Label-Free Colorimetric Nanosensor for the Selective On-Site

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Label-free colorimetric nanosensor for the selective on-site detection of aqueous Al3+ Priyanka Joshi, Ritu Painuli, and Dinesh Kumar ACS Sustainable Chem. Eng., Just Accepted Manuscript • Publication Date (Web): 11 May 2017 Downloaded from http://pubs.acs.org on May 11, 2017

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ACS Sustainable Chemistry & Engineering

Corresponding author Dr. Dinesh Kumar School of Chemical Sciences, Central University of Gujarat, Gandhinagar-382030, India E-mail- [email protected] Authors Priyanka Joshi Department of Chemistry, Banasthali University, Rajasthan-304022, India E-mail- [email protected] Ritu Painuli Department of Chemistry, Banasthali University, Rajasthan-304022, India E-mail- [email protected]

1 ACS Paragon Plus Environment


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Label-free colorimetric nanosensor for the selective on-site detection of aqueous Al3+ Priyanka Joshi1, Ritu Painuli1, and Dinesh Kumar2 1

2

Department of Chemistry, Banasthali University, Rajasthan-304022, India

School of Chemical Sciences, Central University of Gujarat, Gandhinagar-382030, India

Abstract Aluminum is a health hazard element, found abundantly in the environment. Although many methods have been reported for the efficient detection of aluminum, an easy and accessible sensor for fast detection of aqueous aluminum has not been devised to date. In this approach, we have synthesized indole-2-carboxylic acid capped silver nanoparticles (I2CA-AgNPs) using the one-pot method and used them as label-free nanosensors for the detection of Al3+ in the presence of interfering metal ions. I2CA-AgNPs were synthesized by two methods at different temperatures. AgNPs synthesized by heating method were further used as detection probe as they showed a strong and narrow surface plasmon resonance (SPR) peak in the visible region. The sensitivity of the detection probe has been optimized by variations in size and distribution of nanoparticles. Synthesized AgNPs were characterized by UV-Vis spectroscopy, HRTEM, FT-IR, zeta potential and DLS analysis. Based on these results, I2CA-AgNPs could be used as a colorimetric sensor to selectively detect the presence of Al3+. Further, Results are confirmed by theoretical calculations of binding energy by DFT. Moreover, the nanosensor can also be applied to trace aluminum contamination in different types of water samples. The lower detection limit of the proposed method is 0.01 ppm (S/N = 3) which falls in the permissible limit set by USEPA i.e. 50 ppm. Keywords: Silver nanoparticles (AgNPs), indole-2-carboxylic acid (I2CA), Density functional theory (DFT), colorimetric detection, aluminum ions (Al3+), aluminum nanoparticles (AlNPs).


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Introduction In recent years, the development of sensitive and selective detection methods for hazardous metal ions has interested researchers, given their importance in medicine, living systems and the environment [1,2]. However, many of them are toxic even at trace level concentrations [3,4]. Among these toxic metal ions, aluminum is the third most prevalent metallic element in the earth’s crust. It is widely used in aliment additives, pharmaceuticals, and storage/cooking utensils [5]. There is mounting evidence that unregulated amounts of aluminum in the human body cause damage to the nervous system, idiopathic Parkinson’s disease, impairment of memory, Alzheimer’s disease [6], and dialysis encephalopathy [7]. The iron binding protein is the main carrier for Al3+ in plasma. Thus Al3+ can easily enter the brain and reach the placenta and fetus. Aluminum concentrations in the brain should be maintained at 500 W attributed may be due to the metallic oxides. The improved thermal stability of I2CA capped AgNPs could be due to the strong interaction of a stabilizing agent on the surface of the AgNPs. FT-IR analysis Synthesis of nanoparticles was further confirmed by the FT-IR spectra. In the spectra of pure I2CA (Figure 3a), a strong band at 3351 cm-1 and a small band at 3428 cm-1 were observed,


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assigned to the –NH group involved in N-H----O hydrogen bonding and non-associated –NH respectively. A prominent and broadband was observed between 3200-2500 cm-1 which confirm the involvement of -COOH group in intermolecular hydrogen bonding. Strong peaks at 1707 cm1

and 1194 cm-1 were noted which were attributed to C=O and C-O stretching vibration of –

COOH group [44]. However, in the case of I2CA-AgNPs, a large shift in peak position was observed (Figure 3b). After completion of the reaction, the characteristic peak for COOdisappeared. This could be attributed to the decarboxylation of I2CA. Peaks showing the involvement of the N-H group in the N-H----O hydrogen bonding and residual peak for some non-associated –NH group also disappeared with the generation of a new sharp peak in the midst of the broad peak at 3416 cm-1 confirming the involvement of -NH group in the –NH----N hydrogen bonding. Peaks at 1399 cm-1, twin peaks at 1544 cm-1, 1570 cm-1 correspond to C-H, NH-C=O group respectively. Peaks showing the aromatic character in indole ring also disappear. These variations support the mechanism of I2CA oxidation suggested by Sangal et al [45]. As most of the carboxylic acid of indole has pka < 7.0 [46], it is expected that at pH 8.0 carboxylic group of indoles would be present in its anionic form. An abstraction of an electron from the anion generates free radical of I2CA. Removal of a second electron with oxidative decarboxylation results in the generation of a cationic species. Cationic indole is a highly unstable species and hence undergoes attack by OH- group forming 2-hydroxyindole, which exists in its tautomeric form i.e. 2-oxyindoles. Further 2 electrons, 2 H+ oxidation of 2oxyindoles gives dioxindoles (Figure 4). Electrons released in the above procedure were responsible for the reduction of Ag+ to Ag0 which, on nucleation, forms AgNPs and negative charge of dioxindoles provides electrostatic stability to synthesized AgNPs.



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Figure 3. FT-IR spectra of (a) I2CA, (b) I2CA-AgNPs, and (c) I2CA-AgNPs with Al3+.

Figure 4. Schematic representation of Al3+ induced aggregation of I2CA-AgNPs. Cyclic voltammetry analysis 20 ACS Paragon Plus Environment

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The synthesis of AgNPs by I2CA was also confirmed by cyclic voltammetry analysis. To collect cyclic voltammograms of I2CA and I2CA-AgNPs, Pt electrode was utilized as the reference electrode and three cycles were run in the range of potential -1 to 1 V at 100 mV s-1 scan rate. Figure S5a shows that I2CA exhibited one peak at -0.600 V in aqueous media with irreversible nature. During the initial forward scan, an increasingly reducing potential is applied due to which, the cathodic current increase at least over this time, as there are reducible analytes present in the system [47]. At some point after the reduction potential of the analyte is reached, the cathodic current decreases as the concentration of reducible analyte start depleting. This negative potential of I2CA shows its reducing capacity [48]. Correspondingly, Figure S5b depicts a voltammogram for Ag+ ion. Figure S6a-c shows the interaction of I2CA (0.0001 to 0.01 M) with Ag+ ions. Results indicate that Ag+ ions are not completely reduced to Ag0 at 0.0001 M of I2CA. However, upon increasing the concentration of I2CA, cathodic peak current increases linearly from 0.0001 to 0.01 M. This peak corresponds to the complete reduction of Ag+ ion to Ag0 [17].

Selectivity test for Al3+ by I2CA-AgNPs It is a well-known fact that the oxygen and nitrogen containing ligands have a high affinity for metal ions [49]. Based on this fact, we have synthesized I2CA-AgNPs which show high selectivity for the Al3+ ions. Figure 5a displays the UV-Vis extinction spectra before and after adding various metal ions to the I2CA-AgNPs solution. In this series of studies, I2CA-AgNPs led to a significant change in SPR peak, which is attributed due to the formation of a colored complex between ligand and Al3+ while other metal ions led to an only minor change in the SPR peak. The selectivity of probe towards Al3+ was further quantiﬁed by plotting the absorption intensity ratio (A550/A405) of the I2CA-AgNPs solution against different metal ions (10-100 ppm)



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as shown in Figure S7. The Al3+ induced values of A550/A405 are significantly greater than the values observed for other metal ions which show that the value of A550/A405 can be used to display the distinctive interaction between the Al3+ and I2CA-AgNPs. Additionally, the marked bathochromic shift and augmentation in the values of A550/A405 were confirmed by the naked-eye with the color change in the solution of detection probe from brown to reddish-brown immediately after the addition of Al3+ (Figure 5b). After 15 min, it led to the precipitation of I2CA-AgNPs. However, there is no change in the color of the nanoparticles solution with the addition of other environmentally relevant metal ions. It is apparent from Figure 5c that there were significant optical changes for Al3+ ions, irrespective of the presence of other cations. Further, the selectivity towards Al3+ ion was confirmed in synthetic water. We prepared two different types of synthetic water samples (a & b) containing all above-mentioned metal ions. Sample b had additional Al3+ ions while sample a did not have additional Al3+ ions. We interacted both the samples with I2CA-AgNPs and got encouraging results. I2CA-AgNPs sensed Al3+ in sample b even in the presence of other environmentally relevant metal ions and gave negative results with the sample as shown in Inset Figure 5c. The results confirm that the interaction between Al3+ ions and AgNPs are unaffected by the presence of other metal ions. However, the sensor was found to give false positive results when the concentration of other metal ions is higher than 3 ppm in synthetic water samples.


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Figure 5. (a) UV-Vis spectra of the I2CA-AgNPs upon addition of different metal ions, (b) visual colour change of the I2CA-AgNPs upon addition of various metallic ions, and (c) photographic image of the detection systems incubated with mixture of Al3+ and other ions; Inset shows the response of I2CA-AgNPs in synthetic water samples. Theoretical calculation Here, we discuss the binding energy of Al3+ ion and Ga3+ ion for I2CA-AgNPs. This is the most important parameter in the evaluation of the interaction between metal ions and sensor. For the purpose,

the

structure

of

sensor

and

sensor-metal

complex

was

optimized

by

PBE0/LANL2DZ/6-311G**. The optimized structures are displayed in Figure S8. The calculated value of binding energy for Al3+ ion is -135.83 kcal/mol which is much higher than the binding


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energy calculated for Ga3+ (-65.95 kcal/mol). The result shows that the binding strength for Al3+ is higher than Ga3+, which agrees well with experimental results. Sensitivity of the I2CA-AgNPs to Al3+ The performance of the developed Al3+ sensor depends upon the pH of the solution because the pH of the solution not only influences the synthesis of nanoparticles but also affects the interaction between I2CA-AgNPs and Al3+ ions. As we mentioned above, the synthesized I2CAAgNPs have maximum stability at pH 8, but there is not much change observed in the pH range from 7 to 10. We found that the value of A550/A405 was maximum at pH 8.0 and then decreased as shown in Figure 6a. This phenomenon may be due to the formation of aluminum hydroxide precipitates in high alkaline solution [26]. Thus, we performed the whole experiment at pH 8.0. Quantitative analysis was conducted by adding different concentrations of Al3+ into I2CAAgNPs solution and the changes in intensity, width, and position of SPR peak were monitored by UV-Vis spectroscopy. It is apparent from Figure 6b that the intensity of the SPR peak at 405 nm decreases as the function of Al3+ concentration with the generation of a new peak at 550 nm. So, these two wavelengths were chosen to show the amount of monodispersed and aggregated particles, respectively. In the presence of Al3+ ion color of I2CA-AgNPs changes to reddish brown, which undergoes precipitation at higher concentration (Figure 6c). The colorimetric changes in I2CA-AgNPs solution could be due to the interaction of functional groups present on the surface of NPs with Al3+ by metal–ligand interaction; thereby the Al3+ ions induced the aggregation of AgNPs. The plot of A550/A405 against the various concentrations of Al3+ shows the dose response of the assay (Figure 6d). The plot of Al3+ with concentration ranging from 0.5 ppm to 10 ppm shows a linear correlation and value of linear regression coefficients (R2) was 0.9924 (6e). The color of the solution remains like control at an Al3+ concentration of 0.001 ppm.



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Therefore, our sensor’s limit of detection by the naked eye is 0.01 ppm making it suitable for the quantitative determination of Al3+ ions at the ppm level in aqueous solutions. The result was also confirmed by UV-Vis spectra which did not show any change in the characteristic peak of nanoparticles beyond 0.01 ppm of Al3+ [50]. To check the reproducibility with respect to sensing ability of synthesized I2CA-AgNPs, 8 replicate experiments were performed for 0 ppm (blank) and 0.01 ppm of Al3+ (Figure S9). The value of A550/A405 nm for 0.01 ppm Al3+ is significantly similar for all the replicates which confirm their sensing reproducibility [51]. The higher value of A550/A405 was obtained for 0.01 ppm of Al3+ ions than that for blank, but there is no difference in the A550/A405 value between 0.009 ppm and blank which further confirms the LOD is 0.01 ppm (S/N = 3), and the relative standard deviation is 1.3% [52]. The interaction of I2CA-AgNPs with Al3+ was also confirmed by nuclear magnetic resonance (NMR) spectroscopy. Figure S10a and b show the NMR spectra of pure I2CA and I2CA-AgNPs after interaction with Al3+. Results indicate that not much change was observed in the basic unit, only the functional groups take part in interaction with Al3+ ions.


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Figure 6. (a) Bar graph shows the effect of pH on sensing, (b) UV-Vis spectra of I2CA-AgNPs at Al3+ ion concentration of 0.001-10 ppm, (c) color change of I2CA-AgNPs solution upon addition of diWerent concentrations of Al3+ ions under the optimized conditions, (d) a dose-response curve for the detection of Al3+ ion (A550/A405 ratios),

(e) linear calibration plot for the

concentration of Al3+ ion in the range of 0.5 ppm-10 ppm, the absorbance ratio was measured in 29 ACS Paragon Plus Environment


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triplicates for each concentration of Al3+ ion, error bars present standard deviation, HRTEM images of I2CA-AgNPs (f) before and (g) after interaction with Al3+ ion.

HRTEM analyses were carried out in the presence and absence of Al3+ ions, under identical conditions. Figure 6f shows that the synthesized I2CA-AgNPs are apparently monodispersed, and 5 nm to 20 nm in average diameter which undergoes aggregation on the addition of Al3+ (Figure 6g). Further, DLS measurement was carried out to show the aggregation of nanoparticles upon interaction with Al3+. Figure S11a shows the particles had an average diameter of 19 nm in the absence of Al3+ which increases progressively up to 286 nm on increasing the concentration of Al3+. Further the decrease in zeta potential from -25 mV to 21.9 mV confirmed aggregation of I2CA-AgNPs in the presence of Al3+ (Figure S11b) [17]. Based on the observed UV-Vis spectral changes, HRTEM images, FT-IR spectra, zeta potential, and DLS measurements, we propose a possible mechanism for the interaction of AgNPs with Al3+ in an aqueous medium as shown in Figure 4. Upon addition of Al3+ into the AgNPs solution, the intensity of SPR band gradually decreases with the generation of a new peak for Al3+ ions. Al3+ is a hard acid and it tends to co‒ordinate preferably with a hard base such as N and O atom [53,54]. Thus, the Al3+ co‒ordinate with the functional groups (NH–C=O) present on the NPs surface through metal–ligand interactions. As a result, these NPs come closer to each other which leads to the cross-linking aggregation of I2CA-AgNPs, causing a change in the color of the solution from brown to reddish brown. The co‒ordination of Al3+ ion with N and O atom was confirmed by the disappearance of the peaks at 3416 cm-1, 1571 cm-1. The shifting of the peak from 1567 cm-1 to 1538 cm-1 shows the decrease in double bond character in C=O upon its coordination with Al3+ ion and appearance of a new peak at 973 cm-1 confirms co-ordination of


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Al3+ ion (Figure 3c). The high specificity of the I2CA-AgNPs for Al3+ can be explained based on multiple numbers of N and O atom present in the system [55,56]. Energy dispersive X-ray analysis EDX analysis was performed to show the synthesis of I2CA-AgNPs and their interaction with Al3+ ions. Figure S12a shows the characteristic peaks at 3 keV corresponding to Ag characteristic L line [57]. The other peaks with high intensity are due to the C, N, and O which constitute the basic unit of reducing and stabilizing agent I2CA. In Figure S12b the presence of peaks which correspond to the Al3+ ions confirm the interaction of I2CA-AgNPs with Al3+ ions. Interaction of I2CA with AlNPs The formation of AlNPs was confirmed by P-XRD (Figure S13a). Results were in good agreement with the results reported by Murlidhran et al [58] which revealed the face-centered cubic (FCC) arrangement of aluminum. To support the mechanism of Al3+ sensing, we attempted interaction between AlNPs with I2CA but the stumbling block was that the formed AlNPs were not dispersed in an aqueous medium, which was the base for all our previous reactions. To solve this problem, we checked their dispersion in various solvents. They were found to be soluble in acetic acid. I2CA is also soluble in acetic acid. Therefore, acetic acid was chosen as the medium for their interaction. UV-Vis spectra of AlNPs in acetic acid did not show any peak except a small shoulder around 299 nm. No additional peak or any change in UV-Vis spectra of I2CA was observed on addition of AlNPs confirming that there is no interaction between AlNPs and I2CA (Figure S13b). The FESEM image of AlNPs in acetic acid showed that particles get aggregated and move towards the formation of oxides (Figure S13c). Particle size distribution was derived from a histogram measured using multiple FESEM micrographs (Figure S13d). The effects of size variations and distribution of I2CA-AgNPs on sensing



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To know the effect of size on sensing response we considered Ag (8 nm) and Ag (32 nm) particles. With the increasing size of nanoparticles, an increase in sensitivity from 0.01 ppm to 0.005 ppm was observed. The sensitivity of the sensor is mainly governed by shape, orientation, interparticle distance, size and distribution of aggregates (number of particles). As the size of nanoparticles increase, distribution of aggregates increases, which results in a decrease of the interparticle distance between particles. This, in turn, enhances the sensitivity by plasmon coupling of nanoparticles [59]. Another reason for increased sensitivity could be due to increase radiative damping or retardation [60]. Figure 7a shows the UV-Vis spectra of I2CA-AgNPs (32 nm) with Al3+. As the concentration of Al3+ increases, a continuous decrease in intensity was observed with the generation of a new shoulder at 682 nm. Correspondingly, the color of nanoparticles solution changes from greenish black to orange-brown (Figure 7b). The aggregation of nanoparticles was confirmed by HRTEM analysis (Figure 7c). Although the nanoparticles with large size are more sensitive, their stability is lower and this limits their application.


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Figure 7. (a) UV-Vis spectra and, (b) optical image of I2CA-AgNPs (32 nm) in the presence of Al3+, and (c) HRTEM image showing the aggregation of particles in the presence of Al3+. Application of the sensor



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To validate the practical application of the proposed label‒free colorimetric method, we tested its response on tap and pond water samples. However, we could not detect Al3+ in the samples as the concentration of Al3+ in tap and pond water samples were very low which may be less than the sensitivity limit of our proposed method. Tap and pond water samples were spiked with various concentrations of Al3+ in the range of 0.001 ppm to 10 ppm and tested in the system. The visual response of sensor linearly increased with increasing Al3+ concentration as shown in Figure 8. Sensor responses in distilled, tap and pond water are very similar, suggesting that the colorimetric assay can detect Al3+ without being aWected by the interfering tap and pond water environment. To further show the validity of the method, a recovery test method was also performed for the determination of Al3+ on tap and pond water samples. When two different concentrations of Al3+ were spiked and then analyzed using the standard addition method, recovery of Al3+ in the range from 96% to 107.5% was obtained. The observed concentration in tap and pond water sample by our proposed method was very close to the concentration determined by the AAS (Table 1). The sensitivity of this colorimetric sensor was compared to reported methods using nanoparticles as sensors [23-25, 61-63]. The limit of detection of our proposed method is lower or comparable to the other reported methods for Al3+ ion (Table S2). Easy synthesis, short response time, working at physiological pH, and applied to the real water samples makes the present method more advantageous over other reported methods.


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Figure 8. The colorimetric response of I2CA-AgNPs as a function of Al3+ ion concentration in (a) tap water and (b) pond water samples.

Table 1. The recovery results from spiked real water samples Sample

Added amount Found amount (ppm)

Recovery (%)

of Al3+ (ppm)

(Mean ± E, and n = 3)

(Mean ± E, and n = 3) 35

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AAS


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Tap

0.5

0.49 ± 0.01

98 ± 2

0.53

water

2.0

2.1 ± 0.02

105 ± 2.5

0.19

Pond

0.5

0.51 ± 0.019

102 ± 3.8

0.50

Water

2.0

1.98 ± 0.01

99 ± 0.50

0.19

Conclusions The outcomes of this research indicate the development of a novel and selective sensor for the label‒free colorimetric sensing of Al3+. Various conditions such as pH, time, temperature, and concentration of I2CA were studied for the synthesis of nanoparticles. AgNPs synthesized by the heating method is more suitable for the efficient sensing of the metal ion as they show a strong narrow band and require a shorter time for the reduction of Ag+ ions. AgNPs show the good colorimetric response for Al3+ with excellent selectivity as other environmentally relevant metal ions does not show interference with Al3+. The reaction conditions for the experiment were set at 0.001 M AgNO3, 0.01 M I2CA, and pH 8. 100 µL of the metal ion solution was added into 400 µL of I2CA-AgNPs which was suitable for the detection of Al3+ with instant response in Millipore, tap, and pond water samples. The sensor shows high selectivity for Al3+, but at the concentration of 100 ppm of some metal ions (Ni2+, Co2+, and Cr3+) starts to interfere. Theoretical calculation by DFT confirms binding of Al3+ ion with I2CA-AgNPs. When the simultaneous presence of other environmentally relevant metal ions is higher than 3 ppm, sensor gives false positive results. Effect of size on the sensing of Al3+ was also investigated which shows that the large particles show improved selectivity. It has several advantages over other existing techniques for the Al3+ ion sensing- it does not require any complicated instrumentation or modification which simplifies the operation and reduces associated costs. The sensor allows


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the detection of Al3+ ion in concentrations as low as 0.01 ppm by the naked eyes and spectroscopically. ASSOCIATED CONTENT Supporting Information. UV-Vis spectra of I2CA-AgNPs illustrating reproducibility of with respect to size, HRTEM images at different magnification, and histograms representing the synthetic reproducibility with respect to size, Size distribution of I2CA-AgNPs at (a) 405 nm, (b) 427 nm, the calculation of FWHM of I2CA-AgNPs synthesized at (a) 0.01 M, and (b) 0.1 M concentration of I2CA, Thermogram of (a) I2CA, (b) I2CA-AgNPs, Cyclic voltammogram of (a) I2CA, and (b) AgNO3, Cyclic voltammogram of I2CA-AgNPs synthesized with (a) 10 ml, (b) 15 ml, and 20 ml of I2CA, selectivity of I2CA-AgNPs in the presence of different concentration (10-100 ppm) of various heavy metal ions, the graphical structure of (a) I2CA-AgNPs, and it’s complexes with (b) Al3+, and (b)

Ga3+. Structures were optimized by PBE0/LANL2DZ/6-

311G**, Sensing reproducibility of I2CA-AgNPs for Al3+, The reaction condition for the experiment set at 0.001 M AgNO3, 0.01 M I2CA, pH 8, 1H NMR spectra of (a) I2CA, and (b) I2CA-AgNPs after interaction with Al3+ ions, size distribution of I2CA-AgNPs before and after addition of Al3+ ion, Zeta potential distribution of I2CA-AgNPs before and after interaction with Al3+ ions, EDX spectra of (a) I2CA-AgNPs, and (b) I2CA-AgNPs after interaction with Al3+ ions, P-XRD pattern of synthesized AlNPs, UV-Vis spectra of I2CA in presence of AlNPs, FESEM images of AlNPs in acetic acid, histogram of AlNPs, characterization of I2CA-AgNPs with different size, the comparison of reported colorimetric methods with present work in terms of reducing and stabilizing agent, pH, and limit of detection.

Acknowledgments



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We gratefully acknowledge support from the Ministry of Human Resource Development, Department of Higher Education, Government of India under the scheme of Establishment of Centre of Excellence for Training and Research in Frontier Areas of Science and Technology (FAST), vide letter No, F. No. 5-5/201 4-TS. Vll. The authors also thank AIIMS, New Delhi, and University of Rajasthan, Jaipur, for the providing HRTEM facility. Profound gratitude extended to Dr. Ruby Srivastava, DST scientist, CSIR, IICT Hyderabad, and Dr. G. Narhari Sastry, H.O.D., Centre for molecular modeling, CSIR, IICT for computational work. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] ORCID Priyanka Joshi: 0000-0003-0882-4760 Ritu Painuli: 0000-0002-0423-896X Dinesh Kumar: 0000-0001-5488-951X

Notes The authors declare no competing ﬁnancial interest


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For Table of Contents Use Only Label-free colorimetric nanosensor for the selective on-site detection of aqueous Al3+

Priyanka Joshi1, Ritu Painuli1, and Dinesh Kumar2 1

2

Department of Chemistry, Banasthali University, Rajasthan-304022, India

School of Chemical Sciences, Central University of Gujarat, Gandhinagar-382030, India

Graphical abstract

Synopsis



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I2CA capped AgNPs were prepared with balanced properties which are sustainable for the colorimetric detection of Al3+ ions based on a sensing mechanism of aggregation.

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Label-Free Colorimetric Nanosensor for the Selective On-Site

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