Chemically assembled monolayers of fluorophores as chemical sensing materials

Abstract

The development of fluorescent chemical sensors has been an active research topic for many research fields. Design strategies play an important role in the sensing performance of the desired sensors. The use of chemically assembled monolayers of fluorophores to fabricate film sensors has shown several advantages: highly stable, re-useable, non-consumptive, and easy to be made into devices, etc. The present tutorial review gives an overview of the fluorescent film sensors based on chemical monolayer assemblies of fluorophores that have been developed in our laboratory along with some representative publications of others over the past decade. Different sensing mechanisms were taken into account in the sensor designs, including hydrogen-bond formation, static complex with quenchers, and more interestingly, the "spacer layer screening effect". Various neutral organic chemicals and anions were targeted by these film sensors with great selectivity and sensitivity. In particular, the specific "spacer layer screening effect" imparts these particular type of films with tuned selectivity, opening a novel direction in developing fluorescent film sensors.

Epoxy-Terminated Self-Assembled Monolayers Containing Internal Urea or Amide Groups

“…7,8,9,10,11 The chemical modification of Si/SiO 2 surfaces by epoxy groups represents an interesting approach for the covalent immobilization of biomolecules containing amino or thiol groups in one step. 12 Generally, the commercially available (3-glycidoxypropyl)trimethoxysilane (GPTS) is used to functionalize the silica surfaces for the chemical immobilization of small molecules, 13,14,15 polymers, 16,17,18 or biomolecules. 19,20 However, in the case of non atomically flat substrates, this short-chain arm can adopt various orientations and some of epoxide groups may not be accessible to the species to immobilize.…”

Recent advances in fluorescent film sensing from the perspective of both molecular design and film engineering

“…In comparison with the others, organic fluorescent dyes were developed first and enjoy enduring popularity. [15][16][17][18] It is notable that fluorescent sensing films have great advantages in device manufacture and this makes them more favorable for practical applications. Therefore, different methods have been developed for organic fluorophore-based sensing, such as directly dispersing organic fluorophores into the analysis medium, doping them into a polymer matrix, employing them to functionalize nanoparticles, and immobilizing them on a solid surface to construct fluorescent sensing films, etc.…”

“…24 The attractive aspects of organic fluorescent dyes lie in their designable structure, ease of characterization and wide range of available choices. [15][16][17][18][25][26][27] In fact, few commercial fluorescent sensors can operate without their sensing films. [15][16][17][18] It is notable that fluorescent sensing films have great advantages in device manufacture and this makes them more favorable for practical applications.…”

“…[15][16][17][18] Accordingly, in the manufacture of fluorescent sensing films, one must realize that: 1) the sensitivity and selectivity of a fluorescent sensing film are influenced by many factors, and their optimization is the most challenging problem; 2) the stability of a sensing film mainly depends on the chemical nature of the fluorophore, the fabrication strategy and the substrate employed; 3) the response speed of a sensing film is determined by the mass transfer of the analyte across the interface between the bulk phase and the sensing layer, as well as within the sensing layer, and the kinetics of the interaction between the analyte and the sensing sites is also an important factor that affects the sensing speed; and 4) the reversibility of a sensing film relies on the reaction mechanism of the sensing process, as well as the mass transfer of the analyte within the sensing layer. [15][16][17][18] Accordingly, in the manufacture of fluorescent sensing films, one must realize that: 1) the sensitivity and selectivity of a fluorescent sensing film are influenced by many factors, and their optimization is the most challenging problem; 2) the stability of a sensing film mainly depends on the chemical nature of the fluorophore, the fabrication strategy and the substrate employed; 3) the response speed of a sensing film is determined by the mass transfer of the analyte across the interface between the bulk phase and the sensing layer, as well as within the sensing layer, and the kinetics of the interaction between the analyte and the sensing sites is also an important factor that affects the sensing speed; and 4) the reversibility of a sensing film relies on the reaction mechanism of the sensing process, as well as the mass transfer of the analyte within the sensing layer.…”

“…3 A fluorescent sensor is the key part of a sensing device and its development involves both the design and engineering of a sensing molecule. [15][16][17][18] In contrast to previous papers, we review recent progress in the development of organic fluorophore-based fluorescent sensing films and focus on the two key issues in the construction of fluorescent sensor devices: molecular design and film engineering. In contrast to research on fluorescence sensing in the early years, researchers now pay more attention to practical applications of fluorescent sensing molecules.…”