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Cite This: ACS Appl. Mater. Interfaces XXXX, XXX, XXX-XXX
Arginine-Rich Peptide-Induced Supramolecular Self-Assembly of Water-Soluble Anionic Alkynylplatinum(II) Complexes: A Continuous and Label-Free Luminescence Assay for Trypsin and Inhibitor Screening Angela Sin-Yee Law, Margaret Ching-Lam Yeung, and Vivian Wing-Wah Yam* Institute of Molecular Functional Materials (Areas of Excellence Scheme, University Grants Committee (Hong Kong)) and Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, People’s Republic of China S Supporting Information *
ABSTRACT: A water-soluble anionic alkynylplatinum(II) 2,6-bis(benzimidazol-2′-yl)pyridine (bzimpy) complex has been strategically designed and synthesized to show supramolecular self-assembly with cationic arginine-rich peptides through unique noncovalent Pt(II)···Pt(II) and π−π stacking interactions. Upon introduction of trypsin, the arginine-rich peptides can be hydrolyzed into small fragments and deaggregation of the platinum(II) complex molecules is observed. The aggregation− deaggregation process has been probed by UV−vis absorption, emission, and resonance light scattering (RLS) studies. This platinum(II) complex has been employed for developing a new, continuous and label-free luminescence assay for trypsin as well as for inhibitor screening, and has been successfully applied to detect trypsin in diluted serum solutions. KEYWORDS: aggregation, biosensors, platinum, supramolecular chemistry, trypsin assay for the specific delivery of drug molecules.6 Apart from that, arginine-rich peptides have been a topic of interest for the application of gene therapy such as curing genetic diseases and cancer.7,9 Therefore, there has been a high demand to develop new convenient and sensitive assays for arginine-rich peptides, trypsin and its inhibitors, which can be applied to proteomics, medical diagnosis, and therapy. Luminescent square-planar d8 platinum(II) complexes are potential candidates for designing new sensing protocols for biological assays. They have been shown to display unique photophysical and self-assembly properties through the formation of unique Pt(II)···Pt(II) and π−π stacking interactions, and have attracted much attention because of their drastic color changes and significant red to near-infrared (NIR) luminescence enhancement upon supramolecular selfassembly.10−49 These extraordinary properties have made
1. INTRODUCTION As a serine protease, trypsin plays a considerable part in a lot of biological processes, such as protein digestion and regulation of pancreatic function.1 It is formed after its proenzyme trypsinogen has been activated.1 Abnormal trypsin levels are associated with the occurrence and growth of a variety of illnesses, for example, chronic kidney disease,2 acute pancreatitis,2 cancer,3 and inflammation.4 Trypsin is found in lower abundance in serum samples from healthy individuals in comparison to those from acute pancreatitis patients.2 Also, it is undetectable in urine samples from healthy people.5 Thereby, trypsin may be employed as a biomarker for medical diagnosis.2 On the other hand, oligoarginine, which is a substrate of trypsin, is a cell-penetrating peptide and is widely used as a molecular transporter.6−8 The concentration of cell-penetrating peptides used in cellular internalization of biopharmaceuticals is generally very low (micromolar concentration).8 Because of the low cytotoxicity of arginine-rich peptides and the ability of delivering bioactive cargos in cells and tissues, an increasing number of novel arginine-rich molecules have been developed © XXXX American Chemical Society
Received: August 17, 2017 Accepted: October 20, 2017
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DOI: 10.1021/acsami.7b12319 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
Research Article
ACS Applied Materials & Interfaces alkynylplatinum(II) complexes applicable to various assays and sensing protocols. Examples include detection of pH,36 temperature46 and so on. Taking advantage of the self-assembly properties, this class of complexes have been further exploited for possible biological applications, such as in the detection of single-stranded nucleic acid,50 G-quadruplex,51,52 nuclease,51 lysozyme,53 thrombin,53 glucose,54 α-glucosidase,54 human serum albumin,55 heparin,56 kinase,57 phosphatase,57 and phosphate derivatives.57 The exhibition of low-energy red to NIR emission upon aggregation is of considerable interest because this can improve the signal-to-background autofluorescence ratio, which is desirable for analyte detection.58 As platinum(II) complexes are able to undergo aggregation and deaggregation processes through noncovalent Pt(II)··· Pt(II) and π−π stacking interactions which lead to interesting spectroscopic and luminescence changes, it is anticipated that water-soluble alkynylplatinum(II) complexes can act as a versatile probe to investigate the activity of biological analytes in a label-free and real-time manner. In addition, the lack of reports on biological substrate sensing based on the aggregation of water-soluble anionic alkynylplatinum(II) 2,6-bis(benzimidazol-2′-yl)pyridine (bzimpy) complexes has aroused our interest to examine their ability to detect biological analytes and to explore their potential application in diagnostic processes, especially in the early stages of diseases. Herein, a water-soluble anionic alkynylplatinum(II) complex 1 incorporated with sulfonate pendant groups has been designed and synthesized for the luminescence assay of trypsin (Figure 1).
Table 1. Photophysical Data of Alkynylplatinum(II) Bzimpy Complex 1 medium (T (K)) DMF (298)a water (298)a glass (77)c solid (298) solid (77)
λabs (nm) (ε (mol−1 dm3 cm−1)) 330 370 328 470
sh (18450), 352 (19860), sh (17290), 476 (3860) (19190), 350 sh (17830), sh (2450)
λem (nm) (τo (μs)) 566 (
