Langmuir Monolayer Flow across Hydrophobic Surfaces. 2. Sensor Development Using Langmuir Monolayer Flow

Abstract

Two sensing mechanisms utilizing Langmuir monolayer flow, the pressure-driven movement of a Langmuir film into a hydrophobic surface−liquid interface, have been investigated and involve analyte interaction with either the flowing monolayer or stationary film. The sensing aspect is achieved through modulation of the bilayer formation rate. A sensor using this novel transduction mechanism was developed for Cd2+, based on the interaction of divalent cations with the carboxylic headgroup of the flowing monolayer. Aqueous divalent cations associate with an oleic acid monolayer, increasing its viscosity. As a result, the flow rate of the associated monolayer is slower than for the unassociated monolayer. A rudimentary pH sensor was also developed to exemplify flow-based sensing, in which oleyl alcohol flows into the interface between a mixed methyl-carboxylic acid terminated self-assembled monolayer modified gold electrode and water. The flow rate for this system was sensitive to subphase pH. Attenuation of the monolayer flow rate is dependent upon the relative surface concentration of the carboxylic acid moiety in the multicomponent surface monolayer. The major contribution to the modulation of the monolayer flow rate in this system is attributed to solvation thermodynamics of the carboxylate anion macroscopically averaged across the modified electrode surface.

Polymerization of a Cysteinyl Peptidolipid Langmuir Film

“…A Langmuir film at the air−water interface represents a thin film technique that has broad applications in many important disciplines such as chemo- and biosensor developments, , building blocks for nanomaterials, and a model system for mimicking biointerfaces and their functions . At air−solid interfaces, a Langmuir−Blodgett (LB) film and a self-assembled monolayer (SAM) are both thin film techniques that have been well studied. − LB films are physically adsorbed onto the solid substrate surface, while self-assembled monolayers are covalently bonded to the substrate material .…”

Naked-Eye Cadmium Sensor: Using Chromoionophore Arrays of Langmuir−Blodgett Molecular Assemblies

“…Langmuir−Blodgett (L-B) thin-film technique has been a key manufacturing tool in nanotechnology, with applications ranging from biotechnology (membranes and biosensors), gas sensors, and electronic devices to lithography. − Interest in L-B technique is fueled by its merits, which include (a) precise control of the monolayer thickness, (b) homogeneous deposition of the monolayers over large areas, and (c) the possibility of generating multilayer structures with varying layer composition on almost any kind of solid substrate. , It has been observed that L-B monolayers of metal complexes have properties similar to those of supramolecular structures involved in the biosensing of Li + , Na + , K + , Ca 2+ , etc. , Therefore, incorporation of L-B molecular layers of chelating groups onto solid platforms is expected to reveal meaningful applications in sensing techniques and other fundamental studies. However, such implications of L-B film monolayers in toxicity validation have remained only vague conjecture, especially in the emerging areas of naked-eye sensing.…”