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.

Using nanosized metal substrates, surface-enhanced Raman scattering (SERS) is a tool for improving the Raman signal of biomolecules. For detection, SERS has gained much popularity and an important role in determining chemical composition. In the present study, SERS spectra of 2-methyl-4-(4-methylpiperazin-1-yl)-10H-thieno[2,3-b][1,5]benzodiazepine (olanzapine) (MPTB) were investigated on silver and silver-gold metal substrates (SERSitive, Warsaw, Poland) at different concentrations. Also, different chemical and electronic properties are investigated using DFT calculations. The ring and other functional modes in SERS change in frequency values with variations in intensity for all concentrations. The molecule is oriented in a tilted manner with respect to Ag and Ag-Au.

Surface enhanced Raman scattering (SERS) is a spectroscopic technique for trace analysis where the efficiency depends on the substrate. In the present work, concentration-dependent SERS of pioglitazone (EPMT) in silver and silver-gold substrates are reported. The presence and absence of different SERS peaks between the analyte spectra on silver and silver-gold substrates show that there is an orientation change of the analyte adsorbed depending on the surface-active metal. The density functional theory (DFT) method was used to verify the experimental findings obtained from normal Raman and SERS spectra. Theoretical modeling of EPMT and metal clusters are reported and enhancement factors are found from theoretical and experimental results. In the EPMT-Ag-Ag and EPMT-Ag-Au molecular systems, Frontier molecular orbital’s (FMO’s) results highlight charge transfers from Ag-Ag/Ag-Au clusters to the molecule. Furthermore, the SERS enhancement factor values show that EPMT is chemisorbed.

The molecular model is one of the most appealing to explain the peculiar optical properties of Carbon nanodots (CNDs) and was proven to be successful for the bottom up synthesis, where a few molecules were recognized. Among the others, citrazinic acid is relevant for the synthesis of citric acid-based CNDs. Here we report a combined experimental and computational approach to discuss the formation of different protonated and deprotonated species of citrazinic acid and their contribution to vibrational and magnetic spectra. By computing the free energy formation in water solution, we selected the most favoured species and we retrieved their presence in the experimental surface enhanced Raman spectra. As well, the chemical shifts are discussed in terms of tautomers and rotamers of most favoured species. The expected formation of protonated and de-protonated citrazinic acid ions under extreme pH conditions was proven by evaluating specific interactions with H2SO4 and NaOH molecules. The reported results confirm that the presence of citrazinic acid and its ionic forms should be considered in the interpretation of the spectroscopic features of CNDs.

The molecular emission model is the most accredited one to explain the emission properties of carbon dots (CDs) in a low-temperature bottom-up synthesis approach. In the case of citric acid and urea, the formation of a citrazinic acid (CZA) single monomer and oligomers is expected to affect the optical properties of the CDs. It is therefore mandatory to elucidate the possible role of weak bonding interactions in determining the UV absorption spectrum of some molecular aggregates of CZA. Although this carboxylic acid is largely exploited in the synthesis of luminescent CDs, a full understanding of its role in determining the final emission spectra of the produced CDs is still very far to be achieved. To this aim, by relying on purely first-principles density functional theory calculations combined with experimental optical characterization, we built and checked the stability of some molecular aggregates, which could possibly arise from the formation of oligomers of CZA, mainly dimers, trimers, and some selected tetramers. The computed vibrational fingerprint of the formation of aggregates is confirmed by surface-enhanced Raman spectroscopy. The comparison of experimental data with calculated UV absorption spectra showed a clear impact of the final morphology of the aggregates on the position of the main peaks in the UV spectra, with particular regard to the 340 nm peak associated with n-π* transition.

Raman spectroscopy has become an essential analytical technique for field detection and identification of illicit or dangerous materials such as explosives, but its main drawback is low signal intensity. This problem can be circumvented by using surface enhanced Raman spectroscopy (SERS), in which scattering signals increase significantly for analytes adsorbed onto or near nano structured surfaces of the plasmonic materials. However,despite numerous studies, SERS has still not been widely used in real-world applications. The main goal of the studies describe herein was to investigate the possibility of detection of trace amounts of selected explosive materials on various commercial and non-commercial SERS substrates using portable Raman instruments. Our studies have shown that while portable systems suitable for SERS measurement of trace amounts of explosives are readily available, the problem remains in the selection of reliable and reproducible SERS substrates. Among five investigated SERS substrates only two, Klarite 312 and GaN-pillars allowed for trace analysis of all studied explosive materials. In both cases, detected concentrations of explosives ranged from single to hundreds of μg/cm2 depending on the explosive material and the Raman spectrometer used. Based on our findings, it could be concluded that the best SERS substrates for trace analysis of explosives are substrates with hot spots densely and evenly distributed over a whole active area of SERS substrate

Over the last decade several research groups have accomplished the fabrication of 2D periodic and 3D nanocage like structures on different materials using diverse lithographic approaches. Herein, we present the detailed studies on the fabrication of femtosecond (fs) laser‐induced periodic/ripple‐like surface structures on nickel (Ni) substrate in distilled water whereas 3D-like (nanocages) features on Ni substrates in acetone by tailoring the laser processing parameters (pulse energy). The morphological studies of simultaneously obtained Ni nanoparticles (NPs)/nanostructures (NSs) in distilled water/acetone were meticulously studied using transmission electron microscope (TEM) and field emission scanning electron microscope (FESEM). The fabricated Ni periodic/3D-like structures were gold (Au) plated using thermal evaporation technique and subsequently utilized as surface enhanced Raman scattering (SERS) active sensors for detecting the traces of various analyte molecules such as malachite green (MG) and Nile blue (NB). The grooved Ni-Au substrates allowed us to detect extremely low concentrations of MG (500 pM) and NB (5 nM) and, significantly, utilizing a simple, portable Raman spectrometer. Moreover, the substrates have demonstrated superior reproducibility as well as multi-utility nature with a relative standard deviation (RSD) of <17%. Additionally, Au- coated Ni grooved SERS substrates have demonstrated superior sensitivity and reproducibility in comparison to commercially available Ag-based SERS sensors (SERSitive, Poland). The proposed method of fabricating ripple and nanocages of Ni SERS platforms are highly viable to overcome the cost and one-time usage of substrates for on-site detection of several analyte molecules using a portable/hand-held Raman spectrometer.

The majority of analytical chemistry methods requires presence of target molecules directly at a sensing surface. Diffusion of analyte from the bulk towards the sensing layer is random and might be extremely lengthy, especially in case of low concentration of molecules to be detected. Thus, even the most sensitive transducer and the most selective sensing layer are limited by the efficiency of deposition of molecules on sensing surfaces. However, rapid development of new sensing technologies is rarely accompanied by new protocols for analyte deposition. To bridge this gap, we propose a method for fast and efficient deposition of variety of molecules (e.g. proteins, dyes, drugs, biomarkers, amino acids) based on application of the alternating electric field. We show the dependence between frequency of the applied electric field, the intensity of the surface enhanced Raman spectroscopy (SERS) signal and the mobility of the studied analyte. Such correlation allows for a priori selection of parameters for any desired compound without additional optimization. Thanks to the application of the electric field, we improve SERS technique by decrease of time of deposition from 20 h to 5 min, and, at the same time, reduction of the required sample volume from 2 ml to 50 μl. Our method might be paired with number of analytical methods, as it allows for deposition of molecules on any conductive surface, or a conductive surface covered with dielectric layer.

An assessment of the feasibility of using modified surface enhanced Raman scattering substrates (Ag nanoparticles on indium‑tin-oxide glass) for quantitative nanoparticle-enhanced laser induced breakdown spectroscopy (NELIBS) was carried out. Substrates were prepared with different surface coverage from various nanoparticle sizes, and their laser ablation behaviour was tested in detail. It was found that use of those combinations are most beneficial in terms of the signal enhancement factor, which provide the shortest interparticle distances. With the application of 266 nm laser wavelength, long (ms-range) gate width, and optimized laser pulse energy, the best NELIBS signal enhancement was found to be about a factor of three. By using liquid sample deposition by spraying, which was found to provide an even distribution of liquid samples on the substrate surface, successful calibration for Mn, Zn and Cr was performed. The NELIBS signal repeatability from five repeated measurements was found to be comparable to that of LIBS (5–10% RSD). These observations indicate that the NELIBS signal enhancement approach can be used in quantitative analytical applications for liquid samples, if i) the substrate fabrication procedure has good repeatability, ii) surface coverage and nanoparticle size is tightly controlled, iii) a homogenous liquid sample deposition is achieved.

The development of recyclable surface enhanced Raman scattering (SERS) based sensors has been in huge demand for trace level explosives detection. A simple, hybrid Silicon (Si) nanotextured target-based SERS platform is fabricated through patterning micro square arrays (MSA) on Si using femtosecond (fs) laser ablation technique at different fluences. Using the hybrid target Si MSA substrate loaded/decorated with Ag-Au alloy NPs (obtained using femtosecond ablation in liquids) we demonstrate the trace level detection of organic nitro-explosives [picric acid (PA), 2,4-dinitrotoluene (DNT), and 1, 3, 5-trinitroperhydro-1, 3, 5-triazine (RDX)] and their mixtures. The microstructures/nanostructures of MSA fabricated at an input fluence of 9.55 J/cm2, and decorated with Ag-Au alloy NPs, exhibited exceptional SERS enhancement factors (EFs) up to ∼1010 for MB, ∼106 for PA, and ∼104 for RDX with the detection limits obtained being ∼5 pM, ∼36 nM, and ∼400 nM for MB, PA and RDX respectively. Furthermore, we demonstrate these SERS substrates possess good reproducibility (RSD values < 15%) and a superior performance compared to a commercial Ag substrate (SERSitive, Poland). Three binary mixtures, i.e. MB-PA, MB-DNT, PA-DNT at different concentrations, were also investigated using the same SERS substrate to test the efficacy. Further, the SERS spectra of dyes, explosives, and complex mixtures were utilized for discrimination/classification using principal component analysis.

The paper reports on the features and advantages of horizontally oriented flexible silicon nanowires (SiNWs) substrates for surface-enhanced Raman spectroscopy (SERS) applications. The novel SERS substrates are described in detail considering three main aspects. First, the key synthesis parameters for the flexible nanostructure SERS substrates were optimized. It is shown that fabrication temperature and metal-plating duration significantly influence the flexibility of the SiNWs and, consequently, determine the SERS enhancement. Second, it is demonstrated how the immersion in a liquid followed by drying results in the formation of SiNWs bundles influencing the surface morphology. The morphology changes were described by fractal dimension and lacunar analyses and correlated with the duration of Ag plating and SERS measurements. SERS examination showed the optimal intensity values for SiNWs thickness values of 60–100 nm. That is, when the flexibility of the self-assembly SiNWs allowed hot spots occurrence. Finally, the test with 4-mercaptophenylboronic acid showed excellent SERS performance of the flexible, horizontally oriented SiNWs in comparison with several other commercially available substrates.

We show that surface-enhanced Raman spectroscopy (SERS) coupled with principal component analysis (PCA) can serve as a fast, reliable, and easy method for detection and identification of food-borne bacteria, namely Salmonella spp., Listeria monocytogenes, and Cronobacter spp., in different types of food matrices (salmon, eggs, powdered infant formula milk, mixed herbs, respectively). The main aim of this work was to introduce the SERS technique into three ISO (6579:2002; 11290–1:1996/A1:2004; 22964:2006) standard procedures required for detection of these bacteria in food. Our study demonstrates that the SERS technique is effective in distinguishing very closely related bacteria within a genus grown on solid and liquid media. The advantages of the proposed ISO-SERS method for bacteria identification include simplicity and reduced time of analysis, from almost 144 h required by standard methods to 48 h for the SERS-based approach. Additionally, PCA allows one to perform statistical classification of studied bacteria and to identify the spectrum of an unknown sample. Calculated first and second principal components (PC-1, PC-2) account for 96, 98, and 90% of total variance in the spectra and enable one to identify the Salmonella spp., L. monocytogenes, and Cronobacter spp., respectively. Moreover, the presented study demonstrates the excellent possibility for simultaneous detection of analyzed food-borne bacteria in one sample test (98% of PC-1 and PC-2) with a goal of splitting the data set into three separated clusters corresponding to the three studied bacteria species. The studies described in this paper suggest that SERS represents an alternative to standard microorganism diagnostic procedures.