s 16 (2007) 138–143www.elsevier.com/locate/diamond

Diamond & Related Material

Immobilization of horseradish peroxidase via an amino silaneon oxidized ultrananocrystalline diamond

Jorge Hernando a,⁎, Tahmineh Pourrostami a, Jose A. Garrido a, Oliver A. Williams b,Dieter M. Gruen c, Alexander Kromka d, Doris Steinmüller d, Martin Stutzmann a

a Walter Schottky Institut, Technische Universität München, Garching 85748, Germanyb Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439, USA

c Materials Science and Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439, USAd r-Best coating, Hartstoffbeschichtungs GmbH, Erlach 165, 6150 Steinach, Austria

Received 14 November 2005; received in revised form 10 April 2006; accepted 17 April 2006Available online 23 June 2006

Abstract

We discuss the complete functionalization of nitrogen-doped ultrananocrystalline diamond (UNCD) films, starting from an oxidized surface.First, the presence of hydroxyl groups on oxidized nanocrystalline diamond (NCD) was confirmed by fluorescence microscopy. Next, the graftingof a linker molecule such as 3-aminopropylmethyldiethoxysilane on oxidized NCD was confirmed by fluorescence microscopy and X-rayphotoelectron spectroscopy (XPS). Then the horseradish peroxidase (HRP) enzyme was immobilized on silane-modified initially oxidized UNCD.The HRP-modified UNCD was characterized by electrochemical techniques, such as faradaic cyclic voltammetry and the amperometric responseto H2O2. This response to H2O2 is discussed in terms of the layer-by-layer configuration used and the electronic properties of conducting UNCD.© 2006 Elsevier B.V. All rights reserved.

Keywords: Diamond film; Nanocrystalline; Electrochemical; Biomaterials

1. Introduction

Diamond possesses outstanding properties that make it idealfor biochemical applications. On one hand, diamond, consistingonly of carbon atoms, is a per se biocompatible material. On theother hand, and of most importance in order to develop electro-chemical biosensors by means of modified diamond, no othermaterial shows as much versatility as an electrochemical elec-trode as does the electrically conducting diamond [1]. This is dueto the wide potential window, its chemical stability in extremeenvironments, its low background current when compared toother electrode materials, and its semimetallic electronic be-havior. However, the progress in diamond-based biosensors hasbeen usually hindered by the high cost of diamond.

⁎ Corresponding author. Present address: E.T.S.I. Industriales, Universidad deCastilla La Mancha, 13071 Ciudad Real, Spain. Tel.: +34 926 295 300x6425;fax: +34 926 295 361.

E-mail address: jorge.hernando@uclm.es (J. Hernando).

0925-9635/$ - see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.diamond.2006.04.005

Fortunately, the development of conducting ultrananocrys-talline diamond (UNCD) [2], with nearly the same exceptionalproperties as single crystal diamond and at a relatively low cost,is making diamond research and development viable for severalapplications. Recent work has confirmed the progress in thefield of nanocrystalline (NCD) based biosensors [3,4].

The functionalization approach of Yang et al. [3] and Härtl etal. [4] is based on a slow photochemical process to bind amine-terminated hydrocarbon chains on a hydrogen-terminated surface.Here we propose the use of oxidized UNCD surfaces as thestarting point of the functionalization, which requires a differentsurface chemistry. This approach could take advantage of thefabrication of oxidized structures on the nanometer scale withatomic force microscopy [5]. The subsequent functionalization ofthese oxidized structures would allow the design of sensors on thenanoscale, which are characterized by a higher sensitivity anddenser arrays than conventional micro-sized sensor devices.

Here, we present the complete biofunctionalization of anoxidized UNCD surface. First we confirmed the presence ofhydroxyl groups on oxidized NCD surfaces. Next we looked for

139J. Hernando et al. / Diamond & Related Materials 16 (2007) 138–143

a linker molecule that reacts with the hydroxyl groups. Amongthe different alternatives, we decided to make use of the aminoalkoxysilane chemistry, which is very well established in orderto cover hydroxyl-terminated surfaces. The most well knownaminosilane molecule is the 3-aminopropyltriethoxysilane(APTES). This molecule was deposited before on different dia-mond surfaces [6,7]. However, different contributions reportedabout the difficulty of obtaining good monolayers from trieth-oxysilanes, like APTES, due to the formation of thick deposits[8,9]. In our case, an efficient electron transfer between theUNCD surface and the subsequent immobilized enzymes on thesilane-modified UNCD was required and this thick deposit oflinker molecules would constitute a barrier for the transfer.That is why we chose the 3-aminopropylmethyldiethoxysilane(APDEMS) molecule, which was reported to provide a coverageof only one monolayer [8]. The amino end group of this linkerallows further attachment of a biomolecule.

Once the surface was activated with the APDEMSmolecules,the aim was to attach an enzyme layer to study its activity afterthe immobilization on oxidized UNCD. Among the differentpossibilities, the horseradish peroxidase (HRP) enzyme waschosen. HRP catalyzes the reduction of hydrogen peroxide[10,11]. In combination with an electrochemical electrode itallows the indirect detection of H2O2 at lower potentials (∼0 V)than the standard potentials for direct electrochemical monitor-ing of H2O2 (∼0.7 V). HRP-modified electrodes have alreadybeen used to take advantage of this property for the detection ofhydrogen peroxide [12], to detect glucose in combination withglucose oxidase [13], and to fabricate immunosensors [14]. Inour case, the presence and the mediatorless response to H2O2 ofHRP after its immobilization on a silane-modified initially oxi-dized UNCD surface were analyzed by means of electrochem-ical methods. The measured response to H2O2 is discussed interms of the layer-by-layer approach of the functionalization andthe electronic properties of the conducting UNCD material, andcompared to the response of physisorbed HRP on polycrystallinediamond [15].

2. Experimental

2.1. Chemicals and material preparation

Horseradish peroxidase (HRP, EC 1.11.1.7, type II), 3-aminopropylmethyldiethoxysilane (APDEMS) and sulforhoda-mine B acid chloride were purchased from Sigma Aldrich.Rhodamine B isothiocyanate and potassium ferrocyanide werepurchased from Merck. All the other reagents and solvents wereof analytical grade and used without further purification. Milli-QMillipore water was used.

Undoped NCD and nitrogen-doped UNCD samples wereused. All samples were cleaned before any process in an ultra-sonic bath with acetone and isopropanol for 15min each andfinally dried with nitrogen.

The undoped NCDmaterial was grown by hot-wire chemicalvapor deposition from a CH4(5–10%)/H2(95–90%) mixture.The average grain size, estimated from X-ray diffraction ex-periments, was below 20 nm. The surface was H-terminated, as

confirmed by a static water contact angle close to 90°. Theseundoped samples were used for studying the presence of hy-droxyl groups and the process of silanization. They were usedfor X-ray photoelectron spectroscopy (XPS), water contactangle measurements and fluorescence microscopy. Non-struc-tured samples were used for the first two techniques. In the caseof the fluorescence microscopy, patterns of about 4 μm×4 μmoxidized squares, surrounded by H-terminated regions, werefabricated. The patterns were prepared on H-terminated NCDsamples by conventional UV-photolithography. The openedsquares were oxidized in an oxygen plasma. Next the photoresiston the H-terminated regions was cleaned as follows in order toensure its complete removal: ultrasonic bath in acetone for10 min (three times), ultrasonic bath in isopropanol for 10 min,and nitrogen for drying.

The nitrogen-dopedUNCDmaterial was grown bymicrowaveplasma-enhanced chemical vapor deposition (MWPECVD) witha microwave power of 1200 W and a substrate temperature of800 °C. The precursor gas phase was 1.2% CH4 and 10% nitro-gen diluted with argon at a total gas flow of 100 sccm. The grainsize was about 12 nm [2]. The Hall effect showed typical con-ductivities of the order of 100Ω−1 cm−1. The conducting UNCDsamples were used for the electrochemical measurements, sowe named these samples as electrodes. In order to allow theelectrical conduction, two 1 mm×0.1 mm Au/Ti contacts weredeposited on bare samples by thermal evaporation after therequired standard photolithographic steps. The cleaning men-tioned above was also used to remove the photoresist after themetallization process. Oxidation, silanization and HRP immo-bilization were performed on these electrodes. The silane-modified and HRP-modified electrodes were used to study thepresence and the activity of the enzymes.

The size of the grains for both the undoped and the nitrogen-doped materials was comparable. Therefore the results obtainedfor the undoped material, such as the presence of hydroxylgroups and the achievement of the silanization, were expectedto be similar for the nitrogen-doped material.

2.2. Surface modification

2.2.1. OxidationThe oxidation of the plain samples, electrodes, and patterned

samples was achieved with an oxygen–plasma system (TePla100-E). The parameters of the oxidation were 1.4 mbar O2 pres-sure and 200 W plasma power for 5 min. The static water contactangle of the plain samples after the oxidation was below 5°.

2.2.2. SilanizationThe grafting of the APDEMS molecules was performed as

follows. Either immediately after the oxidation of the plainsamples and electrodes, or after the removal of the photoresistfrom the patterned samples, the samples were introduced in anargon glove box (H2Ob1 ppm, O2b1 ppm) where the reactionwith the APDEMS molecules took place. The freshly preparedsolution for the reaction was 0.1 ml APDEMS in 10 mlanhydrous toluene. The samples were immersed in the solutionand the duration of the reaction was 1 h and 30 min at room

Fig. 1. Fluorescence microscopy image of (a) a pattern of oxidized squares afterreaction with sulforhodamine B acid chloride, and (b) a pattern of APDEMS-modified squares after reaction with rhodamine B isothiocyanate.

140 J. Hernando et al. / Diamond & Related Materials 16 (2007) 138–143

temperature. After the process, the samples were rinsed in an-hydrous toluene, anhydrous isopropanol and dried with argon.Then the samples were removed from the glove box and a morethorough cleaning was performed in order to remove any phys-isorbed material. The cleaning consisted of an ultrasonic bath intoluene and isopropanol, each of them for 15 min, and finallynitrogen for drying.

2.2.3. HRP immobilizationThe protocol for the enzyme attachment was similar to the

one described by Härtl et al. [4], unless otherwise specified, andit was carried out immediately after the silanization process. Theelectrodes were immersed in a 2 mg/ml HRP solution in a50 mM pH 6.2 Na-based PBS buffer for 15 h at 4 °C.

2.3. Fluorescence microscopy

Patterned samples, prepared as described previously, wereused for these experiments, in which the presence of bothspecific oxygen groups on the oxidized squares and the silanemolecules after their reaction with the oxidized squares wasinvestigated. To this end, fluorescent probes which reactselectively with either the hydroxyl groups or the amino endgroups of the silane molecules were used. H-terminated regionsare not expected to react with the fluorophores or the silanemolecules. Therefore the achievement of a successful reactionwould provide a clear contrast between the oxidized squares andthe H-terminated surroundings.

Oxygen-terminated diamond may exhibit either carbonyl orhydroxyl groups as reactive sites. Experiments assuming thepresence of carbonyl groups did not show any positive result.That is why we have focussed our interest on the hydroxylgroups, which react with the sulforhodamine B acid chloridefluorophore. The patterned NCD was immersed in a fresh 1 mg/ml fluorophore solution in 50 mM pH 9 (adjusted addingNaOH) Na-based PBS buffer. The reaction was done for 21h atroom temperature, avoiding any exposure to light. After theprocess, the samples were rinsed with the same buffer, cleanedin an ultrasonic bath with acetone and isopropanol, for 15 mineach, and finally dried with nitrogen.

For the labelling of the amine-terminated silane-modifiedpatterned NCD samples, the rhodamine B isothiocyanate fluoro-phore was chosen. A fresh 1mg/ml solution of the fluorophore inanhydrous dimethyl sulfoxide (DMSO) was prepared. The pat-terned sample was immersed in a mixture of 100 μl of theprevious solution and 900 μl of 100 mM pH 10 carbonate buffer.The reaction took place for 21 h at 4 °C, being protected fromlight. The cleaning after the reaction consisted of rinsing incarbonate buffer, cleaning in an ultrasonic bath with DMSO,acetone and isopropanol, for 15 min each, and finally nitrogen.

A Zeiss Axiovert 200 M MAT fluorescence microscope wasused to take the fluorescence images.

2.4. XPS and contact angle measurements

Oxidized and silane-modified NCD plain samples werestudied. The XPS measurements were done in a UHV system

with an EA-10 MCD SPECS analyzer and a RQ20/38 SPECSX-ray source. The Al Kα radiation at 1486.6 eV was used forthe excitation. The C1s, O1s, Si2p, Si2s and N1s peaks wereinvestigated.

Static water contact angle was measured with a home-madeset-up. The reported values are the average of at least threeindependent measurements.

2.5. Electrochemistry

A glass cell with a three electrode set-up was used for theelectrochemical measurements. The reference electrode was anAg/AgCl electrode, and the counter electrode was a Pt wire. Allpotentials are referred to the Ag/AgCl electrode. The electro-chemical measurements were performed using a PrincetonApplied Research PARSTAT 2263 potentiostat. A 100 mM pH6.2 K-based PBS buffer was used as the electrolyte. Theelectrolyte was purged with nitrogen for 1h prior to use and aflow of nitrogen was maintained above the electrolyte surface

90 95 100 105 110

50

100

150

200

250

300

350

(a) Si2p

C

ount

s (a

.u.)

Energy (eV)

390 395 400 405 4101100

1200

1300

1400

1500

1600

(b) N1s

Cou

nts

(a.u

.)

Energy (eV)

Fig. 2. XPS curves of (a) Si2p and (b) N1s for both oxidized (solid squares) andAPDEMS-modified (open circles) NCD samples.

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8

-40

-20

0

20

40

60

80

100

APDEMS HRP

Cur

rent

den

sity

(µA

cm

-2)

Voltage vs Ag/AgCl (V)

Fig. 3. Cyclic voltammetry curves of APDEMS-modified (dash) and HRP-modified (solid) UNCD electrodes in 1 mM K4[Fe(CN)6]·3H2O in 100 mM pH6.2 PBS electrolyte. Scan rate: 50 mV/s.

141J. Hernando et al. / Diamond & Related Materials 16 (2007) 138–143

while measuring. Faradaic cyclic voltammetry was done inelectrolyte containing 1 mM K4[Fe(CN)6]·3H2O. Amperometrywas measured in pure electrolyte, being magnetically stirred at aconstant rate, and H2O2 30% (w/w) was added manually whilemeasuring.

After realizing the different functionalization processes onthe electrodes and in order to perform the electrochemicalmeasurements, the contact metals were covered with a siliconerubber (type RTV-1 from Scrintc GmbH), defining an activearea of about 1 mm2 between the contacts. The exact area of thedevice is calculated from the images obtained with a cameraconnected to an optical microscope. The electrodes were eitherused or stored at 4 °C in a 50 mM pH 6.2 Na-based PBS buffer.

3. Results and discussion

3.1. Fluorescence microscopy

Fig. 1a) shows the fluorescence image of a pattern of oxidizedsquares after reaction with the sulforhodamine B acid chloridefluorophore. A clear contrast can be observed between themodified oxidized squares and the H-terminated surroundings,confirming the presence of reactive hydroxyl groups at thesurface of oxidized NCD films.

Fig. 1b) shows the fluorescence image for a pattern of silane-modified oxidized squares after reaction with the rhodamine Bisothiocyanate fluorophore. Again, a clear contrast can be ob-served between the squares and the surroundings, confirmingthe successful immobilization of APDEMS molecules on theinitially oxidized regions.

3.2. XPS and contact angle measurements

Fig. 2 shows the XPS data for the Si2p andN1s peaks for bothan oxidized NCD sample and a silane-modified NCD sample. Aclear Si2p peak can be observed at about 102 eV, related to theSi–O bond, on the silane-modified NCD. No Si2p peak wasobserved in the oxidized sample. The weak N1s peak, comingfrom the amino end group for the APDEMS-modified sample(Fig. 2b), was also not detected for the oxidized sample. Addi-tional information can be extracted from the integrated intensityof the O1s peak. The silane-modified sample compared to theoxidized sample shows an intensity ratio (OSilane:OOxidized) ofabout 1.7. This increase in the oxygen content for the silane-modified sample suggests a surface coverage closer to a mono-layer rather than a multilayer system, in which a higher ratioshould be expected.

The success of the silanization process was further confirmedby a change in the static water contact angle from below 5° forthe oxidized sample to 51° for the silane-modified sample.

3.3. Electrochemistry

3.3.1. Cyclic voltammetryFig. 3 shows the cyclic voltammetry curves for an APDEMS-

modified and HRP-modified UNCD electrodes in 100 mM pH6.2 PBS electrolyte buffer with a concentration of 1 mM K4[Fe(CN)6]·3H2O. In the case of the APDEMS-modified sample, ananodic current peak due to the oxidation of the mediator, as wellas a cathodic current peak due to the reduction of the oxidizedmediator can be observed. The difference in voltage between thepeaks,ΔEp, is about 495 mV, indicating a very sluggish process

0 5 10 15 20 25 30 35 40 45 50 55 60 65-0.05

-0.04

-0.03

-0.02

-0.01

0.00

0.01

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0.01

0.02

0.03

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rent

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sity

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cm

-2)

H2O

2 concentration (mM)

HRP

APDEMS

Cur

rent

den

sity

(µA

cm

-2)

Time (min.)

Fig. 4. Amperometry of APDEMS-modified and HRP-modified UNCDelectrodes at 0 V while adding H2O2. Aliquots of 0.2 mM H2O2 were addedevery 5min. Inset: cathodic current of the HRP-modified UNCD electrodeversus H2O2 concentration.

142 J. Hernando et al. / Diamond & Related Materials 16 (2007) 138–143

for the electron transfer between the mediator and the electrode.This could be related to the fact that the silane layer acts as ablocking layer for the diffusion of the ferrocyanide mediator tothe electrode surface. However, it should be taken into accountthat this mediator has already been reported to be sensitive to thetermination of diamond surfaces, showing a sluggish electrontransfer (ΔEp=198 mV) for oxygen-terminated polycrystallinediamond surfaces [16].

In the case of the HRP-modified electrode, the shape of theresponse is different. In particular, the response shows a signif-icant intensity decrease, and the anodic current peak is notvisible below 0.7 V, while the cathodic current peak is slightlyshifted to more negative voltages. A clear increase inΔEp occursas compared to the silane-modified electrode. This increase isindicative of a more inefficient electron transfer than for thesilane-modified electrode. Expecting that the only differencebetween both samples is the enzyme layer, this can be explainedby assuming that the enzyme layer further hinders thecommunication between the mediator and the electrode surface.This change in the cyclic voltammetry response has already beenused in the literature in order to identify different functionaliza-tion steps [17,18].

3.3.2. AmperometryOnce the presence of the enzyme on the UNCD surface was

confirmed, the activity of the enzyme was investigated. HRPcatalyzes the reduction of H2O2 [10,11]. After reacting withH2O2 the enzyme is oxidized, and two electrons are required toreduce it back to its initial state. These electrons can be providedby a mediator, or by direct electron transfer from the electrode.Here we only focus on the direct electron transfer from theelectrode to the active center of the enzyme. This transfer ofelectrons is equivalent to the cathodic current that can be mea-sured experimentally. So, in order to determine the sensitivity ofthe HRP-modified UNCD electrode to H2O2, amperometryexperiments were performed. Fig. 4 shows the current of boththe APDEMS-modified electrode and the HRP-modified

electrode as a function of time at 0 V while adding H2O2.Aliquots of 0.2 mMH2O2 were added every 5min. The responseof theHRP-modified electrode is significantly higher than that ofthe APDEMS-modified electrode, as expected for the catalyticactivity of HRP.

The inset of Fig. 4 shows the cathodic current of the HRP-modifiedUNCDelectrode versus the concentration of H2O2. Thecurrent increased linearly up to 1.2 mM H2O2 with a correlationcoefficient of 0.999 and deviated downward from the linearrelationship for higher H2O2 concentrations due to the HRPreaction kinetics. A response of 0.013 μA cm−2 (mMH2O2)

−1 at0 Vwas calculated from the slope of the curve in the linear range.This response was almost unchanged after storage at 4 °C for aperiod of 2 weeks. The detection limit, estimated at a signal tonoise ratio of 3, was equal to 0.062 mM.

The measured response value was much lower than that ofstate-of-the-art gold colloidal modified HRP-based biosensor[19], which was fabricated using an approach that provided amore efficient electron transfer and a higher enzyme loadingthan the layer-by-layer protocol followed here. In our case, thedensest loading attainable was expected to be one monolayer.The formation of a multilayer of enzymes by cross-linking mayhelp to increase this loading. Besides the loading, the electrontransfer is also a very important parameter to control. For anefficient direct electron transfer, the active center of the immo-bilized enzymes requires an appropriate distance and orientationwith respect to the electrode [11]. In our case, the enzymes wererandomly attached to the silane layer, therefore the communi-cation with the electrode was only favored for the well posi-tioned enzymes.

Only a few works on gold have been reported for HRP-basedelectrodes with a linker molecule between the electrode and thebiomolecule [20,21]. In the case of Imabayashi et al. [20], acurrent of 2 nA at 0 V for 0.2 mM H2O2, with an active area of0.8 cm2, was reported. This corresponds to a response of about0.01 μA cm−2 (mM H2O2)

−1, similar to the one obtained in thepresent work.

In the field of diamond electrodes, cross-linked HRP wasphysisorbed on as grown and oxidized polycrystalline diamondand the response to H2O2 was analyzed [15]. From Fig. 5 foundin the paper of Tatsuma et al. we can deduce a response of about0.1 μA cm−2 (mM H2O2)

−1 in the linear range at 0.3 V. Theresponse is higher than that of the present manuscript. This maybe due to the fact of depositing the enzymes directly on thesurface. This would help enhance the electron transfer, as there isno linker molecule in between to hinder the transfer. However,the simple adsorption of the enzymes on the surface can beaffected by their removal from measurement to measurement,what would change and deteriorate the electrode performancewith time. The layer-by-layer immobilization we propose pro-vides a higher stability, as a covalent bonding is expected be-tween the different layers. Another factor to obtain a betterresponse is the application of 0.3 V. However, a voltage of 0.3 Vcould give rise to interference with other analytes.Weminimizedthat effect by applying 0 V.

It is also important to take into account the electronic pro-perties of nitrogen-doped UNCD when analyzing the response.

143J. Hernando et al. / Diamond & Related Materials 16 (2007) 138–143

The semimetallic behavior and the electrical conduction throughthe grain boundaries for nitrogen-doped as grownUNCDare verywell established [2,22]. We observed the same semimetallicbehavior on oxidized UNCD. Therefore, only the grain bound-aries can provide as many electrons as required for the electro-chemical reaction of the enzymes.However, as alreadymentionedbefore, despite of the high density of electrons, the achievement ofthe electron transfer from the electrode to the immobilized en-zyme is also subjected to other conditions, such as the properdistance and orientation of the active center of the enzymes withrespect to the electrode. In the case of nitrogen-doped UNCD,only the enzymes close enough to the grain boundaries and withthe proper orientation can get electrons from the grain boundaries,while those enzymes on the grains that are not close enough to theboundaries do not have the chance to receive charge from thegrain boundaries. As a consequence, only a fraction of the totalamount of immobilized enzymes is contributing to the measuredresponse. And the lower the surface ratio of grain boundaries tograins, the lower will be this fraction. The comparison betweenboron-doped UNCD, in which the grains are expected to beconductive, and nitrogen-doped UNCD will be conducted toinvestigate this point.

4. Conclusions

The complete functionalization of oxidized nitrogen-dopedUNCD with HRP enzymes has been carried out. First, the pre-sence of hydroxyl groups on oxidized NCD was confirmed.Next the attachment of 3-aminopropylmethyldiethoxysilane onoxidized NCD was achieved. Finally the HRP enzyme wasimmobilized on silane-modified initially oxidized UNCD. Themediatorless response of the HRP-modified UNCD electrode toH2O2 was measured electrochemically, obtaining a value of0.01 μA cm−2 (mM H2O2)

−1, comparable to previous HRP-modified gold electrodes with the same layer-by-layer config-uration. Details of the electrical conduction through the grainboundaries in nitrogen-doped UNCD have to be taken intoaccount when quantifying the response of biosensors based onthis type of material.

Acknowledgements

Thanks are due to Dr. Michael Weller for his help with thefluorescence microscopy experiments. We also thank Dr. MartinEickhoff for the XPS measurements.

Jorge Hernando acknowledges the financial support from theAlexander von Humboldt Foundation. Part of the work wasfunded by NaDiNe (Nano Diamond Network) of the AustrianNANO initiative, and by EU FP6 DRIVE (Diamond Researchon Interfaces for Versatile Electronics).

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