Metal binding colloidal gold particles: A versatile scanning force microscope tip calibrator for fluid imaging

One of the primary difficulties of imaging under aqueous solution with the scanning force microscope (SFM) is a lack of reliable tip characterization. The requirements of imaging under solution greatly limit the utility of av ailable standards. We report the synthesis of metal binding colloidal gold (MBG) which allows direct deconvolution of tip shape during sample imaging. Divalent metal ions have been used extensively for binding samples to mica for SFM in fluid, especially biological samples such as DNA. The MBG synth esized here can be imaged bound to mica, demonstrating their usefulness for fluid SFM. Their diameter has been measured and is consistent with the exp ected value. They are shown to be robust to repeated imaging and stable in a variety of conditions. Their ability to be imaged is inhibited by the pre sence of a metal chelator. Finally, these gold particles, in conjunction wi th computational image restoration methods, have been used to analyze plasm id DNA images obtained in aqueous solution. Enabling colloidal gold particl es to bind metals through the attachment of a synthesized polypeptide allow s simpler and faster tip calibration in aqueous solution than calibrations obtained by previously described methods.