Redox actuation of a microcantilever driven by a self-assembled ferrocenylundecanethiolate monolayer: an investigation of the origin of the micromechanical motion and surface stress.

The electrochemically induced motion of free-standing microcantilevers is attracting interest as micro/nanoactuators and robotic devices. The development and implementation of these cantilever-based actuating technologies requires a molecular-level understanding of the origin of the surface stress that causes the cantilever to bend. Here, we report a detailed study of the electroactuation dynamics of gold-coated microcantilevers modified with a model, redox-active ferrocenylundecanethiolate self-assembled monolayer (FcC(11)SAu SAM). The microcantilever transducer enabled the observation of the redox transformation of the surface-confined ferrocene. Oxidation of the FcC(11)SAu SAM in perchlorate electrolyte generated a compressive surface stress change of -0.20 +/- 0.04 N m(-1), and cantilever deflections ranging from approximately 0.8 microm to approximately 60 nm for spring constants between approximately 0.01 and approximately 0.8 N m(-1). A comparison of the charge-normalized surface stress of the FcC(11)SAu cantilever with values published for the electrochemical oxidation of polyaniline- and polypyrrole-coated cantilevers reveals a striking 10- to 100-fold greater stress for the monomolecular FcC(11)SAu system compared to the conducting polymer multilayers used for electroactuation. The larger stress change observed for the FcC(11)SAu microcantilever is attributable to steric constraints in the close-packed FcC(11)SAu SAM and an efficient coupling between the chemisorbed FcC(11)S- monolayer and the Au-coated microcantilever transducer (vs physisorbed conducting polymers). The microcantilever deflection vs quantity of electrogenerated ferrocenium obtained in cyclic voltammetry and potential step/hold experiments, as well as the surface stress changes obtained for mixed FcC(11)S-/C(11)SAu SAMs containing different populations of clustered vs isolated ferrocenes, have permitted us to establish the molecular basis of stress generation. Our results strongly suggest that the redox-induced deflection of a FcC(11)SAu microcantilever is caused by a monolayer volume expansion resulting from collective reorientational motions induced by the complexation of perchlorate ions to the surface-immobilized ferroceniums. The cantilever responds to the lateral pressure exerted by an ensemble of reorienting ferrocenium-bearing alkylthiolates upon each other rather than individual anion pairing events. This finding has general implications for using SAM-modified microcantilevers as (bio)sensors because it indicates that the cantilever responds to collective in-plane molecular interactions rather than reporting individual (bio)chemical events.

[1]  Wenmiao Shu,et al.  Polyelectrolyte brush amplified electroactuation of microcantilevers. , 2008, Nano letters.

[2]  Thomas Thundat,et al.  A novel self-assembled monolayer (SAM) coated microcantilever for low level caesium detection , 2000 .

[3]  T. Thundat,et al.  Observation of the surface stress induced in microcantilevers by electrochemical redox processes. , 2004, Ultramicroscopy.

[4]  H. Rothuizen,et al.  Translating biomolecular recognition into nanomechanics. , 2000, Science.

[5]  Ian J Burgess,et al.  Microcantilever-based sensors: effect of morphology, adhesion, and cleanliness of the sensing surface on surface stress. , 2007, Analytical chemistry.

[6]  M. Calleja,et al.  Role of the gold film nanostructure on the nanomechanical response of microcantilever sensors , 2007 .

[7]  M. Welland,et al.  Measuring surface stress induced by electrode processes using a micromechanical sensor , 1996 .

[8]  H. Abruña,et al.  Electrochemically Controlled Adhesion in Atomic Force Spectroscopy , 1996 .

[9]  Michel Godin,et al.  A differential microcantilever-based system for measuring surface stress changes induced by electrochemical reactions , 2005 .

[10]  B. L. Weeks,et al.  Monitoring the formation of self-assembled monolayers of alkanedithiols using a micromechanical cantilever sensor. , 2007, Langmuir : the ACS journal of surfaces and colloids.

[11]  U. Simon,et al.  Molecular structure of ferrocenethiol islands embedded into alkanethiol self‐assembled monolayers by UHV‐STM , 2006 .

[12]  P. Sorger,et al.  Electronic detection of DNA by its intrinsic molecular charge , 2002, Proceedings of the National Academy of Sciences of the United States of America.

[13]  Carolyn R. Bertozzi,et al.  Coadsorption of ferrocene-terminated and unsubstituted alkanethiols on gold: electroactive self-assembled monolayers , 1990 .

[14]  Rachel A. McKendry,et al.  Physics of Nanomechanical Biosensing on Cantilever Arrays , 2008 .

[15]  G. Whitesides,et al.  Potential-dependent wetting of aqueous solutions on self-assembled monolayers formed from 15-(ferrocenylcarbonyl) pentadecanethiol on gold , 1994 .

[16]  D. Reinhoudt,et al.  Self-assembled monolayers on gold of ferrocene-terminated thiols and hydroxyalkanethiols , 2002 .

[17]  Xuemei Wang,et al.  Potential-controlled molecular machinery of bipyridinium monolayer-functionalized surfaces: an electrochemical and contact angle analysis , 2003 .

[18]  M. Sepaniak,et al.  Enhancing chemi-mechanical transduction in microcantilever chemical sensing by surface modification. , 2003, Ultramicroscopy.

[19]  M. Grattarola,et al.  Micromechanical cantilever-based biosensors , 2001 .

[20]  Arun Majumdar,et al.  Label-free protein recognition two-dimensional array using nanomechanical sensors. , 2008, Nano letters.

[21]  H. Ju,et al.  Effect of electrolytes on the electrochemical behaviour of 11-(ferrocenylcarbonyloxy)undecanethiol SAMs on gold disk electrodes , 1999 .

[22]  James K. Gimzewski,et al.  Surface stress in the self-assembly of alkanethiols on gold , 1997 .

[23]  H. Lang,et al.  A label-free immunosensor array using single-chain antibody fragments. , 2005, Proceedings of the National Academy of Sciences of the United States of America.

[24]  S. Creager,et al.  Determination of the surface pK of carboxylic- and amine-terminated alkanethiols using surface plasmon resonance spectroscopy. , 2008, Langmuir : the ACS journal of surfaces and colloids.

[25]  Stephen D. Evans,et al.  Surface potential studies of alkyl-thiol monolayers adsorbed on gold , 1990 .

[26]  G. Niaura,et al.  Mediated oxidation of ascorbic acid on a homologous series of ferrocene-terminated self-assembled monolayers. , 2007, Langmuir : the ACS journal of surfaces and colloids.

[27]  W. Knoll,et al.  Molecular recognition at self‐assembled monolayers: Optimization of surface functionalization , 1993 .

[28]  Jochen S. Gutmann,et al.  Synthesis and Characterization of Polymer Brushes on Micromechanical Cantilevers , 2004 .

[29]  Roberto Raiteri,et al.  Changes in surface stress at the liquid:solid interface measured with a microcantilever , 2000 .

[30]  L. Abrantes,et al.  Redox induced orientational changes in a series of short chain ferrocenyl alkyl thiols self-assembled on gold(111) electrodes , 2001 .

[31]  Yukari Sato,et al.  Electrochemical characteristics of a gold electrode modified with a self-assembled monolayer of ferrocenylalkanethiols , 1991 .

[32]  R. Bruce Lennox,et al.  Gold−Sulfur Bonding in 2D and 3D Self-Assembled Monolayers: XPS Characterization , 2000 .

[33]  M. Sepaniak,et al.  Cantilever transducers as a platform for chemical and biological sensors , 2004 .

[34]  T. Thundat,et al.  Effect of chain length on nanomechanics of alkanethiol self-assembly , 2007 .

[35]  Hao Jiang,et al.  Bimaterial Microcantilevers as a Hybrid Sensing Platform , 2008 .

[36]  L. G. J. Fokkink,et al.  Potential-Dependent Wetting of Electroactive Ferrocene-Terminated Alkanethiolate Monolayers on Gold , 1994 .

[37]  S. Balasubramanian,et al.  DNA molecular motor driven micromechanical cantilever arrays. , 2005, Journal of the American Chemical Society.

[38]  Roberto Raiteri,et al.  Micromechanics senses biomolecules , 2002 .

[39]  H. Lang,et al.  Multiple label-free biodetection and quantitative DNA-binding assays on a nanomechanical cantilever array , 2002, Proceedings of the National Academy of Sciences of the United States of America.

[40]  Maria T. Cruañes,et al.  Characterization of Charge Transfer Processes in Self-Assembled Monolayers by High-Pressure Electrochemical Techniques , 1995 .

[41]  Ida Lee,et al.  Effect of nanometer surface morphology on surface stress and adsorption kinetics of alkanethiol self-assembled monolayers. , 2006, Ultramicroscopy.

[42]  Vincent Tabard-Cossa,et al.  Nanomechanical cantilever motion generated by a surface-confined redox reaction , 2003 .

[43]  Peter Williams,et al.  Quantitative surface stress measurements using a microcantilever , 2001 .

[44]  S. Creager,et al.  Long-Range Electronic Coupling between Ferrocene and Gold in Alkanethiolate-based Monolayers on Electrodes , 1997 .

[45]  L. Norman,et al.  Electrochemical surface plasmon resonance investigation of dodecyl sulfate adsorption to electroactive self-assembled monolayers via ion-pairing interactions. , 2007, Langmuir : the ACS journal of surfaces and colloids.

[46]  J. Lahann,et al.  A Reversibly Switching Surface , 2003, Science.

[47]  P. Fenter,et al.  Chain-length dependence of the structures and phases of CH3(CH2)n-1 SH self-assembled on Au(111). , 1993, Physical review letters.

[48]  L M Lechuga,et al.  Nanomechanics of the formation of DNA self-assembled monolayers and hybridization on microcantilevers. , 2004, Langmuir : the ACS journal of surfaces and colloids.

[49]  G. Stoney.  The Tension of Metallic Films Deposited by Electrolysis , 1909 .

[50]  J. Colton,et al.  Microcantilevers: sensing chemical interactions via mechanical motion. , 2008, Chemical reviews.

[51]  Harold G. Craighead,et al.  Virus detection using nanoelectromechanical devices , 2004 .

[52]  Yukari Sato,et al.  Mass transport accompanied with electron transfer between the gold electrode modified with 11-ferrocenylundecanethiol monolayer and redox species in solution — an electrochemical quartz crystal microbalance study , 1997 .

[53]  Michel Godin,et al.  Erratum to: "A differential microcantilever-based system for measuring surface stress changes induced by electrochemical reactions" (Sensors and Actuators B 107 (2005) 233-241) , 2006 .

[54]  H. Craighead,et al.  Micro- and nanomechanical sensors for environmental, chemical, and biological detection. , 2007, Lab on a chip.

[55]  K. Uosaki,et al.  Redox-Induced Orientation Change of a Self-Assembled Monolayer of 11-Ferrocenyl-1-undecanethiol on a Gold Electrode Studied by in Situ FT-IRRAS , 1997 .

[56]  Yukari Sato,et al.  Electrochemical quartz crystal microbalance studies of self-assembled monolayers of 11-ferrocenyl-1-undecanethiol: Structure-dependent ion-pairing and solvent uptake , 1994 .

[57]  D. Allara,et al.  Spontaneously organized molecular assemblies. 4. Structural characterization of n-alkyl thiol monolayers on gold by optical ellipsometry, infrared spectroscopy, and electrochemistry , 1987 .

[58]  R. Georgiadis,et al.  Electrostatic surface plasmon resonance: Direct electric field-induced hybridization and denaturation in monolayer nucleic acid films and label-free discrimination of base mismatches , 2001, Proceedings of the National Academy of Sciences of the United States of America.

[59]  Arun Majumdar,et al.  Nanomechanical Forces Generated by Surface Grafted DNA , 2002 .

[60]  M. Porter,et al.  Infrared spectroelectrochemical characterization of ferrocene-terminated alkanethiolate monolayers at gold , 1992 .

[61]  Thomas Thundat,et al.  In situ detection of calcium ions with chemically modified microcantilevers. , 2002, Biosensors & bioelectronics.

[62]  Christiane Ziegler,et al.  Cantilever-based biosensors , 2004, Analytical and bioanalytical chemistry.

[63]  Chih-Ming Ho,et al.  A nanomechanical device based on linear molecular motors , 2004 .

[64]  Charles M. Lieber,et al.  Chemical Force Microscopy , 1997, Microscopy and Microanalysis.

[65]  Yukari Sato,et al.  Dynamic Ellipsometry of a Self-Assembled Monolayer of a Ferrocenylalkanethiol during Oxidation-Reduction Cycles , 1994 .

[66]  M. Molero,et al.  Influence of Spatial Redox Distribution on the Electrochemical Behavior of Electroactive Self-Assembled Monolayers , 2001 .

[67]  P V Bonnesen,et al.  Ultrasensitive detection of CrO4(2-) using a microcantilever sensor. , 2001, Analytical chemistry.

[68]  Marc D. Porter,et al.  Real Time Monitoring of the Electrochemical Transformation of a Ferrocene-Terminated Alkanethiolate Monolayer at Gold via an Adhesion-Based Atomic Force Microscopic Characterization , 1996 .

[69]  Matthew A Cooper,et al.  Nanomechanical detection of antibiotic-mucopeptide binding in a model for superbug drug resistance. , 2008, Nature nanotechnology.

[70]  Wenmiao Shu,et al.  Highly reversible and multi-stage cantilever actuation driven by polyelectrolyte brushes. , 2006, Journal of the American Chemical Society.

[71]  Byungkyu Kim,et al.  Real-time measurement of the contractile forces of self-organized cardiomyocytes on hybrid biopolymer microcantilevers. , 2005, Analytical chemistry.

[72]  I. R. Mcdonald,et al.  Domain formation and system-size dependence in simulations of self-assembled monolayers , 1993 .

[73]  M. Godin,et al.  Redox-induced surface stress of polypyrrole-based actuators. , 2005, The journal of physical chemistry. B.

[74]  C. P. Smith,et al.  Theory of the interfacial potential distribution and reversible voltammetric response of electrodes coated with electroactive molecular films. , 1992, Analytical chemistry.

[75]  Thomas Thundat,et al.  1,6-Hexanedithiol monolayer as a receptor for specific recognition of alkylmercury. , 2005, The Analyst.

[76]  E. Bamberg,et al.  Two-Dimensional Structure of Disulfides and Thiols on Gold(111) , 1998 .

[77]  Panos G. Datskos,et al.  Enhanced chemi-mechanical transduction at nanostructured interfaces , 2001 .

[78]  C. Chidsey,et al.  Free Energy and Temperature Dependence of Electron Transfer at the Metal-Electrolyte Interface , 1991, Science.

[79]  Martin Hegner,et al.  Cantilever array sensors , 2005 .

[80]  Yukari Sato,et al.  Coverage dependent behavior of redox reaction induced structure change and mass transport at an 11-ferrocenyl-1-undecanethiol self-assembled monolayer on a gold electrode studied by an in situ IRRAS–EQCM combined system , 1999 .

[81]  G. Niaura,et al.  Anion effect on mediated electron transfer through ferrocene-terminated self-assembled monolayers. , 2004, Langmuir : the ACS journal of surfaces and colloids.

[82]  Stephen E. Creager,et al.  Redox and ion-pairing thermodynamics in self-assembled monolayers , 1991 .

[83]  James K. Gimzewski,et al.  Surface stress in the self-assembly of alkanethiols on gold probed .by a force microscopy technique , 1998 .

[84]  S. Creager,et al.  REDOX PROPERTIES OF FERROCENYLALKANE THIOLS COADSORBED WITH LINEAR N-ALKANETHIOLS ON POLYCRYSTALLINE BULK GOLD ELECTRODES , 1991 .

[85]  W. Haiss,et al.  Surface stress of clean and adsorbate-covered solids , 2001 .

[86]  Volker Scheumann,et al.  Probing the Electrochemical Deposition and/or Desorption of Self-Assembled and Electropolymerizable Organic Thin Films by Surface Plasmon Spectroscopy and Atomic Force Microscopy , 1999 .

[87]  S. Manalis,et al.  Micromechanical detection of proteins using aptamer-based receptor molecules. , 2004, Analytical chemistry.

[88]  C. E. Bach,et al.  Potential-induced stress in the solid-liquid interface: Au(111) and Au(100) in an HClO4 electrolyte , 1997 .

[89]  Cengiz S. Ozkan,et al.  Analysis, control and augmentation of microcantilever deflections in bio-sensing systems , 2003 .

[90]  H. Sugimura,et al.  Self-assembled mixed monolayer containing ferrocenylthiol molecules : STM observations and electrochemical investigations , 2007 .

[91]  Arun Majumdar,et al.  Chemomechanics of surface stresses induced by DNA hybridization. , 2006, Langmuir : the ACS journal of surfaces and colloids.

[92]  K. Uosaki,et al.  Anion effect on the electrochemical characteristics of a gold electrode modified with a self-assembled monolayer of ferrocenylhexanethiol in aqueous and dichloromethane solutions , 2001 .

[93]  R. Bruce Lennox,et al.  Potential-Induced Defects in n-Alkanethiol Self-Assembled Monolayers Monitored by Impedance Spectroscopy , 2000 .

[94]  Michel Godin,et al.  Surface stress, kinetics, and structure of alkanethiol self-assembled monolayers. , 2004, Langmuir : the ACS journal of surfaces and colloids.

[95]  M. Welland,et al.  Measuring the surface stresses in an electrochemically deposited metal monolayer : Pb on Au(111) , 1996 .

[96]  Thomas Thundat,et al.  Detection of pH variation using modified microcantilever sensors , 2001 .

[97]  L. Lee,et al.  Ferrocenylalkylthiolates as a probe of heterogeneity in binary self-assembled monolayers on gold. , 2006, Langmuir : the ACS journal of surfaces and colloids.

[98]  Rüdiger Berger,et al.  Micromechanical cantilever technique: a tool for investigating the swelling of polymer brushes. , 2007, Langmuir : the ACS journal of surfaces and colloids.

[99]  Yuyuan Tian,et al.  Quantification of Redox-Induced Thickness Changes of 11-Ferrocenylundecanethiol Self-Assembled Monolayers by Electrochemical Surface Plasmon Resonance , 2004 .

[100]  Marilyne Sousa,et al.  Investigating the molecular mechanisms of in-plane mechanochemistry on cantilever arrays. , 2007, Journal of the American Chemical Society.

[101]  L. Abrantes,et al.  In situ Ellipsometric Study of Redox Induced Orientation of a Short Chained Ferrocenylalkylthiol Monolayer Self-Assembled on Gold , 2002 .

[102]  G. Whitesides,et al.  Effect of Surface Wettability on the Adsorption of Proteins and Detergents , 1998 .

[103]  T. Thundat,et al.  Bioassay of prostate-specific antigen (PSA) using microcantilevers , 2001, Nature Biotechnology.

[104]  J. Kjems,et al.  Nanomechanical sensing of DNA sequences using piezoresistive cantilevers. , 2005, Langmuir : the ACS journal of surfaces and colloids.

[105]  James K. Gimzewski,et al.  Stress at the Solid−Liquid Interface of Self-Assembled Monolayers on Gold Investigated with a Nanomechanical Sensor , 2000 .

[106]  Chih-Ming Ho,et al.  Linear artificial molecular muscles. , 2005, Journal of the American Chemical Society.

[107]  George M. Whitesides,et al.  Formation of monolayers by the coadsorption of thiols on gold: variation in the head group, tail group, and solvent , 1989 .

[108]  N. Abbott,et al.  Surface-Driven Switching of Liquid Crystals Using Redox-Active Groups on Electrodes , 2003, Science.

[109]  I. Willner,et al.  Redox Activation of a Polyaniline-Coated Cantilever: An Electro-Driven Microdevice Parts of this research are supported by The Israel Ministry of Science and the Israel Science Foundation. M. Lahav gratefully acknowledges the support of The Clore Israel Foundation Scholars Programme. , 2001, Angewandte Chemie.

[110]  R. Georgiadis,et al.  Kinetic discrimination of sequence-specific DNA-drug binding measured by surface plasmon resonance imaging and comparison to solution-phase measurements. , 2007, Journal of the American Chemical Society.

[111]  Harald Ibach,et al.  The role of surface stress in reconstruction, epitaxial growth and stabilization of mesoscopic structures , 1997 .

[112]  S. Creager,et al.  Reorganization energetics for ferrocene oxidation/reduction in self-assembled monolayers on gold , 1998 .

[113]  A. Guiseppi-Elie,et al.  Growth of electropolymerized polyaniline thin films , 1993 .

[114]  G. Niaura,et al.  Direct Observation of Two Types of Monolayer-Bound Ferricinium Ions on Gold: Implications for Electrocatalysis , 2003 .

[115]  James K. Gimzewski,et al.  An artificial nose based on a micromechanical cantilever array , 1999 .

[116]  A. Chilkoti,et al.  Microcantilever sensing and actuation with end-grafted stimulus-responsive elastin-like polypeptides. , 2007, Langmuir : the ACS journal of surfaces and colloids.