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Multicolor immunosensor is a promising tool for on-site rapid analysis by naked eye without bulky instruments. Herein, a multicolor immunosensor employed a specific nanobody-alkaline phosphatase fusion protein (VHHjd8-ALP) for biosensing of fenitrothion was developed. After one-step indirect competitive immunoassay, the binding VHHjd8-ALP in microplate catalyzed ascorbyl-2-phosphate (AAP) into ascorbic acid, which propose dual readout including multicolor ratiometric visible immunoassay (MRVIA) and multicolor ratiometric fluoroimmunoassay (MRFIA). For MRVIA, K 3 [Fe(CN) 6 ] and Fe3+ was employed for multicolor generation. The substrate AAP can chelate with Fe3+ to form orange AAP-Fe3+ complex. When ALP catalyzed AAP into ascorbic acid, the latter can reduced K 3 [Fe(CN) 6 ] into K 4 [Fe(CN) 6 ], which reacted with Fe3+ to produced Prussian blue via self-assembly. A visible color transition from orange to blue against fenitrothion was obtained. For MRFIA, the generated ascorbic acid etched MnO 2 nanosheet to control the concentration of Na 2 SO 3 , which can convert 9-anthraldehyde into sulfuretted anthracene accompanied by a fluorescent color transition from green to blue. These two methods showed visible multicolor transition against fenitrothion for naked-eye analysis. The recovery and blind samples test verified good accuracy and practicability, which can be used for rapid screening of fenitrothion by a naked-eye semiquantitative analysis mode. [Display omitted] • Multicolor immunoassays were achieved without precious-metal materials. • Color regulation relies on ratiometric changing of dual signals. • The VHHjd8-ALP-based strategy can develop a dual multicolor immunosensor. • They can be used for semiquantitative detection without complex apparatus. [ABSTRACT FROM AUTHOR]

A quinoline-vinyl-dihydroxylphenyl linkage comprising a donor-π-bridge-acceptor structural motif, in which the quinoline serves as an electron-withdrawing core, has been synthesized and used as a fluorescent sensor ( 2 ) for the recognition of Al 3+ and F − by colorimetry/fluorescence. The sensor 2 exhibited little fluorescence due to excited-state intramolecular proton transfer from the hydroxyl oxygens to the nitrogen of the quinoline moiety. By contrast, on coordination of Al 3+ or F − , sensor 2 afforded strong fluorescence. A reversible “off–on” optical switching mode has been constructed by sequential inputs from Al 3+ and F − ions to the sensor 2 via different excitation and emission wavelengths. 1 H NMR and IR spectroscopic analysis revealed that the Al 3+ is coordinated to the quinoline nitrogen and phenolic oxygen atoms, whereas the F − center is only coordinated by two phenolic oxygen atoms. [ABSTRACT FROM AUTHOR]

The performance of a number of rhodamine-triazine derivatives (probe R1 – R4) which utilize rhodamine as the fluorophore with cyanuric chloride as the molecular platform have been evaluated. Spectroscopic analysis revealed that differing structural substitution patterns of the probe resulted in different sensitivity and selectivity for specific metal ions. The probes R1 and R2 were fluorescent/colorimetric probes for Cu 2+ , whilst R3 and R4 were probes for Al 3+ , Cr 3+ and Fe 3+ . The probe R2 exhibited superior recognition for Cu 2+ in neutral aqueous medium, and the optical switching behavior of R2 for Cu 2+ and S 2− could be used to construct a molecular logic gate. In addition, fluorescence imaging of probe R2 for Cu 2+ in living cells was demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: 2-(1-Hydroxy-2-naphthyl)methylene hydrazone (HMNH), with two naphthalene planar conjugated moieties linked by a rotatable Nbond, has been feasibly synthesized. This molecule is characterized by aggregation-induced emission enhancement properties, exhibiting markedly enhanced fluorescence after aggregation in DMF (N,N-dimethylformamide)/H2O mixed solvent. According to spectroscopic data, crystal structure determination, SEM, and fluorescence microscopy, rotation round the intramolecular single bond is hindered by the combined effects of intramolecular hydrogen-bond formation and ordered molecular stacking with aggregate formation, which inhibit non-radiative transitions in the aggregated state. HMNH has excellent metal ion recognition properties, isolated HMNH working as a fluorescence turn-on sensor for Zn2+, but aggregated HMNH with AIEE as a turn-off sensor for Co2+. Using OH− and Zn2+/Co2+ as chemical inputs and the fluorescence signal as output, AND and NAND logic gates operating at the molecular level have been constructed. This single molecule sensor for multiple analytes by isolated or aggregated is promising and has been rarely exploited. [Copyright &y& Elsevier]

Abstract: The synthesis and spectroscopic studies of a thiacalix[4]arene-based sensor of 1,3-alternate-25,27-bis(2-aminoethoxy)-26,28-bis(2-methoxyethyl)-thiacalix[4]arene linked 4-chloro-7-nitrobenzofurazan (NBD-Cl) are described. The properties of the compound were evaluated and show that it is a colorimetric and fluorescence sensor for Ag+ and AcO−. The addition of Ag+ results in a red shift of the absorption spectrum of the sensor, which is clearly visible to the naked eye, accompanied by a strong quenching of the fluorescence. With the addition of AcO−, the fluorescence was severely quenched, and the absorbance increased significantly, with a new absorption band appearing at shorter wavelength. This demonstrated that the multifunctional sensing compound prepared from a novel thiacalix[4]arene was highly selective for AcO−. [Copyright &y& Elsevier]

Abstract: A new flexible tripodal compound 1 linked with three rhodamine groups as fluorophores and recognition sites was synthesized and its sensing behavior toward metal ions was investigated by UV–vis and fluorescence spectroscopy methods. It exhibited excellent selectivity for Cu(II) over miscellaneous metal ions including Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Zn(II), Cd(II), Al(III), Mg(II), Ca(II), Sr(II), Na(I), and K(I). While the fluorescence of the 1-Cu(II) complex could be enhanced significantly upon the addition of Hg(II) compound 1 may therefore be applicable as an OFF-ON fluorescent chemosensor for Cu(II) and Hg(II). [Copyright &y& Elsevier]

A novel fluorescent probe 1 has been synthesized by a microwave reaction, and its ion-binding and fluorescence-sensing properties have been investigated under different solvent conditions. The analysis results indicated that probe 1 can act as a multiple analysis probe by simply tuning the solvent. Probe 1 exhibited high selectively toward Hg 2+ through fluorescence quenching in H 2 O/DMF. In H 2 O/1,4-dioxane solution, probe 1 selectively recognized and discriminated between Ag + and Hg 2+ displaying ratiometric behaviour. Moreover, probe 1 readily recognized the anion F − via the ratiometric fluorescent mode in CH 3 CN. Furthermore, distinct colour changes were observed under UV light, which can be seen by the naked eye and thus used for distinguishing Hg 2+ , Ag + and F − from the other ions screened herein using probe 1 . Interestingly, almost pure white light emission was evident by simply tuning the F − anion-concentration, which makes this system a potential candidate for smart and tunable luminescent materials. [ABSTRACT FROM AUTHOR]

Abstract: A simple structure, a rhodamine fluorescent derivative, was synthesized easily by a one-step condensation reaction of rhodamine B ethylenediamine and acetylacetone. Its structure was characterized by X-ray crystallography, NMR, MS and IR spectroscopy. As a bi-functional and highly selective “OFF–ON” chemosensor for Fe3+ or Cu2+, the derivative displayed a selective fluorescence enhancement effect only with Fe3+ and an absorption enhancement effect only with Cu2+ by modulating the pH value. In an aqueous ethanol medium, Fe3+ formed a 1:1 complex with the derivative at pH 6, while Cu2+ formed a 1:1 complex at pH 8.5. The limits of detection of the ions were low: 3.9×10−9 and 4.8×10−8 molL−1. The derivative also functioned as a fluorescence sensor for CT-DNA, in which the Fe3+ ion that was used as a bridge between the derivative and DNA forming a ternary complex. [Copyright &y& Elsevier]

Abstract: A new rhodamine B schiff-base fluorescent sensor (1) was synthesized by a one-step condensation reaction of rhodamine B ethylenediamine and acetylacetone. The structure of 1 was characterized by single crystal X-ray crystallography, 1H NMR, MS and IR spectroscopy. Studying its fluorogenic and colorimetric behaviors towards various metal ions, high sensitivity and selectivity were achieved for Fe3+ over other commonly coexistent metal ions, which were accompanied by ring opening of a rhodamine spirocycle framework. In the ethanol aqueous medium (v/v=4/6, Tris–HCl buffer, pH=7.0), the presence of Fe3+ induces the formation of a 1-ion complex, which was deduced by spectroscopy, HPLC and electrochemical methods. The limit of detection for Fe3+ determinations was low to 0.11μM (fluorescence measurement) and 1.6μM (UV–vis measurement), respectively, indicating the potential application of 1 for the determination of trace Fe3+ ions in neutral medium. [Copyright &y& Elsevier]

A novel quinoline-functionalized hexahomotrioxacalix[3]arene L was synthesized via Click chemistry and its chemosensing properties with various metal ions were investigated. The chemosensor L exhibited a high selectivity for Fe 3+ with little interference from other environmentally and biologically relevant metal ions, leading to a prominent ‘off-on’ type fluorescent signalling behaviour. Our studies demonstrated that the detection limit on fluorescence response of the sensor to Fe 3+ is in the 10 −7 M range. The mechanism of the interaction between the L and Fe 3+ has been investigated in detail by 1 H NMR spectroscopic titration experiments. [ABSTRACT FROM AUTHOR]

A new pyrenyl appended hexahomotrioxacalix[3]arene L featuring 1,2,3-triazole linkers was synthesized as a fluorescent chemosensor for Zn 2+ in mixed aqueous media. It exhibited high affinity toward Zn 2+ , and the monomer and excimer emission of the pyrene moieties could be adjusted. The binding stoichiometry of the L ·Zn 2+ complex was determined to be 1:1, and the association constant ( K a) was found to be 7.05 × 10 4 M −1 . The binding behavior with Zn 2+ has been confirmed by 1 H NMR spectroscopic analysis. [ABSTRACT FROM AUTHOR]