Easy Design of Colorimetric Logic Gates Based on Nonnatural Base

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Easy Design of Colorimetric Logic Gates Based on Nonnatural Base Pairing and Controlled Assembly of Gold Nanoparticles Li Zhang, Zhong-Xia Wang, Ru-ping Liang, and Jian-ding Qiu Langmuir, Just Accepted Manuscript • DOI: 10.1021/la401887b • Publication Date (Web): 17 Jun 2013 Downloaded from http://pubs.acs.org on June 19, 2013

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Easy Design of Colorimetric Logic Gates Based on Nonnatural Base Pairing and Controlled Assembly of Gold Nanoparticles Li Zhang, Zhong-Xia Wang, Ru-Ping Liang, and Jian-Ding Qiu* Department of Chemistry, Nanchang University, Nanchang 330031, China

ABSTRACT: Utilizing the principles of metal-ion-mediated base pairs (C-Ag-C and T-Hg-T), the pH-sensitive conformational transition of C-rich DNA strand as well as the ligand-exchange process triggered by DL-dithiothreitol (DTT), a system of colorimetric logic gates (YES, AND, INHIBIT, and XOR) can be rationally constructed based on the aggregation of the DNA modified Au NPs. The proposed logic operation system is simple, which consists of only T-/C-rich DNA modified Au NPs and it is unnecessary to exquisitely design and alter the DNA sequence for different multiple molecular logic operations. The nonnatural base pairing combined with unique optical properties of Au NPs promise great potential in multiplexed ion sensing, molecule-scale computers and other computational logic devices.

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INTRODUCTION In recent years, great attention has been attracted in the interactions of nucleic acids with metal ions.1-3 Examples of such novel interactions include the selective incorporation of metal ions as cofactors to promote the catalytic activities of nucleic acid enzymes and the specific binding of certain metal ions such as Hg2+, Ag+, and Cu2+ with nucleosides to form metal-ion-mediated base pairs.4-7 This non-natural base pairing is stabilized by metal-nucleoside coordinative bonds in a manner different from natural hydrogen bonding between complementary nucleosides.8-9 The generation of such additional base pairs would lead not only to expansion of the genetic alphabet but also to novel nucleic acid structures and functions based on the controlled spacing of the metallo-base pairs along the helix axis.10-17 The novel interaction of nucleic acids with metal ions has recently been utilized for the construction of molecular logic gates,18-30 which are crucial for the development of molecular-scale computers and other computational logic devices. In particular, nucleic acid enzymes have proven to be highly useful building blocks for the construction of molecular logic gates based on the fact that their catalytic activities can be allosterically regulated by specific metal ions.18-23 However, these kinds of logic gates typically rely on relatively complex designs for gate switching and frequently require the involvement of RNA or chimeric DNA as operational substrates, which would lead to high construction costs and susceptibility to oligonucleotide degradation. The specific binding of certain metal ions with nucleosides has also been investigated for the DNA logic gate construction and DNA biocomputing.24-30 For example, Park and coworkers have recently designed a novel strategy for construction of molecular logic gates based on the “illusionary” polymerase activity at the mismatched site triggered by metal ions.24 Miyoshi et al. have also conceived a concept for DNA logic gates based on the duplex-quadruplex conversion of the telomere DNA molecules triggered by K+ and H+.25 Furthermore, the multiplexed sensing of Hg2+ and Ag+ ions as well as the logic


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operations were rationally performed by Willner and other researchers.26-28 Although substantial progress has been achieved in logic gate construction based on the metal-ion-mediated base pairs, challenges are still ahead of us. For example, complex designs of DNA sequences required for different multiple molecular logic operations may prove cumbersome. Besides, most of such logic gates operate by gel electrophoresis or fluorescence detection, which often suffers from complex handling procedures and poor portability. Therefore, molecular logic gate systems with simple components and rapid readout are highly demanded. From this perspective, homogeneous colorimetric methods based on the distance-dependent optical properties of Au nanoparticles (Au NPs) could serve as an alternative approach to provide desirable features for the logic gate construction including simple procedure, rapid readout, and little or no required instrumentation.31-36 Along this strategy, we for the first time report a system of metal-ion-mediated DNA logic gates based on colorimetric outputs. Utilizing the unique features that Hg2+ ions could bridge thymine (T) bases while Ag+ ions could specifically bridge cytosine (C) bases, the AND logic system can be constructed based on the ion induced aggregation of the T-/C-rich DNA modified Au NPs, in which the Hg2+ and Ag+ ions are employed as inputs to form the metallo-base pairs along the helix axis and the color changes from red to purple due to the formation of extended polymeric Au NPs/polynucleotide aggregate as output. Moreover, by employing the principles of metal-ion-mediated base pair and the pH-sensitive conformational transition of T-/C-rich DNA strand, another INHIBIT logic gate operation is achieved. Furthermore, by utilizing the unique properties of DL-dithiothreitol (DTT) that could not only remove thiolated oligonucleotides from gold surface through a ligand-exchange process but also react with Hg2+/Ag+ ions to form stable complexes, a XOR logic gate is rationally constructed. To the best of our knowledge, the


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application of colorimetric detection for logic gate operations based on metal-ion-mediated base pair has not been reported to date.

EXPERIMENTAL SECTION Materials and Apparatus. All oligonucleotides were purchased from Shanghai Sangon Biological Co. Ltd. (Shanghai, China). DL-dithiothreitol (DTT, C4H10O2S2) was obtained from Sigma and used without further purification. Hydrogen tetrachloroaurate (III) trihydrate (HAuCl4·3H2O) and trisodium citrate (C6H5Na3O7·2H2O) were obtained from Shanghai Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China). Silver nitrate (AgNO3) was purchased from Tianjin Damao Chemical reagent Co. Ltd. (Tianjin, China), mercuric nitrate (Hg(NO3)2) was

purchased

from

Taixing

Chemical

reagent

Co.

Ltd

(Jiangsu,

China).

Tris(hydroxymethyl)aminoethane (Tris) was obtained from Shanghai Lanji technology Co. Ltd. (Shanghai, China). All chemicals and solvents were of analytical grade and were used without further purification. UV-vis absorption spectra were recorded on a Shimadzu UV-2450 spectrophotometer (Tokyo, Japan). The resonance light scattering (RLS) spectra were performed on a Hitachi F-7000 fluorescence spectrofluorometer (Tokyo, Japan). Transmission electron microscopy (TEM) measurements were conducted on a JEM-2010 transmission electron microscope (JEOL Ltd.). Synthesis and Modification of Au NPs. Au NPs with an average diameter of 13 nm were prepared according to previous references by reducing HAuCl4·3H2O with citrate.37, 38 Briefly, 48 mL of deionized water was mixed with 2 mL of 1% (w/w) HAuCl4 solution to make the final concentration of HAuCl4·3H2O 1 mM. The mixture was then heated under magnetic stirring until it began to boil, then 1 mL of 5% trisodium citrate was added to the solution. Under continuous stirring and boiling, the mixture gradually changed to deep red color within 3 min. After boiling for another 5 min, the solution was cooled to room temperature under vigorous stirring.


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For the modification of Au NPs, the thiol DNA was first activated following literature procedures,39 and then incubated with Au NPs at 25°C for 24 h, the DNA-Au NPs conjugates were allowed to “age” according to reported methods.39 The final concentration of the Au NPs was about 1 nM, and the final concentration of DNA was 2.5 × 10-6 M. Excess reagents were removed by centrifugation at 14000 rpm for 10 min, and then the resulting red oily precipitate was dispersed in 1 mL water. After modification, the Au NPs showed a neglectable shift in the surface plasmon band and an apparent decrease in intensity due to the decrease of particle concentration during the workup of the DNA-modified Au NPs, and further involved high stability in solutions containing elevated salt concentrations. Construction of the Logic Gates. For the YES logic gate construction, equal amount of two sets 1-Au NPs and 2-Au NPs were mixed and then 60 nM Ag+ ions as inputs were added to the solution. The hybridization was performed at 37 oC in Tris-HCl buffer (pH~8.0) for 5 min and the colorimetric responses as well as the corresponding absorption spectra of the solution were then recorded. The “AND” logic gate was performed in a solution containing 2-Au NPs. The hybridization between 2-Au NPs was initiated by the addition of Hg2+ (0.2 mM) and Ag+ (0.6 mM) as inputs at 37

o

C in Tris-HCl buffer (pH~8.0) for 5 min. The colorimetric responses as well as

corresponding absorption spectra of the solution were then recorded. The state of the system was reset by adding NH4OH (EDTA) with the molar ratio of NH4OH/Ag+ (EDTA/Hg2+) increasing from 0 to 2.0 (1.5), and the corresponding ∆λ was recorded. The fabrication procedures in “INHIBIT” logic operations were similar to the above description except that H+ (input A) and metal ions (0.2 mM Hg2+/0.6 mM Ag+, input B) were


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introduced as inputs to control the DNA structural polymorphism and thus the aggregation of 2Au NPs. The “XOR” logic gate was constructed by introducing DTT (1 mM, input A) and metal ions (0.2 mM Hg2+/0.6 mM Ag+, input B) as inputs to control the assembly/disassembly and thus the colorimetric change of 2-Au NPs. The logic gate was operated at 37 oC in Tris-HCl buffer (pH~8.0, containing 50 mM NaNO3) for 30 min.

RESULTS AND DISCUSSION Au NPs with a diameter of 13 nm were chemically modified with the thiolated A-/C-rich DNA 1, T-/C-rich DNA 2, and T-/G-rich DNA 3. Figure 1a outlines the principle for the selective analysis of Ag+ ions by the 1-Au NPs and 2-Au NPs. When 60 nM Ag+ ions were introduced into the mixture containing the two different DNA modified Au NPs (1-Au NPs and 2-Au NPs) in 5 mM Tris-HCl (pH 8.0), a rigid double helix structure formed, in which the C residues of the spatially separated nucleotides were linked by the Ag+ ions, and the solution color changed from red to purple within 5 min. This color change can be attributed to the formation of large DNAlinked three-dimensional aggregates of Au NPs, leading to a red shift in the surface plasmon resonance from λmax = 525 to 598 nm (Figure S1). Control experiments revealed that each solution containing 1-Au NPs or 2-Au NPs subjected to the same amount of Ag+ ions did not lead to any plasmon shift in the UV-vis spectra (Figure S1). On the contrary, Hg2+ ions could be detected based on the hybridization between 2-Au NPs and 3-Au NPs (Figure 1b and the experimental results not shown). The observations described above suggest that the aggregation of DNA modified Au NPs induced by specific metal ions could be utilized for the identification of metal ions. Moreover, this new phenomenon could serve as the basis for novel molecular logic gates through simple incorporation of C-rich and/or T-rich DNA modified Au NPs, in which


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Hg2+ and/or Ag+ ions were used as inputs and the red shift in the surface plasmon resonance or the color change corresponding to the Au NPs aggregation as outputs. To explore this concept, a single-input molecular logic gate, YES gate, was constructed (Figure S2). The YES gate system obediently follows the input (e.g., output 0 if input is 0 and output 1 if input is 1). In this system, Ag+ ions were used as the inputs to trigger the aggregation of 1-Au NPs and 2-Au NPs through the formation of a stable C-Ag-C complex as indicated by the solution color change from red to purple, while no aggregation was observed in the absence of Ag+ ions, a phenomenon that is in accordance with proper execution of the YES logic gate (Figure S2b-2d). Likewise, Hg2+ ions could activate the YES logic gate with the system composed of 2-Au NPs and 3-Au NPs. An AND gate, which gives an output of 1 only if both of the two inputs were held at 1, was constructed next. This gate consisted of 2-Au NPs, and used both Hg2+ and Ag+ ions as inputs (Figure 2). To demonstrate how this logic gate operates, UV-vis absorption spectra, resonance light scattering (RLS) spectra and transmission electron microscopy (TEM) measurements were utilized to monitor the morphology and distribution changes of Au NPs for four input modes. With no input, the (C4T4)3C4 DNA was in the random coil state and the modified Au NPs were in dissociated state with the λmax at 525 nm (Figure 3a). When only one of the ions was added to the logic system, the DNA structure was not changed and consequently no obvious aggregates were formed to induce a visible color change in Au NPs solution (the output was 0). While the simultaneous presence of Hg2+ and Ag+ would induce the DNA undergo a random coil-to-double helix conformation transition as a result of the stable metal-ion-mediated base pairs (T-Hg-T and C-Ag-C). The conformational transition resulted in a remarkable color change of the Au NPs solution from the initial red to a purple color within 1 min (the output was 1), allowing straightforward visualization by the naked eye (inset of Figure 3a). The λmax in the surface plasmon resonance red shifted to 545 nm as a result of the reduced


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inter-nanoparticle distance (Figure 3a). To further evaluate the performance and consistency of our results, we used the RLS method to investigate the molecular logic gate operation. As shown in Figure 3b, in the absence of both Hg2+ and Ag+ or either, relatively weak RLS signals were observed, correlating with the isolated individual Au NPs (Figure 3c). In the (1, 1) state, where both the Hg2+ and Ag+ were present, the RLS intensity remarkably enhanced and the aggregation of Au NPs could be clearly discriminated (Figures 3b and 3c). Obviously, both the RLS results and the TEM characterizations were fully consistent with the absorption results, further confirming the AND logic behavior with a characteristic truth table (Figure 2c). Furthermore, it is interesting to find that the logic system can be reset via introducing a Hg2+ chelator, EDTA or a Ag+ chelator NH4OH. Since EDTA (NH4OH) is able to capture Hg2+ (Ag+) from the T-Hg-T (C-Ag-C) complex, DNA can change from the double helix conformation to random coil again, which resets the logic system to its initial state. As Figure S3a shows, raising the molar ratio of NH4OH/Ag+ up to 2.0 caused the λmax of DNA-Au NPs solution return to about 525 nm (∆λ ~ 0). Similarly, increasing the EDTA/Hg2+ molar ratio led to the blue-shift of the λmax (Figure S3b). The whole AND-Reset cycle resembles the performance of the respective electronic circuitry (Figure 2b). Based on the above concept, additional INHIBIT logic gate was constructed using proton (H+) to control the structure of DNA and consequently the assembly/disassembly of DNA-Au NPs conjugates. The logic system consisted of 2-Au NPs and used both H+ (input A) and Hg2+/Ag+ ions (input B) as inputs (Figure 4). With no inputs (pH~8.0), the (C4T4)3C4 DNA was in random coil state, and the modified Au NPs were in dissociated state (the output was 0), whereas it hybridized to form rigid duplex structure in the presence of Hg2+/Ag+ ions, resulting in Au NPs aggregation with color change from red to purple (the output was 1, inset of Figure 5a). The absorption spectrum displayed a pronounced shift of the surface plasmon resonance of Au NPs


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(Figure 5a) due to the interparticle plasmon coupling as a result of Au NPs aggregation. If input H+ ions were introduced, the (C4T4)3C4 DNA involved conformational transition from random coil to well-packed “i-motif” structure at pH~5.0, due to the formation of intramolecular noncanonical base pairs between cytosine and protonated cytosine (CH+).40 Since the closed “imotif” form is more stable than the single-stranded or duplex form under such experimental conditions,41 the hybridization between 2-Au NPs could be efficiently suppressed even in the presence of Hg2+/Ag+ ions (the output was 0). The absorption spectrum of the system recorded at this state did not show any plasmon shift (Figure 5a), and the corresponding RLS intensity was relatively weak (Figure 5b). To further confirm that the observed spectral shift as well as the enhanced RLS signals were indeed the result of Au NPs aggregation, representative TEM graphs for the four input modes were recorded (Figure 5c). It is clear that the Au NPs were assembled into large aggregates only for (0, 1) mode, while they were in dispersed and isolated states for other three modes, agreeing very well with the results from absorption spectra and RLS measurements. These observations demonstrated that when only Hg2+/Ag+ metal ions were added (input [0, 1]), the output was 1, otherwise it was 0, confirming the INHIBIT logic behavior with a characteristic truth table as shown in Figure 4c. It should be noted that the reset function could also be realized by the addition of EDTA or NH4OH. Combining the above results with the ligand-exchange process by DTT, a XOR logic gate was then constructed. This logic gate system consisted of 2-Au NPs and defined DTT (input A) and Hg2+/Ag+ (input B) as inputs and the color change of the Au NPs solution as output (Figure 6). In the presence of DTT (input [1, 0]), a ligand-exchange process occurred. DTT as a common disulfide reducing agent has been demonstrated to efficiently remove thiolated oligonucleotides from gold surface.42 Since the covalently attached oligonucleotides have been liberated from the Au NPs, the nanoparticles tended to aggregate in ionic strength solution due to the decrease of


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the negatively charged density and thus the electrostatic repulsion between neighboring Au NPs. As shown in the UV-vis absorption spectra, the addition of DTT made the plasmon peak at 525 nm decreasing and meanwhile the shoulder absorption band at 660 nm increasing (Figure S4a). When the concentration of DTT was as low as 1 mM, a color change from red to blue can be discriminated by the naked eye (output 1, inset of Figure S4a). The irreversible aggregation could be verified by the enhanced RLS signals and the state change of dispersion/aggregation of Au NPs by TEM graphs (Figure S4b and Figure S4c). In the presence of Hg2+/Ag+ ions (input [0, 1]), as demonstrated above, the absorption band of the 2-Au NPs solution red shifted to 545 nm (Figure S4a) with a concomitant red-to-purple color change (output 1, inset of Figure S4a), and the aggregation process was confirmed by the RLS signal and TEM graph (Figure S4b and Figure S4c). Thus, the presence of either DTT or Hg2+/Ag+ ions resulted in the aggregation of Au NPs and eventually gave rise to the output of 1, although the aggregation mechanism was different from each other. However, when both inputs were present (input [1, 1]), coexistence of DTT and Hg2+/Ag+ ions led to the formation of very stable complexes between Hg2+/Ag+ ions and DTT,43 which not only prevented the formation of stable metal-ion-mediated base pairs but also suppressed the gold affinity of the thiol groups. Consequently, no color change and surface plasmon resonance shift can be observed (output 0, Figure S4a), and the corresponding RLS intensity was relatively weak (Figure S4b), illustrating the dispersed and isolated state of the Au NPs (Figure S4c). These observations demonstrated that a true output of 1 was obtained when only one of the two inputs was held at 1, whereas a false output of 0 was produced when both inputs were held at either 0 or 1, confirming the XOR logic behavior with a characteristic truth table as shown in Figure 6c.


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To further demonstrate the gate networking necessary for the higher-order circuits with varying degrees of complexity, as shown in Figure S5, the INHIBIT and XOR gates could be combined into a multilevel circuit that enforced an overall OR Boolean behavior.

CONCLUSION In conclusion, we have constructed a conceptually new class of colorimetric molecular-scale logic gate systems making use of the specific interaction between Hg2+ ions and T bases as well as that between Ag+ ions and C bases. Although the concepts of nonnatural base pairing and the logic gates using gold-DNA conjugates are not new, yet, we combine these “two” old concepts into a new approach. The proposed approach includes three unique features different from the conventional ones: (1) the present logic operation is very simple, the logic system consists of only T-/C-rich DNA modified Au NPs and it is unnecessary to exquisitely design and alter the DNA sequence for different multiple molecular logic operations (AND, INHIBIT and XOR logic gates); (2) for the first time we convert the conformational transition of C-/T-rich DNA upon ioninduced logic operation to the colorimetric change of noble metal nanoparticles, which can be monitored by the naked eye; (3) compared with previous reports with unmodified AuNPs as optical sensing elements, the present logic systems can effectly omit the non-selective aggregation, avoiding the background interference and thus potentiating its applications in biological and environmental systems. We believe that the nonnatural base pairing combined with unique optical properties of Au NPs could overcome limitations existed in previous logic gate design, and thus promises great potential in multiplexed ion sensing, molecule-scale computers and other computational logic devices.

AUTHOR INFORMATION Corresponding Author


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*E-mail: [email protected]; Phone: (+86) 791-83969518; Fax: (+86) 791-83969518.

ACKNOWLEDGMENT We greatly appreciate the supports of the National Natural Science Foundation of China (21065006, 21163014 and 21105044) and the Program for New Century Excellent Talents in University (NCET-11-1002).

ASSOCIATED CONTENT Supporting Information Absorption spectra of the mixture of 1-Au NPs and 2-Au NPs with addition of Ag+ ions (Figure S1); Schematic representation of the YES logic gate system (Figure S2); Reset of the AND logic system by NH4OH or EDTA (Figure S3); The results of XOR logic gate (Figure S4); Representation of the multilevel circuit (Figure S5). This material is available free of charge via the Internet at http://pubs.acs.org.

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(26) Freeman, R.; Finder, T.; Willner, I. Multiplexed analysis of Hg2+ and Ag+ ions by nucleic acid functionalized CdSe/ZnS quantum dots and their use for logic gate operations. Angew. Chem. Int. Ed. 2009, 48, 7818-7821. (27) Zhang, G.; Lin, W.; Yang, W.; Lin, Z.; Guo, L.; Qiu, B.; Chen, G. Logic gates for multiplexed analysis of Hg2+ and Ag+. Analyst. 2012, 137, 2687-2691. (28) Li, X.; Sun, L.; Ding, T. Multiplexed sensing of mercury(II) and silver(I) ions: A new class of DNA electrochemiluminescent-molecular logic gates. Biosens. Bioelectron. 2011, 26, 35703576. (29) Li, T.; Wang, E.; Dong, S. Potassium-lead-switched G-quadruplexes: A new class of DNA logic gates. J. Am. Chem. Soc. 2009, 131, 15082-15083. (30) Wang, Z.-G.; Elbaz, J.; Remacle, F.; Levine, R. D.; Willner, I. All-DNA finite-state automata with finite memory. Proc. Natl. Acad. Sci. USA 2010, 107, 21996-22001. (31) Yin, B. C.; Ye, B. C.; Wang, H.; Zhu, Z.; Tan, W. Colorimetric logic gates based on aptamer-crosslinked hydrogels. Chem. Commun. 2012, 48, 1248-1250. (32) Xu, X.; Zhang, J.; Yang, F.; Yang, X. Colorimetric logic gates for small molecules using split/integrated aptamers and unmodified gold nanoparticles. Chem. Commun. 2011, 47, 94359437. (33) Du, J.; Yin, S.; Jiang, L.; Ma, B.; Chen, X. A colorimetric logic gate based on free gold nanoparticles and the coordination strategy between melamine and mercury ions. Chem. Commun. 2013, 49, 4196-4198. (34) Liu, D.; Chen, W.; Sun, K.; Deng, K.; Zhang, W.; Wang, Z.; Jiang, X. Resettable, multireadout logic gates based on controllably reversible aggregation of gold nanoparticles. Angew. Chem. Int. Ed. 2011, 50, 4103-4107. (35) Li, Y.; Han, X.; Deng, Z. Logical regulations of the aggregation/dispersion of gold nanoparticles via programmed chemical interactions. Langmuir, 2011, 27, 9666-9670.


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(36) Ren, J.; Wang, J.; Wang, J.; Wang, E. Colorimetric enantiorecognition of oligopeptide and logic gate construction based on DNA aptamer–ligand–gold nanoparticle interactions. Chem. Eur. J. 2013, 19, 479-483. (37) Frens, G. Controlled nucleation for the regulation of the particle size in monodisperse gold suspensions. Nat. Phys. Sci., 1973, 241, 20-22. (38) Grabar, K. C.; Freeman, R. G.; Hommer M. B.; Natan, M. J. Preparation and characterization of Au colloid monolayers. Anal. Chem. 1995, 67, 735-743. (39) Hill, H. D.; Mirkin, C. A. The bio-barcode assay for the detection of protein and nucleic acid targets using DTT-induced ligand exchange. Nat. protoc. 2006, 1, 324-336. (40) Gehring, K.; Leroy, J.-L.; Gueron, M. A tetrameric DNA structure with protonated cytosinecytosine base pairs. Nature 1993, 363, 561-565. (41) Liu, D.; Balasubramanian, S. A proton-fuelled DNA nanomachine. Angew. Chem. Int. Ed. 2003, 42, 5734-5736. (42) Thaxton, C. S.; Hill, H. D.; Georganopoulou, D. G.; Stoeva, S. I.; Mirkin, C. A. A bio-barcode assay based upon dithiothreitol-induced oligonucleotide release. Anal. Chem. 2005, 77, 8174-8178. (43) Shimron, S.; Elbaz, J.; Henning, A.; Willner, I. Ion-induced DNAzyme switches. Chem. Commun. 2010, 46, 3250-3252.


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Figure Captions Figure 1. Illustration of Au NPs aggregation triggered by metal ions. (a) Aggregation of (C4A4)3C4 modified Au NPs (1-Au NPs) and (C4T4)3C4 modified Au NPs (2-Au NPs) by Ag+ ions. (b) Aggregation of 2-Au NPs and (G4T4)3G4 modified Au NPs (3-Au NPs) by Hg2+ ions. Figure 2. An AND logic gate system consisting 2-Au NPs by using Hg2+ (A) and Ag+ (B) ions as inputs. (a) Illustration of the operational design of the AND gate. (b) Equivalent electronic circuit for the AND-Reset logic operation. (c) Truth table of the AND gate. Figure 3. The results of AND logic gate with different input modes were characterized by colorimetric and UV-vis detection (a), RLS measurement (b), and TEM images (c). Figure 4. An INHIBIT logic gate system consisting 2-Au NPs by using H+ (A) and Hg2+/Ag+ (B) ions as inputs. (a) Illustration of the operational design of INHIBIT gate. (b) Equivalent electronic circuit for the INHIBIT-Reset logic operations. (c) Truth table of the INHIBIT gate. Figure 5. The results of INHIBIT logic gate with different input modes were characterized by colorimetric and UV-vis detection (a), RLS measurement (b), and TEM images (c). Figure 6. A XOR logic gate system consisting 2-Au NPs by using DTT (A) and Hg2+/Ag+ (B) ions as inputs. (a) Illustration of the operational design of XOR gate. (b) Equivalent electronic circuit for the XOR logic operations. (c) Truth table of the XOR gate.


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Figure 1. Illustration of Au NPs aggregation triggered by metal ions. (a) Aggregation of (C4A4)3C4 modified Au NPs (1-Au NPs) and (C4T4)3C4 modified Au NPs (2-Au NPs) by Ag+ ions. (b) Aggregation of 2-Au NPs and (G4T4)3G4 modified Au NPs (3-Au NPs) by Hg2+ ions.


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Figure 2. An AND logic gate system consisting 2-Au NPs by using Hg2+ (A) and Ag+ (B) ions as inputs. (a) Illustration of the operational design of the AND gate. (b) Equivalent electronic circuit for the AND-Reset logic operation. (c) Truth table of the AND gate.


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Figure 3. The results of AND logic gate with different input modes were characterized by colorimetric and UV-vis detection (a), RLS measurement (b), and TEM images (c).


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Figure 4. An INHIBIT logic gate system consisting 2-Au NPs by using H+ (A) and Hg2+/Ag+ (B) ions as inputs. (a) Illustration of the operational design of INHIBIT gate. (b) Equivalent electronic circuit for the INHIBIT-Reset logic operations. (c) Truth table of the INHIBIT gate.


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Figure 5. The results of INHIBIT logic gate with different input modes were characterized by colorimetric and UV-vis detection (a), RLS measurement (b), and TEM images (c).


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Figure 6. A XOR logic gate system consisting 2-Au NPs by using DTT (A) and Hg2+/Ag+ (B) ions as inputs. (a) Illustration of the operational design of XOR gate. (b) Equivalent electronic circuit for the XOR logic operations. (c) Truth table of the XOR gate.


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Easy Design of Colorimetric Logic Gates Based on Nonnatural Base

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