (ii) silver nitrate (AgNO3 – 3, 5, 10 mM) (iii) Chloroauric acid (HAuCl4 – 3, 5, 10 mM), yielding the formation of pure Ge, hybrid Ge-silver (Ag), Ge-gold (Au) nanostructures (NSs) and nanoparticles (NPs). The morphological features and corresponding elemental compositions of Ge, Ge-Ag, and Ge-Au NSs/NPs have been conscientiously studied using different characterization techniques. Most importantly, the deposition of Ag/Au NPs on the Ge substrate and their size variation were thoroughly investigated by changing the precursor concentration. By increasing the precursor concentration (from 3 mM to 10 mM), the deposited Au NPs and Ag NPs’ size on the Ge nanostructured surface was increased from ~46 nm to ~100 nm and from ~43 nm to ~70 nm, respectively. Subsequently, the as-fabricated hybrid (Ge-Au/Ge-Ag) NSs were effectively utilized to detect diverse hazardous molecules (e.g., picric acid and Thiram) via the technique of surface-enhanced Raman scattering (SERS). Our findings revealed that the hybrid SERS substrates achieved at 5 mM precursor concentration of Ag (denoted as Ge-5Ag) and Au (denoted as Ge-5Au) had demonstrated superior sensitivity with the enhancement factors (EFs) of ~2.5×104, 1.38×104 (for PA), and ~9.7×105 and 9.2×104 (for Thiram), respectively. Interestingly, the Ge-5Ag substrate has exhibited ~10.5 times higher SERS signals than the Ge-5Au substrate.
Keywords: SERS, SERS Substrates, Raman, Femtosecond Laser Ablation, Femtosecond Laser
Oliver S. J. Hagger, M. Emre Sener, Imran Khan, Francis Lockwood Estrin, Stefanos Agrotis, Albertus D. Handoko, Ivan P. Parkin and Daren J. Caruana
A helium gas atmospheric pressure plasma jet (APPJ) is used to prepare a silver-based SERS substrate. The Raman enhancement from substrates created using APPJ compares well with two commercially available silver-based SERS substrates and an in-house prepared physical deposition of pre-synthesised silver nanoparticles. An aqueous solution of rudimentary silver salt was required as an ink to deposit zero valent silver in a single step with no post processing. An array of 16 × 16 silver ‘islands’ are printed on borosilicate glass, each island taking 5 seconds to print with a power of < 14 W to sustain the plasma. The SERS response was assessed using 4-mercaptobenzoic acid and rhodamine 6G as model analytes, with a calculated detection limit of 1 × 10−6 M. Also demonstrated is the removal of analyte from the surface after Raman measurement by exposure to helium APPJ doped with oxygen followed by hydrogen to restore zero baseline. This regeneration takes less than 10 seconds and allows for replicate measurements using the same SERS substrate.
Keywords: SERS, Plasma Jet Deposition
Sritam Biswas, Yengkhom Damayanti Devi, Dipjyoti Sarma, Diganta Hatiboruah, Nabadweep Chamuah, Nima D. Namsa, Pabitra Nath
Among the different analytical techniques, surface-enhanced Raman scattering (SERS) approach is a widely used technique for the detection and analysis of various chemicals and biological samples. Present study reports a low- cost, sensitive SERS substrate that has an ability to detect rotavirus in clinical stool samples. The proposed SERS substrate has been fabricated through drop-casting of silver nanoparticles (AgNPs) on a printing-grade paper. Rotavirus particles were extracted from clinical stool samples. The presence of rotavirus antigen in stool samples was confirmed using enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction (PCR), and sequencing. The characteristic Raman peaks of rotavirus (RV) particles in solution were found to be significantly enhanced when Raman signals were recorded from the paper-based SERS substrates. Using the proposed SERS substrate, rotavirus samples with concentration as low as 1% could be reliably recorded by the Raman spec- trometer. The paper SERS substrate reported herein is an extremely cost-efficient platform and may find ap- plications in other research and clinical laboratories as well.
Keywords: SERS, Rotavirus, ELISA, PCR, Paper-based, substrate, Enhancement factor, biosers, bio-sers
Nan Chen, Ting-Hui Xiao, Zhenyi Luo, Yasutaka Kitahama, Kotaro Hiramatsu, Naoki Kishimoto, Tamitake Itoh, Zhenzhou Cheng & Keisuke Goda
Surface-enhanced Raman spectroscopy (SERS) is a powerful tool for vibrational spectroscopy as it provides several orders of magnitude higher sensitivity than inherently weak spontaneous Raman scattering by exciting localized surface plasmon resonance (LSPR) on metal substrates. However, SERS can be unreliable for biomedical use since it sacrifices reproducibility, uniformity, biocompatibility, and durability due to its strong dependence on “hot spots”, large photothermal heat generation, and easy oxidization. Here, we demonstrate the design, fabrication, and use of a metal-free (i.e., LSPR-free), topologically tailored nanostructure composed of porous carbon nanowires in an array as a SERS substrate to overcome all these problems. Specifically, it offers not only high signal enhancement (~106) due to its strong broadband charge-transfer resonance, but also extraordinarily high reproducibility due to the absence of hot spots, high durability due to no oxidization, and high compatibility to biomolecules due to its fluorescence quenching capability.
Keywords: porous carbon nanowire array, porous carbon, nanowire array, enhancement factor, rotavirus RNA, SERS, Paper-based SERS, Silver clusters, DFT, Experimental analysis, theoretical modelling, Raman, photoscience in biology, experimental techniques, Raman spectroscopy, theoretical approaches, single molecules, synthesis methods, ultrafast photochemistry, photoscience at nanoscale, infrared spectroscopy, surface enhanced raman spectroscopy, press, sciene, big scale research,
Kang Soo Lee, Zachary Landry, Fátima C. Pereira, Michael Wagner, David Berry, Wei E. Huang, Gordon T. Taylor, Janina Kneipp, Juergen Popp, Meng Zhang, Ji-Xin Cheng & Roman Stocker
Raman microspectroscopy offers microbiologists a rapid and non-destructive technique to assess the chemical composition of individual live microorganisms in near real time. In this Primer, we outline the methodology and potential for its application to microbiology. We describe the technical aspects of Raman analyses and practical approaches to apply this method to microbiological questions. We discuss recent and potential future applications to determine the composition and distribution of microbial metabolites down to subcellular scale; to investigate the host–microorganism, cell–cell and cell–environment molecular exchanges that underlie the structure of microbial ecosystems from the ocean to the human gut microbiomes; and to interrogate the microbial diversity of functional roles in environmental and industrial processes — key themes in modern microbiology. We describe the current technical limitations of Raman microspectroscopy for investigation of microorganisms and approaches to minimize or address them. Recent technological innovations in Raman microspectroscopy will further reinforce the power and capacity of this method for broader adoptions in microbiology, allowing microbiologists to deepen their understanding of the microbial ecology of complex communities at nearly any scale of interest.
Keywords: non-destructive technique, non-destructive, enhancement factor, rotavirus RNA, SERS, Paper-based SERS, Silver clusters, DFT, Experimental analysis, theoretical modelling, Raman, photoscience in biology, experimental techniques, Raman spectroscopy, theoretical approaches, single molecules, synthesis methods, ultrafast photochemistry, photoscience at nanoscale, infrared spectroscopy, surface enhanced raman spectroscopy, press, sciene, big scale research,
Michael J. Zervas
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2019. Abstract: Detection of cancerous tumors and identification of counterfeit medications are just two examples that demonstrate the chemical specificity provided by Raman Spectroscopy. Yet, the widespread use of Raman Spectroscopy as an analytical tool has been limited to large bench-top systems in controlled laboratory environments. Existing technology, specifically in portable or handheld formats, suffers from a high false detection rate and relatively low sensitivity compared to other spectroscopic techniques. The present work addresses these issues through the design and development of a new system architecture that stochastically modulates the laser excitation wavelength. Small changes in excitation will proportionally shift the Raman scatter while having little effect on other spectral artifacts, including fluorescence. A custom confocal Raman Spectrometer was built and characterized that can rapidly shift the excitation wavelength by selectively straining an externally mounted Fiber Bragg Grating (FBG). When combined with a superluminescent diode (SLED), a modulation bandwidth of over half a nanometer was achieved. The functionality of the system was tested and benchmarked against Raman spectra that have been well characterized in literature. In addition, a novel signal processing approach was used to obtain a difference spectrum from a stochastic input excitation sequence. Simulations were conducted that compare the performance to conventional methods, which were then verified experimentally. Results indicate that the stochastic modulation was able to effectively isolate Raman scatter with a higher SNR compared to conventional methods. Finally, it was demonstrated that the developed system could be applied to Surface Enhanced Raman Spectroscopy (SERS). SERS substrates increase the Raman scatter signal, but also compete with significant fluorescence and a strong background signal. Rhodamine 6G, a fluorescent dye, was tested using the developed system on a SERS substrate. Concentrations on the order of several hundred parts per million (ppm) were successfully measured, with significantly lower limits of detection possible. The experimental data shows that the combination of SERS with stochastically modulated techniques reduces the false detection rate and improves the detection sensitivity by several orders of magnitude, addressing both of the major existing limitations.
Keywords: MIT, Mechanical Engineering, PhD, PhD Thesis, Stochastical, Stochastical Raman Spectrometer, Stochastically Modulated Raman Spectrometer, Raman, SERS, Spectrometer
Malwina Liszewska; Bartosz Bartosewicz; Bogusław Budner; Bartłomiej J. Jankiewicz
Raman spectroscopy has become a standard tool for identification of hazardous materials by first responders. However, despite many advantages of this technique, it has also a limitation, which is low sensitivity. This limitation could be overcome by Surfaced Enhanced Raman Spectroscopy, technique which still waits for real-world applications. In this paper, we present an overview of both methods, Raman and SERS spectroscopies, and examples of their uses for detection and identification of biological, chemical and explosive materials.
Keywords: Raman spectroscopy; SERS; hazardous materials detection
Mahmoud, Ahmed
In the past few decades, surface enhanced Raman scattering (SERS) has been evolving as a powerful analytical technique for the detection of a wide of chemical and biological molecules. The technique can reach a sensitivity of single molecule detection, which triggered plenty of ongoing research. In addition, technological advancements in photonics and nanoscience have resulted in the advent of portable and handheld Raman systems. These devices help SERS analysis move from expensive heavy-equipped research labs to low cost field deployable-research. The development of efficient SERS substrates that can provide signal enhancement by many orders of magnitude is a core component for SERS. The SERS substrates market and research are generally dominated by rigid solid substrates that are fabricated mostly by micro/nanofabrication techniques. Although these methods can provide reproducible substrates, they suffer from usability constraints because of their high cost of fabrication.
Keywords: Flexible SERS substrates, Membrane-supported SERS substrates, In-solution SERS substrates, Silver nanocoral, Gold nanostars, Surface enhanced Raman scattering, SERS substrates, SERS
Ana G. Abril, Mónica Carrera,Vicente Notario, Ángeles Sánchez-Pérez and Tomás G. Villa
Phages have certain features, such as their ability to form protein–protein interactions, that make them good candidates for use in a variety of beneficial applications, such as in human or animal health, industry, food science, food safety, and agriculture. It is essential to identify and characterize the proteins produced by particular phages in order to use these viruses in a variety of functional processes, such as bacterial detection, as vehicles for drug delivery, in vaccine development, and to combat multidrug resistant bacterial infections. Furthermore, phages can also play a major role in the design of a variety of cheap and stable sensors as well as in diagnostic assays that can either specifically identify specific compounds or detect bacteria. This article reviews recently developed phage-based techniques, such as the use of recombinant tempered phages, phage display and phage amplification-based detection. It also encompasses the application of phages as capture elements, biosensors and bioreceptors, with a special emphasis on novel bacteriophage-based mass spectrometry (MS) applications.
Keywords: phage-based proteomics; LC–ESI–MS/MS; mass spectrometry; bacteriophage; bacterial detection; antimicrobials; vaccines
Moram Sree Satya Bharati, Venugopal Rao Soma
This article reviews the most recent advances in the development of flexible substrates used as surface-enhanced Raman scattering (SERS) platforms for detecting several hazardous materials (e.g., explosives, pesticides, drugs, and dyes). Different flexible platforms such as papers/filter papers, fabrics, polymer nanofibers, and cellulose fibers have been investigated over the last few years and their SERS efficacies have been evaluated. We start with an introduction of the importance of hazardous materials trace detection followed by a summary of different SERS methodologies with particular attention on flexible substrates and their advantages over the nanostructures and nanoparticle-based solid/hybrid substrates. The potential of flexible SERS substrates, in conjunction with a simple portable Raman spectrometer, is the power to enable practical/on-field/point of interest applications primarily because of their low-cost and easy sampling.
Keywords: hazardous materials / flexible / surface-enhanced Raman scattering (SERS) / nanomaterials / nanostructures
V. S. Vendamani, Reshma Beeram, S. V. S. Nageswara Rao, A. P. Pathak, and Venugopal Rao Soma
We report results from our extensive studies on the fabrication of ultra-thin, flexible, and cost-effective Ag nanoparticle (NP) coated free-standing porous silicon (FS-pSi) for superior molecular sensing. The FS-pSi has been prepared by adopting a simple wet-etching method. The deposition time of AgNO3 has been increased to improve the number of hot-spot regions, thereby the sensing abilities are improved efficiently. FESEM images illustrated the morphology of uniformly distributed AgNPs on the pSi surface. Initially, a dye molecule [methylene blue (MB)] was used as a probe to evaluate the sensing capabilities of the substrate using the surface-enhanced Raman scattering (SERS) technique. The detection was later extended towards the sensing of two important explosive molecules [ammonium nitrate (AN), picric acid (PA)], and a pesticide molecule (thiram) clearly demonstrating the versatility of the investigated substrates. The sensitivity was confirmed by estimating the analytical enhancement factor (AEF), which was ∼107 for MB and ∼104 for explosives and pesticides. We have also evaluated the limit of detection (LOD) values in each case, which were found to be 50 nM, 1 µM, 2 µM, and 1 µM, respectively, for MB, PA, AN, and thiram. Undeniably, our detailed SERS results established excellent reproducibility with a low RSD (relative standard deviation). Furthermore, we also demonstrate the reasonable stability of AgNPs decorated pSi by inspecting and studying their SERS performance over a period of 90 days. The overall cost of these substrates is attractive for practical applications on account of the above-mentioned superior qualities.
Keywords: explosives, pesticides, low-cost, free-standing, silver, nanoparticles, decorated, porous, silicon, silver nanoparticles decorated porous silicon
Clement Yuen, Xiaohong Gao, James Jia Ming Yong, Prem Prakash, Chalapathy Raja Shobana, Perera Adhikarige Taniya Kaushalya, Yuemei Luo, Yanru Bai, Chun Yang, Peter R. Preiser, Quan Liu
We report a chip based on surface-enhanced Raman scattering (SERS) developed towards malaria field diagnosis. Only a mixture of 10-μl water and 10-μl blood is required as the sample input to the chip. Water is the only lysing agent to hemolyze blood cells while keeping the malaria biomarkers, hemozoin biocrystals, at locally high concentrations within parasites and/or their vacuoles. Then, SERS-active silver nanoparticles are synthesized on site near hemozoin in these concentrated regions when the blood/water mixture flows through and dissolves dried chemical patches that are earlier deposited inside the channel, which subsequently arrives at the detection region for SERS measurements. It should be highlighted that the procedure can be accomplished without a laboratory requirement and the risk of exposure to hazardous chemicals. Additionally, raw chemicals deposited inside the chip are chemically more stable than those readymade SERS substrates, thus the shelf life of the chip can be much longer. Furthermore, the chip yields analytical enhancement factor values ranging from 5.4 × 103 to 1.9 × 106 that are comparable to other ready-made SERS substrates in the literature. This strategy is capable of quantifying hemozoin concentrations in malaria infected human blood with a root-mean-square error of prediction of 0.3 μM, and a detection limit of 0.0025 % parasitemia level for parasites in the ring stage (equivalent to 125 parasites/μl) with a room of extra enhancement by switching the laser to a more suitable wavelength. These results show the feasibility to exploit this cost-effective yet highly sensitive SERS-based technique for malaria field diagnosis.
Keywords: Surface-enhanced Raman scatteringMalaria field diagnosisOn-chip sample preparationNear-analyte nanoparticle synthesisHemozoin detectionRaman spectroscopy