the area designated as "Drought Polygon"(occurrence of dr5lUghts ) is estimatedat 1,083,790.7 km . It is estimated thatonly in serni-arid, the area occupied bynatprally saline soil is more than 90,000km r predorninantly within the DroughtPolygon.

Besides, the growing demand forwater in industrial processes may affectthe local environment in a significantway. Likewise, water scarcity, especiallyin the semi-arid northeast of Brazil,makeswater reuse a factor of high priority andattractiveness [3].

Thus it is important to havemethodologies to assess the impact ofagricultural activities on soi! and water.More specifically,in the case ofapplicationof inputs such as fertilizers and pesticides(herbícides, insecticides, fungicides), andsubstances such as nitrates, nitrites, heavymetals, ions and humic substances, it isessential to constant monitoring of theenvironment in order to know well theeffects and destination of such products

in natural resources [4, 5]. In this case,the tests are almost always expensive andrequire the use ofsophisticated laboratoryequipment. Therefore, the developmentsof sensors that aIlow the determinationof these substances in the laboratory orfield, with techniques of low cost andsimple to perform, are highly desirable.An important feature of the monitoringand surveillance of these substances inthe environrnent [6, 7] is the need for alarge number of tests and measures, bothspatially and temporaIly. To this end, weseek to increasingly sensors, equipmentand the most sirnple, cheap and fast. Thestudy ofconductingpolymers has attractedan enormous scientific and technologicalinterest due to the need of active materiaIsfor sensors in manyapplications. Thesepolymers become electroactive throughthe process of dópíng, with a variety ofsubstances, which allows an increase of itsversatility for use in sensor devices.

Thepotential impact ofnanotechnologyon the sensor market is huge in thedeveloping and developed world alike.Forexample, industry analyst NanoMarketsreports that nanotech sensors generatedglobal revenues of US$2.7billion in 2008and estirnates it will reach US$7.2billionin 2012.

InBrazil,TheNational NanotechnologyLaboratoryAppliedtoAgribusiness,housedat Embrapa' s agricultural instrumentationunit in São Paulo, has developed a cheapoptical sensor incorporating nano-assembled films to evaluate the acidityof natural water supplies. And 'electronictongues' - another kind of polymer sensordeveloped at Embrapa - can be used todistinguish between different mineralwaters and between pure water and watercontaminated by organic matter.

Nanosensor applied to Water Quality - Developing low cost pHsensor to natural water, and applicationof other te...chniques.

Paulo Sergio de Paula Herrmann Jr.Embrapa Instrumentação Agropecuária, National Nanotechnology Laboratonj fi? r Agribusiness, Rua

XV de Novembro1452, P.D. Box 741, Zip Code: 13560-970, São Carlos-SP, Bmzil ,tel: 0-5516 21072911 e-mail: herrmann@cnpdia.embrapa.br

ABSTRACTThe low-cost optical sensor built in strip, was developed froma composite obtained with applicationof in-situ chemical polymerization, using polyaniline in the emeraldine oxidation state, dopedwith HCL onto poly(ethylene terephthalate) (PEl) film, used to measured the pH of water. Theabsorption of UV-Visspectra was used to evaluate the optical response to pH change of naturalwater. The strip showed a reversible color change upon variation of the pH. The pH ranges usedto calibrate the optical sensor were from 2.0 to 12.0.These kinds of sensor show the potentiality toinvestigate lhe pH of the natural water, to application to limnologicstudies, as well as, to investigatethe influence of the ionic strenglh. In this paper were showed new techniques that can be use toconduct research with pesticides in water using electrochemistry and biosensor, and electronictongue with conductive polymers to global quality evaluation.

Key words: disposable nanosensor, optical, low cost, conductive polymers, water quality, newtechniques

r

Introduction

Theevaluation and rri.onitoringofwaterquality are of fundamental importance forthe sustainable use of water resources.The contamination of the environmentand its direct relation to human health,the management of livelihood and themaintenance of ecosystems, has raisedstandards airned at the disposal ofchernicalwaste. The increasing use of pesticides inagriculture and its harrnful effects suchas contamination of soils and watershas drawn the attention of society andscientists to the issue of sustainabledevelopment [1].

In South Ásia total reriewab lefreshwater resources amount to 3655kmand totpl withdrawals for agriculture are842km per year which is by far the highestconsumptive use of water [2].

In Brazil the serni-arid 18% of thenational territory and includes 29% ofthe population of the country, with anextension of 858.000 km2, representingabout 57% of the territory northeast, and

376

New sensor technology copowerful micro-and nanomawill lead to tiny sensors, phígh accuracy for detectinand biochemical' s. The poteof nanotechnology sensor maFor example, the nano market .States reached $ 190 millionshould grow at an average26% to $ 592 million by the[8].

One of the major chaIlecentury will certainly be the dof electronic devices basedpaper products, very lowcost.are beginning to be demonswork of Garnier and colleagthat in 1994a Field EffectTramanufactured of polymeriusing pr íntíng technique.viewpoint of its constructionof substrate for the productionly on the properties desidevice. However, other mateon organic compounds, casuch as polyaniline, polyppolythiophene conductive [9].

Line Patteming Technique

The sensor technologconducting polymers has sinteresting results, especirelated to the development odevices [10-11].It has been shminiaturization and thin filmcould be the best way to have sworking with goodperforrnancthe techniques whichusuallyachieve such systems are not sdue high costs and many compto build up such sensors.and collaborators [12] devLine Patterning Technique, wused to fabricate inexpensive,

377

The line patterning technique wasused to make a maskto developing a low-cost optical sensor, buiIt in the stripe ofpoly(ethylene terephthalate) (PET) film,using a thin film of polyaniline (PANI)in the emeraldine oxidation state [14-15] doped with HCI, by in-situ chemicalpolymerization. The measurementsoccured with conductive polymers dopedand dedoped, and were used to evaluatethe pH of natural water. The absorption ofUV-Visspectra was investigated to evaluatethe optical response of the pH change tonatural water, and the comparison withcommon technique (Horiba system) used Emeraldine-HCI By in situ De.,rositionto measure the value of water pH in the of Polyaniline froma 1 mol"lnatural condition. The sensitivity and HydrochIoric Acid Aqueous Solution.reproducibility was evaluated. The overhead transparency was place

In this paper are demonstrated the in a 1.0 M hydrochloric acid solution

electronic devices [13]. This process isrelatively simple and easy to be carriedout. In this process, commerciaIly availableoffice supplies, as for example overheadtransparency and paper can be used as asubstrate for the fabrication of electrodes.Therefore, it is a new possibility to fabricatedisposable and inexpensive sensors.

The pH of the water is an importantparameter to water quality, because thevalue could determine the toxic effectsof the substances found in the solution.(runoff from agricultural, domestic,and industrial areas may contain iron,aluminum, ammonia, mercury or otherelements). The measurement of the pHin the water has high weigth in theWater Quality Index (WQI).The WQI arecompound by the following parameters:a) Dissolved oxygen; b) Fecal coliform; c)pH; d) Biochernical oxygen demand; e)temperature; f) total phosphate; g)Nitrates;h) Turbidity and i) Total solids. [22].

Optícal pH disposable nanosensor,

potential application of low cost sensorto investigate influence of ionic strengthto desalinization investtgation, carry outstudy of pH in natural water (Iirnnologicand portable water), new other techniquesto evaluate de concentration of pesticidein water (Electrochernistry and biosensor)and global water quality (electronictongue).

Materiais and Methods

with O.lM aniline and O.lM ammoniumpersulfate. The polymerization at 0.0

0

Cwasdone, with the reaction time of 90minutes.Thin strips of PETcoated with PANi werecut with 1.0 em and 6.0cm. The ribbonswere used as sensor of pH in the naturalwaters. All the measurements were carryout at room temperature.The absorbancemeasurement were taken from UV-Visspectrometer Shimadzu 1610, to evaluatethe colorimetric response of the polyanilinein the emeraldine base oxidation, ontopoly(ethylene terephthalate) (PET). Thepolymerization of the composites, usedas a pH sensor, showed a formation ofpolyaniline (PANi)fi the doped emeraldinesalt (ES) formo All the aqueous solutionused in this experíment was prepared withMilli-Qwater. Aniline (Aldrich, Sao Paulo,Brazil) was used after distillation underreduced pressure. Other chemicals wereused as received.

Development of optical pH sensorusing Line Patterning Technique (LPT)

The LPTwas used to design the maskand polyaniline deposition. In the figure1 the sequence for the manufacture ofoptical pH sensor: a) Design of the mask,b) negative image of the mask, c) printingof the mask on PET, d) in-situ synthesis ofPANI, e) removal of the toner with tolueneand methyl ethyl ketone (MEK).

The size of the strip was designedcompatible with PETto the size of portableelectronics. The size of the square todeposition of the active layer (PANI) wasdeterrnined according to the place wherethe light bearn wiII not be dispersed.

uV-Vis spectroscopy of the PETfPANIstripe with different pH

The spectrum of polyaniline obtainedby chernical oxidation is pH dependentbetween a pH 2 -12. In this range theapparent pK is around 7; which is in thephysiologicãl pH range. The electronicabsorption band of polyaniIine sensitiveto pH change is very broad. The figure2 showed the absorption response of thecomposite (in-situ deposition ofpolyanilinecoated PET) with fifteen different pH (2.0,3.0,4.0,4.5,5.0,5.5,6.0,6.5,7.0,7.5,8.0,9.0,10.0,11,0 and 12.0).

-~ I'ronIv..",

11·· ~:~'. ~ .~ ~_:~~~)01-, ' •• ~-, - ~101MnBefote •.,.1. , R~ 01•.•..•.... _ .....,.,.-_.

Fig. 1. Sequence for the develapment of optical sensorusing line patterning technique. Measurement in natural water

The developed system was usedto determine the pH of natural waterdarnrned. Thewater used in the experimentwas collected on ]anuary 6, 2009 at 16:30in Carlos Botelho (Lobo-Broa) reservoir,

378

Itirapina, São Paulo, Bratil I

11' 40,87" S, longitude 47 .'pthe surface are,,! is36.8 Km ;around 22 x 10 m , We colwater samples at different30 and 45 cm), to obtain thesamples from the Lobo-Brrwith the optical system. The :PANI was maintained for fív.1MHClsolution, and after drsame used for the calibration {system. After calibration, tluplaced for five rninutes in the :measured the pH, being inseisystem formeasuring pH Thewith the optical system was COI

the values obtained with a cormeter (Analion).

-Fig. 2. Set of absorption spectra rec

film obtained by in-situ deposition ofemeraldine oxidation state, on

nr,r Jtr-,I' W - /'

I~ __ '" I I .

~J..k" fo

I '\

Fig. 3. Localization of Carlos BotelhiReservoir (SP) [16].

379

Results and Discussion

The colour of PET/PANI stripe ispH dependent, as the protonated andnon-protonated forms of the pANI havedifferent spectral characteristics. Fig.4 shows the calibration curve that wasobtained with the wavelength of 530run.The reproducibility was tested, and valueobtained for 6 different samples were 7.6%to the sarne wavelength. The sensitivity ofthe calibration curve, using a fourth gradepolynornial equation, was approximately0.4 of pH. The minimum measurementof the pH was 1.5 and the maximum was11.9. The equation 1 is a linear relationof the attenuation (I/I) and pH. This isconsidered the calibrâtion equation ofPET/P ANI stripe. The reproducibility wasinvestigated and the standard deviationis considered the measured three times,with immersion time of 5 minutes eachmeasure.

i. ••

11..{ •

•••• {WIJ

Fig. 4. Normalised attenuation curpe oJ the PET/PANIstripe, measured at 530 nm as afunction of

. pH

Where "I" is the measurement ofthe stripe under different pH and "I "is the reference before measure the pl-Isolution.

pH = 1.503-(43.982 'IOg,,( +. )}R> = 0.9882) (1)

The optieal device developed was usedto verified the effeets of the ionic strengthand the nature of the iOAS,using buffersolutions in which different salts (NaCIand KCI)and three conçentrations of 0.15,0.30 and 0.50 moI l-I, with the solutionin the same pH (7.0). Fig. 5 shows therelation between cóncentration (moI l-I)and attenuation response of PET/ PANIstripe, obtained by using NaCI and KCI(in differentconcentrations).

Table I. Values of pH of water(Carlos Botelho reservoir) at variousdepths, obtained with the opticalsystem and commercial electrode.

Depth(em)

pH (commercialSystem)

7.9

pH(Stripe(PET/

·_·i5-·--r--··_··-7.2-·· ·-IR~i.~m.....30 7.7 7.9

"" ~ I". VIO.aClIo IIIOKCI

pH~1.0

7.645

•...

0.111 I!I

••• The data were obtained in the field,during a rainy day, in 01/2009, 16:00hs.The measurement of the pH obtained in15 cm was possible observe a slight trendto acid regime. This eould be a influence ofthe rain in the fisrt layerof natural water .In the depth 30cm and 45 em basically thepH didnt change.

...,s· OM

~••j 6'"

ó

....e.•• 1 : i i J ! ! : ?

0.10 0.15 0.20 0.25 0.30 O,S5 0,40 0.4$ 0,50 assC4ftC«'1tr.tlon (moi· r1•

Fig. 5. Effect ofionicstrength (0.15, 0.30 and 0,50 moil-I, in the samepH (7.0» and nature of the iOllS(NaCIand KCl) on lhe sensor response.

The results obtained show us thepotentiality to beused as disposable sensorto evaluate the influence of ionic strength,and can be applied to investigate the saltconcentration in the water solution.

Application of optical pH in naturalwater

.H

7.a 7,1

_..20

ó',"-

,.~.K·r••....

The pH of natural water eoIleetedfrom various depths, in Carlos Botelho(Lobo-Broa)reservoir, ltirapina-SP, Brazil,was obtained with the PET/PANI opticalsensor. The pH of the water throughthe optical system was compared withmeasurement of the commereiaI pHmeter.Thedata eollectedare showed inTableI.Theproposed optical system has an aceuracyof ± 0.4 pH units, the data obtained are ingood agreement with the pH obtained withthe eommercial system.

I-PETIPANII.-0- .. pHmeter

Fig. 6. The graphic conlain experimental data of therelation of pH with the depth (15, 30 and 45 em) Df

the Broa reserooir.

New Techniques to water qualitymonitoring.

Follow below some of the newtechniques that were developed byresearchers of the Embrapa AgriculturalInstrumentation applied toevaluated waterquality used in soilphysics, límnology andother areas:

380

Nanobiosensors with AFM cafor detecting herbicides

Enzyme inhibitors bind tand decrease their activity. Sincan enzyme activity can kill aor correet a metabolic imbaladrugs are enzyme inhibitors.also used as herbicides andSpecifie interactions betweercan be studied at the molecusing atomic force mieroseoAdhesion, in particular, is goshort-range intermoleeular f(may be controlled by approprizmodification, thus leadingcalled Chemical Force Microse[17, 18]. Figure 7 shows theforce between glass (substrate)without herbicide (diclofop-mthe tip of the Atomic Force M(AFM) coated with enzyme (acarboxylase (ACCase).

.~ .~ ...t _

i-

F-llJ.1 ~ ntl r;Tip .ACe •••.('~3Gl-m ••.w.:W. '

~

AdhulOllf.lu(nNI

Fig.7. Force curve on glass and herbl

Electrochemical detection of Pusing conducting polymers as

Pesticides with acidic char(2,4-D, gliphosate and bent:readily sorbed on the dedopedincreasing the voltammetrieof the CPE2 electrode. Howinteraction was observed bemacidic pesticides and the polyp~

3~1

suggesting that electrostatic interaction aredominant in the sorption of such pesticideswithout doping of the polypyrrole byprotonation, since the paraquat is an ionicpesticide [19].

Electronic Tongue water quality

An electronic tongue based onconducting polymers and a lipid-likematerial (stearic acid, SA) can be usedto distinguish between different mineralwaters and between pure water and watercontaminated by organic matter [20].

The importance of using ultrathin filmsin obtaining high sensitivity, detectingsucrose, quinine, NaCI, and HCl at theparts-per-billion (ppb) leveI. For thatwere compare sensor arrays ma de withnanostructured Langmuir-BIodgett (LB)films and cast films from conductingpolymers, a metaIlic complex, mer-[RuCl (dppb)(Py)] (dppb =PPh (CH) PPh;py = pyridine) (Rupy), and mixtMes àfconducting polymers and Rupy. Thiscould be indicate that the manipulation ofcomposite Rupy/ conductingpolymer filmsmay be tailored to specific applications,particularly because ruthenium complexesmight complex with heavy metaIs [21].

Conclusions

The results obtained in this workindica te that the strip built with PET- PANI nanocomposite produced duringin situ polymerization of aniline ontoPET film, is suitable for a construction ofdisposable optical sensor, which could beuseful to measure pH of the natural water,as weIl the ionic strength .The sensitivityand durability of each optical sensor wereobtained from the experimental results.The analysis of the data showed that couldbe useful to investigation in environrnentalcondition.

Inaddition was showed the potentialityof new techniques (Biosensor with AFMcantilever and Eletrochemistry) applied todetection and quantification of herbicidein water, and electronic tongue to use inglobal water quality. In this paper wasshowed a brief overview of the potentialapplication of low cost sensor to investigateinfIuenceof ionic strength to desalinizationinvestigation, carry out study of pH innatural water.

Acknowledgement

The author would like to thank fortheir contributions, the folIowingmembersof the team: Dr. Silvio Crestana andDr. Washington Luiz de Barros Meioresearchers from Embrapa AgriculturalInstrumentation (CNPDIA), and DrAlexandra ManzoIli (Pos-Doctorate),M.Sc. Clarice Steffens, and M.Sc. JulietaBramorski (Craduated Student) andRafaeIla Takehara, Helio José AntunesFranco (undergràduate student) as amember of the project. AswelI Dr. Fabio deLima Leite (Associate Professor at FederalUniversityofSãoCarlos-Campus Sorocaba,SP, Brazil (UFSCar-Sorocaba, SP, Brazilj)with iWTestigationin Nanobiosensor, Dr.Carlos Mapoel Pedro Vaz and Dr. LuizHenrique Capparellí Mattoso researchersof the CNPDIA that house the NationalNanotechnology Laboratory Appliedto Agribusiness (LNNA) that conductresearches with electrochemistry andelectronic tongue applied to water andfacilities support.

TheCNPq with financial support of thefoIlowing research projects: 485921/2006-5, 490807/2007-0, "NAMITEC NationalInstituteofScience and Technology" (INCT-Namitec,573738/2008-4(CNPq),2008/57862-6 (FAPESP» and macroprogram 3, fromEmbrapa, number 03.08.01.027.00.04.

382

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