Spherical silver nanoparticles as substrates in surface-enhanced Raman spectroscopy for enhanced characterization of ketoconazole

A voltammetric sensor based on a carbon black and chitosan-stabilized gold nanoparticle nanocomposite for ketoconazole determination

A modified glassy carbon electrode with carbon black (CB) and gold nanoparticles (AuNPs) within a crosslinked chitosan (CTS) film is proposed in this work. The electroanalytical performance of the modified CB-CTS-AuNPs/GCE has been evaluated towards the voltammetric sensing of ketoconazole (KTO), a widespread antifungal drug. The nanocomposite was characterized by scanning electron microscopy, X-ray diffraction spectroscopy, and electrochemistry experiments. The evaluation of the electrochemical behaviour of KTO on the proposed modified electrode shows an irreversible oxidation process at a potential of +0.65 V (vs. Ag/AgCl (3.0 mol L^-1 KCl)). This redox process was explored to carry out KTO sensing using square-wave voltammetry. The analytical curve was linear in the KTO concentration range from 0.10 to 2.9 μmol L^-1, with a limit of detection (LOD) of 4.4 nmol L^-1 and a sensitivity of 3.6 μA L μmol^-1. This modified electrode was successfully applied to the determination of KTO in pharmaceutical formulations and biological fluid samples.

Trapping analytes into dynamic hot spots using Tyramine-medicated crosslinking chemistry for designing versatile sensor

HYPOTHESIS

Due to the intrinsic nature of the surface-enhanced Raman scattering (SERS), the detection of molecules with weak binding affinities toward metal substrates is critical for development of a universal SERS sensing platform. We hypothesized the physical trapping of small pesticide molecules for active hot spot generation using tyramine-mediated crosslinking chemistry and silver nanoparticles (Ag NPs) enhances SERS detection sensitivity.

EXPERIMENTS

Tyramine-mediated crosslinking chemistry for sensor application was validated by ultraviolet-visible absorption spectroscopy, scanning electron microscopy, dynamic light scattering, and Raman spectroscopy. SERS sensing platform using tyramine-mediated crosslinking reaction was systematically studied for detection of 1,4-dyethylnylbenzene as a model analyte. This sensor system was applied to detect two other pesticides, thiabendazole and 1,2,3,5-tetrachlorobenzene, which have different binding affinities toward metal surfaces.

FINDINGS

The SERS signal of 1,4-dyethylnylbenzene obtained using this sensor system was 3.6 times stronger than that obtained using the Ag colloidal due to the nanogap of approximately 1.3 nm within the generated hot spots. This sensor system based on tyramine-mediated crosslinked Ag NPs was evaluated as a promising tool to achieve a solution based sensitive detection of various pesticide molecules that cannot be adsorbed on the surfaces of typical SERS substrates such as metal nanoparticles.

Rapid detection of seven indexes in sheep serum based on Raman spectroscopy combined with DOSC-SPA-PLSR-DS model

Hepatic fascioliasis, ketosis of pregnancy, toxemia of pregnancy and other common sheep diseases will directly affect the concentration (/enzymatic activity) of seven indicators, such as cortisol and high-density lipoprotein cholesterol (HDL-C) in sheep serum. Whether the concentrations (/enzymatic activity) of these indicators can be detected quickly will directly affect the prevention of sheep diseases and the targeted adjustment of breeding methods, thereby affecting the economic benefits of sheep breeding. In this research, we established partial least square regression (PLSR), support vector regression based on genetic algorithm optimization (GA-SVR) and extreme learning machine (ELM) models. Due to the large differences in the content of different substances, it is difficult to directly use the RMSE to evaluate the quantitative effect of the model. This study is the first to propose conducting deviation standardization (DS) for the determination results of various substances. To further improve the performance of the model, we use the successive projections algorithm (SPA) to optimize feature extraction and combine it with the better-performing PLSR model for training. The results show that the optimized DOSC-SPA-PLSR-DS quantitative model has better determination results for 101 sheep serum samples. The average RMSE_p* of the concentration of the six substances decreased from 0.0408 to 0.0387, the R_p² increased from 0.9758 to 0.9846, and the running time was reduced from 0.1659 to 0.0008 s. And the determination performance of lipase (LPS) enzymatic activity has also been improved. The results of this research show that sheep serum Raman spectroscopy combined with DOSC-SPA-PLSR-DS optimization can efficiently monitor the concentration (/enzyme activity) of seven indicators in real time and provide a new strategy for future intelligent supervision of animal husbandry.

Investigations on 2-(4-Cyanophenylamino) acetic acid by FT-IR,FT-Raman, NMR and UV-Vis spectroscopy, DFT (NBO, HOMO-LUMO, MEP and Fukui function) and molecular docking studies

Extensive quantum chemical calculation have been carried out to investigate the Fourier Transform Infrared(FT-IR), Fourier Transform Raman(FT-RAMAN) and Nuclear magnetic resonance(NMR), and Ultra Violet-Visible(UV-vis) spectra of 2-(4-Cyanophenylamino) acetic acid. The molecular structure, fundamental vibrational frequencies and intensities of the vibrational bands were interpreted with the aid of optimizations and normal coordinate force field calculations based on density functional theory (DFT) and ab initio HF methods with 6–311++G(d,p) basis set. The theoretical vibrational wavenumbers are compared with the experimental values. The calculated HOMO-LUMO energies were found to be-6.2056 eV and -1.2901 eV which indicates the charge transfer within the molecule. Natural bond orbital analysis has been carried out to explain the charge transfer (or) delocalization of charge due to the intra molecular interactions. Molecular Electrostatic Potential (MEP), First order hyperpolarizability, and Fukui functions calculation were also performed. The thermodynamic properties of the title compound were studied for different temperatures. Molecular docking studies were made on the title compound to study the hydrogen bond interactions and the minimum binding energy was calculated.

Optical sensors based on silver nanoparticles for determination of pharmaceuticals: An overview of advances in the last decade

This review focuses on optical nanosensors based on silver nanoparticles (Ag NPs) and demonstrates their applications in the determination of pharmaceutical compounds in the last decade. Such optical sensors have received high attention in the analytical field owing to their low cost and simplicity since they do not require any complex or expensive instrumentation. This article reviews Ag NP-based optical methods for the determination of pharmaceutical compounds from 2010 to 2020. The reported optical methods are classified into four types: spectrophotometry, spectrofluorimetry, scattering and chemiluminescence. Ag NPs play different roles in the different sensing platforms used by these methods, the details of which are carefully explained in this review. Moreover, the relevant analytical parameters of the developed methods are categorized by role and tabulated. It is hoped that this review will stimulate further research in this field with similar nanostructures.

Facile organic surfactant removal of various dimensionality nanomaterials using low-temperature photochemical treatment

Deep ultraviolet (DUV)-treatment is an efficient method for the removal of high-energy-barrier polymeric or aliphatic organic ligands from nanomaterials. Regardless of morphology and material, the treatment can be used for nanoparticles, nanowires, and even nanosheets. The high-energy photon irradiation from low-pressure mercury lamps or radio frequency (RF) discharge excimer lamps could enhance the electrical conductivity of various nanomaterial matrixes, such as Ag nanoparticles, Bi₂Se₃ nanosheets, and Ag nanowires, with the aliphatic alkyl chained ligand (oleylamine; OAm) and polymeric ligand (polyvinyl pyrrolidone; PVP) as surfactants. In particular, Ag nanoparticles (AgNPs) that are DUV-treated with polyvinyl pyrrolidone (PVP) for 90 min (50-60 °C) exhibited a sheet resistance of 0.54 Ω □^-1, while thermal-treated AgNP with PVP had a sheet resistance of 7.5 kΩ □^-1 at 60 °C. The simple photochemical treatment on various dimensionality nanomaterials will be an efficient sintering method for flexible devices and wearable devices with solution-processed nanomaterials.

Charge transfer-induced enhancement of a Raman signal in a hybrid Ag–GaN nanostructure

A hybrid system consisting of Ag nanoparticles dispersed onto a GaN nanowall network (GaN NWN) exhibited characteristic optical properties and electronic band structure. Surface-sensitive XPS studies of this high-surface-area system revealed the presence of a high surface charge carrier concentration due to dangling bonds, which resulted in a high metal-like surface conductivity. The low coverage of absorbed Ag led to the nanocluster formation, facilitating charge transfer from GaN to Ag, and thereby further increasing the surface charge carriers. Photoluminescence studies revealed the presence of a high density of band tail states at the conduction band, which is significantly (14-fold) larger than in the GaN epilayer. Raman studies show an increase (2.46-fold) in the interfacial strain at the Ag/GaN interface after the deposition of the Ag nanoparticles. We show that these surface modifications increase the density of hot spots, resulting in an intense Raman signal with an enhancement factor of 10⁷. The role of the charge transfer between Ag nanoparticles and GaN NWN in the enhancement of Raman signal has been demonstrated.

The optical properties and electronic band structure of Ag nanoparticles dispersed on a GaN nanowall network were studied. High metal like surface conductivity was revealed, and charge transfer between Ag and GaN was involved in the enhancement of Raman signals.

Nitrogen doped chiral carbonaceous nanotube for ultrasensitive DNA direct electrochemistry, DNA hybridization and damage study

In the interest of developing novel electrocatalyst for high performance DNA biosensing, with distinctive chiral double helix nanostructure, nitrogen doped chiral carbonaceous nanotube (Chiral-CNT) was employed for ultrasensitive label-free DNA biosensing research. Chiral-CNT can quantitative detection of four DNA bases with high sensitivity and selectivity. Without any prehydrolysis and labeling process, direct electrochemistry of single-stranded DNA and double-stranded DNA, qualitative and quantitative detection of DNA hybridization (low detection limit: 0.0268 g L^-1) were realized. Moreover, sensitive detection of DNA damage induced by fenton reagent was also realized with low detection limit of 0.0350 mg mL^-1 and high sensitivity of 7.42 μA mg^-1 mL. The high biosensing performance attributes to the unique chiral structure of Chiral-CNT, leads to efficient interreaction between Chiral-CNT and DNA molecule.

Synergistic effect between silver nanoparticles and antifungal agents on Candida albicans revealed by dynamic surface-enhanced Raman spectroscopy

Identifying the mechanisms of action of new potential antibiotics is a necessary but time-consuming and costly process. We have developed an ultra-rapid, highly sensitive, and reproducible dynamic surface-enhanced Raman spectroscopy (D-SERS) method to discriminate and evaluate the sensitivity of Candida albicans to antifungal agents with different mechanisms by using silver nanoparticles (Ag NPs). Although Ag NPs have been used conventionally for the enhancement of Raman signals, the accompanying influence of Ag NPs on the microbes has not been investigated. Herein, surface charge and concentration of Ag NPs are likely to be the main influencing factors. Then different concentrations of Ag NPs with the same surface charge as C. albicans were prepared to find the optimal conditions for enhancement of Raman signals while minimally affecting tested fungi. Spectral variations were observed with increasing concentrations of Ag NPs, as well as those of antifungal agents, including echinocandin and azole drugs. The results indicated that the combination of sub-lethal Ag NPs and echinocandin drugs revealed potent synergistic effects against fungi. This could be explained by the metabolism of fungi, the result of which has also been verified by transmission electron microscopy (TEM). Lastly, the combination of sub-lethal Ag NPs and echinocandin drugs was used for a mammalian cell toxicity assay to demonstrate whether the optimal combination could cause lower cytotoxicity to mammalian cells. This work opens a window not only for the evaluation of antifungal agents with different mechanisms, but also for the clinical treatment of fungal infections or even new drug development.

Guanidinium ionic liquid-controlled synthesis of zeolitic imidazolate framework for improving its adsorption property

The massive release of rhodamine B (RhB) to water system is an emerging problem, which dramatically threaten environment and human health. The development of an adsorbent with enhanced removal efficiency for RhB is urgently needed. Herein, we report an environment-friendly synthesis of high quality zeolitic imidazolate framework-8 (ZIF-8) and functional ionic liquid@ZIF-8 in water-based system without heat treatment for improving its adsorption property. Guanidinium ionic liquids (ILs) could not only act as greener agents instead of volatile bases and toxic surfactants to efficiently control the nucleation and growth rate of ZIF-8, but also were incorporated as shell material to add specific adsorption sites. The relationship between nanoparticle structure and adsorption performance for RhB was systematically investigated. Due to high surface area (1167 m² g^-1), high porosity (0.79 cm³ g^-1), high crystallinity, nano size (about 100 nm) and monodispersity, the as-obtained ZIF-8 showed improved adsorption capacity toward RhB (80% removal efficiency). Heteropolyanion-based guanidinium IL@meso-ZIF-8 (HPAIL@meso-ZIF-8) exhibited the high RhB uptake capacity of 278 mg g^-1 (higher than most of the reported adsorbents) and effectively removed 99% of RhB within 15 min. The results showed that the adsorption process of prepared materials fitted well with pseudo-second-order kinetics and Langmuir isotherm model. The existence of mesopores in ZIF-8 facilitated the diffusion of RhB and the incorporated guanidinium IL played a significant role in enhancing the adsorption affinity. Moreover, the reusability results revealed the HPAIL@meso-ZIF-8 as a highly efficient adsorbent for RhB removal with satisfactory performance and structural stability. Therefore, HPAIL@meso-ZIF-8 is one of the most promising adsorbents for organic dye removal from water.

Silver-loaded graphene as an effective SERS substrate for clotrimazole detection: DFT and spectroscopic studies

Vibrational infrared, Raman and surface-enhanced Raman scattering (SERS) spectra of clotrimazole (CTZ) were documented and evaluated. Density-functional theory, B3LYP/6-311++G(d,p), approach was implemented to identify the possible conformations, develop the electrostatic potential map, evaluate frontier molecular orbitals and calculate the vibrational spectra of the target compound. The silver-loaded graphene was shown to be an effective SERS substrate for CTZ trace detection. The SERS spectrum showed two enhanced bands at 670 cm^-1 and 700 cm^-1 which confirmed the absorption of the silver substrate through chlorine and nitrogen atoms. A detection limit as low as 5 nM could be reached with a determination coefficient of 0.9988 using the band at 670 cm^-1. The protein-ligand interaction with Secreted Aspartic Proteinase 2 (SAP2) of C. albicans showed that the four stable forms of CTZ maintain a free energy of binding of 6-7 kcal/mol, which could give insights into the mode of action in treating Candidiasis.

Novel electrochemical sensing platform for ultrasensitive detection of cardiac troponin I based on aptamer-MoS2 nanoconjugates

Cardiac troponin I (cTnI) is a specific and sensitive biomarker for the early diagnosis of acute myocardial infarction and for the subsequent clinical treatments. In this work, novel electrochemical sensing platform for sensing of cTnI based on aptamer-MoS₂ nanoconjugates was proposed. For comparison, core-shell Au@SiO₂@Au nanoparticles were also used for sensing of cTnI. The sensing schemes and electrochemical responses of the proposed sensors were investigated by electrochemical impedance spectroscopy (EIS) in 5.0 mM K₃[Fe(CN)₆]/K₄[Fe(CN)₆] (1:1) solution containing 0.1 M KCl, respectively. Results showed that the aptamer-Au@SiO₂@Au based aptasensor shows a linear rage of 10 pM-10.0 μM with the detection limits of 1.23 pM For the aptamer-MoS₂ nanosheets based aptasensor, the linear range for cTnI detection was from 10 pM to 1.0 μM with a lower detection limit of 0.95 pM Meanwhile, both the sensors were successfully applied for detection of cTnI in human blood samples. The two kinds of aptsensors have been successfully used for detecting of cTnI in human blood serums. Moreover, no negligible signal changes could be observed in the presence of non-targets of CK-MB and Myo, suggesting the good potential for clinic diagnosis.

An electrochemical biosensor for microRNA-196a detection based on cyclic enzymatic signal amplification and template-free DNA extension reaction with the adsorption of methylene blue

A simple and sensitive electrochemical biosensor was developed for microRNA-196a detection, which is of important diagnostic significance for pancreatic cancer. It was based on cyclic enzymatic signal amplification (CESA) and template-free DNA extension reaction. In the presence of microRNA-196a, duplex-specific nuclease (DSN) catalyzed the digestion of the 3'-PO₄ terminated capture probe (CP), resulting in the target recycling amplification. Meanwhile, the 3'-OH terminal of CP was exposed. Then, template-free DNA extension reaction was triggered by terminal deoxynucleotidyl transferase (TdT), producing amounts of single-stranded DNA (ssDNA). After ssDNA absorbed numerous methylene blue (MB), an ultrasensitive electrochemical readout was obtained. Based on this dual amplification mechanism, the proposed biosensor exhibited a high sensitivity for detection of microRNA-196a down to 15 aM with a linear range from 0.05 fM to 50 pM. This biosensor displayed high specificity, which could discriminate target microRNAs from one base mismatched microRNAs. It also showed good reproducibility and stability. Furthermore, it was successfully applied to the determination of microRNA-196a in plasma samples. In conclusion, with the excellent analytical performance, this biosensor might have the potential for application in clinical diagnostics of pancreatic cancer.