Qinhan Jin

Sensitive and selective detection of nitrite ion based on fluorescence superquenching of conjugated polyelectrolyte

In recent years, conjugated polyelectrolytes (CPEs) that feature good water-solubility have drawn great attention as optical transducers in high sensitive bio- and chemo-sensors due to their predominant optical/electronic properties and remarkable signal amplification. Herein, a sensitive and selective assay for nitrite ion has successfully been developed based on the fluorescence superquenching of an anionic CPE, PPESO(3). With the sensor format composed of PPESO(3) and H(+), Fe(2+) can easily be oxidized into Fe(3+) in the presence of NO(2)(-), and the later dramatically quenches the fluorescence of PPESO(3). Indeed, the inclusion of conjugated polyelectrolyte into the sensory scheme can give rise to a notable enhancement of fluorescence response, which endows the newly proposed NO(2)(-) probe with high sensitivity. Thus, nitrite ion within a relatively wide concentration range (0-70 microM) can be determined in a rather simple and sensitive manner with a detection limit of 0.62 microM (approximately 28 ppb). Additionally, most other anions such as halogen ions, acetate, sulfate, carbonate, phosphate and even nitrate, show minor interference on the NO(2)(-) detection.

Peptide-induced fluorescence quenching of conjugated polyelectrolyte for label-free, ultrasensitive and selective assay of protease activity

We report here a label-free method for ultrasensitive and selective assay of protease activity based on the peptide-induced fluorescence quenching of conjugated polyelectrolyte (PPESO(3)). It is very interesting to find that there is a critical length of oligo-polyarginine (i.e., Arg(5)) below which 1) the quenching efficiency of PPESO(3) is sharply decreased, and more importantly, 2) the trypsin-catalyzed hydrolysis is greatly slowed down. This opens good opportunities for not only the ultrasensitive assay of trypsin, but the specific detection of other proteases if carefully designing an appropriate peptide length and the cleavage site. Herein, the enzyme selected as a proof of concept is chymotrypsin. Due to the essence that any cleavage of the designed peptide probes will result in a notable decrease or even a complete loss of their capability to quench the emission of PPESO(3), the limits of detection for trypsin and chymotrypsin have been found as low as 0.25 ng/mL (11 pM) and 0.15 ng/mL (6 pM), respectively. Both are superior to those of most previous methods by 1-2 orders or higher.

Au:CdHgTe quantum dots for in vivo tumor-targeted multispectral fluorescence imaging

AbstractNear-infrared gold-doped CdHgTe quantum dots (QDs) with improved photoluminescence and biocompatibility were developed using an aqueous solution route with l-glutathione and l-cysteine as stabilizers. As-prepared Au:CdHgTe QDs were covalently linked to arginine–glycine–aspartic acid (RGD) peptide, anti-epidermal growth factor receptor (EGFR) monoclonal antibody (MAb), and anti- carcinoembryonic antigen-related cell adhesion molecule-1 (CEACAM1) MAb separately. Three Au:CdHgTe QD bioconjugates (QD800-RGD, QD820-anti-CEACAM1, and QD840-anti-EGFR) were successfully used as probes for in vivo tumor-targeted multispectral fluorescence imaging of xenografts. Fluorescence signals from the QD bioconjugates used to detect three tumor markers were spectrally unmixed, and their co-localization was analyzed. The results indicate that multiple tumor markers could be simultaneously detected by multispectral fluorescence imaging in vivo using QD bioconjugates as probes. This approach has excellent potential as an imaging method for the noninvasive exploration and detection of multiple tumor markers in vivo, thereby substantially aiding the diagnosis of cancer.n FigureIn vivo tumor-targeted multispectral fluorescence imaging with Au:CdHgTe quantum dots

Fluorescence turn-on assay for glutathione reductase activity based on a conjugated polyelectrolyte with multiple carboxylate groups

In this work, an anionic conjugated polyelectrolyte (CPE) that features four carboxylate groups on each repeat unit, PPE-(COOK)4, has been designed and synthesized by integrating the two synthetic strategies for conjugated poly(phenylene ethynylene) and dendritic polyamidoamine. Through the installation of multiple functional groups, the proposed CPE has been greatly improved in many aspects, such as the good water solubility, slight aggregation, and relatively high quantum yield. Thanks to the close resemblance in chemical structures between the polymers pendant groups and EDTA, the resulting PPE-(COOK)4 has also been found to show stronger complexation with metal ions, and has further been demonstrated to be an excellent fluorescent probe for Cu2+ with both high sensitivity and remarkable specificity. Moreover, by taking advantage of the distinct fluorescence recovery rates of PPE-(COOK)4/Cu2+ caused by GSH and by GSSG, a novel fluorescence turn-on assay for glutathione reductase (GR) has successfully been developed. With a minimum detectable enzyme concentration of 0.2 mU/mL, this newly proposed GR activity assay is highly sensitive and robust as compared to most spectrophotometric and fluorescent methods.

Detection of mismatched caspase-3 DNA oligonucleotides with an SPR biosensor following amplification by Taq polymerase

AbstractWe demonstrate that base mismatches of caspase-3 DNA sequences can be detected by surface plasmon resonance (SPR) following signal amplification by polymerase from Thermus aquaticus (Taq). The concentration of magnesium ions and the respective dNTPs for polymerase binding to the oligonucleotides on the sensing surface were optimized. Taq polymerase binds to double-stranded DNA that is self-assembled on the gold surface of the biosensor to induce an SPR signal. Experiments are presented on the effect of Mg(II) and dNTP concentrations on the activity of the polymerase on the sensing surface. The detection limits are 50xa0pM, 0.1xa0nM, 0.7xa0nM, 7xa0nM, and 20xa0nM for correctly matched, single-base mismatched, two-base mismatched, three-base mismatched and four-base mismatched DNA of caspase-3, respectively. This is attributed to the optimized experimental conditions, with samples containing 2xa0μM of Mg(II) and 0.3xa0mM of dNTP.n FigureThe process of detecting mismatched caspase-3 DNA oligonucleotides with SPR biosensor