Engineering of Surface Chemistry for Enhanced Sensitivity in Nanoporous Interferometric Sensing Platforms

Abstract

We explore new approaches to engineering the surface chemistry of interferometric sensing platforms based on nanoporous anodic alumina (NAA) and reflectometric interference spectroscopy (RIfS). Two surface engineering strategies are presented, namely (i) selective chemical functionalization of the inner surface of NAA pores with amine-terminated thiol molecules and (ii) selective chemical functionalization of the top surface of NAA with dithiol molecules. The strong molecular interaction of Au ions with thiol-containing functional molecules of alkane chain or peptide character provides a model sensing system with which to assess the sensitivity of these NAA platforms by both molecular feature and surface engineering. Changes in the effective optical thickness of the functionalized NAA photonic films (i.e., sensing principle), in response to gold ions, are monitored in real-time by RIfS. 6-Amino-1-hexanethiol (inner surface) and 1,6-hexanedithiol (top surface), the most sensitive functional molecules from approaches i and ii, respectively, were combined into a third sensing strategy whereby the NAA platforms are functionalized on both the top and inner surfaces concurrently. Engineering of the surface according to this approach resulted in an additive enhancement in sensitivity of up to 5-fold compared to previously reported systems. This study advances the rational engineering of surface chemistry for interferometric sensing on nanoporous platforms with potential applications for real-time monitoring of multiple analytes in dynamic environments.

Critical assessment of relevant methods in the field of biosensors with direct optical detection based on fibers and waveguides using plasmonic, resonance, and interference effects

“…It allows the measurement by RIfS the concentration of organic compounds down to a few parts per million [374]. Approaches to engineer the surface chemistry for interferometric sensing platforms based on this nanoporous anodic alumina is given in [375] whereby RIfS is monitoring in real time. Protein-modified nanoporous anodic alumina platforms can be finally used to observe binding interactions of blood proteins.…”

“…Protein-modified nanoporous anodic alumina platforms can be finally used to observe binding interactions of blood proteins. An example is an assessment of the binding affinity between Hg and transferrin-functionalized pores [375]. Finally, streptavidin-biotin complexes are used to measure thrombin [376].…”

Nanoporous Anodic Alumina Photonic Crystals for Optical Chemo- and Biosensing: Fundamentals, Advances, and Perspectives

“…The sulfhydryl or disulfide moiety of organosulfur molecules has strong affinity toward gold, leading to relatively strong bonds that form stable SAMs [ 120 , 121 ]. The resulting organosulfur-based SAMs can be used for various applications such as support layer for lipid bilayer formation [ 122 ] as well as further functionalization for chemo- and biosensing [ 123 ]. Alkene and alkynes are able to form SAMs on NAA by thermally-induced wet chemical technique [ 97 , 124 ].…”

“…Law et al developed a sensing system combining NAA-FPIs and RIfS to monitor gold–thiol interaction [ 123 ]. NAA-FPIs were functionalized with a range of thiol-containing with different molecular features and backbone sizes.…”

“…Law et al combined NAA-PC platforms with RIfS to develop a sensing system able to monitor in real-time the formation of self-assembled monolayers of thiol molecules ( Figure 14 a,b) [ 123 ]. NAA-PCs with effective medium modulated in a sawtooth-like fashion were coated with gold and exposed to different concentrations of 11-mercaptoundecanoic acid (11-MUA).…”