Nicotinamide adenine dinucleotide immobilized tungsten trioxide nanoparticles for simultaneous sensing of norepinephrine, melatonin and nicotine

Immobilization of Adenosine Derivatives onto Cellulose Nanocrystals via Click Chemistry for Biocatalysis Applications

Adenosine triphosphate (ATP) is a central molecule of organisms and is involved in many biological processes. It is also widely used in biocatalytic processes, especially as a substrate and precursor of many cofactors─such as nicotinamide adenine dinucleotide phosphate (NADP(H)), coenzyme A (CoA), and S-adenosylmethionine (SAM). Despite its great scientific interest and pivotal role, its use in industrial processes is impeded by its prohibitory cost. To overcome this limitation, we developed a greener synthesis of adenosine derivatives and efficiently selectively grafted them onto organic nanoparticles. In this study, cellulose nanocrystals were used as a model combined with click chemistry via a copper-catalyzed azide/alkyne cycloaddition reaction (CuAAC). The grafted adenosine triphosphate derivative fully retains its biocatalytic capability, enabling heterobiocatalysis for modern biochemical processes.

Methylene blue molecularly imprinted polymer for melatonin determination in urine and saliva samples

A highly sensitive and rapid electrochemical sensor was developed for detecting melatonin using a molecularly imprinted polymer (MIP) with methylene blue as the functional monomer and melatonin as the template. The MIP was synthesized via a simple electropolymerization process that did not require an initiating reagent. The sensor demonstrated good selectivity for melatonin against common interferences such as lactate, cytosine, cytidine, urea, ascorbic acid, creatine, creatinine, serotonin, and tryptophan. Melatonin detection was achieved at a potential of 0.60 V vs. Ag/AgCl with a sensitivity of 138.8 ± 4.7 µA µM‒1 in the linear range 0.097 - 200 µM and a limit of detection of 29 nM (3SB/m). The sensor exhibited excellent reproducibility and repeatability for both within (intra) and between (inter) electrodes (%RSD < 3% for n = 3). The sensor was applied to authentic urine and saliva samples with recoveries of 103 ± 1% and 102 ± 1%, respectively.

Melatonin in different food samples: Recent update on distribution, bioactivities, pretreatment and analysis techniques

Melatonin (MLT) plays a significant role on maintaining the basic physiological functions and regulating various metabolic processes in plentiful organisms. Recent years have witnessed an increase in MLT's share in global market with its affluent functions. However, the worrisome quality issues and inappropriate or excessive application of MLT take place inevitably. In addition, its photosensitive properties, oxidation, complex substrate concentration and trace levels leave exact detection of MLT doubly difficult. Therefore, it is essential to exploit precise, sensitive and stable extraction and detection methods to resolve above questions. In this study, we reviewed the distribution and bioactivities of MLT and conducted a comprehensive overview of the developments of pretreatment and analysis methods for MLT in food samples since 2010. Commonly used pretreatment methods for MLT include not only traditional techniques, but also novel ones, such as solid-phase extraction, QuEChERS, microextraction by packed sorbent, solid phase microextraction, liquid phase microextraction, and so on. Analysis methods include liquid chromatography coupled with different detectors, GC methods, capillary electrophoresis, sensors, and so on. The advantages and disadvantages of different techniques have been compared and the development tendency was prospected.

A bio-analytic nanoplatform based on Au post-functionalized CeFeO3 for the simultaneous determination of melatonin and ascorbic acid through photo-assisted electrochemical technology

Both melatonin and ascorbic acid could perform an irreplaceable role in maintaining the ecological balance of the human body and fighting cardiovascular diseases. Herein, a dual-channel photo-assisted electrochemical sensor has been fabricated based on Au post-functionalized CeFeO₃ nanospheres to simultaneously monitor melatonin and ascorbic acid for the first time. Briefly, CeFeO₃ nanospheres are prepared through a hydrothermal and annealing process, and then the reduced Au nanoclusters are anchored on the surface of spheres to afford the CeFeO₃@Au bi-nanospherical sensing probe. Impressively, the pre-fabricated sensor can produce a current signal 11% higher under light than that produced in a dark environment during the electrochemical measurements. Subsequently, the sensor fabricated by our strategy has achieved the simultaneous determination of melatonin and ascorbic acid with the wide detecting ranges of 1 nM-5 μM and 1 nM to 2 μM, and low detection limits of 0.8 nM and 0.4 nM by electrochemical measurements with the presence of the sunlight, and has shown satisfactory recoveries in the real sample measurements, demonstrating that the CeFeO₃@Au bi-nanospherical sensing probe will be an auspicious candidate of advanced electrode material in photo-assisted electrochemical sensing applications.

Recent Advances in Electrochemical and Optical Sensors for Detecting Tryptophan and Melatonin

Tryptophan and melatonin are pleiotropic molecules, each capable of influencing several cellular, biochemical, and physiological responses. Therefore, sensitive detection of tryptophan and melatonin in pharmaceutical and human samples is crucial for human well-being. Mass spectrometry, high-performance liquid chromatography, and capillary electrophoresis are common methods for both tryptophan and melatonin analysis; however, these methods require copious amounts of time, money, and manpower. Novel electrochemical and optical detection tools have been subjects of intensive research due to their ability to offer a better signal-to-noise ratio, high specificity, ultra-sensitivity, and wide dynamic range. Recently, researchers have designed sensitive and selective electrochemical and optical platforms by using new surface modifications, microfabrication techniques, and the decoration of diverse nanomaterials with unique properties for the detection of tryptophan and melatonin. However, there is a scarcity of review articles addressing the recent developments in the electrochemical and optical detection of tryptophan and melatonin. Here, we provide a critical and objective review of high-sensitivity tryptophan and melatonin sensors that have been developed over the past six years (2015 onwards). We review the principles, performance, and limitations of these sensors. We also address critical aspects of sensitivity and selectivity, limit and range of detection, fabrication process and time, durability, and biocompatibility. Finally, we discuss challenges related to tryptophan and melatonin detection and present future outlooks.

Plasmophore Enhancement in Fibroblast Green Fluorescent Protein-Positive Cells Excited by Smoke

Considering the large consumption of nicotine and its sedative/stimulant effect on different organs of the body, the detection of low concentration of this material and its subsequent effect on live animals plays a significant role. Optical detection techniques such as plasmonics are the pioneers in highly sensitive detection techniques. However, for investigating the nicotine/smoke effect on live cells, not only the interaction between cell nicotine should be optimized but also the plasmonic interface should show a high sensitivity to the reception of nicotine by the cell receptors. In this study, the sensitivity of the plasmonic detection system was greatly increased using the coupling of plasmon and fluorophore. This coupling could enhance the main plasmonic signal several orders of magnitude besides improving Δ and Ψ ellipsometry parameters. Benefiting from the green fluorescence proteins, the phase shift and the amplitude ratio between the reflections under s- and p-polarized light enhance considerably which verifies the coupling of the dipole of the fluorescence emitter and the plasmons of the metal nanostructure. For 1 s increase of the maintenance time, we encountered a considerable increase in the Δ values that were 0.15° for T _e = 1 s and 0.24° for T _e = 3 s. Benefiting from extracted ellipsometry parameters, this study could open new avenues toward studying the effect of various types of drugs and stimulants on biological samples using a novel plasmophore platform.