ABSTRACT
Spurred by outstanding optical properties, chemical stability, and facile bioconjugation, plasmonic metals have become the first-choice materials for optical signal transducers in biosensing. While the design rules for surface-based plasmonic sensors are well-established and commercialized, there is limited knowledge of the design of sensors based on nanoparticle aggregation. The reason is the lack of control over the interparticle distances, number of nanoparticles per cluster, or multiple mutual orientations during aggregation events, blurring the threshold between positive and negative readout. Here we identify the geometrical parameters (size, shape, and interparticle distance) that allow for maximizing the color difference upon nanoparticle clustering. Finding the optimal structural parameters will provide a fast and reliable means of readout, including unaided eye inspection or computer vision.
Subject(s)
Gold , Metal Nanoparticles , Gold/chemistry , Metal Nanoparticles/chemistry , ColorimetryABSTRACT
Plasmonic catalysis in the colloidal phase requires robust surface ligands that prevent particles from aggregation in adverse chemical environments and allow carrier flow from reagents to nanoparticles. This work describes the use of a water-soluble conjugated polymer comprising a thiophene moiety as a surface ligand for gold nanoparticles to create a hybrid system that, under the action of visible light, drives the conversion of the biorelevant NAD+ to its highly energetic reduced form NADH. A combination of advanced microscopy techniques and numerical simulations revealed that the robust metal-polymer heterojunction, rich in sulfonate functional groups, directs the interaction of electron-donor molecules with the plasmonic photocatalyst. The tight binding of polymer to the gold surface precludes the need for conventional transition-metal surface cocatalysts, which were previously shown to be essential for photocatalytic NAD+ reduction but are known to hinder the optical properties of plasmonic nanocrystals. Moreover, computational studies indicated that the coating polymer fosters a closer interaction between the sacrificial electron-donor triethanolamine and the nanoparticles, thus enhancing the reactivity.
Subject(s)
Gold , Metal Nanoparticles , Catalysis , Gold/chemistry , Light , Metal Nanoparticles/chemistry , PolymersABSTRACT
The colloidal stability of metal nanoparticles is tremendously dependent on the thermal behavior of polymer brushes. Neat polyethylene glycol (PEG) presents an unconventional upper critical solution temperature in ethanol, where phase segregation and crystallization coexist. This thermal behavior translated to a PEG brush has serious consequences on the colloidal stability in ethanol of gold nanoparticles (AuNPs) modified with PEG brushes upon cooling. We observed that AuNPs (13 nm diameter) stabilized with conventional linear PEG brushes (Mn = 6 and 11 kg mol-1) in ethanol suffer from reversible phase separation upon a temperature drop over the course of a few hours. However, the use of a polymer brush with cyclic topology as a stabilizer prevents sedimentation, ensuring the colloidal stability in ethanol at -25 °C for, at least, four months. We postulate that temperature-driven collapse of chain brushes promotes the interpenetration of linear chains, causing progressive AuNP sedimentation, a process that is unfavorable for cyclic polymer brushes whose topology prevents chain interpenetration. This study reinforces the notion about the importance of polymer topology on the colloidal stability of AuNPs.
ABSTRACT
Circulating DNA (ctDNA) and specifically the detection cancer-associated mutations in liquid biopsies promises to revolutionize cancer detection. The main difficulty however is that the length of typical ctDNA fragments (â¼150 bases) can form secondary structures potentially obscuring the mutated fragment from detection. We show that an assay based on gold nanoparticles (65 nm) stabilized with DNA (Au@DNA) can discriminate single nucleotide polymorphism in clinically relevant ssDNA sequences (70-140 bases). The preincubation step was crucial to this process, allowing sequential bridging of Au@DNA, so that single base mutation can be discriminated, down to 100 pM concentration.
Subject(s)
DNA/genetics , Gold/chemistry , Metal Nanoparticles/chemistry , Polymorphism, Single Nucleotide , Base Sequence , Biosensing Techniques/methods , DNA/chemistry , Immobilized Nucleic Acids/chemistry , Immobilized Nucleic Acids/geneticsABSTRACT
The remote release of nano-objects from a container is a promising approach to transduce chemical events into an optical signal. The major challenge in the development of such a system involves the use of a suitable molecular gate that retains aggregated particles and releases them upon applying an external stimulus. We show proof-of-concept experiments for the release of gold nanoparticles into an aqueous solution upon photodegradation of conjugated polymer thin films. Gold nanoparticles thus transduce light-induced chemical events into an amplified optical signal with a release rate of 2.5 nM per hour, which can be readily detected by the naked eye.
