One‐step synthesis of cationic gold nanoclusters with high catalytic activity on luminol chemiluminescence reaction

A one-pot loop-mediated isothermal amplification platform using fluorescent gold nanoclusters for rapid and naked-eye pathogen detection

Loop-mediated isothermal amplification (LAMP) is a rapid and sensitive nucleic acid testing method for pathogen detection, yet the absence of a straightforward readout strategy remains challenging. We've successfully designed polyethyleneimine-stabilized gold nanoclusters (PEI-AuNCs) as a cationic AuNCs indicator tailored for distinguishing LAMP results, enabling direct visual inspection under UV light. Positive LAMP reactions with PEI-AuNCs, in combination with magnesium pyrophosphate crystals, yield red-fluorescent bulk precipitates visible to the naked eye. To address contamination concerns, we introduced a one-pot reaction by incorporating AuNCs into the lid recess. This one-pot LAMP assay demonstrates exceptional detection capability, identifying Salmonella enterica at concentrations as low as 101 CFU/mL within approximately 50 min, excluding nucleic acid extraction. The platform's versatility, achieved through customizable primers, positions it as a promising molecular diagnostic tool for rapid and visual pathogen detection across scientific disciplines.

Selective synthesis of fluorescent metal nanoclusters over metal nanoparticles

Metal nanoparticles and nanoclusters are pivotal in nanomaterial science, each offering unique properties for diverse applications. Nanoclusters, typically smaller than 2 nm, exhibit distinct optical and electronic characteristics due to quantum confinement, resulting in fluorescence emission. In contrast, metal nanoparticles, sized between 2 and 100 nm, exhibit absorption spectra. Both are synthesized by reducing metal precursors in the presence of a suitable stabilizing agent. While nanoparticles have been the historical research focus, recent attention has shifted to nanoclusters for their exceptional properties and their synthesis has evolved significantly over the past few decades. This review discusses the selective synthesis of nanoclusters over nanoparticles, emphasizing the role of various factors such as ligand concentration (metal-to-ligand ratio), reducing agents, pH, reaction time and temperature, solvents, and assistant reagents. Higher ligand concentrations stabilize smaller nanoclusters by preventing aggregation, while lower concentrations lead to larger nanoparticles. Stronger reducing agents produce smaller, more uniform particles, whereas weaker reducing agents yield larger ones. pH affects nanocluster size and emission properties. Solvents and assistant reagents influence reaction kinetics and material properties. Temperature and reaction time also play critical roles in controlling nanocluster size and properties. These insights guide the optimized synthesis of metal nanoclusters, for their specific applications.

The Molecular Basis of Organic Chemiluminescence

Bioluminescence (BL) and chemiluminescence (CL) are interesting and intriguing phenomena that involve the emission of visible light as a consequence of chemical reactions. The mechanistic basis of BL and CL has been investigated in detail since the 1960s, when the synthesis of several models of cyclic peroxides enabled mechanistic studies on the CL transformations, which led to the formulation of general chemiexcitation mechanisms operating in BL and CL. This review describes these general chemiexcitation mechanisms-the unimolecular decomposition of cyclic peroxides and peroxide decomposition catalyzed by electron/charge transfer from an external (intermolecular) or an internal (intramolecular) electron donor-and discusses recent insights from experimental and theoretical investigation. Additionally, some recent representative examples of chemiluminescence assays are given.

Enhancement effect of 2, 3-dimethyl maleic acid on luminol chemiluminescence reactions and its application in detection of sequence-specific DNA related to hepatitis B virus

2, 3-dimethyl maleic acid (DMMA) was found to enhance luminol-H₂O₂ chemiluminescent (CL) reactions, among which the strongest enhancement effect was observed by using polyethyleneimine-templated gold nanoclusters (PEI-Au NCs) as the catalyst. With the addition of DMMA, the CL signal of the PEI-Au NCs-catalyzed luminol-H₂O₂ reaction enhanced about 630-fold, and a flash-type CL profile was obtained. Mechanism studies showed that the luminophore was still 3-aminophthalate anions in the excited state (3-APA*), and superoxide radical (O₂^·-) played an important role during the CL process. Under the optimized experimental conditions, the lowest concentration of PEI-Au NCs can be detected was 0.168 nM which was 82-fold lower than that without an enhancer. Furthermore, the catalytic activity of biotinylated PEI-Au NCs in the DMMA-enhanced luminol system was similar to PEI-Au NCs, providing a good opportunity for the development of CL bioanalysis platforms using PEI-Au NCs as the label. Thus, the DMMA-enhanced luminol-H₂O₂ system was applied to the CL detection of sequence-specific DNA related to the hepatitis B virus (HBV) using PEI-Au NCs as the label. The CL platform exhibited linearly enhanced CL response with the increasing amount of target DNA ranging from 0.0025 to 0.5 pmol. As low as 0.002 pmol of HBV DNA could be sensitively detected, which was superior to the previously reported methods.

Flower-like Gold Nanoparticles for In Situ Tailoring Luminescent Molecules for Synergistic Enhanced Chemiluminescence

In recent years, gold nanoparticles (AuNPs) have attracted much attention due to their ease of surface modification, excellent biocompatibility, and extraordinary optoelectronic and catalytic activities. Herein, based on a AuNP-catalyzed reaction, a strategy for tailoring luminescent molecules in situ is proposed to trigger an ultrastrong chemiluminescence (CL). In the strategy, flower-like AuNPs are prepared using CL molecular probes (Probe-OH for NaClO/ONOO^-) via one-pot synthesis and subsequently act as a tailor for Probe-OH to generate novel CL molecules, allowing a synergistic CL enhancement about 4 times that of initial Probe-OH. Furthermore, by modification with poly(vinylpyrrolidone) (PVP) on the surface, the CL signals (only for NaClO) are amplified by 100 times based on an intermolecular chemically initiated electron exchange luminescence (CIEEL) mechanism. Given the improved sensitivity and selectivity over Probe-OH, the thus-formed CIEEL nanoplatform (PVP-Au) is successfully developed for detecting NaClO in a wide range of 2.5-100 μM, and the detection limit is 10.68 nM. This work provides unprecedented perspectives for expanding this facile and effective strategy for CL amplification based on AuNP catalysis.

Chemiluminescence assay for kanamycin based on target recycling strategy

A chemiluminescence (CL) sensing strategy for kanamycin residue detection in fish samples was established based on luminol-functionalized gold nanoparticles as CL nanoprobe materials combined with DNA hairpin structure and carboxyl modified magnetic beads. Relying on nucleic acid amplification technology, the system can successfully realize the recycling of kanamycin, so that the biosensor can release a large number of luminol-functionalized gold nanoparticles with excellent CL performance even at a low residual level of kanamycin. The biosensor strategy showed a good linear relationship with kanamycin in the range of 0.09 nM-130 nM, the detection limit was as low as 0.04 nM. This method proves the excellent performance of the sensing strategy and provides a low-cost and high-sensitivity CL analysis strategy for the detection of kanamycin and even other antibiotics.

K+ Ion-Doped Mixed Carbon Nitride: A Daylight-Driven Photocatalyst and Luminophore for Enhanced Chemiluminescence

Photocatalytic production of reactive oxygen species from O₂ at the interface of the photocatalyst is significant to convert luminous energy like daylight into chemical energy and could be momentous for a reactive oxygen species-based chemiluminescence system. Herein, we synthesized a novel K⁺ ion-doped tri-s-triazine/triazine mixed carbon nitride (MCN), in which K⁺ ions were intercalated into the layers in a bridging manner. After a mild daylight treatment for 30 min, the MCN suspension could produce long-lifetime reactive oxygen species and further directly produce intense and stable chemiluminescence emission in the presence of luminol. In particular, the chemiluminescence intensity was 780 times that of H₂O₂-luminol, and MCN could be recycled several times in the chemiluminescence system. The mechanism results revealed a large number of reactive oxygen species that were generated from O₂ on the surface of MCN through a temperate photocatalytic process. In the theoretical calculation, the charge density of N interacting with K⁺ ions was significantly more negative than that at the corresponding position in graphitic carbon nitride, which was beneficial to the adsorption and activation of oxygen, and the narrower band gap suggested that the doping of K⁺ ions was conducive to the intramolecular charge transfer interaction. Then, the long-lifetime reactive oxygen species triggered the conversion of luminol into an excited-state intermediate, which further transferred energy to MCN, producing strong chemiluminescence emission. The K⁺ ion-doped MCN might conduct as an efficient photocatalyst for reactive oxygen species generation, recyclable catalysts, and luminophores in the photoinduced chemiluminescence system.

Determination of organophosphate flame retardant tris(2-chloroethyl)phosphine based on the luminol-H2 O2 chemiluminescence system

Organophosphorus flame retardants (OPFRs) are new types of environmental pollutants, therefore the rapid and sensitive detection of OPFRs is a very important objective. A new experimental phenomenon was found in which tris(2-chloroethyl)phosphine (TCEP), a type of OPFR, could effectively enhance the signal of the luminol-H₂ O₂ chemiluminescence (CL) system. Combined with the controllability of flow injection analysis, a rapid, stable, and sensitive CL method was established. The CL intensity responded linearly to the concentration of TCEP in the range 0.5-100 μg/L (R²  = 0.999) with a low detection limit of 33 ng/L. Relative standard deviation (RSD) was 2.2% (n = 7, c = 100 μg/L). Water samples were labelled and recycled with RSDs of 1.1-5.7% and recoveries of 88.7-116.1%. Based on these results, this study established a new CL detection method for the environmental pollutant TCEP.

Gold nanoclusters: An ultrasmall platform for multifaceted applications

Gold nanoclusters (Au NCs) with a core size below 2 nm form an exciting class of functional nano-materials with characteristic physical and chemical properties. The properties of Au NCs are more prominent and extremely different from their bulk counterparts. The synthesis of Au NCs is generally assisted by template or ligand, which impart excellent cluster stability and high quantum yield. The tunable and sensitive physicochemical properties of Au NCs open horizons for their advanced applications in various interdisciplinary fields. In this review, we briefly summarize the solution phase synthesis and origin of the characteristic properties of Au NCs. A vast review of recent research work introducing biosensors based on Au NCs has been presented along with their specifications and detection limits. This review also highlights recent progress in the use of Au NCs as bio-imaging probe, enzyme mimic, temperature sensing probe and catalysts. A speculation on present challenges and certain future prospects have also been provided to enlighten the path for advancement of multifaceted applications of Au NCs.