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A Supramolecular Sensor Array Using Lanthanide-Doped Nanoparticles for Sensitive Detection of Glyphosate and Proteins Meng Wang,† Hebo Ye,† Lei You,*,† and Xueyuan Chen*,‡ †
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China ‡ Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China S Supporting Information *
ABSTRACT: Lanthanide (Ln3+)-doped nanoparticles (NPs) are an intensive area of research in chemical and materials sciences. Herein a sensor array of Ln3+-doped NPs was developed for the first time toward sensitive molecular sensing based on a novel strategy of the hybridized time-resolved Förster resonance energy transfer (TRFRET) with the indicator displacement assay (IDA) concept (TRFRET-IDA). The sensor platform was generated in situ by binding a series of negatively charged indicators on the surface of ligand-free LiYF4:Ce/Tb NPs. The TR-FRET between NPs and dyes resulted in indicator emission and was employed as a means of removing undesired short-lived background luminescence from the indicator effectively. Displacement of indicators from the NP/indicator ensembles by glyphosate, a common herbicide, led to turn-off of the indicator emission. The sensor array was able to successfully discriminate 11 biologically relevant anions with high accuracy and sensitivity in pure aqueous buffer both qualitatively and quantitatively. Furthermore, the differentiation of six model proteins in the nM range was achieved with 100% accuracy for the classification, thereby demonstrating the versatility of this simple sensor platform. The study of the mechanism of binding and signal modulation further verified TR-FRET-IDA as a reliable sensing paradigm. KEYWORDS: lanthanide, FRET, indicator displacement assay, nanoparticles, sensor array
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INTRODUCTION Anions play key roles in environment,1,2 industrial processes,3 as well as biological systems,4 and most biomolecules, such as proteins, nucleic acids, and fatty acids, contain anionic functionalities. For example, glyphosate is widely used as an herbicide in agriculture, and its overuse can cause adverse effects and pollution.5,6 As a result, the development of costeffective and sensitive sensors for the detection of anions is of great significance.7 These sensors would also provide ample inspirations for biological sensing. The enzyme-linked immunosorbent assay (ELISA) has been employed for quantitative determination of biological anions.8−11 However, its application is limited by the drawbacks of high cost, risk of contamination, and tedious sample preparation.12 In the past decade, a large number of synthetic receptors have been developed for anions, such as transition metal complexes,13 amide/urea containing receptors,14 and pyrrole-based anion receptors.15 Although significant progress has been made, anion sensing in pure aqueous medium remains challenging. In particular, few systems have been reported for the sensitive detection of glyphosate despite its importance. In addition to covalently attached receptor-spacer-reporter paradigm for anion sensing, the indicator-displacement assay (IDA) is currently the other primary analytical tool.16−21 Indicators can be combined reversibly with receptors to create a diverse set of receptor/indicator ensembles, affording a sensor © 2015 American Chemical Society
array with enhanced cross-reactivity, which is particularly useful for the detection of structurally similar analytes and biological targets for which the development of highly specific sensors is challenging.22−24 Recently, nanoparticles (NPs)-based sensor array has been applied in this field as well, leading to examples of detection of biomolecules, such as nucleotides and proteins.25−28 In these systems, the sensor array was created through supramolecular assembly of functionalized NPs (for example, Au, graphene oxides) with different dyes, resulting in quenching of dyes, and upon the dye release after analyte binding to the NPs, the “turn-on” signal was generated.29 However, most dyes used in IDAs have background signals, so the sensitivity of assay could be severely compromised by autofluorescence interference from excess dyes. Time-resolved (TR) technique is an excellent method to eliminate the interference of scattered light and other shortlived autofluorescence (Figure S1).30 By utilizing the long-lived photoluminescence (PL) of lanthanide (Ln3+) chelates, TR luminescent biosensing has achieved remarkable sensitivity,31,32 but highly specialized ligands that require significant synthetic work are generally employed. Recently, lanthanide (Ln3+)doped inorganic nanoparticles (NPs) are generating significant Received: October 9, 2015 Accepted: December 11, 2015 Published: December 11, 2015 574
DOI: 10.1021/acsami.5b09607 ACS Appl. Mater. Interfaces 2016, 8, 574−581
Research Article
ACS Applied Materials & Interfaces interest in molecular sensing and imaging.33−39 Compared to traditional organic fluorophores, Ln3+-doped NPs show many advantages, such as facile preparation and functionalization, higher resistance to photobleaching, as well as lower toxicity and cost.40−43 A variety of analytes, such as carcinoembryonic antigen,44 biothiols,45 DNA,46 CN−,47,48 HS−,49 Zn2+,50 and Ca2+,51 have been detected by means of Förster resonance energy transfer (FRET) assays based on Ln3+-doped NPs. To the best of our knowledge, the exploitation of Ln3+-doped NPs for the creation of sensor array has not been reported. An approach to achieve this would significantly expand the application scope of Ln3+-doped NPs. To make full use of the advantages of Ln3+-doped NPs and overcome the drawbacks of IDAs, herein we developed a sensor array based on a novel strategy of the hybridized TR-FRET with the IDA concept (TR-FRET-IDA) by simply using Ln3+doped NPs as receptors (Figure 1). Because FRET efficiency is
response to external perturbation. We conceive that in NP/dye complex the cationic lanthanide ions on NP surface bind strongly with the anionic dye, leading to the emission of the dye due to the FRET between NP and dye. As a result of the minimal distance between NP donors and dye acceptors, the FRET efficiency can be enhanced. More importantly, the TRFRET signal can be measured free of the interference of shortlived background by setting appropriate delay time and gate time. The binding equilibrium is then altered in the presence of anionic analyte, resulting in rapid displacement of dye from NP surface, and with the suppressed FRET process from NP to free indicators, there would be a decrease in the emission intensity of the dye. As a result, we envision the luminescence “turn-off” of the dye to provide an assay for the detection of anions. By employing an array consisting of a suite of NP/indicator ensembles in conjunction with pattern recognition, characteristic fingerprints could be created, thereby opening the door for the discrimination of closely related analytes. Tetragonal-phase LiYF4 was chosen as the host system owing to its low phonon energy (
