Plant Electrophysiology Volume 662 || Electrochemical Impedance Spectroscopy

Chapter 9Electrochemical Impedance Spectroscopy

E. Azzarello, E. Masi and S. Mancuso

Abstract Electrochemical impedance spectroscopy (EIS) is a method to study thecharacteristics of organic and inorganic materials, based on their passive electricalproperties, determined by the observation of the tissue electrical response to thepassage of external electrical energy. The impedance and phase angles of thematerials is measured by a multiple frequency impedance analyzer (impedancemeter) that is able to scan each sample at different frequencies. Electrochemicalimpedance have been widely used to estimate plant health, their nutrient status,mineral deficiency, presence of viruses, fruit damages, structural cellular variationduring fruit ripening, freeze or chill damages, sensitivity to salinity, and mea-surement of root system growth in trees. In all these studies EIS measurementsprovided a means of nondestructively analyzing variation in intra- and extracel-lular resistances and in the condition of the membranes.The fundamental studiesand some applications of EIS for the field of plant science are described, partic-ularly in relation to root growth and development, seed quality, environmentalstresses, and fruits damages or ripening.

9.1 Introduction

An electric circuit is formed by individual electronic components, through whichelectric current (i) can flow continuously. Voltage (v) is the measure of potentialenergy present in a circuit capable to move electrons from one point to another

E. Azzarello � E. Masi � S. Mancuso (&)Department of Plant, Soil and Environment, University of Florence,Viale delle Idee 30, 50019 Sesto Fiorentino, Italye-mail: [email protected]

A. G. Volkov (ed.), Plant Electrophysiology,DOI: 10.1007/978-3-642-29119-7_9, � Springer-Verlag Berlin Heidelberg 2012

205

one. The opposition to a motion of free electrons in a circuit is called resistance(R) and, similar to voltage, is relative to two points.

Resistance is measured by the ratio between voltage and current (Ohm’s law):

R ¼ v

i: ð9:1Þ

In other words, the Ohm’s law bases on a linear relation between voltage andcurrent.

Indeed, the use of this equation is limited to an ideal resistor that must showthree properties: (1) it follows Ohm’s law at any current and voltage value; (2)resistance value does not depend on frequency; (3) alternate current and voltagesignals, through a resistor, are in phase with each other. Charge carriers are able tomove in materials that conduct electricity. In materials that do not conduct elec-tricity, called dielectrics, all the charges are fixed. It can therefore be said that theresistance of an ideal conductor is 0 while the resistance of an ideal dielectric isinfinite (Ivorra 2003).

The simplest example of a dielectric capacitor consists of two conductingplates placed on either side of a layer of dielectric material, and separated by adistance d (Fig. 9.1). The amount of charge that the dielectric is capable to storedepends on its dimension and on a dielectric parameter called permittivity (e)that indicates the extent to which charge distributions within the material can bedistorted or polarized in response to an applied electric field (Martinez 2007).Capacitance is measured as

C ¼ A

de; ð9:2Þ

where A is the area of the plane electrodes and d the separation distance, whilee = eqe0 is the permittivity, with er indicating relative permittivity and e0 per-mittivity of a vacuum. Capacitance measures the relative amount of charge(Q) that can be stored on a pair of parallel plate for a given amount of voltage (m)when a constant voltage is applied between the electrodes.

C ¼ Q

vð9:3Þ

Fig. 9.1 Schematicrepresentation of the parallel-plate structure related withthe capacitance phenomenon.i = current, +Q=positivecharges, -Q = negativecharges, d = distancebetween the two conductiveplates, A = area of the plate

206 E. Azzarello et al.

If the capacitance increases more charge can be stored when the same potentialis applied.

If the capacitance voltage is constant, no current enters or leaves the capaci-tance. When voltage changes with time, a quantity of current can enter and leavethe capacitor, charging or discharging it. In this way it can be assumed that, if atime varying voltage is applied to a capacitor, some current is able to flow throughthe source (Ivorra 2003).

As described above, resistance obeys the Ohm’s law and the relation betweenvoltage and current can be represented as a relation of magnitudes

Z ¼ Re ¼ R ¼ v

ið9:4Þ

On the contrary, impedance of a capacitor, called capacitive reactance, dependson frequency (f) and is defined as the relation between the input voltage and theinput current for that frequency. It can be calculated as

Z ¼ j1

ð2pfCÞ ; ð9:5Þ

where j2 = -1 is the complex unit (indicating an anticlockwise rotation by p/2relative to the x-axis) that relates to the phase angle.

At low frequencies the capacitor blocks the current flow, causing a very highimpedance modulus. At high frequency, the current is free to flow through thecapacitor that is not enough charged, thus causing a minor opposition to the flow(Ivorra 2003).

As a consequence of this, it can be said that the impedance of a circuit (Fig. 9.2)formed by a resistor and a capacitor in series can be calculated as

Z ¼ Rþ j1

ð2pfCÞ ð9:6Þ

Fig. 9.2 Electrical circuitformed by a resistor and acapacitor in series

9 Electrochemical Impedance Spectroscopy 207

9.2 Impedance Concept

Oliver Heaviside introduced, for the first time, the impedance concept in the 1880s(Filho 2002). Impedance is measured by applying a small alternating current ofknown frequency and small amplitude to a system, determining the amplitude andphase difference of the associated electrical potential that develops across it(Coster et al. 1996). In many materials impedance varies as the frequency of theapplied voltage changes, due to the properties of the material itself. This may bedue to its physical structure, to the chemical processes within it, or to the com-bination of both (Schröder et al. 2004).

Impedance Z is the quotient of the voltage–time function v(t) and the resultingcurrent–time function i(t):

Z ¼ mðtÞiðtÞ ¼

m0senðxtÞi0senðxt þ hÞ ; ð9:7Þ

where v0 and i0 are the maximum voltage and current signals, x = 2pf is theangular frequency, and h is the phase difference between the voltage and thecurrent (Pänke et al. 2008).

In Cartesian coordinates, impedance becomes a complex number, constituted oftwo components (Eq. 9.8–9.11):

Z xð Þ ¼ Zr xð Þ þ jZiðxÞ; ð9:8Þ

where

Zr xð Þ ¼ Zj jcos hð Þ ð9:9Þ

is the real component,

ZiðxÞ ¼ Zj jsenðhÞ ð9:10Þ

is the imaginary component or reactance,

and h ¼ tan�1 Zi

Zrð9:11Þ

is the impedance phase angle. Phase angle is a linear method for the measurementof the relationship between resistance and reactance in series or parallel circuits.Phase angle can range from 0 to 90�. When the angle is 0� the circuit is onlyresistive, at 90� the circuit is only capacitive, while at 45� the circuit has an equalamount of capacitive reactance and resistance (Liedtke 1997).

Finally, the relation between impedance and its individual component (resis-tance and reactance) can be represented as a vector (Fig. 9.3), whose magnitude is:

ZðxÞj j ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

Z2r þ Z2

i

q

: ð9:12Þ


The real and imaginary parts of Z describe the resistance and reactance,respectively. If the real part is plotted on the X-axis and the imaginary part on theY-axis, an impedance spectrum, using the frequency as the parametric variable,is obtained (Fig. 9.4).

9.3 Electrochemical Impedance Spectroscopy

Electrochemical impedance spectroscopy (EIS) is a technology that can investigateelectrical and electrochemical properties of different materials and systems. One ofthe most interesting aspects of EIS is the close correlation that exists between the

Fig. 9.3 Vector diagramshowing relationship betweenresistance (Zr), reactance (Zi),and impedance

Fig. 9.4 Impedancespectrum (plot of reactance(imaginary part) againstresistance (real part) withfrequency as parametricvariable)


behavior of a real system and an idealized model circuit with discrete electricalcomponents (Macdonald 1987).

EIS is a very sensitive technique and, although it does not provide a directmeasure of the physical phenomena, is a valuable analysis method for materialswith high ionic conduction, such as solid and liquid electrolytes, fused salts,ionically conducting glasses, and all materials where conduction involves motionof ion vacant and interstitial. EIS is also valuable in the study of fuel cells,rechargeable batteries, and corrosion (Macdonald 1992).

Of course, the measurements of electrical parameters are also very useful tocharacterize most events or conditions in human, animal, and plant tissues (Cole1972; Lewis et al. 1989).

While in metals the electrical charge carriers are represented by electrons, ionsare the charge carriers in biological tissues, and conductivity is dependent on theirconcentration and diffusion coefficients (Ackmann and Sitz 1984). All biologicaltissues consist of cells and extracellular matrix, an intricate network of macro andsmall molecules, ions, and water. Both extracellular and intracellular medium canbe considered as liquid electrolytes whose viscosity varies with the temperature,decreasing or increasing ions mobility and consequently the resistance. Inside thecell, beside ions and charged molecules (protein, organic acids, etc.), there arenumerous membrane structures with a completely different electrical response.Thus, the impedance of the intracellular medium must be a mixture of conductiveand capacitive properties (Ivorra 2003).

Cell membranes separate intracellular space from the extracellular ones con-tributing to make a barrier for the passage of ions and large molecules. They areformed by a lipid bilayer to which is associated proteins, transport organelles, ionicchannels, and ionic pumps, the basic elements of the membrane active role. Theintrinsic electrical conductance of this structure is very poor and can be approx-imated to a dielectric (Martinez 2007).

The complete organization composed by the extracellular medium, the lipidbilayer membrane, and the intracellular medium forms the conductor–dielectric–conductor structure schematized in Fig. 9.5.

When an alternating electric field is applied to plant tissues, AC (alternatingcurrent) causes polarization and relaxation, leading to changes in amplitude andphase of the applied AC signal (Repo et al. 2000). Based on these changes theimpedance of the sample can be determined. This current is usually appliedthroughout a range of specific frequencies to produce a spectrum of measurements.The polarization of a particular component depends on the sample’s tissue prop-erties as well as on the frequency, on the force of the electrical field applied, on theionic concentration, on the temperature, etc. In general, the smaller the compo-nent’s dimension, the higher the frequency at which the polarization takes place.

In biological samples, the proportion of current passing through the apoplasticand symplastic spaces in a tissue depends on AC frequency (Repo et al. 2000)(Fig. 9.6). The lipid bilayer of plasma membrane contributes to stop the passage ofAC at low frequencies, acting as a capacitor that store energy in an electric field.The only way for current to pass is the apoplast and the total impedance is mostly


due to the resistance of the extracellular space. When frequency increases, also cellmembranes become conductive causing a change in impedance that will becomposed of a parallel combination of intra-and extracellular resistances (Ozier-Lafontaine and Bajazet 2005).

9.3.1 Data Analysis and Interpretation

Modern impedance analyzers allow measuring impedance and phase angle ofmaterials at different frequencies. Many of these analyzers are integrated with

Fig. 9.5 Diagram of the electrical cell model, where the capacitor represents the plasmamembrane, while Re and Ri represent the extra cellular and intracellular fluids, respectively

Fig. 9.6 Schematic diagramof high and low frequenciesflowing through a vegetaltissue


software useful in the evaluation and analysis of the data (Panke et al. 2008)(Fig. 9.7).

Before performing the analysis, it is useful to examine IS data graphically, bothto search for any outliers and to examine the structure of the data that will usuallyreflect the physical processes present that led to that data (Macdonald 1992).The step of the graphics examination is very important to estimate some systemparameters, but only in the simplest cases. When the cases are more complex theuse of complex nonlinear least squares (CNLS) data-fitting of different equivalentcircuits is needed.

After that, an equivalent circuit is used to investigate the nature of the samples.An equivalent circuit is a model composed by a certain number of ideal resistorsand capacitors connected to each other, which produces a frequency response thatis similar to that measured by the impedance experiment (Mancuso and Rinaldelli1996). If a proper equivalent circuit is chosen, the study of tissue properties,according to the changes in the parameters of the model, becomes possible (Zhangand Willison 1992; Zhang and Willison 1993; Repo et al. 1994; Repo and Pulli1996; Ryyppö et al. 1998).

9.3.2 How and What Equivalent Circuit Should be Chosen?

The choice of the equivalent model is crucial to understand the characteristics of thematerials under investigation. The choice depends on the characteristic of the systemunder study and on the intuition of the researcher. There can be potential problemscaused by the fact that equivalent circuits are rarely unique and several circuit modelscan have identical or very similar impedances (Lackermeier et al. 1999).

In order to verify the validity of the chosen circuit, the quality of the fit tothe experimental curve must be evaluated. Whenever possible, the model shouldbe verified before being used. One way to verify the model is to alter a singlecell component and wait for the expected changes in the impedance spectrum(Macdonald 1987).

Fig. 9.7 Custom-designed apparatus to measure impedance spectra in plant


When impedance analyses are applied to vegetal tissues, usually two types ofequivalent circuits are used: lumped circuit (Cole 1940; Hayden et al. 1969; Zhangand Willison 1991, 1992; Harker and Maindonald 1994; Inaba et al. 1995) anddistributed models (Repo and Zhang 1993; Repo et al. 1994). A lumped modelconsists of limited number of ideal resistors and capacitors. One of the firstimportant lumped model was developed by Cole in 1940 and it characterizesbiological tissue into two-branch parallel circuit. In this model R1 and R2 representextracellular and intracellular space resistance, respectively, while C representsmembrane capacitance (Fig. 9.8b).

However, the measurement of complex impedance in different vegetal tissueshas shown that lumped circuits cannot describe all tissues. Generally, stems andneedles of woody plants or other highly differentiated tissues cannot be modeledby a simple lumped circuit, thus distributed circuit elements (DCE) are required(Repo and Pulli 1996; Burr et al. 2001). In fact, impedance spectrum of thesetissues has one or more depressed centers that suggest a distribution of timeconstant (Repo 1994).

DCE-models are more complex than lumped ones; moreover, each componentof the model does not necessarily correspond to a biological structure. Never-theless, they have an excellent fit to the experimental data; thanks to a highlycompact mathematical expression (Cole and Cole 1941; Macdonald 1987). Thesebenefits have led to an increasing use of DCE-models compared to the lumpedones (Kanai et al. 1987; Foster and Schwan 1989; Mancuso and Rinaldelli 1996).

9.3.3 Models Examples

9.3.3.1 The Hayden Model

In the Hayden model different intracellular compartments are represented byapoplasmic resistance R1, symplasmic resistance R2, and plasma membraneresistance R3, while plasma membrane capacitance is represented by C (Fig. 9.8a).

Fig. 9.8 a Hayden model:R1, apoplasmic resistance; R2,symplasmic resistance; R3,plasma membrane resistance.b Simplifed Hayden modelwithout R3


Hayden and collaborators measured impedance in potato and alfalfa tissues(Hayden et al. 1969). They estimated apoplasmic resistance at low frequency; forthe symplasmic one they approximated that the reactive component of impedanceapproaches zero at high frequency.

The real part of the impedance of the circuit of the Hayden model is calculatedas:

X ¼ R1ðR2 þ R3ÞðR1 þ R2 þ R3Þ þ x2C2R1R2R23ðR1 þ R2Þ

ðR1 þ R2 þ R3Þ2 þ x2C2R23ðR1 þ R2Þ

ð9:13Þ

while the imaginary part is:

Y ¼ �xCðR1R3Þ2

ðR1 þ R2 þ R3Þ2x2C2R23ðR1 þ R2Þ

ð9:14Þ

where x is the angular frequency.Actually, the Hayden model can be simplified omitting R3 from the equations,

whenever R3 � R1 and R3 � R2.

X ¼R1 R2ðR1 þ R2Þ þ 1

xC

� �2h i

ðR1 þ R2Þ2 þ 1xC

� �2 ð9:15Þ

and

Y ¼�R2

11

xC

� �


� �2 ð9:16Þ

Therefore, substituting X and Y in the modulus of Z ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

X2 þ Y2p

; the equationbecomes:

Z2 ¼R1R2ðR1 þ R2Þ þ R1

1xC

� �


� �2

" #2

þR2

11

xC

� �


� �2

" #2

ð9:17Þ

and R1 and R2 values can be calculated (see Zhang et al. 1990).

9.3.3.2 Double-Distributed Electrical Circuit Model

In the distributed electrical circuits, resistance, capacitance, and inductance aredistributed continuously throughout the material of the circuit. The distributedelement model is more defined and also more complex than the lumped one. Theimpedance measurements of biological tissues frequently produce impedancespectra composed by two arcs with strongly depressed centers (Repo et al. 2002)(Fig. 9.9); in these cases, a double-distributed model may be used (Paine et al.2001; Repo et al. 2002). As reported in Fig. 9.9, the resistors (R, R1, and R2) of the


model can be calculated from the interceptions of the circles with the x-axis; therelaxation times (s1 and s2) describe the location of the dispersion range on thefrequency and are obtained from the apex of the arcs and plane. The coefficientsW1 and W2 describe the distribution of the relaxation times (Repo et al. 2002).

The Voigt model is a double-DCE model, composed of two distributed ele-ments (DCE1 and DCE2) in series with a resistor (R). Both DCEs are composedby the parallel arrangement of two resistors R1 and R2 and two constant-phaseelements ZCPE1 and ZCPE2. The constant-phase element (CPE) is described as acapacitance that is frequency dependent (Ivorra 2003) and has been introduced toimprove the equivalent electrical circuit models to more closely fit the realimpedance spectra. The impedance of the constant-phase elements is (Macdonald1987):

ZCPE1 ¼1

ðJxC1ÞW1 ð9:18Þ

and

ZCPE2 ¼1

ðJxC2ÞW2 ð9:19Þ

Fig. 9.9 Wessel diagram. Real data plotted along the x-axis and imaginary on the y withfrequency as parametric variable (modified by Repo et al. 2005)


For the impedance of DCEs we get:

1ZDCE1

¼ 1R1þ 1

ZCPE1ð9:20Þ

and

1ZDCE2

¼ 1R2þ 1

ZCPE2ð9:21Þ

Therefore:

ZDCE1 ¼R1

1þ R1ðjxC1ÞW1 ¼R1

1þ jxC1R1

W11

� �W1 ð9:22Þ

and

ZDCE2 ¼R2

1þ R2ðjxC2ÞW2 ¼R2

1þ jxC2R1

W11

� �W2 ð9:23Þ

In this way it is possible to define s1 ¼ C1R1

W11 s1 and s2 ¼ C2R

1W22 and

ZDCE1 ¼R1

1þ ðjxs1ÞW1 and ZDCE2 ¼R2

1þ ðjxs2ÞW2 ð9:24Þ

For the total impedance of the double-DCE model we get:

Z ¼ Rþ ZDCE1 þ ZDCE2 ¼ Rþ R1

1þ ðjxs1ÞW1þR2

1þ ðjxs2ÞW2 ; ð9:25Þ

where x = angular velocity = 2pf

9.3.3.3 Complex Nonlinear Least Squares Data-Fitting

Complex nonlinear least squares data-fitting is a fitting technique that can be usedfor a good characterization of the material-electrode system (Macdonald 1992).Macdonald and Garber (1977) applied this method for the first time to impedancespectroscopy. Thanks to a mathematical model, CNLS shows which parametersare useful for fitting; moreover, it allows fitting very complex models having morethan 10 unknown parameters (Macdonald 1987).

The weighted sum of squares of the real and imaginary residual has to beminimized. A residual is the difference between a data value at a given frequencyand the corresponding value calculated from the model. The weights are calculatedas the inverses of the estimated error variance for a given real data value and forthe corresponding imaginary value (Macdonald 1992).


SðPÞ ¼X

M

j¼1

wj Yj � YCjðPÞ� �2

; ð9:26Þ

where:M total number of data points;wj weight associated with the jth point;Yj jth data point value to be fitted;YCj(P) value calculated fitting function involving the set parameters P.

The initial choice of the parameters is very important: they must be relativelyclose to the real values. On the contrary CNLS method becomes easily divergent.

9.4 EIS Applications in Plants

9.4.1 EIS, Root Growth, and Development

Although the dynamic of root growth is very difficult to study, EIS technique wasinterestingly employed in experiments on growth and morphological studies of theroot system (Dalton 1995; Van Beem et al. 1998; Ozier-La Fontaine et al. 2001;Matsumoto et al. 2001; Rajkai et al. 2002). The use of EIS is based on thecapacitance changes that happen to the system root/soil during root growth.In 2005 Repo and collaborators tried to develop a non-destructive evaluationof plant root growth using EIS. In this study they modeled the IS by a circuitconsisting of a resistor, two Zarc-Cole elements, and a constant-phase element inseries (Fig. 9.10). In a further research conducted in 2005, Ozier-La Fontaine andBajazet aimed to verify experimentally the validity of the relationship betweenroot fresh or dry weight and root capacitance. By measuring EIS using twoAg–AgCl electrodes inserted in the plant stem and into the soil, respectively, theydemontsrated that the root growth was characterized by a modifications in bothelectrical capacitance and resistance components.

The complications caused by the different polarization interfaces betweenconductive mediums and root/soil system, the soil type, and the soil moisturecontent that can interfere with EIS properties may be overcome with experimentconducted in hydroponic culture. In fact, hydroponic culture, representing a sim-plified system, is able to standardize some of the confounding factors of soil.In 2011, Cao and collaborators developed equivalent circuits for estimating willowroot system size nondestructively using the EIS approach. Willows roots weregrown in hydroponic solution and the electrical impedance spectrum was mea-sured inserting one Ag electrode in the middle position of the stem above thesolution, and another at the bottom of the narrow solution container. They preparedthree different setups (one with all the roots immersed in the solution; another one


with a single root immersed in the solution; and the third one with only the stemimmersed in the solution) (Fig. 9.11). For each setup they developed a lumpedmodel as equivalent circuit resulting in a good fit of the measured data.

In the case of the DCE-models a little bit more attention is needed. In fact, evenif they have been used many times (Dalton 1995; Ozier-Lafontaine and Bajazet2005) and with mathematically good fit, the biological interpretation of the dataremains more difficult than using lumped model.

9.4.2 EIS and Seed Quality

Electrical impedance spectroscopy was used to evaluate the seed quality (Paineet al. 2001; Repo et al. 2002). Seeds contain different microstructures as the cell

Fig. 9.10 Electrical circuit consisting of a resistor, two ZARC-Cole elements (ZARC1 andZARC2) and one constant-phase-element (CPE)

Fig. 9.11 Diagram of the experimental setups for the measurement of the impedance spectra ofthe root apparatus. E1 and E2 refer to the Ag electrodes (modified by Cao et al. 2011)


walls, the membranes and the starch grains that are able to modify significantly theionic transport. The physiological changes of these microstructures, due to the ageof the seed, can be followed by corresponding changes in the impedance values.EIS parameters vary between viable and non-viable seeds because of the lost ofmembranes integrity (Priestley 1986). Conventional techniques used to evaluateseed viability are often time consuming and destructive. Compared to them, EISoffers different advantages thanks to its capacity to evaluate seed qualitynoninvasively.

9.4.3 EIS and Environmental Stresses

One of the most important applications of EIS is in the study of stress physiologyand in particular in the evaluation of damages caused by abiotic stresses.

Many interesting researches have been conducted to evaluate freezing and coldtolerance in different woody and herbaceous plant species in relation to coldacclimation. One of the most sensitive mechanisms to low temperatures in plant isthe ionic transport through the cellular membranes, mainly because of alterationsof the H+ and K+ transporting systems (Levitt 1981; Yoshida 1991, 1994; Palta andWeiss 1993; Shabala and Newman 1997). For that reason, monitoring the state ofelectrical impedance can be used as a possible indicator of the initial stage ofchilling stress in plants (Mancuso 2000).

During cold acclimation several changes in the content of cellular sap and cellmembranes occur (Steponkus 1984) that are mirrored in the modification of theelectrical level of cellular constituents and consequently can be detected by EIS(Repo et al. 2005; Zhang and Willison 1991; Zhang et al. 1992; Tsarouhas et al.2000; Vainola and Repo 2000; Luoranen et al. 2004; Repo et al. 2000; Mancusoet al. 2004).

Interestingly, data extrapolated directly from impedance spectra were sufficientto evaluate lethal temperature (LT) in Australian plants (Mancuso et al. 2004).In this research, the impact of temperature injury was estimated as the change inimpedance ratio (low/high frequency) before and after the thermal treatment

DZratio ¼Zlow

Zhigh

after

� Zlow

Zhigh

before

;

where DZratio is the change in the ratio of the impedance to freezing, (Zlow/Zhigh)after

the ratio of the impedance at 1 and 20 kHz after freezing, and (Zlow/Zhigh)before

the ratio of the impedance at 1 and 20 kHz before freezing. The lethal temperaturewas finally estimated as the inflection point of a logistic sigmoid function, plottingDZratio against the temperatures analyzed. This method was also applied to studythe answers of plant tissues to other types of stress, such as heat (Mancuso andAzzarello 2002) and salinity (Mancuso and Rinaldelli 1996).


9.4.4 EIS Analysis on Fruits

Many EIS researches have been conducted on the study of the physiologicalcondition and maturity of fruits and on study of ripening of chill-injured fruits(Weaver and Jackson 1966; Zachariah 1976; Furmanski and Buescher 1979;Lougheed et al. 1981; Inaba et al. 1995; Varlan and Sansen, 1996). EIS has theadvantage to identify easily and fastly the internal condition of the fruit duringripening and cold storage (Klein 1987; Schoorl and Holt 1977), thanks to thecapacity to detect rapid changes associated with physiological dysfunctionand membrane damage (Zhang and Willison 1992; Harker and Forbes 1997).Using this method Harker and Maindonald in 1994 were able to assess changes inthe condition of the cell wall, cell membranes, and intracellular compartmentsduring ripening of nectarine. Similar studies were conducted in peaches, kiwi, andpersimmon with or without chilling injuries (Furmanski and Buescher 1979;Sugiyama et al. 1987; Von Mollendorff et al. 1992; Harker and Maindonald 1994;Harker and Forbes 1997; Bauchot et al. 2000).

9.5 Conclusions

Electrochemical impedance spectroscopy plays an important and fundamental rolein electrochemistry and biological science being a simple, quick, repeatable,and non-destructive technique. Modern impedance analyzers, by widening thefrequency range from the millihertz to megahertz, have made possible a solidincrease in the studies of impedance applied to plant science. All the describedapplications confirm that EIS is a useful tool to assess physiological changes invegetal tissues due to the plant development as well as after the exposure tostresses. The choice of the procedures to estimate the best correlation between theelectrical measurements and the physiological properties of plant tissues remainscrucial for the successful use of this technology.

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Plant Electrophysiology Volume 662 || Electrochemical Impedance Spectroscopy