Imbibition of Femtoliter-Scale DNA-Rich Aqueous Droplets into Porous Nylon Substrates by Molecular Printing

Abstract

This work presents the first reported imbibition mechanism of femtoliter (fL)-scale droplets produced by microchannel cantilever spotting (μCS) of DNA molecular inks into porous substrates (hydrophilic nylon). Differently from macroscopic or picoliter droplets, the downscaling to the fL-size leads to an imbibition process controlled by the subtle interplay of evaporation, spreading, viscosity, and capillarity, with gravitational forces being quasi-negligible. In particular, the minimization of droplet evaporation, surface tension, and viscosity allows for a reproducible droplet imbibition process. The dwell time on the nylon surface permits further tuning of the droplet lateral size, in accord with liquid ink diffusion mechanisms. The functionality of the printed DNA molecules is demonstrated at different imbibed oligonucleotide concentrations by hybridization with a fluorolabeled complementary sequence, resulting in a homogeneous coverage of DNA within the imbibed droplet. This study represents a first step toward the μCS-enabled fabrication of DNA-based biosensors and microarrays into porous substrates.

Printed Electrochemical Biosensors: Opportunities and Metrological Challenges

“…Clearly, an amplification of the signal needs to be implemented in order to reach a competitive LOD. Different amplification strategies have been proposed, demonstrating the possibility to reach femtoand atto-molar concentrations of DNA [187,188], thus improving the sensitivity by almost six orders of magnitude compared to standard quantification without amplification [189]. The methods can be grouped into the following categories: (i) enzyme mediated, exploiting the recycle of a single event by the biocatalytic reaction mediated; (ii) nanomaterial-based, exploiting the high surface area of nanoparticles for the high loading of DNA probes [53]; (iii) nucleic acid-based approaches, implementing the local isothermal amplification of the DNA copies before quantification [161].…”

Artificial Biosystems by Printing Biology

“…In order to deposit the droplet to the surface, the Laplace pressure at the tip/meniscus interface has to be larger than that at the meniscus/substrate one. [75][76][77] The difference between the Laplace pressures arises from different curvatures of the liquid/air interface at the tip/meniscus interface as compared with that at the meniscus/substrate one. The size growth of the droplet continues until a saturation is observed due to the variation with time of the droplet surface curvature at the meniscus/substrate and tip/meniscus.…”

Controlled Surface Adhesion of Macrophages via Patterned Antifouling Polymer Brushes

“…Typically, arrays of 20 Â 20 dot features were spotted via μCS, which deposits small femtoliter-sized droplets on a surface. [57] These droplets can act as reaction vessels where click-reactions take place. [58,61,62] After 20 min of binding, the excess ink was washed away and samples were incubated with fluorescently labeled streptavidin to activate the array for macrophage capture.…”

“…Recently, we have shown the use of “clickable” antifouling polymer brushes as substrate for polymer pen lithography (PPL) [ 55 ] to generate click chemistry based arrays to capture proteins. [ 56 ] However, microchannel cantilever spotting (μCS), where femtoliter‐scale microdroplets of ink are transferred to a substrate by a cantilever carrying a microfluidic channel, [ 57 ] offer an ideal feature size for our purposes, closely resembling the targeted cell size [ 58 ] and offers high accuracy in the generation of microarrays. [ 59 ] Therefore, μCS was chosen as lithographic tool in our approach for providing the desired localized highly specific binding places for adhesion of macrophages of different polarization, while preventing unspecific binding of the macrophages and other macromolecules to the substrate.…”