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. Author manuscript; available in PMC: 2014 May 21.
Published in final edited form as: J Am Chem Soc. 2009 Jun 17;131(23):8211–8220. doi: 10.1021/ja901120f

Figure 8.

Figure 8

Functioning of a diode sensor for streptavidin. A) Experimental current-voltage curves for a single conical nanopore whose tip was modified with biotin and exposed to 0.5 μM solution of streptavidin. The measurements were performed in 10 mM KCl and various pH conditions, at which streptavidin was positively charged (pH 4.2, red squares), negatively charged (pH 8.0, blue triangles) or neutral (pH 5.8, green squares). B) Rectification degree measured at different pH for a single conically shaped nanopore with biotin and streptavidin at the tip. The current-voltage curve flipped at the value of pH that corresponds to the protein isoelectric point (pI). Dashed line (---) is a guide to the eye showing Q = 1, i.e. no rectification. The value of pI for surface immobilized streptavidin as determined by our biosensor is ~5.5.