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.

Review on Lysosomal Metal Ion Detection Using Fluorescent Probes.

Metal ions are indispensable and play an important role in living systems. Metal ions coordinated to metalloenzymes pocket activate the bound substrate and labile metal ions maintaining the ionic balance. The amount of metal ions present in various subcellular compartments of the cells is highly regulated for maintaining cellular homeostasis. An imbalance in the metal ion concentration is related to several diseases and results in serious pathological conditions. Mostly the internalized metal ions are processed in the lysosomal compartment of the cell. A delicate regulation of metal ions in the lysosomal compartment can modulate the lysosomal pH and inhibit hydrolytic enzymes, which ultimately causes lysosomal storage disorders. In the past decade, the understanding and regulation of lysosomal metal ions based on fluorometric methods have gained significant attention. In this review, we have comprehensively summarized the development of various fluorescent reporters over the past five years for a selective and sensitive estimation of lysosomal metal ion concentration. We believe this consolidated and timely review will help researchers working in the areas associated with lysosomal metal ions.

Trivalent metal ion sensor enabled bioimaging and quantification of vaccine-deposited Al3+ in lysosomes.

Extracellular metallic debris is deposited into the well-known 'recycle bins' of the cells named lysosomes. The accumulation of unwanted metal ions can cause dysfunction of hydrolyzing enzymes and membrane rupturing. Thus, herein, we synthesized rhodamine-acetophenone/benzaldehyde derivatives for the detection of trivalent metal ions in aqueous media. In solution, the synthesized probes exhibited a 'turn-on' colorimetric and fluorometric response upon complexation with trivalent metal ions (M3+). Mechanistically, M3+ chelation enables the appearance of a new emission band at approximately 550 nm, which verifies the disruption of the closed ring and the restoration of conjugation on the xanthene core in rhodamine 6G derivatives. Exclusive localization of the biocompatible probes at the lysosomal compartment favored the quantification of deposited Al3+. Moreover, the novelty of the work lies in the detection of Al3+ deposited in the lysosome that originated from hepatitis B vaccines, which shows their efficiency for near future in vivo applications.

Mitochondria-Directing Fluorogenic Probe: An Efficient Amyloid Marker for Imaging Lipid Metabolite-Induced Protein Aggregation in Live Cells and Caenorhabditis elegans.

The design and development of optical probes for sensing neurotoxic amyloid fibrils are active and important areas of research and are undergoing continuous advancements. In this paper, we have synthesized a red emissive styryl chromone-based fluorophore (SC1) for fluorescence-based detection of amyloid fibrils. SC1 records exceptional modulation in its photophysical properties in the presence of amyloid fibrils, which has been attributed to the extreme sensitivity of its photophysical properties toward the immediate microenvironment of the probe in the fibrillar matrix. SC1 also shows very high selectivity toward the amyloid-aggregated form of the protein as compared to its native form. The probe is also able to monitor the kinetic progression of the fibrillation process, with comparable efficiency as that of the most popular amyloid probe, Thioflavin-T. Moreover, the performance of SC1 is least sensitive to the ionic strength of the medium, which is an advantage over Thioflavin-T. In addition, the molecular level interaction forces between the probe and the fibrillar matrix have been interrogated by molecular docking calculations which suggest the binding of the probe to the exterior channel of the fibrils. The probe has also been demonstrated to sense protein aggregates from the Aß-40 protein, which is known to be responsible for Alzheimer's disease. Moreover, SC1 exhibited excellent biocompatibility and exclusive accumulation at mitochondria which allowed us to successfully demonstrate the applicability of this probe to detect mitochondrial-aggregated protein induced by an oxidative stress indicator molecule 4-hydroxy-2-nonenal (4-HNE) in A549 cell lines as well as in a simple animal model like Caenorhabditis elegans. Overall, the styryl chromone-based probe presents a potentially exciting alternative for the sensing of neurotoxic protein aggregation species both in vitro as well as in vivo.

Rationally designed far-red emitting styryl chromones and a magnetic nanoconjugate for strip-based 'on-site' detection of metabolic markers.

The global burden of liver damage and renal failure necessitates technology-aided evolution towards point-of-care (POC) testing of metabolic markers. Hence in the prevalence of current health conditions, achieving on-site detection and quantifying serum albumin (SA) can contribute significantly to halting the increased mortality and morbidity rate. Herein, we have rationally designed and synthesized far-red emitting, solvatofluorochromic styryl chromone (SC) derivatives SC1 and SC2, and SC2-conjugated fluorescent magnetic nanoparticles (SCNPs) for sensing SA with a fluorogenic response via interacting at an atypical drug binding site. In solution, the highly sensitive and selective fluorogenic response was evaluated by the prominent amplification and blue-shift in the emission maxima of the probes from deep red to dark yellow through an intermediate orange emission. The transformation of the fluorogen into a fluorophore was manifested through spectroscopic measurements. The stabilization of the probes at protein pockets was ascribed to the non-covalent interactions, such as H-bonding, cation-π, and hydrophobic interactions, as unveiled by docking studies. The practical applications revealed the novelty of SC derivatives through (a) the capability to detect SA isolated from real blood samples via a turn-on fluorescence response; (b) the design of a simple, cheap, and portable test-strip using a glass-slide loaded with solid-state emissive SC2, which provided differential emission color of the SC2-HSA complex in solution and the solid-state with increasing concentration of HSA. Moreover, a smartphone-based color analysis application was employed to obtain the ratio of green and red (G/R) channels, which was utilized for quantitative detection of HSA; (c) the biocompatibility of the SC1 was ascertained through confocal laser scanning microscopic imaging (CLSM). Detailed investigation showed that SC1 could entirely localize in the mitochondria and evolve as a promising biomarker for distinguishing cancer cells from normal cells. Additionally, the validation of uncommon binding of SC1 and SC2 between domains I and III was determined using competition experiments with a known site-specific binder and molecular docking studies. This unique property of the probes can be further exploited to understand the cellular intake of HSA-drug complexes in the multifaceted biological system. These results find the utility of SC derivatives as small molecule-based chemosensors for at-home SA detection and as a biomarker for cancer.

Water-soluble optical sensors: keys to detect aluminium in biological environment.

Metal ion plays a critical role from enzyme catalysis to cellular health and functions. The concentration of metal ions in a living system is highly regulated. Among the biologically relevant metal ions, the role and toxicity of aluminium in specific biological functions have been getting significant attention in recent years. The interaction of aluminium and the living system is unavoidable due to its high earth crust abundance, and the long-term exposure to aluminium can be fatal for life. The adverse Al3+ toxicity effects in humans result in various diseases ranging from cancers to neurogenetic disorders. Several Al3+ ions sensors have been developed over the past decades using the optical responses of synthesized molecules. However, only limited numbers of water-soluble optical sensors have been reported so far. In this review, we have confined our discussion to water-soluble Al3+ ions detection using optical methods and their utility for live-cell imaging and real-life application.

1,6-Addition of 1,2,3-NH triazoles to para-quinone methides: Facile access to highly selective N1 and N2 substituted triazoles.

The regioselective syntheses of N1 and N2 substituted triazoles through a 1,6-addition reaction of 1,2,3-NH triazoles to p-quinone methide were achieved under mild reaction conditions. The present reactions showed superior results in terms of selectivity, mild reaction conditions, short reaction time and broad substrate scope with good functional-group compatibility. Considering the high synthetic value of N1- and N2-substituted compounds and p-QM related research, the present strategy will greatly benefit researchers in various fields.