Wettability-based ultrasensitive detection of amphiphiles through directed concentration at disordered regions in self-assembled monolayers

Abstract

Various forms of ecological monitoring and disease diagnosis rely upon the detection of amphiphiles, including lipids, lipopolysaccharides, and lipoproteins, at ultralow concentrations in small droplets. Although assays based on droplets’ wettability provide promising options in some cases, their reliance on the measurements of surface and bulk properties of whole droplets (e.g., contact angles, surface tensions) makes it difficult to monitor trace amounts of these amphiphiles within small-volume samples. Here, we report a design principle in which self-assembled monolayer–functionalized microstructured surfaces coated with silicone oil create locally disordered regions within a droplet’s contact lines to effectively concentrate amphiphiles within the areas that dominate the droplet static friction. Remarkably, such surfaces enable the ultrasensitive, naked-eye detection of amphiphiles through changes in the droplets’ sliding angles, even when the concentration is four to five orders of magnitude below their critical micelle concentration. We develop a thermodynamic model to explain the partitioning of amphiphiles at the contact line by their cooperative association within the disordered, loosely packed regions of the self-assembled monolayer. Based on this local analyte concentrating effect, we showcase laboratory-on-a-chip surfaces with positionally dependent pinning forces capable of both detecting industrially and biologically relevant amphiphiles (e.g., bacterial endotoxins), as well as sorting aqueous droplets into discrete groups based on their amphiphile concentrations. Furthermore, we demonstrate that the sliding behavior of amphiphile-laden aqueous droplets provides insight into the amphiphile’s effective length, thereby allowing these surfaces to discriminate between analytes with highly disparate molecular sizes.

Advancements in droplet reactor systems represent new opportunities in chemical reactor engineering: A perspective

“…The topographies of slippery isotropic liquid-infused porous surfaces are independent of the measuring direction, and the physical properties remain constant throughout the material. [142] They have shown great potential for applications in biomedical detection [143][144][145][146][147] and water harvesting. [148] To date, most reported research has focused on the manipulation of droplet movement on these surfaces using a variety of electric, [149] thermal, [150,151] and magnetic stimuli.…”

Endotoxinanalytik: Alternative zum Pfeilschwanzkrebs

“…Für dieses Verteilungsverhalten des Analyten gibt es ein thermodynamisches Modell. 8) Die gelöcherten Oberflächen ermöglichen es nach Yao et al, Endotoxine bei Konzentrationen von vier bis fünf Größenordnungen unterhalb der kritischen Mizellbildungskonzentrationen (CMA) mit dem bloßen Auge zu detektieren. Für die Zukunft wird es darauf ankommen, die Versuchsbedingungen auf Endotoxine oder auch auf Lipide, Lipopolysaccharide, Lipoproteine oder andere Amphiphile zu optimieren.…”

A phenothiazine-functionalized pyridine-based AIEE-active molecule: a versatile molecular probe for highly sensitive detection of hypochlorite and picric acid

“…[24][25][26] Meanwhile, anion-responsive ligand-functionalized conjugated nanoparticles provide accurate and sensitive anion detection mechanisms through uorescence quenching or enhancement mechanisms. 27,28 Phenothiazine-based conjugated compounds exhibit high sensing performance due to their strong uorescence properties, [29][30][31] and the sulfur atom shows the interaction ability towards anions like ClO − . The compounds which contain nitrogen heteroatoms have shown interactions with picric acid.…”