Development of a Hydration Sensor Integrated on Fabric

Gilles Marchand, Alain Bourgerette, Michel Antonakios, Yvon Colletta, Nadine David, Franc;oise Vinet and Coralie Gallis

Abstract- The main purpose of the European project

ProeTEX is to develop equipment to improve safety,

coordination and efficiency of emergency disaster intervention

personnel like fire-fighters or civil protection rescuers. The

equipment consists of a new generation of "smart" garments,

integrating wearable sensors which will allow monitoring

position and activity of the user, as well as environmental

variables of the operating field in which rescuers are working

and physiological parameters among whom there is the

dehydration.The dehydration of emergency disaster personnel

can lead to severe physiological consequences being able to go

until the death. The follow-up of the sodium ions concentration

in the sweat allows to evaluate this dehydration state in real

time by a non invasive method and to react quickly in the event

of problem. This paper deals with the development of an Ionic

Selective Electrode sensor and its transfer on fabrics. The

performances were evaluated in terms of sensitivity, selectivity

and reproducibility initially in model solution and then in

natural sweat. A portable electronic board connected to the

sensing part is described too. This board drives the

electrochemical and temperature sensors for analog acquisition

and converts measurement data to digital value. Signal

processing is implemented on the electronic board in order to

correct raw data (gain, offset) and to convert them to ion

concentrations

I. INTRODUCTION

The work described in this paper is part of the ProeTEX

project, a European Integrated Project aiming at

developing a new generation of equipments for the market of

emergency operators, like Civil Protection rescuers and fire­

fighters. Among the numerous sensors integrated in the inner

garment, the dehydration sensor appears as one of most

essential. Indeed, during interventions on disasters, the

emergency personnel are exposed to extreme physical

conditions and an important physiological consequence can

be the dehydration. Thus, an abnormal loss of sodium in the

sweat can lead to a hypo or hyper-natremia [1,2] and this

abnormal concentration of sodium in the blood-plasma can

eventually generate a cerebral oedema and its ultimate

consequence is the death. Thus, following the sodium

concentration in the sweat seems to be an important

parameter to ensure the good health of the emergency

personnel. However, this application requires a portable and

not much bulky device in order to not hinder the firefighter

during intervention. This paper deals with the integration of

Manuscript received November 17, 2009 .. This work was supported by the European Community Framework Programme VI, IST Programme, Contract n.26987. Authors are with CEAlLETI-Minatec- Department of Technology for Biology and Health 17 rue des Martyrs 38054 Grenoble, France (corresponding author to provide phone: 33-4 38 78 23 81; fax: 33-4 38 78 57 87 ; e-mail: gilles.marchand@cea.fr).

an Ionic Selective Electrode (ISE) sensor on fabric able to

detect and quantify selectively Na+ ions in natural sweat and

the development of a portable electronic board connected to

the sensing part driving several ISEs and temperature sensors

and converting electrical measurement data to ions

concentration.

I. CHARACTERISTICS AND TECHNOLOGY

II-l ISE Developement

The developed electrochemical sensor consists of host

molecule included in a conducting polymer, to perform

specific transducer that precisely and selectively measures

the sodium concentration. Thus, the complexation of the

targeted ion (with positive charges) by the host molecule

leads to a modification of the electrochemical response of the

sensing part. This modification is followed by the evolution

of the open circuit potential (OCP). Firstly, we have

developed a metallic coating on fabric (constituted of

cottonlelasthanne: 95/5) by chemical approaches to realize

patterned electrodes (Figure 1). More precisely, a solution containing an organo-metallic fluid (PdC12/SnC12), which

physical properties can be controlled, was locally deposited

to create a metallic pattern. Afterwards the fabric was

immersed in a copper ions solution and the growth of copper

metal by autocatalytic deposition on the patterning area took

place. Next, the fabric was immersed successively in a nickel

ions bath and gold ions bath. The deposited nickel serves as

a diffusion barrier to the underlying copper and permits the

gold layer formation by an electroless process. Thus, the

deposited nickel is oxidized and dissolved into solution

while the gold in solution is reduced in metal on the nickel

surface. Then, the patterned gold areas are used as electrodes

for electrochemical measurements.

In this application, an electrochemical cell is constituted

of four electrodes - 3 working electrodes (EO, ETl and ET2)

to insure the reproducibility of the measurement and one

reference electrode. This electrochemical cell is coupled with

a temperature probe to enhance reliability of the

measurement since electrochemical measurement depends on

temperature. On the working electrodes, a polypyrrole

was deposited at I.2V versus Ag/ AgCl electrode in trapping

4-tert -butylcalix[ 4 ]arene tetraaceticacid tetraethylester

(Figure 2) [3]. This host molecule is able to complex

selectively Na+ ions in a solution containing competitors.

The functionalized electrodes are called Ionic Selective

Electrodes [4,5].

Fig.1 Picture of a gold electrodes network realized according to a chemical procress

Fig.2 Picture of gold electrodes functionalized with a conducting polymer (dark colour) and connected to a flexible sheet compatible with a Samtec connector. The fourth gold electrode corresponds to the reference electrodes. A temperature probe is coupled with the electrochemical cell.

1I-2 Electronic Board Development

The electrochemical sensor was connected to a portable

electronic board, named RPMCV I, which drives the sensing

part and achieves the signal processing to convert the

electrical information in sodium ions concentration. This

prototype includes: il analogical parts (regulation,

generators, commutation matrix), iii control block

(microcontroller MSP430-F I6 I I pulsated at 8MHz)

integrating software for communication and signal

processing, iiil connection to electrochemical cells via

Samtec connector, ivl RS485 protocol to communicate with a

data concentrating module. A particular attention was

carried on the integration to be wearable and low power of

components.

11-3 Measurement Management

The electronic acquires first raw data from an open

circuit potential techniques. The goal is that these data are

processed on the electronic board in order to provide directly

Na+ concentration as output of the system.

The method has been tested to perform calibration with

model solutions (NaCI solutions) and to fit curve in order to

convert raw data to ion concentration. Four algorithms

(polynomial regression models (orders k = 2 and 3), linear

regression model and logarithmic regression model) were

tested and the first tests show that the polynomial regression

model (order k = 2) seems the most adapted for our

measurements.

This approach with regression model was implemented on

the microcontroller of the electronic board.

Fig.3 Picture of the electronic board RPMCYI. Dimensions: 4 9 x 4 2mm

III- MEASUREMENT VALIDATIONS

III-lISE Performances

The sensor performances were evaluated initially with

model solutions and then with synthetic sweat solutions

(solution containing 6mM de KCI, l. ImM de CaCh,

O.22mM de MgCh. and variable concentration of NaCI).

400

5' 350 ,;, a. U 300 0 I- - I-- r- r- -

250 - - I-- r- r- -

200 - - f- - f- f- -

150 -2.9 -1.7 -1.4 -1,2 -2.9 -1.7 -1.4 -1.2 -2,9

Log [Na+]

Fig. 4 Evolution of OCP when Na+ concentrations increase and decrease

The validation consisted on the demonstration of the sensor

sensitivity towards a Na+ concentrations variation. As shown

in Figure 4, we observed a correlation between Na+

concentration and OCP modification with a relative standard

deviation of 10% and a sensitivity of 2mV/mM (in the range

1.25-62.5mM). The selectivity (K+, Ca2+, Mg

2+ were tested)

and the reversibility of the sensor were proven as well.

III-2 Electronic Board Performances

The electronic board was tested initially with fictive

electrochemical cell. The electrochemical cell was simulated

with a voltage generator (Time Electronics 1044 voltage

calibrator). Applied voltage varied from 20 mV to 200mV.

Standard deviation and offset voltage were controlled as

shown in table 1 A. Then, the electronic was connected to

the sensing part deposited on textile and the obtained

measurements for different Na+ concentrations were

compared with the ones obtained with a commercial

potentiostat (Auto lab PGSTST 100 from Ecochemie BV).

The values reported in the Table 1 show that the measured

values with the electronic board RPMCV I are very similar to

the ones measured with Autolab potentiostat PGSTATlOO.

III-3 Biochemical Validations

The characterization of the sensing part associated to the

electronic part was then performed on natural sweat. In a

preliminary step, an abacus curve was performed with

different solutions of known Na+ concentrations

((polynomial regression model). Afterwards, the Na+ sensor

was immersed in natural sweat carefully collected. The open

circuit potential was reported on the abacus curve and a

concentration of 38.9mM was determined.

In the same time, the samples were analyzed with classical

equipment used in biochemistry labs (Hitachi 912 using ionic

selective electrodes). A value of 34.8mM was found.

Therefore, these experiments allowed to validate the correct

functioning of this sensor in natural sweat.

IV CONCLUSIONS

This paper introduces part of the work done during the

European Integrated Project ProeTEX, whose aim is the

development of a new generation of "smart" garments for

emergency intervention personnel. Among the numerous

integrated sensor, an electrochemical sensor, specific of Na+

ions, was developed and transferred on fabrics. After

connexion to a portable electronic board driving the sensing

part and converting the electrical signals to ions

concentrations, the sensor was validated with natural sweat.

In the future evaluation, this sensor will be integrated in

firefighters inner garments and tested in real conditions.

ACKNOWLEDGMENT

The authors wish to thank our collaborators at Sofileta,

Smartex and CSEM for their assistance during this work.

TABLE 1 A- Standard deviation and offset voltage function of applied voltage ; B- Comparison of performances Autolab PGSTAT 100 potentiostat vs RMPCVl board

Applied Standard deviation (mV) Offset voltage (mV)

voltage ETO ETl ET2 ETO ETl ET2

(mV) 20 0,10 0,11 0,16 0,4 7 0,83 0,05 4 0 0,12 0,12 0,12 0,4 3 0,73 0,04 60 0,11 0,10 0,15 0,33 0,71 0,05 80 0,12 0,11 0,12 0,33 0,65 0,08 100 0,15 0,11 0,06 0,29 0,60 0,12 120 0,11 0,13 0,10 0,33 0,59 0,13 14 0 0,13 0,15 0,11 0,25 0,56 0,24 160 0,10 0,14 0,14 0,23 0,54 0,21 180 0,11 0,16 0,13 0,18 0,4 3 0,31 200 0,13 0,13 0,14 0,15 0,4 1 0,32

Concentration Na+ Xl X2 X3

Autolab

Medium value (mV) 16,51 14,37 8,59

Standard deviation �mV2 0,09 0,30 0,09

RPMCVl

Medium Value(mV) 16,93 13,97 9,13

Standard deviation �mV2 0,06 0,04 0,051

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