Smartphone-Enabled Colorimetric Trinitrotoluene Detection Using

Subscriber access provided by UB + Fachbibliothek Chemie | (FU-Bibliothekssystem)

Article

Smartphone Enabled Colorimetric Trinitrotoluene Detection Using Amine-Trapped Polydimethylsiloxane Membranes Ning Tang, Luye Mu, Hemi Qu, Yanyan Wang, Xuexin Duan, and Mark A. Reed ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b03314 • Publication Date (Web): 06 Apr 2017 Downloaded from http://pubs.acs.org on April 8, 2017

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

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

Page 1 of 29

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

ACS Applied Materials & Interfaces

Smartphone Enabled Colorimetric Trinitrotoluene Detection Using Amine-Trapped Polydimethylsiloxane Membranes Ning Tang, † Luye Mu, †, ‡ Hemi Qu, † Yanyan Wang, † Xuexin Duan,*, † and Mark A. Reed ‡,§ †

State Key Laboratory of Precision Measuring Technology & Instruments, Tianjin University,

Tianjin 300072, China ‡

Department of Electrical Engineering, Yale University, New Haven, Connecticut 06520, USA

§

Department of Applied Physics Yale University, New Haven, Connecticut 06520, USA

KEYWORDS: Trinitrotoluene, Polydimethylsiloxane, Colorimetric, Smartphone, Point-of-Care

ABSTRACT: In this work, a smartphone-enabled platform for easy and portably colorimetric analysis of 2,4,6-trinitrotoluene (TNT) using amine-trapped PDMS is designed and implemented. The amine-trapped polydimethylsiloxane (PDMS) is simply prepared by immersing the cured PDMS in aminosilane solutions forming an amine-containing polymer. After contacting with TNT-containing solutions, the colorless PDMS showed a rapid colorimetric change which can be easily identified by the naked eye. The amine-trapped PDMS was carefully optimized to achieve visible detection of TNT at concentrations as low as 1µM. Using an integrated camera in the smartphone, pictures of colored PDMS membranes can be analyzed by a home-developed

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

Page 2 of 29

mobile application. Thus, the TNT amount can be precisely quantified. Direct TNT detection in real samples (e.g. drinking, tap and lake waters) is demonstrated as well. Smartphone-enabled colorimetric method using amine-trapped PDMS membranes realizes a convenient and efficient approach towards a portable system for field TNT detections.

1. INTRODUCTION Polydimethylsiloxane (PDMS) is an elastomer with many advantages, such as high flexibility, optical transparency, low cost, and biocompatibilty. It has been extensively used for various applications ranging from soft lithography to microfluidics.1 PDMS has been used extensively in solid phase extraction due to its porous structure,2 however, less has been reported on the utilization of their porous structure for sensing application in liquid.3 The porosity of PDMS makes it highly permeable to small molecules, and therefore it can be utilized for molecular absorptions.4 2,4,6-Trinitrotoluene (TNT), the primary military explosive among nitroaromatic compounds, has been known as one of the most commonly used, mutagenic, and refractory pollutant, which not only poses a security threat, but also brings about environmental issues, especially water contamination.5-8 Contamination of groundwater with TNT has become a key security issue due to its biological persistence, toxicity and mutagenicity.9-10 People exposed to TNT over an enduring period of time showed an increased tendency to suffer from anemia or liver failures.11-14 Due to these concerns, TNT detection has attracted significant attentions. Methods have been developed for selective TNT detection using ion-mobility spectroscopy,15


Page 3 of 29

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


mass spectrometry,16 gas or liquid chromatography,17 electrochemical detection,18 and enzymatic assays.19 However, the employment of these methods require complicated measurement protocols and preconcentration procedures, and has therefore largely been restricted to laboratories.20 Furthermore, the inherently bulky nature and poor portability render these costly instrument-based approaches unsuitable for on-site analysis. Consequently, there is great demand for the development of a miniaturized system that is compact, low cost, easy to use, highly sensitive and selective for field TNT detection.21-22 One candidate for easy and quick detection of TNT is the colorimetric probe by using enzyme23-24 or chemical functionalized nanoparticles,25-28 which is essentially based on donor-acceptor (D-A) interactions between TNT (acceptor) and primary amines (donor).29-32 Colorimetric sensors are prevalent as portable sensors due to their rapid detection, and easy observation by the naked eye.33-35 Gold nanoparticles (AuNPs) labeling is one of the most efficient methods to achieve color signal amplification, and has been widely used in colorimetric detection in the past decade.36-37 However, a significant drawback of these colorimetric sensors is the high cost of their realization and complex surface functionalization process, which could not meet the demand of low-cost for portable sensors. In addition, the use of nanoparticles is also a potential environmental hazard.38 In this work, we developed a simple, label-free and environmentally friendly colorimetric TNT detection strategy using amine-trapped polydimethylsiloxane (PDMS) membrane based on its porous structure. Unlike the use of sophisticated surface chemical modification techniques,



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 4 of 29

the amine-trapped PDMS were simply prepared by immersing the cured PDMS membrane into an aminosilane solution, forming a stable amine-trapped PDMS membrane. Due to its hydrophobicity and porous structure, the amine-trapped PDMS will absorb and enrich TNT molecules from their aqueous solutions. The absorbed TNT can be detected based on the specific color responses (red shift) through interactions between TNT and the primary amines trapped inside the PDMS, resulting in the formation of the Meisenheimer complex.39-42 Due the transparency of PDMS, the color change induced by the TNT-amine reactions can be easily identified by the naked eye (Figure 1a). The intensity of the color is proportional to the amount of Meisenheimer complexes created, which is dependent on the amount of absorbed TNT. This allow for the direct quantification of TNT absorption through quantifying the color of the PDMS. Smartphone-based devices have attracted much attention in recent years due to their ability of mobile healthcare delivery and personalized medicine,43 resulting in the development of a number of point-of-care (POC) analyses such as colorimetric detection.44-46 Thus, through the camera of the smartphone and a home-built analysis program, which we termed GeTNT, the color change with the RGB color components can be quantified (Figure 1b).


Page 5 of 29

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


Amino-Polymer Trapping In PDMS

a Aminosilane Incubation (R-NH2: )

PDMS

b

TNT

Colorimetric Detection

PDMS@NH2

PDMS@NH2+TNT

Smartphone NEXT QUIT

Analysis PDMS@NH2+TNT

Figure 1. Cartoon shows (a) the preparation of the amine-trapped PDMS and TNT detection through colorimetric reaction; (b) TNT quantification using a handheld device (smartphone) and home-built APP (GeTNT).

2. EXPERIMENTAL SECTION Materials:

3-(Ethoxydimethylsilyl)propylamine

(APMES,

97%),

3-Aminopropyl-

(diethoxy)- methylsilane (APDES, 97%), (3-Aminopropyl)triethoxysilane (APTES, ≥98%), and 1H,1H,2H,2H-Perfluordecyltrichlorosilane (PFDTS, 96%) were purchased from Aladdin Industrial Corporation without further purification. 2,4,6-Trinitrotoluene and 2,4-dinitrotoluene solution (1mg/mL in methyl alcohol) were obtained from the TMRM. Polydimethylsiloxane (PDMS) was prepared by SYLGARD 184 SILICONE ELASTOMIER. Composite PDMS Membranes: The PDMS membranes was first prepared by casting the liquid prepolymer of the PDMS base and the curing agent in a 10:1 (w/w) ratio onto a silicon wafer which containing an anti-adhesion layer (PFDTS). The mixture was then degassed for 10 min to remove air bubbles. After curing at 80 °C for half an hour, the films were cooled to room 5 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 6 of 29

temperature and peeled off from the silicon wafer. The average value of the thickness of the PDMS membrane was determined by digital caliper (readable to ±0.01 mm) at least four spots on the same membrane. Functionalization and Characterization of PDMS Membranes: PDMS membranes were directly immersed in the aminosilanes containing ethanol solution (10%, 20%, 30%, 40%, 50%, V/V respectively) for 48 hours without any other treatment. The wetting property and chemical bonding structure of amine-trapped PDMS membranes were analyzed with contact angle (CA) measurements (JC2000DM, Zhongchen, China) and Fourier transform infrared (FT-IR) spectrometer (Vertex 70V, Bruker Optics, Germany), respectively. Color Intensity Measurement and Analysis: Upon immersed the amine-trapped PDMS into TNT solution, a red color appeared immediately. The UV-Vis absorption spectroscopy of the red color PDMS membranes were detected by using a microplate reader (Thermal Scientific, Multiskan GO), and the spectroscopy range was set to 300 - 800 cm-1. The intensity of the images was first analyzed with the Adobe Photoshop software (version CS 6). Five points in the image were randomly selected and averaged to compute the RGB component values, and a common background of the controlled PDMS was subtracted. The adjusted intensity I was calculated using the following equation: I = 1−

I R + IG + I B I rR + I rG + I rB

(1)

where I R , I G , I B and I rR , I rG , I rB represent the RGB component intensity of target PDMS and reference PDMS (In this case, we regarded the amine-trapped PDMS reacted with 0 µM TNT as 6 ACS Paragon Plus Environment

Page 7 of 29

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


reference PDMS), respectively.

3. RESULTS AND DISCUSSION 3.1. Characterization of the Amine-Trapped PDMS and Their Reactions with TNT. The key step in our approach is the fabrication of amine-trapped PDMS with high amine content while retaining the chemical-reactivity of the primary amine inside the PDMS, so that it can further react with TNT. We found a simple approach to incorporate aminosilanes inside of PDMS by simply immersing a thin piece of cured PDMS into the aminosilane solutions (e.g. 3-Aminopropyl(diethoxy)methylsilane (APDES), 30% v/v ethanol solution). Ethanol can swell PDMS and enhance its porous structures, thus allowing the aminosilanes to diffuse into the PDMS, forming a transparent amine-trapped PDMS membrane. In order to illustrate the porous structure of PDMS, a confirmatory research was performed at first (Figure S1). To verify the reactive status of the incorporated amines, FT-IR was applied to characterize the amine-trapped PDMS. Figure 2a shows the FT-IR spectroscopy of bare PDMS and amine-trapped PDMS. In the FT-IR spectroscopy of amine-trapped PDMS (PDMS @ NH2), N-H bond vibration peaks at 3345 cm-1 and 1411 cm-1 are clearly identified. A strong band at 1048 cm-1 is observed as well which is due to the formation of Si-O-Si bonds as a result of the crosslink between aminosilanes.47 These results suggest that the PDMS has been successfully modified with aminosilane and the primary amines are preserved. Due to the crosslink between the silanes, an aminosilane polymer network is formed within the PDMS membrane, thus



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

Page 8 of 29

improving its stability within PDMS and preventing it from leaking out of the membrane. UV-Vis absorption spectroscopy was used to study the interactions of amine-trapped PDMS with TNT. As shown in Figure 2b, after the incubation of the amine-trapped PDMS in TNT aqueous solutions (25µM) for 10 mins, absorption peaks at 461 nm and 532 nm can be easily identified. In control experiments, bare PDMS, amine-trapped PDMS, and amine-trapped PDMS incubated in 2,4-Dinitrotoluene (DNT; an analog molecule of TNT) did not show any absorption peaks. These spectroscopy results are in agreement with the colorimetric results that only amine-trapped PDMS incubated in TNT can turn red (Figure S2). We believe the color change is due to the formation of the Meisenheimer complex between the selected nitro aromatic and primary amines based on the strong charge transfer by acid-base pairing interaction (Figure S3).31, 40, 42, 48 However, DNT, which is a well-known structural analogue of TNT, cannot form such a complex. This is due to fact that TNT is a Bronsted-Lowry acid that is more inclined to be deprotonated at the methyl group by an amine group.31 On the contrary, due to one fewer electron withdrawing nitro group in DNT, the benzene ring is not electron-poor enough to form the Meisenheimer complex. All of these results show that the amine-trapped PDMS can be used as a simple and portable colorimetric probe for TNT detection with excellent selectivity. Moreover, UV-Vis was applied to analyze the same amine-trapped PDMS reaction with different concentrations of TNT (Figure 2c). It clearly shows that the absorbance at 461 nm increases with increasing concentrations of TNT. Figure 2d shows a good linear relationship between the absorbance values extracted at 461 nm and TNT concentrations ranging from 1 µM


Page 9 of 29

to 500 µM (correlation coefficient: 0.99115). It indicates that the color change is proportion to the amount of TNT and forms the basic principle to quantify the TNT amount using the amine-trapped PDMS as a colorimetric probe.

3345 NH3

b

2889 CH3

0.40 1411 NH3

PDMS@NH2

1500

1470

1440

1410

1380

-1

1350

Wavenumber(cm )

Absorbance

a

0.35

PDMS PDMS@NH2

0.30

PDMS@NH2+DNT

0.25

PDMS@NH2+TNT

0.20 0.15 0.10 0.05

4000

3000

0.00

1048 Si-O-Si

PDMS 2000

1000

1200

1150

1100

300 1050

1000

400

950

Wavenumber(cm )

500

600

700

800

Wavelength(nm)

-1

Wavenumber(cm )

-1

4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0

500 µM 250 µM 100 µM 50 µM 25 µM 5 µM 1 µM 0.5 µM 0.2 µM 0.1 µM 0.05 µM

300

400

500

600

700

800

Absorbance(At 461nm)

d

c Absorbance

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


4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0

Adj. R-Squar

0

100

Wavelength(nm)

200

300

0.99115

400

500

Concentration(µM)

Figure 2. (a) FT-IR spectroscopy of PDMS and amine-trapped PDMS; (b) UV-Vis absorption spectroscopy of PDMS, amine-trapped PDMS and in the presence of DNT (25 µM), and TNT (25 µM) aqueous solutions; (c) Absorption spectroscopy of amine-trapped PDMS incubated with different concentrations of TNT (0.05 – 500 µM); (d) Linear correlation of the absorbance values at 461 nm as a function of TNT concentrations.

3.2. Optimization of the Amine-Trapped PDMS Membrane. To further improve the limit of detection (LOD) of the TNT detection, the amine-trapped PDMS membrane needs to be optimized. As shown in Figure S3, the formation of the Meisenheimer complex is the main reason for the color change. The amount of the complex mainly depends on the content of amine 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 29

groups within the PDMS membranes. Therefore, we tested a number of ways to improve the amount of the trapped amines. First, three different aminosilanes (APMES, APDES, APTES) (Figure 3a), which have similar chemical structures but different amino/ethoxy ratios were used and compared for their ability to form the Meisenheimer complex, quantified by UV-vis. Figure 3a provides a comparison of the absorbance values of the TNT detection (25 µM) by the amine-trapped PDMS modified with three different aminosilanes. It clearly shows that the amine-trapped PDMS modified by aminosilanes with fewer ethoxy groups have stronger absorptions. This is due to the fact that the ethoxy group is easily hydrolyzed to form the hydroxyl group (-OH). The formation of the (O-H· · ·N) hydrogen bonds between hydroxyl and amino group will block the primary amine binding with TNT, thus decreasing the number of chemically active primary amines with increasing ethoxy content. We also noticed that there is no significant difference between APMES and APDES in terms of the absorbance at 461 nm, which is likely due to the crosslink between aminosilanes and PDMS resulting in the disappearance of some hydroxyl groups. When considering the low-cost benefits, we finally chose the APDES to modify the PDMS. The volume concentration of the aminosilanes to modify the PDMS also plays a role in the degree of amination. As shown in Figure 3b, by increasing the concentration of the APDES from 10% to 50% in ethanol, with fixed incubation time (20 mins), the TNT absorbance values increase as well. However, the absorbance value at 461 nm of 30%, 40%, and 50% of APDES is very close, which indicates that the amount of amine saturates within the PDMS membrane when


Page 11 of 29

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


using >30% of APDES. Furthermore, we also compared the effects of silane modification time. Figure 3c provides the absorption values obtained from APDES (30% in ethanol) modified PDMS with different silane incubation time. As shown from the results, there is almost no difference in absorbance value after 48 hours' incubations. Therefore, the optimal modification time is 48 hours. Due to the porous structure of PDMS, the amount of TNT absorption would increase with increasing thickness of the PDMS. However, increasing PDMS thickness may also affect the diffusion of TNT into the PDMS membranes. Thicker PDMS may require longer incubation time to get a uniform color change throughout. Thus, the thickness of PDMS membranes needs to be optimized as well. Figure 3d shows the responses of PDMS membranes with different thickness to different TNT concentrations (100, 50, 25 µM, respectively) with fixed incubation time (30 mins). The absorbance value at 461 nm increases as the thickness of PDMS membrane increases from 0.32 to 0.48 mm, and decreases when the thickness becomes greater than 0.5 mm. The available volume to trap TNT is certainly larger with thicker PDMS; however, the diffusion speed limits the transport of TNT into the membrane such that the effective volume available for absorption no longer increases for membranes thicker than 0.5 mm. Therefore, in order to be able to detect low concentrations of TNT (< 25 µM) in a reasonable time, we chose the PDMS membrane with a thickness of 0.4-0.5 mm for rest of the experiments. Besides the thickness, the surface area of the PDMS membrane may also play a role. Since PDMS can be easily molded into micro-sized structures, we designed and prepared



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 29

micro-channels on the surface of PDMS to increase the contact area between PDMS and TNT solution. As shown in Figure 3e, indeed, the absorption values of the amine-trapped PDMS with micro channels are enhanced compared to flat PDMS after incubating with the same TNT solutions. In principle, the surface area is larger with deeper channels, which will facilitate TNT diffusion into PDMS membrane. However, from the contact angle measurement, it shows that the available surface area is actually lower when using high aspect ratio micro-channels (Figure S4). In other words, although increasing the depth of the channels is in favor of expanding the surface area, large channel depth will reduce the wetting property of the PDMS membrane, actually resulting in the decrease of effective contact area. Actually, increasing the distance between channels can improve the hydrophilicity, but to a certain extent, may reduce the effective area. Therefore, this result indicates that, in the case of the 100 µm distance between two channels, there exists an optimal channel depth for the best performance of the colorimetric detection. In order to find the optimal channel depth, micro channels with different depth were investigated (Figure 3e). It is evident that the absorbance increases as the depth of channel increasing from 0 to 20 µm, but decreases as the depth is greater than 50 µm. As a consequence, the optimum depth of the PDMS membrane varies between 10 to 20 µm. As mentioned above, the PDMS structure, the concentration, the incubation time and the types of aminosilanes have been optimized to achieve maximum primary amine content. The trapping of the aminosialnes are due to the fact that both the aminosilanes and the PDMS are hydrophobic and the cross-linked aminosilanes may interact with the backbones of the PDMS.


Page 13 of 29

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


As PDMS is a flexible elastomer, the backbone of PDMS can be extended by stretching the PDMS, thus increasing this interaction and the amount of trapped silanes. To test this hypothesis, we compared the TNT detection result under different levels of PDMS stretch treatment. The PDMS membranes were clamped and mechanically stretched to a certain degree (0%, 25%, 50%, respectively) in one direction (Figure 3f). The stretched samples were then incubated in the APDES ethanol solution (30%) for 48 hours, followed by TNT detection after relaxing to their original state. From the value of the absorbance at 461 nm (Figure 3f), it clearly shows that the PDMS modification under stretching conditions significantly improved TNT absorption, which confirms our hypothesis that stretching of PDMS will increase the loading of trapped aminosilanes and further increase the amount of Meisenheimer complex. It is also apparent that the absorbance value increases as the degree of stretching increases, which suggests that the stretch treatment plays a critical role in the improvement of colorimetric sensitivity.



a

b

0.5

10% 20% 30% 40% 50%

Absorbance

0.4

0.30 0.25 0.15 0.10 0.05 0.00 400

500

600

700

0.2 0.1

300

c

0.20

300

0.3

0.0

APMES APDES APTES


Absorbance

0.35

800

Wavelength(nm)

0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.2

e

100 µM 50 µM 25 µM

500

600

700

800

0.26 0.24 0.22 0.20 0.18 0.16 0.14 20

40

60

80

100

Modification Time(hours) 1.0 200 µm 100 µm 50 µm 20 µm 3 µm 0 µm

0.8

Absorbance

d

400

Wavelength(nm)

0


0.6 0.4 0.2 0.0

0.4

0.6

0.8

1.0

1.2

300

1.4

Thickness(mm)

400

500

600

700

800

Wavelength(nm)

f Fixture

PDMS


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 29

1.8

50%

25%

1.5

0

1.2 0.9 0.6 0.3 0.0

100 µM

50 µM

25 µM

TNT Concentration

Figure 3. (a) PDMS membranes modified with three different aminosilanes (APMES, APDES, APTES) and their comparisons to TNT sensing; UV-VIS absorption results of (b) different concentrations and (c) incubation time of APDES modified PDMS after contacting with 25µM TNT solution. (d) PDMS membranes with different thickness response to different concentrations of TNT; (e) The effects of different microchannels on the surface of the PDMS membrane to the TNT detection; (f) Schematic of the uni-axial stretch of PDMS membrane and their effects on the TNT detection. 14 ACS Paragon Plus Environment

Page 15 of 29

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


3.3. Colorimetric Response to TNT. For TNT detection, the optimized amine-trapped PDMS membranes were cut into small strips (e.g. 0.5 × 0.5 cm) and immersed into vials containing various concentrations of TNT aqueous solutions with fixed incubation time (20 mins). A gradual change to red color can be clearly observed with increasing the concentration of TNT (Figure 4a). The LOD here is defined as the least amount of TNT in the contaminated water that was capable of resulting a colored change detectable merely by the naked eye. As shown in Figure 4a, the LOD of TNT detection by the naked eye with our method is around 1 µM. The LOD obtained by this simple amine-trapped PDMS probe, avoiding the use of expensive material, can be as good as the previously reported LOD,48 although not comparable to that of the precise instruments.49 It is possible to detect a much lower concentration of TNTs with UV-Vis spectroscopy (LOD: 0.05 µM), as we have shown in Figure 2c. In real world aqueous samples, there might exist a large amount of interfering ions (e.g. salt ions, metal ions) that could influence TNT detection. To further explore our method using amine-trapped PDMS in daily life, experiments were conducted by directly dissolving TNT molecules into drinking, tap and lake water without any extra purification steps (Figure 4b). Although there are many interfering ions in lake water, the amine-trapped PDMS did not show any color change even after 1 hour incubation without TNT added. On the contrary, red color can be quickly observed from the samples containing TNT molecules from drinking, tap, and lake waters, which indicates that the amine-trapped PDMS has excellent selectivity for TNT detection in practical applications and can be used in different environments (e.g. security check points,



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 29

sewage treatment center etc.).

a μM 100μ μM μM 250μ 2mM 1mM 500μ

50μ μM 25μ μM μM 5μ

μM 0μ μM 2μ μM 1μ

b 5μ μM 2μ μM 1μ μM

0.1μ μM 0μ μM

Drinking Water Tap Water Lake Water

Figure 4. (a) A gradual change in color of PDMS membranes after contact with various concentrations of TNT solutions; (b) Real sample detections using the amine-trapped PDMS.

3.4. TNT Quantifications by the Color Intensity. Although colorimetric methods offer a simple approach for TNT detection, the amount of TNT cannot be precisely determined by the naked eye only. In principle, UV-Vis spectroscopy can be used for TNT quantification by reading out the absorption values at 461 nm (Figure 2c). However, due to the relatively large optical setup, there are limitations for real time, on-site quantifications. Here, a cell phone compatible application (named GeTNT) is developed using the Android Studio platform, which enables the use of any hand-held device with a camera (e.g. smartphone) as a portable tool to quantify the TNT amount absorbed within the amine-trapped PDMS. The RGB component values were first taken by Photoshop (Figure 5a). Unlike the algorithms used by the previous researcher,50 we directly extract the mean RGB values to


Page 17 of 29

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


calculate the adjust intensity I . A concentration-dependent curve (Figure 5b) was fitted with the adjusted intensity at different TNT concentrations by equation (2): log[TNT ] = 3.81098 × I − 6.07676

(2)

where [TNT ] represents the concentrations of TNT. This adequate linearity (correlation coefficient: 0.97649) indicated reliability of the smartphone enabled system for TNT quantification. Based on this fitting, GeTNT is developed to measure the concentrations of unknown samples (Figure S5), and the detection limit of this system is as low as 1 µM. The smartphone enabled system using amine-trapped PDMS showed a great advantage compared with other biosensors that use complex biomarkers and large instruments for TNT detections,25, 51 which cannot be easily used for on-site detections. Although the ambient light poses a limitation on the colorimetric sensing by smartphone, a box with constant brightness can be made to avoid the outside light. Moreover, in order to prove the effect of smartphone models with different cameras on the detection results is small, a comparative experiment was performed (Figure S6). Ultimately, the combination of the amine-trapped PDMS and the hand-held device provided a low-cost portable system for precise mobile detection of TNT. It is worth mentioning that the versatile smartphone enabled quantification system could also be extended to other in-field colorimetric sensing such as environment monitoring, food safety evaluation, and point of care monitoring, etc.



a

b TNT Concentration(M)

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 29

1E-3 1E-4 1E-5 1E-6 0.0

Adj. R-Squar

0.2

0.4

0.6

0.97649

0.8

1.0

Adjusted intensity

Figure 5. (a) RGB intensities obtained from image of the amine-trapped PDMS after reacting with 5 µM TNT by Photoshop; (b) Linear fitting of the RGB intensities as a function of the logarithm values of different TNT concentrations.

3.5. Kinetics of TNT Detection Using the Amine-Trapped PDMS Membrane. The accumulation and reaction of TNT with primary amines inside the PDMS membrane has different kinetics compared to chemical reactions in solvent. The diffusion rate of TNT inside of PDMS and their reaction rate with trapped amines play key roles in the kinetics. In order to get a deeper insight into the color change process, the following mathematical model was adopted to depict the kinetics of the diffusion and reaction of TNT inside of the PDMS membrane: PDMS t = A1 (1 − e − k1t ) + A2 (1 − e − k2t ) PDMS e

(3)

Where PDMSt and PDMSe are the experimental absorbance peak value at 461 nm at time t and after reaching equilibrium, respectively. As shown in equation (3), there are four fitting parameters, namely A1 , A2 , k1 and k 2 , where A1 and A2 are the relative contributions of two barriers (surface and diffusion barriers) controlling the overall process (with A1 + A2 =1), and k1 and k 2 are the corresponding surface and diffusion kinetic rate constants, respectively. According to

this double exponential model, described and utilized earlier by Kondo52 and Fletcher,53 the 18 ACS Paragon Plus Environment

Page 19 of 29

fitting results clearly shows the satisfactory fitting of the experimental data as shown in Figure 6. It suggests that TNT absorption process can be divided into two steps: the first is fast which is related to the TNT molecules reaction with amines on the surface of the PDMS membrane; the second is slower which is attributed to their diffusion and reaction in the porous framework structures of PDMS membrane. From the kinetics data, we can conclude that the colorimetric reaction reaches saturation around 30 mins, but practically, obvious color change can be clearly observed within 5 mins incubation using the optimized amine-trapped PDMS for most concentrations plotted in Figure 5.


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


4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0

500 µM 250 µM 100 µM 50 µM 25 µM 5 µM 2 µM 1 µM

0

10

20

30

40

50

60

Time(min) Figure 6. The absorption values at 461 nm of aminated PDMS in contact with various TNT concentrations as a function of time.

4. CONCLUSION In summary, we have designed and developed a novel smartphone-enabled colorimetric platform (amine-trapped PDMS) for field TNT detection. The amine-trapped PDMS was simply



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 29

prepared by immersing cured PDMS membranes in aminosilane solutions to form an amino-containing polymer network trapped inside the PDMS membrane. The surface structure, the thickness, and the stretching status of the PDMS, the concentration, the incubation time and the types of the aminosilanes have all been carefully optimized to achieve maximum amino content in PDMS to improve the LOD of the TNT detection. TNT concentrations as low as 1 µM were successfully detected merely by the naked eye. To precisely quantify the TNT, a smart phone-compatible colorimetric analyzing program is developed as well. TNT in real sample detection (drinking, tap, and lake waters) was demonstrated to prove the utility of such a method in real world applications. Thus, the smartphone enabled colorimetric probe using amine-trapped PDMS provides a simple, low-cost, portable and efficient platform to detect TNT sensitively and selectively. Although this work is mainly focused on TNT detection using amine-trapped PDMS, the use of PDMS’s porous structure combined with other chemical functionalization approaches can be further applied to many other analytical applications (e.g. ion detection and biosensing etc.).

ASSOCIATED CONTENT Supporting Information. The verification of porous structure of PDMS; The specificity of the amine-trapped PDMS; Acid-base pairing interaction; Contact angle images; Workflow of the GETNT APP; Comparison between various smartphones with different cameras. This material is available free of charge via the Internet at http://pubs.acs.org.


Page 21 of 29

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


AUTHOR INFORMATION Corresponding Author * Tel. /Fax: +86 2227401002. E-mail: [email protected].

ORCID Xuexin Duan: 0000-0002-7550-3951. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT The authors gratefully acknowledge financial support from the Natural Science Foundation of China (NSFC no. 61674114), Tianjin Applied Basic Research and Advanced Technology (14JCYBJC41500), and the 111 Project (B07014).

REFERENCES (1) Mukhopadhyay, R., When PDMS isn't the Best. Anal. Chem. 2007, 79 (9), 3248-3253. (2) Landín, P.; Llompart, M.; Lourido, M.; Cela, R., Determination of Tri‐Through Heptachlorobiphenyls in Water Samples by SPME‐GC‐MS‐MS: Comparison of PDMS and PDMS‐DVB Coatings. J. Microcolumn Sep. 2001, 13 (7), 275-284. (3) Juchniewicz, M.; Stadnik, D.; Biesiada, K.; Olszyna, A.; Chudy, M.; Brzózka, Z.; Dybko, A.,



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 29

Porous Crosslinked PDMS-Microchannels Coatings. Sens. Actuators, B 2007, 126 (1), 68-72. (4) Toepke, M. W.; Beebe, D. J., PDMS Absorption of Small Molecules and Consequences in Microfluidic Applications. Lab Chip 2006, 6 (12), 1484-1486. (5) Won, W. D.; DiSALVO, L. H.; Ng, J., Toxicity and Mutagenicity of 2, 4, 6-Trinitrotoluene and Its Microbial Metabolites. Appl. Environ. Microbiol. 1976, 31 (4), 576-580. (6) Kaplan, D. L., Biological Degradation of Explosives and Chemical Agents. Curr. Opin. Biotechnol. 1992, 3 (3), 253-260.

(7) Van Beelen, P.; Burris, D. R., Reduction of the Explosive 2, 4, 6‐Trinitrotoluene by Enzymes from Aquatic Sediments. Environ. Toxicol. Chem. 1995, 14 (12), 2115-2123. (8) Hartter, D., The Use and Importance. Toxicity of nitroaromatic compounds 1985, 1. (9) Hawari, J.; Beaudet, S.; Halasz, A.; Thiboutot, S.; Ampleman, G., Microbial Degradation of Explosives: Biotransformation Versus Mineralization. Appl. Microbiol. Biotechnol. 2000, 54 (5), 605-618. (10) Van Dillewijn, P.; Couselo, J. L.; Corredoira, E.; Delgado, A.; Wittich, R.-M.; Ballester, A.; Ramos, J. L., Bioremediation of 2, 4, 6-Trinitrotoluene by Bacterial Nitroreductase Expressing Transgenic Aspen. Environ. Sci. Technol.

2008, 42 (19), 7405-7410.

(11) Reifenrath, W. G.; Kammen, H. O.; Palmer, W. G.; Major, M. M.; Leach, G. J., Percutaneous Absorption of Explosives and Related Compounds: An Empirical Model of Bioavailability of Organic Nitro Compounds from Soil. Toxicol. Appl. Pharmacol. 2002, 182 (2), 160-168. (12) Adamia, G.; Ghoghoberidze, M.; Graves, D.; Khatisashvili, G.; Kvesitadze, G.; Lomidze, E.;


Page 23 of 29

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


Ugrekhelidze, D.; Zaalishvili, G., Absorption, Distribution, and Transformation of TNT in Higher Plants. Ecotoxicol. Environ. Saf. 2006, 64 (2), 136-145. (13) Yinon, J.; Hwang, D., Applications of Liquid Chromatography—Mass Spectrometry in Metabolic Studies of Explosives. J. Chromatogr. A 1987, 394 (1), 253-257. (14) Jiamjitrpanich, W.; Parkpian, P.; Polprasert, C.; Laurent, F.; Kosanlavit, R., The Tolerance Efficiency of Panicum Maximum and Helianthus Annuus in TNT-Contaminated Soil and nZVI-Contaminated Soil. J. Environ. Sci. Health, Part A 2012, 47 (11), 1506-1513. (15) Wallis, E.; Griffin, T. M.; Popkie Jr, N.; Eagan, M. A.; McAtee, R. F.; Vrazel, D.; McKinly, J. Instrument Response Measurements of Ion Mobility Spectrometers in Situ: Maintaining Optimal System Performance of Fielded Systems. Defense and Security, International Society for Optics and Photonics: 2005; pp 54-64.

(16) Håkansson, K.; Coorey, R. V.; Zubarev, R. A.; Talrose, V. L.; Håkansson, P., Low‐Mass Ions Observed in Plasma Desorption Mass Spectrometry of High Explosives. J. Mass Spectrom. 2000, 35 (3), 337-346. (17) Moore, D., Instrumentation for Trace Detection of High Explosives. Rev. Sci. Instrum. 2004, 75 (8), 2499-2512.

(18) Ho, M. Y.; D’Souza, N.; Migliorato, P., Electrochemical Aptamer-Based Sandwich Assays for the Detection of Explosives. Anal. Chem. 2012, 84 (10), 4245-4247. (19) Smith, R. G.; D'Souza, N.; Nicklin, S., A Review of Biosensors and Biologically-Inspired Systems for Explosives Detection. Analyst 2008, 133 (5), 571-584.



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 29

(20) Geng, Y.; Ali, M. A.; Clulow, A. J.; Fan, S.; Burn, P. L.; Gentle, I. R.; Meredith, P.; Shaw, P. E., Unambiguous Detection of Nitrated Explosive Vapours by Fluorescence Quenching of Qendrimer Films. Nat. Commun. 2015, 6. (21) Czarnik, A. W., A Sense for Landmines. Nature 1998, 394 (6692), 417-418. (22) Lichtenstein, A.; Havivi, E.; Shacham, R.; Hahamy, E.; Leibovich, R.; Pevzner, A.; Krivitsky, V.; Davivi, G.; Presman, I.; Elnathan, R., Supersensitive Fingerprinting of Explosives by Chemically Modified Nanosensors Arrays. Nat. Commun. 2014, 5. (23) Morais, S.; Carrascosa, J.; Mira, D.; Puchades, R.; Maquieira, Á., Microimmunoanalysis on Standard Compact Discs to Determine Low Abundant Compounds. Anal. Chem. 2007, 79 (20), 7628-7635. (24) Su, X.; Teh, H. F.; Lieu, X.; Gao, Z., Enzyme-Based Colorimetric Detection of Nucleic Acids Using Peptide Nucleic Acid-Immobilized Microwell Plates. Anal. Chem. 2007, 79 (18), 7192-7197. (25) Jiang, Y.; Zhao, H.; Zhu, N.; Lin, Y.; Yu, P.; Mao, L., A Simple Assay for Direct Colorimetric Visualization of Trinitrotoluene at Picomolar Levels Using Gold Nanoparticles. Angew. Chem. 2008, 120 (45), 8729-8732.

(26) Dasary, S. S.; Senapati, D.; Singh, A. K.; Anjaneyulu, Y.; Yu, H.; Ray, P. C., Highly Sensitive and Selective Dynamic Light-Scattering Assay for TNT Detection Using p-ATP Attached Gold Nanoparticle. ACS Appl. Mater. Interfaces 2010, 2 (12), 3455-3460. (27) Vilela, D.; González, M. C.; Escarpa, A., Sensing Colorimetric Approaches Based on Gold


Page 25 of 29

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


and Silver Nanoparticles Aggregation: Chemical Creativity Behind the Assay. A review. Anal. Chim. Acta 2012, 751, 24-43.

(28) Mohan, M.; Chand, D. K., Visual Colorimetric Detection of TNT and 2, 4-DNT Using As-Prepared Hexaazamacrocycle-Capped Gold Nanoparticles. Anal. Methods 2014, 6 (1), 276-281. (29) Bernasconi, C. F., Kinetic and Spectral Study of Some Reactions of 2, 4, 6-Trinitrotoluene in Basic Solution. I. Deprotonation and Janovsky Complex Formation. J. Org. Chem. 1971, 36 (12), 1671-1679. (30) Walker, N. R.; Linman, M. J.; Timmers, M. M.; Dean, S. L.; Burkett, C. M.; Lloyd, J. A.; Keelor, J. D.; Baughman, B. M.; Edmiston, P. L., Selective Detection of Gas-phase TNT by Integrated Optical Waveguide Spectrometry Using Molecularly Imprinted Sol–Gel Sensing Films. Anal. Chim. Acta 2007, 593 (1), 82-91. (31) Tu, R.; Liu, B.; Wang, Z.; Gao, D.; Wang, F.; Fang, Q.; Zhang, Z., Amine-Capped ZnS-Mn2+ Nanocrystals for Fluorescence Detection of Trace TNT Explosive. Anal. Chem. 2008, 80 (9), 3458-3465.

(32) Vashist, S. K.; Lam, E.; Hrapovic, S.; Male, K. B.; Luong, J. H., Immobilization of Antibodies and Enzymes on 3-Aminopropyltriethoxysilane-Functionalized Bioanalytical Platforms for Biosensors and Biagnostics. Chem. Rev. 2014, 114 (21), 11083-11130. (33) Taton, T. A.; Mirkin, C. A.; Letsinger, R. L., Scanometric DNA Array Detection with Nanoparticle Probes. Science 2000, 289 (5485), 1757-1760.



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 29

(34) Alexandre, I.; Hamels, S.; Dufour, S.; Collet, J.; Zammatteo, N.; De Longueville, F.; Gala, J.-L.; Remacle, J., Colorimetric Silver Detection of DNA Microarrays. Anal. Biochem. 2001, 295 (1), 1-8. (35) Ma, Z.; Sui, S. F., Naked‐Eye Sensitive Detection of Immunoglubulin G by Enlargement of Au Nanoparticles in Vitro. Angew. Chem. 2002, 41 (12), 2176-2179. (36) Kim, D.; Daniel, W. L.; Mirkin, C. A., Microarray-Based Multiplexed Scanometric Immunoassay for Protein Cancer Markers Using Gold Nanoparticle Probes. Anal. Chem. 2009, 81 (21), 9183-9187.

(37) Yeh, C.-H.; Hung, C.-Y.; Chang, T. C.; Lin, H.-P.; Lin, Y.-C., An Immunoassay Using Antibody-Gold Nanoparticle Conjugate, Silver Enhancement and Flatbed Scanner. Microfluid. Nanofluid. 2009, 6 (1), 85-91.

(38) Hardman, R., A Toxicologic Review of Quantum Dots: Toxicity Depends on Physicochemical and Environmental Factors. Environ. Health Perspect. 2006, 165-172. (39) Kuş, M.; Okur, S., Electrical Characterization of PEDOT:PSS Beyond Humidity Saturation. Sens. Actuators, B 2009, 143 (1), 177-181.

(40) Ban, R.; Zheng, F.; Zhang, J., A Highly Sensitive Fluorescence Assay for 2,4,6-Trinitrotoluene Using Amine-Capped Silicon Quantum Dots as A Probe. Anal. Methods 2015, 7 (5), 1732-1737. (41) Gusain, A.; Joshi, N. J.; Varde, P. V.; Aswal, D. K., Flexible NO Gas Sensor Based On Conducting

Polymer


Page 27 of 29

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


Poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT). Sens. Actuators, B 2017, 239, 734-745. (42) Xu, S.; Lu, H., Mesoporous Structured MIPs@CDs Fluorescence Sensor for Highly Sensitive Detection of TNT. Biosens. Bioelectron. 2016, 85, 950-956. (43) Vashist, S. K.; Mudanyali, O.; Schneider, E. M.; Zengerle, R.; Ozcan, A., Cellphone-Based Devices for Bioanalytical Sciences. Anal. Bioanal. Chem. 2014, 406 (14), 3263-3277. (44) Shen, L.; Hagen, J. A.; Papautsky, I., Point-of-Care Colorimetric Detection With a Smartphone. Lab Chip 2012, 12 (21), 4240-4243. (45) Vashist, S. K.; Schneider, E. M.; Luong, J. H., Commercial Smartphone-Based Devices and Smart Applications for Personalized Healthcare Monitoring and Management. Diagnostics 2014, 4 (3), 104-128.

(46) Vashist, S. K.; Luppa, P. B.; Yeo, L. Y.; Ozcan, A.; Luong, J. H., Emerging Technologies for Next-Generation Point-of-Care Testing. Trends Biotechnol. 2015, 33 (11), 692-705. (47) Kim, B. Y.; Hong, L. Y.; Chung, Y. M.; Kim, D. P.; Lee, C. S., Solvent‐Resistant PDMS Microfluidic Devices with Hybrid Inorganic/Organic Polymer Coatings. Adv. Funct. Mater. 2009, 19 (23), 3796-3803.

(48) Hughes, S.; Dasary, S. S.; Begum, S.; Williams, N.; Yu, H., Meisenheimer Complex Between 2, 4, 6-Trinitrotoluene and 3-Aminopropyltriethoxysilane and Its Use for A Paper-Based Sensor. Sensing and Bio-Sensing Research 2015, 5, 37-41. (49) Feng, L.; Tong, C.; He, Y.; Liu, B.; Wang, C.; Sha, J.; Lü, C., A Novel FRET-Based



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 29

Fluorescent Chemosensor of β-cyclodextrin Derivative for TNT Detection in Aqueous Solution. J. Lumin. 2014, 146, 502-507.

(50) Vashist, S. K.; van Oordt, T.; Schneider, E. M.; Zengerle, R.; von Stetten, F.; Luong, J. H., A Smartphone-Based Colorimetric Reader for Bioanalytical Applications Using the Screen-Based Bottom Illumination Provided by Gadgets. Biosens. Bioelectron. 2015, 67, 248-255. (51) Bernards, D. A.; Macaya, D. J.; Nikolou, M.; DeFranco, J. A.; Takamatsu, S.; Malliaras, G. G., Enzymatic Sensing with Organic Electrochemical Transistors. J. Mater. Chem. 2007, 18 (1), 116-120. (52) Kondo, A.; Kojima, N.; Kajiro, H.; Noguchi, H.; Hattori, Y.; Okino, F.; Maeda, K.; Ohba, T.; Kaneko, K.; Kanoh, H., Gas Adsorption Mechanism and Kinetics of an Elastic Layer-Structured Metal–Organic Framework. J. Phys. Chem. C 2012, 116 (6), 4157-4162. (53) Fletcher, A. J.; Cussen, E. J.; Bradshaw, D.; Rosseinsky, M. J.; Thomas, K. M., Adsorption of Gases and Vapors on Nanoporous Ni2 (4, 4'-bipyridine) 3 (NO3) 4 Metal-Organic Framework Materials Templated with Methanol and Ethanol: Structural Effects in Adsorption Kinetics. J. Am. Chem. Soc. 2004, 126 (31), 9750-9759.

TOC 28 ACS Paragon Plus Environment

Page 29 of 29


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


Smartphone-Enabled Colorimetric Trinitrotoluene Detection Using

Recommend Documents