Simple Fluorescence Turn-On Chemosensor for Selective Detection of Ba2+ Ion and Its Live Cell Imaging

Recent advances in the fluorimetric and colorimetric detection of cobalt ions

Cobalt is an essential metal to maintain several functions in the human body and is present in functional materials for numerous applications. Thus, to monitor these functions, it is necessary to develop suitable probes for the detection of cobalt. Presently, researchers are focused on designing different chemosensors for the qualitative and quantitative detection of the metal ions. Among the numerous methods devised for the identification of cobalt ions, colorimetric and fluorimetric techniques are considered the best choice due to their user-friendly nature, sensitivity, accuracy, linearity and robustness. In these techniques, the interaction of the analyte with the chemosensor leads to structural changes in the molecule, causing the emission and excitation intensities (bathochromic, hyperchromic, hypochromic, and hypsochromic) to change with a change in the concentration of the analyte. In this review, the recent advancements in the fluorimetric and colorimetric detection of cobalt ions are systematically summarized, and it is concluded that the development of chemosensors having distinctive colour changes when interacting with cobalt ions has been targeted for on-site detection. The chemosensors are grouped in various categories and their comparison and the discussion of computational studies will enable readers to have a quick overview and help in designing effective and efficient probes for the detection of cobalt in the field of chemo-sensing.

Selective and pH-Independent Detection of Ba2+ in Water by a Benzo-21-crown-7-Functionalized BODIPY

Herein, we report on highly Ba2+ selective fluorescence sensing in water by a fluorescent probe consisting of a benzo-21-crown-7 as a Ba2+ binding unit (ionophore) and a tetramethylated BODIPY fluorophore as a fluorescence reporter. This fluorescent probe showed a Ba2+ induced fluorescence enhancement (FE) by a factor of 12±1 independently of the pH value and a high Ba2+ sensitivity with a limit of detection (LOD) of (17.2±0.3) μM. Moreover, a second fluorescent probe consisting of the same BODIPY fluorophore, but a benzo-18-crown-6 as a cation-responsive binding moiety, showed an even higher FE upon Ba2+ complexation by a factor of 85±3 and a lower LOD of (13±3) μM albeit a lower Ba2+ selectivity. The fluorescence sensing mechanism of Ba2+ was further investigated by time-resolved fluorescence as well as transient absorption spectroscopy (TAS) and it turned out that within these probes a blocking of a photoinduced electron transfer (PET) by Ba2+ is very likely responsible for the FE.

Luminous Insights: Exploring Organic Fluorescent "Turn-On" Chemosensors for Metal-Ion (Cu+2, Al+3, Zn+2, Fe+3) Detection

There are several metal ions that are vital for the growth of the environmental field as well as for the biological field but only up to the maximum limit. If they are present in excess, it could be hazardous for the human health. With the growing technology, a series of various detection techniques are employed in order to recognize those metal ions, some of them include voltammetry, electrochemical methods, inductively couples, etc. However, these techniques are expensive, time consuming, requires large storage, advanced instrumentation, and a skilled person to operate. So, here comes the need of a sensor and it is defined as a miniature device which detects the substance of interest by giving response in the form of energy change. So, from past few decades, many sensors have been formulated for detecting metal ions with some basic characteristics like selectivity, specificity, sensitivity, high accuracy, lower detection limit, and response time. Detecting various metal ions by employing chemosensors involves different techniques such as fluorescence, phosphorescence, chemiluminescence, electrochemical, and colorimetry. The fluorescence technique has certain advantages over the other techniques. This review mainly focuses on the chemosensors that show a signal in the form of fluorescence to detect Al+3, Zn+2, Cu+2, and Fe+3 ions.

Rhodamine-based fluorescent sensors for the rapid and selective off-on detection of salicylic acid and their use in plant cell imaging

Salicylic acid (SA) is a key hormone that regulates plant growth and immunity, and understanding the physiologic processes induced by SA enables the development of highly pathogen-resistant crops. Here, we report the synthesis of three new SA-sensors (R1-R3) from hydroxyphenol derivatives of a rhodamine-acylhydrazone scaffold and their characterization by NMR and HRMS. Spectroscopic analyses revealed that structural variations in R1-R3 resulted in sensors with different sensitivities for SA. Sensor R2 (with the 3-hydroxyphenyl modification) outperformed R1 (2-hydroxyphenyl) and R3 (4-hydroxyphenyl). The SA-detection limit of R2 is 0.9 μM with an ultra-fast response time (<60 s). In addition, their plant imaging indicated that designed sensor R2 is useful for the further study of SA biology and the discovery and development of new inducers of plant immunity.

A multifunctional cucurbit[6]uril-based supramolecular assembly for fluorescence sensing of TNP and Ba2+ and information encryption

Both nitroaromatic compounds (NACs) and heavy metal ions are accumulative high-risk environmental pollutants, so high-sensitivity detection of these environment pollutants is necessary. In this work, a cucurbit[6]uril (CB[6]) based luminescent supramolecular assembly [Na₂K₂(CB[6])₂(DMF)₂(ANS)(H₂O)₄](1) (CB[6] = cucurbit[6]uril, ANS^2- = 8-Aminonaphthalene-1,3,6-trisulfonic acid ion) has been synthesized under solvothermal conditions, using ANS^2- as a structural inducer. Performance studies have shown that 1 exhibits excellent chemical stability and easy regeneration ability. It can highly selective sensing of 2,4,6-trinitrophenol (TNP) through fluorescence quenching with a strong quenching constant (K_sv = 2.58 × 10⁴ M^-1). Additionally, the fluorescence emission of 1 can be effectively enhanced with Ba²⁺ in aqueous solution (K_sv = 5.57 × 10³ M^-1). More impressively, Ba²⁺@1 was successfully used as anti-counterfeiting fluorescent ink functional material with strong information encryption function. This work illustrates the application prospects of luminescent CB[6]-based supramolecular assembly in environmental pollutants detection and information anti-counterfeiting for the first time, which extends the multifunctional application scope of CB[6]-based supramolecular assembly.

Robust solvatochromic carbon quantum dots for selective detection of water and Sn4+ and specific lipid imaging

Developing carbon quantum dots (CQDs) with the solvatochromic effect and exploring multifunctional applications remains challenging. Herein, robust solvatochromic carbon quantum dots (RS-CQDs) with emission shift up to ∼62 nm from yellow to red was fabricated by the hydrothermal method. The RS-CQDs was used to detect water and Sn⁴⁺ in the linear ranges and limits of detection of 2.0-97.6% and 0.14% and 6.24-53.18 μM and 66.3 nM, respectively, and was further applied to determine Sn⁴⁺ in practical water samples with satisfactory results. In addition, RS-CQDs exhibited bright red emission in oil media with a 9.7-fold increase in fluorescence relative to aqueous media, making them a wash-free probe for specifically staining lipids. Compared to the commercial lipid marker BODIPY 493/503, the RS-CQDs-based probe has significant advantages, such as longer emission, larger Stokes shift, and better photostability, ensuring that RS-CQDs-based marker can implement real-time and wash-free monitoring and imaging of lipids in living cells, liver tissues, zebrafish embryos, and zebrafish larvae. This study provides a novel research direction for the development of metal-doped CQDs by demonstrating RS-CQDs as the viability of fluorescence probes for water and Sn⁴⁺ detection and the efficiency of RS-CQDs as a fluorescent marker for lipid imaging.

N,Zn-Doped Fluorescent Sensor Based on Carbon Dots for the Subnanomolar Detection of Soluble Cr(VI) Ions

The development of a fluorescent sensor has attracted much attention for the detection of various toxic pollutants in the environment. In this work, fluorescent carbon dots (N,Zn-CDs) doped with nitrogen and zinc were synthesized using citric acid monohydrate and 4-pyridinecarboxyaldehyde as carbon and nitrogen sources, respectively. The synthesized N,Zn-CDs served as an "off" fluorescence detector for the rapid and sensitive detection of hexavalent chromium ions (Cr(VI)). The zinc metal integrated into the heteroatomic fluorescent carbon dot played a functional role by creating a coordination site for the hydrogen ions that were displaced after the addition of Cr to the solution matrix. The stepwise addition of Cr(VI) effectively quenched the fluorescence intensity of the N,Zn-CDs, and this phenomenon was attributed to the internal filter effect. A low detection limit of 0.47 nmol/L for Cr(VI) was achieved in the fluorescence experiments. Real water samples were used to evaluate the practical application of N,Zn-CDs for the quantification of Cr(VI). The results show acceptable recoveries and agreement with ion chromatography-ultraviolet spectrometry results. These good recoveries indicate that the fluorescence probe is very well suited for environmental measurements.

DNAzyme-based biosensors for mercury (Ⅱ) detection: Rational construction, advances and perspectives

Mercury contamination is one of the most severe issues in society due to its threats to public health and the ecological system. However, traditional methods for mercury ion detection are still limited by their time-consuming procedures, requirement of expensive instruments, and low selectivity. In recent decades, tremendous progress has been made in the development of functional nucleic acid-based, especially DNAzyme sensors for mercury (Ⅱ) (Hg²⁺) determination, including RNA-cleaving DNAzymes and G-quadruplex-based DNAzymes in particular. Researchers have heavily studied the construction of Hg²⁺ sensors, mainly originating from in vitro selection-derived DNAzymes, by incorporating T-Hg²⁺-T recognition moieties in existing DNAzyme scaffolds, and interfacing Hg²⁺-sensitive sequences with nanomaterials. In the last case, the employment of materials (as quenchers, signal transducers and DNA immobilizers) enriches the application scenarios of current Hg²⁺-DNAzymes, due to a combination of their functions. We summarize a broad range of sensing approaches, including optical, electrochemical, and other sensing methods, and compare their features. This review elaborates on the rational design strategies for engineering DNAzymes to selectively sense Hg²⁺, critically discusses their properties in different application scenarios, and summarizes recent advances in this field. Additionally, current progress, challenges and future perspectives are also discussed. This minireview provides deeper insights into the chemistry of these functional nucleic acids when working with Hg²⁺, explains the design ideas of DNAzyme-sensors in each platform, and reveals potential opportunities in developing more advanced DNAzyme sensors for the highly selective and sensitive recognition of Hg²⁺. ENVIRONMENTAL IMPLICATION: Mercury is one of the most toxic metallic contaminants due to its high toxicity, non-biodegradability, and serious human health risks when accumulated in the body. In the recent decade, intensive studies have focused on exploring mercury sensors by combining DNAzymes with various sensing methods, paving a promising avenue to gain ultra-high sensitivity and selectivity. However, so far, no review has introduced the recent advances on DNAzyme-based sensors for mercury detection in a critical way. In this review, we comprehensively summarized the studies on DNAzyme-based sensors for mercury detection using various sensing techniques including optical, electrochemical and other sensing methods.

Natural polyphenol-based nanoengineering of collagen-constructed hemoperfusion adsorbent for the excretion of heavy metals

Designing a hemoperfusion adsorbent for the excretion therapy of toxic heavy metals still remains a great challenge due to the biosafety risks of non-biological materials and the desired highly efficient removal capacity. Herein, inspired from the homeostasis mechanism of plants, natural polyphenols are integrated with collagen matrix to construct a polyphenol-functionalized collagen-based artificial liver (PAL) for heavy metals excretion and free radicals scavenging therapy. PAL presents high adsorption capacities for Cu²⁺, Pb²⁺, and UO₂²⁺ ions, up to 76.98 μmol g^-1, 106.70 μmol g^-1, and 252.48 μmol g^-1, respectively. Remarkably, PAL possesses a high binding affinity for UO₂²⁺, Pb²⁺, and Cu²⁺ ions even in the complex serum environment with the presence of biologically-relevant ions (e.g., Mg²⁺, Ca²⁺ ions). Low hemolysis ratio (1.77%), high cell viability (> 85%), high plasma recalcification time (17.4 min), and low protein adsorption (1.02 μmol g^-1) indicate outstanding biocompatibility of this material. This natural polyphenol/collagen-based fully bio-derived hemoperfusion adsorbent provides a novel and potentially applicable strategy for constructing a hemoperfusion adsorbent for heavy metal ions excretion therapy with efficiency and biosafety.

Luminescent Dimeric Oxalate-Bridged Eu3+/Tb3+-Implanted Arsenotungstates: Tunable Emission, Energy Transfer, and Detection of Ba2+ Ion in Aqueous Solution

Two cases of lanthanide (Ln)-implanted arsenotungstates, K₁₇Na₂H₅[{(As₂W₁₉O₆₇(H₂O))Ln(H₂O)₂}₂(C₂O₄)]·87H₂O (Ln = Eu (1), Ln = Tb (2)) and their codoped derivatives Eu_xTb_1-x-POM (x = 0.01 (3), x = 0.04 (4), x = 0.1 (5), x = 0.2 (6)) were prepared and further characterized by powder X-ray diffraction, infrared spectra, and thermogravimetric analyses. An X-ray structural analysis of 1 and 2 indicates that they both present a dimeric oxalate-bridged Ln³⁺-implanted lanthanide arsenotungstate polyanion structure. Under the O → W LMCT excitation at 265 nm of arsenotungstate polyanions, the emissions of Ln³⁺ ions in 1 and 2 are sensitized and the lifetimes are prolonged. Codoped compounds 3-6 demonstrate a color-tunable emission from green to red by adjusting the Eu³⁺/Tb³⁺ ratio. Emission spectra and time-resolved emission spectroscopic studies were performed for 3 to further authenticate the energy transfer processes from excited arsenotungstates to the Eu³⁺ and Tb³⁺ metal ions and also between the Eu³⁺ and Tb³⁺ centers. More interestingly, 1 is an effective fluorescent probe for the recognition and detection of Ba²⁺ ions in aqueous solution. The optical properties of the Ln-implanted arsenotungstate compounds not only expressly reveal distinctive energy transfer processes in those compounds but also broaden the application of POM-based materials in the fluorescence sensing field.

Review on Nanoparticles and Nanostructured Materials: Bioimaging, Biosensing, Drug Delivery, Tissue Engineering, Antimicrobial, and Agro-Food Applications

In the last few decades, the vast potential of nanomaterials for biomedical and healthcare applications has been extensively investigated. Several case studies demonstrated that nanomaterials can offer solutions to the current challenges of raw materials in the biomedical and healthcare fields. This review describes the different nanoparticles and nanostructured material synthesis approaches and presents some emerging biomedical, healthcare, and agro-food applications. This review focuses on various nanomaterial types (e.g., spherical, nanorods, nanotubes, nanosheets, nanofibers, core-shell, and mesoporous) that can be synthesized from different raw materials and their emerging applications in bioimaging, biosensing, drug delivery, tissue engineering, antimicrobial, and agro-foods. Depending on their morphology (e.g., size, aspect ratio, geometry, porosity), nanomaterials can be used as formulation modifiers, moisturizers, nanofillers, additives, membranes, and films. As toxicological assessment depends on sizes and morphologies, stringent regulation is needed from the testing of efficient nanomaterials dosages. The challenges and perspectives for an industrial breakthrough of nanomaterials are related to the optimization of production and processing conditions.

Intelligent demethylase-driven DNAzyme sensor for highly reliable metal-ion imaging in living cells

The accurate intracellular imaging of metal ions requires an exquisite site-specific activation of metal-ion sensors, for which the pervasive epigenetic regulation strategy can serve as an ideal alternative thanks to its orthogonal control feature and endogenous cell/tissue-specific expression pattern. Herein, a simple yet versatile demethylation strategy was proposed for on-site repairing-to-activating the metal-ion-targeting DNAzyme and for achieving the accurate site-specific imaging of metal ions in live cells. This endogenous epigenetic demethylation-regulating DNAzyme system was prepared by modifying the DNAzyme with an m⁶A methylation group that incapacitates the DNAzyme probe, thus eliminating possible off-site signal leakage, while the cell-specific demethylase-mediated removal of methylation modification could efficiently restore the initial catalytic DNAzyme for sensing metal ions, thus allowing a high-contrast bioimaging in live cells. This epigenetic repair-to-activate DNAzyme strategy may facilitate the robust visualization of disease-specific biomarkers for in-depth exploration of their biological functions.

Construction of a simple dual-channel fluorescence chemosensor for Cu2+ ion and GSSG detection and its mitochondria-targeting bioimaging applications

Numerous chemosensors have been developed for next-generation detection systems because of their ease of use and promising characteristics to distinguish signals between various analytes binding. However, given their typically poor emission response and arduous preparation methods, very few chemosensing probes have been commercialized to date. In this work, a simple, naphthoquinone-based mitochondria-targeting chemosensor (CIA) has been fabricated for the simultaneous detection of Cu²⁺ and GSSG (glutathione oxidized) through an "on-off" mode in a buffered semi-aqueous solution. Significantly, the CIA chemosensor showed a sensitive detection response towards Cu²⁺ and GSSG with low detection limits (0.309 μM, and 0.226 μM, respectively). In addition, the detection mechanism of CIA was thoroughly verified and confirmed using numerous analytical techniques. Furthermore, CIA was utilized as a sequential fluorescence biomarker to detect Cu²⁺ in human cervical cancer cell lines. These findings indicate that the chemosensor CIA can discriminate human cancer cells from normal cells. The CIA was also confirmed to possess the ability to target mitochondria. More importantly, the present CIA chemosensor detected Cu²⁺ in zebrafish larvae, indicating the probe has tissue penetration ability.

Mitochondria-targeted acridine-based dual-channel fluorescence chemosensor for detection of Sn4+ and Cr2O72- ions in water and its application in discriminative detection of cancer cells

The goal of the present work was to fabricate a new low-cost, easy-to-prepare, dual-channel fluorescence chemosensor comprised of acridine-diphenylacetyl moieties (NDA) to enable remarkable Sn⁴⁺ detection in water and biological medium. The resulting NDA-Sn⁴⁺ complex was utilized for the distinguished identification of Cr₂O₇^2- ions from other anions and biomolecules. These investigations involve the absorption, fluorescence, and electrochemical methods for the detection of Sn⁴⁺ and Cr₂O₇^2- ions in pure water. The mechanism for NDA-mediated Sn⁴⁺ detection was experimentally determined by FT-IR, NMR titrations, mass (ESI) analyses, and DFT calculations. The obtained results indicate that the NDA chemosensor possessed excellent performance characteristics including good water solubility and compatibility, quick response time (less than 10 s), high sensitivity (Sn⁴⁺ = 0.268 μM and Cr₂O₇^2- = 0.160 μM), and selectivity against coexisting metals, anions, amino acids, and peptides. The chemosensor NDA induced negligible toxicity in live cells and was successfully utilized as a biomarker for the tracking of Sn⁴⁺ in human normal and cancer cells. More importantly, NDA demonstrates distinguished recognition of Sn⁴⁺ in human cancer cells rather than in normal live cells. Additionally, NDA was shown to act as a mitochondria-targeted probe in FaDu cells.

A dual-channel colorimetric and ratiometric fluorescence chemosensor for detection of Hg2+ ion and its bioimaging applications

A new colorimetric and ratiometric fluorescence chemosensor 4-((3-(octadecylthio)-1,4-dioxo-1,4-dihydronaphthalen-2-yl)amino)benzenesulfonamide (4DBS) was synthesized and investigated for the selective detection of Hg²⁺ in DMSO-H₂O (9:1, v/v) solution. The chemosensor was efficiently synthesized in two steps via Michael-like addition and nucleophilic substitution reactions. The ratiometric fluorescence turn-on response was obtained towards Hg²⁺, and its fluorescence emission peak was red-shifted by 140 nm with an associated color change from light maroon to pale yellow due to the intramolecular charge transfer effect. The formed coordination metal complex was further evaluated by FT-IR, ¹H NMR, and quantum chemical analyses to confirm the binding mechanism. The detection process was sensitive/reversible, and the calculated limit of detection for Hg²⁺ was 0.451 µM. Furthermore, 4DBS was effectively utilized as a bioimaging agent for detection of Hg²⁺ in live cells and zebrafish larvae. Additionally, 4DBS showed distinguishing detection of Hg²⁺ in cancer cells in comparison with normal cells. Thus, 4DBS could be employed as an efficient bioimaging probe for discriminative identification of human cancer cells.

Mitochondria-targeted dual-channel colorimetric and fluorescence chemosensor for detection of Sn2+ ions in aqueous solution based on aggregation-induced emission and its bioimaging applications

Several fluorescence and colorimetric chemosensory for Sn²⁺ detection in an aqueous media have been reported, but applications remain limited for discriminative Sn²⁺ detection in live human cells and zebrafish larvae. Herein, a mitochondria-targeted Sn²⁺ "turn-on" colorimetric and fluorescence chemosensor, 2CTA, with an aggregation-induced emission (AIE) response was developed. The sensing of Sn²⁺ was enabled by a reduction-enabled binding pathway, with the conversion of -C˭O groups to -C-OH groups at the naphthoquinone moiety. The color changed from light maroon to milky white in a buffered aqueous solution. The chemosensor 2CTA possessed the excellent characteristics of good water solubility, fast response (less than 10 s), and high sensitivity (79 nM) and selectivity for Sn²⁺ over other metal ions, amino acids, and peptides. The proposed binding mechanism was experimentally verified by means of FT-IR and NMR studies. The chemosensor 2CTA was successfully employed to recognize Sn²⁺ in live human cells and in zebrafish larvae. In addition, a colocalization study proved that the chemosensor had the ability to target mitochondria and overlapped almost completely with MitoTracker Red. Furthermore, a bioimaging study of live cells demonstrated the discriminative detection of Sn²⁺ in human cancer cells and the practical applications of 2CTA in biological systems.

Simple fluorescence optosensing probe for spermine based on ciprofloxacin-Tb3+ complexation

We developed a facile detection method of spermine based on the fluorescence (FL) quenching of the ciprofloxacin-Tb3+ complex, which shows astrong green emission. Ciprofloxacin (CP) makes efficient bondings to Tb3+ ion as a linker molecule through carboxylic and ketone groups to form a kind of lanthanide coordination polymer. The addition of spermine that competes with Tb3+ ions for the interaction with CP due to its positive charge brings about weakened coordination linkage of CP and Tb3+. The probe exhibited high sensitivity, selectivity, and good linearity in the range of 2-180 μM with a low limit of detection of 0.17 μM. Moreover, we applied this method on the paper strip test (PST), along with the integration of a smartphone and Arduino-based device. The practical reliability of the developed probe was evaluated on human serum samples with acceptable analytical results.

Microscopic Afterglow Bioimaging by Ultralong Organic Phosphorescent Nanoparticles in Living Cells and Zebrafish

Compared with short-lived emission probes featuring fluorescence imaging , the use of phosphorescent probes imparts the advantage of long-lived signal persistence that distinguishes against background fluorescence interference. However, the realization of ultralong organic phosphorescent (UOP) probes with an ultralong emission lifetime in an aqueous medium is still a challenge. Here, we present a rational strategy for obtaining UOP nanoparticles (NPs) in an air-saturated aqueous medium prepared using an organic phosphor (PDBCz) and a surfactant polymer (PVP), named PDBCz@PVP, showing an ultralong emission lifetime of 284.59 ms and a phosphorescence quantum efficiency of 7.6%. The excellent phosphorescence properties and water solubility of PDBCz@PVP make it a promising candidate for biological imaging. The as-prepared PDBCz@PVP NPs possess excellent luminescence intensity as well as illustrious biocompatibility both in vitro and in vivo. We demonstrate their use as an efficient phosphorescent nanoprobe both in living cells and zebrafish by capturing their afterglow emission signals under microscopy observation for the first time, realizing convenient and fast bioimaging with low cost, which allows for anti-fluorescence interference and shows promise for the future theragnostic applications in nanomedicine.

Demonstration of Selective Single-Barium Ion Detection with Dry Diazacrown Ether Naphthalimide Turn-on Chemosensors

Single-molecule fluorescence imaging (SMFI) of gas-phase ions has been proposed for "barium tagging," a burgeoning area of research in particle physics to detect individual barium daughter ions. This has potential to significantly enhance the sensitivity of searches for neutrinoless double-beta decay (0νββ) that is obscured by background radiation events. The chemistry required to make such sensitive detection of Ba²⁺ by SMFI in dry Xe gas at solid interfaces has implications for solid-phase detection methods but has not been demonstrated. Here, we synthesized simple, robust, and effective Ba²⁺-selective chemosensors capable of function within ultrapure high-pressure ¹³⁶Xe gas. Turn-on fluorescent naphthalimide-(di)azacrown ether chemosensors were Ba²⁺-selective and achieved SMFI in a polyacrylamide matrix. Fluorescence and NMR experiments supported a photoinduced electron transfer mechanism for turn-on sensing. Ba²⁺ selectivity was achieved with computational calculations correctly predicting the fluorescence responses of sensors to barium, mercury, and potassium ions. With these molecules, dry-phase single-Ba²⁺ ion imaging with turn-on fluorescence was realized using an oil-free microscopy technique for the first time-a significant advance toward single-Ba²⁺ ion detection within large volumes of ¹³⁶Xe, plausibly enabling a background-independent technique to search for the hypothetical process of 0νββ.

A Highly Selective Turn-on Fluorescent and Naked-eye Colourimetric Dual-channel Probe for Cyanide Anions Detection in Water Samples

A highly selective turn-on fluorescent and naked-eye colourimetric dual-channel probe for cyanide anions (CN-) has been designed and characterized. In the mixed solution (DMSO / H₂O, 9:1, v / v), only CN- could cause an increase in the UV absorption intensity and the corresponding fluorescence intensity increased, and other anions had no significant effect on the probe. After treatment with cyanide in the probe solution, the solution showed a noticeable colour change, from light yellow to purple. Moreover, a fluorescence spectrophotometer can be used to observe that the fluorescence intensity of the solution is significantly enhanced. The response of the colourimetric and fluorescent dual-channel probe to CN- was attributed to nucleophilic addition, and the mechanism was determined by ¹H NMR spectroscopy. In addition, this probe was used to detect CN- in actual water samples, including river water, drinking water, and tap water. The spiked CN- recovery rate is very high (97.2%-100.06%), and analytical precision is also very high (RSD < 2%), which shows its feasibility and reliability for detecting cyanide ions in actual water samples.

Inner filter effect as a sensitive sensing platform for detection of nitrofurantoin using luminescent drug-based carbon nanodots

In the present paper, a sensitive and selective inner filter effect sensing platform was designed to detect nitrofurantoin (NIT) in pharmaceutical dosage form. Nitrogen and phosphorus co-doped carbon nanodots (CNDs) prepared via solvothermal treatment of folic acid and phosphoric acid. The prepared CNDs exhibit greenish fluorescence at 470 nm when excited at 340 nm with fluorescence quantum yield up to 40%. The CNDs exhibit high stability in various pH, temperature, and ionic strength which adds valuable merits to its pharmaceutical applications. The emission is quenched in the presence of absorber (here NIT) while the fluorophores were not quench by the presence of common pharmaceutical excipients. A fluorometric assay was fabricated to determine NIT in capsules by quenching of the CNDs. The linear response for the proposed method was from 5.0 μM to 90 μM with the detection limit being 1.4 μM. To validate the method, the recovery of NIT in spiked sample was measured which was 96.6% -103.3%. The method was applied to the determination of NIT in pharmaceutical capsule samples, with comparable results of a reference method stated by the British Pharmacopeia (BP). Furthermore, the sub-acute toxicity studies of CNDs were investigated using normal male Balb/c mice forcefully drunk with 3 different dosages of CNDs. Animals did not produce treatment related signs of toxicity or mortality in any of the animals tested during the 28 days observation period. Additionally, no significant (P > 0.05) changes in the body weight, haematological and biochemical parameters compared with the control group were not revealed. Similarly, histopathological examination of the internal vital organs did not show any morphological alterations.

A label-free multifunctional nanosensor based on N-doped carbon nanodots for vitamin B12 and Co2+ detection, and bioimaging in living cells and zebrafish

Multifunctional N-doped carbon nanodots (N-CNDs) with a fluorescence (FL) quantum yield (QY) of 13.6% have been synthesized via a facile one-step hydrothermal process using Artemisia annua and 1,2-ethylenediamine as precursors. As-prepared N-CNDs showed excellent FL properties and were developed as a multifunctional sensing platform for vitamin B₁₂ (VB₁₂) and Co²⁺ determination, and bioimaging in living cells and zebrafish. The FL of N-CNDs is quenched efficiently in the presence of VB₁₂ on the basis of the inner filter effect (IFE) or Co²⁺ by static quenching, respectively. EDTA as a masking agent enables Co²⁺ to be effectively eliminated and N-CNDs were used to selectively detect VB₁₂ in the presence of both VB₁₂ and Co²⁺. The present FL nanosensor can detect VB₁₂ and Co²⁺ in the linear ranges of 0.5-35 μM and 2.5-25 μM with the corresponding detection limits of 47.4 nM and 230.5 nM, respectively. The study proved that the determination of Co²⁺ was based on the static quenching to form a complex between the amino group of N-CNDs and Co²⁺. Inspired by these outstanding properties, practical applications of this nanosensor for the detection of VB₁₂ in actual samples (human serum, egg yolk, VB₁₂ tablets and VB₁₂ injection) and Co²⁺ in water samples were further verified with satisfactory results. The as-constructed N-CNDs have negligible toxicity and good biocompatibility, which facilitates utilization of N-CNDs in bioimaging of A549 cells and zebrafish, and sensing VB₁₂ in living cells.

Macrocyclic "tet a" derived colorimetric sensor for the detection of mercury cations and hydrogen sulphate anions and its bio-imaging in living cells

A mono-N-substituted probe L containing a bromosalicylaldehyde pendant arm attached to a tetraazamacrocyclic "tet a" moiety was synthesized via straight forward reaction. The probe L crystallizes in a monoclinic P2₁/n space group. The probe L displayed quick sensitivity and selectivity towards Hg²⁺ ions due to its hopeful Chelation Enhancement Quenching (CHEQ) feature. Interestingly, the probe L exhibits turn-off fluorescence response to Hg²⁺ ion and turn-on fluorescence signals to HSO₄^- ions. When the probe L was complexed with HSO₄^- in 1:1 mode (L + HSO₄^- formation), improved turn-on fluorescence emission was detected due to the chelation enhanced fluorescence effect through sensor complex. The macrocyclic "tet a" probe L exhibited a binding constant value of 3.89 × 10⁶ M^-1 and 5.58 × 10⁵ M^-1 for Hg²⁺ and HSO₄^-, respectively. Probe L exhibited good selectivity to Hg²⁺ rather than other common metal ions and HSO₄^- over other common anions. The limit of detection (LOD) of Hg²⁺ and HSO₄^- were found to be 1 nM and 7 μM, respectively. The time-resolved fluorescence emission single-photon counting study was used to determine the average lifetime value for the probe L and L + HSO₄^- ions as 0.47 and 1.02 ns, respectively. The practical application of the probe in visualizing intracellular Hg²⁺ and HSO₄^- ions distribution in live Artemia salina was demonstrated. Furthermore, the probe L with Hg²⁺cations was found to be cytotoxic against breast cancer cells in nature and can be delivered as an anticancer agent. Besides the probe L with HSO₄^- exhibit strong fluorescence emission with low cytotoxicity, and it can be recommended for live-cell imaging.