Changmin Yu

A PEGylated Fluorescent Turn‐On Sensor for Detecting Fluoride Ions in Totally Aqueous Media and Its Imaging in Live Cells

Owing to the considerable significance of fluoride anions for health and environmental issues, it is of great importance to develop methods that can rapidly, sensitively and selectively detect the fluoride anion in aqueous media and biological samples. Herein, we demonstrate a robust fluorescent turn-on sensor for detecting the fluoride ion in a totally aqueous solution. In this study, a biocompatible hydrophilic polymer poly(ethylene glycol) (PEG) is incorporated into the sensing system to ensure water solubility and to enhance biocompatibility. tert-Butyldiphenylsilyl (TBDPS) groups were then covalently introduced onto the fluorescein moiety, which effectively quenched the fluorescence of the sensor. Upon addition of fluoride ion, the selective fluoride-mediated cleavage of the Si-O bond leads to the recovery of the fluorescein moiety, resulting in a dramatic increase in fluorescence intensity under visible light excitation. The sensor is responsive and highly selective for the fluoride anion over other common anions; it also exhibits a very low detection limit of 19 ppb. In addition, this sensor is operative in some real samples such as running water, urine, and serum and can accurately detect fluoride ions in these samples. The cytotoxicity of the sensor was determined to be Grade I toxicity according to United States Pharmacopoeia and ISO 10993-5, suggesting the very low cytotoxicity of the sensor. Moreover, it was found that the senor could be readily internalized by both HeLa and L929 cells and the sensor could be utilized to track fluoride level changes inside the cells.

A low cytotoxic and ratiometric fluorescent nanosensor based on carbon-dots for intracellular pH sensing and mapping.

Intracellular pH plays a critical role in the function of cells, and its regulation is essential for most cellular processes. In this study, we demonstrate a fluorescence resonance energy transfer (FRET)-based ratiometric pH nanosensor with carbon-dot (CD) as the carrier. The sensor was prepared by covalently linking a pH-sensitive fluorescent dye (fluorescein isothiocyanate, FITC) onto carbon-dot. As the FRET donor, the carbon-dot exhibits bright fluorescence emission as well as λex-dependent photoluminescence emission, and a suitable excitation wavelength for the donor (CD) can be chosen to match the energy acceptor (fluorescein moiety). The fluorescein moieties on a CD undergo structural and spectral conversion as the pH changes, affording the nanoplatform a FRET-based pH sensor. The CD-based system exhibits a significant change in fluorescence intensity ratio between pH 4 and 8 with a pKa value of 5.69. It also displays excellent water dispersibility, good spectral reversibility, satisfactory cell permeability and low cytotoxicity. Following the living cell uptake, this nanoplatform with dual-chromatic emissions can facilitate real-time visualization of the pH evolution involved in the endocytic pathway of the nanosensor. This reversible and low cytotoxic fluorescent nanoplatform may be highly valuable in a variety of biological studies, such as endocytic trafficking, endosome/lysosome maturation, and pH regulation in subcellular organelles.

A fluorescent ratiometric nanosensor for detecting NO in aqueous media and imaging exogenous and endogenous NO in live cells

As an endogenously generated signal-inducing agent in the immune, cardiovascular and nervous systems, nitric oxide (NO) is involved in various biological processes and a large number of pathologies. Hence, sensitive and reliable detection of NO in biological samples and inside living cells has been of great interest. Herein, we reported a carbon-dot-based fluorescent ratiometric nanosensor for NO detection in water and imaging in living cells. Ratiometric sensing is realized through the fluorescence resonance energy transfer (FRET) process, and the carbon dots (CDs) serve as both the energy donor and the anchoring site for the NO probe moiety, which turns into the energy acceptor in the presence of NO. This nanosensor is highly selective for NO, and is operable in totally aqueous media with a very low detection limit of 3 nM. Due to the biocompatible nature and small size of the carbon dots, the nanosensor exhibits very low cytotoxicity and can easily permeate through the cell membrane. The nanosensor is capable of tracking the exogenous NO levels in several cell lines such as Hela, L929 and Raw 264.7 cells, and it can be also used to visualize the endogenously produced NO in the Raw 264.7 macrophage cell line.

Hyperbranched polyester-based fluorescent probe for histone deacetylase via aggregation-induced emission.

Aberrant expression of histone deacetylases (HDACs) is related to various types of cancer and is associated with increased proliferation of tumor cells. Hence, the detection of HDAC activities is of great significance for medical sciences as well as biological diagnostics. Herein, we report a hyperbranched polyester-based one-step fluorescent assay for HDAC. This assay system consists of two water-soluble components: the hyperbranched polyester coupled with the acetylated lysine groups (H40-Lys(Ac)) and the negatively charged TPE derivative bearing two sulfonic acid groups (TPE-2SO3(-)). HDAC triggers the deacetylation of H40-Lys(Ac), thereby turning the electroneutral polymer into the positively charged one. Consequently, complexation occurs between the positively charged polymer and the negatively charged TPE-2SO3(-), thereby leading to the formation of nanoaggregates due to electrostatic interaction. Eventually, the fluorescence enhancement as a result of AIE effect is achieved. This assay system is operable in aqueous media with very low detection limit of 25 ng/mL. The system is capable of detecting HDAC in such biological fluid as serum, and this strategy may provide a new and effective approach for enzyme assay.

A fast-responding fluorescent turn-on sensor for sensitive and selective detection of sulfite anions

A robust fluorescent turn-on sensor with a detection limit of 10 nM was developed for detecting sulfite anions in water and real beverage samples. For this sensitive sensor, the reaction of sulfite with the quenching moiety of the probe led to the enhanced fluorescent emission.

Ratiometric fluorescence assay for γ-glutamyltranspeptidase detection based on a single fluorophore via analyte-induced variation of substitution

The first ratiometric fluorescent probe for γ-glutamyltranspeptidase (GGT) was developed, which functions through GGT-induced variation of substitution and subsequent changes in photophysical properties. It can detect GGT in human serum, and be used to visualize the endogenous GGT in ovarian cancer cells.

A polylysine-based fluorescent probe for sulfite anion detection in aqueous media via analyte-induced charge generation and complexation

Sulfite is widely used as a preservative in food and beverages; and human exposure to SO2 (which is easily transformed into sulfite) has become increasingly widespread. Overdose or inhalation of sulfite may induce many respiratory responses and a number of diseases. Hence, it is important to achieve rapid, sensitive and selective detection of sulfites. Herein, we report a robust fluorescent turn-on probe for sulfite anions via the analyte-induced charge generation and AIE effect (the aggregation induced emission effect). The two-component sensing system comprises a modified polylysine with benzoic aldehyde side groups and a positively charged tetraphenylethene bearing two quaternary ammonium groups. In the presence of sulfite anions, the benzoic aldehyde groups on polylysine side chains react with sulfite and turn into negatively charged groups, leading to the complexation between the polymer chains and the positively charged fluorophores (TPE-2N+) and eventually achieving the fluorescence enhancement of the system as a result of the AIE effect. The integration of the water-soluble biopolymer and AIE-active fluorophore ensures that the system is operable in totally aqueous media (100% water), which is beneficial for applications in food quality control, environmental pollution monitoring and biological assays. Furthermore the system exhibits highly selective and sensitive fluorescent turn-on detection for sulfite, with the detection limit of 3.6 μM. Moreover, it can be used in real samples such as red wine, beer and rainwater, and there is no need for special sample pretreatment.

A silica nanoparticle-based sensor for selective fluorescent detection of homocysteine via interaction differences between thiols and particle-surface-bound polymers.

Biothiols play crucial roles in maintaining biological systems; among them, homocysteine (Hcy) has received increasing attention since elevated levels of Hcy have been implicated as an independent risk factor for cardiovascular disease. Hence, the selective detection of this specific biothiol, which is a disease-associated biomarker, is very important. In this paper, we demonstrate a new mesoporous silica nanoparticle-based sensor for selective detection of homocysteine from biothiols and other common amino acids. In this fluorescent sensing system, an anthracene nitroolefin compound was placed inside the mesopores of mesoporous silica nanoparticles (MSNs) and used as a probe for thiols. The hydrophilic polyethylene glycol (PEG 5000) molecules were covalently bound to the MSN surface and used as a selective barrier for Hcy detection via different interactions between biothiols and the PEG polymer chains. The sensor can discriminate Hcy from the two low-molecular mass biothiols (GSH and Cys) and other common amino acids in totally aqueous media as well as in serum, with a detection limit of 0.1 μM. This strategy may offer an approach for designing other MSN-based sensing systems by using polymers as diffusion regulators in sensing assays for other analytes.

Low molecular weight PEIs modified by hydrazone-based crosslinker and betaine as improved gene carriers.

Low-molecular-weight polyethyleneimine (LMW PEI) exhibits poorer transfection efficiency but lower cytotoxicity compared to high-molecular-weight polyethyleneimine (such as PEI 25kDa). To enhance the gene transfection performance of LMW PEI, we herein demonstrate a new strategy for modifying LMW PEI. A crosslinker containing an acid-labile hydrazone bond (hydrazone-based crosslinker) was synthesized and used to crosslink PEI 1.8kDa and convert it into higher-molecular-weight polycations. And the crosslinked polycations were further modified by incorporating a betaine monomer [N,N-dimethyl(acrylamidopropyl)ammonium propane sulfonate, DMAAPS] onto their surfaces. The molar percentages of the incorporated betaine molecules to amino groups on the polycations were determined as 21.2%, 36.0% and 77.2%, respectively. Molecular weights of the modified polycations were measured using capillary viscometry at pH 7.4 and 5.0, respectively, and the degradation of the polymers in acidic solution was confirmed. The PEIs modified with hydrazone and betaine (PEI-Hdz-DMAAPS) exhibit much lower cytotoxicity than PEI 25K, and they also show no or little hemolytic effect with their hemolysis rates around 5%. PEI-Hdz-DMAAPS21.2%/DNA and PEI-Hdz-DMAAPS36.0%/DNA complexes exhibit high transfection efficiencies, which are comparable to or higher than that of PEI 25K/DNA complex in the absence or presence of 10% serum. With these improved gene delivery properties, the PEI-Hdz-DMAAPS samples have great potential for serving as efficient gene carriers. This strategy may provide some insights for constructing some other biocompatible materials.