AC electrokinetic immobilization of organic dye molecules

Eva-Maria Laux,Ralph Hölzel,Frank F Bier,Christian Wenger

doi:10.1007/s00216-020-02480-4

Abstract

The application of inhomogeneous AC electric fields for molecular immobilization is a very fast and simple method that does not require any adaptions to the molecule’s functional groups or charges. Here, the method is applied to a completely new category of molecules: small organic fluorescence dyes, whose dimensions amount to only 1 nm or even less. The presented setup and the electric field parameters used allow immobilization of dye molecules on the whole electrode surface as opposed to pure dielectrophoretic applications, where molecules are attracted only to regions of high electric field gradients, i.e., to the electrode tips and edges. In addition to dielectrophoresis and AC electrokinetic flow, molecular scale interactions and electrophoresis at short time scales are discussed as further mechanisms leading to migration and immobilization of the molecules.Graphical

Highlights

Spatial manipulation and immobilization of small objects is a central experimental step in a broad spectrum of scientific applications that aim at ordered structures in the nanorange as well as in bioanalytic applications, where analytes of interest can be concentrated or moved to specific sites for further reactions or detection
Their distribution onto electrode tips, bases, and surfaces was dependent on the applied frequency, and it was monitored in real time by fluorescence microscopy
Regions of interest were chosen at the tips, bases, and surfaces of the electrodes to cover all types of areas that are expected to attract differing amounts of molecules with the amounts being influenced mainly by the curvature of the electrode structure, causing electric field inhomogeneities, and a stronger dielectrophoretic force. 10 regions of interest were selected for the tips, bases, and surfaces each

Summary

Introduction

Spatial manipulation and immobilization of small objects is a central experimental step in a broad spectrum of scientific applications that aim at ordered structures in the nanorange as well as in bioanalytic applications, where analytes of interest can be concentrated or moved to specific sites for further reactions or detection. The objects’ dimensions that have been spatially manipulated by dielectrophoretic forces are getting smaller and smaller, from biological objects like cells [1] with dimensions of tens of micrometers or carbon nanotubes with diameters of few nanometers and lengths of several micrometers [2], reaching down to nanoparticles with diameters of only a few nanometers in all three dimensions [3], e.g., zinc oxide nanoparticles with a diameter of 9 nm [4], core-shell CdSe quantum dots with a diameter of 8 nm [5], or gold nanoparticles as small as 5 nm [6] or 2 nm [7] in diameter. Protein sizes are typically in the low nanometer range in all three dimensions, and they belong to the smallest objects handled in AC electrokinetic experiments so far

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Discussion

Conclusion