A Study of Small Molecule-Based Rhodamine-Derived Chemosensors and their Implications in Environmental and Biological Systems from 2012 to 2021: Latest Advancement and Future Prospects.

Rhodamine-based chemosensors have sparked considerable interest in recent years due to their remarkable photophysical properties, which include high absorption coefficients, exceptional quantum yields, improved photostability, and significant red shifts. This article presents an overview of the diverse fluorometric, and colorimetric sensors produced from rhodamine, as well as their applications in a wide range of fields. The ability of rhodamine-based chemosensors to detect a wide range of metal ions, including Hg+2, Al3+, Cr3+, Cu2+, Fe3+, Fe2+, Cd2+, Sn4+, Zn2+, and Pb2+, is one of their major advantages. Other applications of these sensors include dual analytes, multianalytes, and relay recognition of dual analytes. Rhodamine-based probes can also detect noble metal ions such as Au3+, Ag+, and Pt2+. They have been used to detect pH, biological species, reactive oxygen and nitrogen species, anions, and nerve agents in addition to metal ions. The probes have been engineered to undergo colorimetric or fluorometric changes upon binding to specific analytes, rendering them highly selective and sensitive by ring-opening via different mechanisms such as Photoinduced Electron Transfer (PET), Chelation Enhanced Fluorescence (CHEF), Intramolecular Charge Transfer (ICT), and Fluorescence Resonance Energy Transfer (FRET). For improved sensing performance, light-harvesting dendritic systems based on rhodamine conjugates has also been explored for enhanced sensing performance. These dendritic arrangements permit the incorporation of numerous rhodamine units, resulting in an improvement in signal amplification and sensitivity. The probes have been utilised extensively for imaging biological samples, including imaging of living cells, and for environmental research. Moreover, they have been combined into logic gates for the construction of molecular computing systems. The usage of rhodamine-based chemosensors has created significant potential in a range of disciplines, including biological and environmental sensing as well as logic gate applications. This study focuses on the work published between 2012 and 2021 and emphasises the enormous research and development potential of these probes.

A fluorescence turn "on-off" imaging probe for sequential detection of Al3+ and L-Cysteine in HeLa cells.

At this "Aluminum Age", exposure to aluminum (metallic or ionic form) is inevitable and inestimable. The presence of aluminum in biological systems is evident but more often aluminum toxicity is less understood. Therefore, the presence of biologically reactive aluminum needs to be identified and quantified. Alongside metals, L-cysteine, an essential amino acid, plays a pivotal role in the homeostasis of cellular oxidative and reductive stress. However, excess (<7g) could be lethal and can lead to death. Thus, in-situ selective detection of aluminum and L-cysteine is of larger interest. Here we report a fluorogenic probe (R) for the sequential selective detection and quantification of Al3+ and L-cysteine in a semi-aqueous medium (3:7; water: DMSO). The probe (R) was synthesized by a one-step acid-mediated condensation reaction between pyridine-3,4-diamine and 2-hydroxy-1-napthaldehyde. The synthesized probe was characterized using 1H and 13C NMR, and HR-Mass spectroscopic techniques. The probe (R) is non-emissive in nature, but on recognition of Al3+, the probe R showed "turn-on" emission (bright yellow colour) showing two emission maxima (522 nm and 547 nm), and no naked eye observable color change. Other competing cations do not show any noticeable fluorescence outcome. The R + Al3+ ensemble can specifically detect L-cysteine among all the essential amino acids by showing a fluorescence "turn-off" response. The sensing mechanism of Al3+ is obeying the chelation-enhanced fluorescence (CHEF) effect. The binding constant of R + Al3+ is 0.3 × 104 M-1. The limit of detection (LoD) for Al3+ and L-cysteine are 2.02 × 10-7 M and 0.5 × 10-5 M respectively. The probe (R) can show maximum efficiency within the pH range (7.0-10.0). The probe is found non-toxic (>80 % cell viability with 15 µM concentration) and employed for the in-vitro fluorescence imaging in the HeLa cell.

A near-infrared fluorescent probe with a substantial Stokes shift designed for the detection and imaging of ß-galactosidase within living cells and animals.

ß-Galactosidase serves as a pivotal biomarker for both cancer and cellular aging. The advancement of fluorescent sensors for tracking ß-galactosidase activity is imperative in the realm of cancer diagnosis. We have designed a near-infrared fluorescent probe (PTA-gal) for the detection of ß-galactosidase in living systems with large Stokes shifts. PTA-gal exhibits remarkable sensitivity and selectivity in detecting ß-galactosidase, producing near-infrared fluorescent signals with a remarkably low detection limit (2.2 × 10-5 U/mL) and a high quantum yield (0.30). Moreover, PTA-gal demonstrates biocompatibility and can effectively detect ß-galactosidase in cancer cells as well as within living animals.

Ratiometric Fluorescent Probe for the Detection of Nanomolar Phosgene in Solution and Gaseous Phase: Advancing Crime Detection Applications.

Phosgene, an exceptionally hazardous gas, poses a grave concern for the health and safety of the general public. The present study describes a fluorescent ratiometric probe for phosgene employing 2-(naphthalen-2-yl) benzo[d]oxazol-5-amine (NOA) with an amino group as the recognition site. NOA detects phosgene through the intramolecular charge transfer mechanism. The electron-rich amine group of NOA attacks the electrophilic carbonyl group of phosgene, resulting in a quick response within 20 s. NOA demonstrates a low detection limit of 60 nM while maintaining high selectivity and sensitivity toward phosgene. The final product was isolated and verified by nuclear magnetic resonance spectroscopy. The probe can detect phosgene not just quickly in a solution environment but also in its solid state. The probe's applications in fingerprint imaging and bioimaging are also demonstrated.

Single Step Solid State Synthesis of Carbon Nanoparticles for Instantaneous Detection of Fe (III) in Water Samples.

Though iron is one of the vital micronutrients in biological systems excess of which is associated with various illness. Consumption of contaminated water and crops because of its extensive industrial utility is one of the major sources for excess iron in living beings. Hence, we have designed a sensor based on carbon nanoparticles for the detection of Fe (III) and we have also attempted to estimate Fe (III) in spiked water samples. Carbon nanoparticles (CNP) with quantum yield of 40.2 % was synthesized by solid state synthesis from aromatic molecular precursors unlike conventional synthesis methodology. The particle size, stability and optical properties of CNP were investigated by microscopic and spectroscopic techniques. CNP manifested a naked color change from colorless to yellow in presence of Fe (III) and 72 % of CNP's emission was quenched at 487 nm on excitation at 377 nm by Fe (III). The detection time was less than a second and limit of detection was calculated as 0.248 µM. The mechanistic aspect of detection was investigated and applicability of CNP was examined in spiked water samples.

One-step synthesis of a pH switched pyrene-based fluorescent probe for ratiometric detection of HS- in real water samples.

Only a few probes are suited for highly acidic environments and sensitive to pH values below 4. Thus, finding a solution for detecting strong acidic (pH value below 2) conditions is still challenging. Herein, we constructed and created a pH-switched fluorescent probe based on pyrene and a heteroatom containing pyridine unit. When exposed to acidic environments (pH 2.0), the probe's fluorescence redshifted with distinct colour and fluorescence changes owing to protonation on the nitrogen atom containing pyridine moiety, which could be deprotonated by HS- selectively compared to other competing analytes. Pyr can detect HS- with a rapid response within 5 s and showed very good quantum yield under acidic environments. The sensing mechanism was confirmed by Density Functional Theory (DFT) studies using the B3LYP and 6-31G+ (d) basis sets. Furthermore, the probe was utilized to monitor HS- in actual water samples and identify H2S gas by a simple paper strip test.

ESIPT-PET based triphenylamine-anthraquinone probe for the detection of phosgene: DFT studies, real-time application in soil samples and test strips.

Public health and safety are gravely jeopardised by phosgene, a highly toxic gas. In this study, phosgene was detected by the excited-state intramolecular proton transfer (ESIPT) and photoelectron transfer (PET) mechanisms utilising a fluorescent probe built from a triphenylamine-anthraquinone core structure (TPAAQ) with carbonyl and imidazole moieties as recognition sites. TPAAQ undergoes nucleophilic substitution and cyclization reactions with phosgene to form a six-membered ring. This results in a quick reaction with good selectivity, high sensitivity, and a detection limit of 22.83 nM. With the aid of high-resolution mass spectrometry and 1H NMR spectroscopy, the mechanism for sensing was verified. The ESIPT and PET mechanism of the probe was confirmed through DFT and TDDFT studies. In addition, we could detect phosgene in soil samples with detection limits of 0.1583 ppm, 0.233 ppm and 1.047 ppm for field soil, clay soil and sandy soil, respectively, and created a fluorescent test strip to identify phosgene. The fluorescent test strip's colour change from light reddish to yellow is visible to the unaided eye under 365 nm UV light.

Expeditious fluorimetric detection of bilirubin by simple imidazole derived luminophore and it's pragmatic applicability in spiked biological fluids.

Bilirubin is an indispensable biomarker for liver diseases. Utilizing organic molecules as sensor platform for effective detection of bilirubin are little. In addition, the reported fluorophores required longer incubation time for detection. Hence, herein we have attempted to design an imidazole derivative 4-(3H-imidazo[4,5-b]pyridin-2-yl)-N,N-diphenylaniline (IMI) from triphenylamine and pyridine units which could detect bilirubin swiftly without any incubation period. IMI manifested an instant quenching of emission in presence of bilirubin with limit of detection (LOD) 11.74 × 10-6 mol L-1. The mechanistic aspect of detection involves coexistence of both static and dynamic quenching which was suitably justified. Finally, the pragmatic application of IMI was performed in bio-fluids.

Dual-Responsive Benzo-Hemicyanine-Based Fluorescent Probe for Detection of Cyanide and Hydrogen Sulfide: Real-Time Application in Identification of Food Spoilage.

Colorimetric and fluorescent probes have received a lot of attention for detecting lethal analytes in realistic systems and in living things. Herein, a dual-approachable Benzo-hemicyaninebased red-emitting fluorescent probe PBiSMe, for distinct and instantaneous detection of CN- and HS- was synthesized. The PBiSMe emitted red fluorescence (570 nm) can switch to turn-off (570 nm) and blue fluorescence (465 nm) in response to CN- and HS-, respectively. Other nucleophilic reagents, such as reactive sulfur species (RSS) and anions, have no contact or interference with the probe; instead, a unique approach is undertaken to exclusively interact with CN- and HS- over a wide pH range. The measured detection limits for CN- (0.43 µM) and HS- (0.22 µM) ions are lower than the World Health Organization's (WHO) recommended levels in drinking water. We confirmed 1:1 stoichiometry ratio using Job's plot and observed good quantum yield for both analytes. The probe-coated paper strips were used to detect the H2S gas produced by food spoilage (such as eggs, raw meat, and fish) via an eye-catching visual response. Moreover, fluorescence bioimaging studies of living cells was done to confirm the probe's potential by monitoring the presence of CN- and HS- in a living system.

Recent Advancements in the Design and Development of Near Infrared (NIR) Emitting Fluorescent Probes for Sensing and their Bio-Imaging Applications.

Fluorescent bio-imaging will be the future in the medical diagnostic for visualising inner cellular and tissues. Near-infrared (NIR) emitting fluorescent probes serve dynamically for targeted fluorescent imaging of live cells and tissues. NIR imaging is advantageous because of its merits like deep tissue penetration, minimum damage to the tissue, reduced auto fluorescence from the background, and improved resolution in imaging. The Development of the NIR emitting probe was well explored recently and growing drastically. In this review, we summarise recent achievements in NIR probes in between 2018-2021. The merits and future applications have also been discussed in this review.

Benzodioxole grafted spirooxindole pyrrolidinyl derivatives: synthesis, characterization, molecular docking and anti-diabetic activity.

A highly stereoselective, three-component method has been developed to synthesize pyrrolidine and pyrrolizidine containing spirooxindole derivatives. The interaction between the dipolarophile α,ß-unsaturated carbonyl compounds and the dipole azomethine ylide formed in situ by the reaction of 1,2-dicarbonyl compounds and secondary amino acids is referred to as the 1,3-dipolar cycloaddition reaction. The reaction conditions were optimized to achieve excellent stereo- and regioselectivity. Shorter reaction time, simple work-up and excellent yields are the salient features of the present approach. Various spectroscopic methods and single crystal X-ray diffraction examinations of one example of compound 6i validated the stereochemistry of the expected products. The anti-diabetic activity of the newly synthesized spirooxindole derivatives was tested against the α-glucosidase and α-amylase enzymes. Compound 6i was found to exhibit potent inhibition activity against α-glucosidase and α-amylase enzymes which is further evidenced by molecular docking studies.

A two photon fluorescent probe for highly selective detection and endogenous imaging of hydrogen sulfide.

Hydrogen sulfide (H2S), one of redox-active sulfur species, is known as a signaling molecule and an antioxidant in biological tissues to maintain cellular functions. The development of selective and sensitive H2S detection is important to understand the role of H2S in vivo. Herein, a new two-photon probe NNE was developed to detect hydrogen sulfide using 6-acetyl-N-methyl-2-naphthylamine with an attachment of 7-nitrobenzo-oxadiazole. The probe NNE exhibits high selectivity towards hydrogen sulfide over other anions. Nucleophilic substitution of H2S leads to a turn-on response with 28-fold enhancement in quantum yield (from 0.004 to 0.117). NNE shows a high sensitivity towards hydrogen sulfide with an extremely low detection limit at 6.8 nM. Furthermore, the probe NNE exhibits two-photon excited fluorescence, making it a suitable probe for monitoring H2S distribution in live cells and tissues without background fluorescence interference.

Specific two-photon fluorescent probe for cysteine detection in vivo.

Cysteine (Cys), an essential amino acid, plays several crucial functions in numerous biological processes. Notably, the detection of Cys is critical to disease diagnosis. Fluorescent probes that can quickly detect Cys will help to study the mechanism of certain diseases. Herein, a new fluorescent probe, ANP, which is based on 6-acetyl-N-methyl-2-naphthyl amine, has been developed for Cys detection over Hcy and GSH in vivo. The addition of thiol on α,ß-unsaturated ketone promotes 87-fold fluorescence turn-on response with a 65 nM limit of detection. The high two-photon efficiency of the probe ANP (cross-section = 22.3) makes it a suitable probe for evaluating Cys in living cells without background fluorescence interference. Its application was extended to monitor the Cys distribution in live cells and tissues.

Ratiometric Probe for Rapid Naked Eye Detection of Toxic Hydrazine: Real Time Application in Strip Test, Spray Test and Soil Analysis.

Striking colorimetric probe (CynH) for abrupt detection of hydrazine under complete aqueous solution was achieved. The water soluble probe was designed with electron "push-pull" strategy by coupling of 4-hydroxy benzaldehyde and 2, 3, 3-trimethylindolinine. The positively charged N-propylated indolinine make the probe completely soluble in water. The probe yields eye catching selective detection of hydrazine over other competing analytes with high sensitivity. Obvious colour change was observed from colourless to appearance of bright pink colour with hydrazine. It reacts quickly with hydrazine within 2 min and makes the probe an effective candidate for practical application. The real time application was demonstrated using paper strip to detect hydrazine vapour. This probe is superior to earlier reported probes because of its effective sensing of hydrazine displayed with various applications including real-time strip based sensing, spray test and soil analysis. In all the examinations, the probe yields distinct response with rapid naked eye colour change which overcomes the drawbacks of previous reports.

Synthesis, in vitro and in silico anti-bacterial analysis of piperine and piperic ester analogues.

A set of 12 analogues of piperine was designed, replacing the amide functional group of the molecule with different aliphatic and aromatic ester functional groups. Molecular docking studies of these molecules with FDA-approved target proteins for anti-bacterial drugs were done. The binding energy of the proteins and the ligands were low and the analogues were found to be drug-like based on the ADME results; hence, the molecules were synthesized. The synthesized compounds were tested for their anti-bacterial property against six bacterial species via Agar well-diffusion method. Acinetobacter baumannii, Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Enterococcus faecalis and Staphylococcus epidermidis were the strains tested. The overall susceptibility is higher in gram-positive. The analogues showed better activity than piperine. The analogues, propyl piperic ester (P3) and 2-fluorophenyl piperic ester (P9) and 4-fluorophenyl piperic ester (P10) showed comparatively bigger inhibition zones for all the strains.

Triple Action Sensing Behaviour of a Single Receptor for the Detection of Multiple Analytes via Different Approaches.

The thiosemicarbazide based receptor was synthesized with 4-(diethylamino)salicylaldehyde and N- phenyl-thiosemicarbazide by the simple condensation method and the properties were studied under the naked eye, UV-Vis and fluorescence studies etc. The synthesized receptor detects cyanide, cobalt, and mercury in acetonitrile medium. The observed color changes included colourless to yellow for cyanide, colourless to green for cobalt and colourless to yellow for mercury which were seen under naked eye without the aid of any instruments. Furthermore, the cyanide bound receptor detects Cr3+ by the relay recognition method. The detection limit of receptor with cyanide, cobalt & mercury was found to be 5.8 × 10- 7 M, 3.6 × 10- 7 M and 8.1 × 10- 7 M respectively. Experimental results were verified by DFT calculations. Receptor was successfully employed in the construction of INHIBIT and IMPLICATION logic gates.

"Covalent-Assembly"-Triggered Striking Far-Red to near-Infrared Emitting Fluorescent Probe for Abrupt Detection of Nerve-Agent Mimic (DCP): Real Time Application in Monitoring the Presence of Trace Amounts in Soil and Live Cells.

Detection of chemical warfare agents (CWA) by simple and rapid methods with real-sample applications are quite inevitable in order to ease the threats to living systems caused by uncertain terror attacks and wars. Herein we have developed the first far-red to near infra-red (NIR) probe based on a covalent assembly approach for the detection of trace amounts of nerve agent mimic diethyl chloro phosphate (DCP) in soil and their fluorescent bio imaging in live cells. The probe features abrupt fluorescence turn on sensing of DCP with fluorescence quantum yield Φ = 0.622. It senses DCP selectively over other analytes in excellent sensitivity with a detection limit of 6.9 nM. In real time, the probe treated strips were employed to detect the DCP vapor effectively with eye catching fluorescence response. The presence of trace amounts of these acute warfare agents in the environment were monitored by soil analysis. Further fluorescent bio imaging was carried out to monitor trace level DCP in living cells using the HeLa cell line.

Nanomolar Detection of H2S in an Aqueous Medium: Application in Endogenous and Exogenous Imaging of HeLa Cells and Zebrafish.

The homeostasis of short-lived reactive species such as hydrogen sulfide/hypochlorous acid (H2S/HOCl) in biological systems is essential for maintaining intercellular balance. An unchecked increase in biological H2S concentrations impedes homeostasis. In this report, we present a molecular probe pyrene-based sulfonyl hydrazone derived from pyrene for the selective detection of H2S endogenously as well as exogenously through a "turn-off" response in water. The structure of the receptor is confirmed by Fourier-transform infrared spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopy, electrospray ionization mass spectrometry, and single-crystal X-ray diffraction studies. The receptor shows excellent green emission in both the aqueous phase and solid state. Quenching of green emission of the receptor is observed only when H2S is present in water with a detection limit of 18 nM. Other competing anions and cations do not have any influence on the receptor's optical properties. The efficiency of H2S detection is not negatively impacted by other reactive sulfur species too. The sensing mechanism of H2S follows a chemodosimetric reductive elimination of sulfur dioxide, which is supported by product isolation. The receptor is found to be biocompatible, as evident by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and its utility is extended to endogenous and exogenous fluorescence imaging of HeLa cells and zebrafish.

Reduced Graphene Oxide Supported Molybdenum Oxide Hybrid Nanocomposites: High Performance Electrode Material for Supercapacitor and Photocatalytic Applications.

Using a simple solution based synthesis route, hexagonal MoO3 (h-MoO3) nanorods on reduced graphene oxide (RGO) sheets were prepared. The structure and morphology of resulting RGO-MoO3 nanocomposite were characterized using X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). The optical property was studied using UV-Visible diffuse reflectance spectroscopy (UV-Vis DRS) and photoluminescence spectroscopy (PL). The RGO-MoO3 nanocomposites were used as an electrode for supercapacitor application and photocatalyst for photodegradation of methylene blue (MB) and rhodamine B (RhB) under visible light irradiation. We demonstrated that the RGO-MoO3 electrode is capable of delivering high specific capacitance of 134 F/g at current density of 1 A/g with outstanding cyclic stability for 2000 cycles. The RGOMoO3 photocatalyst degrades 95% of MB dye within 90 min, and a considerable recyclability up to 4 cycles was observed. The quenching effect of scavengers test confirms holes are main reactive species in the photocatalytic degradation of MB. Further, the charge transfer process between RGO and MoO3 was schematically demonstrated.

Naphthalimide based smart sensor for CN-/Fe3+ and H2S. Synthesis and application in RAW264.7 cells and zebrafish imaging.

Achieving selective detection of target analytes in aqueous media continues to be an arduous proposition. Herein, we report the conceptualization and synthesis of a novel tailor-fit molecular probe R based on 1,8-naphthalimide which acts as a trifunctional molecular sensor for CN-, Fe3+ and H2S. R shows colorimetric and fluorometric "on-off" relay recognition for CN- (red colour and orange emission) and Fe3+ (no colour and no emission) in 5% H2O + DMSO medium which is experimentally ascertained to be a tandem deprotonation-protonation process and is supported by 1H-NMR titration. Among all RSS (Reactive Sulphur Species), R shows selectivity for H2S through red colouration. Other coexistent anions, cations and RSS cause no discernible perturbation to the detection process. The detection of H2S is attributed to a chemodosimetric reduction of the nitro to amino group as evidenced by a potentiometric titration assay. The experimental observations are well supported by DFT theoretical calculation. The K a for CN-/Fe3+ are 1.4 × 104 M-1, 6.07 × 104 M-1 respectively and photochemical yield of R + CN- is 0.86. Limit of detections for CN-, Fe3+ and H2S are 17.5 nM, 8.69 µM and 8.1 µM respectively. Receptor R is effective for real time applications, bio-compatible and has been successfully employed for confocal fluorescence imaging of RAW264.7 cell and zebrafish.