Naked-eye Sensor Research Articles

Carbon dots as naked eye sensors.

Optical sensors are always fascinating for chemists due to their selectivity, sensitivity, robustness and cost-effective nature. Moreover, these sensors provide the facility of onsite detection without employing any instrumental technique. A number of such visual sensors including carbon dots (CDs) have been reported for selective detection of many ionic and molecular species. This review elaborates the utilization of CDs as colorimetric sensors. Carbon dots (CDs) are being synthesized from a large number of natural and synthetic carbon source materials using a variety of methods. CDs can also be tuned chemically by doping, to impart the desired sensing properties. Therefore, the development of CDs with selective sensing properties enables extremely low detection limits and has thus gained substantial attention.

Synthesis, spectrophotometric and DFT studies of new Triazole Schiff bases as selective naked-eye sensors for acetate anion

ABSTRACT Selective anion sensors can be used in the colourimetric detection of certain anions. In the present study, two new 1,2,4-triazole derivatives containing thiol group and azo moiety 3a (nitrile derivative) and 3b (methoxy derivative) were synthesised by condensation of 4-(4-amino-5-mercapto-4 H-1,2,4-triazol-3-yl)phenol (1) and aromatic aldehydes containing azo groups 2a and 2b under acidic conditions. The nitrile derivative 3a acted as a selective naked-eye sensor for acetate anions in a mixture of dimethyl sulphoxide and water (9:1 by volume). It interacted with the acetate anions in a 1:2 stoichiometry with strong positive cooperativity and an overall association constant (β12) exceeding 2 × 108 M−2. The detection limit of 3a towards the acetate anion was found to be 0.66 × 10−5 M. The DFT studies showed that both 3a and 3b were similar in their electronic properties, but the internal charge transfer for 3a was responsible for the positive response to acetate anions.

Magnetic bead-enzyme assemble for triple-parameter telomerase detection at single-cell level.

In this work, we developed a triple-parameter strategy for the detection of telomerase activity from cancer cells and urine samples. This strategy was developed based on magnetic bead-enzyme hybrids combined with fluorescence analysis, colorimetric assay, or adenosine triphosphate (ATP) meter as readout. The application of magnetic bead-enzyme hybrids has the advantages of magnetic separation and signal amplification. These detection methods can be used individually or in combination to achieve the optimal sensing performance and make the results more convincing. Among them, the ATP meter with portable size had easy operation and low cost, and this response strategy provided a higher sensitivity at the single-cell level. The designed strategy was suitable as naked-eye sensor and point-of-care testing (POCT) for rapid assaying of telomerase activity. Graphical abstract Magnetic bead-enzyme assemble for triple-parameter telomerase detection.

Nitrogen-doped carbon dot threads as a "turn-off" fluorescent probe for permanganate ions and its hydrogel hybrid as a naked eye sensor for gold(III) ions.

Highly fluorescent nitrogen-doped carbon dot (NCD) threads were synthesized via simple pyrolysis of citric acid, p-hydroxybenzoic acid, and ammonia. The NCDs show excitation-independent behavior with maximum excitation and emission wavelengths of 350nm and 435nm, respectively. The developed probe was used as a turn-off fluorescent sensor for the selective and sensitive determination of permanganate ions in aqueous media. The probe's hydrogel hybrid displayed a beautiful purple color demonstrating its potential as a naked eye sensor for gold detection. The ratiometric sensor exhibited excellent selectivity towards permanganate ions over 27 other ions with a linear range of 510nM to 2μM, a detection limit of 170nM, and a linear regression value (R2) of 0.9944. Similarly, the linear range and limit of detection for gold ions was 3.89-20μM and 1.285μM, respectively. The synthesized NCDs were also used as a fluorescent ink as well as a naked eye marker in association with a gold solution demonstrating its potential forensic and anti-counterfeiting applications. Graphical abstract.

Uniform and Easy-To-Prepare Glycopolymer-Brush Interface for Rapid Protein (Anti-)Adhesion Sensing.

Glycopolymers have emerged as powerful and versatile glycan analogues for the investigation of cellular signal transduction. In this study, a layer of the glycopolymer-brush (GlyB) interface was functionalized on the surface of gold substrates. In order to enhance the capability and accessibility of this transducer interface, a combined protocol of copper(0)-mediated living radical polymerization (Cu(0)-LRP) with subsequent "CuAAC" click reaction was utilized to synthesize a set of novel glycopolymer precursors with a tunable scaffold structure and pyranose ligands. The resulting glycopolymer exhibited a fine-tuned molecular weight with a minor dispersity of 1.27. Through surface plasmon resonance (SPR) analysis, various GlyB interfaces exhibiting different saccharide moieties (glucose, mannose, and galactose) were examined to study their adhesion or antiadhesion potential toward three types of proteins, concanavalin A, bovine serum albumin, and peanut agglutinin (PNA). The strong affinity between poly(galactose) and PNA was further employed to construct a proof-of-concept aggregation-mediated sensing system. This minimal naked-eye sensor that consisted of only two substances, namely, gold nanoparticles and glycopolymers, was characterized and tested for its potential in protein quantification.

Sensitive Naked‐eye and Fluorescence Determination of Acetylcholinesterase Activity using Cu/Ag Nanoclusters Based on Inner Filter Effect

AbstractIn this work, a novel naked eye and fluorescence sensor for acetylcholinesterase (AChE) determination based on copper/silver nanoclusters (Cu/Ag NCs) was developed. L‐Histidine protected Cu/Ag NCs were prepared and exhibited superior properties compared with copper nanoclusters, with the quantum yield increased from 4.3% to 13.2%. The fluorescence of Cu/Ag NCs can be easily quenched by 2‐nitro‐5‐thiobenzoate anion (TNB) owing to the inner filter effect. TNB is the product between 5′‐Dithiobis‐(2‐nitrobenzoic acid) (DTNB) and thiols. However, AChE can specially catalyze acetylthiocholine (ATCh) to hydrolyze and release biothiols (TCh). Based on this, the determination of AChE was achieved by introducing DTNB. A naked eye sensor was also constructed owing to the color change.

Size-tunable Au@Ag nanoparticles for colorimetric and SERS dual-mode sensing of palmatine in traditional Chinese medicine

Palmatine is a protoberberine alkaloid separated from several plants and application as an anti-inflammatory and antibacterial agent in the therapy of gastrointestinal and genitourinary disorder. Thus, the fast quantification of palmatine is important in clinic medical assays. Herein, we report simple, fast and sensitive colorimetric visualization and surface-enhanced Raman spectroscopy (SERS) dual-mode detection of palmatine basing on bimetallic size tunable silver shell capped gold nanoparticles (Au@Ag NPs). Interesting, the best signals output for dual-mode sensing of palmatine were both 5 nm Ag shell thickness of Au@Ag NPs. Meanwhile, we found that the addition of NaHSO4 significantly improves the aggregating sensitivity of Au@Ag NPs to trace palmatine. Upon exposure to 0.1 μM level palmatine, NaHSO4-optimized Au@Ag NPs solution exhibits a highly sensitive color change from orange to green and rapid aggregation kinetics within the initial 5 min, which can directly be seen with the naked eye and monitored by UV–vis absorbance spectra. In addition, we measured palmatine by SERS with the excellent enhancement effect of Au@Ag NPs for further increase the sensitivity and selectivity. More importantly, other protoberberine alkaloids do not interfere with this dual-mode sensor due to the different interaction force between Au@Ag NPs and these alkaloids, and the applicability of the sensor is well demonstrated in real samples with satisfactory results. This provide a fast and simple assay for the rapid detection of palmatine in traditional Chinese medicine, the limit of detection (LOD) is 0.13 μM by the naked eye and 0.10 μM by UV–vis spectroscopy. Therefore, the size-tunable of NaHSO4-optimized Au@Ag NPs can be used not only as a naked-eye sensor of palmatine, but also as a highly selective SERS probe.

Synthesis, Photo-, and Ionochromic Properties of Indolyl(thienyl)maleimides with Terpyridine Receptor

Indolyl(thienyl)maleimides with terpyridine receptor in the bridge part have been synthesized. Irradiation of their toluene solutions with light at λ = 436 nm has led to the formation of cyclic isomers. The reverse ring opening reaction has occurred during the photolysis with visible light (λ > 500 nm). 1-(4-([2,2′:6′,2″-Terpyridin]-4′-yl)phenyl)derivatives have exhibited the properties of chromogenic naked-eye sensors to Fe2+ cations in acetonitrile solution, changing the solution color from bright-orange to red.

Metal ion chemosensors based on diaza-18-crown-6 coupling with azobenzene dye.

Novel naked-eye cation-selective chemosensors were developed from derivatives of diaza-18-crown-6 bearing one or two azobenzenes functionalized with o-acetic acid or p-nitro groups. The chromogenic acid and nitro derivatives exhibited solvatochromic effects with a majority of quinone-hydrazone tautomer in DMSO. The study of sensing properties of all molecules towards several metal ions showed that the one and two nitro-bearing N1 and N2 derivatives responded selectively to Cr3+ in MeCN with a color change from pink to colorless. They also showed selectivity for Hg2+ in DMSO with a color change from purple to light yellow. The detection limit of N1 and N2 that render visual difference to the naked eye are 0.21 ppm and 0.31 ppm for Cr3+ in MeCN, and 1.20 ppm and 1.00 ppm for Hg2+ in DMSO, while that obtained from 3σ method are 0.08 ppm and 0.03 ppm for Hg2+ in DMSO. These results demonstrate a potential use of p-nitro azobenzene diaza-18-crown-6 as naked-eye sensors, notably for Cr3+ that brings acute toxic to aquatic life.

A novel 1,8-naphthalimide as highly selective naked-eye and ratiometric fluorescent sensor for detection of Hg2+ ions

A novel colorimetric and ratiometric fluorescent chemosensor, 2-(2-mercaptophenyl)-1H-benzo[de]isoquinoline-1,3-(2H)-dione (L3) is reported for Hg2+ ions. The selective binding of Hg2+ to L3 afforded new absorbance and fluorescence peaks at 438 nm and 480 nm, in addition to the existing bands of L3 at 332 nm and 376 nm. It also showed apparent colour change from colourless to yellowish green and weak fluorescent to bright yellowish green strong fluorescent due to selective binding of Hg2+ ion. The sensor forms a 1:1 stoichiometry with high binding constants (3.89 × 104 mol−1L) and limit of detection 1.74 × 10-8 M with high selectivity and sensitivity towards Hg2+ in the presence of other interfering metal ions. More importantly, it has good practicability in environmental water sample. The outcome of photo-physical experiment has also been in good accordance with the time-resolved fluorescence life decays and the density functional theory (DFT) estimations. Moreover, the L3-Hg2+ solution displayed high colorimetric and fluorimetric reversibility via the addition of KI. This reversibility in fluorescence showed potential applicability of chemosensor L3 as “on–off–on” naked eye sensor.

A simple sensor based on 1,8-naphthalimide with large Stokes shift for detection of hypochlorous acid in living cells.

Hypochlorous acid (HOCl), one of the most reactive and deleterious reactive oxygen species (ROS), plays a vital role in many pathological and physiological processes. However, as a result of the highly reactive and diffusible nature of HOCl, its uncontrolled production may lead to an adverse effect on host physiology. Because of its biological importance, many efforts have been focused on developing selective fluorescent probes to image HOCl. However, it is still challenging to design a fluorescent probe with exclusive selectivity towards HOCl. In this study, a novel fluorescent probe for HOCl, Probe 1 was rationally designed based on 1,8-naphthalimide. As the concentration of HOCl increased, the fluorescence intensity of the probe gradually decreased, and the solution color changed from yellow-green to colorless, indicating this is a “naked-eye sensor”. Probe 1 has a large Stokes shift (120 nm), which can effectively avoid fluorescence self-absorption. In addition, Probe 1 shows excellent selectivity to HOCl among different ions including common ROS, high sensitivity, fast response (<2 min), high fluorescence quantum yield (Φ = 0.93) and low detection limit (0.237 μM). Finally, the imaging results in HeLa cells showed that the probe could be used for the detection of exogenous and endogenous HOCl, and proved the potential of the probe as a biosensor for the detection of HOCl.

Chemical traffic light: A self-calibrating naked-eye sensor for fluoride

We report a low-cost sensing platform for effective naked-eye detection of fluoride ion in aqueous media. The sensor is based on silicon complex of 5,10,15-tritolylcorrole (SiTTCorr) deposited on paper support and designed in a particular way that permits it to perform in a unique sensing event an internal sensor self-calibration and subsequent analysis of fluoride ion in a concentration range from 20 [Formula: see text]g/L to 200 mg/L with a LOD 9 [Formula: see text]g/L, much lower than the WHO guideline value of 1.5 mg/L for fluoride in drinking water. The influence of tetradodecylammonium chloride (TDACl) anion exchanger addition to the performance of SiTTCorr-based sensors was studied and the sensor with optimal ionophore: exchanger [Formula: see text] 2:1 ratio demonstrated the highest sensitivity. The evident color variation of SiTTCorr-based optode from dark pink to intense green occurred upon addition of increasing concentrations of fluoride. A smartphone application equipped with home-written color intensity analysis software as a detector of developed sensor output permitted fluoride content quantification in bottled water and toothpaste samples. Moreover, since at the quantification step the SiTTCorr color variation was significant for the red component of visible light and increase of fluoride content evidently changed this color from red to yellow and then to green, the developed optode was compared to a kind of chemical traffic light, able to detect the presence of fluoride in permitted, borderline or dangerous concentrations, respectively.

The naked-eye NH3 sensor based on fluorinated graphene

Graphene has aroused continual and tremendous interest in gas sensing applications because of its unique properties. However, the graphene-based sensors still meet limitations such as inconvenient device fabrication, sustained power supply, specific measuring equipment, etc. Here, we find that fluorinated graphene (FG) shows an obvious color change (from white to dark yellow) in the presence of NH3 which can be observed directly by the naked eye. PL measurement shows that the sensitivity of color change can reach a high value of ca. 4.05% ppm−1. The density functional theory calculations reveal that the F atoms on FG increase the adsorption ability and charge transfer of NH3 molecules, resulting in the efficient color change. This work develops a naked-eye sensor which needs no device fabrication, power supply or measuring equipment, thus, can be potentially used to manufacture a cheap, sensitive and miniaturized NH3 sensor.

Ultrasensitive Colorimetric and Ratiometric Detection of Cu2+: Acid-Base Properties, Complexation, and Binding Studies.

Herein, we report the synthesis and characterization of a chemosensor, 5-(diethylamino)-2-(2,3-dihydro-1H-perimidin-2-yl)phenol (HL), synthesized from a condensation between 4-(diethylamino)salicylaldehyde and 1,8-diaminonaphthalene. Upon investigation of the sensing properties of HL, it was found that this sensor may be employed for simple yet efficient detection of Cu2+ in aqueous methanol solutions. The selective and ratiometric response to Cu2+ yielded an outstandingly low limit of detection of 3.7 nM by spectrophotometry and is also useful as a naked-eye sensor from 2.5 μM. The system was studied by spectrophotometric pH titrations to determine Cu2+ binding constants and complex speciation. Binding of Cu2+ to HL occurs in 1:1 stoichiometry, in good agreement with high-resolution electrospray ionization mass spectrometry (ESI-HRMS) results, Cu2+ titrations, and Job’s plot experiments, while the coordination geometry was tentatively assigned as square pyramidal by spectroscopic studies.

A rhodamine/copper complex as selective and naked-eye sensor for arginine

A rhodamine/copper complex as selective and naked-eye sensor for arginine

Spherical nanocellulose-based highly efficient and rapid multifunctional naked-eye Cr(VI) ion chemosensor and adsorbent with mild antimicrobial properties

To meet the challenges of sustainable growth it is imperative to develop smart multifunctional materials with high cost-effectiveness and positive environmental impact. In this study we report a spherical nanocellulose (SNC)-based multifunctional material, SNC-Chemosensor, which acts as naked-eye sensor, rapid adsorbent and antimicrobial agent. It showed fluorescent quenching properties for Cr(VI) ions, which was studied under different Cr(VI) ions concentrations. At extremely low concentration a high fluorescent intensity was observed. Detection limits of Cr(VI) ions was obtained to be less than 30 ppb from 100 ppm which is well below their maximum contamination standard in drinking water. SNC-Chemosensor also shows rapid Cr(VI) ions adsorption from their aqueous solutions even at pH 7.0 contrary to that is reported in literature. Also, SNC-Chemosensor can be regenerated by using 0.1 N NaOH as a desorbing agent. SNC-Chemosensor has mild biocidal activity as observed against the representative microorganisms Gram (+), S. aureus, Gram (−), E. coli and A. niger.

Design and one-pot synthesis of a novel pyrene based fluorescent sensor for selective “turn on”, naked eye detection of Ni2+ ions, and live cell imaging

A novel pyrene based fluorescent probe, 4-phenyl-2-(pyren-1-yl)-1,8-naphthyridine (Pyr-1), was designed and synthesized through tandem cyclization of pyrenealdehyde, amine and alkyne in the presence of quinolinium modified β-CD (Qun-β-CD) in water. Pyr-1 was characterized by 1H NMR, 13C NMR and ESI–MS spectra and was used as a selective “turn-on” and naked eye sensor for Ni2+ ion over other cations. The localized frontier molecular orbitals (DFT studies) and the solvent polarity dependent photoluminescence characteristics strongly validate the presence of photo induced electron transfer from pyrene to 1,8-naphthyridine unit in Pyr-1. Upon Ni2+ addition, the fluorescence was shifted to 450 nm due to the formation of a square planar 2:1 complex of pyr-1 with Ni2+ at room temperature even in the presence of other interfering ions such as Cd2+ and Hg2+. The resultant excimer emission and conquest of photoinduced electron transfer (PET) from pyrene moiety to the 1,8-naphthyridine part is supported by DFT studies. The sensor also exhibited very low cytotoxicity and strong fluorescence emission in living cells, indicating its potential applicability as a novel chemosensor for selective detection of Ni2+ ions in biological environment also.

Plasmonic and fluorescent sensors of metal ions in water based on biogenic gold nanoparticles

Gold nanoparticles (AuNPs) were synthesized using a rapid, single step, and completely green biosynthetic method employing aqueous Citrus paradisi (grapefruit) extract, which was used as both the reducing and capping agent. Au(III) ions were rapidly reduced by the aqueous grapefruit extract, leading to the formation of highly stable and crystalline colloidal AuNPs, confirmed by the surface plasmon resonance (SPR) peak centered at 544 nm in the UV–Vis spectra. Biogenic AuNPs have been evaluated as plasmonic, fluorescent and naked-eye sensors of Pb2+, Ca2+, Hg2+, Zn2+ and Cu2+ ions in aqueous media, with a good performance and selectivity. Of the three methods used for metal ions sensing, fluorescent sensors shows better results, specifically with Ca2+, Cu2+ and Pb2+. Copper was detected by both plasmonic and fluorescent methods.

Design and synthesis of 1,4-benzothiazine hydrazide as selective and sensitive colorimetric and turn-on fluorometric sensor for Hg2+ detection in aqueous medium

A highly colorimetric and fluorimetric chemosensor, 3-oxo-[1,4]-benzothiazin-2-ylidene acetohydrazide (L2) is reported for the mercury detection. In HEPES-buffered solution (CH3CN: H2O, 1:2, v/v, pH 7.2), L2 showed a characteristic absorption peak at 340 nm, after addition of Hg2+ induces color change from light yellow to purple with significantly enhancement in absorbance at 340 nm and a new band centered at 550 nm with red-shift of 110 nm. Furthermore, the L2 exhibited high sensitivity and selectivity overall emission change of more than 100-fold fluorescence intensity enhancement towards Hg2+ ion with a 1:1 binding stoichiometry (1.938 × 103 M−1 binding constant within detection limit as low as 5.4 × 10−8 M) in water samples. Apart from this, theoretical elucidation of the experimental outcome has also been supported by applying density functional theory (DFT) to the ligand and the complex. In situ, the solution of L2 + Hg2+ complex displayed high reversibility by I− through Hg2+ displacement approach. This reversibility in fluorescence suggested that the promising applicability of chemosensor as “off–on–off” naked eye sensor and practical applicability of L2 as an INHIBIT logic gate based on the emission changes with the inputs of Hg2+ and I− was investigated.

Highly sensitive naked eye detection of Iron (III) and H2O2 using poly-(tannic acid) (PTA) coated Au nanocomposite

In the present study, we present a room temperature-, one-pot method for the synthesis of functional poly (tannic acid) (PTA)-based core@shell nanocomposites (core@PTA). The addition of tannic acid (TA) to gold (Au) salt solutions at mildly alkaline pH induced reduction of the metal salts to Au nanoparticles (NPs) while TA was oxidized and self-polymerized before encapsulating the AuNPs to form Au@PTA. Through the use of coordination chemistry, the synthesized Au@PTA was utilized as a naked eye sensor for iron (III) ions and H2O2. In the presence of Fe3+, Au@PTA aggregated and resulted in visible color change, showing high selectivity towards Fe3+ with visual detection limit of 20 μM. Extension of the approach is used to detect H2O2 with visual detection limit of 0.4 μM. Observation of the UV–vis spectra after the addition of analytes for the two detection systems revealed an additional peak in the H2O2 detection system at ∼ 650 nm. This is due to the presence of “wire-like” oligomer structures in the H2O2 detection system as opposed to nanocomposite aggregation observed in the former system.