Using Graphene Quantum Dots as Photoluminescent Probes for

Sep 5, 2013 - Using Graphene Quantum Dots as Photoluminescent Probes for Protein Kinase Sensing. Citing Articles; Related Content. Citation data is ma...
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Using Graphene Quantum Dots as Novel Photoluminescent Probes for Protein Kinase Sensing Ying Wang, Li Zhang, Ru-Ping Liang, Jian-Mei Bai, and Jian-Ding Qiu Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/ac401807b • Publication Date (Web): 05 Sep 2013 Downloaded from http://pubs.acs.org on September 18, 2013

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Analytical Chemistry

Using Graphene Quantum Dots as Novel Photoluminescent Probes for Protein Kinase Sensing Ying Wang, Li Zhang, Ru-Ping Liang, Jian-Mei Bai, Jian-Ding Qiu* Department of Chemistry, Nanchang University, Nanchang 330031, P. R. China

*Corresponding author Jian-Ding Qiu Department of Chemistry, Nanchang University, Nanchang 330031, P. R. China Phone: +86-791-8396-9518 ; Fax: +86-791-8396-9518; E-mail: [email protected]

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Analytical Chemistry

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ABSTRACT A simple and sensitive photoluminescence (PL) assay for the activity of protein kinase was established based on the selective aggregation of phosphorylated peptide-graphene quantum dots (GQDs) conjugates triggered by Zr4+ ions coordination. With more sophisticated design on the peptide substrate sequences, detecting other enzymes could also be possible. Under optimal conditions, a linear relationship between the decreased PL intensity of peptide-GQDs and the concentration of casein kinase II (CK2) in the range from 0.1 U mL-1 to 1.0 U mL-1 with a detection limit of 0.03 U mL-1 (3σ) was obtained. The EC50 value (enzyme concentration at which 50% substrate is converted) of CK2 was evaluated to be 0.34 U mL-1. The proposed method showed potential applications in kinase inhibitor screening. To demonstrate the potential of this GQDs-based platform for screening kinase inhibitors in real biological systems, the inhibition of CK2 phosphorylation activity by four different inhibitors, ellagic acid, 5,6Dichloroben-zimidazole-l-β-D-ribofuranoside (DRB), emodin, and quercetin, was tested in human serum by comparing signals from samples incubated with inhibitors against that without any inhibitor. As expected, in the presence of inhibitors, the PL intensity increased with the increasing efficiency of inhibitor. The IC50 value (inhibitor concentration producing 50% inhibition) of ellagic acid was estimated to be 0.041 µM. The developed protocol provided a new and promising tool for the analysis of both enzyme and its inhibitors with low cost and excellent performance.

KEYWORDS: protein kinase, graphene quantum dot, photoluminescence quenching, inhibitor.

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Analytical Chemistry

INTRODUCTION Graphene, a two-dimensional carbon material, has sparked great excitement within the scientific community due to its fascinating and unusual physical and chemical properties.1,2 Nevertheless, as graphene is a zero-bandgap semiconductor, the possibility of observing its luminescence is highly unlikely,3 and its optoelectronic applications have so far been limited. To generate an electronic band gap in graphene, various methods such as opening the bandgap through doping,4 manipulating graphene oxide (GO) through partial reduction and surface passivation,5,6 and cleaving GO materials into nanoscale graphene quantum dots (GQDs)7,8 have been used to induce photoluminescence (PL). Among them, the GQDs fabrication and the tuning of their optical properties have become the most active area. In theoretical and experimental studies, GQDs with