Journal of Hazardous Materials 280 (2014) 46–54

Contents lists available at ScienceDirect

Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat

Specific and ultrasensitive ciprofloxacin detection by responsive photonic crystal sensor Rong Zhang a , Yong Wang a , Li-Ping Yu a,b,∗ a b

Department of Chemistry, School of Science, Tianjin University, Tianjin 300072, China State Key Laboratory of Medicinal Chemical Biology, Nankai University, Tianjin 300071, China

h i g h l i g h t s • Sensor was designed by integrating complexes into responsive photonic crystal. • Ternary tryptophan–zinc(II)–ciprofloxacin complexes were chosen for sensing. • Excellent sensing of ciprofloxacin was achieved in aqueous media.

a r t i c l e

i n f o

Article history: Received 7 February 2014 Received in revised form 30 May 2014 Accepted 13 July 2014 Available online 23 July 2014 Keywords: Ciprofloxacin Responsive photonic crystal.

a b s t r a c t A new approach for specific and ultrasensitive measurement of ciprofloxacin has been developed by integrating ternary complexes into responsive photonic crystal (RPC). Tryptophan was first immobilized within the polyacrylamide hydrogel substrates of RPC. The determination of ciprofloxacin was via the existence of zinc(II) ions that function as a ‘bridge’ to form specific tryptophan–zinc(II)–ciprofloxacin complexes step by step, which resulted in a stepwise red-shift of the diffraction wavelength. A maximum wavelength shift from 798 to 870 nm for ciprofloxacin was observed when the RPC film was immersed in 10−4 M ciprofloxacin. A linear relationship has been obtained between the  of diffraction peak and logarithm of ciprofloxacin concentration at pH 5.0 in the range of 10−10 to 10−4 M. And the least detectable concentration in present work is about 5 × 10−11 M. The results demonstrated that the as-designed ternary complexes-based RPC sensor exhibited high sensitivity, satisfactory specificity and excellent recoverability for sensing of ciprofloxacin in aqueous media and were validated by detecting ciprofloxacin in the eye-drop sample. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Ciprofloxacin (CIP) is one of the most widely prescribed fluoroquinolone antibiotics, which is active against a broad spectrum of Gram-negative and -positive bacteria, and widely used in health care and agricultural industries to treat human and animal diseases [1,2]. Although benefits of the use of CIP in medicine are obvious, CIP is also proved to be interfering with biological systems and exhibits toxic effects on cells, organs, organisms and populations even at low concentrations [3]. The enrichment of the antibiotics like CIP in environment may pose serious threats to the ecosystem and human health by inducing proliferation of bacterial drug resistance [4]. Therefore, it is crucial to develop sensitive and effective methods for the careful monitoring of CIP in various samples.

∗ Corresponding author. Tel.: +86 22 27403475; fax: +86 22 27403475. E-mail address: [email protected] (L.-P. Yu). http://dx.doi.org/10.1016/j.jhazmat.2014.07.032 0304-3894/© 2014 Elsevier B.V. All rights reserved.

Up to now, many methods have been developed for the determination of CIP, which mainly include fluorescence spectroscopy [5], capillary electrophoresis [6], microbiological method [7], highperformance liquid chromatography (HPLC) [8,9], enzyme-linked immunosorbent assay (ELISA) [10,11] and various spectrophotometric methods [12,13]. The existing detection methods are usually limited to professional operators and expensive equipment [10], even microbiological method and HPLC are timeconsuming and require extensive sample cleanup [11]. Moreover, the immunoreagents are often expensive and the establishment of an ELISA system for determination of CIP residues is too costly for routine laboratories [11]. Herein, new methods with low-cost, feasible and time-saving procedures are demanded urgently. Recently, much attention has been paid to the responsive photonic crystals (RPCs) which have fascinating optical properties that can be exploited for various applications including biological and chemical sensors [14,15]. In many cases, the tunable photonic effects of RPCs were endued by integrating stimuli-sensitive

R. Zhang et al. / Journal of Hazardous Materials 280 (2014) 46–54

hydrogels into photonic crystal structures. The commonly used strategy for design and fabrication of RPCs is to fill hydrogels into the interstitial spaces of photonic crystal templates to form composite materials [15]. These responsive photonic materials have dielectrically periodical structures that can alter their diffraction wavelength or intensities upon exposure to physical or chemical stimuli, such as temperature [14,16,17], pH [18,19] and specific analytes [16,20–23]. RPCs as sensors usually have larger diffraction wavelength shifts as well as better sensitivity in response to the external stimuli, owing to the greater volume change of polymer networks [22,24–26]. Our group has explored a novel sensing platform based on the integration of hydrogel photonic crystals and ternary complexes [27]. Copper(II) complexes have been designed involving tetracycline as the primary ligand and glycine as the secondary ligand, and a gradual diffraction wavelength red-shift of the hydrogel photonic crystals was observed when ternary complexes formed stepwise on its surface. The integrated hydrogel photonic crystals can undergo a large swelling change and still retain the molecular recognition ability during the ligand-binding event, by which we realized a signal amplification chance for highly sensitive glycine detection [27]. In the present work, a ternary complexes-based RPC sensor was designed and fabricated for the sensing of CIP. Tryptophan (Trp) was immobilized within the hydrogels by polymerization with an acrylamide matrix, which was filled into the interstitial spaces of polystyrene photonic crystal template. Zinc(II) was chosen to act as a “bridge” between Trp and CIP to form ternary Trp–zinc(II)–CIP complexes for detection of CIP. Remarkable diffraction wavelength red-shifts were observed during the stepwise ligand-binding event via construction of appropriate photonic crystal structures and complex systems. After a series of optimization of polymerization, pH, ionic strength and the concentration of Trp and zinc(II), the ternary complexes-based RPC sensor exhibited admirable sensitivity, satisfactory specificity, rapid responsiveness and excellent recoverability for the determination of CIP.

2. Materials and methods 2.1. Reagents and instrumentation l-Tryptophan (l-Trp), ciprofloxacin (CIP), styrene, sodium dodecylsulfonate (SDS), ammonium persulfate (APS), acrylamide (AMD), acrylic acid (AA), zinc acetate, acetic acid, N,N methylenebisacrylamide (BIS), sodium acetate and other affiliated chemicals used were of analytical reagent grade and from local suppliers. Styrene was vacuum-distilled to remove inhibitors prior to use. Other solvents and chemicals were used without further purification unless specially mentioned. All containers and glass slides (50 × 20 mm2 ) for photonic crystal growth were cleaned by rinsing with a H2 SO4 –H2 O2 mixture and deionized water. The buffer solution was prepared by 0.1 M acetic acid and 0.1 M sodium acetate. When used, the pH was adjusted by adding additional acetic acid or sodium acetate solution. The stock standard solutions of zinc(II) and CIP were prepared by dissolving a certain amount of the relevant chemicals in pH buffer solutions, and the standard solutions of lower concentrations were prepared by diluting the stock solutions with pH buffer solutions. The stock standard solutions were stored at room temperature before use. Scanning electron microscopy (Nova NanoSEM 430, FEI) operating at 25 kV was used to observe structures of photonic crystal templates and the Trp-immobilized RPC film. pH meter (FE20 K, Shanghai, China) was used to measure the pH value.

47

The optical responses of diffraction peaks were measured by using a 380–1050 nm fiber optic spectrometer (JKHQ-D1, Tianjin, China) at the vertical direction. And the measurement location was fixed by focusing the incident light on one dot. After each measurement of diffraction peak, the film was always washed in dilute hydrochloric acid and thoroughly rinsed with deionized water to recover the blank state for the next detection. For a series of concentrations, the detection followed the sequence from low to high concentrations to eliminate interference. Before each spectral scan, the pH of all solutions was adjusted and the final pH value was checked. 2.2. Self-assembly of polystyrene photonic crystal template The monodispersed polystyrene colloids with the diameter of about 210 nm were synthesized by emulsion polymerization as described in reference [28]. Templates of photonic crystal were prepared from the obtained monodispersed polystyrene colloids by using the vertical deposition method. Clean glass slides were vertically inserted into treated container in which polystyrene colloids were fully dispersed in deionized water (1:20, v/v). The containers were put in a 43 ◦ C water bath for about 2–3 days. The polystyrene photonic crystal templates were obtained after the solvent was evaporated completely. 2.3. Preparation of Trp-immobilized RPC film Immobilization of Trp within photonic crystal structures was along with the polymerization procedure of polyacrylamide. Herein, AMD and AA used as functional monomers were mixed with Trp in 4 mL of deionized water to form a stable complex. Appropriate amounts of BIS as cross-linker and APS as initiator were added. Following a sufficient homogenization, the mixture of precursors was infiltrated into the above polystyrene photonic crystal template by using a capillary-attraction-induced method and the interstitial space between the closely packed spheres was filled with the solution through the capillary effects. After thermal polymerization in an oven at 50 ◦ C for about 5 h, the Trp-immobilized RPC was obtained. The non-immobilized polymer was prepared in the same way without Trp. The effects of pH on the optical responses of Trp-immobilized RPC hydrogel were measured in the acetic acid–sodium acetate buffer solution from pH 2.0–7.0. The RPC film was soaked in 10 mL of 10−3 M zinc(II) buffer solution of different pH value for 15 min at room temperature before starting the spectral scan. The nonimmobilized film was detected in the same way in order to make comparison with the immobilized film. The effects of ionic strength on the diffraction peak of the Trpimmobilized RPC film were measured in the 10−3 M zinc(II) solution mixing with KNO3 in the concentration range from 0 to 1 M at the optimum pH value. 2.4. Swelling study The swelling behaviors of the RPC film were carried out by immersing the dried film in 0.1 M acetic acid and 0.1 M sodium acetate buffer solution (pH 5.0) at room temperature. The water absorbed was determined by weighing the film after wiping at regular time intervals. Swollen gels were weighed by an electronic balance and the measurements were continued until a constant weight was reached. 2.5. Formation of Trp–zinc(II) binary complex In all cases, the Trp-immobilized RPC film was soaked in 10 mL of buffer solutions of various zinc(II) concentrations for 15 min at

48

R. Zhang et al. / Journal of Hazardous Materials 280 (2014) 46–54

room temperature until it reached a swelling equilibrium, and then a maximum diffraction peak was recorded.

deionized water. The Trp–zinc(II) binary complex on the surface of RPC film should be rebuilt in advance for each measurement. 2.7. Sample detection

2.6. Determination of CIP After formation of Trp–zinc(II) binary complex, the RPC film without any treatments was then immersed in 10 mL of CIP buffer solution for another 15 min at room temperature until it reached a new swelling equilibrium again, in which the ternary Trp–zinc(II)–CIP complexes was formed, and a subsequent diffraction peak shifts could be observed and recorded. Both the CIP and zinc(II) could be washed off after the film was soaked in 0.01 M dilute hydrochloric acid and then washed thoroughly with

The Ciprofloxacin Hydrochloride Eyedrops was purchased from a local drugstore. The sample solution was prepared by diluting 1 mL of eye drops into 100 mL with buffer solution which was adjusted to the optimum pH value. For determination of CIP in real CIP eye drops sample, the RPC film was immersed into 10 mL of 10−3 M zinc(II) solution at the optimum pH for 15 min at room temperature firstly and then the diffraction peak was observed when the binary RPC film was immersed into 10 mL diluted sample solution, thus CIP was detected in terms of the diffraction peak shift

Fig. 1. SEM photographs with (a) high magnifications and (b) low magnifications of polystyrene photonic crystal template. SEM photographs with (d) high magnifications and (e) low magnifications of tryptophan-immobilized RPC film. Cross-view SEM images of (c) polystyrene photonic crystal template and (f) tryptophan-immobilized RPC film.

R. Zhang et al. / Journal of Hazardous Materials 280 (2014) 46–54

49

compared to the diffraction peak of binary complex. The standard curve for quantitative determination of real samples was established in a concentration range of CIP from 10−10 to 10−4 M. 3. Results and discussion Three steps were involved in this work in order to get the ternary complexes-based RPC sensor, which included immobilization of Trp within acrylamide photonic crystal structures, formation of a Trp–zinc(II) binary system and formation of a ternary Trp–zinc(II)–CIP system for detection of CIP. The scheme of the overall protocol for the construction and recognition of the RPC is in accord with a previous work in our group [27]. 3.1. Immobilization of Trp within acrylamide photonic crystal structures Immobilized RPC was fabricated by filling responsive acrylamide material into the interstitial spaces of polystyrene photonic crystal templates. Fig. 1a and b is the top view of a polystyrene photonic crystal template in different magnifications, and Fig. 1c is the cross-view SEM image. A face-centered cubic (fcc) close-packed structure of the photonic crystal template can be seen clearly from these pictures. The immobilization of Trp within photonic crystal structures was along with the polymerization procedure of hydrogel. After optimization, the Trp-immobilized RPC film was prepared by placing the monomers (42 mmol, 66.6% AMD, 20 mmol, 31.7% AA) together with the ligand (0.098 mmol, 0.16% Trp) in a glass container along with the cross-linker (0.58 mmol, 0.92% BIS) and initiator (0.39 mmol, 0.62% APS), all dissolved in 4 mL of deionized water. After polymerization in an oven at 50 ◦ C for about 5 h, Trpimmobilized RPC film with a highly ordered opal photonic crystal structure was obtained, different magnifications and cross-view SEM image of the film were shown in Fig. 1d, e and f. 3.2. Formation of Trp–zinc(II) binary system The inherent indole group in its molecular structure makes it possible for Trp to form a complexation between indolyl and metal ions, which has already been utilized in the solid-phase extraction [29,30]. Immobilization of Trp in the RPC film enabled us to introduce a binding system for metal ions on the surface of the RPC film. In our present work, formation of Trp–zinc(II) binary complex was investigated firstly by measuring responses in terms of varying immobilized Trp. The RPC film contained 0, 0.01, 0.04, 0.08, 0.12, 0.16, 0.19 and 0.23 mol% Trp were fabricated and their optical responses to 10−3 M zinc(II) were measured in a pH 5.0 solution. Generally, the binding capacity of the responsive surface depends on the amount of the immobilized ligand. Diffraction wavelength shift of the RPC film immobilized with different contents of Trp is demonstrated in Fig. 2. It could be clearly seen that the content of Trp do play an important role in the response properties of the immobilized RPC film. Diffraction wavelength shift of immobilized RPC film increased gradually with increasing Trp content, and the maximum wavelength shift was achieved when the content of Trp arrived at 0.16 mol%. It was probably because that there were more ligands provided to uptake more zinc(II) ions when more Trp were immobilized within the RPC film, which resulted in greater diffraction wavelength shift. However, it was also experimentally demonstrated that the diffraction shift no longer increased when the content of Trp continuously increased from 0.16 to 0.23 mol%, which was probably limited by the amount of AMD and AA in the film. Consequently, 0.16 mol% was chosen for an optimum Trp content for preparation of immobilized RPC film.

Fig. 2. Optical responses of tryptophan-immobilized RPC film to 10−3 M zinc(II) with increasing amount of immobilized tryptophan, in which  is the diffraction peak difference between 10−3 M zinc(II) buffer solution and pure buffer solution.

In order to obtain a satisfactory RPC sensor, it is also very important to investigate other parameters which probably influence the sensitivity and response properties of the ternary complexes-based RPC sensor. In the present work, the effects of pH and ion strength were also investigated to optimize the sensing properties of the RPC sensor for CIP.

3.3. Effect of pH pH is one of the most important parameters which affect the complexing of zinc(II) ions in solution. The formation of the binary Trp–zinc(II) complex and the maximum diffraction shift of the RPC film can be achieved by optimization of the pH. The influence of the pH was firstly investigated in the 10−3 M zinc(II) buffer solutions with a pH range of 2.0–7.0 at room temperature. The diffraction  was calculated to estimate the effect of the pH, which is the diffraction peak difference between the 10−3 M zinc(II) buffer solutions at various pH and the pure buffer solutions without zinc(II) at the corresponding pH. The relationship between  and pH is shown in Fig. 3a. It was found that the diffraction shift of the Trpimmobilized RPC film in response to zinc(II) was increasing when the pH value increased from 2.0 to 5.0. But when the pH changed from 5.0 to 7.0, the diffraction shift was decreased slowly, and there was a sharp increase from 4.0 to 6.0. Herein, the effect of the pH from 4.0 to 6.0 was then investigated in detail with an increment of 0.5 (Fig. 3b). The maximum diffraction shift responded to zinc(II) was up to 91 nm at pH 5.0. Diffraction peaks of the RPC in pure buffer solutions and 10−3 M zinc(II) buffer solutions was presented in the range of pH 2.0–4.5 (Fig. 3c) and pH 5.0–7.0 (Fig. 3d). At higher pH values more than 5.5, the diffraction shift was reduced probably due to the formation of Zn(OH)2 or Zn(OH)+ [29]. All subsequent experiments were carried out at the optimum pH 5.0.

3.4. Effect of ionic strength Influence of ionic strength on the formation of Trp–zinc(II) binary complex was also studied. We experimentally examined the RPC film in response to 10−3 M zinc(II) solutions which contained 0, 0.01, 0.1, 1, 10, 100 and 1000 mM KNO3. As shown in Fig. 4, the response of the Trp-immobilized RPC film changes slightly with the continuing increase of the concentration of KNO3 from 0 to 1000 mM in the buffer solution. It is illustrated that the effect of ionic strength on the formation of Trp–zinc(II) binary complex can be negligible since the presence of KNO3 in the solution has so little influence on the volume change of the hydrogel.

50

R. Zhang et al. / Journal of Hazardous Materials 280 (2014) 46–54

Fig. 3. Effect of pH on responsive properties of tryptophan-immobilized and non-immobilized RPC film to zinc(II) in the range of (a) pH 2.0–7.0 and (b) pH 4.0–6.0.  is the diffraction peak difference between 10−3 M zinc(II) buffer solution and pure buffer solution. The diffraction peaks of the RPC sensor in buffer solutions and the corresponding 10−3 M zinc(II) solutions in the range of (c) pH 2.0–4.5 and (d) pH 5.0–7.0.

3.5. Effect of the zinc(II) content in preparation of the Trp–zinc(II) binary complex Zinc(II) is non-poisonous and indispensable for our life, as well as a transition metal that is apt to form a series of complexes with pharmaceutical molecular including amino acids and antibiotics [31,32]. The interaction between zinc(II) and Trp, and the complexation between zinc(II) and CIP have been reported previously [31,32]. Zinc(II) thus was chosen to play a role of “bridge” to form a Trp–zinc(II)–CIP complexes and pursue a sensing of CIP.

We investigated the diffraction wavelength at different concentrations of zinc(II) in order to obtain the optimal zinc(II)complexing RPC film for the detection of CIP. Fig. 5 presents the response of the RPC film’s diffraction wavelength to the varying zinc(II) concentrations. It was observed that the diffraction peak exhibited continuous red-shifts as the zinc(II) concentrations increase. When the film was soaked in the pure buffer solution, the maximum diffraction peak was 707 nm, and then it red-shifted from 707 to 719 nm in the presence of 10−9 M zinc(II) (pH 5.0). Furthermore, it continued to red shift to 771 nm when the solution was replaced by 10−5 M zinc(II) solution (pH 5.0). When the

Fig. 4. (a) Effect of ionic strength on the formation of tryptophan–zinc(II) complex in the presence of 10−3 M zinc(II). (b) Diffraction response of the tryptophan-immobilized RPC film to 10−3 M zinc(II) in buffer solutions of various ionic strength.

R. Zhang et al. / Journal of Hazardous Materials 280 (2014) 46–54

51

Fig. 5. Responses of tryptophan-immobilized RPC film to zinc(II) ranging from 10−9 to 10−2 M.

Fig. 7. Swelling behavior of the RPC film in 0.1 M acetic acid and 0.1 M sodium acetate buffer solution (pH 5.0).

concentration of zinc(II) was increased to 10−3 M, the maximum diffraction peak was 798 nm and a maximum red-shift was up to 91 nm compared to that in the pure buffer solution. The wavelength shift can be attributed to the formation of Trp and zinc(II) binary complex. Therefore, the binary RPC formed in 10−3 M zinc(II) solution was chosen for the following detection of CIP.

the concentration of CIP in the range of 10−10 to 10−4 M. A linear relationship of  = 9.35 log c + 110.41 has been obtained between the  of diffraction peak and logarithm of CIP concentration (log c) (Fig. 6b) at pH 5.0, in which  is the wavelength difference between the ternary complexes RPC and the binary complex RPC.

3.6. Formation of ternary Trp–zinc(II)–CIP system for detection of CIP

3.7. Swelling dynamic and response time

The determination of CIP was conducted under the pH identical to that for the binary system. It can be confirmed that the Trp–zinc(II)–CIP ternary complexes do form since the diffraction wavelength had a significant red-shift compared to the binary complexed RPC. The RPC film fixed at 10−3 M zinc(II) solution was examined for wavelength shift with varying CIP concentrations ranging from 10−10 to 10−4 M. As shown in Fig. 6a, it is clearly seen the diffraction wavelength gradually red-shift with the increasing concentration of CIP. The maximum diffraction wavelength shift was up to 870 nm when the RPC film was immersed in 10−4 M CIP. Our ternary complexes-based RPC sensor displayed a high sensitivity for the determination of CIP. A distinct redshift of 13 nm can be observed directly when the concentration of CIP was as low as 10−10 M. The least detectable concentration in present work is about 5 × 10−11 M, which is far below the detection limits of some other methods such as capillary electrophoresis (70 ␮g L−1 ) [6], microbiological method (5100 ␮g kg−1 ) [7], and spectrophotometric method (0.5 ␮g mL−1 ) [13]. Moreover, a gradual and considerable red-shift was found in proportion to

The percentage swelling (%S) of the RPC film was calculated from the following relation: %S = (mt − m0 )/m0 × 100, where mt is the mass of the swollen gel at time t, and m0 is the initial mass of the dry film [34]. Swelling isotherm of the RPC film was shown in Fig. 7. It can be seen that the percentage swelling of the RPC film increases with time until about 10 min, then the value of percentage swelling becomes constant which means it reaches an equilibrium percentage swelling. In addition, the effect of the response time on the sensing characteristic of the RPC film was also performed. In the response time measurements, the diffraction peak was monitored until diffraction peak ceased shift. The Trp-immobilized RPC film was firstly soaked in 10 mL of buffer solution (pH 5.0) for 15 min, and then it was immersed in 10 mL of 10−3 M zinc(II) solution (pH 5.0), the diffraction peak of the Trp-immobilized RPC film was measured every 1 min until the wavelength no longer shift. And then the binary complexed RPC was soaked in 10 mL of 10−4 M CIP solution (pH 5.0), the diffraction peaks were measured every 1 min again. It can be clearly seen that the wavelength of the diffraction peak is no longer changed when the Trp-immobilized RPC film was immersed

Fig. 6. (a) Diffraction wavelength shift of the RPC sensor fixed at 10−3 M zinc(II) in response to ciprofloxacin ranging from 10−10 to 10−4 M. (b) Relationship between logarithm of ciprofloxacin concentrations and the diffraction peak shift ().

52

R. Zhang et al. / Journal of Hazardous Materials 280 (2014) 46–54

Fig. 8. Time dependence of the RPC film in (a) 10−3 M zinc(II) solution and (b) 10−4 M CIP solution.

Fig. 9. Diffraction response of the RPC sensor to CIP for recoverability test.

in the zinc(II) solution in about 13 min (Fig. 8a) and the response time of 15 min for the detection CIP is used (Fig. 8b). In this work, the chosen soaking time of 15 min for any concentration is proved to be sufficient for diffusion and swelling equilibrium to occur. Our RPC sensor has a rapid responsiveness to CIP and the detection is fast in our present work. In the reported work, the detection time of CIP by the fluorescence spectroscopy method is more than 20 min [5], ELISA method costs about 2 h [10,11] and microbiological method needs several hours [7]. 3.8. Recoverability In the present work, the RPC sensor was required to be immersed in the solution and followed by washing with 0.01 M hydrochloric acid after a series of detections. Thus, the recoverability of the RPC sensor is very important for the accuracy of the determination. Repeated experiments in our work revealed that the RPC sensor has favorable recoverability without significant changes in diffraction peak after over several cycles. To examine the recoverability, the Trp-immobilized RPC film was firstly immersed in the buffer solution (pH 5.0) to reach a stable blank state, and then soaked in 10−3 M zinc(II) buffer solution to form the Trp–zinc(II) binary complex. With the presence of zinc(II), the diffraction peak had a red-shift from 707 to 798 nm. In the step of the formation of ternary complexes, it had a further red-shift from 798 to 870 nm when exposed to CIP. As presented in Fig. 9, the diffraction wavelength of the RPC sensor can shift back to the original value after it was washed by hydrochloric acid and deionized water because the zinc(II) and CIP were both washed off on the occasion. Fig. 10 demonstrates five cycles of the diffraction wavelength changes. It can be clearly seen that the diffraction response of the RPC sensor was not affected over five cycles, and it can be easily recovered.

Fig. 10. Diffraction response of tryptophan-immobilized RPC film over five cycles.

3.9. Response mechanism The response mechanism of ternary complexes-based RPC sensor is based on the volume change of hydrogel triggered by the external stimulus, i.e. the presence of the target chemical molecules. Molecular-recognition groups are usually functionalized on their polymer chains of the hydrogels for the selective binding of the target molecules. The volume change of the hydrogel could cause the variation of the separation distance between the colloidal spheres, thus resulting in the shift of the diffraction wavelength. The Trp, in whose molecular structure there is a hydrophilic amino group and a hydrophilic carboxyl group as well as a hydrophobic group of indole, was dissolved in aqueous solution along with the functional monomers of AMD and AA. After a sufficient mixing and polymerization, multiple hydrogen bondings are expected to occur between the amino and carboxyl groups of Trp and the carboxyl groups of AA [33], while leaving the hydrophobic group of indole outside the polymer chains to play a key role as a ligand for complexing with zinc(II) ions [29]. In the presence of zinc(II), the bonding between the indole ligand and these zinc(II) cations localize the positive charge on the gel network and cause an increase in osmotic pressure within the gel owing to the introduction of mobile counterions to the bonded cations, thus leading to the swelling of the hydrogel and a red shift of the diffraction [15]. Furthermore, with the existing of CIP, whose oxygens of the carboxyl are tend to coordinate with zinc(II) ions [31,32], the formation of ternary complexes Trp–zinc(II)–CIP will induce the further osmotic pressure changes, resulting in the further swelling changes and red-shifts of diffraction peaks. The sketch map of the complexation mechanism of ternary Trp–zinc(II)–CIP complexes is shown

R. Zhang et al. / Journal of Hazardous Materials 280 (2014) 46–54

53

Fig. 11. Complexation mechanism of the ternary complexes-based RPC sensor.

Fig. 12. The different responsiveness of tryptophan-immobilized RPC film to 10−3 M zinc(II), copper(II), magnesium(II) and aluminum(III) (pH 5.0).

in Fig. 11, and the response of the RPC to CIP is considered to be roughly the same mechanism as our previous work [27]. 3.10. Interference discussion The responsiveness of Trp-immobilized RPC film to different metal ions was investigated under the optimal pH conditions of zinc(II) to estimate the interference in the step of the formation of Trp–zinc(II) binary system. The maximum diffraction peak of the RPC film was examined by immersing the film into 10 mL of 10−3 M copper(II), magnesium(II) and aluminum(III) solutions (pH 5.0), respectively. As is shown in Fig. 12, copper(II), magnesium(II) and aluminum(III) resulted in much smaller responses to the Trpimmobilized RPC film compared to zinc(II). It is indicated that the common co-existed metal ions such as copper(II), magnesium(II) and aluminum(III) do little contribution to the diffraction shift of the RPC film, and zinc(II) has the strongest trend to form complexes with Trp under pH 5.0. It is thus can be deduced that their

Fig. 13. Diffraction response of the RPC sensor to the eye drops sample.

interference can be entirely negligible in the step of formation of a Trp–zinc(II) binary system when the separate concentration of copper(II), magnesium(II) and aluminum(III) is less than 10−3 M. In view of the interference of the third step of the formation of ternary complexed RPC system for detection of CIP, other fluoroquinolone antibiotics such as ofloxacin, norfloxacin and enoxacin were carefully considered. It is fortunate that other fluoroquinolone antibiotics caused little interference of the determination of CIP in our work because our whole protocol was performed in an aqueous media of pH 5.0, where the enoxacin and ofloxacin were usually absence due to their extreme low solubility in aqueous solution. Since the probable coexist concentrations of the similar drugs are far low than the analyte, their interferences then can be ignored practically. 3.11. Application The developed method was validated by determining CIP in commercial eye drops. When the RPC sensor was exposed to the

54

R. Zhang et al. / Journal of Hazardous Materials 280 (2014) 46–54

sample solution, it was obvious that there was a significant redshift of diffraction peak in response to the sample (as shown in Fig. 13). According to the linear equation of the standard curve method in the range of 10−10 to 10−4 M CIP, it can be calculated that the content of CIP in the eye drops sample is about 10−8 M. It is demonstrated that the newly developed method makes a quick and convenient detection of CIP possible. 4. Conclusions In this paper, a new approach for detecting CIP in liquid samples was developed, which was based on the design of ternary complexes-based RPC sensor. Using the ternary complexes, the swelling of the RPC sensor may change dramatically over a small range of external parameter variation, by which we can amplify the response signal. The proposed method exhibits good recoverability, high sensitivity and specific responsiveness, and it is relatively easy and cheap to perform as well. Acknowledgments This work was supported by the National Natural Science Foundation of China (No. 21245006) and the Foundation of State Key Laboratory of Medicinal Chemical Biology (No. 20130468). References [1] H. Chen, L.Q. Ma, B. Gao, Influence of Cu and Ca cations on ciprofloxacin transport in saturated porous media, J. Hazard. Mater. 262 (2013) 805–811. [2] C. Girardi, J. Greve, M. Lamshöft, I. Fetzer, A. Miltner, A. Schäffer, M. Kästner, Biodegradation of ciprofloxacin in water and soil and its effects on the microbial communities, J. Hazard. Mater. 198 (2011) 22–30. [3] B.D. Witte, J. Dewulf, K. Demeestere, H.V. Langenhove, Ozonation and advanced oxidation by the peroxone process of ciprofloxacin in water, J. Hazard. Mater. 161 (2009) 701–708. [4] T.A. Gad-Allah, M.E.M. Ali, M.I. Badawy, Photocatalytic oxidation of ciprofloxacin under simulated sunlight, J. Hazard. Mater. 186 (2011) 751–755. [5] L.M. Du, Q.Q. Xu, J.M. Yuan, Fluorescence spectroscopy determination of fluoroquinolones by charge-transfer reaction, J. Pharm. Biomed. Anal. 33 (2003) 693–698. [6] M. Hernández, C. Aguilar, F. Borrull, M. Calull, Determination of ciprofloxacin, enrofloxacin and flumequine in pig plasma samples by capillary isotachophoresis—capillary zone electrophoresis, J. Chromatogr. B 772 (2002) 163–172. [7] A. Monteroa, R.L. Althausb, A. Molinac, I. Berrugac, M.P. Molinaa, Detection of antimicrobial agents by a specific microbiological method (Eclipse100®) for ewe milk, Small Ruminant Res. 57 (2005) 229–237. [8] H. García Ovando, N. Gorla, C. Luders, G. Poloni, C. Errecalde, G. Prieto, I. Puelles, Comparative pharmacokinetics of enrofloxacin and ciprofloxacin in chickens, J. Vet. Pharmacol. Ther. 22 (1999) 209–212. [9] J. Manceau, M. Gicquel, M. Laurentie, P. Sanders, Simultaneous determination of enrofloxacin and ciprofloxacin in animal biological fluids by high-performance liquid chromatography: application in pharmacokinetic studies in pig and rabbit, J. Chromatogr. B 726 (1999) 175–184. [10] K. Hu, X.Y. Huang, Y.S. Jiang, W. Fang, X.L. Yang, Monoclonal antibody based enzyme-linked immunosorbent assay for the specific detection of ciprofloxacin and enrofloxacin residues in fishery products, Aquaculture 310 (2010) 8–12.

[11] J. Duan, Z.H. Yuan, Development of an indirect competitive ELISA for ciprofloxacin residues in food animal edible tissues, J. Agric. Food Chem. 49 (2001) 1087–1089. [12] S. Mostafa, M. El-Sadek, E.A. Alla, Spectrophotometric determination of ciprofloxacin, enrofloxacin and perfloxacin through charge transfer complex formation, J. Pharm. Biomed. Anal. 27 (2002) 133–142. [13] Z.Q. Zhang, Y.C. Jiang, H.T. Yan, Indirect determination of ciprofloxacin by flow injection flame AAS based on forming complex with Fe(III), At. Spectrosc. 24 (2003) 27–30. [14] M. Honda, T. Seki, Y. Takeoka, Dual tuning of the photonic band-gap structure in soft photonic crystals, Adv. Mater. 21 (2009) 1801–1804. [15] J.P. Ge, Y.D. Yin, Responsive photonic crystals, Angew. Chem. Int. Ed. 50 (2011) 1492–1522. [16] J.H. Holtz, J.S.W. Holtz, C.H. Munro, S.A. Asher, Intelligent polymerized crystalline colloidal arrays: novel chemical sensor materials, Anal. Chem. 70 (1998) 780–791. ¨ [17] C.G. Schafer, M. Gallei, J.T. Zahn, J. Engelhardt, G.P. Hellmann, M. Rehahn, Reversible light-, thermo-, and mechano-responsive elastomeric polymer opal films, Chem. Mater. 25 (2013) 2309–2318. [18] H.L. Jiang, Y.H. Zhu, C. Chen, J.H. Shen, H. Bao, L.M. Peng, X.L. Yang, C.Z. Li, Photonic crystal pH and metal cation sensors based on poly(vinyl alcohol) hydrogel, New J. Chem. 36 (2012) 1051–1056. [19] Y.J. Lee, P.V. Braun, Tunable inverse opal hydrogel pH sensors, Adv. Mater. 15 (2003) 563–566. [20] C.E. Reese, S.A. Asher, Photonic crystal optrode sensor for detection of Pb2+ in high ionic strength environments, Anal. Chem. 75 (2003) 3915–3918. [21] M. Ben-Moshe, V.L. Alexeev, S.A. Asher, Fast responsive crystalline colloidal array photonic crystal glucose sensors, Anal. Chem. 78 (2006) 5149–5157. [22] F.Y. Lin, L.P. Yu, Thiourea functionalized hydrogel photonic crystal sensor for Cd2+ detection, Anal. Methods 4 (2012) 2838–2845. [23] S. Kado, H. Otani, Y. Nakahara, K. Kimura, Highly selective recognition of acetate and bicarbonate by thiourea-functionalised inverse opal hydrogel in aqueous solution, Chem. Commun. 49 (2013) 886–888. [24] L.Q. Wang, F.Y. Lin, L.P. Yu, A molecularly imprinted photonic polymer sensor with high selectivity for tetracyclines analysis in food, Analyst 137 (2012) 3502–3509. [25] Y.X. Zhang, P.Y. Zhao, L.P. Yu, Highly-sensitive and selective colorimetric sensor for amino acids chiral recognition based on molecularly imprinted photonic polymers, Sens. Actuator B Chem. 181 (2013) 850–857. [26] X.Y. Liu, H.X. Fang, L.P. Yu, Molecularly imprinted photonic polymer based on␤cyclodextrin for amino acid sensing, Talanta 116 (2013) 283–289. [27] M. Liu, L.P. Yu, A novel platform for sensing an amino acid by integrating hydrogel photonic crystals with ternary complexes, Analyst 138 (2013) 3376–3379. [28] J.Y. Wang, Y. Cao, Y. Feng, F. Yin, J.P. Gao, Multiresponsive inverse-opal hydrogels, Adv. Mater. 19 (2007) 3865–3871. [29] M. Ghaedi, K. Niknam, K. Taheri, H. Hossainian, M. Soylak, Flame atomic absorption spectrometric determination of copper, zinc and manganese after solid-phase extraction using 2,6-dichlorophenyl-3,3-bis(indolyl)methane loaded on Amberlite XAD-16, Food Chem. Toxicol. 48 (2010) 891–897. [30] M. Ghaedi, K. Niknamb, A. Shokrollahi, E. Niknama, H.R. Rajabi, M. Soylak, Flame atomic absorption spectrometric determination of trace amounts of heavy metal ions after solid phase extraction using modified sodium dodecyl sulfate coated on alumina, J. Hazard. Mater. 155 (2008) 121–127. [31] M. Zupanèiè, R.C. Koroˆsec, P. Bukovec, The thermal stability of ciprofloxacin complexes with magnesium(II), zinc(II) and cobalt(II), J. Therm. Anal. Calorim. 63 (2001) 787–795. [32] M. Patel, M. Chhasatia, P. Parmar, Antibacterial DNA interaction studies of zinc(II) complexes with quinolone family member, ciprofloxacin, Eur. J. Med. Chem. 45 (2010) 439–446. [33] M.N. Lin, X. Li, W.Y. Zhang, X.G. Ying, Preparation and properties of porous l-tryptophan imprinted latex membrane from core-shell emulsion, J. Appl. Polym. Sci. 127 (2013) 2067–2073. [34] E. Karadag, O.B. Uzum, D. Saraydin, Swelling equilibria and dye adsorption studies of chemically crosslinked superabsorbent acrylamide/maleic acid hydrogels, Eur. Polym. J. 38 (2002) 2133–2141.

Specific and ultrasensitive ciprofloxacin detection by responsive photonic crystal sensor.

A new approach for specific and ultrasensitive measurement of ciprofloxacin has been developed by integrating ternary complexes into responsive photon...
3MB Sizes 0 Downloads 4 Views