A Rational Calibration Strategy for Accurate and Sensitive Colorimetric

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A Rational Calibration Strategy for Accurate and Sensitive Colorimetric Detection of Iodide and L-thyroxine Based on Gold Triangular Nanoplates Hang Ren, Tong Li, Rui Ling, Junmin Bi, Chenling Zhang, Zhenglong Wu, and Weidong Qin ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.9b02129 • Publication Date (Web): 18 Aug 2019 Downloaded from pubs.acs.org on August 19, 2019

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ACS Sustainable Chemistry & Engineering

A Rational Calibration Strategy for Accurate and Sensitive Colorimetric Detection of Iodide and L-thyroxine Based on Gold Triangular Nanoplates

Hang Ren a, Tong Li a, Rui Ling a, Junmin Bi a, Chenling Zhang b, Zhenglong Wu c, Weidong Qin a,*

a College

of Chemistry, Beijing Normal University, No. 19, XinJieKouWai Street,

Beijing 100875, P. R. China b

Institute of Hydrogeology and Environmental Geology, Chinese Academy of

Geological Sciences, No. 92, East Zhongshan Road, Zhengding, Hebei, 050803, P. R. China c Analytical

and Testing Center, Beijing Normal University, No. 19, XinJieKouWai

Street, Beijing 100875, P. R. China

* Corresponding authors: Weidong Qin, E-mail: [email protected]; Tel: +86-10-58802531

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ABSTRACT We developed a sensitive and accurate colorimetric method to detect iodide (I ― ) and L-thyroxine by etching gold triangular nanoplates (AuTNPs) in the presence of H2O2. The morphological changes of the AuTNPs resulted in vivid color variations of the nanoprism dispersion, accompanied by a blue shift of the in-plane localized surface plasmon resonance (LSPR) peak, enabling visual and photometric sensing. To improve the accuracy and the linear range, the overlapping out-of-plane and in-plane LSPR peaks of the AuTNPs were deconvoluted, and a new calibration model was established by plotting the square of the in-plane LSPR wavelength shift against the concentration of the analytes. Under the optimum conditions, the limits of detection (LODs) for iodide reached 1 μM and 50 nM by naked eye and photometry, respectively, and the corresponding LODs for L-thyroxine were 200 and 13.7 nM. Importantly, improved accuracy and linear range were obtained by the new data processing strategy. The method was applied in detecting iodide in tap and drinking water samples and L-thyroxine in pharmaceutical tablets, indicating its potential for real sample analysis.

KEYWORDS: Gold triangular nanoplates; Colorimetry; Iodide; L-Thyroxine; Lightinduced deiodination; Etching; Deconvolution

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INTRODUCTION Iodine species is known as an essential micronutrient in human thyroids, where the thyroid hormone (T4) is synthesized. Deficiency of iodine results in goiter, cretinism and sterility, whereas excessive iodine intake can cause thyroid autoimmunity (Hashimoto's thyroiditis) and even some thyroid cancers.1 To address this issue, the US Food, Drug Administration (FDA) and the World Health Organization (WHO) recommend a daily value of 150 μg for iodine,2 and 130 countries over the world have mandatory legislation for salt iodization.3 In China, the use of iodized table salt was implemented in the early 1980s, and a concentration of 150 μg/L (1.2 μM) was recommended in drinking water.4 Drinking water is the most common source for iodine administration, and detecting iodine species in drinking waters is a crucial step for solving the problem of endemic thyroid dysfunctions. On the other hand, hypothyroidism is often clinically treated using pharmaceutical formulations containing thyroid hormones, among which levothyroxine (L-T4) is the most commonly prescribed.5 However, L-T4 possesses a low therapeutic index; overdose may lead to adverse cardiac and/or metabolic effects. Therefore, it is important to verify whether the real content of L-T4 in a drug is in consistent with the claimed value.

Gold nanomaterials have high extinction coefficients at their local surface plasmon resonance (LSPR) absorption bands. Importantly, the LSPR wavelengths of these gold nanomaterials are dependent on their sizes, shapes and interparticle distances,6, 7 as well as on the chemical and physical properties of the dispersion medium.6, 8-10 These unique properties render gold nanomaterials ideal chromogenic components in cost3



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effective, rapid colorimetric detection.11, 12 Gold triangular nanoplates (AuTNPs) are two-dimensional anisotropic nanostructures. When truncated, the wavelength of the in-plane dipole LSPR becomes blue-shifted as the electron density across the nanoprism surface changes.13 Because human eyes are more sensitive to color variations than to optical density changes,14, 15 the AuTNP-based method is expected to have high naked-eye detection sensitivity. Nonetheless, only a limited number of such AuTNP-based sensing applications have been reported.16

Another family of Au-based nanostructures often employed for colorimetric detection are gold nanorods (AuNRs).17, 18 As elongated nanoparticles, AuNRs are characterized by their easily-tuned aspect ratios (length to width) and long longitudinal LSPR wavelengths extending to the near-infrared band, potentially providing wide response ranges. However, compared to the approaches based on AuNRs, the AuTNP-etching based colorimetry used in this experiment has two advantages. (1) Preparation of the AuTNPs is facile. While seeding-growth of AuNRs usually takes hours, the seedless protocol can produce high-quality AuTNPs within 10 min.19 (2) Owing to their unique geometric shapes, colorimetry based on etching of AuTNPs is able to provide higher sensitivity for low-concentration analytes (which will be discussed in R&D section).

One inherent limitation for the gold nanomaterial-based colorimetry is its poor linearity. To address this problem, a variety of empirical calibration relationships have been proposed in quantitative analysis, for instance, 𝐴λ1/𝐴λ2 versus C, 𝐴λ versus log 4


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∆λ

C, 𝐴λ1/𝐴λ2 versus log C, Δλ versus C, ΔA versus C and log (∆λ𝑚𝑎𝑥) versus log C (where, A, λ, Δλ and C are absorbance, wavelength, wavelength shift and concentration of analyte, respectively).20 By comparison, the situation is more complex for AuTNPs. Since the in-plane dipole and the out-of-plane dipole LSPR peaks are relatively close, intensive etching causes a large blue shift of the longwavelength peak, potentially leading to peak overlapping and thereby making it difficult to read out the accurate wavelength values. Therefore, it is a challenge to construct calibration curves with good linearity and wide range for accurate quantitation using AuTNPs as colorimetric substrates. In this context, exploring new data processing approaches is desirable.

Herein, we report a colorimetric method for directly determining iodine species by iodide-mediated etching of AuTNPs and indirectly determining L-T4 by adopting a UV-photodegradation pretreatment. The influences of hydrogen peroxide (H2O2) concentration, hydrochloric acid (HCl) concentration, etching time and dehalogenation time were investigated and optimized. Importantly, on the basis of the etching mechanisms, the relationship between the wavelength shift of the LSPR and the concentration of iodide was studied, and a model for calibration was established. Finally, the method was applied to detect iodine species in drinking water and tap water as well as L-T4 in tablets. This research extends the application scope of both light-induced dehalogenation and AuTNP-based colorimetry, provides an alternative detection method for iodinated organic compounds, and shows promising potential in environmental analysis and quality control in the pharmaceutical industry.

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EXPERIMENTAL SECTION Chemicals Gold (III) chloride trihydrate (HAuCl4•3H2O) was purchased from Sinopharm Chemical Reagent (Shanghai, China). L-Ascorbic acid (AA) and cetyltrimethylammonium chloride (CTAC) were purchased from J&K Scientific (Beijing, China). Sodium hydroxide (NaOH) and potassium iodide (KI) were products of Xilong Scientific Co., Ltd. (Shanghai, China). L-Thyroxine sodium [sodium o-(4hydroxy-3,5-diiodophenyl)- 3,5-diiodo-L-tyrosinate] was obtained from Sangon Biotech (Shanghai, China), H2O2 (30 wt%) and HCl were supplied by Beijing Chemical Plant (Beijing, China). Ultrapure water was prepared by a Milli-Q system (Millipore, MA, USA) and used throughout all experiments.

Synthesis, Purification and Characterization of AuTNPs AuTNPs were synthesized following a one-pot seedless growth protocol reported previously with minor modifications (refer to Supporting Information).19 The asprepared AuTNP dispersion was purified by removing the background constituents that would potentially cause errors in the detection, e.g., AA, I ― and HAuCl4. In brief, 10.00 mL of AuTNP dispersion was centrifuged at 10000 × g for 15 min. After 9.90 mL of the supernatant aqueous phase was carefully removed, the AuTNPs were redispersed in 9.90 mL of 0.01 M CTAC solution so that well-dispersed colloids were obtained due to the interparticle electrostatic repulsion. After four redispersioncentrifugation cycles, the AuTNPs were finally dispersed in 2 mL of 0.01 M CTAC solution. With this procedure, the background reagents in the original AuTNP 6


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dispersion were subjected to a 2 × 109-fold dilution such that the residues would not bring about significant interference. For example, the concentration of I ― , originally 75 μM, was reduced to 3.75 × 10-14 M.

The extinction spectra of the AuTNPs were recorded from 400 to 800 nm at a resolution of 1 nm on a UV-2450 UV-vis spectrophotometer (Shimadzu, Kyoto, Japan) using a 1-cm optical path quartz cuvette. The morphology of the AuTNPs was observed by a TF20 (200 kV, FEI Tecnai, Oregon, USA) transmission electron microscope (TEM). Photographs of the AuTNP dispersions before and after etching were taken using a built-in smartphone camera on an iPhone 6 (Apple Incorporation, CA, USA).

Pretreatment of Real Samples Tap water from the lab (Chemistry Building, Beijing Normal University, Beijing, China) and drinking water bought from a local supermarket were filtered through 0.22-μm filters prior to analysis. Five L-T4 tablets (50 μg L-T4/tablet, Euthyrox, Merck, Darmstadt, Germany) were weighed and ground, and an aliquot of the powders equivalent to 50 μg of L-thyroxine sodium was weighed and dissolved in 50 mL of 20 mM NaOH solution under ultrasonication. The resultant suspension was centrifuged at 10000 × g for 10 min, and supernatants of appropriate volumes were collected for the subsequent dehalogenation experiments.

Light-Induced Dehalogenation Before the experiment, 4 mL of the L-T4 standard solution (prepared in 20 mM 7



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NaOH) or the as-prepared tablet sample solution was transferred to a 5-mL Pyrex bottle. No other reagents were added before light irradiation. The solution was placed 15 cm in front of a 175 W mercury arc lamp (Yugu Electronics, Guangzhou, China) and stirred at 2000 rpm. After irradiation, the solution was neutralized with 100 mM HCl, filtered with a 0.22-μm filter, and stored in the dark at 4 °C before use.

Detection of 𝐈 ― and L-T4 by Iodide-Mediated Etching Iodide-containing standards and water samples, and deiodinated L-T4 standards and L-T4 tablet solutions were used as test solutions, whereas ultrapure water was employed as a reagent blank. Briefly, in a 2-mL clean centrifuge tube, 1000 μL of test solution or reagent blank was mixed with 100 μL of AuTNP dispersion, followed by 20 μL of 100 mM HCl and 80 μL of 1 M H2O2 (the pH value of the final solution was 2.44). The resultant AuTNP solution was mixed thoroughly and incubated in a water bath at 50 °C for etching. Ten minutes later, the solution was cooled to room temperature in the open air. The absorption spectra of the as-treated AuTNP solution were photometrically measured in triplicate. The average wavelengths of the in-plane dipole LSPR peaks of AuTNPs etched in the presence of the test solutions (λ) and the reagent blank (λ0) were recorded, from which the wavelength shifts were obtained by Δλ = λ0 - λ. Calibration curves were established by plotting (Δλ)2 against the corresponding concentrations of the analytes in the standard solutions.

RESULTS AND DISCUSSION Sensing Mechanisms Iodide has been applied in etching of gold nanostructures for various purposes.21-25 In 8


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the presence of H2O2, the inorganic iodide ion-mediated oxidative etching of AuTNPs can be represented by the following reactions:

2I − + 2H 2+ + H2 O2 → I2 + 2H2 O

(1)

I2 + I − → I3−

(2)

2 Au0 + I3− + I − → 2 AuI2−

(3)

I ― is oxidized to I2 by H2O2 (Eq. 1) and then forms I3― (Eq. 2), which oxidizes A u0 to AuI2― (Eq. 3). The etching mechanism was investigated and the products of Au+-halide complexes were verified by mass spectrometry in several publications.23-25 In our experiment, the product of AuI2― was also detected after the etching reactions (Figure S1). Moreover, it was proposed that cetyltrimethylammonium ion (CTA+) could form ion-association compounds with the Au+-halide complexes23, 24, favoring the reaction in Eq. 3. Etching of the AuTNPs can be characterized by colorimetry. As shown in Figure 1A(a), the as-prepared AuTNPs possessed out-of-plane dipole- and in-plane dipole LSPR peaks located at approximately 540 and 620 nm, respectively. Introduction of either I ― (Figure 1A, b) or H2O2 (Figure 1A, c) alone did not induce any wavelength shift or color change of the dispersion, implying the unsuccessful etching of the AuTNPs. However, when I ― and H2O2 were introduced simultaneously to the dispersion, a significant blue shift of the in-plane dipole LSPR band was detected, and a color change of the AuTNPs was observed (Figure 1A, d), which were the consequences of morphological transitions of the AuTNPs. The phenomena in conditions c and d of Figure 1A were similar to the results reported by other researchers.22 Although H2O2 possessed strong oxidation ability in acidic 9



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solution, the redox potentials for AuCl4― /Au0 and AuCl2― /Au0 are 1.002 and 1.154 V, respectively, higher than the corresponding values for AuI4― /Au0 (0.560 V) and AuI2― /Au0 (0.578 V).26, 27 Moreover, compared to Cl ― , l ― bound much more strongly with Au0 on AuTNPs by chemisorption, inducing corrosion or reconstruction of the adsorbed facets.22 Therefore, in acidic conditions, H2O2 initialized the iodide ion-mediated oxidative etching of AuTNPs, and the morphological changes of the nanostructures were reflected by colorimetry, which was not interfered by chloride.

Figure 1 (A) Absorption spectra of AuTNPs after etching with (a) ultrapure water, (b) 1 mM KI and 2 mM HCl, (c) 200 mM H2O2 and 2 mM HCl, and (d) 0.015 mM KI, 200 mM H2O2 and 2 mM HCl. (B) Absorption spectra of AuTNPs after etching with (e) intact L-T4 and (f) 2 μM photodegraded L-T4 in the presence of 200 mM H2O2 and 2 mM HCl. The insets are the images of the corresponding AuTNP dispersions in cuvettes. The high-resolution TEM images of AuTNPs: C, intact; D, etched by 2 μM photodegraded L-T4; E, etched by 20 μM photodegraded L-T4. The scale bars are 100 nm. The reaction was conducted at 50 °C for 10 min.

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Each L-thyroxine molecule contains four iodine atoms. UV irradiation led to sequential cleavage of C-I bonds on hydroxyphenoxy and phenylalanine groups of LT4, yielding iodide,5, 28 which can be detected thereafter by the present sensing system. As shown in Figure 1B, with the addition of intact L-T4, the AuTNP dispersion remained the original color, and the UV-vis absorption spectra did not change, indicating that no etching occurred in the absence of iodide. However, introducing the photodegraded L-T4 solution turned the AuTNP dispersion from blue to red (Figure 1B, inset), accompanied by a blue shift of the in-plane dipole LSPR peak. To further elucidate the mechanism, TEM analysis was employed. Figure 1C indicates that sharp AuTNPs with edge lengths of approximately 60 nm and thicknesses of approximately 15 nm were obtained by the one-pot seedless growth protocol, and were truncated in the presence of 2 μM photodegraded L-T4 (Figure 1D). According to the Gibbs–Thomson effect, a convex surface has higher surface energy than a flat surface. In this context, the AuTNP edges are more stable than the sharp “tips”, where the corrosion occurs more easily, resulting in "snipped" triangular nanoplates. Nonetheless, the etching taking place on the edges cannot be ignored. Nanoprisms are twinned {111} crystals with convex and concave side facets,29 and the convex side facets have higher surface energy and lower stability because of the Gibbs–Thomson-like effect. The above mechanisms suggest that etching preferentially occurs on the sharp “tips” of the nanoprisms, followed by the convex side facets. Therefore, the AuTNPs undergo morphological transitions starting from sharp triangular prisms to “snipped” triangular, hexagonal and, ultimately, disk-like nanoplates (Figure 1E) as the etching process progresses.

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Strategies for Quantitation The wavelength shift (Δλ) of the in-plane dipole LSPR reflects the extent of etching,30 which is represented by the average edge length (noted le, Figure 2A) of the snips removed from the triangular prisms. For this reason, Δλ is often employed as a parameter in constructing calibration curves.31 Nevertheless, the quantitation usually suffers from the limitations of narrow linearity and, occasionally, inaccuracy.

Two aspects contribute to these limitations. One is the difficulty in accurately measuring the wavelength of the in-plane dipole LSPR peak, particularly when it severely overlaps with the out-of-plane dipole LSPR peak (exemplified in the left trace of Figure 2B). To solve this problem, the overlapping peaks should be deconvoluted. Another is the calibration model itself. If the analyte is the etchant that directly leads to corrosion of the gold nanoprisms, a calibration curve depending on the Δλ–C relation might not be the best choice.

Assuming that the volume of the etching solution is V and the concentration of the etchant is 𝐶, the amount of etchant is 𝑉 × 𝐶. Assuming that there are N identical AuTNPs with thickness of ℎ in the etching solution and, after etchant-depletion reaction, the three snips removed from each AuTNP are all equilateral triangle prisms with an average edge length of le, the total volume of the etched part of the nanoprisms can be expressed as 3 ×

3 2 4 𝑙𝑒

× ℎ × 𝑁. By assuming that N, ℎ and V are

constants, one can derive that 𝑙𝑒2 ∝ 𝐶.

Because Δλ can be easily measured by colorimetric analysis, to establish a workable 12


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calibration model, the relationship between Δλ and 𝑙𝑒 should be studied. To this end, an FDTD method was employed to simulate the extinction wavelength of the in-plane dipole LSPR of the 60-nm-edge × 15-nm-thickness AuTNPs, which were used in our experiments, with snips of lengths varying from 0 to 16 nm. The simulated wavelength for the intact AuTNPs was 623 nm (Figure S2), consistent with the experimental results (ca. 620 nm). Moreover, the plot of Δλ versus 𝑙𝑒 demonstrated good linearity, with R2 = 0.9925 (Figure S3). The above results suggest that the (Δλ)2– C regression can be used to establish a calibration curve (Figure 2C). Note that although the theoretical simulations suggest a wide linear range between Δλ and 𝑙𝑒, one should bear in mind that a high extent of etching would result in rounding AuTNPs and, consequently, deviation from the (Δλ)2–C linearity. However, the (Δλ)2–C regression can provide better linearity than that of Δλ–C, particularly for the cases of low- and medium-degree etched AuTNPs, which are transformed into snipped triangular or hexagonal nanoplates.

Figure 2 Schematic illustration of the quantitation strategy. (A) Iodide-mediated etching of gold nanoprisms; (B) deconvolution of the overlapping LSPR peaks, in 13



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which the blue and red dotted lines are the original extinction spectra obtained from intact and etched AuTNPs, respectively. The corresponding solid lines are extracted in-plane and out-of-plane dipole LSPR peaks, and the in-plane dipole LSPRs have longer wavelengths than the out-of-plane dipole LSPRs. The inset indicates that after peak fitting, the wavelength of the in-plane dipole LSPR peak is different from the merged one, revealing that deconvolution is helpful in enhancing accuracy. (C) a (Δλ)2–C regression based on the deconvoluted data.

Theoretical Comparison with AuNRs in Sensitivity Because the aspect ratio determines the wavelength of the lower-energy LSPR band of an anisotropic nanostructure, to investigate rationally, we choose 60-nm-length × 15-nm-width AuNRs for comparison, which have the same aspect ratio as the AuTNPs used in this work. The detailed calculation and simulation results are presented in the Supporting Information. First, according to the etching mode of AuNRs (Figure S4), a linear relation between Δλ and C was deduced. Second, under identical etching parameters, the etched edge lengths for AuTNPs and the corresponding etched lengths for AuNRs were calculated (Table S1). Third, the corresponding LSPR wavelengths of etched AuNRs were predicted by FDTD simulation (Figure S5) and the wavelength shifts were calculated (Table S1, Figure S6). It was found that the simulated wavelengths of AuNRs were close to those having the same aspect ratios,32 suggesting the effectiveness of the FDTD parameters. Moreover, owing to the different morphologies, the wavelength shifts in AuTNPs and AuNRs varied differently with the etching extent, which was represented by etched volume of the nanostructures. Figure S7 indicates that larger wavelength shifts are 14


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obtained using AuTNPs as colorimetric substrates than using AuNRs when the etched volume is less than 700 nm3 per nanostructure. The results imply that if both nanostructures are used for the detection of iodide, which acts as an etchant, AuTNPs can provide a lower detection limit than AuNRs.

Optimization of Experimental Conditions To improve the analytical performance of the method, the crucial experimental parameters, i.e., H2O2 concentration, HCl concentration and etching time, were investigated and optimized based on the LSPR wavelength shift of the AuTNPs caused by 10 μM I ― .

The wavelength shift increased gradually with H2O2 concentration in the range of 0.4 mM–200 mM, and leveled off when the concentration of H2O2 was further increased (Figure S8A). A higher H2O2 concentration favored the oxidation of I ― to I2, and the experiments suggest that equilibrium was reached at a H2O2 concentration of 200 mM. The acidity of the etching solution was adjusted with HCl. Introducing HCl from 0 (pH 4.86) to 0.5 mM (pH 3.15) sharply increased the wavelength shift, and the highest sensitivity was obtained when the concentration reached 2 mM (pH 2.44, Figure S8B). The concentration of HCl played an important role in etching, because acidic conditions are favorable for the oxidation of iodide ions to iodine by H2O2. Regarding the etching time, the wavelength shift increased during the etching process, reaching a maximum at 10 min (Figure S8C). It should be noted that within the concentration ranges of iodide and deiodinated L-T4 investigated in this report, no additional wavelength shift was observed with prolonged etching time, revealing that 15



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iodide species were depleted within the 10-min etching reaction. Based on the above experiments, the concentrations of H2O2 and HCl in the etching solution were fixed at 200 mM and 2 mM (pH 2.44), respectively, and the etching time was 10 min for the subsequent experiments.

Interference Studies The influences of the potentially interfering ions, including F ― , Cl ― , Br ― , Ac ― , C2O4― , CO32 ― , SO32 ― , SO42 ― , PO43 ― , Na + , Mg2 + , Ba2 + , Co2 + , Ni2 + , Cu2 + , Zn2 + , Hg2 + , Pb2 + , Cd2 + and Fe3 + , were studied under the optimal conditions. As shown in Figure 3 (the corresponding UV-vis spectra are shown in Figure S9), 10 μM I ― could trigger a large LSPR peak shift, along with a color change of the AuTNP dispersion from blue to purple. In contrast, the presence of the foreign ions, i.e., a 4-fold concentration of Br ― , 10-fold concentrations of other anions (Figure 3A) and 20-fold concentrations of metal ions (Figure 3B), did not result in significant interference with the detection. The results showed the excellent selectivity of this sensing system, which is attributed to the strong binding strength between Au0 and I ― and the strong oxidation tendency of AuI ― .22 The reason for the slight colorimetric response to Br ― ions may arise from their affinity for Au0 surfaces and from the spontaneous oxidation tendency of AuBr ― . Nonetheless, compared with those of I ― , both the binding strength of Br ― with Au0 and the oxidation tendency of AuBr ― are much weaker.33 Bromide is prohibited in drinking water, but it exists at trace levels in surface water. According to a WHO report,34 the maximal bromide content in drinking water for infants was 2 mg/L, corresponding to a molar concentration of 25 μM, which is lower than the 40 μM concentration used in this 16


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experiment. Mercury ions oxidized Au0 to Au+ in the presence of Cl ― at the beginning of the etching reaction,35 leading to a colorimetric change. In fact, the maximal content of Hg2 + in drinking water was set to 1 ng/mL (~ 5 nM) by the Chinese government,36 and 2 ng/mL (~ 10 nM) by the United States Environmental Protection Agency guidelines,37 both of which are at least 4 orders lower than the concentration of Hg2 + employed in the experiment. Although Fe3

+

and Cu2

+

could catalyze the conversion of H2O2 into hydroxyl radicals (HO·),38 which were efficient etchants for the AuTNPs, chloride in the etching solution could react with HO· to form the much less reactive species 𝐶𝑙·2― in acidic environments (refer to Supporting Information for detailed equations).39 Moreover, complexation between Fe3

+

and Cl - would also impede the Fenton-like reaction.40 Hence, the results

suggest that the method can be applied to sensing I ― in drinking water.

Figure 3 Selectivity of the AuTNP-based iodide sensor under the optimal conditions. (A) Wavelength shift of the AuTNP solution in the presence of 10 μM I ― , 4-fold Br ― , and 10-fold other anions. (B) Wavelength shift of the AuTNP solution in the presence of 10 μM I ― and 20-fold metal ions, i.e., Na + , Mg2 + , Ba2 + , Co2 + , Ni2 + , Cu2 + , Zn2 + , Hg2 + , Pb2 + , Cd2 + and Fe3 + . The error bars represent the standard deviations of three independent measurements. The inset images show the 17



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corresponding color changes of the solutions.

Performance of the Method Iodide The color changes caused by I ― from 1 μM could be readily distinguished by the naked eye (Figure S10A), allowing visual detection of iodide concentrations in drinking water that is in compliance with the guideline of the Chinese government, in which the iodine content was set to 150 μg/L (1.2 μM).4 The absorbance spectra indicate that the wavelength of the in-plane dipole LSPR of the AuTNPs blue-shifted progressively with increasing I ― concentration from 0 to 30 μM (Figure S10B). Figure 4B depicts a good linear relationship (R2 = 0.9715) between (Δλ)2 and CI ― over the range of 0.20–30 μM, which shows a wider linear range and better linearity than that of the Δλ–CI ― plotting (Figure 4A), indicating that our calibration strategy is effective. Nevertheless, it was found that the peaks corresponding to the in-plane and the out-of-plane dipole plasmon resonances gradually overlapped with increasing iodide concentration, which might give rise to errors in wavelength measurement. To improve accuracy, the partially merged peaks were deconvoluted by Gaussian fitting using PeakFit software (SeaSolve Software, MA, USA). The overlapping peaks were successfully resolved, with R2 values between 0.9980 and 0.9998 (Table S2). Using the wavelength values of the extracted in-plane dipole LSPR peak, we found that the reconstructed plot of (Δλ)2 against CI ― (Figure 4C) had better linearity (R2 = 0.9955) over the range of 0.2−30μM, enabling more accurate measurement.

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The limit of detection (LOD) of this colorimetric sensor for I ― , defined as the concentration giving a signal-to-noise ratio of 3, was estimated to be 50 nM (6.3 μg/L); the limit of quantification (LOQ), at a signal to noise ratio of 10, was determined to be 0.166 μM. As listed in Table S3, our method is more sensitive than the gold nanosphere-based colorimetric assays,41, 42 the silver-coated gold nanobipyramid-based method,31 and the electrochemical method.43, 44 Strikingly, it is even comparable to high-performance liquid chromatography (HPLC).45 The linear range and correlation coefficient of our calibration curve are among the best of the gold nanomaterial-based colorimetric methods (Table S3).

To further demonstrate the effectiveness of our calibration and deconvolution strategies, AuTNPs of larger dimensions were prepared (averaging 70 nm in edge length, refer to Figure S11 of Supporting Information for TEM images). Owing to the longer LSPR wavelength (657 nm versus 620 nm for the 60-nm AuTNPs), a wider range for the (Δλ)2–C regression with good linearity was obtained (2–120 μM, R2 = 0.9914, Figure S12 of the Supporting Information). Through the new calibration strategies, the quantitation performances of the AuTNP-based colorimetry were substantially improved.

Figure 4 Influences of regression and deconvolution strategies. In (A) and (B), Δλ 19



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values were obtained from the original spectra; in (C), Δλ values were obtained from the extracted spectra.

L-T4 To quantitatively detect L-T4, the influence of light irradiation time on the deiodination efficiency was investigated. Our experiments indicated that an irradiation time of 180 min afforded complete deiodination of L-T4 (refer to Figure S13 and Figure S14 in the Supporting Information). Figure 5A indicates that the presence of 200 nM L-T4 in the etching solution produced distinguishable color changes. The UVvis spectra depict that the LSPR peak gradually blue-shifted with increasing L-T4 concentration (Figure 5B). The LOD and LOQ by photometry were 13.7 and 45.6 nM, respectively, suggesting that the sensing system can be used for quantitative analysis of L-T4. Additionally, the regression of (Δλ)2 versus the concentration of LT4 showed good linearity over the range of 0.02–5 μM, with R2 = 0.9905 (inset of Figure 5C). This calibration provides better linearity than the Δλ–C plot (Figure S15). The deviations from linearity at higher L-T4 concentrations may be attributed to the progressive transformation of AuTNPs to disc nanoplates, toward which our calibration model does not work well.

20


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Figure 5 (A) Images and (B) absorption spectra of the AuTNPs treated with etching solutions containing 200 mM H2O2, 2 mM HCl and different concentrations of photodegraded L-T4. (C) (Δλ)2–C relations. The inset shows the calibration curve.

Practical Applications Tap water and drinking water samples spiked with I ― to varying concentrations were chosen for analysis. The water samples without addition of I ― could not induce color changes, suggesting that the I ― concentrations were below the LOD of the photometric method (50 nM). These results may be reasonable. The tap water in the laboratory is from surface water (Kunming Lake). In another lake which is approximately 3 kilometers from the water source, the I ― concentration was 21



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determined to be 80 ± 5 nM by a standard Sandell−Kolthoff reaction method.46 Therefore, the final concentration of iodide in the tap water is likely below 50 nM, because during the disinfection process a considerable fraction of I ― is converted to organic iodides,47, 48 which are not detectable by the direct etching method. The AuTNP-based sensing system could accurately detect I ― spiked in water samples, with recoveries ranging from 91% to 106% (Table 1), indicating its applicability in environmental analysis.

Table 1 Determination of I ― in water samples (n = 6) Sample

Tap water

Drinking water

Added (μM)

0

1.0

5.0

0

1.0

5.0

Found (μM)

nda

0.94

5.3

nda

0.91

4.6

Recovery (%)

94

106

91

92

RSD (%)

2.5

2.6

2.9

2.8

Color

a nd,

not detected.

To demonstrate the applicability of light-induced deiodination/AuTNP-based colorimetry for the detection of L-T4 in complex matrices, we employed commercial thyroxine tablets as an example. For comparison, the tablets were also analyzed by a previously reported HPLC-mass spectrometry (MS) method,49 with slight modification (refer to the Supporting Information for details). The results (Figure S16 and Table S4) indicate that our method has good accuracy and precision (recoveries ≥ 22


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95%, RSD ≤ 2.8%), comparable with those of the HPLC-MS technique, demonstrating its promising applicability in pharmaceutical analysis.

CONCLUSIONS In summary, a colorimetric platform based on AuTNPs was established for the direct sensing of iodide and indirect sensing of L-T4. The AuTNP-based colorimetry method showed high sensitivity and excellent selectivity for visual and photometric detection of iodide. The nonenzymatic light-induced deiodination protocol afforded complete deiodination of the L-thyroxine molecules without introducing any foreign chemicals to the sample, favoring the subsequent selective colorimetric detection. The content of L-T4 in a pharmaceutical formulation was successfully detected, in good agreement with the manufacturer's claimed values and with the results by a HPLC-MS method. More importantly, our data processing strategy incorporating peak deconvolution and (Δλ)2–C regression provided a wider linear range and offered more accurate detection. The results suggest that the method can be applied in the colorimetric sensing of trace iodine species and iodinated organic compounds in the environment and in pharmaceuticals.

ACKNOWLEDGEMENTS This work was supported by the National Natural Science Foundation of China (21575017)

Supporting Information 23



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Synthesis of AuTNPs, mass spectra of the etch products, the process and results of FDTD simulation, optimization of experimental conditions, images and absorption spectra of the AuTNPs with different interfering ions, images and absorption spectra of the AuTNPs etched by different concentrations of iodide, results of the peak deconvolution, comparison of analytical performances, influence of the irradiation time, photodegradation degree of L-thyroxine, the calibration curve between wavelength shift (obtained from the original spectra) and the concentrations of L-T4, HPLC-MS experiments and results, detection of thyroxine in tablet sample solution by the AuTNP-based probe and HPLC-MS.

24


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REFERENCE (1)

Laurberg, P.; Pedersen, I. B.; Knudsen, N.; Ovesen, L.; Andersen, S., Environmental iodine

intake affects the type of nonmalignant thyroid disease. Thyroid 2001, 11 (5), 457-469, DOI 10.1089/105072501300176417. (2)

Trumbo, P. R., FDA regulations regarding iodine addition to foods and labeling of foods

containing

added

iodine.

Am.

J.

Clin.

Nutr.

2016,

104

Suppl

3,

864S-867S,

DOI

10.3945/ajcn.115.110338. (3)

Codling, K.; Rudert, C.; Begin, F.; Pena-Rosas, J. P., The legislative framework for salt

iodization in Asia and the Pacific and its impact on programme implementation. Public Health Nutr. 2017, 20 (16), 3008-3018, DOI 10.1017/S1368980017001689. (4)

Li, J. X.; Wang, Y. X.; Xie, X. J.; Zhang, L. P.; Guo, W., Hydrogeochemistry of high iodine

groundwater: a case study at the Datong Basin, northern China. Environ. Sci.: Processes Impacts 2013, 15 (4), 848-859, DOI 10.1039/c3em30841c. (5)

Kazemifard, A. G.; Moore, D. E.; Aghazadeh, A., Identification and quantitation of sodium-

thyroxine and its degradation products by LC using electrochemical and MS detection. J. Pharmaceut. Biomed. 2001, 25 (5-6), 697-711, DOI 10.1016/S0731-7085(01)00370-3. (6)

Chakraborty, A.; Fernandez, A. C.; Som, A.; Mondal, B.; Natarajan, G.; Paramasivam, G.;

Lahtinen, T.; Hakkinen, H.; Nonappa; Pradeep, T., Atomically Precise Nanocluster Assemblies Encapsulating Plasmonic Gold Nanorods. Angew. Chem. Int. Ed. Engl. 2018, 57 (22), 6522-6526, DOI 10.1002/anie.201802420. (7)

Xu, S.; Ouyang, W.; Xie, P.; Lin, Y.; Qiu, B.; Lin, Z.; Chen, G.; Guo, L., Highly Uniform

Gold Nanobipyramids for Ultrasensitive Colorimetric Detection of Influenza Virus. Anal. Chem. 2017, 89 (3), 1617-1623, DOI 10.1021/acs.analchem.6b03711. (8)

Kim, J. H.; Lee, T. R., Thermo- and pH-Responsive Hydrogel-Coated Gold Nanoparticles.

Chem. Mater. 2004, 16 (19), 3647-3651, DOI 10.1021/cm049764u. (9)

Frost, R.; Wadell, C.; Hellman, A.; Molander, S.; Svedhem, S.; Persson, M.; Langhammer,

C., Core–Shell Nanoplasmonic Sensing for Characterization of Biocorona Formation and Nanoparticle Surface Interactions. ACS Sens. 2016, 1 (6), 798-806, DOI 10.1021/acssensors.6b00156. (10) Langhammer, C.; Larsson, E. M.; Kasemo, B.; Zoric, I., Indirect nanoplasmonic sensing: ultrasensitive experimental platform for nanomaterials science and optical nanocalorimetry. Nano Lett. 2010, 10 (9), 3529-3538, DOI 10.1021/nl101727b. (11) Taghdisi, S. M.; Danesh, N. M.; Ramezani, M.; Emrani, A. S.; Abnous, K., Novel Colorimetric Aptasensor for Zearalenone Detection Based on Nontarget-Induced Aptamer Walker, Gold Nanoparticles, and Exonuclease-Assisted Recycling Amplification. ACS Appl. Mater. Inter. 2018, 10 (15), 12504-12509, DOI 10.1021/acsami.8b02349. (12) Sanromán-Iglesias, M.; Lawrie, C. H.; Schäfer, T.; Grzelczak, M.; Liz-Marzán, L. M., The sensitivity limit of nanoparticle biosensors in the discrimination of single nucleotide polymorphism. ACS Sens. 2016, 1 (9), 1110-1116, DOI 10.1021/acssensors.6b00393. (13) Hu, H. Q.; Zhou, J. Y.; Kong, Q. S.; Li, C. X., Two-Dimensional Au Nanocrystals: Shape/Size Controlling Synthesis, Morphologies, and Applications. Part. Part. Syst. Char. 2015, 32 (8), 796-808, DOI 10.1002/ppsc.201500035. (14) Ma, X.; Lin, Y.; Guo, L.; Qiu, B.; Chen, G.; Yang, H. H.; Lin, Z., A universal multicolor 25



Page 26 of 34

immunosensor for semiquantitative visual detection of biomarkers with the naked eyes. Biosens. Bioelectron. 2017, 87, 122-128, DOI 10.1016/j.bios.2016.08.021. (15) Ma, X.; He, S.; Qiu, B.; Luo, F.; Guo, L.; Lin, Z., Noble Metal Nanoparticle-Based Multicolor Immunoassays: An Approach toward Visual Quantification of the Analytes with the Naked Eye. ACS Sens. 2019, 4 (4), 782-791, DOI 10.1021/acssensors.9b00438. (16) Chang, C. C.; Wang, G. Q.; Takarada, T.; Maeda, M., Iodine-Mediated Etching of Triangular Gold Nanoplates for Colorimetric Sensing of Copper Ion and Aptasensing of Chloramphenicol. ACS Appl. Mater. Inter. 2017, 9 (39), 34518-34525, DOI 10.1021/acsami.7b13841. (17) Lin, Y.; Xu, S. H.; Yang, J.; Huang, Y. J.; Chen, Z. T.; Qiu, B.; Lin, Z. Y.; Chen, G. N.; Guo, L. H., Interesting optical variations of the etching of Au Nanobipyramid@Ag Nanorods and its application as a colorful chromogenic substrate for immunoassays. Sensor. Actuat. B: Chem. 2018, 267, 502-509, DOI 10.1016/j.snb.2018.04.060. (18) Ma, X.; Chen, Z.; Kannan, P.; Lin, Z.; Qiu, B.; Guo, L., Gold Nanorods as Colorful Chromogenic Substrates for Semiquantitative Detection of Nucleic Acids, Proteins, and Small Molecules with the Naked Eye. Anal. Chem. 2016, 88 (6), 3227-3234, DOI 10.1021/acs.analchem.5b04621. (19) Chen, L.; Ji, F.; Xu, Y.; He, L.; Mi, Y. F.; Bao, F.; Sun, B. Q.; Zhang, X. H.; Zhang, Q., Highyield seedless synthesis of triangular gold nanoplates through oxidative etching. Nano Lett. 2014, 14 (12), 7201-7206, DOI 10.1021/nl504126u. (20) Zhang, Y. L.; McKelvie, I. D.; Cattrall, R. W.; Kolev, S. D., Colorimetric detection based on localised surface plasmon resonance of gold nanoparticles: Merits, inherent shortcomings and future prospects. Talanta 2016, 152, 410-422, DOI 10.1016/j.talanta.2016.02.015. (21) Zhang, Z. Y.; Chen, Z. P.; Cheng, F. B.; Zhang, Y. W.; Chen, L. X., Highly sensitive on-site detection of glucose in human urine with naked eye based on enzymatic-like reaction mediated etching of gold nanorods. Biosens. Bioelectron. 2017, 89, 932-936, DOI 10.1016/j.bios.2016.09.090. (22) Weng, G. J.; Dong, X. J.; Li, J. J.; Zhao, J. W., Halide ions can trigger the oxidative etching of gold nanorods with the iodide ions being the most efficient. J. Mater. Sci. 2016, 51 (16), 7678-7690, DOI 10.1007/s10853-016-0050-1. (23) Zhang, Z.; Chen, Z.; Wang, S.; Cheng, F.; Chen, L., Iodine-Mediated Etching of Gold Nanorods for Plasmonic ELISA Based on Colorimetric Detection of Alkaline Phosphatase. ACS Appl. Mater. Inter. 2015, 7 (50), 27639-27645, DOI 10.1021/acsami.5b07344. (24) Zhang, Z.; Chen, Z.; Chen, L., Ultrasensitive Visual Sensing of Molybdate Based on Enzymatic-like Etching of Gold Nanorods. Langmuir 2015, 31 (33), 9253-9259, DOI 10.1021/acs.langmuir.5b02113. (25) Li, T.; Bi, J. M.; Ren, H.; Ling, R.; Zhang, C. L.; Wu, Z. L.; Qin, W. D.; Jiao, P., A gold nanorod-based plasmonic platform for multi-logic operation and detection. Nanotechnology 2019, 30 (5), 9, DOI 10.1088/1361-6528/aaf043. (26) Khan, Z.; Singh, T.; Hussain, J. I.; Hashmi, A. A., Au(III)-CTAB reduction by ascorbic acid: preparation and characterization of gold nanoparticles. Colloids Surfaces B 2013, 104, 11-17, DOI 10.1016/j.colsurfb.2012.11.017. (27) Hojo, M.; Yamamoto, M.; Okamura, K., Dilute nitric or nitrous acid solution containing halide ions as effective media for pure gold dissolution. Phys Chem Chem Phys 2015, 17 (30), 19948-19956, DOI 10.1039/c5cp02288f. (28) Reinwein, D.; Rall, J. E., Nonenzymatic Deiodination of Thyroid Hormones by Flavin 26


Page 27 of 34 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


Mononucleotide and Light. J. Biol. Chem. 1966, 241 (7), 1636-1643. (29) Millstone, J. E.; Hurst, S. J.; Metraux, G. S.; Cutler, J. I.; Mirkin, C. A., Colloidal gold and silver triangular nanoprisms. Small 2009, 5 (6), 646-664, DOI 10.1002/smll.200801480. (30) Kelly, K. L.; Coronado, E.; Zhao, L. L.; Schatz, G. C., The Optical Properties of Metal Nanoparticles: The Influence of Size, Shape, and Dielectric Environment. J. Phys. Chem. B 2003, 107 (3), 668-677, DOI 10.1021/jp026731y. (31) Qi, Y.; Zhu, J.; Li, J. J.; Zhao, J. W., Multi-mode optical detection of iodide based on the etching of silver-coated gold nanobipyramids. Sensor. Actuat. B: Chem. 2017, 253, 612-620, DOI 10.1016/j.snb.2017.06.180. (32) Sekhon, J. S.; Verma, S. S., Optimal Dimensions of Gold Nanorod for Plasmonic Nanosensors. Plasmonics 2010, 6 (1), 163-169, DOI 10.1007/s11468-010-9182-3. (33) Saa, L.; Coronado-Puchau, M.; Pavlov, V.; Liz-Marzan, L. M., Enzymatic etching of gold nanorods by horseradish peroxidase and application to blood glucose detection. Nanoscale 2014, 6 (13), 7405-7409, DOI 10.1039/c4nr01323a. (34) Cotruvo, J.; Fawell, J. K.; Giddings, M.; Jackson, P.; Magara, Y.; Ngowi, A. V. F.; Ohanian, E.

Bromide

in

drinking-water.

https://www.who.int/water_sanitation_health/dwq/chemicals/Fourth_Edition_Bromide_Final_January_ 2010.pdf (accessed August 7 2019). (35) Zou, R. X.; Guo, X.; Yang, J.; Li, D. D.; Peng, F.; Zhang, L.; Wang, H. J.; Yu, H., Selective etching of gold nanorods by ferric chloride at room temperature. CrystEngComm 2009, 11 (12), 2797– 2803 DOI 10.1039/b911902g. (36) Standards

for

drinking

water

quality.

http://c.gb688.cn/bzgk/gb/showGb?type=online&hcno=73D81F4F3615DDB2C5B1DD6BFC9DEC86 (accessed August 7 2019). (37) National

Primary

Drinking

Water

https://www.epa.gov/sites/production/files/2016-06/documents/npwdr_complete_table.pdf

Regulations. (accessed

August 7 2019). (38) Maciel, R.; Sant'Anna, G. L., Jr.; Dezotti, M., Phenol removal from high salinity effluents using Fenton's reagent and photo-Fenton reactions. Chemosphere 2004, 57 (7), 711-719, DOI 10.1016/j.chemosphere.2004.07.032. (39) Machulek, A.; Moraes, J. E. F.; Vautier-Giongo, C.; Silverio, C. A.; Friedrich, L. C.; Nascimento, C. A. O.; Gonzalez, M. C.; Quina, F. H., Abatement of the Inhibitory Effect of Chloride Anions on the Photo-Fenton Process. Environ. Sci. Technol. 2007, 41 (24), 8459-8463, DOI 10.1021/es071884q. (40) Luna, A. J.; Chiavone-Filho, O.; Machulek, A., Jr.; de Moraes, J. E.; Nascimento, C. A., PhotoFenton oxidation of phenol and organochlorides (2,4-DCP and 2,4-D) in aqueous alkaline medium with high chloride concentration. J. Environ. Manage. 2012, 111, 10-17, DOI 10.1016/j.jenvman.2012.06.014. (41) Zhang, J.; Xu, X. W.; Yang, C.; Yang, F.; Yang, X. R., Colorimetric iodide recognition and sensing by citrate-stabilized core/shell Cu@Au nanoparticles. Anal. Chem. 2011, 83 (10), 3911-3917, DOI 10.1021/ac200480r. (42) Zeng, J. B.; Cao, Y. Y.; Lu, C. H.; Wang, X. D.; Wang, Q. R.; Wen, C. Y.; Qu, J. B.; Yuan, C. G.; Yan, Z. F.; Chen, X., A colorimetric assay for measuring iodide using Au@Ag core-shell nanoparticles coupled with Cu2+. Anal. Chim. Acta 2015, 891, 269-276, DOI 10.1016/j.aca.2015.06.043. 27



Page 28 of 34

(43) de Souza, F. C.; Vegas, C. G.; da Silva, D. A. I.; Ribeiro, M. S.; Cabral, M. F.; de Melo, M. A.; Mattos, R. M. T.; Faria, R. B.; D'Elia, E., Amperometric and potentiometric determination of iodide using carbon electrodes modified with salophen complex. J. Electroanal. Chem. 2016, 783, 49-55, DOI 10.1016/j.jelechem.2016.10.056. (44) Ciftci, H.; Tamer, U., Electrochemical determination of iodide by poly(3-aminophenylboronic acid) film electrode at moderately low pH ranges. Anal. Chim. Acta 2011, 687 (2), 137-140, DOI 10.1016/j.aca.2010.12.019. (45) Nguyen, V. T. P.; Piersoel, V.; El Mahi, T., Urine iodide determination by ion-pair reversedphase high performance liquid chromatography and pulsed amperometric detection. Talanta 2012, 99, 532-537, DOI 10.1016/j.talanta.2012.06.028. (46) Jia, Y. X.; Zheng, W. S.; Zhao, X. H.; Zhang, J. J.; Chen, W. W.; Jiang, X. Y., Mixing-toAnswer Iodide Sensing with Commercial Chemicals. Anal. Chem. 2018, 90 (13), 8276-8282, DOI 10.1021/acs.analchem.8b02126. (47) Ding, G. Y.; Zhang, X. R., A picture of polar iodinated disinfection byproducts in drinking water by (UPLC/)ESI-tqMS. Environ. Sci. Technol. 2009, 43 (24), 9287-9293, DOI 10.1021/es901821a. (48) Yang, Y.; Komaki, Y.; Kimura, S. Y.; Hu, H. Y.; Wagner, E. D.; Marinas, B. J.; Plewa, M. J., Toxic impact of bromide and iodide on drinking water disinfected with chlorine or chloramines. Environ. Sci. Technol. 2014, 48 (20), 12362-12369, DOI 10.1021/es503621e. (49) Gregorini, A.; Ruiz, M. E.; Volonte, M. G., A derivative UV spectrophotometric method for the determination of levothyroxine sodium in tablets. J. Anal. Chem. 2013, 68 (6), 510-515, DOI 10.1134/s1061934813060075.

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For Table of Contents Use Only

Synopsis: The accuracy and linearity of the gold triangular nanoplate-based colorimetry is significantly improved by incorporating peak deconvolution and new calibration strategy.

29



Figure 1 (A) Absorption spectra of AuTNPs after etching with (a) ultrapure water, (b) 1 mM KI and 2 mM HCl, (c) 200 mM H2O2 and 2 mM HCl, and (d) 0.015 mM KI, 200 mM H2O2 and 2 mM HCl. (B) Absorption spectra of AuTNPs after etching with (e) intact L-T4 and (f) 2 μM photodegraded L-T4 in the presence of 200 mM H2O2 and 2 mM HCl. The insets are the images of the corresponding AuTNP dispersions in cuvettes. The high-resolution TEM images of AuTNPs: C, intact; D, etched by 2 μM photodegraded L-T4; E, etched by 20 μM photodegraded L-T4. The scale bars are 100 nm. The reaction was conducted at 50 °C for 10 min. 83x59mm (600 x 600 DPI)


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Figure 2 Schematic illustration of the quantitation strategy. (A) Iodide-mediated etching of gold nanoprisms; (B) deconvolution of the overlapping LSPR peaks, in which the blue and red dotted lines are the original extinction spectra obtained from intact and etched AuTNPs, respectively. The corresponding solid lines are extracted in-plane and out-of-plane dipole LSPR peaks, and the in-plane dipole LSPRs have longer wavelengths than the out-of-plane dipole LSPRs. The inset indicates that after peak fitting, the wavelength of the in-plane dipole LSPR peak is different from the merged one, revealing that deconvolution is helpful in enhancing accuracy. (C) a (Δλ)2–C regression based on the deconvoluted data. 83x54mm (600 x 600 DPI)



Figure 3 Selectivity of the AuTNP-based iodide sensor under the optimal conditions. (A) Wavelength shift of the AuTNP solution in the presence of 10 μM I^-, 4-fold Br-, and 10-fold other anions. (B) Wavelength shift of the AuTNP solution in the presence of 10 μM I^-and 20-fold metal ions, i.e., Na^+, Mg^(2+), Ba^(2+), Co^(2+), Ni^(2+), Cu^(2+), Zn^(2+), Hg^(2+), Pb^(2+), Cd^(2+) and Fe^(3+). The error bars represent the standard deviations of three independent measurements. The inset images show the corresponding color changes of the solutions. 83x43mm (600 x 600 DPI)


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Figure 4 Influences of regression and deconvolution strategies. In (A) and (B), Δλ values were obtained from the original spectra; in (C), Δλ values were obtained from the extracted spectra. 83x20mm (600 x 600 DPI)



Figure 5 (A) Images and (B) absorption spectra of the AuTNPs treated with etching solutions containing 200 mM H2O2, 2 mM HCl and different concentrations of photodegraded L-T4. (C) (Δλ)2–C relations. The inset shows the calibration curve. 83x127mm (600 x 600 DPI)


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A Rational Calibration Strategy for Accurate and Sensitive Colorimetric

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