Dye Displacement Research Articles

Fluorescence Turn-ON Displacement Assays with Cucurbit[7]uril-Thiophenylpyridinium Complexes as Host-Dye Reporter Pairs.

The N-methyl-4-thiophenylpyridinium cation (ThioPy) is a high affinity (Kd ca. 5 nM), fast-exchanging fluorescent probe for cucurbit[7]uril (CB7). The CB7/ThioPy complex shows a unique fluorescence turn-ON response upon displacement by an analyte in sensing application. This enabled the development of a real-time fluorescence assay with the MRFA peptide for the protease thermolysin, which is also suitable for the cancer biomarker cathepsin B. Moreover, liposome encapsulation of CB7/ThioPy in large unilamellar vesicles (LUVs) provided mechanistic insight into intravesicular dye displacement reactions.

Entropically driven binding of Camptothecin in the minor groove of salmon testes DNA

The present study focuses on binding association of Camptothecin (CMT) towards natural deoxy-ribonucleic acid (salmon testes, ST) under physiological conditions of pH 7.4. Extensive spectroscopic and computational techniques have been employed to elucidate thermodynamics of the said interaction. UV and fluorescence analyses portrays significant intensity changes (hyper-chromic and hypsochromic) in the spectra, which confirms effective CMT binding to ST DNA. The McGhee-von Hipple method and Scatchard plot analyses estimated the binding affinities in 105 M−1 range. Associated thermodynamic data revealed spontaneous and exothermic nature of binding. Temperature-dependent fluorescence showed negative change in enthalpy and positive change in entropy, leading to the formation of a 1:1 adduct. Non-polyelectrolytic forces appeared to be the driving force of the ligand-DNA interaction, according to salt-dependent fluorescence. Dye displacement assay, viscosity study, DNA melting, iodide quenching, urea denaturation assay examined the minor groove nature of CMT. In silico docking study examined precise molecular representations of the minor groove binding mechanism that formed between the complex, and the study's findings were consistent with the experimental results. Simulation studies also validated the experimental analysis and docking data. These findings could expedite the process of creating new and improved CMT molecular derivatives and help in the creation of DNA-targeted medicines, which may be beneficial from a pharmaceutical point of view.

A Minor Groove Binder with Significant Cytotoxicity on Human Lung Cancer Cells: The Potential of Hesperetin Functionalised Silver Nanoparticles.

Natural drug functionalised silver (Ag) nanoparticles (NPs) have gained significant interest in pharmacology related applications due to their therapeutic efficiency. We have synthesised silver nanoparticle using hesperetin as a reducing and capping agent. This work aims to discuss the relevance of the hesperetin functionalised silver nanoparticles (H-AgNPs) in the field of nano-medicine. The article primarily investigates the anticancer activity of H-AgNPs and then their interactions with calf thymus DNA (ctDNA) through spectroscopic and thermodynamic techniques. The green synthesised H-AgNPs are stable, spherical in shape and size of 10 ± 3nm average diameter. The complex formation of H-AgNPs with ctDNA was established by UV-Visible absorption, fluorescent dye displacement assay, isothermal calorimetry and viscosity measurements. The binding constants obtained from these experiments were consistently in the order of 104 Mol-1. The melting temperature analysis and FTIR measurements confirmed that the structural alterations of ctDNA by the presence of H-AgNPs are minimal. All the thermodynamic variables and the endothermic binding nature were acquired from ITC experiments. All these experimental outcomes reveal the formation of H-AgNPs-ctDNA complex, and the results consistently verify the minor groove binding mode of H-AgNPs. The binding constant and limit of detection of 1.8μM found from the interaction studies imply the DNA detection efficiency of H-AgNPs. The cytotoxicity of H-AgNPs against A549 and L929 cell lines were determined by in vitro MTT cell viability assay and lactate dehydrogenase (LDH) assay. The cell viability and LDH enzyme release are confirmed that the H-AgNPs has high anticancer activity. Moreover, the calculated LD50 value for H-AgNPs against lung cancer cells is 118.49µl/ml, which is a low value comparing with the value for fibroblast cells (269.35µl/ml). In short, the results of in vitro cytotoxicity assays revealed that the synthesised nanoparticles can be considered in applications related to cancer treatments. Also, we have found that, H-AgNPs is a minor groove binder, and having high DNA detection efficiency.

Interaction between antidepressant drug trazodone with double-stranded DNA: Multi-spectroscopic and computational analysis

Trazodone (TZD) is an antidepressant drug used to treat major depressive and sleeping disorders. Elevated doses of trazodone are associated with central nervous system depression, which manifests as nausea, drowsiness, confusion, vertigo, exhaustion, etc. To develop a clinically viable active pharmaceutical compound with minimal adverse effects, it is imperative to possess a comprehensive knowledge of the drug's action mechanism on DNA. Hence, we investigate the mode of interaction between trazodone and DNA utilizing various spectroscopic and computational techniques. Studies using UV–vis titration showed that the DNA and trazodone have an effective interaction. The magnitude of the Stern-Volmer constant (KSV) has been calculated to be 5.84 × 106 M−1 by the Lehrer equation from a steady-state fluorescence study. UV–vis absorption, DNA melting, dye displacement, and circular dichroism studies suggested that trazodone binds with DNA in minor grooves. Molecular docking and molecular dynamic simulation demonstrated that the TZD-DNA system was stable, and the mode of binding was minor groove. Furthermore, ionic strength investigation demonstrates that DNA and trazodone do not have a substantial electrostatic binding interaction.

HSA and DNA binding analysis of antiviral drug cidofovir: Spectroscopic and molecular docking techniques

This article discusses the interaction of antiviral drug cidofovir (CDV) with biomolecules (HSA and DNA) under simulated physiological conditions (pH 7.4). The binding propensity of CDV with DNA was assessed through UV–visible absorption spectroscopy, fluorescence spectroscopy, and molecular docking. The results of fluorescence spectroscopy indicated that the binding of CDV to DNA induced fluorescence quenching through a static quenching mechanism, with a binding constant of 1.03 × 103 M−1 at 293 K. The groove mode of CDV binding to calf thymus DNA (ct-DNA) was validated using dye displacement assays. The results from molecular docking confirmed the binding mode and supported the findings obtained through spectroscopic techniques. Furthermore, the binding propensity of CDV with HSA was assessed through fluorescence spectroscopy, UV–visible absorption spectroscopy, and docking simulation. The fluorescence data indicated that CDV quenches the intrinsic fluorescence of the protein through a static quenching process, with a binding constant of 5.60 × 103 M−1 at 293 K. Meanwhile, the results of docking simulation confirmed our spectroscopic findings.

Exploring the mechanism of interaction of glipizide with DNA: Combined in vitro and bioinformatics approach

DNA, vital for biological processes, encodes hereditary data for protein synthesis, shaping cell structure and function. Since revealing its structure, DNA has become a target for various therapeutically vital molecules, spanning antidiabetic to anticancer drugs. These agents engage with DNA-associated proteins, DNA–RNA hybrids, or bind directly to the DNA helix, triggering diverse downstream effects. These interactions disrupt vital enzymes and proteins essential for maintaining cell structure and function. Analysing drug–DNA interactions has significantly advanced our understanding of drug mechanisms. Glipizide, an antidiabetic drug, is known to cause DNA damage in adipocytes. However, its extract mechanism of DNA interaction is unknown. This study delves into the interaction between glipizide and DNA utilizing various biophysical tools and computational technique to gain insights into the interaction mechanism. Analysis of UV–visible and fluorescence data reveals the formation of complex between DNA and glipizide. The binding affinity of glipizide to DNA was of moderate strength. Examination of thermodynamic parameters at different temperatures suggests that the binding was entropically spontaneous and energetically favourable. Various experiments such as thermal melting assays, viscosity measurement, and dye displacement assays confirmed the minor grove nature of binding of glipizide with DNA. Molecular dynamics studies confirmed the glipizide forms stable complex with DNA when simulated by mimicking the physiological conditions. The binding was mainly favoured by hydrogen bonds and glipizide slightly reduced nucleotide fluctuations of DNA. The study deciphers the mechanism of interaction of glipizide with DNA at molecular levels.

Investigation of Rare Earth Element Binding to a Surface-Bound Affinity Peptide Derived from EF-Hand Loop I of Lanmodulin.

Bioinspired strategies have been given extensive attention for the recovery of rare earth elements (REEs) from waste streams because of their high selectivity, regeneration potential, and sustainability as well as low cost. Lanmodulin protein is an emerging biotechnology that is highly selective for REE binding. Mimicking lanmodulin with shorter peptides is advantageous because they are simpler and potentially easier to manipulate and optimize. Lanmodulin-derived peptides have been found to bind REEs, but their properties have not been explored when immobilized on solid substrates, which is required for many advanced separation technologies. Here, two peptides, LanM1 and scrambled LanM1, are designed from the EF-hand loop 1 of lanmodulin and investigated for their binding affinity toward different REEs when surface-bound. First, the ability of LanM1 to bind REEs was confirmed and characterized in solution using circular dichroism (CD), nuclear magnetic resonance (NMR), and molecular dynamics (MD) simulations for Ce(III) ions. Isothermal titration calorimetry (ITC) was used to further analyze the binding of the LanM1 to Ce(III), Nd(III), Eu(III), and Y(III) ions and in low-pH conditions. The performance of the immobilized peptides on a model gold surface was examined using a quartz crystal microbalance with dissipation (QCM-D). The studies show that the LanM1 peptide has a stronger REE binding affinity than that of scrambled LanM1 when in solution and when immobilized on a gold surface. QCM-D data were fit to the Langmuir adsorption model to estimate the surface-bound dissociation constant (Kd) of LanM1 with Ce(III) and Nd(III). The results indicate that LanM1 peptides maintain a high affinity for REEs when immobilized, and surface-bound LanM1 has no affinity for potential competitor calcium and copper ions. The utility of surface-bound LanM1 peptides was further demonstrated by immobilizing them to gold nanoparticles (GNPs) and capturing REEs from solution in experiments utilizing an Arsenazo III-based colorimetric dye displacement assay and ultraviolet-visible (UV-vis) spectrophotometry. The saturated adsorption capacity of GNPs was estimated to be around 3.5 μmol REE/g for Ce(III), Nd(III), Eu(III), and Y(III) ions, with no binding of non-REE Ca(II) ions observed.

A dual-mode biosensor based on silica inverse opal photonic crystals modulated electrochemiluminescence and dye displacement colorimetry for the sensitive detection of synthetic cathinone in water environment

To address the challenges posed by signal capacity limitations and the reliance of sensing methods on single analytical information, this study developed an electrochemiluminescence (ECL) and colorimetric dual-mode sensing platform for the precise detection of 4-chloroethcathinone (4-CEC) in water environments. Firstly, the accurate alignment of the reflection wavelength of appropriately sized silica inverse opal photonic crystals (SIOPCs) with the ECL emission wavelength of luminescent metal-organic frameworks (PCN-224) has been achieved via diameter modulation. This innovative design, which cleverly utilized the band-edge effect, improved the luminous intensity of the ECL sensor, leading to a significant boost in analytical performance. Secondly, the establishment of a colorimetric detection method for confirming the presence of 4-CEC in samples through visual observation of color changes was achieved by employing an aptamer-based dye displacement reaction, utilizing differential binding affinities between the aptamer and both the sulforhodamine B (SRB) and 4-CEC. Under the optimal experimental conditions, the dual-mode sensor demonstrated ECL detection of limits (LOD) of 2.6 × 10−13 g/L and colorimetric LOD of 6.5 ng/L for 4-CEC. These findings highlighted the tremendous potential of developing streamlined and efficient dual-signal readout platforms using ECL aptamer sensors for the precise determination of other Synthetic cathinones (SCs) in water environments.

Probing the interaction of an antiviral drug 8-methoxy-3-nitro-2-(4-methoxyphenyl)-2H-chromene (MNC) with DNA by experimental and computational approach

Deoxyribonucleic acid (DNA) is a major target in research pertaining to antiviral and anticancer therapies since it is the principal genetic material that controls vital biological functions. The complex relationship between calf thymus DNA (ct-DNA) and 8-Methoxy-3-nitro-2-(4-methoxyphenyl)-2H-chromene (MNC), an anticancer drug derivative of 2-aryl-3-nitro-2H-chromenes, is explored in this work. Using various spectroscopic methods such as fluorescence, circular dichroism (CD), UV–visible, isothermal titration calorimetry (ITC) experiment, and molecular docking calculations, this study elucidates the binding characteristics and affinity between MNC and ct-DNA. Through predominant groove binding and moderate intercalation, MNC demonstrates a complicated binding pattern with DNA at the minor groove, as shown by the UV–Vis spectra and emission-based dye displacement investigations. DNA undergoes a little conformational change that MNC induces, as shown by CD spectroscopy. The thermodynamics parameters such as the binding constant, binding enthalpy, and binding free energy of DNA-MNC interaction, as calculated by the ITC experiment, were approximately ∼ 104 M−1, −26 kcal mol−1, and 6 kcal/mol, respectively. The binding process is enthalpy driven implying a stabilizing contact of MNC with DNA and the entropic penalty (−TΔS = +20.1 kcal mol−1) points to a reduction in the degree of freedom of movement. The molecular docking investigation also estimates the similar interaction energy and binding locations of MNC with DNA. Interestingly, MNC attaches to the surface of the DNA via electrostatic interactions; a stronger attachment through van der Waals and hydrophobic contacts within the minor groove follows this. These studies are anticipated to provide researchers with important direction for designing new drug molecules for further biomolecular investigations.

Single-use dye displacement colorimetry assay based on molecularly imprinted polymers: Towards fast and on-site detection of xylazine in alcoholic beverages

The use of the veterinary tranquilizer xylazine as an adulterant poses a major health problem in the world. Involuntary consumption of this drug (e.g. spiked beverages and suicidal attempts) leads to loss of consciousness and even death. In this work, a probe for the fast, visual detection of xylazine in alcoholic beverages is proposed. The technology is based on xylazine-specific molecularly imprinted polymers that were loaded with methylene blue to generate a dye-displacement assay. The assay displayed high selectivity when evaluated against common compounds present in beverages. Optimal assay conditions were found at pH ≥ 7 and alcohol contents <15 v/v%. Furthermore, the assay was evaluated in a real gin and tonic sample and displayed a linear regime of 1.5–4 mM and a LOD of 1.36 mM. Implementation of the assay in a portable device resulted in a much faster xylazine detection (under 30 s) in a spiked gin & tonic sample.

Exploring the binding mechanism of Pomalidomide drug with CT-DNA: Insights from multi-spectroscopic, molecular docking and simulation studies

Exploration of the interaction of a thalidomide analogue immunomodulatory and anti-angiogenic drug pomalidomide (POD) with calf thymus DNA (CT-DNA) was carried out using multi-spectroscopic (UV–Vis, fluorescence, and circular dichroism), molecular docking and metadynamics simulation studies in Tris–HCl buffer (pH 7.4). The results revealed that POD binds to the nucleic acid via groove binding mode. The proposed binding mode is strongly supported by competitive dye displacement assay using ethidium bromide (EB) and rhodamine B (RB) dyes, KI quenching studies and viscosity measurements. The thermodynamic parameters such as ∆Ho (60 kJ mol−1), ∆So (297 JK−1 mol−1) and ∆Go (-22 kJ mol−1) indicated that the POD/CT-DNA interaction is spontaneous and is stabilized predominantly by hydrophobic forces. The proposed groove binding mode of interaction of POD with CT-DNA was further confirmed by a computer-aided molecular docking studies and analysis of free energy surface contour derived from the molecular simulation study.

Critical assessment of interactions between ct-DNA and choline-based magnetic ionic liquids: evidences of compaction.

Ionic liquids (ILs) have become an alternative green solvent for storage and for stability of DNA. However, an in-depth understanding of binding and molecular interactions between ILs and DNA is needed. In this respect, magnetic ILs (MILs) are promising due to their tunable physicochemical properties. Various spectroscopic techniques and molecular simulations have been employed to unravel the critical factors of the strength and binding mechanism of MILs with DNA. UV-vis spectra unravel the multimodal binding of MILs with DNA, and the intrusion of IL molecules into the minor groove of DNA has been observed from dye displacement studies. Fluorescence correlation spectroscopic studies and scanning electron microscopy confirm the compaction of the DNA. ITC and molecular docking studies estimate the binding affinity of DNA with MILs, of ∼7 kcal mol-1. The 1 μs long-MD simulations give insight into the structural changes in the DNA in the MIL environment. Due to strong interaction with choline ions in the close vicinity, DNA helixes bend or squeeze in length and dilate in diameter (elliptical → spherical), leading to compaction. The post-MD parameters suggest a stronger interaction with [Ch]2[Mn] IL than with [Ch][Fe] IL; hence, the former induces DNA compaction to a more significant extent. Furthermore, decompaction is observed with the addition of sodium salts and is characterized using spectroscopic methods.

Supramolecular complexation of phenylephrine by cucurbit[7]uril in aqueous solution.

Cucurbiturils (CBn) are known to establish stable host-guest complexes with a variety of drug molecules. Herein, the supramolecular complexation between cucurbit[7]uril (CB7) and phenylephrine hydrochloride is reported in aqueous solution. Phenylephrine forms inclusion complex with CB7 with high binding affinity (Kaffinity = 4.0 × 106 M-1), which allows for the development of a fluorescence-based sensing assay applying the dye displacement strategy. The structure of the host-guest inclusion complex is investigated by 1H NMR spectroscopy, in which complexation-induced chemical shifts indicate the immersion of the aromatic ring inside the hydrophobic cavity of CB7. Density functional theory (DFT) calculations support the 1H NMR results, and reveal that the complex is stabilized through intermolecular interactions between the polar groups on the phenylephrine and the carbonyl rims of CB7, as well as the hydrophobic effect. Moreover, preferential binding of phenylephrine in its protonated over the neutral form results in a complexation-induced pKa shift.

Agglomeration effect of nanoparticles on foam stability of nonionic surface-active liquid: experimental and density functional theory studies

Innovative applications of foam are the need of time which fundamentally depends on the stability of the foam. In the present research work, the static foam behavior of the nonionic surfactant Tween-20 in the presence and absence of Titanium dioxide nanoparticles (TiO2-NPs) was investigated. The role of TiO2-NPs on foaming power based on foam height and foamability was studied at different temperatures. At 29 ± 1 0C, maximum foam height for Tween 20 (5% surfactant solution in distilled water) without and with TiO2-NPs was increased from 45.60 to 60.30 cm exhibiting 32.25% increase. In view of studying foam stability, axial dye displacement rate (ADDR) test was performed without and with nanoparticles where TiO2-NPs resist liquid drainage. TiO2 -NPs and Tween-20 form intermolecular hydrogen bonding which helps to enhance the foam stability as revealed by the density functional theory (DFT) studies. However, TiO2 -NPs have tendency to agglomerate if zeta potential value is low that severely affect the foaming power and foamability.

Mechanistic investigation into the binding property of Yohimbe towards natural polymeric DNAs

DNA interactions with multivalent ligand(s) have increasingly become the subject of substantial research. For several small molecules with therapeutic potential, nucleic acids serve as their primary molecular target. Such interaction has been shown to affect transcription or replication, ultimately leading to apoptotic cell death. As a result, researchers are becoming increasingly interested in understanding how small molecules interact with DNA making it possible to develop new, DNA-specific drugs. The bioactive indole alkaloid, Yohimbe (Yohimbine; Yh) has been broadly studied in pharmacological properties while its binding mode to DNA has not been explicated so far. This study adopted molecular modelling and multi-spectroscopic methods to investigate the interaction between Yohimbine and herring testes (HT DNA) in physiological conditions. Minor hypochromic and bathochromic shifts of fluorescence intensity were observed, suggesting the binding of Yh to HT DNA. The Scatchard plot analyses using the McGhee-von Hipple method revealed non-cooperative binding and affinities in the range of 105 M−1. The thermodynamic parameters suggested exothermic binding, which was favoured by negative enthalpy and positive entropy changes from temperature-dependent fluorescence experiments. Salt-dependent fluorescence suggested that the interaction between the ligand and DNA was governed by non-polyelectrolytic forces. The results of iodide quenching, urea denaturation assay, dye displacement, and in silico molecular docking, suggested groove binding of Yh to HT DNA. Thus, the groove binding mechanism of interaction was validated by both biophysical and computational techniques. The structural elucidation and energetic profiling of Yh's interaction with naturally occurring polymeric DNA can be useful to the development of DNA-targeted therapeutics.

Deciphering the binding mechanism of an anti-cancer phytochemical plumbagin with calf thymus DNA using biophysical and in silico techniques.

Plumbagin (PLM), a plant derivative, is well known for a wide range of therapeutic effects in humans including anti-cancer, anti-inflammatory, anti-oxidant, and anti-microbial. Cytotoxic and genotoxic potential of this phytochemical has been studied which demands further insight. DNA being a major target for several drugs was taken to study against PLM to understand its effects on the cellular system. UV-Vis spectroscopy has indicated the binding of PLM to ctDNA and dye displacement assays have confirmed the formation of PLM-ctDNA complex. The insignificant changes in circular dichroism spectra suggested that PLM is not affecting the structural makeup of the ctDNA, hence the binding could be peripheral and not intercalating. Further, the relative viscosity and minimal change in melting temperature upon the complex formation supported this finding and confirmed the groove binding of PLM. Molecular docking analysis and simulation studies also show PLM as a minor groove binder to DNA and provide details on the interaction dynamics of PLM-DNA complex. Docking followed by a 100ns simulation reveals the negative Gibbs free energy change (∆G = -6.6kcalmol-1), and the formation of a stable complex. The PLM- DNA complex with stable dynamics was further supported by different parameters including RMSD, RMSF, SASA, Rg, and the energy profile of interaction. This study provides an insight into the cytotoxic and genotoxic mechanism of PLM which can be a crucial step forward to exploit its therapeutic potential against several diseases including cancer.

Multi-spectroscopic, calorimetric and molecular dynamics evaluation on non-classical intercalation of antiviral drug Molnupiravir with DNA

The interaction of an antiviral drug Molnupiravir (MOL) with calf thymus DNA (CT-DNA) was investigated using a series of biophysical techniques. A significant hyperchromism with a blue shift nm in the UV-Vis spectra indicated a high binding affinity of MOL for CT-DNA with binding constants in the order of 105 M−1. Competitive fluorescent dye displacement assays with ethidium bromide (EB) and Hoechst 33258 suggested an intercalative mode of binding of MOL with CT-DNA. Thermodynamic profiles determined using fluorescence titration and isothermal titration calorimetric (ITC) analysis matched well with each other. The negative free energy change revealed that the MOL/CT-DNA complexation is a spontaneous process. The negative values of enthalpy and entropy changes indicated that H-bonding and van der Walls interactions play dominant roles in stabilizing the complex. A decrease in viscosity of CT-DNA solution upon adding MOL indicated a partial intercalation mode of binding which was well supported by circular dichroism (CD) spectral and effect of KI and denaturation studies. Molecular docking and metadynamics simulation studies clearly showed the partial intercalation of the pyrimidine ring of MOL into the base pairs of DNA. Free energy surface (FES) contour indicated that the drug/DNA complex is stabilized by H-bonding and pi-pi/pi-cation interactions. Communicated by Ramaswamy H. Sarma

Highly sensitive detection of bacteria (E. Coli) endotoxin using novel PANI-benzimidazole-Ag nanocomposite by DMMB dye displacement assay

In the present study, a new biochemical biosensor material of conductive Silver (Ag) reinforced polyaniline (PANI)-Benzimidazole copolymer nanocomposite was fabricated via in situ chemical oxidative polymerization method for the detection of endotoxin. The fabricated PANI-Benz-Ag nanocomposite was characterized by FTIR, XRD, UV–visible spectrometer, DSC, TGA, Zeta-potential, SEM, TEM, and Confocal fluorescence imaging microscopy. The measured particle size, zeta-potential, and conductivity of the PANI-Benz-Ag nanocomposite were 4.942 nm, −10.4 mV, and 73.7 μS cm−1 respectively. The crystallite size of Ag nanoparticles was around 67 nm calculated by XRD analysis and TGA analysis was carried out to determine weight loss and thermal stabilities of PANI-Benz and PANI-Benz-Ag nanocomposite. The endotoxin (E. coli) bacteria detection ability of the synthesized PANI-Benz-Ag nanocomposite-based biochemical biosensor using DMMB dye displacement assay through the hitchhiking method by confocal fluorescence microscopy was found to be simple and effective. Endotoxin (E. coli) can form a stable interaction with other bioactive molecules and thus it binds readily with Ag-doped PANI-Benzimidazole nanocomposite. Further, the DMMB dye displacement assay method is more accurate and sensitive than the other existing methods for the detection of endotoxin.

Isolation and characterization of the quinclorac-specific aptamer toward a colorimetric sensor for the visual detection of quinclorac in water and soil

Quinclorac is an herbicide widely used in rice production, and its residue in water and soil poses significant threats to aquatic organisms and subsequent crops. We herein isolated a group of aptamers with high binding affinity to quinclorac using library-immobilized SELEX. Notably, one of these aptamers (Apt.Q1) demonstrated excellent specificity and affinity to quinclorac, with dissociation constant (Kd) of 8.7 ± 2.4 µM and no interference from structurally similar pesticides. Molecular dynamics simulations identified the G-rich loop in Apt.Q1 as the potential binding domain, and circular dichroism analysis revealed the conformational transition from hairpin to G-triplex structure upon quinclorac interaction. Moreover, a one-step, label-free colorimetric biosensor was developed based on quinclorac-mediated displacement of Cy7 dye and Apt.Q1 for detecting quinclorac within 1 min with a detection limit of 237 nM and RSD<5%. Assessment of quinclorac residues in soil and river water using the biosensor demonstrated recoveries of 89–92%. The study not only provided a promising bio-receptor for developing various quinclorac biosensors but also provided a cost-effective tool for rapidly screening quinclorac in environment. Specifically, the investigation of the recognition mechanism between Apt.Q1 and quinclorac lays a theoretical foundation for designing more sensitive and reliable sensing platforms for quinclorac detection.

Exploring the cytotoxicity on human lung cancer cells and DNA binding stratagem of camptothecin functionalised silver nanoparticles through multi-spectroscopic, and calorimetric approach

The influence of nanoparticles inside the human body and their interactions with biological macromolecules need to be explored/studied prior to specific applications. The objective of this study is to find the potential of camptothecin functionalised silver nanoparticles (CMT-AgNPs) in biomedical applications. This article primarily investigates the binding stratagem of CMT-AgNPs with calf thymus DNA (ctDNA) through a series of spectroscopic and calorimetric methods and then analyses the anticancer activity and cytotoxicity of CMT-AgNPs. The nanoparticles were synthesized using a simple one pot method and characterized using UV–Visible, fourier transform infrared (FTIR) spectroscopy, X-ray diffraction and high-resolution transmission electron microscopy (HRTEM). The average size of CMT-AgNPs is 10 ± 2 nm. A group of experimental techniques such as UV–Visible spectrophotometry, fluorescence dye displacement assay, circular dichroism (CD) and viscosity analysis unravelled the typical groove binding mode of CMT-AgNPs with ctDNA. The CD measurement evidenced the minor conformational alterations of double helical structure of ctDNA in the presence of CMT-AgNPs. The information deduced from the isothermal titration calorimetry (ITC) experiment is that the binding was exothermic and spontaneous in nature. Moreover, all the thermodynamic binding parameters were extracted from the ITC data. The binding constants obtained from UV absorption experiments, fluorescence dye displacement studies and ITC were consistently in the order of 104 Mol−1. All these results validated the formation of CMT-AgNPs–ctDNA complex and the results unambiguously confirm the typical groove binding mode of CMT-AgNPs. An exhaustive in vitro MTT assay by CMT-AgNPs and CMT against A549, HT29, HeLa and L929 cell lines revealed the capability of CMT-AgNPs as a potential anticancer agent.