Zhengqing Qi

Near-infrared BODIPY-based two-photon ClO− probe based on thiosemicarbazide desulfurization reaction: naked-eye detection and mitochondrial imaging

Hypochlorite serves as a significant antimicrobial agent in the human immune system, and its detection is of great importance. Herein, a novel near-infrared BODIPY-based ClO- fluorescent probe (NCS-BOD-OCH3) was designed and synthesized. The emission bands of NCS-BOD-OCH3 concentrated at 595 nm and 665 nm. Since the electron withdrawing group 1,3,4-oxadiazole was formed after the desulfurization reaction, the fluorescence intensity of NCS-BOD-OCH3 decreased significantly in THF/H2O (v/v, 1 : 1, buffered with 10 mM PBS pH = 7.4), which is visible to the naked eye with an obvious color change. NCS-BOD-OCH3 can realize the two-photon up-converted fluorescence emission. The low detection limit was calculated from the titration results, with the figure for NCS-BOD-OCH3/ClO- being 1.15 × 10-6 M. The result of living cell imaging experiment demonstrated that NCS-BOD-OCH3 can successfully detect ClO- in living cells and can serve as a NIR mitochondrial imaging agent. It is an excellent platform for developing NIR ClO- fluorescent probes.

A smart two-photon fluorescent platform based on desulfurization–cyclization: a phthalimide–rhodamine chemodosimeter for Hg2+ NIR emission at 746 nm and through-bond energy transfer

A smart two-photon fluorescent platform based on desulfurization–cyclization was developed by attaching rhodamine to a cyanine skeleton through the Knoevenagel reaction. Based on the platform, a CyRSN probe was rationally designed and synthesized, in which morpholinyl naphthalimide and modified rhodamine thiohydrazide were linked to form a structure of monothio-bishydrazide. The probe exhibits excellent two-photon properties toward Hg2+ under Ti:sapphire pulsed laser 800 nm irradiation, allowing the naked-eye signal and fluorescence “turn-on” signal at 746 nm to be obviously distinguished. The addition of Hg2+ to the probe ensured that the naphthalimide donor and modified rhodamine acceptor were connected with electronically conjugated bonds (1,2,4-oxadiazole). Hence, a typical TBET process took place, resulting in an increase of the modified rhodamine NIR emission at 746 nm by about 34-fold as well as a decrease of the naphthalimide emission at 540 nm and producing a colorimetric change from pale yellow to green. The chemodosimeter exhibits a stable response for Hg2+ over other metal ions with a detection limit of 1.91 × 10−7 M, high sensitivity, a rapid response time, and pH independence under neutral conditions (pH 6.0–10.0). In addition, the CyRSN probe was successfully applied in the detection and quantification of Hg2+ in water samples with satisfactory recovery results.

A conjugated BODIPY–triphenylamine multi-aldoxime: Sonogashira coupling, ratiometric chemodosimeter and rapid detection of hypochlorite with two-photon excited fluorescence

A conjugated BODIPY–triphenylamine multi-aldoxime (BTN) was designed and synthesized by the Sonogashira coupling reaction. The chemodosimeter showed a red emission (670 nm), fast response (within seconds), high selectivity and good sensitivity towards hypochlorite based on the redox reaction of four aldoximes. BTN possessed two original absorption peaks at 366 nm and 588 nm, respectively, corresponding to fluorescence emissions at 440 nm and 660 nm, which exhibited a ratiometric change in the presence of hypochlorite. With the addition of hypochlorite, the redox reaction of aldoxime led to the termination of isomerization of the CN bond, the fluorescence intensity at 660 nm gradually changed from weak to strong, accompanied by a slight 10 nm red-shift; in contrast, the fluorescence intensity began to decrease at 440 nm. Moreover, as the two-photon excited fluorescent NaOCl probe, BTN afforded an enhanced signal response for hypochlorite at 686 nm under two-photon excitation (λTPEFex = 800 nm). Meanwhile, successful imaging of living cells was carried out for BTN towards hypochlorite in A-549 cells. The results demonstrated that BTN had potential application prospects and was promising for practical application in biological systems and environmental systems.

Tunable double-resonance dimer structure for surface-enhanced Raman scattering substrate in near-infrared region

Plasmonic resonance with Fano lineshape has attracted a great deal of recent interest. Here we design a new structure with a dimer grating upon a gold film separated by a layer of silica spacer, which has two resonant modes corresponding to the dimer’s localized surface plasmon resonance and the surface plasmon resonance excited by the dimer grating. This structure has three advantages for near-infrared detection in water. First, it provides two resonant modes to enhance the excitation and scattered signals of surface-enhanced Raman scattering. Second, coupling of these two modes results in a Fano resonance, providing a higher electric field enhancement. Finally, the dimer provides more flexible tunability compared to a single disk structure.

A two-step method to synthesize water-dispersible Mn:ZnSe/ZnO core/shell quantum dots with pure dopant emission

In this work, water-dispersible Mn:ZnSe/ZnO core/shell quantum dots (QDs) with pure dopant emission were prepared via a two-step method. Compared with the traditional organometallic approach, this two-step method has many advantages, such as using low-cost and non-toxic chemicals, low reaction temperature and simple operation. Moreover, the obtained Mn:ZnSe/ZnO core/shell QDs also showed superior properties to those prepared by the aqueous solution synthesis, such as narrow emission and good monodispersity. The influence of the storage time of Mn:ZnSe QDs in organic medium, the amount of MPA and temperature during the period of ZnO shell deposition on the photo-luminescence (PL) properties was investigated. Under optimal conditions, MPA-capped Mn:ZnSe/ZnO QDs with an average diameter of 2.6 nm and a dopant PL quantum yield (QY) of 30% in water were produced.