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In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains. Accepted Manuscript ChemComm www.rsc.org/chemcomm http://www.rsc.org/Publishing/Journals/guidelines/AuthorGuidelines/JournalPolicy/accepted_manuscripts.asp http://www.rsc.org/help/termsconditions.asp http://www.rsc.org/publishing/journals/guidelines/ ChemComm RSCPublishing COMMUNICATION This journal is © The Royal Society of Chemistry 2012 J. Name., 2012, 00, 1-3 | 1 Cite this: DOI: 10.1039/x0xx00000x Received 00th January 2012, Accepted 00th January 2012 DOI: 10.1039/x0xx00000x www.rsc.org/ Water soluble polymers, solid polymer membranes, and coated fibres as smart sensory materials for the naked eye detection and quantification of TNT in aqueous media. Jesús L. Pablos, Miriam Trigo-López, Felipe Serna, Félix C. García, José M. García* This study developed sensory polymeric materials for the colorimetric sensing of TNT in aqueous media. Solid films and coated fabrics permitted the detection of TNT, through colour change, and its quantification, by taking a picture of the materials and processing their RGB parameters to define the evolved colour. The detection of explosives by non-specialised personnel using rapid, cheap techniques is a challenging issue that has arisen from societal concern about their widespread use in mining industries, military endeavours, and terrorist attacks. The detection and quantification of explosives is twofold, through vapour detection and in solution. The former is related to homeland security and humanitarian efforts such as demining, for instance, and the latter with forensic and criminal investigations and environmental control and remediation. Among the broad set of explosives, 2,4,6- trinitrotoluene (TNT) is one of the most widely used in civil and military applications, and its detection in solution in groundwater or extraction from soil is necessary for the control and remediation of abandoned military sites, industrial waste, and spills by explosive- related industries because nitroaromatics are blood and liver toxins that can be absorbed by the skin or gastrointestinal tract.1 In the same way, TNT’s detection in solutions of washed scrap-metals and residues are essential in terrorist strike investigations. With these needs in mind, we undertook the preparation of water-soluble polymers, solid sensory polymer membranes with gel behaviour, and smart fibres made from polymer-coated yarns as colorimetric chemosensing materials for the naked eye detection of TNT in aqueous solutions.2-6 The well-known formation of highly coloured complexes of the electron-deficient aromatic ring of TNT with Lewis bases, such as amines, alkoxy, and hydroxyl groups, under mild conditions, also called the Meisenheimer complexes,7-11 has been exploited for the detection of nitroaromatics using colour changes through UV/Vis spectroscopy. Following this approach, we engaged in the preparation of colorimetric chemosensory polymeric materials using a costless commercial acrylic monomer, 2- (dimethylamino)ethyl methacrylate (DMAEMA), which contains an amine group as a colorimetric sensory moiety for TNT. This was a different methodology than that usually followed to achieve sensitivity and the selectivity challenges encountered in explosive sensing, which is usually carried out using conjugative polymers and is typically based on fluorescence quenching,12,13,14,15 and not in colour variations. Both the thermically initiated radical homopolymerisation of DMAEMA and copolymerisation of DMAEMA with the hydrophilic co-monomer 2-hydroxyethyl acrylate (2HEA) rendered water soluble linear polymers, L100 and L50, respectively (Scheme 1), whose colourless solution in water containing organic solvents developed red colours in the presence of TNT. The addition of a crosslinker to DMAEMA or to a mixture of DMAEMA/DMAEMA permitted the preparation of film shaped solid membranes with thicknesses of 110 μm, both lipophilic and hydrophilic and with gel and organogel behaviour, named M100 and M50, respectively (Scheme 1). The membranes were colourless and transparent and were cut with an office puncher into easily handled sensory discs with diameters of 5 mm. The immersion of the sensory discs in solutions containing TNT turned them reddish in minutes. Moreover, the coating of white cotton fibres and yarns allowed for the preparation of intelligent garment pieces that turned reddish upon coming into contact with organic/aqueous solutions containing TNT. Apart from the visual detection of TNT and its quantification by the UV/Vis technique, the solid materials also permitted its quantification using the colour definition, or the RGB parameters, of a digital picture taken with a conventional camera or smartphone, avoiding the use of time-consuming techniques requiring operation by skilled, specialised personnel.16-18 A reference membrane Mref, without sensory amine motifs, was also prepared for comparative and control purposes (Scheme 1). The polymers were characterised as sensory materials prior to testing. Thermal resistance is a key parameter of materials for final applications and was evaluated for the membranes using thermogravimetric analysis (TGA) (Table S1 and Figure S1). The decomposition temperatures of membranes that resulted in 5% loss under a nitrogen atmosphere (T5) were approximately 250 ºC, indicating that the materials had a reasonably good thermal stability for sensing applications. The chemical constitution of the Mref, as derived by FTIR spectra (Figure S2), corresponded to the proposed structure (νOH = 3033-3696 cm-1, broad signal; νC=O = 1721 cm-1), and its spectral pattern resembled the structure of the well-known poly(2-hydroxyethyl methacrylate).19 No significant changes were observed between Mref and M50; in M100, the absence of the hydroxyl group was in accordance with the absence of υ-OH Page 1 of 3 ChemComm C h em ic al C o m m u n ic at io n s A cc ep te d M an u sc ri p t CO 2 | app solv par mo tak org and resp low che term Fur pro org L10 tho dat in r Sch cop col che am was How obs as S6) wh par as a Fig met to aro wit upo con sys How OMMUNICATIO J. Name., 2012 proximately 340 vent uptake, i.e rameter in the d lecules enter t es place, by d ganogel phase. d 54%, and in a pectively. It ha wer than 100% emicals into th ms of mechan rthermore, these ovided it with an ganic and aqueo 00 and L50, the se of the mem a confirmed th relation to the c heme 1. Sens polymer and b) ourlessness and After charac emosensors was ine with TNT s the case w wever, the sens served upon the 2,4-dinitrotolue ). This interacti ich are species rtial transfer of a Lewis base, t gure S7 reveals thyl groups of a lower field, matic proton re th the TNT.21,2 on extraction w nsequently, the tems for this p wever, the Me ON 2, 00, 1-3 00 cm-1. The so e., the hydrophi design of solid the membrane, diffusion into The SSPs of t acetone they we as been proven % is appropriat he membrane a nical properties e data showed n amphiphilic c ous environmen characterisatio mbranes (Figure he structure and comonomer mol sory material membranes, w d transparency. cterisation, the s evaluated. It leads to the d with the sensin sing was highly e addition of ot ene (2,4-DNT) ion is based on in equilibrium f electronic char to the aromatic s a gradual shi tertiary amine , along with t esonance, confi 22 Forensic and with organic so ideal testing m purpose are org eisenheimer com olvent-swelling licity and lipop sensory materia which is whe the solvent-ric the membranes ere 41% and 38 n that a SSP h te for both th and maintainin s, of the wate that the constit character useful nts. In relation t on data were in es S3-S5 and T d composition o lar ratio. preparation an with pictures sh e material’s is known that evelopment of ng acrylic mo y specific and n ther nitroaroma and 4-nitrotol n the Meisenhe m, including cha rge from an am nucleus of the ft in the proto and the methy the downfield rming the inter d environment olvents usually edia in lab proo ganic solvents mplex formatio g percentage (S philicity, is a str als because the re the sensing ch membrane g s in water were 8% for M100 and higher than 40% e rapid diffusi g the tractabil er-swelled mat tution of the m l for detection i to the linear pol n full agreemen Table S2). The of the copolym nd codes: a) howing the mat performance the interaction a reddish colo onomer DMAE no colour chang atic compounds luene (4-NT) (F imer-like comp arged species, a mine group, beh nitro-compoun n resonances f ylene group (N- shift of the T raction of DMA tal samples pre y contain wate of-of-concept se enriched with on is described SP) or rategic e target event gel or e 61% d M50, % and ion of lity, in terials. material in both lymers nt with NMR mer L50 linear terials’ as a n of an our, as AEMA. ge was s, such Figure plexes, and the having nds.8,20 for the -CH2-) TNT’s AEMA epared er, and ensory water. d to be strong behav (80:2 S8). W and conce enviro curve detec and 1 In used senso UV/V detec 9.0x1 reaso previo L100 spray as de conta T using in dia imme TNT Meise TNT other S12) mono the tw imme M) in record 25-30 exper instab the de TNT the co devel TNT three comp (PC1) three titrati (the p The p depth LOD/ and 1 these the d consi mater smart W colori fabric cotton DMA T gly affected by viour of the m 0, v:v), resultin We chose aceto forensic applic entrated at low onmental conc es (Figure S9) tion (LOD) an .7x10-4 M, resp n a similar fash to prepare sens ory dimethylam Vis titration cu tion of TNT w 10-5/2.7x10-4 M nably good for ously reported and L50 were ys with which to emonstrated in act with TNT (sh The solid sensor g a conventiona ameter. Colour ersing the disc for 2-3 min enheimer comp was highly sel nitroaromatic when followin omer DMAEM wo sensory me ersed in a quart n an acetone:w ded periodicall 0 min was ad riments was co bility of Meisen ecomposition o acetone:water olourless discs i lopment (Figure concentration RGB paramete ponent analysis ), which gave RGB paramete ion curves ([TN principal comp procedure is sho h in recent pu /LOQ were 1.1 .4x10-4/4.3x10- were conclude detection of dering that the rials, in situ, tphone/laptop. We extended ou imetric detectio cating wearable n fabric were c AEMA and EG This journal is © y the presence monomer in dr ng in an enhanc one because it is cations, it is w temperature, cerns, and it using the UV nd limit of qua pectively.24 hion, stock wate sory acetone:w mino motif con urves (Figures with a LOD/L for L50 and L10 r the detection data.11,25 Mor an environme o detect in situ the detection o hown in the vid ry kits were man l office sheet p r changes were s in an aceton nutes, indicati plexes. Moreov lective, with th compounds, su g the same beh A in solution. T embranes, senso tz cuvette conta ater solution (8 y every 45 s (F equate, and th onsidered to b nheimer comple of TNT in soluti (80:20, v/v) so into the solution e 1). A visual of 1x10-3 M. A ers of each dis s (PCA), extra an account of > ers, thus permit NT] vs. CP1) w onent paramete own in a cartoo ublications by 1x10-4/3.5x10-4 -4 M for M50. In d to be extreme TNT. This c e quantification and using the ur study to the p on of TNT, as a e chemical poly coated with the DMMA. 1x1 c The Royal Socie of water,11,23 s ry acetone and nced response in s a common so cheap, sample , it does not gave satisfacto V/Vis techniqu antification (LO ter solutions of water (80:20, v:v oncentration of S10 and S11 LOQ of 4.2x10 00, respectively of TNT in solu reover, the aqu ental friendly the presence o of cotton fibre deo provided as nufactured from paper punch to c e visible to th ne:water (80:20 ing the effici ver, the rapid v he materials rem uch as 2,4-DNT haviour that exh To determine th ory discs of M taining a solutio 80:20, v:v), an (Figure S13). A he optimal tim be 1 h when a exes under amb tion.10 A naked olution was carr n for 1 h and ob colour change After photograp sc were process acting one pri > 96% of the tting the simple with a concomit ers are shown on in Figure S1 y our Research M for the sen n light of previo ely sensitive se conclusion wa n was carried he hardware an preparation of s an attractive cl ymeric sensors. e sensory polym cm cotton fabric Journal Na ty of Chemistry 2 so we analysed d in acetone:w n the latter (Fig lvent for extrac es can be rap present impor ory TNT titra e, with a limi OQ) of 5.7x10- f L100 and L50 w v) solutions wi f 1.2 mEq/L. ) allowed for 0-5/1.3x10-4 M y. These limits w utions accordin ueous solution tool for prepa of TNT in surfa s that had bee s ESI). m the M100 and cut out discs 5 he naked eye a 0, v/v) solution ient formation visual detection maining silent w T and 4-NT (Fig hibited the sen he response tim M100 and M50 w on of TNT (1x nd the spectra w A detection tim me for the sen accounting for bient conditions eye titration of ried out by dipp bserving the co was observed phing the discs, sed using princ incipal compon information on e elaboration of ant noise reduc in Table S3-S 14 and describe h Group.26,27 sory material M ously reported d ensory materials as especially out with cost nd software o smart fibres for ass of substrate Fibres from w mer prepared f cs were coated w ame 2012 d the water gure ction pidly rtant ation it of -5 M were ith a The the and were ng to s of aring aces, n in M50 mm after n of n of n of with gure sory me of were x10-2 were me of nsing the and f the ping olour at a , the cipal nent n the f 2D ction S13). ed in The M100 data, s for true tless of a r the e for white from with Page 2 of 3ChemComm C h em ic al C o m m u n ic at io n s A cc ep te d M an u sc ri p t Jou This 61, sma (see the v/v M. visu pol be dig 2.4 resp imm two than bec nee was sen coa loss tou wh coa con Fig pho film ace par ach dep con Fig dip from titra from ana In s solu that put col film pro lim urnal Name s journal is © Th 47, 27, 12 and art fabrics with e picture in Fig sensory disc, t v) containing co The colour c ually related w lymer content ( quantified with gital picture, giv x10-3 and 1.8x pectively. The mersing the coa o minutes, an n that corresp cause of the c eded for the dif s highly dimin nsory material f ating increased s of garment co uch with the low ich full garmen ated fabrics cou nventional garm gure 1. Titratio otographs of th ms, M100 and etone:water (80 rameters (R, G hieved via princ pict the colour ncentrations. gure 2. Digital ped for 2 min m 1x10-5 M to ation curve usi m the three di alysis. summary, we p uble polymers a t permitted the tting the senso our developmen ms and coated f ocessing the RG mits of detectio e Royal Society o d 6%, by weigh h references F61 gure S15). Fol the fabrics were oncentrations of hanges were o ith the TNT co (Figure 2). Sim h the colour de ving rise, for in x10-3 M for th e picture show ated fabrics in impressive resp ponding to the oated fibres’ h ffusion of TNT nished when r from one hundr the rigidity of t omfort, though t wer polymer c nts could be pre uld be used to ments. on of TNT usin he sensory dis M50, were ta 0:20, v/v) for 1 G, B) to one cipal componen r variations ca l picture taken nutes in TNT s o 5x10-2 M, usi ng the single p igital colour p repared sensory and solid-film s e colorimetric d ors into contac nt was observed fabrics permitte GB parameters t on between th of Chemistry 201 ht, of the senso 1, F47, F27, F12, lowing the pro e immersed in a f TNT ranging f observed in m oncentration and milarly, the TNT finition of each nstance, to LOD he coated fabri wn in Figure the media cont ponse time. Th e sensory mem high sensory s into the sensor reducing the c red of microns t the cotton fabric this increase w ontaining fabri epared. On the sew small TNT ng the RGB par scs. These pict aken after imm 1 h, and the re principal com nt analysis. The aused by diffe n from squares solutions of co ing acetone as principal compo arameters via y polymeric ma shaped network detection of TN ct with solutio d in minutes. P ed the explosiv that defined the he micro and 12 ory polymer to , and F6, respec ocedure describ acetone:water ( from 1x10-5 to inutes and cou d the fabric’s se T concentration h fabric taken f D values of 1.1 ics F47, F12, an 2 was taken taining TNT fo his time was s mbranes, most surface and the ry membranes, cross section o to a thin coatin c, with a conco as not apparent ics, F12 and F6 other hand, all T sensory label rameters from tures of the se mersing the di eduction of the mponent (PC1 e pictures of the erences in the s of lab coat oncentrations ra a solvent (left onent (PC1) ob principal comp aterials, both as ks, and coated f NT in solution. ons containing ictures of the se ve’s quantificati e digital colours d millimolar r render ctively bed for (80:20, 5x10-2 uld be ensory n could from a 1x10-3, nd F6, n after or only shorter likely e time which of the ng. The omitant t to the 6, from of the ls into digital ensory scs in e three ) was e discs e TNT fabric anging ft), and btained ponent s linear fabrics Upon TNT, ensory ion by s, with ranges. Appli can b impro havin Note Depar Plaza jmigu † E prepar of the memb demon 1 W 2 T W 3 M 4 Y C 5 S 6 M G 7 J. 8 F 9 H 20 10 Y B 11 E 12 S 44 13 A an 14 S 13 15 J. R 16 K 10 17 D 18 J. A 19 S 17 20 E 22 21 Y K 22 H 23 23 T 24 L (L of re M 25 G Fo 26 H A 27 S. G ications in the e envisaged fro ovement of the ng primary inste es and refer rtamento de Quí de Misael uel@ubu.es; Tel: lectronic Supple ration and chara e colorimetric branes, principa nstrating video. W.D. McNally, T race chemical Wiley-Interscienc M. E. Germain an Y. Salinas, R. M Costero, M. Parra . J. Toal and W. M.C. ChuangJ.R Galik,T.Y. Chou, Meisenheimer, . Terrier, Chem. H. Chen, H.W. C 004, 15, 998. Y. Liu, H.H. Wan B, 2011, 160, 114 . Ercag, A. Uzer . Rochat and T. 488. A. Alvarez, A. S nd A. Sanz-Med . W. Thomas, G 339. M. 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DOI: Sens. 2012, 968, r, Y. 2013, urves ation n the x10-3 y)). nton, arcía, . M. Page 3 of 3 ChemComm C h em ic al C o m m u n ic at io n s A cc ep te d M an u sc ri p t