Considerable amount of research has been carried out on designing and improving metal-recognition methodologies in environmental and biological media. The development of fluorescent-based techniques has proven to be an important milestone for non-invasive metal detection and quantification in a multichannel environment. Metals as natural components of the Earth's crust are generally present in trace concentrations in environmental samples, wherein humic substances have a complexation affinity toward them. Iron, zinc and copper are the 1st, 2nd and 3rd most abundant elements that are indispensable to the human body in trace amounts as they play crucial roles in many biological processes. However, unregulated amounts either an excess or deficiency may exacerbate deterioration of the vital organs and trigger the progression of complications. In addition to these three essential elements, mercury is widely considered to be one of the most hazardous pollutants and highly dangerous elements due to its recognized accumulative and toxic effects in the environment and in biological media. In the present study, we attempted to summarize all the recently developed fluorescent signaling materials for the detection of Cu2+, Fe2+/Fe3+, Zn2+ and Hg2+. The spectral shifts in the molecules on metal chelation, the mode of complexation and the stoichiometries of the resulting adducts have been discussed in detail. Furthermore, we highlight molecules that have been reported as an intracellular metal detector via bioimaging, which can be useful for the future design and development of cell-viable and membrane-permeable molecular probes.

Optical sensor: a promising strategy for environmental and biomedical monitoring of ionic species

Our designed chemosensor, rhodamine-HBT-dyad (RHD), selectively detects two biologically important ions (Al3+ and Zn2+) at two different wavelengths (‘naked-eye’ colors red and green, respectively) through two different mechanisms (i.e. FRET and ESIPT) at ppm level. The sensor can also detect the Al3+ ion through displacement of the Zn2+ ion in vivo.

FRET based ‘red-switch’ for Al3+ over ESIPT based ‘green-switch’ for Zn2+: dual channel detection with live-cell imaging on a dyad platform

We have developed a novel coumarin-based chemosensor H 2 L with ICT character bearing the hydrazone of substituted phenol, synthesized by the condensation of 2-hydroxy-4-methylbenzohydrazide with 3-acetylcoumarin. The fluorescence spectra of the receptor H 2 L demonstrated that the sensor could selectively recognize Al 3+ over other metal ions and the detection limit was found in the micromolar concentration range. Sensing capability of the receptor for Al 3+ was reversible. Cu 2+ complex of H 2 L was structurally characterized which gave the basis for possible structure of Al 3+ complex of H 2 L. The Turn On fluorescence of H 2 L is based on intramolecular charge transfer (ICT), chelation enhanced fluorescence (CHEF) and C N isomerization to serve as fluorescent chemosensor in DMF-water solvent mixture. The receptor H 2 L showed a remarkably red-shifted absorption spectrum in the presence of Al 3+ in DMF. B3LYP-SCRF/6-31G* density functional theory explains the ICT mechanism.

A schiff base ligand of coumarin derivative as an ICT-Based fluorescence chemosensor for Al3+

A chemosensor 3-[(2-hydroxybenzylidene)-amino]-1H-pyridin-2-one (HL) for multi-ions was synthesized and characterized by single-crystal X-ray diffraction. HL is a turn-on fluorescence chemosensor for Al3+, F−, and CN− ions in DMSO. F− and CN− anions could be further distinguished by the ratiometric absorption spectrometry method. Job plot and 1H NMR data showed that the binding stoichiometries of HL with Al3+, F−, or CN− all were 1:1. Further observations of 1H NMR titration and ESI-MS showed that the possible fluorescent species of Al3+ with HL was [AlL(OH)(DMSO)2]+ in DMSO. The spectroscopic observations of the Al(III) complex showed that the two oxygen atoms and one imine nitrogen atom of HL were coordinated to the Al(III) ion. While the crystal structure of the Ni(II)-L complex confirmed the tridentate coordination mode of HL in the complexes. The experimental results revealed that HL and F− ion formed hydrogen bond in DMSO, while CN− attacked the carbon atom at –C N of HL to undergo a nucleophilic addition. The theoretical calculations confirmed that HL showed very weak fluorescence because of the excited-state intramolecular proton transfer (ESIPT). The turn-on sensing of HL to Al3+, F−, and CN− ions arose from the inhibition of ESIPT. MTT tests showed that HL was low toxic to cells. Also, HL could probe intracellular Al3+ and F− ions by bioimaging.

A turn-on fluorescence chemosensor for Al3+, F− and CN− ions, and its application in cell imaging

Simultaneous bioimaging recognition of Al3+ and Cu2+ in living-cell, and further detection of F− and S2− by a simple fluorogenic benzimidazole-based chemosensor

A tetrazole derivative 1-[(1H-tetrazol-5-ylimino)methyl]naphthalen-2-ol (H2L) as a fluorescent chemosensor for Al3+ in DMSO and Zn2+ in DMF was designed and synthesized. From 1H NMR data, the Job plot and the ESI-MS spectrum, 1:1 stoichiometric complexation between H2L and Al3+/Zn2+ was found in DMSO and DMF, respectively. The theoretical calculations at the level of B3LYP/6-311G** for the ground state and TD-B3LYP/6-311G** for the excited state revealed the sensing mechanism is the inhibition of excited state intramolecular proton transfer (ESIPT). And the possible fluorescent species formed in the DMSO and DMF solutions were deduced to be [Al(HL)(OH)(NO3)(H2O)(DMSO)] and [Zn(HL)(OH)(H2O)(DMF)]. What's more, it is confirmed that H2L could be used to detect Al3+ and Zn2+ in cells by bioimaging.

A tetrazole-based fluorescence “turn-on” sensor for Al(III) and Zn(II) ions and its application in bioimaging

A memristor is a kind of nonlinear two-port circuit element with memory characteristics, whose resistance value is subject to being controlled by the voltage or current on both its ends, and thus it has broad application prospects. At present, most of the memristor application research is based on the change of resistance and memory characteristics, which involves how to make the memristor change according to the desired trajectory. Aiming at this problem, a resistance tracking control method of memristors is proposed based on iterative learning controls. This method is based on the general mathematical model of the voltage-controlled memristor, and uses the derivative of the error between the actual resistance and the desired resistance to continuously modify the control voltage, making the current control voltage gradually approach the desired control voltage. Furthermore, the convergence of the proposed algorithm is proved theoretically, and the convergence conditions of the algorithm are given. Theoretical analysis and simulation results show that the proposed algorithm can make the resistance of the memristor completely track the desired resistance in a finite time interval with the increase of iterations. This method can realize the design of the controller when the mathematical model of the memristor is unknown, and the structure of the controller is simple. The proposed method can lay a theoretical foundation for the application research on memristors in the future.

/pdf/resistance-tracking-control-of-memristors-based-on-iterative-fgfsg4qo.pdf

Jin-Ping Qiao

Papers

A tetrazole-based fluorescence “turn-on” sensor for Al(III) and Zn(II) ions and its application in bioimaging

Resistance Tracking Control of Memristors Based on Iterative Learning