Fluorescence Shift Research Articles

Mapping the formation of gemcitabine-immunoglobulin nanoparticles and the subsequent activity against pancreatic cancer cells.

This research involved the synthesis of Gemcitabine-immunoglobulin nanoparticles (GIgG NPs) and the exploration of their apoptotic mechanisms in targeting Panc-1 cancer cells. A desolvation technique for synthesis was applied, resulting in the heterogeneous clustering of IgG molecules with several Gemcitabine molecules. The DLE and DEE were determined to be 6.8 ± 0.32 % and 93.28 ± 2.88 %, respectively. Dynamic Light Scattering (DLS) and imaging analysis indicated a size of 122.1 nm, a PDI of 0.21, and a zeta potential of -23.78 mV. Fluorescence spectroscopy revealed a reduction and shift in the intrinsic fluorescence of IgG as the Gemcitabine concentration increased. ITC data showed that the binding sites (n) for IgG were 0.96, suggesting roughly one Gemcitabine binding site per IgG molecule, while for GIgG NPs, the n value was measured at 0.84. The binding constant (Kb) for IgG-Gemcitabine was 2.06 × 105 M-1, while for GIgG NPs, it was 1.26 × 105 M-1. The Gibbs free energy (ΔG°) for IgG-Gemcitabine was -30.41 kJ/mol, while for GIgG NPs it was -29.18 kJ/mol. Moreover, negative ΔH° and positive ΔS° values suggested that hydrogen bonds and hydrophobic interactions could facilitate the formation of the complex. Molecular docking analysis indicated that nonpolar interactions and intermolecular solvation play a role in the binding of Gemcitabine to IgG. The release kinetics aligned closely with the Korsmeyer-Peppas and Higuchi models for the pH-sensitive release of Gemcitabine. The IC50 of Gemcitabine for Panc-1 cancer cells dropped seven-fold when encapsulated in GIgG NPs, demonstrating enhanced cytotoxicity and selective targeting of cancer cells. Mechanisms for inducing apoptosis were evident via increased effectiveness, gene expression alteration, caspase activation, and oxidative stress. These results indicate that GIgG NPs could serve as a potential therapeutic option for the targeted treatment of pancreatic cancer.

Towards a Quantitative Description of Proteolysis: Contribution of Demasking and Hydrolysis Steps to Proteolysis Kinetics of Milk Proteins.

The hydrolysis of proteins by proteases (proteolysis) plays a significant role in biology and food science. Despite the importance of proteolysis, a universal quantitative model of this phenomenon has not yet been created. This review considers approaches to modeling proteolysis in a batch reactor that take into account differences in the hydrolysis of the individual peptide bonds, as well as the limited accessibility (masking) for the enzymes of some hydrolysis sites in the protein substrate. Kinetic studies of the proteolysis of β-casein and β-lactoglobulin by various proteolytic enzymes throughout the whole degree of hydrolysis are reviewed. The two-step proteolysis model is regarded, which includes demasking of peptide bonds as a result of opening of the protein structure at the first stage, then hydrolysis of the demasked peptide bonds. To determine the kinetics of demasking, the shift in Trp fluorescence during opening of the protein substrate is analyzed. Two stages of demasking and secondary masking are also considered, explaining the appearance of unhydrolyzed peptide bonds at the end of proteolysis with decreasing enzyme concentrations. Proteolysis of a nanosized substrate is considered for the example of tryptic hydrolysis of β-CN micelles, leading to the formation and degradation of new nanoparticles and non-monotonic changes in the secondary protein structures during proteolysis.

Tailored hydrothermal platforms for fluorescent Q-dots with theranostic application.

This study explores the fluorescence properties of the hydrothermal reaction of citric acid and urea under different conditions, as they have attracted considerable attention in recent years. However, so far, the detailed formation process and the precise chemical structure of the resulting fluorescent products remain inadequately understood. The results reveal that under mild conditions, fluorescence is mainly due to organic molecules, identified as citrazinic acid through acid treatment with spectroscopic techniques. Moreover, the fluorescence shifts towards carbonized quantum dots (CDs) is both temperature and reaction duration-dependent. Comparative analysis versus graphene quantum dots and citrazinic acid elucidated differences in solution properties, including excitation-dependency, photobleaching and fluorescence lifetime. With reference to previous findings in literature, this study provides for an innovative, detailed understanding on the evolution of fluorescent species, by tuning the reaction conditions. Hence, they propose for excellent future strategic application in the nanotechnology and theranostic fields.

Determining the Relative Affinity of ORPs for Lipid Ligands Using Fluorescence and Thermal Shift Assays.

Lipid transfer proteins (LTPs) are specialized proteins that convey specific lipids across the cytosol to regulate the lipid composition of organelles and the plasma membrane. Quantifying to which extent these LTPs recognize and transfer various lipid species and subspecies is of prime interest todefine their cellular role(s). Here, we describe how to measure in vitro the relative affinity of Osh6p, a yeast phosphatidylserine (PS)/phosphatidylinositol 4-phosphate (PI(4)P) exchanger belonging to the oxysterol-binding protein(OSBP)-related protein (ORP) family, for PS and phosphoinositide subspecies. First, we detail how to produce and purify Osh6p with high purity. Secondly, we describe how to measure its ability to bind PS, PI(4)P, and PI(4,5)P2 by FRET-based and thermal shift assays using liposomes of defined composition. These protocols can allow further analysis of other ORPs or inspire the design of assays to characterize other LTPs. Notably, they can be helpful in defining how LTPs transfer phospholipids subspecies as a function of their acyl chains' length and unsaturation degree and, therefore, whether they can contribute to regulating the acyl chain composition of cell membranes.

An Ultrahigh Affinity DNA Aptamer for Quinine and Its Intrinsic Fluorescence Based Label-Free Detection.

Measuring quinine is critical for the detection of its overdose, understanding its pharmacological and toxicological effects, and monitoring its pollution. While a previously reported aptamer named MN4 can bind quinine, it was not selected for it, leading to compromised binding affinity and specificity. In this work, a new quinine aptamer was isolated using the library immobilization capture-SELEX technique. The Q1 aptamer has a Kd value of 10 nM determined by an isothermal titration calorimetry experiment and 45 nM in a fluorescence binding assay. A 3.5 nM quinine limit of detection was obtained based on the aptamer binding-induced quenching of the intrinsic fluorescence of quinine. A large blue shift in fluorescence was observed for quinine upon binding to Q1, whereas binding to MN4 led to a very small red shift, indicating different ways of quinine binding by these two aptamers. Q1 did not bind cocaine based on NMR spectroscopy and fluorescence assays also indicated excellent selectivity against other tested molecules. This work has supplied a high affinity aptamer for quinine that can be useful for its detection and fundamental aptamer binding studies. It also highlights the advantages of using capture-SELEX to isolate aptamers for small molecules.

Novel förster resonance energy transfer (FRET)-based ratiometric fluorescent probe for detection of cyanides by nucleophilic substitution of aromatic hydrogen (SNArH)

The development of novel fluorescent probes for real-time detection of cyanides (CN−) in environmental and biological systems has become a significant focus in chemical sensing. Particularly, ratiometric fluorescence sensing offers a unique method for precise and quantitative detection of cyanides, even under complex conditions. We report herein the design of a new ratiometric fluorescent probe for cyanides based on modulation of Förster resonance energy transfer (FRET) coupled with novel cyanide-induced nucleophilic substitution of aromatic hydrogen (SNArH). The target probe (R1) is developed by introducing coumarin fluorophores as FRET donors into a 3-nitro-naphthalimide acceptor, which is easily synthesized and exhibits a colorimetric change from colorless to faint yellow and a significant ratiometric fluorescence shift (Δλ = 114 nm) upon cyanide binding. A clear ratiometric signal at I582/I468 was obtained, with a limit of detection of 5.69 μM. The sensing mechanism was confirmed through 1H NMR titration and LC-MS analysis. Additionally, R1-loaded strips were easily prepared, serving as a portable device for detecting CN− with visible color changes. The probe R1 has been successfully utilized for real-time monitoring of cyanide in food materials and water samples. Importantly, fluorescence bioimaging studies in HeLa cells were conducted, demonstrating the probe’s capability for ratiometric detection of exogenous CN− in living systems.

A method to spatially assess multipass spray deposition patterns via UV fluorescence and weed population shifts

AbstractSpray deposition patterns from agricultural sprayers are traditionally sampled discretely along a field transect accounting for 0.5% or less of the treated area. Such methods may not fully capture the dimensional variability inherent in large‐scale, multiple‐pass spray applications, especially evident from an agricultural spray drone (ASD). This study investigated the utilization of UV‐fluorescent dye and nighttime aerial imaging techniques to assess large‐scale, multipass spray deposition patterns. Accuracy of digital hue from UV‐fluorescent photography to predict deposition of proxy dye was confirmed via fluorometry assessed intensity levels of extracted UV‐fluorescent dye from 384 Petri dishes placed prior to treatment. Results showed that ASD applications, regardless of nozzle type, exhibited greater spatial variability within the target area compared to ride‐on sprayer applications, primarily due to overapplication. Additionally, the ASD generated spray drift to adjacent nontarget areas that was at least three times more than that of ride‐on and spray‐gun sprayers. Multipass deposition was further assessed via in situ smooth crabgrass infestation following treatment with quinclorac or topramezone by multipass ASD or hand‐held, four‐nozzle spray boom. Weed infestation annotated from overlaid grids with 9.3‐dm2 ground resolution inconsistently detected spatial heterogeneity between transects assessed along the center and edge of each sprayer pass. The ASD controlled smooth crabgrass 11% more than the hand‐held sprayer, albeit with an 18% increase in spray drift to nontarget areas, similar to the UV‐fluorescence study. Digitally assessed average hue of fluorescence photography appears to be a viable method to assess multidimensional and continuous spatial relationships of spray deposition.

An Aggregation-Induced Emissive Platinum(II) Metallacycle as the Energy Donor of Rhodols for Ratiometric Detection of Hydrazine.

Industry-produced hydrazine (N2H4) is released into the environment, posing a major risk to human health and the ecosystem. Therefore, it is imperative to develop an effective and convenient method for the detection of N2H4. Herein, artificial light-harvesting systems (ALHSs) for N2H4 detection were constructed by applying an aggregation-induced emission-active platinum(II) metallacycle (TPEMc) as the energy donor and rhodols (P1, P2, and P3) as the energy acceptors. The ratiometric fluorescence probes based on ALHSs for N2H4 showed obvious signal amplification and lower limits of detection compared to those of rhodols (P1, P2, P3) alone. The TPEMc-rhodols systems clearly demonstrated a noticeable increase in fluorescence intensity at 550 nm and an obvious fluorescent color shift from cyan to yellow in the presence of N2H4. Fascinatingly, N2H4 could be visually and quantitatively detected in water by the TPEMc-rhodol systems paired with smartphone RGB analysis. Therefore, the combination of platinum(II) metallacycle with rhodols is a promising strategy for simple, sensitive, and visual detection of N2H4.

Chloroplast ATP synthase restricts photosynthesis under fluctuating light in tomato but not in maize

Photosynthesis in fluctuating light requires coordinated adjustments of diffusion conductance and biochemical capacity, but the role of chloroplast ATP synthase activity (gH+) in dynamic photosynthesis is not well understood. In this study, we measured gas exchange, chlorophyll fluorescence and electrochromic shift signals in fluctuating light for leaves of tomato (Solanum lycopersicum) and maize (Zea mays). During the transition from sun to shade, simultaneous increases in gH+, effective quantum yield of PSII, and net CO2 assimilation rate (AN) occurred in tomato but uncoupled in maize, indicating that gH + limited AN during the sun-to-shade transition in tomato but not in maize. During the shade-to-sun transition, gH + increased simultaneously with stomatal conductance, mesophyll conductance and Rubisco carboxylation capacity in tomato, suggesting that gH+ is an overlooked factor affecting light induction of AN in tomato. By comparison, gH + maintained at high levels in maize and its AN was mainly restricted by stomatal conductance. Our results reveal that the kinetics of gH+ in fluctuating light differs between species, and chloroplast ATP synthase may be a potential target for improving dynamic photosynthesis in crops such as tomato.

A novel coumarin-naphthalimide-based ratiometric fluorescent probe for efficiently monitoring of hydrazine in environmental water.

A novel coumarin-naphthalimide-based ratiometric fluorescent probe, called XPT, was synthesized with the aim of achieving high sensitivity and anti-interference for N2H4 detection. The probe XPT consists of coumarin species and naphthalimide species, which act as the energy donor and acceptor, respectively. The phthalimide group functions as the recognition unit for N2H4. Without the presence of hydrazine, the naphthalimide remains in a non-fluorogenic phthalimide mode, disrupting the FRET signal. However, the phthalimide group undergoes the Gabriel reaction to an amine, which induces FRET and consequently causes a shift in the emitted fluorescence from 468 to 528 nm when N2H4 was added. The results of the study demonstrated that XPT exhibits high sensitivity with a limit of detection 2.2 μM, as well as selectivity. Furthermore, it is remarkable that the distribution of N2H4 in real water samples can be monitored by XPT.

Samarium, nitrogen co-Doped carbon dots for detection of Epinephrine: Theoretical and experimental

In this study we have developed a highly sensitive optical sensor for the detection of epinephrine using carbon dots co-doped with samarium and nitrogen (Sm,N-CDs) with a very low detection limit of 28.1 nM and a broad linear dynamic range from (0–105 nM). Various techniques were employed to characterize the synthesized material, aiming to understand its morphological and physicochemical characteristics. The synergistic effect of the synthesized Sm,N-CDs demonstrated excellent optical performance, high selectivity and photostability. Additionally, good recovery findings were obtained when the sensor’s viability for Epinephrine detection in biological fluid samples that had been spiked was evaluated. In addition, we have developed an smartphones-based sensor to record the solution’s fluorescent color shift as it is being sensed. Using a mobile phone application to examine the green, red, and blue values from these photos, the comparable LOD was found to be 17.21 μM in a (0–90 μM) wide linear range of concentration. This straightforward, affordable, and quick screening device is highly demanding for the on-the-spot identification of the analytes at remote locations where advanced instrumentation is typically unavailable. Density functional theory was used to examine energy, stability, band gap, and how Ep interacted with the Sm,N-CDs nanoparticles.

Urinary Extracellular Vesicles as a Readily Available Biomarker Source: A Simplified Stratification Method.

Urine, a common source of biological markers in biomedical research and clinical diagnosis, has recently generated a new wave of interest. It has recently become a focus of study due to the presence of its content of extracellular vesicles (EVs). These uEVs have been found to reflect physiological and pathological conditions in kidney, urothelial, and prostate tissue and can illustrate further molecular processes, leading to a rapid expansion of research in this field In this work, we present the advantages of an immunoaffinity-based method for uEVs' isolation with respect to the gold standard purification approach performed by differential ultracentrifugation [in terms of purity and antigen presence. The immunoaffinity method was made feasible by combining specific antibodies with a functionalized polymethacrylate polymer. Flow cytometry indicated a significant fluorescence shift, validating the presence of the markers (CD9, CD63, CD81) and confirming the effectiveness of the isolation method. Microscopy evaluations have shown that the morphology of the vesicles remained intact and corresponded to the expected shapes and dimensions of uEVs. The described protocol is inexpensive, fast, easy to process, has good reproducibility, and can be applied to further biological samples.

Carbon dots with tunable excitation-independent fluorescence and organelle-specific targeting via core graphitization and surface groups engineering

Single-emission fluorescence and non-specific cellular organelle-targeting limit the application of carbon dots (CDs) in bio-imaging. Here, we proposed an adjustable strategy for synthesis of four CDs: Tm1-, Tm2-, Tma-, and Tp-CDs. The synthetic scheme was designed with tartaric acid and m-/p-phenylenediamine as precursors and water/acetone as solvent through hydrothermal/solvothermal synthesis and (or) column chromatography isolation. The maximum productivity of the CDs was 56.2 % and the highest fluorescence quantum yield was 47.8 %. These CDs emitted excitation-independent blue, green, and yellow fluorescence, respectively. The red shift of CDs fluorescence was caused by increasing graphitized conjugated sp2 domain and graphitic nitrogen content of carbon core. The hydrophilicity/lipophilicity and protonation ability of CDs determined their cellular uptake, intracellular trafficking and subcellular targets, including endoplasmic reticulum, lysosomes and nucleus. These CDs have the potential application in fluorescence visualization of live bacteria and in the organelle-targeted imaging of living mammalian, fungal, and plant cells. The study provides novel insights into rational design of CDs with multi-color fluorescence and organelle-specific targeting in live cells.

An NIR Type I Photosensitizer Based on a Cyclometalated Ir(III)-Rhodamine Complex for a Photodynamic Antibacterial Effect toward Both Gram-Positive and Gram-Negative Bacteria.

Type I photosensitizers offer an advantage in photodynamic therapy (PDT) due to their diminished reliance on oxygen levels, thus circumventing the challenge of hypoxia commonly encountered in PDT. In this study, we present the synthesis and comprehensive characterization of a novel type I photosensitizer derived from a cyclometalated Ir(III)-rhodamine complex. Remarkably, the complex exhibits a shift in absorption and fluorescence, transitioning from "off" to "on" states in aprotic and protic solvents, respectively, contrary to initial expectations. Upon exposure to light, the complex demonstrates the effective generation of O2- and ·OH radicals via the type I mechanism. Additionally, it exhibits notable photodynamic antibacterial activity against both Gram-positive and Gram-negative bacteria, demonstrated through in vitro and in vivo experiments. This research offers valuable insights for the development of novel type I photosensitizers.

Smart films based on semiconductor heterojunctions of mechanoluminescent sulfide and sulfur oxide for stress sensing and anti-counterfeiting applications

Mechanoluminescent (ML) materials offer significant potential for remote stress sensing and distribution. However, creating highly sensitive and responsive ML materials remains a challenge. In this study, mechanoluminescent semiconductor materials have been successfully prepared as Mn2+ doped ZnS-SrZnOS heterojunction composites. These materials exhibit high-resolution stress distribution visualization and rapid response, captured via camera recording. Notably, they possess a low stress triggering threshold, reaching the KPa level, and respond within milliseconds. Furthermore, it was found that by adjusting the doping concentration of Mn2+ within the heterojunction, the material utilizes its bimodal emission capability to manipulate the fluorescence shift and achieve optical anti-counterfeiting. The synthesis of smart films by combining the material with polydimethylsiloxane matrix had enabled the achievement of collision detection, information hiding and optical anti-counterfeiting. These results suggest that the prepared smart films have wide range of optical sensing applications.

Dual-Mode Ce-MOF Nanozymes for Rapid and Selective Detection of Hydrogen Sulfide in Aquatic Products.

Increasing concern over the safety of consumable products, particularly aquatic products, due to freshness issues, has become a pressing issue. Therefore, ensuring the quality and safety of aquatic products is paramount. To address this, a dual-mode colorimetric-fluorescence sensor utilizing Ce-MOF as a mimic peroxidase to detect H2S was developed. Ce-MOF was prepared by a conventional solvothermal synthesis method. Ce-MOF catalyzed the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by hydrogen peroxide (H2O2) to produce blue oxidized TMB (oxTMB). When dissolved, hydrogen sulfide (H2S) was present in the solution, and it inhibited the catalytic effect of Ce-MOF and caused the color of the solution to fade from blue to colorless. This change provided an intuitive indication for the detection of H2S. Through steady-state dynamic analysis, the working mechanism of this sensor was elucidated. The sensor exhibited pronounced color changes from blue to colorless, accompanied by a shift in fluorescence from none to light blue. Additionally, UV-vis absorption demonstrated a linear correlation with the H2S concentration, ranging from 200 to 2300 µM, with high sensitivity (limit of detection, LOD = 0.262 μM). Fluorescence intensity also showed a linear correlation, ranging from 16 to 320 µM, with high selectivity and sensitivity (LOD = 0.156 μM). These results underscore the sensor's effectiveness in detecting H2S. Furthermore, the sensor enhanced the accuracy of H2S detection and fulfilled the requirements for assessing food freshness and safety.

Abstract A003: Unwinding the complexities of helicases as compelling drug targets in oncology

Abstract In recent years, helicases have moved to the forefront of research as novel drug targets for a variety of human diseases, including cancer. As critical components of the cell cycle and DNA repair, these enzymes offer an attractive point of therapeutic intervention. Recent bioinformatic endeavours such as the Cancer DepMap have further highlighted the essentiality of these proteins in the progression of numerous cancers. Inhibitors of Werner helicase (WRN) entered Phase I evaluation in 2023, after studies highlighted its role in tumours with microsatellite instability (MSI) and impaired mismatch repair (MMR). Building on these advances, helicases now represent a significant drug target class and are the subject of intense research. However, these targets present significant complexities in their prosecution. Hit finding and robust validation of these putative active compounds remains challenging, with high attrition rates and significant sensitivity to false positives. Resultant hits require thorough biological characterisation via both biochemical and biophysical methods, alongside determination of selectivity against other closely related family members, to increase confidence in their provenance before commencing a detailed drug discovery project. To exemplify these approaches, we have profiled three commercially available WRN inhibitors from two chemical series through a selection of biochemical and biophysical assays. The three compounds exhibit excellent selectivity against 6 distinct helicase/translocase targets. In Michaelis-Menten mechanism of Inhibition studies, we defined contrasting mechanisms of inhibition for the two series and were also able to identify time dependent inhibition with one compound series. Analysing binding interactions of the compounds against protein and protein:substrate complexes, via a fluorescent thermal shift assay (FTSA) and microscale thermophoresis (MST), enabled us to further understand and interrogate the mechanism of inhibition. Herein, we describe some of our experiences, learnings and best practices when prosecuting these compelling, but challenging, targets. Citation Format: Yael Mamane, Zoe Caple, Katie Chapman, Ian Henderson, Allan Jordan, Vanessa Lyne, Cynthia Okoye, Laurent Rigoreau, Ganesh Kadamur, Stuart Thomson, Chris Tomlinson, Jana Wolf. Unwinding the complexities of helicases as compelling drug targets in oncology [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Expanding and Translating Cancer Synthetic Vulnerabilities; 2024 Jun 10-13; Montreal, Quebec, Canada. Philadelphia (PA): AACR; Mol Cancer Ther 2024;23(6 Suppl):Abstract nr A003.

Distinguishing the transitions of fluorescence spectra of tryptophan-134 and 213 in BSA induced by bindings of UV filters, oxybenzone-3, and avobenzone

Abstract Oxybenzone-3 (OBZ) and avobenzone (ABZ), commercially available ultraviolet-light filters for sunscreens, are known to induce photosensitizing allergy as an adverse effect, similar to an analgesic ketoprofen (KTP) due to their benzophenone moiety. The present study focused on OBZ and ABZ's protein binding compared to the related analgesics, KTP, diclofenac (DCF), and ibuprofen (IBP). The bovine serum albumin (BSA) was used as a protein model, measuring the fluorescent spectral peak shifts (i) and Stern–Volmer analysis (i) of its intrinsic tryptophans. Moreover, their adsorption types (iii) were verified using the singular value decomposition (SVD) computation of fluorescence spectra. For (i), (ii), and (iii), KTP and DCF caused a no-shift peak, an ordinary dynamic quenching, and a simple Langmuir adsorption. We found OBZ exhibiting (i) red-shift and (ii) including static quenching, ABZ suggesting (i) blue-shift and (iii) binding to multiple bind sites, and IBP indicating (i) blue-shift and (iii) multivalent bindings. Integrating the results, it can be understood that OBZ interacts with subdomain IA (around W134) in BSA, while ABZ interacts with subdomain IIA (around W213) in BSA. Moreover, IBP is bound to BSA with a cooperative effect, certified by Hill's plot. OBZ and ABZ had their individual binding sites on a protein, suggesting the exchange between OBZ and ABZ might reduce their own adverse effect. The present study verified the effectiveness of the SVD computation in distinguishing the details of the adsorption manner of ligands around the intrinsic fluorescent probes.

Unveiling the multifaceted applications of pamoic acid carbon dots (PACDs) in sensing and oncology

In our research we explore the world of PACDs, carbon dots synthesized from pamoic acid through a single step pyrolysis method. Our findings reveal that PACDs have capabilities of serving as sensitive and selective sensors in both colorimetric and fluorescent modes. They are particularly effective, at colorimetrically and fluorometrically detecting ferric ions and can also act as fluorometric sensors for pH.When ferric ions are introduced an interesting transformation occurs. A noticeable change in color unfolds before our eyes, under 365 nm UV light the fluorescence shifts from green to blue while in daylight it changes from a yellow to a deep ink blue. Notably these detection techniques can precisely measure ferric ions within concentrations ranging from 5 µM to 80 µM with a detection limit of 0.1 µM for fluorescence response. Additionally, they can detect ferric ions colorimetrically within the range of 5 µM to 45 µM with a detection limit of 3.8 µM.Furthermore, the PACDs exhibit a capability to adapt to different pH levels. In alkaline environments with a pH range between 8 and 11 the fluorescence signal demonstrates a response that directly correlates with pH levels and slightly shifts its position. In contrast under acidic conditions a noticeable shift, towards blue is observed in the fluorescence signal leading to a change in color from green to blue when exposed to UV light. This shift persists as the fluorescence signal directly correlates with decreasing pH levels in settings.Apart from their proficiency in ferric ion detection and pH monitoring, the PACDs also demonstrate potential in cancer research. Through an assessment using the MTT assay it was discovered that the PACDs exhibit cytotoxic effects against five different cancer cell lines; HCT 116, MDA MB 231, Hep3B, MCF 7 and HeLa. The findings are promising as the PACDs show IC50 values of 12.5 µg/ml 6.25 µg/ml 25 µg/ml 50 µg/ml and 100 µg/ml for these cell lines. This research highlights the versatility and potential of PACDs as a tool, in both sensing applications and oncology research.

Detection mechanism and solvent effects of the 3‐hydroxy‐2‐(4‐(pyrrolidin‐1‐yl)phenyl)benzo[g]quinolin‐4(1H)‐one (PBQ) probe

AbstractHydroxy‐2‐(4‐(pyrrolidin‐1‐yl)phenyl)benzo[g]quinolin‐4(1H)‐one (PBQ) is a ratiometric fluorescent probe based on excited‐state intramolecular proton transfer (ESIPT). PBQ‐1 is the reaction product following its exposure to phosgene. Density functional theory (DFT) and time dependent density functional theory (DFT) have been used to study the excited state dynamics of PBQ and PBQ‐1 in different solvents. The results show that the reaction of PBQ with a transition from charge‐transfer excitation to local excitation before and after the reaction. It becomes more difficult for PBQ in the excited state to transfer proton with increasing solvent polarity. The product PBQ‐1 undergoes a molecular structure twist, and the angle of twisting decreases with increasing solvent polarity, resulting in a lower degree of rotational freedom of the hydroxyl group (5‐OH) at the 5th carbon position, which makes it more susceptible to ESIPT reactions. Therefore, PBQ‐1 is more susceptible to ESIPT as solvent polarity increases. Our theoretical calculations also elucidate the cause of the blue shift of PBQ fluorescence and the impact of the twisting intramolecular charge transfer phenomenon on the solvent effect. Furthermore, our study provides the theoretical guidance for the designing probe based on excited state intramolecular proton transfer.