Routine and timely sub-picoNewton force stability and precision for biological applications of atomic force microscopy.
Force drift is a significant, yet unresolved, problem in atomic force microscopy (AFM). We show that the primary source of force drift for a popular class of cantilevers is their gold coating, even though they are coated on both sides to minimize drift. Drift of the zero-force position of the cantilever was reduced from 900 nm for gold-coated cantilevers to 70 nm (N = 10; rms) for uncoated cantilevers over the first 2 h after wetting the tip; a majority of these uncoated cantilevers (60%) showed significantly less drift (12 nm, rms). Removing the gold also led to ∼10-fold reduction in reflected light, yet short-term (0.1-10 s) force precision improved. Moreover, improved force precision did not require extended settling; most of the cantilevers tested (9 out of 15) achieved sub-pN force precision (0.54 ± 0.02 pN) over a broad bandwidth (0.01-10 Hz) just 30 min after loading. Finally, this precision was maintained while stretching DNA. Hence, removing gold enables both routine and timely access to sub-pN force precision in liquid over extended periods (100 s). We expect that many current and future applications of AFM can immediately benefit from these improvements in force stability and precision.
JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309, United States.
Allison B
AB
Churnside
Ruby May A
RM
Sullan
Duc M
DM
Nguyen
Sara O
SO
Case
Matthew S
MS
Bull
Gavin M
GM
King
Thomas T
TT
Perkins
D004247:DNA / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D013997:Time Factors
D006046:Gold; D004247:DNA