Selective Colorimetric Sensor Research Articles

A facile colorimetric sensor for ketoprofen detection in milk: Integrating molecularly imprinted polymers with Cu-doped Fe3O4 nanozymes

A facile and efficient detection method is required to address the potential health risks of ketoprofen (KP) in animal-derived foods. Herein, we integrated molecularly imprinted polymers (MIPs) with Cu-doped Fe3O4 nanozymes (Fe3O4–Cu) to develop a selective colorimetric sensor for KP detection. Chitosan and glutaraldehyde were used as functional monomers and cross-linkers to fabricate proposed the MIPs@Fe3O4–Cu. On KP addition, it was specifically captured by the imprinted cavities, thereby blocking the channels between chromogenic substrates and Fe3O4–Cu. Based on this rationale, a selective colorimetric sensor utilizing MIPs@Fe3O4–Cu was established, exhibiting a linear range of 0.25–100 μM and a detection limit of 0.073 μM. The developed method was validated through its application in milk samples, yielding satisfactory recoveries with low relative standard deviations. This efficient and selective colorimetric sensor holds immense significance for KP detection in complex samples.

Bifunctional Pt-loaded steel slag matrix composites for the detection and degradation of tetracycline antibiotics

In this paper, a method for the simultaneous detection and degradation of tetracycline antibiotics (TCs) in water was investigated. Calcium silicate hydrate (CSH), FeO and calcium aluminate hydrate (CAH) were isolated from steel slag as carriers for Pt monomers. The produced Pt-modified modified steel slag (ALANH-Pt) possessed both peroxidase activity and photocatalytic properties. As a result, a sensitive and selective colorimetric sensor was exploited on the basis of ALANH-Pt for tetracycline (TC), oxytetracycline (OTC), and doxycycline (DOX), which exhibited a detection limit (LOD) of 1.696 μM, 0.999 μM and 3.607 μM, respectively. In addition, the degradation rate for TCs could be achieved 82 % within 60 min. The possible mechanisms of detection and degradation are discussed based on ESR spectroscopy, revealing the generation of hydroxyl radicals (OH), superoxide radicals (O2−) and holes (h+). The degradation pathway of TC was inferred by HPLC-MS. The selectivity of the colorimetric sensing platform and the application of the bifunctional ALANH-Pt to real water samples were investigated. This work provides a new idea that allows for the simultaneous detection and degradation of TCs, and offers a new approach to the utilization of steel slag.

Selective colorimetric sensors and diagnostic microfiber yarn for carbonyl groups via ion-pairing dyes with plural chromatic behaviors

An ideal chemo-responsive dye requires several essential features, including a facile preparation method, a broad range of dynamic color changes, and colorimetric responses to multiple stimuli. Herein, we present a simple and reliable procedure for synthesis of chemo-responsive dye from ion-pair formation of oppositely charged dyes. The ion-pairing dye exhibits various colorimetric responses to pH levels and amine concentrations, indicating that the dye has plural chromatic behaviors and wide visible spectrum: ‘halochromism’ and ‘solvatochromism’. Due to this, our colorimetric sensors can selectively identify various carbonyl groups such as ketone, aldehyde, and carboxylic acid, in which the detection limits range from a minimum of 0.019 to maximum of 2.506 ppm. Furthermore, the sensing array composed of a single ion-pairing dye enables the generation of easily identifiable color-patterns as unique fingerprints for each carbonyl groups across a range of gas levels. Based on these colorimetric responses to carbonyl groups, we develop dye-loaded microfiber yarn for biomarker diagnosis, which can check for the presence of acetone gas in the exhaled breaths and confirm whether an individual is in the optimal ketosis state or not.

Copper oxide nanosheets as an effective nanozyme with haloperoxidase-like activity for the colorimetric detection of H2O2 and glucose

Copper oxide nanosheets (CuO NSs) have been successfully obtained by exploiting an effective one-step approach of sugar-blowing method followed by calcination. The nanosheets were characterized by several techniques like X-ray powder diffraction (XRD), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Impressively, CuO NSs display haloperoxidase (HPO) like catalytic activity which catalyses the oxidation of chloride ions by H2O2 giving rise to reactive chlorine species (RCS). A sensitive and selective colorimetric sensor was then demonstrated via the oxidation of chromogenic substrate 3,3′,5,5′- tetramethylbenzidine (TMB) by the novel nanoenzyme CuO NSs through the generation of RCS for H2O2 and glucose detection with limit of detection of 109 nM and 21 nM in the linear ranges of 4.6 µM to 769 µM and 0.22 µM to 19.57 µM respectively. Additionally, the methodology is validated for the analysis of glucose in real samples.

Sensitive and selective colorimetric sensor detection of Sn (II): An aqueous, paper, and gel-based method by green biomimetic silver nanoparticles

Tin contamination in waters due to mining and natural activities in high concentrations can threaten human health. This research presents the development of a sensitive and selective colorimetric sensor in aqueous, paper, and gel-based to detect Sn2+. The development of such sensors is promising, with attractive advantages such as intense color, fast naked-eye response, and simple continuous fabrication. The addition of Sn2+ ions will change the color of the medium because curcumin (Cur) interacts with Sn2+, causing a decrease in free Cur, silver nanoparticles (AgNPs) becoming less stable, and a change in particle size. Colorimetric changes in Sn2+ were achieved by visual inspection within 10 min for aqueous-based and 20 min for paper and gel-based. The good linear relationship (R2 = 0.9999) between Sn2+ and Δ absorption with a detection limit of up to 66.99 µg/L. This method is relatively scalable in determining Sn2+ and shows good recovery between 80 and 105 %. This colorimetric sensor gives good sensitivity to Sn2+ metal ions which is expected to become the basic technology for developing in-situ sensors to monitor Sn2+ levels in tin industrial waste.

A Schiff base functioning as a highly selective colorimetric sensor for Cu2+ ion

In this study, we employed a Schiff base ligand (L = 6,6′-((1E,1′E)-(cyclohexane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(2,4-di-tert-butylphenol)) to serve as a chemosensor exclusively for detecting Cu2+ ions over other metal ions and anions in a THF:H2O mixture (7:3, v/v). L exhibits an absorption band at 330 nm, which undergoes a bathochromic shift to 377 nm upon interaction with solely Cu2+ ions, suggesting a restricted internal charge transfer process of L. Analysis via ESI-MS and Job’s plot confirmed a 1:1 stoichiometric ratio between L and Cu2+. L demonstrated the capability to detect Cu2+ ions at a concentration as low as 0.46 μM. Furthermore, we investigated the effectiveness of L in developing molecular logic gates and its applications in analyzing Cu2+ in water samples.

Sunlight-assisted green synthesis of gold nanocubes using horsetail leaf extract: A highly selective colorimetric sensor for Pb2+, photocatalytic and antimicrobial agent

This work aims to establish a novel approach for the selective synthesis of gold nanoparticles (Au NPs) with defined shape and size as well as excellent colloidal stability via a facile and environmentally friendly manner. The polar extract from the leaves of the plant E. diffusum (EDLE), also known as horsetail, was used to synthesize gold NPs (EDLE@Au NPs). Fourier-transform infrared (FTIR) and UV–visible spectroscopy, scanning electron microscopy-energy dispersive X-rays (SEM-EDX), PXRD, dynamic light scattering (DLS), and zeta potential (ZP) were used to characterize as-synthesized EDLE@Au NPs. The SEM imaging revealed the cubic shape of EDLE@Au NPs. Interestingly, EDLE@Au NPs interacted with different metal ions, and a shift in the LSPR band to a higher wavelength was observed only in the case of Pb2+ ions. This provided a basis for using the EDLE@Au NPs as a selective colorimetric sensor for Pb2+ ions. A linear range of 20–350 µM and a limit of detection of 4.4 µM for Pb2+ detection was achieved. To elucidate the sensing mechanism, DLS and zeta potential analyses were carried out after addition of Pb2+. A significant decrease in the zeta potential along with an increase in the particle size of the Au NPs was observed after the addition of Pb2+, suggesting the aggregation of the nanoparticles. Further, the results of the antimicrobial study showed that EDLE@Au NPs were active against both gram-positive and gram-negative bacteria. An exceptional photocatalytic activity with 96.5% degradation efficiency of EDLE@Au NPs was examined against methylene blue dye.

A smartphone-based colorimetric assay using Cu-tannic acid nanosheets (Cu-TA NShs) as a laccase-mimicking nanozyme for visual detection of quercetin in vegetables.

Theinteraction of Cu-tannic acid nanosheets (Cu-TA NShs) as nanozyme in a surfactant solution of CTAB under relatively acidic conditions is shown toexhibit a catalytic effect on quercetin (Qur). This catalytic property of Cu-TA NShs, which mimics laccase enzyme with many advantages, has been applied todeveloping a selective colorimetric sensor for the determination of trace amounts of Qur in vegetable samples. This strategy presents a desirable linear relationship between the absorbance signal intensity and the concentrations of Qur from 0.350 to 32.09 µM with a detection limit (LOD) of 0.064 µM (S/N = 3). The feasibility of the proposed portable colorimetric sensor for in situ analysis of the real samples has been validated with the high-performance liquid chromatography (HPLC) method as reference method, and two-tailed test (t test) statistical analysis certifies good agreement between the results. This enzyme-free and sensitive naked-eye sensor with the smartphone-based color map is promising to provide technical support for the rapid and visual detection of Qur in vegetables.

Robust Synthesis of GO-PtNPs Nanocomposites: A Highly Selective Colorimetric Sensor for Mercury Ion (II) Detection

Robust Synthesis of GO-PtNPs Nanocomposites: A Highly Selective Colorimetric Sensor for Mercury Ion (II) Detection

Highly Selective Colorimetric Sensor of Mercury(II) Ions by Andrographolide-Stabilized Silver Nanoparticles in Water and Antibacterial Evaluation.

Silver nanoparticles (AgNPs) are well known for their exceptional properties and versatility in various applications. This study used andrographolide as a biochemical stabilizer to synthesize AgNPs (andro-AgNPs). The andro-AgNPs were characterized by using UV-vis spectroscopy, revealing a surface plasmon resonance peak at 440 nm. Fourier transform infrared spectroscopy was also used to confirm the presence of AgNPs. Transmission electron microscopy was used to investigate the morphology of andro-AgNPs, which showed a spherical shape with an average diameter of 18.30 ± 5.57 nm (n = 205). Andro-AgNPs were utilized as a colorimetric sensor to detect mercury ions (Hg2+) in water, and the optimized detection conditions were evaluated using UV-vis spectroscopy with a linear range of 15-120 μM. The limit of detection and the limit of quantification for Hg2+ detection were found to be 11.15 and 37.15 μM, respectively. Furthermore, andro-AgNPs exhibited antibacterial properties against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. The results imply that andro-AgNPs hold promising potential for future biomedical applications.

Flavonoid-incorporated starch and poly(vinyl alcohol) film: Sensitive and selective colorimetric sensor for copper identification and quantification in beverages and environmental samples

Colorimetric sensors based on an eco-friendly sensor molecule immobilized into a polymer matrix have broad applications for detecting trace elements. However, their potential for quantitative analysis of these elements remains little explored. Here, we incorporated rutin or quercetin into films based on starch, poly(vinyl alcohol), and glycerol to detect and quantify Cu2+ in different matrices. The films were characterized by colorimetric assays, thickness, and solubility analyses, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and mechanical assays. Incorporating the flavonoids in the film decreased its solubility, tensile strength, and modulus of elasticity, while increased its cross-sectional surface irregularity. XRD and DSC results indicated an increase in film crystallinity in the presence of rutin or quercetin. FTIR analyses showed a more effective incorporation of quercetin than rutin in the polymeric matrix, which was confirmed by flavonoid release studies from the film. The film containing quercetin exhibited selectivity in identifying copper in liquid matrices, changing its color from light yellow to dark yellow. An analytical method to quantify Cu2+ was developed, presenting a linear response range of 0.20–1.20 mg L−1, with detection and quantification limits of 0.060 and 0.20 mg L−1, respectively, very lower than other methods based on polymeric matrices containing natural dyes. The method was successfully applied for Cu2+ determination in cachaça and tap water samples, achieving high accuracy (96–104% of recovery) and precision (relative standard deviation < 6.7%). Our findings represent an advancement in the field of sensors based on natural dyes, demonstrating that such sensors can achieve high sensitivity without the need for complex sample preparation methods.

Synthesis of Ag nanoparticles for selective dual detection of glutathione and dopamine using N, N-dimethyl-p-phenylenediamine mediated colorimetric probe

We report a simple and easy method to synthesize Ag nanoparticles (Ag NPs) and demonstrate its potential for the detection of glutathione (GSH) and dopamine (DA) via colorimetric assay. The Ag NPs were found to be monodispersed and spherical with a size of 5 ± 2 nm. The X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM) investigations revealed the formation of crystalline Ag NPs. The colour of N, N-dimethyl-p-phenylenediamine assay changed from dark pink to colourless when the concentration of GSH was increased from 1 to 40 μM. Notably, the suspension colour changed from dark pink to blue when a similar set of experiments were performed with DA. The UV/Visible and interference experiments of Ag NPs exhibited excellent sensitivity and selectivity against both GSH and DA even after the addition of 40 μM of different interference biomolecules. The calculated limit of detection (LOD) was 141 and 245 nM for GSH and DA, respectively. The real-time analysis with serum samples showed satisfactory recovery percentages of >95 and 80–90% for GSH and DA, respectively. Hence, the Ag NPs reported here have huge potential to serve as a sensitive and selective colorimetric sensor for the detection of GSH and DA for diverse applications ranging from catalysis to cancer therapy and theranostics.

Dual-mode highly selective colorimetric and smartphone-based paper sensors utilizing silver nanoparticles for ultra-trace level omeprazole detection in complex matrices

The present work focuses on the synthesis and optimization of highly stable, bare silver nanoparticles (AgNPs) as colorimetric sensor for trace-level detection of omeprazole. A novel approach combining AgNPs-based paper sensor and smartphone technology enables real-time analysis of omeprazole. The color change observed by the naked eye and shift in localized surface plasmon resonance (LSPR) were used to construct calibration curves. Both LSPR-based colorimetric sensing and paper-based sensing approaches were utilized for omeprazole detection in complex matrices. The limits of detection (LODs) were determined as 15 nM and 240 nM, with linear dynamic ranges of 0.05–40 µM and 0.1–50 µM, respectively. Recovery studies demonstrated % recoveries within the acceptable range of 90–110% and relative standard deviation (RSD) below 2%. Detailed characterizations including Fourier-Transform Infrared - (FTIR) Spectroscopy, Dynamic Light Scattering (DLS), zeta potential, Atomic Force Microscopy (AFM), and Field-Emission Scanning Electron Microscopy (FE-SEM) provided insights into sensing mechanism. This work offers a promising and practical solution for real-time omeprazole analysis with potential applications extending beyond pharmaceutical formulations. The developed colorimetric sensor based on AgNPs demonstrates high stability, sensitivity, and versatility, making it suitable for on-site and point-of-care omeprazole detection in various samples, including serum, plasma, urine, sea water, and tap water.

Facile Synthesis of Oxidized Boron Nanosheets for Chemo- and Biosensing.

As recently emerging nanomaterials, boron nanosheets (BNSs) have attracted more and more attention in various fields such as supercapacitors, photodetectors, bioimaging, and electrocatalysis due to their advantages of good biological compatibility, environmental friendliness, and good electro-optical properties. However, the study and application of BNSs in chemical and biological sensing are still in the infant stage, mainly due to the requirement of complicated, high-cost, and time-consuming preparation strategies. In this work, a new class of BNSs, namely oxidized-BNSs (i.e., ox-BNSs), were easily and rapidly synthesized by chemically treating boron powder with diluted HNO3 in a very short time (less than 15 min). The composition, morphology, optical property, and peroxidase mimetic activity of obtained ox-BNSs were investigated in detail. The prepared ox-BNSs were several-layered nanosheets with abundant oxygen-containing groups, emitted blue fluorescence, and possessed good intrinsic peroxidase mimetic activity, based on which a sensitive and selective colorimetric sensor was developed for detection of H2O2 and glucose. The new easy preparation strategy and good sensing performances of the prepared ox-BNSs would greatly stimulate the study and application of BNSs in chemo- and biosensing.

Porous biocompatible colorimetric nanofiber-based sensor for selective ammonia detection on personal wearable protective equipment

Colorimetric sensors are economical and power-free devices for gas detection. Ammonia is used in several industries and overexposure can lead to death. In this study, we demonstrate a simple, single-step fabrication of a sensitive and selective colorimetric ammonia sensor. This sensor is based on simple pH-indicator immobilized electrospun mat and was able to detect ammonia concentrations as low as 0.5 ppm with a fast response time of 10 s. The core-shell bi-polymer nanofiber mat was produced using single nozzle electrospinning with a PDMS shell for selectivity. We overcome the main weakness of colorimetric ammonia sensing which is its response to pH liquids and aerosol by the addition of PDMS shell making it suitable for personal protective equipment (PPE) in industrial environments. The detection range is adjustable by controlling the thickness of the PDMS shell without compromising the other performances of the sensor. Smart PPEs with integrated colorimetric sensors could potentially be used by workers in industrial settings to detect the presence of toxic ammonia gas in a visual way.

N,N-dicarboxymethyl Perylene-diimide-modified CdV2O6 Nanorods for Colorimetric Sensing of H2O2 and Pyrogallol.

Theperoxidase-like activity of CdV2O6 nanorods has been considerablyimproved by modification with N, N-dicarboxymethyl perylene-diimide (PDI) as a photosensitizer. The peroxidase-like behaviors are evaluated by virtue of the colorlesschromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB), which is fast changed into blue oxTMB in the presence of H2O2 inonly 90s. PDI-CdV2O6 exhibits high stability at elevated temperatures and PDI-CdV2O6 retains more than 70% of itscatalytic activity over a wide range of 15 to 60°C. Thecatalytic mechanism of PDI-CdV2O6 is ascribed to the synergistic interaction between PDI and CdV2O6 and the generation of •O2- radicals. Based on the enhanced peroxidase-like activity of PDI-CdV2O6, a selective colorimetric sensor has been constructedfor H2O2 and pyrogallol (PG) with detection limits of 36.5μM and 0.179μM, respectively. Thefeasibility of the proposed sensing platform has been validated by detecting H2O2 in milk and pyrogallol in tap water.

Pyrene derived imine functionalized moiety for highly selective colorimetric detection of Cu2+ ion real time sample with supportive DFT studies

Schiff base probe 4-hydroxy-N-(pyrene -1-yl-methylene) benzo hydrazide (PyrBH) has been synthesized and rationally designed as a rapid and highly selective colorimetric sensor for Cu2+ ions in the semi-aqueous medium. Structural characterization of PyrBH was confirmed by NMR, FT-IR, and HRMS spectral techniques. The cation binding affinity with the PyrBH probe was confirmed colorimetric study using the UV-Visible spectral method. The probe PyrBH exhibits a colorimetric response from colourless to yellow solutions containing Cu2+ ions. UV-Visible studies confirmed the formation of a 1:1 stoichiometry complex with a calculated binding constant Ka value (3.464 × 10-5 M) of suggests stable complex formation between the Cu2+ ions and the sensing PyrBH probe. The limit of detection (LOD) was found to be 2.19 × 10-7 M. The fabrication of test paper strips with the probe was done to detect the presence of Cu2+ ions in the real sample. The DFT & TD-DFT computational analysis was used to determine the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels, which it associates with satisfactory correlation.

A highly selective Hg2+ colorimetric sensor and antimicrobial agent based on green synthesized silver nanoparticles using Equisetum diffusum extract.

Plasmonic nanoparticles such as Ag have gained great interest in the biomedical domain and chemical analysis due to their unique optical properties. Herein, we report a simple, cost-effective, and highly selective colorimetric sensor of mercury(ii) based on E. diffusum (horsetail) extract-functionalized Ag nanoparticles (ED-AgNPs). The ED-AgNPs were synthesized by exploiting the coordination of Ag+ with the various functional groups of ED extract under sunlight exposure for only tens of seconds. ED-AgNPs (63 nm) were characterized using various techniques such as UV-vis, FTIR, DLS, SEM and EDX. FTIR spectra suggested the successful encapsulation of the AgNPs surface with ED extract and XRD confirmed its crystalline nature. This ED-AgNPs colorimetric sensor revealed remarkable selectivity towards Hg2+ in aqueous solution among other transition metal ions through a redox reaction mechanism. Besides, the sensor exhibited high sensitivity with rapid response and a detection limit of 70 nM. The sensor demonstrated feasibility for Hg(ii) detection in spiked tap and river water samples. In addition, the synthesized ED-AgNPs revealed enhanced antimicrobial activity with higher efficacy against the Gram-positive bacterium (L. monocytogenes with an inhibition zone of 18 mm) than the Gram-negative bacterium (E. coli with an inhibition zone of 10 mm). The simplicity and adaptability of this colorimetric sensor render it a promising candidate for on-site and point-of-care detection of heavy metal ions in diverse conditions.

A ruthenium nitrosyl complex-based highly selective colorimetric sensor for biological H2S and H2S-NO cross-talk regulated release of NO.

A ruthenium nitrosyl complex (1·NO) and 1·NO incorporated phospholipid-based liposomes (Lip-1·NO) were reported for highly selective colorimetric detection of H2S. The probe 1·NO "cross-talks" with H2S and releases nitric oxide (NO) in the process. The detection limit for H2S was found to be 0.31 μM and 0.45 μM in the cases of 1·NO and Lip-1·NO, respectively. The DAF-FM DA assay has been performed to confirm the H2S-induced NO release from 1·NO and Lip-1·NO. The sensing of H2S was also verified by ESI-MS and FT-IR spectroscopy. It was also observed that external stimuli, H2S and light worked in an almost similar way to release NO as observed by UV-Vis spectroscopy. A molecular logic gate operation "OR" was applied to the probe 1·NO in combination with inputs 'light' and 'H2S' to give the output 'NO release'. Hence, the probe 1·NO performs the dual work of sensing H2S with a colorimetric response, releasing NO upon cross-talk between NO and H2S.

Synthesis of tetrazine-tetracyanobutadienes and their transformation into pyridazines via inverse-electron demand Diels-Alder cycloaddition (IEDDA).

We report the synthesis of novel triphenylamine-tetrazine-tetracyanobutadiene based asymmetric and symmetric push-pull chromophores (1T and 1DT) by [2 + 2] cycloaddition-retroelectrocyclization of tetrazine connected electron-rich ethynyl triphenylamine with tetracyanoethene (TCNE). The electron-deficient tetrazine and tetracyanobutadiene (TCBD) moieties in 1T and 1DT create strong intramolecular charge transfer (ICT) interactions with TPA units, resulting in strong visible absorption with red edges reaching up to 700 nm (bandgaps of 1.79-1.89 eV). Furthermore, the structural, optical, and electronic properties of 1T and 1DT have been further tuned by transforming tetrazine units into pyridazines (1T-P and 1DT-P) via inverse-electron demand Diels-Alder cycloaddition (IEDDA). The relatively electron-donating character of pyridazine raised the HOMO and LUMO energies and widened the bandgap by ∼0.2 eV. This is the first synthetic strategy which allows two levels of tuning of the properties. 1DT acts as a selective colorimetric sensor for CN-via a nucleophilic attack on the dicyanovinyl unit of TCBD. The transformation results in a distinct colour change from orange to brown, while no change was observed for a range of anions tested (F-, Br-, HSO4-, NO3-, BF4-, and ClO4-).