TECHNICAL NOTE pubs.acs.org/ac
Quantum Dot Layer-by-Layer Assemblies as Signal Amplification Labels for Ultrasensitive Electronic Detection of Uropathogens Yun Xiang,*,† Haixia Zhang,† Bingying Jiang,‡ Yaqin Chai,† and Ruo Yuan*,† †
Key Laboratory of Ministry of Education on Luminescence and Real-Time Analysis, School of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715, PR China, and ‡ School of Chemistry and Chemical Engineering, Chongqing University of Technology, Chongqing 400040, PR China. ABSTRACT: The preparation and use of a new class of signal amplification label, quantum dot (QD) layer-by-layer (LBL) assembled polystyrene microsphere composite, for amplified ultrasensitive electronic detection of uropathogen-specific DNA sequences is described. The target DNA is sandwiched between the capture probes immobilized on the magnetic beads and the signaling probes conjugated to the QD LBL assembled polystyrene beads. Because of the dramatic signal amplification by the numerous QDs involved in each single DNA binding event, subfemtomolar level detection of uropathogen-specific DNA sequences is achieved, which makes our strategy among the most sensitive electronic approach for nucleic acid-based monitoring of pathogens. Our signal amplified detection scheme could be readily expanded to monitor other important biomolecules (e.g., proteins, peptides, amino acids, cells, etc.) in ultralow levels and thus holds great potential for early diagnosis of disease biomarkers.
I
dentification and quantification of bacterial pathogens is of great importance for food safety, clinical diagnosis, environmental monitoring and biodefense because of the rapid growth and deleterious effects of these pathogens on human health.14 For example, some strains of E. coli have been identified to cause different symptoms such as bloody diarrhea, hemorrhagic colitis, hemolytic uremic syndrome, and renal failure.5 However, traditional culture-based methods for uropathogen detections normally require 23 days to complete the processes, which are generally time-consuming and laborious.6 The development of techniques for sensitive, rapid, accurate, portable, and low-cost uropathogen detection is thus highly desired. Recently, nucleic acid-based electrochemical (EC) biosensors for bacterial pathogen detections via monitoring sequencespecific DNA or RNA from the target bacterial cells have attracted considerable research attention due to two main advantages of these approaches. First, the inherent advantages of EC devices such as the size, speed, sensitivity, portability, and cost can favorably meet the requirements for point-of-care or field detection of bacterial pathogens. Second, nucleic acid-based bacterial detection schemes could offer high sensitivities and low detection limits owing to the convenient incorporation of various signal amplification strategies into the assay protocols. These signal amplification routes are commonly based on using labels such as nanoparticles,712 enzymes,1317 intercalators,1824 and nanocarriers for loading multiple tags.2529 Among these amplification strategies, the nanocarriers-based method is potentially attractive because of its substantial signal amplification nature induced by the numerous tags involved in each single DNA hybridization event. In this study, we report on the preparation of a new class of signal amplification tag, the quantum dot (QD) nanoparticle r 2011 American Chemical Society
layer-by-layer (LBL) assemblies, by alternating attachment of streptavidin (STV) and biotin-conjugated CdS QDs, respectively, onto the surfaces of nanosized polystyrene (PS) particles. For proof-of-concept demonstration, the resulting QD LBL assemblies were further used as labels for highly sensitive, electronic detection of sequence-specific DNA targets from the E. coli uropathogens (position 432461 according to the 50 30 nucleotide sequence of the 16s rRNA gene).30 With our new amplification labels, a large number of CdS QDs, instead of one single CdS QD, are involved in each DNA recognition event. These surface-captured QDs release numerous Cd2þ ions upon acid dissolution, and the analytical signal is thus expected to be dramatically amplified. Moreover, square wave voltammetric (SWV) stripping is demonstrated to be highly sensitive for monitoring trace metal ions (e.g., Zn, Cd, Pb, Ga, In, etc.). The coupling of the inherent signal amplification nature of the LBL assembled QDs with the high sensitivity of the SWV technique is shown herein to achieve subfemtomolar level detection of uropathogen-specific DNA sequences.
’ EXPERIMENTAL SECTION Chemicals and Materials. Sodium bis(2-ethylhexyl)sulfosuccinate (AOT), cysteamine hydrochloride, 2-mercaptoethane sulfonate, 3-mercaptopropionic acid (MPA), 2-(N-morpholino) ethanesulfonic acid (MES), N-(3-dimethylamminopropyl)-N0 -ethylcarbodiimide hydrochloride (EDC), N-hydroxysulfosuccinimid Received: March 3, 2011 Accepted: April 25, 2011 Published: April 25, 2011 4302
dx.doi.org/10.1021/ac200564r | Anal. Chem. 2011, 83, 4302–4306
Analytical Chemistry sodium salt (NHS), STV, and bovine serum albumin (BSA) were purchased from Sigma (St. Louis, MO). Hg2þ standard solution was received from the Chinese CRM/CM Information Center (Beijing, China). STV-coated magnetic Dynabeads (MyOne Streptavidin C1, 1.0 μm in diameter) and monodispersed carboxyl polystyrene beads (0.2 μm in diameter) were obtained from Invitrogen Corp. (Oslo, Norway) and BaseLine ChromTech Research Centre (Tianjin, China), respectively. All oligonucleotides were purchased from Shanghai Sangon Biological Engineering Technology and Services Co., Ltd. (Shanghai, China), and the sequences of these oligonucleotides were as follows: SH-ploy-T10-biotin, 50 -biotin-TTTTTTTTTT-(CH2)6SH-30 ; capture probe, 50 -biotin-TATTAACTTTACTCC-30 ; signaling probe, 50 -CTTCCTCCCCGCTGA-biotin-30 ; complementary target, 50 -TCAGCG GGGAGGAAGGGAGTAAAGTTAATA-30 ; noncDNA, 50 -CTG GGGTGAAGTCGTAACAAGGTAACCGTAGGGGAAC-30 ; single-base mismatch DNA, 50 -TCAGCTGGGAGGAAGGGAGTAAAGTTAATA-30 . Apparatus. TEM images and UVvis spectra were recorded by a Philips TECNAI 10 microscope (Philips Fei Co., OR) and a UVvis 8500 spectrometer (Techcomp Ltd., China), respectively. Preparation of the STV-CdS and Biotin-CdS Bioconjugates. The CdS QDs were first synthesized according to a previous reported procedure.31 To prepare the STV-CdS bioconjugates, the CdS QDs were first functionalized with carboxyl groups by suspending the CdS quantum dots (3.2 mg) in MPA (300 μL, 50 mM) and mixing for 2 h. The excess MPA were removed by centrifugation at 10 000 rpm for 30 min. The resulting QDs were then resuspended and mixed in MES buffer (0.1 M, pH 5.9) containing EDC (400 mM) and NHS (100 mM) for 30 min. This is followed by centrifugation at 10 000 rpm for 30 min and removal of the supernatant. Next, an aliquot (240 μL) of phosphate buffer solution (30 mM, pH 8.0) containing STV (2 mg mL1) was mixed with the above QDs for 1 h. Finally, the STV-CdS were collected by centrifugation at 10 000 rpm for 30 min, removal of the supernatant, and resuspended in PBS (10 mM, pH 7.4) for further use. The biotin-CdS bioconjugates were prepared by mixing the SHpolyT10-biotin (1 μM) with a CdS QD suspension (0.2 mg mL1, 500 μL) overnight at room temperature, followed by centrifugation at 10 000 rpm for 45 min, removal of supernatant, and resuspension in PBS. Preparation of the STV-PS beads. An aliquot (25 μL) of PS beads was transferred into a centrifuge vial and washed twice with PBS. The beads were then resuspended in MES buffer (0.1 M, pH 5.9) containing EDC (400 mM) and NHS (100 mM) and mixed for 1 h, followed by centrifugation at 5000 rpm and washing with PBS. Next, STV (200 μL, 0.2 mg mL1 in PBS) was added and incubated with the beads for 1 h. After washing twice with PBS, the resulting STV-PS were resuspended in PBS (50 μL) for further use. Preparation of the PS-(CdS)n and Signaling Probe Conjugated PS-(CdS)4 Assemblies. In brief, the STV-PS beads (2.5 μL) were transferred into a centrifuge vial, and the CdS-biotin (10 μL) and PBS-BSA (50 μL, 0.15% BSA, pH 7.4) were added to the vial and incubated for 30 min. Subsequently, the PS-biotinCdS bioconjugates were centrifuged at 5000 rpm for 10 min to remove the supernatant. These beads were washed three times with PBS-T (0.1% Tween 20, pH 7.4) to remove any nonspecifically adsorbed CdS-biotin conjugates. Next, the STV-CdS (10 μL, 0.2 mg mL1) in PBS-BSA were incubated with the beads for 30 min, followed by centrifugation at 5000 rpm for
TECHNICAL NOTE
10 min to remove the supernatant and washed with PBS-T. Additional CdS layer could be attached by using the above procedure consecutively to obtain the PS-(CdS)n assemblies. After the attachment of the second STV-CdS layer (n = 4), the signaling probe (2 μM) was incubated with the PS-(CdS)4 for 30 min, followed by centrifugation and washing with PBS. The signaling probe conjugated PS-(CdS)4 assemblies were then resuspended in PBS. DNA Hybridization Assay. The capture probe was immobilized on the STV-coated magnetic beads according to the procedures recommended by the manufacturer. In brief, the STV-coated magnetic beads (5 μL) were transferred into a centrifuge vial and washed twice with Tris-HCl buffer (TB, 5 mM, containing 0.5 mM EDTA, 1 M NaCl, pH 7.5). Then, the magnetic beads were suspended and incubated in the capture probe solution (50 μL, 6.5 μM in TB) for 30 min with gentle mixing. The beads were washed twice with TB and incubated with the target DNA solution at various concentration in the hybridization buffer (1 M PBS containing 1% BSA, pH 7.2) for 30 min. The magnetic beads were washed three times with PBS and incubated with the signaling probe conjugated PS-(CdS)4 assemblies for 30 min with gentle shaking. Finally the magnetic beads were washed with PBS, and nitric acid (50 μL, 1 M) was added to the tube to dissolve the CdS QDs. After 1 h of mixing, the solution was transferred into a glass cell containing 0.2 M acetate buffer (10 ppm Hg2þ, pH 5.2) for measurement. EC Measurements. A conventional three-electrode configuration was used for the measurements, with a glassy carbon working electrode (3 mm in diameter, CH Instruments Inc., Shanghai, China), an Ag/AgCl (3 M KCl) reference electrode, and a platinum wire counter electrode in connection to an EC workstation (CHI 852C, CH Instruments Inc., Shanghai, China). The SWV stripping detection involved in a 1 min pretreatment at þ0.6 V, 2 min accumulation at 1.1 V, and scanning the potential from 1.0 to 0.3 V with a potential step of 4 mV, a frequency of 25 Hz, and an amplitude of 25 mV. Data processing was made using the “linear baseline correction” function of the CHI 852C software.
’ RESULTS AND DISCUSSION As the first step toward the preparation of the QD LBL assemblies (PS-(CdS)n), we synthesized the STV and biotinconjugated CdS QDs, respectively. The STV-CdS conjugates were obtained through covalent attachment of STV to the CdS QDs, and the biotin-CdS were prepared through ligand exchange of the surface-capped thiol groups on the QDs by SH-polyT10biotin. The selection of polyT10 as a bridge to impart biotin onto the CdS QD surfaces was based on the consideration that selfassembly of DNA molecules to nanoparticles could lead to highly stable bioconjugates owing to the strong interparticle electrostatic repulsions.32 The formation of the PS-(CdS)n assemblies is based on the strong affinity interactions between the biotin-CdS and STVCdS, and the stepwise fabrication process is illustrated in Scheme 1. The biotin-CdS QDs were first attached to the STV-PS beads through biotin-STV affinity interactions. The surface-attached biotin-CdS QDs acted as linkers for the subsequent coating of the second layer of STV-CdS QDs. The PS-(CdS)n assemblies could thus be prepared through simple alternating attachment of biotin-CdS and STV-CdS QDs. The strong bindings between biotin and STV are expected to greatly 4303
dx.doi.org/10.1021/ac200564r |Anal. Chem. 2011, 83, 4302–4306
Analytical Chemistry improve the stability of the LBL assemblies compared with other assemblies prepared through electrostatic interactions.3336 The transmission electron microscopy (TEM) image of the resulting PS-(CdS)4 assemblies provides evidence for the formation of CdS QD LBL composite on the PS beads. From the representative TEM images in Figure 1A,B, we can see randomly distributed nonuniform nanostructures corresponding to the Scheme 1. Illustration of the Stepwise Preparation of the PS-(CdS)n Assemblies
Figure 1. TEM images of (A) PS beads and (B) PS-(CdS)4 assemblies. (C) UVvis absorption spectra of the PS-(CdS)n assemblies: (a) PS beads, (b) n = 1, (c) n = 3, and (d) n = 5. (D) Stripping voltammetric response of the PS-(CdS)n assemblies from n = 1 to n = 5 upon acid dissolution of the CdS QDs. SWV measurements were carried out in 0.2 m acetate buffer (10 ppm Hg2þ, pH 5.2) with a 1 min pretreatment at þ0.6 V, 2 min accumulation at 1.1 V, and by scanning the potential from 1.0 to 0.3 V with a potential step of 4 mV, a frequency of 25 Hz, and an amplitude of 25 mV (error bars: SD, n = 3).
TECHNICAL NOTE
assembled CdS QDs on the PS surfaces after the self-assembly process (Figure 1B). The fabrication process for the PS-(CdS)n assemblies was also monitored by UVvis spectroscopy. The resulting absorption spectra are displayed in Figure 1C, from which a well-defined maximum absorption of the CdS QDs at 400 nm is observed after the attachment of the first layer of the biotin-CdS (curve b in Figure 1C). In addition, the absorption intensity of CdS increases gradually as the number of CdS QD layer increases, indicating the attachment of more and more CdS QDs to the PS beads. On the basis of the concentration change of the CdS QDs suspension along with the absorption intensity37,38 before and after the coating step, the number of CdS QDs deposited on each PS bead was estimated to be 6.7 104 after the attachment of the first layer and 9.2 104 after the fourth layer, respectively. The formation of the PS-(CdS)n assemblies was further evaluated by monitoring the voltammetric stripping peak of Cd2þ after acid dissolution of the LBL assembled CdS QDs. As shown in Figure 1D, the stripping current intensity of Cd2þ increases and exhibits a dependence upon the number of CdS QD layer deposited onto the PS beads, which further indicates the successful preparation of the PS-(CdS)n assemblies. For a proof-of-concept application of the CdS QD LBL assemblies in EC assays, we selected the PS-(CdS)4 assemblies as the effective labels for ultrasensitive detection of sequence-specific DNA from the E. coli uropathogens. Our new signal amplification protocol for ultrasensitive EC DNA detection based on the PS-(CdS)4 labels is illustrated in Scheme 2, which involves immobilization of the biotin-modified capture probe on the STV-coated magnetic beads, hybridization of the target DNA with the capture probe and the signaling probe conjugated to the PS-(CdS)4 assemblies, acid dissolution of the captured CdS QDs, and EC monitoring of the released Cd2þ. In order to show the dramatic signal amplification capability of our assay approach, we compared our PS-(CdS)4-based detection route with the conventional single CdS QD label-based one for DNA detection. Figure 2 displays the hybridization cadmium responses of the conventional single CdS QD and the CdS QD LBL assembled PS-(CdS)4 labels for 10 pM and 100 fM target, respectively. A small EC stripping response (0.054 μA) of Cd2þ is obtained for a significant higher target concentration (10 pM, 100-fold) using the single CdS QD labels (Figure 2A). However, about a 17-fold EC signal enhancement (0.95 μA) for the significantly lower target concentration (100 fM) is observed by using the PS-(CdS)4 labels (Figure 2B). This comparison
Scheme 2. Schematic Representation of the PS-(CdS)4 Assembly-Labeled DNA Hybridization Assay Protocola
a
(A) Formation of the sandwich complexes through a dual hybridization event, (B) dissolution of the assembled CdS QDs with nitric acid, and (C) stripping voltammetric monitoring of the released Cd2þ. Other conditions are as in Figure 1D. 4304
dx.doi.org/10.1021/ac200564r |Anal. Chem. 2011, 83, 4302–4306
Analytical Chemistry
Figure 2. Square wave voltammograms for the DNA hybridization assays with different labels (A) single CdS with 10 pM target DNA and (B) PS-(CdS)4 assembly with 100 fM target DNA. Other conditions are as in Figure 1D.
TECHNICAL NOTE
The selectivity of the PS-(CdS)4-labeled signal amplification approach was investigated against noncomplementary and single-base mismatch sequences, respectively (Figure 3C). The presence of 10 pM noncomplementary sequences (curve b in Figure 3C) shows no significant increase in the Cd2þ stripping peak compared with that of the control experiment (0 nM target, curve a in Figure 3C). Although the presence of 10 pM singlebase mismatch DNA sequences (curve c in Figure 3C) causes a small increase in the Cd2þ stripping peak, the addition of a 10fold lower concentration of the target DNA (1 pM) leads to a dramatic increase (24-fold and 5-fold, respectively, compared with the noncomplementary and single-base mismatch sequences) in the Cd2þ stripping peak (curve d in Figure 3C). These results indicate that our assay protocol is also coupled with good selectivity.
’ CONCLUSIONS In conclusion, we have demonstrated the preparation of the PS-(CdS)n assemblies through simple biological self-assembly in a LBL fashion. The surface assembled multilayer CdS QDs dramatically amplified the analytical signal in EC detection of the sequence-specific DNA target from the E. coli uropathogens, leading to the monitoring of DNA down to the subfemtomolar level. A further increase in the number of CdS QD layers is expected to push down the detection limit. Such an attractive signal-amplified ultrasensitive DNA detection scheme could be readily expanded to other important biomolecules (e.g., proteins, peptides, small molecules, cells, etc.) in connection to different molecular recognition events. Our QD LBL assembly based assay protocol could thus offer numerous versatile opportunities for the early diagnosis of different diseases. Figure 3. A) Square wave voltammograms for increasing DNA target concentration: (a) 0 fM, (b) 0.5 fM, (c) 5 fM, (d) 10 fM, (e) 100 fM, (f) 1 pM, (g) 10 pM. (B) The corresponding calibration plot for the target DNA in the range from 0.5 fM to 10 pM. (C) Square wave voltammograms for (a) blank solution with no target DNA, (b) 10 pM noncDNA, (c) 10 pM single-base mismatch DNA, and (d) 1 pM cDNA target. Other conditions are as in Figure 1D.
clearly demonstrates the substantial signal amplification capability of the PS-(CdS)4 labels due to the large number of LBL assembled CdS QDs involved in the DNA binding events and the enormous Cd2þ released upon acid dissolution. The sensitivity of the PS-(CdS)4-labeled dual DNA hybridization assay was investigated by varying the target DNA concentration. From Figure 3A we can see that the stripping response of Cd2þ increases accordingly as the target DNA concentration is elevated from 0.5 fM to 10 pM. The corresponding calibration plot of log[c] vs the stripping current response of Cd2þ exhibits a dynamic range from 0.5 fM to 10 pM (Figure 3B). A detection limit of 0.22 fM is estimated based on the signal-to-noise characteristics (S/N = 3). This attractive detection limit, which is basically due to the enormous tags involved in each single DNA hybridization event, is among one of the most sensitive strategies for DNA detection.30,3945 The high sensitivity and simple assay protocol of our approach makes it a promising alternative for the PCR-based DNA detections. A series of six repetitive measurements of 1 pM target DNA yielded a relative standard deviation of 6.2% for the Cd2þ peaks, suggesting a good reproducibility of the assay protocol.
’ AUTHOR INFORMATION Corresponding Author
*Phone: þ86-23-68252277 (Y.X. and R.Y.). E-mail: yunatswu@ swu.edu.cn (Y.X.),
[email protected] (R.Y.).
’ ACKNOWLEDGMENT This work is supported by National Natural Science Foundation of China (Grant No. 20905062 and Grant No. 20675064), Natural Science Foundation Project of Chongqing City (Grant CSTC-2009BB5052), State Key Laboratory of Electroanalytical Chemistry (Grant SKLEAC2010009), China Postdoctoral Science Foundation (Grants 20090460715 and 201003305), Fundamental Research Funds for the Central Universities (Grant XDJK2009B013), research funds from Southwest University (Grant SWUB2008078), and Start-up Fund of Chongqing University of Technology. ’ REFERENCES (1) Torres-Chavolla, E.; Alocilja, E. C. Biosens. Bioelectron. 2009, 24, 3175. (2) Lazcka, O.; Campo, F. J. D.; M~unoz, F. X. Biosens. Bioelectron. 2007, 22, 1205. (3) Kim, J.; Yoon, M. Y. Analyst 2010, 135, 1182. (4) Heo, J.; Hua, S. Z. Sensors 2009, 9, 4483. (5) Ho, J. A.; Hsu, H. W.; Huang, M. R. Anal. Biochem. 2004, 330, 342. (6) Leoni, E.; Legnai, P. P. J. Appl. Microbiol. 2001, 90, 27. (7) Rosi, N. L.; Mirkin, C. A. Chem. Rev. 2005, 105, 1547. 4305
dx.doi.org/10.1021/ac200564r |Anal. Chem. 2011, 83, 4302–4306
Analytical Chemistry (8) Wang, J. Small 2005, 1, 1036. (9) Erdem, A. Talanta 2007, 74, 318. (10) Ozsoz, M.; Erdem, A.; Kerman, K.; Ozkan, D.; Tugrul, B.; Topcuoglu, N.; Erken, H.; Taylan, M. Anal. Chem. 2003, 75, 2181. (11) Karadeniz, H.; Erdem, A.; Caliskan, A.; Pereira, C. M.; Pereira, E. M.; Ribeiro, J. A. Electrochem. Commun. 2007, 9, 2167. (12) Pumera, M.; Castaneda, M. T.; Pividori, M. I.; Eritja, R.; Merkoci, A.; Alegret, S. Langmuir 2005, 21, 9625. (13) Lumley-Woodyear, T.; Campbell, C.; Heller, A. J. Am. Chem. Soc. 1996, 118, 5504. (14) Patolsky, F.; Lichtenstein, A.; Willner, I. Nat. Biotechnol. 2001, 19, 253. (15) Azek, F.; Grossiord, C.; Joannes, M.; Limoges, B.; Brossier, P. Anal. Biochem. 2000, 284, 107. (16) Bakker, E.; Qin, Y. Anal. Chem. 2006, 78, 3965. (17) Domínguez, E.; Rincon, O.; Narvaez, A. Anal. Chem. 2004, 76, 3132. (18) Kerman, K.; Ozkan, D.; Kara, P.; Meric, B.; Gooding, J. J.; Ozsoz, M. Anal. Chim. Acta 2002, 462, 39. (19) Jin, Y.; Yao, X.; Liu, Q.; Li, J. Biosens. Bioelectron. 2007, 22, 1126. (20) Teles, F. R. R.; Prazeres, D. M. F.; Lima-Filho, J. L. Sensors 2007, 7, 2510. (21) Ahmed, M. U.; Idegami, K.; Chikae, M.; Kerman, K.; Chaumpluk, P.; Yamamura, S.; Tamiya, E. Analyst 2007, 132, 431. (22) Fixe, F.; Branz, H. M.; Louro, N.; Chu, V.; Prazeres, D. M. F.; Conde, J. P. Biosens. Bioelectron. 2004, 19, 1591. (23) Nie, L.; Guo, H.; He, Q.; Chen, J.; Miao, Y. J. Nanosci. Nanotechnol. 2007, 7, 560. (24) Kelley, S. O.; Boon, E. M.; Barton, J. K.; Jackson, N. M.; Hill, M. G. Nucleic Acid Res. 1999, 27, 4830. (25) Yu, X.; Munge, B.; Patel, Y.; Jensen, G.; Bhirde, A.; Gong, J. D.; Kim, S. N.; Gillespie, J.; Gutkind, J. S.; Papadimitrakopoulos, F.; Rusling, J. F. J. Am. Chem. Soc. 2006, 128, 11199. (26) Mani, V.; Chikkaveeraiah, B. V.; Patel, V.; Silvio Gutkind, J.; Rusling, J. F. ACS Nano 2009, 3, 585. (27) Du, D.; Zou, Z.; Shin, Y.; Wang, J.; Wu, H.; Engelhard, M. H.; Liu, J.; Aksay, I. A.; Lin, Y. Anal. Chem. 2010, 82, 2989. (28) Wang, J.; Liu, G.; Rasul, M. J. Am. Chem. Soc. 2003, 126, 3010. (29) Bae, S. W.; Cho, M. S.; Hur, S. S.; Chae, C. B.; Chung, D. S.; Yeo, W. S.; Hong, J. I. Chem.—Eur. J. 2010, 16, 11572. (30) Chumbimuni-Torres, K. Y.; Wu, J.; Clawson, C.; Galik, M.; Walter, A.; Flechsig, G. U.; Bakker, E.; Zhang, L.; Wang, J. Analyst 2010, 135, 1618. (31) Willner, I.; Patolsky, F.; Wasserman Angew. Chem., Int. Ed. 2001, 40, 1861. (32) Hu, M.; He, Y.; Song, S.; Yan, J.; Lu, H.; Weng, L.; Wang, L.; Fan, C. H. Chem. Commun. 2010, 46, 6126. (33) Bi, S.; Zhou, H.; Zhang, S. Biosens. Bioelectron. 2009, 24, 2961. (34) Munge, B.; Liu, G. D.; Collins, G.; Wang, J. Anal. Chem. 2005, 77, 4662. (35) Du, D.; Zou, Z.; Shin, Y.; Wang, J.; Wu, H.; Engelhard, M. H.; Liu, J.; Aksay, I. A.; Lin, Y. Anal. Chem. 2010, 82, 2989. (36) Srivastava, S.; Kotov, N. A. Acc. Chem. Res. 2008, 41, 1831. (37) Yu, W. W.; Qu, L. H.; Guo, W. Z.; Peng, X. G. Chem. Mater. 2003, 15, 2854. (38) Zhang, D.; Huarng, M. C.; Alocilja, E. C. Biosens. Bioelectron. 2010, 26, 1736. (39) Wu, J.; Chumbimuni-Torres, K. Y.; Galik, M.; Thammakhet, C.; Haake, D. A.; Wang, J. Anal. Chem. 2009, 81, 10007. (40) Liao, J. C.; Mastali, M.; Gau, V.; Suchard, M. A.; Møller, A. K.; Bruckner, D. A.; Babbitt, J. T.; Li, Y.; Gornbein, J.; Landaw, E. M.; McCabe, E. R. B.; Churchill, B. M.; Haake, D. A. J. Clin. Microbiol. 2006, 44, 561. (41) Mastali, M.; Babbitt, J. T.; Li, Y.; Landaw, E. M.; Gau, V.; Churchill, B. M.; Haake, D. A. J. Clin. Microbiol. 2008, 46, 2707. (42) Wang, J.; Liu, G. D.; Rasul Jan, M.; Zhu, Q. Electrochem. Commun. 2003, 5, 1000. (43) Zhu, N.; Zhang, A.; He, P.; Fang, Y. Z. Analyst 2003, 128, 260.
TECHNICAL NOTE
(44) Cui, D.; Pan, B.; Zhang, H.; Gao, F.; Wu, R.; Wang, J.; He, R.; Asahi, T. Anal. Chem. 2008, 80, 7996. (45) Dong, H. F.; Yan, F.; Ji, H. X.; Wong, D. K. Y.; Ju, H. X. Adv. Funct. Mater. 2010, 20, 1173.
4306
dx.doi.org/10.1021/ac200564r |Anal. Chem. 2011, 83, 4302–4306
