Abstract
The sensing of small molecules poses the challenge of developing devices able to discriminate between compounds that may be structurally very similar. Here, attention has been paid to the use of self-assembled monolayer (SAM)-protected gold nanoparticles since they enable a modular approach to tune single-molecule affinity and selectivity simply by changing functional moieties (i.e., covering ligands), along with multivalent molecular recognition. To date, the discovery of monolayers suitable for a specific molecular target has relied on trial-and-error approaches, with ligand chemistry being the main criterion used to modulate selectivity and sensitivity. By using molecular dynamics, we showcase that either individual molecular characteristics and/or collective features such as ligand flexibility, monolayer organization, ligand local ordering, and interfacial solvent properties can also be exploited conveniently. The knowledge of the molecular mechanisms that drive the recognition of small molecules on SAM-covered nanoparticles will critically expand our ability to manipulate and control such supramolecular systems.
Highlights
Sensitive, selective chemical and biological sensors are highly demanded in a broad range of applications in chemistry, biology, healthcare, medicine, and environmental protection
Deepening the knowledge of the basic principles governing molecular sensing at the monolayer surface has the potential to critically expand our ability to manipulate self-assembled monolayer (SAM)-AuNP-based devices. To this purpose, taking advantage of the molecular view offered by molecular dynamics (MD) calculations, we show how recognition occurs at the surface of three differently designed SAM-AuNPs, and we decipher which molecular features of both the coating ligand and monolayer affect the identification and discrimination of six small amphiphilic molecules (Scheme 1)
Even though the multivalent nature of these systems is an important feature and synergistic effects between binding sites could arise through cooperative recognition, we focus here on profiling molecular forces and ligand properties regulating the recognition of small molecules on SAM-AuNPs, leaving the detailed investigation of multivalency for a further study
Summary
Selective chemical and biological sensors are highly demanded in a broad range of applications in chemistry, biology, healthcare, medicine, and environmental protection. The development of more efficient, low-cost, versatile, and miniaturized sensors requires continuous advancements in technology, coupled with fundamental knowledge in chemistry, biology, and materials science.[1−3] In. 2012, on recognizing the considerable potential for nanotechnology to facilitate the development of sensitive, adaptable devices for detection, identification, and quantification of substances, the National Nanotechnology Initiative launched its fifth Nanotechnology Signature Initiative (NSI), entitled “Nanotechnology for Sensors and Sensors for Nano-technology: Improving and Protecting Health, Safety, and the Environment” (or the Sensors NSI).[4] Engineered nanomaterials possess characteristics that might advance both the recognition and transduction steps of a probing event, as well as the signal-to-noise ratio, thanks to the miniaturization of the sensor elements.[5,6] sensing at the nanoscale may be viewed as a natural fit. Only a small number of analyte molecules are needed to produce a measurable signal, allowing both a reduction of sample volumes and a miniaturization of sensors.[7]
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