Ultra-large scale AFM of lipid droplet arrays: investigating the ink transfer volume in dip pen nanolithography

Abstract

There are only few quantitative studies commenting on the writing process in dip-pen nanolithography with lipids. Lipids are important carrier ink molecules for the delivery of bio-functional patters in bio-nanotechnology. In order to better understand and control the writing process, more information on the transfer of lipid material from the tip to the substrate is needed. The dependence of the transferred ink volume on the dwell time of the tip on the substrate was investigated by topography measurements with an atomic force microscope (AFM) that is characterized by an ultra-large scan range of 800 × 800 μm(2). For this purpose arrays of dots of the phospholipid1,2-dioleoyl-sn-glycero-3-phosphocholine were written onto planar glass substrates and the resulting pattern was imaged by large scan area AFM. Two writing regimes were identified, characterized of either a steady decline or a constant ink volume transfer per dot feature. For the steady state ink transfer, a linear relationship between the dwell time and the dot volume was determined, which is characterized by a flow rate of about 16 femtoliters per second. A dependence of the ink transport from the length of pauses before and in between writing the structures was observed and should be taken into account during pattern design when aiming at best writing homogeneity. The ultra-large scan range of the utilized AFM allowed for a simultaneous study of the entire preparation area of almost 1 mm(2), yielding good statistic results.

Locally Controlled Growth of Individual Lambda‐Shaped Carbon Nanofibers

“…With increasing cycle number, the volume declines nearly exponentially to a volume of (0.0336 ± 0.0081) µm³ ( n = 5) for the tenth cycle (see dashed line in Figure c). This exponential decline is a well‐known phenomenon in DPN and allows for a controlled writing after conditioning of the tip …”

A diffusive ink transport model for lipid dip-pen nanolithography

“…11 Molecular inkswith the prominent example of the thiol ink on a gold substrate systemhave been widely analyzed and models that encompass not only the surface diffusive stage but also the whole transport process have been developed. Some initial quantitative studies conducted previously addressed the writing process, 15,16 the thickness dependence on the tip speed and humidity, 17 membrane stack organization, 18 and the accurate height characterization of multilayer thickness by precise calibration of fluorescence microscopy. They retain the fluidity aspect of liquid systems, due to their fluid properties.…”

Writing Behavior of Phospholipids in Polymer Pen Lithography (PPL) for Bioactive Micropatterns

“…In L-DPN, feature size strongly depends on the dwell time and—in the case of line writing—on tip speed [4,20,21]. For PPL, feature sizes can be generally dependent on dwell time, but also change with contact pressure (cf.…”

“…However, it is interesting to notice that the absolute area values share the same range throughout the three experiments, in contrast to the intensity values. Altogether, the results indicate that the ink flow rate increases in relation to the environmental RH and to the ink load on the pyramids, similar to L-DPN [21,24]. That the area is less influenced than intensity by the amount of transferred ink indicates that high ink flow rates tend to create multi-layered (hence higher) spots [22].…”

“…When comparing the outcome at different humidity, it can be observed that the variation in feature intensity from different tips (given by the error bars) is—relative to the overall intensity—increasing with decreasing humidity. This implies a more irregular replenishing of lipid ink at the tip apex for lower humidity, compatible with the more viscous state of the lipid ink at low hydration [21].…”