Junhua Yu

Shuttle-based fluorogenic silver cluster biolabels

Most molecular/cellular labeling utilizes organic dyes conjugated to bioactive molecules through general organic/inorganic chemistry. Though shortcomings of organic dyes such as poor photostability[1] and low brightness[2] limit observable copy numbers, lack of selectivity in labeling often more seriously limits their application in live cell imaging and single molecule studies[3]. Specificity can be addressed through antibodies and other strong affinity pairs such as avidin-biotin[4, 5], but direct covalent technologies are crucial at sub-pM concentrations, as this is beyond the binding limits of antibody-based affinities. Genetically encoded fluorescent proteins are an excellent solution for specific fluorescent labeling in live cells, but disadvantageous organic dye photophysical instabilities (blinking and bleaching) remain, coupled with the potential perturbation due to large label size[6]. Attempts to overcome photoinstabilities of organic labels have produced much brighter quantum dot labels[7], but, while providing excellent signals, these emitters introduce additional problems such as large physical size, aggregation, toxicity, polyvalency, and strong fluorescence intermittency[8–10]. Simultaneously addressing concerns of brightness, photostability, monovalency, size, and fluorescence intermittency, newly emerging silver cluster-based labels offer excellent potential as molecular labeling agents[11–15]. Spectrally-pure emitters have been produced ranging from the blue to the near IR, with fluorescence quantum yields (ΦF) up to 40% and hydrodynamic radii of the fully assembled ssDNA-encapsulated SCs of ~2.5 nm[16]. Moreover, at bulk and single molecule levels, SCs also show both excellent brightness and photostability[17].

Live Cell Surface Labeling with Fluorescent Ag Nanocluster Conjugates

DNA‐encapsulated silver clusters are readily conjugated to proteins and serve as alternatives to organic dyes and semiconductor quantum dots. Stable and bright on the bulk and single molecule levels, Ag nanocluster fluorescence is readily observed when staining live cell surfaces. Being significantly brighter and more photostable than organics and much smaller than quantum dots with a single point of attachment, these nanomaterials offer promising new approaches for bulk and single molecule biolabeling.

Optically modulated fluorophores for selective fluorescence signal recovery.

Fluorescence imaging in biological sciences is hindered by significant depth-dependent signal attenuation and highly fluorescent backgrounds. We have developed optically modulated near-IR-emitting few-atom Ag nanodots that are selectively and dynamically photobrightened upon simultaneous excitation with a secondary laser, enabling high-sensitivity image extraction to reveal only the demodulated fluorophores. Image demodulation is demonstrated in high-background environments to extract weak signals from completely obscuring background emission.

Photoelectrochemical properties of TiO2 electrodes sensitized by porphyrin derivatives with different numbers of carboxyl groups

Abstract The photochemical and photoelectrochemical properties of two porphyrin derivatives with different numbers of carboxyl groups were investigated. The two porphyrin derivatives are 5-(4-carboxyphenyl)-10,15,20-tritolylporphyrin (H2TC1PP) and 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (H2TC4PP). The interaction between the porphyrin and TiO2 is determined by the UV–vis spectra. Differences in adsorption behavior of the two porphyrin derivatives on the TiO2 electrode surface were observed. The IR data suggest that both of the porphyrins adsorb by bridging or bidentate chelate coordination on the TiO2 surface. Comparing the luminescence spectra of the two porphyrins in solution and the solid state, no spectral difference was observed. However, we found that the variation in the number of carboxyl groups has an influence on the fluorescence spectra of the adsorbed TiO2 electrode. Furthermore, we measured and compared the incident photon-to-current conversion efficiency (IPCE) and the light-to-electrical conversion efficiency of the porphyrin-sensitized solar cell. These results revealed that the number of functional groups influenced the photoelectrochemical properties of the cell.

Detection of hydrogen peroxide with chemiluminescent micelles

The overproduction of hydrogen peroxide is implicated in the progress of numerous life-threatening diseases and there is a great need for the development of contrast agents that can detect hydrogen peroxide in vivo. In this communication, we present a new contrast agent for hydrogen peroxide, termed peroxalate micelles, which detect hydrogen peroxide through chemiluminescence, and have the physical/chemical properties needed for in vivo imaging applications. The peroxalate micelles are composed of amphiphilic peroxalate based copolymers and the fluorescent dye rubrene, they have a ‘stealth’ polyethylene glycol (PEG) corona to evade macrophage phagocytosis, and a diameter of 33 nm to enhance extravasation into permeable tissues. The peroxalate micelles can detect nanomolar concentrations of hydrogen peroxide (>50 nM) and thus have the sensitivity needed to detect physiological concentrations of hydrogen peroxide. We anticipate numerous applications of the peroxalate micelles for in vivo imaging of hydrogen peroxide, given their high sensitivity, small size, and biocompatible PEG corona.

A pH-insensitive, ratiometric chemosensor for citrate using europium luminescence.

A chemoselective sensor for the citrate anion has been devised, based on a new europium complex that offers ratiometric analysis of the long-lived emission.

Autofluorescence generation and elimination: a lesson from glutaraldehyde

Glutaraldehyde causes especially high autofluorescence. It reacted with proteins and peptides to generate visible to near-IR emitters. A model indicated that ethylenediamine and a secondary amine in the molecule were key components for the formation of emissive species. The mechanism enables us to control the generation and elimination of autofluorescence.

Colorimetric and fluorescent dual detection of paraquat and diquat based on an anionic polythiophene derivative

We have developed a colorimetric and fluorescent dual-response probe for the detection of paraquat and diquat in aqueous solutions based on an anionic polythiophene derivative. The detection limit of this approach can be as low as 10(-9) M by fluorescence measurements.

DNA-encapsulated silver nanodots as ratiometric luminescent probes for hypochlorite detection

DNA-encapsulated silver nanodots are noteworthy candidates for bio-imaging probes, thanks to their excellent photophysical properties. The spectral shift of silver nanodot emitters from red to blue shows excellent correlations with the concentration of reactive oxygen species, which makes it possible to develop new types of probes for reactive oxygen species (ROS), such as hypochlorous acid (HOCl), given the outstanding stability of the blue in oxidizing environments. HOCl plays a role as a microbicide in immune systems but, on the other hand, is regarded as a disease contributor. Moreover, it is a common ingredient in household cleaners. There are still great demands to detect HOCl fluxes and their physiological pathways. We introduce a new ratiometric luminescence imaging method based on silver nanodots to sensitively detect hypochlorite. The factors that influence the accuracy of the detection are investigated. Its availability has also been demonstrated by detecting the active component in cleaners.PACS82; 82.30.Nr; 82.50.-m

The triplet excited state changes of amphiphilic porphyrins with different side-chain length in AOT reverse micelles

Two amphiphilic porphyrins terminated with carboxyl were studied in AOT/iso-octane/water reverse micelles, intending to mimic the relationship between microenvironments in organism and the amphiphilic properties of porphyrins for photodynamic therapy (PDT) drugs. The quenching of porphyrins by methyl viologen chloride and the laser flash photolysis experiments show that the longer side-chain length would promote the firm embedding of porphyrin molecules in the interfacial region of reverse micelles. Such an embedding may shift porphyrins from aggregated to monomeric form in reverse micelles and, accordingly, the slower excited state decay may increase the efficiency of the photosensitizer in PDT. The effect of amphiphilic properties on the status of porphyrins in microenvironments provides a light on the synthesis of other amphiphilic porphyrins for PDT drugs.