Turn-on Fluorescence Chemosensor for Zn2+ Ion Using Salicylate Based Azo Derivatives and their Application in Cell-Bioimaging

Novel imidazo[1,2,4] triazole derivatives: Synthesis, fluorescence, bioactivity for SHP1

The Src homology 2 domain-containing protein tyrosine phosphatase 1 (SHP1) is a convergent node for oncogenic cell-signaling cascades. Consequently, SHP1 represents a potential target for drug development in cancer treatment. The development of efficient methods for rapidly tracing and modulating the SHP1 activity in complex biological systems is of considerable significance for advancing the integration of diagnosis and treatment of the related disease. Thus, we designed and synthesized a series of imidazo[1,2,4] triazole derivatives containing salicylic acid to explore novel scaffolds with inhibitory activities and good fluorescence properties for SHP1. The photophysical properties and inhibitory activities of these imidazo[1,2,4] triazole derivatives (5a-5y) against SHP1PTP were thoroughly studied from the theoretical simulation and experimental application aspects. The representative compound 5p exhibited remarkable fluorescence response (P: 0.002) with fluorescence quantum yield (QY) of 0.37 and inhibitory rate of 85.21 ± 5.17% against SHP1PTP at the concentration of 100 μM. Furthermore, compound 5p showed obvious aggregation caused quenching (ACQ) effect and had high selectivity for Fe3+ ions, good anti-interference and relatively low detection limit (5.55 μM). Finally, the cellular imaging test of compound 5p also exhibited good biocompatibility and certain potential biological imaging application. This study provides a potential way to develop molecules with fluorescent properties and bioactivities for SHP1.

Recent Advances in Fluorescent Probes for Zinc Ions Based on Various Response Mechanisms

Zinc is a vital metal element with extensive applications in various fields such as industry, metallurgy, agriculture, food, and healthcare. For living organisms, zinc ions are indispensable, and their deficiency can lead to physiological and metabolic abnormalities that cause multiple diseases. Hence, there is a significant need for selective recognition and effective detection of free zinc ions. As a probe method with high sensitivity, high selectivity, real-time monitoring, safety, harmlessness and ease of operation, fluorescent probes have been widely used in metal ion identification studies, and many convenient, low-cost and easy-to-operate fluorescent probes for Zn²⁺ detection have been developed. This article reviews the latest research advances in fluorescent chemosensors for Zn²⁺ detection from 2019 to 2023. In particular, sensors working through photo-induced electron transfer (PET), excited state intramolecular proton transfer (ESIPT), intramolecular charge transfer (ICT), fluorescence resonance energy transfer (FRET), chelation-enhanced fluorescence (CHEF), and aggregation-induced emission (AIE) mechanisms are described. We discuss the use of various recognition mechanisms in detecting zinc ions through specific cases, some of which have been validated through theoretical calculations.

Fluorescent Azobenzene-Containing Compounds: From Structure to Mechanism

The reversible photoisomerization of azobenzenes has been extensively studied to construct systems with optical responsiveness; however, this process limits the luminescence of these compounds. Recently, there have been many efforts to design and synthesize fluorescent azobenzene compounds, such as inhibition of electron transfer, inducing aggregation, and metal-enhancement, which make the materials ideal for application in fluorescence probes, light-emitting devices, molecular detection, etc. Herein, we review the recently reported progress in the development of various fluorescent azobenzenes and summarize the possible mechanism of their fluorescence emission. The potential applications of these materials are also discussed. Finally, in order to guide research in this field, the existing problems and future development prospects are discussed.

A novel tetrapeptide fluorescence sensor for early diagnosis of prostate cancer based on imaging Zn2+ in healthy versus cancerous cells

Zinc as a biomarker can be used to diagnose the early stage prostate cancer, while ZIP1 protein, a zinc transporter is significantly down-regulated in prostate cancer cells. This behavior leads to the apparent alteration of the enrichment ability for zinc between early prostate cancer tissues and healthy tissues. This difference inspires us to develop a novel Zn²⁺ sensor that applies to the clinic diagnosis of early prostate cancer. We designed a tetrapeptide sensor H₂L (Dansyl-Gly-Pro-Trp-Gly-NH₂) according to the photo-induced electron transfer principle (PET), and it performed adequately in Zn²⁺ imaging of prostate cell lines. Based on the assessment of Zn²⁺ enrichment ability, there was distinctly lower Zn²⁺ concentrate in prostate cancer cell lines than healthy prostate epithelial cells. Furthermore, H₂L displayed high sensitivity with a detection limit as low as 49.5 nM, and high specificity for Zn²⁺ detection. Also the low toxicity and the superior cell permeability of H₂L made the imaging of Zn²⁺ ions detection safe and rapid. We expect that H₂L to be a powerful tool for early diagnosis of prostate cancer and a good indicator for the precise resection of cancer tissue during surgery.

A coumarin-based turn-on chemosensor for selective detection of Zn(II) and application in live cell imaging

A 2-oxo-2H-chromene-3-carbohydrazide (CHB) was synthesized by the reaction of salicylaldehyde with diethyl malonate and hydrazine hydrate. The recognition behaviors of CHB to Zn²⁺ were investigated and the results showed that CHB exhibits well selectivity and sensitivity to Zn²⁺ with fast response in PBS (pH = 7.24, 60% DMF), the co-existed cations and anions could not interfere the recognition between CHB and Zn²⁺. Besides, the detection limit of CHB for Zn²⁺ was calculated to be 0.95 μM. Furthermore, DFT, EI-MS data and Job's plot were applied for determining the sensing mechanism of CHB with Zn²⁺ and the results showed that a type of 2:1 complex was formed between CHB and Zn²⁺ with the binding constant was 1.32 × 10⁴ M^-2. At last, probe CHB was successfully applied for the imaging of Zn²⁺ in living cells.

Thieno[3,2-c]pyran: an ESIPT based fluorescence “turn-on” molecular chemosensor with AIE properties for the selective recognition of Zn2+ ion

Thieno[3,2-c]pyran was synthesized as a fluorescent turn-on chemosensor for the selective recognition of Zn²⁺ ions with a low detection limit (0.67 μM), and it also exhibited AIE properties.

Development of a near infrared novel bioimaging agent via co-oligomerization of Congo red with aniline and o-phenylenediamine: experimental and theoretical studies

With a view to study the effect of insertion of a multifunctional dye moiety on the photo physical properties of conducting polymers, the present paper reports for the first time the homopolymerization and co-oligomerization of Congo red (CR) dye with aniline and o-phenylenediamine. The co-oligomerization was established by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (1H-NMR), and ultraviolet-visible (UV-vis) spectroscopy while the morphology was examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The theoretical as well as experimental data of 1H-NMR as well as IR studies confirmed the co-oligomer formation while ultraviolet-visible spectroscopy studies revealed a dynamic change in the optical properties upon variation of co-oligomer composition. X-ray diffraction studies established a crystalline morphology of oligomers. Live cell confocal imaging studies revealed that the co-oligomers could be effectively used in NIR imaging.

Subtle structural variation in azine/imine derivatives controls Zn2+ sensitivity: ESIPT-CHEF combination for nano-molar detection of Zn2+ with DFT support

Excited-state intra-molecular proton transfer (ESIPT)-active imine and azine derivatives, structurally characterised by XRD, and denoted L1, L2, L3 and L4, possess weak fluorescence. The interaction of these probes with Zn²⁺ turns ON the fluorescence to allow its nano-molar detection. Among the four ESIPT-active molecules, L2, L3 and L4 are bis-imine derivatives while L1 is a mono-imine derivative. Among the three bis-imine derivatives, one is symmetric (L3) while L2 and L4 are unsymmetrical. The lowest detection limits (DL) of L1, L2, L3 and L4 for Zn²⁺ are 32.66 nM, 36.16 nM, 15.20 nM and 33.50 nM respectively. All the probes bind Zn²⁺ (10⁵ M⁻¹ order) strongly. Computational studies explore the orbital level interactions responsible for the associated photo-physical processes.

Single crystal X-ray structurally characterised ESIPT-active weakly fluorescent imine and azine derivatives undergo Zn²⁺ assisted turn ON fluorescence.