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Institute Silicon Photovoltaics

Sensing of biomolecules

The substrate is functionalized by a linker molecule with an anchoring part where the recognition element is bound. The next step is the specific binding of the peptide, antibody etc. as sketched in Fig. 1 coupled with a detection of the recognition process by means of mass change as measured by QCM or optical verification (fluorescence spectroscopy, in-situ infrared spectroscopy) or electrical measurements (impedance spectroscopy, voltammetry).

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Fig. 1: Scheme of a bio-sensing layer with linker molecule to the surface, recognition element (e.g. biotin), and streptavidin (high affinity to biotin) that will immobilize by biotin for further investigations.

The linker molecule can be grafted onto the substrate surface by different techniques. We use:

  1. Electrochemical deposition via diazonium salts followed by the amide bonding of the anchor [1-4], see Fig. 2.
  2. Chemical deposition via hydrosylation [5] followed by the amide bonding of the anchor (Fig. 3).
enlarged view

Fig. 2: Preparation scheme of the bio-sensing layer by use of carboxyl, amino or maleimide groups via the diazonium route.

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Fig. 3: Chemical functionalization of Si-H surface by hydrosylation.


The bio-sensing layer using route 3 in Fig. 2 (direct maleimide functionalization) showed a 7-times higher sensitivity towards the anti-GST antibody than CB4-1 antibody (Fig. 4). The detection of the specific binding event of the antibody was performed using Flow-Injection-Analysis Quartz-Crystal-Microbalance (FIA-QCM) and voltametric measurements [4].

enlarged view

Fig. 4: (a) Frequency response of the Au electrodes (QCM) modified by maleimidophenyl and cys-peptide as a function of time after addition of the solutions of specifically binding anti-GST antibody and non-specific CB4-1 antibody with different concentrations from 0.08 to 50 µg/ml; (b) electrical response of a Si electrode modified by maleimidophenyl and cys-peptide after addition of anti-GST antibody and CB4-1 antibody.



Large-area graphene based sensor

Graphene is a conducting substrate that can be functionalized homogeneously [6,7] and transferred to any other material conducting or non-conducting without any remarkable loss of functionality [7].

Fig. 5: Top: Sketch of the surface functionalization of graphene by maleimido-phenyl (MP) via electrochemical reduction of p-Maleimidobenzene-tetrafluoroborate. Bottom: Functionalization of graphene on copper and subsequent transfer on another substrate (here oxidized Si wafer).

Fig. 6: Raman spectra of a) unmodified graphene (Gr) transferred on glass, b) maleimidophenyl (MP) functionalized graphene on copper; MP/Gr transferred to c) thick SiO2 layer on Si, to d) Au/Si and to e) PTFE foil. The spectra are shifted vertically for clarity. The * marked bands are due to PTFE. Excitation with 488 nm.


references

[1] Infrared spectroscopic study of the amidation reaction of aminophenyl modified Au surfaces and p-nitrobenzoic acid as model system; Zhang, X.; Sun, G.; Hinrichs, K.; Janietz, S.; Rappich, J.; Phys Chem Chem Phys 12 (2010), 12427-12429.

[2] Infrared spectroscopic ellipsometry (IRSE) and X-ray photoelectron spectroscopy (XPS) monitoring the preparation of maleimide-functionalized surfaces: from Au towards Si (111); Sun, G.; Hovestaedt, M.; Zhang, X.; Hinrichs, K.; Rosu, D.M.; Lauermann, I.; Zielke, C.; Vollmer, A.; Löchel, H.; Ay, B.; Holzhütter, H.-G..; Schade, U.; Esser, N.; Volkmer, R.; Rappich, J.; Surf. Interface Anal. 43 (2011) 1203–1210.

[3] Chehimi M.M.; editor. Aryl diazonium salts: new coupling agents in polymer and surface science. Weinheim: Wiley-VCH Verlag; 2012; ISBN 10: 3527329986 / 3-527-32998-6

[4] Electrochemical functionalization of gold and silicon surfaces by a maleimide group as a biosensor for immunological application; Zhang, X.; Tretjakov, A.; Hovestaedt, M.; Sun, G.; Syritski, V.; Reut, J.; Volkmer, R.; Hinrichs, K.; Rappich, J.; Acta Biomaterialia 9 (2013) 5838–5844.

[5] In situ monitoring of the electronic properties and the pH stability of grafted Si(111); Aureau, D.; Rappich, J.; Moraillon, A.; Allongue, P.; Ozanam, F.; Chazalviel, J.-N.; J. Electroanal. Chem. 646 (2010) 33–42.

[6] Quantifying the electrochemical maleimidation of large area graphene; Rösicke, F.; Gluba, M.A.; Hinrichs, K.; Sun, G.; Nickel, N.H.; Rappich, J.; Electrochem. commun. 57 (2015) 52.

[7] Functionalization of any substrate using covalently modified large area CVD graphene; Rösicke, F.; Gluba, M.A.; Shaykhutdinov, T.; Sun, G.; Kratz, C.; Rappich, J.; Hinrichs, K.; Nickel, N.H.; Chem. Commun. 53 (2017) 9308.