Evaporative preconcentration and cryopreservation of fluorescent analytes using superhydrophobic surfaces

Abstract

The preconcentration of analytes is important in biochemical analysis as it offers the ability to detect trace species, and increase signal-to-noise ratios when using optical sensing. A strong advantage of the evaporation technique lies in its ability to operate without any external energy source. We have found that the evaporation of droplets on typical surfaces is susceptible to the coffee staining effect that leaves remnant fluorescence on the surface. This is less pronounced with hydrophobic surfaces but shown here to be still significant. The use of a superhydrophobic surface is demonstrated to engender minuscule fluorescent material losses. The difficulty of locating a droplet on this surface is addressed here using wells in which a depth of 0.51 mm with 7 ml analyte volume was found to accommodate a comfortable tilt working range of up to 19 . Experiments revealed preconcentration rates to be faster with lower humidity but maximal concentrations were achieved using 50% relative humidity. We have also shown the ability to attain solid-liquid state changes of the spherical shaped droplets of analytes using subzero temperatures. This allows for tandem preconcentration and cryopreservation without any analyte transfer, leading to the advantages of minimal sample handling loss and contamination. With EGFP used as a model protein, we found no deterioration in fluorescence for up to 8 freeze-thaw cycles.

Liquid Body Formation from a Semispherical Superhydrophobic Well on a Small Incline

“…11,12,20 The introduction of a semispherical well on the SH surface presents a possible capacity to support additional hysteresis of the drop through the edges (of the well). The capability of edges to provide additional constraining on liquids has been harnessed in various applications.…”

Particle deposition after droplet evaporation on ultra-hydrophobic micro-textured surfaces

“…This phenomenon opens the possibility to sort and extract individual particles, which has many practical interests: for instance in biological cells sorting or in catalysis localization in epitaxial growth. This has also important consequences in evaporation-induced preconcentration of cells suspensions [24,25].…”

A superhydrophobic manhole for drops

“…5,6 More recently, this has been extended to the sensing of nanoparticles 7 which despite their many advantageous features can be harmful if inadvertently released to the environment. [11][12][13] In the process of evaporative pre-concentration, it is desirable to have the lowest area of solid-liquid contact and adhesion to minimize entity deposition on the solid substrate. [11][12][13] In the process of evaporative pre-concentration, it is desirable to have the lowest area of solid-liquid contact and adhesion to minimize entity deposition on the solid substrate.…”