Signal-On Detection of Dopamine and Tyrosinase Using Tris(hydroxypropyl)phosphine as a New Lucigenin Chemiluminescence Coreactant

Dopamine (DA) is a very imperative neurotransmitter in our body, since it contributes to several physiological processes in our body, for example, memory, feeling, cognition, cardiovascular diseases, and hormone secretion. Meanwhile, tyrosinase is a critical biomarker for several dangerous skin diseases, including vitiligo and melanoma cancer. Most of the reported chemiluminescent (CL) methods for monitoring DA and tyrosinase are signal-off biosensors. Herein, we introduce a new chemiluminescent "signal-on" system, lucigenin-tris(hydroxypropyl)phosphine (THPP), for the selective determination of DA and tyrosinase. THPP is well known as a versatile and highly water-soluble sulfhydryl-reducing compound that is more highly stable against air oxidation than common disulfide reductants. By employing THPP for the first time as an efficient lucigenin coreactant, the lucigenin-THPP system has shown a high CL response (approximately 16-fold) compared to the lucigenin-H2O2 classical CL system. Surprisingly, DA can remarkably boost the CL intensity of the lucigenin-THPP CL system. Additionally, tyrosinase can efficiently catalyze the conversion of tyramine to DA. Therefore, lucigenin-THPP was employed as an ultrasensitive and selective signal-on CL system for the quantification of DA, tyrosinase, and THPP. The linear ranges for the quantification of DA, tyrosinase, and THPP were 50-1000 nM, 0.2-50 μg/mL, and 0.1-800 μM, respectively. LODs for DA and tyrosinase were estimated to be 24 nM and 0.18 μg/mL, respectively. Additionally, the CL system has been successfully employed for the detection of tyrosinase in human serum samples and the assay of DA in human serum samples as well as in dopamine injection ampules with excellent obtained recoveries.

Biosensors; a novel concept in real-time detection of autophagy

Autophagy is an early-stage response with self-degradation properties against several insulting conditions. To date, the critical role of autophagy has been well-documented in physiological and pathological conditions. This process involves various signaling and functional biomolecules, which are involved in different steps of the autophagic response. During recent decades, a range of biochemical analyses, chemical assays, and varied imaging techniques have been used for monitoring this pathway. Due to the complexity and dynamic aspects of autophagy, the application of the conventional methodology for following autophagic progression is frequently associated with a mistake in discrimination between a complete and incomplete autophagic response. Biosensors provide a de novo platform for precise and accurate analysis of target molecules in different biological settings. It has been suggested that these devices are applicable for real-time monitoring and highly sensitive detection of autophagy effectors. In this review article, we focus on cutting-edge biosensing technologies associated with autophagy detection.

Recent Advancements on Self-Immolative System Based on Dynamic Covalent Bonds for Delivering Heterogeneous Payloads

The precisely spatial-temporal delivery of heterogeneous payloads from a single system with the same pulse is in great demand in realizing versatile and synergistic functions. Very few molecular architectures can satisfy the strict requirements of dual-release translated from single triggers, while the self-immolative systems based on dynamic covalent bonds represent the "state-of-art" of ultimate solution strategy. Embedding heterogeneous payloads symmetrically onto the self-immolative backbone with dynamic covalent bonds as the trigger, can respond to the quasi-bio-orthogonal hallmarks which are higher at the disease's microenvironment to simultaneously yield the heterogeneous payloads (drug A/drug B or drug/reporter). In this review, the modular design principles are concentrated to illustrate the rules in tailoring useful structures, then the rational applications are enumerated on the aspects of drug codelivery and visualized drug-delivery. This review, hopefully, can give the general readers a comprehensive understanding of the self-immolative systems based on dynamic covalent bonds for delivering heterogeneous payloads.

Dual Chemiexcitation by a Unique Dioxetane Scaffold Gated by an OR Logic Set of Triggers

Chemiexcitation of phenoxy-1,2-dioxetane chemiluminescent luminophores is initiated by electron transfer from a meta-positioned phenolate ion to the peroxide-dioxetane bond. Here we report the development of a unique 1,2-dioxetane chemiluminescent scaffold with chemiexcitation gated by an OR logic dual-set of triggering events. This scaffold is composed of meta-dihydroxyphenyl-1,2-dioxetane-adamantyl molecules, equipped with acrylic acid and chlorine substituents, that chemiexcitation under physiological conditions. A dual-mode chemiluminescent probe, armed with two different triggering substrates designed for activation by the enzymes β-galactosidase and alkaline phosphatase, was synthesized. The probe emitted intense light signals in the response to each enzyme, demonstrating its ability to serve as a single-component chemiluminescent sensor for dual-analyte detection. We also demonstrated the ability of the probe to detect β-galactosidase and phosphatase activities in bacteria. This is the first 1,2-dioxetane scaffold capable of responding to two different chemiexcitation events from two different positions on the same dioxetane molecule. We anticipate that the OR-gated mode of chemiexcitation, described herein, will find utility in the preparation of chemiluminescent probes with a dual-analyte detection/imaging mode.

Hydrogen-bond-driven self-assembly of chemiluminophore affording long-lasting in vivo imaging

Developing chemiluminescence probe with a slow kinetic profile, even a constant emission within analytical time, would improve the analytical sensitivity, but still remains challenging. This work reports a novel strategy to afford long-lasting in vivo imaging by developing a self-assembled chemiluminophore HPQCL-Cl via the introduction of the hydrogen-bond-driven self-assembled dye HPQ to Schaap's dioxetane. Compared with classical chemiluminophore HCL, self-assembled HPQCL-Cl was isolated from the physiological environment, thereby lowering its deprotonation and prolonging its half-life. Based on HPQCL-Cl, the long-lasting in vivo imaging of 9L-lacz tumor was achieved by developing a β-gal-responsive probe. Its signals remained constant (<5% change) for about 20 min, which may provide a wide time window for the determination of β-gal. This probe also showed high tumor-to-normal tissue ratio throughout tumor resection, highlighting its potential in image-guided clinical surgery.

An Activatable Near-Infrared Afterglow Theranostic Prodrug with Self-Sustainable Magnification Effect of Immunogenic Cell Death

Herein, we report an activatable near-infrared (NIR) afterglow theranostic prodrug that circumvents high background noise interference caused by external light excitation. The prodrug can release hydroxycamptothecin (HCPT) in response to the high intratumoral peroxynitrite level associated with immunogenic cell death (ICD), and synchronously activate afterglow signal to monitor the drug release process and cold-to-hot tumor transformation. The prodrug itself is an ICD inducer achieved by photodynamic therapy (PDT). PDT initiates ICD and recruits first-arrived neutrophils to secrete peroxynitrite to trigger HCPT release. Intriguingly, we demonstrate that HCPT can significantly amplify PDT-mediated ICD process. The prodrug thus shows a self-sustainable ICD magnification effect by establishing an "ICD-HCPT release-amplified ICD" cycling loop. In vivo studies demonstrate that the prodrug can eradicate existing tumors and prevent further tumor recurrence through antitumor immune response.

Synthesis and Evaluation of Ubiquitin-Dioxetane Conjugate as a Chemiluminescent Probe for Monitoring Deubiquitinase Activity

The removal of ubiquitin (Ub) from a modified protein or Ub chain is a process that occurs regularly by the ubiquitin-proteasome system. This process is known to be mediated by various deubiquitinating enzymes (DUBs) in order to control the protein's half-life and its expression levels among many other signaling processes. Since the function of DUBs is also involved in numerous human diseases, such as cancer, there is an obvious need for an effective diagnostic probe that can monitor the activity of these enzymes. We have developed the first chemiluminescence probe for detection of DUBs activity. The probe was prepared by conjugation of the chemically synthesized C-terminally activated Ub(1-75) with a Gly-enolether precursor. Subsequent oxidation, under aqueous conditions, of the enolether conjuagate with singlet-oxygen furnished the dioxetane probe Ub-CL. This synthesis provides the first example of a dioxetane-luminophore protein conjugate. The probe's ability to detect deubiquitinating activity was successfully validated with three different DUBs. In order to demonstrate the advantage of our new probe, comparison measurements for detection of DUB UCH-L3 activity were performed between the chemiluminescent probe Ub-CL and the well-known Ub-AMC probe. The obtained data showed significantly higher S/N, for probe Ub-CL (>93-fold) in comparison to that observed for Ub-AMC (1.5-fold). We anticipate that the successful design and synthesis of the turn-ON protein-dioxetane conjugate probe, demonstrated in this work, will provide the insight and motivation for preparation of other relevant protein-dioxetane conjugates.

Powerful Chemiluminescence Probe for Rapid Detection of Prostate Specific Antigen Proteolytic Activity: Forensic Identification of Human Semen

The prostate specific antigen (PSA), a serine protease with chymotrypsin-like activity, is predominantly expressed in the prostate and is considered as the most common marker in use to identify and follow the progress of prostate cancer. In addition, it is also now accepted as a marker for detecting semen in criminal cases. Here, we describe the design, synthesis, and evaluation of the first chemiluminescence probe for detection of PSA enzymatic activity. The probe activation mechanism is based on a catalytic cleavage of a specific peptidyl substrate, followed by a release of a phenoxy-dioxetane luminophore, that then undergoes efficient chemiexcitation to emit a green photon. The probe exhibits a significant turn-on response upon reaction with PSA and produces strong light emission signal with an extremely high signal-to-noise ratio. Comparison of the chemiluminescence probe with an analogous fluorescence probe showed superior detection capability in terms of response time and sensitivity. In addition, the probe was able to efficiently detect and image human semen traces on fabric, even after 3 days from sample preparation. The advantageous sensitivity and simplicity of a chemiluminescence assay to detect seminal fluid was effectively demonstrated by on-site measurements using a small portable luminometer. It is expected that the new chemiluminescence probe would be broadly useful for numerous applications in which PSA detection or imaging is required.

Activity-Based Optical Sensing Enabled by Self-Immolative Scaffolds: Monitoring of Release Events by Fluorescence or Chemiluminescence Output

Functional molecular scaffolds comprised of self-immolative adaptors are being used in widespread applications in the fields of enzyme activity analyses, signal amplification, and bioimaging. Optically detected chemical probes are very promising compounds for sensing and diagnosis, since they present several attractive features such as high specificity, low detection limits, fast response times, and technical simplicity. During the last two decades, we have developed several distinct molecular scaffolds that harness the self-immolative disassembly feature of these adaptors to amplify chromogenic output for diagnosis and drug delivery applications. In order to study the molecular behavior of the various amplification systems, an optical output, used to monitor the progress of the disassembly pattern, was required. Therefore, over the course of our research, diverse molecular scaffolds that produce an optical signal in response to a disassembly step, were evaluated. These optically active scaffolds have been incorporated into self-immolative dendrimers and self-immolative polymers to implement unique disassembly properties that result with linear and exponential signal amplification capabilities. In addition, some scaffolds, aimed for linker technology, were used in delivery systems to monitor release of drug molecules. The optical signal used to monitor the release event could be produced by analysis of reporter molecules with chromogenic or fluorogenic properties. Recently, we have also developed molecular scaffolds modified to produce a chemiluminescent signal to monitor the self-immolative disassembly step. The main advantage of these scaffolds over others is the use of chemiluminescence as an output signal. It is well-known that chemiluminescence is considered as one the most sensitive diagnostic methods due to its high signal-to-noise ratio. The unique structures of the self-immolative chemiluminescence scaffolds have been used in the design of three different distinctive concepts: self-immolative chemiluminescence polymers, auto-inductive amplification systems with chemiluminescence signal and monitoring of drug release by a chemiluminescence output. Furthermore, we reported the design and synthesis of the first theranostic prodrug for the monitoring of drug release achieved by a chemiluminescence mode of action. Quinone-methide elimination has proven to serve as a valuable functional tool for composing molecular scaffolds with self-immolative capabilities. Such scaffolds function as molecular adaptors that can almost simultaneously release a target molecule with an accompanied emission of a light signal that is used to monitor the release event. We anticipate that these self-immolative scaffolds will continue to find utility as functional linkers in various chemical and biological research areas such as drug delivery, theranostic applications, and as molecular sensors with signal amplification.

Lighting up alkaline phosphatase in drug-induced liver injury using a new chemiluminescence resonance energy transfer nanoprobe

We present a new nanoprobe based on chemiluminescence resonance energy transfer for in vivo imaging of drug-induced alkaline phosphatase (ALP). This probe exhibits the perfect degrees of high sensitivity and specificity for real-time monitoring of ALP levels to directly evaluate drug-induced liver injury.