Colorimetric sensors for rapid detection of various analytes

Synthesis and characterization of novel tricyanofuran hydrazone probe: solvatochromism, density-functional theory calculation and selective fluorescence, and colorimetric determination of iron (III)

A tricyanofuran hydrazone (TCFH) spectroscopic probe was produced to visually recognize Fe(III) ions in aqueous environments. The synthesis was started by reacting tricyanofuran with 4-aminophenol diazonium chloride. All the synthesized compounds were characterized by spectroscopic analyses. TCFH showed distinctive solvatochromic behaviour in various organic polar solvents due to intramolecular charge transfer. Its behaviour towards sensing Fe(III) was studied using ultraviolet-visible spectrophotometry. The sensing behaviours of the proposed probe for other metal ions, namely Co(II), Cr(III), Mg(II), Pb(II), Cd(II), Ba(II), Hg(II), Mn(II), Ni(II), Cu(II), Zn(II), Ca(II), Al(III), Na(I) and K(I), were also investigated, but no spectral changes were observed, indicating the probe's potential use as a highly selective and Fe(III)-sensitive colorimetric and fluorescent chemical sensor. The TCFH probe using EtOH/H₂ O (5:1; v/v) served as a colorimetric and fluorescent chemosensor for identification of Fe(III) by the naked eye owing to both its high sensitivity and selectivity towards Fe(III) compared with the other examined metal ions. The proposed TCFH probe can therefore be utilized as an effective spectroscopic sensor for Fe(III). Both colorimetric and fluorescence recognition of the analyte depended on the concentration of Fe(III) ions and was accomplished at a pH of 7. A rapid colour change from yellow to red occurred when an aqueous solution of Fe(III) ions was added. The intensity of the colour increased at higher Fe(III) concentrations. Cyclic voltammetry measurements in the dimethylformamide solvent indicated a nonreversible redox potential. This study also explained the possible mechanisms for both solvatochromism and the detection of Fe(III) through TCFH-Fe(III) complex formation. The binding constant of the generated TCFH-Fe(III) complex was explored. Computational modelling was conducted to explain the deprotonation-triggered changes that occur in the photophysical properties of TCFH dyes.

Spatially isolated redox processes enabled by ambipolar charge transport in multi-walled carbon nanotube mats

This work demonstrates a simple dual-well device which enables spatially isolated solutions to undergo complementary redox reactions. The device functions by the ambipolar transport of charge carriers between two spatially isolated poly(dimethylsiloxane) (PDMS) microwells through an underlying multi-walled carbon nanotube (MWCNT) mat. This MWCNT mat enables charge carriers, produced from the decomposition of an analyte in one solution, to drive a redox reaction in a spatially isolated second colorimetric read-out solution via a potential difference between the wells. As proof-of-concept a visible colorimetric read-out was shown using an enzyme, cytochrome c (reduced in 16 h), and the visualizing reagent 3,3',5,5'-tetramethylbenzidine (TMB) (oxidized in 2.5 h) for the detection of dithionite and hydrogen peroxide, respectively, without any external energy input. We discuss the origin of this phenomenon and highlight the ability of MWCNTs to accept and transport both electrons and holes efficiently between spatially isolated solutions giving rise to a highly versatile sensor suitable for use in simple, low-cost point-of-care diagnostics.

Colorimetric Sensing of Volatile Organic Compounds Produced from Heated Cooking Oils

Measurement of cooking-associated air pollution indoors is an integral part of exposure monitoring and human health risk assessment. There is a need for easy to use, fast, and economical detection systems to quantify the various emissions from different sources in the home. Addressing this challenge, a colorimetric sensor array (CSA) is reported as a new method to characterize volatile organic compounds produced from cooking, a major contributor to indoor air pollution. The sensor array is composed of pH indicators and aniline dyes from classical spot tests, which enabled molecular recognition of a variety of aldehydes, ketones, and carboxylic acids as demonstrated by hierarchical clustering and principal component analyses. To demonstrate the concept, these CSAs were employed for differentiation of emissions from heated cooking oils (sunflower, rapeseed, olive, and groundnut oils). Sensor results were validated by gas chromatography-mass spectrometry analysis, highlighting the potential of the sensor array for evaluating cooking emissions as a source of indoor air pollution.

Metallothionein dependent-detoxification of heavy metals in the agricultural field soil of industrial area: Earthworm as field experimental model system

Earthworms are known to reclaim soil contamination and maintain soil health. In the present study, the concentration of DTPA extractable heavy metals, Cd, Cu, Cr, Pb, and Zn in vermicasts and tissues of the earthworms (anecic: Lampito mauritii; epigeic: Drawida sulcata) collected from the soils of four different industrial sites, Site-I (Sago industry), Site-II (Chemplast industry), Site-III (Dairy industry) and Site-IV (Dye industry) have been studied. The heavy metals in industrial soils recorded were 0.01-326.42 mg kg^-1 with higher Cu, Cr, and Zn contents while the vermicasts showed lower heavy metal loads with improved physicochemical properties and elevated humic substances. The higher humic substances dramatically decreased the heavy metals in the soil. The bioaccumulation factors of heavy metals (mg kg^-1) are in the order: Zn (54.50) > Cu (17.43) > Cr (4.54) > Pb (2.24) > Cd (2.12). The greatest amount of metallothionein protein (nmol g^-1) was recorded in earthworms from Site-IV (386.76) followed by Site-III (322.14), Site-II (245.82), and Site-I (232.21). Drawida sulcata can produce a considerable amount of metallothionein protein than Lampito mauritii as the metallothionein production is dependent upon the presence of pollutants. The molecular docking analysis indicates a binding score of 980 for Cd, Cr and Cu, and 372 for Zn. Pb may bind with a non-metallothionein protein of earthworms and bio-accumulated in the internal chloragogenous tissues. Metallothionein neutralizes the metal toxicity and controls the ingestion of essential elements.

Development of a gold nanoparticles-based colorimetric sensor for the indirect determination of ammonium dinitramide and tetryl

Ammonium dinitramide (ADN) is a strong, environmentally friendly oxidizer used in composite solid rocket propellants. As there is no reliable colorimetric sensor for ADN assay applicable to in-field screening, we developed a sensitive and practical sensing method to determine it in the presence of other explosives and possible interferents, based on the detection of nitrite formed from ADN degradation under UV light in a slightly alkaline (i.e. of lower alkalinity than needed to hydrolyze nitramines) solution by a nanoparticle-based colorimetric sensor. The ADN-derived nitrite formed a colored product via a Griess reaction using gold nanoparticles modified with 4-aminothiophenol (4-ATP-AuNPs) along with a coupling reagent N-(1-naphthyl)ethylene diamine (NED) for forming an azo dye. The method used for ADN detection could also be applied to tetryl samples at a different wavelength. The limit of detection (LOD) was 0.012 mg L^-1 for ADN and 0.615 mg L^-1 for tetryl. Interference effects of energetic materials like trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and pentaerythritol tetranitrate (PETN) to ADN determination could be overcome. In addition, common soil ions did not adversely affect the nanosensor performance. The developed method was statistically validated against reference voltammetric, UV, and HPLC methods using t- and F- tests.

Development of a novel colorimetric thermometer based on poly(N-vinylcaprolactam) with push–π–pull tricyanofuran hydrazone anion dye

Thermochromic poly(N-vinylcaprolactam-co-tricyanofuran hydrazone) [poly(VC-co-TCFH)] gel labeled with a halochromic chromophore was developed using traditional free radical polymerization.

Simple Development of Novel Reversible Colorimetric Thermometer Using Urea Organogel Embedded with Thermochromic Hydrazone Chromophore

Thermochromic urea (U) organogel immobilized with a thermochromic tricyanofuran hydrazone (TCFH) chromophore was developed. Thermochromic TCFH chromophore bearing two nitro functional groups on a hydrazone recognition unit was synthesized via an azo-coupling reaction of tricyanofuran (TCF) heterocyclic moiety containing an active methyl group with the diazonium chloride salt of 2,4-dinitroaniline comprising two strongly electron-withdrawing nitro groups. The molecular structure of both intermediates and TCFH dye were characterized by several analytical methods, including 1H NMR, 13C NMR, IR, mass spectroscopy (MS), and elemental analysis. The thermochromic responsiveness could be attributed to the charge delocalization of TCFH as well as to the presence of an intramolecular charge transfer. The generated organogel displayed a thermoreversible sol–gel transition associated with color change. The origin of the monitored thermochromism is a conformational change of the tricyanofuran hydrazone backbone due to the temperature-driven deprotonation–protonation reversible process. The prepared urea–tricyanofuran hydrazone (UTCFH) thermometer acted as a diagnostic tool providing an instant color change between yellow, orange, red and purple upon changing the temperature of the UTCFH organogel in dimethyl sulfoxide (DMSO). This color change was proportionally correlated with increasing the temperature from 44 to 63 °C. The UTCFH organogel composed of urea and push-π-pull hydrazone type tricyanofuran chromophore immobilized physically in the urea organogel was found to function as a temperature-driven chromic thermometer. This chromogenic UTCFH organogel in DMSO displayed a phase transition at 41–48 °C. The morphological properties of the gel internal fibrous nanostructure (80–120 nm) were monitored by scanning electron microscopy (SEM). The colorimetric measurements were monitored by UV–Vis absorption spectroscopy. The chromogenic thermometer demonstrated a good reversibility without fatigue. The mechanism accounting for thermochromism of UTCFH organogel is proposed.

Polymer Electrochromism Driven by Metabolic Activity Facilitates Rapid and Facile Bacterial Detection and Susceptibility Evaluation

The electrochromism of a water-soluble naturally oxidized electrochromic polymer, ox-PPE, is harnessed for rapid and facile bacterial detection, discrimination, and susceptibility testing. The ox-PPE solution shows distinct colorimetric and spectroscopic changes within 30 min when mixed with live bacteria. For the underlying mechanism, it is found that ox-PPE responds to the reducing species (e.g. cysteine and glutathione) released by metabolically active bacteria. This reduction reaction is ubiquitous among various bacterial strains, with a noticeable difference that enables discrimination of Gram-negative and Gram-positive bacterial strains. Combining ox-PPE with antibiotics, methicillin-susceptible and -resistant S. aureus can be differentiated within 2.5 h. Proof-of-concept demonstration of ox-PPE for antimicrobial susceptibility testing is carried out by incubating E. coli with various antibiotics. The obtained minimum inhibition concentrations are consistent with the conventional culture-based methods, but with the procedure time significantly shortened to 3 h.

Disposable and Low-Cost Colorimetric Sensors for Environmental Analysis

Environmental contamination affects human health and reduces the quality of life. Therefore, the monitoring of water and air quality is important, ensuring that all areas are acquiescent with the current legislation. Colorimetric sensors deliver quick, naked-eye detection, low-cost, and adequate determination of environmental analytes. In particular, disposable sensors are cheap and easy-to-use devices for single-shot measurements. Due to increasing requests for in situ analysis or resource-limited zones, disposable sensors’ development has increased. This review provides a brief insight into low-cost and disposable colorimetric sensors currently used for environmental analysis. The advantages and disadvantages of different colorimetric devices for environmental analysis are discussed.

Clinical Applications of Visual Plasmonic Colorimetric Sensing

Colorimetric analysis has become of great importance in recent years to improve the operationalization of plasmonic-based biosensors. The unique properties of nanomaterials have enabled the development of a variety of plasmonics applications on the basis of the colorimetric sensing provided by metal nanoparticles. In particular, the extinction of localized surface plasmon resonance (LSPR) in the visible range has permitted the exploitation of LSPR colorimetric-based biosensors as powerful tools for clinical diagnostics and drug monitoring. This review summarizes recent progress in the biochemical monitoring of clinical biomarkers by ultrasensitive plasmonic colorimetric strategies according to the distance- or the morphology/size-dependent sensing modes. The potential of colorimetric nanosensors as point of care devices from the perspective of naked-eye detection is comprehensively discussed for a broad range of analytes including pharmaceuticals, proteins, carbohydrates, nucleic acids, bacteria, and viruses such as Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). The practical suitability of plasmonic-based colorimetric assays for the rapid visual readout in biological samples, considering current challenges and future perspectives, is also reviewed.

A paper-based colorimetric sensor array for discrimination and simultaneous determination of organophosphate and carbamate pesticides in tap water, apple juice, and rice

A colorimetric paper-based sensor is proposed for the rapid monitoring of six major organophosphate and carbamate pesticides. The assay was constructed by dropping gold and silver nanoparticles on the hydrophilic zones of a paper substrate. The nanoparticles were modified by L-arginine, quercetin, and polyglutamic acid. The mechanism of sensing is based on the interaction between the pesticide and the nanoparticles. The color of nanoparticles changed during the interactions. A digital camera recorded these changes. The assay provided a unique response for each studied pesticide. This method can determine six individual pesticides including carbaryl, paraoxon, parathion, malathion, diazinon, and chlorpyrifos. The limit of detection for these pesticides were 29.0, 22.0, 32.0, 17.0, 45.0, and 36.0 ng mL^-1, respectively. The assay was applied to simultaneously determine the six studied pesticides in a mixture using the partial least square method (PLS). The root mean square errors of prediction were 11, 8.7, 9.2, 10, 12, and 11 for carbaryl, paraoxon, parathion, malathion, diazinon, and chlorpyrifos, respectively. The paper-based device can differentiate two types of studied pesticide (organophosphate and carbamate) as well as two types of organophosphate structures (oxon and thion). Furthermore, this sensor showed high selectivity to the pesticides in the presence of other potential species (e.g., metal ions, anions, amino acids, sugar, and vitamins). This assay is capable of determining the pesticide compounds in tap water, apple juice, and rice samples.Graphical abstract.

Tetramethylammonium Hydroxide-doped Starch Film as a Colorimetric Sensor for Trinitrotoluene Detection

A tetramethylammonium hydroxide (TMAH)-doped starch film was developed for trinitrotoluene (TNT) detection. A purple Janowsky anion was obtained from the reaction of TNT with released TMAH. When the film was used in conjunction with digital image colorimetry (DIC), rapid quantitative analysis of TNT was achieved. The Red-Green-Blue (RGB) intensities analyzed from digital photographs of the purple product were used to establish calibration curves for TNT. A wide linear range (2.5 to 50 mgL^-1) with good linearity (R² > 0.99) was achieved for the quantification of TNT. Good precision (1.73 to 3.74%RSD) was obtained for inter-day tests (n = 5). The films were applied to test four post-blast soil samples and two positive results were observed. The concentrations quantified by DIC were in good agreement with spectrophotometry. The film was able to be stored in a freezer for 3 months with <4.3% change in performance.

Click chemistry as a tool in biosensing systems for sensitive copper detection

Copper detection for diagnostic purposes is an appealing field due to the important biological role copper plays as a trace metal. A convenient strategy for sensing copper is to utilize its catalytic ability. Therefore, this review summarizes approaches for copper determination by Cu^I-catalyzed azide/alkyne cycloaddition (CuAAC). The concept was introduced in 2006 and all contributions made up to the middle of 2020 are covered in this review. The issue is divided into three categories: electrochemical, visual, and fluorescence-based methods. The advantages, as well as the disadvantages, of every group, are discussed in detail. The methodology which allows for the determination of copper content in water and human biological samples from 5 s up to 48 h without complex instrumentation are discussed. The reported range of limit of detection (LOD) was 0.38 aM-20 μM, with 1-10 nM being the typical range. The most successful strategies involved using DNA chains or enzymes in the sensing systems.

Washable Colorimetric Nanofiber Nonwoven for Ammonia Gas Detection

The colorimetric sensor is a facile, cost-effective, and non-power-operated green energy material for gas detection. In this study, the colorimetric sensing property of a meta-aramid/dye 3 nanofiber sensor for ammonia (NH₃) gas detection was investigated. This colorimetric sensor was prepared using various dye 3 concentrations via electrospinning. Morphological, thermal, structural, and mechanical analyses of the sensor were carried out by field-emission scanning electron microscopy, thermogravimetric analysis, Fourier-transform infrared spectroscopy, and a universal testing machine, respectively. A homemade computer color matching machine connected with a gas flow device characterized the response of the meta-aramid/dye 3 nanofiber colorimetric sensor to various exposure levels of NH₃ gas. From the results, we confirmed that this colorimetric green energy sensor could detect ammonia gas in the concentration of 1-10 ppm with a sensing response time of 10 s at room temperature. After washing with laundry detergent for 30 min, the colorimetric sensors still exhibited sensing property and reversibility.

Polysaccharides as the Sensing Material for Metal Ion Detection-Based Optical Sensor Applications

The incorporation of a proper sensing material towards the construction of high selectivity optical sensing devices is vital. Polysaccharides, such as chitosan and carrageenan, are among the bio-based sensing materials that are extensively employed due to their remarkable physicochemical attributes. This paper highlights the critical aspects of the design of suitable polysaccharides for the recognition of specific analytes through physical and chemical modifications of polysaccharide structure. Such modifications lead to the enhancement of physicochemical properties of polysaccharides and optical sensor performance. Chitosan and carrageenan are two materials that possess excellent features which are capable of sensing target analytes via various interactions. The interaction between polysaccharides and analytes is dependent on the availability of functional groups in their structure. The integration of polysaccharides with various optical sensing techniques further improves optical sensor performance. The application of polysaccharides as sensing materials in various optical sensing techniques is also highlighted, particularly for metal ion sensing.

Electrostatically controlled plasmonic effects of gold nanoparticles with indigo-carmine functionation for rapid and straightforward colorimetric detection of Cu2+ ions

A colorimetric sensor is fabricated for effective on-site monitoring of Cu²⁺ ions content based on the distance-dependent optical properties of gold nanoparticles-polyvinyl alcohol-citrate (Au-NPs-PVA-Cy) which plasmonic effect electrostatically was controlled by PVA-Cy stabilizing indigo-carmine (IC) functionalizing. The surface-modified gold nanoparticles were extremely stable with a strong affinity toward Cu²⁺ ions. Citrate ion was employed as a cross-linking agent for pairs of Au-NPs-PVA-Cy and IC for stabilizing coordination between Cu²⁺ ion and IC. The active materials were characterized by UV-Vis, SEM, DLS, XRD, FT-IR, and EDS analyses. The sensor response toward Cu²⁺ ion was found to be linear in the range of 0.0974 to 3.27 μM with the limit of detection and quantification values of 0.021 and 0.07 μM, respectively. The sensor represents good sensitivity and stability, promisingly suggesting this device for the accurate and repeatable determination of Cu²⁺ in real water samples. The effect of different foreign ions on the selectivity of the sensor was checked. The sensor has a long shelf life in comparison to other similar colorimetric sensors. Also, it shows a repeatable response with RSD% of 2.02%. Thus, the sensing of Cu²⁺ ions based on the electrostatically control plasmonic of Au-NPs-PVA-Cy was developed with proper signaling based on the color change from dark blue to light blue as readily seen by the naked eye. Furthermore, the efficient environmental applicability of this simple and rapid determination of the Cu²⁺ sensor is proved.

Reduced texaphyrin: A ratiometric optical sensor for heavy metals in aqueous solution

We report here a water-soluble metal cation sensor system based on the as-prepared or reduced form of an expanded porphyrin, texaphyrin. Upon metal complexation, a change in the redox state of the ligand occurs that is accompanied by a color change from red to green. Although long employed for synthesis in organic media, we have now found that this complexation-driven redox behavior may be used to achieve the naked eye detectable colorimetric sensing of several number of less-common metal ions in aqueous media. Exposure to In(III), Hg(II), Cd(II), Mn(II), Bi(III), Co(II), and Pb(II) cations leads to a colorimetric response within 10 min. This process is selective for Hg(II) under conditions of competitive analysis. Furthermore, among the subset of response-producing cations, In(III) proved unique in giving rise to a ratiometric change in the ligand-based fluorescence features, including an overall increase in intensity. The cation selectivity observed in aqueous media stands in contrast to what is seen in organic solvents, where a wide range of texaphyrin metal complexes may be prepared. The formation of metal cation complexes under the present aqueous conditions was confirmed by reversed phase high-performance liquid chromatography, ultra-violet-visible absorption and fluorescence spectroscopies, and high-resolution mass spectrometry.

A review on colorimetric methods for determination of organophosphate pesticides using gold and silver nanoparticles

This review (with 99 refs.) summarizes the progress that has been made in colorimetric (i.e. spectrophotometric) determination of organophosphate pesticides (OPPs) using gold and silver nanoparticles (NPs). Following an introduction into the field, a first large section covers the types and functions of organophosphate pesticides. Methods for colorimetric (spectrophotometric) measurements including RGB techniques are discussed next. A further section covers the characteristic features of gold and silver-based NPs. Syntheses and modifications of metal NPs are covered in section 5. This is followed by overviews on enzyme inhibition-based assays, aptamer-based assays and chemical (non-enzymatic) assays, and a discussion of specific features of colorimetric assays. Several Tables are presented that give an overview on the wealth of methods and materials. A concluding section addresses current challenges and discusses potential future trends and opportunities. Graphical abstractSchematic representation of organophosphate pesticide determinations based on aggregation of nanoparticles (particular silver or gold nanoparticles). This leads to a color change which can be determined visually and monitored by a red shift in the absorption spectrum.

White Eggshells: A Potential Biowaste Material for Synergetic Adsorption and Naked-Eye Colorimetric Detection of Heavy Metal Ions from Aqueous Solution

In the present work, we have utilized a simple, no-cost, unmodified eggshell powder as a naked-eye colorimetric detector, which on simple dispersion in aqueous solution of metal ions exhibited characteristic color change from white to pale green, pale blue, yellow, pale yellow, dark yellow, pale pink, blue, and brown for metal ions V⁴⁺, Cr³⁺, Cr⁶⁺, Fe²⁺, Fe³⁺, Co²⁺, Cu²⁺, and Ag⁺, respectively. The effects of various parameters like concentration of metal ions, pH, temperature, and adsorbent dosage were investigated by batch sorption experiments. Also, Freundlich and Langmuir models were used to describe the adsorption isotherm. The eggshell powder before and after adsorption was characterized qualitatively by the naked-eye and quantitatively by diffuse reflectance spectroscopy-UV, Fourier transform infrared, atomic absorption spectroscopy, powder X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy, Brunauer-Emmett-Teller, zeta potential, and X-ray photoelectron spectroscopy techniques. In addition, the competitive adsorption of metal ions in mixtures and the recycle experiments were carried out to prove the sustainability of the material. Further, the red, green, and blue alterations were extracted from the colorimetric array and subjected to hierarchical clustering analysis using the Ward method by calculating the Euclidean distance, which displayed facile discrimination of 10 heavy metal ions at 1 mM level. Thus, the unmodified eggshell powder has been proven to be an impressive value-added sustainable material for synergistic metal adsorption and colorimetric naked-eye detection of a series of metal ions with detection limits of 10^-4 M for Fe³⁺, Fe²⁺, and Cu²⁺; 10^-3 M for Cr³⁺, Cr⁶⁺, Ag⁺, and Co²⁺; and 5 × 10^-3 M for V⁴⁺.

Enhanced Colorimetric Signal for Accurate Signal Detection in Paper-Based Biosensors

Paper-based colorimetric biosensors combine the use of paper with colorimetric signal detection. However, they usually demonstrate lower sensitivities because a signal amplification procedure has not been used. Stopping the reaction of colorimetric signal generation is often used in lab-based assays in order to amplify and stabilize the colorimetric signal for detection. In this study, the generation of a stopped colorimetric signal was examined for accurate and enhanced signal detection in paper-based biosensors. The colorimetric reaction in biosensors is usually based on the interaction between the enzyme horseradish peroxidase (HRP) and a selected chromogenic substrate. The two most commonly used HRP substrates, 3,3’,5,5’-tetramethylbenzidine (TMB) and 2’-azinobis (3-ethylbenzothiazoline-6-sulfonic-acid) (ABTS), were compared in terms of their ability to generate a stopped colorimetric signal on membrane. The stopped colorimetric signal was visible for TMB but not for ABTS. Moreover, the generation of stopped colorimetric signal was dependent on the presence of polyvinylidene-difluoride (PVDF) membrane as the separation layer. With PVDF the colorimetric signal (color intensity) was higher (TMB: 126 ± 6 and ABTS: 121 ± 9) in comparison to without PVDF (TMB: 110 ± 2 and ABTS: 102 ± 4). The TMB stopped colorimetric signal demonstrated a more stable signal detection with lower standard deviation values. To conclude, a stopped colorimetric signal can be generated in paper-based biosensors for enhanced and accurate signal detection.

Curcumin nanoparticle doped starch thin film as a green colorimetric sensor for detection of boron

A tapioca starch film doped with curcumin nanoparticles was successfully fabricated and applied as a novel green colorimetric sensor for detection of boron in wastewater. Curcumin nanoparticles (curn, 30-90 nm) extracted from turmeric powder were used as a green probe, while tapioca starch was used as a natural support substrate. A yellow thin film (51 μm thick) fabricated on a used plastic spoon turned red-brown after immersion in boron solution (pH 9) for 15 min with excellent selectivity. The film costs only 0.0007 USD, while the cost of the sensor (curn-film on new plastic spoon) was 0.004 USD. After use the film could be completely washed from the plastic, it being biodegradable, while the used plastic spoon could be re-used to fabricate a new sensor at least 10 times. The good 1.52%RSD precision was obtained across three lots fabricated. When the curn-film was used in conjunction with digital image colorimetry (DIC), a simple and rapid quantification of boron was achieved. The green color layer in reflected light image of the red-brown product (I_G) provided the highest sensitivity (64 ± 1 a.u. L mg^-1) and the lowest detection limit of 0.052 ± 0.001 mg L^-1. The intra-day testing (9 films) had 2.41 to 4.34%RSD, while the inter-day testing had 2.29 to 5.66%RSD (15 films, 5 days). Accuracy in terms of relative error for control samples (0.40 mg L^-1) was +3.63%. Wastewater samples from Para-rubber wood processing plant were quantified by curn-film and DIC, giving 4248 ± 391 mg L^-1 boron concentration with no significant difference to ICP determination at 95% confidence level. The sensors after storage in a desiccator for a year gave readings changed by only +3.5% and -2.1% relative to freshly prepared sensors.

Anthocyanin immobilization in carboxymethylcellulose/starch films: A sustainable sensor for the detection of Al(III) ions in aqueous matrices

A robust and sustainable sensor for the detection of Al(III) ions in water was developed by immobilization of anthocyanin (AN) from black rice in a film formed by carboxymethylcellulose (CMC) and starch. Characterization of the films was performed using solubility, thickness, FTIR, and mechanical analysis. The film exhibited an irreversible color change from red to purple in response to the presence of Al(III). The best colorimetric response of the sensor was observed at pH 4.5 and a time of 60 min, achieving the detection of 3 mg L^-1 of Al(III). For concentrations higher than 5 mg L^-1, the sensor response time decreased to 20 min. The minimum Al(III) concentration detected with the naked eye was lower than the maximum permissible concentrations in aqueous effluents according to different legislations, indicating the potential of this study to develop sensors for the detection of Al(III).

A novel chromone based colorimetric sensor for highly selective detection of copper ions: Synthesis, optical properties and DFT calculations

In this work, a new chromone based colorimetric sensor (ChrCS) was developed for highly selective detection of copper ions in semi-aqueous media. Evaluation of color and spectral changes displayed by the developed sensor shows that the sensor can be applied to detect copper ions in the presence of other competing metal ions and anions. The developed sensor, which contains biologically active chromone ring, shows excellent selectivity at microlevel for Cu²⁺ with a color change from colorless to yellow. Job's plot based on spectroscopic data showed the complex formation between ChrCS and Cu²⁺ ions has the stoichiometric ratio of 1:1 (ChrCS-Cu²⁺ complex). In addition, the binding constant of the ChrCS to Cu²⁺ was determined using the Benesi-Hildebrand equation. Furthermore, the test papers of the developed ChrCS were successfully prepared and employed to detect different concentration Cu²⁺ (10^-3 M to 10^-7 M) in aqueous solution. Importantly, sensor ChrCS was applied to detect Cu²⁺ ions in real water samples. To better understand the optical character of ChrCS and the effect of metal ion titration, density functional theory (DFT) calculations at the B3LYP/6-31 + G(d,p) level were performed for ChrCS and its complex ChrCS-Cu²⁺. Furthermore, on the basis of the Job's plot analysis DFT calculations, and reversible nature of the developed sensor, the sensing mechanism was demonstrated.

Revealing Lectin-Sugar Interactions with a Single Au@Ag Nanocube

An individual nanoparticle-based plasmonic nanotechnology was used for real-time monitoring of lectin-sugar interactions, which could be designed as novel plasmonic nanobiosensors for the detection of trace concanavalin A (ConA) with high sensitivity and selectivity. The localized surface plasmon resonance (LSPR) spectra of Au@Ag nanocubes (NCs) are linearly shifted to a long wavelength with an increasing concentration of ConA. In fact, each Au@Ag NC can act as a nanobiosensor for the quantified detection of trace ConA, which enables the miniaturization of the biosensor system to nanoscale. Furthermore, the results demonstrated the perfect biosensing ability with the dual channel of dark-field microscopy images and LSPR spectra. We expect that this nanobiosensor system can provide an alternative important method for monitoring the specific binding of lectin-sugar at a single nanoparticle surface.

Combining gold nanoparticle-based headspace single-drop microextraction and a paper-based colorimetric assay for selenium determination

A novel method combining headspace single-drop microextraction with a paper-based colorimetric assay was developed. Headspace single-drop microextraction using a microdrop containing unmodified gold nanoparticles (AuNPs) as both the extractant and the colorimetric probe was used for the sensitive and selective determination of Se(IV). The method relies on the color change of the microdrop solution caused by the adsorption of in situ-generated hydrogen selenide on the surface of AuNPs. Following extraction, the microdrop was spotted onto cellulose paper, and scanometric-assisted digital image analysis was used for selenium quantification. The analytical variables affecting the method sensitivity, including the drop volume, the concentrations of KBH₄, HCl, and AuNP solutions, and the extraction time, were studied. Under the optimal conditions, a linear correlation between the colorimetric signal and Se(IV) concentration in the range from 15-100 μg L^-1 with a limit of quantification of 12 μg L^-1 was achieved. The repeatability of the method was studied by the calculation of intraday and interday precision for the standard solutions at concentrations of 20 and 70 μg L^-1. The batch-to-batch reproducibility of the AuNPs synthesized under the same conditions was also assessed. The relative standard deviations were less than 7%. The method provided satisfactory results for the determination of selenium in real samples.

Silver Nanoparticle-Based Assay for the Detection of Immunoglobulin Free Light Chains

There is a wide spectrum of malignant diseases that are connected with the clonal proliferation of plasma cells, which cause the production of complete immunoglobulins or their fragments (heavy or light immunoglobulin chains). These proteins may accumulate in tissues, leading to end organ damage. The quantitative determination of immunoglobulin free light chains (FLCs) is considered to be the gold standard in the detection and treatment of multiple myeloma (MM) and amyloid light-chain (AL) amyloidosis. In this study, a silver nanoparticle-based diagnostic tool for the quantitation of FLCs is presented. The optimal test conditions were achieved when a metal nanoparticle (MNP) was covered with 10 particles of an antibody and conjugated by 5-50 protein antigen particles (FLCs). The formation of the second antigen protein corona was accompanied by noticeable changes in the surface plasmon resonance spectra of the silver nanoparticles (AgNPs), which coincided with an increase of the hydrodynamic diameter and increase in the zeta potential, as demonstrated by dynamic light scattering (DLS). A decrease of repulsion forces and the formation of antigen-antibody bridges resulted in the agglutination of AgNPs, as demonstrated by transmission electron microscopy and the direct formation of AgNP aggregates. Antigen-conjugated AgNPs clusters were also found by direct observation using green laser light scattering. The parameters of the specific immunochemical aggregation process consistent with the sizes of AgNPs and the protein particles that coat them were confirmed by four physical methods, yielding complementary data concerning a clinically useful AgNPs aggregation test.

Bio-Recognition in Spectroscopy-Based Biosensors for *Heavy Metals-Water and Waterborne Contamination Analysis

: Microsystems and biomolecules integration as well multiplexing determinations are key aspects of sensing devices in the field of heavy metal contamination monitoring. The present review collects the most relevant information about optical biosensors development in the last decade. Focus is put on analytical characteristics and applications that are dependent on: (i) Signal transduction method (luminescence, colorimetry, evanescent wave (EW), surface-enhanced Raman spectroscopy (SERS), Förster resonance energy transfer (FRET), surface plasmon resonance (SPR)); (ii) biorecognition molecules employed (proteins, nucleic acids, aptamers, and enzymes). The biosensing systems applied (or applicable) to water and milk samples will be considered for a comparative analysis, with an emphasis on water as the primary source of possible contamination along the food chain.

Dermal Tattoo Biosensors for Colorimetric Metabolite Detection

Tattooing is a ubiquitous body modification involving the injection of ink and/or dye pigments into the dermis. Biosensors in the form of tattoos can be used to monitor metabolites in interstitial fluid. Here, minimally invasive, injectable dermal biosensors were developed for measuring pH, glucose, and albumin concentrations. The dermal pH sensor was based on methyl red, bromothymol blue, and phenolphthalein, which responded to a pH range from 5.0 to 9.0. The dermal glucose sensor consisted of glucose oxidase, 3,3',5,5'-tetramethylbenzidine, and peroxidase that detected concentrations up to 50.0 mmol L^-1 . The dermal albumin sensor consisted of 3',3'',5',5''-tetrachlorophenol-3,4,5,6-tetrabromosulfophthalein to measure concentrations up to 5.0 g L^-1 . The sensors were multiplexed in ex vivo skin tissue and quantitative readouts were obtained using a smartphone camera. These sensors can be used to manage of acid-base homeostasis, diabetes, and liver failure in point-of-care settings.

Breath analysis of cancer in the present and the future

Most of the currently used diagnostics for cancerous diseases have yet to meet the standards of screening, as they are insufficiently accurate and/or invasive and risky. In this review, we describe the rationale, the progress made to date, and the potential of analysing the exhaled volatile organic compounds as a pathway for enabling early diagnosis of cancer and, therefore, for achieving better clinical prognosis and survival rates. The review highlights the major advancements made in this field, from fundamentals, up to translational phases and clinical trials, with a special emphasis on sensing platforms based on nanomaterials. The prospects for breath analysis in early cancerous disease are presented and discussed.

Label free aptasensor for ultrasensitive detection of tobramycin residue in pasteurized cow's milk based on resonance scattering spectra and nanogold catalytic amplification

TOB aptamer can be adsorbed on the AuNPs surface to form AuNPs-aptamer complexation to prevent AuNPs aggregation in high salt solution. When TOB was added to the AuNPs solution, the aptamer would bind with TOB and depart from the AuNPs surface. The amount of the AuNPs-aptamer complexation depends on the TOB concentration. Different concentration of AuNPs-aptamer can catalyze the reduction reaction of CuSO₄ to produce different size Cu₂O particle. The resonance scattering peak intensities are correlated with the Cu₂O size. Large size Cu₂O particle as a resonance scattering spectroscopy probe can remarkable improve the TOB detection sensitivity. We have succeeded to detect the trace TOB in aqueous solutions. The linear range and limit of detection were 0.50-17 nM and 0.19 nM, respectively. This simple and inexpensive method exhibited high sensitivity and selectivity, which was successfully used to detect TOB in milk. The results indicated the accuracy and precision were satisfied.

Precise, direct, and rapid detection of Shigella Spa gene by a novel unmodified AuNPs-based optical genosensing system

Early detection of infectious bacteria is a necessity for combating infectious diseases. Due to low infectious dose of Shigella, rapid and sensitive detection is needed. Compared to the presented genes, Spa gene can be introduced as a novel sequence for all species of Shigella detection. Herein, the possibility of Spa genes for detection of four species of Shigella was investigated for the first time by AuNPs-based optical genosensing system. In this method, AuNP-DNA probes were hybridized with Spa gene sequence. When the complementary target is present, it prevents the aggregation of the complex under acid environment and the solution remains red whereas in the absence of the specific sequence, it turns to purple. Therefore, visual detection is possible with bare eye. The comparison of this Optical DNA biosensor and PCR-based method showed that the proposed method is simple, cost-effective, rapid operation, with high or comparable detection limit of (LOD and LOQ: 8.14 and 26.6 ng mLl^-1, respectively), without need of any expensive techniques, and equipments compared to the conventional methods. In conclusion, the described method may develop into a platform that could be utilized for detection of various bacterial species with high accuracy and prompt screening of samples.

Synthesis and living cell imaging of a novel fluorescent sensor for selective cupric detection

Copper is an important element indispensable for human life and health. Many copper-determining probes have been created for exploring its functional behavior in various cell types but few of them contains both fluorescent and colorimetric characters. In the present study, we developed a set of copper probes by synthesizing several novel thiophene-based Schiff bases in order to make a suitable sensor for quantifying and imaging copper in living cells. We find that the ligand FS-1 has a splendid selectivity and affinity toward Cu²⁺ among the common divalent metal ions. Living cell imaging show that FS-1 has a robust and repetitive fluorescence response in the presence of Cu²⁺ only in the cytosolic space of Hepg2 cell and not in the other cells examined. These data suggest that we have developed a new copper probe that can be used as a Cu²⁺ fluorescent and colorimetric sensor for in vivo and in vitro copper studies.

Development of three ways molecular logic gate based on water soluble phenazine fluorescent 'selective ion' sensor

New hydrophilic fluorescent selective ion sensor based on phenazine and phthalazine moieties, 1,1'-(phenazine-2,3-diyl)-bis(3-(1,4-dihydroxyphthalazin-6-yl)urea) (1), has been designed, synthesized and characterized. Interestingly, sensor 1 exhibits prominent "turn-on" and "turn-off" fluorogenic signaling at 580 nm towards Fe²⁺ & AcO^- and Sr²⁺ & Cu²⁺, respectively. The fluorescence titration experiments shed light on the nature of the interaction between 1 and guest molecules (Fe²⁺, Sr²⁺, Cu²⁺ and AcO^-), which divulge that 1 is flexible enough to orient itself according to the size of the guest molecule. Water mediated excited-state intramolecular proton transfer (ESIPT) and photo-induced electron transfer (PET) mechanisms are responsible for the dual behavior of 1, which binds with guest molecules in 1:1 stoichiometry. Based on the significant duplex fluorescence response of 1, a molecular logic gate keypad lock with sixteen "on" passwords for a storage system has been developed.

Test strips based on iron(iii)-impregnated alginate/polyacrylonitrile nanofibers for naked eye screening of tetracycline

Tetracycline (TC) is an inexpensive broad-spectrum antibiotic used to treat infectious diseases and to promote growth in animals. However, driven by economic interest, abuse of TC poses a serious threat to human beings, and it remains a significant challenge to create easy-to-use TC colorimetric test strips for public use. Herein, we present a strategy to prepare free-standing, nanofibrous structured test strips with tortuous porous structure and large surface area by combining polyacrylonitrile nanofibrous membranes (PAN NMs), alginate, and Fe3+. In this approach, alginate was first functionalized on the PAN NMs and then, Fe3+ was assembled into the alginate to construct a TC-sensing surface. The resultant test strips exhibited the following integrated properties: fast sensing process (10 min), low naked eye detection limit (5 μg kg-1), excellent anti-interference ability, and satisfactory reusability. Furthermore, the TC concentration-dependent color change (yellow to maroon) was quantitatively visualized by an iPhone read-out hue parameter. All the findings indicate that this intriguing approach may pave the way for versatile designing of NMs to serve as a preventive treatment for the public.