Hongguang Lu

An FRET-based ratiometric chemosensor for in vitro cellular fluorescence analyses of pH

Ratiometric fluorescence sensing is an important technique for precise and quantitative analysis of biological events occurring under complex conditions by simultaneously recording fluorescence intensities at two wavelengths and calculating their ratios. Herein, we design a ratiometric chemosensor for pH that is based on photo-induced electron transfer (PET) and binding-induced modulation of fluorescence resonance energy transfer (FRET) mechanisms. This ratiometric chemosensor was constructed by introduction of a pH-insensitive coumarin fluorophore as an FRET donor into a pH-sensitive amino-naphthalimide derivative as the FRET acceptor. The sensor exhibited clear dual-mission signal changes in blue and green spectral windows upon pH changes. The pH sensor was applied for not only measuring cellular pH, but also for visualizing stimulus-responsive changes of intracellular pH values.

Highly Efficient Far Red/Near‐Infrared Solid Fluorophores: Aggregation‐Induced Emission, Intramolecular Charge Transfer, Twisted Molecular Conformation, and Bioimaging Applications

The development of organic fluorophores with efficient solid-state emissions or aggregated-state emissions in the red to near-infrared region is still challenging. Reported herein are fluorophores having aggregation-induced emission ranging from the orange to far red/near-infrared (FR/NIR) region. The bioimaging performance of the designed fluorophore is shown to have potential as FR/NIR fluorescent probes for biological applications.

Using fluorine-containing amphiphilic random copolymers to manipulate the quantum yields of aggregation-induced emission fluorophores in aqueous solutions and the use of these polymers for fluorescent bioimaging

Two new series of aggregation-induced emission (AIE) fluorophore-containing amphiphilic copolymers possessing the segments of a monomeric AIE fluorophore, N-(2-hydroxypropyl)methacrylamide (HPMA), [2-(methacryloyloxy)ethyl]trimethylammonium chloride (MATMA), and/or 2,2,2-trifluoroethyl methacrylate (TFEMA) were synthesized. Photophysical properties were investigated using UV-Vis absorbance and fluorescence spectrofluorometry. The increases of molar fractions of the hydrophobic AIE fluorophores and/or the trifluoroethyl moieties result in the higher quantum yields of the AIE fluorophores in the polymers. Using 1-mol% of AIE fluorophores with the tuning of molar fractions of TFEMA, 40% quantum yield was achieved, whereas only less than 10% quantum yield was obtained for the polymers without the TFEMA segments. The quantum yield difference indicates the importance of the fluorine segments for getting high quantum yields of the AIE fluorophores. These polymers were explored for fluorescent bioimaging using human brain glioblastoma U87MG and human esophagus premalignant CP-A cell lines. All the polymers are cell permeable and located in the cellular cytoplasma area. Cellular uptake was demonstrated to be through endocytosis, which is time and energy dependent. The polymers are non-cytotoxic to the two cell lines. Because the polymers contain (19)F segments, we studied the spin-lattice relaxation time (T1) and spin-spin relaxation time (T2) of these polymers. T1 and T2 are the two important parameters for the evaluations of the capacity of these polymers for further applications in (19)F magnetic resonance imaging ((19)F MRI). Structure influence on T1 and T2, especially for T2, was observed. These new multifunctional materials are the first series of fluorinated polymers with AIE fluorophores for bioapplications.

Label-free fluorescence turn-on detection of Pb2+ based on AIE-active quaternary ammonium salt of 9,10-distyrylanthracene

A label-free fluorescence turn-on approach for the selective sensing of Pb2+ based on quaternary ammonium salt of 9,10-distyrylanthracene with aggregation-induced emission (AIE) property was developed through Pb2+-induced allosteric G-quadruplex (G4). The method is simple, easy to operate, cost-effective, and provides good sensitivity and selectivity.

New ratiometric optical oxygen and pH dual sensors with three emission colors for measuring photosynthetic activity in Cyanobacteria

Photosynthetic algae and cyanobacteria have been proposed for producing biofuels through a direct photoconversion process. To accelerate the efforts of discovering and screening microbes for biofuel production, sensitive and high throughput methods to measure photosynthetic activity need to be developed. Here we report the development of new ratiometric optical oxygen and pH dual sensors with three emission colors for measuring photosynthetic activities directly. The dual sensor system can measure oxygen (O(2)) generation and pH increase resulted from carbon dioxide (CO(2)) consumption simultaneously. The sensor was prepared by a copolymerization of three monomeric probes, an intra-reference probe (IRP) which does not respond to pH or O(2), a probe for pH sensing (pHS), and an O(2) probe for O(2) sensing (OS) with 2-hydroxyethyl methacrylate (HEMA) and acrylamide (AM). After polymerization, the three probes were chemically immobilized in an ion and O(2) permeable poly(2-hydroxyethyl methacrylate)-co-polyacrylamide (PHEMA-co-PAM) matrix. The resulted sensing films (membranes) exhibited three emission colors with well separated emission spectra, covering blue, green, and red emission windows, under 380 nm light excitation. Responses of the sensors to pH and dissolved O(2) were investigated in buffers and cyanobacterial cell cultures (Synechocystis sp. PCC 6803). In spite of the strong autofluorescence from cyanobacteria, the sensors were able to determine the pH values and dissolved O(2) concentrations accurately and reproducibly. The measured results using the optical sensors were well in accordance with measurements using electrodes with minimal experimental variations. The sensors were further applied for evaluation of photosynthetic activities of Synechocystis sp. PCC 6803 at the exponential and stationary phases. The results were consistent with biological observation that the photosynthetic activity in the exponential phase was higher than that in the stationary phase.

Synthesis, characterization, two-photon absorption, and optical limiting properties of triphenylamine-based dendrimers

Three π-conjugated dendrimers (Ph-G0, Ph-G1 and Ph-G2) bearing triphenylamine moieties have been synthesized through a convergent synthetic strategy without any protection–deprotection chemistry. The linear photophysical properties, two-photon absorption (TPA), and optical limiting behavior of the dendrimers were investigated in solution at room temperature. Linear absorption and emission spectra revealed a bathochromic shift and decreased fluorescence quantum yields with increasing dendrimer generation. A strong cooperative effect in the TPA absorption of these dendrimers was observed. The TPA cross-sections increase gradually with the proportion of triphenylamine units and the maximum value of the TPA cross-section can reach 5690 GM for Ph-G2. These triphenylamine-based dendrimers exhibited efficient two-photon optical limiting under femtosecond excitation.

Pluronic F127–folic acid encapsulated nanoparticles with aggregation-induced emission characteristics for targeted cellular imaging

In this work, fluorescence amplified organic nanoparticles (NPs) are synthesized by incorporation of the hydrophobic aggregation-induced emission (AIE) fluorophores, 9,10-bis(4-butoxystyryl) anthracene (BOSA) and/or bis(4-(N-(2-naphthyl)phenylamino)-phenyl)fumaronitrile (NPAPF), using biocompatible Pluronic F127–folic acid adduct (F127–FA) as the encapsulation matrix. The emission spectrum of BOSA donor overlaps well with the absorption spectrum of NPAPF acceptor, resulting in a 3.0-fold amplified NPAPF emission signal via fluorescence resonance energy transfer (FRET). The obtained BOSA–NPAPF co-loaded F127–FA nanoparticles (NPs) show a large Stokes shift of 245 nm, high water dispersibility, and low cytotoxicity. Application of these NPs for targeted cellular imaging is successfully demonstrated using folate receptor (FR)-overexpressed MCF-7 breast cancer cells as an example. Using the F127–FA as the encapsulation matrix, the folate-functionalized AIE NPs show bright fluorescence signals and specific targeting effect for FR-overexpressed cancer cells. These studies indicate that the F127–FA encapsulated AIE NPs are efficient fluorescent probes for biological imaging.

A dual sensor for real-time monitoring of glucose and oxygen

A dual glucose and oxygen sensor in a polymer format was developed. The dual sensor composed of a blue emitter as the glucose probe, a red emitter as an oxygen probe, and a yellow emitter as a built-in reference probe which does not respond to either glucose or oxygen. All the three probes were chemically immobilized in a polyacrylamide-based matrix. Therefore, the dual sensor possesses three well separated emission colors and ratiometric approach is applicable for analysis of the glucose and oxygen concentration at biological conditions. The sensor was applied for real-time monitoring of glucose and oxygen consumption of bacterial cells, Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis), and mammalian cells of mouse macrophage J774 and human cervical cancer HeLa cell lines. On the other hand, in order to achieve satisfactory sensing performance for glucose, compositions of the matrices among poly(2-hydroxyethyl methacrylate), polyacrylamide, and poly(6-aminohexyl methacrylamide) which is a linker polymer for grafting the glucose probe, were optimized.

Aggregation-Induced-Emissive Molecule Incorporated into Polymeric Nanoparticulate as FRET Donor for Observing Doxorubicin Delivery.

Tetraphenylethene (TPE) derivatives characterized with distinct aggregation-induced-emission, attempted to aggregate with doxorubicin (Dox) to formulate the interior compartment of polymeric nanoparticulate, served as fluorescence resonance energy transfer (FRET) donor to promote emission of acceptor Dox. Accordingly, this FRET formulation allowed identification of Dox in complexed form by detecting FRET. Important insight into the Dox releasing can be subsequently explored by extracting complexed Dox (FRET) from the overall Dox via direct single-photon excitation of Dox. Of note, functional catiomers were used to complex with FRET partners for a template formulation, which was verified to induce pH-responsive release in the targeted subcellular compartment. Hence, this well-defined multifunctional system entitles in situ observation of the drug releasing profile and insight on drug delivery journey from the tip of injection vein to the subcellular organelle of the targeted cells.

Construction of Supramolecular Nanoassembly for Responsive Bacterial Elimination and Effective Bacterial Detection

There is an urgent need for developing novel strategies for bacterial detection and inhibition. Herein, a multifunctional nanomaterial based on mesoporous silica nanoparticles (MSNs) is designed, loaded with amoxicillin (AMO), and surface-coated with 1,2-ethanediamine (EDA)-modified polyglycerol methacrylate (PGEDA), cucurbit[7]uril (CB[7]), and tetraphenylethylene carboxylate derivatives (TPE-(COOH)4) by the layer-by-layer (LbL) self-assembly technique. When bacteria contacts with this nanoassembly, the binding of anionic bacterial surface toward the cationic PGEDA layer of this material can reduce or break the interactions between PGEDA layer and TPE-(COOH)4 layer, leading to attenuated TPE-(COOH)4 emission due to the weakening of aggregation-induced emission (AIE) effect. Furthermore, upon adding adamantaneamine (AD), the more stable AD⊂CB[7] complex forms and PGEDA is liberated through competitive replacement, thus leading to the release of AMO and resulting in much higher antibacterial ability of this nanomaterial. This newly designed nanomaterial possesses dual functions of controllable antibacterial activity against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli, and bacterial detection ability in aqueous media, suggesting that the design of this multifunctional antibacterial material will provide a simple, effective, and rapid way to control the activity of antimicrobial and open up an alternative new avenue for bacterial detection and elimination.