Natural Cyclodextrins as Efficient Boosters of the Chemiluminescence of Luminol and Isoluminol: Exploration of Potential Applications

Boosting Photon Emission from the Chemiluminescence of Luminol Based on Host-Guest Recognition for the Determination of Dopamine

Modulating the photon emission of the luminophore for boosting chemiluminescence (CL) response is very crucial for the construction of highly sensitive sensors via the introduction of functionalized materials. Herein, the integration of the emitter and coreactant accelerator into one entity is realized by simply assembling cucurbit[7]uril (CB[7]) on the surface of gold nanoparticles (AuNPs) through simple assembly via a Au-O bond. The loaded CB[7] on the AuNPs improves their catalytic capacity for the generation of hydroxyl radicals(•OH). Moreover, the host-guest recognition interaction between luminol and CB[7] enables the capture of luminol on AuNPs efficiently. Also, the intramolecular electron-transfer reaction between the luminol and •OH enables the CL response more effectively in the entity, which greatly boosts photon emission ca 100 folds compared with the individual luminol/H2O2. The host-guest recognition between luminol and CB[7] is revealed by Fourier transform infrared spectroscopy, electrochemical, and thermogravimetric characterization. Moreover, the proposed CL system is successfully used for the sensitive and selective determination of dopamine (DA) based on a synergistic quenching mechanism including the competition quenching and radical-scavenging effect from DA. The present amplified strategy by integrating recognized and amplified elements within one entity simplifies the sensing process and holds great potential for sensitive analysis based on the self-enhanced strategies.

Vanillin-Catalyzed highly sensitive luminol chemiluminescence and its application in food detection

Among various chemiluminescence (CL) systems, luminol-H₂O₂ system is used extensively due to its cheapness and sensitivity. Herein, 4-hydroxy-3-methoxybenzaldehyde, known as vanillin, was firstly found to be able to catalyze H₂O₂ very efficiently to produce ^•OH and O₂^•-, which can be used to enhance the CL of luminol-H₂O₂ as Co⁺. In alkaline aqueous solution, vanillin catalyzed the dissociation of H₂O₂ into active ^•OH and O₂^•- radicals and accelerated luminol-H₂O₂ reaction to emit strong CL signal. Combining the stabilizing function of β-CD, CL intensity of luminol-H₂O₂ was enhanced further. Thus, dual-signal amplification of luminol-H₂O₂ chemiluminescence based on the catalyzing function of vanillin and the stabilizing function of β-CD was proposed and its mechanism was explored deeply in the manuscript. Interestingly, vanillin is a highly prized flavor compound broadly used as food additive, however, the excessive intake of vanillin is harmful to human and thus the determination of vanillin is very important. On the basis of the luminol-β-CD-H₂O₂/vanillin reaction, a low-cost, rapid and simple CL sensor has been established to detect vanillin. The sensor was able to detect vanillin in the range of 1.0 μM ∼ 75 μM with a detection limit of 0.89 μM (S/N = 3). It can also be used for CL imaging detection with satisfactory results.

Untapped toolbox of luminol based polymers

The present state of luminol based polymers is highlighted with the challenges and the respective strategies for the advancement of this versatile class of polymers.

Turn-on chemiluminescence probes and dual-amplification of signal for detection of amyloid beta species in vivo

Turn-on fluorescence imaging is routinely studied; however, turn-on chemiluminescence has been rarely explored for in vivo imaging. Herein, we report the design and validation of chemiluminescence probe ADLumin-1 as a turn-on probe for amyloid beta (Aβ) species. Two-photon imaging indicates that ADLumin-1 can efficiently cross the blood-brain barrier and provides excellent contrast for Aβ plaques and cerebral amyloid angiopathy. In vivo brain imaging shows that the chemiluminescence signal of ADLumin-1 from 5-month-old transgenic 5xFAD mice is 1.80-fold higher than that from the age-matched wild-type mice. Moreover, we demonstrate that it is feasible to further dually-amplify signal via chemiluminescence resonance energy transfer (DAS-CRET) using two non-conjugated smart probes (ADLumin-1 and CRANAD-3) in solutions, brain homogenates, and in vivo whole brain imaging. Our results show that DAS-CRET can provide a 2.25-fold margin between 5-month-old 5xFAD mice and wild type mice. We believe that our strategy could be extended to other aggregating-prone proteins.

Efficient Cascade Resonance Energy Transfer in Dynamic Nanoassembly for Intensive and Long-Lasting Multicolor Chemiluminescence

Light emission induced by chemical reactions, known as chemiluminescence (CL), has been widely used for bioassays, biosensors, imaging, and illumination applications. Most known CL systems exhibit flash-type single-color light emissions, which limit their applications. Long-lasting multicolor CL in aqueous solutions is highly desirable, especially for biological applications, but remains a challenge. Herein, we report a simple strategy of achieving highly efficient cascade Förster resonance energy transfer (FRET) in the dynamic nanoassembly of β-cyclodextrin (β-CD), CL reagents, and fluorophores in aqueous solution, which emits intensive multicolor CL with adjustable wavelength within 410-610 nm. β-CD can bind CL reagents and fluorophores to form a dynamic nanoassembly. These nanoassemblies can bring the included luminescent intermediate and fluorophores into close proximity and proper alignment, which should greatly enhance the FRET efficiency between luminescent intermediate and fluorophores. Indeed, the cascade FRET efficiency in this supramolecular nanoassembly reaches up to 92%, which is comparable with the cascade FRET systems based on covalently linked donors and acceptors. By using hydroxypropyl methylcellulose as the thickener to slow the diffusion (to elongate the CL emission), and using Ca(OH)₂ solid (a low solubility strong base) as buffer to maintain the pH in the optimal range for the CL reaction, this nanoassembly system has been further developed to achieve slow-diffusion-controlled catalytic CL reactions, which enables long-lasting multicolor CL in aqueous solution that is visible to naked eyes and lasts for more than 20 h. The multicolor CL systems can be used to prepare transformable two-dimensional multicolor codes for encryption application.

Chemiluminescent self-reporting supramolecular transformations on macromolecular scaffolds

We introduce the synthesis of a self-reporting system with chemiluminescent output, which is regulated via dynamic supramolecular complex formation.

Improving Luminol Blood Detection in Forensics

The aim of this study was to develop chemical improvements to the original Weber protocol, in order to increase the intensity and time length of light emission and to eliminate false-positive reactions. The intensity and duration of light were measured on serial blood dilutions using a plate reader chemiluminometer. Blood stains of various concentrations were impregnated in pure cellulose, dried, and luminol solution was added with/without the potential enhancers. An in silico study was also conducted, aiming to demonstrate the enhancing mechanism of hemoglobin denaturation using 8 M urea. The luminol blood detection test revealed important improvements after urea pretreatment or in the presence of monochloro-triazinyl-β-cyclodextrin. This approach also eliminated the false-positive reaction from sodium hypochlorite. These improvements could provide a higher sensitivity under particular circumstances such as old or washed blood stains, leading to a better localization for further DNA typing and higher quality photographic analysis.

Quantitative ROESY analysis of computational models: structural studies of citalopram and β-cyclodextrin complexes by (1) H-NMR and computational methods

Complexation of racemic citalopram with β-cyclodextrin (β-CD) in aqueous medium was investigated to determine atom-accurate structure of the inclusion complexes. (1) H-NMR chemical shift change data of β-CD cavity protons in the presence of citalopram confirmed the formation of 1 : 1 inclusion complexes. ROESY spectrum confirmed the presence of aromatic ring in the β-CD cavity but whether one of the two or both rings was not clear. Molecular mechanics and molecular dynamic calculations showed the entry of fluoro-ring from wider side of β-CD cavity as the most favored mode of inclusion. Minimum energy computational models were analyzed for their accuracy in atomic coordinates by comparison of calculated and experimental intermolecular ROESY peak intensities, which were not found in agreement. Several least energy computational models were refined and analyzed till calculated and experimental intensities were compatible. The results demonstrate that computational models of CD complexes need to be analyzed for atom-accuracy and quantitative ROESY analysis is a promising method. Moreover, the study also validates that the quantitative use of ROESY is feasible even with longer mixing times if peak intensity ratios instead of absolute intensities are used.

Revealing interaction between sulfobutylether-β-cyclodextrin and reserpine by chemiluminescence and site-directed molecular docking

The host-guest interaction between sulfobutylether-β-cyclodextrin (SBE-β-CD) and reserpine (RSP) is described using flow injection-chemiluminescence (FI-CL) and site-directed molecular docking methods. It was found that RSP could inhibit the CL intensity produced by a luminol/SBE-β-CD system. The decrease in CL intensity was logarithmic over an RSP concentration range of 0.03 to 700.0 nM, giving a regression equation of ∆I = 107.1lgCRES  + 186.1 with a detection limit of 10 pM (3σ). The CL assay was successfully applied in the determination of RSP in injection, saliva and urine samples with recoveries in the range 93.5-106.1%. Using the proposed CL model, the binding constant (KCD-R ) and the stoichiometric ratio of SBE-β-CD/RSP were calculated to be 7.4 × 10(6)  M(-1) and 1 : 1, respectively. Using molecular docking, it was confirmed that luminol binds to the small cavity of SBE-β-CD with a nonpolar interaction, while RSP targeted the larger cavity of SBE-β-CD and formed a 1 : 1 complex with hydrogen bonds. The proposed new CL method has the potential to become a powerful tool for revealing the host-guest interaction between CDs and drugs, as well as monitoring drugs with high sensitivity.

Luminol-based bioluminescence imaging of mouse mammary tumors

Polymorphonuclear neutrophils (PMNs) are the most abundant circulating blood leukocytes. They are part of the innate immune system and provide a first line of defense by migrating toward areas of inflammation in response to chemical signals released from the site. Some solid tumors, such as breast cancer, also cause recruitment and activation of PMNs and release of myeloperoxidase. In this study, we demonstrate that administration of luminol to mice that have been transplanted with 4T1 mammary tumor cells permits the detection of myeloperoxidase activity, and consequently, the location of the tumor. Luminol allowed detection of activated PMNs only two days after cancer cell transplantation, even though tumors were not yet palpable. In conclusion, luminol-bioluminescence imaging (BLI) can provide a pathway towards detection of solid tumors at an early stage in preclinical tumor models.

Interaction between monomers of two surfactants derived from the [Ru(2,2'-bpy)(3)](2+) complex and α, β and γ-cyclodextrins: formation of [2]- and [3]-pseudorotaxanes

Two new surfactants derived from the tris(2,2'-bipyridine) ruthenium(II) complex, [Ru(2,2'-bpy)(3)](2+), were synthesized and characterized: the double-tailed [Ru(2,2'-bipy)2(4,4'-(C(11)H(23))(2)-2,2'-bipy)](2+) surfactant (RuC11) and the mono-tailed [Ru(2,2'-bipy)(2)(4-(CH(3))-4'-(C(13)H(27))-2,2'-bipy)](2+) surfactant (RuC13). The main characteristic of these species is the presence of an inorganic complex as the polar head of the surfactant with interesting luminescence properties, which were used to study the interaction of these cationic surfactants with α-, β- and γ-cyclodextrins (CD). The results showed the formation of [2]- and [3]-pseudorotaxanes. The binding constant values as well as the stoichiometry of the complexes formed were obtained; the results were confirmed, from a qualitative point of view, with NMR spectra.

Study on the luminescence behavior of sulfobutylether-β-cyclodextrin with risperidone and its analytical application

The interaction of sulfobutylether-β-cyclodextrin (SBE-β-CD) with risperidone (RISP) was first described with luminol-SBE-β-CD chemiluminescence (CL) system by flow injection analysis (FIA). In luminol-SBE-β-CD CL system, the 1:1 SBE-β-CD···luminol(*) complexation could enhance CL intensity of luminol and produce the effect of complexation enhancement of CL (CEC). It was found that RISP could quench the CL intensity of SBE-β-CD···luminol(*) and caused the effect of complexation enhancement of quenching (CEQ), the formation constant K(R-CD) 3.4×10(4) L mol(-1) and the stoichiometric ratio 1:1 of RISP···SBE-β-CD complex were obtained by the proposed CL model. Association degree α 0.036 of RISP···SBE-β-CD complex was also given by CL method. Based on the linear relationship to the decrement of luminol-SBE-β-CD-RISP CL intensity and the logarithm of RISP concentration, RISP also can be quantified in the linear range of 3.0-500.0 nmol L(-1) with a detection limit of 1.0 nmol L(-1) (3σ). The proposed method was successfully applied to monitoring excreted RISP in human urine. It was found that RISP reached its maximum after oral administration for 1.5 h with the total excretion of 14.26% within 8.5 h; the elimination rate constant k and half-life time t(1/2) were 0.474 and 1.5 h, respectively.

Mg-Al-carbonate layered double hydroxides as a novel catalyst of luminol chemiluminescence

The interlayer carbonate in Mg-Al layered double hydroxides as a novel catalyst of luminol chemiluminescence has been reported for the first time, which has great potential in further applications of luminol chemiluminescence for sensitive sensors, catalyst-conjugated probes.