Macromolecular Systems with MSA-Capped CdTe ... - ACS Publications

Subscriber access provided by UNIV OF LETHBRIDGE

Article

Macromolecular Systems with MSA capped CdTe and CdTe/ZnS Core/Shell Quantum Dots as Superselective and Ultrasensitive Optical Sensors for Picric Acid Explosive Priyanka Dutta, Dilip Saikia, Nirab Chandra Adhikary, and Neelotpal Sen Sarma ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b07660 • Publication Date (Web): 20 Oct 2015 Downloaded from http://pubs.acs.org on October 21, 2015

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

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

Page 1 of 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

ACS Applied Materials & Interfaces

Macromolecular Systems with MSA capped CdTe and CdTe/ZnS Core/Shell Quantum Dots as Superselective and Ultrasensitive Optical Sensors for Picric Acid Explosive Priyanka Dutta1, Dilip Saikia2, Nirab Chandra Adhikary2, Neelotpal Sen Sarma1,* 1Advanced

Materials Laboratory, Physical Sciences Division, Institute of Advanced

Study in Science and Technology, Guwahati – 781 035, India 2Plasma

Section, Physical Sciences Division, Institute of Advanced Study in Science

and Technology, Guwahati-781035, India *Corresponding author, E-mail: [email protected] Tel No. +91 361 2912073. Fax: +91 361 2279909.

ABSTRACT: This work reports the development of highly fluorescent materials for the selective and efficient detection of picric acid explosive in the nM range by fluorescence quenching

phenomenon.

Polyvinylalcohol

grafted

polyaniline

(PPA)

and

its

nanocomposites with MSA capped CdTe quantum dots (PPA-Q) and with MSA capped CdTe/ZnS core/shell quantum dots (PPA-CSQ) are synthesized in a single step free radical polymerization reaction. The thermal stability and photo stability of the polymer increases in the order PPA < PPA-Q < PPA-CSQ. The polymers show remarkably high selectivity and efficient sensitivity towards picric acid and the quenching efficiency for PPA-CSQ reaches up to 99 %. The detection limit of PPA, PPA-Q and PPA-CSQ for picric acid are found to be 23 nM, 1.6 nM and 0.65 nM respectively which is remarkably low. The mechanism operating in the quenching phenomenon is proposed to be a combination of a strong Inner Filter Effect (IFE) and ground state electrostatic interaction between the polymers and picric acid. A portable and cost effective electronic device for 1 ACS Paragon Plus Environment


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

the visual detection of picric acid by the sensory system is successfully fabricated. The device was further employed for quantitative detection of picric acid in real water samples. KEYWORDS: Polymer nanocomposites, fluorescence quenching, quantum dots, core/ shell quantum dots, picric acid sensing. INTRODUCTION: Enormous number of terrorist activities throughout the world has led to the urgent need for the development of efficient and selective sensors for the detection of trace number of explosives. Among the diverse chemicals used in such deadly weapons, nitro containing and nitroaromatic compounds cover a wide range of such explosives.1,2 Picric acid (2,4,6-trinitrophenol) is found to be a highly dangerous polynitrated aromatic explosive and its deadly effects are even worse than the well-known explosive 2,4,6trinitrotoluene (TNT).3,4 Besides being a dangerous explosive material, picric acid is also considered to be a highly toxic environment pollutant. Because of its high solubility in water, its exposure can easily contaminate soil and groundwater causing serious threat to human health and environment.5 Picric acid causes severe health effects including skin and eye irritation and severe respiratory disorders.6,7 Thus the development of potential picric acid sensors with high sensitivity and selectivity is of utmost importance in the present scientific world. Among the various analytical techniques used for the detection of picric acid, fluorescence based sensing is highly employed because of its high sensitivity and quick response time.8-10 Forster resonance energy transfer (FRET),11 Photoinduced electron transfer (PET),12 Ratiometric detection13, Inner Filter Effect (IFE)14 and Aggregation Induced Emission (AIE)15 are some of the well-known mechanisms for fluorescence 2 ACS Paragon Plus Environment

Page 2 of 34

Page 3 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


based sensing phenomenon. Inner Filter Effect is the reabsorption of emitted light of the fluorescent probe by the analyte resulting in fluorescent quenching. Recently, IFE has gained much interest in the development of efficient sensors which does not require the establishment of covalent linkage of the probes with the analyte.16,17 Rong et. al in 2015 established a novel approach towards picric acid sensing by graphitic carbon nitride nanosheets based on Inner Filter Effect.18 Among the various probes, semiconducting polymers are immensely useful as chemosensors because of their high stability, high sensitivity and better mechanical properties.19,20 Luminescent metal organic frameworks have also been reported for the efficient detection of nitroaromatic explosives in alcoholic medium.21 Organic dyes and conjugated polymers for nitroaromatic explosive sensing in non-aqueous media have been reported.22,23 Ratiometric NIR fluorescent sensor for PA based on charge transfer in CH3CN had been constructed by Xu et al.24 Quantum dots are primarily inorganic nanoparticles possessing unique photophysical properties.25 Core shell quantum dots are highly functionalized materials having modified properties and are finding diverse applications as sensors, catalysis, in optoelectronics and other biomedical applications.26,27 Willner et al. used CdSe/ZnS QDs as fluorescent probes to detect TNT or trinitrotriazine (RDX).28 CdTe/CdS core/shell QDs and hybrid CdTe QDs have also been reported as fluorescent probes for detecting nitroaromatic explosives.29,30 In our earlier work, we have seen that the incorporation of nanoparticles in semiconducting polymers increases the surface charge of the polymers which enhances various properties of such polymers for diverse applications.31,32 Thus, in the present work, we have synthesized electron rich CdTe and CdTe/ ZnS core/ shell QDs at controlled conditions using MSA as the capping agent. Electron rich nanocomposites were then prepared by incorporating these QDs in polyvinlyalcohol grafted polyaniline via single step free-radical polymerization reaction.

3 ACS Paragon Plus Environment


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

The polymers are found to be efficient probes for the selective detection of highly electron deficient picric acid explosive in aqueous medium. The formation of ZnS shell over the CdTe core increases the stability and quantum yield of the QD and reduces its toxicity to a large extent. Furthermore, the remarkably low detection limit and real sample analysis of the CdTe/ ZnS core/ shell nanocomposite makes them suitable probes for selective and efficient sensing of PA in aqueous medium. Materials and Methods: Materials: Polyvinyl alcohol (LOBA CHEMIE), Aniline (MERCK), AIBN (SPECTROCHEM), DMSO (MERCK), Cadmium chloride (MERCK), Sodium Borohydride (Merck), Mercapto succinic acid (Loba Chemie), Sodium telluride (Loba Chemie), Citric acid (Fischer Scientific), Borax powder (Fischer Scientific), Zinc chloride (MERCK) and Sodium sulphide (MERCK) were used without further purification. Picric acid (PA) was purchased from SIGMA and stored in 50% water because of safety reasons. 3,5dinitrosalisylic acid (DNSA), 1,4-dinitrobenzene (DNB), 2-nitrophenol (2-NP), 4nitrophenol (4-NP) and nitrobenzene (NB) were purchased from MERCK. Synthesis of CdTe-MSA and CdTe-MSA/ ZnS core/ shell quantum dots: CdTe-MSA quantum dots are synthesized at pH 8 and collected after 1 hour as reported earlier.33 MSA capped CdTe/ZnS Core/Shell quantum dots are synthesized by a one-pot approach34 in addition to an extra step for the shell formation over the core QD. At first, 3 mM CdCl2, 0.75 mM Na2TeO3 and 9 mM MSA solutions were mixed with a buffer containing Borax and Citric acid. The reaction mixture is stirred properly for 5 min and pH is maintained at pH 8. Suitable amount of NaBH 4 is then added to the reaction 4 ACS Paragon Plus Environment

Page 4 of 34

Page 5 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


mixture and the colorless solution turns light yellow. This indicates the initiation of nucleation of nanocrystals and the solution was refluxed at 100 oC for 20 minutes. Thereafter, 3 mM 20 ml solutions of each ZnCl2 and Na2S were added to the reaction mixture followed by addition of 1.8 ml of 0.1 M MSA solution. The samples formed are the required CdTe/ZnS core/ shell quantum dots and are collected after 1 hour.

Scheme 1: Synthetic route for preparation of the QDs with their proposed structures Scheme 1 shows the possible reaction steps in the synthesis of CdTe/ZnS core/ shell quantum dots, where Cd2+ of CdCl2 and Te2- of Na2TeO3 react with MSA to form MSA capped CdTe quantum dot (Step-I). The electron affinity of the capping agent MSA is same towards Cd, Zn and S because of their same oxidation state. Hence, CdTe QD surface adsorbs Zn and S atom to form a shell of ZnS over CdTe core (Step-II).



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

Synthesis of the polymers: Polyvinyl alcohol (PVA) (1 g, DP=1,700-1,800) dissolved in DMSO, Aniline (8.4 ml, 0.09 mol) and the initiator AIBN (0.05 g) was mixed together and degassed. After the complete removal of oxygen, the above solution was sealed and placed in a thermostat at 60 oC for 2 days. The tube was then opened and the reaction mixture was poured into ethanol to precipitate the polymer. It was further washed with hot water and after extraction, 2.5 g of polyvinylalcohol grafted polyaniline was isolated and dried at 50 oC. It is designated as PPA. FT-IR: ῡ (cm-1) = 3381, 3010, 2922, 1647, 1445, 1314, 1140, 1017, and 921. 1H NMR (DMSO): δ (ppm) = 4.2-4.67 (for –OH proton), 3.8 (-CH proton), 1.3-1.7 (-CH2 protons), 4.94 (s, -NH proton), 6.43 (t, 1H), 6.5 (d, 2H) and 6.9 (t, 2H). Now, 5 ml solution of MSA capped CdTe quantum dots (pH 8) was added to the PVA (1 g, DP=1,700-1,800) solution in DMSO and stirred overnight so that the QDs are well dispersed into the polymer matrix. After that, aniline (8.4 ml, 0.09 mol) along with AIBN (0.05 g) was added to the above solution and degassed. Again, the solution, after complete removal of oxygen was placed in a thermostat at 60 oC for 2 days. The tube was then opened and the reaction mixture was allowed to precipitate in ethanol. It was then washed with hot water and then 2.8 g nanocomposite gel of PVA-g-PPA-CdTe quantum dots was extracted which is designated as PPA-Q. FT-IR: ῡ (cm-1) = 3380, 3010, 2921, 1647, 1443, 1315, 1152, 1016, and 921. 1H NMR (DMSO): δ (ppm) = 4.24.67 (for –OH proton), 3.8 (-CH proton), 1.3-1.7 (-CH2 protons), 4.94 (s, -NH proton), 6.43 (t, 1H), 6.5 (d, 2H) and 6.9 (t, 2H). The above procedure was adopted with 5 ml solution of MSA capped CdTe/ZnS core/ shell quantum dots (pH 8) to synthesize 2.7 g of the corresponding nanocomposite and is designated as PPA-CSQ. FT-IR: ῡ (cm-1) = 3381, 3010, 2922, 1647, 1445, 1315,


Page 6 of 34

Page 7 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


1159, 1015, and 922. 1H NMR (DMSO): δ (ppm) = 4.2-4.67 (for –OH proton), 3.8 (-CH proton), 1.3-1.7 (-CH2 protons), 4.94 (s, -NH proton), 6.43 (t, 1H), 6.5 (d, 2H) and 6.9 (t, 2H). Note: The polymer PVA-g-polyaniline was synthesized using four different concentrations of aniline i.e. 0.3 mol, 0.6 mol, 0.9 mol and 1.2 mol. The best fluorescence property was obtained for the one prepared using 0.9 mol. Further increase in the amount of aniline did not enhance the fluorescence property. This may be due to inefficient grafting of aniline with the PVA matrix. Hence, the concentration of aniline was fixed at 0.9 mol and the nanocomposites were also prepared using the same concentration. The FT-IR and 1H-NMR spectra of the polymers are provided in Figure S1 and S2 in the Supporting Information section. Figure 1 gives the pictures of the synthesized gels at normal light and at UV light of wavelengths 254 nm and 365 nm.

Figure 1: Pictures of the gels under normal light and UV light Methods: FT-IR measurements: Fourier Transformed Infrared spectra (FT-IR) of the samples were recorded with a NICOLATE 6700 FT-IR Spectrophotometer in the range of 6007 ACS Paragon Plus Environment


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

4000 cm-1 with 64 scans. The samples were prepared in the form of thin films and the spectra was recorded in the ATR transmission mode. NMR Measurements: 1H NMR spectra of the polymers in solution state were recorded on a Bruker 400 MHz NMR spectrometer using DMSO as the solvent. The internal standard is tetramethylsilane (TMS) relative to which the chemical shifts appear in the 1H

NMR spectrum.

TEM analysis: Few drops of CdTe and CdTe/ZnS core/shell quantum dot solutions were dispersed into a 3 mm copper grid covered with carbon film. The samples were dried at room temperature. TEM analysis was carried out on a JEOL JEM 2100 transmission electron microscope operating at 200 kV. FESEM characterization: Surface morphological study of the polymers were carried out with a SIGMA – VP (ZEISS) Scanning Electron Microscope at an accelerating voltage of 5 kV. Thin films of the polymers were prepared with thickness 0.3 mm for the study. EDX study was carried out to measure the elemental distribution of the quantum dots and the polymers with the help of Carl Zeiss Ʃigma VP using EHT 20kV. Thermal properties analysis: The thermal stability of the polymers were studied with the help of Thermo Gravimetric Analysis (TGA) using Perkin Elmer TGA 4000 at a heating rate of 10oC per minute with a constant N2 flow rate of 20 ml/min within a temperature range of 35-800 oC. XRD characterization: The powder X-ray Diffraction (PXRD) study was carried out with a Bruker D8 Advance diffractometer using Cu Kα (λ= 1.54 Ǻ) as the incident ray operating at 40 kV and 40 mA in the angular range 2θ =5 - 80ο. Sample preparation for DLS and Spectroscopic studies: The polymer samples were dispersed in DMSO in the concentration 0.1 g/ml. Thereafter, 30 µL of the above solution 8 ACS Paragon Plus Environment

Page 8 of 34

Page 9 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


is dispersed in 3 ml of distilled water and is used for the DLS and spectroscopic studies. Thus the solvent media used for all photophysical experiments of the undoped polymer and the QDs doped polymers is 1:100 of DMSO: H2O. PA solution was prepared in distilled water for the PL experiments. For real time analysis, PA solutions were prepared in IASST tap water and drinking water and were used thereafter for PL experiments. DLS Measurements: Zeta potential was measured at 25oC in Malvern Nano ZS90 in a glass cuvette with zeta dip cell electrode. Spectroscopic experiments (UV-Vis and PL study): UV-Vis spectra were recorded at 25oC using 1800 SHIMADZU UV-Vis spectrophotometer. PL studies were carried out using Cary Eclipse spectrophotometer with halogen lamp as the excitation source and at a constant scan rate of 240 nm s-1. The excitation and emission slit widths were taken to be 5 nm and the detector voltage was kept at 550 V. Quartz cells (4×1×1 cm) with high vacuum Teflon stopcocks were taken for spectral measurements. Time-Resolved Photoluminescence study: Time resolved photoluminescence (TRPL) study is carried out using Edinburg Instruments FSP920, Picosecond Timeresolved cum Steady State Luminescence Spectrometer. An LED source of wavelength 290 nm is used as the excitation source. Cyclic Voltammetry (CV) experiments: CV measurements were done using a Gamry Reference 3000 Potentiostat/Galvanostat instrument with a three-electrode system. The electrodes used are glassy carbon working electrode, Ag/Ag+ reference electrode and a platinum wire counter electrode with 0.5 M KCl aqueous solution as electrolyte. RESULTS AND DISCUSSIONS: Characterization of QDs: 9 ACS Paragon Plus Environment


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

Page 10 of 34

The TEM and HRTEM images of the QDs are provided in Figure 2. HRTEM images shows that the particle size of the CdTe QDs ranges about 5-6 nm, while CdTe/ ZnS core/ shell QDs ranges about 6-7 nm. The HRTEM images shows that the QDs are nearly spherical in shape with distinct lattice fringes. The formation of core around the spherical shell can be clearly observed in the HRTEM image of the core/ shell QD. The interplanar spacing was found to be 0.31 nm for CdTe and 0.27 nm for the ZnS shell. The presence of Cd, Te and S in MSA capped CdTe QD and that of Cd, Te, Zn and S in CdTe/ ZnS core/ shell QD was verified from the EDX spectra provided in Figure S3 in the Supporting Information section. Crystal structure analysis of CdTe and CdTe/ ZnS QDs by PXRD technique reveals the formation of cubic zinc blende crystal structure. The observed diffraction peaks at 24°, 40° and 46.9° corresponds to (111), (220) and (311) lattice plane of CdTe cubic zinc blende structure. The peaks at 27° and 44.3° for CdTe/ZnS CS QD corresponds to (111) and (220) lattice plane. The shift in the peaks towards larger 2θ values corresponds to the formation of the ZnS shell over the CdTe core.35 From the FT-IR spectra, the presence of peak at 1325 cm-1 indicates the presence of sulphide groups in the CdTe and the CdTe/ ZnS core/ shell QDs. The absence of –SH peak in the range 2500-2600 cm-1 indicates the cleavage of thiol moiety and the formation of S-Cd bond in CdTe QD and S-Zn bond in CdTe/ ZnS core shell QD. The XRD and FT-IR spectra of the QDs are provided in Figure S3 in the Supporting Information section. Zeta potential studies further shows that the surface charge of the MSA capped CdTe QDs is around -28 mV and that of MSA capped CdTE/ ZnS core/shell QD is 40 mV. The effect of different pH on the PL spectra of the core/shell QD were also checked and it is provided in Figure S4 in the Supporting Information. The best fluorescence intensity was obtained for pH 8 and hence it was incorporated into the polymers.


Page 11 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


Figure 2: (A) TEM and (B) HRTEM image of CdTe QDs; (C) TEM and (D) HRTEM image of CdTe/ ZnS core/ shell QDs Thermal stability and crystalline properties of the polymers: The polymers shows sharp peaks at 2 theta values of 15 and 17 as shown in the XRD spectra in Figure 3 A. The crystalline property of the polymers further increases after the incorporation of quantum dots. In case of PPA-Q and PPA-CSQ, the presence of small peaks at 2 theta values of 24, 40 and 47 corresponds to (111), (220) and (311) diffraction planes of the zinc blende structure of CdTe. The XRD spectra of PPA-Q and PPA-CSQ are almost similar in appearance. The TGA spectra of the polymers in Figure 3 B shows that the thermal stability of the polymers increases to a large extent after the 11 ACS Paragon Plus Environment


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

Page 12 of 34

incorporation of QDs. The addition of the CdTe/ ZnS core/ shell QD further increases the thermal stability. The weight loss at 200 oC is 25 % for PPA, 10 % for PPA-Q and 9 % for PPA-CSQ. Complete degradation of the polymers occurs at around 530 oC for PPA, 550

oC

for PPA-Q and 600

oC

for PPA-CSQ. This clearly elucidates the

comparatively much higher thermal stability of the CdTe/ZnS core shell nanocomposite.

Figure 3: (A) XRD spectra and (B) TGA analysis of the polymers FESEM and EDX spectra of the polymers: FESEM images of the polymers as shown in Figure 4, displays the presence of clusters of nanoparticles of size around 100 nm in the polymer crosslinks. The presence of Cd, Te and S in the EDX spectra confirms the presence of MSA capped CdTe Qds in PPA-Q. Similarly, the presence of Cd, Te, Zn and S in the EDX spectra confirms the presence of MSA capped CdTe/ ZnS core shell QDs in PPA-Q. EDX mapping of the polymers displayed the percentage composition of the different elements in the polymers as provided in Figure 4. The percentage elemental composition of all the polymers is provided in Table S1 and the mapping of PPA and PPA-Q in Figure S5 in the Supporting Information section. EDX spectra were also taken at different regions of the polymer material and it confirmed uniform elemental composition throughout.


Page 13 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


Figure 4: FESEM image and EDX spectra of the polymers; EDX mapping of the polymer PPA-CSQ



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

Page 14 of 34

Photophysical properties: The polymers PPA, PPA-Q and PPA-CSQ shows strong absorption peaks at 287 nm, 290 nm and 291 nm. The emission peaks of the polymers PPA, PPA-Q and PPACSQ were obtained at around 333, 340 and 350 nm, respectively, on excitation at 270 nm. It was clearly observed that the incorporation of quantum dots increases the fluorescence intensity of the polymers. The absorption and emission spectra of the polymers are given in Figure S6 in the Supporting Information. Again, the impregnation of CdTe and CdTe-ZnS core/ shell quantum dots induces high photostability in the polymer which further increases their widespread applications. The photostability study of the polymers is depicted in Figure S7 in the Supporting Information. Sensitivity studies: The sensitivity of the polymers were tested in presence of picric acid and it was found that the polymers displayed selectively good sensitivity for picric acid compared to other compounds. The PL intensities of the polymers gradually decreases on the addition of picric acid which implies that sensing occurs via fluorescence quenching methods. The quenching efficiency of the polymers increases in the nanocomposites compared to PPA and in PPA-CSQ, the PL intensity completely quenches after addition of 20 nM picric acid solution. The quenching efficiency is observed to be 81 % for PPA, 94 % for PPA-Q and 99 % for PPA-CSQ. Figure 5 shows the PL quenching studies after the addition of picric acid in the polymers.


Page 15 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


Figure 5: Fluorescence quenching of the polymers in presence of PA Selectivity and Interference study: The sensing ability of these polymers were checked in presence of other nitroaromatic, nitroaliphatic, non-nitroaromatic and non-aromatic compounds as well. The compounds chosen for the study were 2-nitrophenol (2-NP), 4-nitrophenol (4-NP),



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

Page 16 of 34

3,5-dinitrosalicylic said (3,5-DNSA), 1,4-dinitrobenzene (1,4-DNB), nitrobenzene (NB), benzoic acid (BA), benzoyl chloride (BC), benzene, chloroform, nitromethane (NM) and nitroethane (NE). It was observed that the PL intensity of the polymers remains slightly differs in presence of these analytes. The best selectivity was obtained for PPA-CSQ and it was clearly observed that PPA-CSQ selectively senses only picric acid rather than all the above mentioned analytes. The selectivity of the polymers was also tested in presence of different metal ions such as Na+, Li+, Ca2+, Ba2+ and various other heavy metals such as Cd2+, Pb2+, Cr2+, Hg2+, Co2+, Ni2+, Cu2+ and Zn2+ ions. The PL intensity of the polymers slightly changes in presence of the metal ions. Figure 6 A and 6 B shows the selectivity of PPA-CSQ in presence of all these compounds and metal ions. The interference of all the above compounds and metal ions were tested in the picric acid sensing phenomenon of the polymers. It was experimentally studied that the effect of these interferents in the PA quenching efficiency of the polymers is very less. The interference study of PPA-CSQ showed that the effect of all above interferents in its PA quenching phenomenon is almost negligible as shown in Figure 6 C and 6 D. The high selectivity may be attributed to the lack of proper binding sites for metal ions. Interference study of the polymers PPA and PPA-Q is provided in Figure S8 and Figure S9 in the Supporting Information section.


Page 17 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


Figure 6: Selectivity study of PPA-CSQ in presence of (A) chemicals, and (B) metal ions; Interference of (C) chemicals, and (D) metal ions, in PA sensing Stern-Volmer plots and TRPL study: Stern Volmer (SV) plots were plotted to get a deeper understanding of the process taking place in the PL quenching phenomenon. Figure 7 shows that the plot of Io/I vs PA concentration gives a straight line at low concentration bending upwards at higher concentration. The Stern-Volmer constant from the linear fitted SV plot is calculated directly from the slope. The non-linear SV plots confirms either selfabsorption or the presence of an additional energy transfer mechanism. The SternVolmer binding constant (Ksv) of the polymers as obtained from the slope of the SV plots are 2.12 × 107 for PPA, 4.73 × 108 for PPA-Q and 1.74 × 109 for PPA-CSQ. To gain further insight into the mechanism, time resolved photoluminescence (TRPL) study was carried out to differentiate between static and dynamic quenching.



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

Page 18 of 34

Figure 7: Stern-Volmer plots of the polymers in presence of PA Figure 8 shows the TRPL spectra of the polymers in absence and in presence of PA. The TRPL measurements of the polymers were carried out in absence of PA and in presence of a definite concentration of PA viz. 50 nM for PPA, 20 nM for PPA-Q and 10 nM for PPA-CSQ. Since the PL lifetime of the polymers remained unchanged on addition of analytes, this suggests the presence of static quenching phenomenon via formation of a ground state electrostatic interactions. Table 1 shows the lifetime and 2 values of the polymers in absence and presence of analytes.

Figure 8: TRPL spectra of the polymers in absence and in presence of PA 18 ACS Paragon Plus Environment

Page 19 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


Table 1: Lifetime and 2 values of the polymers in absence and presence of PA. TRPL Datas

PPA

PPA + PA

PPA-Q

PPA-Q + PA

PPACSQ

PPACSQ + PA

ns)

0.82

0.84

0.90

0.919

0.977

0.978

2

0.94

0.99

1.03

1.027

1.06

1.079

Mechanism: The mechanism operating in picric acid sensing is proposed to be a combination of a strong Inner Filter Effect (IFE) and ground state electrostatic interaction between the polymers and picric acid. The high sensitivity of the polymers towards PA and the non-linear SV plots suggests the possibility of either excited state energy transfer from the luminescent polymers to the non-luminescent analyte (FRET), or re-absorption of the emitted light of the polymer by the quencher (IFE). Both in case of Forster Resonance Energy Transfer (FRET) and Inner Filter Effect (IFE), there is an efficient overlap between the emission band of the donor and the absorption band of the acceptor.18 Since the lifetime of the probes remained unchanged on adding PA in the TRPL study, the possibility of excited state energy transfer via FRET is ruled out. Thus the predominant factor behind the quenching mechanism is a strong Inner Filter Effect along with some electrostatic interactions. Figure 9 shows a large overlap between the normalized emission band of the polymers and the normalized absorption band of PA. The area of spectral overlap for PPA is 61.02, for PPA-Q is 76.01 and for PPA-CSQ is 84.14. The overlap is the largest for PPA-CSQ which ensures efficient IFE leading to the remarkably high quenching efficiency. Due to efficient spectral overlap, the probes also get nearer to each other which in turn increases the electrostatic interactions between the polymer and the analyte. The overlap with all other nitroaromatic



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

Page 20 of 34

compounds is given in Figure S10 in the Supporting Information. The comparatively much less spectral overlap with other analytes is another reason behind the selective sensitivity of the polymers towards PA.

Figure 9: Overlap between the emission band of the polymer and the absorption band of PA Electrostatic interaction brings the probes in close proximity which may result in electron transfer between the polymer and picric acid. To further check the probability of electron transfer mechanism, cyclic voltammetry (CV) study of the polymers were carried out as shown in Figure S11 in the Supporting Information. The HOMO and LUMO levels of the polymers were calculated based on cyclic voltammetry study.36 The calculated values of HOMO are -5.34 eV for PPA, -5.08 eV for PPA-Q and -4.74 eV for PPA-CSQ. Again, the values of LUMO were found to be -4.7 eV for PPA, -4.47 eV for PPA-Q and -4.33 eV for PPA-CSQ. The HOMO and LUMO levels of PA and picrate ion were taken from literature.9 Cyclic Voltammetry study confirmed the absence of excited state electron transfer since the LUMO of the polymers lies below the LUMO of picric acid. Again, since the polymers are negatively charged, the probability of ground state electron transfer from the picrate ion to the polymer is also not possible. This further rules out the possibility of electron transfer mechanism.


Page 21 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


In addition to the strong Inner Filter Effect (IFT), electrostatic interactions such as H-bonding between the basic NH group of the e- rich polymer and the –OH group of picric acid is another reason which leads to ground state acid-base electrostatic interactions. Such type of electrostatic interaction was reported by Sun et al., between the amine group of Bovine Serum Albumin (BSA) and the picrate ion.37 The luminescence in the polymer is mainly due to the presence of the conjugated system aniline. The proposed mechanism describes that there is charge transfer from the QDs to the polymer. The surface charge of the QDs is electrically negative and hence there is charge transfer from the QDs to the nitrogen of aniline which makes the nitrogen more electron rich and facilitates efficient bonding with the –OH group of picric acid. Hence, after the addition of QDs the sensing efficiency of the polymers toward picric acid increases. Again, the –OH group of picric acid is highly acidic due to the presence of three electron withdrawing –NO2 groups and easily reacts with the basic amine group of aniline. To check the probability of interaction of the polymer with any acid, we have checked selectivity tests with benzoic acid and 3,5-dinitrosalicylic acid which showed no change in the fluorescence intensity. Further evidence was collected from UV spectroscopic measurements as given in Figure S12 in the Supporting Information. It was observed that there is a decrease in the absorbance peak of PPA-CSQ at 291 nm after the addition of PA along with the formation of the absorption peak for PA at 350 nm. The absence of shift in the λmax value of the polymer upon addition of PA further confirms the absence of any ground state complex formation. The fluorescence quenching occurs due to the presence of weaker electrostatic interactions such as Hbonding between the –OH group of picric acid and the –NH group of the basic polymer. The electrostatic interaction of the polymers with picric acid is diagrammatically represented in Scheme 2.



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

Page 22 of 34

Scheme 2: Schematic representation of the electrostatic interaction The electrostatic interaction is further confirmed by zeta potential (ζ) provided in Figure S13 in the Supporting Information section. The ζ value of CdTe QD is -28 mV and that of CdTe/ZnS core shell QD is -40 mV. The electronegative QDs induces charge transfer from the QD to the polymer and thus the surface negative charge of the nanocomposites increases. The incorporation of highly electronegative CdTe/ ZnS QDs (ZP = -40 mV) increases the surface negative charge of the nanocomposite and the ζ of the PPA-CSQ nanocomposite is found to be -14.7 mV. This further reduces to -4.48 mV after the addition of picric acid. This is a solid evidence of the strong electrostatic interaction taking place between the polymer and picric acid.


Page 23 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


Sensing experiments in real samples: Practical applications of the sensory systems was investigated by studying the PL quenching efficiency of the polymers in real samples. Real sample analysis was performed by preparing picric acid solutions in IASST tap water and drinking water. It was found that the PL quenching efficiency is least affected in case of drinking water compared to that of tap water. This is because the polymers lack proper binding sites for metal ions due to which it selectively senses picric acid. This increases the probability of in field application of these polymers as efficient and selective sensing materials for picric acid. The real sample analysis for PA sensing is depicted in Figure S14 in the Supporting Information. Limit of Detection (LOD) of the polymers: The excellent quenching efficiency of the polymers is supported by an extremely low limit of detection for picric acid as shown in Figure 10. Detection limit of the polymers decreases to a large extent after the doping of CdTe and CdTe/ZnS quantum dots in the polymer. The detection limit is found to be in the nM range for the polymers and PPACSQ shows a remarkably low detection limit of 0.65 nM picric acid.

Figure 10: Determination of the limit of detection of the polymers for PA



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

Page 24 of 34

This value of detection limit is very low compared to many other earlier reported works. A comparative study is also carried out to show the advantages and better LOD of our sensory system over earlier reported PA sensors in Table 2. Table 2: Comparative values of LODs of PPA-Q and PPA-CSQ with earlier reported sensors: Sl. no. 1. 2. 3.

Sensor systems

LOD for PA

Ref.

Phosphole Oxide

2.03 mM

38

Cationic bispyrene fluorophore, Py-dilM-Py Self-assembled pentacenequinone derivative

1×

10-6

M

39

3.5 × 10-7 M

40

4.

Sodium dodecyl sulfate (SDS)

1 μM

41

5.

Eu(III) based metal organic frameworks

1 × 10-7 M

42

6.

DNSA-SQ

70 nM

43

7.

Isobenzotriazolophanes

19 ppm

44

8.

Tripyrenyl Truxene

0.15 ppm

45

9.

PPA-Q

1.6 nM

10.

PPA-CSQ

0.65 nM

(Our system) (Our system)

Fabrication of an electronic device for visual observation of picric acid sensing: The highly fluorescent property of the polymers has been used to design an electronic device for the visual detection of picric acid in aqueous media. The circuit diagram of the electronic device is provided in Figure S15 in the Supporting Information, and it consists of a photo diode, a UV LED, an operational amplifier and a Power Supply unit (PSU). The polymer PPA-CSQ was considered for this application. We have observed that the PPA-CSQ emits blue light under the UV light of 365 nm. Hence 395 nm 2-pin through-hole UV LED was used to excite the polymer and was fitted with a cuvette to illuminate the polymer solution from bottom side. A visible light photodiode SFH2270R was used in this circuit for accurate light detection from the 24 ACS Paragon Plus Environment

Page 25 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


photoluminescence of the sample. The amplifier IC OP07 was used for converting the photodiode current into an output voltage. At last a digital voltmeter was used for measuring the output voltage from the amplifier circuit.

Figure 11: (A) Photograph of the circuit designed for PA detection at switched off condition, (B) Voltmeter reading of the polymer illuminated by UV LED, (C) Voltmeter reading of the polymer with PA illuminated by UV LED showing the quenching effect, and (D) Plot of Voltage vs PA concentration in real samples added to the polymer; Error bar represents the standard deviation of three consecutive voltmeter readings. The polymer PPA-CSQ was initially dispersed in DMSO in the concentration 0.1 g/ml. After that it was diluted with 10 times distilled water and the solvent system used was 1:10 DMSO: H2O. Thus the concentration of the polymer used for this experiment is 0.01 g/ml in the solvent mixture 1:10 DMSO: H2O solution. Initially the cuvette containing the polymer solution was kept in a dark condition. When the cuvette sample 25 ACS Paragon Plus Environment


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

Page 26 of 34

was illuminated from bottom by glowing the UV LED, blue light was emitted from the solution. The photodiode connected to the cuvette then sense the blue light and the corresponding voltage was obtained from its reverse current with the help of the operational amplifier. The picture of the entire circuit at switched off condition is given in Figure 11 A. The voltage corresponding to the photoluminescence of the polymer sample after illuminating with UV LED was found to be 2.3 V as shown in Figure 11 B. On addition of 2 µM PA, the photoluminescence of the polymer quenches and the voltmeter reading was found to be 1.1 V as shown in Figure 11 C which clearly shows the quenching effect. The above experiment was repeated with real water samples. We have used IASST tap water to prepare the polymer solution in the ratio 1:10 of DMSO: H2O. A stock solution of 10 µM picric acid was then prepared in tap water and increasing amount of PA were added to the polymer solution to obtain the corresponding voltmeter readings. It was observed that the voltage decreases on increasing the amount of PA added. The initial voltmeter reading for the fluorescent sample was found to be 2.2 V. On addition of 2 µM PA, the fluorescence quenches completely and the voltmeter reading was found to be 1.1 V. Figure 11 D shows the gradual decrease in voltage displayed with increasing concentration of PA in real water samples. The plot is statistically linear as the value of the correlation coefficient is found to be 0.986. Such a prototype can be easily used for the infield detection of picric acid in real samples and further emphasizes on the advantages of this sensory system. Conclusion: In this work, we have demonstrated the synthesis and characterization of a new class of polymers, PPA, PPA-Q and PPA-CSQ, as highly efficient and selective sensors for picric acid explosive in aqueous media.

PVA grafted polyaniline and its


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


nanocomposites with MSA capped CdTe and CdTe/ZnS core/ shell quantum dots were syntheiszed by free radical polymerization reaction. The proposed sensing phenomenon involves the combination of a strong Inner Filter Effect (IFE) and electrostatic interactions between the probes and the analyte. The incorporation of negatively charged QDs enhances the electron density of the polymers which helps in effective interaction with highly electron deficient picric acid. Detection limit of the PPA-CSQ polymer is remarkably low and is found to be 0.65 nM. An electronic device was successfully fabricated to visualize the quantitative detection of picric acid by PPA-CSQ. These electron rich fluorescent polymers, especially PPA-CSQ, may be used for the infield selective sensing of picric acid which is a well-known dangerous explosive and an extremely toxic environment pollutant. Supporting Information: FT-IR and 1H-NMR of the polymers, EDX, XRD and FT-IR spectra of the QDs, PL spectra of the core/shell QD at different pH, EDX mapping of PPA and PPA-Q, percentage elemental composition of the polymers, UV and PL of the polymers, interference and selectivity study of PPA and PPA-Q, spectral overlap of PPACSQ with other nitroaromatic analytes, UV of PPA-CSQ before and after addition of PA, zeta potential plots of the polymers before and after adding PA, CV plots of the polymers, real sample analysis and circuit diagram of the device fabricated for PA sensing are provided in this section. This material is available free of charge via the Internet at http://pubs.acs.org. Acknowledgment Authors would like to thank Department of Information Technology (DeitY), Government of India for project No. 1(2)/2011-M&C. PD would like to thank DST, Govt. of India and IASST, Guwahati for fellowship. Authors would like to thank Saugata Sahu and Akhtar Hussain, CIF, IITG for the TRPL analysis. PD would like to thank Sameer 27 ACS Paragon Plus Environment


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

Page 28 of 34

Hussain for his valuable suggestions regarding the mechanism. Authors would also like to thank Aloke Ghosh, Bikash Sharma and Aziz Khan for their help in the instrumentation section. References: (1)

Thomas, S. W.; Joly, G. D.; Swager, T. M. Chemical Sensors Based on Amplifying Fluorescent Conjugated Polymers, Chem. Rev. 2007, 107, 1339-1386.

(2)

Sohn, H.; Sailor, M. J.; Magde, D.; Trogler, W. C. Detection of Nitroaromatic Explosives Based on Photoluminescent Polymers Containing Metalloles, J. Am. Chem. Soc. 2003, 125, 3821-3830.

(3)

Akhavan, J. The Chemistry of Explosives, 3rd edition; Royal Society of Chemistry, 2011; Chapter 1, 1-22.

(4)

Hamric, J. T. High Temperature Explosive System Containing Trinitromesitylene, United States Patent 3515604, 1970.

(5)

Nipper, M.; Qian, Y.; Carr, R. S.; Miller, K. Degradation of Picric Acid and 2,6-DNT in Marine Sediments and Waters: The Role of Microbial Activity and Ultra-violet Exposure, Chemosphere 2004, 56, 519-530.

(6)

Safety Data Sheet for Picric Acid, Resource of National Institute of Health.

(7)

Ashbrook, P. C.; Houts, T. A. Picric Acid, ACS Div. Chem. Health Safety 2003, 10, 27.

(8)

Germain, M. E.; Knapp, M. J. Optical Explosives Detection: from Color changes to Fluorescence Turn-On, Chem. Soc. Rev. 2009, 38, 2543-2555.

(9)

Hussain, S.; Malik, A. H.; Afroz, M. A.; Iyer, P. K. Ultrasensitive Detection of Nitroexplosive – Picric Acid via a Conjugated Polyelectrolyte in Aqueous Media and Solid Support, Chem. Commun. 2015, 51, 7207-7210.


Page 29 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


(10) Gole, B.; Bar, A. K.; Mukherjee, P. S. Modification of Extended Open Frameworks with Fluorescent Tags for Sensing Explosives: Competition between Size Selectivity and Electron Deficiency, Chem. Eur. J. 2014, 20, 2276-2291. (11) Nagarkar, S. S.; Joarder, B.; Chaudhari, A. K.; Mukherjee, S.; Ghosh, S. K. Highly Selective Detection of Nitro Explosives by a Luminescent Metal–Organic Framework, Angew. Chem. 2013, 125, 2953-2957. (12) Gole, B.; Shanmugaraju, S.; Bar, A. K.; Mukherjee, P. S. Supramolecular Polymer for Explosives Sensing: Role of H-bonding in Enhancement of Sensitivity in the Solid State, Chem. Commun. 2011, 47, 10046-10048. (13) Liu, B.; Tong, C.; Feng, L.; Wang, C.; He, Y.; Lu, C. Water-Soluble Polymer Functionalized CdTe/ZnS Quantum Dots: A Facile Ratiometric Fluorescent Probe for Sensitive and Selective Detection of Nitroaromatic Explosives, Chem. Eur. J. 2014, 20, 2132-2137. (14) Wang, Y.; Xiong, L.; Geng, F.; Zhang, F.; Xu, M. Design of a Dual-Signaling Sensing System for Fluorescent Ratiometric Detection of Al3+ ion based on the Inner-Filter Effect, Analyst, 2011, 136, 4809-4814. (15) Gogoi, B.; Sarma, N. S. Curcumin-Cysteine and Curcumin-Tryptophan Conjugate as Fluorescence Turn On Sensors for Picric Acid in Aqueous Media, ACS Appl. Mater. Interfaces 2015, 21, 11195-11202. (16) Shao, N.; Zhang, Y.; Cheung, S.; Yang, R.; Chan, W.; Mo, T.; Li, K.; Liu, F. Copper Ion-Selective Fluorescent Sensor Based on the Inner Filter Effect Using a Spiropyran Derivative, Anal. Chem. 2005, 77, 7294–7303. (17) Zhai, Y.; Jin, L.; Wang, P.; Dong, S. Dual-functional Au–Fe3O4 Dumbbell Nanoparticles for Sensitive and Selective Turn-On Fluorescent Detection of Cyanide based on the Inner Filter Effect, Chem. Commun. 2011, 47, 8268–8270. 29 ACS Paragon Plus Environment


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

Page 30 of 34

(18) Rong, M.; Lin, L.; Song, X.; Zhao, T.; Zhong, Y.; Yan, J.; Wang, Y.; Chen, X. A Label-Free Fluorescence Sensing Approach for Selective and Sensitive Detection of 2,4,6-Trinitrophenol (TNP) in Aqueous Solution Using Graphitic Carbon Nitride Nanosheets, Anal. Chem. 2015, 87, 1288−1296. (19) Sohn, H.; Calhoun, R. M.; Sailor, M. J.; Trogler, W. C. Detection of TNT and Picric Acid on Surfaces and in Seawater by Using Photoluminescent Polysiloles, Angew. Chem. 2001, 113, 2162-2163. (20) Dutta, P.; Kalita, B.; Gogoi, B.; Sarma, N. S. Development of Macroporous coPolyesters of Glyceryl Methacrylate with Acrylonitrile and Styrene for Electrical Sensing of Ammonia Vapor, J. Phys. Chem. C 2015, 119, 17260-17270. (21) Pramanik, S.; Zheng, C.; Zhang, X.; Emge, T. J.; Li, J. New Microporous MetalOrganic Framework Demonstrating Unique Selectivity for Detection of High Explosives and Aromatic Compounds, J. Am. Chem. Soc. 2011, 133, 4153-4155. (22) Toal, S. J.; Magde, D.; Trogler, W. C. Luminescent Oligo(tetraphenyl)silole Nanoparticles as Chemical Sensors for Aqueous TNT, Chem. Commun. 2005, 5465-5467. (23) Gole, B.; Song, W.; Lackinger, M.; Mukherjee, P. S. Explosives Sensing by Using Electron-Rich Supramolecular Polymers: Role of Intermolecular Hydrogen Bonding in Significant Enhancement of Sensitivity, Chem. Eur. J. 2014, 20, 1366213680. (24) Xu, Y.; Li, B.; Li, W.; Zhao, J.; Sun, S.; Pang, Y. Protein-Based Sensitive, Selective and Rapid Fluorescence Detection of Picric Acid in Aqueous Media, Chem. Commun. 2013, 49, 4764-4766.


Page 31 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


(25) Zhu, H.; Song, N.; Lian, T. Controlling Charge Separation and Recombination Rates in CdSe/ZnS Type I Core−Shell Quantum Dots by Shell Thicknesses, J. Am. Chem. Soc. 2010, 132, 15038-15045. (26) Chaudhuri, R. G.; Paria, S. Core/Shell Nanoparticles: Classes, Properties, Synthesis, Mechanisms, Characterization and Applications, Chem. Rev. 2012, 112, 2373-2433. (27) Karele, S.; Gosavi, S. W.; Urban, J.; Kularni, S. K. Nanoshell Particles: Synthesis, Properties and Applications, Curr. Sci. 2006, 91, 1038-1052. (28) Freeman, R.; Finder, T.; Bahshi, L.; Gill, R.; Willner, I. Functionalized CdSe/ZnS QDs for the Detection of Nitroaromatic or RDX Explosives, Adv. Mater. 2012, 24, 6416-6421. (29) Yunsheng, X.; Lei, S.; Changqing, Z. Turn-On and Near-Infrared Fluorescent Sensingfor 2, 4, 6-Trinitrotoluene Based on Hybrid (Gold Nanorod)−(Quantum Dots) Assembly, Anal. Chem. 2011, 83, 1401-1407. (30) Zhang, K.; Zhou, H.; Mei, Q.; Wang, S.; Guan, G.; Liu, R.; Zhang, J.; Zhang, Z. Instant Visual Detection of Trinitrotoluene Particulates on Various Surfaces by Ratiometric Fluorescence of Dual-Emission Quantum Dots Hybrid, J. Am. Chem. Soc. 2011, 133, 8424-8427. (31) Dutta, P.; Dass, N. N.; Sarma, N. S. Stimuli Responsive Carbon Nanocomposite Hydrogels with Efficient Conducting Properties as a Precursor to Bioelectronics, React. Funct. Polym. 2015, 90, 25-35. (32) Dutta, P.; Dass, N. N.; Chowdhury, D.; Sarma, N. S. Oil-sorbent to Hydrosorbent Switching in Poly-9-octadecenylacrylate and Poly-9-octadecenylacrylate/Au Nanocomposites, Chem. Eng. J. 2013, 225, 202-209.



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

Page 32 of 34

(33) Chakravarty, S.; Saikia, D.; Sharma, P.; Adhikary, N. C.; Thakur, D.; Sarma, N. S. A Supramolecular Nanobiological Hybrid as a PET Sensor for Bacterial DNA Isolated from Streptomyces Sanglieri, Analyst 2014, 139, 6502-6510. (34) Gogoi, M.; Deb, P.; Kostka, A. Differential Tunability Effect on the Optical Properties of Doped and Undoped Quantum Dots, Phys. Status Solidi A 2012, 209, 1543-1551. (35) Jing, L.; Ding, K.; Kalytchuk, S.; Wang, Y.; Qiao, R.; Kershaw, S. V.; Rogach, A. L.; Gao, M. Aqueous Manganese-Doped Core/Shell CdTe/ZnS Quantum Dots with Strong Fluorescence and High Relaxivity, J. Phys. Chem. C 2013, 117, 18752−18761. (36) Kalita, A.; Subbarao, N. V. V.; Iyer, P.K. Large-Scale Molecular Packing and Morphology-Dependent High Performance Organic Field-Effect Transistor by Symmetrical Naphthalene Diimide Appended with Methyl Cyclohexane, J. Phys. Chem. C 2015, 119, 12772−12779. (37) Sun, X.; Ma, X.; Kumar, C. V.; Lei, Y. Protein-Based Sensitive, Selective and Rapid Fluorescence Detection of Picric Acid in Aqueous Media, Anal. Methods 2014, 6, 8464–8468. (38) Shiraishi, K.; Sanji, T.; Tanaka, M. Trace Detection of Explosive Particulates with a Phosphole Oxide, ACS Appl. Mater. Interfaces 2009, 7, 1379-1382. (39) Ding, L.; Bai, Y.; Cao, Y.; Ren, G.; Blanchard, G. J.; Fang, Y. Micelle-Induced Versatile Sensing Behavior of Bispyrene-Based Fluorescent Molecular Sensor for Picric Acid and PYX Explosives, Langmuir 2014, 30, 7645-7653. (40) Bhalla, V.; Gupta, A.; Kumar, M.; D. Rao, D. S. S.; Prasad, S. K. Self-Assembled Pentacenequinone Derivative for Trace Detection of Picric Acid, ACS Appl. Mater. Interfaces 2013, 5, 672-679.


Page 33 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


(41) Ding, L.; Bai, Y.; Cao, Y.; Ren, G.; Blanchard, G. J.; Fang, Y. Micelle-Induced Versatile Sensing Behavior of Bispyrene-Based Fluorescent Molecular Sensor for Picric Acid and PYX Explosives, Langmuir 2014, 30, 7645-7653. (42) Zhou, X. H.; Li, L.; Li, H. H.; Li, A.; Yang, T.; Huang, W.; A Flexible Eu(III)-based Metal–Organic Framework: Turn-Off Luminescent Sensor for the Detection of Fe(III) and Picric Acid, Dalton Trans. 2013, 42, 12403-12409. (43) Xu, Y.; Li, B.; Li, W.; Zhao, J.; Sun, S.; Pang, Y. “ICT-Not-Quenching” Near Infrared Ratiometric Fluorescent Detection of Picric Acid in Aqueous Media, Chem. Commun. 2013, 49, 4764-4766. (44) Venkatesan, N.; Singh, V.; Rajakumar, P.; Mishra, A. K. Isobenzotriazolophanes: A New Class of Fluorescent Cyclophanes as Sensors for Aromatic Nitro Explosives–Picric Acid, R. Soc. Chem. Adv. 2014, 4, 53484-53489. (45) Samang, P.; Raksasorn, D.; Sukwattanasinitt, O.; Rashatasakhon, P. A Nitroaromatic Fluorescence Sensor from a Novel Tripyrenyl Truxene, R. Soc. Chem. Adv. 2014, 4, 58077-58082.



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

TOC GRAPHIC Circuit designed for PA detection system showing the polymer with and without PA illuminated by UV LED and the quenching effect. 392x120mm (96 x 96 DPI)

ACS Paragon Plus Environment

Page 34 of 34

Macromolecular Systems with MSA-Capped CdTe ... - ACS Publications

Recommend Documents