Abstract: Improved methods for preparing thiolate passivated gold nanoparticles are provided resulting in a narrower size distribution. By alternating oxidation and reduction of the particles, after oxidation, the thiolates may be readily displaced with a different thiol, followed by reduction to prevent further reaction. Proteins can be rigidly bound to the gold nanoparticles by binding an scFv for a target protein to the gold nanoparticles, where the scFv prior or subsequent to binding to the gold nanoparticles may be complexed with the target protein. The protein is rigidly held and its structure readily determined using electron microscopy.