Modification of indium tin oxide with dendrimer-encapsulated nanoparticles to provide enhanced stable electrochemiluminescence of Ru(bpy)3(2+)/tripropylamine while preserving optical transparency of indium tin oxide for sensitive electrochemiluminescence-based analyses

Flexible and Dynamic Light-Guided Electrochemiluminescence for Spatiotemporal Imaging of Photoelectrochemical Processes on Hematite

Here, we report an electrochemiluminescence (ECL)-based approach for imaging of local photoelectrochemical processes on hematite in a spatially and temporally controlled manner. The local processes were guided by flexible and dynamic light illumination, not requiring any prepatterned conductive features or photomasks, with a digital micromirror device (DMD). The imaging approach was based on light-addressable electrochemical reactions on hematite, resulting in photoinduced ECL emission for spatiotemporally resolved imaging of photoelectrochemical processes selectively guided by light illumination. After clarifying the capability of hematite as a photosensitive electrode, we validated that the illuminated hematite exhibited stable light-guided ECL emission in correspondence with the illuminated area, with a spatial resolution of 0.8 μm and a temporal resolution of 1 μs, even over a long period of 6 h. More importantly, this study exemplified the simple yet effective ECL-based approach for electrochemical visualization of local photoelectrochemical processes guided by flexible and dynamic adjustment of light illumination in a spatiotemporally controlled way.

Electrochemiluminescence of iridium(III)/ruthenium(II) complexes with naphthyl tags in solutions and host-guest thin films

Herein we report electrochemiluminescence (ECL) generation from three new iridium(III)/ruthenium(II) (Ir(III)/Ru(II)) complexes with naphthyl (nap) tags in solutions and host-guest thin films. In comparison with its parent structure, the addition of a nap tag to [4-(2-naphthalenyl)-1,10-phenanthroline]bis(2,2'-bipyridine)ruthenium(II) results in a 6.1-fold enhancement in the ECL efficiency. Moreover, the nap tag enables the non-covalent immobilization of Ir(III)/Ru(II) complexes via host-guest interactions. Therefore, a molecular thin film was constructed by hydrophobic effects between the cavity of β-cyclodextrin and the nap tags, which emits stable and strong ECL emission in the presence of tri-n-propylamine (TPrA). These results give a mechanistic insight into ECL generation from (Ir(III)/Ru(II)) complexes with host-guest recognition tags and may help in the development of host-guest thin film-based ECL sensors.

A novel self-enhanced electrochemiluminescent aptamer sensor based on ternary nanocomposite PEI/RuSi-MWCNTs for the detection of profenofos residues in vegetables

In this work, a novel ternary nanocomposite of PEI/RuSi-MWCNTs was designed and synthesized for the first time, which an ultrasensitive and self-enhanced electrochemiluminescent (ECL) aptasensor was developed for the detection of profenofos residues in vegetables. The self-enhanced complex PEI-Ru (II) enhanced the emission and stability of ECL, and the multi-walled carbon nanotubes (MWCNTs) acted as an excellent carrier and signal amplification. The PEI/RuSi-MWCNTs were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM) and energy dispersive spectrometer (EDS). The incorporation of gold nanoparticles (AuNPs) improved the performance of the sensor and provided a platform for the immobilization of the aptamer. The results of the experiment showed that the presence of profenofos significantly suppressed the electrochemiluminescence intensity of the sensor. The detection sensitivity of the aptamer sensor was in the range of 1 × 10-2 to 1 × 103 ng/mL. Under optimal conditions, the limit of detection (LOD) of the sensor for profenofos was 1.482 × 10-3 ng/mL. The sensor had excellent stability, reproducibility and specificity. The recoveries of the sensor ranged from 92.29 % to 106.47 % in real sample tests.

Galvanic Bipolar Electrode Arrays with Self-Driven Optical Readouts

In this work, we report a bipolar electrode (BPE) array system with self-driven optical readouts of the faradic current flowing through the BPEs. The BPE array system is based on the spontaneous redox reactions that are respectively occurring at opposite poles of the BPEs with appropriate electrocatalysts on the poles; this system is analogous to one consisting of galvanic electrochemical cells. The galvanic BPE array system operates in a self-powered mode that requires there to be neither a direct electrical connection nor external electrical polarization to each BPE. Importantly, the appropriate electrocatalysts on the poles play a critical role in the galvanic BPE array system to induce the spontaneous redox reactions occurring at the poles of BPEs. Moreover, the galvanic BPE array system provides self-driven optical readouts, including fluorometric and colorimetric ones, to report the faradaic current resulting from the spontaneous redox reactions on the BPE poles. Based on the unique benefits that the galvanic BPE array system has over conventional BPEs, we demonstrated the promising potential of galvanic BPE arrays for the simple yet rapid and quantitative screening of electrocatalysts for the oxygen reduction reaction as well as sensitive sensing of H2O2 in parallel.

A Sensitive Electrochemiluminescence Urea Sensor for Dynamic Monitoring of Urea Transport in Living Cells

A multiple signal-amplified electrochemiluminescence (ECL) urea sensor was designed based on a self-enhanced probe and SiO₂ photonic crystals for dynamic tracking of urea transmembrane transport. The self-enhanced probe (AuNR@Ru-LA) prepared by loading polyethyleneimine (PEI), lactobionic acid (LA), and Ru(dcbpy)₃²⁺ on gold nanorods (AuNRs) generated an initial ECL signal, and then the intensity was multiple-amplified by the enhanced light-scattering effect of SiO₂ photonic crystals and the co-reaction with urea. The as-prepared sensor exhibited excellent performance for the detection of urea in the range of 1.0 × 10^-10 to 1.0 × 10^-4 M with a detection limit of 8.8 × 10^-11 M at (3σ)/S. The AuNR@Ru-LA probes were labeled on HepG2 cells to construct a cytosensor with a detection range of 1.0 × 10³ to 2.0 × 10⁶ cells mL^-1. In addition, the dynamic changes of the extracellular urea concentration were tracked by monitoring the ECL signal of the cytosensor to study urea transmembrane transport. The developed strategy realized the amplification of multiple ECL signals and the tracking of urea transmembrane transport, which provided a novel dynamic detection method for small biomolecules.

Shell-Isolated Nanoparticle-Enhanced Electrochemiluminescence

Enhanced electrochemiluminescence (ECL) aims to promote higher sensitivity and obtain better detection limit. The core-shell nanostructures, owing to unique surface plasmon resonance (SPR) enabling distance-dependent strong localized electromagnetic field, have attracted rising attention in enhanced ECL research and application. However, the present structures usually with porous shell involve electrocatalytic activity from the metal core and adsorption effect from the shell, which interfere with practical SPR enhancement contribution to ECL signal. Herein, to exclude the interference and unveil exact SPR-enhanced effect, shell-isolated nanoparticles (SHINs) whose shell gets thicker and becomes pinhole-free are developed by modifying pH value and particles concentration. Furthermore, allowing for the distribution of hotspots and stronger enhancement, excitation intensity and ECL reaction layer thickness are mainly investigated, and several types of SHINs-enhanced ECL platforms are prepared to fabricate distinct hotspot distribution via electrostatic attraction (submonolayer) and a layer-by-layer deposition method (monolayer). Consequently, the strongest enhancement up to ≈250-fold is achieved by monolayer SHINs with 10 nm shell, and the platform is applied in a "turn-off" mode sensing for dopamine. The platform provides new guidelines to shell preparation, interface engineering and hotspots fabrication for superior ECL enhancement and analytical application with high performance.

Molecularly imprinted sensing platform based on electrochemically modified graphite paper for efficient detection of 3-monochloropropane-1,2-diol

In this study, a molecularly imprinted polymer (MIP) electrochemical sensor based on electrochemically modified graphite paper (EM-GP) was developed for the detection of 3-MCPD for the first time. To this end, Prussian blue (PB) was electrodeposited on EM-GP to yield uniformly distributed PtNPs. The successful preparation of Pt@PB/EM-GP was verified by SEM, Raman spectroscopy, XRD,XPS, and EDS. MIP was then prepared by CV electropolymerization with template molecules (3-MCPD), and density functional theory (DFT) at M06-2X/6-31 + g (d,p) level was used to calculate the molecular-level interaction between 3-MCPD and MIP. Under the optimum conditions, the dynamic linear range of the sensing platform varied from 1 × 10^-8mol/L to 5 × 10^-5mol/L with a detection limit estimated to 5 × 10^-9 mol/L (S/N = 3). Overall, these findings look promising for the construction of selective and quick detection platforms of 3-MCPD in food samples.

Progress and challenges in sensing of mycotoxins using molecularly imprinted polymers

Mycotoxin is toxic secondary metabolite formed by certain filamentous fungi. This toxic compound can enter the food chain through contamination of food (e.g., by colonization of toxigenic fungi on food). In light of the growing concerns on the health hazards posed by mycotoxins, it is desirable to develop reliable analytical tools for their detection in food products in both sensitive and efficient manner. For this purpose, the potential utility of molecularly imprinted polymers (MIPs) has been explored due to their meritful properties (e.g., large number of tailor-made binding sites, sensitive template molecules, high recognition specificity, and structure predictability). This review addresses the recent advances in the application of MIPs toward the sensing of various mycotoxins (e.g., aflatoxins and patulin) along with their fabrication strategies. Then, performance evaluation is made for various types of MIP- and non-MIP-based sensing platforms built for the listed target mycotoxins in terms of quality assurance such as limit of detection (LOD). Further, the present challenges in the MIP-based sensing application of mycotoxins are discussed along with the future outlook in this research field.

Three-Dimensional TEM Study of Dendrimer-Encapsulated Pt Nanoparticles for Visualizing Structural Characteristics of the Whole Organic-Inorganic Hybrid Nanostructure

Here, we report three-dimensional (3-D) visualization of dendrimer-encapsulated Pt nanoparticles (Pt DENs) by using 3-D electron tomography to reveal intricate structural characteristics of their whole organic-inorganic hybrid nanostructure. We reconstructed the 3-D spatial volume of Pt DENs by back-projecting a tilt series of two-dimensional (2-D) projections of Pt nanoparticles encapsulated inside dendrimers negatively stained with uranyl acetate. The direct 3-D visualization of Pt DENs elucidated their encapsulation characteristics with the spatial imaging of Pt nanoparticles embraced inside dendrimers in three dimensions. The encapsulation characteristics of Pt DENs were further verified with selective electrochemical poisoning experiments. In addition, quantitative 3-D structural characterization of Pt DENs provided more accurate and precise size distributions of nanoparticles than those obtained from conventional 2-D transmission electron microscopy analysis relying only on a 3-D structure projected on a 2-D plane.

Mechanistic Insight into a Novel Ultrasensitive Nicotine Assay Base on High-Efficiency Quenching of Gold Nanocluster Cathodic Electrochemiluminescence

Monitoring nicotine concentrations in human fluids is extremely crucial owing to the harmful effect of nicotine on human health. Herein, it is shown that nicotine could quench the cathodic electrochemiluminescence (ECL) of gold nanoclusters (AuNCs) with high efficiency. The ECL quenching mechanism of nicotine was studied in detail using various experimental tools and theoretical calculations. It was concluded that the strongly oxidizing intermediate SO₄^•-, produced from K₂S₂O₈, could oxidized nicotine, resulting in ECL emission quenching. On the basis of this high-efficiency ECL quenching of the AuNCs/K₂S₂O₈ system, a recyclable, ultrasensitive, and selective ECL sensing platform for nicotine detection was proposed. Even in the absence of any complex signal amplification techniques, the ECL sensor for nicotine detection showed an unprecedentedly low detection limit of 7.0 × 10^-13 M (S/N = 3) and a wide linear range over 8 orders of magnitude. Most remarkably, it could be successfully used for nicotine detection in human urine samples. This is expected to promote the investigations and applications on nicotine-related diseases. We believe that the proposed ECL platform can hold great prospects for commercialization in biomedical fields and tobacco industries.

Nanocage-confined electrochemiluminescence for the detection of dopamine released from living cells

Herein we report an electrochemiluminescent nanocage array (ENA) in which luminophores are physically confined. The ENA can function as a solid sensor for the detection of dopamine released from living cells on the basis of its quenching effect on the ECL signal.

Facile Preparation of WO3-x Dots with Remarkably Low Toxicity and Uncompromised Activity as Co-reactants for Clinical Diagnosis by Electrochemiluminescence

The exceptional nature of WO_3-x dots has inspired widespread interest, but it is still a significant challenge to synthesize high-quality WO_3-x dots without using unstable reactants, expensive equipment, and complex synthetic processes. Herein, the synthesis of ligand-free WO_3-x dots is reported that are highly dispersible and rich in oxygen vacancies by a simple but straightforward exfoliation of bulk WS₂ and a mild follow-up chemical conversion. Surprisingly, the WO_3-x dots emerged as co-reactants for the electrochemiluminescence (ECL) of Ru(bpy)₃ ²⁺ with a comparable ECL efficiency to the well-known Ru(bpy)₃ ²⁺ /tripropylamine (TPrA) system. Moreover, compared to TPrA, whose toxicity remains a critical issue of concern, the WO_3-x dots were ca. 300-fold less toxic. The potency of WO_3-x dots was further explored in the detection of circulating tumor cells (CTCs) with the most competitive limit of detection so far.

Simple and rapid nicotine analysis using a disposable silica nanochannel-assisted electrochemiluminescence sensor

Nicotine analysis is essential to medicine, toxicology and the tobacco industry. However, no simple, portable and disposable method was developed to meet their demands. Here, we report a simple, rapid and disposable silica nanochannel (SAN)-based electrochemiluminescence (ECL) sensor for nicotine analysis by simply assembling a SAN electrode with a paper cover. The sensing principle of the disposable sensor is based on the size exclusion effect and charge selectivity, which obviously prolong the sensor service time. We find that the sensor exhibits good specificity to nicotine, and most of the complex matrices are unlikely to impact the detection. The performance of the disposable sensor in cigarettes, e-cigarettes, nicotine gums, and lozenges is fully validated, showing satisfactory linearity, sensitivity (a limit of detection of 27.82 nM), and accuracy (a recovery between 96.00% and 106.51%). The disposable sensor can be potentially applied for on-site nicotine analysis.

Oxygen-Resistant Electrochemiluminescence System with Polyhedral Oligomeric Silsesquioxane

We report the oxygen-resistant electrochemiluminescence (ECL) system from the polyhedral oligomeric silsesquioxane (POSS)-modified tris(2,2'-bipyridyl)ruthenium(II) complex (Ru-POSS). In electrochemical measurements, including cyclic voltammetry (CV), it is shown that electric current and ECL intensity increase in the mixture system containing Ru-POSS and tripropylamine (TPrA) on the indium tin oxide (ITO) working electrode. The lower onset potential (E_onset) in CV is observed with Ru-POSS compared to tris(2,2'-bipyridyl)ruthenium(II) complex (Ru(bpy)₃²⁺). From the series of mechanistic studies, it was shown that adsorption of Ru-POSS onto the ITO electrode enhances TPrA oxidation and subsequently the efficiency of ECL with lower voltage. Moreover, oxygen quenching of ECL was suppressed, and it is proposed that the enhancement to the production of the TPrA radical could contribute to improving oxygen resistance. Finally, the ECL-based detection for water pollutant is demonstrated without the degassing treatment. The commodity system with Ru(bpy)₃²⁺ is not applicable in the absence of degassing with the sample solutions due to critical signal suppression, meanwhile the present system based on Ru-POSS was feasible for estimating the amount of the target even under aerobic conditions by fitting the ECL intensity to the standard curve. One of critical disadvantages of ECL can be solved by the hybrid formation with POSS.

A Robust Longitudinal Co-culture of Obligate Anaerobic Gut Microbiome With Human Intestinal Epithelium in an Anoxic-Oxic Interface-on-a-Chip

The majority of human gut microbiome is comprised of obligate anaerobic bacteria that exert essential metabolic functions in the human colon. These anaerobic gut bacteria constantly crosstalk with the colonic epithelium in a mucosal anoxic-oxic interface (AOI). However, in vitro recreation of the metabolically mismatched colonic AOI has been technically challenging. Furthermore, stable co-culture of the obligate anaerobic commensal microbiome and epithelial cells in a mechanically dynamic condition is essential for demonstrating the host-gut microbiome crosstalk. Here, we developed an anoxic-oxic interface-on-a-chip (AOI Chip) by leveraging a modified human gut-on-a-chip to demonstrate a controlled oxygen gradient in the lumen-capillary transepithelial interface by flowing anoxic and oxic culture medium at various physiological milieus. Computational simulation and experimental results revealed that the presence of the epithelial cell layer and the flow-dependent conditioning in the lumen microchannel is necessary and sufficient to create the steady-state vertical oxygen gradient in the AOI Chip. We confirmed that the created AOI does not compromise the viability, barrier function, mucin production, and the expression and localization of tight junction proteins in the 3D intestinal epithelial layer. Two obligate anaerobic commensal gut microbiome, Bifidobacterium adolescentis and Eubacterium hallii, that exert metabolic cross-feeding in vivo, were independently co-cultured with epithelial cells in the AOI Chip for up to a week without compromising any cell viability. Our new protocol for creating an AOI in a microfluidic gut-on-a-chip may enable to demonstrate the key physiological interactions of obligate anaerobic gut microbiome with the host cells associated with intestinal metabolism, homeostasis, and immune regulation.

A Facile and Scalable Route to the Preparation of Catalytic Membranes with in Situ Synthesized Supramolecular Dendrimer Particle Hosts for Pt(0) Nanoparticles Using a Low-Generation PAMAM Dendrimer (G1-NH2) as Precursor

Since the first reports of Cu dendrimer-encapsulated nanoparticles (DENs) published in 1998, the dendrimer-templating method has become the best and most versatile method for preparing ultrafine metallic and bimetallic nanoparticles (1-3 nm) with well-defined compositions, high catalytic activity, and tunable selectivity. However, DENs have remained for the most part model systems with limited prospects for scale up and integration into high-performance and reusable catalytic modules and systems for industrial-scale applications. Here, we describe a facile and scalable route to the preparation of catalytic polyvinylidene fluoride (PVDF) membranes with in situ synthesized supramolecular dendrimer particles (SDPs) that can serve as hosts and containers for Pt(0) nanoparticles (2-3 nm). These new catalytic membranes were prepared using a reactive encapsulation process similar to that utilized to prepare Pt DENs by addition of a reducing agent (sodium borohydride) to aqueous complexes of Pt(II) + G4-OH/G6-OH polyamidoamine (PAMAM) dendrimers. However, the SDPs (2.4 μm average diameter) of our new mixed matrix PVDF-PAMAM membranes were synthesized in the dope dispersion without purification prior to film casting using (i) a low-generation PAMAM dendrimer (G1-NH₂) as particle precursor and (ii) epichlorohydrin, an inexpensive functional reagent, as cross-linker. In addition, the membrane PAMAM particles contain secondary amine groups (∼1.9 mequiv per gram of dry membrane), which are more basic and thus have higher Pt binding affinity than the tertiary amine groups of the G4-OH and G6-OH PAMAM dendrimers. Proof-of-concept experiments show that our new PVDF-PAMAM-G1-Pt/membranes can serve as highly active and reusable catalysts for the hydrogenation of alkenes and alkynes to the corresponding alkanes using (i) H₂ at room temperature and a pressure of 1 bar and (ii) low catalyst loadings of ∼1.4-1.6 mg of Pt. Using cyclohexene as model substrate, we observed near quantitative conversion to cyclohexane (∼98%). The regeneration studies showed that our new Pt/membrane catalysts are stable and can be reused for five consecutive reaction cycles for a total duration of 120 h including 60 h of heating at 100 °C under vacuum for substrate, product, and solvent removal with no detectable loss of cyclohexene hydrogenation activity. The overall results of our study point to a promising, versatile, and scalable path for the integration of catalytic membranes with in situ synthesized SDP hosts for Pt(0) nanoparticles into high-throughput modules and systems for heterogeneous catalytic hydrogenations, an important class of reactions that are widely utilized in industry to produce pharmaceuticals, agrochemicals, and specialty chemicals.

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.

Highly Stable Mesoporous Luminescence-Functionalized MOF with Excellent Electrochemiluminescence Property for Ultrasensitive Immunosensor Construction

In this work, a novel mesoporous luminescence-functionalized metal-organic framework (Ru-PCN-777) with high stability and excellent electrochemiluminescence (ECL) performance was synthesized by immobilizing Ru(bpy)₂(mcpbpy)²⁺ on the Zr₆ cluster of PCN-777 via a strong coordination bond between Zr⁴⁺ and -COO^-. Consequently, the Ru(bpy)₂(mcpbpy)²⁺ could not only cover the surface of PCN-777 but also graft into the interior of PCN-777, which greatly increased the loading amount of Ru(bpy)₂(mcpbpy)²⁺ and effectively prevented the leaching of the Ru(bpy)₂(mcpbpy)²⁺ resulting in a stable and high ECL response. Considering the above merits, we utilized the mesoporous Ru-PCN-777 to construct an ECL immunosensor to detect mucin 1 (MUC1) based on proximity-induced intramolecular DNA strand displacement (PiDSD). The ECL signal was further enhanced by the enzyme-assisted DNA recycling amplification strategy. As expected, the immunosensor had excellent sensitivity, specificity, and responded wide linearly to the concentration of MUC1 from 100 fg/mL to 100 ng/mL with a low detection limit of 33.3 fg/mL (S/N = 3). It is the first time that mesoporous Zr-MOF was introduced into ECL system to assay biomolecules, which might expand the application of mesoporous metal-organic frameworks (MOFs) in bioanalysis. This work indicates that the use of highly stable mesoporous luminescence-functionalized MOFs to enhance the ECL intensity and stability is a feasible strategy for designing and constructing high-performance ECL materials, and therefore may shed light on new ways to develop highly sensitive and selective ECL sensors.

Solid state electrochemiluminescence from homogeneous and patterned monolayers of bifunctional spirobifluorene

Electrochemiluminescence (ECL) from self-assembled monolayers of a spirobifluorene dye covalently linked to a transparent ITO surface is reported.

Near-infrared electrochemiluminescence from orange fluorescent Au nanoclusters in water

We report the unusual generation of near-IR electrochemiluminescence from orange fluorescent Au nanoclusters soluble in water.

Single Cell Electrochemiluminescence Imaging: From the Proof-of-Concept to Disposable Device-Based Analysis

We report here the development of coreactant-based electrogenerated chemiluminescence (ECL) as a surface-confined microscopy to image single cells and their membrane proteins. Labeling the entire cell membrane allows one to demonstrate that, by contrast with fluorescence, ECL emission is only detected from fluorophores located in the immediate vicinity of the electrode surface (i.e., 1-2 μm). Then, to present the potential diagnostic applications of our approach, we selected carbon nanotubes (CNT)-based inkjet-printed disposable electrodes for the direct ECL imaging of a labeled plasma receptor overexpressed on tumor cells. The ECL fluorophore was linked to an antibody and enabled to localize the ECL generation on the cancer cell membrane in close proximity to the electrode surface. Such a result is intrinsically associated with the unique ECL mechanism and is rationalized by considering the limited lifetimes of the electrogenerated coreactant radicals. The electrochemical stimulus used for luminescence generation does not suffer from background signals, such as the typical autofluorescence of biological samples. The presented surface-confined ECL microscopy should find promising applications in ultrasensitive single cell imaging 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.

PAMAM dendrimers: A multifunctional nanomaterial for ECL biosensors

Polyamido amine (PAMAM) dendrimers have been shown to function as electrochemiluminescence (ECL) co-reactant and have the inherent capability of improving immobilization of molecules on surfaces due to their dendritic structure. Here, we investigated the combination of both of these properties as the basis for biosensor development. Dendrimers with 5, 8, 10 and 16 terminal amine groups, respectively, were used. These were covalently coupled to biotin as model recognition site, and tagged with Ru(bpy)₃²⁺ via adsorption. Due to their hydrophilicity, Ru-dendrimers showed significantly improved electrochemical activity in comparison to the standard tripropylamine (TPA) assisted ECL and similar luminescence yields even though 10 fold less dendrimer concentration was required in comparison to TPA. Best signals were obtained for D8 and D10 dendrimers. These Ru-dendrimers were subsequently used for the quantification of streptavidin, as its binding to the biotin-tag caused a proportional decrease in ECL signal with a dynamic range of 5nM to 1μM. These preliminary studies demonstrate that PAMAM dendrimers can function as responsive signal generators in solution-based ECL-bioassays with an assumed even higher impact when being immobilized directly on the electrode-surface.

Enhanced anodic electrochemiluminescence of CdTe quantum dots based on electrocatalytic oxidation of a co-reactant by dendrimer-encapsulated Pt nanoparticles and its application for sandwiched immunoassays

A first immunosensor using Fe₃O₄@SiO₂-Pt DENs for carrier separation and signal amplification in the CdTe QD-TPrA anodic ECL system.