Biofunctionalization of carbon nanofiber tips for scanning probe microscopy using thin Au coating and immobilized biorecognition molecules

Individual carbon nanofibers (CNFs) synthesized on the apices of tetrahedral-type Si cantilever tips via argon-ion (Ar⁺) bombardment, i.e., CNF-tipped scanning probe microscopy (SPM) probes, were sputter coated with a Au film without undergoing any obvious deformations. Indentations made using the Au-coated CNF tips showed that the buckling force of the tips increased with the thickness of the Au film. The CNF tip coated with a thin Au film less than approximately 8 nm in thickness elastically buckled when subjected to mechanical deflection, which was similar to the bare CNF tips. After annealing the Au-coated CNF-tipped SPM probes, we biofunctionalized them by immobilizing thiol-derivatized, single-stranded DNA (ssDNA) molecules, used as representative biorecognition molecules, on the Au(1 1 1)-coated surfaces. The ability of the immobilized ssDNA molecules to bind with complimentary RNA targets was confirmed via field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy-based analysis of quantum dots bound to the ssDNA/RNA hybrids formed on the surfaces of the biofunctionalized CNF-tipped SPM probes.