Table 1. Mean square end-to-end distances of the 627 bp fragment at different adsorption/imaging conditions.

	[PL] (mg ml–1)	Deposition conditionsa	L (nm)b	<R2> (nm2)c	Number of molecules
TIF	1.0	10 mM NaCl	200	6300	75
	1.0	50 mM NaCl	195	7500	135
	0.005	10 mM NaCl	197	8300	97
	0.005	50 mM NaCl	188	16 400	68
	0.003	10 mM NaCl	197	16 900	94
	0	10 mM NaCl, 2 mM MgCl2	203	19 600	77
TIA	0.001	50 mM NaCl	198	18 600	50

TIF, tapping in fluid; TIA, tapping in air.

^aThe DNA was bound to the surfaces in 10 mM HEPES, pH 8.0 plus the given salt conditions.

^bThe contour lengths L represent the average length of the DNAs traced and smoothed as described in Materials and Methods (note that eight pixels are removed from the original paths by smoothing).

^cThe theoretical <R²> for a complete surface equilibration of the 627 bp fragment is equal to 22 200 nm² [calculated using equation 9 in Rivetti et al. (29) for the average contour length of the smoothed DNA paths of all samples (197 nm) and a DNA persistence length of 50 nm]. The theoretical value for trapping is 9600 nm² [calculated using equations 10 and 11 in Rivetti et al. (29)].