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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Plasmonics has drawn significant attention in the area of biosensors for decades due to the unique optical properties of plasmonic resonant nanostructures. While the sensitivity and specificity of molecular detection relies significantly on the resonance conditions, significant attention has been dedicated to the design, fabrication, and optimization of plasmonic substrates. The adequate choice of materials, structures, and functionality goes hand in hand with a fundamental understanding of plasmonics to enable the development of practical biosensors that can be deployed in real life situations. Here we provide a brief review of plasmonic biosensors detailing most recent developments and applications. Besides metals, novel plasmonic materials such as graphene are highlighted. Sensors based on Surface Plasmon Resonance (SPR), Localized Surface Plasmon Resonance (LSPR), and Surface Enhanced Raman Spectroscopy (SERS) are presented and classified based on their materials and structure. In addition, most recent applications to environment monitoring, health diagnosis, and food safety are presented. Potential problems related to the implementation in such applications are discussed and an outlook is presented.

The introduction of N doping atoms in the carbon network of Carbon Dots is known to increase their quantum yield and broaden the emission spectrum, depending on the kind of N bonding introduced. N doping is usually achieved by exploiting amine molecules in the synthesis. In this work, we studied the possibility of introducing a N–N bonding in the carbon network by means of hydrothermal synthesis of citric acid and hydrazine molecules, including hydrated hydrazine, di-methylhydrazine and phenylhydrazine. The experimental optical features show the typical fingerprints of Carbon Dots formation, such as nanometric size, excitation dependent emission, non-single exponential decay of photoluminescence and G and D vibrational bands in the Raman spectra. To explain the reported data, we performed a detailed computational investigation of the possible products of the synthesis, comparing the simulated absorbance spectra with the experimental optical excitation pattern. The computed Raman spectra corroborate the hypothesis of the formation of pyridinone derivatives, among which the formation of small polymeric chains allowed the broad excitation spectra to be experimentally observed.

Bacteria will likely become our most significant enemies of the 21st century, as we are approaching a post-antibiotic era. Bacteriophages, viruses that infect bacteria, allow us to fight infections caused by drug-resistant bacteria and create specific, cheap, and stable sensors for bacteria detection. Here, we summarize the recent developments in the field of phage-based methods for bacteria detection. We focus on works published after mid-2017. We underline the need for further advancements, especially related to lowering the detection (below 1 CFU/mL; CFU stands for colony forming units) and shortening the time of analysis (below one hour). From the application point of view, portable, cheap, and fast devices are needed, even at the expense of sensitivity.

Surface enhanced raman scattering (SERS) technique has been widely implemented for the detection/quantification of numerous compounds. The development of reusable SERS substrates through regeneration is a constant concern of scientists in the field, related to the sustainability of the method. Cold atmospheric plasma (CAP) is an advantageous green method well-known for its effectiveness towards the successful degradation of organic molecules and materials’ activation/modification. In the present study, we explored for the first time nanosecond pulsed dielectric barrier discharge (NSP-DBD) plasma as a rapid, energy efficient method for SERS solid substrates regeneration, implemented either directly in the gas or in the liquid phase as well as through immersion of the substrates in plasma activated water (PAW). We investigated the critical cold plasma factors (e.g. feeding gas, plasma treatment and retention time) in order to propose the most cost-effective alternative and shed light on the underlying regeneration mechanisms. The different SERS analysis case scenarios (analyte’s class , concentration andcross check) were considered, in order to simulate real SERS measurements conditions/requirements. In practical terms, such an approach will contribute to a significant reduction of the detection costs, revealing the NSP-DBD process as a flexible, fast, green, effective and low-cost solution towards the SERS substrates regeneration.

Natural dyes pose problems concerning their non-invasive identification in artefacts when most of the techniques usually employed for “in-situ” analysis of coloring materials are used. Nowadays, surface-enhanced Raman spectroscopy (SERS) is currently employed to recognise dyes extracted from textiles, as well as applied to extractionless analysis directly on fibers. Nevertheless, there is still a demand for a method based on SERS suitable for the “in-situ” identification of the dyes on intact fabrics in museums. The enhancement of the Raman scattering in SERS is due to two different mechanism, an electromagnetic and a chemical one. The former contributes to the SERS intensification in an order of magnitude of 1010, while the latter of 102. Therefore, in principle, the SERS enhancement can be observed also in absence of a chemisorption and thus, a dry-state analysis leading to a completely non-invasive approach should be possible. In this context, we are studying the possibility of using thin films obtained by deposition of silver colloids on an optically transparent support, i.e. a glass slide, to prepare in an easy way SERS probes suitable for “in situ” analysis by means of portable Raman instrumentation. Silver nanospheres obtained by different methods [2,3] or, alternatively, silver nanostars [4] were deposited on glass slides functionalised with (3-aminopropyl)trimethoxysilane, to promote the adherence and prevent the so-called “coffee ring” effect. The films were tested for the identification of anthraquinonic dyes by a portable Raman micro-probe in mock-up samples of dyed textile fibres. The possibility of embedding the nanoparticles into a polymeric matrix will be also considered to ensure higher stability and a lower impact on the examined object. Finally, we exploited for the first time, at least to the best of our knowledge, commercial electrochemically-deposited substrates (SERSitive) to observe dry-state SERS, obtaining positive results that encourage in perspective to experiment the electrochemical path to produce suitable substrates for our purposes.

Detection and estimation of various biomolecular samples are often required in research and clinical laboratory applications. Present work demonstrates the functioning of a surface-enhanced Raman scattering (SERS) substrate that has been obtained by drop-casting of citrate-reduced gold nanoparticles (AuNPs) of average dimension of 23 nm on a bare blu-ray digital versatile disc (BR-DVD) substrate. The performance of the proposed SERS substrate has been initially evaluated with standard Raman active samples, namely malachite green (MG) and 1,2-bis(4-pyridyl)ethylene (BPE). The designed SERS substrate yields an average enhancement factor of 3.2 106 while maintaining reproducibility characteristics as good as 94% over the sensing region of the substrate. The usability of the designed SERS substrate has been demonstrated through the detection and analysis of purified rotavirus double-stranded RNA (dsRNA) samples in the laboratory environment condition. Rotavirus RNA concentrations as low as 10 ng/μL could be detected with the proposed sensing scheme.

Epinephrine is a naturally occurring Catecholamine neurotransmitter, playing a key role in the fight-orflight response in the body. Surface Enhanced Raman Spectroscopy (SERS) is regarded as an ideal detection technique due to its specificity and sensitivity. Here, we report the experimental SERS detection of Epinephrine solution down to 10 μM using a simple, inexpensive A4-paper-based substrate coated with silver nanoparticles. We also perform Density Functional Theory (DFT) calculations of the Epinephrine molecule in the presence of small silver clusters Agn (n = 1-4) to understand the chemical interactions between the molecule and the clusters. It is observed that there are two different minima for the Epinephrine-Ag4 complexes; one of these shows an increase in the calculated Raman activity, and the other shows an increase in the stability, with increasing number of atoms in the silver cluster. These observations are further investigated and explained through the calculation of the interaction energies, reactivity parameters, electrostatic properties and Natural Bond Orbital (NBO) analysis.

Insulin is a peptide hormone produced by beta cells of pancreatic islets. In type 1 diabetes mellitus, these islets are destroyed by the body’s own immune system, no insulin is produced and the blood glucose level is increased. Nowadays, efforts in combatting type 1 diabetes focus on the transplantation of islets immunoprotected in microspheres made of non-covalently crosslinked hydrogels. The functionality of the encapsulated islets is retained, while the hydrogel matrix allows permeation of the produced insulin into the bloodstream. The applicability of these microspheres has been extensively studied in vivo. However, prior to biological models, a dynamic detection method to monitor the production of insulin and its diffusion through the microspheres is still missing. Herein, we apply the Surface Enhanced Raman Scattering (SERS) technique to detect physiologically relevant concentrations of insulin using planar Ag SERS substrates, while considering their implementation for monitoring insulin diffusion through alginate matrices. Insulin was detected after drying SERS planar substrates in a concentration range of 10-3- 10-12 M. Additionally, we demonstrated the decrease in the deposition time using an alternating electric field. Moreover, the in situ monitoring of the SERS signal from insulin molecules has certain limitations when conducting experiments for SERS substrates submerged in water. As the secretion of insulin and its diffusion across the immunoprotective microspheres is a dynamic process, the development of an adequate detection method is expected to lead to a better understanding of these processes as a function of time, matrix composition, and glucose intake.