Glutathione Modified Gold Nanoparticles for Sensitive Colorimetric

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Glutathione Modified Gold Nanoparticles for Sensitive Colorimetric Detection of Pb2+ ions in Rain Water Polluted by Leaking Perovskite Solar Cells Yaming Yu, Ying Hong, Peng Gao, and Mohammad Khaja Nazeeruddin Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b03515 • Publication Date (Web): 23 Nov 2016 Downloaded from http://pubs.acs.org on November 23, 2016

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Analytical Chemistry

Glutathione Modified Gold Nanoparticles for Sensitive Colorimetric Detection of Pb2+ ions in Rain Water Polluted by Leaking Perovskite Solar Cells Yaming Yua, b, Ying Honga, Peng Gaob, Mohammad Khaja Nazeeruddinb a

College of Materials Science and Engineering, Huaqiao University, 361021 Xiamen, China Group for Molecular Engineering of Functional Materials, Institute of Chemical Science and Engineering, École Polytechnique Fédérale de Lausanne, CH-1950 Sion, Switzerland

b

ABSTRACT: In the past few years, the advent of lead halide perovskite solar cells (PSCs) has revolutionized the prospects of the third- generation photovoltaics and the reported power conversion efficiency (PCE) has been updated to 22%. Nevertheless, two main challenges including the poisonous content of Pb and the vexing instability toward water still lie between the lab based PSCs technology and large scale commercialization. With this background, we firstly evaluated Pb2+ concentration from the rain water samples polluted by three types of market promising PSCs with inductively coupled plasma mass spectrometry measurements (ICPMS) as a case study. The influence of possible conditions (pH value and exposure time) on the contents of Pb2+ from the three PSCs was systematically compared and discussed. Furthermore, an optimized glutathione functionalized gold nanoparticles (GSHAuNPs) colorimetric sensing assay was used to determine Pb2+ leaking from PSCs for the first time. The Pb2+-induced aggregation of sensing assay could be monitored via both naked eye and UV–Vis spectroscopy with a detection limit of 15 nM and 13 nM, which are all lower than the maximum level in drinking water permitted by WHO. The quantitative detection results were compared and in good agreement with that of ICP-MS. The results indicate that the content of Pb2+ from three PSCs are in the same order of magnitude under various conditions. By the use of the prepared GSH-AuNPs self-assembled sensing assay, the fast and onsite detection of Pb2+ from PSCs can be realized.

Organic-inorganic lead halide perovskites solar cells (PSCs) as third-generation solar cells with certified efficiencies up to 22 %1 have been reported. It is proverbially believed that the PSCs have the promise to compete with the currently commercial available silicon and cadmium–tellurium thin-film photovoltaic technologies due to the simple, flexible and cost efficient manufacture.2 Behind the flowers and applause to the fast rising device performance, PSCs are suffering from the notorious instability over the long-term under ambient andatmospheric conditions.3,4 Aiming at mass production and globally extensive application, PSCs community has to face the concerns over the potential environmental impacts of heavily used toxic lead elements against the background of vexing instability.5 Unlike the prevailing decorative lead glass and protective lead coat, lead element existing inside a lead halide perovskites is in the form of lead ion (Pb2+), which is readily soluble inside a electrolyte solution e.g. rain water. Pb2+ is one of the oldest known and most widely studied toxins due to its causing adverse health effects from lead exposure, particularly in children.6 A variety of symptoms have been attributed to lead poisoning when introducing it into the human body, such as abdominal pain, vomiting, muscle paralysis, mental confusion, memory loss, and anemia.7,8 To address the above concerns, researchers have made pioneer attempts to recognize the potential toxicity of broken perovskite panels. Hailegnaw et al. evaluated the impact of rain on methylammonium lead iodide perovskite films by gravimetric and ICPMSmeasurements.9 Later on, Fabini quantified the total lead

content of halide perovskite PV devices that would be required to supply current electricity needs in the United States and evaluated the upper bound on possible lead pollution during the service life of this technology, which was compared with select historical and current sources of lead pollution in the U.S.5 More recently, Babayigit el. al. assessed the toxicity of Pb and Sn based perovskite solar cells in model organism Danio rerio.10,11 Those seminal works broadened our horizons to understand the possible consequences of Pb2+ leakage from PSCs modules for environment, organisms or human body. Despite the situation that the fixed and sealed PSCs panels are seriously broken in the worse scenario which may not happen easily, Pb2+ will leak from the panels even though there is a small crack during a rainy weather. Then it will be a nightmare that the lead-contaminated food or drinks enter the gastrointestinal tract of humans. A stitch in time save nine. To prevent the catastrophe, it is critical and meaningful to develop methods for the fast, sensitive and on-site detection of Pb2+ leaked from failed PSC panels. Although the commercial available instruments such as ICP-MS,12 inductively coupled plasmaatomic emission spectrometry (ICP-AES),13 as well as ion selective electrodes and flame photometry (ISEFP),14 can be used to determine the contents of Pb2+, they cannot meet the fast and on-site detection due to the complicated preparation and economic reasons. Gold nanoparticles (AuNPs) are widely employed in the application of Pb2+ ion sensors based on localized surface plasmon resonance (LSPR) effect.15,16 LSPR is one of the most im-

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portant properties of the AuNPs, which is induced by the collective oscillation of free electrons in the conduction band on the surface of nanoparticles. The location and intensity of LSPR peak are sensitive to the local refractive index surrounding the nanoparticles, which make it possible to detect the Pb2+ by naked eye. However, the limit of detections (LODs) obtained from these reports are normally higher than the WHO’s reference standards for drinking water (10 ppb).17 Efforts have been made to increase the detection limit of metal ions through ligand molecule screening (e.g. DNA or peptides) or size control of AuNPs. Glutathione, as one of the most used ligands has been employed to modify various gold/silver nanostrutures for the purpose to detect metal ions such as Pb2+,15,18,19 Cr3+ and Cr6+,20 Co2+,21 as well as As3+.22 Meanwhile, a lot of aspects have been focused on and tried to explain the features of these sensing systems, including the reasons of selectivity towards certain cations. Recently, core–satellite AuNPs structures were developed and able to provide higher sensitivity compared with unique size AuNPs.17,23–25 To the best of our knowledge, there was no application of core–satellite AuNPs based colorimetric methods to selectively detect Pb2+ ions from perovskite films. In this paper, we took the first try in comparing and evaluating Pb2+ dissolution in acidic aqueous solution from PSCs with three types of perovskite compositions (CH3NH3PbI3, FA0.85MA0.15Pb(I0.85Br0.15)3 and Csx(MA0.17FA0.83)(100−x)Pb(I0.83Br0.17)3) featuring high efficiency26–28 by using highly sensitive colorimetric method based on core–satellite AuNPs. The experiment was designed to mimic a critical structure failure in those solar cells in a rainy day, which would result in the full degradation of the perovskite absorber material when being exposed to the ambient. The dissolution of the decomposed products (including HI, HBr, methyl ammonium (MA), formamidinium (FA), Pb2+, Cs+ etc.) in water may readily leach into surroundings.10,29,30 There is an acute need to assess the impact of this leakage and the determination of Pb2+ is the first critical step. Taking advantage of

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the colorimetric sensing assays it is possible to realize fast detection of Pb2+ from the decomposed PSCs on-time. Firstly, two kinds of simulated rain water with different pH were used to immerse the PSCs. Then the self-assembled core–satellite GSH-AuNPssensing system was optimized systematically to find the LOD for Pb2+ from perovskite films. In this study, we realized a detection limit of 13 nM and 15 nM by UV-Vis and naked-eyes, respectively, which are lower than the WHO standard limit (10 ppb). As a complimentary study, the contents of Pb2+ from the two simulated rain water that immersed the PSCs were also evaluated by ICP-MS. This research broadened the applications for gold nanoparticle sensing assays and provided a new avenue for the detection of Pb2+ from perovskite solar cells as well. Materials and methods Instruments The contents of Pb2+ were determined via ICP-MS (PerkinElmer NexION 350D). UV-Vis absorption spectra were recorded by using PerkinElmer Lambda 950 spectrophotometer. The morphology and size of GSH-AuNPs were characterized by transmission electron microscopy (TEM H-7650, Hitachi, Japan). Determination of Pb2+ via ICP-MS PbI2 standard stock solution was prepared by dissolving 20 mg of PbI2 in 100 mL of water containing 0.03% of HNO3 with continuous sonication for about 10 hours. A serious of PbI2 standard solutions with various concentrations for ICP-MS were obtained by further diluting the prepared stock solution according to the experiment requirement. Perovskite films (1.4cm×2.4cm×200nm), were dissolved in 10 ml of the prepared aqueous solution with different pH value. The aqueous solutions with pH of 4.5 and 5.6 were prepared by diluting aqueous solutions of HNO3 and acetic acid to ca. 0.1 mM, respectively, until the required pH was obtained.

Figure 1. (a) Photograph of the three types perovskite films before and after rain water immersion for 10 seconds and after annealing at 100 °C for 30 mins; Pb2+ contents in the contaminated rain water (b) pH = 5.6 and (c) pH = 4.5 depending on PSC types and dipping time.


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Synthesis and functionalization of AuNPs AuNPs were obtained by the improved Frens method.31 The sodium citrate was used as a reducing agent to reduce HAuCl4. Different sized AuNPs were prepared by adjusting the ratio of sodium citrate and HAuCl4. The small sized AuNPs was obtained as follows. 90 mL ultrapure water was put in a 250 ml round bottom flask. 5 mL of HAuCl4·4H2O (5×10-3 mol/L) was added under vigorous stirring. Then, 5 mL of sodium citrate (1.7×10-2 mol/L) was added in the above solution. The mixed solution was heated to boiling, and kept for 10 minutes. After that, the product was cooled naturally to room temperature. In this process, the color of solution was slightly changed from yellow into wine red. The theoretical concentration of AuNPs solution was 2.5×10-3 mol/L and the average diameter was 20.6±1.4 nm (measured by TEM). The maximum absorption peak was at about 520 nm. The big sized AuNPs was synthesized as follows. 93 mL ultrapure water was put in a 250 ml round bottom flask and 5 mL of HAuCl4·4H2O solution (5×10-3 mol/L) was added under vigorous stirring. Then, 2 mL of sodium citrate (1.7×10-2 mol/L) was injected in the above solution. The mixed solution was heated to boiling, and kept for 10 minutes. After that, the product was cooled naturally to room temperature. In this process, the color of solution was changed from yellow into wine red and finally turned purple. The average diameter was about 30.0±3.9 nm (measured by TEM). The maximum absorption peak was at about 530 nm. The solutions with different sized AuNPs (total volume was 10 ml) were mixed under stirring. Then, 60 µL of GSH (2.5×10-3 M) was injected into the mixed solution. The solution was kept under stirring for 1 hour and then the GSHAuNPs were obtained. Colorimetric detection of Pb2+ Different ions (4 µM) were added into a solution containing GSH-AuNPs, respectively. The mixtures reacted at room temperature for 20 minutes to get the collection of photograph and then were transferred separately into a cuvette for the detection of absorbance. The absorption ratios of A700/A520 versus the concentration of Pb2+ were used for calibration. Results and discussion Evaluation of Pb2+ from three types of perovskite films immersed into simulated rain water

It is known that the perovskite film would degrade when interacting with water even under mild humidity condition, and giving PbX2 (X = Br, I) and ammonium halide ions.9,10,29 Here, we employed three kinds of perovskite films with up to 20% efficiency as reported, 26–28 which are pure MAPbI3 (PSC-1), FA0.85MA0.15Pb(I0.85Br0.15)3 (PSC-2) and Csx(MA0.17FA0.83)(100−x)Pb(I0.83Br0.17)3 (PSC-3), respectively. The degradation products of all the three types of PSCs are shown in Schemes 1 to 3. It is worth noting that the amount of mixed Br and Cs from PSC-2 and PSC-3 are minor and can be ignored in comparison with Pb and I in the film. The instance change of the three perovskite films were seen when dropped into water for only 10 seconds. The color of films changed from dark brown or black into yellow immediately (Figure 1a). This fast colour conversion indicates that a very fast destruction of the perovskite structure. Most of CH3NH3+ , CH(NH2)2+ and halide ions as well as certain amount of Pb2+ are removed from the FTO/TiO2 substrate through fast outdiffusion. The decomposed yellow substrates were then annealed at 100 °C for 30 mins. Several dark lines appeared on the annealed films, indicating the reversible reaction happened where little amount of CH3NH3I and/or NH=CH-NH3I remained on the substrates. X-ray diffraction (XRD) of the films before and after water dipping was measured to reveal the change in PSCs structures. (Figure S1) After exposure to rain water, only PbI2 with the characteristic (001) peak at ~12o remained and no peaks from the (110) perovskite at ~14o anymore, indicating the total degradation of perovskite films. This is in accord with the previous studies and the yellow films suggest that not all the PbI2 were dissolved in the simulated rain water.9 It is imperative and meaningful to sort out how much solvable toxic ions will be released from these three types of promising PSCs when the sealed cells are broken and exposed to rainwater. pH of normal rain in nature is about 5.6 and the rain with pH below 5.6 is called acid rain. Here, two types of simulated rainwater with pH at 5.6 and 4.5 were used to immerse the lab made PSCs with a structure of FTO/c-TiO2/mpTiO2/perovskite/Spiro-OMeTAD and an area of 3.75 cm2. ICP-MS measurements were performed to understand how the pH of rainwater and exposure time would affect the mass of solvated Pb2+ after immersion treatment. Solutions were taken from 10 mL of rainwater as a function of time (1h, 3h and 1day) and diluted for ICP-MS. Figure 1 and Table S1 show the contents of Pb2+ measured from three PSCs under different immersion conditions.

CH NH PbI

CH NH + + 3 (Scheme 1)

(NHCHNH ). (CH NH ). Pb(I. Br. )

0.85(NHCHNH ) + 0.15(CH NH ) + + 2.55 + 0.45'( (Scheme 2)

Cs* [(NHCHNH ). (CH NH )., ](.) Pb(I. Br., )

(100 − 0)[0.83(NHCHNH ) + (0.17CH NH ) ] + 023 + + 2.49 + 0.51'( (Scheme 3) from the smaller slope in the curves. (Figure 1b) The concentrations of Pb2+ measured after one day reached 2~ 2.7 Sample solutions from normal rain water with pH=5.6 were mmol/L. Generally, all the cells decomposed in the same trend studied firstly. For samples taken after 1 hour, a jump in the 2+ in the normal rain water. However, for samples taken from concentrations of Pb from all three PSCs was observed from acidic rain water with pH=4.5, the increasedconcentrations of 0 to about 0.7 mmol/L. Then a slower increase in the concenPb2+ (~ 1.7 mmol/L) in the water samples are more than twice trations was followed in the next two hours as can be seen



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of the levels in the case of normal rain water. Obviously, pH affects significantly the solubility of lead components in the perovskite film in the early emersion stage (1h and 3h). After another 3 hours, the concentrations of Pb2+ from PSC-1 and PSC-3 increased only slightly. In contrast, with PSC-2 the Pb2+ concentration raised significantly to 2.44 mmol/L. After one day, the Pb2+ concentrations in all the water samples increased to contiguous levels similar with that of pH=4.5. (Figure 1c) The much accelerated dissolution of Pb2+ in PSC-2 in the early stage of water dipping might be attributed to the synergistic effect of the specific composition in the perovskite film under this more acidic condition. After one day, the Pb2+ concentrations between samples from different films and rain water type approach to similar range. Overall, there exists a two-stage out-diffusion or dissolution procession when the perovskite films are dipped in rain water: a fast step and a slow step. The fast step happened within one hour due to the fact that the ammonium halides are assisting the solvation of lead halides. When the ammonium halides are totally diffused into the water phase, the solvation of lead halides slows down until the rain water is saturated. Core–satellite aggregation of AuNPs as indicator for detection of Pb2+ After the study of dissolution behavior of different PSCs in rain water, it is imperative to detect the Pb2+ ions inside the contaminated rain water, which has the chance to further pollute the soil, underground water, river and lakes. The toxicity of lead to human body is due in general, to its binding affinity to thiol and cellular phosphate groups of numerous enzymes, proteins, and cell membrane,32 thus we can make use of the amino acids (e.g. glutathione GSH) decorated gold nanoparticles to bind with Pb2+ ions via the chelating ligands.15 (Figure 2a) This is a self-assembly procession which can be visualized by transmission electron microscope (TEM) (Figure 2bc), UVVis Figure 2d) measurement and even naked eye. To realize the core–satellite AuNPs structure, two kinds of GSH modified gold nanoparticles with different sizes were synthesized. The dispersed and self-assembled gold nanoparticles after Pb2+ addition were firstly characterized by UV-Vis spectrometer. It can be seen from Figure 2d that there is only one distinct plasmon band at 520 nm for the unmodified AuNPs solution. Upon addition of GSH, the absorption peak slightly shifted to around 523 nm. From the TEM image in Figure 2b, we can see that the GSH-AuNPs are separately dispersed. When Pb2+ containing solution is added to the GSHAuNPs solution, the intensity of the plasmon peak at 520 nm significantly decreases and a new peak located at 700 nm was observed, which is attributed to the plasmon coupling after aggregation of AuNPs. The formed core–satellite structure can

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be revealed in Figure 2c. The absorbance at 520 and 700 nm is related to the extent of dispersed and aggregated states of AuNPs respectively. Therefore, the ratio between the absorbance at 700 nm and that at 520 nm (A700/A520) was used to express the ratio of aggregated AuNPs to dispersed AuNPs.

Figure 2. (a) Chemical structure of GSH; Representative TEM images of dispersed GSH-AuNPs (b) and the aggregated GSHAuNPs after interaction with Pb2+ (c); UV-Vis spectra (d) and Raman spectra (e) of AuNPs, GSH-AuNPs and GSH-AuNPs in the presence of Pb2+. Raman spectroscopy was further employed to understand the self-assembled process of the gold nanoparticles induced by Pb2+ (Figure 2e). The S-H stretching peak at 2524 cm-1 in pure GSH (Figure 2ei) disappeared after the modification of gold nanoparticles (Figure 2eii and iii), which can be attributed to the formation of Au-S bond between thiol group from GSH and gold nanoparticles.33 The peak at 1106 cm-1 and 1110 cm-1 in Figure 2eii,iii corresponding to the C-N and C-C stretching is enhanced comparing to those in Figure 2ei. 33 After the addition of Pb2+, peaks corresponding to the bending of C–H bonds at 1463 and 1582 cm-1 as well as gold–GSH vibration at 279 cm-1 in Figure 2eiii are enhanced greatly than that in Figure 2ei and 2eii.34 Moreover, the peak at 775 cm-1 in Figure 2ei assigning to –COO- bending is blue-shifted to 745 cm-1 in Figure 2eii and disappears in Figure 2eiii. The peak at 1628 cm-1 corresponding to amide I in Figure 2ei is red-shifted to 1680 cm-1 in Figure 2eii and disappears in Figure 2eiii. The above mentioned disappeared peaks are due to the coordination of carboxylic and amino groups with Pb2+. Optimization of the indicator recipe for colorimetric detection of Pb2+


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Figure 3. Influence of (a) ratio of two size of AuNPs (v:v), (b) the concentration of GSH, (c) pH value and (d) concentration of NaCl on the ratios of A700/A520 for GSH-AuNPs system in the absence and presence of Pb2+. In view of the complicated decomposed products from perovassist the aggregation of the AuNPs.15 So in our recipe, the 2+ skite solar cells according to Scheme 1 to 3, an effective Pb influence of NaCl on the ratio of A700/A520 in the presence of indicator should have reasonable sensitivity, selectivity and Pb2+ was studied and shown in Figure 3d. The ratio of anti-interference ability. In this regard, parameters to prepare A700/A520 increased significantly with the increase in the conthe indicator such as the ratio of two-sized AuNPs, concentracentration of NaCl from 15 mM to 20 mM and levelled off at tion of GSH, pH and concentration of NaCl need to be opti20 mM, which suggested that 20 mM of NaCl was sufficient mized. UV–Vis absorption of GSH modified AuNPs solution for the formation of aggregation. Therefore, 20 mM of NaCl with various ratios between two different sizes (V30 nm / V20 nm) was selected for the GSH-AuNPs sensing assay. of 1:3, 1:2, 1:1, 2:1, 3:1, 4:1 and 5:1 in the presence of 5 µM Selectivity and limit of detection test of the sensing assay as Pb2+ were recorded. Ideally, the optimized ratio of 30 nm Pb2+ indicator AuNPs to 20 nm AuNPs was expected to be equal to the amount of 20 nm AuNPs to fully cover the surface of 30 nm In order to study the influence of other ions on Pb2+ binding to AuNPs. Meanwhile, the ratio of A700/A520 should reach maxiGSH-AuNPs, several cations and anions were employed to mum, indicating that the introduced Pb2+ ions trigger the hightest the selectivity of the indicator. It is shown obviously that est aggregation. According to Figure 3a, when V30 nm/V20 nm from Figure 4 that 4 µM of Na+, Zn2+, Fe3+, Hg2+, Cd2+, Ca2+, equals 2:1 (in the presence of Pb2+) the A700/A520 showed the Ce+, K+, Ag+, Cu2+, Li+, CH3NH3+, CH(NH2)2+, I-, F-, Br-, Acmaximum ratio. Further increasing the ratio of volume (V30 and Cl- alone had no obvious effect on the color of the self/V ), A /A reached a plateau. Therefore, a ratio of 2:1 20 nm 700 520 nm assembled sensing assay (Figure S2). However, as the addition (v/v) of 30 nm GNPs to 20 nm GNPs was selected for the folof 4 µM of Pb2+ alone, the colour of the indictor solution lowing experiment. changed from red to blue. Moreover, competitive experiments Various concentrations of GSH with 0, 5, 10, 15, 20, 25, 30, were performed in the presence of Pb2+ (4 µM) with other ions 35 and 40 µM were employed to functionalize the AuNPs (V30 (X) above mentioned. The ratios of A700/A520 from the mix2+ tures of Pb2+ with X changed similarly with that from Pb2+ nm/V20 nm = 2:1) (Figure 3b). In the presence of 5 µM Pb , the ratio of A700/A520 increased significantly with the increase in alone, which indicated that the sensing system possessed exthe concentration of GSH and levelled off above 10 µM, cellent selectivity for Pb2+ ion. which would be chosen for the modification of AuNPs. The linear range of the GSH-AuNPs sensing assay was examA pH titration of GSH-AuNPs was carried out and the influined with different concentrations of Pb2+ under the above ence of pH in the range of 2.4 - 10.0 on the ratio of A700/A520 mentioned optimized conditions. The photograph of the senswas investigated. It is observed (Figure 3c) that, in the absence ing solutions with Pb2+ concentration varying between 0-4.5 2+ of Pb , the ratio of A700/A520 equals around 0.1 in the pH µM was shown in Figure 4b. The addition of merely 0.015 µM range from 4.0 to 10.0, indicating that there is no aggregation could induce visible color change from red to blue. Figure 4c and the GSH-AuNPs can be kept stable and uniformly distribplots the ratio of A700/A520 versus the concentration of Pb2+. uted. This is important for a potential chemical indicator. In The ratio of A700/A520 is sensitive to Pb2+ and increased as the 2+ the presence of Pb , the ratio of A700/A520 kept constant at pH concentration of Pb2+ increased. A linear correlation existed from 2.5 to 8.0 and then decreased slightly from 8.0 to 10.0. between the ratio of A700/A520 and the concentration of Pb2+ in Therefore, the pH values from 4.0 to 8.0 are suitable for the the range of 0.03-2 µM (R2=0.99). The LOD at an S/N ratio of 2+ detection of Pb . We choose pH = 5.0 for the following ex3 for Pb2+ was calculated to be 13 nM. The detection limit periment and at this pH value, the amino group in GSH can be from both naked-eye and UV-Vis linear curve are lower than protonated and two carboxyl groups are deprotonated in terms the maximum level in drinking water permitted by WHO (10 of the pKa of GSH.17 ppb, 48 nM). NaCl is known to speed up the color change by screen the repulsion between the negatively charged AuNPs, so as to



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Figure 4. (a) A700/A520 upon the addition of Pb2+ and/or selected ions to GSH-AuNPs sensing assay. Black bars represent the addition of single interferential ions (4 µM) and red bars are the addition of Pb2+ (4 µM) in the presence of interferential ion (X) (4 µM). (b) Plot of A700/A520 value of GSH-AuNPs as a function of the concentration of Pb2+; (c) Photograph of GSH-AuNPs sensing assay for the color change at different concentrations of Pb2+. On the basis of the F-test and t-test, the results from our apCase study of the Pb2+ indicator in detecting lead halide proach are in good agreement with those from ICP-MS. PSCs contaminated samples To demonstrate the potential applications of the prepared selfassembled sensing assay as Pb2+ indicator, we attempted to detect Pb2+ from PSCs immersed rain water. As shown in Figure 5, our AuNPs based colorimetric assay clearly and qualitatively shows the existence of Pb2+ inside the acidic rain water that soaked the three types PSCs. It means that our straightforward colorimetric method can make instant qualitative detection of Pb2+. Moreover, it is possible to estimate thatthe amounts of Pb2+ from PSC-1 and PSC-2 are around 1µM based on Figure 4c. To precisely determine the concentration of Pb2+ in rinsed rain water, a standard addition method was Figure 5. Photographs of GSH-AuNP based colorimetric assay in employed. According to the results of ICP-MS (Table S1) and the absence (a) and presence of Pb2+ in 5 µL diluted washing rain the detecting range of this system, the lead content of the samwater (PH = 5.6) from PSC-1(b), PSC-2(c) and PSC-3(d). ple water could be detectable even after diluting 10000 times. 2+ Table 1 lists the concentrations of Pb in those samples tested by this Pb2+ indicator and ICP-MS. The diluted samples exclude interferences from other components in the solutions. Table 1. Determination of the concentrations of Pb2+ in three PSCs by self-assembled gold nanoparticles and ICP-MS. samples

Self-assembled gold nanoparticles (mol/L, n=3)

ICP-MS (mol/L, n=3)

F test

t test

PSC-1

(2.49±0.205)×10-3

(2.67±0.0799)×10-3

6.58

1.41

PSC-2

(2.60±0.187)×10

-3

-3

PSC-3

(2.52±0.0157)×10-3

(2.47±0.0583)×10

(2.68±0.0694)×10-3

Conclusions In summary, to evaluate the lead-leaking behavior of a broken perovskite solar cell, we for the first time treated lab made three typical PSCs that have been reported to give the highest efficiencies with simulated normal rain and acidic rain water.

10.27

1.14

5.13

1.51

The analysis by ICP-MS revealed a two stage dissolution of Pb2+ ions and strong influence of pH value in the uptake of Pb2+ ions. There is no significant difference in the final Pb2+ concentrations among the three types of perovskite films and both rain water samples after 1 day soaking.


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Analytical Chemistry (7)

Given the complicated chemical composition in the perovskite-soaked rain water, the optimized glutathione modified gold nanoparticles (GSH-AuNPs) colorimetric sensing assay as a Pb2+ indicator showed excellent sensitivity, selectivity and anti-interference ability in determining the Pb2+ from PSCs. The Pb2+-induced aggregation of sensing assay could be monitored via both naked eye and UV–Vis spectroscopy with a detection limit of 15 nM and 13 nM, which are all lower than the maximum level in drinking water permitted by WHO. The quantitative detection results were compared and in good agreement with that of ICP-MS. By the use of the prepared GSH-AuNPs self-assembled sensing assay, a fast and on-site detection of Pb2+ leaked from PSCs in water could be realized. The work to make test strips based the GSH-AuNPs is under way in our lab.

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ASSOCIATED CONTENT

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Supporting Information (17)

The Supporting Information is available free of charge on the ACS Publications website. Additional Pb contents, characterization of PSCs films and photographs as noted in text (PDF).

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AUTHOR INFORMATION

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Corresponding Author

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* Corresponding authors: [email protected], [email protected], [email protected].

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ACKNOWLEDGMENT

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This work was financially supported by the National Natural Science Foundation of China (21404045), the Natural Science Foundation of Fujian Province (China) (2015J05025), Scientific Research Foundation for the Returned Overseas Chinese Scholars (State Education Ministry, China), Educational Commission of Fujian Province (China) (JA13017), Promotion Program for Young and Middle-aged Teacher in Science and Technology Research of Huaqiao University (ZQN-PY406) and Project Funding for Talent of Huaqiao University (13BS102). Y.M.Y gratefully acknowledges financial support from the China Scholarship Council (CSC, Grant No. 201508350028). The authors wish to thank Mr. Yi Zhang for providing perovskite films and Dr. Heron Vrubel for performing ICP-MS measurements.

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