Fluorescent Test Paper Research Articles

Naked eye colorimetric multifunctional sensing of nitrobenzene, Cr(VI) and Fe(III) with a new green emission Ag6S6 multi-metal-cluster

With the increasing need of detecting chemical pollutants, modern analytical instruments show many advantages but also have some common drawbacks such as high operational cost and tedious pretreatment procedures. Thus, developing a fast, simple, and convenient colorimetric sensing system is a challenge. Here, a new Ag6S6 cluster-based coordination compound formulated as Ag6(dmpymt)6 (1) (Hdmpymt = 4,6-dimethylpyrimidine-2-thione) was synthesized under solvothermal condition and displayed apparently green luminescence emission and good stabilities in water and some organic solvents. Fluorescence experiments illustrated that 1 displayed efficiently naked eye colorimetric sensing for nitrobenzene (NB), Cr(VI), and Fe(III) ions by fluorescence quenching in the emulsions. The possible sensing mechanisms are attributed to the competitive absorption of excitation wavelength energy between the analytes and the compound 1. Furthermore, the fluorescent test papers of 1 were prepared as well and showed efficient, convenient, and easily recycled characteristics, presenting a potential sensing application for the environmental concerns.

Ratiometric fluorescent test paper based on silicon nanocrystals and carbon dots for sensitive determination of mercuric ions.

Classical dye absorption-based pH test papers are widely used to measure the degree of acidity of media for quantification or semi-quantification by the observation of the naked eye on the variation of colour. However, it remains a challenging task to extend portable and cheap methods to a wide range of analytes for accurate quantification. Here, we report a dosage-sensitive test paper for the assay of mercury ions (Hg2+) with wide colour evolution. The ratiometric fluorescent probe was prepared by mixing blue-emission silicon nanocrystals (Si NCs) and red-emission carbon dots (r-CDs). The Si NCs serve as the reaction site and the r-CDs as the internal reference. Upon the addition of Hg2+, the blue fluorescence of the Si NCs was quenched, while the red fluorescence of the r-CDs remained constant, resulting in the consecutive fluorescence colour changes from blue to orange red. The probe demonstrates high selectivity and sensitivity of the visualization assay of Hg2+ with a detection limit of 7.63 nM. Moreover, we printed the ratiometric fluorescence probe result onto a piece of filter paper to prepare a test paper, which represents an on-site, sensitive, rapid and cost-effective method for the visual determination of Hg2+ by the naked eye.

A multi-chemosensor based on Zn-MOF: Ratio-dependent color transition detection of Hg (II) and highly sensitive sensor of Cr (VI)

Accurate and visual methods aimed to pollution monitoring were insistent demands of scientists. For this purpose, a novel metal-organic framework (MOF), formulated as [Zn(tpbpc)2]·solvent (Htpbpc = 4′-[4,2′;6′,4′′]-terpyridin-4′-yl-biphenyl-4-carboxylic acid), has been isolated and structurally characterized; it exhibits unique (2,8)-connected 8T20 (MOF.ttd) topology with binuclear [Zn2(COO)4N4]n secondary building units (SBUs) as 8-c nodes and tpbpc− ligands as 2-c nodes. Strikingly, this is the first multi-responsive MOFs fluorescent sensor for simultaneously detecting Hg2+, CrO42− and Cr2O72− ions with high sensitivity and low detection limits in aqueous solution. Meanwhile, the fluorescent sensor for Hg2+ exhibits a color transition in seconds which can be observed by the naked eyes. What is more, the chemosensor based on the Zn-MOF for detecting Cr(VI) ions possesses a very low detection down to 10−8 M, which is the lowest detection limit among all reported up to date. Importantly, the luminescence can be fast regenerated and its sensing ability can be recycled for more than six times. In addition, the simple MOF-based fluorescent test paper was successfully prepared, which provided a reliable and visual detection of Hg2+, CrO42− and Cr2O72− in practical application.

Semi-quantitative and visual assay of copper ions by fluorescent test paper constructed with dual-emission carbon dots.

A novel, simple and effective dual-emissive fluorescent probe for the sensitive and selective detection of Cu(ii) has been developed by mixing blue carbon dots and orange carbon dots, with a sensitive detection limit of 7.31 nM. The blue fluorescence can be selectively quenched by Cu(ii), while the orange fluorescence is a internal reference, resulting in a distinguishable fluorescence color change from blue to orange under a UV lamp. Meanwhile, its as-prepared text paper provides a convenient and simple approach for the visual detection of Cu(ii) and successfully applied in real water samples, with a dose-discerning ability as low as 50 nM. The methodology reported here opens a novel pathway toward the real applications of fluorescent test papers.

Highly selective, rapid-functioning and sensitive fluorescent test paper based on graphene quantum dots for on-line detection of metal ions

In this study, test papers based on N-doped graphene quantum dots and graphene quantum dots were designed and prepared.

Synthesis of Dicyanovinyl-Substituted 1-(2-Pyridyl)pyrazoles: Design of a Fluorescent Chemosensor for Selective Recognition of Cyanide.

A fluorescence "turn-off" probe has been designed and successfully applied to detect cyanide (CN-) based on a Michael-type nucleophilic addition reaction and intramolecular charge transfer (ICT) mechanism. For this research, a family of 3-aryl-4-(2,2-dicyanovinyl)-1-(2-pyridinyl)pyrazoles as donor-π-acceptor (D-π-A) systems have been synthesized in 58-66% overall yield, by a three-step synthesis sequence starting from p-substituted acetophenones. The substituted p-methoxyphenyl showed good fluorescence emission and large Stokes shifts in different solvents due to its greater ICT. Likewise, this probe evidenced high selectivity and sensitivity and fast recognition for CN- with a detection limit of 6.8 μM. HRMS analysis, 1H NMR titration experiments, and TD-DFT calculations were performed to confirm the mechanism of detection and fluorescence properties of the chemodosimeter of CN-. Additionally, fluorescent test paper was conveniently used to detect cyanide in aqueous solution.

Grey level replaces fluorescent intensity: Fluorescent paper sensor based on ZnO nanoparticles for quantitative detection of Cu2+ without photoluminescence spectrometer

This work uses ZnO nanoparticles as the probe and a case, proving that the grey level can replace fluorescent intensity to realize a quantitative detection function of paper-based Cu2+ sensor. Portable Cu2+ test papers were obtained through dipping filter papers in as-prepared ZnO sol possessing the Cu2+ quenching property. Based on grey level which is obtained through ordinary digital camera and computer, the detection function of the fabricated Cu2+ test paper is extended from qualitative detection relied on naked eyes to quantitative detection whose detection range is calculated to be 10–1000μM. The fabricated test papers also could resist the interruption of some competing ions and is a potential candidate for portable Cu2+ detection device with quantitative function. Since the strategy of replacing fluorescence intensity by grey level is based on the map relationship between the fluorescence intensity and the digital signal (grey level), it is promising to be applied to other fluorescent test papers to gain quantitative test papers aimed at corresponding chemicals. At the same time, the mechanism of Cu2+-induced fluorescence quenching was also investigated by fluorescence lifetime, UV–vis spectra, and photoluminescence spectra. And a static quenching mechanism based on the non-fluorescence complex formed by Cu2+ and Ox− is brought up.

Profuse color-evolution-based fluorescent test paper sensor for rapid and visual monitoring of endogenous Cu2+ in human urine

The fluorescent paper for colorimetric detection of metal ions has been widely fabricated using various sensing probes, but it still remains an elusive task to design a test paper with multicolor variation with target dosages for accurate determination. Herein, we report a profuse color-evolution-based fluorescent test paper sensor for rapid and visual monitoring of Cu2+ in human urine by printing tricolor probe onto filter paper. The tricolor probe consists of blue-emission carbon dots (bCDs), green-emission quantum dots (gQDs) and red-emission quantum dots (rQDs), which is based on the principle that the fluorescence of gQDs and rQDs are simultaneously quenched by Cu2+, whereas the bCDs as the photostable internal standard is insensitive to Cu2+. Upon the addition of different amounts of Cu2+, the ratiometric fluorescence intensity of the tricolor probe continuously varied, leading to color changes from shallow pink to blue with a detection limit of 1.3nM. When the tricolor probe solution was printed onto a sheet of filter paper, as-obtained test paper displayed a more profuse color evolution from shallow pink to light salmon to dark orange to olive drab to dark olive green to slate blue to royal blue and to final dark blue with the increase of Cu2+ concentration compared with dual-color probe-based test paper, and dosage scale as low as 6.0nM was clearly discriminated. The sensing test paper is simple, rapid and inexpensive, and serves as a visual platform for ultrasensitive monitoring of endogenous Cu2+ in human urine.

Dual-Colored Carbon Dot Ratiometric Fluorescent Test Paper Based on a Specific Spectral Energy Transfer for Semiquantitative Assay of Copper Ions.

Classical pH test papers are widely used to measure the acid-base degree of media in a qualitative or semiquantitative manner. However, the extension of portable and inexpensive methods to a wide range of analytes so as to eliminate the tediousness of instrumental assays remains unsuccessful. Here, we report a novel kind of dual-colored carbon dot (CD) ratiometric fluorescent test paper for the semiquantitative assay of copper ions (Cu2+) by a dose-sensitive color evolution. The preparation of the test paper is based on the following two interesting findings: on the one hand, residual p-phenylenediamine at the surface of as-synthesized red CDs (r-CDs) efficiently binds Cu2+ ions to produce a strong visible absorption that overlaps the emission of blue CDs (b-CDs); on the other hand, the Cu2+ ions render the adsorption of small b-CDs onto the surface of larger r-CDs through their dual-coordinating interactions with the surface ligands of both r-CDs and b-CDs. These two mechanisms lead to a specific spectral energy transfer to quench the fluorescence of b-CDs with a sensitive detection limit of 8.82 nM Cu2+, whereas the red fluorescence of r-CDs is unaffected as a stable internal standard. Ratiometric fluorescent test papers have been prepared using a mixture of r-CDs and b-CDs (1:7) as ink by jetprinting on a piece of paper. With the addition of Cu2+ ions, the blue test paper produces a consecutive wide-colored evolution from blue to orange-red, with a dose-discerning ability as low as 25 nM.

A Water‐Stable Dual‐Channel Luminescence Sensor for UO22+ Ions Based on an Anionic Terbium(III) Metal–Organic Framework

A stable 3D TbIII -based metal-organic framework [Tb(BPDC)2 ]⋅(CH3 )2 NH2 (DUT-101) was synthesized, and it is the first efficient dual-channel luminescence sensor for aqueous UO22+ ions. DUT-101 contains an anionic three-dimensional framework and protonated dimethylamine molecules embedded within the channels. The intense green emission of DUT-101 could be highly selectively and sensitively quenched by UO22+ ions even in the presence of other competing metal ions. A possible sensing mechanism was proposed based on both suppression of luminescence resonance energy transfer and enhancement of intermolecular electron transfer. Furthermore, visual green fluorescent test papers based on DUT-101 were fabricated and could be used to discriminate UO22+ ions among various metal ions.

Facile preparation of fluorescent Au nanoclusters-based test papers for recyclable detection of Hg2+ and Pb2+

A simple, portable and recyclable method has been developed for on-site and real-time detection of Hg2+ and Pb2+ by naked eyes by using Au nanoclusters-based test paper as the fluorescent sensor. The high specificity of Hg2+ and Pb2+ to Au nanoclusters provided excellent selectivity over 15 kinds of other ions. Interestingly, an apparent fluorescent quenching of the test paper was shown when exposed to Hg2+, while a significant fluorescent enhancement was observed in the presence of Pb2+, which could be attributed to aggregation-induced fluorescence quenching and enhancement. The limit of detection for Hg2+ and Pb2+ by naked eyes was 5μM and 50μM, respectively. More importantly, the cyclic utilization of the test paper was achieved by immersing the test papers into ethylenediamine tetraacetic acid to recover the fluorescence of the test paper, which contributed to reducing resource consumption. Otherwise, the GSH-AuNCs test paper was competent for a practical application in environmental water samples with strong anti-interference ability.

A single dual-emissive nanofluorophore test paper for highly sensitive colorimetry-based quantification of blood glucose

Fluorescent test papers are promising for the wide applications in the assays of diagnosis, environments and foods, but unlike classical dye-absorption-based pH test paper, they are usually limited in the qualitative yes/no type of detection by fluorescent brightness, and the colorimetry-based quantification remains a challenging task. Here, we report a single dual-emissive nanofluorophore probe to achieve the consecutive color variations from blue to red for the quantification of blood glucose on its as-prepared test papers. Red quantum dots were embedded into silica nanoparticles as a stable internal standard emission, and blue carbon dots (CDs) were further covalently linked onto the surface of silica, in which the ratiometric fluorescence intensity of blue to red is controlled at 5:1. While the oxidation of glucose induced the formation of Fe3+ ions, the blue emission of CDs was thus quenched by the electron transfer from CDs to Fe3+, displaying a serial of consecutive color variations from blue to red with the dosage of glucose. The high-quality test papers printed by the probe ink exhibited a dosage-sensitive allochromatic capability with the clear differentiations of ~5, 7, 9, 11mM glucose in human serum (normal: 3–8mM). The blood glucose determined by the test paper was almost in accordance with that measured by a standard glucometer. The method reported here opens a window to the wide applications of fluorescent test paper in biological assays.

A novel europium metal-organic framework as luminescent probe for detecting Al3 +

A novel three-dimensional europium metal-organic framework (Eu-MOF), [Eu(L)(OAc)(DMA)]n (1), has been successfully obtained based on a newly designed ligand 4′-(3,5-dicarboxyphenyl)-4,2′:6′,4″-terpyridine (H2L). The structure of 1 was established by single crystal X-ray diffraction technique, and structure analysis shows that two Eu3+ in 1 are 4-fold bridged by two η1:η1:μ2 carboxylates from L2− and the other two η1:η2:μ2 carboxylates from acetic acid, respectively. The binuclear [Eu2] were further linked by L2− to form a 3D framework. The investigations on luminescent properties reveal that 1 can detect Al3+ quickly with relatively high sensitivity and selectivity. More importantly, it displays high thermal and solvent stability. Additionally, a self-made fluorescence test paper fabricated based on 1 was used to detect Al3+ in practice.

Selective detection of picric acid by a fluorescent ionic liquid chemosensor

A fluorescent ionic liquid with a dansylamide chromophore was designed and synthesized, which exhibited strong green fluorescence both in the solution and in the condensed phase. As a fluorescent sensor, this ionic probe showed highly sensitive and selective detection of nitroaromatic explosives, especially for picric acid (PA). Theoretical calculations and NMR studies have demonstrated that a ground-state charge transfer through a protonation process and favorable electrostatic π–π interactions between ionic probe and PA may be responsible to the fluorescence quenching mechanism. Moreover, the resonance energy transfer (RET) studies explained the higher sensitivity and selectivity of this ionic probe towards PA than other nitro-containing explosives. A fluorescent test paper was also prepared for the on-site and accurate detection of PA, which provided a new clue of thoughts for instant and highly selective detection of nitroaromatic explosives.

A rapid and facile fluorimetric method for detecting formaldehyde

2-amino-6-(piperazin-1-yl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (NPz) was rationally designed and synthesized as a rapid and facile fluorimetric derivatization reagent for detecting formaldehyde. Compared with the other fluorimetric derivatization reagents, NPz possessed a marked advantage on the time consumption. Upon addition of formaldehyde, NPz showed an obvious fluorescence enhancement at room temperature within 4min. The fluorescent test papers loaded with NPz were prepared and applied in the detection of formaldehyde qualitatively.

High photoluminescent carbon nanodots and quercetin-Al3+ construct a ratiometric fluorescent sensing system

Highly blue fluorescent carbon nanodots (CNDs) were synthesized by the hydrothermal method from citric acid and diethylenetriamine with the quantum yield of about ∼86%. Quercetin (QCT) and its fluorescent metal-ion complex (QCT-Al3+) can efficiently coordinate on the surface of CNDs, the emission of CNDs at 429nm completely overlapped with the absorption peak of QCT-Al3+ at 428nm. Therefore, a ratiometric fluorescence sensor for Al3+ was developed based on fluorescence resonance energy transfer (FRET) with CNDs as donor and QCT-Al3+ as acceptor. A linear calibration of F429/F481 versus aluminum ion concentration was obtained within 1–20 and 20–60μM, along with a detection limit of 558nM. Moreover, the ESIPT–FRET ratiometric fluorescence system based on the CNDs/QCT-Al3+ was applied for fluorescent test papers with satisfying resolution.

A symmetric pseudo salen based turn-on fluorescent probe for sensitive detection and visual analysis of zinc ion

A turn-on fluorescence probe for zinc ion has been synthesized, which contains a symmetric pseudo salen moiety as zinc recognition site. The multidentate salen ligand chelates with zinc ions, and generates the rigidity of the zinc complex, which subsequently results in a dramatic fluorescence enhancement of the probe. Mass spectral and spectroscopic results reveal that the reaction proceeds rapidly in a 1 to 1 stoichiometric manner to form a clean zinc complex. We have demonstrated that the fluorescence probe not only has high selectivity for zinc ion over other biological relevant ions but also shows high sensitivity for zinc ion with a detection limit of 83nM. A fluorescence test paper has been developed by incorporating the probe on a polyamide fiber paper. The fluorescence color of the test paper became bright green–yellow under UV lamp when water sample containing zinc ions was dropped on it, suggesting its potential application in the measurement of zinc ions.