Decoupling competing surface binding kinetics and reconfiguration of receptor footprint for ultrasensitive stress assays

Cantilever arrays have been used to monitor biochemical interactions and their associated stress. However, it is often necessary to passivate the underside of the cantilever to prevent

unwanted ligand adsorption, and this process requires tedious optimization. Here, we show a way to immobilize membrane receptors on nanomechanical cantilevers so that they can function

without passivating the underlying surface. Using equilibrium theory, we quantitatively describe the mechanical responses of vancomycin, human immunodeficiency virus type 1 antigens and

coagulation factor VIII captured on the cantilever in the presence of competing stresses from the top and bottom cantilever surfaces. We show that the area per receptor molecule on the

cantilever surface influences ligand–receptor binding and plays an important role on stress. Our results offer a new way to sense biomolecules and will aid in the creation of ultrasensitive

biosensors.

We thank the EPSRC Grand Challenge in Nanotechnology for Healthcare (EP/G0620064/1), I-sense EPSRC IRC in Early Warning Sensing Systems for Infectious Diseases (EP/G062064/1), Royal Society

(RS), Targanta Therapeutics, Bio Nano Consulting (BNC), the European Union FP7 Project VSMMART Nano (managed by BNC) for funding. The authors also thank J. Russat (London Centre for

Nanotechnology), S. Sivachelvam (London Centre for Nanotechnology), M. Rehak (Sphere Fluidics, UK), R.A. Weiss (University College London) C.T. Verrips (QVQuality, Utrecht), T. Philips

(Utrecht University), M. Morfini (University of Florence), T. Cass (Imperial College), V. Emery (Surrey Business School) and G. Aeppli (Paul Scherrer Institut) for the kind gift of materials

and for helpful discussions. The glycoprotein antigens (gp140CN54 and gp140UG37) to llama antibody fragments were provided by the Centre for AIDS Reagents, National Institute for Biological

Standards and Control (NIBSC) of the UK Medicines & Healthcare Products Regulatory Agency (MHRA).

Samadhan B. Patil, Manuel Vögtli, Benjamin Webb and Joseph W. Ndieyira: These authors contributed equally to this work

London Centre for Nanotechnology and Departments of Medicine and Physics, University College London, 17–19 Gordon Street, London, WC1H 0AH, UK

Samadhan B. Patil, Manuel Vögtli, Benjamin Webb, Rachel A. McKendry & Joseph W. Ndieyira

Department of Materials, Imperial College London, London, SW7 2AZ, UK

Division of Infection & Immunity, University College London, Cruciform Building, Gower Street, London, WC1E 6BT, UK

UCL Institute for Liver and Digestive Health, Royal Free Hospital, London, NW3 2QG, UK

Department of Chemistry, Jomo Kenyatta University of Agriculture and Technology, Nairobi, PO Box 62000, Kenya

J.W.N. designed the experiments. J.W.N. and M.V. performed the experiments on antibiotics. J.W.N., S.B.P. and B.W. performed the experiments on HIV antigen detections. J.W.N. and S.B.P.

formulated the mathematical model to decouple competing surface binding kinetics at Au (top surface of cantilever) and Si (bottom surface of cantilever). J.W.N. performed the experiments on

blood clotting proteins and wrote the paper. All authors discussed the results and commented on the manuscript.

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