Observed Color Changes Research Articles

A novel azo-triazolopyridine-based dual naked-eye chemosensor for the selective detection of CN− and Cu2+ ions

A new chemosensor incorporating a triazolopyridine and an azo chromophore was synthesized and employed as a colorimetric sensor. Visual investigations for detecting anions and cations revealed that the sensor acts as a highly sensitive and selective chromogenic detector for cyanide (CN−) and copper (Cu2+) ions. The observable color change from yellow to deep orange for Cu2+ and from yellow to purple for CN− allows for detecting these ions without the need for advanced equipment, even with the naked eye. The sensor’s limit of detection (LOD) was determined to be 0.02 μM for CN− ions and 1.13 μM for Cu2+ ions. The Job plot indicated that the sensor binds to CN− and Cu2+ with a stoichiometric ratio of 1:1 and 2:1, respectively. The ability to accurately and selectively distinguish Cu2+ and CN− ions makes this sensor valuable for various analytical applications, including environmental monitoring and chemical analysis. Its capacity to produce noticeable and distinct color changes enables the rapid and straightforward detection of these hazardous ions, making it a practical choice for real-world applications. The quantum yield of A-TAP/Cu2+ was 54 % at a λmax (maximum absorbance) of 450 nm, while that of A-TAP/CN− was 62 % at 538 nm, using a reference sensor with a λmax of 380 nm.

Development of an on-site real-time dual detection method for norovirus and rotavirus using RPA-CRISPR/Cas12,13

Norovirus (NoV) and rotavirus (RoV) are the two most prevalent foodborne viruses responsible for infectious gastroenteritis, with high contamination rates in fruits and vegetables. Monitoring and accurately identifying these pathogens are crucial for preventing human foodborne illnesses. Therefore, developing a rapid, highly specific, and sensitive detection method for NoV and RoV is essential. An on-site real time dual detection method for Noroviruses of genogroup I (GI-NoV) and Rotavirus of group A (A-RoV) was established by integrating Recombinase Polymerase Amplification (RPA) with the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-associated protein (Cas) system. The DNA amplification products generated by multiplex RPA were simultaneously detected by Cas12a and Cas13a in a single tube. Utilizing the trans-cleavage preferences of Cas12a and Cas13a, the specific cleavage of DNA and RNA probes carrying different fluorescent groups within the reaction system was achieved. The results indicated that the established dual detection method had a detection limit of 102 copies/μL for GI-NoV and A-RoV. Specificity assay showed the established method only detected GI-NoV and A-RoV, with no cross-reactivity with other four foodborne viruses. Furthermore, the detection capability of this method was validated in strawberries and lettuce. The method enables the simultaneous detection of GI-NoV and A-RoV in fresh produce at 37 °C within 60 min. Detection results were interpreted by measuring fluorescence values or observing color changes under blue light at the end of the reaction. This technique required minimal instrumentation, provided excellent visual representation of results, and served as a technical reference for the rapid on-site detection of foodborne viruses in food matrices.

Solution plasma synthesis of nitrogen-doped carbon dots from glucosamines: Comparative fluorescence modulation for dopamine detection

The intriguing fluorescence characteristics of carbon dots (CDs) have led to many sensor applications, particularly for dopamine (DA), a molecule linked to various diseases. This study prepares CDs from glucose and glucosamine (nitrogen-free and nitrogen-containing precursors) using a simple solution plasma process (SPP). We explore how nitrogen elements and counterions in glucosamine (hydrochloride and sulfate) affect CD properties and their ability to modulate fluorescence for DA detection. Glucosamine offers three advantages over glucose: (i) single-step CD synthesis via SPP, (ii) enhanced fluorescence of CDs, and (iii) improved fluorescence response to DA. We investigate the DA detection capabilities of N,S-CDs (from glucosamine sulfate) and N,Cl-CDs (from glucosamine hydrochloride). Both can sense DA with distinct photoluminescence responses. N,S-CDs show selectivity and fluorescence brightening upon DA interaction, with a detection limit of 33.05 μM. N,Cl-CDs demonstrate higher sensitivity with a lower detection limit of 0.1212 μM through fluorescence quenching. Silver ions (Ag+) may also contribute to N,Cl-CDs quenching; however, the observed color change to gray due to silver nanoparticle (AgNP) formation helps pinpoint the quenching substance. The varied photoluminescence responses arise from different surface functional groups: N,S-CDs have amino-rich surfaces, while N,Cl-CDs have conjugated carbonyl-rich surfaces. This study illustrates the mechanisms of DA detection and AgNP formation, suggesting the potential of CDs in medical diagnostics as selective tools for disease diagnosis. Additionally, we compare the DA sensing methodology of our CDs with existing literature, highlighting the advantages of our sensor.

Rational design of an isatin-based colorimetric and solvatochromic receptor for carbonate ions and its application in molecular-scale logic gates & memory units

A simple and highly sensitive isatin-based colorimetric sensor ISAT 3(a-d) was synthesized through a single-step reaction. The as-prepared receptor ISAT 3b with carbonate ions (CO32− ions) shows a significant red shift in the UV–visible absorption spectra and a visible color change from pale yellow to pink. Also, the receptor ISAT 3b shows unique solvatochromic behavior with CO32− ions in different aprotic solvents and solvent compositions. Moreover, the receptor’s pink coloration (absorption maxima at 544 nm) with CO32− ions could be reversible by adding HSO4− ions (attain initial pale-yellow color, absorption maxima at 425 nm), which can be repeatable. The observed color changes with spectral shift and reversibility of the receptor with CO32− ions and HSO4− ions provide “ON-OFF” switching for applying molecular logic gates. Receptors exhibited properties, such as reversibility and repeatability, benefit the design of a molecular-scale sequential memory unit with a display of “Writing-Reading-Erasing-Reading”. The real sample analysis was also carried out to prove the practical applicability of receptor (ISAT 3b) for detecting CO32− ions.

An Optical Au3+ Sensor Based on layer-by-layer PEI/PAA-Rho thin Films on ITO.

This study presents the development of a sensitive and selective gold ion (Au3+) sensor utilizing layer-by-layer (LbL) assembled thin films composed of polyethylenimine (PEI) and poly (acrylic acid) (PAA) conjugated with rhodamine (Rho). The first study revealed that the polymeric sensors (PAA-Rho) demonstrated significant selectivity and sensitivity in their colorimetric and fluorescence responses to Au3+ compared to other metal ions. In their spirolactam form, the polymeric sensors were non-fluorescent but could selectively transform into the fluorescent ring-opened amide form upon interaction with Au3+ ions, resulting in fluorescence enhancement and observable color changes. Common co-existing metal ions showed negligible interference in the detection of Au3+. The LbL sensor exhibited a linear increase in absorbance with the addition of bilayers, confirming successful film deposition. Surface morphology analysis using SEM, along with structural confirmation via ATR-FTIR and XRD, further validated the sensor's capability to detect cation. Results demonstrated that the LbL sensor exhibited selectivity for Au3+ ions within the range 1 × 10-6 to 1 × 10-3 M. This approach offers an easily understandable and intrinsically sensitive means for detecting Au3+ ions in both environmental and biological applications.

Fluorescence and Colorimetric Dual-Readout Detection of Tetracycline Using Leucine-Conjugated Iron Oxide Quantum Dots.

This study developed a dual-readout system utilizing fluorescence and colorimetry based on iron oxide quantum dots (IO-QDs) for detecting tetracycline (TCy). IO-QDs were synthesized within 6 h using L-leucine as a surface modifier, achieving a more efficient route. Upon interaction with TCy, IO-QDs exhibited a significant decrease in fluorescence response and observable color changes, while fluorescence lifetime remained consistent regardless of TCy presence. Moreover, IO-QDs' fluorescence response remained stable across various temperatures. The Förster resonance energy transfer distance of less than 2 nm and a quenching constant of 2.90 × 1012 M-1s-1 indicated static quenching in the presence of TCy. Additionally, significant changes in observed and corrected fluorescence efficiency suggested the involvement of the inner filter effect in the fluorescence quenching of IO-QDs. The synthesized IO-QDs were then utilized for selective and rapid fluorescence-based TCy detection, showing a linear range of 0.5 to 80 μM. Simultaneously, a colorimetric method for TCy detection was established, demonstrating a good linear relationship within the range of 0.5 to 20 μM. The detection limits for TCy were determined as 0.539 and 0.329 μM using fluorescence and colorimetric approaches, respectively. Furthermore, IO-QDs were applied to detect real samples, and the dual-readout probe exhibited satisfactory recoveries, confirming the practical reliability of the developed method for analyzing milk and drinking water samples.

Enhancing thermal stability and corrosion resistance of carbon-carbon composites with iridium coatings deposited by electron beam physical vapor deposition

Abstract Carbon–carbon (C−C) composites are extensively used in high-temperature environments such as Combustor Liners and Turbine Blades in jet engines and Throat Inserts, Nozzle Extensions and Exit Cones in rocket engines due to their excellent thermal stability and mechanical properties. However, at temperatures exceeding 800 °C, these composites require additional protection to prevent degradation. This study aims to investigate the behavior of C−C composites when coated with high-purity metallic iridium using Electron Beam Physical Vapor Deposition (EBPVD). The research problem focuses on enhancing the high-temperature performance and corrosion resistance of C−C composites for aerospace applications. The methodology involves depositing a uniform 5.6 microns thick iridium coating on C−C substrates and characterizing the coating’s microstructure, hardness, and corrosion resistance. FESEM micrographs reveal that the iridium coating adheres uniformly to the substrate without any seepage, and XRD analysis confirms an FCC crystal structure with a densely packed grainy surface. Corrosion tests were conducted using a BIOLOGIC electrochemical workstation in a sodium chloride environment indicate a corrosion rate of 0.00307 mm year−1. The Nyquist, Bodo plots, and Taffel plots were constructed for the better understanding of the corrosion mechanism. While the OCP was constructed to understand the stability and the corrosion resistance of the C−C samples. Microhardness of the coating, measured under a normal applied load of 0.20 N, is 702 HV. The coated samples also could withstand thermal shocks between −40 °C and 1500 °C for 40 h without observable damage or color change. These findings demonstrate the potential of iridium-coated C−C composites to maintain structural integrity and performance in extreme aerospace environments, significantly impacting the field by providing a reliable protective solution for high-temperature applications.

Dual-mode iodine sensing: Colorimetric and electrochemical detection methods using functionalized gold nanoparticles

Iodine in natural and treated waters exists mainly as iodide, iodate, and molecular iodine (I2). I2 is a highly volatile and reactive species impacting biological and chemical systems. Iodine, a vital micronutrient, is essential for human and animal growth and metabolism. It also plays a crucial role in synthesising artificial adrenaline within the metabolic processes of humans and animals. It is also widely used as an antiseptic, disinfectant, and for emergency water disinfection. Moreover, iodine deficiency can result in various diseases, especially hypothyroidism and goitre. Given its critical functions, it is imperative to have a straightforward, dependable, and efficient method for monitoring iodine levels. This study introduces a simple and innovative I2 detection system based on its reactivity, toxicity, and role as an indicator of oxidative conditions in water. It operates in terms of based on optical and electrochemical signal changes, utilising the anti-aggregation mechanism of gold nanoparticles (AuNPs) and 6-mercaptohexanol (MHA) for sensitive and selective detection under mild conditions. I2 determination is achieved by observing the colour change in AuNPs, which is influenced by competitive interactions between MHA, I2, and AuNPs. The optical detection system, with its low detection limit (LOD=260 nM), is based on the straightforward observation of colour changes. On the other hand, the electrochemical detection method utilises changing redox peaks observed in anodic region, providing selective and sensitive I2 detection (LOD=100 nM). The probe effectively detects the presence of I2 in real water samples as a practical application. Moreover, the proposed method revolutionises I2 detection by incorporating a smartphone for signal reading, eliminating the need for specialised equipment and significantly reducing the detection cost. This cost-effective approach carries the potential to expedite on-site and naked-eye I2 detection, opening up new possibilities for research and application.

Thermochromic Properties of 3C-, 6H- and 4H-SiC Polytypes up to 500°C

The thermochromic properties (color change with temperature) of n type doped SiC wafers of different polytypes (3C, 4H and 6H) have been investigated up to 500°C under air. It was found that 3C-SiC color passes from bright yellow at room temperature to deep orangeat 500°C leading to a color contrast (ΔE) as high as 64. The hexagonal polytypes undergo also a color change upon heating but far less pronounced, with ΔE values <20. All these semiconductors undergo band gap shrinkage upon heating which effect largely participated to the observed color change. This effect is very sensitive for 3C polytypesince its bandgap is already in the visible energy range at room temperature. The thermochromicity of 3C-SiC was found to be reversible thanks to its thermal stability and its resistance towards oxidation.

Investigating Ion-Coupled Electron Transfer of Conducting Polymers

After years of basic and applied studies of electron transfer in redox active films, the fundamentals of ion transfer during the exchange remain to be understood. Empirically, the processes are ion-transport limited. Using a conducting polymer as a model system, we aim to study the relationship between electron and ion transfer during redox switching.We work on electrochromic conducting polymers because of their observable and detectable color changes in addition to the current during the redox switching. Tracing optical signals can enhance the understanding of electrical signals from redox reactions. When a potential is applied to the electroactive polymer, its color will change from lighter to darker or vice versa. Keeping in mind that absorbances are additive, the ratio of the contents that make up the overall color of the polymer changes. This ratio change is directly proportional to the amount of matter under inter-conversion during the redox reaction.This study aims to explore the ion-electron mechanism in conductive polymers using the simultaneous Spectro-CV method. To achieve this, we conducted cyclic voltammetry at exceptionally high scanning rates, leveraging the conductive polymer's color-changing property. At these high rates, ion movement was restricted due to limited time for forward and backward motion, potentially reaching a point of stagnation. The investigation focused on whether the polymer would continue changing color, providing insights into ion-electron transfer. In addition, we are conducting EIS measurements alongside simultaneous Spectro-CV measurements and attempting to fit the impedance response of the polymer with an appropriate model. We aim to track the time constants provided by the polymer at different voltage values and understand the corresponding physical processes associated with these time constants. Additionally, we aim to use our EIS model to validate the desired redox current information obtained from optical data. We mathematically reach the faradaic portion of the total current with EIS and compare the results obtained from optical data.

Azo Based Chromogenic Sensor: An Approach for Naked Eye Detection of Biologically Relevant Anions and Metal Cations

Abstract: It was previously reported that azo compounds are vigorous and chemically stable compounds and well-known chromophores. Having different chromophores, the azo dyes act as probing units for capturing the charged particles either by electron transfer or deprotonation mechanisms. The probing efficiency usually exhibits in the magnitude of variations in UV absorbance, NMR peaks and visually observed color changes. The sensing application is a prerequisite for numerous analytical techniques involved in pharmaceutical as well as pathological discipline. In the last two decades, numerous azo based sensors have been developed, which render low cost and effective sensing approaches towards ionic diagnosis through instantaneous eye beaming chromogenic change. This sensing approach is simple, cost-effective, and precise and provides reliable quantitative and qualitative statistics of an analyte present in a complex environment. Our present study culminates the recent progress on the synthesis of azo compounds and their chromogenic sensing application towards various reactive analytes through reviewing spectral variations and colorimetric observations. This review article assesses the potential of azo dyes in chromogenic sensing for different analytes. We believe this review will be of interest and important for researchers working on designing azo-based chromogenic sensors.

Control of the size distribution of AuNPs for colorimetric sensing by pulsed laser ablation in liquids

Gold nanoparticles (AuNPs) are extensively employed in colorimetric sensing, taking advantage of their optical properties to detect variables via observable color changes. These properties are primarily driven by localized surface plasmon resonance (LSPR), particularly pronounced in AuNPs within the visible spectrum. In this study, AuNPs were synthesized via pulsed laser ablation in liquids (PLAL) with a laser pulse energy (Ep) ranging from 25 mJ to 75 mJ. Size distributions, hydrodynamic diameters, polydispersity indices (PDI), absorbance intensity, and LSPR were characterized. Spherical AuNPs with FCC structure were synthesized, exhibiting a maximum absorption peak centered at approximately 529 nm wavelength and a size range between 50 nm and 178 nm, easily adjustable depending on the laser pulse energy used in the synthesis process. An anomalous behavior was noted at Ep=50 mJ, exhibiting three peaks in size distribution, high PDI, low absorbance intensity, and indistinct LSPR. By extending the ablation time from 10 min to 30 min, particle size decreased alongside lower PDI. Size distributions transitioned from three to two peaks, absorbance increased, and LSPR became readily identifiable. These findings underscore the size control over AuNP characteristics achievable through PLAL synthesis parameters, promising significant implications for the optimization of colorimetric sensor design and development.

A novel fluorescence sensor film for hydroquinone based on a graphene quantum dots-nano activated carbon composite

A novel film sensor, composed of graphene quantum dots-nano activated carbon, chitosan, and PVA, offers a simple and effective hydroquinone (HQ) detection. This film exhibits impressive HQ adsorption under ambient conditions (room temperature, pH 7, 3 h) and utilizes a readily observable fluorescence color change for quantification. Upon HQ binding, the film's fluorescence color shifts from yellow-green to blue, enabling a linear detection range of 1.0–150 mg⋅L−1 based on intensity analysis of the blue component (B value). Calibration curves generated on the same day (n = 3) exhibit high precision, with standard deviations of the linear equation parameters below 0.014 and a low detection limit of 0.5 mg⋅L−1. The film exhibits exceptional stability, retaining its color and performance for up to 20 days. This stability is further corroborated by recovery experiments utilizing HQ-spiked water samples at concentrations of 2.5 mg⋅L−1 and 40 mg⋅L−1, where recoveries of 106 % and 95 % were achieved, respectively. These results demonstrated the sensor's reliable quantification capabilities. Notably, the sensor exhibited insignificant interference from commonly co-existing substances such as ethanol, ascorbyl glucoside, arbutin, kojic acid, and methylene blue. However, Cu²⁺, Fe³⁺, and catechol did cause some interference. This versatility, coupled with its straightforward operation, makes the film sensor a promising candidate for on-site HQ detection in diverse environmental monitoring applications.

A Cobalt(II) based coordination architecture for efficient colorimetric sensing of ammonia and amine vapors

This work presents the design, synthesis, and characterization of a new cobalt (II) based coordination architecture, {[Co(toua)(4,4′-bpy)].2H2O}n (1); where toua is 3,6,9-trioxaundecanaote and 4,4′-bpy is 4,4′-bipyridine tailored for efficient sensing of ammonia and amines. The formation and identity of 1 was confirmed by elemental analysis, spectroscopic study (FTIR and UV–visible spectroscopy), PXRD, XPS, FESEM, and BET analysis. The colorimetric sensing capability of 1 towards ammonia and various smaller-sized amines in the vapor phase through observable color changes is explored in this study. Their interaction with 1 is elucidated through FTIR, UV–Visible and Fluorescence spectroscopy, FESEM, and TCSPC analysis. The fluorescence sensing experiments demonstrate a remarkable quenching/enhancement effect with the addition of ammonia and various amines, showcasing the compound’s sensitivity and selectivity. The quenching/enhancement efficiency follows the order: NH3>Ethylenediamine (EDA)>1,3-diaminopropane (DAP)>n-propylethylenediamine (n-PEDA), following the molecular dimensions and steric hindrance surrounding nitrogen atoms. Hydrogen bonds and host-guest interactions, including (C–H)pyridinium⋅⋅⋅N interactions, are identified as the driving forces for the sensing process. Additionally, the paper reveals a rare occurrence of both “turn-off” and “turn-on” sensing behavior for the same compound, showcasing its versatility. The calculated RSD for the fluorometric sensor was found to be 1.03 % calculated from its triplicate readings at 240 nm. Limits of detection (LODs) and Limit of Quantification (LOQs) for NH3 (0.52 μM, and 1.74 μM) EDA (1.2 μM, and 4.2 μM), DAP (3.1 μM, and 10.5 μM), and n-PEDA (3.3 μM, and 11.2 μM) respectively) underscore the effective sensing capabilities of 1. The robustness of 1 upon exposure to amines was confirmed by PXRD. These findings justify that 1 is a promising vaporchromic probe for the fast and selective detection of ammonia and amines.

An enhanced multifunctional chitosan-based active packaging film reinforced with cinnamon essential oil encapsulating onion peel anthocyanins

The fabrication of bio-hybrid composites utilizing polymers, nanomaterials, essential oils, and other substances is gaining popularity due to its multi-functionality and application across various fields. Many industries today effectively employ innovative composite and multilayer materials by considering their benefits in several areas. In particular, the food industry uses innovative, multi-functional packaging materials based on biodegradability to accomplish multiple tasks. Many researchers have recently shown interest in an innovative and intelligent food packaging film with indicators for real-time food safety and protection. It is preferable to use anthocyanins, as an indicator in the active packaging film to track the freshness of food by observing color changes in the packaged film upon a shift in pH. In the current investigation, ethanol was used as a solvent to obtain anthocyanin-rich onion peel extracts (AROPE), using conventional and ultrasound-assisted extraction techniques, which were then used as an indicator in the packaging films. To develop antioxidant and pH-sensing films, anthocyanin-rich onion peel extract was blended into the chitosan and cinnamon essential oil matrix. Films displayed significant color variations in acidic and alkaline environments over short periods making them easy to perceive with the naked eye. For real-world applications, the fabricated films mechanical, structural, and physical characteristics were further explored. Because of their sensory qualities, colors, and antimicrobial benefits, these novel chitosan-based films could be ideal for food packaging to enhance food security.

Portable Sensing Platform for the Visual Detection of Iodide Ions in Food and Clinical Samples

The detection of iodide ions (I−), despite challenges due to low concentrations and potential masking, is crucial for studying physiological processes and diagnosing diseases. A colorimetric sensor was developed to improve I− ion monitoring and facilitate on-site detection based on filter paper, which is a cost-effective platform. The sensor observed color changes in response to the exposure of hydrogen peroxide (H2O2), 3,3′,5,5′-tetramethylbenzidine (TMB), from colorless to yellowish brown. The sensor demonstrated a detection limit of 0.125 × 10−6 M for I− ions in a relatively wide range of 0.01 to 15 × 10−6 M under optimized conditions including gel concentration, temperature, incubation time, TMB and H2O2 concentration, and pH. Furthermore, the proposed sensor was successfully employed in a variety of applications, such as biological (urine and blood serum), food (egg yolk and snacks), and environmental samples (tap water). The study established effective recoveries in complex media for visual on-site I− ion monitoring, indicating the developed assay as a potent, affordable, and practical platform.

Effect of silver nanoparticles synthesized by Lecanicillium lecanii and their combinations with insecticides (Sivanto and Deltamethrin) on larvae and adults of Tribolium confusum Duv. (Tenebrionidae : Coleoptera)

This research focused on developing a nanopesticide derived from silver nanoparticles (AgNPs) synthesized through the metabolic activities of the fungus Lecanicillium lecanii Gams & Zare 2001). The study aimed to assess its efficacy against the flour beetle Tribolium confusum and explore its synergistic effects with two chemical pesticides, Sivanto 20% and deltamethrin 2.5%. Biotinylated AgNPs were successfully produced using the biomass of the fungus L. lecanii. Characterization of silver nanoparticles was achieved through the observable color change of silver nitrate solution (AgNO₃) from a clear or watery state to red, brown, or dark red, confirmed by UVV is spectroscopy, with the highest absorption peak at 420 nm, indicative of silver element absorption. Transmission electron microscope images illustrated that the biologically prepared AgNPs with L. lecanii exhibited spherical shapes with sizes ranging from 12 to 40 nanometers. Various concentrations of nanopesticide, Sivanto, and deltamethrin were tested for the treatment of grains. A concentration of 1 ml/L of deltamethrin showed superior performance, with the mortality ratio increasing with prolonged exposure. Both Sivanto and deltamethrin (0.5 ml/L and 0.4 ml/L) caused 100% mortality, followed by the nanopesticide (30% concentration), reaching a corrected mortality rate of 39.3% against adults of T. confusum. In the larval experiment, the mortality rate was high when applying AgNPs at a concentration of 100%, comparable to Sivanto 0.5 ml/L under similar conditions. Deltamethrin exhibited complete mortality at a 1 ml/L concentration. [ Keywords: Silver Nanoparticles, Lecanicillium lecanii, Tribolium confusum

Design and Fabrication of Biosensor for a Specific Microbe by Silicon-Based Interference Color System.

In this paper, one of the great challenges faced by silicon-based biosensors is resolved using a biomaterial multilayer. Tiny biomolecules are deposited on silicon substrates, producing devices that have the ability to act as iridescent color sensors. The color is formed by a coating of uniform microstructures through the interference of light. The system exploits a flat, RNA-aptamer-coated silicon-based surface to which captured microbes are covalently attached. Silicon surfaces are encompassed with the layer-by-layer deposition of biomolecules, as characterized by atomic force microscopy and X-ray photoelectron spectroscopy. Furthermore, the results demonstrate an application of an RNA aptamer chip for sensing a specific bacterium. Interestingly, the detection limit for the microbe was observed to be 2 × 106 CFUmL-1 by visually observed color changes, which were confirmed further using UV-Vis reflectance spectrophotometry. In this report, a flexible method has been developed for the detection of the pathogen Sphingobium yanoikuyae, which is found in non-beverage alcohols. The optimized system is capable of detecting the specific target microbe. The simple concept of these iridescent color changes is mainly derived from the increase in thickness of the nano-ordered layers.

Green production of functionalized few-layer borophene decorated with cerium-doped iron oxide nanoparticles for repeatable hydrogen peroxide detection

Functionalized few-layer borophene (FFB) was prepared using gallnut extract and coffee waste extract as natural exfoliating and stabilizing agents in an environmentally friendly ultrasonic and high shear exfoliation. Here, a facile precipitation method was employed to grow iron oxide nanoparticles doped with cerium (Ce-FeONPs) onto the surface of FFB. This intriguing combination of materials yielded Ce-FeONPs nanoparticles that exhibited exceptional peroxidase-like activity, efficiently catalyzing the conversion of 3,3′,5,5′-tetramethylbenzidine (TMB) to a blue oxidized TMB (oxTMB) in the presence of hydrogen peroxide (H2O2). Additionally, the introduction of FFB contributes a reducibility effect to the catalytic oxidation of TMB, facilitating the restoration of the oxTMB to TMB. Thus, FFB-Ce-FeONPs showcase intriguing properties encompassing both oxidative and reductive characteristics, suggesting their potential as a reagent for repeated detection of H2O2. Moreover, a colorimetric sensing system enabled the liner detection of H2O2 spanning a concentration range from 0.08 to 1 mM, with a detection limit of 0.03 mM. Noteworthily, FFB-Ce-FeONPs demonstrated sustained efficacy over ten successive recycling cycles, as indicated by consistent slopes and observable color changes. In summary, this work reports the first application of nanoenzymes in repetitive H2O2 detection. Even after ten multiple cycles, the detection limit remains virtually unaltered, underscoring the robustness and enduring effectiveness of the engineered nanomaterial. The proposed simultaneous oxidation and reduction strategies for detecting H2O2 showed a commendable capability in ten cycles of H2O2 detection, thus providing a promising approach in the field of H2O2 detection.

Structural Colored Based Humidity Sensor Consisting of High Resolution 3D Printed Photonic Crystal Coated with Ultrathin Responsive Hydrogels.

Today, humidity sensors have become an integral part of the daily lives. In particular, humidity sensors using an electronic measuring principle have become the standard. Although these sensors have proven to be a stable measurement method, they have some disadvantages, such as their long response time or the danger of using them in explosiveenvironments. This work introduces photonic crystals as an alternative optical measurement approach. The novel technology of ultra-fast two-photon polymerisation printing is combined with a thin-film deposition process, namely iCVD. This allows to print large area high-precision 3D templates, which are subsequently coated with a humidity responsive hydrogel thin film (p(HEMA) of 20nm.The limits of 2PP technology are being pushed allowing the production ofs table and periodic large-area 3D structures. The flexible customization of hydrogels for ambient conditions make them exceptionally promising for a wide range of sensing applications. Additionally, optical methods for measuring humidity seem to be an excellent alternative to overcome the limitations for current state of the art humidity sensors. The optical detection of changes in ambient air humidity is achieved by observing color changes of the printed structure within the visible wavelength range.