Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 1298–1303

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A paper-based chemiluminescence device for the determination of ofloxacin Wei Liu ⇑, Yumei Guo, Huifang Li, Mei Zhao, Zesheng Lai, Baoxin Li Key Laboratory of Analytical Chemistry for Life Science of Shaanxi Province, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi’an 710062, China

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 AgNPs are used on CL paper-based

device for determination of OFLX.  AgNPs can greatly enhance the CL

signal of luminol–H2O2–OFLX system on paper.  Wax-printing method was used here for the device fabrication process.

a r t i c l e

i n f o

Article history: Received 5 June 2014 Received in revised form 3 September 2014 Accepted 4 September 2014 Available online 28 September 2014 Keywords: Paper-based analytical device Chemiluminescence Silver nanoparticle Ofloxacin

a b s t r a c t Paper-based devices are biodegradable and have been used in diagnosis and environmental analysis field. In this work, a wax-printed paper-based analytical device combined with silver nanoparticles (AgNPs) catalyzed luminol chemiluminescence (CL) system for the determination of ofloxacin (OFLX) was presented. It was based on the enhancement of CL intensity of luminol–H2O2–OFLX system by AgNPs. Wax-printing fabrication technique was used to make the simple circle shaped paper device and large scale chips can be fabricated at the same time. Under the selected experimental conditions, a linear relationship was obtained between the CL intensity and the concentration of OFLX in the range from 1.0  10 9 g/mL to 1.0  10 6 g/mL with a detection limit of 3.0  10 10 g/mL. This method has been successfully applied to the determination of OFLX in eyedrop samples. Ó 2014 Elsevier B.V. All rights reserved.

Introduction Paper-based analytical devices (PADs), which were first proposed by Whitesides’ group [1], have gained much more interest than before due to their attractive advantages such as low cost [2] and simplicity [3]. Nowadays, it is believed to be one of the cheapest platforms available for developing assays because paper has the main features of high abundance, biodegradability, and excellent chemical compatibility with many applications [4,5]. ⇑ Corresponding author. Tel.: +86 29 81530726; fax: +86 29 81530727. E-mail addresses: [email protected], [email protected] (W. Liu). http://dx.doi.org/10.1016/j.saa.2014.09.059 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

Many reports on PADs have been directed toward the development of fabrication [6] and functionalization [7,8] methods. The most common used detection method is colorimetry which was based on visually comparing the color intensity of the reaction spots by naked eye or camera phones [9–11]. However, there is an emerging trend of establishing some new analytical methods on PADs to meet the needs of simplicity, portability and sensitivity. Recently, PADs combined with electrochemical (EC) [12] and CL [13] detection methods have been widely used in clinical diagnosis [14], food quality control [15] and environmental monitoring fields [16]. Due to its high sensitivity and wide dynamic range, CL has been proven to be a powerful analytical tool for PADs [17,13]. In

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Fig. 1. (A) UV–vis absorption spectrum of AgNPs and (B) TEM image of AgNPs.

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Fig. 2. Schematic diagram and assay procedure (1) sample injector; (2) CL detector; (3) ultraweak luminescence analyzer; (4) personal computer.

the last two years, several papers have been published by Yu’s group with very lower detection limits about CL detection method combining with PADs [17,13,18,19]. But most of their work was based on the oxidase enzyme reactions and traditional enzymelinked immunosorbent assay (ELISA) immunoassay method with CL detection. As we all know, luminol system [20–22] is a very common CL system which has been investigated for many years. Some metal nanoparticles such as gold nanoparticles (AuNPs) or AgNPs can be used as catalysts to enhance the inherent sensitivity in CL system which is now an expanding area [23,24]. Cui and his co-workers have systematically investigated the catalytic action of AuNPs in luminol–H2O2 CL reactions [25]. However, according to the excellent catalytic character of metal nanoparticles, few papers were reported on the nanoparticle catalyzed CL system on the PADs [26–28]. In this work, OFLX was detected by CL on PAD with AgNPs for the first time. OFLX is the second generation fluoroquinolones [29] and widely used in the treatment of urinary tract infections and respiratory tract infections. Hence, it is necessary to find an effective method to recognize and determine the concentration of OFLX to control the purity of the drug. Different detection methods including spectrophotometry [30], nuclear magnetic resonance (NMR) [31], high performance liquid chromatography (HPLC) [32] and fluorescence [33] have been proposed for the determination of OFLX. The CL systems [34–37] including [Ru(bipy)2+ 3 ]–Ce(IV)

system, potassium permanganate–sodium sulfite system, sulfitePbO2 system, cerium(IV)-sulfite system have been used for OFLX detection with lower detection limits. We have seen a paper [38] based on AuNPs catalyzed luminol CL system for the determination of OFLX with the detection limit of 8.0 ng/mL. Here, with AgNPs coated on the paper surface, OFLX can be detected on the paperbased device with higher sensitivity. By using the wax printing method [39] to fabricate the paper-based chip, the proposed CL system was applied for the determination of OFLX in eyedrop samples with the detection limit of 3.0  10 10 g/mL. It is found that the proposed paper-based chip provides a number of advantages such as high sensitivity, simple operation and high throughput analysis for the determination of fluoroquinolone derivative. This work is useful for on-site environmental testing of pesticides, drugs or environmental pollutants in remote regions. Experimental Reagents and materials OFLX, AgNO3 and NaBH4 were obtained from Sinopharm Group Chemical Reagent Company (Shanghai, China). Sodium citrate and H2O2 were purchased from Xi’an Chemical Reagent Company (Xi’an, China). The eyedrop samples were purchased from Wuhan Yuancheng Gongchuang Technology Co., Ltd. (China). The stock

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The CL intensity was measured and recorded with a model IFFSA Chemiluminescence Analyzer (Xi’an Remex Electronic Sci. Tech. Co. Ltd., Xi’an, China). The acquisition and treatment of CL signal were performed using RFL-1 software running under Windows XP (Xi’an Remax, China). The results of UV were obtained using Shimadzu UV-1800 recording spectrophotometer (Beijing Purkinje, China). The transmission electron microscopy (TEM) images of AgNPs were taken using a Hitachi H-600 TEM (Tokyo, Japan). The paper-based chip was fabricated by Xerox Phaser 8560N color printer (Japan). Preparation and characterization of AgNPs Silver colloid was prepared according to the literature [40]. Briefly, a 25 mL 1  10 3 mol/L AgNO3 aqueous solution was added to 75 mL 2  10 3 mol/L NaBH4 aqueous solution in the ice bath with vigorous stirring simultaneously. Ten minutes later, a 5 mL 1% (w/w) trisodium citrate aqueous solution was added to stabilize AgNPs. The colloid was stirred for another 20 min and stored at 4 °C for 2 days before use. All glassware used was cleaned in a bath of freshly prepared 3:1 HNO3–HCl, rinsed thoroughly in water and dried in air prior to use. The size and monodispersity of the obtained nanoparticles was determined by transmission electron microscopy (TEM) (JEM-2100, Japan) and the diameter of particles was about 15 ± 5 nm as shown in Fig. 1B. According to Su’s [41]

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Fig. 3. Schematic diagram of the CL behavior of OFLX on PAD, (1) blank signal of luminol–H2O2; (2) signal of luminol–H2O2–AgNPs; (3) signal of luminol–H2O2– OFLX (OFLX: 10 8 g/mL); (4 and 5) signals of luminol–H2O2–AgNPs with different concentration of OFLX. (4) OFLX: 10 8 g/mL; (5) OFLX: 10 7 g/mL; luminol, 0.4 mM; H2O2, 0.1 mM; pH, 12.0.

solution of OFLX (5.0  10 4 g/mL) was prepared by dissolving OFLX (25.0 mg) in 2 mL of 0.1 mol/L sodium hydroxide solution and diluting with deionized water to 50 mL. Working standard solutions of OFLX were freshly diluted with deionized water. The 2.5  10 2 mol/L stock solution of luminol (3-aminophthalhydrazide) (Kangpei Technology Co., China, 98%) was prepared by dissolving luminol (4.43 g) in 0.1 mol/L sodium hydroxide and then diluted to 1 L with water. The luminol solution was stored in the dark for one week prior to use to ensure that the reagent had stabilized. Working solutions of H2O2 were freshly prepared by dilution of a 30% reagent solution (Shanghai, China). All chemicals and reagents were of analytical grade and used without further purification. Millipore Milli-Q water (18 MX/cm) was used in all experiments. Whatman chromatography paper #1 (WCP#1) (200.0 mm  200.0 mm) was purchased from Sigma (USA).

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Concentration of luminol (×10-4 M) Fig. 4. Parameter optimization for CL on the PAD. (A) Influence of the pH value. (0.1 mM H2O2, 0.4 mM luminol); (B) influence of the concentration of H2O2. (0.4 mM luminol, pH:12.0); (C) influence of the concentration of luminol (0.1 mM H2O2, pH:12.0).

work, the concentration of AgNPs in this work was 6.3  10 11 M. The UV–vis absorption spectra were also done. From Fig. 1A, it can be seen that the freshly prepared AgNPs has a notable absorption peak at about 390 nm.

Preparation of paper-based chip by wax-printing method The following are the detail procedure to fabricate the paperbased chip. Firstly, the paper microzone plates were designed using Corel draw X6 (the dimension of the paper zones was 6 mm while

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W. Liu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 1298–1303

the distance between two zones was 2 mm). Then, the wax patterns were printed onto the surface of the paper with wax printer. At last, the wax-printed paper was put in an oven and baked at 120 °C for 5 min. So the printed wax can melt and penetrate through the whole paper to form the hydrophobic patterns. It will be ready for use after cooling to room temperature. The whole piece of the paper was cut into a single paper microzone one by one. CL assay procedure on PAD As shown in Fig. 2, the CL signal was measured using a computerized ultraweak luminescence analyzer. After the paper device was cooled to room temperature, 5 lL of the mixture solution of AgNPs and OFLX of different concentration was dropped on the paper zone and dried for 20 min. The PAD was put on the bottom of the device holder which was fixed on the bottom of the cassette. When the CL intensity was detected by photomultiplier tube (PMT), the cassette can be shut with a black metallic cover. 10 lL mixture solutions of luminol and H2O2 were dropped onto the paper device through the injection hole on top of the cassette by an injector. The CL signal was detected and amplified by the PMT. Data acquisition and treatment was performed with RFL software running under Windows XP. The concentration of sample was quantified by the peak height of the CL signal. Results and discussion Optimization of the paper’s type

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Whatman chromatography paper 3 MM were used. But Whatman chromatography paper 3 MM is so thick that the melted wax was difficult to penetrate the whole paper to form the hydrophobic walls on the paper. So we chose Whatman chromatography paper #1 as the substrate in our experiment. Owing to the porous structure of paper, the melted wax can penetrate into the paper to decrease the hydrophilicity of the paper remarkably and form hydrophobic walls. But the unprinted area can still maintain good hydrophilicity, flexibility and three-dimensional porous structure. According to the stability of the signal and the consumption of reagent, the dimension of 6 mm of the paper zones was the best choice. CL behavior of this AgNPs catalyzed luminol system

Because paper has become an appealing material for portable analytical applications, the paper’s quality is vital for the later use. Different type of paper was tried here to choose the appropriate one to meet our demands. At first, printing paper, quantitative filter paper, filter paper and qualified filter paper were tried for CL detection. Comparing to the printing paper, the hydrophilicity and repeatability of the printing paper were very poor. For the other three kinds of filter paper, the results showed that the CL signals of the blank sample were high and the repeatability was still not good. The problem is that the thickness of filter paper and qualified filter paper was not always the same which was in the range of 10–250 lm. The thickness of paper affects the optical path length, scattering, assay sensitivity, and volume of fluid required for an assay. While, the repeatability was improved a lot when Whatman chromatography paper #1 and

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Table 1 Tolerable concentration for the 1.0  10 8 g/mL OFLX (

A paper-based chemiluminescence device for the determination of ofloxacin.

Paper-based devices are biodegradable and have been used in diagnosis and environmental analysis field. In this work, a wax-printed paper-based analyt...
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