Characterization of single 1.8-nm Au nanoparticle attachments on AFM tips for single sub-4-nm object pickup
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NANO EXPRESS
Open Access
Characterization of single 1.8-nm Au nanoparticle attachments on AFM tips for single sub-4-nm object pickup Hui-Wen Cheng1, Yuan-Chih Chang2, Song-Nien Tang3, Chi-Tsu Yuan4, Jau Tang5 and Fan-Gang Tseng1,5*
Abstract This paper presents a novel method for the attachment of a 1.8-nm Au nanoparticle (Au-NP) to the tip of an atomic force microscopy (AFM) probe through the application of a current-limited bias voltage. The resulting probe is capable of picking up individual objects at the sub-4-nm scale. We also discuss the mechanisms involved in the attachment of the Au-NP to the very apex of an AFM probe tip. The Au-NP-modified AFM tips were used to pick up individual 4-nm quantum dots (QDs) using a chemically functionalized method. Single QD blinking was reduced considerably on the Au-NP-modified AFM tip. The resulting AFM tips present an excellent platform for the manipulation of single protein molecules in the study of single protein-protein interactions. Keywords: Au nanoparticle; AFM; Quantum dots; Blinking
Background Scanning tunneling microscopy (STM) [1] and atomic force microscopy (AFM) [2] have revolutionized surface sciences by enabling the study of surface topography and other surface properties at the angstrom-to-micrometer scale. The three major functions of AFM include imaging, spectroscopy (i.e., force-distance curve), and manipulation (nanolithography). AFM techniques employ a very sharp tip as a probe to scan and image surfaces. Spectroscopic information is acquired through forces generated between the tip and the sample when the probe is brought into proximity with the sample surface, according to Hooke's law. Xie et al. [3] classified nanolithographic techniques into two groups: force-assisted and bias-assisted nanolithography. In AFM, the interactive force between the tip of the probe and the sample surface is determined according to the deflection of a microfabricated cantilever with the tip positioned at the free end. Modifying the probe enables researchers to explore a range of surface characteristics. AFM probes with individual microparticles or nanoparticles * Correspondence: [email protected] 1 Department of Engineering and System Science, National Tsing Hua University, 101, Section 2, Kuang-Fu Road, Hsinchu 30013, Taiwan 5 Research Center for Applied Sciences, Academia Sinica, 128, Section 2, Academia Road, Taipei 11529, Taiwan Full list of author information is available at the end of the article
attached to the cantilever/tip have been widely used to measure surface forces in AFM and near-field scanning optical microscopy (NSOM) [4] as the geometry and composition of the particle can be well controlled. Ducker et al. [5,6] were pioneers in the attachment of microspheres to a tipless AFM cantilever with resin. Their colloidal probe technique employed a laser-pulled micropipette attached to an optical microscope. Mak et al. [7] improved this method through their dual wire technique, in which glue and a microsphere are simultaneously applied to a cantileve
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