Interdigitated Electrodes (IDEs)

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1 Interdigitated NanoElectrodes for sensing: fabrication and characterization Irene Fernandez-Cuesta, Jesús García, Jahir Orozco, César Fernández-Sánchez, Antoni Baldi, Xavier Borrisé and Francesc Pérez-Murano NILSIS CNM - Institute of Barcelona: Multidisciplinar: collaboration between groups -> chemistry + biology + nanofabrication Fabrication and characterization of NanoBioSensors

Interdigitated Electrodes (IDEs) Biosensors, electrochemical sensors, nanoparticles detection 1. IDEs: Introduction 2. Fabrication 3. Characterization a. Voltamperometry, I(V) b. Impedances, Z(f) c.

2 Interdigitated Electrodes (IDEs) Biosensors, electrochemical sensors, nanoparticles detection 1. IDEs: Introduction 2. Fabrication 3. Characterization a. Voltamperometry, I(V) b. Impedances, Z(f) c. Nanoparticles Insulating substrate Metallic electrodes Using IDEs for Sensing 1.Voltamperometry: measurement of electrochemical current coming from red/ox reactions in the electrodes. V A 2. Impedimetric Spectroscopy: measurement of the resistivity and capacitance of the solution, as a function of the frequency. Z ~ V Centro Nacional de Microelectrónica

3 Why nano IDEs for sensing For the detection and quantification of nano entities (i.e. virus, proteins, nanoparticles ) the sensitivity increases when the size of the electrode is similar to the size of the objetc. Nanopartículas (p.ej) MICRO NANO Fabrication Institut de Microelectrònica de Barcelona

4 Design: 300x300µm -Combination of MICRO and NANO fabrication. - Aligning marks added, to facilitate the electron beam lithography -Contacts were designed with standard size, so the samples can be bounded to a PCB. Two different geometries 3 mm Aligning Marks 100x100µm 200x200µm 3 mm 1. Optical lithography 2. EBL Centro Nacional de Microelectrónica Fabrication: RESULTS Width=150nm Pitch=450nm Width=180nm Pitch=230nm

5 Fabrication: Packaging PCB PMMA Characterization

Voltamperometry V ox A w g + w I lim = mbnfc * D 0,637 ln 2,55 0, 19 w g 2 2 w w 0,05 tlim 14 D D m = number of digits b = length of the digits n = number of e - involved in the red/ox process F =

detection increases if: m», b», w«, w»wg Nanoelectrodes K. Aoki, M. Morita, O. Niwa, H. Tabei. J. Electroanal.

6 Voltamperometry V ox A w g + w I lim = mbnfc * D 0,637 ln 2,55 0, 19 w g 2 2 w w 0,05 tlim 14 D D m = number of digits b = length of the digits n = number of e - involved in the red/ox process F = Faraday constant c* = concentration of red/ox species D = difussion coefficient of the redox species w g = width of the gap between electrodes w = width of the electrodes w g w g + w 2 Ox The detection increases if: m», b», w«, w»wg Nanoelectrodes K. Aoki, M. Morita, O. Niwa, H. Tabei. J. Electroanal. Chem, 256 (1988) 269 Centro Nacional de Microelectrónica Voltamperometry Voltammograms First tests: reduction of ferricianure V A Fe(CN) e - Fe(CN) 6 4-, E 0 =+0.35V KNO 3 + Fe(CN) KNO 3 (not active) 40 Ferricianure 0 Corriente I (na) 20 0 Corriente I (na) [Fe(CN) 3- ] 6 1mM in KNO Potencial (V) Potencial (V) Ultra-micro vs. micro electrode

Voltamperometry Chronoamperometry -> > CALIBRATION OF THE SENSOR Fix potential. Additions of active species of known concentration and volume.

10-5 M Dopamine, 10-4 M Phosphate Dopamine, 10-5 M Dopamine, 3. 10-5 M Dopamine, 10-4 M Dopamine, 3. 10-4 M Dopamine, 10-3 M Dopamine, 3.

0 Dopamine Concentration (mm) + 2H + + 2e - After calibration, the electrode can be used to determine the concentration of unknown solutions.

7 Voltamperometry Chronoamperometry -> > CALIBRATION OF THE SENSOR Fix potential. Additions of active species of known concentration and volume. I (na) 30 0 V 15 0 HO HO Chronoamperometry +0.5 V Time (s) + NH 3 Phosphate Dopamine, 10-5 M Dopamine, M Dopamine, 10-4 M Phosphate Dopamine, 10-5 M Dopamine, M Dopamine, 10-4 M Dopamine, M Dopamine, 10-3 M Dopamine, M Dopamine, 10-3 M I (na) Dopamine in Phosphate (Ph=7.4) O O + NH 3 Calibration (I at t>45s) Sensitivity: 30nA/mM Dopamine Concentration (mm) + 2H + + 2e - After calibration, the electrode can be used to determine the concentration of unknown solutions. Sweeping Frequency Z ~ V Impedance Spectroscopy 95% of the current comes from a height below 2L. Nanoelectrodes (L<<) Electric Field -Changes in the conductivity and the capacitance of the solution can be detected. -Nanoparticles (or nano-objetcs) can be detected.

Impedances Electric Model 1 3 2 3.- SUBSTRATE: Eventhough it is an insulator, it also creates a parasitic capacitance. 2 1 1.

8 Impedances Electric Model SUBSTRATE: Eventhough it is an insulator, it also creates a parasitic capacitance DOBLE LAYER: the surface of the electrode is charged -> opposite sign charges (ions) are attracted/induced -> dobule layer capacitance DOUBLE LAYER Gold The thickness of the doble layer depends on the concentration of ions in the solution 2.- DISOLUCIÓN: Each disolution or media has a different behaviour, associated to the quantity of charges/ions, their movility in the solution, its nature, etc. [C y R del medio] 3 - High frequency: solution - Low Frequency: doble layer - High resistivity medias: substrate Impedances Dependence on the conductivity Aqueous Solutions of NaCl, with different concentrations (i.e., the number of ions is changed -> the resistivity of the media varies) 2,0e-11 1,5e-11 C 1,0e-11 NaCl solutions (aq) 10-1 M DI H 2 O 5*10-5 M 10-3 M 10-2 M 5,0e Frequency (Hz) More ions -> better doble layer -> we keep on seeing it even for high frequencies

9 Impedances Dependence on ε r Measurements in different liquids with different permitivity (i.e., the capacity of charge storage is different). Z'' -1.5e7-1.0e7-5.0e6 Complex plane: Z vs Z C (F) 1.2e e-11 THF (ε r =7.5) Hexane (ε r =1.89) Air (ε r =1) 8.0e Validation of the model: in apolar medias we don t see the double layer Frequency (Hz) Acetonitrile (ε r =36.6) Etanol (ε r =25.3) DI water (ε r =80.1) e6 2.50e6 7.50e6 1.25e7 Z' Higher ε, more capacitance of the solution Nano Particles

10 Latex Nanoparticles (φ=300nm) 1 µm High concentration In the case of a high quantity of nanoparticles on the surface, the capacity decreases, mainly for low frequency. 2.8e * e-11 DI water nide04 - H2Odes h r - t0.z nide04-1% - 300nm - sec y di - t0.z 1.110e-11 Low concentration For low concentrations of nanoparticles, the capacity at high frequency decreases. As it is shown in the graph, very low changes can be detected. C 1.8* e-11 C 1.3e * % np 8.0e F requency 10 5 (H z) Frecuency (Hz) C 1.085e % nanopartículas DI water 0.003% nanopartículas 1.060e Frequency (Hz) Conclusions -We have designed and fabricated gold nanoelectrodes onto an insolating substrate (SiO 2 ) by a combination of micro and nanofabrication. -Electrochemical current measurements have demonstrated the good performance of the sensor. Furthermore, chronoamperometric measurements allow the calibration of the device. -Impedance spectroscopy measurements have also shown the good performance of the sensor. The response varies for different solutions, changing the conductivity or the permitivity of the media.. -Preliminary results of the detection of nanoparticles have been shown.

Lecture 4. Conductance sensors. ChemFET. Electrochemical Impedance Spectroscopy. py Practical consideration for electrochemical biosensors.

Lecture 4. Conductance sensors. ChemFET. Electrochemical Impedance Spectroscopy. py Practical consideration for electrochemical biosensors. Lecture 4 Conductance sensors. ChemFET. Electrochemical Impedance Spectroscopy. py Practical consideration for electrochemical biosensors. Conductivity I V = I R=, L - conductance L= κa/, l Λ= κ /[ C]