Iodine-Mediated Etching of Triangular Gold Nanoplates for

Subscriber access provided by UNIVERSITY OF ADELAIDE LIBRARIES

Article

Iodine-Mediated Etching of Triangular Gold Nanoplates for Colorimetric Sensing of Copper Ion and Aptasensing of Chloramphenicol Chia-Chen Chang, Guoqing Wang, Tohru Takarada, and Mizuo Maeda ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b13841 • Publication Date (Web): 14 Sep 2017 Downloaded from http://pubs.acs.org on September 18, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Iodine-Mediated Etching of Triangular Gold Nanoplates for Colorimetric Sensing of Copper Ion and Aptasensing of Chloramphenicol Chia-Chen Chang,* Guoqing Wang, Tohru Takarada, and Mizuo Maeda Bioengineering Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan

Abstract

A colorimetric method for fast, simple, and selective detection of Cu2+ was developed using I–mediated etching of triangular gold nanoplates (AuNPLs). The method was based on our finding that Cu2+ efficiently promoted this etching in the presence of SCN–. The etching process was accompanied by a dramatic color change from blue to red, allowing for visual and spectroscopic detection of Cu2+ with a detection limit of 10 µM and 1 µM, respectively. By incorporating molecular recognition by a DNA aptamer into this method, visual detection of chloramphenicol was also achieved with a detection limit of 5 µM.

Keywords: gold nanoplate, copper ion, etching, aptamer, chloramphenicol

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 30

INTRODUCTION Various gold nanomaterials, such as gold nanoparticles (AuNPs) and gold nanorods (AuNRs), have been widely utilized for chemical and biological sensing, primarily because they exhibit unique optical and catalytic properties. Over the past two decades, a number of studies have been carried out to develop various probes by incorporating molecular recognition events into gold nanomaterials.1,2 Among them, two-dimensional triangular gold nanoplates (AuNPLs) that exhibit highly shape-dependent localized surface plasmon resonance (LSPR) have shown promise in a diverse range of sensing applications.3 Nonetheless, only a limited number of AuNPL-based assays have been reported, despite the great attention paid to the development of sensors in general.4 Colorimetric sensing has the advantages of being cost-effective and permitting visual readout of target molecules with the naked eye prior to instrumental analyses.5 Moreover, such assays are easily adaptable to a smartphone-based device or a portable spectrophotometer, making them suitable for on-site analysis and point-of-care testing.6 We have recently reported a colorimetric gene mutation assay using non-cross-linking aggregation of DNA-functionalized AuNPLs.7 It is further expected that various analytes will be detectable by using AuNPLs in a more facile manner. In the present study, we attempt to develop two AuNPL-based sensing systems for metal ions and antibiotics. Copper ion (Cu2+) is an essential trace metal ion that is involved in numerous physiological and pathological events, such as hemoglobin synthesis and oxidative phosphorylation, due to the fact that redox enzymes often require copper ions as a catalytic cofactor. Nevertheless, excessive Cu2+ intake is highly toxic to the human body and causes serious neurological diseases.8 Thus, detection of Cu2+, especially in drinking water, has already been widely performed by various


2

Page 3 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


analytical methods, including optical sensing,9 microcantilever-based detection,10 and fluorescent assay.11 Although these approaches have great advantages over conventional bench-top assays, they require complicated and expensive equipment. Because such requirements can be a serious obstacle for on-site analysis and point-of-care testing, interest is converging on visual methods for Cu2+ detection. For example, silver-coated AuNPs and AuNRs have been employed for a detection probe based on the copper-mediated leaching of silver.12,13 Nevertheless, the synthetic procedures of gold nanocomposites are usually time-consuming, owing to the multiple steps. Recently, Cu2+ sensing methods based on the catalytic etching of bare AuNPs14 and AuNRs15,16 have been reported; however, they usually require a high reaction temperature over 70°C and highly acid or basic conditions, which limit their practical application. For example, the colorimetric methods based on the thiosulfate-mediated etching system14,15 are carried out in alkaline solutions, because thiosulfate ions become unstable at pH18 MΩcm) from a Milli-Q system was used for all experiments. Transmission electron microscopy (TEM) was performed on a JEM 1230 TEM (JEOL) operated at an accelerating voltage of 80 kV. The pH values of solutions were measured with a MP230 pH meter (Mettler-Toledo). The zeta potential of AuNPLs was determined using a Zetasizer Nano ZS instrument (Malvern). Raman and absorption spectra were obtained on a LabRam


4

Page 5 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


spectrometer (Horiba) and a Cary 50 UV/Vis spectrophotometer (Varian), respectively. All photographs were recorded by a Xiaomi Redmi Note 2 smartphone. Synthesis of AuNPLs. AuNPLs were synthesized according to the rapid one-pot seedless growth method.24 Initially, 100 mM CTAC (6.4 mL) was added to ultrapure water (32 mL). Next, 10 mM KI (300 µL), 25 mM HAuCl4 (320 µL), and 100 mM NaOH (81 µL) were sequentially introduced to the diluted CTAC solution. Then, 64 mM AA (320 µL) was injected into the mixture solution before gentle mixing. After the solution color changed from yellow to colorless, 100 mM NaOH (40 µL) was added into the mixture solution, followed by rapid shaking for 3 s. This led to the solution color change from colorless to blue. Finally, the mixture solution was allowed to stand for 10 min. The resulting solution was used for the following study without further purification, mainly due to avoidance of undesired aggregation that could cause loss of the final products. The final concentrations of AuNPL, CTAC, AA, and KI were 0.13 nM, 16 mM, 0.52 mM, and 76 µM, respectively. The concentration of AuNPL was determined using an extinction coefficient of 4.2 x 109 m-1cm-1.7 Detection of Cu2+ with KI. The AuNPL dispersion (50 µL) was first diluted with ultrapure water (130 µL). Then, 100 mM KI (10 µL) was added into the dispersion, followed by the addition of different concentrations of Cu(NO3)2 (10 µL). The final concentration of KI was 5 mM. The resultant solution was allowed to stand for 20 min at room temperature for color changes. Detection of Cu2+ with KI and KSCN. The AuNPL dispersion (50 µL) was first diluted with ultrapure water (136 µL). Then, 0.1 M KSCN (4 µL) was added into the dispersion, followed by the addition of different concentrations of Cu(NO3)2 (10 µL). The resultant solution was allowed to stand for 2.5 min at room temperature for color changes. In addition, the tap water spiked with 15 µM Cu(NO3)2 was used as a model practical sample. Quantitative analysis of Cu2+ was


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 30

conducted following the procedure described above. The initial concentration of KI that originated from the AuNPL dispersion was 76 µM; thus, the final concentration of KI was 19 µM. Detection of CAP. The 2.5 µM CAP-binding DNA aptamer (4 µL) was added into the AuNPL dispersion (50 µL), accompanied by the addition of TE buffer (15 µL). After an incubation at room temperature for 15 min, different concentrations of CAP (20 µL) were mixed with the solution. The

resultant

solution

was

allowed

to

stand

for

15

min

at

room

temperature. Subsequently, 100 mM KSCN (1 µL) and 16 mM Cu(NO3)2 (10 µL) were sequentially introduced to the mixture solution. After 10 min, the absorption spectra were measured by a UV/Vis spectrophotometer. The final concentration of KI was 38 µM. For the practical application, 100 µg/mL of formula milk (Meiji, Japan) was spiked with 20 µM CAP to be used as a model sample. The color changes were monitored following the procedure described above.

RESULTS AND DISCUSSION Detection of Copper Ions. In the current study, we demonstrated the applicability of bare AuNPLs for Cu2+ sensing. As shown in Figure 1A, characteristic LSPR bands were observed for the prepared AuNPLs around 630 nm. Interestingly, the bands were blue-shifted and decreased in intensity in the presence of Cu(NO3)2. The observed shift indicated the size and shape changes of AuNPLs.24 TEM images of the AuNPLs with Cu(NO3)2 are shown in Figure 1B. The initial AuNPLs showed a triangular shape with an edge length over 100 nm. When the concentration of Cu(NO3)2 was 10 µM, the morphology of the AuNPLs evolved from triangular to circular. When we further increased the concentration of Cu(NO3)2 to 1000 µM, we observed smaller circularand triangular-shaped nanomaterials; the representative diameter or edge was found to be at least


6

Page 7 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2-fold smaller than the edge length of the original AuNPLs. These results indicate that Cu2+ promoted the etching of triangular AuNPLs. A previous study reported a simple and rapid method to synthesize AuNPLs via seedless growth in a slightly alkaline solution (pH 8) containing CTAC, AA, and KI.24 To understand the mechanism of the present Cu2+-assisted AuNPL etching, we investigated the dependence of the Cu2+-assisted etching speed on the concentration of CTAC, AA, and KI. In the case of CTAC, the increase of CTAC concentration led to a red shift of the LSPR bands, indicating that CTAC inhibited the AuNPL etching (Figure S1). The zeta-potential measurement revealed that the surface charge of AuNPLs became more positive with increasing CTAC concentration (Figure S1). These results strongly suggested that CTAC was adsorbed onto the AuNPL surfaces to prohibit the access of Cu2+ due to the electrostatic repulsion and steric hindrance. Next, we investigated the effect of AA on the AuNPL etching. When the AA concentration was increased, the LSPR bands were also red-shifted to be almost identical to those of the initial AuNPLs (Figure S2). Therefore, the etching was strongly inhibited by an excess amount of AA, probably due to the reduction of Cu2+ to Cu+ by AA. Finally, we examined the effect of KI concentration on the Cu2+-assisted etching. Without Cu2+, the portion of the LSPR bands from 500 nm to 600 nm was gradually augmented with increasing KI concentration (Figure 2A). This observation was consistent with the previous work by Chen and co-workers that identified the oxidative etching of AuNPLs by KI.24 However, with 1 mM Cu(NO3)2, the LSPR bands were blue-shifted with a dramatic increase in intensity in a KI-concentration-dependent manner; the solution color was changed from blue to red, suggesting that KI was firmly associated with the Cu2+-assisted etching (Figure 2B). The ratio of the absorbance at 550 nm and 630 nm (A550/A630) was used to evaluate the degree of the AuNPL etching, because large A550/A630 values are generally


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 30

observed for truncated small triangular or circular AuNPLs. As shown in Figure 2C, the A550/A630 value with 1 mM Cu(NO3)2 was significantly larger than that without Cu(NO3)2 at various KI concentrations ranging from 0 to 5 mM. For example, in the presence of 5 mM KI, the A550/A630 value with 1 mM Cu(NO3)2 was 2-fold larger than that without Cu(NO3)2. Taken together, these findings showed that the dependence of the etching on the concentrations of CTAC, AA, and KI was in line with the fact that the I–-mediated AuNPL etching process was accelerated by Cu2+. The solution chemistry of the iodide-mediated Au etching is enormously complicated, mainly due to possible formation of many different iodine and iodide species in the solutions.25 Here, we hypothesized that the present Cu2+-assisted I–-mediated AuNPL etching consisted of three steps: the oxidation of I– by Cu2+ to generate I2, the formation of tri-iodide ion (I3–) from I– and I2,24 and the oxidation of Au0 to Au+ by I3– and I–.26 These steps can be respectively described as follows: 2+

−

2Cu + 4I → 2CuI ↓ + I 2 −

(1)

–

I + I2→ I3 −

(2) −

–

2Au + I3 + I → 2AuI2

(3)

We confirmed the production of I2 by monitoring the absorption spectra of KI solution in the presence and absence of Cu2+. When 1 mM Cu(NO3)2 was added to the KI solution, two characteristic peaks appeared at 290 nm and 350 nm, accompanying the solution color change from colorless to yellow (Figure S3).27 By contrast, no peak was found without Cu(NO3)2. The significant color change induced by Cu2+ was due to the formation of I2, which was immediately converted to I3−.28 Thus, it was strongly suggested that the I–-mediated AuNPL etching was promoted by Cu2+ through the production of I3−.


8

Page 9 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


This finding prompted us to develop a simple colorimetric method to detect Cu2+. As expected, the color change of the AuNPL etching solutions containing 5 mM KI was induced in a Cu(NO3)2-concentration-dependent manner (Figure S4). However, we found that the metal-ionselectivity was insufficient, because some other divalent and trivalent metal ions also induced slight color changes (Figure S5). In particular, the color change induced by 100 µM FeCl3 was found to be almost equal to the change by 1 µM Cu(NO3)2. This is because Fe3+ is also capable of oxidizing I– to generate I2.29 To minimize such interference by Fe3+, which may coexist with Cu2+ in real samples, we employed potassium thiocyanate (KSCN) as a masking agent because SCN– provided greater stability constant for the formation of the iron(III)–thiocyanate complex but had poor coordination ability with Cu2+.30 In addition, we expected that SCN– also promoted the AuNPL etching for the following reasons. I2 is known to adsorb preferentially on CuI precipitate. The thus-adsorbed I2 can be readily substituted with SCN– to react with I–, according to eq 2.31 In addition, SCN– directly reacts with CuI to produce I– as follows32: −

−

SCN + CuI ↓→ CuSCN + I

(4)

The regenerated I– also reacts with I2 to yield I3–. Therefore, SCN– can work as an accelerating agent, as well as a masking agent. As shown in Figure S6, the addition of 2 mM KSCN into the reaction solution actually improved both the selectivity and efficiency of the Cu2+-induced AuNPL etching. The overall reaction schemes are depicted in Scheme 1. Figure 3 shows the results of Cu2+ detection using the present method under the optimized conditions. We measured both the absorption spectra and the color changes of the AuNPL etching solutions at different concentrations of Cu(NO3)2. Prior to these measurements, we determined the appropriate reaction time to be 2.5 min in order to achieve the greatest masking effect against Fe3+ (Figure S7). No effect of pH was observed on the etching reaction under


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 30

acidic and neutral conditions, strongly suggesting that the pH adjustment was not required (Figure S8). As the concentration of Cu(NO3)2 increased, the absorbance at 630 nm gradually decreased, thereby producing the color change from blue through purple and red to colorless (Figure 3A). We obtained a good linear response of this colorimetric sensor from 1 µM to 1 mM Cu(NO3)2 with a detection limit (LOD) of 1 µM. The LOD was sufficiently lower than the maximum permissible level in drinking water (Japan standard, ~15.7 µM33; USA standard, ~20.5 µM34). Compared with organic dye-based colorimetric methods, the synthesis of AuNPLs is straightforward and time-effective. For example, the preparation of Cd2+-based organic dye typically requires 3 days and more.35 Besides, the use of hazard chemicals such as Cd2+ in the synthetic procedure is problematic to human health. Additionally, our method is characterized by its rapidity and simplicity compared to recently reported analytical assays, as well as other gold nanomaterial-based colorimetric methods (Table S1). It should be noted that the detection time of our assay was less than 5 min, which was shorter than that of almost all the preceding methods. We also assessed the improved selectivity of our assay using SCN– (Figure 4). The other metal ions induced no color change. To further verify the selectivity for the practical detection of Cu2+, we prepared a sample mixture containing all of the other metal ions employed in this study. Approximately 8-fold higher normalized absorption intensity was obtained in the sample mixture spiked with Cu(NO3)2, compared to that without Cu(NO3)2. This result indicated that the current method had sufficient selectivity toward Cu2+. In addition, no effects of various counter anions of Cu2+ were observed (Figure S9). Furthermore, we demonstrated the practical use of the current Cu2+ assay by using tap water samples. The average concentration of Cu2+ in tap water in Japan has been reported to be 315 nM.36 Considering that the maximum permissible level of Cu2+ in


10

Page 11 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


drinking water in Japan is ~15.7 µM, as described above, we spiked 15 µM of Cu2+ into a tap water sample. Using the current assay, we succeeded in observing a color change from blue to purple for this spiked sample (Figure S10). Thus, the present colorimetric assay should be practically useful, especially in a state of emergency, for visually detecting Cu2+ in tap water that exceeds the Japan standard.

Detection of Antibiotics. Subsequently, we applied the current Cu2+-assisted I–-mediated AuNPL etching to aptameric sensing of antibiotics. Although aptamers have been widely used in bio-sensing, it still remains challenging to construct sensing systems using long, highly-folded aptamers.37 In general, planar Au substrates have a certain degree of affinity for nucleobases.38 Moreover, CTAC-stabilized AuNPLs have highly positively-charged surfaces. We therefore assumed that DNA aptamers were adsorbed onto the surface of CTAC-stabilized AuNPLs through the electrostatic interaction and the coordinate Au–N bonding. By utilizing the competition between the adsorption of the aptamers and the molecular recognition by the aptamers, we tried to develop bio-sensing systems based on the current AuNPL etching. As an analyte, we selected chloramphenicol (CAP), an antibiotic widely used in veterinary and human medicine. The previously selected DNA aptamer targeting CAP has a long sequence (80 bases) with a complicated secondary structure (Figure S11).23 We performed the zeta-potential measurement and the surface-enhanced Raman scattering measurement to investigate the interaction between the aptamer and the AuNPL (Figure S12). The results showed that the aptamer was capable of binding to the AuNPL surface. In the presence of CAP, the folded aptamer was almost completely detached from the AuNPL surface, due to the formation of a complex with CAP. This is because the complex formation through the folding of the DNA


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 30

aptamer39 was able to break the coordination bonding between Au and the nucleobase and/or could attenuate the electrostatic interaction between the phosphate group of the aptamer and CTA+.40 We combined the molecular recognition of CAP by the DNA aptamer with the present AuNPL etching. Figure 5A and B show the absorption spectra and the color changes before and after the AuNPL etching, respectively. The absorption spectra under the different conditions exhibited the same absorption peak before the etching reaction (Figure 5A), whereas all the absorption intensities decreased after the etching (Figure 5B). Compared to the sample without the aptamer and CAP (Figure 5B(a)), no change of the absorbance was observed for the reaction solution involving CAP (Figure 5B(b)), demonstrating that CAP caused no effect on the AuNPL etching rate. By contrast, the absorbance for the reaction solution involving the aptamer (Figure 5B(c)) was ∼1.3-fold higher at 610 nm than that without the aptamer and CAP (Figure 5B(a)), indicating deceleration of the AuNPL etching by the adsorption of the aptamer onto the AuNPL surface. As expected, when CAP was added into the aptamer-bound AuNPL solutions (Figure 5B(d)), the absorbance at 610 nm was decreased until it was almost identical to that of the reaction solution without the aptamer and CAP (Figure 5B(a)). These results demonstrated that CAP caused the dissociation of the aptamer from the AuNPL surface, thereby recovering the AuNPL etching. Therefore, the Cu2+-assisted I–-mediated AuNPL etching can be at least partially restricted by the adsorption of the DNA aptamers on the AuNPL surfaces. The complex formation between the aptamer and CAP can restart this etching reaction, due to the desorption of the aptamer from the AuNPL surfaces. The proposed mechanism is shown in Figure 5C. To achieve the greatest color change, we optimized the incubation time with CAP to be 10 min (Figure S13). As shown in Figure 6, a gradual decrease in the absorbance at 610 nm,


12

Page 13 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


accompanied by a blue shift of the LSPR bands and a distinct color change from blue to red, was observed as the CAP concentration increased from 0 to 2000 µM; the LOD was determined to be 5 µM. The sensitivity of the current method was not as high as that of recently reported ones (Table S2). However, it should be emphasized that this colorimetric assay requires no high-cost instruments and no time-consuming washing steps, both of which should be highly advantageous to on-site pre-screening of the analyte. The therapeutic concentration range for CAP has been reported to be 10–20 µg/mL (31–62 µM); an excessive level (>25 µg/mL) of CAP exhibits toxicity to human health.41 Hence, from a diagnostic perspective, the sensitivity of our assay was high enough for the commonly accepted range in clinical monitoring of CAP. The selectivity of the present CAP assay was also high enough, because different antibiotics, such as ampicillin (AMP), streptomycin (STR), and tetracycline (TEC), were not detected by this assay (Figure 7). We also succeeded in detecting CAP in the sample mixture where these other antibiotics coexisted. Moreover, by using the current assay, we observed the expected absorption spectral change for the milk powder sample spiked with 20 µM CAP (Figure S14). These results indicate the potential use of this assay for real samples.

CONCLUSIONS In summary, we identified the Cu2+-assisted I–-mediated etching of AuNPLs and exploited this reaction to develop a colorimetric Cu2+ assay by using SCN– as a promoter. Compared to the previously reported Cu2+ sensors, the current method required shorter measurement time and exhibited higher sensitivity. We further applied this Cu2+-assisted I–-mediated AuNPL etching to the aptameric detection of antibiotics. This was achieved by combining the CAP recognition by the DNA aptamer and the inhibition of the AuNPL etching by the adsorption of the aptamer onto


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 30

the AuNPL surface. The current strategy could be readily used to detect various chemical and biological molecules by employing appropriate aptamers. Therefore, this detection method should be useful for various purposes, including environmental assessment and medical diagnostics.


14

Page 15 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.xxxxxxx. Comparison of sensing performance with previously reported methods, additional absorption and Raman spectroscopic data, and zeta potential analysis data (PDF)

AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected]. Phone: +81-48-467-9312. ORCID Chia-Chen Chang: 0000-0001-5466-4724 Tohru Takarada: 0000-0001-6906-5812 Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS C. C. C. acknowledges the support of the Taiwan Postdoctoral Research Abroad Program (1052917-I-564-034). This work was supported by JSPS KAKENHI Grant Number JP25220204 and by a Grant for Molecular Systems Research provided by RIKEN.


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 30

REFERENCES (1)

Sasidharan, A.; Monteiro-Riviere, N. A. Biomedical Applications of Gold Nanomaterials: Opportunities and Challenges. WIREs Nanomed. Nanobiotechnol. 2015, 7 (6), 779–796.

(2)

Yang, X.; Yang, M.; Pang, B.; Vara, M.; Xia, Y. Gold Nanomaterials at Work in Biomedicine. Chem. Rev. 2015, 115 (19), 10410–10488.

(3)

Hu, H.; Zhou, J.; Kong, Q.; Li, C. Two-Dimensional Au Nanocrystals: Shape/Size Controlling Synthesis, Morphologies, and Applications. Part. Part. Syst. Charact. 2015, 32 (8), 796–808.

(4)

Scarabelli, L.; Coronado-Puchau, M.; Giner-Casares, J. J.; Langer, J.; Liz-Marzán, L. M. Monodisperse Gold Nanotriangles: Size Control, Large-Scale Self-Assembly, and Performance in Surface-Enhanced Raman Scattering. ACS Nano 2014, 8 (6), 5833–5842.

(5)

Song, Y.; Wei, W.; Qu, X. Colorimetric Biosensing Using Smart Materials. Adv. Mater. 2011, 23 (37), 4215–4236.

(6)

Wu, T. H.; Chang, C. C.; Vaillant, J.; Bruyant, A.; Lin, C. W. DNA Biosensor Combining Single-Wavelength Colorimetry and a Digital Lock-In Amplifier within a Smartphone. Lab Chip 2016, 16 (23), 4527–4533.

(7)

Wang, G.; Akiyama, Y.; Takarada, T.; Maeda, M. Rapid Non-Crosslinking Aggregation of DNA-Functionalized Gold Nanorods and Nanotriangles for Colorimetric SingleNucleotide Discrimination. Chem. - Eur. J. 2016, 22 (1), 258–263.


16

Page 17 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(8)

Crisponi, G.; Nurchi, V. M.; Fanni, D.; Gerosa, C.; Nemolato, S.; Faa, G. Copper-Related Diseases: From Chemistry to Molecular Pathology. Coord. Chem. Rev. 2010, 254 (7–8), 876–889.

(9)

Lin, S.; Chang, C. C.; Lin, C. W. A Reversible Optical Sensor Based on Chitosan Film for the Selective Detection of Copper Ions. Biomed. Eng. Appl. Basis Commun. 2012, 24 (5), 453–459.

(10) Zhao, H.; Xue, C.; Nan, T.; Tan, G.; Li, Z.; Li, Q. X.; Zhang, Q.; Wang, B. Detection of Copper Ions Using Microcantilever Immunosensors and Enzyme-Linked Immunosorbent Assay. Anal. Chim. Acta 2010, 676 (1–2), 81–86. (11) Wu, Y.; Tan, Y.; Wu, J.; Chen, S.; Chen, Y. Z.; Zhou, X.; Jiang, Y.; Tan, C. Fluorescence Array-Based Sensing of Metal Ions Using Conjugated Polyelectrolytes. ACS Appl. Mater. Interfaces 2015, 7 (12), 6882–6888. (12) Lou, T.; Chen, L.; Chen, Z.; Wang, Y.; Chen, L.; Li, J. Colorimetric Detection of Trace Copper Ions Based on Catalytic Leaching of Silver-Coated Gold Nanoparticles. ACS Appl. Mater. Interfaces 2011, 3 (11), 4215–4220. (13) Wang, X.; Chen, L.; Chen, L. Colorimetric Determination of Copper Ions Based on the Catalytic Leaching of Silver from the Shell of Silver-Coated Gold Nanorods. Microchim. Acta 2014, 181 (1–2), 105–110. (14) Liu, R.; Chen, Z.; Wang, S.; Qu, C.; Chen, L.; Wang, Z. Colorimetric Sensing of Copper(II) Based on Catalytic Etching of Gold Nanoparticles. Talanta 2013, 112, 37–42.


17


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 30

(15) Chen, Z.; Liu, R.; Wang, S.; Qu, C.; Chen, L.; Wang, Z. Colorimetric Sensing of Copper(II) Based on Catalytic Etching of Gold Nanorods. RSC Adv. 2013, 3 (32), 13318– 13323. (16) Zhang, Z.; Chen, Z.; Qu, C.; Chen, L. Highly Sensitive Visual Detection of Copper Ions Based on the Shape-Dependent LSPR Spectroscopy of Gold Nanorods. Langmuir 2014, 30 (12), 3625–3630. (17) Green, T. A. Gold Electrodeposition for Microelectronic, Optoelectronic and Microsystem Applications. Gold Bull. 2007, 40, 105–114. (18) Elmahdi, S.; Ligia V. D.; Salina, P. Antibiotic Resistance of Vibrio Parahaemolyticus and Vibrio Vulnificus in Various Countries: A Review. Food Microbiol. 2016, 57, 128–134. (19) Armenta, S.; de la Guardia, M.; Abad-Fuentes, A.; Abad-Somovilla, A.; Esteve-Turrillas, F. A. Highly Selective Solid-Phase Extraction Sorbents for Chloramphenicol Determination in Food and Urine by Ion Mobility Spectrometry. Anal. Bioanal. Chem. 2016, 408 (29), 8559–8567. (20) Huang, X.; Liu, Q.; Yao, S.; Jiang, G. Recent Progress in the Application of Nanomaterials in the Analysis of Emerging Chemical Contaminants. Anal. Methods 2017, 9 (19), 2768– 2783. (21) Wu, S.; Zhang, H.; Shi, Z.; Duan, N.; Fang, C.; Dai, S.; Wang, Z. Aptamer-Based Fluorescence Biosensor for Chloramphenicol Determination Using Upconversion Nanoparticles. Food Control 2015, 50, 597–604.


18

Page 19 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(22) Hao, L.; Gu, H.; Duan, N.; Wu, S.; Wang, Z. A Chemiluminescent Aptasensor for Simultaneous Detection of Three Antibiotics in Milk. Anal. Methods 2016, 8 (44), 7929– 7936. (23) Mehta, J.; Van Dorst, B.; Rouah-Martin, E.; Herrebout, W.; Scippo, M.-L.; Blust, R.; Robbens, J. In Vitro Selection and Characterization of DNA Aptamers Recognizing Chloramphenicol. J. Biotechnol. 2011, 155 (4), 361–369. (24) Chen, L.; Ji, F.; Xu, Y.; He, L.; Mi, Y.; Bao, F.; Sun, B.; Zhang, X.; Zhang, Q. High-Yield Seedless Synthesis of Triangular Gold Nanoplates through Oxidative Etching. Nano Lett. 2014, 14 (12), 7201–7206. (25) Qi, P. H.; Hiskey, J. B. Electrochemical Behavior of Gold in Iodide Solutions. Hydrometallurgy 1993, 32, 161–179. (26) Chow, A.; Beamish, F. E. Studies of Titrimetric and Spectrophotometric Methods for the Determination of Gold. Talanta 1963, 10 (8), 883–890. (27) Kireev, S. V.; Shnyrev, S. L. Study of Molecular Iodine, Iodate Ions, Iodide Ions, and Triiodide Ions Solutions Absorption in the UV and Visible Light Spectral Bands. Laser Phys. 2015, 25 (7), 075602. (28) Winger, R. J.; König, J.; House, D. A. Technological Issues Associated with Iodine Fortification of Foods. Trends Food Sci. Technol. 2008, 19 (2), 94–101. (29) Zhu, Y.; Li, C.; Zhang, J.; She, M.; Sun, W.; Wan, K.; Wang, Y.; Yin, B.; Liu, P.; Li, J. A Facile

FeCl3/I2-Catalyzed

Aerobic

Oxidative

Coupling


Reaction:

Synthesis

of

19


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 30

Tetrasubstituted Imidazoles from Amidines and Chalcones. Org. Lett. 2015, 17 (15), 3872– 3875. (30) Li, F.; Wang, J.; Lai, Y.; Wu, C.; Sun, S.; He, Y.; Ma, H. Ultrasensitive and Selective Detection of Copper (II) and Mercury (II) Ions by Dye-Coded Silver Nanoparticle-Based SERS Probes Biosens. Bioelectron. 2013, 39, 82–87. (31) Meites, L. Idometric Determination of Copper. Anal. Chem. 1952, 24 (10), 1618–1620. (32) Chen, W. M.; Wu, X. S.; Geng, J. F.; Chen, J.; Chen, D. B.; Jin, X.; Jiang, S. S. An Accurate Method of Iodometric Titration to Measure Copper Valence of High-Tc Superconductors. J. Supercond. 1997, 10 (1), 41–44. (33) Japan Drinking Water Regulations. http://www.mhlw.go.jp/stf/seisakunitsuite/bunya/ topics/bukyoku/kenkou/suido/kijun/kijunchi.html (accessed 20170409). (34) Table of Regulated Drinking Water Contaminants. https://www.epa.gov/ground-water-anddrinking-water/table-regulated-drinking-water-contaminants (accessed 20170409). (35) Qiao, C.; Qu, X.; Yang, Q.; Wei, Q.; Xie, G.; Chen, S.; Yang, D. Instant High-Selectivity Cd-MOF Chemosensor for Naked-Eye Detection of Cu(II) Confirmed using in Situ Microcalorimetry. Green Chem. 2016, 18 (4), 951–956. (36) Database of Water Quality of Aqueduct. http://www.jwwa.or.jp/mizu/list.html (accessed 20170409). (37) Liu, J. Adsorption of DNA onto Gold Nanoparticles and Graphene Oxide: Surface Science and Applications. Phys. Chem. Chem. Phys. 2012, 14 (30), 10485–10496.


20

Page 21 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(38) Kimura-Suda, H.; Petrovykh, D. Y.; Tarlov, M. J.; Whitman, L. J. Base-Dependent Competitive Adsorption of Single-Stranded DNA on Gold. J. Am. Chem. Soc. 2003, 125 (30), 9014–9015. (39) Pilehvar, S.; Mehta, J.; Dardenne, F.; Robbens, J.; Blust, R.; De Wael, K. Aptasensing of Chloramphenicol in the Presence of Its Analogues: Reaching the Maximum Residue Limit. Anal. Chem. 2012, 84 (15), 6753–6758. (40) Cho, H.; Yeh, E.C.; Sinha, R.; Laurence, T. A.; Bearinger, J. P.; Lee, L. P. Single-Step Nanoplasmonic VEGF165 Aptasensor for Early Cancer Diagnosis. ACS Nano 2012, 6 (9), 7607–7614. (41) Hammett-Stabler, C. A.; Johns, T. Laboratory Guidelines for Monitoring of Antimicrobial Drugs. Clin. Chem. 1998, 44 (5), 1129–1140.


21


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 30

Figure 1. (A) Absorption spectra and (B) TEM images of AuNPLs after I–-mediated etching with 0, 10, and 1000 µM Cu(NO3)2 at room temperature for 30 min.


22

Page 23 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. Effect of KI on the AuNPL etching. (A) Absorption spectra of AuNPLs after I–mediated etching without Cu(NO3)2 at different concentrations of KI at room temperature for 30 min. The inset shows photographs of the etching solution. (B) Absorption spectra of AuNPLs after I–-mediated etching with 1 mM Cu(NO3)2 at different concentrations of KI. The inset shows photographs of the etching solutions. (C) Relationship between the absorption spectral change and the KI concentration with and without Cu(NO3)2. The absorption spectral data shown in (A) and (B) were used. The error bars are the standard deviation of the mean from three measurements.


23


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 30

Scheme 1. Schematic representation of the proposed mechanism for the Cu2+-assisted I–mediated AuNPL etching.


24

Page 25 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. (A) Photographs and (B) absorption spectra of the reaction solution of the I–-mediated AuNPL etching with 2 mM KSCN and different concentrations of Cu(NO3)2 at room temperature for 2.5 min. (C) Calibration curve for the Cu2+-assisted I–-mediated AuNPL etching. Inset: the linearity between the logarithmic concentration of Cu2+ in µM and the normalized absorbance response. The data shown in (B) were used. A630X and A6300 are the normalized absorbance of AuNPLs at 630 nm in the presence and absence of Cu2+, respectively. The final concentrations of AuNPL and KI were 32 pM and 19 µM, respectively. The red line shown in the inset represents the linear least-squares fit for each data set. The error bars are the standard deviation of the mean from three measurements.


25


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 30

Figure 4. (A) Photographs and (B) absorbance changes of the reaction solution of the metal-ionassisted I–-mediated AuNPL etching with 2 mM KSCN and 100 µM of various metal salts at room temperature for 2.5 min. Mix stands for the reaction solution containing all the metal salts except for Cu(NO3)2 at 100 µM each. The error bars are the standard deviation of the mean from three measurements.


26

Page 27 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. Absorption spectra of the reaction solution (A) before and (B) after the Cu2+-assisted I– -mediated AuNPL etching with 2 mM KSCN under the different conditions at room temperature for 5 min. The inset shows photographs of the etching solution. (C) Schematic representation of the proposed mechanism for the CAP detection based on the Cu2+-assisted I–-mediated AuNPL etching.


27


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 30

Figure 6. (A) Photographs and (B) absorption spectra of the reaction solution of the AuNPL etching with 1.6 mM Cu(NO3)2, 1 mM KSCN, and 100 nM aptamer in the presence of various amounts of CAP at room temperature for 10 min. (C) Calibration curve for the Cu2+-assisted I–mediated AuNPL etching in the presence of CAP. Inset: the linearity between the logarithmic concentration of CAP in µM and the normalized absorbance response. The data shown in (B) were used. A610X and A6100 are the normalized absorbance of AuNPLs at 610 nm in the presence and absence of CAP, respectively. The final concentrations of AuNPL and KI were 64 pM and 38 µM, respectively. The red line shown in the inset represents the linear least-squares fit for each data set. The error bars are the standard deviation of the mean from three measurements.


28

Page 29 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7. (A) Photographs and (B) absorbance changes of the reaction solution of the AuNPL etching with 1.6 mM Cu(NO3)2, 1 mM KSCN, and 100 nM aptamer in the presence of 50 µM of various antibiotics (AMP: ampicillin; TEC: tetracycline; and STR: streptomycin) at room temperature for 10 min. Mix stands for the solutions including all the antibiotics except for CAP at 50 µM each. The error bars are the standard deviation of the mean from three measurements.


29


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 30

For TOC

Cu2+-assisted Etching


30

Iodine-Mediated Etching of Triangular Gold Nanoplates for

Recommend Documents