Development of a Si-rhodamine-based NIR fluorescence probe for highly specific and quick response of Hg2+ and its applications to biological imaging

A novel reversible fluorescent probe for sequential detection of Al3+ and HPO42- based on caffeic acid and its applicability in cell imaging

In this work, we focused on synthesizing a new fluorescent probe HBA based on caffeic acid for detecting Al3+/HPO42- by the mode of "off-on-off". HBA alone exhibited a weak fluorescence emission in aqueous solution. When Al3+ was added into the HBA solution, a significant green fluorescence was found at 498 nm. However, the introduction of HPO42- to the solution of [HBA-Al3+] complex induced the disappearance of green fluorescence. The detection limit of HBA was calculated as low as 41.7 nM for Al3+ and 62.1 nM for HPO42-, respectively. Probe HBA exhibited good cell-membrane penetrability and had the potential to trace Al3+/HPO42- in biological systems.

A novel "turn on" fluorescence probe based on a caffeic acid skeleton for detecting Al3+ and bioimaging application

The specificity detection of Al³⁺ is important for monitoring life health and environmental pollution. A fluorescence enhancement probe based on caffeic acid HAM was synthesized for detecting Al³⁺ with high sensitivity and good selectivity. When Al³⁺ was added in the aqueous solution of HAM, the formation of HAM-Al³⁺ complexes inhibited the PET process, which led to great enhancement of fluorescence. The addition of other metal ions cannot induce the change of fluorescence intensity. The sensing mechanism was proved by ¹H NMR titration, MS, and Job's plot. Moreover, probe HAM exhibited excellent properties, such as high sensitivity (LOD = 0.168 μM), fast response time (30 s), wide pH range (3-11), and good interference ability. Based on the above results, probe HAM was used to explore its bioimaging application in biological samples.

Recent progress of TP/NIR fluorescent probes for metal ions

Metal ions are of significance in various pathological and physiological processes. As such, it is crucial to monitor their levels in organisms. Two-photon (TP) and near-infrared (NIR) fluorescence imaging has been utilized to monitor metal ions because of minimal background interference, deeper tissue depth penetration, lower tissue self-absorption, and reduced photodamage. In this review, we briefly summarize recent progress from 2020 to 2022 of TP/NIR organic fluorescent probes and inorganic sensors in the detection of metal ions. Additionally, we present an outlook for the development of TP/NIR probes for bio-imaging, diagnosis of diseases, imaging-guided therapy, and activatable phototherapy.

Molecular probes for fluorescent sensing of metal ions in non-mammalian organisms

While metal ions play an important role in the proper functioning of all life, many questions remain unanswered about exactly how different metals contribute to health and disease. The development of fluorescent probes, which respond to metals, has allowed greater understanding of the cellular location, concentration and speciation of metals in living systems, giving a new appreciation of their function. While the focus of studies using these fluorescent tools has largely been on mammalian organisms, there has been relatively little application of these powerful tools to other organisms. In this review, we highlight recent examples of molecular fluorophores, which have been applied to sensing metals in non-mammalian organisms.

Fluorescent and Colorimetric Dual-Mode Strategy Based on Rhodamine 6G Hydrazide for Qualitative and Quantitative Detection of Hg2+ in Seafoods

In this study, a rapid fluorescent and colorimetric dual-mode detection strategy for Hg²⁺ in seafoods was developed based on the cyclic binding of the organic fluorescent dye rhodamine 6G hydrazide (R6GH) to Hg²⁺. The luminescence properties of the fluorescent R6GH probe in different systems were investigated in detail. Based on the UV and fluorescence spectra, it was determined that the R6GH has good fluorescence intensity in acetonitrile and good selective recognition of Hg²⁺. Under optimal conditions, the R6GH fluorescent probe showed a good linear response to Hg²⁺ (R² = 0.9888) in the range of 0-5 μM with a low detection limit of 2.5 × 10^-2 μM (S/N = 3). A paper-based sensing strategy based on fluorescence and colorimetric analysis was developed for the visualization and semiquantitative analysis of Hg²⁺ in seafoods. The LAB values of the paper-based sensor impregnated with the R6GH probe solution showed good linearity (R² = 0.9875) with Hg²⁺ concentration in the range of 0-50 μM, which means that the sensing paper can be combined with smart devices to provide reliable and efficient Hg²⁺ detection.

A novel peptide-based fluorescent probe for highly selective detection of mercury (II) ions in real water samples and living cells based on aggregation-induced emission effect

A new fluorescent probe TPE-GHK was synthesized containing a tetrastyrene (TPE) derivative as fluorophore and classical tripeptide (Gly-His-Lys-NH₂) as a receptor based on the aggregation-induced emission (AIE) mechanism. TPE-GHK displayed high selectivity and rapid fluorescent "turn-on" response to Hg²⁺ among other competitive metal ions. The 2:1 complex binding mechanism of TPE-GHK toward Hg²⁺ was verified by fluorometric titration, Job's plots, and ESI-HRMS spectra. The fluorescent emission showed a good linear response in the range of 0-1.0 μM with the low detection limit of 28.6 nM. Meanwhile, TPE-GHK exhibited the excellent biocompatibility and low toxicity and was successfully applied in monitoring Hg²⁺ in living CAKI 2 cells, which demonstrated its potential application in environment and biological science. More importantly, TPE-GHK could be used to detect Hg²⁺ in two real water samples and also was successfully designed as test strips.