Electrochemiluminescence Monitoring of the Ligand Exchange Process of Gold Nanoclusters.

Electrochemiluminescence (ECL) is rapidly emerging as an excellent electrochemical analytical technique for the specific and sensitive detection of various biomarkers and hazardous trace metals. Among ECL emitters, gold nanoclusters (AuNCs) have proven to be excellent luminophores due to their remarkable luminescent properties, stability, and biocompatibility. However, the low ECL efficiency of AuNCs precludes their application in ultrasensitive biosensing. One of the key reasons for the low ECL efficiency of AuNCs is the nonradiative energy transitions arising from intramolecular vibrations and rotations of the ligands on the surface of AuNCs. Herein, we explore the ECL of Zn2+/Au22(SG)18/PDA nanoclusters (NCs), where Zn2+ and 2,6-pyridinedicarboxaldehyde (PDA) activate the restriction of intramolecular motion (RIM) through aggregation-induced emission (AIE) to aggregation-induced enhanced emission (AIEE). This effect is achieved via cross-linking of Zn2+ and PDA with glutathione on the surface of Au22(SG)18, resulting in a significant enhancement of ECL emission compared to Au22(SG)18 NCs alone. A sensitive ECL sensing system was devised with Zn2+/Au22(SG)18/PDA as the ECL emitter, with triethylamine (TEA) as the coreactant, for the detection of Cu2+ and histidine in the linear ranges of 0.1 to 40 μM and 1 to 85 μM, respectively, with detection limits of 0.705 and 1.928 μM, respectively.

WARNING : The light-emitting molecular structures responsible for the chemiluminescence and fluorescence phenomena are not necessarily the same!

Gold nanoclusters (Au NCs) with excellent optical properties and biocompatibility have become one of the most promising electrochemiluminescence (ECL) emitters. However, the low efficiency and poor stability of Au NCs restrict their applications in ECL. Herein, by supramolecular assembly of L-arginine (Arg) and 4-hydroxy-2-mercapto-6-methylpyrimidine (MTU) on the surface of Au NCs, Arg/MTU-Au NCs with enhanced ECL efficiency and stability were prepared. Compared with the MTU-stabilized Au NCs (MTU-Au NCs), the ECL efficiency of Arg/MTU-Au NCs increased by 24.8 times. As a proof-of-concept, a sensitive biosensing platform was constructed for sensitive detection of hemoglobin (Hb) in urine using Arg/MTU-Au NCs as ECL emitters. The proposed ECL detection platform provides a feasible strategy for the detection of biomarkers in urine and has broad application prospects in disease screening and clinical marker detection.

Bulky Thiolate-Protected Silver Nanocluster Ag ₂₁₃ (Adm-S) ₄₄ Cl ₃₃ with Excellent Electrocatalytic Performance toward Oxygen Reduction

Electrochemiluminescence (ECL) is a phenomenon in which light is emitted from the excited state of a redox-active material generated by electrochemical reactions. Among light-emitting device, ECL devices have various advantages in terms of structure and ease of fabrication, and therefore, they are expected as next generation emitting devices. Concerning to the ECL device, we have reported the improvement of emission response, ECL intensity and stability of the ECL device by employing alternating current (AC)-driven method.[1] Nevertheless, we found that the ECL intensity and long-term stability of the system were not enough, and improvement should be required for practical use. In terms of improving the ECL intensity, several researchers have reported that the brightness of the Ru(bpy)3 2+-based ECL could be improved by adding metal oxide nanoparticles (NPs) into the ECL solution. However, the underlying mechanisms of the enhancements were not clarified.[2], [3] The purpose of this study is to elucidate the mechanism of this ECL enhancement. We first investigated the change in the ECL intensity and long-term stability of the ECL device upon addition of the TiO2 NPs to the Ru(bpy)3 2+-based ECL solution. With the addition of the TiO2 NPs into the solution, the emission luminescence of the ECL device increased to 165 cd/m2, which was 1.4 times higher than the device without the addition of TiO2 NPs (120 cd/m2). Without the TiO2 NPs, the half-life time of the ECL device was ~250 s, in contrast to that of the ECL device with the TiO2 NPs, which was expended by a factor of 4 to ~1000 s. Thus, the ECL intensity and long-term stability of the device were greatly improved by adding TiO2 NPs in the Ru(bpy)3 2+-based ECL solution. To reveal the influence of the TiO2 NPs on achieving the high emission luminescence and long-term stability, we measured the optical and electrochemical properties of the Ru(bpy)3 2+-based ECL solution in detail. Increases in the photoluminescence for Ru(bpy)3 2+ were observed by adding the TiO2 NPs. This indicated that the suppression of the radiationless quenching of the excited states would improve the ECL intensity. In terms of the long-term stability, electron transfer between the Ru(bpy)3 2+ and TiO2 NPs was suggested by the detailed electrochemical measurements. Electron transfer occurred from the reduced species of Ru(bpy)3 2+ to the TiO2 NPs, and subsequently, from the TiO2 NPs to the oxidized species of Ru(bpy)3 2+. This kind of electron transfer is thought to improve the balance between the redox reactions in the ECL device, leading to long-term stability. Reference [1] T. Nobeshima et al., J. Mater. Chem., 20, 10630 (2010). [2] N. Itoh, J. Electrochem. Soc., 156, J37 (2009). [3] N. Itoh, Matrials, 3, 3729 (2010).

In most cases of semiconductor quantum dot nanocrystals, the inherent optical and electrochemical properties of these interesting nanomaterials do not translate into expected efficient electrochemiluminescence or electrogenerated chemiluminescence (ECL) because of the surface-state induction effect. Thus, their low ECL efficiencies, while very interesting to explore, limit their applications. As their electrochemistry is not well-defined, insight into their ECL mechanistic details is also limited. Alternatively, gold nanoclusters possess monodispersed sizes with atomic precision, low and well defined HOMO-LUMO energy gaps, and stable optical and electrochemical properties that make them suitable for potential ECL applications. In this Account, we demonstrate strong and sustainable ECL of gold nanoclusters Au25z (i.e., Au25(SR)18z, z = 1-, 0, 1+), Au38(SR)24, and Au144(SR)60, where the ligand SR is 2-phenylethanethiol. By correlation of the optical and electrochemical features of Au25 nanoclusters, a Latimer-type diagram can be constructed to reveal thermodynamic relationships of five oxidation states (Au252+, Au25+, Au250, Au25-, and Au252-) and three excited states (Au25-*, Au250*, and Au25+*). We describe ECL mechanisms and reaction kinetics by means of conventional ECL-voltage curves and novel spooling ECL spectroscopy. Notably, their ECL in the presence of tri-n-propylamine (TPrA), as a coreactant, is attributed to emissions from Au25-* (950 nm, strong), Au250* (890 nm, very strong), and Au25+* (890 nm, very strong), as confirmed by the photoluminescence (PL) spectra of the three Au25 clusters electrogenerated in situ. The ECL emissions are controllable by adjustment of the concentrations of TPrA· and Au25-, Au250, and Au25+ species in the vicinity of the working electrode and ultimately the applied potential. It was determined that the Au25-/TPrA coreactant system should have an ECL efficiency of >50% relative to the Ru(bpy)32+/TPrA, while those of Au250/TPrA and Au25+/TPrA reach 103% and 116%, respectively. Au25-* is the main light emission source for Au25z in the presence of benzoyl peroxide (BPO) as a coreactant, with a relative efficiency of up to 30%. For Au38, BPO leads to the Au38-* excited state, which emits light at 930 nm. In the Au38/TPrA coreactant system, we find that highly efficient light emission at 930 nm is mainly from Au38+* (and also Au383+*), with an efficiency 3.5 times that of the Ru(bpy)32+/TPrA reference. We show that the ECL and PL of the various Au38 charge states, namely, Au382-, Au38-, Au380, Au38+, Au382+, and Au384+, have the same peak wavelength of 930 nm. Finally, we demonstrate ECL with a peak wavelength of 930 nm from the Au144/TPrA coreactant system, which is released from the electrogenerated excited states Au144+* and Au1443+*. In our opinion, these gold nanoclusters represent a new class of effective near-IR ECL emitters, from which applications such as bioimaging, biological testing, and medical diagnosis are anticipated once they are made water-dispersible with hydrophilic capping ligands.

Remarkable increase in electrochemiluminescence of isomeric bipyridine-based covalent organic frameworks via regulating the direction of imine linkage for sensing application.

A simple and sensitive approach to monitor the spectrum change during the electrochemiluminescence process and reveal the mutual promotion between g-C3N4 and co-reactant of S2O82-

Electrogenerated chemiluminescence of a cationic cyclometalated iridium complex–Nafion modified electrode in neutral aqueous solution

The redox nature and electrochemiluminescence (ECL) of highly crystallized organometal halide perovskite CH3NH3PbBr3 nanocrystals (NCs) in aqueous medium were investigated for the first time. CH3NH3PbBr3 NCs could be electrochemically reduced to negative charge states by injecting electrons into the lowest unoccupied molecular orbitals and oxidized to positive charge states by removing electrons from the highest occupied molecular orbitals; charge transfer between NCs with positive and negative charge states could produce ECL. The redox sequence of CH3NH3PbBr3 NCs played an important role in the generation of charge-transfer-mediated ECL; transient ECL could be achieved only by electrochemically reducing positive-charged NCs in an annihilation route. A large redox current was unfavorable for ECL. Charge mobility within CH3NH3PbBr3 NCs had an important effect on ECL intensity in a co-reactant route, which is promising for photovoltaic and optoelectronic device applications. Importantly, the ECL spectra of CH3NH3PbBr3 NCs were almost identical to their photoluminescence spectra, with a maximum emission around 535 nm and full width at half-maximum around 25 nm; this might open a way to obtaining monochromatic ECL using highly crystallized NCs as emitters, which makes them promising for use in color-selective ECL analysis.

Introduction Electrochemiluminescence (ECL) is the chemical luminescence reaction catalyzed by electrochemically active species. In the case of luminol-based ECL, the oxidation of luminol at the electrode and the reactive oxygen species (ROS) as coreactant result in excited intermediate and the release of photon upon relaxation. ECL is used in immunoassay and nucleic acid studies for its advantages such as low background and requiring no external light source. Many of these studies use H2O2 as target or coreactant since many biologically relevant events involve H2O2 and the results are often analyzed by the increase in ECL intensity. Particularly, many enzyme-based ECL that targets H2O2 are reported to date. In this study, catalase enzyme was used to take advantage of its fast turnover rate. However, use of enzymes are sometimes troublesome due to spontaneous reaction upon mixture containing enzyme and its substrate. We addressed this issue by generating substrate for enzyme that utilizes oxygen derivatives at electrode surface by oxygen reduction reaction (ORR). Also, magnetic nanoparticles are used for collection of target species to electrode proximity to elicit concentration effect. Therefore, combination of ORR-ECL and magnetic nanoparticles provide powerful tool for highly sensitive detection system. In this study, we report signal-off ECL using enzyme modified magnetic beads and electro-generated substrate reaction on a small volume multi-chamber screen printed electrode. Materials and Method Catalase enzyme was coupled to NHS modified magnetic nanoparticle (φ200 nm, Tamagawa Seiki) and the absorption spectra and enzyme activity of catalase modified magnetic nanoparticle (CAT-MB) were evaluated using spectroscopic method. For ECL measurement, screen printed electrode with 73 chambers (diameter 200 μm x height 10 μm) was used to limit the reaction volume to about 300 pL. Chambers were filled with solution containing CAT-MB and luminol and magnetic nanoparticles were attracted to the electrode surface using external magnet. Cover glass was placed on top of the electrode chip to cover the chambers to prevent diffusion of enclosed species. The substrate for catalase was electro-generated at the electrode surface. Constant negative potential was applied during the pretreatment time thereby generating ROS. ECL of chambers were recorded with image intensifier and electron magnifying CCD camera mounted on upright microscope. The enclosed catalase enzymes catalyzed H2O2 thus diminish of ECL intensity was observed with increasing magnetic particle concentrations. Electro-generation of ROS species on electrode surface was evaluated with various conditions including electrode pretreatment potential and pretreatment time to control the amount of ROS formed. Results and Discussion Spectroscopic characterization revealed absorbance peak shift from 280 nm to 220 nm from free catalase in aqueous phase to CAT-MB, respectively. Enzyme activity of CAT-MB was found to be lowered by factor of 10 compared to calculated value and the detection limit of CAT-MB was 0.2 μg/mL. The reduced enzyme activity was attributed to the structural modification of catalase molecule during the modification process. ROS electro-generation conditions were investigated by changing the pretreatment potential and time. Starting potential of CV sweep was changed from -1000 to 0 mV with 100 mV interval and the observed ECL intensity showed exponential reduction as the starting potential moved to more positive. Pretreatment time of 20 to 60 seconds were tested at various pretreatment potential and the ECL imaging at -500 mV showed clear difference in brightness at different pretreatment time conditions. The effect of bare magnetic nanoparticles and the use of external magnet on ECL response was also tested. Quantitative ECL imaging analysis using different concentrations of CAT-MB showed that this system can detect 1 ng/mL of magnetic nanoparticle on a multi-chamber chip, and each chamber was estimated to contain average of 5 magnetic nanoparticles. Conclusion In summary, this study successfully developed highly sensitive enzyme modified magnetic particle detection system using the combination of small volume multi-chamber electrode and magnet nanoparticles. Detection was conducted by observing the reduction of ECL signal caused by decomposition of H2O2 electro-generated at the electrode surface by catalase modified on the magnetic nanoparticles enclosed in small chambers. Difference in ECL signal with few nanoparticles as low as average of 5 magnetic nanoparticles in a chamber was detected.

Gold nanoclusters (Au NCs) are potential electrochemiluminescence (ECL) emitters that have been increasingly studied in ECL sensing due to their excellent biocompatibility and electrochemical properties. However, their small size is not conducive to further separation and immobilization, resulting in their low ECL intensity. In this work, a new strategy was designed to form heterostructure Au [email protected]3C2 in situ as a luminophore based on the unique reducibility of Ti3C2, which greatly enhanced the ECL intensity. Here, Au NCs are firmly anchored on the surface of Ti3C2 through O atoms, and Au-O-Ti acts as the connection between Au NCs and Ti3C2. In addition, Ti3C2 with good conductivity is used as the carrier to increase the loading of Au NCs. Through skilful combination with CHA and the lateral cutting characteristics of CRISPR-Cas12a, an ECL biosensor was constructed to detect miRNA-155 with good specificity and sensitivity. The linear range was from 0.1 fM to 1.0 nM with a detection limit as low as 35.7 aM. This research has laid a solid foundation for the development of high efficiency Au NC luminophores and sensitive ECL platforms for clinical and biological analysis.

As a versatile post-synthesis modification method, ligand exchange reaction exhibits great potential to extend the space of accessible nanoclusters. In this review, we summarized this process for thiolate-protected gold nanoclusters. In order to better understand this reaction we will first provide the necessary background on the synthesis and structure of various gold clusters, such as Au25(SR)18, Au38(SR)24, and Au102(SR)44. The previous investigations illustrated that ligand exchange is enabled by the chemical properties and flexible gold–sulfur interface of nanoclusters. It is generally believed that ligand exchange follows a SN2-like mechanism, which is supported both by experiments and calculations. More interesting, several studies show that ligand exchange takes place at preferred sites, i.e. thiolate groups –SR, on the ligand shell of nanoclusters. With the help of ligand exchange reactions many functionalities could be imparted to gold nanoclusters including the introduced of chirality to achiral nanoclusters, size transformation and phase transfer of nanoclusters, and the addition of fluorescence or biological labels. Ligand exchange was also used to amplify the enantiomeric excess of an intrinsically chiral cluster. Ligand exchange reaction accelerates the prosperity of the nanocluster field, and also extends the diversity of precise nanoclusters.

A cellular NO sensor based on aggregation-induced electrochemiluminescence and photoelectron transfer of a novel ruthenium(II) complex

Based on the phenomenon that each of chlorpromazine (CPZ), promethazine (PMZ), chlorpromazine sulfoxide (CPZSO) and promethazine sulfoxide (PMZSO) could enhance the electrochemiluminescence (ECL) intensity of tris(2,2'-bipyridyl) ruthenium, a novel and sensitive method was proposed for the simultaneous determination of CPZ, PMZ and their main metabolites using capillary electrophoresis (CE) coupled with ECL detection. The influences of several experimental parameters were explored. The optimum experimental conditions were as follows: detection potential of 1. 20 V (Ag/AgCl), 40 mmol/L of phosphate buffer solution (pH 6.5) containing 5 mmol/L tris(2,2'-bipyridyl) ruthenium in ECL detection cell, running buffer solution of 18 mmol/L (pH 4.8), sample injection of 8 s at 11 kV, and separation voltage of 13.5 kV. The detection limits (3sigma) of this method were 8.3 x 10(-7) g/L for CPZ, 7.2 x 10(-6) g/L for PMZ, 1.9 x 10(-5) g/L for CPZSO and 3.7 x 10(-6) g/L for PMZSO. The linear ranges of ECL intensity versus mass concentration of medicaments were 7. 1 x 10(-6) - 6. 3 x 10(-3) g/L for CPZ, 7.5 x 10(-5) - 4.6 x 10(-3) g/L for PMZ, 9.7 x 10(-5) - 3.6 x 10(-3) g/L for CPZSO and 8.1 x 10(-5) - 7.7 x 10(-3) g/L for PMZSO. The relative standard deviations (RSDs) of the four target compounds were not more than 3% for ECL intensity and 1% for migration time. This method has the merits of simplicity, speediness, sensitivity, small sample injection, and free from interference. This method was successfully utilized to directly and simultaneously detect CPZ, PMZ, CPZSO and PMZSO in urine samples of pet dogs.