Observed Color Changes Research Articles

Electrospun colourimetric sensors for detecting volatile amines

Volatile amines are present in our daily life as a result of chemical manufacturing, agriculture and farming, release by rotten food or exhalation under certain medical conditions or diseases. An efficient, fast and low-cost method for detecting these compounds is desired due to their often-toxic nature. The development of a highly sensitive electrospun colourimetric sensor for the detection of volatile amines is reported here. Composite microfibrous meshes were obtained by incorporating activated furan adducts (FAs) into electrospun polymer meshes. Volatile amines penetrate into the amorphous polymer matrix where the ring-opening reaction with FAs yields strongly coloured donor-acceptor Stenhouse adducts (DASAs), resulting in an easily observable visible mesh colour change. Different FAs were evaluated, including a highly reactive FA yielding 3rd generation DASAs. The colourimetric responses were assessed qualitatively and quantitatively by RGB (red, green and blue) colour analysis. The sensors showed a detection range with high sensitivity down to the low-ppb range. Additionally, the covalent attachment of FAs to a polymer backbone anchored them inside the fibres and successfully prevented leaching. Thus, the cytotoxic effect of leached FAs was eliminated, as shown by indirect and direct contact tests with human fibroblasts.

Dopamine and Melamine Binding to Gold Nanoparticles Dominates Their Aptamer-Based Label-Free Colorimetric Sensing.

Target-directed aptamer adsorption by gold nanoparticles (AuNPs) has been widely used to develop label-free colorimetric biosensors. However, the potential interactions between target molecules and AuNPs have not been considered, which may lead to misinterpretation of analytical results. In this work, the detection of dopamine, melamine, and K+ was studied as model systems to address this problem. First, dopamine and two control molecules all induced the aggregation of citrate-capped AuNPs with apparent Kd's of 5.8 μM dopamine, 51.6 μM norepinephrine, and 142 μM tyramine. Isothermal titration calorimetry measured the aptamer Kd to be 1.9 μM dopamine and 16.8 μM norepinephrine, whereas tyramine cannot bind. Surface enhanced Raman spectroscopy confirmed direct adsorption of dopamine, and the adsorbed dopamine inhibited the adsorption of DNA. Using a typical salt-induced colorimetric detection protocol, a similar color response was observed regardless of the sequence of DNA, indicating the observed color change reflected the adsorption of dopamine by the AuNPs instead of the binding of dopamine by the aptamer. For this label-free sensor to work, the interaction between the target molecule and AuNPs should be very weak, while dopamine represents an example of strong interactions. For the other two systems, the melamine detection did not reflect aptamer binding either but the K+ detection did, suggesting melamine also strongly interacted with AuNPs, whereas K+ had very weak interactions with AuNPs. Since each target molecule is different, such target/AuNP interactions need to be studied case-by-case to ensure the sensing mechanism.

Aptamer-Conjugated Polydiacetylene Colorimetric Paper Chip for the Detection of Bacillus thuringiensis Spores.

A colorimetric polydiacetylene (PDA) paper strip sensor that can specifically recognize Bacillus thuringiensis (BT) HD-73 spores is described in this work. The target-specific aptamer was combined with PDA, and the aptamer-conjugated PDA vesicles were then coated on polyvinylidene fluoride (PVDF) paper strips by a simple solvent evaporation method. The PDA-aptamer paper strips can be used to detect the target without any pre-treatment. Using the paper strip, the presence of BT spores is directly observable by the naked eye based on the unique blue-to-red color transition of the PDA. Quantitative studies using the paper strip were also carried out by analyzing the color transitions of the PDA. The specificity of this PDA sensor was verified with a high concentration of Escherichia coli, and no discernable change was observed. The observable color change in the paper strip occurs in less than 1 h, and the limit of detection is 3 × 107 CFU/mL, much below the level harmful to humans. The PDA-based paper sensor, developed in this work, does not require a separate power or detection device, making the sensor strip highly transportable and suitable for spore analysis anytime and anywhere. Moreover, this paper sensor platform is easily fabricated, can be adapted to other targets, is highly portable, and is highly specific for the detection of BT spores.

Novel absorbance peak of gentisic acid following the oxidation reaction.

Gentisic acid (GA), a metabolite of acetylsalicylic acid (ASA), and homogentisic acid (HGA), which is excreted at high levels in alkaptonuria, are divalent phenolic acids with very similar structures. Urine containing HGA is dark brown in color due to its oxidation. We recently reported a new oxidation method of HGA involving the addition of sodium hydroxide (NaOH) with sodium hypochlorite pentahydrate (NaOCl·5H2O), which is a strong oxidant. In the present study, we attempted to oxidize GA, which has a similar structure to HGA, using our method. We herein observed color changes in GA solution and analyzed the absorption spectra of GA after the addition of NaOH with NaOCl·5H2O. We also examined the oxidation reaction of GA using a liquid chromatography time-of-flight mass spectrometer (LC/TOF-MS). The results obtained indicated that GA solution had a unique absorption spectrum with a peak at approximately 500 nm through an oxidation reaction following the addition of NaOH with NaOCl·5H2O. This spectrophotometric method enables GA to be detected in sample solutions without expensive analytical instruments or a complex method.

Characterization of Ag/ZnS/Ag multilayered film as transparent electrode for organic light-emitting diode

Ag/ZnS/Ag (AZA) multilayer films with various ZnS interlayer thicknesses were deposited on glass substates by thermal vacuum evaporation. The transmittance, reflectance, and sheet resistance of the films were investigated for their use as the transparent electrode of an organic light-emitting diode (OLED). A transmittance peak and reflectance valley showed red-shift by changing the interlayer thickness and thus corresponded well. The sheet resistance of the AZA multilayer films was lower than that of indium tin oxide, which is suitable for usage as a transparent electrode for OLED. Next, the OLED devices with AZA multilayer films of different interlayer thicknesses were fabricated, and the device performance and electroluminescence (EL) spectra were evaluated. Unexpectedly, the emission color of AZA-OLED changed from yellow to sky blue when the thickness of ZnS interlayer went from 30 nm to 60 nm. According to the correspondence between EL and reflectance spectra, the observed color change can be attributed to the dominance of a microcavity effect rather than plasmon-induced color filtering. The calculated external quantum efficiency was the highest when the ZnS interlayer thickness was 30 nm compared to the other AZA-OLEDs and conventional OLEDs.

Colorimetric detection of fluoxetine using citrate-capped silver nanoparticles

A novel colorimetric assay has been presented for the detection of fluoxetine using citrate-capped silver nanoparticles (CIT-Ag NPs) as a colorimetric sensor. The detection of fluoxetine was accomplished by observing color change of CIT-Ag NPs solution from yellow to dark brown due to aggregation induced by fluoxetine. The aggregation of CIT-Ag NPs was characterized by various techniques including UV–Vis spectrometry, scanning electron microscopy, Fourier transform infrared spectroscopy, dynamic light scattering, and zeta potential. A characteristic absorption peak of CIT-Ag NPs at 400 nm was red shifted and surface plasmon resonance band became broad due to addition of fluoxetine. Under optimized conditions, linear calibration curve was obtained within concentration range of 2–10 μg/ml with detection limit of 0.18 µg/ml. Furthermore, the developed colorimetric assay was found to be simple, sensitive, reproducible, and selective towards a number of pharmaceutical additives. It involved sensing of fluoxetine by naked eye within few minutes without requiring any complicated instrumentation. Colorimetric platform was applied to detect fluoxetine in pharmaceutical formulation, and biological fluids including spiked human urine and blood serum samples.

Isolation of PlANS and PlDFR genes from herbaceous peony (Paeonia lactiflora Pall.) and its functional characterization in Arabidopsis and tobacco

Flower colour, which is largely determined by anthocyanin, is an important ornamental value of herbaceous peony (Paeonia lactiflora Pall.). Anthocyanin synthesis genes encode enzymes acting at different stages of flavonoid biosynthetic pathway. In this research, we cloned anthocyanin synthesis genes PlANS and PlDFR from red dominated herbaceous peony cultivar ‘Hongyanzhenghui’ and explore their functionality with respect to colour formation by genetic engineering techniques. The over-expression vectors pB1301-PlANS and pB1301-PlDFR were constructed and transformed as heterologous genes into Arabidopsis thaliana (A. thaliana) and tobacco (K326). The quantitative real-time PCR results showed the over expression of PlANS and PlDFR in transgenic plants from 10 to 1600 times. Phenotypic observation and HPLC detection at OD 525 nm also revealed the elevated anthocyanin content in the transgenic Arabidopsis. The a* and c* value of transgenic flower increased 3–4 times compared with control tobacco which are consistent with the observed colour change. Taken together, our findings showed that PlANS, PlDFR is participated in the anthocyanin biosynthesis pathway which could provide a theoretical basis for further research of flower colour in herbaceous peony. Our results provided an important research work of two P. lactiflora genes which are related to the red petal colour formation. It provides a theoretical basis for further identification of flower colour-related gene function study in P. lactiflora.

Comment on “Synthesizing Gold Nanoparticles Using Honey in Basic Solution under Leidenfrost Conditions To Aid Students in Reliably Reproducing Observable Color Changes”

This letter aims to respond to the claim of Mortier and co-workers in “Synthesizing Gold Nanoparticles Using Honey in Basic Solution under Leidenfrost Conditions To Aid Students in Reliably Reproducing Observable Color Changes” concerning the difficulty of the experimental repetition of Elbahri and co-workers’ concept. Here, we not only scientifically address this claim but also present some video links demonstrating and stressing the easiness of the experimental procedures and the high reproducibility of the outcomes.

Temperature-induced storage quality changes in pumpkin and safflower cold-pressed oils

Cold-pressed pumpkin and safflower seeds oils were stored at 2 ± 1 °C, 20 ± 1 °C and 40 ± 1 °C for 8 weeks. Measurements of lipid quality parameters were performed every 2 weeks. Throughout storage the emission and synchronous fluorimetric spectra of investigated oils were registered and colour L*, a*, b* parameters were determined. It was found that pumpkin oil, regardless of storage temperature, maintains high quality over the entire examined period. Safflower oil demonstrated relatively low oxidative stability, especially when stored at 20 and 40 °C. Evaluated activation energy of oxidation was 82.9 and 36.5 kJ/mol for pumpkin seed and safflower oil, respectively. Emission spectra determined the nature of changes occurring in investigated oils at all storage temperatures. Registered synchronous spectra connected with the principal component analysis (PCA) allowed the crucial factors influencing the oil quality to be identified. In addition, regression models were used to determine the parameters causing the observed colour changes of the examined products.

Laser-patterned paper-based sensors for rapid point-of-care detection and antibiotic-resistance testing of bacterial infections

Antimicrobial resistance (AMR) has been identified by the World Health Organisation as a global threat that currently claims at least 25,000 deaths each year in Europe and 700,000 globally; the number is projected to reach 10 million per year between 2015 and 2050. Therefore, there is an urgent need for low-cost but reliable point-of-care diagnostics for early screening of infections especially in developing countries lacking in basic infrastructure and trained personnel. This work is aimed at developing such a device, a paper-based microfluidic device for infection testing by an unskilled user in a low resource setting. Here, we present our work relating to the use of our laser-patterned paper-based devices for detection and susceptibility testing of Escherichia coli, via a simple visually observable colour change. The results indicate the suitability of our integrated paper devices for timely identification of bacterial infections at the point-of-care and their usefulness in providing a hugely beneficial pathway for accurate antibiotic prescribing and thus a novel route to tackling the global challenge of AMR.

Fast Optical Sensing of Metals: A Case Study of Cu2+ Assessment in Soils

In this paper we report an application of a novel porphyrin ligand, Zn(II)TPP-BPI-crown (ZnPC), functionalized with two dibenzo-crown-ether moieties as cation-sensitive ionophore. The test on the optical response of ZnPC ligand inside PVC-based polymeric membranes towards different cations (Na+, K+, Li+, Ca2+, Mg2+, Co2+, Cd2+, Pb2+, Zn2+, Cu2+ and NH4+) were performed. The influence of the lipophilic site functionalization on the ZnPC optode response was investigated. The visibly (naked eye) observed color change of sensing material from green to red demonstrated the suitability of the ZnPC-based optodes to perform fast monitoring of Cu(II) ions in the concentration range between 6.6 × 10−7 and 2.4 × 10−2 mol l−1, with a low detection limit (estimated by s/n = 3 method) of 0.03 mg l−1, which is lower than WHO guideline value of 2 mg l−1 for natural waters. The membranes with the best composition were deposited onto paper support and employed for the express analysis of copper(II) ion in aqueous soil extracts. The results obtained were in a good agreement with a standard ASS method, thus suggesting the utility of developed sensors for aims of express environmental monitoring.

Theoretical insights into a colorimetric azo-based probe to detect copper ions.

In the present study, a colorimetric azobenzene-based probe (AZO 1) was reported that exhibits high selectivity toward Cu2+ and undergoes a red to yellow colour change upon its detection. Density functional theory (DFT) calculations were carried out to investigate the mechanism of the probe discoloration. The differences in the binding energies of complexes of 2 : 1 and 1 : 1 stoichiometry indicated that a two-step complexation process takes place as the Cu2+ content increases. However, the calculated absorption spectra suggested that a significant colour change would only be observed for the 1 : 1 AZO 1 : Cu2+ complex. A HOMO–LUMO electronic transition was a key factor for the blue shift of the absorption bands of the probe. Further studies indicated that solvent molecules participate in the complexation and that the presence of the o-methoxy group in AZO 1 led to formation of an octahedral complex because of the additional chelating site. A significant change in the conformation of AZO 1, namely the rotation of the N,N-di(carboxymethyl)amino group around the N–CAr bond by approximately 90°, resulted in a larger HOMO–LUMO energy gap, and the corresponding alteration of the intramolecular charge transfer (ICT) from the N,N-di(carboxymethyl)amino group to the phenyl ring led to the observed colour change.

Green Synthesis of Zinc Oxide Nanoparticles from (Punica granatum L) Pomegranate Aqueous Peel Extract

The biosynthesis of Zinc oxide nanoparticles (ZnONPs) was done under alkaline conditions (pH 12) and temperature ≥ 80 ◦C. Mixing 10% of aqueous pomegranate peel extract (PPE) with 0.1 molar of zinc nitrate [Zn (NO3)2.6H2O], mixture was stirred at 70-80 ◦C for 15 minute and then left at room temperature overnight. The result was separated and centrifuged at 4000 rpm for 10 minutes. This process was repeated three times then the precipitate was collected and dried for using. ZnONPs were characterized by visual observation of color changes, estimate duration of synthesis compared to weight of ZnONPs was the result, UV-visible analysis, Fourier transform infrared (FT-IR), X- ray diffraction (XRD) and Scanning electron microscope (SEM). The results of this line, investigate the proper condition for ZnONPs synthesis. Result of FT-IR showed functional group related to Zn-O at (613.38 to 580.59 cm_1), whereas the result of X-RD at 2 theta diagnose the type of oxide formation as ZnO and determined particle size were found in range (20 - 30 nm). Finally, SEM image was shown crystals shape of ZnO nanoparticles. In conclusion, PPE acts as reducing agent used in synthesis of ZnO in Nano-scale size via easy and simple method.

A simple fluorophore-imine ensemble for colorimetric and fluorescent detection of CN- and HS- in aqueous solution.

Colorimetric and fluorescent detection of cyanide and hydrogen sulfide ions has been effected using a simple organic probe in H2O:DMSO (20:80, v/v) medium. The probe exhibits a colour change from pale-yellow to red upon addition of these analytes under normal light and fluorescent change from green to red under UV lamp. Other competitive ions show no observable colour or fluorescence change. The binding constants of cyanide and hydrogen sulfide ions with the probe determined using fluorescence titration data are found to be 2.1×104 and 1.6×104 M-1, respectively. The probe fluorimetrically detects the analytes in a wide pH range (4-10). 1H and 13C NMR studies suggest that the probe senses cyanide ion through deprotonation and nucleophilic addition mechanism and hydrogen sulfide ion via deprotonation mechanism. Detection limits of cyanide and hydrogen sulfide are determined to be 0.15 and 1μM, respectively. The practical utility of the probe has been demonstrated by same dual mode detection of cyanide in food materials like bitter almond, cassava flour and sprouting potato.

Long secondary periods in luminous red giant variables

ABSTRACT The origin of long secondary periods (LSPs) in red giant variables is unknown. We investigate whether stellar pulsations in red giants can explain the properties of the LSP variability. VIJHKs light curves obtained by OGLE and the IRSF/SIRIUS survey in the Small Magellanic Cloud are examined. The sample of oxygen-rich LSP stars shows evidence of a phase lag between the light curves of optical and near-IR band. The change in radius contributes to the bolometric change roughly half as much as the change in temperature, implying that the change in effective temperature plays an important role in the luminosity change associated with the LSPs. We have created numerical models based on the spherical harmonics to calculate the light amplitudes of dipole mode variability and have found that the models can roughly reproduce the amplitude–amplitude relations (e.g. (ΔI, ΔH)). The LSP variability can be reproduced by the dipole mode oscillations with temperature amplitude of ≲100 and ≲150 K for oxygen-rich stars and most carbon stars, respectively. Radial pulsation models are also examined and can reproduce the observed colour change of the LSPs. However, there is still an inconsistency in length between the LSP and periods of radial fundamental mode. On the other hand, theoretical period–luminosity relations of the dipole mode corresponding to so-called oscillatory convective mode were roughly consistent with observation. Hence, our result suggests that the observations can be consistent with stellar pulsations corresponding to oscillatory convective modes.

Cheese Whey and Ricotta Whey for the Growth and Encapsulation of Endogenous Lactic Acid Bacteria

The aim of this study was to compare the ability of endogenous Lactobacillus paracasei ATR6 to grow in unsupplemented bovine cheese whey (CW) and ricotta whey (RW), and to evaluate the efficiency of these media as encapsulating agents for the spray-drying (SD) of this bacterium. Growth assays indicated that both CW and RW are adequate culture media since L. paracasei ATR6 grew satisfactorily (~ 4 log cycles) in both compared to the control medium (skimmed milk). Concerning their potential as encapsulating agents, results showed that survival rates after SD were similar for CW and RW (> 78%), as were the yields (> 47%) of this process. CW allowed the formation of smaller capsules (5.31 ± 1.27 μm) than RW (15.21 ± 7.24 μm), with lower moisture: 8.60% and 13.52%, respectively. Powders were stored at 25 °C for 60 days, during which CW and RW maintained satisfactory bacterial viability. Water activity increased, yet remained below 0.3. Moisture content of CW and RW powders was relatively stable throughout the 60 days; however, values obtained in this study are considered to lie outside the adequate range (4–7%) for product stability. We did not observe color changes in CW and RW microcapsules during storage. Due to its lower protein content, RW offered less protection, which led to higher loss in acidification ability of the strain. CW and RW are suitable culture media and encapsulating agents for the growth of L. paracasei ATR6; however, the former offered better protection, which enabled the maintenance of biological activity.

Process optimization for green synthesis of gold nanoparticles mediated by extract of Hygrophila spinosa T. Anders and their biological applications

Plant extract-mediated green synthesis of gold nanoparticles (AuNPs) and their biomedical application is currently gaining huge interest in the field of nanotechnology . In the present study, AuNPs were synthesized using Hygrophila spinosa aqueous extract (HSAE). The formation of AuNPs was confirmed by observing color change and characteristic absorbance peak for surface plasmon resonance by UV–Vis spectroscopy. Different reaction parameters such as HSAE concentration, salt concentration, pH, reaction time and temperature were optimized for biosynthesis of AuNPs. The NPs were characterized for particle size, surface morphology , crystallinity , elemental composition and surface functionalities. Cytotoxicity of the AuNPs was studied against different cancer cell lines by MTT assay and antioxidant potential as total antioxidant capacity was also evaluated. The biosynthesized AuNPs were small in size and negatively charged. Phytochemical screening of HSAE, and FTIR spectrum of synthesized AuNPs demonstrated participation of various groups of chemical compounds as capping and stabilizing agents in biosynthesis of AuNPs. The green synthesized AuNPs exhibited significantly higher anticancer activity compared to HSAE against breast, ovarian, glioblastoma/brain and multi-drug resistant ovarian cancer cell lines. Antioxidant activity of the synthesized AuNPs was less than HSAE. The biosynthesized AuNPs could be studied further to access their potency in the treatment and imaging of various cancers. • Green synthesis of AuNPs has been carried out with Hygrophila spinosa aqueous extract (HSAE). • Concentration of HAuCl 4 solution, pH, reaction incubation temperature & time, and concentration of HSAE have been optimized for synthesis of AuNPs. • Characterization by UV–Vis, FTIR, SEM, TEM, EDS and XRD confirm that HSAE could synthesize AuNPs. • Synthesized AuNPs exhibited promising antioxidant and anticancer activities.

Rational design of colorimetric sensing for a customer-oriented index range using plasmonic substrates

Both beneficial matter and harmful matter widely spread in aqueous solutions. Various approaches have been developed to identify them qualitatively and quantitatively. In particular, colorimetric sensing, relying on an observable environment-induced color change, is a readily accessible approach to detect signals via our naked eyes, with no need for extra optoelectronic devices. Here we propose a colorimetric sensing scheme with enhanced performance using plasmonic metasurfaces. By judiciously selecting the structure parameters, the plasmonic resonance can be flexibly tuned at the entire visible range. Along with a pair of polarizers to filter the polarization states of the incident light and output reflection, a plasmonic metasurface, supporting bright colors, can serve as an efficient colorimetric sensing substrate. As an example, a figure of merit can be obtained as high as 1175°/RIU in the demodulation of the hue. Significantly, the sensing capability can be designed according to the selected solvent with a specified refractive index, which promises a target-oriented colorimetric sensing scheme.

Plasmonic colored nanopaper: a potential preventive healthcare tool against threats emerging from uncontrolled UV exposure

Preventive healthcare is crucial to hinder or delay the onset of disease, furthermore it contributes to healthy and productive lifestyles and saves resources allocated to public health. Herein, we explore how the plasmonic coupling of silver and gold nanoparticles embedded within nanopaper allows for potential preventive healthcare tools based on a change in plasmonic color. Particularly, we selected UV radiation exposure as a potential threat to health to be monitored via plasmonic colored nanopaper (PCN). Uncontrolled UV radiation exposure is not only known to provoke epidermal damage, but also to trigger leaching of hazardous compounds from polycarbonate containers. In this context, we engineered UV-responsive PCN devices whose sensing mechanism is based on UV photodegradation of silver nanoparticles. Since absorbance and scattering of metal nanoparticles strongly depend on their size and inter-particle distance, the resulting PCN detectors are able to warn of the potential UV radiation-induced threat via a visually observable plasmonic color change with a yellowish/reddish transition. Epidermal experiments with tattoo-like PCN devices prove the resulting detectors can change in color upon safe dose of sun exposure. Moreover, PCN detectors stuck on polycarbonate containers also change in color after moderate sun exposure. This cost-effective and lightweight nanophotonic device leads to a versatile preventive healthcare tool.

Thin Functional Polymer Films by Electropolymerization.

Intrinsically conducting polymers (ICPs) have been widely utilized in organic electronics, actuators, electrochromic devices, and sensors. Many potential applications demand the formation of thin polymer films, which can be generated by electrochemical polymerization. Electrochemical methods are quite powerful and versatile and can be utilized for investigation of ICPs, both for educational purposes and materials chemistry research. In this study, we show that potentiodynamic and potentiostatic techniques can be utilized for generating and characterizing thin polymer films under the context of educational chemistry research and state-of-the-art polymer research. First, two well-known bifunctional monomers (with only two linking sites)—aniline and bithiophene—and their respective ICPs—polyaniline (PANI) and polybithiophene (PBTh)—were electrochemically generated and characterized. Tests with simple electrochromic devices based on PANI and PBTh were carried out at different doping levels, where changes in the UV-VIS absorption spectra and color were ascribed to changes in the polymer structures. These experiments may attract students’ interest in the electrochemical polymerization of ICPs as doping/dedoping processes can be easily understood from observable color changes to the naked eye, as shown for the two polymers. Second, two new carbazole-based multifunctional monomers (with three or more linking sites)—tris(4-(carbazol-9-yl)phenyl)silanol (TPTCzSiOH) and tris(3,5-di(carbazol-9-yl)phenyl)silanol (TPHxCzSiOH)—were synthesized to produce thin films of cross-linked polymer networks by electropolymerization. These thin polymer films were characterized by electrochemical quartz crystal microbalance (EQCM) experiments and nitrogen sorption, and the results showed a microporous nature with high specific surface areas up to 930 m2g−1. PTPHxCzSiOH-modified glassy carbon electrodes showed an enhanced electrochemical response to nitrobenzene as prototypical nitroaromatic compound compared to unmodified glassy carbon electrodes.