Surface-enhanced infrared attenuated total reflection spectroscopy based on carbon nanomaterials

Abstract

This cumulative dissertation focuses on studying the potential of carbon nanomaterials in surface-enhanced infrared absorption (SEIRA) spectroscopy, which is based on four peer-reviewed journal articles. The introduction of this dissertation outlines the motivation and theoretical background. Namely, fundamentals and challenges of SEIRA as well as conventional Fourier transform infrared (FTIR) spectroscopy are introduced. As promising enhancing materials serving as SEIRA substrates, carbon nanomaterials, and particularly graphene, graphene oxide, and carbon-based nanodots are highlighted in respect of their extraordinary properties and advantages vs. commonly used noble metals. Given the advantage of analyzing aqueous samples with enhanced sensitivity, infrared attenuated total reflection (ATR) configurations are beneficial to SEIRA applications with the basic principles and merits likewise introduced. Latest progress, applications, and challenges in SEIRA spectroscopy utilizing graphene-based nanomaterials as the signal-enhancing substrate are reviewed in an associated journal article.

The research presented in this dissertation provides innovative platforms for SEIRA sensing, in particular in-situ and real-time SEIRA monitoring of molecular species in aqueous environments. Firstly, graphene-decorated ATR prisms serving as a novel and efficient platform for simultaneously enhancing multiple characteristic IR bands of molecules in aqueous phase was successfully developed for the first time, and also enabled recording the temporal evolution of the entire molecular vibrational fingerprints. Generic applicability of the proposed platform was verified via various molecules with aromatic moieties.

Secondly, readily obtained water-dispersible carbon nanodots (CNDs) that were drop-casted onto the ATR waveguide surface have demonstrated the pronounced ability to notably enhance the IR signals of a variety of analytes in aqueous solutions. The potential of this CNDs-based SEIRA was further confirmed by quantitatively assaying adenine solutions at low concentration levels in a label-free fashion.

Thirdly, graphene oxide (GO) with distinct advantages vs. hydrophobic graphene including excellent water dispersibility, ease of preparation, and capability to interact with a wider range of molecules based on non-covalent interactions has been proved an even more universally applicable material inducing selective chemical enhancement in SEIRA scenarios. In addition, GO eliminated potential interferences from dispersing agents or processing residues common to procedures involving graphene.

Consequently, carbon nanomaterials-based SEIRA methods established in this dissertation have demonstrated (i) pronounced IR signal enhancement effects, (ii) simple experimental procedures, and (iii) convenient operation free from toxic agents, harsh experimental conditions, and sophisticated fabrication/sampling routines. Last but not least, these studies are of particular importance for facilitating fundamental understanding on the chemical enhancement mechanisms in SEIRA spectroscopy.