Near-infrared Fluorescent Chemosensor Research Articles

A near-infrared fluorescent chemosensor with a remarkably large Stokes shift for the ultrasensitive detection of tyrosinase activity and bioimaging in living cells and mouse xenograft model

Tyrosinase (TYR) plays an important role in melanin formation and is regarded as the biomarker for melanoma cancer. Highly sensitive and selective detection of TYR activity in live cells may enhance the comprehension on the mechanism of TYR in living organisms and promote the prognosis and precise diagnosis of TYR related diseases. Herein, an “off-on” near-infrared fluorescent chemosensor EQR-TYR was developed that could detect TYR with high anti-interference ability. The evaluation of TYR activity was established in terms of the relationship between fluorescent intensity of EQR-TYR and TYR activity. Importantly, EQR-TYR showed various advantages, such as good water-solubility, low detection limit of TYR (0.035 U/mL), remarkably large Stokes shift (130 nm) and fast response (1 h). The application of EQR-TYR was successfully demonstrated by monitoring different TYR expressions in living cells and xenograft tumor mouse model, indicating its good biocompatibility. We anticipate that the novel chemosensor will provide an alternative for monitoring TYR activity in complex biological systems.

Sensing mechanism of a ratiometric near-infrared fluorescent chemosensor for cysteine hydropersulfide: Intramolecular charge transfer

Previous studies have shown that the cysteine hydropersulfide (Cys-SSH) as the sulfur donor is crucial to sulfur-containing cofactors synthesis. Recently, a selective and sensitive near-infrared ratiometric fluorescent chemosensor Cy-DiSe has been designed and synthesized to detect Cys-SSH spontaneously. Herein, by means of the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) approaches, the sensing mechanism has been thoroughly explored. According to our calculations, the experimental data have been reproduced. The results indicate the intramolecular charge transfer (ICT) is the reason for changes in fluorescence wavelengths. Compared with the chemosensor Cy-DiSe, the larger energy gap of Cy induced by ICT mechanism leads to the blue-shift of the absorption and emission spectra, which guarantees that Cy-DiSe can become a ratiometric fluorescent chemosensor to detect Cys-SSH.

A nitroxyl-responsive near-infrared fluorescent chemosensor for visualizing H2S/NO crosstalk in biological systems

We present a near-infrared (NIR) fluorescent probe, NR-HNO, which was successfully applied to visualizing H2S/NO "crosstalk" by the fluorescence detection of nitroxyl with a fast response time (5 min) and a large Stokes shift (131 nm) in living cells and tissue; it was also used to image nitroxyl in live mice.

A near-infrared chemosensor for determination of trivalent aluminum ions in living cells and tissues

A near-infrared fluorescent chemosensor (NIR-Rh) is developed for detecting trivalent aluminum ions (Al3+). In the NIR chemosensor, Fisher aldehyde is introduced to the structure of rhodamine dyes in order to extend the wavelength of absorption and emission. To the best of our knowledge, this is the first example of near-infrared fluorescent chemosensors that is applied in the detection of aluminum ions in biological samples. It exhibits a highly sensitive “turn-on” fluorescent response toward Al3+ with a 77-fold fluorescence intensity enhancement under 2 equiv. of Al3+ added. The chemosensor can be applied to the quantification of Al3+ with a linear range covering from 1.0 × 10−7 to 2.0 × 10−5 M with the detection limit of 3.0 × 10−8 M. Most importantly, the fluorescence changes of the chemosensor are remarkably specific for Al3+ in the presence of other metal ions, which meet the selective requirements for practical application. Moreover, the response behavior of NIR-Rh towards Al3+ is pH independent in neutral condition (pH 6.0–8.0). The response of the chemosensor is fast (less than 90 s) and the chemosensor is chemically reversible. Furthermore, the ring-opening mechanism of the NIR-Rh spirolactam induced by Al3+ and the 1:1 stoichiometric structure between NIR-Rh and Al3+ were supported by Job's plot, NMR, MS and DFT theoretical calculations. In addition, the proposed chemosensor has been used to detect Al3+ in living cells and tissues with satisfying results.

A near-infrared squaraine dye for cascade recognition of copper ion and biological phosphate and its application in IMPLICATION logic gate

A near-infrared fluorescent chemosensor based on squaraine has been synthesized, and its cascade recognition for copper ion, biological phosphate PPi, and amino acids has also been investigated by spectroscopic techniques. SQ-1 exhibits high selectivity and sensitivity for sensing Cu2+ over other metal ions by reversibly forming a [SQ-1-Cu2+] complex. By tandem ligand exchange, PPi and amino acids can remove Cu2+ from the complex and restore the spectral signal of SQ-1, which can be used for cascade recognition of these biologically active species. Notably, an IMPLICATION logic gate can be constructed based on this bifunctional chemosensing system.

DFT/TD-DFT calculations on the sensing mechanism of a dual response near-infrared fluorescent chemosensor for superoxide anion and hydrogen polysulfides: photoinduced electron transfer

Fluorescence quenching by the PET process in HCy-FN.

A Cu2+-selective fluorescent chemosensor based on BODIPY with two pyridine ligands and logic gate

A novel near-infrared fluorescent chemosensor based on BODIPY (Py-1) has been synthesized and characterized. Py-1 displays high selectivity and sensitivity for sensing Cu2+ over other metal ions in acetonitrile. Upon addition of Cu2+ ions, the maximum absorption band of Py-1 in CH3CN displays a red shift from 603 to 608nm, which results in a visual color change from pink to blue. When Py-1 is excited at 600nm in the presence of Cu2+, the fluorescent emission intensity of Py-1 at 617nm is quenched over 86%. Notably, the complex of Py-1–Cu2+ can be restored with the introduction of EDTA or S2−. Consequently, an IMPLICATION logic gate at molecular level operating in fluorescence mode with Cu2+ and S2− as chemical inputs can be constructed. Finally, based on the reversible and reproducible system, a nanoscale sequential memory unit displaying “Writing–Reading–Erasing–Reading” functions can be integrated.

A turn-on near-infrared fluorescent chemosensor for selective detection of lead ions based on a fluorophore–gold nanoparticle assembly

A turn-on fluorescent chemosensor of Pb(2+) in the near-infrared (NIR) region, which is based on the Pb(2+)-tuned restored fluorescence of a weakly fluorescent fluorophore-gold nanoparticle (AuNPs) assembly, has been reported. In this fluorophore-AuNP assembly, NIR fluorescent dye brilliant cresyl blue (BCB) molecules act as fluorophores and are used for signal transduction of fluorescence, while AuNPs act as quenchers to quench the nearby fluorescent BCB molecules via electron transfer. In the presence of Pb(2+), fluorescent BCB molecules detached from AuNPs and restored their fluorescence due to the formation of a chelating complex between Pb(2+) and glutathione confined on AuNPs. Under the optimal conditions, the present BCB-AuNP assembly is capable of detecting Pb(2+) with a concentration ranging from 7.5 × 10(-10) to 1 × 10(-8) mol L(-1) (0.16-2.1 ng mL(-1)) and a detection limit of 0.51 nM (0.11 ng mL(-1)). The present BCB-AuNP assembly can be used in aqueous media for the determination of Pb(2+) unlike common organic fluorescent reagents, and also shows advantages of NIR fluorescence spectrophotometry such as less interference, lower detection limit, and higher sensitivity. Moreover, the present method was successfully applied for the detection of Pb(2+) in water samples with satisfactory results.