Sensing behavior and logic operation of a colorimetric fluorescence sensor for Hg(2+)/Cu(2+) ions

A terpyridyl-rhodamine hybrid fluorescent probe for discriminative sensing of Hg (II) and Cu (II) in water and applications for molecular logic gate and cell imaging

Sensitive and discriminative sensing of more than one analyte with a single fluorescent probe is significant and challenging. Herein a new terpyridyl-rhodamine hybrid, namely TRH, has been rationally designed and prepared with two responsive groups in the molecular structure, which facilitate the discriminative detection of Hg2+ and Cu2+ ions in water with detection limits of 4.9 and 53.3 nM by ratiometric fluorescence change (F595/F485) and fluorescence quenching, respectively. Investigations show that the selectivity to Hg2+ ions can be attributed to Hg2+-promoted spirolactam ring opening and further hydrolysis, followed by a through-bond energy transfer (TBET) process. The selective fluorescence quenching to Cu2+ ions probably can be ascribed to the binding Cu2+ to terpyridyl that triggers a ligand-to-metal charge transfer (LMCT) process, which can also efficiently inhibit the TBET process induced by Hg2+ ions and promotes the discriminative sensing of Cu (II) and Hg (II). In addition, the fluorescent responses to Hg2+ and Cu2+ ions cover a wide pH range. Moreover, a combinatorial logic gate with the functions of NOR and INHIBIT has been fabricated by using Hg2+ and Cu2+ ions as chemical input signals, and fluorescence at 485 and 595 nm as output signals. Besides, TRH also exhibits sensitive and discriminative sensing ability to Hg2+ and Cu2+ ions by the fluorescence of rhodamine fluorophore. Significantly, based on the fluorescence signal output of rhodamine moiety, TRH can be used as a tracer for the discriminative sensing of Hg2+ and Cu2+ ions by using living cells.

Importance of BODIPY-based Chemosensors for Cations and Anions in Bio-imaging Applications

Background:

Chemosensor compounds are useful for sensitive selective detection of cations and anions with fluorophore groups in an attempt to develop the effective selectivity of the sensors. Although familiar fluorescent sensors utilizing inter-molecular interactions with the cations and anions, an extraordinary endeavor was executed the preparation of fluorescent-based sensor compounds. 4,4-difluoro-4- bora-3a,4a-diaza-s-indacene (Bodipy) and its derivatives were firstly used as an agent in the imaging of biomolecules due to their interesting structures, complexation, and fluorogenic properties. Among the fluorescent chemosensors used for cations and anions, Bodipy-based probes stand out owing to the excellent properties such as sharp emission profile, high stability, etc. In this review, we emphasize the Bodipy-based chemosensor compounds, which have been used to image cations and anions in living cells, because of as well as the biocompatibility and spectroscopic properties.

Methods:

Research and online content related to chemosensor online activity is reviewed. The advances, sensing mechanisms and design strategies of the fluorophore exploiting selective detection of some cation and anions with Bodipy-based chemosensors are explained. It could be claimed that the using of Bodipy-based chemosensors is very important for cations and anions in bio-imaging applications.

Results:

Molecular sensors or chemosensors are molecules that show a change can be detected when affected by the analyte. They are capable of producing a measurable signal when they are selective for a particular molecule. Molecular and ion recognition that it is important in biological systems such as enzymes, genes, environment, and chemical fields. Due to the toxic properties of many heavy metal ions, it is of great importance to identify these metals due to their harmful effects on living metabolism and the pollution they create in the environment. This process can be performed with analytical methods based on atomic absorption and emission. The fluorescence methods among chemosensor systems have many advantages such as sensitivity, selectivity, low price, simplicity of using the instrument and direct determination in solutions. The fluorescence studies can be applied at nanomolar concentrations.

Conclusion:

During a few decades, a lot of Bodipy-based chemosensors for the detection of cations & anions have been investigated in bio-imaging applications. For the Bodipy-based fluorescent chemosensors, the Bodipy derivatives were prepared by different ligand groups for the illumination of the photophysical and photochemical properties. The synthesized Bodipy-based chemosensors have remarkable photophysical properties, such as a high quantum yield, strong molar absorption coefficient etc. Moreover, these chemosensors were successfully implemented on living organisms for the detection of analytes.

A Pyrazolo Imine-based Colorimetric and Turn-on Fluorescent Sensor Probe for Determination of Hg2+ Ion and its Application in Test Paper Strips

In this work, we synthesized diethylamino substituted pyrazolo imine (3) fluorescent probe for recognition of Hg²⁺ ion.The sensor probe 3 can detect Hg²⁺ by colorimetric method, and there is a 10-fold enhancement in fluorescence response. When the fluorescent probe bound with Hg²⁺ ion, turn-on fluorescence was observed via the coordination. Probe 3 has an excellent selectivity toward Hg²⁺ in the CH₃ CN/H₂ O (8:2, v/v) solution with low limit of detection and high binding association constant of 551 parts per billion (ppb) and 6.6067 × 10⁶  m^-1 for 3+Hg²⁺ , respectively. Furthermore, the formation of 3+Hg²⁺ complex with 1:1 binding mode was evidenced by Job's plot, ¹ H NMR spectroscopy and Mass analysis. In addition, probe 3 is a feasible option to detect Hg²⁺ in various sources of water samples. Bio-imaging experiments have demonstrated that probe 3 can be used to monitor Hg²⁺ in Escherichia coli bacterial cell. The sensor 3 was also used for paper strip application to detect Hg²⁺ ion.

A BODIPY derivative for colorimetric fluorescence sensing of Hg2+, Pb2+ and Cu2+ ions and its application in logic gates

A BODIPY-based colorimetric and fluorescent chemosensor 1 anchored with dipyridylamino (DPA) receptor has been designed, synthesized and characterized. It exhibited a simultaneous sensitive recognition for Cu²⁺, Hg²⁺ and Pb²⁺ ions. With the addition of these three kinds of metal ions into 1 in CH₃CN, its initial absorption maximum displayed obvious blue shifts, and the color changes of the solution could be clearly observed by naked eyes. Besides, the fluorescence intensity was significantly enhanced accompanied with the appearance of new emission peaks at 587 nm for Pb²⁺ and Hg²⁺ ions and 545 nm for Cu²⁺ ions. These results were attributed to the π-deconjugation between N-pyridyl and the BODIPY group due to the binding of metal ions with the BODIPY and DPA groups. Based on the sensing behaviors of 1, three logic gates (OR, INHIBT and combinational logic gate) were constructed correspondingly.

A NIR-BODIPY derivative for sensing copper(II) in blood and mitochondrial imaging

In order to develop NIR BODIPY for mitochondria targeting imaging agents and metal sensors, a side chain modified BODIPY (BPN) was synthesized and spectroscopically characterized. BPN has NIR emission at 765nm when excited at 704nm. The emission at 765nm responded differently to Cu²⁺ and Mn²⁺ ions, respectively. The BPN coordinated with Cu²⁺ forming [BPNCu]²⁺ complex with quenched emission, while Mn²⁺ induced aggregation of BPN with specific fluorescence enhancement. Moreover, BPN can be applied to monitor Cu²⁺ in live cells and image mitochondria. Further, BPN was used as sensor for the detection of Cu²⁺ ions in serum with linear detection range of 0.45μM-36.30μM. Results indicate that BPN is a good sensor for the detection of Cu²⁺ in serum and image mitochondria. This study gives strategies for future design of NIR sensors for the analysis of metal ions in blood.

Colorimetric and fluorescent sensing of a new FRET system via [5]helicene and rhodamine 6G for Hg2+ detection

A “visually colorimetric” and fluorometric sensor based on [5]helicene connected to rhodamine 6G via a hydrazide moiety was designed and prepared for the highly sensitive and selective detection of Hg²⁺.

Triple detection modes for Hg2+ sensing based on a NBD-fluorescent and colorimetric sensor and its potential in cell imaging

The sensor provides highly Hg²⁺-sensitivity and can enhance the emission in live cell.

Diaminomalenonitrile-decorated cholesterol-based supramolecular gelator: aggregation, multiple analyte (hydrazine, Hg2+ and Cu2+) detection and dye adsorption

A low molecular weight gelator (LMWG) containing a diaminomalenonitrile functional group 1 forms supramolecular gels from DMF–H₂O and 1,2-dichlorobenzene. The DMF/H₂O gel is multi-analyte responsive (Hg²⁺, Cu²⁺ and hydrazine) with practical applications in dye adsorption from water.

A New Reactive 1,8-Naphthalimide Derivative for Highly Selective and Sensitive Detection of Hg2

A 1,8-naphthalimide derivative with a reactive aliphatic hydroxyl was designed and synthesized as a fluorescent probe. Its structure was characterized by IR, ¹H NMR, ¹³C NMR, LC-MS and HPLC. The probe showed high selectivity and sensitivity to Hg²⁺ over other metal ions such as Pb²⁺, Na⁺, K⁺, Cd²⁺, Cr³⁺, Zn²⁺, Cu²⁺, Ni²⁺, Ca²⁺, Fe³⁺, Fe²⁺, Co²⁺, Mn²⁺ and Mg²⁺ in MeCN/H₂O (15/85, v/v). The increase in fluorescence intensity was linearly proportional to the concentration of Hg²⁺ in the range of 18-40 μM with a detection limit of 1.38 × 10^-7 mol/L. The probe could work in a pH span of 4.3-9.0 and respond to Hg²⁺ quickly with strong anti-interference ability. Job's plot suggested a 1:2 complex of the probe and Hg²⁺.

A multifunctional Schiff base as a fluorescence sensor for Fe3+ and Zn2+ ions, and a colorimetric sensor for Cu2+ and applications

Chemosensors play important parts in the selective recognition of ions, which is widely applied in various fields of environment, industry and biological sciences. In this work, a chemosensor for multi-metal ions based on rhodamine B derivative was synthesized, which could selectively recognize various metal ions in different solvent system. The addition of Cu²⁺ caused the color change from colorless to pink in EtOH/H₂O (v/v=1:1) solvent system, which could be quickly identified by the naked eyes with a detection limit of 8.27×10^-8M. In ethanol solution system, the addition of Fe³⁺ and Zn²⁺ caused different fluorescence changes with the detection limit of 2.12×10^-7M and 6.64×10^-7M respectively. The binding ratios are 1:1 (1-Cu²⁺), 2:1 (1-Fe³⁺) and 1:1 (1-Zn²⁺), respectively. Meanwhile, the probe 1 was used to detect the trace metal ions in real water samples. Besides, the probe 1 showed sensitive fluorescence signals for Fe³⁺ in biological cells. The experimental results further verify the application value of the sensor.

BODIPY dyes with thienyl- and dithienylthio-substituents – synthesis, redox and fluorescent properties

Novel thienyl- and dithienylthio-BODIPYs were synthesized, which displayed unusual crystal packing and luminescence.