Raman Spectroscopy Techniques Research Articles

Spatially Quantitative Imaging of Enzyme Activity in a Living Cell.

Enzyme activity plays a key role in cell heterogeneity. Its spatially quantitative imaging in a living cell not only directly displays but also helps people to understand cell heterogeneity. Current methods are hard to achieve due to the short intracellular retention or lack of internal reference of the imaging probes. Herein, we rationally designed a self-referenced Raman probe Val-Cit-Cys(StBu)-Pra-Gly-CBT (Yne-CBT) which takes an intracellular cathepsin B (CTSB)-initiated CBT-Cys click reaction to yield a long-retained cyclic dimer in cell. In the meantime, Raman signal changes of its two chemical bonds (C≡C and C≡N) after the reaction are used for self-referencing and quantitative Raman imaging of CTSB activity. In vitro experiments demonstrated that, with shell-isolated nanoparticle-enhanced Raman spectroscopy technique, 20 μM Yne-CBT was able to quantitatively detect CTSB activity with a limit of detection of 61.4 U L-1. Under a homemade microfluidic channel, Yne-CBT was successfully applied for spatially quantitative imaging CTSB activity in a living cell. Our strategy provides people with a facile method to directly and quantitatively display cell heterogeneity.

Crystallographic symmetry increasing in the pressure-induced phase transition of the hydrogen-bonded organic crystal 1-methylhydantoin.

In situ high-pressure Raman spectroscopy and synchrotron angular dispersive x-ray diffraction techniques, combined with first-principles calculations, have been performed to investigate the 1-methylhydantoin (C4H6N2O2, 1-MH) molecular crystal. High-pressure experiments have shown that phase I (monoclinic system) begins to transform into phase II (orthorhombic system) at pressures above 4.0GPa, and the transformation range is from 4.0 to 14.2GPa. It is proposed that the mechanism of phase transition is the interlayer contraction and rearrangement of the hydrogen-bonding network due to the enhanced strong hydrogen-bonded interactions at high pressures. This study provides some theoretical basis for this rare pressure-induced phase transition from low symmetry to high symmetry in organic supramolecular polymorphism.

Evaluation of Breast Cancer Gene Type 1 (BRCA1) Protein Levels in Cancer Tissue Using Surface-Enhanced Raman Spectroscopy.

Raman spectroscopy is a chemical process that utilizes the interaction between light and matter to get significant insights into the structure or characteristics of matter. Raman spectroscopy techniques, such as quantitative evaluation, early diagnostic capabilities, and elucidation of the spectral properties of tissues, are excellent candidates for use in research. In cancer, changes in genes and proteins expressed by related genes are associated with a poor prognosis and aggressive tumor characteristics. Due to modifications and regulatory steps in protein translation, the results of the messenger RNA (mRNA) expression of genes may not correctly reflect the results of protein expression. For this reason, the mRNA and protein expressions of genes are studied in parallel in molecular studies on cancer. In our study, the breast cancer gene type 1 (BRCA1) gene, which is frequently studied in breast cancer and is relatively more difficult to measure by traditional methods due to its high molecular weight, was selected, and protein quantification was performed in tissue samples by Raman spectroscopy. With Raman spectroscopy, it is possible to obtain rapid and precise quantitative results even with a small amount of sample, so it is quite advantageous compared to traditional methods. In our study, we performed surface-enhanced Raman spectroscopy (SERS) to analyze the quantitative protein amount. SERS is a highly sensitive method for detecting compounds at low concentrations. For this purpose, magnetic nanoparticles modified with protein antibodies were used, and the target protein was withdrawn from the complex environment and transferred to an appropriate buffer environment. The calibration curve for BRCA1, which plots Raman intensity against concentration, was derived by calculating the average response reading from duplicate assays conducted under identical conditions. The BRCA1 protein levels of cells were determined from the regression curve of the BRCA1 protein. The relation between the concentration of BRCA1 protein and SERS spectrum intensity was determined to be logarithmic in the range of 300 µg·mL-1 to 292 ng·mL-1 (R2 = 0.9928, limit of detection = 10.41 µg·mL-1, and limit of quantitation = 31.24 µg·mL-1).

Flexible Fe-Doped NiO/Ni-Foam Substrate Nano-System Based Electrode with Tunable Opto-Electrochemical Attributes for Supercapacitor Applications

Abstract This work underlines the modification and effect of iron doping on different characteristics of NiO nanoparticles. The facile hydrothermal method was followed to form pristine and iron doped( 4% and 8% ) NiO sample. The X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), transmission electron microscopy (TEM), UV–Vis spectroscopy and Raman spectroscopy techniques were employed for the identification of phase, morphology, microstructural details and optical property of the as synthesized Fe doped NiO samples. XRD measurements of the as synthesized Fe doped NiO samples revealed the polycrystalline nature with the crystallite size varying from 11nm – 20nm showing hexagonal structure. Surface morphology investigation carried out by using SEM showed the varied morphology of as synthesized samples . UV-Vis investigation revealed a red shift with increasing iron doping content, which corresponds to a decrease in optical bandgap values from 3.4eV for pure NiO to 2.2eV for 8% Fe doped NiO sample thus giving a wide tunable absorption bandgap . The study of cyclovoltammetry and PEIS demonstrates the novelty of this work showing exceptionally high electrochemical performance in a three-electrode system with highest specific capacitance of 977F/g at scan rate of 20mV/sec for 8% doped sample .

Electrochemical detection of catechol with a disposable carbon nanotube paste electrode modified with CTAB

Abstract The accurate and rapid detection of catechol which is a class of highly toxic organic phenolic compounds, is of great importance for the protection of environment and human health. In this work, a novel electrochemical sensor for catechol was constructed by modifying multi-walled carbon nanotube paste microelectrode with a cationic surfactant of cetyltrimethylammonium bromide (CTAB) through a simple and controllable adsorption method. Electrochemical experiment results show that the modified electrode has good electrocatalytic effect to the electrochemical response of catechol. The electrochemical response mechanism of the sensor to catechol were investigated through using many analytical methods, including scanning electron microscopy, energy-dispersive spectroscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, and electrochemical techniques. Under the optimal fabrication and application conditions, the response current of catechol on the sensor exhibits a good linear relationship with its concentration from 1.0 μmol/L ~ 7.0 mmol/L with a sensitivity of 1.33 nA/(μmol/L) and a low detection limit of 15 nmol/L (S/N = 3). Applying the sensor in the detection of catechol in tap water samples and urine samples, the results were satisfactory, indicating its good application prospect.

Evaluation of 1064 nm Raman for meat and bone meal species discrimination: From raw form to chemical and physical components

The 1064 nm Raman spectroscopy technique was employed to characterize raw, bone fragments (BF), meat fragments (MF), lipid, and residue of meat and bone meal (MBM) samples. Employing three chemometric algorithms, species discrimination models were optimized for the aforementioned sample types, indicating that the presence of BF favored discriminant analysis for poultry samples, yielding a classification error of 0.000. The species discrimination model constructed using Raman spectra combined with PLS-DA algorithm for residue samples was found to be overall optimal, with classification error for four species samples all below 0.061. A detailed analysis of the BF related spectral variables contributing significantly to PLS-DA discriminant analysis was conducted. Finally, this study established the complementarity of Raman spectroscopy in species discrimination analysis from both a physical and chemical components perspective, laying the theoretical groundwork for the development of a high-precision 1064 nm Raman spectroscopic analysis method for MBM species discrimination.

Chiral Phonon, Valley Polarization, and Inter/Intravalley Scattering in a van der Waals ReSe2 Semiconductor.

Exploring valley manipulatable layered semiconductors is highly significant for valleytronic devices. Here, we report the phonon chirality and resulting inter/intravalley scattering in valley polarized van der Waals (vdW) layered ReSe2 by linearly/circularly polarized Raman (L/CPR), transmission (L/CPT), and photoluminescence (L/CPL) spectroscopic techniques. L/CPR combined with scanning transmission electron microscopy determines the Re chains' direction and displays the existence of chiral phonons. The LPT discloses the energetic valley polarization between the Re chains and its perpendicular crystal axis directions. Intriguingly, the valley polarization strength depends on the layer thickness even in a micrometer scale and abnormaly increases with temperature increase. Further, CPT manifests the optical rotation in ReSe2 due to strong chiral phonon-photon coupling. More essentially, L/CPL unveils a strong exciton-like effect (Stokes shift) that can be interpreted from the inter/intravalley scattering related to the (chiral) phonon-carrier coupling. This investigation suggests a promising platform based on a low-symmetry vdW ReSe2 semiconductor for exploring valley physics and fabricating valley(opto)tronic nanodevices.

Study of morphology, phase composition, optical properties, and thermal stability of hydrothermal zirconium dioxide synthesized at low temperatures.

Oxide nanoparticles exhibit unique features such as high surface area, enhanced catalytic activity, and tunable optical and electrical properties, making them valuable to various industry applications as well as for the development of new research projects. Nowadays, ZrO2 nanoparticles are widely used as catalysts and precursors in ceramic technology. Hydrothermal synthesis with metal salts is one of the most common methods for producing stable tetragonal-phase zirconium dioxide nanoparticles. However, hydrothermal synthesis requires relatively high process temperatures (160-200°C) and the use of advanced heat-resistant autoclaves capable of maintaining high pressure. This paper investigates how different precursors (ZrOCl₂·8H₂O and ZrO(NO₃)₂·2H₂O) and synthesis temperatures (110-160°C) affect the phase composition, optical properties, size, and shape of ZrO₂ nanoparticles produced by hydrothermal synthesis without calcination. In addition, the effect of temperature exposure in the range of 100-1000°C on the phase stability of the synthesized nanoparticles was studied. X-ray diffraction and Raman spectroscopy techniques were used to determine the structure and phase composition, while the optical properties were examined through the analysis of transmission and absorption spectra in the visible and UV ranges. It was found that the obtained particles at synthesis temperatures of 110-130°C have predominantly cubic c-ZrO2 phase, which changes to monoclinic phase when heated above 500°C. Analysis of visible and UV spectroscopy data reveals that the experimental samples have pronounced absorption in the middle UV range (200-260nm) and have an energy band gap Eg varying from 4.8 to 5.1eV. The hydrothermal powders synthesized in this study can be used as absorbers in the mid-UV range and as reinforcing additives in the preparation of technical ceramics.

Highly Strained AlGaAs‐GaAsP Nanomembranes‐Based High‐Performance Diode

AbstractNanomembranes (NMs) made from single‐crystalline inorganic semiconductors offer unique properties, such as flexibility, transparency, and tunable bandgaps, making them suitable for complex device integration and next‐generation high‐power devices. In this study, the fabrication of a high‐performing emitter and base (E‐B) diode using transferable NMs of n‐AlGaAs/p‐GaAsP is demonstrated. Using a modified epitaxial lift‐off and transfer method, a single‐crystalline n‐AlGaAs/p‐GaAsP fragile NMs transfer onto ultrathin oxide (UO) grown GaN and Si substrates. The crystalline quality of the NMs is characterized by X‐ray diffraction and Raman spectroscopy techniques before and after transfer, no noticeable degradation has been found in its crystalline quality. In addition, atomic force microscopy and scanning electron microscopy images confirm the smooth surface and uniformity of the NMs over the whole substrate without any formation of cracks, respectively. Kelvin probe force microscopy demonstrates the formation of a nanoscale contact potential barrier at the interface of the E‐B diode. Furthermore, current–voltage (I–V) measurements demonstrate that the performance of the NM‐based E‐B diode is comparable to that of a rigid diode on the as‐grown sample. The findings highlight the potential of the epitaxial lift‐off and transfer method for the heterogeneous integration of III–V semiconductor materials to overcome the lattice‐mismatch limitations.

Classification and Identification of Foodborne Bacteria in Beef by Utilising Surface-Enhanced Raman Spectroscopy Coupled with Chemometric Methods.

The detection and classification of foodborne pathogenic bacteria is crucial for food safety monitoring, consequently requiring rapid, accurate and sensitive methods. In this study, the surface-enhanced Raman spectroscopy (SERS) technique coupled with chemometrics methods was used to detect and classify six kinds of foodborne pathogenic bacteria, including Salmonella typhimurium (S. typhimurium), Escherichia coli (E. coli) O157:H7, Staphylococcus aureus (S. aureus), Listeria monocytogenes (L. monocytogenes), Listeria innocua (L. innocua), and Listeria welshimeri (L. welshimeri). First, silver nanoparticles (AgNPs) with different particle sizes were prepared as SERS-enhanced substrates by changing the concentration of sodium citrate, and the volume ratio of silver nanosol to bacterial solution was optimised to obtain the optimal SERS signal. Then, principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used to classify the SERS spectra of six bacteria at three classification levels (Gram type level, genus level and species level), and appropriate classification models were established. Finally, these models were validated on 540 spectra using linear discriminant analysis (LDA), achieving an average accuracy of 95.65%. Overall, it was concluded that the SERS technique combined with chemometrics methods could achieve the rapid detection and classification identification of foodborne pathogenic bacteria, providing an effective means for food safety monitoring.

Antimony (Sb)-doped PbTe nanostructured alloys with improved optical and thermoelectrical characterizations for clean energy applications

The current work investigates the influence of antimony doping on the morphology, optical behavior, and thermoelectric performance of PbTe nanostructures fabricated using the hydrothermal method. Analyses employing X-ray diffraction (XRD) and Raman spectroscopy techniques asserted the existence of the cubic phase, a defining characteristic of PbTe compounds. The morphology and internal structure of the samples are examined by the scanning and high-resolution transmission electron microscopes. The photoluminescence spectra show a band gap energy around 3.0 eV which is higher than that of the bulk sample. Raman spectra show three peaks corresponding to longitudinal optical (LO) phonon mode and higher-harmonic multiphonon process of PbTe. The PL spectra exhibit a strong peak at the wavelength 401 nm which is ascribed to a recombination of excitons and/or shallowly trapped electron–hole pairs. The thermoelectric properties are studied in the temperature range of 300–500 K and confirm the domination of p-type conduction in the whole temperature range. The electrical conductivity (σ) versus temperature showed thermally activated behavior as the charge carrier mobility is activated and the average carrier kinetic energy increases with temperature. Activation energy was obtained from the plots of Ln σ as a function of 1000/T. The recorded values were found at 62, 50,73 and 34 meV for x = 0, 0.04, 0.06 and 0.08, respectively. The Seebeck coefficients (S) of the synthesized nanostructures revealed a dominance of p-type conduction due to consistently positive S values. The S-T plots exhibit an initial increase in S with temperature at lower values (T < Tₛ). However, a transition occurs at a specific temperature (Tₛ), marked by a step change in S from positive to negative values, followed by a decrease in S with further temperature rise (T > Tₛ). The highest Seebeck coefficient was observed around 196.2 μV/ K and recorded at 418 K for the sample of x=0.04 Sb content. The largest power factor was recorded at 13.6×10-5 W. m-1. K-2, obtained for pure PbTe at 438 K due to the high value of electrical conductivity.

A Review of Non-Destructive Raman Spectroscopy and Chemometric Techniques in the Analysis of Cultural Heritage.

Today, there is an increasing concern and effort for protection, conservation, and restoration of cultural heritage materials. Non-invasive analytical methodologies such as Raman spectroscopy offers various advantages such as high speed, robust identification, low cost, and in-site analysis. Previous contributions highlighted the potential of Raman spectroscopy combined with multivariate statistics for identification and quality evaluation of cultural heritage materials such as paints, fiber, dyes, woods, stones, inks, and textile materials. Especially, application of chemometrics and multivariate statistics algorithms opens new horizons for scientists and inspectors. In conclusion, the paper provided an overview of the state-of-the-art uses of multivariate statistically equipped Raman spectroscopy methods for evaluation of cultural heritage and art materials with illustrations from previous research studies.

Feasibility Study of Label-Free Raman Spectroscopy forParathyroid Gland Identification.

We aim to evaluate the feasibility of Raman spectroscopy for parathyroid gland (PG) identification during thyroidectomy. Using a novel side-viewing handheld Raman probe, a total of 324 Raman spectra of four tissue types (i.e., thyroid, lymph node, PG, and lipid) commonly encountered during thyroidectomy were rapidly (< 3 s) acquired from 80 tissue sites (thyroid [n = 10], lymph node [n = 10], PG [n = 40], lipid [n = 20]) of 10 euthanized Wistar rats. Two partial least-squares (PLS)-discriminant analysis (DA) detection models were developed, differentiating the lipid and nonlipid (i.e., thyroid, lymph node, and PG) tissues with an accuracy of 100%, and PG, lymph node, and thyroid could be detected with an accuracy of 98.4%, 93.9%, and 95.4% respectively. This work demonstrates the feasibility of Raman spectroscopy technique for PG identification and protection during thyroidectomy at the molecular level.

Challenges in Raman spectroscopy of (micro)Plastics: The interfering role of colourants

Rising plastic consumption leads to widespread microplastic (MP) contamination. Raman spectroscopy is widely used for MP identification due to its ability to analyse particles as small as 1 μm. However, it faces challenges such as interference from pigments and additives. In this study, we aim to assess the accuracy of Raman micro-spectroscopy in identifying coloured plastic samples by applying various oxidative treatments to eliminate the possible interference effect caused by colourants associated with the sample. Standard and coloured microplastics were analysed using a Raman imaging microscope. Coloured plastics were treated with H2O2 30%, Sodium hypochlorite 5%, and Fenton reagent (H2O2 30% and Ferrous sulphate 0.2 M) for 24, 48, and 72 h. The Raman spectra were acquired after treatment to assess the impact of the treatment procedure on the polymer identification. Our results revealed that colourants significantly impact Raman spectra by peak broadening and/or fluorescence effects, which reduces identification accuracy and match scores Red pigments particularly obscure polymer identification. Treatments like oxidation and Fenton's reagent showed limited effectiveness. Additives in plastic samples can affect the accuracy of polymer identification by the Raman spectroscopy technique. Common treatment procedures do not improve the accuracy of identification. In order to improve the reliability of Raman analysis, essential factors such as utilizing multiple excitation lasers and appropriate CCD detectors, establishing a comprehensive reference library of colourants and additives, and employing advanced techniques like time-gated Raman spectroscopy or Surface-Enhanced Raman Spectroscopy (SERS) should be considered.

Characterization of PbMo0.3W0.7O4 Crystal: A Potential Material for Photocatalysis and Optoelectronic Applications

AbstractPbMo0.3W0.7O4 semiconductor crystal, which contains the balanced ratios of Mo and W, is grown for the first time by Czochralski method. The structural and optical properties of the crystal are investigated in detail in the present study. Structural analysis shows that crystal has tetragonal structure like PbMoO4 and PbWO4 compounds. The optical characteristics are studied by transmission, Raman, FTIR and photoluminescence methods. The bandgap energy is found to be 3.18 eV, and the positions of the conduction and valence bands are determined. The vibrational characteristics are studied by means of Raman and FTIR spectroscopy techniques. Photoluminescence spectrum presents three peaks around 486, 529, and 544 nm which fall into the green emission spectral range. Taking into account the properties of the compound, it is stated that PbMo0.3W0.7O4 (or Pb(MoO4)0.3(WO4)0.7) has the potential to be used in water splitting applications and optoelectronic devices that emit green light.

Structural, optical, and dielectric properties of double perovskite NdBaFeTiO6

NdBaFeTiO6 compound was synthesized successfully through solid-state reaction method. The compound was found to have a crystalline cubic double perovskite (DP) structure with space group Pm-3m by XRD analysis. Structural refinement was performed to investigate the detail of the structure and was found consistent with the experimental results. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and elemental mapping were used to analyze the morphology and elemental composition, revealing the existence of expected chemical composition and uniform distribution of elements within the material. FTIR and Raman spectroscopic techniques were utilized to investigate the vibrational modes and bonding configurations present in the synthesized sample. XPS spectra confirms the existence of photoelectron peaks associated with constituent elements, and also reveals the lattice oxygen and oxygen vacancies. Optical absorbance measurements showed that this material possesses a significant band gap energy of around 4eV, making it a promising candidate for a variety of technological applications. The electrical properties of this double perovskite were investigated using dielectric measurements, both frequency and temperature dependent. At low temperatures, the dielectric constant behaves independently. At higher temperatures, the thermal energy sufficiently enhances the mobility of charge carriers, thereby causing an elevation in dielectric constant of the order of 104 and 103 at low and high frequencies respectively. Moreover, the temperature dependence of the dielectric constant varies for different frequencies.

Evaluation of silver nanoformulated plant extracts against larvae of the fall armyworm, Spodoptera frugiperda (J. E. Smith), under laboratory and field conditions

AbstractThe fall armyworm, Spodoptera frugiperda (J. E. Smith), is a destructive pest of Zea mays (maize) and other agricultural crops. The synthetic insecticides predominantly used against this pest lead to pest resistance, environmental contamination and health hazards. This study evaluated nanoformulated aqueous extracts of some promising local plant species against third instar larvae of S. frugiperda under laboratory and field conditions. The initial screening bioassay showed highest larval mortality with a 20% extract of Nicotiana tabacum L. (66.67%), followed by Azadirachta indica A. Juss. (53.33%), Withania somnifera L. (46.67%), Melia azedarach L. (40%) and Dodonaea viscosa Jacq. (33.33%). The two most effective plant extracts (A. indica and N. tabacum) were further nanoformulated with silver nitrate (AgNO3) and bioassayed against S. frugiperda larvae using different concentrations. The results showed that these nanoformulated extracts caused significant larval mortality, with LC50 (lethal concentration that kills 50% of the population) and LT50 (lethal time to kill 50% of the population) values of 37.36 and 28.21% at 72 h, and 52.19 and 33.25 h at 80% concentration, respectively. Field experiments on Zea mays L. (maize) plants showed maximum larval reduction by nanoformulated A. indica extract (48%), followed by N. tabacum extract (36%), whereas 80% and 20% larval reduction was noted for the positive (SuperLock®, emamectin benzoate and tebufenozide) and the negative (water) controls, respectively. Furthermore, characterization of both silver nanoparticles‐based plant extract formulations was performed using ultraviolet–visible (UV–vis) spectroscopy, Raman spectroscopy and scanning electron microscopy (SEM) techniques, which confirmed the formation of silver nanoparticles. It is concluded that nanoformulated plant extracts can be an effective alternative to synthetic pesticides in combatting S. frugiperda and other lepidopteran pests.

Surface-enhanced Raman spectroscopy for the rapid identification of fosfomycin resistant and sensitive strains of E. Coli

Development of rapid detection and discrimination technique for the antibiotic resistant and sensitive bacterial strains is required for this purpose, Surface-enhanced Raman spectroscopy (SERS) technique is considered to have great potential. To develop a fast and sensitive detection and discrimination methodology based on SERS technique along with chemometric tools for the differentiation among fosfomycin sensitive and resistant Escherichia coli (E. coli.) strains. In this research work, three E. Coli strains resistant to fosfomycin with three fosfomycin sensitive E. coli strains were characterized in which silver nanoparticles were employed as SERS substrate. Moreover, MATLAB 7.8 (2009a) was used for the preprocessing, baseline correction and normalization of SERS spectra. Using principal component analysis (PCA) and partial least squares discriminant analysis (PLSDA), several E. Coli strains were identified on the basis of their distinctive SERS spectral properties. The differentiating SERS spectral features which can be associated with the resistance and sensitivity against fosfomycin antibiotic, are obtained by comparing mean SERS spectrum of strains of resistant E. coli with sensitive E. coli strains. Chemometric techniques, such as principal components analysis, have been proven effective for qualitative analysis. Additionally, PLSDA was employed to classify the SERS spectra acquired from the pellets of several bacterial strains. SERS is a useful analytical method for quickly differentiating between E. Coli strains that are sensitive to fosfomycin and those that are resistant to it.

Drug expiration study using Raman spectroscopy and super paramagnetic clustering

Currently, there is a belief that drugs used after the expiration date no longer work, or even these can cause some damage. In the present work, several types of drugs on the market with different expiration dates are analyzed to find out if these, with the expired expiration date, present spectroscopic differences from those drugs whose expiration date is still valid. This study used the Raman spectroscopy technique to determine the chemical composition of drugs. To measure the drug Raman spectra, Horiba equipment, LabRam HR800, was used with an Olympus confocal microscope focusing a laser of 830 nm and 17 mW on the drugs through a 50 X Leica long-range objective. The Super Paramagnetic Clustering (SPC) method was applied to classify the Raman spectra. In the SPC method, the clustering process is based on a phenomenon of clustering observed in nature at the atomic level and perfectly described by a statistical physics model known as the Potts model, which describes the interacting spins on a crystalline lattice. This clustering method allows for identifying hierarchical structures in the spectra data banks. Fourteen drugs were analyzed, including 2 capsules, 5 tablets, 2 liquid samples, 4 ointments, and one spray with 1 to 3 expired expiration dates. Comparing drugs with expiration dates that are still valid and expired, the SPC results applied to the Raman spectra showed that, although some drugs indicated chemical differences, others indicated no chemical differences, even among those with up to two expired expiration dates. The results showed that Raman spectroscopy and SPC are excellent tools for discriminating between expired and non-expired drugs. The Principal Components Analysis (PCA) was also applied as a cross-checking method of the SPC result, obtaining consistent results. To our knowledge, it is the first preliminary result evaluating the usefulness of Raman spectroscopy and SPC in identifying expired drugs distributed on the market.

Single gold nanowire-nanoparticles conjugated system: Fabrication and sensing application

Single-entity-based sensing platform has many advantages for real-time assays, such as single-molecule analysis, or targets detection in confined environment. In this contribution, a new single Au nanowire (NW) – Au@Pt/Au nanoparticles (Au@Pt/Au NPs) conjugated system was established and used for the detection of thrombin by using surface-enhanced Raman spectroscopy (SERS) technique. This method was mainly based on electrostatic attraction between the capture (thrombin aptamer) and probe molecules (crystal violet, CV) on the surface of Au NW - Au@Pt/Au NPs conjugation, reducing the adsorption of CV molecules on conjugation surface, and resulting the decrease of SERS signals. The addition of thrombin could bind with thrombin aptamer due to specific interaction, leading to the decrease of electrostatic effect from thrombin aptamer for CV diffusion to conjugation surface, and the SERS signals could be recovered. This thrombin sensing method showed high sensitivity and selectivity, and the linear range for thrombin assay was 0.01 nM–100 nM with a detection limit of 1.35 pM. This single Au NW - Au@Pt/Au NPs conjugation has more SERS hotspots and small overall size, which offers unparalleled advantages over other sensing system and can be applicable for real time analysis, especially at single molecule/cell level.