Ultrasensitive and highly selective "turn-on" fluorescent sensor for the detection and measurement of melatonin in juice samples

Ratio-fluorescence sensor based on carbon dots and PtRu/CN nanozyme for efficient detection of melatonin in tablet

The identification and quantification of melatonin (MT) are crucial for early diagnosis of disorders associated with circadian rhythm disruption. Herein, novel blue-emissive carbon dots (BCDs) were synthesized through an improved hydrothermal treatment using serine and malic acid as reductant and carbon source. The excellent optical properties of the as-obtained BCDs were used for ratiometric sensing by strategically constructing a MT sensing system integrating BCDs with C3N4 nanosheets loaded with platinum/ruthenium nanoparticles (PtRu/CN). In this system, H2O2 activated the peroxidase-like activity of PtRu/CN to generate •OH and 1O2 for oxidizing the colorless o-phenylenediamine (OPD) into yellow 2,3-diaminophenazine (DAP) with fluorescence emission at 565 nm. Concurrently, the fluorescence emission of BCDs at 439 nm was quenched by the generated DAP via the static quenching and inner filter effect (IFE) process. However, MT rapidly scavenged the generated free radicals to reverse the ratio fluorescence signal. The developed BCDs/PtRu/CN/OPD/H2O2 sensing platform enabled quantitative analysis of MT at concentrations ranging from 0.06 to 600 μmol/L with a low detection limit of 23.56 nmol/L. Moreover, smartphone-based RGB sensing of MT was successfully developed for rapid visualization and portable processing. More broadly, novel insights into the preparation of carbon dots with sensitive fluorescence sensing properties were presented, promising for future considerations.

Dispersive Solid Phase Extraction of Melatonin with Graphene/Clay Mixtures and Fluorescence Analysis in Surfactant Aqueous Solutions

In this work, the dispersive solid phase extraction (dSPE) of melatonin using graphene (G) mixtures with sepiolite (SEP) and bentonite (BEN) clays as sorbents combined with fluorescence detection has been investigated. The retention was found to be quantitative for both G/SEP and G/BEN 4/96 and 10/90 w/w mixtures. G/clay 4/96 w/w mixtures were selected to study the desorption process since the retention was weaker, thus leading to easier desorption. MeOH and aqueous solutions of the nonionic surfactant Brij L23 were tested as desorbents. For both clays and an initial sample volume of 25 mL, a percentage of melatonin recovery close to 100% was obtained using 10 or 25 mL of MeOH as desorbent. Further, using a G/SEP mixture, 25 mL as the initial sample volume and 5 mL of MeOH or 60 mM Brij L23 solution as the desorbent, recoveries of 98.3% and 90% were attained, respectively. The whole method was applied to herbal tea samples containing melatonin, and the percentage of agreement with the labeled value was 86.5%. It was also applied to herbal samples without melatonin by spiking them with two concentrations of this compound, leading to recoveries of 100 and 102%.

Recent Advances in Nanomaterials Based Optical Sensors for the Detection of Melatonin and Serotonin

In this review paper we discussed the detection of melatonin and serotonin by using various optical methods. Melatonin and serotonin are very necessary body hormones these are also called neuroregulatory hormones secreted by pineal gland in brain by pinealocytes and shape of pineal gland is cone like. Sensitive detection of melatonin and serotonin in pharmacological samples and human serum is crucial for human beings, lots of research publications available in literature for melatonin and serotonin and we overviewed these papers. We have deeply reviewed many research papers where sensitively sensing of melatonin and serotonin occurs, by using of various interfering agents and nanomaterials. This review aims presenting colorimetry, fluorometry and spectrophotometric detection of melatonin (MEL) and serotonin (SER) by using different metal oxides, carbon nanomaterials (nanosheets, nanorods, nanofibers) and many other agents. Nanomaterials typically possess favourable optical, electrical and mechanical characteristics, they provide up new avenues for enhancing the efficacy of sensors. It is crucial to provide an optical sensors platform that is dependable, sensitive and low price. The development of sensors and biosensors to use nanomaterials for neurotransmitters has advanced significantly in recent years. There are currently many developing biomarkers in biological fluids, and bionanomaterial-based biosensor systems, as well as clinical and pharmacological settings, have garnered significant interest. Biomarkers have been found using optical devices in a quick, selective and sensitive manner. Our aim is to compile all the data that already published on MEL, SER sensing and comparison of each method, we mainly focused on principle, observations, sensitivity, selectivity, limit of detection, mechanism behind the reaction, effect of temperature, pH and concentration. In the last of this paper, we discuss some challenges of these methods and future projects.

Ratiometric fluorescent sensing of melatonin based on inner filter effect and smartphone established detection

Melatonin (MLT) is a crucial neurohormone having inhibitory effects over various types of cancer. In this work, 3,6-Diaminocarbazole (DAC), a fluorescent probe is utilized to detect MLT in a highly sensitive, selective and facile way. The unique feature of present work is that MLT is sensed by ratiometric fluorescent technique based on the inner filter effect (IFE) using DAC at an emission wavelength of 310 nm. As a result, a noticeable change in color from red to cyan is observed and the quantitative analysis of fluorescence signals at these wavelengths are used to detect MLT observing a linear relationship between the ratio of emission intensities and the concentration of MLT over a linear range of 0 to 78 μM. DAC can accurately measure the detailed quantity of MLT with a limit of detection of 30 nM and has proved to be an efficient sensing probe due to its excellent molar absorptivity and high photoluminescence quantum yield (PLQY). Sensing characterization was carried out UV-Vis, steady-state, and time- resolved fluorescence spectroscopic techniques. The smartphone app "RGB colour detector" value has been successfully linked with the considerable detectable color changes of DAC on addition of MLT. HOMO-LUMO have been calculated using DFT with B3LYP/6-31G(d,p) level and band gaps of 3.77 eV and 4.91 eV were found for DAC and MLT, respectively. Electrons are not allowed energetically to transfer from MLT to DAC, as is evident from their band gaps. Therefore, IFE can be considered the foremost method in fluorescence quenching of present investigation. The developed sensor was verified by spiking of MLT in human serum.

Preparation of fluorescent sensor based on Zn metal-organic framework for detection and determination of raloxifene as an anticancer drug

Breast cancer is the second leading cause of death for women worldwide. Raloxifene (RLX) is a somewhat effective drug in lowering cholesterol, preventing and treating invasive breast cancer in postmenopausal women with osteoporosis, and does not interfere with breast tissue. Nevertheless, considering the possibility of risk in biological function due to excessive use of anticancer drugs and the adverse effects of drugs in wastewater on plants, animals, and aquatic, it is useful to determine the concentration of RLX in water and human body fluids. Here, a fluorescent metal-organic framework (MOF) nanoparticle based on trinuclear zinc clusters called Zn-MOF was presented, which is a high-performance and fast-response fluorescent chemosensor that can be used to detect RLX based on the fluorescence quenching medium in water. FTIR, XRD, SEM, and EDS analyses were used to identify the functional group and determine the structure and morphology of Zn-MOF. pH range 3-10. The prepared nanoparticles showed symmetric emission with excitation at a wavelength of 310.0 nm. The performance of the proposed fluorescent nanosensor was proportional to the quenching of the fluorescent signal with increasing RLX concentration at 404.0 nm; the quenching fluorescence response was linear in RLX concentration from 0.7 to 350 ng/mL with a significant detection limit equal to 0.485 nM.

A Turn-Off Fluorescent Biomimetic Sensor Based on a Molecularly Imprinted Polymer-Coated Amino-Functionalized Zirconium (IV) Metal-Organic Framework for the Ultrasensitive and Selective Detection of Trace Oxytetracycline in Milk

Developing sensitive and effective methods to monitor oxytetracycline residues in food is of great significance for maintaining public health. Herein, a fluorescent sensor (NH₂-UIO-66 (Zr)@MIP) based on a molecularly imprinted polymer-coated amino-functionalized zirconium (IV) metal-organic framework was successfully constructed and first used for the ultrasensitive determination of oxytetracycline. NH₂-UIO-66 (Zr), with a maximum emission wavelength of 455 nm under 350 nm excitation, was prepared using a microwave-assisted heating method. The NH₂-UIO-66 (Zr)@MIP sensor with specific recognition sites for oxytetracycline was then acquired by modifying a molecularly imprinted polymer on the surface of NH₂-UIO-66 (Zr). The introduction of NH₂-UIO-66 (Zr) as both a signal tag and supporter can strengthen the sensitivity of the fluorescence sensor. Thanks to the combination of the unique characteristics of the molecularly imprinted polymer and NH₂-UIO-66 (Zr), the prepared sensor not only exhibited a sensitive fluorescence response, specific identification capabilities and a high selectivity for oxytetracycline, but also showed good fluorescence stability, satisfactory precision and reproducibility. The fabricated sensor displayed a fluorescent linear quenching in the OTC concentration range of 0.05-40 μg mL^-1, with a detection limit of 0.012 μg mL^-1. More importantly, the fluorescence sensor was finally applied for the detection of oxytetracycline in milk, and the results were comparable to those obtained using the HPLC approach. Hence, the NH₂-UIO-66 (Zr)@MIP sensor possesses great application potential for the accurate evaluation of trace oxytetracycline in dairy products.

Metal-organic framework-based nanomaterials as opto-electrochemical sensors for the detection of antibiotics and hormones: A review

Increasing trace levels of antibiotics and hormones in the environment and food samples are concerning and pose a threat. Opto-electrochemical sensors have received attention due to their low cost, portability, sensitivity, analytical performance, and ease of deployment in the field as compared to conventional expensive technologies that are time-consuming and require experienced professionals. Metal-organic frameworks (MOFs) with variable porosity, active functional sites, and fluorescence capacity are attractive materials for developing opto-electrochemical sensors. Herein, the insights into the capabilities of electrochemical and luminescent MOF sensors for detection and monitoring of antibiotics and hormones from various samples are critically reviewed. The detailed sensing mechanisms and detection limits of MOF sensors are addressed. The challenges, recent advances, and future directions for the development of stable, high-performance MOFs as commercially viable next-generation opto-electrochemical sensor materials for the detection and monitoring of diverse analytes are discussed.

Ultrasound-assisted synthesis of europium doped BPO4 nanoparticles; a new approach for Zn2+ (aq) detection

In this work, europium ion was doped into boron phosphate nanoparticles (BPO₄) using an ultrasonic method followed by the calcination process. The nanoparticles were characterized by various techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy, transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy, and scanning electron microscopy (SEM). Doping of europium ion into the BPO₄ host crystal was proved by cell volume calculation from XRD patterns, the shift in Raman spectra, and photoluminescence properties. In addition, the europium doped boron phosphate (BPE) as a fluorescence sensor for the quantification of Zn²⁺ cation was studied. The obtained results showed the enhancement and shift of the photoluminescence peak from 292 to 340 nm. The sensor's selectivity toward this ion was verified in the presence of a variety of common interfering cations. Surprisingly, BPE revealed excellent selectivity and sensitivity towards Zn²⁺ in the presence of Pb²⁺, Na⁺, Fe²⁺, Al³⁺, Ca²⁺, Mg²⁺, Cu²⁺, Co²⁺, Ni²⁺, Mn²⁺, Cd²⁺, Hg²⁺, Ba²⁺ and Fe³⁺ cations. The fluorescence response was linearly proportional to the Zn²⁺concentration. After the addition of trace amounts of Zn²⁺ ions into the aqueous solution, a significant enhancement of fluorescence emission occurred with the detection limit of 0.3 μM.

Magnetic nanoparticles based on cerium MOF supported on the MWCNT as a fluorescence quenching sensor for determination of 6-mercaptopurine

In this study, a new magnetic nanocomposite was developed as an efficient and fast-response fluorescence quenching sensor for determination of anticancer drug 6-mercaptopurine (6-MP). For this purpose, the needle-shape fluorescence metal-organic framework of cerium (Ce-MOF) were successfully synthesized on the surface of multiwalled carbon nanotubes using 1,3,5-benzenetricarboxylic acid ligand via a facile solvothermal assisted route and magnetized. The accuracy of the proposed synthesis was confirmed using the FT-IR, FE-SEM, XRD, and VSM methods. The obtained product as presented the fluorescence emission in 331 nm by excitation of 293 nm in excitation/emission slit widths of 10.0 nm. The operation of suggested method is based on quenching the fluorescence signal in accordance with increasing the 6-MP concentration. The proposed assay effectively detected the trace amount of 6-MP in the linear range of 1.0 × 10^-6 to 7 × 10^-5 M. The limit of detection and limit of quantification were obtained as 8.6 × 10^-7 and 2.86 × 10^-6 M, respectively. The analyte molecule was determined in real samples with satisfactory recoveries between 98.75 and 105.33.