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The lysosomal targeted ratiometric fluorescent BD probe reveals excellent application performance in the fields of selective monitoring of the lysosome pH of living cells, real-time dynamic monitoring of autophagy, and document anti-counterfeiting.

A mitochondrial pH sensing fluorescent probe namely 2-(2-(6-hydroxynaphthalen-2-yl)vinyl)-3-(6-(triphenyl-phosphonio)hexyl)benzothiazol-3-ium bromide (HTBT2) was designed and facilely synthesized via the Knoevenagel condensation reaction. HTBT2 displayed a linear fluorescence enhancement at 612 nm in response to pH changes between 8.70 and 7.20. The pK

A lysosome-targeting and polarity-specific fluorescent probe CPM has been rationally designed for cancer diagnosis and imaging. We have successfully shown that lysosome polarity may serve as an ubiquitious marker for cancer detection. The potential of CPM for cancer diagnosis has also been demonstrated at the levels of live cells, organs, whole animal, and clinical patient tissue samples.

We present the first Golgi-targeted small-molecular pH-sensitive fluorescent probe RSG, which allows an off-on fluorescence response to Golgi acidification with high sensitivity and specificity. RSG has been successfully used for real-time monitoring of Golgi pH changes induced by drug treatment at the cellular level, as well as by the LPS-mediated inflammation in vivo.

Lysosomes are acidic organelles containing many hydrolytic enzymes responsible for degrading macromolecules. Aberrant lysosomal pH changes are known to associate with lysosomal dysfunctions linking to various diseases including cancer and neurodegenerative disorders. Thus, it is of paramount importance to monitor lysosomal pH changes in order to investigate the pathological conditions. We report herein two novel, highly sensitive and fast responsive carbazole-based ratiometric fluorescent probes with different emission wavelengths, namely MCDBI and MCDI for lysosomal pH detection and imaging. Importantly, the MCDBI and MCDI probes bearing indole and benzoindoles as acid-sensing sites exhibit pKa values of 4.26 and 4.51, respectively, which are ideal for the quantitative analysis of lysosomal pH changes in living cells. These probes exhibited a strong pH-dependent behavior and responded linearly and rapidly to minor pH fluctuations. Moreover, the two biocompatible probes are highly lysosomal targeting, sensitive towards H+ over metal ions and some bioactive molecules, and exhibit excellent photostability and good reversibility. These probes have excellent cell membrane permeability and are further applied successfully to monitor lysosomal pH fluctuations in the lysosomes of HepG2 cells.

A mitochondrial-targeted pH fluorescent probe 4-(2-(6-hydroxynaphthalen-2-yl)vinyl)-1-methylpyridin-1-ium was facilely synthesized via the carbon–carbon double bond bridging of 6-hydroxy-2-naphthaldehyde and 1,4-dimethylpyridinium iodide salt. The probe exhibited remarkable pH-dependent behavior in the linear range of 7.60–10.00, with a pKa value of 8.85 ± 0.04 near mitochondrial pH. A significantly large Stokes shift of 196 nm was obtained, which reduces the interference of excitation light. Application of the probe in live HepG2 cells indicated that the probe had excellent mitochondrial targeting ability and was successfully used to visualize mitochondrial pH fluctuations in live cells.

Intracellular pH, especially cytoplasmic pH (~7.2) plays a crucial role in cell functions and metabolism. A ratiometric fluorescent probe namely, 6-(2-(benzothiazol-2-yl)vinyl)naphthalen-2-ol (BTNO) was facilely synthesized by the condensation of 6-hydroxy-2-naphthaldehyde and 2-methylbenzothiazole. BTNO exhibited a remarkable ratiometric emission (F456/F526) enhancement in response to a pH change with a linear range of pH = 9.50–7.00 and a pKa value of 7.91 ± 0.03, which is desirable for measuring and monitoring the cytoplasmic pH fluctuations. In addition, because of the high fluorescence quantum yield of BTNO (Φ = 0.88 in DMSO and 0.61 in water relative to quinine sulfate solution in 0.1 M H2SO4), the interferences of the probe on the physiological functions could be greatly reduced. This could also provide enhanced measurement sensitivity. The successful demonstration of BTNO in detecting and monitoring the intracellular pH changes in live HeLa cells via a ratiometric approach confirmed that BTNO held a practical potential in biomedical research.

As an effective lysosomal biomarker for oxidative stress status, cysteine (Cys) plays an important role in lysosomal proteolysis. Herein, we report the first lysosome-targetable fluorescence probe (MCAB) for Cys-selective detection based on nucleophilic addition reaction of sulfhydryl toward a α, β-unsaturated ketone and demonstrate its application to lysosomal-targetable imaging. MCAB is designed based on a α, β-unsaturated ethanoylcarbazole as the fluorophore and the thiols reaction site, and a methylcarbitol unit as a lysosome-targetable group. Upon reacting with Cys, this probe turns on highly specific fluorescence signals linearly proportional to Cys concentrations over the range of 0–300 μM. MCAB detects Cys with a rapid response time (within 12 min) and low limit of detection (0.38 μM). MCAB is highly selective to Cys over other similar biothiols including homocysteine (Hcy) and glutathione (GSH). Moreover, it also exhibits significant lysosomal-targetable ability, which is ideal for lysosomal Cys-selective imaging. Using MCAB, we have successfully visualized the fluctuation endogenous Cys in lysosomes under oxidative stress status in real-time.