Featuring research from the group of Prof. Dr Mei Yan at the University of Jinan, Key Laboratory of Chemical Sensing & Analysis in Universities of Shandong, Jinan, China

As featured in:

Electrophoretic separation in a microfluidic paper-based analytical device with an on-column wireless electrogenerated chemiluminescence detector A microfluidic paper-based analytical device was further exploited by coupling with electrophoretic separation technique for the first time.

See Mei Yan, Nianqiang Li et al., Chem. Commun., 2014, 50, 5699.

www.rsc.org/chemcomm Registered charity number: 207890

ChemComm

Published on 10 January 2014. Downloaded by University of Waterloo on 30/10/2014 02:15:21.

COMMUNICATION

Cite this: Chem. Commun., 2014, 50, 5699 Received 25th December 2013, Accepted 10th January 2014 DOI: 10.1039/c3cc49770d

View Article Online View Journal | View Issue

Electrophoretic separation in a microfluidic paper-based analytical device with an on-column wireless electrogenerated chemiluminescence detector† Lei Ge,a Shaowei Wang,a Shenguang Ge,a Jinghua Yu,a Mei Yan,*a Nianqiang Li*b and Jiadong Huanga

www.rsc.org/chemcomm

In this work, a microfluidic paper-based analytical device was further exploited by coupling with an electrophoretic separation technique for the first time. A low-cost, simple, portable, and disposable microfluidic paper-based electrophoretic device with an on-column wireless electro-generated chemiluminescence detector was demonstrated.

As an alternative to first-generation microfluidic devices, research efforts on microfluidic paper-based analytical devices (m-PADs) have recently expanded significantly to focus on developing novel fabrication techniques, inventing new functional concepts, and designing prototype devices for a variety of analytical applications.1 Among these functional concepts, independent and multiplex separation functions are important for building total analysis systems on m-PADs. However, in this regard, only Kubota’s group has successfully demonstrated the simultaneous separation of two compounds using thin-layer chromatography (TLC) on m-PADs coupled with an electrochemical detector.2 As a very well established technique, the equipment as well as the experimental procedure of TLC is simple and low-cost. However, this technique in its present form suffers from a major drawback: a poor flow profile with a linear flow rate of the mobile phase.3 The inverse relationship between flow rate and the distance migrated by the mobile phase front in the paper channel results in a progressively slower migration rate of the mobile phase, which narrows the application field of TLC and negatively influences its separation efficiency in m-PADs. Recently, the introduction of an electrokinetic flow technique into m-PADs by Chakraborty’s group4 showed great potential for overcoming the above problem. In the presence of an external electric field, the analytes would be driven through the macroporous paper channel by electrophoretic transport, and thus the flow rate would be independent of the separation channel length. Inspired by this technique, electrophoretic separation was introduced into m-PADs a

Key Laboratory of Chemical Sensing & Analysis in Universities of Shandong, School of Chemistry and Chemical Engineering, University of Jinan, Jinan 250022, P. R. China. E-mail: [email protected] b School of Information Science and Engineering, University of Jinan, Jinan 250022, China. E-mail: [email protected] † Electronic supplementary information (ESI) available. See DOI: 10.1039/c3cc49770d

This journal is © The Royal Society of Chemistry 2014

Scheme 1 (A) Board-A: (1) pierced reservoir zones, (2) pierced sample zone, (3) Z-cBPE. (B) Wax pattern for m-PED: (4) ECL reporting zone, (5) paper reservoir, (6) paper channel. (C) Board-B: (7) gold driving electrode, (8) pierced hole. (D) Scenograph of the m-PED after clamping between board-A and board-B. (E) The size and relative position of the sample zone, Z-cBPE, and paper channel.

in this work and a simple, portable, and disposable microfluidic paper-based electrophoretic device (m-PED) was fabricated (details in ESI†) for the first time from paper sheets patterned into the hydrophilic channel and zones bound by wax (the hydrophobization and insulation agent). The configuration of the wax pattern for this m-PED (Scheme 1B) comprised a hydrophilic paper channel (Scheme 1B(6)) interconnecting two paper reservoirs (Scheme 1B(5), 20 mm in diameter) and one ECL reporting zone (Scheme 1B(4), 5.0 mm in diameter). This m-PED had a total area of 75.0 mm  30.0 mm. To drive the electrophoretic separation in this m-PED, a compatibly designed device-holder (Fig. S3, ESI†), comprising two circuit boards named board-A (Scheme 1A) and board-B (Scheme 1C), was designed to grip the m-PED (Scheme 1D and Fig. S3, ESI†) during its connection to a home-made electrophoretic power supply (Scheme S1, ESI†) through two gold driving electrodes (Scheme 1C(7)) on board-B. The detection of analytes following electrophoretic separation in m-PADs is much more challenging than detection following TLC in m-PADs. The characteristics which make electrophoresis an attractive

Chem. Commun., 2014, 50, 5699--5702 | 5699

View Article Online

Communication

ChemComm

The ECL intensities (peak height) were plotted as a function of amino acid concentration. The ECL emission from the m-PED was investigated first. The applied separation voltage (Eapp) was 330 V. The potential gradient (V0) is given by eqn (1):

Published on 10 January 2014. Downloaded by University of Waterloo on 30/10/2014 02:15:21.

V0 (V mm 1) = Eapp/(LSC + Rreservoir (20 mm) + 2 mm + 2 mm) (1)

Scheme 2 Schematic representation of the detection and reporting process on the Z-cBPE: (a) wax penetrated paper, (b) hydrophilic paper channel, (c) copper anode of the Z-cBPE, (d) gold cathodic end of the Z-cBPE, (e) modified ECL reporting zone, (f) cellulose fibers, (g) board-A, (h) board-B.

Here, LSC (Scheme 1E) is the length of the paper separation channel and Rreservoir is the diameter of the paper reservoir. For the investigation of ECL emission, LSC was held constant at 20 mm as a model. It has been reported that, under this constant potential gradient, the potential difference applied to the Z-cBPE (DEBPE) only depends on the external width of the Z-cBPE (WBPE, Scheme 1E) along the separation channel9 and could be calculated by the following eqn (2): DEBPE = V0  WBPE

separation technique also make detection difficult. Among the available detection methods in m-PADs,1 electro-generated chemiluminescence (ECL) offers considerable promise as a detection method coupled with electrophoretic separation.5 Wireless ECL detection based on bipolar electrodes (BPEs)6 has recently attracted much attention due to their inherent advantages, such as its ease of integration into portable devices and the lack of direct electrical connection required between it and an external power supply. In this work, a novel Z-shaped composite BPE (Z-cBPE, Scheme 2) was designed on board-A (Scheme 1A(3)) and employed as the on-column wireless ECL detector of this m-PED, which could physically separate the ECL reporting from the electrophoretic separation channel, avoiding the addition of the ECL reagent into the electrophoresis medium. This configuration not only reduced the analytical cost remarkably, but also eliminated the mutual interference between the electrophoretic separation and ECL reaction. In this work, three electro-inactive amino acids (serine, aspartic acid, and lysine) were chosen as model analytes to illustrate the construction and performance of the m-PED, capable of simultaneously performing electrophoretic separation and quantitative ECL determination. Due to the electro-inactivity of these amino acids, copper was employed as the anode in this Z-cBPE to perform the electrocatalytic oxidation of the amino acids under strongly alkaline conditions (50 mM NaOH as the electrophoresis medium).7 Under these experimental conditions, the amino acids migrated from the cathode to the anode. In view of the negative charge carried by each of these amino acids, this was not unexpected as their electrophoretic migration rate (toward the anode) surpasses that of the tortuous electroosmotic flow in the paper channel.4 Detailed operational procedures of this m-PED are described in the ESI.† As shown in Scheme 2, when the copper anodic sensing pole (Scheme 2c) was electrochemically activated through the electrocatalytic oxidation of the amino acids, ECL is emitted from the cadmium sulfide nanoparticles (CdS NPs)-potassium persulfate (K2S2O8) ECL system8 in the ECL reporting zone (Scheme 2e) at the gold cathodic end (Scheme 2d) of this Z-cBPE. Due to charge conservation, the intensity of the ECL reporting event is related to the electrochemical reaction process at the sensing pole. The generated ECL signal was then captured by the photomultiplier through the hole on board-B (Scheme 1C(8)).

5700 | Chem. Commun., 2014, 50, 5699--5702

(2)

Thus, the DEBPE could be controlled by changing WBPE. Fig. 1 and Table S2 (ESI†) showed the electropherogram profiles and data of

Fig. 1 Electropherogram profiles of (A) 54 pM serine, (B) 0.12 nM aspartic acid, and (C) 0.67 nM lysine. The insets show the ECL intensity as a function of WBPE.

This journal is © The Royal Society of Chemistry 2014

View Article Online

Published on 10 January 2014. Downloaded by University of Waterloo on 30/10/2014 02:15:21.

ChemComm

each amino acid using eleven m-PEDs with different DEBPE. The ECL intensity (IECL) for the oxidation of each amino acid was also recorded as a function of DEBPE. With increasing DEBPE, the IECL for these amino acids increased quickly and reached their maximum values at 2.35 V, which correlated well to the potential differences calculated from Fig. S5 (ESI†), indicating that the electrical coupling between the anode and cathode reactions on this Z-cBPE was reliable. Thus, for continuous and sensitive detection of these amino acids in the m-PED, 2.35 V was selected as the DEBPE in the following experiments. Furthermore, from Fig. 1 and Table S2 (ESI†), it can be seen clearly that the migration times of these amino acids in the m-PED were quite different, indicating that these amino acids could be simultaneously separated by this m-PED. In addition, the relative standard deviations (RSD) of peak height and migration time were o5.0% and r1.5% for each amino acid, respectively. These results indicate that this m-PED holds the potential for simultaneous separation and detection of these amino acids. Optimizing the electrophoretic separation of these amino acids in this m-PED with regard to separation speed and resolution required a high potential gradient. Therefore, detailed evolution of the electrophoretic separation of these amino acids in this m-PED was performed under different potential gradients. In this study, according to eqn (1), control of the potential gradient was carried out just through changing the LSC. The potential gradient for electrophoretic separation was optimized by changing the LSC in the range of 10 mm to 30 mm. It is notable that, according to eqn (2), the WBPE should be changed correspondingly to maintain the DEBPE at 2.35 V.

Fig. 2 Electropherogram profiles of the amino acid mixture containing 54 pM serine, 0.12 nM aspartic acid, and 0.67 nM lysine in m-PEDs with different LSC (A–E). (F) Electropherogram profiles of the amino acid mixture containing different concentrations of amino acids in the m-PED with LSC = 20 mm. From top to bottom, cserine = 5.4 nM, 0.54 nM, and 54 pM; caspartic acid = 12.0, 1.2, and 0.12 nM; clysine = 67.0, 6.7, and 0.67 nM.

This journal is © The Royal Society of Chemistry 2014

Communication

The electrophoretic separation results are recorded in Table S3 (ESI†) and the electropherograms are shown in Fig. 2. As shown in Fig. 2A–E and Table S3 (ESI†), the resolution (R) between each amino acid increased with increasing LSC, while the ECL intensities decreased with increasing LSC. This may be attributed to the increased migration time that further increased the diffusion of the analytes. The diffusion of the analytes in the paper channel during the separation could broaden the separation peak and lower the peak height, thus reducing the ECL intensities as well as the detection sensitivity. It can also be seen in Table S3 (ESI†) that a complete separation (R 4 1.5) between serine and aspartic acid was obtained with a LSC of 20 mm. For LSC longer than 20 mm the resolution increased, however, the time required to perform the separation and detection also increased (Fig. 2A–E). Thus, an LSC of 20 mm (WBPE = 313 mm) was selected in this work for the complete separation of these amino acids as well as highly sensitive detection in a relatively short time (6 min compared with paper-based TLC devices2). In addition, increased amino acid concentrations led to an increased anodic current and, because of the charge balance, a correspondingly high cathodic current (Scheme 2), which in turn boosted the generation of ECL emission (Fig. 2F). Furthermore, the RSDs of the peak heights and the migration times were also o5.0% and r1.5% for these amino acids. These results further proved that this m-PED had high reproducibility and precision during manufacture and operation and could be suitable for the accurate separation and detection of these amino acids. The analytical capabilities of this m-PED were verified by applying 1.0 mL electrophoresis medium containing serine, aspartic acid, and lysine at various concentrations into the separation channel. All the calibration plots showed good linear relationships between the ECL intensities and the logarithm values of the analyte concentrations in the range of 54 pM to 0.38 mM for serine, 0.12 nM to 6.5 mM for aspartic acid, and 0.5 nM to 1.7 mM for lysine (Fig. S6, ESI†). The linear regression equations were IECL = 8303lg[serine (nM)] + 12830 (R = 0.9981), IECL = 6702lg[aspartic acid (nM)] + 7616 (R = 0.9984), and IECL = 8390lg[lysine (nM)] + 3202 (R = 0.9982). The limits of detection (3s) for serine, aspartic acid, and lysine were 13 pM, 34 pM, and 0.17 nM, respectively, which were much lower than in previously reported work.7 This study reported for the first time the successful coupling of an electrophoretic separation technique into m-PAD with on-column wireless ECL detection. Whilst the introduction of such an electrophoretic separation scheme appears contrary to the principle of simplicity and the inexpensive nature of m-PADs, the advantages of relative rapidness, repeatability, and sensitivity helps offset this concern. These separations were achieved without resorting to an expensive and sophisticated electrophoretic power supply as well as on-column electrical de-coupling devices. The advantages of this m-PED are the inherent miniaturization of devices for hand-held testing as well as their low-power requirements and low-cost (Bo$0.02 per device, including the consumption of materials and the depreciation of equipment) for single-use applications. This m-PED provided an integrated potential for multiplex separation and detection on m-PAD. Furthermore, the wireless ECL detector based on BPE allowed the fabrication of a simpler and more compact m-PED. Finally, this novel Z-cBPE, as a powerful wireless

Chem. Commun., 2014, 50, 5699--5702 | 5701

View Article Online

Communication

Published on 10 January 2014. Downloaded by University of Waterloo on 30/10/2014 02:15:21.

detector, holds great potential for the detection of other analytes through changing the electrode material and the WBPE. Thus, we believe this m-PED will be extensively useful in the fields of analytical research. This work was financially supported by the Natural Science Research Foundation of China (21277058, 51003039, 51273084) and the Natural Science Foundation of Shandong Province, China (ZR2012BZ002).

Notes and references 1 (a) A. W. Martinez, S. T. Phillips and G. M. Whitesides, Anal. Chem., 2010, 82, 3; (b) R. Pelton, TrAC, Trends Anal. Chem., 2009, 28, 925; (c) E. Nery and L. Kubota, Anal. Bioanal. Chem., 2013, 405, 7573; (d) A. K. Yetisen, M. S. Akram and C. R. Lowe, Lab Chip, 2013, 13, 2210; (e) D. Ballerini, X. Li and W. Shen, Microfluid. Nanofluid., 2012, 13, 769.

5702 | Chem. Commun., 2014, 50, 5699--5702

ChemComm ˜o Kfouri, M. H. de Oliveira Piazetta, 2 R. F. Carvalhal, M. Sima A. L. Gobbi and L. T. Kubota, Anal. Chem., 2010, 82, 1162. 3 S. Mendez, E. M. Fenton, G. R. Gallegos, D. N. Petsev, S. S. ´pez, Langmuir, 2009, Sibbett, H. A. Stone, Y. Zhang and G. P. Lo 26, 1380. 4 P. Mandal, R. Dey and S. Chakraborty, Lab Chip, 2012, 12, 4026. 5 M. Su, W. Wei and S. Liu, Anal. Chim. Acta, 2011, 704, 16. 6 (a) M.-S. Wu, B.-Y. Xu, H.-W. Shi, J.-J. Xu and H.-Y. Chen, Lab Chip, 2011, 11, 2720; (b) M.-S. Wu, G.-s. Qian, J.-J. Xu and H.-Y. Chen, Anal. Chem., 2012, 84, 5407; (c) M.-S. Wu, D.-J. Yuan, J.-J. Xu and H.-Y. Chen, Chem. Sci., 2013, 4, 1182; (d) X. Zhang, C. Chen, J. Li, L. Zhang and E. Wang, Anal. Chem., 2013, 85, 5335. 7 J. Ye and R. P. Baldwin, Anal. Chem., 1994, 66, 2669. 8 G. Jie, B. Liu, H. Pan, J.-J. Zhu and H.-Y. Chen, Anal. Chem., 2007, 79, 5574. 9 (a) W. Zhan, J. Alvarez and R. M. Crooks, J. Am. Chem. Soc., 2002, ´, K.-F. Chow, E. Sheridan, B.-Y. Chang, 124, 13265; (b) F. O. Mavre J. A. Crooks and R. M. Crooks, Anal. Chem., 2009, 81, 6218.

This journal is © The Royal Society of Chemistry 2014

Electrophoretic separation in a microfluidic paper-based analytical device with an on-column wireless electrogenerated chemiluminescence detector.

In this work, a microfluidic paper-based analytical device was further exploited by coupling with an electrophoretic separation technique for the firs...
3MB Sizes 0 Downloads 3 Views