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Contents lists available at ScienceDirect

Sensors and Actuators B: Chemical

jo ur nal home page: www.elsev ier .com/ locate /snb

icrofluidic electronic tongue

ristiane M. Daikuzonoa, Cleber A.R. Dantasb, Diogo Volpatib,c, Carlos J.L. Constantinod,aria H.O. Piazzettae, Angelo L. Gobbie, David M. Taylor f, Osvaldo N. Oliveira Jr. c,

ntonio Riul Jr. g,∗

PPGCM, Universidade Federal de São Carlos/UFSCAR, campus Sorocaba, SP, BrazilPOSMAT, Universidade Estadual Paulista/UNESP, Bauru, SP, BrazilSão Carlos Institute of Physics, University of São Paulo, São Carlos, SP, BrazilDFQB, FCT – Univ. Estadual Paulista/UNESP, Presidente Prudente, SP, BrazilLNNano, Centro Nacional de Pesquisa em Energia e Materiais/CNPEM, Campinas, SP, BrazilSchool of Electronic Engineering, Bangor University, Bangor, United KingdomDFA, IFGW, Universidade Estadual de Campinas/UNICAMP, Campinas, SP, Brazil

r t i c l e i n f o

rticle history:vailable online xxx

eywords:icrofluidics

ayer-by-layerlectronic tongue

a b s t r a c t

Fast, simple inspection of liquids such as coffee, wine and body fluids is highly desirable for food, beverageand clinical analysis. Electronic tongues are sensors capable of performing quantitative and qualitativemeasurements in liquid substances using multivariate analysis tools. Earlier attempts to fulfil this taskusing only a few drops (microliters) of sample did not yield rational results with non-electrolytes e.g.sucrose (sweetness). We report here the fabrication and testing of a microfluidic e-tongue able to dis-tinguish electrolytes from non-electrolytes, covering also the basic tastes relevant to human gustativeperception. The sensitivity of our device is mainly attributed to the ultrathin nature of an array formed bynon-selective sensing units. The electronic tongue is composed of an array of sensing units designed witha microchannel stamped in a poly(dimethylsiloxane) (PDMS) matrix and sealed onto gold interdigitatedelectrodes (IDEs). The IDEs are then coated in situ with a 5-bilayer film deposited by the layer-by-layer(LbL) technique. The cationic layer is derived from polyallylamine chloride (PAH). The anionic layer iseither poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) PEDOT:PSS, polypyrrole or nickel tetra-

sulfonated phthalocyanine. When compared to a conventional electronic tongue our system is threetimes faster and requires only microliters of sample. Applying Principal Component Analysis to the datayields a high correlation for all substances tested. This microfluidic e-tongue has the potential for pro-ducing low-cost, easily integrated, multi-functional sensor for food, beverages, in addition to clinical andenvironmental applications.

© 2014 Elsevier B.V. All rights reserved.

. Introduction

Microfluidics is at the interface of Physics, Medical Sciences,ngineering and Chemistry, bringing the benefits of reduced sizend, hence small test volumes, low waste and fast response as wells the potential for small, portable and integrated devices [1–3].ithin this context, it is highly desirable to develop platforms

ncorporating micro-analytical tools for food, beverage, phar-

Please cite this article in press as: C.M. Daikuzono, et al., Micrhttp://dx.doi.org/10.1016/j.snb.2014.09.112

aceutical, clinical and environmental investigations in liquidamples. An electronic tongue (e-tongue) is a multisensory systemsing multivariate analysis for the quantitative and qualitative

∗ Corresponding author. Tel.: +55 19 35215336; fax: +55 19 35214147.E-mail addresses: riul@ifi.unicamp.br, riul@ufscar.br (A. Riul Jr.).

ttp://dx.doi.org/10.1016/j.snb.2014.09.112925-4005/© 2014 Elsevier B.V. All rights reserved.

inspection of a solution [4]. Microfluidic systems incorporatingthe e-tongue concept reported to date have not been used withnon-electrolyte substances [5,6]. We present here a method thatbenefits from the manipulation of nanostructured layers andsamples inside a microchannel to create a microfluidic electronictongue able to distinguish all basic tastes (sour, salt, sweet, bitterand umami) at sensitivities below the human threshold.

Several types of e-tongue systems have been reported in theliterature [7]. The device reported here is based on measuring theimpedance of a sensor array composed of ultrathin films depositedonto interdigitated electrodes [8,9]. Briefly, the distinct electrical

ofluidic electronic tongue, Sens. Actuators B: Chem. (2014),

characteristic of the nanostructured materials used to form indi-vidual sensing units creates a fingerprint of the solution analyzed,with the ultrathin nature of the films yielding a highly sensitive sen-sor. Since we do not perform potential-dependent measurements,

IN PRESSG ModelS

2 and Actuators B xxx (2014) xxx–xxx

ti

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Table 1LbL parameters used to build multilayers inside a PDMS microchannel.

Material Concentration(mg/mL)

pH LbL multilayer formed Based onreference

PAH 0.5 8 (PAH/NiTsPc)n=5 [19]NiTsPc 0.5 8PAHa 0.5 4.8 (PAH/PPy)n=5 [20]PPya 1.12 3.1PAH 0.5 3.5 (PAH/PEDOT:PSS)n=5 [21]PEDOT:PSS 0.1 3.5

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here is no need to use the three-electrode cell normally employedn electrochemistry.

Various methods can be used to assemble nanostructures.he layer-by-layer technique (LbL) is a simple, versatile, bottom-p procedure for multilayer formation on free surfaces [10]nd in confined geometries e.g. inside microchannels [11–13].here are several reports on nanostructured thin films insideicrochannels using dynamic layer-by-layer (LbL) deposition,

ut only one is related to electronic tongues or taste sensors.acesko et al. [5] reported a surface acoustic wave microfluidicensor having a 10 mL chamber; however, our system requiresnly 200 �L of sample and uses impedance spectroscopy ashe detection method, thus obviating the need for a piezoelec-ric substrate. Zou et al. [14] used a system analogous to ourso check protein binding at an electrode surface and observed

significant reduction in time analysis and reagent volumes.im et al. [15] reported a bioelectronic super-taster, incorpo-ating the human bitter-taste receptor protein immobilized on

single-walled carbon-nanotube field-effect-transistor (SWCNT-ET) with a lipid membrane which exhibited a surprising humanongue-like sensitivity. Nonetheless, fabrication of the field-effectevice requires many assembly steps including the immobiliza-ion of a composite lipid membrane between source and drainollowed by the integration into a microfluidic system. Hossein-abaei and Nemati [6] reported the concept of a microfluidiclectronic tongue, which was used only for strong electrolytessourness and saltiness). Measurements for bitterness and sweet-ess, such as sucrose (non-electrolyte) and caffeine, were noterformed.

In this study, we describe the fabrication and testing of aicrofluidic taste sensor, in which sensing is undertaken byeasuring the impedance between co-planar, interdigitated

old electrodes coated with nanostructured films. The devices formed by integrating individual sensing units comprising-bilayer films deposited in situ within each microchannelsing the layer-by-layer approach. Every bilayer is composedf polyallylamine chloride (PAH) as the cationic layer andither poly(3,4-ethyenedioxythiophene):poly(styrenesulfonate)PEDOT:PSS), polypyrrole (PPy) or nickel phthalocyanine (NiTsPc)s the anionic layer. Each sensing unit requires only 200 �L ofamples and presents a much faster analysis than a conventionaletup (needs ∼ 50 mL for sampling), providing also high correla-ion between data acquired in triplicate. Indeed, different devicesntegrated into microfluidic systems enable a variety o distinctesigns in an e-tongue system for producing low-cost, easily

ntegrated, multi-functional sensors that can be directed for apecific application for food, beverages, clinical and environmentalnalysis.

. Materials and methods

PAH, NiTsPc, PEDOT:PSS and PPy were purchased fromigma–Aldrich and used as received. Sodium chloride (NaCl),-glutamic acid monosodium salt hydrate (monosodium gluta-ate), sucrose (C12H22O11), hydrochloric acid (HCl) and caffeine

8H10N4O2 (anhydrous) were of analytical grade and purchasedrom Vetec, Quemis and Synth, and used as received. All solutionsere prepared with ultrapure water from a Direct-Q5 Millipore

ystem, with aqueous solutions of NaCl, sucrose (C12H22O11), HCl,onosodium glutamate and caffeine (C8H10N4O2) prepared at

mM concentration for e-tongue analysis.

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Gold interdigitated electrodes (IDEs) comprising 30 pairs ofngers 40 �m wide, 3 mm long with an inter-electrode gap of0 �m (cell constant ∼13.7 mm) were fabricated onto glass slidest the Brazilian Nanotechnology National Laboratory (LNNano).

a Both PAH and PPy solutions were prepared in a 0.5 M L−1 NaCl solution, withn = number of deposited bilayers.

Microchannels 490 �m wide, 50 �m high and 12.5 mm long wereengraved in a PDMS matrix, again at LNNano. The IDEs and PDMSmicrochannels were placed in an oxygen plasma (SE80/Barrel AsherPlasma Technology: 100 mTorr and 70 W) for 15 s [16–18]. Afterplasma treatment, the PDMS microchannel was placed in contactwith the IDEs and manually pressed for a few seconds, irreversiblysealing the device, as illustrated in Fig. 1.

LbL films were successfully deposited at room temperatureinside such sealed microchannels, with multilayers systematicallybuilt-up in a controlled manner by sequentially passing freshpolyelectrolytes through the microchannel at 1000 �L/h using aHamilton micro-syringe housed in a Cole Parmer syringe pump,as illustrated in Fig. 1a. The LbL deposition inside the PDMSmicrochannel was adapted from the dynamic LbL depositionmethod [12,13], based on results from reported conventional LbLassembly [19–21] in order to guarantee good adsorption betweenconsecutive layers. 15 min was adopted as the deposition timewith the LbL parameters specified in Table 1.

The LbL films were characterized using impedance and Ramanspectroscopies. Impedance measurements were acquired from 1 Hzto 1 MHz using an impedance analyser (Solartron Analytical, Model1260A), with a 20 mV amplitude signal to assure linear response ofthe system [22]. Impedance data was collected during the depo-sition of each layer in the LbL film fabrication. For the analysis ofdifferent tastants impedance data was also recorded after rinsingthe LbL films in Milli-Q water. The presence of the LbL-depositedfilms in the microchannels was confirmed using Raman microscopy(Renishaw in-Via model), equipped with an optical microscope(500× magnification) and a 633 nm laser. Micrographs and spec-tra were obtained both before and after rinsing the films with avolume of ultrapure water 800 times higher than the volume ofthe microchannel. Several input laser powers were used in orderto optimize the signal-to-noise ratio, without compromising thephysical integrity of the samples.

The e-tongue comprised an array of sensing units formed withLbL films (described in Table 1) deposited onto IDEs inside PDMSmicrochannels. After rinsing the LbL films, the microchannelswere filled at 1000 �L/h with 1 mM aqueous solutions of NaCl(saltiness), C12H22O11 (sweetness), HCl (sourness), C8H10N4O2 (bit-terness) and l-glutamic acid monosodium salt hydrate (umami)for e-tongue analysis at room temperature. Four impedance spec-tra covering the range 1 Hz–1 MHz were acquired for each solutiontested, in order to check possible variations during the data acqui-sition. Three independent sets of measurements were also takenfor each analyte tested, with Principal Component Analysis (PCA)plots built with data taken in the kHz region, following previousworks [8]. In short, PCA is a statistical tool used to reduce dimen-sionality in multivariate data analysis [7,23], with PC1 explainingthe highest variance of original variables, PC2 explaining the sec-

ofluidic electronic tongue, Sens. Actuators B: Chem. (2014),

ond highest variation of original variables, etc. The PCA scoreplots were obtained using MATLAB (version 10), where groupsplaced close to each other correspond to samples with similarbehaviour.

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LbL a

3

pm[ciiiPL

qbfwdPLs

kcotmcpowt

Fec

face area with the surrounding solution. The electrical behaviourthen appears to arise from a combination of electrical double-layercapacitance (dependent on surface area) and the capacitance of the

Fig. 1. (a) Schematic view of the experimental setup used in the dynamic

. Results and discussion

After deposition of each LbL monolayer on the substrate, therogress of the adsorption is generally monitored using UV–viseasurements at a wavelength characteristic of the materials used

24]. Due to the difficulties in obtaining UV–vis data in the presentase owing to the presence of the gold interdigitated electrodesn the sealed device, LbL growth was monitored using in situmpedance spectroscopy measurements. Fig. 2 illustrates typicalmpedance data of the first adsorbed bilayer, acquired with theDMS microchannel filled with polyelectrolytes during dynamicbL deposition.

The inverse dependence of the impedance modulus |Z*| on fre-uency in Fig. 2 shows that capacitive behaviour dominates sampleehaviour in the measured frequency range up to ca. 10 kHz. There-ore, as in previous publications [7–9,25], electrical measurementsere restricted to measuring the capacitance at 1 kHz. Exampleata are given in Fig. 3 for the sequential adsorption of PAH/PPy andAH/NiTsPc LbL films in identical microchannels. PAH/PEDOT:PSSbL films displayed similar behaviour as for PAH/PPy (results nothown).

The changes in capacitance in Fig. 3 are similar to the well-nown overcompensation effect due to adsorption of oppositelyharged polyelectrolyte layers [26,27]. Albeit the trends are inpposite directions depending on the polyelectrolyte used, the sys-ematic change after each deposition step clearly indicates that the

aterial adsorbed onto the electrode affects the cell impedance,orroborating the literature in that IDEs are highly sensitive to the

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resence of charged layers [28,29]. Simple addition of one layernto another should lead to a capacitance that decreases inverselyith number of layers. For the PAH/NiTsPC films, the downward

rend in capacitance is evident with a good linear relationship

ig. 2. Impedance modulus acquired with the PDMS microchannel filled with poly-lectrolytes during the dynamic LbL deposition. A simplified equivalent electricircuit schematized inside.

ssembly; (b) cross-section view of the LbL film inside the microchannel.

between C and 1/n (results not shown). The slope obtained is thecapacitance for a singly deposited bilayer; however, the resultingcapacitance per unit area for a PAH/NiTsPC is ∼2 nF/cm2, an unre-alistic value when compared with lipids in the literature, possiblybecause the adsorbed multilayers are not a homogeneous dielec-tric film at that interface [27,30]. It is worth mentioning that thesame tendency of decreasing capacitance with increasing numberof deposited layers was observed for PAH/PSS [27] and PAH/CuTsPcLbL films (results not presented here).

On the other hand, an upward trend in capacitance is observedfor PAH/PPy and PAH/PEDOT:PSS (results not shown) for increas-ing layer deposition. Similar results in impedance behaviour wereobserved in the literature with other materials [29]. Most likely, thebilayers are deposited as open structures leading to a large inter-

ofluidic electronic tongue, Sens. Actuators B: Chem. (2014),

Fig. 3. Changes in capacitance during growth of (a) PAH/PPy and (b) PAH/NiTsPcLbL films deposited under flow conditions, with electrolytes kept 15 min inside thePDMS microchannel.

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FuP

dabhfpiiUfidsabLm

etiRFgiofpmrdcCdPLcsai

eiomrPft

Fig. 5. Raman spectra of PDMS, cast films and LbL films deposited inside PDMS

ig. 4. Variation of the T parameter in the CPE element due to the polyelectrolytessed in the dynamic LbL process inside a PDMS microchannel: (a) PAH/PPy and (b)AH/NiTsPc.

eposited LbL thin film gathered into a complex overall impedancet the electrode/electrolyte interface. A possible explanation mighte a change in the permeability of the LbL matrix formed due to aigher mobility of charges between non-contact parts at the inter-

ace within the conducting polymers, due to water and small ionsermeation [26,31]. As a result, the permittivity will change with

ncreasing number of deposited layers due to the redistribution ofons at the charged sites, changing the overall observed behaviour.nfortunately, developing an analytical description for an LbL filmlled with a polyelectrolyte solution which includes the effect of theouble-layer and film thickness is not a trivial problem. The modelhould consider at least the presence of charges from moleculesdsorbed onto the bilayer surface, effects arising from the redistri-ution of ions in the intermolecular spaces within the multilayerbL film and geometrical capacitance assigned to the adsorbedacromolecules at the electrode/electrolyte interface [26,27].To a first approximation, the results in Fig. 2 would be as

xpected from a capacitance in series with a resistance, the lat-er dominating the behaviour at higher frequencies [32]. Fittingn Fig. 2 was made using Z-View software and a simplified seriesC equivalent electric circuit. A closer inspection of the plots inig. 2 indicates that at lower frequencies a series RC circuit is aood approximation for changes in the dielectric properties of thenterface as “ZCPE = [T(jω)P]−1”, where T is an empirical (capacitiver resistive) element, j is the imaginary number, ω is the angularrequency and P is an empirical constant representing a constanthase element (CPE). Briefly, when P = 1 the constant phase ele-ent behaves like a pure capacitor, for P = 0 CPE represents a pure

esistor, and 0 < P < 1 characterizes impurities, distribution and/oriffusion of charges, electrode surface roughness and other interfa-ial phenomena [22,33]. The phase of the impedance related to thePE element is dependent on the P parameter only, and is indepen-ent of the frequency of the applied signal. From the fitted results

was found to be similar (∼0.9) for all the dynamically depositedbL films. This value for P is certainly attributed to interfacial pro-esses, since film roughness depends on the number of layers, ando should depend on the parameter T, as indicated in Fig. 4. Oncegain, the PAH/PEDOT:PSS behaviour (results not shown) was sim-lar to that observed with PAH/PPy.

Raman spectra were obtained from a PDMS plate from poly-lectrolyte films cast from solutions and from the LbL films formednside the PDMS microchannel. All LbL spectra in Fig. 5 werebtained from films deposited onto the gold IDEs inside theicrochannel region thus reinforcing the Raman signal due to light

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eflection. The main characteristic peaks of the materials in theDMS plate and cast films were also observed in the LbL filmsormed inside the microchannel. Assignment of spectral featureso their characteristic vibrational modes is given in Tables 2–4 in

microchannels. The laser line used to obtain the Raman was 633 nm for all thematerials characterized.

the Supporting Information. The adsorption of materials inside thePDMS microchannel is immediately confirmed by simple compar-ison of the spectra of the LbL and cast films. Spectra were obtainedfor PDMS because its Raman signal becomes active when the laserbeams pass through the sealing layer, which could induce misin-terpretation of the spectral data.

Raman mapping inside the PDMS microchannel region wasundertaken at the edge between the channel and the sealed region,along distinct positions of the IDEs. The peak intensity of PPy at1600 cm−1 along the AB line is plotted in Fig. 6, using a colour scale.The dark segment in Fig. 6 (vertical AM line) indicates absence ofmaterial (PPy in this case) in the sealed region, confirming thatgood sealing had been achieved. This is a crucial factor in this sort ofapplication, as leakage would lead to a higher contact area betweenliquid samples and the IDEs potentially leading to erroneous results.Lighter regions along the MB line are associated with the intensityof the 1600 cm−1 peak, corroborating the presence of the nano-structured PAH/PPy LbL film inside the PDMS microchannel. Similarresults supporting the well-sealed microchannels were observedwith the other two materials (results not shown).

All chips were thoroughly washed using ultrapure water witha volume thousands of times larger than that of the microchan-nel, with Raman mappings acquired before and after washings,as illustrated in Fig. 7, in order to check the adsorption of differ-ent LbL materials. All spectra acquired along the line indicated inFig. 7 (for PAH/NiTsPc in this case) are plotted side-by-side, with themicroscope image representing the region inside the microchannelwhere the map was collected. Before washing the spectral intensitywas non-uniform, revealing a trend of thicker film at the border, as

−1

ofluidic electronic tongue, Sens. Actuators B: Chem. (2014),

seen by following the intensity of the 1555 cm peak assigned toNiTsPc. After washing, the spectral intensity becomes more uniformshowing that excess, loosely bound material was removed.

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Fig. 6. Raman mapping along the line AB (60 �m long) at the edge of the microchan-n −1

ab

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Fig. 7. Raman mapping for the PAH/NiTsPc film LbL deposited under static con-

microfluidic e-tongue preserves good performance, even thoughthe active area for sensing in the microfluidic device is muchsmaller (ca. 17%) than that of the same device where the electrode

el. The colour scale in the AB bar is related to the peak intensity at 1600 cmssigned to the Ppy vibrational mode, while M (dotted line) represents the midpointetween sealed and open microchannel.

In another approach, random Raman mapping of the 1555 cm−1

eak intensity was undertaken at ten distinct regions both beforend after the washing, again confirming the regular intensity ofhe Raman signal after washing and hence the uniform distribu-ion of materials inside the microchannel (Fig. S1 in Supportingnformation). Different chips were analyzed and in all cases bet-er planarization and homogeneity of the film surface inside the

icrochannel was observed after washing. This is indicative of aossible reduction of aggregates and a more planar film profile, asormally observed in conventional LbL structures [12].

As a proof of concept in real application a microfluidic e-ongue was assembled, composed of bare gold IDEs with a PDMS

icrochannel sealed onto it, and 3 distinct microchannels eachith a different LbL material: 5-bilayer PAH/NiTsPc, PAH/Ppy and

AH/PEDOT:PSS LbL films deposited inside, similar to Fig. 1. Solu-ions representing basic tastes were then introduced into the

icrochannels under flow conditions (1000 �L/h) and impedanceata were obtained at 1 kHz for all sensing units. The results fromhe distinct sensing units were combined and analyzed using theCA approach, as presented in Fig. 8.

Good correlation (PC1 + PC2 ∼ 99%) of all basic tastes, including

Please cite this article in press as: C.M. Daikuzono, et al., Micrhttp://dx.doi.org/10.1016/j.snb.2014.09.112

on-electrolytes such as sugar, was achieved using only tworincipal Components, both under static (results not shown) andow conditions. In addition, considering molar concentrationselow the human threshold for saltiness and sweetness (usually

ditions before and after washing. All spectra collected along the line inside themicrochannel and onto the gold electrode, as represented in the microscope image,are plotted side-by-side making it possible to compare in terms of spectral intensity.

∼10 mM), only small data dispersion was observed in 3 inde-pendent sets of measurements. It is important to mention thehigher dispersion for sucrose, a natural difficulty in measuring anon-electrolyte. Therefore, good distinction could be achieved forbasic tastes, which can be confirmed by zooming on the regionwhere water and caffeine are grouped. This also indicates that the

ofluidic electronic tongue, Sens. Actuators B: Chem. (2014),

Fig. 8. Microfluidic e-tongue differentiating basic tastes under flow (1000 �L/h)conditions inside a PDMS microchannel. 1 mM aqueous solutions of (�) HCl, (�)NaCl, (�) l-glutamic acid monosodium salt hydrate, (�) caffeine, (×) sucrose, (©)Milli-Q water.

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6 C.M. Daikuzono et al. / Sensors and A

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ig. 9. Microfluidic e-tongue responding to distinct concentrations of sucrose addedn 1 mM HCl solution. (�) sucrose 1 mM; (�) 10−1 M, (�) 10−2 M, (×) 10−3 M , (�)0−4 M, (©) HCl 1 mM.

rea is not limited by a microchannel. Furthermore, using floweasurements and small volumes (of the order of microliter)

educe the time for a complete analysis to one third of that for aonventional set-up, which requires at least 50 mL for sampling.

Despite the reduced electrode area available with theicrochannel set-up, the microfluidic e-tongue affords good cor-

elation for electrolytes and non-electrolytes, responding also touppression effects (sweetening the sour in Fig. 9), where elec-rolyte and non-electrolyte substances are mixed at low molaroncentrations. The addition of small amounts of sucrose in 1 mMCl solution yields a shift in PC2, with the data associated with

owest (sucrose + HCl) solution approaching the region for 1 mMCl. A “non-linear” behaviour can also be expected in Fig. 9, as theoping of PEDOT:PSS and PPy in acidic solutions will be tangled byhe sucrose addition in the (sucrose + HCl) solution. Furthermore,his microfluidic approach for an e-tongue can be easily upgraded,reating the opportunity for future multiple functionalities andntegration that can be readily adapted either in specific investi-ation or simply in conventional applications of a taste sensor.

. Conclusions

A taste sensor has been fabricated based on gold interdigi-ated electrodes sealed in a PDMS microchannel. A sensing filmas deposited onto the electrodes using the LbL technique. In situ

mpedance spectroscopy analysis was used to confirm, at each step,he successful deposition of polyelectrolyte bilayers. A simplifiedquivalent electric circuit based on a constant phase element ineries with a resistor was used to describe the cell behaviour. Ramannalysis supports the presence of the ultrathin films inside theicrochannel, indicating a more planar LbL film after washing, sim-

lar to observations with conventional LbL films. When comparedo a conventional e-tongue system the results presented here show

strong reduction in time needed for analysis. The sample vol-me and hence waste is reduced. In addition, high correlation isbtained in the analysis of tastants and more complex liquid sys-ems (sucrose added to HCl). The concept presented is promisingor producing low-cost, portable sensors with possible integrationf multiple functionalities in one single microfluidic device.

cknowledgements

Authors are grateful to FAPESP (Proc No. 08/06504-2),NNano/CNPEM (Grant No. LMF 16439), CNPq, CAPES, INEO (Granto. 573762/2008-2), nBioNet for financial support, and Luciano M.ogueira for kindly participating in the discussion of the data.

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ppendix A. Supplementary data

Supplementary data associated with this article can be found, inhe online version, at http://dx.doi.org/10.1016/j.snb.2014.09.112.

[

PRESSctuators B xxx (2014) xxx–xxx

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iographies

ristiane Margarete Daikuzono received degree in Biological Physics fromniversidade Estadual Paulista/UNESP (2010), M.Sc. in Materials Science from Uni-ersidade Federal de São Carlos/UFSCar (2013) and is currently as a PhD student inscola de Engenharia de Sao Carlos/USP, Brazil, under the supervision of Prof. Drsvaldo N. Oliveira Jr.

leber Aparecido Rocha Dantas obtained his degree in physics from the Univer-idade Estadual Paulista/UNESP (2006), master’s degree (2009) and Ph.D. (2013) inaterials Science and Technology at the same University (UNESP/POSMAT). He is

urrently professor at Faculdade de Engenharia de Sorocaba (FACENS).

iogo Volpati has a degree in Physics (2005), with M.Sc. (2008) and Ph.D. (2012)egrees in Materials Science & Technology by Sao Paulo State University – UNESP.ince then he is a post-doctoral researcher at São Carlos Institute of Physics (Univer-ity of Sao Paulo – USP), being currently a postdoctoral visitor at Durham University,K. His research interests include nanostructured films, as well as physical chem-

stry of interfaces probed with sum-frequency generation spectroscopy, FTIR-basedechniques, Raman scattering and associated surface-enhanced phenomena (SERS

Please cite this article in press as: C.M. Daikuzono, et al., Micrhttp://dx.doi.org/10.1016/j.snb.2014.09.112

nd SERRS).

arlos José Leopoldo Constantino received a degree in Physics from Institutoe Física de São Carlos-USP (1993) and also a degree in Production Engineeringrom Universidade Federal de São Carlos (1997). M.Sc. in Applyied Physics from

PRESSctuators B xxx (2014) xxx–xxx 7

Instituto de Física de São Carlos-USP (1995) and Ph.D. in Science and Materials Sci-ence Engineering, both from Instituto de Física de São Carlos-USP (1999). Currently isa lecturer at Depto de Física, Química e Biologia (FCT, UNESP) in Presidente Prudente(SP, Brazil).

Maria Helena de Oliveira Piazzetta received a degree in chemistry from Methodistof Piracicaba University (UNIMEP) in 1989. She worked for 20 years in R&D Lab-oratories. Since 2000 she has been working with microelectromechanical systems(MEMS) at the Brazilian Synchrotron Light Lab. Her expertise lies in lithography,etching processes, electroplating and chemical deposition at LNNano (CNPEM).

Angelo LuizGobbi obtained his MSc in semiconductor physics from University ofCampinas in 1988 studying amorphous silicon solar cells. From 1986 to 2000 heworked at Telebras with optoelectronics devices. In 2000 he moved to LNLS, whereis the head of Microfabrication Laboratory at LNNano (CNPEM).

David Martin Taylor holds a Personal Chair in the University of Wales and headsOrganic Electronics Research at Bangor. He was gained both his B.Sc. in ElectronicEngineering and Ph.D. from the University of Wales. His Ph.D. awarded for a the-sis entitled “Electrical Characteristics of Polymeric Materials”. Professor Taylor is aFellow of the Institute of Physics (IOP) and has served on the Committee of the IOPStatic Electrification Group for many years. He is also a Member of the Institution ofEngineering and Technology and a Chartered Engineer.

Osvaldo N. Oliveira Junior is a physics professor at Instituto de Física de São Carlos,Universidade de São Paulo, Brazil. He received his Ph.D. from the University of Wales,Bangor (UK), in 1990. His research interests include nanostructured films, especiallyfor applications in sensing and biosensing, and natural language processing. He hassupervised over 30 Ph.D. and M.Sc. students, authored ca. 340 papers in refereedjournals, and filed 6 patents. He is currently an associate editor for the Journal ofNanoscience and Nanotechnology. In 2006 he received the Elsevier Scopus Awardas one of the most productive Brazilian scientists in terms of number of publicationsand citations.

Antonio Riul Junior obtained his Ph.D. in Materials Science and Engineering from

ofluidic electronic tongue, Sens. Actuators B: Chem. (2014),

University of São Paulo (USP, São Carlos) in 1998, with post-doctoral experience atthe University of Wales, Bangor (UK) (1998–2000) and at EMBRAPA/CNPDIA, SãoCarlos (SP – Brazil) (2000–2002). He is currently as Associate Professor at Universi-dade Estadual de Campinas/UNICAMP (Campinas, SP–Brazil), with research interestsin microfluidics, nanostructured thin films in sensors and electronic tongues.