Delineating a Tailor-Made Fluorescent Probe Designed for the Selective Detection of Tyrosinase

A dicyanoisophorone based fluorescent probe (E)-2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-en-1-ylidene)malononitrile (DCIP-OH) was developed for the selective sensing of tyrosinase in apple extract and live cells. The probe was obtained by the condensation of 2-(3,5,5-trimethylcyclohex-2-en-1-ylidene)malononitrile with 4-hydroxybenzaldehyde. Upon interaction with tyrosinase, the probe exhibited absorbance switching from 417 nm to 357 nm, accompanied by a slight increase in absorption value and an isosbestic point observed at 373 nm. Additionally, a reduction in emission intensity at 592 nm was observed. Furthermore, we successfully employed the probe for sensing of tyrosinase in apple extract and conducted inhibition studies by using kojic acid. LOD was determined to be ~0.4 nM. Moreover, the biocompatible nature of DCIP-OH enabled its effective localization in epithelial-like melanoma cells, B16F10, where it demonstrated successful fluorescent probing of intracellular tyrosinase.

Ultrasensitive detection of tyrosinase with click reaction-combined dark-field imaging platform

Tyrosinase (TYR) is an essential oxidase that is responsible for the regulation of multiple physiological processes and diseases. Achieving the trace and reliable detection of TYR in complex biological samples is of great significance for the diagnosis of TYR-related diseases, but which faces a great challenge. In this study, we developed an ingenious and powerful method for the ultrasensitive detection of TYR by click reaction-combined dark-field microscopy. This method begins with the formation of cuprous ions (Cu+) based on the reduction of copper ions (Cu2+) by ascorbic acid (AA). Subsequently, the formed Cu+ can catalyze the crosslinking between azide- and alkyne-functionalized gold nanoparticles, causing a significant red-shift in the scattering spectrum. However, AA can chelate with TYR, which inhibits the generation of Cu+ and subsequent click reaction, thus achieving TYR-controlled scattering spectral shift. The proposed sensing platform shows a good linear detection range of 0.01-0.8 U/L with a low detection limit of 0.003 U/L, which is three orders of magnitude lower than the best performance of TYR sensing probes reported to date. Most importantly, the strategy has the ability to reliably and accurately detect TYR in serum sample, suggesting its potential clinical application in diagnosing TYR-related diseases. This visual sensing platform offers promising prospects for future research in enzymatic analysis and biomedical diagnostics.

Recent advances in FRET probes for mitochondrial imaging and sensing

Mitochondria, as essential organelles in cells, play a crucial role in cellular growth and apoptosis. Monitoring mitochondria is of great importance, as mitochondrial dysfunction is often considered a hallmark event of cell apoptosis. Traditional fluorescence probes used for mitochondrial imaging and sensing are mostly intensity-based and are susceptible to factors such as concentration, the probe environment, and fluorescence intensity. Probes based on fluorescence resonance energy transfer (FRET) can effectively overcome external interference and achieve high-contrast imaging of mitochondria as well as quantitative monitoring of mitochondrial microenvironments. This review focuses on recent advances in the application of FRET-based probes for mitochondrial structure imaging and microenvironment sensing.

Fabrication of FRET based nano sensor from biomass-derived fluorescent carbon quantum dots and naphthalimide for ratiometric detection of nitric oxide: To examine nitrite levels in meat samples

Nitric oxide (NO) is a ubiquitous, gaseous, free radical signaling molecule which plays a key role in physiological and pathological processes. Literature reports revealed that the conventional methods such as colorimetry, electron paramagnetic resonance (EPR), electrochemical etc. to detect NO are costly, time consuming and lack resolution, particularly in aqueous or biological system. Thus, in this context, herein we have developed covalently linked biomass derived carbon quantum dots (CQDs) and naphthalimide based nano sensor system for FRET based ratiometric detection of nitric oxide (NO) in pure aqueous media. The CQDs derived from orange peels were characterized using UV-visible absorption, fluorescence spectroscopy, PXRD, TEM, FT-IR and zeta potential studies. Further, the obtained CQDs were functionalized with amine functionality, and subsequently linked with naphthalimide derivative (5) using terephthaldehyde through covalent bond formation. The conjugation of naphthalimide (5) and functionalized CQDs was studied using DLS, zeta potential, FT-IR and time resolved fluorescence spectroscopy. The excitation of developed nano sensor system at λ_ex 360 nm results in fluorescence emission at λ_em 530 nm which establishes the FRET pair between the CQDs and naphthalimide unit. However, in the presence of NO, the observed FRET pair abolishes due to the cleavage of NO susceptible imine bond. The developed sensor demonstrates high selectivity towards NO with limit of detection (LOD) and limit of quantification (LOQ) of 15 nM and 50 nM respectively. Further, the developed sensor system was also utilized for indirect detection of nitrite (NO₂^-) in food samples for food safety and monitoring.

Persistent and Efficient Multimodal Imaging for Tyrosinase Based on Two-Photon Excited Fluorescent and Room-Temperature Phosphorescent Probes

Tyrosinase is crucial to regulate the metabolism of phenol derivatives, playing an important role in the biosynthesis of melanin pigments, whereas an abnormal level of tyrosinase would lead to severe diseases. It is rather necessary to develop a sensitive and selective imaging tool to assess the level of tyrosinase in vivo. We thoroughly researched the luminous mechanism of the existing TPTYR probe and provided design strategies to improve its two-photon excited fluorescence properties. The designed probes benza2-TPTYR and product benza2-TPTYR-coumarin have large two-photon absorption cross sections at the NIR spectral region (41 GM/706 nm, 71 GM/852 nm), while benza2-TPTYR-coumarin possesses easily distinguishable spectrum in the visible region and a high fluorescence efficiency (Φ_F = 0.27). What is more, novel two-photon excited multimodal imaging based on the pure organic small molecule benza1-TPTYR-coumarin (61 GM/936 nm) is proposed first, simultaneously possessing strong instantaneous fluorescent (563.79 nm) and persistent room-temperature phosphorescent emissions (767.68 nm, 0.54 ms).

Synthesis and photophysical properties of photostable 1,8-naphthalimide dyes incorporating benzotriazole-based UV absorbers

We developed a series of blue-emitting 1,8-naphthalimide dyes covalently attached to 2-(2-hydroxyphenyl)-2H-benzotriazoles that retard photodegradation of the fluorophore. The dyes displayed weaker fluorescence emissions than the parent 1.8-naphthalimide. Quantum chemical calculations suggested that the decreased fluorescence was caused by the nonradiative deactivation promoted through the excited state intramolecular proton transfer (ESIPT) in benzotriazole components. The dyes' phosphorescences in a degassed solution at 77 K were more efficient than that of the parent 1.8-naphthalimide, indicating a possible deactivation pathway through intersystem crossing. PMMA films doped with these dyes showed higher resistance against photoaging than the film doped with an equimolar mixture of constituent 1.8-naphthalimide and the benzotriazole derivatives. Thus, the covalently linked benzotriazole units slow fluorophore degradation not only by preferential absorption of harmful UV light, which is found in the film with a simple mixture of two components, but also by the nonradiative deactivation involved in benzotriazole units.

Highly photostable blue fluorescence dyes were developed by hybridization of 1,8-naphthalimides with benzotriazole-based UV absorbers enabling a non-radiative energy dissipation process of excited-state intramolecular proton transfer (ESIPT).

One-pot synthesis of a peroxidase-like nanozyme and its application in visual assay for tyrosinase activity

Both single-atom nanozymes (SAzymes) and protein-template metal nanoparticles have attracted comprehensive attention in several respects owing to their excellent catalytic performance, green facile synthesis process, and robustness. Herein, the peroxidase-like activity of single-atom copper anchored on bovine hemoglobin-template gadolinium nanoparticles (Cu,Gd@BHb^FITC NPs) were successfully synthesized and two sensitive turn-on fluorescence strategies for tyrosinase (TYR) activity sensing were proposed for the first time. For strategy Ⅰ, TYR sensing was carried out from 1.00 to 7.80 U/mL with the detection limit (LOD) of 0.20 U/mL based on the fluorescence resonance energy transfer (FRET) between the fluorescein isothiocyanate (FITC) and the in situ generated polydopamine dots (PDA-dots). For strategy Ⅱ, The LOD of TYR was 0.05 U/mL with the linear range of 0.40-19.70 U/mL based on the elimination of inner-filter effect (IEF) between FITC and the reaction product (RC) of phenol and 4-Aminoantipyrine (AAP). The smartphone-assisted sensing platform was applied to construct the on-site detection of TYR with both strategies. The developed probe possessed good selectivity and was successfully utilized to TYR detection in serum samples.

Highly stable fluorescent probe based on mesoporous silica coated quantum dots for sensitive and selective detection of Cd2

Cadmium ions have been of crucial concern due to the high biological toxicity and serious environmental risks. Various fluorescent Cd-sensitive probes have been reported with improved sensing properties, but still severely suffer from poor stability and insufficient selectivity. In this work, a stable fluorescent probe based on silica encapsulated quantum dots (QDs) have been developed for rapid, sensitive and selective detection of cadmium ion. To improve fluorescence stability, the strategy of mesoporous silica encapsulation was adopted, in which the mesoporous silica shell offers numerous channels for Cd²⁺. Further, the Forster Resonance Energy Transfer (FRET) system, where QDs@mSiO₂and rhodamine B (RB) are used as donors and acceptors respectively, has been constructed, in which the mesoporous silica shell also serves as spacers with tunable thickness for controlling the QD-RB distance. Under optimal conditions, the probes possess a sensitive fluorescence response with a detection limit of 1.25μM. Visual detection can be realized by the obvious fluorescence changes of the FRET system. In addition, the FRET system shows promising sensing performances both in tap water samples and rice-washed water samples, confirming a great potential for practical application.

Trends in small organic fluorescent scaffolds for detection of oxidoreductase

Oxidoreductases are diverse class of enzymes engaged in modulating the redox homeostasis and cellular signaling cascades. Abnormal expression of oxidoreductases including thioredoxin reductase, azoreductase, cytochrome oxidoreductase, tyrosinase and monoamine oxidase leads to the initiation of numerous disorders. Thus, enzymes are the promising biomarkers of the diseased cells and their accurate detection has utmost significance for clinical diagnosis. The detection method must be extremely selective, sensitive easy to use, long self-life, mass manufacturable and disposable. Fluorescence assay approach has been developed potential substitute to conventional techniques used in enzyme's quantification. The fluorescent probes possess excellent stability, high spatiotemporal ratio and reproducibility represent applications in real sample analysis. Therefore, the enzymatic transformations have been monitored by small activatable organic fluorescent probes. These probes are generally integrated with enzyme's substrate/inhibitors to improve their binding affinity toward the enzyme's catalytic site. As the recognition unit bio catalyzed, the signaling unit produces the readout signals and provides novel insights to understand the biochemical reactions for diagnosis and development of point of care devices. Several structural modifications are required in fluorogenic scaffolds to tune the selectivity for a particular enzyme. Hence, the fluorescent probes with their structural features and enzymatic reaction mechanism of oxidoreductase are the key points discussed in this review. The basic strategies to detect each enzyme are discussed. The selectivity, sensitivity and real-time applications are critically compared. The kinetic parameters and futuristic opportunities are present, which would be enormous benefits for chemists and biologists to understand the facts to design and develop unique fluorophore molecules for clinical applications.

Recent advances in the construction and analytical applications of carbon dots-based optical nanoassembly

Recently, more and more attention has been focused on the construction and analytical applications of optical nanoassembly through combining carbon dots (CDs) with various other functional nanomaterials. The rational design and manufacture of CDs-based optical nanoassembly will be critical to meeting the needs of analytical science. The last decade has witnessed the immense potential of CDs-based optical nanoassembly in multiple sensing applications owing to their controlled optical properties, adjustable surface chemistry and microscopic morphology. This feature article collects the recent advances in the research and development of CDs-based optical nanoassembly and their applications in analytical sensors, aiming to provide vital insights and suggestions to inspire their broad sensing applications.

3-Aminophenyl Boronic Acid Functionalized Quantum-Dot-Based Ratiometric Fluorescence Sensor for the Highly Sensitive Detection of Tyrosinase Activity

Using the commercially available and economical 6-hydroxycoumarin (6-HC) as the substrate, a dual-emission ratiometric fluorescence sensor was developed to detect tyrosinase (TYR) activity based on 3-aminophenyl boronic acid functionalized quantum dots (APBA-QDs). TYR can catalyze 6-HC, a monohydroxy compound, to form a fluorescence-enhancing o-hydroxy compound, 6,7-dihydroxycoumarin. Owing to the special covalent binding between the o-hydroxyl and boric acid groups, APBA-QDs react with 6,7-dihydroxycoumarin to form a five-membered ring ester dual-emission fluorescence probe for TYR. With an increase in TYR activity, the fluorescence at 675 nm originating from the QDs is gradually quenched, whereas that at 465 nm owing to 6,7-dihydroxycoumarin increases. Referencing the decreasing signal of the dual-emission probe at 675 nm to measure the increasing signal at 465 nm, a ratiometric fluorescence method was established to detect the TYR activity with high sensitivity and selectivity. Under the conditions optimized via response surface methodology, a linear range of 0-0.05 U/mL was obtained for the TYR activity. The detection limit was as low as 0.003 U/mL. This sensing strategy can also be adopted for the rapid screening of the TYR inhibitors.

Fast tyrosinase detection in early stage melanoma with nanomolar sensitivity using a naphthalimide-based fluorescent read-out probe

We report an expeditious approach for selective tyrosinase detection in early stage melanoma with nanomolar sensitivity using a napthalimide-based fluorescent probe.

Electrochemistry-Regulated Recyclable SERS Sensor for Sensitive and Selective Detection of Tyrosinase Activity

Tyrosinase (TYR) which can catalyze the oxidation of catechol is recognized as a significant biomarker of melanocytic lesions, thus developing powerful methods for the determination of TYR activity is highly desirable for the early diagnosis of melanin-related diseases, including melanoma. Herein, we develop a novel portable and recyclable surface-enhanced Raman scattering (SERS) sensor, prepared by assembling gold nanoparticles and p-thiol catechol ( p-TC) on an ITO electrode, for detecting TYR activity via the SERS spectral variation caused by the conversion of p-TC into its corresponding quinone under TYR catalysis. The developed SERS sensor has a rapid response to TYR within 1 min under the optimized conditions and shows high selectivity for TYR with the detection limit at 0.07 U/mL. Importantly, this SERS sensor can be easily regulated by applying negative voltage to achieve circular utilization, favoring the automation of SERS detection. Furthermore, the presented recyclable SERS sensor can perform well on both the determination of TYR activity in serum and the assessment of TYR inhibitor, demonstrating huge potential in the sensitive, selective, and facile detection of TYR activity for disease diagnosis and drug screening related with TYR.

A colorimetric and near -infrared ratiometric fluorescent probe for the determination of endogenous tyrosinase activity based on cyanine aggregation

A ratiometric fluorescent probe for TYR activity with high sensitivity was developed based on the H-aggregation of a cyanine dye.

A highly selective naphthalimide-based ratiometric fluorescent probe for the recognition of tyrosinase and cellular imaging

Upon the addition of tyrosinase to the probe solution, the monophenolic unit is oxidized to o-dihydroxy and consequently releases the 4-aminonaphthalimide unit.