Spectral Intensity Changes Research Articles

Silver shelled gold nanorods for sensitive detection of cholesterol and triglycerides

We report the synthesis of bimetallic plasmonic nanostructure of silver shelled gold nanorods (Ag–Au NRs), subsequently employed for the selective detection of cholesterol (Cho) and triglycerides (TGl) utilizing Surface Enhanced Raman Spectroscopy (SERS). In this direction, the gold nanorods (Au NRs) were synthesized via seed mediated growth method followed by forming a silver shell with reduction of AgNO3 onto Au NRs. Ag–Au NRs showed significantly augmented SERS property owing to hybridization of Localized Surface Plasmon Resonances (LSPR) of silver and gold. The enhanced plasmonic property was thus employed for biosensing. For this, two different Raman reporter molecules, 5,5′–dithiobis–(2–nitrobenzoic acid) (DTNB) and 4–aminothiophenol (4ATP) were immobilized separately on Ag–Au NRs to synthesize SERS active nanoprobes, before the attachment of the bioreceptors – cholesterol oxidase (ChOx) and lipase (Lp) to form ChOx–DTNB–Ag–Au NRs and Lp–4ATP–Ag–Au NRs. These nanoprobes were then utilized for the quantification of Cho and TGl via liquid mode Raman spectroscopic study. The change in SERS spectral intensity of DTNB and 4ATP were systematically recorded in reference to the baseline sample to mark the calibration for both Cho and TGl. Additionally, interference studies considering effects of ascorbic acid, glucose, sodium and potassium ion were performed to unveil excellent selectivity of the proposed method.

Water-Mediated Charge Transfer and Electron Localization in a Co3Fe2 Cyanide-Bridged Trigonal Bipyramidal Complex.

The effects of temperature and chemical environment on a pentanuclear cyanide-bridged, trigonal bipyramidal molecular paramagnet have been investigated. Using element- and oxidation state-specific near-ambient pressure X-ray photoemission spectroscopy (NAP-XPS) to probe charge transfer and second order, nonlinear vibrational spectroscopy, which is sensitive to symmetry changes based on charge (de)localization coupled with DFT, a detailed picture of environmental effects on charge-transfer-induced spin transitions is presented. The molecular cluster, Co3Fe2(tmphen)6(μ-CN)6(t-CN)6, abbrev. Co3Fe2, shows changes in electronic behavior depending on the chemical environment. NAP-XPS shows that temperature changes induce a metal-to-metal charge transfer (MMCT) in Co3Fe2 between a Co and Fe center, while cycling between ultrahigh vacuum and 2 mbar of water at constant temperature causes oxidation state changes not fully captured by the MMCT picture. Sum frequency generation vibrational spectroscopy (SFG-VS) probes the role of the cyanide ligand, which controls the electron (de)localization via the superexchange coupling. Spectral shifts and intensity changes indicate a change from a charge delocalized, Robin-Day class II/III high spin state to a charge-localized, class I low spin state consistent with DFT. In the presence of a H-bonding solvent, the complex adopts a localized electronic structure, while removal of the solvent delocalizes the charges and drives an MMCT. This change in Robin-Day classification of the complex as a function of chemical environment results in reversible switching of the dipole moment, analogous to molecular multiferroics. These results illustrate the important role of the chemical environment and solvation on underlying charge and spin transitions in this and related complexes.

In-situ surface-enhanced Raman scattering on imidazole-based ionic liquids at variable temperatures

Ionic liquids (ILs) are unique solvents with a broad liquid temperature range. However, little has so far been done to investigate the ionic structures of ILs as a function of temperature. This can be performed by surface-enhanced Raman scattering (SERS) technique to effectively investigate the ionic structure and interface reaction of ILs at different temperature. Herein, in-situ SERS spectra of 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl) and 1-carboxyethyl-3-methylimidazolium chloride ([HO2CEtMIm]Cl) ILs adsorbed on silver substrates at variable temperatures were recorded to study the adsorption behaviors and enhancement mechanisms. The results suggested interaction between [EMIm]Cl and silver substrate through N-atoms with the imidazole ring standing on the substrate. The enhancement mechanism of silver substrates toward [EMIm]Cl originated from the combination of electromagnetic enhancement (EM) and chemical enhancement (CM). At temperatures of 25–200 °C, no significant changes in the adsorption behavior and ionic structure of [EMIm]Cl on the silver substrate surface were observed. However, a further temperature rise resulted in changes in SERS spectral intensity of [EMIm]Cl owing to the aggregation of silver particles, as well as the increment in the amount of adsorbed molecules. Besides, [HO2CEtMIm]Cl interacted with the silver substrate through the carboxyl group, resulting in a molecular configuration that greatly influenced the adsorption behavior of [HO2CEtMIm]Cl. Compared to [EMIm]Cl, the imidazole ring of [HO2CEtMIm]Cl was located farther away from the substrate surface, leading to weaker SERS enhancement. Finally, the temperature variation did not affect the adsorption behavior and ionic structure of [HO2CEtMIm]Cl on the substrate surface. Overall, these results look promising for future studies of ionic structure and interface reaction of various ILs for advanced synthesis processes.

Photosynthetic adaptation strategies in peppers under continuous lighting: insights into photosystem protection.

Energy efficient lighting strategies have received increased interest from controlled environment producers. Long photoperiods (up to 24 h - continuous lighting (CL)) of lower light intensities could be used to achieve the desired daily light integral (DLI) with lower installed light capacity/capital costs and low electricity costs in regions with low night electricity prices. However, plants grown under CL tend to have higher carbohydrate and reactive oxygen species (ROS) levels which may lead to leaf chlorosis and down-regulation of photosynthesis. We hypothesize that the use of dynamic CL using a spectral change and/or light intensity change between day and night can negate CL-injury. In this experiment we set out to assess the impact of CL on pepper plants by subjecting them to white light during the day and up to 150 µmol m-2 s-1 of monochromatic blue light at night while controlling the DLI at the same level. Plants grown under all CL treatments had similar cumulative fruit number and weight compared to the 16h control indicating no reduction in production. Plants grown under CL had higher carbohydrate levels and ROS-scavenging capacity than plants grown under the 16h control. Conversely, the amount of photosynthetic pigment decreased with increasing nighttime blue light intensity. The maximum quantum yield of photosystem II (Fv/Fm), a metric often used to measure stress, was unaffected by light treatments. However, when light-adapted, the operating efficiency of photosystem II (ΦPSII) decreased and non-photochemical quenching (NPQ) increased with increasing nighttime blue light intensity. This suggests that both acclimated and instantaneous photochemistry during CL can be altered and is dependent on the nighttime light intensity. Furthermore, light-adapted chlorophyll fluorescence measurements may be more adept at detecting altered photochemical states than the conventional stress metric using dark-adapted measurements.

A novel algorithm for highly sensitive and rapid hotspot detection in HTS magnets using quasi-continuous fiber Bragg gratings

Most optical fiber sensors based on Brillouin/Rayleigh scattering, and discrete fiber Bragg gratings (FBGs) cannot offer the speed and distributed sensing with operation in a cryogenic environment < 80 K necessary for superconducting magnet protection. An ultra-long fiber Bragg grating (ULFBG) comprised of quasi-continuous FBGs has the potential to rapidly detect the occurrence of a thermal hot spot in high-temperature superconducting magnets. However, processing the data for detection purpose is challenging. This is because the spectrum of an ULFBG is complex, and the hotspot induced spectral changes are difficult to identify. In this paper, we present the novel Spectral Intensity Change (SIC) algorithm to 1) extract the region of interest within the spectrum based on unique change patterns, 2) identify the direction of temperature change, and 3) process the isolated spectral data to signal hotspot events. To demonstrate the effectiveness of the algorithm, three ULFBGs with sensing lengths of 0.2, 0.5 and 1.9 m are used to detect events of temperature variations. Using the algorithm, ULFBG sensors not only can identify a hot spot event rapidly and accurately but also achieve a significantly enhanced signal to noise ratio (SNR) at 80 K. The SIC algorithm has the potential to be implemented for real-time hotspot and quench detection in superconducting magnets.

Long-term repeatability improvement using beam intensity distribution for laser-induced breakdown spectroscopy

The relatively low measurement repeatability has long been considered as a major obstacle to the widespread use and commercialization of laser-induced breakdown spectroscopy (LIBS). Although many efforts have been made to improve the signal repeatability in the short term, how to improve the long-term signal repeatability is critical in practical applications and has rarely been studied. Moreover, the mechanisms behind the degradation of long-term repeatability are not fully revealed. This study proposes a new method to improve the long-term repeatability of LIBS measurement, which modifies the spectral intensity based on laser beam intensity distribution. It first pre-processes the beam intensity distribution profiles and spectral intensity. Then the relationship between the relative deviations of beam and spectral intensities is modelled using Partial Least Squares Regression (PLSR). The proposed method was tested on copper and silicon samples, and the spectra and laser beam intensity distribution were recorded for more than thirty days. Day-to-day variations in beam intensity distribution were observed. Such variations can lead to changes in spectral intensity, resulting in degraded signal repeatability. By modifying the spectral intensity, the long-term signal repeatability was improved. Specifically, in terms of day-mean spectral intensity, the valid correction rates were above 70% for both of copper silicon sample in most cases. Long-term RSD decreased from ∼13.5% to ∼4% for copper and decreased from ∼10.7% to 6.5% for silicon sample. These results indicate that the proposed method provides a viable method for improving the long-term repeatability of LIBS measurement.

Determination of Radiation Dose Leading to Molecular Chain Destruction of Amino Acids

The soft X-ray absorption spectroscopy (XAS) spectra of Alanine, L- and D-phenylalanine, and L- and D-tyrosine dissolved in a solid state were measured at BL17SU of SPring-8. The spectra exhibited characteristic features dependent on the molecular structure. It was found that almost the same spectra were obtained for Alanine and Phenylalanine, while for Tyrosine, the spectral shape indicated a drastic change owing to the existence of the oxygen 1s → π* transitions of COO¯. It is found that the X-ray irradiation promotes the destruction reaction of amino acids and changes the spectral shape during the spectroscopic measurement. The molecular destruction rate by X-ray was estimated from the change of spectral intensity as a function of irradiation time. Our results indicate that the ratio of the destruction rate depends on the molecular structure and is facilitated by the oxygen 1s → π* transitions.

Efficiently driving protein-based fragment screening and lead discovery using two-dimensional NMR.

Fragment-based drug discovery (FBDD) and validation of small molecule binders using NMR spectroscopy is an established and widely used method in the early stages of drug discovery. Starting from a library of small compounds, ligand- or protein-observed NMR methods are employed to detect binders, typically weak, that become the starting points for structure-activity relationships (SAR) by NMR. Unlike the more frequently used ligand-observed 1D NMR techniques, protein-observed 2D 1H-15N or 1H-13C heteronuclear correlation (HSQC or HMQC) methods offer insights that include the mechanism of ligand engagement on the target and direct binding affinity measurements in addition to routine screening. We hereby present the development of a set of software tools within the MestReNova (Mnova) package for analyzing 2D NMR for FBDD and hit validation purposes. The package covers three main tasks: (1) unsupervised profiling of raw data to identify outlier data points to exclude in subsequent analyses; (2) batch processing of single-point spectra to identify and rank binders based on chemical shift perturbations or spectral peak intensity changes; and (3) batch processing of multiple titration series to derive binding affinities (KD) by tracing the changes in peak locations or measuring global spectral changes. Toward this end, we implemented and evaluated a set of algorithms for automated peak tracing, spectral binning, and variance analysis by PCA, and a new tool for spectral data intensity comparison using ECHOS. The accuracy and speed of the tools are demonstrated on 2D NMR binding data collected on ligands used in the development of potential inhibitors of the anti-apoptotic MCL-1 protein.

Changes in the Fluorescence of Biological Particles Exposed to Environmental Conditions in the National Capitol Region

A variety of methods have been used to study atmospheric bioaerosols. A common technique employed for the detection and measurement of bioaerosols is the measurement of the autofluorescence of biological particles when excited by ultraviolet light. We examined the changes in the fluorescence spectra of bioaerosols when exposed to ambient outdoor conditions for periods of several hours. The bioaerosols in this study were contained in a Captive Aerosol Growth and Evolution (CAGE) chamber that employed two rotating drums constructed with an exterior FEP Teflon film to allow sunlight to penetrate and an inner ePTFE membrane to allow ambient trace gasses to permeate the drums. The bioaerosols were periodically measured with a TSI UV-APS (excited at 355 nm) and a single-particle fluorescence spectrometer (excited at 351 and 263 nm). The data indicate changes in both fluorescence spectral profile and intensity from Bacillus thuringiensis var. kurstaki spores and MS2 bacteriophage particles during the experiments. The changes observed in these particles appear to be due to a combination of the environmental conditions rather than attributable to any single factor. The results of this study indicate that bioaerosols are significantly altered by atmospheric aging processes and that these changes may affect measurements by ultra-violet light induced fluorescence (UV-LIF) or other spectroscopic techniques.

Simulation system of lighting environment for optical imaging test

In order to overcome the shortcomings of the solar simulator in the aspect of the performance testing for optical imaging system, a lighting environment simulation system is designed. We select dysprosium lamp, xenon lamp and multiple LEDs as light sources of the solar simulator, and the change of the sun zenith angle is simulated by using the symmetrical method of the light source. Also, the light intensity is controlled by adjusting the output current of the power supply. Lighting environment simulation system not only can simulate spectral irradiance and intensity change of real solar, but also can simulate the real sun depending on the season and the angle of illumination period. This system provided a technical support for the performance testing of optical imaging systems.

Investigation of fluconazole susceptibility to Candida albicans by MALDI-TOF MS and real-time PCR for CDR1, CDR2, MDR1 and ERG11

BackgroundC. albicans is a pathogenic yeast that is the most common cause of fungal infections in humans. Unfortunately, the yeast’s resistance to the antifungal medication fluconazole (FLC) is increasing; furthermore, testing its susceptibility to FLC by conventional methods takes time, resulting in treatment failure. The susceptibility of C. albicans to FLC was investigated using MALDI-TOF Mass Spectrometry and Real-time PCR tests for CDR1, CDR2, MDR1 and ERG11. Overall, 32 C. albicans strains made up of four reference strains (three FLC susceptible [S] and one FLC resistant [R], one spontaneous mutant strain [FLC susceptible-dose-dependent (SDD)] and 27 clinical strains obtained from two Thai University Hospitals) were tested for susceptibility to FLC. The following tests were performed: SensititreYeastOne and broth microdilution method, FLC resistant expression mechanism by Real-time PCR, and the major peak determination by MALDI-TOF MS.ResultsThe change of CDR1 and CDR2 mRNA expression was only significantly observed in SDD and R strains. MALDI-TOF MS was performed after incubation for six hours; the change of mass spectral intensity at range 3376–3382 m/z (major peak) was significantly related to FLC susceptibility as SDD (decreased at 4 µg/mL and increased at 8 µg/mL), S (all increased), and R (all slightly decreased or no change). All 27 clinical strains showed FLC minimum inhibitory concentrations (MIC range 0.25-2 µg/mL), no change in CDR1 and CDR2 expression and S major peak type. The FLC resistant C. albicans with CDR1and CDR2 expression may possibly affect the change of mass spectral intensity at range 3376–3382 m/z.ConclusionsThe MALDI-TOF MS may be used to simultaneously classify and predict FLC resistant C. albicans strains associated with CDR1 and CDR2 expression. Further studies are essential to clarify the methodology and improve the reliability of this assay for routine diagnosis.

Two-Trace Two-Dimensional Correlation Spectroscopy Study of the Crystallization Behavior of Bioplastics.

A pair of attenuated total reflection infrared (ATR IR) spectra obtained during the crystallization of bioplastic copolymer poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] or PHBHx from the melt by spontaneous cooling were examined using the two-trace two-dimensional correlation spectroscopy (2T2D-COS) analysis. Unlike conventional difference spectra, 2T2D spectra showed unexpected details for the patterns of spectral intensity changes, clearly revealing the existence of two distinct populations of crystalline contributions, attributed to the well-ordered primary crystals and the less ordered secondary crystals, in addition to the amorphous component. The 2T2D spectrum sorts out highly overlapped bands associated with different constituents of the system, based on the fundamental properties and constraint imposed on a pair of spectra. Hetero-mode asynchronous 2T2D correlation analysis between the congested CH-stretching region and better resolved carbonyl-stretching region further indicates that the increase in the intensities of certain methyl and methylene bands during the crystallization process is mostly associated with the growth of the well-ordered primary crystals of PHBHx instead of the formation of the secondary crystals in the confined inter-lamellar space.

High-Performance Electro-Optic Manipulation by Plasmonic Light Absorber With Nano-Cavity Field Confinement

Narrowband light absorber with multi-band plasmonic resonances is numerically investigated for high-performance electrical manipulation via introducing the electro-optic (EO) medium in the slit array based grating structure. A maximal absorption efficiency of 99.5% is achieved. The spectral shift sensitivity reaches 0.99 nm/V. Besides, the large spectral intensity change is also obtained due to the use of sharp resonances, which therefore ensures the high signal-to-noise ratio for the manipulation process. It is observed that the strong surface plasmon resonance and the localized optical cavity modes can introduce the differential responses for the multiple modes under the optical adjusting process and also for the EO manipulation process. These features not only contribute to produce the new EO modulator platforms based on the light absorbers but also pave new ways for the cavity-enhanced high-performance EO operation. Moreover, the absorption properties can be well maintained in a wide range of the structural parameters, indicating the high tolerance of the fabrication process. The findings can pave new insights into the high-performance manipulations via the narrowband absorbers with strong electromagnetic field enhancement and hold wide applications in dynamic switching, filtering, displaying, etc.

Periodic properties of Laguerre-Gaussian correlated Schell-model beams in a gradient-index fiber

The explicit expressions of the cross-spectral density (CSD) and the propagation factor of Laguerre-Gaussian correlated Schell-model (LGCSM) beams propagation in a gradient-index (GRIN) fiber were derived. The statistical properties, such as the spectral intensity, the spectral degree of coherence (DOC) and the propagation factor of LGCSM beams in a GRIN fiber are illustrated numerically. Our results show that the beams spectral intensity and spectral DOC change periodically in a GRIN fiber. We can adjust the initial beam parameters of LGCSM beams, such as the beam order, the transverse beam width and the transverse coherence width, to control the distributions of the spectral intensity and the spectral DOC of the beams in the output plane of a GRIN fiber. Furthermore, the propagation factor of the beams remains invariant on propagation and it is determined only by the initial beam parameters. Our results may be useful in optical fiber communications.

Foliage Intensity is an Important Cue of Habitat Location for Empoasca onukii.

For many herbivorous insects, vision is more important than olfaction in the prealighting stage of host habitat location. Tea leafhoppers, Empoasca onukii (Hemiptera, Cicadellidae), are serious pests that preferentially inhabit the tender leaves of tea plants across China. Here, we investigated whether tea leafhoppers could distinguish foliage colors associated with different leaf ages and use this visual cue to guide suitable habitat location from short distances. Similar to honeybees, the adult E. onukii has an apposition type of compound eye, and each ommatidium has eight retinular cells, in which three spectral types of photoreceptors are distributed, with peak sensitivities at 356 nm (ultraviolet), 435 nm (blue), and 542 nm (green). Both changes in spectral intensity and hue of reflectance light of the host foliage were correlated with varying leaf age, and the intensity linearly decreased with increasing leaf age. Behavioral responses also showed that adult E. onukii could discriminate between the simulated colors of host foliage at different leaf ages without olfactory stimuli and selected the bright colors that strongly corresponded to those of tender leaves. The results suggest that, compared with the spectral composition (hue), the intensity of light reflectance from leaves at different ages is more important for adult leafhoppers when discriminating host foliage and could guide them to tender leaves at the top of tea shoots.

High-Q plasmonic graphene absorbers for electrical switching and optical detection

In this work, we report an intensive theoretical study on the achieving of multiple ultra-sharp and near-unity absorption in a cavity enabled graphene absorber. The plasmonic-induced magnetic resonance, i.e., magnetic plasmon is excited and localized efficiently via the one-dimensional metallic oblique slit array. The slit concentrates highly for the plasmonic field in a limited spatial cavity and simultaneously intensifies the graphene-field coupling, which leads to the emergency of the multi-band high-quality (Q) factor (190) ultra-sharp perfect absorption. Although the graphene-slit interaction area is just 17.7% of the structural size, the maximal absorption efficiency reaches 99.8%. In the near-infrared range, a large spectral intensity change of 82% is achieved when the graphene’s Fermi energy is manipulated by a slight value of 0.03 eV, which directly introduces a viewable switching process between the operation “on” and “off” states. The optical sensing sensitivity is also up to 1276 nm/RIU and the FOM factor reaches 106. During the application for temperature detecting, the resolution limit can be as down as 3 × 10−3 °C (K), suggesting a desirable temperature detector. Moreover, polarization-adjustable and angle-insensitive properties for the plasmonic graphene absorber could further promote enormous applications for the active optoelectronic devices.

Vibrational Sum Frequency Generation Study of the Interference Effect on a Thin Film of 4,4'-Bis(N-carbazolyl)-1,1'-biphenyl (CBP) and Its Interfacial Orientation.

Molecular organization of vapor-deposited organic molecules in the active layer of organic light-emitting diodes (OLEDs) has been a matter of great interest as it directly influences various optoelectronic properties and the overall performance of the devices. Contrary to the general assumption of isotropic molecular orientation in vacuum-deposited thin-film OLEDs, it is possible to achieve an anisotropic molecular distribution at or near the surface under controlled experimental conditions. In this study, we have used interface-specific vibrational sum frequency generation (VSFG) spectroscopy to determine the orientation of a low-molecular weight OLED material, 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP), at free (air) and buried (CaF2) interfaces. VSFG spectra were measured at four different polarization combinations for five different thicknesses of the CBP film. The spectral shift and VSFG intensity changes with the film thickness can be accurately modeled by considering the optical interference effect of the signals coming from the CBP/air and CBP/CaF2 interfaces. A global fitting of the experimental spectra for all thicknesses along with theoretical simulations reveal that the long molecular axis of CBP is oriented at an angle of ∼58° (47-70°) from the surface normal at the air/CBP interface, whereas at the CBP/CaF2 interface, the angle is ∼48° (43-52°). Such a change in the angle (∼10°) suggests that the CBP molecule tends to orient more vertically (edge-on) at the buried CaF2 interface, which may be attributed to the intermolecular π-π stacking interaction between adjacent CBP molecules.

Nano carbides-mediated acceleration of energy release behavior of amorphous boron during ignition and combustion

Action mechanism of nano titanium carbide (nTiC), nano zirconium carbide (nZrC), and nano silicon carbide (nSiC) was studied using a concentrated ignition experimental system, an X-ray diffractometer and a scanning electron microscope. Each nano-carbide was mixed with B in mass ratio of 2/8 and then pressed into tablets, respectively. Furthermore, a sample of amorphous B was also prepared as the control group. All the three nano-carbides showed positive influence on the ignition of B. During the first stage of combustion, only nTiC could increase the maximum emission spectral intensity of the sample, while both nTiC and nZrC helped to increase that during the second stage of combustion. Although the addition of nano-carbides intensified the energy release rate of B (except nSiC), the expansion and diffusion of generated carbon dioxide took large amounts of heat away and reduced the surface temperature of the samples The temperature change in solid-phase exhibited a relationship with the spectral intensity change in gas-phase. The temperature increase was slow during the ignition delay stage, while the first combustion stage proceeded with rapid increase in surface temperature. The high-temperature areas regressed during the second combustion stage, accompanied by the gradual stopping of gas-phase reactions. The components and microstructure of the condensed combustion products (CCPs) were analyzed after the ignition experiment. Results showed that both nTiC and nZrC could react with B to generate corresponding metal borides, capable of promoting the ignition of B. Moreover, the catalysis of produced TiO2 and ZrO2 explain the increase of emission spectral intensity during the second combustion stage. A lot of micropores formed in the CCPs after adding nTiC, which showed a destructive effect of generated gaseous CO2 on the surface oxide layer. In general, nTiC is the top accelerant for B oxidation in this study, while nSiC is at the bottom.

High-performance plasmonic oblique sensors for the detection of ions

Efficient optical sensing is desirable for a wide range of applications. For sensors, the spectral factors of the sensitivity (S) and the figure of merit (FoM) and the intensity change related figure of merit (FOM*) are all the key factors in sensing measurement. In this work, we propose and demonstrate a novel high-performance plasmonic sensor platform using a resonant cavity array grating under oblique excitation. An ultra-sharp absorption mode with a bandwidth down to 1.3 nm is achieved when the oblique angle is 7.5°. During the sensing of the Na+ (Cl−) ions in the solution, the spectral S and FoM factors reach 568 nm RIU−1 (refractive index unit) and 436 nm RIU−1, respectively. The minimum detection limit is as low as 3.521 × 10–6 RIU. The FOM* factor is simultaneously up to 907. Moreover, the spectral intensity change is up to 57% when only a 1% concentration change is introduced into the solution. The detection limit of the concentration of the ions can be as low as 0.002%. The sensor has great potential applications due to its ultrahigh S, FoM, and FOM*.

Spectrophotometric study of the interaction of active pharmaceutical ingredients with colloidal silver nanoparticles capped by sulfonato-calix[6]arene derivatives

ABSTRACT Three sulfonato-calix[6]arene derivatives, namely para-sulfonato-calix[6]arene, calix[6]arene-O-propyl-3-sulphonate and para-sulfonato-calix[6]arene-O-propyl-3-sulphonate have been used as capping agents for silver nanoparticles. The sulfonato-calix[6]arene derivatives were demonstrated to stabilise the nanoparticles, and to act as ligands for molecular recognition at the surface of the nanoparticles. The nanoparticles were characterised by UV-visible spectroscopy, dynamic light scattering, zeta potential and scanning electron microscopy. The localised surface plasmon resonance of the nanoparticles was shown to be highly sensitive to the local environment, and was used to evaluate molecular interactions with four active pharmaceutical ingredients: streptomycin, gentamycin, D-penicillamine and chloramphenicol. Changes in spectral intensity and wavelength have shown that the interactions are dependent on both the nature of the active pharmaceutical ingredient and that of the calix[6]arene receptor.