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A 2-hydroxyl phenyl imino modified phenanthro[9,10- d ]imidazole probe (PPIP) was synthesized and its aggregation-induced emission enhancement (AIEE) phenomenon in aqueous medium was characterized by the Tyndall phenomena, morphologies of scanning electron microphotograph (SEM) as well as the enhanced fluorescence intensities. The AIEE-active PPIP in aggregated states exhibited a sensitive detection for Cu2+ along with the elimination of fluorescence intensity; subsequently, in situ PPIP- Cu2+ complex showed selective fluorescence "turn-on" for Cr3+, providing a potential platform for tandem recognition of Cu2+ and Cr3+. The 1:1 M ratio between PPIP and Cu2+ was confirmed by Job's plot, 1H NMR spectra, mass spectra and density functional theory (DFT) calculations. The detection limits for Cu2+ and Cr3+ were 4.127 × 10−2 μM and 9.404 × 10−1 μM, respectively. Moreover, this successive recognition could be utilized to construct the molecular logic gates by the fluorescence changes. In addition, PPIP was successfully employed for quantitative detecting Cu2+ in real water samples with satisfactory results. 2-Hydroxy phenyl imino modified phenanthro[9,10- d ]imidazole: An AIEE-active sensor for "turn-off" determination of Cu2+ and subsequent "turn-on" recognition of Cr3+. Unlabelled Image • An AIEE-active PPIP probe based on phenanthro[9,10- d ]imidazole was designed and synthesized; • An "on-off-on" fluorescence platform for tandem recognition of Cu2+ and Cr3+ was established. • The quantitative detecting Cu2+ in real water samples was realized. [ABSTRACT FROM AUTHOR]

[Display omitted] • Changes of characteristic groups are aim to understand the extraction process. • The four CQAs of SMF are rapidly determined in extraction process. • A fast modeling method based on TQSM without determining the index components. Swertia mussotii Franch. (SMF), a traditional Tibetan medicine, which has miraculous effect on treating hepatitis diseases. However, there is no research on its entire production process, and invisible production process has seriously hindered the SMF modern development. In this study, principal component analysis (PCA), subtractive spectroscopy, and two-dimensional correlation spectroscopy (2D-COS) were used to explain changes of characteristic groups in the extraction process. Four main characteristic peaks at 1884 nm, 1944 nm, 2246 nm and 2308 nm were identified to describe the changes of molecular structure information of total active components in SMF extraction process. In addition, multi critical quality attributes (CQAs) models were established by near-infrared spectroscopy (NIRS) combined with the total quantum statistical moment (TQSM). The coefficients of determination (R2 eval and R2 ival) were both greater than 0.99. The ratios of the standard deviation of validation to the standard error of the prediction (RPD e and RPD i) were greater than five. The quantitative model of AUC T could save time on primary data measurement by not requiring determination of indicator components compared with others. In conclusion, these results demonstrated that it was feasible to understand the SMF extraction process through AUC T and characteristic groups. These could realize the visual digital characterization and quality stability of the SMF extraction process. [ABSTRACT FROM AUTHOR]

Raman spectra were measured for Langmuir–Blodgett (LB) films of C16NaphOH and C10AzoNaphC4N-SDS on Calcium Fluorite substrate for the first time. In order to find out favorable excitation condition, Raman spectra of the single and multi-monolayer LB films excited at different lines at 244, 514, 633 and 778 nm are recorded and compared in the present study. Raman spectrum of the monolayer LB film of C16NaphOH excited by 244 nm demonstrate that excellent signal to noise is achieved even for one monolayer LB film with an extremely short integrating time as 60 s because of being resonantly enhanced, while no meaningful spectra were recorded under the same condition for the monolayer LB film of C10AzoNaphC4N-SDS because of burning. Using a HeNe 633 nm excitation the problem with strong substrate fluorescence was partially solved, since under these conditions this fluorescence is mainly outside the fingerprint region of the LB film molecules (1000–2000 cm−1). Therefore by using the HeNe laser excitation, Raman spectra with high signal to noise ratio of LB films of C16NaphOH were collected and shown in this paper. These findings stress again the necessity to define an appropriate Raman system for this special application of LB film diagnosis. [Copyright &y& Elsevier]

Surface-enhanced Raman scattering (SERS) of 4-mercaptopyridine (4-mpy) adsorbed on HNO3 etched silver foil, chemically deposited silver films (silver mirror) and silver colloids were measured. The SERS study has revealed that 4-mpy was adsorbed onto the three kinds of silver surfaces by a sulfur–silver bond with the plane of pyridine ring being normal to the silver substrates. The structure of 4-mpy adsorbed on the silver surfaces depends largely on the pH values of environment. When the pH values of the environment are changed, the structure of 4-mpy adsorbed on silver surfaces can easily be altered through a protonation or deprotonation reaction occurring on the N atom of the pyridine ring, and the modified structure shows unique characters on the SERS spectrum. Owing to the remarkable enhancement ability of SERS technique and characteristic spectrum of different species, a monolayer of 4-mpy assembled on a silver mirror holds potential as a H+ sensor for highly sensitive detection of the proton concentration in an aqueous solution. [ABSTRACT FROM AUTHOR]

Ag+ and SCN− play extremely important roles in the fields of the physiology and environment. In this work, on the basis of phenanthro[9,10- d ]imidazole derivative (DIPIP) which can exhibit the aggregation-induced emission (AIE) properties in aqueous solution, we achieved a sequential on-off-on switch for Ag+ and SCN− with high selectivity and sensitivity. A remarkable fluorescence quenching effect of Ag+ on the probe DIPIP was observed with 1:2 stoichiometry, Subsequently, the fluorescence intensity of in situ generated DIPIP -Ag+ ensemble was easily switched on after the interaction between Ag+ and SCN−, which was attributed to the stronger affinity of SCN− to capture Ag+. In particular, the extreme limits of detection (LOD) for Ag+ and SCN− in standard solutions were as low as to be 74.5 nM and 7.8 nM, respectively. Furthermore, the probe DIPIP and the DIPIP -Ag+ ensemble could be used to detect Ag+ in the real water and SCN− in smoker saliva samples, respectively. In addition, the sequential "on-off-on" fluorescence mode of DIPIP to Ag+ and SCN− were also successfully applied in living HeLa cells. Unlabelled Image • Fluorescent probe DIPIP was designed and prepared; • DIPIP had obvious AIE activity; • A "on-off-on" sequential detection for Ag+ and SCN– with the extreme lower LOD was studied; • The responses of DIPIP to Ag+/AgNPs and of Ag+ to SCN− were applied in water and saliva samples. • Mode of the sequential sensing was realized in cells imaging. [ABSTRACT FROM AUTHOR]

[Display omitted] • The selective enhancement mechanism in SERS for two types of Au nanoparticles was elucidated. • SERS spectra of probe molecules demonstrated the importance of specific SERS tags in determining the main enhancement factors. • 2T2D-COS results showed the relationship between nanoparticle type and SERS enhancement. The selective enhancement mechanism in surface-enhanced Raman scattering (SERS) is demonstrated. Two different types of single nanoparticles (Au nanosphere and Au nanorod) were used to investigate the role of the localized surface plasmon resonance (LSPR) in SERS spectra by using the two-trace two-dimensional (2T2D) correlation spectroscopy. The SERS intensities of three probe molecules, 4-mercaptobenzoic acid (4-MBA), 4-aminothiophenol (4-ATP), and 4-bromobenzenethiol (4-BBT), respectively, were enhanced but slightly different when adsorbed on Au nanospheres and Au nanorods. 2T2D correlation SERS spectra clearly showed that even with the same shape of Au nanoparticles, the main factors influencing the SERS enhancement can vary depending on the specific type of SERS tags used. Such subtle difference could not be clearly identified by the conventional spectral analysis. This result sheds light on potential applications of 2T2D correlation spectroscopy. For 4-MBA molecules, the a 1 and b 2 modes are mainly affected by the Au nanospheres and Au nanorods. For 4-ATP molecules, the a 1 and b 2 modes related to C–S stretching combined with C–C stretching band are mainly affected by Au nanorods and Au nanospheres. For 4-BBT molecules, the a 1 and b 2 modes of C–C (aromatic ring) stretching band are mainly affected by Au nanorods and Au nanospheres. This study offers valuable insights into the relationship between nanoparticle shape and SERS enhancement. [ABSTRACT FROM AUTHOR]

A multilayer LB film and a casting film of reversed duckweed polymer ES-3 on Au-evaporated glass slides were investigated by Fourier Transform infrared grazing reflection–absorption spectroscopy. It is found that the two kinds of ordered ultrathin films have different orientation of alkyl chains, nearly perpendicular to the substrate surface for the LB film while rather tilted for the casting film. The studies on their thermal transition behaviors indicate that both of the films have three phase transition processes, respectively, occurring near 65, 105 and 140 °C for the former while near 80, 105 and 140 °C for the latter, but show different transition behavior in the each corresponding transition process. It is referred that at room temperature there are island-like domain structures formed in the LB film, but no ones in the casting film; however, the latter can form the domain structures between the first two transition points due to the desorption of solvents. The formation of domain structure seems to play two important roles, one of which is to make alkyl chains more perpendicular to the substrate surface, and the other to make alkyl chains more packed closely. Thermal cyclic experiments reveal that neither of the films could return to its original state after thermal cyclic treatment up to the temperature, which is above the third transition point, although its alkyl chain becomes highly ordered again. [Copyright &y& Elsevier]

[Display omitted] • In 2 O 3 NPs were firstly used as SERS substrates. • The CT mechanism of SERS is confirmed by the spectra. • Providing new semiconductor substrates for SERS applications. Surface-enhanced Raman scattering (SERS) has outstanding merits in biochemical molecular analysis, and the development of new SERS substrates is the focus of research. Herein, In 2 O 3 nanoparticles (NPs) were synthesized by a high temperature pyrolysis method with cubic phase and small particle size at 10 nm. The structures and properties of In 2 O 3 NPs were characterized by X–ray powder diffraction (XRD), transmission electron microscope (TEM) and other characterization methods. Additionally, the SERS spectra of In 2 O 3 -MBA with the enhancement factor (EF) up to 1.22 × 104 is discussed. The results demonstrate that there is a charge transfer (CT) effect revealed between the adsorbed molecules of 4-mercaptobenzoic acid (4-MBA) and the substrates of In 2 O 3 NPs, and it could be excited by long wavelength energy. Based on the In 2 O 3 NPs, the study is beneficial to develop more potential semiconductor SERS substrates. [ABSTRACT FROM AUTHOR]

Abstract Norfloxacin (NFX) is an antibacterial agent belonging to the fluoroquinolone family of drugs, known to bind bovine serum albumin (BSA). Surface-enhanced Raman scattering (SERS) and fluorescence spectroscopy in combination with molecular docking were explored to investigate the binding interaction between NFX with Bovine serum albumin (BSA) at a physiological condition. This study focused on identifying the binding site and relevant interaction mechanisms between NFX and BSA. Spectrophotometric titration with molecular docking results demonstrated that the binding site of NFX on BSA was located in sub-domain IIA. The principle binding site was identified within a hydrophobic cavity which is surrounded by the residues Leu 197, Arg 198, Ser 201, Ala 209, Trp 213, Ser 343, Leu 346, Lys 350, Ser 453, Leu 480, Val 481, and the binding force was mainly hydrophobic interaction and hydrogen bond interaction. In addition, the absorptive orientation of the NFX molecule on the colloidal surface underwent a set of changes during the process of NFX binding to BSA. Graphical Abstract Unlabelled Image Highlights • The combination of SERS and molecular docking were explored to investigate the binding site of Norfloxacin on BSA. • The absorptive geometry of Norfloxacin with BSA on the self-assembled monolayer film was confirmed. • The detailed binding position and relevant interaction mechanism of Norfloxacin to BSA were obtained. [ABSTRACT FROM AUTHOR]

The reliable and ultrasensitive detection of antibiotic drug residue is of great interest for environmental protection and human health. Herein, we propose a simple SERS strategy based on Ag nanoparticles (NPs) as substrate with the assistance of aggregation agent (MgSO 4 ) for the SERS investigation and the high sensitive detection of antibiotic drug carbenicillin disodium (CBDM). The density functional theory calculation was performed for the assignment and identification of Raman bands of the CBDM molecule. The results indicate that the CBDM molecule is close to the Ag NP substrate surface through the carboxyl group. The CBDM molecules on Ag NP substrate exhibit the largest SERS enhancement, when the concentration of MgSO 4 is 1 × 10 −2  mol/L and the pH value of CBDM solution is 6. By this SERS method, the limit of detection of CBDM is 0.63 × 10 −8  mol/L, which is lower than the standard of European Union for the maximum residue limit of antibiotic drug (1.2 × 10 −8  mol/L). And, a quantitative detection method of CBDM can be established. There is a good linear relationship (R 2  = 0.9908) in the concentration range of 1.0 × 10 −8 –1.0 × 10 −3  mol/L. It proves that the proposed SERS method is a simple, rapid (within 6 min), reliable and highly sensitive scheme with a good reproducibility for the detection of CBDM. And, the proposed SERS strategy can also be applied for the high sensitive detection and identification of other antibiotic drug (penicillin). [ABSTRACT FROM AUTHOR]

p-Aminothiophenol (PATP) is a preferred molecule in research on surface-enhanced Raman scattering (SERS) because of its unique characteristics of high spectral activity, easily induced charge-transfer (CT), and sensitivity to molecular structural changes. However, some aspects are still unclear, such as the initial steady state of PATP on noble metallic substrates without strong additional excitation with incident and/or induced electromagnetic radiation. Information about the initial steady state, especially the intrinsic CT state, is of great importance to elucidate the dynamic processes of CT and/or molecular structural changes under additional excitation. To investigate the native state of an adsorbed molecule, a suitable probe method that does not disrupt the native state of the whole system, including both molecules and substrates, is required. SERS is not applied in this context because of its use of high-energy visible and near-infrared light. Herein, a low-energy probe method, surface-enhanced infrared-absorption (SEIRA) spectroscopy, is employed as a suitable method for studying the native adsorption state of PATP on silver nanoisland films. The molecular structure and adsorption state were investigated. The intrinsic CT state received particular attention by analyzing the CT-related vibration of B 2 modes. Using Fourier transform infrared (FTIR), transmission SEIRA and reflection SEIRA spectroscopy, we explained why the relative intensities of some bands were different under different conditions. A quasi-standing orientation of PATP adsorbed on the substrates was also confirmed. More importantly, we demonstrated that there is no perceptible CT between PATP and silver nanoisland films; in contrast, CT generally occurs in a disruptive manner in SERS. Density functional theory (DFT) calculations and the selection rules for infrared (IR) transmission and reflection-absorption spectroscopy were used to analyze the spectra throughout the paper. SEIRA proved to be an effective technique to explore the native adsorption state of molecules without the excessive external disturbance induced by excitation. The results are very important in providing insight into molecules in surface-interface chemistry, enhanced spectroscopy and photoelectronics. [ABSTRACT FROM AUTHOR]

Glyphosate is one of the most commonly-used and non-selective herbicides in agriculture, which may directly pollute the environment and threaten human health. A simple and effective approach to assessment of its damage to the natural environment is thus quite necessary. However, traditional chromatography-based detection methods usually suffer from complex pretreatment procedures. Herein, we propose a simple and sensitive method for the determination of glyphosate by combining ninhydrin reaction and surface-enhanced Raman scattering (SERS) spectroscopy. The product (purple color dye, PD) of the ninhydrin reaction is found to SERS-active and directly correlate with the glyphosate concentration. The limit of detection of the proposed method for glyphosate is as low as 1.43 × 10 − 8 mol·L − 1 with a relatively wider linear concentration range (1.0 × 10 − 7 -1.0 × 10 − 4 mol·L − 1 ), which demonstrates its great potential in rapid, highly sensitive concentration determination of glyphosate in practical applications for safety assessment of food and environment. [ABSTRACT FROM AUTHOR]

In this study, we have investigated the effect of the surface morphologies of the zinc oxide (ZnO) substrates on surface enhanced Raman spectroscopy (SERS). During synthetic process, the self-assembly monolayers (SAMs) with different terminal groups are used as templates to induce the nucleation and growth of Zn(NO 3 ) 2 ·6H 2 O crystals, then different morphologies micro-nano ZnO powders are obtained by annealing Zn(NO 3 ) 2 ·6H 2 O crystals at 450 °C. The products obtained at different conditions are characterized by means of X-ray diffraction (XRD) patterns, scanning electron microscopy (SEM) and Raman spectra. The as-prepared ZnO micro-sized particles have been used the efficient Surface enhanced Raman scattering (SERS) substrates, and the SERS signals of 4-mercaptopyridine (Mpy) probe molecules are much influenced by the morphologies of the ZnO structures. Results indicated that the more (0001) facets appear in the of ZnO morphology, the greater degree of charge-transfer (PCT) for the SERS enhancement on the surface of semiconductors is achieved. The chemical interaction between ZnO structures and Mpy molecules plays a very important role in the SERS enhancement. [ABSTRACT FROM AUTHOR]

With the explosive application of methyl salicylate (MS) molecules in food and cosmetics, the further detection of MS molecules becomes particularly important. Here we investigated the detection of MS molecules based on surface-enhanced Raman scattering (SERS) in a novel molecule/assistant/metal system constructed with MS, 4,4′-(hexafluoroisopropylidene) bis (benzoic acid) and Ag nanoparticles (AgNPs). The minimum detection concentration is 10 −4  M. To explore the function of assisted reagent, we also referred another system without assistant molecules. The result demonstrates that SERS signals were not acquired, which proves that the assistant molecules are critical for the capture of MS molecules. Two possible mechanisms of MS/assistant/AgNPs system were speculated through two patterns of hydrogen bonds. The linker molecules acted as the role of the bridge between metallic substrates and target molecules through the molecular recognition. This strategy is very beneficial to the expanding of MS detection techniques and other hydrogen bond based coupling detections with SERS. [ABSTRACT FROM AUTHOR]

4-Mercaptophenylboronic Acid (4-MPBA) plays pivotal role in various fields. The orientation and existing form of the 4-MPBA strongly depend on the pH value of the media. The general aim of this work is to obtain information about the structure changes of 4-MPBA absorbed on Ag nanoparticles in different pH environment. Surface-enhanced Raman spectroscopy (SERS) technique is a simple and rapid method to study adsorption phenomena at molecule level. The investigation is done by means of SERS. In order to interpret the experimental information, a series of SERS spectra is carried out. The relative intensities of the totally symmetric (a 1 mode) and non-totally symmetric (b 2 mode) bands in the SERS spectra of 4-MPBA change depend on the environmental pH values, which is a manifestation of charge transfer (CT) processes. The degree of charge transfer increases with the pH value of the media changing from acidity to alkalinity. The structure changes of MPBA had been carried out in different pH environment. We envision that this approach will be of great significance in related fields of 4-MPBA-involved detection. [ABSTRACT FROM AUTHOR]

[Display omitted] • A rapid and sensitive SERS strategy using a portable Raman spectrometer was described. • β-CD-AgNPs was synthesized as SERS substrate to determine Thiram (THI) and atrazine (ATZ). • LOD was 2.42 × 10-9 mol L-1 (0.58 ppb) for THI and 7.26 × 10-9 mol L-1 (1.56 ppb) for ATZ. • Determination via SERS of THI in apple and ATZ in apple and water Samples. In this work, a rapid and sensitive strategy was developed to determine thiram (THI) and atrazine (ATZ) by surface-enhanced Raman scattering (SERS) technology. β-cyclodextrin modified silver nanoparticles (β-CD-AgNPs) were synthesized using β-CD as a reducing agent and encapsulating agent under alkaline conditions and employed as SERS substrate. The existence of β-CD can capture the molecules to form host–guest complex and fix molecular orientation in its cavity, thus ensuring the enhanced SERS signal intensity of THI and ATZ. The linear response extends from 2.56 × 10-8 to 2.56 × 10-3 mol/L for THI and 3.08 × 10-8 to 3.08 × 10-3 mol/L for ATZ, with the limits of detection (LOD) of 2.42 × 10-9 mol/L for THI and 7.26 × 10-9 mol/L for ATZ, respectively. The application of the proposed method in real samples including apple and water were investigated, and the results would help promote the application of SERS technology as a powerful analytical tool for detecting other pesticide residues. It is expected that this SERS strategy will provide great value for rapid detecting pesticide residues in food products and environmental systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mixed valence Ce doping forms multiple doping energy levels in TiO 2 and enriches its Ess. • Multiple levels and abundant Ess greatly enhance CT efficiency from substrate to molecule for boosted SERS. • SERS EF of Ce 0.010 Ti 0.990 O 2 is 2.2 × 106 and detection limit is 10−10 mol/L. • Ce 0.010 Ti 0.990 O 2 SERS substrate shows a high uniformity and stability. Considering the variable valence characteristics of rare earth elements, they can be in a variety of valence forms coexistence. Doping of rare earth element with different valence states may produce different energy levels to tune the semiconductor energy band structure. We utilize rare earth element Ce doping TiO 2 for the development of high-performance semiconductor surface-enhanced Raman scattering (SERS) substrates based on an energy-level tuning strategy. Ce doping not only forms multiple energy levels including Ce3+ and Ce4+ metal doping energy levels in the bandgap of TiO 2 , but also enriches the surface state level of TiO 2 itself, which together promote the separation of photogenerated carriers and improve charge transfer efficiency between substrates and absorbed molecules. This endows TiO 2 semiconductor substrate with a higher SERS enhancement factor, which can reach 2.2 × 106. The detectable concentration of methylene blue can be as low as 10−10 mol/L. Moreover, the semiconductor substrate exhibits excellent uniformity and stability. This study not only provides a new strategy to develop excellent semiconductor SERS substrate with multiple energy levels, but also lays the foundation for promising practical application of semiconductor substrate. [ABSTRACT FROM AUTHOR]

In the WTG-PLS approach, first, the UV–vis spectrum was decomposed into several sub-signals by WT, and the selected sub-signals with GWO was reconstructed into an effective signal (S); Then the moment variables were calculated from the signal S by TCM method and further selected with GWO algorithm; Finally, PLS was used to establish the quantitative WTG-PLS model. [Display omitted] • A novel WTG-PLS approach to the spectral analysis of complex samples was developed. • The proposed approach was applied to the analysis of trace homogeneous catalysts in chemical production and obtained the satisfactory results. • Compared with MCR-ALS and PLS models, the WTG-PLS model was more accurate and reliable. • This study not only successfully solved the practical problem in chemical enterprises, but also provided a new idea for the analysis of complex samples. As one of the important factors in chemical production, catalyst content directly affects the process of reaction and the quality of products. The quantitative analysis of trace catalyst in homogeneous reaction system is still faced with great challenges. In this work, a simple and effective approach to the rapid determination of trace homogeneous catalyst (THC) was proposed based on UV–vis spectrophotometry. Wavelet transform and Tchebichef curve moment methods were combined with gray wolf algorithm to extract the feature information from the original UV–vis spectra of samples. Then the partial least-squares model was established. The predictive correlation coefficient (R p 2) was 0.9842, and the limit of quantification was 0.07 ‰. The intra-day and inter-day precision were 3.97 % and 4.36 %, respectively. The spiked recoveries of three different concentrations in actual samples were between 97.6 and 101.9 %. The results indicated that the obtained model was satisfactory and could be used in practical measurement. Compared with the conventional modeling methods, the proposed approach was more accurate and reliable, which provided a feasible new pathway for enterprise product quality control. [ABSTRACT FROM AUTHOR]

Raman spectroscopy, surface-enhanced Raman spectroscopy (SERS) and density functional theory (DFT) simulations were employed to study 5-amino-2-mercaptobenzimidazole (5-A-2MBI) molecules. Ag colloids were used as SERS substrates which were prepared by using hydroxylamine hydrochloride as reducing agent. Raman vibration modes and SERS characteristic peaks of 5-A-2MBI were assigned with the aid of DFT calculations. The molecular electrostatic potential (MEP) of 5-A-2MBI was used to discuss the possible adsorption behavior of 5-A-2MBI on Ag colloids. The spectral analysis showed that 5-A-2MBI molecules were slightly titled via the sulfur atoms adhering to the surfaces of Ag substrates. The obtained SERS spectral intensity decreased when lowering the 5-A-2MBI concentrations. A final detection limit on the concentration of 5 × 10 − 7 mol · L − 1 was gained. SERS proved to be a simple, fast and reliable method for the detection and characterization of 5-A-2MBI molecules. [ABSTRACT FROM AUTHOR]

In this paper, 4-mercaptobenzoic acid (4-MBA/pMBA) was designed as a model molecule for theoretical and experimental studies of the molecule structure. Density functional theory (DFT) calculations have been performed to predict the IR and Raman spectra for the molecule. In addition, Fourier transform infrared (FTIR) and Raman spectra of the compound have been obtained experimentally. Based on the modeling results obtained at the B3LYP/6-311++G ∗∗ level, all FTIR and Raman bands of the compound obtained experimentally were assigned. Our calculated vibrational frequencies are in good agreement with the experimental vales. The molecular electrostatic potential surface calculation was performed and the result suggested that the 4-MBA had two hydrogen bond donors and three hydrogen bond acceptors. HOMO–LUMO gap was also obtained theoretically at B3LYP/6-311++G ∗∗ level. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three types of DNA nanogels were assembled by the branched DNA units. • SERS has been successfully exploited for the structural analysis of DNA nanogels. • The mechanism for enhancing the SERS signal of DNA gels has been suggested. The direct characterization of DNA nanogels at the atomic level is desirable and of great significance, however, has been challenging because of structural complexity and the larger size of nanogels. Herein, we demonstrated a simple, sensitive and reliable SERS (Surface-enhanced Raman spectroscopy)-based approach towards direct monitoring microstructures, such as three types of nanogels crosslinked by DNA G-quadruplex, i-motif and GC duplex. The achievement is attributed to the detection of featured Raman bands corresponding to the formation of Watson-Crick and Hoogsteen hydrogen bonds as well as C·C+ base pairs. Importantly, this work reveals that the silver nanoparticles attaching on the surface of nanogels can form local 'hotspots' and produce high-quality of Raman spectra under the assistance of iodide, aluminum ions and dichloromethane, therefore, shows great potential for wide applications in accurate characterization of various DNA nanostructures. [ABSTRACT FROM AUTHOR]

At present, fluorescence spectroscopy, ultraviolet spectroscopy and infrared spectroscopy are usually used to detect drug molecules, however the information about using Raman spectroscopy to detect drug molecules is very few. In this work normal Raman spectroscopy and surface-enhanced Raman spectroscopy were utilized to study benzylpenicillin sodium (NaBP). The results show that NaBP is close to the surface of silver substrate through the carboxyl group, and the detection limit of NaBP is reduced to 1 × 10 −7 mol/L. Accordingly, the quantitative analysis of NaBP can be carried out in the range of 1 × 10 −4 –1 × 10 −7 mol/L concentration. And it is proved that NaBP is not stable in acid and alkali conditions and the decomposition reaction is very complex. [ABSTRACT FROM AUTHOR]

Ginsenosides in plant samples have been extensively studied because protopanaxadiol saponins are ubiquitous in Chinese patent medicines, in which they can be used in promoting human health as the main active ingredients. A method for rapid determination of two ginsenosides (Rg1 and Re) in Naosaitong (NST) samples using near-infrared reflectance spectroscopy (NIRS) is studied to determine the contents of ginsenoside Rg1 and Re in this work. Partial least square (PLS) regression was used for building the calibration models, and the effects of spectral preprocessing and variable selection on the models are investigated for optimization of the models. A total of 93 samples were scanned by NIRS, and also by high performance liquid chromatography coupled to a diode array detector to determine the contents of ginsenoside Rg1 and Re. The calibration models for Rg1 and Re had high values of the coefficient of determination ( R 2 ) (0.9766 and 0.9764) and low root mean square error of cross validation (RMSECV) (0.0136 and 0.0104), and the values of the standard error of prediction set (SEP) are 0.00764 and 0.0103, which indicate a good correlation between reference values and NIRS predicted values. The overall results show that NIRS could be applied for the rapid determination of the contents of ginsenosides in Ginseng byproducts for pharmaceuticals that develop high-quality Chinese patent medicines. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering (SERS) and fluorescence spectroscopy were employed to probe the interaction of the pharmaceutical and natural product molecules, ginsenoside Rb1, Rd, Rg3 and compound K (CK), with human serum albumin (HSA). Normal Raman spectra of these four ginsenosides were obtained from solid powder on glass slide. Based on the unsplit peak at 1445 cm −1 , the stacking modes of ginsenoside Rb1, Rd, Rg3 and CK were quite similar, when the deconvolution of alkyl chain was not occurred. SERS spectra of ginsenoside Rb1, Rd, Rg3 and CK were obtained from a colloidal silver surface on a self-assembled SERS substrate, the most enhanced modes were those with certain motions perpendicular to the metal surface, such as C24 C25 stretch and C H out-of-plane bending from alkyl chain. The SERS spectra were used to predict similar perpendicular orientation of flexible alkyl chain and parallel orientation of carbocyclic rings on Ag colloid particles. Therefore, when combined with HSA, the transformations of four ginsenosides still exhibit similar, although in different binding cavities in subdomain IIA and IIIA by making the methyls at C26 and C27 perpendicular plugging into the hydrophobic site of HSA, while the aglycone and glucose nearby are perpendicularly exposed outside to fit other suitable active targeting sites. [ABSTRACT FROM AUTHOR]

In this paper, ninhydrin was designed as a model molecule for theoretical and experimental studies of the molecule structure. Density functional theory (DFT) calculations have been performed to predict the IR and Raman spectra for the molecule. In addition, Fourier transform infrared (FTIR) and Raman spectra of the compound have been obtained experimentally. Based on the modeling results obtained at the B3LYP/6-311++G** level, all FTIR and Raman bands of the compound obtained experimentally were assigned. Our calculated vibrational frequencies are in good agreement with the experimental values. The molecular electrostatic potential surface calculation was performed and the result suggested that the ninhydrin had two potential hydrogen bond donors and four potential hydrogen bond acceptors. HOMO–LUMO gap was also obtained theoretically at B3LYP/6-311++G** level. [ABSTRACT FROM AUTHOR]

In this work, the structural parameters of the title molecule (MTT) have been obtained at the B3LYP/6-311++G ** level of theory. The two phenyl rings and the two heterocyclic rings are found in four different planes. The tetrazolium ring was connected with other three rings and their distances are also different in decrease order of 1.461 Å (from tetrazolium ring to carbon connected phenyl) > 1.445 Å (from tetrazolium ring to nitrogen connected phenyl) > 1.425 Å (from tetrazolium ring to thiazolyl ring). Fourier transform infrared (FTIR) and Raman spectra of the compound were obtained experimentally. All FTIR and Raman bands of the compound obtained experimentally were assigned based on the modeling results obtained at the B3LYP/6-311++G ** level. The calculated vibrational frequencies were in good agreement with the experimental values. In addition, the UV–Vis spectra were obtained experimentally and theoretically. Considering the effect of the PCM modelling error, the calculated absorbance peaks obtained at the B3LYP/6-311++G ** level were also in good agreement with the experimental values. The HOMO–LUMO gap was predicted to be 1.83 eV at the B3LYP/6-311++G ** level. [ABSTRACT FROM AUTHOR]

[Display omitted] • ITO NPs were used as SEIRA substrates for the first time. • The free carrier density is regulated and the LSPR absorptions are tuned by the heteroatoms doping of tin. • The SEIRA property is affected by the doping of semiconductors. • Provide ideas for improving semiconductor SEIRA substrates based on adjusting doping contents. The application of surface enhanced infrared absorption (SEIRA) is severely restricted in many fields due to the SEIRA substrates are constructed mainly from expensive noble metals. Therefore, the development of new SEIRA substrates other than the noble metallic ones is very valuable. Here we introduced a new semiconductor SEIRA substrate, the indium tin oxide (ITO) nanoparticles (NPs), to study the SEIRA property. The results demonstrate that the ITO NPs show the SEIRA property and the enhancement is dependent to the doping ratio of the heteroatoms of tin. The ITO NPs with the 5% atomic doping ratio show the highest SEIRA enhancement factor (EF), which is about 24. The limit of detection (LOD) of the 1,1′-dicarboxyferrocene (dcFc) molecule was as low as 10−5 mol/L. The present study proves that the tin-doped indium oxide can be used as a new and inexpensive semiconductor SEIRA substrate. It also proves that the doped semiconductor NPs have strong potentials for being used as emerging SEIRA substrates. [ABSTRACT FROM AUTHOR]

Highlights: [•] Silver nanotriangles array with long ranged periodicity was fabricated on the surface of glass wafer. [•] High enhancement of the fluorescent intensity of the target antibodies was obtained by the silver nanotriangles array. [•] High sensitivity and good reproducibility for antibodies detection was obtained by the 2D silver nanotriangles array. [ABSTRACT FROM AUTHOR]

Highlights: [•] Most of the fundamentals vibrations agree well with the predicted frequencies. [•] Hydrogen bond donors and acceptors are predicted. [•] The vibrational spectra of 4-MPH are investigated experimentally and theoretically. [ABSTRACT FROM AUTHOR]

Highlights: [•] Stacking modes and spatial positions of alkyl are influenced by C20 hydroxyl. [•] 20(R/S)-ginsenoside Rg3’s alkyl share similar parallel orientation on Ag. [•] Glucose plug into HSA when carbocycle and alkyl exposed outside. [ABSTRACT FROM AUTHOR]

Highlights: [•] The first time using SERS and molecular docking to study the interaction of caffeine with HSA. [•] The absorptive geometry of caffeine on HSA was elucidated. [•] The pyrimidine ring of caffeine was considered to be the main binding group to HSA. [•] Detailed information about the binding site of caffeine on HSA was obtained. [ABSTRACT FROM AUTHOR]

[Display omitted] • ATO NPs were firstly used as SERS substrates and conformed to the CT mechanism. • Free carrier densities in CBs of ATO NPs defected the SERS ability and CT effect. • Provides idea for improving semiconductor SERS substrates based on adjusting doping. Surface-enhanced Raman scattering (SERS) has been applied in many fields, but still has the limitation of widespread applications on semiconductor substrates. In this work, a series of antimony-doped tin oxide (ATO) nanoparticles (NPs) have been synthesized by a hydrothermal method and were used as SERS substrates for the first time. Interestingly, a charge transfer (CT) effect was revealed between the probing molecules of 4-mercaptobenzoic acid (4-MBA) and the substrates of ATO NPs, which accounts for the SERS enhancement and shows dependence to the Sb ions doping ratios in ATO NPs. By considering the energy level diagram of the ATO–MBA complexes and the doping theory of semiconductors, this phenomenon is believed to connect to the variance of the optical band gap energy (E g), which is accompanied with the changes of free charge carrier densities in conduction bands (CBs) of ATO NPs due to different doping contents. The study of the E g - or free-charge-carrier-density-dependent property of the semiconductor-based SERS provides a new point of view for the development of new semiconductor SERS substrates and also contributes to the SERS CT mechanism. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a new proposal for the quantitative evaluation of divalent metal ions (M2+) is developed by the use of the competitive resonance Raman (RR)-based method. Upon excitation with light of the appropriate wavelength (532nm), a strong electric field is generated that couples with the resonance of the complex (zincon-M2+), increasing the character signals of these complexes, resulting in sensitive detection. Herein, the RR probe, zincon-M2+ complex that the RR intensity gets lower with the decreasing of the M2+ concentration, which leads to the transformation of the Raman information. As a result, by using the proposed RR-based method, we could find the liner calibration curves of Cu2+ and Ni2+, which show the potential in quantitative evaluation of an unknown sample. In addition, the abundant fingerprint information shows that RR leads to the successful analysis of a blended solution, which contains two ions: Cu2+ and Ni2+. [Copyright &y& Elsevier]

Abstract: By the aim of constructing surfaces for multi-component and multifunctional bioassay, a microsphere lithography technique was employed to control the surface morphology. Two kinds of protein molecules (antibodies) were used as building blocks. As a result, dual-component biocompatible surfaces with alternate immunoglobulin micropatterns were fabricated. The employed antibodies included human Immunoglobulin G (IgG) and rabbit IgG, which composed nanometer scale surface arrays on the surfaces. The antibodies were identified specially by immunoreactions with labeled antigens of fluorescein isothiocyanate (FITC)-antihuman IgG and tetramethylrhodamine-5-(and 6)-isothiocyanate (TRITC)-antirabbit IgG. The immune responses were confirmed by confocal fluorescence (FL) microscopy. A study on the sensitivity and quantification was done by using surface-enhanced resonance Raman scattering (SERRS) spectroscopy. The obtained SERRS spectra showed satisfactory resolution in the multi-component detection objects. No interference was observed from inner- or interactions of detecting molecules. The detection limits for both of the antigens reached to as low as 1ng/mL, which was comparable to FL method. Meanwhile, a good linear relationship between SERRS peak intensity and the logarithm of antigens’ concentrations (from 1ng/mL to 1mg/mL) were observed. The results demonstrated that SERRS is a very promising detection technique for multi-component immunoassay, and has great potential applications in biotechnology and biochemistry. [Copyright &y& Elsevier]

Abstract: TiO2 and Mn-doped TiO2 (1%, 3% and 5%) nanoparticles (NPs) were synthesized by a sol-hydrothermal method for surface-enhanced Raman spectroscopy study. When using the 4-mercaptobenzoic acid (4-MBA) as the probing molecule, optimum SERS signals were observed on the Mn–TiO2 (3%) samples. On the 3% Mn doped TiO2 substrate, 4-MBA molecules exhibit a higher SERS intensity by a factor of six as compared with the native enhancement of 4-MBA adsorbed on pure TiO2 NPs. The possible mechanism for the phenomena is also discussed. This study opens up a new dimension for the family of SERS substrates. [Copyright &y& Elsevier]

Abstract: Raman and surface-enhanced Raman scattering (SERS) spectroscopy were employed to probe the interaction of the flavonol drugs, kaempferol and galangin, with human serum albumin (HSA). SERS spectra of both flavonol derivatives were obtained from a colloidal silver surface in physiological condition, based on the high performance of the enhanced substrate, the most enhanced modes of kaempferol and galangin were those with certain motions perpendicular to the metal surface. The SERS spectra were allowed to predict similar orientation geometry for both of the drugs on the colloidal surface with minor difference. In addition, both flavonols–HSA complexes were prepared in different concentration ratios and the orientated differences between kaempferol and galangin were investigated by SERS. [Copyright &y& Elsevier]

Abstract: In this study, a nanoscale protein chip is prepared by using an etched polystyrene (PS) template. This protein chip can be directly used for immunoassay, with the help of Surface Enhanced Raman Scattering (SERS) spectra. Some glass slides submerged in aldehyde is initially prepared, modified with antibodies, human immunoglobulin G (IgG). Then PS arrays are self-assembled on these slides with the Langmuir–Blodgett method. The PS template pattern is transferred to the human IgG substrate using an etching process—slides are exposed to O2 plasma for 90s. The PS nanoparticles are then washed away using phosphate buffered saline solution. Next, the slides are dipped into bovine serum albumin solution to ensure that the anti IgG would bond only to the human IgG. At this moment, a patterned protein chip is obtained. When used for protein detection, the protein chip could be immersed into labeled specificity antigen solution. Here we chose fluorescein isothiocyanate anti-human IgG. After washing, only bonded antigens remain. Fluorescence microscopy and SERS is used to characterize the samples. The SERS spectra intensity shows liner correlation with the concentration of anti-human IgG. All the experiments are conducted in a phosphate buffered saline solution at 37°C for 2h. [Copyright &y& Elsevier]

Abstract: A new kind of Ag/Cu2S composite micro/nanostructures has been prepared via a convenient galvanic reduction method. SEM images of these micro/nanostructures showed that Ag nanoparticles with the size of around 50–100nm were well deposited on the surface of Cu2S micro/nanostructures. The SEM images also indicated that the Ag nanoparticles were preferentially grown on the big polygonal Cu2S microstructures, which could be explained by a localization of the electrons on the surface of the polygonal Cu2S microstructures after the electron transfer step. Owing to the introduction of Ag nanoparticles on the surface of Cu2S micro/nanostructures, the resulting Ag/Cu2S composite micro–nanostructures could be used as a versatile substrate for surface enhanced Raman scattering. [Copyright &y& Elsevier]

Abstract: Pefloxacin mesylate, a broad-spectrum antibacterial fluoroquinolone, has been widely used in clinical practice. Therefore, it is very important to detect the concentration of Pefloxacin mesylate. In this research, the near-infrared spectroscopy (NIRS) has been applied to quantitatively analyze on 108 injection samples, which was divided into a calibration set containing 89 samples and a prediction set containing 19 samples randomly. In order to get a satisfying result, partial least square (PLS) regression and principal components regression (PCR) have been utilized to establish quantitative models. Also, the process of establishing the models, parameters of the models, and prediction results were discussed in detail. In the PLS regression, the values of the coefficient of determination (R 2) and root mean square error of cross-validation (RMSECV) of PLS regression are 0.9263 and 0.00119, respectively. For comparison, though applying PCR method to get the values of R 2 and RMSECV we obtained are 0.9685 and 0.00108, respectively. And the values of the standard error of prediction set (SEP) of PLS and PCR models are 0.001480 and 0.001140. The result of the prediction set suggests that these two quantitative analysis models have excellent generalization ability and prediction precision. However, for this PFLX injection samples, the PCR quantitative analysis model achieved more accurate results than the PLS model. The experimental results showed that NIRS together with PCR method provide rapid and accurate quantitative analysis of PFLX injection samples. Moreover, this study supplied technical support for the further analysis of other injection samples in pharmaceuticals. [Copyright &y& Elsevier]

Abstract: Surface-enhanced Raman scattering (SERS) of 4,4′-azopyridine (AZPY) on silver foil substrate was measured under 1064nm excitation lines. Density-functional theory (DFT) methods were used to calculate the structure and vibrational spectra of models such as Ag–AZPY, Ag4–AZPY and Ag6–AZPY complexes with B3LYP/6-31++G(d,p)(C,H,N)/Lanl2dz(Ag) basis set. The Raman bands of AZPY were identified on the ground of analog computation of potential energy distribution. The calculated spectra of Ag4–AZPY and Ag6–AZPY models were much approximated to the experimental results than that of Ag–AZPY model. The DFT results showed that the angles between two pyridyl rings keep 0° from AZPY to Ag–AZPY, Ag4–AZPY and Ag6–AZPY model. The energy gaps between the HOMO and LUMO changed from 363 to 1140nm for AZPY-Ag complexes according to the DFT results. An conclusion was conceived that chemical enhancement mechanism may play an important role in the SERS of AZPY on silver substrate. [Copyright &y& Elsevier]

Abstract: It is important to monitor quality of tobacco during the production of cigarette. Therefore, in order to scientifically control the tobacco raw material and guarantee the cigarette quality, fast and accurate determination routine chemical of constituents of tobacco, including the total sugar, reducing sugar, Nicotine, the total nitrogen and so on, is needed. In this study, 50 samples of tobacco from different cultivation areas were surveyed by near-infrared (NIR) spectroscopy, and the spectral differences provided enough quantitative analysis information for the tobacco. Partial least squares regression (PLSR), artificial neural network (ANN), and support vector machine (SVM), were applied. The quantitative analysis models of 50 tobacco samples were studied comparatively in this experiment using PLSR, ANN, radial basis function (RBF) SVM regression, and the parameters of the models were also discussed. The spectrum variables of 50 samples had been compressed through the wavelet transformation technology before the models were established. The best experimental results were obtained using the (RBF) SVM regression with γ =1.5, 1.3, 0.9, and 0.1, separately corresponds to total sugar, reducing sugar, Nicotine, and total nitrogen, respectively. Finally, compared with the back propagation (BP-ANN) and PLSR approach, SVM algorithm showed its excellent generalization for quantitative analysis results, while the number of samples for establishing the model is smaller. The overall results show that NIR spectroscopy combined with SVM can be efficiently utilized for rapid and accurate analysis of routine chemical compositions in tobacco. Simultaneously, the research can serve as the technical support and the foundation of quantitative analysis of other NIR applications. [Copyright &y& Elsevier]

Abstract: The molecular geometry and vibrational frequencies of 4,4′-bipyridine (BPE) in the ground state were calculated using density functional theory (DFT) methods (B3LYP) with 6-31++G(d,p) basis set. The optimized geometric bond lengths and bond angles are obtained by DFT employing the hybrid of Beckes non-local three parameter exchange and correlation functional and Lee–Yang–Parr correlation functional. Fourier transform infrared (FT-IR), Fourier transform Raman (FT-Raman) and near-infrared surface-enhanced Raman scattering (NIR-SERS) spectra of BPE on the silver foil substrate have been recorded. All FT-IR, FT-Raman and NIR-SERS band were assigned on the basis of the B3LYP/6-31++G(d,p) method. The vibrational frequencies obtained by DFT(3LYP) are in good agreement with observed results. The NIR-SERS of BPE excited by 1064nm laser line is little difference with that excited by visible laser line. This phenomenon is result to the increase of the contribution of CHEM enhancement effect. Surface selection rules derived from the electromagnetic enhancement model were employed to infer the orientations of BPE on the silver foil substrate surface. Some vibrational frequency which are sensitive to the planar or non-planar structure of BPE, and to the dihedral angle were concluded. [Copyright &y& Elsevier]

Abstract: We obtained the high-quality Raman spectra of 4-mercaptopyridine (4-Mpy) adsorbed on CdS microclusters. The Raman signals were enhanced relative to the same molecules in solution. We compared the Raman spectra of 4-Mpy molecules adsorbed on CdS microclusters and Ag substrate. The difference of 4-Mpy molecules adsorbed on semiconductor and metal substrate was revealed. The results demonstrated that adsorbed species on semiconductor CdS can be detected by SERS spectroscopy. [Copyright &y& Elsevier]

Abstract: We describe a simple method to synthesize triangular silver nanoparticles by photoreducing the silver ions by citrate. A noteworthy difference of the present method as compared with the previous photo-induced methods is that good shape control over the nanoparticles can be realized in the absence of soft templates or polymer directing agents. The formation process of the silver nanoparticles was investigated by UV–vis spectroscopy and transmission electron microscopy (TEM). It was found that the concentration of reactant plays important role in the morphology control of produced silver nanoparticles. As one of the applications of these nanoparticles, they were used as surface-enhanced Raman scattering substrates and 1,4-bis[2-(4-pyridyl)ethenyl]-benzene (BVPP) was used as a Raman probe to evaluate the enhancement ability of the triangular silver nanoparticles. [Copyright &y& Elsevier]

Abstract: Ag/CdTe nanocomposite was prepared via self-organization process by electrostatic interaction between positively charged CdTe quantum dots and negatively charged Ag nanoparticles and examined with respect to their optical properties. The positively charged CdTe quantum dots and negatively charged Ag nanoparticles were synthesized separately by modifying nanoparticles surface with cationic and anionic thiol compounds, respectively. The result showed that the mixing ratio of Ag nanoparticles to CdTe quantum dots is an important parameter for controlling resulting composites. The resulting solution is optically transparent if one component is in excess. Photoluminescence of CdTe quantum dots undergoes considerably quenching if CdTe nanocrystals are in excess and SERS spectra of BVPP absorbed on Ag colloid became stronger if Ag nanoparticles are in excess. Nevertheless, while the ratio is approximately 1, micrometer-sized solid composite is obtained with the elapse of 1h after mixing. SERS spectra for solid composite only exhibit the signals of the CdS nanocrystal which reflected that prolonged refluxing during the synthesis leads to a partial hydrolysis of the thiols and to the incorporation of the sulfur from the thiol molecules into the the growing nanoparticles to form mixed CdTe(S) nanocrystal, similar to CdTe/CdS core/shell structure. From the results, we conclude that optical properties of Ag/CdTe are dependent on the mixing ratio of both nanoparticles. [Copyright &y& Elsevier]

Abstract: The FTIR spectra were measured for a self-assembled film of the anti-ferroelectric liquid crystal (AFLC) molecules over a temperature range of 40–150°C. The frequency and intensity variations of the infrared spectra were discussed in terms of changes in molecular orientation, conformation and intra- and/or inter-molecular interaction during phase transitions. The two-dimensional (2d) correlation analysis revealed that two hydrocarbon chains have different orientation behaviors, the shorter hydrocarbon chain is parallel to molecular long axis and the longer one is perpendicular to it. The splitting of the Cing band indicated that the s-cis and the s-trans conformers of the ester group coexist in the self-assembly film. During the phase transitions, in mesogen part the Cdjacent to the chiral part is first response with temperature changing, following the Cetween two phenyl rings, and eventually the phenyl rings; and the respondence with temperature of methyl is slower than that of methylene in alkyl chains. [Copyright &y& Elsevier]

[Display omitted] • A fundamental analysis of 4-CPH is proposed systematically. • The protonation of 4-CPH involves a depolarization effect. • A pH-dependent frequency shift of cyano in 4-CPH is observed and interpreted. 4-Cyanophenylhydrazine (4-CPH) is an organic synthesis intermediate. To date, several products derived from 4-CPH have been well studied; however, 4-CPH itself has not been extensively investigated. Herein, we performed vibrational and theoretical analyses of 4-CPH. Density functional theory (DFT) calculations were applied to predict the IR and Raman spectra of 4-CPH, which were compared with the experimental spectra. The calculated and experimental spectral results were in good agreement, except for an abnormal transformation of the protonated 4-CPH cyano group (C≡N), which was observed in the theoretical IR spectrum. Several wavefunction analyses revealed that this transformation was due to the protonation-induced depolarization of the molecule. Moreover, we verified the applicability of 4-CPH as a probe for surface-enhanced Raman spectroscopy (SERS). We observed a pH-dependent shift in the cyano bond frequency within the silent region and determined, as a novel discovery, that this shift was induced by 4-CPH protonation. Our results provide considerable, fundamental information that confirms the potential of 4-CPH as a SERS probe. [ABSTRACT FROM AUTHOR]

• A novel PS/Ag/ZIF-8 SERS substrate composite was successfully prepared. • The as-prepared PS/Ag/ZIF-8 substrate could exhibit outstanding SERS property. • The SERS behavior of the substrate exhibit a laser wavelength-dependence CT effect. In this work, the monodisperse polystyrene colloidal particles/Ag/zeolite imidazole framework (PS/Ag/ZIF-8) substrate was successfully prepared and served as SERS active substrate. The composition, structure and morphology of the PS/Ag/ZIF-8 substrates were studied by XRD, SEM, UV–Vis and XPS measurements. The main finding of this study was that the as-prepared PS/Ag/ZIF-8 substrate could exhibit outstanding SERS property when 4-mercaptobenzoic acid (4-MBA) was used as the SERS probes. The SERS mechanism was attributed to the combined effect of the electromagnetic enhancement and chemical enhancement (CT). In addition, the SERS behavior of the sandwich PS/Ag/ZIF-8 substrate exhibit a laser wavelength-dependence CT effect with changing the laser source (473 nm, 514 nm, 633 nm and 785 nm). The wavelength-dependence CT mechanism were discussed briefly in the article. The results showed that the chemical interaction in the structure is a necessary condition for occurrence of the CT. The CT process can be evaluated quantitatively by the charge transfer degree (ρ CT). Moreover, the enhancement factor (EF) of 1.23 × 106 was obtained with 4-MBA probes adsorbed on the synthesized PS/Ag/ZIF-8 substrate. More importantly, our research may open the door for developing the SERS substrate research with the well-studied metal–organic frameworks nanostructures materials. [ABSTRACT FROM AUTHOR]

• A bifunctional ratiometric naked-eye fluorescence sensor (BIBC) was developed for turn-on detection of H+ and Al3+. • The detection limit (DL) of BIBC for Al3+ was calculated to be as low as 1.58 μM. • BIBC shows good time-stability in cellar imaging with dual-channel for detection H+ and Al3+. • BIBC shows high sensitivity and accuracy for detection Al3+ in various real samples. Abnormal changes in H+ and Al3+ concentrations in living cells can alter neurological diseases. A small-molecule sensor combined with a fluorescence imaging technique holds great promise for monitoring changes in proton and metal-ion concentration. In this work, a bifunctional ratiometric naked-eye fluorescence sensor (BIBC) was developed for turn-on detection of H+ and Al3+ in H 2 O/EtOH (v / v = 1:1) mixtures. BIBC exhibits a p K a value of 4.58 within a linear pH variation from 4.1 to 4.7 (R2 = 0.9939). Moreover, the fluorescence intensity ratio (I 566 nm / I 524 nm) shows a good linear relationship (R2 = 0.9965) within an Al3+ concentration range of 7.0–10.0 μM. The detection limit (DL) for the sensor was calculated to be 1.58 μM. The practical application of BIBC for Al3+ detection in real samples was further discussed, and satisfactory results were obtained. Furthermore, the sensor was applied to real-time visualization of changes in H+ and Al3+ concentration in living cells, with great photostability and low cytotoxicity observed. Fluorescence images of H+ and Al3+ were collected by using a fluorescence microscope in a dual-channel configuration, wherein they were labeled green and yellow, respectively. [ABSTRACT FROM AUTHOR]

Methotrexate (MTX) is a drug with broad-spectrum antitumor activity that is of great importance in therapeutic drug monitoring applications. In this essay, the two-step modified concentrated Ag colloid with the assistance of KF and MgSO 4 was used as the SERS active substrate for the ultrasensitive detection of MTX and its commercial formulations (tablets). It can be found that the two-step modification of the samples is a crucial procedure to remove the by-products in the synthesis of Ag colloid and further concentrate the Ag colloid. Under the optimal detection conditions, the minimum detection concentration of MTX is 1 × 10−16 mol/L. And, there is a good linear relationship over a wide concentration range of 1 × 10−16–1 × 10−6 mol/L. The labelled amounts of the two manufacturers of MTX commercial tablets are in the range of 96.4–104.3% with the RSDs between 1.8% and 3.5% by this method, which are in accordance with the methodological requirements. These results prove that the proposed SERS method exhibits a good reproducibility and ultra-high sensitivity for the detection of the antitumor drug MTX. Unlabelled Image • Modified Ag colloid was used as SERS substrate for detection of methotrexate (MTX). • Two-step modifying of sample by KF and MgSO 4 is essential for ultrasensitive detection. • The detection limit of MTX is 1 × 10−16 mol/L, far lower than the reported methods. • There is a good linear relation in wide concentration range (1 × 10−16–1 × 10−6 mol/L). • Proposed method can also perform ultrasensitive detection for MTX commercial tablets. [ABSTRACT FROM AUTHOR]