Direct and Indirect Chemiluminescence: Reactions, Mechanisms and Challenges

Molecular mechanism for the unusual enhancement of the second-step chemiluminescence production from the carcinogenic tetrabromohydroquinone and H2O2

We have found recently that two-step intrinsic hydroxyl radical (·OH)-dependent chemiluminescence (CL) could be produced by carcinogenic tetrahaloquinone and H2O2. However, the first-step CL was too fast to clearly detect the stepwise generation of ·OH and CL, and to distinguish the exact dividing point between the first-step and second-step CL. Here we found that, extremely clear two-step intrinsic CL could be produced by the relative slow reaction of tetrabromohydroquinone (TBHQ) with H2O2, which was directly dependent on the two-step ·OH generation. Interestingly, the second-step, but not the first-step CL production of TBHQ/H2O2 (CRET donor) was markedly enhanced by fluorescein (a typical xanthene dye, CRET acceptor) through a unique chemiluminescence resonance energy transfer (CRET) process. The novel CRET system of TBHQ/H2O2/fluorescein was successfully applied for the sensitive detection of TBHQ with the detection limit as low as 2.5 µmol/L. These findings will help to develop more sensitive and highly efficient CL or CRET systems and specific CL sensor to detect the carcinogenic haloquinones, which may have broad environmental applications.

Theoretical investigation on triphenylamine coelenteramide for bioinspired OLED application using thiophene rings in π-bridge

As light emitter of most marine organisms bioluminescence, coelenteramide (CLM) received much attention due to some exciting application in the field of bioinspired organic light-emitting devices (OLED). Nevertheless, native CLM only emit bright blue light. In order to obtain light of different colors, two CLM analogues, TPA-CLM and TPA-TP-CLM were designed by introduction of triphenylamine group and (thiophene) π-bridge. On the other hand, because the light emitter, CLM was produced by the chemical reaction which originates from the oxidation of bioluminescent substrate, coelenterazine (CLZ), it must be evaluated if and how substituent group tune the chemiluminescent (CL) reaction mechanism, firstly. In this article, the complete chemiluminescent reaction mechanism of TPA-CLZ and TPA-TP-CLZ and the photophysical properties of light emitters, TPA-CLM and TPA-TP-CLM were investigated by (time-dependent) density functional theory, (TD) DFT calculations. The calculations indicate that the introduction of triphenylamine and π-bridge minimally affect the complete reaction process. For the light emitters, TPA-CLM and TPA-TP-CLM, the calculation results indicate that the injection abilities of hole and electron can be largely improved by introduction of triphenylamine and π-bridge. The absorption and emission spectra appeared at longer wavelengths than native CLM. These results illustrate that TPA-CLM and TPA-TP-CLM are good candidates for bioinspired OLED application.

Stimuli-Responsive Polymer-Based Nanosystems for Cancer Theranostics

Stimuli-responsive polymers can respond to internal stimuli, such as reactive oxygen species (ROS), glutathione (GSH), and pH, biological stimuli, such as enzymes, and external stimuli, such as lasers and ultrasound, etc., by changing their hydrophobicity/hydrophilicity, degradability, ionizability, etc., and thus have been widely used in biomedical applications. Due to the characteristics of the tumor microenvironment (TME), stimuli-responsive polymers that cater specifically to the TME have been extensively used to prepare smart nanovehicles for the targeted delivery of therapeutic and diagnostic agents to tumor tissues. Compared to conventional drug delivery nanosystems, TME-responsive nanosystems have many advantages, such as high sensitivity, broad applicability among different tumors, functional versatility, and improved biosafety. In recent years, a great deal of research has been devoted to engineering efficient stimuli-responsive polymeric nanosystems, and significant improvement has been made to both cancer diagnosis and therapy. In this review, we summarize some recent research advances involving the use of stimuli-responsive polymer nanocarriers in drug delivery, tumor imaging, therapy, and theranostics. Various chemical stimuli will be described in the context of stimuli-responsive nanosystems. Accordingly, the functional chemical groups responsible for the responsiveness and the strategies to incorporate these groups into the polymer will be discussed in detail. With the research on this topic expending at a fast pace, some innovative concepts, such as sequential and cascade drug release, NIR-II imaging, and multifunctional formulations, have emerged as popular strategies for enhanced performance, which will also be included here with up-to-date illustrations. We hope that this review will offer valuable insights for the selection and optimization of stimuli-responsive polymers to help accelerate their future applications in cancer diagnosis and treatment.

Methods for detecting of cardiac troponin I biomarkers for myocardial infarction using biosensors: a narrative review of recent research

Background and Objective

In cardiovascular diseases (CVDs), acute myocardial infarction (AMI) is considered one of the leading causes of human death, and its diagnosis mainly relies on the detection of the cardiac biomarker troponin I. Traditional detection methods have certain limitations, which has prompted the development of methods with higher sensitivity and specificity. In recent years, biosensors, as an emerging technology, have been widely applied in the clinical medicine and biodetection fields. We retrieved and reviewed relevant articles published over the past 3 years and subsequently summarized the research progress of different types of biosensors in detecting cardiac troponin I and the challenges faced in achieving simple, specific, and portable point-of-care testing (POCT) technology for bedside rapid detection. The aim of this review is to serve as reference for the early diagnosis and treatment of CVDs.

Methods

This study searched for relevant literature published from 2019 to 2022 in the PubMed database of the National Center for Biotechnology Information (NCBI). The keywords used were as follows: "cardiac troponin I", "biosensor", "point-of-care testing", "electrochemical detection", and "surface-enhanced Raman spectroscopy".

Key Content and Findings

The review found that biosensor technology has high specificity and sensitivity in the detection of cardiac troponin I and is simpler and more convenient than is traditional laboratory testing. Its vigorous development can facilitate the diagnosis of AMI earlier and faster.

Conclusions

This study reviewed the progress of cardiac troponin I detection based on biosensing strategies. We found that cardiac troponin I detection methods based on biosensing strategies have their own advantages and disadvantages in clinical applications, and their sensitivity has been constantly improved. In the future, the detection of cardiac troponin I using biosensing technology will be simpler, faster, more sensitive, and portable.

A Reappraisal of the Utility of L-012 to Measure Superoxide from Biologically Relevant Sources

The detection of superoxide anion (O2●-) in biological tissues remains challenging. Barriers to convenient and reproducible measurements include expensive equipment, custom probes, and the need for high sensitivity and specificity. The luminol derivative, L-012, has been used to measure O2●- since 1993 with mixed results and concerns over specificity. The goal of this study was to better define the conditions for use and their specificity. We found that L-012 coupled with depolymerized orthovanadate, a relatively impermeable tyrosine phosphatase inhibitor, yielded a highly sensitive approach to detect extracellular O2●-. In O2●- producing HEK-NOX5 cells, orthovanadate increased L-012 luminescence 100-fold. The combination of L-012 and orthovanadate was highly sensitive, stable, scalable, completely reversed by superoxide dismutase, and selective for O2●- generating NOXes versus NOX4, which produces H2O2. Moreover, there was no signal from cells transfected with NOS3 (NO●) and NOS2(ONOO-). To exclude the effects of altered tyrosine phosphorylation, O2●- was detected using non-enzymatic synthesis with phenazine methosulfate and via novel coupling of L-012 with niobium oxalate, which was less active in inducing tyrosine phosphorylation. Overall, our data shows that L-012 coupled with orthovanadate or other periodic group 5 salts yields a reliable, sensitive, and specific approach to measuring extracellular O2●- in biological systems.

Photodynamic Therapy: From the Basics to the Current Progress of N-Heterocyclic-Bearing Dyes as Effective Photosensitizers

Photodynamic therapy, an alternative that has gained weight and popularity compared to current conventional therapies in the treatment of cancer, is a minimally invasive therapeutic strategy that generally results from the simultaneous action of three factors: a molecule with high sensitivity to light, the photosensitizer, molecular oxygen in the triplet state, and light energy. There is much to be said about each of these three elements; however, the efficacy of the photosensitizer is the most determining factor for the success of this therapeutic modality. Porphyrins, chlorins, phthalocyanines, boron-dipyrromethenes, and cyanines are some of the N-heterocycle-bearing dyes' classes with high biological promise. In this review, a concise approach is taken to these and other families of potential photosensitizers and the molecular modifications that have recently appeared in the literature within the scope of their photodynamic application, as well as how these compounds and their formulations may eventually overcome the deficiencies of the molecules currently clinically used and revolutionize the therapies to eradicate or delay the growth of tumor cells.

Design and synthesis of a small molecular NIR-II chemiluminescence probe for in vivo-activated H2S imaging

Chemiluminescence (CL) with the elimination of excitation light and minimal autofluorescence interference has been wieldy applied in biosensing and bioimaging. However, the traditional emission of CL probes was mainly in the range of 400 to 650 nm, leading to undesired resolution and penetration in a biological object. Therefore, it was urgent to develop CL molecules in the near-infrared window [NIR, including NIR-I (650 to 900 nm) and near-infrared-II (900 to 1,700 nm)], coupled with unique advantages of long-time imaging, sensitive response, and high resolution at depths of millimeters. However, no NIR-II CL unimolecular probe has been reported until now. Herein, we developed an H2S-activated NIR-II CL probe [chemiluminiscence donor 950, (CD-950)] by covalently connecting two Schaap's dioxetane donors with high chemical energy to a NIR-II fluorophore acceptor candidate via intramolecular CL resonance energy transfer strategy, thereby achieving high efficiency of 95%. CD-950 exhibited superior capacity including long-duration imaging (~60 min), deeper tissue penetration (~10 mm), and specific H2S response under physiological conditions. More importantly, CD-950 showed detection capability for metformin-induced hepatotoxicity with 2.5-fold higher signal-to-background ratios than that of NIR-II fluorescence mode. The unimolecular NIR-II CL probe holds great potential for the evaluation of drug-induced side effects by tracking its metabolites in vivo, further facilitating the rational design of novel NIR-II CL-based detection platforms.

Elucidation of an Aggregate Excited State in the Electrochemiluminescence and Chemiluminescence of a Thermally Activated Delayed Fluorescence (TADF) Emitter

The electrochemistry, electrochemiluminescence (ECL), and chemiluminescence (CL) properties of a thermally activated delayed fluorescence (TADF) emitter 4,4'-(1,2-dihydroacenaphthylene-5,6-diyl)bis(N,N-diphenylaniline) (TPA-ace-TRZ) and three of its analogues were investigated. TPA-ace-TRZ exhibits both (a) delayed onset of ECL and (b) long-persistent luminescence, which we have attributed to the formation of an aggregate excited state in excimer or exciplex form. The evidence of this aggregate excited state was consistent across ECL annihilation and coreactant pathways as well as in CL. The absolute ECL efficiency of TPA-ace-TRZ using benzoyl peroxide (BPO) as a coreactant was found to be 0.028%, which was 9-fold stronger than the [Ru(bpy)₃]²⁺/BPO reference coereactant system. Furthermore, the absolute CL quantum efficiency of TPA-ace-TRZ was determined to be 0.92%. The performance and flexibility of the TADF emitter TPA-ace-TRZ under these various emissive pathways are highly desirable toward applications in sensing, imaging, and light-emitting devices.

Chemiluminescent polymeric nanoprobes for tumor diagnosis: A mini review

Chemiluminescence (CL), a distinct luminescent process by taking advantage of chemical reactions rather than external light source, has recently attracted considerable research interests due to its high sensitivity and low background signal. The sensitivity and specificity of chemiluminescent signals in complex tumor microenvironment provide a sound basis for accurate detection of tumors. Various chemiluminescent nanoprobes with superior performance have been obtained by structural modification of chemiluminescent units or introduction of fluorescent dyes. In this review, we focused on the recent progress of chemiluminescent polymeric systems based on various chromophore substrates, including luminol, peroxyoxalates, 1, 2-dioxetanes and their derivatives for tumor detecting. And we also emphasized the design strategies, mechanisms and diagnostic applications of representative chemiluminescent polymeric nanoprobes. Finally, the critical challenges and perspectives of chemiluminescent systems usage in tumor diagnosis were also discussed.

2D MXene-Based Biosensing: A Review

MXene emerged as decent 2D material and has been exploited for numerous applications in the last decade. The remunerations of the ideal metallic conductivity, optical absorbance, mechanical stability, higher heterogeneous electron transfer rate, and good redox capability have made MXene a potential candidate for biosensing applications. The hydrophilic nature, biocompatibility, antifouling, and anti-toxicity properties have opened avenues for MXene to perform in vitro and in vivo analysis. In this review, the concept, operating principle, detailed mechanism, and characteristic properties are comprehensively assessed and compiled along with breakthroughs in MXene fabrication and conjugation strategies for the development of unique electrochemical and optical biosensors. Further, the current challenges are summarized and suggested future aspects. This review article is believed to shed some light on the development of MXene for biosensing and will open new opportunities for the future advanced translational application of MXene bioassays.

Organic persistent luminescence imaging for biomedical applications

Persistent luminescence is a unique visual phenomenon that occurs after cessation of excitation light irradiation or following oxidization of luminescent molecules. The energy stored within the molecule is released in a delayed manner, resulting in luminescence that can be maintained for seconds, minutes, hours, or even days. Organic persistent luminescence materials (OPLMs) are highly robust and their facile modification and assembly into biocompatible nanostructures makes them attractive tools for in vivo bioimaging, whilst offering an alternative to conventional fluorescence imaging materials for biomedical applications. In this review, we give attention to the existing limitations of each class of OPLM-based molecular bioimaging probes based on their luminescence mechanisms, and how recent research progress has driven efforts to circumvent their shortcomings. We discuss the multifunctionality-focused design strategies, and the broad biological application prospects of these molecular probes. Furthermore, we provide insights into the next generation of OPLMs being developed for bioimaging techniques.

Mo2C as Pre-Catalyst for the C-H Allylic Oxygenation of Alkenes and Terpenoids in the Presence of H2O2

In this study, commercially available molybdenum carbide (Mo2C) was used, in the presence of H2O2, as an efficient pre-catalyst for the selective C-H allylic oxygenation of several unsaturated molecules into the corresponding allylic alcohols. Under these basic conditions, an air-stable, molybdenum-based polyoxometalate cluster (Mo-POM) was formed in situ, leading to the generation of singlet oxygen (1O2), which is responsible for the oxygenation reactions. X-ray diffraction, SEM/EDX and HRMS analyses support the formation mainly of the Mo6O192− cluster. Following the proposed procedure, a series of cycloalkenes, styrenes, terpenoids and methyl oleate were successfully transformed into hydroperoxides. After subsequent reduction, the corresponding allylic alcohols were produced with good yields and in lab-scale quantities. A mechanistic study excluded a hydrogen atom transfer pathway and supported the twix-selective oxygenation of cycloalkenes on the more sterically hindered side via the 1O2 generation.

Ultrasound triggered organic mechanoluminescence materials

Ultrasound induced organic mechanoluminescence materials have become one of the focal topics in wireless light sources since they exhibit high spatiotemporal resolution, biocompatibility and excellent tissue penetration depth. These properties promote great potential in ultrahigh sensitive bioimaging with no background noise and noninvasive nanodevices. Recent advances in chemistry, nanotechnology and biomedical research are revolutionizing ultrasound induced organic mechanoluminescence. Herein, we try to summarize some recent researches in ultrasound induced mechanoluminescence that use various materials design strategies based on the molecular conformational changes and cycloreversion reaction. Practical applications, like noninvasive bioimaging and noninvasive optogenetics, are also presented and prospected.

Tuning the Intramolecular Chemiexcitation of Neutral Dioxetanones by Interaction with Ionic Species

The intramolecular chemiexcitation of high-energy peroxide intermediates, such as dioxetanones, is an essential step in different chemi- and bioluminescent reactions. Here, we employed the Time-Dependent Density Functional Theory (TD-DFT) methodology to evaluate if and how external stimuli tune the intramolecular chemiexcitation of model dioxetanones. More specifically, we evaluated whether the strategic placement of ionic species near a neutral dioxetanone model could tune its thermolysis and chemiexcitation profile. We found that these ionic species allow for the “dark” catalysis of the thermolysis reaction by reducing the activation barrier to values low enough to be compatible with efficient chemi- and bioluminescent reactions. Furthermore, while the inclusion of these species negatively affected the chemiexcitation profile compared with neutral dioxetanones, these profiles appear to be at least as efficient as anionic dioxetanones. Thus, our results demonstrated that the intramolecular chemiexcitation of neutral dioxetanones can be tuned by external stimuli in such a way that their activation barriers are decreased. Thus, these results could help to reconcile findings that neutral dioxetanones could be responsible for efficient chemi-/bioluminescence, while being typically associated with high activation parameters.

Electrogenerated chemiluminescence of luminol at a boron-doped diamond electrode for the detection of hypochlorite

Electrogenerated chemiluminescence (ECL) of luminol at a boron-doped diamond electrode has been used for hypochlorite determination. The presence of H₂O₂ induces the generation of the ECL signals of luminol. In contrast, the presence of hypochlorite oxidizes luminol directly to decrease the ECL signals of luminol. Accordingly, a decrease of the ECL signals of luminol in the presence of H₂O₂ was used as the signal response for hypochlorite detection. A linear decrease of ECL signals with the NaClO concentration in the range from 0 to 20 μM was observed with a sensitivity of 18.56 a.u. μM^-1 cm^-2. An estimated detection limit of 0.88 μM was achieved, which is around one order lower than the detection limit obtained using the normal electrochemical method with the same electrode. The system also provides a good selectivity towards Cu²⁺ and Na⁺. A reproducibility of 3.40%RSD was noted for 15 repetitive measurements. The analytical performance was found to be favourable in comparison to those of other typical electrochemical and electrochemiluminescence methods, indicating that it is applicable for real sample detection.

Comparison of the oxidative respiratory burst and mitogen-induced leukocyte responses of camels, goats, sheep, and cows

Background and Aim:

The reports from the Ministry of Agriculture and Fisheries suggest that camels suffer less compared to goats, sheep, and cows from a number of common infectious diseases in Oman. However, there is no immunological evidence to substantiate this claim. This present study is, therefore, an attempt to study the immunological responses of camels, goats, sheep, and cows by comparing their oxidative respiratory burst of peripheral blood leukocytes (PBLs) as a marker of innate immunity occurring during phagocytosis and the mitogenic responses of their peripheral blood mononuclear leukocytes (PBMLs) as a marker of their adaptive immune response.

Materials and Methods:

Ten female adult animals (n = 10) were selected from each species (goats, sheep, and cows). The goats, sheep, and cows were maintained at the Agricultural Experiment Station, while camels were kept at the Royal Camel Corps (RCC). Blood samples were collected from the jugular vein in 7 mL of heparin and ethylenediaminetetraacetic acid vacutainer tubes. The oxidative respiratory burst of PBLs was measured using a chemiluminescence (CL) assay. Reactants consisted of 75 mL of whole blood diluted (1:50), 75 mL of luminol/isoluminol, and 75 mL of zymosan opsonized with non-heat inactivated serum/heat-inactivated serum or non-opsonized zymosan. CL responses were measured as relative light units and expressed as the mean count per minute and peak CL values. The mitogenic response of PBMLs to concanavalin A (Con-A), phytohemagglutinin (PHA), and pokeweed mitogen (PWM) was tested using a WST-8 assay and read spectrophotometrically at 450 nm.

Results:

The present findings showed that camel PBLs generate significantly higher CL responses, both intracellularly as well as extracellularly, with zymosan opsonized with autologous serum. Camel PBLs demonstrated a significantly higher (p = 0.001) response when stimulated with zymosan opsonized with heat-inactivated serum compared to those of goat, sheep, and cow lymphocytes from camels exhibited significantly higher (p = 0.001) stimulation indices (SI) with Con-A, PHA, and PWM.

Conclusion:

The present study suggests that camels are capable of mounting both superior innate as well as adaptive immune responses and provide immunological evidence supporting the belief of some authors, who have proposed that camels are less susceptible to a number of common infectious diseases than other domesticated ruminants.

Biomimetic Radical Chemistry and Applications

Some of the most interesting aspects of free radical chemistry that emerged in the last two decades are radical enzyme mechanisms, cell signaling cascades, antioxidant activities, and free radical-induced damage of biomolecules. In addition, identification of modified biomolecules opened the way for the evaluation of in vivo damage through biomarkers. When studying free radical-based chemical mechanisms, it is very important to establish biomimetic models, which allow the experiments to be performed in a simplified environment, but suitably designed to be in strict connection with cellular conditions. The 28 papers (11 reviews and 17 articles) published in the two Special Issues of Molecules on "Biomimetic Radical Chemistry and Applications (2019 and 2021)" show a remarkable range of research in this area. The biomimetic approach is presented with new insights and reviews of the current knowledge in the field of radical-based processes relevant to health, such as biomolecular damages and repair, signaling and biomarkers, biotechnological applications, and novel synthetic approaches.