Changes In Spectral Response Research Articles

A highly selective turn-on fluorescent and naked-eye colorimetric sensor for cyanide detection in food samples and its application in imaging of living cells

A novel highly selective oligothiophene-benzothiazole based sensor 3TBN has been developed for “naked-eye” colorimetric and fluorescent “turn-on” detection of cyanide in aqueous DMSO media. The sensor 3TBN exhibited distinct visual color and spectral changes in response to cyanide anion (CN−) over other tested anions. A good linear relationship was clearly observed between the fluorescence enhancement of the sensor 3TBN and the concentration of CN− in the wide range of 0–40 μM with a low detection limit of 0.46 μM. The sensing mechanism based on the nucleophilic addition reaction of the sensor with CN− on the cyanovinyl electrophilic CC group has been well confirmed. Economically viable paper-based colorimetric test strips of 3TBN were fabricated to effectively detect the CN− ions in water. More importantly, as a cost-effective and selective fluorescent sensor, the sensor 3TBN has been successfully employed for detection of CN− in food samples and fluorescence bioimaging in living HeLa cells.

A Microscopic Model of the Electrochemical Vibrational Stark Effect: Understanding VSF Spectroscopy of (bi)Sulfate on Pt(111)

Much work over the past several decades has demonstrated that the vibrational frequencies of adsorbates on metal surfaces in ultra-high vacuum (UHV) shift with changing surface coverage. Extensive theoretical efforts have shown that this shift can be quantitatively understood as the result of dipole-dipole interaction. A similar phenomenon is known from spectro-electrochemistry (the so-called electrochemical Vibrational Stark Effect (VSE)): the vibrational frequency of the adsorbate is observed to change as a function of applied external potential. Typically this potential-dependent change in adsorbate frequency is assumed to be linear (or piece-wise linear) with applied bias and thus changes in slope are assigned to changes in adsorbate structure or chemical reactions. Here we measure the change in spectral response of the (bi)sulfate anion adsorbed on a Pt(111) working electrode with changes in applied bias and quantitatively interpret the results using a microscopic model of the VSE that explicitly accounts for the effect of dipole-dipole interaction. Using this model we show that changes in external bias that cause a linear change in molecular polarizability can induce a nonlinear change in the center frequency and intensity of the spectral response of the adsorbed (bi)sulfate: the nonlinearity of the VSE depends both on the local field at potential of zero charge and also the relative change induced by external bias. These results imply that essentially all spectroelectrochemical studies that have attributed chemical significance to changes in slope of spectral parameters with applied bias should be revisited, as potential dependent dipole-dipole interaction can induce such changes independent of any structural or chemical change.

The role of singing style in song adjustments to fluctuating sound conditions: A comparative study on Mexican birds

Many bird species adjust their songs to noisy urban conditions by which they reduce masking and counteract the detrimental impact on signal efficiency. Different species vary in their response to level fluctuations of ambient noise, but it remains unclear why they vary. Here, we investigated whether noise-dependent flexibility may relate to singing style and signal function of the flexible acoustic trait. Species with highly variable songs may generally be more flexible and strongly repetitive singers may be more limited to stray from their stringent patterns. We exposed males of four passerine species with contrasting singing styles (repertoire size, immediate or eventual variety singing and syllable diversity) to three experimental sound conditions: 1) continuous urban noise; 2) intermittent white noise and 3) conspecific song playback. We found no spectral or temporal changes in response to experimental noise exposure in any of the four species, but significant temporal adjustment to conspecific playback in one of them. We argue that the consistency in song frequency and timing may have signal value, independent of singing style, and therefore be an explanation for the general lack of noise-dependent flexibility in the four species of the current study.

Spectral characterization of plastic scintillation detector response as a function of magnetic field strength

The purpose of this work was to characterize intensity and spectral response changes in a plastic scintillation detector (PSD) as a function of magnetic field strength. Spectra measurements as a function of magnetic field strength were performed using an optical spectrometer. The response of both a PSD and PMMA fiber were investigated to isolate the changes in response from the scintillator and the noise signal as a function of magnetic field strength. All irradiations were performed in water at a photon beam energy of 6 MV. Magnetic field strengths of (0, ±0.35, ±0.70, ±1.05, and ±1.40) T were investigated. Four noise subtraction techniques were investigated to evaluate the impact on the resulting noise-subtracted scintillator response with magnetic field strength. The noise subtraction methods included direct spectral subtraction, the spectral method, and variants thereof. The PMMA fiber exhibited changes in response of up to 50% with magnetic field strength due to the directional light emission from erenkov radiation. The PSD showed increases in response of up to 10% when not corrected for the noise signal, which agrees with previous investigations of scintillator response in magnetic fields. Decreases in the erenkov light ratio with negative field strength were observed with a maximum change at −1.40 T of 3.2% compared to 0 T. The change in the noise-subtracted PSD response as a function of magnetic field strength varied with the noise subtraction technique used. Even after noise subtraction, the PSD exhibited changes in response of up to 5.5% over the four noise subtraction methods investigated.

INTEGRAL/SPI γ-ray line spectroscopy

Context. The space based γ-ray observatory INTEGRAL of the European Space Agency (ESA) includes the spectrometer instrument “SPI”. This is a coded mask telescope featuring a 19-element Germanium detector array for high-resolution γ-ray spectroscopy, encapsulated in a scintillation detector assembly that provides a veto for background from charged particles. In space, cosmic rays irradiate spacecraft and instruments, which, in spite of the vetoing detectors, results in a large instrumental background from activation of those materials, and leads to deterioration of the charge collection properties of the Ge detectors.Aim. We aim to determine the measurement characteristics of our detectors and their evolution with time, that is, their spectral response and instrumental background. These incur systematic variations in the SPI signal from celestial photons, hence their determination from a broad empirical database enables a reduction of underlying systematics in data analysis. For this, we explore compromises balancing temporal and spectral resolution within statistical limitations. Our goal is to enable modelling of background applicable to spectroscopic studies of the sky, accounting separately for changes of the spectral response and of instrumental background.Methods. We use 13.5 years of INTEGRAL/SPI data, which consist of spectra for each detector and for each pointing of the satellite. Spectral fits to each such spectrum, with independent but coherent treatment of continuum and line backgrounds, provides us with details about separated background components. From the strongest background lines, we first determine how the spectral response changes with time. Applying symmetry and long-term stability tests, we eliminate degeneracies and reduce statistical fluctuations of background parameters, with the aim of providing a self-consistent description of the spectral response for each individual detector. Accounting for this, we then determine how the instrumental background components change in intensities and other characteristics, most-importantly their relative distribution among detectors.Results. Spectral resolution of Ge detectors in space degrades with time, up to 15% within half a year, consistently for all detectors, and across the SPI energy range. Semi-annual annealing operations recover these losses, yet there is a small long-term degradation. The intensity of instrumental background varies anti-correlated to solar activity, in general. There are significant differences among different lines and with respect to continuum. Background lines are found to have a characteristic, well-defined and long-term consistent intensity ratio among detectors. We use this to categorise lines in groups of similar behaviour. The dataset of spectral-response and background parameters as fitted across the INTEGRAL mission allows studies of SPI spectral response and background behaviour in a broad perspective, and efficiently supports precision modelling of instrumental background.

Stability Monitoring of the VIIRS Day/Night Band over Dome C with a Lunar Irradiance Model and BRDF Correction

The unique feature of the Visible Infrared Imager Radiometer Suite (VIIRS) day/night band (DNB) is its ability to take quantitative measurements of low-light scenes at night. In order to monitor the stability of the high gain stage (HGS) of the DNB, nighttime observations over the Dome C site under moonlight are analyzed in this study. The Miller and Turner 2009 (MT2009) lunar irradiance model has been used to simulate lunar illumination over Dome C. However, the MT2009 model does not differentiate the waxing and waning lunar phases. In this paper, the MT-SWC (SeaWiFS Corrected) lunar irradiance model differentiating the waxing and waning lunar phases is derived by correcting the MT2009 model using lunar observations made by the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS). In addition, a top of atmosphere (TOA) bi-directional reflectance distribution function (BRDF) model during nighttime over Dome C is developed to remove the angular dependence from the nighttime TOA reflectance. The long-term stability monitoring of the DNB high-gain stage (HGS) reveals a lower reflectance factor in 2012 in comparison to the following years, which can be traced back to the change in relative spectral response (RSR) of National Oceanic & Atmospheric Administration’s (NOAA’s) Interface Data Processing Segment (IDPS) VIIRS DNB in April 2013. It also shows the radiometric stability of DNB data, with long-term stability of less than 1.58% over the periods from 2013 to 2016. This method can be used to monitor the radiometric stability of other low-light observing sensors using vicarious calibration sites under moonlight illumination.

Day-1 INSAT-3DR Vicarious Calibration Using Reflectance-Based Approach Over Great Rann of Kutch

This study describes the post-launch calibration for visible (VIS) and shortwave infrared (SWIR) bands of Indian National Satellite System (INSAT)-3DR imager over Great Rann of Kutch (GROK) on Day-1 (15th September 2016), when the first time INSAT-3DR Imager camera was switched on. In order to account the characterization of errors and undetermined post-launch changes in sensor spectral response, this calibration activity was performed and extended for its monitoring to Day-56 (since the Day-1; 09th November 2016). A reflectance based technique is used in the present study. The surface reflectance and atmospheric variables were measured over the site as per solar and viewing geometry of the INSAT-3D scan. Top of atmosphere (TOA) spectral radiances were computed using 6SV (second simulation of the satellite signal in the solar spectrum) radiative transfer code with the in situ measurements as well as spectral response function of each channel. Preliminary results of the Day-1 vicarious calibration yield gain coefficients of 0.974 and 0.820 for VIS and SWIR channels respectively despite the inhomogeneity of the ground target caused by sufficient sub-surface soil moisture. In extension of the present study, the obtained gain coefficients were 1.001 and 0.9887 for VIS and SWIR, respectively, during Day-56 which indicates the performance of sensor is within the range of pre-launch laboratory calibration.

Synthesis and electrochemical and spectroscopic studies of a N,N,N',N'-tetraphenylbenzidine-bridged bis(2,2'-bipyridine) ligand and diruthenium complex

A N,N,N',N'-tetraphenylbenzidine-bridged bis(2,2'-bipyridine) ligand and corresponding diruthenium complexes were synthesized and characterized. They show rich multistep redox processes due to the stepwise oxidations of the amine units and ruthenium components. Their absorption and emission spectral changes in response to electrochemical stimulus were examined by spectroelectrochemical measurements. DFT and TDDFT calculations were performed to complement the experimental results.

Signal processing trade-offs for the quality assessment of acoustic color signatures

Acoustic color is a representation of the spectral response over aspect, typically in 2-D. The two natural axes for this representation are frequency and the aspect to the object. It is intuitive to assume finer resolution in the two dimensions would lead to more information extractable for improved quality. However, with conventional linear track data collection methods, there is an inherent trade-off between signal processing decisions and the amount of information that can be utilized without loss of quality. In this work, how the information distribution is affected with choices of representation domain will be presented. The quality metrics including resolution, signal-to-noise-ratio, and other metrics will be discussed in the context of various signal processing choices and parameters. Other representation approaches as extensions of acoustic color will also be explored, such as time-evolving acoustic color that shows how the spectral response changes within a ping cycle.

Hyperspectral radiometer for automated measurement of global and diffuse sky irradiance

An automated hyperspectral radiometer for the measurement of global and diffuse sky irradiance, SkySpec, has been designed for providing the SMEAR-Estonia research station with spectrally-resolved solar radiation data. The spectroradiometer has been carefully studied in the optical radiometry laboratory of Tartu Observatory, Estonia. Recorded signals are corrected for spectral stray light as well as for changes in dark signal and spectroradiometer spectral responsivity due to temperature effects. Comparisons with measurements of shortwave radiation fluxes made at the Baseline Surface Radiation Network (BSRN) station at Tõravere, Estonia, and with fluxes simulated using the atmospheric radiative transfer model 6S and Aerosol Robotic Network (AERONET) data showed that the spectroradiometer is a reliable instrument that provides accurate estimates of integrated fluxes and of their spectral distribution. The recorded spectra can be used to estimate the amount of atmospheric constituents such as aerosol and column water vapor, which are needed for the atmospheric correction of spectral satellite images.

Chiral Discrimination of Diamines by a Binaphthalene-Bridged Porphyrin Dimer.

A pair of 1,1'-binaphthalene-bridged bisporphyrins, (R)- and (S)-H1, were designed to examine their chiral discrimination abilities toward a range of model diamines by using UV-vis absorption, CD, and 1H NMR spectroscopy with the assistance of DFT molecular modeling. The spectroscopic titrations revealed that (R)-/(S)-H1 could encapsulate (R)-/(S)-DACH and (R)-/(S)-PPDA in the chiral bisporphyrin cavities, leading to the selective formation of sandwich-type 1:1 complexes via dual Zn-N coordination interactions. In particular, the chiral recognition energy (ΔΔG°) toward (R)-/(S)-DACH was evaluated to be -4.02 kJ mol-1. The binding processes afforded sensitive CD spectral changes in response to the stereostructure of chiral diamines. Remarkable enantiodiscrimination effects were also detected in the NMR titrations of (R)-/(S)-H1, in which the nonequivalent chemical shift (ΔΔδ) can reach up to 0.57 ppm for (R)-/(S)-DACH. However, due to the large steric effect, another chiral diamine ((R)-/(S)-DPEA) could not be sandwiched in the chiral bisporphyrin cavity; therefore, (R)-/(S)-DPEA could hardly be discriminated by (R)-/(S)-H1. The present results demonstrate a chiral bisporphyrin host with integrated CD and NMR chiral sensing functions and also highlight the binding-mode-dependent character of its enantiodiscrimination performance for different chiral guests.

Robust, sensitive and facile method for detection of F−, CN− and Ac− anions

Sensing of F−, CN− and Ac− is important from the viewpoint of both medically and environmentally. Particularly, sensing of the anions in 100% water by a colorimetric chemical sensor is a highly difficult task as water molecules interfere the sensing mechanism. In this regard, sensor R1, having azo and nitrophenyl groups as signaling units and thiourea as a binding site was prepared. This sensor exclusively detected CN− ion over other testing anions in 30% aq. DMSO solution by exhibiting distinct spectral and visual color changes. However, in 15% aq. DMSO solution, R1 exhibited obvious spectral and color changes in response to F−, CN− and Ac−. On the other hand, we have also designed sensor, R2, having same signaling units of R1, but a different binding site of urea group. Surprisingly, in contrast to R1, R2 exhibited obvious spectral and color changes in 5% aq. DMSO solution only. Further, economically viable “test stripes” were prepared in a facile mode to detect the CN− in 100% aqueous solution. Such stripes can serve as a practical colorimetric probe for “in the field” detection of the ions and thus avoid additional expensive equipment.

Signal processing trade-offs for the representation and quality assessment of acoustic color signatures

Acoustic color is a representation of an object, typically 2-D, which is constructed to show the evolution of the spectral response over the aspect of the object. The two natural axes for this representation are frequency and the aspect to the object. It is intuitive to assume finer resolution in both dimensions would lead to more information extractable for improved quality. However, with conventional linear track data collection methods, there is an inherent trade-off between signal processing decisions and the amount of information that can be utilized without loss of quality. In this work, this trade-off is investigated for an object with a simple geometry, and various quality metrics are discussed. For objects with spectral response that changes slowly over aspect, quality can be improved with methods such as synthetic aperture sonar processing. However, the effect of these processing decisions can depend on the type of object being represented. Other representation approaches as extensions of acoustic color will also be explored, such as time-evolving acoustic color that shows how the spectral response changes within a ping cycle.

Detection of cyanide ions in aqueous solutions using cost effective colorimetric sensor

Cyanide (CN̄) is one of the most toxic material to the human and environment. It is very important to develop the diagnostic tools for the detection of CN̄ ions. Moreover, detection of the ions in an aqueous medium is a challenging task as water molecules interfere with the sensing mechanism. In this context, we prepared chemical sensor, S1, having anthraquinone as a signaling unit and thiourea as a binding site. This sensor exhibited distinct visual color and spectral changes in response to CN̄ ion over other testing anions in 50% aq. DMSO solution. However, in 20% aq. DMSO solution, S1 exhibited obvious spectral and color changes in response to CN̄, fluoride (F̄), acetate (Ac̄) and benzoate (Bz̄). Another sensor, S2, having a same signaling unit with that of S1, but a different binding site of urea group. In contrast to S1, S2 exhibited obvious spectral and color changes to F̄ in 2.5% aq. DMSO solution. NMR titration results suggested that the spectral and colorimetric responses were due to the formation of host-guest complex and deprotonation events. Finally, economically viable paper-based colorimetric “test stripes” of S1 were fabricated to detect the CN̄ ions in 100% aqueous solution.

Stack of Nano-Films on Optical Fiber End Face for Label-Free Bio-Recognition

This paper presents a study on sensing capabilities of stacks of nano-films deposited on a single-mode optical fiber's end face for application in label-free bio-recognition. The stack consist of five nano-films of periodically interchanging materials characterized by different refractive indices ( n at ${\rm{\lambda \,= \,{\text{1550}}\,{\text{nm}}}}$ ), aluminum AlxOy ( $n\,{\rm{\sim {\text{1.58}}\,{\text{RIU}}}}$ ) and titanium TiOx ( $n\,{\rm{\sim {\text{2.42}}\,{\text{RIU}}}}$ ) oxides layers. The stack was deposited with the reactive magnetron sputtering technique. It has been found that the structures show sensitivity to refractive index of surrounding liquid (74.4 nm/RIU and 44.3 dBm/RIU) and negligible sensitivity to variations of temperature. Moreover, we show that these structures when functionalized can be used for selective detection of biological layer formation on their surface. In this study, a biotin-avidin complex was used to show a label-free bio-recognition capability of the approach. Avidin concentration of 1 mg/ml induced shift of the resonance wavelength and change in reflected power by 3 nm and 0.8 dBm, respectively, when BSA, which is nonspecific to biotin, resulted in a negligible change in spectral response. The approach seems to be very interesting, especially when such advantages as batch device fabrication, sensor robustness, and fully automatized stack deposition process are taken into account.

Reflectance-based vicarious calibration of INSAT-3D using high-reflectance ground target

This study is carried out as the post-launch calibration for visible (IMG-VIS) and shortwave (IMG-SWIR) bands of INSAT-3D imager and visible (SND-VIS) band of Indian National Satellite System (INSAT)-3D sounder over land site (Little Rann of Kutch (ROK), Gujarat) on five clear-sky days. This calibration activity is performed to account for the characterisation errors or undetermined post-launch changes in sensor spectral response. We had measured the surface reflectance and atmospheric variables at the site synchronising with the viewing and solar geometry of the INSAT-3D scan. Top of atmosphere (TOA) spectral radiances were computed using 6SV (Second Simulation of the Satellite Signal in the Solar Spectrum) radiative transfer (RT) code with the surface reflectance and atmospheric variables as well as spectral response function (SRF) of each channel. The uncertainties involved due to spatial variability of site and variation in aerosol type in calibration coefficients were also computed. MODIS Bidirectional Reflectance Distribution Function (BRDF) product is used to account the effect of surface anisotropy on TOA spectral radiance. Comparison between 2014 and 2015 vicarious calibration results, indicate that the INSAT-3D measured radiance are stable within 0.38%, 0.18% and 0.13% for IMG-VIS, IMG-SWIR and SND-VIS, respectively. 6SV simulated atmospherically corrected reflectances were found to match much better with the observed surface reflectance in the inverse mode for all three bands. Comparing these results with the previous year’s analysis, there is no indication of major change in calibration coefficients for all three bands of INSAT-3D.

Optimizing Coupling Region as Sensing Area in Optical Ring Resonator Sensor Applications

Optical Ring Resonators (ORR), whether based on fiber optics or an optical micro ring on substrate structures have been studied and explored extensively to be used for optical sensor applications. The outstanding advantage of optical ring resonator structure is its spectral response shape change due to the variations of the refractive index of the surrounding medium, medium loss due to absorption and scattering, and coupling loss between waveguides in the optical ring structure. The change of spectral response due to the variations of optical medium on the optical ring structure is a phenomenon that can be used to sense the optical property change of physical or biological materials. Some developments of Waveguide (WG) ORR sensors are in progress mostly for bio-sensor applications, since it is free from Electromagnetic Interference (EMI) and is non-physically destructive. In this paper, we discuss our research in developing optical bio-sensor in the form of a WG optical ring resonator. The focus of the research is optimizing the coupling region as sensing area to obtain the optimal coupling coefficient for the most sensitive sense. The results show that the variations of coupling coefficient is not linear with respect to the resonant peak output, such that we are able to locate the most sensitive coupling coefficient to sense.

CMOS Image Sensor and System for Imaging Hemodynamic Changes in Response to Deep Brain Stimulation

Deep brain stimulation (DBS) is a therapeutic intervention used for a variety of neurological and psychiatric disorders, but its mechanism of action is not well understood. It is known that DBS modulates neural activity which changes metabolic demands and thus the cerebral circulation state. However, it is unclear whether there are correlations between electrophysiological, hemodynamic and behavioral changes and whether they have any implications for clinical benefits. In order to investigate these questions, we present a miniaturized system for spectroscopic imaging of brain hemodynamics. The system consists of a 144 ×144, [Formula: see text] pixel pitch, high-sensitivity, analog-output CMOS imager fabricated in a standard 0.35 μm CMOS process, along with a miniaturized imaging system comprising illumination, focusing, analog-to-digital conversion and μSD card based data storage. This enables stand alone operation without a computer, nor electrical or fiberoptic tethers. To achieve high sensitivity, the pixel uses a capacitive transimpedance amplifier (CTIA). The nMOS transistors are in the pixel while pMOS transistors are column-parallel, resulting in a fill factor (FF) of 26%. Running at 60 fps and exposed to 470 nm light, the CMOS imager has a minimum detectable intensity of 2.3 nW/cm(2) , a maximum signal-to-noise ratio (SNR) of 49 dB at 2.45 μW/cm(2) leading to a dynamic range (DR) of 61 dB while consuming 167 μA from a 3.3 V supply. In anesthetized rats, the system was able to detect temporal, spatial and spectral hemodynamic changes in response to DBS.

Parametric variation of gamma frequency and power with luminance contrast: A comparative study of human MEG and monkey LFP and spike responses

Gamma oscillations contribute significantly to the manner in which neural activity is bound into functional assemblies. The mechanisms that underlie the human gamma response, however, are poorly understood. Previous computational models of gamma rely heavily on the results of invasive recordings in animals, and it is difficult to assess whether these models hold in humans. Computational models of gamma predict specific changes in gamma spectral response with increased excitatory drive. Hence, differences and commonalities between spikes, LFPs and MEG in the spectral responses to changes in excitatory drive can lead to a refinement of existing gamma models. We compared gamma spectral responses to varying contrasts in a monkey dataset acquired previously (Roberts et al., 2013) with spectral responses to similar contrast variations in a new human MEG dataset. We found parametric frequency shifts with increasing contrast in human MEG at the single-subject and the single-trial level, analogous to those observed in the monkey. Additionally, we observed parametric modulations of spectral asymmetry, consistent across spikes, LFP and MEG. However, while gamma power scaled linearly with contrast in MEG, it saturated at high contrasts in both the LFP and spiking data. Thus, while gamma frequency changes to varying contrasts were comparable across spikes, LFP and MEG, gamma power changes were not. This indicates that gamma frequency may be a more stable parameter across scales of measurements and species than gamma power. The comparative approach undertaken here represents a fruitful path towards a better understanding of gamma oscillations in the human brain.

Charge transfer inefficiency in the pre- and post-irradiated Swept Charge Device CCD236

This paper describes the mapping of spectral response of an e2v technologies Swept Charge Device (SCD) CCD236 pre and post irradiation with a 10 MeV equivalent proton fluence of 5.0 × 108 protons cm−2. The CCD236 is a large area (4.4 cm2) X-ray detector which will be used in India's Chandrayaan-2 Large Soft X-ray Spectrometer (CLASS) and China's Hard X-ray Modulation Telescope (HXMT). To enable the suppression of surface dark current, clocking is performed continuously resulting in a linear readout. As such the flat field illumination used to measure any change in spectral response over a conventional Charge-Coupled Devices (CCDs) is not possible. An alternative masking technique has been used to expose pinpoint regions of the device to Mn-Kα and Mn-Kβ X-rays, enabling a local map of spectral response to be built up over the device. This novel approach allows for an estimation of the Charge Transfer Inefficiency (CTI) of the device to be made by allowing the creation of a CTI scatter plot similar to that typically observed in conventional CCDs.