Endogenous Photosensitizers in Human Skin

Endogenous photosensitizers play a critical role in both beneficial and harmful light-induced transformations in biological systems. Understanding their mode of action is essential for advancing fields such as photomedicine, photoredox catalysis, environmental science, and the development of sun care products. This review offers a comprehensive analysis of endogenous photosensitizers in human skin, investigating the connections between their electronic excitation and the subsequent activation or damage of organic biomolecules. We gather the physicochemical and photochemical properties of key endogenous photosensitizers and examine the relationships between their chemical reactivity, location within the skin, and the primary biochemical events following solar radiation exposure, along with their influence on skin physiology and pathology. An important take-home message of this review is that photosensitization allows visible light and UV-A radiation to have large effects on skin. The analysis presented here unveils potential causes for the continuous increase in global skin cancer cases and emphasizes the limitations of current sun protection approaches.

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.

Advances on Hormones and Steroids Determination: A Review of Voltammetric Methods since 2000

This article presents advances in the electrochemical determination of hormones and steroids since 2000. A wide spectrum of techniques and working electrodes have been involved in the reported measurements in order to obtain the lowest possible limits of detection. The voltammetric and polarographic techniques, due to their sensitivity and easiness, could be used as alternatives to other, more complicated, analytical assays. Still, growing interest in designing a new construction of the working electrodes enables us to prepare new measurement procedures and obtain lower limits of detection. A brief description of the measured compounds has been presented, along with a comparison of the obtained results.

Molecularly Imprinted Polymers in Diagnostics: Accessing Analytes in Biofluids

Bio-applied molecularly imprinted polymers (MIPs) are biomimetic materials with tailor-made synthetic recognition sites, mimicking biological counterparts known for their sensitive and selective analyte detection. MIPs, specifically designed for biomarker analysis...

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.

Graphene-Based Sensors for the Detection of Bioactive Compounds: A Review

Over the last years, different nanomaterials have been investigated to design highly selective and sensitive sensors, reaching nano/picomolar concentrations of biomolecules, which is crucial for medical sciences and the healthcare industry in order to assess physiological and metabolic parameters. The discovery of graphene (G) has unexpectedly impulsed research on developing cost-effective electrode materials owed to its unique physical and chemical properties, including high specific surface area, elevated carrier mobility, exceptional electrical and thermal conductivity, strong stiffness and strength combined with flexibility and optical transparency. G and its derivatives, including graphene oxide (GO) and reduced graphene oxide (rGO), are becoming an important class of nanomaterials in the area of optical and electrochemical sensors. The presence of oxygenated functional groups makes GO nanosheets amphiphilic, facilitating chemical functionalization. G-based nanomaterials can be easily combined with different types of inorganic nanoparticles, including metals and metal oxides, quantum dots, organic polymers, and biomolecules, to yield a wide range of nanocomposites with enhanced sensitivity for sensor applications. This review provides an overview of recent research on G-based nanocomposites for the detection of bioactive compounds, providing insights on the unique advantages offered by G and its derivatives. Their synthesis process, functionalization routes, and main properties are summarized, and the main challenges are also discussed. The antioxidants selected for this review are melatonin, gallic acid, tannic acid, resveratrol, oleuropein, hydroxytyrosol, tocopherol, ascorbic acid, and curcumin. They were chosen owed to their beneficial properties for human health, including antibiotic, antiviral, cardiovascular protector, anticancer, anti-inflammatory, cytoprotective, neuroprotective, antiageing, antidegenerative, and antiallergic capacity. The sensitivity and selectivity of G-based electrochemical and fluorescent sensors are also examined. Finally, the future outlook for the development of G-based sensors for this type of biocompounds is outlined.

Molecularly Imprinted Polymer Micro- and Nano-Particles. A review

In recent years, molecularly imprinted polymers (MIPs) have become an excellent solution to the selective and sensitive determination of target molecules in complex matrices where other similar and relative structural compounds could coexist. Although MIPs show the inherent properties of the polymers, including stability, robustness, and easy/cheap synthesis, some of their characteristics can be enhanced, or new functionalities can be obtained when nanoparticles are incorporated in their polymeric structure. The great variety of nanoparticles available significantly increase the possibility of finding the adequate design of nanostructured MIP for each analytical problem. Moreover, different structures (i.e., monolithic solids or MIPs micro/nanoparticles) can be produced depending on the used synthesis approach. This review aims to summarize and describe the most recent and innovative strategies since 2015, based on the combination of MIPs with nanoparticles. The role of the nanoparticles in the polymerization, as well as in the imprinting and adsorption efficiency, is also discussed through the review.

Tin disulfide-graphene oxide-β-cyclodextrin mediated electro-oxidation of melatonin hormone: an efficient platform for electrochemical sensing

Here, we have developed an electrochemical sensor based on integrated 2D materials including tin disulfide (SnS2) nanoflakes, graphene oxide (GO), and β-cyclodextrin (β-CD) forming a ternary nanocomposite decorated on a screen-printed electrode (SPE) for the electrochemical detection of melatonin. Hydrothermally synthesized SnS2 was mixed with GO/β-CD to prepare the ternary composite via an ultra-sonication process. The nanocomposite was characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and field emission transmission electron microscopy (FEG-TEM). The electrochemical performance of the modified electrode was investigated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). The electrochemical sensor exhibited a linearity range from 1 nM to 100 μM with the lowest detection limit of 0.17 nM. The sensor was successfully applied for the detection of melatonin in commercial drugs and human saliva, which showed a consistent result with the Enzyme-Linked Immuno-Sorbent Assay (ELISA).

Molecularly Imprinted Polymers in Electrochemical and Optical Sensors

Molecular imprinting is the process of template-induced formation of specific recognition sites in a polymer. Synthetic receptors prepared using molecular imprinting possess a unique combination of properties such as robustness, high affinity, specificity, and low-cost production, which makes them attractive alternatives to natural receptors. Improvements in polymer science and nanotechnology have contributed to enhanced performance of molecularly imprinted polymer (MIP) sensors. Encouragingly, recent years have seen an increase in high-quality publications describing MIP sensors for the determination of biomolecules, drugs of abuse, and explosives, driving toward applications of this technology in medical and forensic diagnostics. This review aims to provide a focused overview of the latest achievements made in MIP-based sensor technology, with emphasis on research toward real-life applications.

Real-Time Detection of Melatonin Using Fast-Scan Cyclic Voltammetry

Melatonin is an important hormone whose functions span from regulating circadian rhythm in the brain to providing anti-inflammatory properties in the immune system. Melatonin secretion from the pineal gland is known; however, the mechanism of melatonin signaling in the immune system is not well understood. The lymph node is the hub of the immune system, and melatonin secretion from lymphocytes was proposed to be an important source specifically for regulating cytokine secretion. Methods exist to quantify the concentration of melatonin within biological samples; however, they often suffer from either a lack of selectivity for melatonin over common biological interferences or temporal resolution, which is not amenable to measuring real-time signaling dynamics. Here, we have characterized an electrochemical method for optimal melatonin detection with subsecond resolution using fast-scan cyclic voltammetry at carbon-fiber microelectrodes. The oxidation peaks detected for melatonin were at 1.0, 1.1, and 0.6 V. Evidence for electrode fouling of the tertiary peak was present; therefore, an optimized waveform was developed scanning from 0.2 to 1.3 V at 600 V/s. The optimized waveform eliminated the detection of fouling products on the electrode with a 24 ± 10 nM limit of detection. Melatonin was distinguished between biological interferences, and codetection with the major synthetic precursor, serotonin, was possible. This method was used to detect melatonin in live lymph node slices and provides the first real-time measurements within the lymph node using FSCV. Real-time detection of melatonin dynamics could provide useful information on the mechanism of immunomodulation during inflammatory disease.

Recent Progress of Imprinted Nanomaterials in Analytical Chemistry

Molecularly imprinted polymers (MIPs) are a type of tailor-made materials that have ability to selectively recognize the target compound/s. MIPs have gained significant research interest in solid-phase extraction, catalysis, and sensor applications due to their unique properties such as low cost, robustness, and high selectivity. In addition, MIPs can be prepared as composite nanomaterials using nanoparticles, multiwalled carbon nanotubes (MWCNTs), nanorods, quantum dots (QDs), graphene, and clays. This review paper aims to demonstrate and highlight the recent progress of the applications of imprinted nanocomposite materials in analytical chemistry.

Facile and novel synthesis of palladium nanoparticles supported on a carbon aerogel for ultrasensitive electrochemical sensing of biomolecules

Highly stable palladium nanoparticles (Pd NPs) supported on a porous carbon aerogel (Pd/CA) prepared by a facile microwave reduction route is reported. The as-prepared Pd/CA composites were characterized by various techniques, viz. XRD, Raman, SEM-EDX, FE-TEM, BET, and TGA. The Pd NPs were found to disperse uniformly in the porous carbon matrix, which possesses a large surface area (851.8 m² g^-1) and pore volume (3.021 cm³ g^-1). The Pd/CA composite was found to possess extraordinary electrocatalytic activity and excellent selectivity for simultaneous detection of dopamine (DA) and melatonin (ML). The Pd/CA-modified electrode exhibited a wide linear response range for electrochemical sensing of DA (0.01-100 μM) and ML (0.02-500 μM) with a detection limit of 0.0026 and 0.0071 μM, respectively. In addition, the electrochemical sensor reported herein was successfully applied for the detection of DA and ML in human serum and urine samples, revealing perspective practical applications.

Molecular imprinting polymers and their composites: a promising material for diverse applications

Molecular imprinted polymerization is considered one of the most useful preparation strategies to obtain highly selective polymeric materials called molecular imprinted polymers (MIPs).

A fluorescence switch sensor for detection of virginiamycin based on graphene oxide-supported carbon quantum dots and molecularly imprinted polymer

A fluorescence switch sensor was developed for the detection of virginiamycin, which was based on graphene oxide-supported carbon quantum dots (GO/C-dots) as the signal indicator and molecularly imprinted polymer (MIP) as the recognition template.

Introduction of selectivity and specificity to graphene using an inimitable combination of molecular imprinting and nanotechnology

Recently, the nanostructured modified molecularly imprinting polymer has created a great attention in research field due to its excellent properties such as high surface to volume ratio, low cost, and easy preparation/handling. Among the nanostructured materials, the carbonaceous material such as 'graphene' has attracted the tremendous attention of researchers owing to their fascinating electrical, thermal and physical properties. In this review article, we have tried to explore as well as compile the role of graphene-based nanomaterials in the fabrication of imprinted polymers. In other words, herein the recent efforts made to introduce selectivity in graphene-based nanomaterials were tried collected together. The major concern of this review article is focused on the sensing devices fabricated via a combination of graphene, graphene@nanoparticles, graphene@carbon nanotubes and molecularly imprinted polymers. Additionally, the combination of graphene and quantum dots was also included to explore the fluorescence properties of zero-band-gap graphene.

Electrochemical investigations of 8-hydroxydeoxyguanosine and its determination at an edge plane pyrolytic graphite electrode

Electrochemical oxidation of 8-hydroxydeoxyguanosine (8-OHdG) and its detection with low detection limit is reported at pyrolytic graphite electrode.

Structural and electrochemical characterization of carbon ion beam irradiated reduced graphene oxide and its application in voltammetric determination of norepinephrine

A high energy carbon ion beam irradiated sensor has been used for the sensitive determination of norepinephrine.

A new electrochemical sensor based on a nitrogen-doped graphene/CuCo2O4 nanocomposite for simultaneous determination of dopamine, melatonin and tryptophan

An electrochemical sensor was fabricated for the simultaneous determination of dopamine, melatonin and tryptophan in biological and pharmaceutical samples.

β-Cyclodextrin/chitosan–magnetic graphene oxide–surface molecularly imprinted polymer nanocomplex coupled with chemiluminescence biosensing of bovine serum albumin

In this report, a sensitive and selective chemiluminescence biosensor for bovine serum albumin coupled with surface molecularly imprinted nanocomplex using β-cyclodextrin/chitosan–magnetic graphene oxide as backbone material was investigated.