Functional Bioelectronic Interfaces on Electrolessly Deposited Gold for Bioelectronic Applications Brian L. Hassler, Neeraj Kohli, Lavanya Parthasarathy, Robert Ofoli, Ilsoon Lee, and R. Mark Worden. Chemical Engineering and Materials Science Michigan State University East Lansing, Michigan

Presentation Outline Background on sensing mechanisms Formation of the gold interface Interface formation/characterization Lipid bilayer with membrane protein Bioelectronic interface with dehydrogenase Summary

Sensing Mechanisms Electrochemical: oxidation/reduction Conductive substrates Gold Optical: fluorescence, luminescence Clear substrates Glass Plastics

Formation of Gold Film Treat with oxygen plasma Deposit polyelectrolyte mulilayers Poly(acrylic acid) (PAA) Poly(allylamine hydrochloride) (PAH) Deposit colloidal gold Seed by reductive deposition of gold salt

SEM-Time (after colloidal solution)(20 minutes seeding) (40 minutes seeding)(60 minutes seeding)

EDS-Analysis Au Si

Development and Characterization of Lipid Based Interfaces Interface development Interface characterization Fluorescence recovery after patterned photobleaching (FRAPP ) Determine mobile fraction Determine diffusion coefficient

Interface Development Lipid bilayer formation DGP: 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine- N-[3-(2-pyridyldithio) propionate] DPGP: 1,2-di-O-phytanyl-sn-glycero-3- phosphoethanolamine NBD-PE: 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine- N-(7-nitro-2-1,3-benzoxadiazol-4-yl) (A) Cystamine, DPGP, and DGP in ethanol (B) DPGP and NBD-PE in 0.1 M NaCl (A)(B)

Fringe patterns using Ronchi ruling Excitation wavelength ( =488 nm) Emission ( =510 nm) Bleaching time (3 1-s pulses) (a) Bleached area(b) Area Interrogated

FRAPP Results Diffusion coefficient 0.12 ± 0.06×10 -8 cm 2 s -1 Mobile fraction 0.87 ± 0.10 Wright, L. L.; Palmer, A. G.; Thompson, N. L. Biophysical Journal 1988, 54,

Development of Dehydrogenase Based Bioelectronic Devices Interface development Interface characterization Cyclic voltammetry Chronoamperometry

Reaction Mechanism

Cyclic Voltammetry on Glass Scan Parameters Initial potential: 400 mV Final potential: -200 mV Scan rate: 100 mV s -1 Results Turnover rate= 69.8 s -1 Sensitivity= 2.0 A mM -1 Saturation current= 60 A

Cyclic Voltammetry on Polystyrene Scan Parameters Initial potential: 400 mV Final potential: -200 mV Scan rate: 100 mV s -1 Results Turnover rate= 47.2 s -1 Sensitivity= 1.7 A mM -1 Saturation current= 43 A

Comparison Hassler and Worden, Biosensors and Bioelectronics (2005), In press

Chronoamperometry Procedure Step change in potential Plot current vs. time Characterization Equation for current decay Evaluation of constants k et = Electron transfer constant Q= Charge associated with oxidation/reduction = Surface coverage I=k et Q exp(-k et t)+k et Q exp(-k et t) =Q/(nFA)

Chronoamperometry on Glass Potentials: Initial: 400 mV Final: -200 mV Results: Electron transfer coefficients k et = 3.2×10 2 s -1 k et = 3.5×10 1 s -1 Surface coverage = 3.0× mol cm -2

Chronoamperometry on Polystyrene Potentials: Initial: 400 mV Final: -200 mV Results: Electron transfer coefficients k et = 4.2×10 2 s -1 k et = 2.1×10 2 s -1 Surface coverage = 6.3× mol cm -2 = 2.1× mol cm -2

Comparison Hassler and Worden, Biosensors and Bioelectronics (2005), In press

Summary Designed bioelectronic interfaces Electrolessly deposited gold Lipid bilayers Dehydrogenase enzymes Characterized interfaces Optical Techniques FRAPP Electrochemical Cyclic voltammetry Chronoamperometry

Acknowledgements Funding Michigan Technology Tri-Corridor Department of Education GAANN Fellowship Undergraduate participants Sean OBrien Craig Pereira

Thank You

Polyelectrolyte Multilayers Formation of films PAH (+) Water PAA (-) Water Formation of films Multilayer architectures Salt Concentration pH Formation of films Advantages of polyelectrolytes Ease of formation Molecule inclusion Controllable thickness

Lipids Used DGP DPGP NBD-PE

Stamp PAH (+ve) Glass slide PAH Technique PAA(-ve)

Cyclic Voltammetry Procedure Linear change in potential Plot current vs. potential Controlled/measured variables Peak current (I p ) Area (A) Scan rate (v) Concentration (C * )

Dehydrogenase Enzymes Dehydrogenase enzymes Catalyze electron transfer reactions Activity easily measured electrochemically Bioelectronic applications Often require cofactor (e.g., NAD(P) + ) Challenge: regenerating cofactor after reaction S P NAD(P) + NAD(P)H Dehydrogenase Enzyme Reaction cofactorenzyme MED ox MED red Cofactor Regenerationmediator

Channel Protein Incorporation Bottom leaflet Upper leaflet Protein Incorporation 5×10 -7 M Valinomycin in NaCl Equilibration Time= 1 h (A)(B) (C)

Impedance Spectroscopy Interface Design Lipid bilayer Lipids with valinomycin Interface Characterization Lipid bilayer Valinomycin containing bilayer C m =0.5 F cm -2 C dl = 4.1 F cm -2 R m = 8 K cm 2 RsRs CmCm RmRm CdlCdl