Modification of Indium Tin Oxide with Dendrimer-Encapsulated Nanoparticles To Provide Enhanced Stable Electrochemiluminescence of Ru(bpy)₃²⁺/Tripropylamine While Preserving Optical Transparency of Indium Tin Oxide for Sensitive Electrochemiluminescence-Based Analyses

Here, we report highly enhanced stable electrogenerated chemiluminescence (ECL) of Ru­(bpy)₃²⁺ (bpy = 2,2′-bipyridyl) with tripropylamine (TPrA) coreactant on indium tin oxide (ITO) electrodes modified with amine-terminated dendrimers encapsulating catalytic nanoparticles while maintaining optical transparency of ITO and feasibility of the modified ITOs to sensitive ECL-based assays. As model systems, we prepared Pt and Au dendrimer-encapsulated nanoparticles (DENs) using amine-terminated sixth-generation poly­(amido amine) dendrimers and subsequently immobilized the DENs onto ITO surfaces via electrooxidative grafting of the terminal amines of dendrimers to the surfaces. The resulting DEN-modified ITOs preserved good optical transparency of ITO and exhibited highly catalyzed electrochemical oxidation of Ru­(bpy)₃²⁺/TPrA, leading to significantly increased ECL emission. Especially, the Pt DEN-modified ITO electrode provides negligible transmittance drop, i.e., only ∼1.99% over the entire visible region, and exhibited not only much enhanced (i.e., ∼213-fold increase compared to ECL obtained from bare ITO) but also stable ECL emission under consecutive potential scans from 0.00 to 1.10 V for 10 cycles, which allowed ∼329 times more sensitive ECL-based analysis of nicotine using the Pt DEN-modified ITO compared with the use of bare ITO

Tailoring Catalytic Activity of Pt Nanoparticles Encapsulated Inside Dendrimers by Tuning Nanoparticle Sizes with Subnanometer Accuracy for Sensitive Chemiluminescence-Based Analyses

Here, we report the size-dependent catalysis of Pt dendrimer-encapsulated nanoparticles (DENs) having well-defined sizes over the range of 1–3 nm with subnanometer accuracy for the highly enhanced chemiluminescence of the luminol/H₂O₂ system. This size-dependent catalysis is ascribed to the differences in the chemical states of the Pt DENs as well as in their surface areas depending on their sizes. Facile and versatile applications of the Pt DENs in diverse oxidase-based assays are demonstrated as efficient catalysts for sensitive chemiluminescence-based analyses

Repetitively Coupled Chemical Reduction and Galvanic Exchange as a Synthesis Strategy for Expanding Applicable Number of Pt Atoms in Dendrimer-Encapsulated Pt Nanoparticles

In this study, we report the controllable synthesis of dendrimer-encapsulated Pt nanoparticles (Pt DENs) utilizing repetitively coupled chemical reduction and galvanic exchange reactions. The synthesis strategy allows the expansion of the applicable number of Pt atoms encapsulated inside dendrimers to more than 1000 without being limited by the fixed number of complexation sites for Pt²⁺ precursor ions in the dendrimers. The synthesis of Pt DENs is achieved in a short period of time (i.e., ∼10 min) simply by the coaddition of appropriate amounts of Cu²⁺ and Pt²⁺ precursors into aqueous dendrimer solution and subsequent addition of reducing agents such as BH₄^–, resulting in fast and selective complexation of Cu²⁺ with the dendrimers and subsequent chemical reduction of the complexed Cu²⁺ while uncomplexed Pt²⁺ precursors remain oxidized. Interestingly, the chemical reduction of Cu²⁺, leading to the formation of Cu nanoparticles encapsulated inside the dendrimers, is coupled with the galvanic exchange of the Cu nanoparticles with the nearby Pt²⁺. This coupling repetitively proceeds until all of the added Pt²⁺ ions form into Pt nanoparticles encapsulated inside the dendrimers. In contrast to the conventional method utilizing direct chemical reduction, this repetitively coupled chemical reduction and galvanic exchange enables a substantial increase in the applicable number of Pt atoms up to 1320 in Pt DENs while maintaining the unique features of DENs

Enhanced Electrogenerated Chemiluminescence of Phenylethynylpyrene Derivatives: Use of Weakly Electron-Donating Group as a Substituent

A weakly donating group (<i>n</i>-propyl) has been used as a substituent at the <i>para</i>-position of the phenyl group for a series of phenylethynylpyrene derivatives where the number of phenylethynyl peripheral arms appended to the pyrene core is varied. This system markedly improved the concurrent stability of both cation and anion radicals and consequently greatly improved electrogenerated chemiluminescence (ECL). Density functional theory (DFT)-based theoretical calculations supported the associated photophysical and electrochemical properties of the series compounds

Enhanced Electrogenerated Chemiluminescence of Phenylethynylpyrene Derivatives: Use of Weakly Electron-Donating Group as a Substituent

A weakly donating group (<i>n</i>-propyl) has been used as a substituent at the <i>para</i>-position of the phenyl group for a series of phenylethynylpyrene derivatives where the number of phenylethynyl peripheral arms appended to the pyrene core is varied. This system markedly improved the concurrent stability of both cation and anion radicals and consequently greatly improved electrogenerated chemiluminescence (ECL). Density functional theory (DFT)-based theoretical calculations supported the associated photophysical and electrochemical properties of the series compounds

Peptide Arrays Identify Isoform-Selective Substrates for Profiling Endogenous Lysine Deacetylase Activity

This paper reports the development of a class of isoform-selective peptide substrates for measuring endogenous lysine deacetylase (KDAC) activities in cell culture. The peptides were first identified by comparing the substrate specificity profiles of the four KDAC isoforms KDAC2, KDAC3, KDAC8, and sirtuin 1 (SIRT1) on a 361-member hexapeptide array wherein the two C-terminal residues to the acetylated lysine were varied. The arrays were prepared by immobilizing the peptides to a self-assembled monolayer of alkanethiolates on gold and could therefore be analyzed by a mass spectrometry technique termed SAMDI (self-assembled monolayers for matrix assisted laser desorption/ionization time-of-flight mass spectrometry). Arrays presenting the selective substrates were treated with nuclear extracts from HeLa, Jurkat, and smooth muscle cells and analyzed to measure endogenous deacetylase activities. We then use the arrays to profile KDAC activity through the HeLa cell cycle. We find that the activity profile of the KDAC3 selective peptide closely mirrors the changing acetylation state of the H4 histone, suggesting a role for this enzyme in cell cycle regulation. This work is significant because it describes a general route for identifying selective substrates that can be used to understand the differential roles of members of the deacetylase enzyme family in complex biological processes and further because the label-free approach avoids perturbation of enzyme activity that has plagued fluorescence-based assays

Spontaneous Pt Deposition on Defective Surfaces of In₂O₃ Nanocrystals Confined within Cavities of Hollow Silica Nanoshells: Pt Catalyst-Modified ITO Electrode with Enhanced ECL Performance

Although the deposition of metallic domains on a preformed semiconductor nanocrystal provides an effective pathway to access diverse hybrid nanocrystals with synergistic metal/semiconductor heterojunction interface, those reactions that take place on the surface of semiconductor nanoscrystals have not been investigated thoroughly, because of the impediments caused by the surface-capping organic surfactants. By exploiting the interfacial reactions occurring between the solution and nanoparticles confined with the cavities of hollow nanoparticles, we propose a novel nanospace-confined strategy for assessing the innate reactivity of surfaces of inorganic semiconductor nanoparticles. This strategy was adopted to investigate the newly discovered process of spontaneous Pt deposition on In₂O₃ nanocrystals. Through an in-depth examination involving varying key reaction parameters, the Pt deposition process was identified to be templated by the defective In₂O₃ surface via a unique redox process involving the oxygen vacancies in the In₂O₃ lattice, whose density can be controlled by high-temperature annealing. The product of the Pt-deposition reaction inside the hollow silica nanoparticle, bearing In₂O₃-supported Pt catalysts inside the cavity protected by a porous silica shell, was proved to be an effective nanoreactor system which selectively and sustainably catalyzed the reduction reaction of small-sized aromatic nitro-compounds. Moreover, the surfactant-free and electroless Pt deposition protocol, which was devised based on the surface chemistry of the In₂O₃ nanoparticles, was successfully employed to fabricate Pt-catalyst-modified ITO electrodes with enhanced electrogenerated chemiluminescece (ECL) performance