Acylhydrazone Functionalized Triphenylamine-Based Fluorescent Probe for Cu2+: Tunable Structures of Conjugated Bridge and Its Practical Application

Novel fluorescent probes were constructed for the convenient and rapid analysis of Cu2+ ions, taking advantages of the the triphenylamine backbone as chromophore and acylhydrazone group as the Cu2+ recognition site. Especially, probe T2 could act as a dual-channel probe towards Cu2+ through both fluorescent and colorimetric method. Through the fluorescent method, the detection limit of probe T2 was calculated to be as low as 90 nmol/L and there was a good linear relationship between the intensity change and the concentration of Cu2+ ions. By virtue of the two-phase liquid-liquid extraction method, probe T2 could be successfully applied in practical extraction and separation of Cu2+. Furthermore, by applying a "turn-off-turn-on" circle, compound T2 could act as a sensitive probe towards S2- anions through the indirect approach and the detection limit of complex T2-Cu2+ for S2- anion was found to be 110 nmol/L.

Highly Selective and Sensitive Colorimetric and Fluorimetric Sensor for Cu2

A newly designed fluorescent and colorimetric probe was synthesized and selective detection of cu²⁺ was successful in aqueous medium. The design strategy exhibited strongly fluorescent when binding with cu²⁺ based on the change in structure between spirocyclic to a non-cyclic form of rhodamine based dye. The UV visible spectra of probe (6GS2) exhibited three absorption peaks at 229, 309 and 530 nm respectively. The emission spectra of fluorescent probe exhibited wavelength at 550 nm. The peak intensity increases during the addition of copper ion to probe through n-π transition. The probe characterized by different techniques like NMR, absorption, emission, mass and test strips methods. Graphical Abstract .

Two-photon imaging of aptamer-functionalized Copolymer/TPdye fluorescent organic dots targeted to cancer cells

Fluorescent organic dots (O-dots) recently have emerged as a new class of promising contrast reagents for two-photon fluorescence (TPF) imaging. However, most of these developed two-photon absorption (TPA) O-dots have no tumor-targeting group, which hampers their wide application for targeted tumor imaging. Herein, we fabricated Sgc8c aptamer-mediated TPA O-dots as a proof-of-concept of the sensing platform for targeted imaging in live cells or deep tissues. The O-dots composed of trans-4-[p-(N, N-diethylamino)styryl]-4'-(dimethyl amino) stilbene (DEAS) emerged as TPA organic emissive cores and encapsulation by using poly (methyl methacrylate-co-methacrylic acid) (PMMA-co-MAA) as polymeric encapsulating matrix to form DEAS/PMMA-co-MAA O-dots via a co-precipitation strategy. The obtained O-dots enabled an extremely high TPA absorption cross-section, bright two-photon fluorescence (excitation at 720 nm; emission at 412 nm and 434 nm), excellent cell-permeability and high penetration depth. Sgc8c aptamer, as a protein tyrosine kinase-7 (PTK7) receptor-targetable ligand, was further anchored on the surface of O-dots to obtain DEAS/PMMA-co-MAA@Sgc8c nanoprobes by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC)-mediated coupling reaction. Guided by Sgc8c aptamer, DEAS/PMMA-co-MAA@Sgc8c nanoprobes could be rapidly internalized into target acute lymphoblastic leukemia cells (CEM) cells with high specificity and great efficiency. It was also performed that two-photon images of TPA nanoprobes exhibited high two-photon brightness not only in target CEM cells, but also in mouse liver tissue slices even a depth of up to 210 μm. In our perception, it is highly promising that this nanoprobe provides a valuable tool for in vivo targeted imaging.

Execution of julolidine based derivative as bifunctional chemosensor for Zn2+ and Cu2+ ions: Applications in bio-imaging and molecular logic gate

A simple julolidine based chemosensor (JT) was designed and synthesized by single condensation step. JT displayed excellent selectivity and sensitivity with on-off responses towards Zn²⁺ and Cu²⁺ over other biologically relevant metal ions in aqueous media. Upon addition of Zn²⁺ ions, JT exhibited a significant blue shift in emission followed by turn-on enhancement while with Cu²⁺, the fluorescence intensity of JT was completely vanished. The 1:1 binding affinity between JT and Zn²⁺/Cu²⁺ was proposed by Job's plot analysis. The detection limit for Zn²⁺ and Cu²⁺ ions reached at 3.5 × 10^-8 M and 1.46 × 10^-6 M, respectively. The sensing mechanism of JT with Zn²⁺/Cu²⁺ was supported by DFT calculations. Based on photophysical studies and its reversibility environment with EDTA, molecular logic gates were fabricated. Furthermore, JT was successfully established to detect intracellular Zn²⁺ ions in live cells by turn-on response.

A novel fluoro-chromogenic Cu2+ probe for living-cell imaging based on rhodamine 6G-pyridine conjugation

A novel fluoro-chromogenic rhodamine spirolactam probe (RP) has been prepared through the condensation of rhodamine hydrazine and 2-acetylpyridine, which displayed the detection of Cu²⁺ with high selectivity over a large number of other common metal ions. It shows a "turn-on" response to paramagnetic Cu²⁺ with an about 12-fold enhancement, and a color change from colorless to red that is observable by the naked eye. These changes are ascribed to the ring-opening of the spirolactam in RP, and subsequent host-guest coordination. The 2:1 binding stoichiometry of RP to Cu²⁺ was confirmed by Job's and B-H plots. The resulting fluorescence enhancement can be used to detect Cu²⁺ at concentrations from 2.0 to 20.0 μM with a limit of detection of 0.21 μM, which was lower than the maximum allowable Cu²⁺ level set by the WHO. Finally, RP has been utilized to monitor Cu²⁺ in living cells and natural water. Graphical abstract.

GB, Latiyan S, Jain S. Remarkably selective biocompatible turn-on fluorescent probe for detection of Fe3+ in human blood samples and cells

The robust nature of a biocompatible fluorescent probe is demonstrated, by its detection of Fe³⁺ even after repeated rounds of quenching (reversibility) by acetate in real human blood samples and cells in vitro.

Achieving selectivity for copper over zinc with luminescent terbium probes bearing phenanthridine antennas

A family of terbium probes was synthesized and evaluated for the luminescence detection of copper and zinc in water at neutral pH. Each probe incorporates a terbium ion chelated by a macrocyclic polyaminocarboxylate and conjugated to either one, two, or three phenanthridine antennas via a diamine linker. All three probes, Tb-1Phen, Tb-2Phen, and Tb-3Phen, exhibit similar responses toward copper and zinc. In each case, the terbium-centered time-gated phosphorescence decreases upon binding either Cu^I or Cu^II but not upon addition of Zn^II. The phosphorescence of Tb-2Phen is also not significantly affected by other metal ions including Mg^II, Ca^II, Mn^II, Fe^II, Ni^II, Cd^II, and Hg^II. Tb-1Phen, on the other hand, responds weakly to Mn^II, Fe^II and Ni^II. The lack of affinity of each probe for Zn^II was further confirmed by competition experiments with Cu^I and Cu^II. Notably, whereas the terbium-centered emission of each probe is quenched upon copper coordination, the phenanthridine-centered luminescence emission is not. As such, each probe functions as a ratiometric probe for the selective detection of copper over zinc. Theoretical calculations further demonstrate that the turn off response of the probe is due to an increase in the distance separating the lanthanide ion from its phenanthridine antennas upon coordination of copper, which in turn decreases the efficiency of terbium sensitization by the phenanthridines.

A new water-soluble heteronuclear PdII–AuI pincer complex as two-photon luminescent probe for biological Co2+ detection

A new water-soluble heteronuclear Pd^II–Au^I pincer complex was synthesized and investigated for biological Co²⁺ detection.

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

In this review, we cover the recent developments in fluorogenic and chromogenic sensors for Cu²⁺, Fe²⁺/Fe³⁺, Zn²⁺and Hg²⁺.

RuNH2@AuNPs as two-photon luminescent probes for thiols in living cells and tissues

Two-photon luminescent sensors have emerged as promising molecular tools for imaging biomolecules in living systems. Here, we present hybrid gold nanocomposites RuNH2@AuNPs as luminescence off-on probes in response to thiols, which can replace the Ru(II) complexes on the surfaces of the AuNPs to release the luminophore RuNH2. The liberated Ru(II) complexes exhibit strong two-photon luminescence and a large two-photon absorption cross section by using the two-photon excitation wavelength at 800 nm. Furthermore, the probe responses toward thiols with high selectivity and insensitivity to pH over the biologically relevant pH range. This two-photon probe can visualize biological thiols levels in live cells as well as in living mouse tissues at depths of 80-170 μm by two-photon microscopy.

Truxene-cored π-expanded triarylborane dyes as single- and two-photon fluorescent probes for fluoride

Two triarylboranes were synthesized and they exhibited high selectivity and sensitivity to fluoride as both single-photon and two-photon fluorescent probes.

Two-photon fluorescent probe for cadmium imaging in cells

A novel two-photon excited fluorescent probe for cadmium (named as TPCd) was designed and synthesized utilizing a prodan (6-acetyl-2-methoxynaphthalene) derivative as the two-photon fluorophore and an o-phenylenediamine derivative as the Cd(2+) chelator, which possessed favorable photophysical properties and good water-solubility. The probe was designed with a photoinduced electron transfer (PET) mechanism and thus was weakly fluorescent itself. After binding with Cd(2+) which blocked the PET process, the fluorescence intensity of the probe was enhanced by up to 15-fold under one-photon excitation (OPE) and 27-fold under two-photon excitation (TPE), respectively. The two-photon action cross-section (Φδ) of the TPCd-Cd complex at 740 nm reached 109 GM compared to 3.6 GM for free TPCd, indicating the promising prospect of the probe in two-photon application. TPCd chelated Cd(2+) with 1 : 1 stoichiometry, and the apparent dissociation constant (K(d)) was 6.1 × 10(-5) M for the one-photon mode and 7.2 × 10(-5) M for the two-photon mode. The probe responded to Cd(2+) over a wide linear range from 0.1 to 30 μM with a detection limit of 0.04 μM. High selectivity of the probe towards Cd(2+) was acquired in Tris-HCl/sodium phosphate buffer. The probe was pH-independent in the biologically relevant pH range and non-toxic to living cells at reasonable concentration levels, warranting its in vivo applications. Through two-photon microscopy imaging, the probe was successfully applied to detect Cd(2+) uptake in living HepG2 cells.