Naked-eye Sensor Research Articles

Highly selective and sensitive colorimetric chemosensor using PVA/chitosan ion-imprinted nanofibers for copper ion detection and removal

Herein, a highly efficient colorimetric chemosensor incorporating ion-imprinted electrospun nanofiber was developed for the removal and detection of Cu2+ ions. In this regard, PVA/chitosan composites were used as the polymeric matrix, and 1-(2-pyridylazo)-2-naphthol was employed for complex formation. The prepared naked-eye sensor was characterized using Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, atomic force microscopy, differential scanning calorimetry, thermogravimetric analysis, and X-ray diffraction analysis, revealing the morphological, structural, and molecular properties of the sensor.The results showed that the colorimetric chemosensor based on copper-imprinted nanofiber (Cu–INF) possesses higher selectivity for Cu2+ compared to interference ions. The selectivity coefficient (k) and relative selectivity coefficient (K′) indicated the selective behavior of Cu–INF in the adsorption of Cu2+ in binary systems including Cu2+/Co2+, Cu2+/Ni2+, and Cu2+/Zn2+.Furthermore, the ion-imprinted nanofiber was used for the preconcentration of copper ions, demonstrating a high adsorption capacity of 128.205 mg g−1 for Cu2+. The equilibrium adsorption isotherm and adsorption kinetics of Cu2+ on Cu–INF followed the Freundlich adsorption isotherm and a pseudo-second-order model, respectively. The developed sensor exhibited a linear detection range of 5 × 10−8 - 2 × 10−7 M with a limit of detection (LOD) of 1.07 × 10−8 M for copper ions. The results indicated satisfactory adsorption and successful detection of Cu2+ at trace concentrations.

A rational design of metal doped C20 fullerene based sensor for the selective detection of ethyl butyrate as COVID-19 biomarker

The detection of ethyl butyrate as a COVID-19 biomarker in exhaled breath could be a novel, rapid, less expensive, painless and non-invasive technique compared to a costly, painful and time-consuming PCR test. The potential of alkaline earth metals doped C20 fullerenes (M@C20) was explored as sensing materials to detect ethyl butyrate selectively. The ethyl butyrate (EB) exhibited the physisorption on pristine C20 fullerene with adsorption energy of -4.16 kcal/mol, while chemisorption was observed with M@C20 fullerenes. The frontier molecular orbital analysis demonstrates enhanced stability of complexes, attributed to widened Eg gaps during EB adsorption onto M@C20 fullerenes. The notable shift in λmax values in the visible region suggests using M@C20 fullerenes as UV–visible-based naked-eye sensors. The infrared analysis showed a red shift in the carbonyl bond stretching frequency of ethyl butyrate upon adsorption onto M@C20 fullerenes. The red shift resulted from charge transfer from ethyl butyrate to M@C20. These findings establish the foundation for utilizing M@C20 fullerenes in IR-based handheld sensing devices. The minimum recovery time (6.8 s) demonstrates Ca@C20 fullerene as a promising, reusable sensor for detecting ethyl butyrate at human body temperature. Our results pave the way to design rapid, reusable sensors for detecting ethyl butyrate.

A new multifunctional phenanthroline-derived probe for colorimetric sensing of Fe2+ and fluorometric sensing of Zn2.

A new phenanthroline derivativebearing imidazole group, (2-(3,5-di(pyridin-4-yl)phenyl)-1-p-tolyl-1H-imidazo[4,5-f][1,10]phenanthroline) (1), has been devised. 1can be used as a multifunctionalprobe exhibiting a highly sensitive colorimetric response to Fe2+ and a selectively ratiometric fluorescent response to Zn2+in a buffer-ethanol solution. The absorption enhancement accompanied by a visual color change from colorless to red upon addition of Fe2+, makes 1a suitable naked-eye sensor for Fe2+. Moreover, 1displayed a Zn2+-induced red-shift of emission (44 nm) showing a color change from blue to light cyan under a 365-nm UV lamp. Its practical imaging applicability for intracellular Zn2+was confirmed in HeLa cells using a confocal microscope. The improved emission properties and cell imaging capability would provideanew approach forfluorescencesensationfor Zn2+.

DFT-D3 and TD-DFT Studies of the Adsorption and Sensing Behavior of Mn-Phthalocyanine toward NH3, PH3, and AsH3 Molecules.

This study employs density functional theory (DFT) calculations at the B3LYP/6-311+g(d,p) level to investigate the interaction of XH3 gases (X = N, P, As) with the Mn-phthalocyanine molecule (MnPc). Grimme's D3 dispersion correction is applied to consider long-range interactions. The adsorption behavior is explored under the influence of an external static electric field (EF) ranging from -0.514 to 0.514 V/Å. Chemical adsorption of XH3 molecules onto the MnPc molecule is confirmed. The adsorption results in a significant decrease in the energy gap (Eg) of MnPc, indicating the potential alteration of its optical properties. Quantum theory of atoms in molecules (QTAIM) analysis reveals partially covalent bonds between XH3 and MnPc, and the charge density differenc (Δρ) calculations suggest a charge donation-back donation mechanism. The UV-vis spectrum of MnPc experiences a blue shift upon XH3 adsorption, highlighting MnPc's potential as a naked-eye sensor for XH3 molecules. Thermodynamic calculations indicate exothermic interactions, with NH3/MnPc being the most stable complex. The stability of NH3/MnPc decreases with increasing temperature. The direction and magnitude of the applied electric field (EF) play a crucial role in determining the adsorption energy (Eads) for XH3/MnPc complexes. The Eg values decrease with an increasing negative EF, which suggests that the electrical conductivity (σ) and the electrical sensitivity (ΔEg) of the XH3/MnPc complexes are influenced by the magnitude and direction of the applied EF. Overall, this study provides valuable insights into the suggested promising prospects for the utilization of MnPc in sensing applications of XH3 gases.

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.

Highly selective and sensitive recognition of multi-ions in aqueous solution based on polymer-grafted nanoparticle as visual colorimetric sensor

A novel, selective and sensitive colorimetric sensor for naked-eye detection and adsorption of multi-ions in aqueous solution was synthesized using hybridization of organic–inorganic phase. The polymer-grafted nanoparticles (PGNPs) was synthesized via atom transfer radical polymerization (ATRP) of monomers on modified TiO2 NPs and applied under optimized conditions for naked-eye detection: sensor mass: 15 mg; response time: 30 s with limits of detection (LODs) as small as 10, 1, 0.5, and 1 ppb Hg (II), Cd (II), Cu (II), and UO2 (II) at pH = 8, 9, 6, and 7, respectively. The efficient selectivity of the naked eye sensor to multi-ions in the presence of various ions was affirmed wherein the color of the chemosensor in the presence of Hg (II), Cd (II), Cu (II), and UO2 (II) shifted from gray to violet, orange, green and yellow, respectively. The salient advantages of this method comprise expeditious, selectable, high reproducibility, with reasonable adsorption capacity (133 mg g-1) and inexpensive nature for rapid detection of heavy metal ions contamination in aqueous solution in an inexpensive manner. The adsorption mechanism was studied via adsorption kinetics and adsorption isotherm models and the accuracy of the chemosensor has been confirmed and supported by XRD, FT-IR, TGA, 1H-NMR, SEM, TEM, EDX mapping, DLS, BET, and EDS analysis.

An azo-receptor immobilized mesoporous honeycomb silica framework as a solid-state chromogenic sensor for capturing ultra-trace cadmium ions from environmental/industrial samples

A solid-state naked-eye sensor composed of a mesoporous honeycomb structured silica monolith impregnated with a DMTHBD receptor offers a simple, rapid and eco-benign approach for the selective sensing of trace Cd2+, with brilliant color transitions.

Design and fabrication of a new sol-gel based sensor for the visual detection of oxalate and investigation of the effect of boiling on the oxalate content of some foods

Sol–gel chemistry is a unique method for constructing high-performance flexible sensors. Sol-gel silica matrices doped with a controlled amount of sensing agent (dopant) lead to the fabrication of suitable sensors. According to this knowledge, we decided to describe the development and performance characteristics of the sol-gel glasses with a nanoporous structure as the novel naked eye sensor for fast detection of oxalate based on the incorporation of indole inside pores of the silica matrix obtained by sol–gel technology. Several sols were made with different water: alkoxide ratios and pHs to design a highly sensitive and selective thin film without dopant leaching. The Field emission scanning electron microscopy (FE-SEM) technique was employed to evaluate the surface morphology and porosity growth. Also, the sol–gel films were characterized by Fourier-transform infrared (FTIR) spectroscopy. The optimum performance in terms of sensitivity, leaching, and response time was achieved using water: alkoxide ratio of 4:1, water acidity (HCl concentration) of 0.01 M, and ethanolic solution of Indole 0.01 mol L-1. The calibration plot was obtained within 0.01–6.00 μg mL−1 of oxalate with a detection limit value of 0.005 μg mL−1. Meanwhile, the prepared sensor exhibited excellent and acceptable RSDs for both inter-day and intra-day precision. The present sensor was used to measure oxalate in various samples and investigate the effects of the celeryʼs cooking time and the brewing duration of tea on oxalate content.

Fluorescence Naphthalene Cationic Schiff Base Reusable Paper as a Sensitive and Selective for Heavy Metals Cations Sensor: RSM, Optimization, and DFT Modelling.

Heavy metals are particularly damaging contaminants in the environment, and even trace concentrations represent a risk to human health due to their toxicity. To detect the heavy metals of Mn2+ and Co2+ ions, a novel selective reusable paper-based Fluorescence naked-eye sensor based on naphthalene cationic Schiff base (NCSB) was synthesized and confirmed using FT-IR, 1H-NMR, and MS tools. Based on a blue to colorless color change in the aqueous solution, the NCSB sensor is utilized to Mn2+ and Co2+ cations selectively among other metal ions (Fe2+, Cu2+, Mg2+, Ni2+, Zn2+, Cd2+, Hg2+, Pb2+, Sn2+ and Cr3+). In the aqueous medium, the NCSB sensor displayed high sensitivity, with limits of detection (LOD) values of 0.014 µM (14.08 nM) and 0.041 µM (41.47 nM) for Mn2+ and Co2+ cations, respectively. The paper-based sensor naked-eye detected Mn2+ and Co2+ cations in water at concentrations as low as 0.65 µM (65 nM) and 0.086 µM (86 nM), respectively. It was discovered that 5min of incubation time and a pH range of 7 to 11 were optimal for the complexation reaction between the Mn2+ and Co2+ ions and the NCSB sensor. Through a static quenching process, the interaction of the different metal ions with the Schiff base group in the NCSB molecule results in the development of a ground-state non-fluorescent complex. NCSB sensor was also successfully applied in analysis of Mn2+ and Co2+ in environmental water with good recoveries of 94.8-105.9%. The theoretical calculations based on density functional theory (DFT) studies are in support of experimental interpretations. The links between the input factors and the anticipated response were evaluated using the quadratic model of the response surface methodology (RSM) modeling.

Naked eye sensors for on-site pesticide detection: a review

Naked eye sensors for on-site pesticide detection: a review

Chromoionophoric probe imbued porous polymer monolith as a Three-in-One Solid-state Naked-eye sensor for the selective sensing and recovery of Ultra-trace Lead, Mercury, and cadmium ions from Industrial/Environmental samples

This article presents a simple, low-cost, eco-benign, and portable naked-eye solid-state sensor for the selective and sensitive colorimetric detection and recovery of ultra-trace concentrations of Pb(II), Hg(II) and Cd(II) from environmental/industrial sources. For solid-state sensing, an indigenously synthesized polymer monolith, i.e., poly(VAn-EGDMA), in-built with high surface area and interlinked meso-/macro-pore network serves as a template for the voluminous and uniform decoration of chromoionophoric probe molecules, i.e., 2-((1H-benzo[d]imidazol-2-yl)diazenyl)-4-methoxyphenol (IDMP) onto the monolith perforations via. direct immobilization technique. The structural and surface topological properties of poly(VAn-EGDMA) monolith and probe-loaded polymer, i.e., IDMP@poly(VAn-EGDMA) sensor, are characterized through FE-SEM, HR-TEM, EDAX, XPS, p-XRD, SAED, FT-IR, BET and BJH analysis. The IDMP@poly(VAn-EGDMA) sensor forms a selective/stable metal complex through visually imposing enhanced charge transfer color transitions from its original canary yellow to dark denim blue, brownish green and lapis blue for varying concentrations of Pb(II), Hg(II) and Cd(II), respectively. The sensor reusability has been tested by decomplexing the IDMP-Mn+ complex with 0.1 M HCl and repeating the sensor performance consistently for eight consecutive cycles. The IDMP@poly(VAn-EGDMA) sensor exhibits pH-dependent ion-sensing, demonstrating a wide linear response range for Pb(II) (0–200 ppb), Hg(II) (0–150 ppb), and Cd(II) (0–150 ppb), with a detection limit of 0.44, 0.56, and 0.52 ppb, respectively. The three-in-one sensor exhibits pH-dependent sequential selectivity, chemical/thermal stability, and data reliability/reproducibility, thus proving effective for on-spot sensing of various sources of contaminated samples.

Synthesis of two novel fluorescein appended dipyromethanes (DPMs): Naked-eye chemosensors for fluoride, acetate and phosphate anions

Two novel fluorescein based dipyromethane probes DPM1 and DPM2 were constructed from a simple and easily accessible fluorescein dye, and were fully characterized by means of standard spectroscopic techniques. Studies of the DPM1 and DPM2, investigated using UV–vis spectroscopy with different anions in CH3CN/DMSO, displayed selective colorimetric sensing towards fluoride, acetate and phosphate anions. Moreover, the fluorescence analysis was also accomplished with DPM1/DPM2, revealing the enhancement in the emission spectra of the fluoride, acetate and phosphate anions. From the studies, we noticed that the DPM1/DPM2 having spirolactone ring is non-fluorescent, which upon addition of the fluoride, phosphate and acetate, underwent ring-opening, resulting in the generation of strong fluorescence. The solid state images divulges that DPM1 shows green fluorescence and DPM2 displayed dark green fluorescence upon irradiating with UV-light of wavelength 254 nm. We infer that such types of naked eye sensors might reveal the potential applications in the selective and sensitive detection of fluoride/acetate/phosphate, and/or other biologically significant anions in nearby future.

Heterocycle-derived organosilatranes as naked eye sensors for Sn2+ ions and their potential inhibiting activity against HIV-1 protease via a computational approach

Nitrogen-based heterocycles are frequently present in active pharmaceutical products.

Correction: Heterocycle-derived organosilatranes as naked eye sensors for Sn2+ ions and their potential inhibiting activity against HIV-1 protease via a computational approach

Correction for ‘Heterocycle-derived organosilatranes as naked eye sensors for Sn2+ ions and their potential inhibiting activity against HIV-1 protease via a computational approach’ by Gurjaspreet Singh et al., New J. Chem., 2023, 47, 12608–12619, https://doi.org/10.1039/d3nj01484c.

Chromoionophore decorated renewable solid-state polymer monolithic naked eye sensor for the selective sensing and recovery of ultra-trace toxic cadmium ions in aqueous environment

In the present study, we report an intelligent solid-state chemosensor by embedding a chromo-ionophoric probe (MQP), i.e., (Z)− 4-methoxy-2-(quinolin-8-yldiazenyl)phenol) onto a bimodal meso-/macro-porous monolithic polymer template for the target-specific sensing of toxic cadmium(II) ions. The MQP probe anchored polymeric sensor material imposes rapid detection kinetics upon interaction with cadmium ions through concentration proportionate visual colour transitions from pale pink to red wine. The unique structural and surface properties of sensor material for the target-specific ion-sensing amidst matrix constituents have been analyzed using p-XRD, TEM-SAED, SEM-EDAX, XPS, FT-IR, and BET/BJH analysis. The analytical sensing performance of the MQP sensor material has been studied by optimizing various physicochemical parameters. For the efficient detection of ultra-trace Cd(II) ions, a solution pH range of 7.5–8.5, solution temperature of ≥ 30 °C, response kinetics of ≥ 25 s, and a linear response range of 0–300 µg/L, with excellent ion-selectivity/-sensitivity. The limit of detection and quantification for the MQP sensor material for Cd(II) ion-sensing is 0.32 and 1.10 µg/L, respectively. The proposed solid-state naked-eye sensor adopts a simple and low-cost fabrication procedure for continuously monitoring natural and industrial water samples. The sensor is reusable for up to eleven repeated cycles and exhibits excellent data reliability/reproducibility for the quantitative detection and recovery of ultra-trace Cd(II) ions.

High porosity silica aerogel thin film to monitoring vanadium: Synthesis, characterization and implementation

Sol–gel chemistry is a very unique method for constructing high-performance flexible sensors. Sol-gel silica matrices doped with a controlled amount of sensing agent (dopant) lead to the fabrication of suitable sensors. According to this knowledge, we decided to describe the development and performance characteristics of the sol-gel glasses with a nanoporous structure as novel naked eye sensor for fast detection of vanadium (V) based on physical entrapment of 4-(2-pyridylazo) resorcinol inside pores of the silica matrix obtained by sol–gel technology. To design a highly sensitive and selective thin film without dopant leaching, several sols were made with different water: alkoxide ratios and pHs. In summary, this study revealed that the characteristics of porous matrix as well as its average pore size could play significant roles in almost all critical parameters affecting the sensor performance, including sensitivity, selectivity, and response time. The FE-SEM technique equipped with EDAX was also employed to evaluate the surface morphology, porosity growth, and elemental identification of the thin films. The calibration plot was obtained within 0.004–3.000 μg mL−1 of vanadium (V) with a detection limit value of 0.0014 μg mL−1.

Simple chalcone-based chemosensor for colorimetric naked-eye detection of Al3+ and Cu2+ ions

A highly selective and sensitive Al3+ and Cu2+ ion receptor (4-(dimethylamino)-2′-hydroxychalcone) was designed, synthesized, and characterized via standard techniques such as FT-IR and 1H NMR spectroscopy and GC-MS. The solvatochromism and keto–enol tautomerism of the material were studied in various solvents. The selectivity of the receptor was investigated using UV–visible and fluorescence spectrophotometry. The receptor was found to behave as a highly selective colorimetric turn-on sensor for the Al3+ ion by changing color from yellow to red with an association constant of 1.62 × 104 M−1 and a low detection limit of 1.02 × 10−7, and as a turn-off sensor for Cu2+ with an association constant of 4.98 × 104 M−1 and detection limit of 9.62 × 10−7. The present investigation confirms that the receptor acts as a selective fluorescence probe for the detection of Cu2+ ions. The highlight of this work is that the receptor is effective as a naked-eye sensor for Al3+ and Cu2+ ions.

Highly Sensitive Colorimetric Naked-Eye Detection of HgII Using a Sacrificial Metal-Organic Framework.

This study has developed a specific, easy, and novel approach to designing a sacrificial metal-organic framework (MOF) that can detect and measure the amount of Hg2+ in aqueous and nonaqueous solutions using the naked eye. The functionalized [Zn(oba)(RL3)0.5]n·1.5DMF (TMU-59) provides the ability of simple visual assessment or colorimetric readout without sophisticated analytical equipment. Because of the special interaction with Hg2+, degradation of the structure of this unique MOF causes the solution to change color from colorless to a pink that is easily recognizable to the naked eye. The presence of a methyl group plays a major role in naked-eye detection by a qualitative sensor. Furthermore, this qualitative sensor data for the production of a simple, instant, and portable red, green, and blue (RGB)-based quantitative sensor were used to determine the concentration of Hg2+ in different specimens. As a turn-off fluorescence sensor, this unique structure is also capable of detecting Hg2+ at very low concentrations (the limit of detection is 0.16 ppb). To the best of our knowledge, TMU-59 is the first MOF-based naked-eye sensor that can successfully and specifically display the presence of Hg2+ through a major color change.

Radiochromic Hydrogen-Bonded Organic Frameworks for X-ray Detection.

Porous materials have been investigated as efficient photochromic platforms for detecting hazardous radiation, while the utilization of hydrogen bonded organic frameworks (HOFs) in this field has remained intact. Herein, two HOFs were synthesized through self-assembly of tetratopic viologen ligand and formic acid (PFC-25, PFC-26), as a new class of "all-organic" radiochromic smart material, opening a gate for HOFs in this field. PFC-26 is active upon both X-ray and UV irradiation, while PFC-25 is only active upon X-ray irradiation. The same building block yet different radiochromic behaviors of PFC-25 and PFC-26 allow us to gain a deep mechanistic understanding of the factors that control the detection specificity. Theoretical and experimental studies reveal that the degree of π-conjugation of viologen ligand is highly related to the threshold energy of triggering a charge transfer, therefore being a vital factor for the particularity of radiochromic materials. Thanks to its convenient processibility, nanoparticle size, and UV silence, PFC-25 can be further fabricated into a portable naked-eye sensor for X-ray detection, which shows obvious color change with the merits of high transmittance contrast, good sensitivity (reproducible dose threshold of 3.5 Gy), and excellent stability. The work exhibits the promising practical potentials of HOF materials in photochromic technology.

Solution Blowing Spinning Technology towards Green Development of Urea Sensor Nanofibers Immobilized with Hydrazone Probe.

Cellulose has been one of the most widespread materials due to its renewability, excellent mechanical properties, biodegradability, high absorption ability, biocompatibility and cheapness. Novel, simple and green colorimetric fibrous film sensor was developed by immobilization of urease enzyme (U) and tricyanofuran hydrazone (TCFH) molecular probe onto cellulose nanofibers (CNF). Cellulose acetate nanofibers (CANF) were firstly prepared from cellulose acetate using the simple, green and low cost solution blowing spinning technology. The produced CANF was exposed to deacetylation to introduce CNF, which was then treated with a mixture of TCFH and urease enzyme to introduce CNF-TCFH-U nanofibrous biosensor. CNF were reinforced with tricyanofuran hyrazone molecular probe and urease enzyme was encapsulated into calcium alginate biopolymer to establish a biocomposite film. This CNF-TCFH-U naked-eye sensor can be applied as a disposable urea detector. CNF demonstrated a large surface area and was utilized as a carrier for TCFH, which is the spectroscopic probe and urease is a catalyst. The biochromic CNF-TCFH-U nanofibrous biosensor responds to an aqueous medium of urea via a visible color signal changing from off-white to dark pink. The morphology of the generated CNF and CNF-TCFH-U nanofibrous films were characterized by different analytical tools, including energy-dispersive X-ray patterns (EDX), polarizing optical microscope (POM), Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM). SEM images of CNF-TCFH-U nanofibers demonstrated diameters between 800 nm and 2.5 μm forming a nonwoven fabric with a homogeneous distribution of TCFH/urease-containing calcium alginate nanoparticles on the surface of CNF. The morphology of the cross-linked calcium alginate nanoparticles was also explored using transmission electron microscopy (TEM) to indicate an average diameter of 56–66 nm. The photophysical performance of the prepared CNF-TCFH-U was also studied by CIE Lab coloration parameters. The nanofibrous film biosensor displayed a relatively rapid response time (5–10 min) and a limit of detection as low as 200 ppm and as high as 1400 ppm. Tricyanofuran hydrazone is a pH-responsive disperse dye comprising a hydrazone detection group. Determination of urea occurs through a proton transfer from the hydrazone group to the generated ammonia from the reaction of urea with urease.