This review discusses the advances in fluorescent Schiff base sensors for metal ion detection with a focus on the strategies, mechanistic insights, and applications.

Fluorescent Schiff base sensors as a versatile tool for metal ion detection: strategies, mechanistic insights, and applications

A novel phenolphthalein-based fluorescent sensor for Al3+ sensing in drinking water and herbal tea samples.

Recent advancement on chromo-fluorogenic sensing of aluminum(III) with Schiff bases

Viscosity activated NIR fluorescent probe for visualizing mitochondrial viscosity dynamic and fatty liver mice

Lysosomal viscosity fluctuation is related to various diseases such as diabetes, neurodegenerative diseases, and cancer. We designed and synthesized four novel pH-insensitive fluorescent viscosity probes ( Lyso-QAP1–4 ) using a quinolinium as the fluorophore and acceptor group while an internal amino benzene ring was incorporated as a donor group and a targeting group for monitoring the viscosity change of lysosomes. Lyso-QAP1–4 possessed a highly sensitive response toward viscosity change with red emission at around 625–640 nm (excited around 570–580 nm), excellent water solubility, good photostability, favorable membrane permeabilization, and moderate cytotoxicity. Colocalization study proved that Lyso-QAP1–4 probes exhibited fast lysosomal detection (within 15 min) without influencing effect from other microenvironments like pH, polarity, and interferent species but Lyso-QAP4 (without a phenyl ring on C2 of quinolinium) also localized in nucleus. Importantly, we demonstrated that a phenyl ring on C2 of quinolinium and an internal amino benzene played an important role in the lysosome specificity. Lyso-QAP1–4 probes can be applied for intracellular viscosity detection. Moreover, Lyso-QAP3 was successfully applied to living cell imaging for cellular and lysosomal viscosity changes. These results suggest that Lyso-QAP3 would provide new opportunities for biomedical diagnosis and imaging applications. • Quinolinium as fluorophore while an internal amino benzene ring as a lysosomal targeting group. • pH-insensitivity to avoid the loss of fluorescence intensity when pH changed. • The phenyl ring on C2 of quinolinium of Lyso-QAP1-3 altered the specificity from nucleus to lysosomes. • Fast lysosome fluorescence imaging within 15 min to detect intracellular viscosity. • Lyso-QAP3 was suitable to detect the lysosomal viscosity change induced by chloroquine. 

Quinolinium-based viscosity probes for lysosome imaging and tracing lysosomal viscosity changes in living cells

A highly selective colorimetric, absorption and fluorescence probe for Al3+ detection based on a new Schiff base compound

A bifunctional sensitive fluorescence probe based on pyrene for the detection of pH and viscosity in lysosome.

Thermo-responsive nanogels, poly(NIPAM–AAM) were prepared by a facile method of free radical one-pot precipitation based on monomeric N-isopropylacrylamide (NIPAM). At the same time, surface carboxyl group-modified fluorescent conjugated polymer nanoparticles (PNPs–COOH) were immobilized in the nanogel networks by hydrogen bonding to show bright green photoluminescence and outstanding thermo-responsive properties with a typical two-phase Tai Chi structure. Poly(NIPAM–AAm)–PNPs–COOH displays a larger change of hydrodynamic diameter (Dh) and a reversible volume transition from ∼150 nm at 40 °C to ∼1.0 μm at 4 °C. The change will cause apoptosis of cells to finish flash chill treatment. Meanwhile, the fluorescence of poly(NIPAM–AAm)–PNPs–COOH demonstrates reversible quenching and recovery with the expansion and collapse of the nanogel network induced by temperature changes. In addition, when adding Fe3+, the fluorescence of poly(NIPAM–AAm)–PNPs–COOH can be quenched due to the chelation between the PNPs–COOH and Fe3+ and then recovered in the presence of hydrogen sulfide because the chelate is broken; this was attributed to the stronger affinity between Fe3+ and S2−. Therefore, the fluorescence nanoplatform, Fe3+/poly(NIPAM–AAm)–PNPs–COOH, was successfully used to detect endogenous hydrogen sulfide in living A549 cells.

Yi-lin Mu

Papers

A highly selective colorimetric, absorption and fluorescence probe for Al3+ detection based on a new Schiff base compound

A bifunctional sensitive fluorescence probe based on pyrene for the detection of pH and viscosity in lysosome.

Thermo-sensitivity of hybrid nanogels for specific endogenous hydrogen sulfide detection and efficient flash chill treatment