Label-free SERS detection of relevant bioanalytes on silver-coated carbon nanotubes: The case of cocaine

Au Ordered Array Substrate for Rapid Detection and Precise Identification of Etomidate in E-Liquid Through Surface-Enhanced Raman Spectroscopy

Etomidate (ET), a medical anesthetic, is increasingly being incorporated into e-liquids for consumption and abuse as a new psychoactive substance (NPS), leading to significant social issues. In this work, large-area Au micro- and nano-structured ordered arrays were engineered as surface-enhanced Raman spectroscopy (SERS) substrates for fast detection and precise identification of ET and its metabolites. This ordered array, characterized by abundant electromagnetic enhancement hotspots and structural uniformity, imparts unique properties to the SERS substrate, including ultra-sensitivity, spectral signal reproducibility, and precise quantitative capabilities. Furthermore, it effectively mitigates interference from the complex matrix of e-liquids, facilitating the rapid detection of trace amounts of ET molecules. This SERS rapid detection technology can act as a preliminary screening method for gold-standard spectroscopic analysis, facilitating the on-site rapid screening of suspicious samples and thereby enabling efficient detection and precise verification.

Ultra-trace SERS detection of cocaine and heroin using bimetallic gold-silver nanostars (BGNS-Ag)

A rapid, in-field, and reliable method for the detection of illegal drugs of abuse in biological fluids without any sample pretreatment would potentially be helpful for law enforcement, drug control officials, and public healthcare. In this study, we presented a cost-effective and highly reproducible solution-based surface-enhanced Raman scattering (SERS) platform utilizing a portable Raman instrument for fast sensitive SERS detection of illegal drugs, such as cocaine, and heroin in human urine without any sample preprocessing. The SERS platform was constructed for the first time by combining the superior SERS enhancement properties of bimetallic silver-coated gold nanostars (BGNS-Ag) and the advantages of suitable alkaline metal salts such as NaI for SERS signal amplification. The effects of the silver thickness of BGNS-Ag and alkaline salts on the SERS performance were investigated in detail; we observed that the maximum SERS enhancement was obtained for BGNS-Ag with the maximum silver thickness (54 ± 5 nm) in presence of NaI salt. Our SERS platform shows ultra-high sensitivity of cocaine and heroin with a limit of detection (LOD) as low as 10 pg/mL for cocaine and 100 pg/mL for heroin, which was 100 times lower than that of the traditional silver nanoparticle-based illegal drug detection. As a demonstration, the platform was further applied to detect cocaine and heroin spiked in human urine without any sample preprocessing achieving a LOD of 100 pg/mL for cocaine and 1 ng/mL for heroin. Overall, our SERS detection platform shows potential for rapid, onsite, ultra-low-cost portable applications for trace detection of illegal drugs and biomarkers.

Recent advances in non-plasmonic surface-enhanced Raman spectroscopy nanostructures for biomedical applications

Surface-enhanced Raman spectroscopy (SERS) is an emerging powerful vibrational technique offering unprecedented opportunities in biomedical science for the sensitive detection of biomarkers and the imaging and tracking of biological samples. Conventional SERS detection is based on the use of plasmonic substrates (e.g., Au and Ag nanostructures), which exhibit very high enhancement factors (EF = 1010 -1011 ) but suffers from serious limitations, including light-induced local heating effect due to ohmic loss and expensive price. These drawbacks may limit detection accuracy and large-scaled practical applications. In this review, we focus on alternative approaches based on plasmon-free SERS detection on low-cost nanostructures, such as carbons, oxides, chalcogenides, polymers, silicons, and so forth. The mechanism of non-plasmonic SERS detection has been attributed to interfacial charge transfer between the substrate and the adsorbed molecules, with no photothermal side-effects but usually less EF compared with plasmonic nanostructures. The strategies to improve Raman signal detection, through the tailoring of substrate composition, structure, and surface chemistry, is reviewed and discussed. The biomedical applications, for example, SERS cell characterization, biosensing, and bioimaging are also presented, highlighting the importance of substrate surface functionalization to achieve sensitive, accurate analysis, and excellent biocompatibility. This article is categorized under: Diagnostic Tools > Diagnostic Nanodevices Diagnostic Tools > Biosensing Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.

Present and Future of Surface-Enhanced Raman Scattering

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article.

Highly Efficient Photoinduced Enhanced Raman Spectroscopy (PIERS) from Plasmonic Nanoparticles Decorated 3D Semiconductor Arrays for Ultrasensitive, Portable, and Recyclable Detection of Organic Pollutants

Semiconductor materials have become competitive candidates for surface-enhanced Raman scattering (SERS) substrates; however, their limited SERS sensitivity hinders the practical applications of semiconductors. Here, we develop a hybrid substrate by integrating anatase/rutile TiO₂ heterostructure with dense plasmonic hotspots of Ag nanoparticle (AgNPs) for efficient photoinduced enhanced Raman spectroscopy (PIERS). The PIERS mechanism is systematically investigated by means of a portable Raman instrument. When ultraviolet (UV) light irradiates the substrate, the TiO₂-Ag hybrid arrays produce remarkable charge-transfer enhancement, which can be ascribed to the highly efficient charge separation driven by heterojunction and transfer from TiO₂ heterostructure to AgNPs. This platform allows for the rapid detection of multifold organic species, including malachite green (MG), crystal violet (CV), rhodamine 6G (R6G), thiram, and acephate, and as high as 27.8-fold enhancement over the normal SERS is achieved, representing the highest PIERS magnification up to the present time. The intensive PIERS enhancement makes it ultrasensitively detect analyte concentration of an order of magnitude lower than that of SERS method. The improved sensitivity and resolution can be readily realized by simple UV irradiation, which represents a major advantage of our PIERS methodology. Besides, the integration of uniform TiO₂ heterostructure arrays with AgNPs generates superior signal reproducibility with relative standard deviation (RSD) value of less than 14%. In addition, the detected molecules on the substrate can be eliminated by photocatalytic degradation after PIERS measurements by using UV irradiation, which makes the substrate reusable for 15 cycles. The ultrahigh sensitivity, superior reproducibility, and excellent recyclability displayed by our platform may provide new opportunities in field detection analysis coupled with a portable Raman instrument.

Optical Biosensors for Label-Free Detection of Small Molecules

Label-free optical biosensors are an intriguing option for the analyses of many analytes, as they offer several advantages such as high sensitivity, direct and real-time measurement in addition to multiplexing capabilities. However, development of label-free optical biosensors for small molecules can be challenging as most of them are not naturally chromogenic or fluorescent, and in some cases, the sensor response is related to the size of the analyte. To overcome some of the limitations associated with the analysis of biologically, pharmacologically, or environmentally relevant compounds of low molecular weight, recent advances in the field have improved the detection of these analytes using outstanding methodology, instrumentation, recognition elements, or immobilization strategies. In this review, we aim to introduce some of the latest developments in the field of label-free optical biosensors with the focus on applications with novel innovations to overcome the challenges related to small molecule detection. Optical label-free methods with different transduction schemes, including evanescent wave and optical fiber sensors, surface plasmon resonance, surface-enhanced Raman spectroscopy, and interferometry, using various biorecognition elements, such as antibodies, aptamers, enzymes, and bioinspired molecularly imprinted polymers, are reviewed.

Molecular Affinity Agents for Intrinsic Surface-Enhanced Raman Scattering (SERS) Sensors

Research at the interface of synthetic materials, biochemistry, and analytical techniques has enabled sensing platforms for applications across many research communities. Herein we review the materials used as affinity agents to create surface-enhanced Raman spectroscopy (SERS) sensors. Our scope includes those affinity agents (antibody, aptamer, small molecule, and polymer) that facilitate the intrinsic detection of targets relevant to biology, medicine, national security, environmental protection, and food safety. We begin with an overview of the analytical technique (SERS) and considerations for its application as a sensor. We subsequently describe four classes of affinity agents, giving a brief overview on affinity, production, attachment chemistry, and first uses with SERS. Additionally, we review the SERS features of the affinity agents, and the analytes detected by intrinsic SERS with that affinity agent class. We conclude with remarks on affinity agent selection for intrinsic SERS sensing platforms.

Development of surface-enhanced Raman spectroscopy application for determination of illicit drugs: Towards a practical sensor

Surface-enhanced Raman spectroscopy (SERS) has been widely applied to identify or detect illicit drugs, because of the ability for highly specific molecular fingerprint and independence of aqueous solutions impact. We summarize the progress in determination of illicit drugs using SERS, including trace illicit drugs, suspicious objects and drugs or their metabolites in real biological system (urine, saliva and so on). Even though SERS detection of illicit drugs in real samples still remains a huge challenge because of the complex unknown environment, the efficient sample separation and the improved hand-held Raman analyzer will provide the possibility to make SERS a practically analytical technique. Moreover, we put forward a prospective overview for future perspectives of SERS as a practical sensor for illicit drugs determination. Perhaps the review is not exhaustive, we expect to help researchers to understand the evolution and challenges in this field and further interest in promoting Raman and SERS as a practical analyzer for convenient and automated illicit drugs identification.

Conformational sensitivity of surface selection rules for quantitative Raman identification of small molecules in biofluids

Biofluid analysis by surface-enhanced Raman scattering (SERS) is usually hindered by nonspecific interferences. It is challenging to drive targeted molecules towards sensitive areas with specific capture and quantitative recognition in complex biofluids. Herein, a highly specific and quantitative SERS analyzer for small molecule dopamine (DA) in serum is demonstrated on a portable Raman device by virtue of a transducer of mercaptophenylboronic acid (MPBA) and a site-directed decoration of plasmonic Ag dendrites on a superhydrophobic surface. Theoretical simulations of molecular vibrations and charge distributions demonstrate the predomination of Raman surface selection rules in molecular reorientation upon the binding of DA. This recognition event is translated into ratiometric changes in the spectral profile which evidences excellent capability on SERS quantitation. The rules can well distinguish DA from its common interferents including fructose, glucose, sucrose and ascorbic acid which all generate weak but completely opposite spectral changes. Moreover, benefitting from the wettability difference, the target DA in diluted serum can be specifically enriched on a transducer-capped Ag surface, and the adsorption of other interferences is resisted by superhydrophobic features. It paves a new way for labelling a single SERS tag to simultaneously realize the identification and quantification of small molecules in complex biological media.

Common Aspects Influencing the Translocation of SERS to Biomedicine

This review overviews the impact in biomedicine of surface enhanced. Raman scattering motivated by the great potential we believe this technique has. We present the advantages and limitations of this technique relevant to bioanalysis in vitro and in vivo and how this technique goes beyond the state of the art of traditional analytical, labelling and healthcare diagnostic technologies.

Surface enhanced Raman scattering sensor for highly sensitive and selective detection of ochratoxin A

An aptamer based SERS sensor was developed to detect picomolar concentrated ochratoxin solutions using an OPLS model.

Bioanalytical applications of surface-enhanced Raman spectroscopy: de novo molecular identification

Surface enhanced Raman scattering (SERS) has become a powerful technique for trace analysis of biomolecules. The use of SERS-tags has evolved into clinical diagnostics, the enhancement of the intrinsic signal of biomolecules on SERS active materials shows tremendous promise for the analysis of biomolecules and potential biomedical assays. The detection of the de novo signal from a wide range of biomolecules has been reported to date. In this review, we examine different classes of biomolecules for the signals observed and experimental details that enable their detection. In particular, we survey nucleic acids, amino acids, peptides, proteins, metabolites, and pathogens. The signals observed show that the interaction of the biomolecule with the enhancing nanostructure has a significant influence on the observed spectrum. Additional experiments demonstrate that internal standards can correct for intensity fluctuations and provide quantitative analysis. Experimental methods that control the interaction at the surface are providing for reproducible SERS signals. Results suggest that combining advances in methodology with the development of libraries for SERS spectra may enable the characterization of biomolecules complementary to other existing methods.

Two-Dimensional Zirconium-Based Metal-Organic Framework Nanosheet Composites Embedded with Au Nanoclusters: A Highly Sensitive Electrochemical Aptasensor toward Detecting Cocaine

Two-dimensional (2D) zirconium-based metal-organic framework nanosheets embedded with Au nanoclusters (denoted as 2D AuNCs@521-MOF) were prepared via a one-pot method under mild conditions. The optimized 2D AuNCs@521-MOF nanosheets not only possessed high specific surface area, physicochemical stability, and good electrochemical activity but also exhibited strong bioaffinity toward biomolecule-bearing phosphate groups. Consequently, a large amount of cocaine aptamer strands can be immobilized onto the substrate modified by 2D AuNCs@521-MOF nanosheet, further leading to the formation of a constructed biosensitive platform, which can be used to successfully detect cocaine through the specific binding interactions between cocaine and aptamer strands. The results demonstrated that the 2D AuNCs@521-MOF-based aptasensor had high sensitivity for detecting cocaine within the broad concentration range of 0.001-1.0 ng·mL^-1 and the low limit of detection of 1.29 pM (0.44 pg·mL^-1) and 2.22 pM (0.75 pg·mL^-1) as determined by electrochemical impedance spectroscopy and differential pulse voltammetry, respectively. As expected, with the advantages of high selectivity, repeatability, stability, and simple operation, this new strategy is believed to exhibit great potential for simple and convenient detection of cocaine.

Pharmacokinetics-on-a-Chip Using Label-Free SERS Technique for Programmable Dual-Drug Analysis

Synergistic effects of dual or multiple drugs have attracted great attention in medical fields, especially in cancer therapies. We provide a programmable microfluidic platform for pharmacokinetic detection of multiple drugs in multiple cells. The well-designed microfluidic platform includes two 2 × 3 microarrays of cell chambers, two gradient generators, and several pneumatic valves. Through the combined use of valves and gradient generators, each chamber can be controlled to infuse different kinds of living cells and drugs with specific concentrations as needed. In our experiments, 6-mercaptopurine (6MP) and methimazole (MMI) were chosen as two drug models and their pharmacokinetic parameters in different living cells were monitored through intracellular SERS spectra, which reflected the molecular structure of these drugs. The dynamic change of SERS fingerprints from 6MP and MMI molecules were recorded during drug metabolism in living cells. The results indicated that both 6MP and MMI molecules were diffused into the cells within 4 min and excreted out after 36 h. Moreover, the intracellular distribution of these drugs was monitored through SERS mapping. Thus, our microfluidic platform simultaneously accomplishes the functions to monitor pharmacokinetic action, distribution, and fingerprint of multiple drugs in multiple cells. Owing to its real-time, rapid-speed, high-precision, and programmable capability of multiple-drug and multicell analysis, such a microfluidic platform has great potential in drug design and development.

Diverse Applications of Nanomedicine

The design and use of materials in the nanoscale size range for addressing medical and health-related issues continues to receive increasing interest. Research in nanomedicine spans a multitude of areas, including drug delivery, vaccine development, antibacterial, diagnosis and imaging tools, wearable devices, implants, high-throughput screening platforms, etc. using biological, nonbiological, biomimetic, or hybrid materials. Many of these developments are starting to be translated into viable clinical products. Here, we provide an overview of recent developments in nanomedicine and highlight the current challenges and upcoming opportunities for the field and translation to the clinic.

SERS activity with tenfold detection limit optimization on a type of nanoporous AAO-based complex multilayer substrate

Most of SERS applications are constricted by heterogeneous hotspots and aggregates of nanostructure, which result in low sensitivity and poor reproducibility of characteristic signals. This work intends to introduce SERS properties of a type of SERS-active substrate, Au-CuCl2-AAO, which is innovatively developed on a porous anodic alumina oxide (AAO) template. Spectral measuring results of Rhodamine 6G (R6G) on this substrate optimized by controlling morphology and gold thickness showed that enhancement factor (2.30 × 10(7)) and detection limit (10(-10) M) were both improved and represented better performance than its template AAO. Homogenous hot spots across the region of interest were achieved by scanning SERS intensity distribution for the band at 1505 cm(-1) in 5 × 5 μm(2) area. Furthermore, the promising SERS activity of the flower-patterned substrate was theoretically explained through simulation of the electromagnetic field distribution. In addition, this SERS substrate is proposed for applications within the field of chemical and biochemical analyses.

Surface-enhanced Raman scattering substrate based on cysteamine-modified gold nanoparticle aggregation for highly sensitive pentachlorophenol detection

A new surface-enhanced Raman scattering (SERS) substrate based on cysteamine-modified gold nanoparticles (AuNPs) on the glass surface has been developed for the monitoring of pentachlorophenol (PCP) in water samples.

Multi-functional DNA-based synthesis of SWNTs@(TiO2/Ag/Au) nanocomposites for enhanced light-harvesting and charge collection in DSSCs

Based on multi-functional DNA templates, SWNTs@(TiO₂/Ag/Au) nanocomposites were synthesized to enhance the light-harvesting and charge collection efficiency of DSSCs.

Bionanotechnology. Colloidal nanoparticles as advanced biological sensors

Colloidal nanoparticle biosensors have received intense scientific attention and offer promising applications in both research and medicine. We review the state of the art in nanoparticle development, surface chemistry, and biosensing mechanisms, discussing how a range of technologies are contributing toward commercial and clinical translation. Recent examples of success include the ultrasensitive detection of cancer biomarkers in human serum and in vivo sensing of methyl mercury. We identify five key materials challenges, including the development of robust mass-scale nanoparticle synthesis methods, and five broader challenges, including the use of simulations and bioinformatics-driven experimental approaches for predictive modeling of biosensor performance. The resultant generation of nanoparticle biosensors will form the basis of high-performance analytical assays, effective multiplexed intracellular sensors, and sophisticated in vivo probes.

Au nanorod quartets and Raman signal enhancement: towards the design of plasmonic platforms

Quartets of Au nanorods were designed by combining the methodologies of lateral and longitudinal assemblies. A high electric field prevailing at the quartet junctions results in large enhancement in the Raman signals of molecules. FDTD simulations showed that the displacement of the lateral dimers in quartets expands the scope of hot spot distribution.

Facile formation of ordered vertical arrays by droplet evaporation of Au nanorod organic solutions

Droplet evaporation is a simple method to induce organization of Au nanorods into ordered superstructures. In general, the self-assembly process occurs by evaporation of aqueous suspensions under strictly controlled experimental conditions. Here we present formation of large area ordered vertical arrays by droplet evaporation of Au nanorod organic suspensions. The uncontrolled (free air) evaporation of such suspensions yielded to formation of ordered nanorod domains covering the entire area of a 5 mm diameter droplet. Detailed investigation of the process revealed that nanorods organized into highly ordered vertical domains at the interface between solvent and air on a fast time scale (minutes). The self-assembly process mainly depended on the initial concentration of nanorod solution and required minimal control of other experimental parameters. Nanorod arrays displayed distinct optical properties which were analyzed by optical imaging and spectroscopy and compared to results obtained from theoretical calculations. The potential use of synthesized arrays as surface-enhanced Raman scattering probes was demonstrated with the model molecule 4-aminobenzenthiol.

Gold Nanowire Forests for SERS Detection

Simple wet chemistry has been applied to control the vertical growth of gold nanowires on a glass substrate. As a consequence, the longitudinal localized surface plasmon band position can be tuned from 656 to 1477 nm in a few minutes by simply controlling the growth rate and time. This allowed us to select the optimum conditions for maximum electromagnetic enhancement and performance in surface enhanced Raman scattering (SERS) detection. SERS measurements confirmed the uniform and reproducible distribution of the nanowires on the substrate, with the subsequent high reproducibility of hot spot formation. Detection of malachite green in water and of 1-naphthalenethiol from the gas phase are demonstrated as proof-of-concept applications of these three-dimensional SERS substrates.

Ultra sensitive label free surface enhanced Raman spectroscopy method for the detection of biomolecules

We present a proof of concept for a novel nanosensor for the detection of ultra-trace amounts of bio-active molecules in complex matrices. The nanosensor is comprised of gold nanoparticles with an ultra-thin silica shell and antibody surface attachment, which allows for the immobilization and direct detection of bio-active molecules by surface enhanced Raman spectroscopy (SERS) without requiring a Raman label. The ultra-thin passive layer (~1.3 nm thickness) prevents competing molecules from binding non-selectively to the gold surface without compromising the signal enhancement. The antibodies attached on the surface of the nanoparticles selectively bind to the target molecule with high affinity. The interaction between the nanosensor and the target analyte result in conformational rearrangements of the antibody binding sites, leading to significant changes in the surface enhanced Raman spectra of the nanoparticles when compared to the spectra of the un-reacted nanoparticles. Nanosensors of this design targeting the bio-active compounds erythropoietin and caffeine were able to detect ultra-trace amounts the analyte to the lower quantification limits of 3.5 × 10(-13)M and 1 × 10(-9)M, respectively.

Raman scattering of linear chains of strongly coupled Ag nanoparticles on SWCNTs

We compare the Raman scattering properties of hybrid nanostructures consisting of Ag nanoparticles (NPs) in disordered and aligned arrangements on single-walled carbon nanotubes (SWCNTs) as a result of chemical and photoreduction methods. In the latter case, the unique structure of the very small Ag NP (from 4 to 7 nm) chains generated an extremely large mode at 969 cm(-1) that was assigned to the sulphate-silver interaction at the NP surface. Another strong mode was present at 1201 cm(-1) and was assigned to an IR-active mode of sodium dodecyl sulphate (SDS); this mode was observed because the symmetry changes altered the selection rules. We demonstrate that both the UV photoreduction of silver and the presence of SWCNTs are necessary to produce this very strong Raman scattering. The Raman modes of the SWCNTs are also significantly modified by the presence of Ag NP chains along the nanotubes.

Metal-dielectric-CNT nanowires for femtomolar chemical detection by surface enhanced Raman spectroscopy

A highly sensitive substrate for surface enhanced Raman spectroscopy (SERS) is formed by arrays of gold-coated metallic carbon nanotubes having a nanoinsert of high-k dielectric (hafnia) as an energy coupling barrier. Repeated femtomolar detection of 1,2 bis-(4-pyridyl)-ethylene in solution demonstrates the critical contribution of this plasmonic energy coupling barrier to the enhanced chemical sensitivity.

Cysteamine-modified silver nanoparticle aggregates for quantitative SERS sensing of pentachlorophenol with a portable Raman spectrometer

Cysteamine-modified silver nanoparticle aggregates has been fabricated for pentachlorophenol (PCP) sensing by surface-enhanced Raman spectroscopy (SERS) using a portable Raman spectrometer. The cysteamine monolayers could preconcentrate PCP close to the substrate surface through the electrostatic interaction, which makes the SERS detection of PCP possible. Moreover, the Raman bands of cysteamine could be used as the internal spectral reference in the quantitative analysis. Qualitative detection of PCP was carried out by SERS without any sample pretreatment. Quantitative analysis of PCP was further realized based on the prepared substrate, as the log-log plot of normalized SERS intensity of PCP versus its concentrations exhibits a good linear relationship. The SERS signals collected on 20 randomly selected points show that the relative standard deviation of the normalized Raman intensity is 5.8%, which indicates the substrate had good uniformity. The PCP sensor also shows good long-term stability in the analyte solution. The substrate was cyclic immersed into PCP and methanol solution; after several cycles, the sensor still had good adsorption to PCP, which revealed the sensor has good reusability. Coupling with a portable Raman spectrometer, the cysteamine-modified silver nanoparticle aggregates have the potential to be used for in situ and routine SERS analysis of PCP in environmental samples.

Surface-Enhanced Raman scattering-based detection of the interactions between the essential cell division FtsZ protein and bacterial membrane elements

Surface-enhanced Raman scattering (SERS) spectroscopy has been applied to detect the interaction of the FtsZ protein from Escherichia coli, an essential component of the bacterial division machinery, with either a soluble variant of the ZipA protein (that provides membrane tethering to FtsZ) or the bacterial membrane (containing the full-length ZipA naturally incorporated), on silver-coated polystyrene micrometer-sized beads. The engineered microbeads were used not only to support the bilayers but also to offer a stable support with a high density of SERS hot spots, allowing the detection of ZipA structural changes linked to the binding of FtsZ. These changes were different upon incubating the coated beads with FtsZ polymers (GTP form) as compared to oligomers (GDP form) and more pronounced when the plasmonic sensors were coated with natural bacterial membranes.

Multiplex optical sensing with surface-enhanced Raman scattering: a critical review

Multiplex analysis permits the detection of several analytical targets at the same time. This approach may permit to draw a rapid and accurate diagnostic about the health of an individual or an environment. Among the analytical techniques with potential for multiplexing surface-enhanced Raman scattering (SERS) offer unique advantages such as ultrasensitive detection down low the deconvolution times, a unique signature containing all the vibrational information of the target molecules, and the possibility of performing the experiments even in very demanding environments such as natural or biological fluids. Here we review the late advances in multiplex SERS including the direct methods, those aided by the surface functionalization of the plasmonic nanoparticles and the use of SERS encoded particles.

Aptamer sensor for cocaine using minor groove binder based energy transfer

We report on an optical aptamer sensor for cocaine detection. The cocaine sensitive fluorescein isothiocyanate (FITC)-labeled aptamer underwent a conformational change from a partial single-stranded DNA with a short hairpin to a double-stranded T-junction in the presence of the target. The DNA minor groove binder Hoechst 33342 selectively bound to the double-stranded T-junction, bringing the dye within the Förster radius of FITC, and therefore initiating minor groove binder based energy transfer (MBET), and reporting on the presence of cocaine. The sensor showed a detection limit of 0.2 μM. The sensor was also implemented on a carboxy-functionalized polydimethylsiloxane (PDMS) surface by covalently immobilizing DNA aptamers. The ability of surface-bound cocaine detection is crucial for the development of microfluidic sensors.

SERS assisted ultra-fast peptidic screening: a new tool for drug discovery

Herein we present a direct label-free ultra-fast method for the identification and classification of the active members of a combinatorial library directly on the solid support used for their synthesis. The method is based on the appropriate functionalization of polyethylene glycol grafted polystyrene (TentaGel®) microbeads with Au@Ag nanoparticles, the use of these materials directly as solid-phase supports for the synthesis of combinatorial libraries of peptides and the subsequent SERS analysis for identification of each peptide on each bead.

Protein-based SERS technology monitoring the chemical reactivity on an α-synuclein-mediated two-dimensional array of gold nanoparticles

The enhancement of weak Raman signals has been challenged to obtain high-quality signals of surface-enhanced Raman scattering (SERS). By employing the Parkinson's disease-related protein of α-synuclein, we introduce SERS-active gold nanoparticles (AuNPs) individually isolated with an ultrathin α-synuclein shell and their 2-D array into a tightly packed monolayer on a glass support, which permits a quantitative SERS measurement of phthalocyanine tetrasulfonate (PcTS), a chemical ligand of the pathological protein. Subsequently, the PcTS-bound SERS substrate was also shown to be capable of discriminating two biologically important metal ions of iron and copper by detecting copper ion to the sub-ppm level in a highly selective manner via the in situ chemical reaction of metal chelation to PcTS. The strategy of using the protein-based 2-D AuNP SERS platform, therefore, could be further developed into a custom-made protein-based biosensor system for the detection of not only specific chemical/biological ligands of the immobilized coat proteins but also their biochemical reactivities.