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A simple and sensitive colorimetric method for the determination of propafenone by silver nanoprobe
Sensors and Actuators B 174 (2012) 133–139
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Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
A simple and sensitive colorimetric method for the determination of propafenone by silver nanoprobe Ji-chun Qu a,b , Yan-ping Chang a,b , Yan-hua Ma a,b , Jin-min Zheng a,b , Hong-hong Li a,b , Qian-qian Ou a,b , Cuiling Ren a,b , Xing-guo Chen a,b,c,∗ a
National Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, China Department of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, China c Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province, Lanzhou 730000, China b
a r t i c l e
i n f o
Article history: Received 6 June 2012 Received in revised form 20 August 2012 Accepted 21 August 2012 Available online 28 August 2012 Keywords: Visual colorimetric detection PPF Silver nanoparticles (AgNPs) Aggregation
a b s t r a c t A simple, rapid and ultrasensitive colorimetric method for the determination of propafenone, based on the specific recognition property of propafenone with the unique optical properties of AgNPs, has been developed. The addition of propafenone induced the citrate to be desorbed from the surface of the AgNPs, leading to the aggregation of the AgNPs, accompanied by a dramatic surface plasmon absorption band shift and thereby results in their yellow-to-red even purple color change. The concentration of propafenone can be determined by monitoring with the naked eyes or a UV–Vis spectrophotometer. The detection limit of the present method for propafenone was 2.4 M. The proposed method is a promising mean for on-site detection of propafenone in actual samples without costly instruments. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Propafenone (PPF) is one of the most important anti-arrhythmic drugs for ventricular and supraventricular arrhythmias. It is a class Ic antiarrhythmic drug that acts on the Nav 1.5 and KCNH2 (hERG) ion channels and has weak -blocking effects [1]. The overdose of PPF has been reported to be associated with features of severe seizures [2], cardiovascular and CNS toxicity [3], even with similar life-threatening symptoms in which cardiac features predominate with QRS/QTc prolongation and ventricular arrhythmias [4]. Therefore, the quantification of PPF is usually required in clinical assay. Some analytical methods for the detection of PPF have been established, including LC [5–8], HPLC [9–11] and so on. These methods have the advantages of high sensitivity and good selectivity. However, these protocols, which usually require specialized equipment or complicated procedures, are somewhat laborious, time-consuming, expensive, and unsuitable for real-time detection. Therefore, it is still a challenge to develop a method for expedient, rapid and real-time detection of PPF. Colorimetric sensors, which require minimal instrumentations and make on-site realtime sensing even easier, are free of the above problems.
∗ Corresponding author at: National Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, China. Tel.: +86 931 8912763; fax: +86 931 8912582. E-mail address: [email protected] (X.-g. Chen). 0925-4005/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2012.08.045
Metal nanomaterials such as silver nanoparticles (AgNPs) and Au nanoparticles (AuNPs) have been found wide applications as ideal reporters for colorimetric detection owing to their unique optical and electric properties [12–15]. The major advantage of Au/AgNPs-based assays is that the molecular recognition events can be transformed into color changes, which can be observed by the naked eye. Moreover, the extraordinarily high absorption coefficient of Au/AgNPs enables the colorimetric assay to be sensitive. Additionally, AgNPs have shown some unique characteristics and advantages over AuNPs to a certain degree since they possess much higher absorption coefficients than AuNPs of the same size [16,17], which can achieve approximately 100-fold [18,19]. This allows sensitive colorimetric detection with minimal material consumption. More importantly, the cost of the preparation of AgNPs is much lower when compared with AuNPs. On this account, AgNPs have gained more popularity than AuNPs. The dispersed solution of AgNPs is yellow in color, while it will change to red or even purple because of aggregation. Contrary to previous reports, in which citrate is considered to be a “magic” component critically required for the formation of silver nanoparticles, Zhang et al. have determined that the ligands which can selectively adhere to Ag (1 1 1) facets can be expanded to many di- and tricarboxylate compounds whose two nearest carboxylate groups are separated by two or three carbon atoms. They have also found that the widely used secondary ligand can be replaced by many hydroxyl and thiol [20] groups-containing compounds or even removed entirely while still producing nanoparticles of excellent uniformity and
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solution under vigorous stirring. After stirring for 20 min, 0.01 g sodium borohydride (freshly prepared) in 10 mL water was added at room temperature (25 ◦ C) and the dark colloidal silver nanoparticles were produced. During the reaction, the dark colloidal solution changed to bright yellow and the stirring was stopped after 1 h. The prepared AgNPs suspension could be used after 2 h. The AgNPs suspension was stored in the dark under 4.0 ± 2.0 ◦ C to remain stable for several weeks.
2.4. Procedures for the detection of PPF
Scheme 1. Schematic illustration of the colorimetric assay for PPF induced the noncrosslinking AgNPs aggregation.
stability [20,21]. Lin et al. have fabricated a facile colorimetric DA (dopamine) biosensor based on the special interaction between DA and AgNPs, in which the stabilizing citrate ions were displaced by the chemisorbed DA and the surface charges were partly neutralized [22]. It is well known that colloidal stability can be adjusted by modifying surface charges and aggregation can be induced due to the loss of surface charges [22–24]. Our strategy was inspired by the probability that the PPF ligands could displace the citrate ions on the AgNPs and the surface charges of the AgNPs would be reduced significantly. As a result, the AgNPs aggregated and the color of the solution changed from bright yellow to red and then purple. Based on this phenomenon, a simple colorimetric assay for PPF was established (Scheme 1). To the best of our knowledge, this method is the first example of using the special interaction between PPF and AgNPs to fabricate a facile colorimetric PPF biosensor with high sensitivity and good selectivity.
In a typical experiment for detecting PPF, 20.0 mL of cit-AgNPs was placed in a 100.00 mL volumetric flask and the solution was diluted to 100.00 mL with water and mixed thoroughly. To investigate the effect of pH of the buffer solutions on PPF detection, 0.05 M HCl or NaOH solution was used to adjust the pH. Then, 3.0 mL of the prepared cit-AgNPs aqueous solution and 30.0 L different amount of PPF were sequentially added into 5.0 mL calibrated test tube to incubate for a certain time, and the absorption spectra of the sensing system with varying concentration of PPF were collected by UV–Vis spectrophotometer.
2.5. Influence of the ionic strength on AgNPs 30 L PPF (1 mM) with different amount of NaCl (1.0 M) making the ionic strength ranging from 3.66 × 10−3 M to 7.49 × 10−3 M were added into the solution including 600 L AgNPs (0.5 mM), 2.4 mL distilled water (pH 9.0). The reactions were performed for 20 min at 25 ◦ C, and then the absorbance was measured.
2. Materials and methods 2.1. Chemicals
2.6. Detection of the PPF in actual samples
Propafenone hydrochloride was purchased from Sigma–Aldrich. Sodium citrate, silver nitrate (AgNO3 , 99%), sodium borohydride (NaBH4 , 98%), KCl, NaCl, glucose, lactose and starch were received from Tianjin Guangfu Institute (China). Propafenone hydrochloride tablets were obtained from Shandong Junan Pharmaceutical Ltd. (Shandong, China). All the reagents were of analytical grade and used as received without further purification. The ultra-water prepared using Milli-XQ equipment was used throughout the experiment.
Firstly, three pieces of propafenone hydrochloride tablet were ground to powder and weighed. Secondly, the obtained powder (approximately 210 mg) was immersed in a suitable amount of methanol. Thirdly, the mixture was dispersed under ultrasonication for 30 min and kept for a few hours to ensure that the PPF was extracted completely from the sample. Then, the mixture was centrifuged and the supernatant containing PPF was collected, which was spined to dryness by a rotary evaporator. Finally, the obtained PPF powder was further dissolved with water, making sure the final concentration of PPF in the solution was within the working range. In order to further explore the practicality of the proposed colorimetric method, standard addition method was applied to detect PPF. To confirm the accuracy of the present procedure, recovery test was also investigated. This method was also applied to urine samples for the determination of PPF. For this purpose the urine of a healthy female volunteer was precipitated to obtain the clear yellowish urine sample after centrifuging at 3000 rpm for 15 min. The recovery of PPF was determined by standard addition method. Three different levels of PPF concentration (10, 20, 25 M) were added into the sample, respectively, and three replicates were performed at each level for measurement. These samples were diluted with a ratio of urine to distilled water of 1:6. Then 30 L of the diluted urine was added into the solution containing 600 L AgNPs (0.5 mM), and 2.37 mL distilled water (pH 9.0). The reactions were carried out at 25 ◦ C for 20 min. After the reactions, we measured the absorbance of the solution by using a TU-1901 double beams UV–Vis spectrophotometer.
2.2. Apparatus TEM analysis was performed on a Hitachi-6000 transmission electron microscope (TEM, Japan). UV–Vis absorption spectra were measured on a TU-1901 double beams UV–Vis spectrophotometer (Purkinje General Instrument Co. Ltd., China) with a 1.0 cm path length quartz cuvette. Photographs of the AgNPs suspension used for visual colorimetric detection were captured by a Nikon 4500 digital camera. A pH-3C digital pH meter (Xiaoshan Scientific Instrument Plant, Zhejiang, China) was used to measure the pH values. 2.3. Synthesis of AgNPs The citrate modified AgNPs (cit-AgNPs) were prepared with modified Creighton method [25,26], which employed sodium citrate as a stabilizer [23]. Briefly, 1.00 mL 50 mM sodium citrate aqueous solution was added into 39 mL 0.64 mM AgNO3 aqueous
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Fig. 1. Representative TEM images of AgNPs in the absence (A) and presence of 1.5 × 10−5 M (B) and 3.5 × 10−5 M (C) PPF.
3. Results and discussion 3.1. Characterization of AgNPs The morphology of the cit-AgNPs was observed by a transmission electron microscope. As shown in Fig. 1A, by and large, AgNPs are dispersed in aqueous solution with an average size of 10.0 nm. When added PPF, it could be observed that the plasmon resonance dampened and had a red shift from 395 nm to 520 nm (Fig. 2B), and the color change was sensitive to PPF concentrations. The citAgNPs gradually turned to red and purple along with the increase of PPF, implying the increased aggregation state of AgNPs. Meanwhile, the TEM image (Fig. 1) of cit-AgNPs in the presence of PPF also confirmed the PPF-stimulated aggregation of AgNPs and the aggregation was intensified with the increasing amount of PPF. This dampening and red shifting were the results of particles assembly due to hybridization, which could be observed with the naked eyes in the form of a color change from bright yellow to pale red then purple. 3.2. Detection principle of PPF using cit-AgNPs as colorimetric probe Because electrostatic force can counteract the effects of Van der Waals’ force between AgNPs, AgNPs can be stabilized in aqueous solution by coating it with negatively charged citrate ions [27]. The surface silver atoms of cit-AgNPs can interact with the tridentate ligand PPF, which contains three groups ( OH, NH , COOH), through coordination interactions. As a result, PPF ligands could displace the citrate ions on the surface of AgNPs. In the experiments, when PPF was added into AgNPs solution, the positively charged
PPF ligands displaced the citrate ions on the surface of AgNPs and then neutralized the surface charges. As a result, the loss of surface charges decreased the electrostatic repulsion among these AgNPs, which induced the aggregation of AgNPs. Simultaneously, the color of the AgNPs solution changed with spectral variations as shown in Fig. 2. In order to explore the real reason, the control experiment was carried out using a series of pharmaceuticals (metoprolol tartrate, propranolol, (−)-pseudoephedrine, (−)-ephedrine) as a substitute of PPF. The mechanism of the detection in the aggregation of nanoparticles can be investigated by following the interaction of AgNPs with the above series of model compounds whose structures were shown in Fig. 2A. UV–Vis absorption was observed on the addition of any one of them to AgNPs indicating the displacement of citrate ions. However, no obvious phenomenon was observed in any case except PPF. The change in color was not observed for these compounds having a hydroxyl and an imino group or a hydroxyl and a carboxyl group at positions adjacent to each other, while PPF with all of the three groups at the proper position caused a rapid yellow-to-red color change (Fig. 2B). These results clearly demonstrated that such substructures except PPF have low coordination ability which could not displace citrate on the cit-AgNPs surface for the facile aggregation of AgNPs and cause a color change. Simultaneously, glutathione (GSH) stabilized AgNPs (GSH-AgNPs) nanomaterials were synthesized to be used as the control as well, The coordination ability of PPF with the surface silver atoms of cit-AgNPs is between citrate and GSH, so it can displace citrate but not GSH (Fig. 3). Scheme 1 depicts the mechanism of colorimetric detection of PPF by cit-AgNPs. The special interaction between PPF and AgNPs rendered this method facile, economic, highly sensitive and selective. Therefore, a simple and selective colorimetric assay for PPF detection could be carried out.
Fig. 2. The chemical structures of a series of pharmaceuticals studied (A), photographic images and UV–Vis spectra of cit-AgNPs solution containing these compound — 0: control; 1: propranolol; 2: (−)-pseudoephedrine; 3: propafenone; 4: (−)-ephedrine; 5: metoprolol tartrate. (B) The experiments were performed at an ionic strength of 3.66 × 10−3 M, pH of 9.0, reaction temperature of 25 ◦ C and reaction time of 20 min. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of the article.)
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Fig. 3. The GSH–AgNPs nanomaterials have been synthesized to be used as control. 0: GSH–AgNPs; 1: GSH–AgNPs with 1.00 × 10−4 M PPF; 2: GSH–AgNPs with 3.23 × 10−4 M PPF.
3.3. Factors influencing of colorimetric detection 3.3.1. Effect of pH The interaction of AgNPs and PPF could be affected by the pH of the solution. PPF is a monoprotic base with pKa = 9.30 and the pH of the solution can affect the form of PPF in aqueous solution. So we investigated the effect of the pH of the solution in the range from 7.0 to 10.0 (Fig. 4). The pH of the AgNPs solution was adjusted with hydrochloric acid or sodium hydroxide. To take 2.5 × 10−5 M PPF for example, the profile of absorption ratio (A520 /A395 ) versus the pH of the solution was obtained, as shown in Fig. 4. It could be seen that the absorption ratio (A520 /A395 ) was very low in weak acidic and basic media (pH <8.0) and strong basic media (pH >10.0), and the highest absorption ratio (A520 /A395 ) was obtained at pH 9.0 (Fig. 4b). At low pH (pH <8.0) protonated PPF could not displace sodium citrate located on the surface of the cit-AgNPs. Meanwhile, the surface charges of the cit-AgNPs cannot be partly neutralized and then the electrostatic force counteract the effects of Van der Waals’ force between AgNPs, which cannot induce the aggregation of the AgNPs and also cannot cause a yellow-to-red even purple color change. So PPF can be not determined at low pH. Furthermore, at relatively low pH (pH <7.0), the AgNPs might partially aggregate themselves and could not interact with PPF as well. But at high pH (pH 9), few protonated PPF (pKa = 9.30) can partly neutralize the surface charges of the AgNPs and induce their aggregation, thus results in a yellow-to-red even purple color change. With pH
Fig. 4. Effect of pH of the solution on the absorption ratio (A520 /A395 ), the AgNPs solution was mixed without PPF (a) or with 2.5 × 10−5 M PPF (b). The experiments were performed at an ionic strength of 3.66 × 10−3 M, reaction temperature of 25 ◦ C and reaction time of 20 min.
Fig. 5. Effect of reaction time on the absorption ratio (A520 /A395 ), the AgNPs solution was mixed with 1.0 × 10−5 M PPF. The experiments were performed at an ionic strength of 3.66 × 10−3 M, pH of 9.0 and reaction temperature of 25 ◦ C.
>10.0, PPF is absolutely unprotonated and the solubility of it was much lower so that it could not induce the aggregation of AgNPs [28]. Additionally, at relatively high pH (pH >10.0), the AgNPs might partially aggregate and could not interact with PPF as well, which could be confirmed by the control experiments (Fig. 4a). Thus, pH 9.0 was chosen as the optimum condition. 3.3.2. Effect of reaction time The reaction time between AgNPs and PPF is a key point that affects the colorimetric assays. The relationship between reaction time and absorption ratio (A520 /A395 ), as shown in Fig. 5, was investigated by adding 30.0 L 1.0 mM PPF solution into 3.0 mL AgNPs solution. It can be seen that the absorption ratio (A520 /A395 ) increased gradually from 2 min to 18 min and kept steady from 18 min to 22 min. This demonstrated that the aggregation of AgNPs almost completed within 20 min. Thus, the reaction time was chosen as 20 min. 3.3.3. Effect of temperature From Fig. 6 we can see that the suitable temperature was 25 ◦ C, as at 25 ◦ C the absorption ratio (A520 /A395 ) was the highest, and when the temperature was below or above 25 ◦ C the absorption ratio reduced. So 25 ◦ C was chosen as optimum temperature.
Fig. 6. Effect of reaction temperature on the absorption ratio (A520 /A395 ), the AgNPs solution was mixed with 1.0 × 10−5 M PPF. The experiments were performed at an ionic strength of 3.66 × 10−3 M, pH of 9.0 and reaction time of 20 min.
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Fig. 7. Effect of ionic strength on the absorption ratio (A520 /A395 ), the AgNPs solution was mixed with 1.1 × 10−5 M PPF. The experiments were performed at an ionic strength of 3.66 × 10−3 M, pH of 9.0, reaction temperature of 25 ◦ C and reaction time of 20 min.
3.3.4. Effect of ionic strength The experimental results shown that the absorption ratio (A520 /A395 ) firstly increased then decreased with the increase of ionic strength of solution, it reached the highest point when the ionic strength of solution was 4.59 × 10−3 M, as can be seen in Fig. 7. However, the ionic strength of the solution with the diluted urine was 3.84 × 10−3 M, while in the pharmaceutical samples it was 3.66 × 10−3 M which is equal to the ionic strength of the detection solution without actual samples, as the pharmaceutical samples were not making any changes to the ionic strength of the detection solution since it is quite pure after a series of treatment. Furthermore, there is no obvious difference with A520/395 when the ionic strength is between 3.66 × 10−3 M and 3.84 × 10−3 M. So 3.66 × 10−3 M was chosen as the optimum ionic strength. 3.4. Analytical parameters Under the optimum conditions, the colorimetric assay was processed directly using the AgNPs suspension in glass tubes to detect different amounts of PPF. The picture of AgNPs solution in the presence of different concentration of PPF in the range of 0.5 × 10−6 to 40 × 10−6 M was shown in Fig. 8. The color of the AgNPs solution got changed as the order of yellow → red → purple → dark by
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Fig. 9. Visual color changes and the absorbance ratio of the AgNPs solution in the presence of 2.5 × 10−5 M PPF or 5.0 × 10−4 M other analytes. The experiments were performed at an ionic strength of 3.66 × 10−3 M, pH of 9.0, reaction temperature of 25 ◦ C and reaction time of 20 min.
increasing PPF concentration (Fig. 8A). So, the concentration of PPF could be roughly discriminated by naked eyes compared with the standard colorimetric picture. Furthermore, there was a good linear relationship between the absorbance change (A520/395 ) of AgNPs and the concentration of PPF in the range of 1.0 × 10−5 –3.5 × 10−5 M. The standard regression equation was A520/395 = 1.55lg c + 7.87, R2 = 0.9986 and the limit for detection of PPF was 2.4 × 10−6 M (Fig. 8B). The selectivity of this method was investigated following the general procedure in the presence of 2.5 × 10−5 M PPF or some potential interfering substances such as common metal ions, sugars, amino acids, and pharmaceuticals. The absorption spectra were used to monitor the aggregation of AgNPs. It was found that common metal ions (K+ , Na+ ), saccharides (glucose, lactose,) and amino acids (dl-glucose, l-Phe, and l-Tyr) as well as urea could be allowed at very high concentration (20–100 times higher than PPF) without any color change. While aggregation does not occur in the presence of a considerable excess of common medicine such as metoprolol tartrate, propranolol, (−)-pseudoephedrine, and (−)-ephedrine at concentration of 50 mM, indicating that there was no significant interference between any other interferences and AgNPs (Fig. 9). Generally speaking, there are no significant interactions between AgNPs and any other interference.
Fig. 8. Photographic images of AgNPs solution containing various concentrations of PPF ranging from 5.0 × 10−7 to 4.0 × 10−5 M. From 0 to 13, they are 0, 5.0 × 10−7 , 7.5 × 10−7 , 1.0 × 10−6 , 2.5 × 10−6 , 5.0 × 10−6 , 7.5 × 10−6 , 1.0 × 10−5 , 1.5 × 10−5 , 2.0 × 10−5 , 2.5 × 10−5 , 3.0 × 10−5 , 3.5 × 10−5 and 4.0 × 10−5 , respectively (A). Inset (B) is the calibration curve between A520 /A395 and concentration of PPF. The experiments were performed at an ionic strength of 3.66 × 10−3 M, pH of 9.0, reaction temperature of 25 ◦ C and reaction time of 20 min.
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Table 1 Determination results of PPF in propafenone hydrochloride tablets. The experiments were performed at an ionic strength of 3.66 × 10−3 M, pH of 9.0, reaction temperature of 25 ◦ C and reaction time of 20 min. Specified (mg/piece)
Found (mg/piece)
Average (mg/piece)
R.S.D. (%, n = 5)
Average error (%)
50.0
50.2, 49.3, 50.9, 50.7, 49.2
50.1
1.56
0.2
Table 2 Recovery results of PPF in propafenone hydrochloride tablets using the proposed method. The experiments were performed at an ionic strength of 3.66 × 10−3 M, pH of 9.0, reaction temperature of 25 ◦ C and reaction time of 20 min. Sample
Detected amount (10−5 M)
Added amount (10−5 M)
Found amount (10−5 M)
R.S.D. (%, n = 5)
Recovery (%, n = 3)
1 2 3
1.33 1.99 2.65
2.67 2.00 1.33
4.08 4.00 3.94
1.48 0.79 1.34
103.0 100.5 97.0
Table 3 Determination results of PPF in urine sample using the proposed method. The experiments were performed at an ionic strength of 3.84 × 10−3 M, pH of 9.0, reaction temperature of 25 ◦ C and reaction time of 20 min.
a
Sample
Detected amount (10−5 M)a
Added amount (10−5 M)
Found amount (10−5 M)
R.S.D. (%, n = 3)
Recovery (%, n = 3)
0 1 2 3
– – – –
0 1.00 2.00 2.50
0 1.06 1.91 2.47
0.50 4.65 2.97
106.0 95.0 98.8
Not detectable.
3.5. Determination of PPF in actual samples
Acknowledgements
PPF from pharmaceutical products was determined by the method under the optimum conditions. The results were listed in Tables 1 and 2. It was shown that the recoveries for PPF ranged from 97% to 103%. The relative standard deviation (R.S.D.) of each three parallel experiments was below 2%. In order to further explore the practical applicability of the present colorimetric method, the amount of PPF in urine was detected. The results of the determination and recovery were shown in Table 3. It showed that the average recoveries for PPF ranged from 95% to 106% at three spiked levels. The relative standard deviation (R.S.D.) of each three parallel experiments was below 5%. The high analytical precision and good recovery results suggested that this colorimetric method was reliable and could be widely applied in the biological samples testing.
This work was supported by the National Natural Science Foundation of China (No. 21075056) and the Fundamental Research Funds for the Central Universities (No. lzujbky-2011-28).
4. Conclusion The rational design and construction of optically active ligand capped nanoparticles for pharmaceutical separation and detection was of intense current interest. In this study, we have developed a novel nanoparticle-based biosensing platform using citrate-capped AgNPs as probe element and demonstrated its feasibility in the application of recognition of PPF based on absorption chemistry. This AgNPs-based probe design offers many advantages, including simplicity of preparation and manipulation compared with other methods that employ specific strategies. More importantly, our present sensor can achieve the goal of translating a selective molecular recognition event into an appreciable color change via the aggregation of AgNPs. The mechanism of color change and the effect of experimental conditions were studied using absorption spectrometry, and the detection limit of 2.4 × 10−6 M for PPF using this novel colorimetric probe can be achieved. This colorimetric analytical method without the use of expensive instruments is so convenient, economic and speedy that it has flourishing prospects in pharmaceutical analytical chemistry.
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Biographies Jichun Qu received her BS degree in chemistry from Sichuan University (China) in 2010. She entered Lanzhou University (China) in 2010, majored in analytical chemistry. Now, she is engaged in the preparation and application of nanometerials. Yanping Chang received her BS degree in chemistry from Luoyang Normal University in 2009. She entered Lanzhou University (China) in 2009, majored in analytical chemistry. Now, she is engaged in the preparation and application of nanometerials. Yanhua Ma received her BS degree in chemistry from Liaocheng University (China) in 2009. She is successive postgraduate and doctoral programs of study in Lanzhou University (China), majored in analytical chemistry. Now, she is engaged in the areas of capillary electrophoresis and the preparation and application of nanometerials. Jinmin Zheng received her BS degree in biology from China University of Mining and Technology in 2009. She entered Lanzhou University (China) in 2010, majored in analytical chemistry. Now, she is engaged in the preparation and application of nanometerials. Honghong Li received her BS degree in chemistry from Northwest Normal University (China) in 2009. She entered Lanzhou University (China) in 2009, majored in analytical chemistry. Now, she is engaged in the preparation and application of nanometerials. Qianqian Ou received her BS degree in chemistry from Xinyang Normal University (China) in 2009. She entered Lanzhou University (China) in 2009, majored in analytical chemistry. Now, she is engaged in the preparation and application of nanometerials. Cuiling Ren received her BS degree in chemistry from Lanzhou University (China) in 2004. She was successive postgraduate and doctoral programs of study in Lanzhou University (China), majored in analytical chemistry. She received her PhD degree in analytical chemistry from Lanzhou University (China) in 2010. Now she is a lecturer of Lanzhou University (China). Her research interests are in the preparation and application of nanometerials. Xingguo Chen received his BS, MS and PhD degree in analytical chemistry from Lanzhou University (China) in 1982, 1987 and 1994, respectively. Now he is a full professor of Lanzhou University (China). His research interests are in the areas of capillary electrophoresis and nanometerials.
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Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
A simple and sensitive colorimetric method for the determination of propafenone by silver nanoprobe Ji-chun Qu a,b , Yan-ping Chang a,b , Yan-hua Ma a,b , Jin-min Zheng a,b , Hong-hong Li a,b , Qian-qian Ou a,b , Cuiling Ren a,b , Xing-guo Chen a,b,c,∗ a
National Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, China Department of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, China c Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province, Lanzhou 730000, China b
a r t i c l e
i n f o
Article history: Received 6 June 2012 Received in revised form 20 August 2012 Accepted 21 August 2012 Available online 28 August 2012 Keywords: Visual colorimetric detection PPF Silver nanoparticles (AgNPs) Aggregation
a b s t r a c t A simple, rapid and ultrasensitive colorimetric method for the determination of propafenone, based on the specific recognition property of propafenone with the unique optical properties of AgNPs, has been developed. The addition of propafenone induced the citrate to be desorbed from the surface of the AgNPs, leading to the aggregation of the AgNPs, accompanied by a dramatic surface plasmon absorption band shift and thereby results in their yellow-to-red even purple color change. The concentration of propafenone can be determined by monitoring with the naked eyes or a UV–Vis spectrophotometer. The detection limit of the present method for propafenone was 2.4 M. The proposed method is a promising mean for on-site detection of propafenone in actual samples without costly instruments. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Propafenone (PPF) is one of the most important anti-arrhythmic drugs for ventricular and supraventricular arrhythmias. It is a class Ic antiarrhythmic drug that acts on the Nav 1.5 and KCNH2 (hERG) ion channels and has weak -blocking effects [1]. The overdose of PPF has been reported to be associated with features of severe seizures [2], cardiovascular and CNS toxicity [3], even with similar life-threatening symptoms in which cardiac features predominate with QRS/QTc prolongation and ventricular arrhythmias [4]. Therefore, the quantification of PPF is usually required in clinical assay. Some analytical methods for the detection of PPF have been established, including LC [5–8], HPLC [9–11] and so on. These methods have the advantages of high sensitivity and good selectivity. However, these protocols, which usually require specialized equipment or complicated procedures, are somewhat laborious, time-consuming, expensive, and unsuitable for real-time detection. Therefore, it is still a challenge to develop a method for expedient, rapid and real-time detection of PPF. Colorimetric sensors, which require minimal instrumentations and make on-site realtime sensing even easier, are free of the above problems.
∗ Corresponding author at: National Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, China. Tel.: +86 931 8912763; fax: +86 931 8912582. E-mail address: [email protected] (X.-g. Chen). 0925-4005/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2012.08.045
Metal nanomaterials such as silver nanoparticles (AgNPs) and Au nanoparticles (AuNPs) have been found wide applications as ideal reporters for colorimetric detection owing to their unique optical and electric properties [12–15]. The major advantage of Au/AgNPs-based assays is that the molecular recognition events can be transformed into color changes, which can be observed by the naked eye. Moreover, the extraordinarily high absorption coefficient of Au/AgNPs enables the colorimetric assay to be sensitive. Additionally, AgNPs have shown some unique characteristics and advantages over AuNPs to a certain degree since they possess much higher absorption coefficients than AuNPs of the same size [16,17], which can achieve approximately 100-fold [18,19]. This allows sensitive colorimetric detection with minimal material consumption. More importantly, the cost of the preparation of AgNPs is much lower when compared with AuNPs. On this account, AgNPs have gained more popularity than AuNPs. The dispersed solution of AgNPs is yellow in color, while it will change to red or even purple because of aggregation. Contrary to previous reports, in which citrate is considered to be a “magic” component critically required for the formation of silver nanoparticles, Zhang et al. have determined that the ligands which can selectively adhere to Ag (1 1 1) facets can be expanded to many di- and tricarboxylate compounds whose two nearest carboxylate groups are separated by two or three carbon atoms. They have also found that the widely used secondary ligand can be replaced by many hydroxyl and thiol [20] groups-containing compounds or even removed entirely while still producing nanoparticles of excellent uniformity and
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solution under vigorous stirring. After stirring for 20 min, 0.01 g sodium borohydride (freshly prepared) in 10 mL water was added at room temperature (25 ◦ C) and the dark colloidal silver nanoparticles were produced. During the reaction, the dark colloidal solution changed to bright yellow and the stirring was stopped after 1 h. The prepared AgNPs suspension could be used after 2 h. The AgNPs suspension was stored in the dark under 4.0 ± 2.0 ◦ C to remain stable for several weeks.
2.4. Procedures for the detection of PPF
Scheme 1. Schematic illustration of the colorimetric assay for PPF induced the noncrosslinking AgNPs aggregation.
stability [20,21]. Lin et al. have fabricated a facile colorimetric DA (dopamine) biosensor based on the special interaction between DA and AgNPs, in which the stabilizing citrate ions were displaced by the chemisorbed DA and the surface charges were partly neutralized [22]. It is well known that colloidal stability can be adjusted by modifying surface charges and aggregation can be induced due to the loss of surface charges [22–24]. Our strategy was inspired by the probability that the PPF ligands could displace the citrate ions on the AgNPs and the surface charges of the AgNPs would be reduced significantly. As a result, the AgNPs aggregated and the color of the solution changed from bright yellow to red and then purple. Based on this phenomenon, a simple colorimetric assay for PPF was established (Scheme 1). To the best of our knowledge, this method is the first example of using the special interaction between PPF and AgNPs to fabricate a facile colorimetric PPF biosensor with high sensitivity and good selectivity.
In a typical experiment for detecting PPF, 20.0 mL of cit-AgNPs was placed in a 100.00 mL volumetric flask and the solution was diluted to 100.00 mL with water and mixed thoroughly. To investigate the effect of pH of the buffer solutions on PPF detection, 0.05 M HCl or NaOH solution was used to adjust the pH. Then, 3.0 mL of the prepared cit-AgNPs aqueous solution and 30.0 L different amount of PPF were sequentially added into 5.0 mL calibrated test tube to incubate for a certain time, and the absorption spectra of the sensing system with varying concentration of PPF were collected by UV–Vis spectrophotometer.
2.5. Influence of the ionic strength on AgNPs 30 L PPF (1 mM) with different amount of NaCl (1.0 M) making the ionic strength ranging from 3.66 × 10−3 M to 7.49 × 10−3 M were added into the solution including 600 L AgNPs (0.5 mM), 2.4 mL distilled water (pH 9.0). The reactions were performed for 20 min at 25 ◦ C, and then the absorbance was measured.
2. Materials and methods 2.1. Chemicals
2.6. Detection of the PPF in actual samples
Propafenone hydrochloride was purchased from Sigma–Aldrich. Sodium citrate, silver nitrate (AgNO3 , 99%), sodium borohydride (NaBH4 , 98%), KCl, NaCl, glucose, lactose and starch were received from Tianjin Guangfu Institute (China). Propafenone hydrochloride tablets were obtained from Shandong Junan Pharmaceutical Ltd. (Shandong, China). All the reagents were of analytical grade and used as received without further purification. The ultra-water prepared using Milli-XQ equipment was used throughout the experiment.
Firstly, three pieces of propafenone hydrochloride tablet were ground to powder and weighed. Secondly, the obtained powder (approximately 210 mg) was immersed in a suitable amount of methanol. Thirdly, the mixture was dispersed under ultrasonication for 30 min and kept for a few hours to ensure that the PPF was extracted completely from the sample. Then, the mixture was centrifuged and the supernatant containing PPF was collected, which was spined to dryness by a rotary evaporator. Finally, the obtained PPF powder was further dissolved with water, making sure the final concentration of PPF in the solution was within the working range. In order to further explore the practicality of the proposed colorimetric method, standard addition method was applied to detect PPF. To confirm the accuracy of the present procedure, recovery test was also investigated. This method was also applied to urine samples for the determination of PPF. For this purpose the urine of a healthy female volunteer was precipitated to obtain the clear yellowish urine sample after centrifuging at 3000 rpm for 15 min. The recovery of PPF was determined by standard addition method. Three different levels of PPF concentration (10, 20, 25 M) were added into the sample, respectively, and three replicates were performed at each level for measurement. These samples were diluted with a ratio of urine to distilled water of 1:6. Then 30 L of the diluted urine was added into the solution containing 600 L AgNPs (0.5 mM), and 2.37 mL distilled water (pH 9.0). The reactions were carried out at 25 ◦ C for 20 min. After the reactions, we measured the absorbance of the solution by using a TU-1901 double beams UV–Vis spectrophotometer.
2.2. Apparatus TEM analysis was performed on a Hitachi-6000 transmission electron microscope (TEM, Japan). UV–Vis absorption spectra were measured on a TU-1901 double beams UV–Vis spectrophotometer (Purkinje General Instrument Co. Ltd., China) with a 1.0 cm path length quartz cuvette. Photographs of the AgNPs suspension used for visual colorimetric detection were captured by a Nikon 4500 digital camera. A pH-3C digital pH meter (Xiaoshan Scientific Instrument Plant, Zhejiang, China) was used to measure the pH values. 2.3. Synthesis of AgNPs The citrate modified AgNPs (cit-AgNPs) were prepared with modified Creighton method [25,26], which employed sodium citrate as a stabilizer [23]. Briefly, 1.00 mL 50 mM sodium citrate aqueous solution was added into 39 mL 0.64 mM AgNO3 aqueous
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Fig. 1. Representative TEM images of AgNPs in the absence (A) and presence of 1.5 × 10−5 M (B) and 3.5 × 10−5 M (C) PPF.
3. Results and discussion 3.1. Characterization of AgNPs The morphology of the cit-AgNPs was observed by a transmission electron microscope. As shown in Fig. 1A, by and large, AgNPs are dispersed in aqueous solution with an average size of 10.0 nm. When added PPF, it could be observed that the plasmon resonance dampened and had a red shift from 395 nm to 520 nm (Fig. 2B), and the color change was sensitive to PPF concentrations. The citAgNPs gradually turned to red and purple along with the increase of PPF, implying the increased aggregation state of AgNPs. Meanwhile, the TEM image (Fig. 1) of cit-AgNPs in the presence of PPF also confirmed the PPF-stimulated aggregation of AgNPs and the aggregation was intensified with the increasing amount of PPF. This dampening and red shifting were the results of particles assembly due to hybridization, which could be observed with the naked eyes in the form of a color change from bright yellow to pale red then purple. 3.2. Detection principle of PPF using cit-AgNPs as colorimetric probe Because electrostatic force can counteract the effects of Van der Waals’ force between AgNPs, AgNPs can be stabilized in aqueous solution by coating it with negatively charged citrate ions [27]. The surface silver atoms of cit-AgNPs can interact with the tridentate ligand PPF, which contains three groups ( OH, NH , COOH), through coordination interactions. As a result, PPF ligands could displace the citrate ions on the surface of AgNPs. In the experiments, when PPF was added into AgNPs solution, the positively charged
PPF ligands displaced the citrate ions on the surface of AgNPs and then neutralized the surface charges. As a result, the loss of surface charges decreased the electrostatic repulsion among these AgNPs, which induced the aggregation of AgNPs. Simultaneously, the color of the AgNPs solution changed with spectral variations as shown in Fig. 2. In order to explore the real reason, the control experiment was carried out using a series of pharmaceuticals (metoprolol tartrate, propranolol, (−)-pseudoephedrine, (−)-ephedrine) as a substitute of PPF. The mechanism of the detection in the aggregation of nanoparticles can be investigated by following the interaction of AgNPs with the above series of model compounds whose structures were shown in Fig. 2A. UV–Vis absorption was observed on the addition of any one of them to AgNPs indicating the displacement of citrate ions. However, no obvious phenomenon was observed in any case except PPF. The change in color was not observed for these compounds having a hydroxyl and an imino group or a hydroxyl and a carboxyl group at positions adjacent to each other, while PPF with all of the three groups at the proper position caused a rapid yellow-to-red color change (Fig. 2B). These results clearly demonstrated that such substructures except PPF have low coordination ability which could not displace citrate on the cit-AgNPs surface for the facile aggregation of AgNPs and cause a color change. Simultaneously, glutathione (GSH) stabilized AgNPs (GSH-AgNPs) nanomaterials were synthesized to be used as the control as well, The coordination ability of PPF with the surface silver atoms of cit-AgNPs is between citrate and GSH, so it can displace citrate but not GSH (Fig. 3). Scheme 1 depicts the mechanism of colorimetric detection of PPF by cit-AgNPs. The special interaction between PPF and AgNPs rendered this method facile, economic, highly sensitive and selective. Therefore, a simple and selective colorimetric assay for PPF detection could be carried out.
Fig. 2. The chemical structures of a series of pharmaceuticals studied (A), photographic images and UV–Vis spectra of cit-AgNPs solution containing these compound — 0: control; 1: propranolol; 2: (−)-pseudoephedrine; 3: propafenone; 4: (−)-ephedrine; 5: metoprolol tartrate. (B) The experiments were performed at an ionic strength of 3.66 × 10−3 M, pH of 9.0, reaction temperature of 25 ◦ C and reaction time of 20 min. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of the article.)
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Fig. 3. The GSH–AgNPs nanomaterials have been synthesized to be used as control. 0: GSH–AgNPs; 1: GSH–AgNPs with 1.00 × 10−4 M PPF; 2: GSH–AgNPs with 3.23 × 10−4 M PPF.
3.3. Factors influencing of colorimetric detection 3.3.1. Effect of pH The interaction of AgNPs and PPF could be affected by the pH of the solution. PPF is a monoprotic base with pKa = 9.30 and the pH of the solution can affect the form of PPF in aqueous solution. So we investigated the effect of the pH of the solution in the range from 7.0 to 10.0 (Fig. 4). The pH of the AgNPs solution was adjusted with hydrochloric acid or sodium hydroxide. To take 2.5 × 10−5 M PPF for example, the profile of absorption ratio (A520 /A395 ) versus the pH of the solution was obtained, as shown in Fig. 4. It could be seen that the absorption ratio (A520 /A395 ) was very low in weak acidic and basic media (pH <8.0) and strong basic media (pH >10.0), and the highest absorption ratio (A520 /A395 ) was obtained at pH 9.0 (Fig. 4b). At low pH (pH <8.0) protonated PPF could not displace sodium citrate located on the surface of the cit-AgNPs. Meanwhile, the surface charges of the cit-AgNPs cannot be partly neutralized and then the electrostatic force counteract the effects of Van der Waals’ force between AgNPs, which cannot induce the aggregation of the AgNPs and also cannot cause a yellow-to-red even purple color change. So PPF can be not determined at low pH. Furthermore, at relatively low pH (pH <7.0), the AgNPs might partially aggregate themselves and could not interact with PPF as well. But at high pH (pH 9), few protonated PPF (pKa = 9.30) can partly neutralize the surface charges of the AgNPs and induce their aggregation, thus results in a yellow-to-red even purple color change. With pH
Fig. 4. Effect of pH of the solution on the absorption ratio (A520 /A395 ), the AgNPs solution was mixed without PPF (a) or with 2.5 × 10−5 M PPF (b). The experiments were performed at an ionic strength of 3.66 × 10−3 M, reaction temperature of 25 ◦ C and reaction time of 20 min.
Fig. 5. Effect of reaction time on the absorption ratio (A520 /A395 ), the AgNPs solution was mixed with 1.0 × 10−5 M PPF. The experiments were performed at an ionic strength of 3.66 × 10−3 M, pH of 9.0 and reaction temperature of 25 ◦ C.
>10.0, PPF is absolutely unprotonated and the solubility of it was much lower so that it could not induce the aggregation of AgNPs [28]. Additionally, at relatively high pH (pH >10.0), the AgNPs might partially aggregate and could not interact with PPF as well, which could be confirmed by the control experiments (Fig. 4a). Thus, pH 9.0 was chosen as the optimum condition. 3.3.2. Effect of reaction time The reaction time between AgNPs and PPF is a key point that affects the colorimetric assays. The relationship between reaction time and absorption ratio (A520 /A395 ), as shown in Fig. 5, was investigated by adding 30.0 L 1.0 mM PPF solution into 3.0 mL AgNPs solution. It can be seen that the absorption ratio (A520 /A395 ) increased gradually from 2 min to 18 min and kept steady from 18 min to 22 min. This demonstrated that the aggregation of AgNPs almost completed within 20 min. Thus, the reaction time was chosen as 20 min. 3.3.3. Effect of temperature From Fig. 6 we can see that the suitable temperature was 25 ◦ C, as at 25 ◦ C the absorption ratio (A520 /A395 ) was the highest, and when the temperature was below or above 25 ◦ C the absorption ratio reduced. So 25 ◦ C was chosen as optimum temperature.
Fig. 6. Effect of reaction temperature on the absorption ratio (A520 /A395 ), the AgNPs solution was mixed with 1.0 × 10−5 M PPF. The experiments were performed at an ionic strength of 3.66 × 10−3 M, pH of 9.0 and reaction time of 20 min.
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Fig. 7. Effect of ionic strength on the absorption ratio (A520 /A395 ), the AgNPs solution was mixed with 1.1 × 10−5 M PPF. The experiments were performed at an ionic strength of 3.66 × 10−3 M, pH of 9.0, reaction temperature of 25 ◦ C and reaction time of 20 min.
3.3.4. Effect of ionic strength The experimental results shown that the absorption ratio (A520 /A395 ) firstly increased then decreased with the increase of ionic strength of solution, it reached the highest point when the ionic strength of solution was 4.59 × 10−3 M, as can be seen in Fig. 7. However, the ionic strength of the solution with the diluted urine was 3.84 × 10−3 M, while in the pharmaceutical samples it was 3.66 × 10−3 M which is equal to the ionic strength of the detection solution without actual samples, as the pharmaceutical samples were not making any changes to the ionic strength of the detection solution since it is quite pure after a series of treatment. Furthermore, there is no obvious difference with A520/395 when the ionic strength is between 3.66 × 10−3 M and 3.84 × 10−3 M. So 3.66 × 10−3 M was chosen as the optimum ionic strength. 3.4. Analytical parameters Under the optimum conditions, the colorimetric assay was processed directly using the AgNPs suspension in glass tubes to detect different amounts of PPF. The picture of AgNPs solution in the presence of different concentration of PPF in the range of 0.5 × 10−6 to 40 × 10−6 M was shown in Fig. 8. The color of the AgNPs solution got changed as the order of yellow → red → purple → dark by
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Fig. 9. Visual color changes and the absorbance ratio of the AgNPs solution in the presence of 2.5 × 10−5 M PPF or 5.0 × 10−4 M other analytes. The experiments were performed at an ionic strength of 3.66 × 10−3 M, pH of 9.0, reaction temperature of 25 ◦ C and reaction time of 20 min.
increasing PPF concentration (Fig. 8A). So, the concentration of PPF could be roughly discriminated by naked eyes compared with the standard colorimetric picture. Furthermore, there was a good linear relationship between the absorbance change (A520/395 ) of AgNPs and the concentration of PPF in the range of 1.0 × 10−5 –3.5 × 10−5 M. The standard regression equation was A520/395 = 1.55lg c + 7.87, R2 = 0.9986 and the limit for detection of PPF was 2.4 × 10−6 M (Fig. 8B). The selectivity of this method was investigated following the general procedure in the presence of 2.5 × 10−5 M PPF or some potential interfering substances such as common metal ions, sugars, amino acids, and pharmaceuticals. The absorption spectra were used to monitor the aggregation of AgNPs. It was found that common metal ions (K+ , Na+ ), saccharides (glucose, lactose,) and amino acids (dl-glucose, l-Phe, and l-Tyr) as well as urea could be allowed at very high concentration (20–100 times higher than PPF) without any color change. While aggregation does not occur in the presence of a considerable excess of common medicine such as metoprolol tartrate, propranolol, (−)-pseudoephedrine, and (−)-ephedrine at concentration of 50 mM, indicating that there was no significant interference between any other interferences and AgNPs (Fig. 9). Generally speaking, there are no significant interactions between AgNPs and any other interference.
Fig. 8. Photographic images of AgNPs solution containing various concentrations of PPF ranging from 5.0 × 10−7 to 4.0 × 10−5 M. From 0 to 13, they are 0, 5.0 × 10−7 , 7.5 × 10−7 , 1.0 × 10−6 , 2.5 × 10−6 , 5.0 × 10−6 , 7.5 × 10−6 , 1.0 × 10−5 , 1.5 × 10−5 , 2.0 × 10−5 , 2.5 × 10−5 , 3.0 × 10−5 , 3.5 × 10−5 and 4.0 × 10−5 , respectively (A). Inset (B) is the calibration curve between A520 /A395 and concentration of PPF. The experiments were performed at an ionic strength of 3.66 × 10−3 M, pH of 9.0, reaction temperature of 25 ◦ C and reaction time of 20 min.
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Table 1 Determination results of PPF in propafenone hydrochloride tablets. The experiments were performed at an ionic strength of 3.66 × 10−3 M, pH of 9.0, reaction temperature of 25 ◦ C and reaction time of 20 min. Specified (mg/piece)
Found (mg/piece)
Average (mg/piece)
R.S.D. (%, n = 5)
Average error (%)
50.0
50.2, 49.3, 50.9, 50.7, 49.2
50.1
1.56
0.2
Table 2 Recovery results of PPF in propafenone hydrochloride tablets using the proposed method. The experiments were performed at an ionic strength of 3.66 × 10−3 M, pH of 9.0, reaction temperature of 25 ◦ C and reaction time of 20 min. Sample
Detected amount (10−5 M)
Added amount (10−5 M)
Found amount (10−5 M)
R.S.D. (%, n = 5)
Recovery (%, n = 3)
1 2 3
1.33 1.99 2.65
2.67 2.00 1.33
4.08 4.00 3.94
1.48 0.79 1.34
103.0 100.5 97.0
Table 3 Determination results of PPF in urine sample using the proposed method. The experiments were performed at an ionic strength of 3.84 × 10−3 M, pH of 9.0, reaction temperature of 25 ◦ C and reaction time of 20 min.
a
Sample
Detected amount (10−5 M)a
Added amount (10−5 M)
Found amount (10−5 M)
R.S.D. (%, n = 3)
Recovery (%, n = 3)
0 1 2 3
– – – –
0 1.00 2.00 2.50
0 1.06 1.91 2.47
0.50 4.65 2.97
106.0 95.0 98.8
Not detectable.
3.5. Determination of PPF in actual samples
Acknowledgements
PPF from pharmaceutical products was determined by the method under the optimum conditions. The results were listed in Tables 1 and 2. It was shown that the recoveries for PPF ranged from 97% to 103%. The relative standard deviation (R.S.D.) of each three parallel experiments was below 2%. In order to further explore the practical applicability of the present colorimetric method, the amount of PPF in urine was detected. The results of the determination and recovery were shown in Table 3. It showed that the average recoveries for PPF ranged from 95% to 106% at three spiked levels. The relative standard deviation (R.S.D.) of each three parallel experiments was below 5%. The high analytical precision and good recovery results suggested that this colorimetric method was reliable and could be widely applied in the biological samples testing.
This work was supported by the National Natural Science Foundation of China (No. 21075056) and the Fundamental Research Funds for the Central Universities (No. lzujbky-2011-28).
4. Conclusion The rational design and construction of optically active ligand capped nanoparticles for pharmaceutical separation and detection was of intense current interest. In this study, we have developed a novel nanoparticle-based biosensing platform using citrate-capped AgNPs as probe element and demonstrated its feasibility in the application of recognition of PPF based on absorption chemistry. This AgNPs-based probe design offers many advantages, including simplicity of preparation and manipulation compared with other methods that employ specific strategies. More importantly, our present sensor can achieve the goal of translating a selective molecular recognition event into an appreciable color change via the aggregation of AgNPs. The mechanism of color change and the effect of experimental conditions were studied using absorption spectrometry, and the detection limit of 2.4 × 10−6 M for PPF using this novel colorimetric probe can be achieved. This colorimetric analytical method without the use of expensive instruments is so convenient, economic and speedy that it has flourishing prospects in pharmaceutical analytical chemistry.
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Biographies Jichun Qu received her BS degree in chemistry from Sichuan University (China) in 2010. She entered Lanzhou University (China) in 2010, majored in analytical chemistry. Now, she is engaged in the preparation and application of nanometerials. Yanping Chang received her BS degree in chemistry from Luoyang Normal University in 2009. She entered Lanzhou University (China) in 2009, majored in analytical chemistry. Now, she is engaged in the preparation and application of nanometerials. Yanhua Ma received her BS degree in chemistry from Liaocheng University (China) in 2009. She is successive postgraduate and doctoral programs of study in Lanzhou University (China), majored in analytical chemistry. Now, she is engaged in the areas of capillary electrophoresis and the preparation and application of nanometerials. Jinmin Zheng received her BS degree in biology from China University of Mining and Technology in 2009. She entered Lanzhou University (China) in 2010, majored in analytical chemistry. Now, she is engaged in the preparation and application of nanometerials. Honghong Li received her BS degree in chemistry from Northwest Normal University (China) in 2009. She entered Lanzhou University (China) in 2009, majored in analytical chemistry. Now, she is engaged in the preparation and application of nanometerials. Qianqian Ou received her BS degree in chemistry from Xinyang Normal University (China) in 2009. She entered Lanzhou University (China) in 2009, majored in analytical chemistry. Now, she is engaged in the preparation and application of nanometerials. Cuiling Ren received her BS degree in chemistry from Lanzhou University (China) in 2004. She was successive postgraduate and doctoral programs of study in Lanzhou University (China), majored in analytical chemistry. She received her PhD degree in analytical chemistry from Lanzhou University (China) in 2010. Now she is a lecturer of Lanzhou University (China). Her research interests are in the preparation and application of nanometerials. Xingguo Chen received his BS, MS and PhD degree in analytical chemistry from Lanzhou University (China) in 1982, 1987 and 1994, respectively. Now he is a full professor of Lanzhou University (China). His research interests are in the areas of capillary electrophoresis and nanometerials.