ELECTROCHEMICAL SENSORSFOR OCEANOGRAPHY:

From Glass Electrodes to Nanosubmarines

Joseph WangDepartment of Nanoengineering,

UCSD

HISTORICAL PROSPECTIVE

pH Glass electrode Oxygen Clark electrode Mercury drop electrodes

ELECTROCHEMICAL SENSORSBackground: Rely on measurements ofelectrical quantities (e.g. current, potential)and their relationship to chemicalparameters (usually concentration).

In the widely-used amperometric sensors(e.g., oxygen electrode), a potential isapplied onto the working electrode to drivean electron-transfer reaction, and theresultant current is measured.Potentiometric devices (e.g. pH sensors)rely on potential measurements.

-0.8-0.6-0.4-0.20.0

Potential / V

Cur

rent

Why Electrochemical Detection?• High Sensitivity and Selectivity (toward EA species)

• EC ‘loves’ salt (including 0.54M NaCl)

• Inherent Miniaturization

• Advanced Microfabrication

• Low Power Requirements (+low costs)

• Rapid (Temporal) Detection

• Easy to use

Electrochemical devices offer great promise for in-situ worksand autonomous platforms!

EC Sensors

Meeting the 4 S Requirements forSuccessful in-situ Monitoring:Sensitivity – Extremely high (down to pM)Selectivity – Towards electroactive species,

with potential overlapping peaksSpeed – Extremely fast (down to msec)Stability – Limited (due to surface fouling)

Properties of Controlled-Potential Techniques

SpeedWorking Detection (time per Response

Technique* Electrode‡ Limit, M cycle), min Shape---------------------------------------------------------------------------------------------DC polarography DME 10-5 3 WaveNP polarography DME 5x10-7 3 WaveDP polarography DME 10-8 3 PeakDP voltammetry Solid 5x10-7 3 PeakSW polarography DME 10-8 0.1 PeakAC polarography DME 5x10-7 1 PeakChronoamperometry Stationary 10-5 0.1 TransientCyclic voltammetry Stationary 10-5 0.1-2 PeakStripping voltammetry Bi SPE, MFE 10-10 3-6 PeakAdsorptive stripping HMDE, Bi 10-10 2-5 PeakvoltammetryAdsorptive stripping Solid 10-9 4-5 PeakVoltammetryAdsorptive-catalytic HMDE, Bi 10-12 2-5 Peakstripping voltammetry

*DC = direct current; NNP = normal pulse; DP = differential pulse; SW = square wave.

From: Analytical Electrochemistry, J. Wang, 2006 (Wiley)

Determination of the zinc complexingcapacity in seawater by cathodicstripping voltammetry, C. van denBerg, Marine Chemistry, 1985

In situ voltammetric measurements innatural waters: Future prospects andchallenges, J. Buffle, Electroanalysis,1993

Measurement of copper and zinc in SanDiego Bay by automated anodicstripping voltammetry, A. Zirino, EST,1978

Direct determination of iodide inseawater by cathodic stripping squarewave voltammetry, G. Luther, Anal.Chem., 1988.

Major Contributions of Buffle, Luther, Zirino, Florence,van den Berg, and many more……….in-situ and speciation studies since the1970s…………..

The speciation of trace elements inwaters, T.M. Florence, Talanta, 1982.

My Own Journey (PhD in late 1970s)

TOWARDS FIELD DEPLOYABLE DEVICESTraditionally, laboratory-based electrochemical measurements have

relied on relatively bulky and expensive electrodes, such as the rotatingdisc electrode or the static mercury drop electrodes (SMDEs) (with theirheavy motor or large mercury reservoir, respectively). Such electrodeswere combined with large cells (of 20-50 ml solution volume), theoperation of which required careful cleaning, oxygen removal, solutionstirring,, standard additions and replacement with new solution.

We would like to replace the conventional, cumbersome approachwith more imaginary ones (that meet the field demands of the 21st

Century).

1994: Tools Developed Towards Cleanup of DOE National Labs Upon theEnd of the Cold War (e.g., remote sensors for groundwater monitoring ofCr and U).

Changing the way we do electrochemistry!!!

From Bulky Mercury and Rotating Electrodes to Solid-State Microfabricated and Flexible Microelectrodes

DME

Thin and thick-filmmicrofabricated electrodes

Rotating disc electrode: RDECurrent electrode strips

MINIATURIZED ANALYZERS

FROM BULKY EC ANALYZERS TO ADVANCED HAND-HELD ANALYZERS

1980s and 1990s

TOWARDS PORTABLE INSTRUMENTATION

1990s: Towards Submersible Sensors

Remote Metal Sensors and Hand-Held Explosive Analyzers

The new devices allow us to move the measurement from the central laboratory to thefield, and to perform them rapidly, reliably and inexpensively (eliminating errors and

delays associated with sampling and storage to the main laboratory.

Plume Tracking

Flexible Wetsuit Sensors Nano-submarines forEnvironmental Remediation

Wearable (Tattoo) Devices

21st Century Devices

DISPOSABLE FLEXIBLE ELECTRODES AND MINIATURIZED ANALYZERS

SUBMERSIBLE/REMOTEELECTROCHEMICAL SENSORS

Goal: Obtaining a fast and accurate return ofchemical data in a timely, safe, and cost-effectivemanner.

Benefits: Assessment of pollutant gradient; earlywarning of pollution events and security threats;characterization of hostile environments; Industrialprocess control.

Minimizing the errors, cost, and delays associatedwith the collection and transport of discrete samples.

REMOTE STRIPPINGELECTRODES

(FOR METALPOLLUTANTS)

REMOTEBIOSENSORS

(FOR ORGANICPOLLUTANTS)

REMOTE MODIFIEDELECTRODES

(FOR ORGANICPOLLUTANTS)

REMOTE UCSDSENSORS

Fast return of the chemical information in a safe and timely manner.Effective monitoring of priority pollutants and threat compounds.

Assessment of chemical gradients

Metal Analyzers

Of the available analytical techniques fortrace metal determinations (AAS, ICP, NA,ASV), electrochemical (stripping) methods offerremarkable sensitivity, combined with portable,low-cost/power instrumentation.

Scope of ASV and AdSV of Trace Metals

Stripping Voltammetry:Electrolytic or Adsorptive Preconcentration

WHY STRIPPING ANALYSIS?

Electrochemical stripping analysishas always been recognized as apowerful tool for measuring tracemetals. Its remarkable sensitivity(and pM detection limits) areattributed to the ‘built-in’preconcentration step, duringwhich the target metals aredeposited onto the workingelectrode.

In-Situ STRIPPING ANALYSIS OFTRACE METALS

THE POTENTIAL-TIMEWAVEFORM

THE RESULTINGVOLTAMMOGRAM

THE POTENTIAL-TIMEWAVEFORM

THE RESULTINGVOLTAMMOGRAM

MICROMACHINED STRIPPING FLOW MICROANALYZER

MEMSASV

For incorporation onto various monitoring platforms

REPRODUCIBILITY

Because of the toxicity of mercury, alternative (‘environmentally friendly’)electrode materials are highly desired for field applications. Bismuthelectrodes offer a very favorable performance and serve as attractivealternative to mercury electrodes. Bismuth stripping electrodes thus holdgreat promise for on-site and in-situ metal measurements.

Increasing levels of Zn, Cdand Pb in 10 ppb steps.

From Mercury to Bismuth Electrodes Wang, Anal. Chem. 2000

REMOTE SENSING OF TRACEMETAL CONTAMINANTS

Wang et al, Anal. Chem. 34(1995)1481

STRIPPING-BASED SUBMERSIBLE PROBE, WITHA GOLD-FIBER MICROELECTRODE,

FOR IN-SITU MONITORING OFTRACE METALS

Originally developed for Groundwater Monitoring

Electrodeconnections

Long shielded cable

Reference electrode

Counter electrodeWorking electrode

PVC type housing

Quick disconnect environmentally-sealed connector

REMOTE ELECTROCHEMICAL SENSOR

WHAT ARE THE CHALLENGESTO SUBMERSIBLE ELECTROCHEMICAL PROBES?

Sensitivity, selectivity and reversibility

Changes of natural conditions (pH, salinity,

oxygen, temperature, convection)

Stability and baseline drift (Surface fouling under

prolonged operation; adsorption of macromolecules)

Robust in-situ calibration (How the quanititate?)

Power (harvesting energy from environment)

Signal handling and transmission

Remote Stripping Probes

Obstacles to Submersible Operation:Traditional use of mercury electrodes, oxygenremoval, supporting electrolyte, or solution stirring.

Solutions:Use of gold or bismuth electrodes, potentiometricstripping operation, and of ultramicroelectrodes (thatoffer efficient deposition from unstirred solution andoperation in low ionic-strength media).

UCSD Remote Submersible Sensors

Real-time in-situ monitoring of priority pollutants and threat compounds.

Wang, Anal. Chem. 67, 1481(1995).

Anal. Chem. 1995

SILVER REMOTE SENSING ELECTRODE

Anal. Chim. Acta 1996

Stability ingroundwater (A)and river water (B)samples

Discharge from a KodakPlant into Lake Ontario

Mapping of San Diego Bay for Heavy MetalContaminants

Anal. Chim. Acta 1995

‘Lab on a Gondola’

Monitoring Trace Hg and Cu in Venice’sGrand Canal

REMOTE SENSING OF METALS THAT CANNOTBE PLATED ELECTROLYTICALLY (Fe, Cr, U, V,

Mo, Ni)

USE OF ADSORPTIVE STRIPPING PROTOCOLSBASED ON THE ADSORPTIVE ACCUMULATIONOF CERTAIN COMPLEXES OF THE TARGET

METAL

M+n + L ML+n MLads+n

REQUIRE NEW PROBE DESIGN, WITHDELIVERY OF THE LIGAND SOLUTION

Extension to Adsorptive Accumulation:

ADSORPTIVE STRIPPING VOLTAMMETRY

Accumulation and stripping steps in adsorptive stripping measurements of ametal ion in the presence of an appropriate chelate agent (L).

AdSV: LAB-ON-A-CABLE

REMOTE Cr STRIPPING SENSOR(W/ An internal delivery of DTPA)

Stability and Carry-Over

Analyst 1999

IN-SITU SENSORS FOR METALSPECIATION

DIFFERENTIATION BETWEEN METAL SPECIESOF DIFFERENT SIZES.IN-SITU MANIPULATION OF COLLECTEDMETAL (via delivery of acid or ligand).ELIMINATION OF ERRORS INDUCED BYSAMPLE COLLECTION AND STORAGE(contamination, disturbance of equilibrium).

ELECTROCHEMICAL SENSORSFOR EXPLOSIVES IN MARINE ENVIRONMENTS

The presence of the electroactivenitro group makes nitroaromatic andnitramine explosives makes them idealcandidates for electrochemical detection.Such nitro group is an excellent electronacceptor and its reduction can beexploited for sensitive and selectiveelectrochemical detection.

For Review: Electroanalysis 19(2007)415

Tools Developed for Security Applications (ONR CSME Program):

In Situ Monitoring of Explosives

Common nitroaromatic and nitramine explosives

EXPLOSIVE DETECTION INMARINE ENVIRONMENTS

Distinct electrochemical signatures

REMOTE TNT SENSOR

Calibration Data : 250 ppb increments in sea water

-0.8-0.6-0.4-0.20.0

Potential / V

Cur

rent

0

4

8

12

0 1 2 3Conc. / ppm

Cur

rent

/ µA

5 µA

a

l

REMOTE TNT SENSOR

-0.7-0.5-0.3-0.1

Potential / V

Cur

rent

3µA

High Stability:

60 repetitive measurementsof 0.7 ppm TNT for 5 h in seawater.

HAND-HELD DIVER TNT SENSOR

SENSOR HEAD

POCKET PC ELECTRONIC

HAND-HELDDIVER UNIT

Dual Detection: Direct Comparison to Fluorescence of T. Swager (MIT)

RESPONSE NEAR SOURCE

Deployment Onto U.S. Navy UnderwaterUnmanned Vehicle

U.S. Navy unmanned

underwater vehicle,

The Remus

TOWARDS ARTIFICIAL DOLPHINES

High sensitivity (down to 1 ppb)and high speed (1-2 sec runs)

DEPLOYMENT ONTO UNDERWATER VEHICLES:Towards “Artificial Dolphins”

Carbon-FiberElectrode Assembly

SENSOR ASSEMBLY ONTO THE AUV

REMUS body ADCP Collar Nose Cone

PV with electronicsElectrode Unit

Connector

TNT sensor integrated onto the REMUS UUV

UNMANNED UNDERWATER VEHICLE (UUV)

Plume-tracking and Source localization:

Finding/following plume to source(ONR CSME Program)

0

1

2

3

0 50 100 150 200 250 300 350 400Run number

Cur

rent

/ uA

AUV TNT Map: Repetitive SWV Scan, every 2 sec

Duck Mission, NC (6/24/03)

Electrochemical Arrays for Multiple Injuries

Parallel Detection of Various Forms of Injury

Towards Wearable Devices: Textile-Based Sensor Arrays

Printed Sensor on Gore-Tex Fabric

Stencil Patternfor Array

FabricationBiosensor ArrayLayout

‘Lab-on-a-Sleeve’Textile-based Wearable Explosive Sensors

Square wave voltammograms (left) of GORE-TEXfabric-based sensors to DNT (A) and TNT (B).Electroanalysis 2010

On-Body Wearable Devices: Wetsuit Sensors(for divers and surfers)

Analyst 2011

Monitoring environmental pollutants andsecurity threats in marine environments

Printable Wetsuit Sensors

Underwater garments are highlycompatible with the thick-film (screen-

printing) fabrication process

Wearable electrochemical sensors onunderwater garments comprised of the

synthetic rubber neoprene.Analyst 2011

Wearable screen-printed electrochemicalsensors on underwater garments

Cyclic voltammograms for 5 mM ferricyanide at SPE on flexibleneoprene (A) and rigid alumina (B) substrates. C) Effect of ten 10

repeated bending operations. D) Relative currents obtained for theredox peaks of (C).

Wearable Wetsuit Sensor

Survive large mechanical deformations.

Wetsuit-based biosensing of phenolic contaminants

Enzyme (tyrosinase) immobilization on awearable substrate towards amperometricbiosensing of phenolic contaminants in

seawater. A tyrosinase-containing carbon inkwas employed for printing the amperometric

biosensor.Analyst 2011

Underwater Copper Monitoring

Stripping voltammograms for trace copper in untreatedseawater at the Au-modified neoprene SPE.

A) response to increasing copper concentrations in 10ppb steps. Deposition for 2 min at -1.0V. B) Calibrationcurve. C,D) Stability of the system with 100 ppb copper

over a 50 min period.

Analyst 2011

Wearable Wetsuit System (‘Lab-on-a-Wetsuit’):Direct integration of a miniaturized potentiostat (supporting electronics)

directly on the underwater garments

Wearable Wetsuit System:Integration of a miniaturized potentiostat directly on

the underwater garments

An encapsulated (watertight)miniaturized potentiostat that

provides the wearer with avisual ‘YES’ / ‘NO’ digital format

(via the illumination of a lightemitting diode).

Wearable epidermal chemical sensingdevices based on

integration of tattoo-transfer and thick-film fabrication processes.

Withstand the mechanical stresses (pinching,stretching, bending) relevant to epidermal wear.

Chem Comm2012

WEARABLE TATTOO pH SENSOR

Keep Smiling and responding

Analyst 2013

Under MechanicalStrain

In 2008

Moving to UCSD and Becoming a Nanoengineer….

GOING NANO! TOWARDS NANOSUBMARINES

1 meter

1 micrometer(1 millionth of a meter)

Barcode

GOING NANO! TOWARDS NANOSUBMARINES!

Locating explosives

or cancer cells

Nanomotors - UCSD Propulsion Mechanisms

Tt

Towards Nanosubmarines

The motion of synthetic micromotors has received a considerable fundamental andpractical interest over the past decade. Bubble-propelled catalytic tubular microenginesoffer great promise for various practical applications due to their efficient propulsion invarious real-life media.

High propulsion power of thePANI/Pt microtube engines:JACS 2011

Bubble-Propelled Catalytic Microengines:Bilayer Polymer-Platinum Microtubular Engines

Advanced Motion Control - Towards complex movement patterns

Micromotor-based strategy for water-quality testing based onchanges in the propulsion behavior of artificial biocatalytic

microswimmers in the presence of aquatic pollutants.

(analogous to changes in the swimming behavior andsurvival of natural fish used for toxicity testing.)

Nanofish for Water-Quality Testing

ACS Nano 2013

TOWARDS ENVIRONMENTAL REMEDIATION:Superhydrophobic Alkanethiol-Coated Microsubmarines for

Effective Removal of Oil

ACS NANO 2012

The new SAM-modified micromotors thus offer a rapid highlyefficient collection and transport of oil droplets in aqueousenvironments through the interaction with the hydrophobicalkanethiol monolayer coating.

Nano Letters, 2011

‘On-the-Fly’ Hybridization: ss-DNA-Functionalized micromotorsas selective transporters of complementary nucleic acid.

Motion-based Pathogen DetectionCatalytic nanomotors ‘racing’ following hybridization assays of

different E. coli cells

Direct detection of raw bacterial ribosomal RNA without isolation or purification steps

Nature Comm., 2010

Conclusions

Electrochemical devices are highlysuitable for decentralized on-site and in-situ marine survey. Over the past 2decades such devices have undergo adramatic change towards high-quality ,user-friendly, compact (hand-held)instruments. These developments shouldhave a substantial impact on marinesurveys and ocean science.

THANK YOU!!!!

Josephwang@ucsd.edu

$$$$$$$ DOE, EPA, ONR $$$$$$$$