Rapid and specific sensing of gallic acid with a photoelectrochemical platform based on polyaniline-reduced graphene oxide-TiO2

Fluorescent silver hydrosol for the dual fluorometric sensing of gallic acid and Cd2

Herein, silver-enhanced fluorescence was obtained using a small molecule of salicylaldehyde (SL) in an alkaline solution in the presence of silver nitrate. Ag+ was reduced to Ag0, while SL was oxidized to the quinone form OSL. OSL was a very weak fluorophore and exhibited metal-enhanced fluorescence (MEF) in the presence of proximal silver nanoparticle surfaces. MEF was selectively quenched by gallic acid and restored by Cd2+. Thus, a dual-sensing platform was obtained for gallic acid [limit of detection (LOD) = 1.77 × 10-5 M; linear detection range = 10-8 to 5 × 10-5 M)] and Cd2+ (LOD = 2.4 × 10-6 M; linear detection range = 5 × 10-8 to 10-6 M) in a one-pot. The observed lightning rod effect and higher radiative decay rate were ascribed to MEF, while replacing the capping agents was responsible for the tuning of MEF. The sensing protocol was applied to natural samples from real sample sources, and satisfactory results were obtained.

Electrochemical study of an enhanced platform by electrochemical synthesis of three-dimensional polyaniline nanofibers/reduced graphene oxide thin films for diverse applications

This work reports the electrochemical fabrication of thin films comprising polyaniline nanofibers (PANI) in conjunction with graphene oxide (GO) and reduced graphene oxide (rGO) on ITO substrate, along with examining the electrochemical properties, with a focus on the influence of the substrate and electrolyte in the electrodeposition methods. The study explores the electrochemical characteristics of these thin films and establishes a flexible framework for their application in diverse sectors such as sensors, supercapacitors, and electronic devices. It analyzes the impact of the substrate and electrolyte in electrodeposition techniques. The effects were studied using techniques such as cyclic voltammetry and chronoamperometry. The fabrication process of PANI/GO and PANI/rGO thin films involved the integration of rGO within PANI via electropolymerization, conducted under sulfuric acid. GO was synthesized by modifying the well-known Hummers' method and characterized by X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). SEM showed the diameters of the formed PANI were between 40 and 150 nm, which helped to intertwine the rGO nanosheets with PANI nanofibers to form thin films. The electrochemical behavior of the PANI/rGO thin films was examined using cyclic voltammetry (CV) and chronoamperometry in different electrolytes, including sulfuric acid (H₂SO₄) and potassium nitrate (KNO₃). The CV profiles exhibited distinct oxidation and reduction peaks, with variations in the voltammogram morphology attributed to the nature of the electrolyte and the substrate employed during the electrodeposition process. These results highlight the critical role of both the substrate and electrolyte in governing the electrochemical performance of PANI/rGO thin films. The findings from this study demonstrate a versatile approach for the fabrication of PANI/graphene-based thin films with tunable electrochemical properties, and such a strategy has great application to fabricating other thin film composites for supercapacitors or other control source frameworks requiring enhanced charge storage and electrochemical responsiveness.

Functionalized cyanostilbene-based nano-AIEgens: multipoint binding interactions for improved sensing of gallic acid in real-life food samples

Cyano-substituted stilbene (CSS) derivatives have been synthesized that can form luminescent nanoscopic assemblies in an aqueous medium. The optical properties of such materials, as governed by the relative ratios of their monomer and aggregated forms, are found to be susceptible to pH and temperature of the medium. The compound with boronic acid attached at the terminal positions shows a turn-on fluorescence response (LOD: 15.4 ppb) with gallic acid (GA). The mechanistic studies indicate that the 1,2-diol unit of GA is involved in ester formation with the boronic acid residue, while the carboxylic end engages in hydrogen bonding interaction with the nitrile unit. Such multi-point binding interaction provides better selectivity over other structurally similar analytes. Moreover, the distinct aggregation properties of such boronate ester derivatives are responsible for the GA-specific optical response. The sensory system has been utilized for the determination of the levels of GA derivatives in tea (green tea and black tea) and various fruit (mango, orange, guava, pomegranate) extracts. In all cases, the estimated values of GAE were found to be in the same range reported by others. Finally, low-cost, chemically-modified paper strips have been designed for rapid, on-location detection of GA.

Unveiling the Latest Developments in Molecularly Imprinted Photocatalysts: A State-of-the-Art Review

Responding to the growing concerns about environmental pollutants, scientists are increasingly turning to innovative solutions rooted in the field of environmental science. One such promising avenue combines the robustness of traditional photocatalysis with the precision of molecular imprinting, leading to the proposition of molecularly imprinted photocatalysts (MIPCs). These MIPCs hold the potential to specifically target and eliminate environmental pollutants, marking them as a promising tool in modern environmental remediation. As researchers delve deeper into this field, the design and optimization of MIPCs have become hotbeds for scientific inquiry. This comprehensive overview delves into the multifaceted approaches to MIPC design, elucidating on aspects like the selection of appropriate photocatalytic bases, the pivotal role of templates, the choice of monomeric building blocks, and the integration of effective cross-linking agents. However, as with all burgeoning technologies, the development of MIPCs is not without its challenges. These potential impediments to the successful innovation and implementation of MIPCs are also explored.

A novel electrochemical sensor based on an Fe–N–C/AuNP nanohybrid for rapid and sensitive gallic acid detection

An Fe–N–C/AuNP nanohybrid was combined with a glassy carbon electrode to construct a novel electrochemical sensor for rapid detection of gallic acid (GA). The sensor exhibited excellent performance to detect GA with a wide linear response range and low detection limit.

A non-enzymatic photoelectrochemical sensor based on g-C3N4@CNT heterojunction for sensitive detection of antioxidant gallic acid in food

Gallic acid (GA) is found in a wide range of natural plants and is relevant to the health of human beings. Here, a photoelectrochemical sensing platform based on g-C₃N₄@CNT heterojunction has been prepared for the highly sensitive and selective detection of GA. Under the light of xenon lamp, the photocurrent of g-C₃N₄@CNT is 7 times higher than that of g-C₃N₄. And the sensor generates 4 times more photocurrent in the presence of GA than without GA. This sensor has a wide linear range from 10 nM to 10 μM with a limit of detection as low as 2 nM. Also, the abundant amino groups of g-C₃N₄ provide excellent selectivity for the sensor. Furthermore, the sensor can be used for the analysis of GA in black tea samples, which provides a novel and rapid method for the detection of GA in food samples.

Facile one pot microbe-mediatedin situsynthesis and antibacterial activity of reduced graphene oxide-silver nanocomposite

The present research deals with the development of a novel bioinspiredin situfabrication of reduced graphene oxide (rGO)-silver nanoparticle (AgNPs) nanocomposite (rGO@AgNCs) using microbes namelyPseudomonas aeruginosa(PA) andStaphylococcus aureus(SA). The fabricated rGO@AgNCs were characterized using Ultraviolet-visible (UV-Vis) spectroscopy, Fourier-transform infrared spectroscopy (FTIR), particle size analysis, polydispersity index (PDI), zeta potential analysis, energy dispersive x-ray analysis (EDAX), Raman spectroscopy, powder x-ray diffraction (PXRD), high-resolution transmission electron microscopy (HR-TEM) analysis, etc. Furthermore, the rGO@AgNCs-PA and rGO@AgNCs-SA interaction with serum protein, pH stability study, andin vitrodissolution of AgNPs were also performed. The research findings of the proposed study demonstrated the simultaneous reduction of graphene oxide (GO) and AgNPs and the formation of rGO@AgNCs in the presence of microbes. Thein vitrodissolution studies of rGO@AgNCs composites showed better AgNPs dissolution with controlled release and offered remarkable matrix integrity throughout the dissolution period. The size and stability of rGO@AgNCs-PA and rGO@AgNCs-SA had no significant changes at physiological pH 7.4. A minimal decrease in the zeta potential of rGO@AgNCs was observed, which may be due to the weak interaction of nanocomposites and albumin. The antibacterial application of the synthesized nanocomposite was evaluated against a pathogenic mastitis-forming bacterium. The obtained results suggested an admirable antibacterial activity of synthesized nanocomposites against the tested microbes. This knowledge will assist the scientific fraternity in designing novel antibacterial agents with enhanced antibacterial activity against various veterinary pathogens in near future.

Electrochemical sensor for the non-enzymatic reduction of hydrogen peroxide and oxidation of gallic acid using a polyamidoblack-10B (PAB)-modified electrode

A novel electrochemical sensor for the oxidation of gallic acid and reduction of hydrogen peroxide using a paraffin impregnated graphite electrode modified with polyamidoblack 10B is developed.

A photoelectrochemical sensor for glutathione based on Bi2S3-modified TiO2 nanotube arrays

A novel photoelectrochemical sensor for the determination of glutathione based on Bi2S3-modified TiO2 nanotube arrays. Under the excitation of visible light, glutathione can be oxidized by the holes created by the Bi2S3/TiO2 NTAs.

Novel detection method for gallic acid: A water soluble boronic acid-based fluorescent sensor with double recognition sites

As one of the widespread phenols in nature, gallic acid (GA) has attracted a subject of attention due to its extensive biological properties. It is very important and significant to develop a sensitive and selective gallic acid sensor. In recent years, owing to their reversible covalent binding with Lewis bases and polyols, boronic acid compounds have been widely reported as fluorescence sensors for the identification of carbohydrates, ions and hydrogen peroxide, etc. However, boronic acid sensors for specific recognition of gallic acid have not been reported. Herein, a novel water-soluble boronic acid sensor with double recognition sites is reported. When the concentration of gallic acid added was 1.1 × 10^-4 M, the fluorescence intensity of sensor 9b decreased by 80%, followed by pyrogallic acid and dopamine. However, the fluorescence of the sensor 9b combined with other analytes such as ATP, sialic acid, and uridine was basically unchanged, indicating that the sensor 9b had no ability to recognize these analytes. Also, sensor 9b has a fast response time to gallic acid at room temperature, and has a high binding constant (12355.9 ± 156.89 M^-1) and low LOD (7.30 × 10^-7 M). Moreover, gallic acid content of real samples was also determined, and the results showed that this method has a higher recovery rate. Therefore, sensor 9b can be used as a potential tool for detecting biologically significant gallic acid in actual samples such as food, medicine, and environmental analysis samples.

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.

Enhanced Photoelectrochemical Water-Splitting Property on TiO2 Nanotubes by Surface Chemical Modification and Wettability Control

We report a simple method to control the photoelectrochemical (PEC) water-splitting performance of TiO₂ nanotube arrays (NTs) by surface chemical modification. Four types of modifier molecules with different surface energy and functional groups, including amine (-NH₂), n-alkane (-C_nH_2n+1), perfluoroalkyl (-F), and polymer molecule (-polymer), were self-assembled to the surface of TiO₂ NTs, which could change the surface chemical composition and wettability from superhydrophilicity to hydrophobicity. Interestingly, different from expected results, photoelectrochemical measurement results show that the n-octadecyltrichlorosilane-modified TiO₂ nanotube arrays with a contact angle of about 134° present the highest PEC property with doubled photocurrent density and more negative onset potential. And the total PEC performance order of the monolayers-modified TiO₂ NTs is (-C_nH_2n+1) > (-F) > (-NH₂) > (-OH, pristine TiO₂) > (-polymer), which is due to the molecular monolayers modification being able to suppress the recombination of photogenerated electrons and holes and facilitate water oxidation by regulating the interface electric double layer, whereas a thick polymer layer on the photoelectrode surface would affect the light absorbance and decrease the PEC performance. Further investigation indicates that the surface energy and wettability of the TiO₂ photoelectrode adjusted by surface modification also have an important influence on the interface reaction of water oxidation and the adsorption/desorption of newly formed oxygen, which also provides a new method for controlling the surface photocatalytic reactions.

New Perspectives on the Efficacy of Gallic Acid in Cosmetics & Nanocosmeceuticals

BACKGROUND

Gallic acid (GA-3,4,5-trihydroxybenzoic acid), a phenolic phytochemical, is a ubiquitous secondary metabolite found in most plants, with appreciable concentrations in grapes seed, rose flowers, sumac, oak and witch hazel. GA often results from the hydrolysis of terpenes and the polyphenol tannic acid.

APPLICATIONS

It exhibits powerful antioxidant, anti-inflammatory, antimicrobial, and anti-cancer activities. Most intriguing benefit has been reported to be on the skin. Due to these beneficial properties, GA and its derivatives (e.g. lipid-soluble phenols such as synthetic gallic esters aka gallates) have been extensively used as an adjuvant in a number of therapeutic formulations, as a substitute of hydrocortisone in children with atopic dermatitis (AD) and other skin conditions (hyperpigmentation, wound healing), and as a cosmetic ingredient. GA has a USFDA GRAS status (generally recognized as safe), exhibiting fairly low systemic toxicity and associated mortality at acute doses in many experimental models. Despite anti-skin aging benefits obtained with relatively safe GA formulations, few cases of gallate-induced skin allergic have been reported in humans. Therefore, approaches to improve the bioavailability and biodegradability of this poor-water soluble and non-biodegradable phenolic compound are warranted.

PURPOSE

This review has focused on the recently reported biological activities pertaining to the skin as well as the pharmacological properties of GA and its derivatives with special emphasis on its use in (nano-) cosmetic formulations. Since this is an evolving area of research, an adequate emphasis has been placed upon advantages and disadvantages of various nanoformulations.

Simple "signal-on" photoelectrochemical aptasensor for ultrasensitive detecting AFB1 based on electrochemically reduced graphene oxide/poly(5-formylindole)/Au nanocomposites

A simple "signal-on" photoelectrochemical (PEC) aptasensor is constructed for Aflatoxin B1 (AFB1) detection based on electrochemically reduced graphene oxide/poly(5-formylindole)/Au (erGO/P5FIn/Au) nanocomposites. The nanocomposites are synthesized by simple electrochemical deposition method and show good photoelectrochemical performance. Poly(5-formylindole) (P5FIn) can generate electron-hole pairs under light irradiation, leading to the formation of robust cathode photocurrent. Au can be acted as signal amplifier due to the high conductivity. The erGO is used to immobilize AFB1 aptamer chain by π-π stacking interaction between the carbon six-membered ring in graphene and the C-N heterocyclic ring in nucleobases of ssDNA. After the insulating AFB1 aptamer chain is fixed to the electrode, the signal of PEC sensor is "OFF". In the process of AFB1 detection, the aptamer chain detaches from the surface of erGO, which results in "ON" of the sensor signal. Based on this design, this constructed PEC aptasensor shows a high sensitivity for AFB1 with a wide linear detection range (LDR) from 0.01 ng mL^-1 to 100 ng mL^-1. The limit of detection (LOD) is 0.002 ng mL^-1. This PEC sensor also exhibits good stability, selectivity, specificity, and satisfactory practical sample analysis ability. This work may provide a new promising PEC platform for AFB1 detection as well as some other small molecules analysis.

A laser-induced TiO2-decorated graphene photoelectrode for sensitive photoelectrochemical biosensing

Direct-laser-writing of TiO₂-decorated graphene on indium-tin oxide glass was demonstrated to fabricate a unique photoelectrode for sensitive photoelectrochemical biosensing.

Synthesis and Applications of Molecularly Imprinted Polymers Modified TiO₂ Nanomaterials: A Review

Titanium dioxide (TiO₂) nanomaterials have caused a widespread concern in the past several decades for their bulk characteristics and potential applications in many different areas. Lately, the combination between molecularly imprinted polymers (MIPs) and TiO₂ nanomaterials have been proven to improve the relative adsorption capacity, selectivity and accelerate the rate of mass transfer of analyte which is not possible using TiO₂ alone. Considering the unique performance of the MIPs modified TiO₂ nanomaterials, this review intends to give an overview of the recent progresses in the development of MIPs modified TiO₂ nanomaterials, the potential applications of their tailor-made characteristics. The limitations and challenges in this practically promising nanomaterials have also been raised and summarized. By means of the points raised in this article, we would like to provide some assistance for further development of preparation methodologies and the expansion of some potential applications in the field of MIPs modified TiO₂ nanomaterials.

Photoelectrochemical device based on Mo-doped BiVO4 enables smart analysis of the global antioxidant capacity in food

For a healthy diet, which is an extension of a high quality lifestyle, tremendous attention has been focused on using antioxidant capacity indicators for food inspections and health guides. Although photoelectrochemical transducers have broadened our horizons for global antioxidant activity analysis, a growing body of foods and beverages needs to be quantified in the visible region and the necessary photoelectrochemical instrumentalization is still in its infancy. Generally, BiVO4 is considered as an ideal starting material for antioxidant surveillance under visible light irradiation. However, it is subjected to unsatisfied charge collection and utilization in practical applications. Herein, we studied the effects of successive molybdenum substitution of vanadium on the photocatalytic behavior of BiMo x V(1-x)O4 under visible light illumination. A superior photocurrent density was obtained for BiMo0.015V0.985O4 due to the flower-like architecture and favorable crystalline form. At the same time, this superhybrid BiMo0.015V0.985O4 composite successfully acted as a sensing unit in a photoelectrochemical platform for antioxidant capacity evaluation in foodstuffs. The related mechanism was further unearthed and discussed in-depth. Such a straightforward yet cogent principle was also applied to our integrated device for the "smart" analysis of the global antioxidant capacity, whereby collected data can be treated as a nutritive value index for routine quality control in the food industry. On the basis of this achievement, it is anticipated that mobile app-based quantitative antioxidant capacity detection will soon be realized.

Carbon-Coated Mesoporous TiO2 Nanocrystals Grown on Graphene for Lithium-Ion Batteries

Graphene-based hybrids have been well studied as advanced catalysts and high-performance electrode materials. In this Article, we have fabricated a novel graphene@mesoporous TiO2 nanocrystals@carbon nanosheet by a simple one-step solvothermal method. We have found that titanocene dichloride can act as an extraordinary source with multiple roles for forming TiO2 nanocrystals, ultrathin carbon outer shells, and cross-linkers to binding TiO2 nanocrystals on graphene surface. Moreover, it also serves as a controlling agent to produce mesoporous structure on TiO2 nanocrystals. The loading-concentration of mesoporous TiO2 nanocrystals on graphene sheets can be well controlled by adjusting the initial content of titanocene dichloride. The as-obtained graphene@mTiO2@carbon nanosheets possess a uniform sandwich-like structure, highly crystalline mesoporous TiO2 nanocrystals, a high surface area of ∼209 m(2)/g, and a large pore volume of ∼0.68 cm(3) g(-1). When used as anodes for LIBs, the resultant nanosheets show a high reversible capacity (∼145 mAh/g), good rate capability, and long cycling life (capacity remains 110 mAh/g after 100 cycles at a current density of 0.2 A/g). We believe that our method represents a new path way to synthesize novel nanostructured graphene-based hybrids for future applications.

Biomolecule-free, selective detection of o-diphenol and its derivatives with WS2/TiO2-based photoelectrochemical platform

Herein, a novel photoelectrochemical platform with WS2/TiO2 composites as optoelectronic materials was designed for selective detection of o-diphenol and its derivatives without any biomolecule auxiliary. First, catechol was chosen as a model compound for the discrimination from resorcinol and hydroquinone; then several o-diphenol derivatives such as dopamine, caffeic acid, and catechin were also detected by employing this proposed photoelectrochemical sensor. Finally, the mechanism of such a selective detection has been elaborately explored. The excellent selectivity and high sensitivity should be attributed to two aspects: (i) chelate effect of adjacent double oxygen atoms in the o-diphenol with the Ti(IV) surface site to form a five/six-atom ring structure, which is considered as the key point for distinction and selective detection. (ii) This selected WS2/TiO2 composites with proper band level between WS2 and TiO2, which could make the photogenerated electron and hole easily separated and results in great improvement of sensitivity. By employing such a photoelectrochemical platform, practical samples including commercial clinic drugs and human urine samples have been successfully performed for dopamine detection. This biomolecule-free WS2/TiO2 based photoelectrochemical platform demonstrates excellent stability, reproducibility, remarkably convenient, and cost-effective advantages, as well as low detection limit (e.g., 0.32 μmol L(-1) for dopamine). It holds great promise to be applied for detection of o-diphenol kind species in environment and food fields.

An efficient optical-electrochemical dual probe for highly sensitive recognition of dopamine based on terbium complex functionalized reduced graphene oxide

A novel organic-inorganic hybrid sensor based on diethylenetriaminepentaacetic acid (DTPA) modified reduced graphene oxide (RGO-DTPA) chelated with terbium ions allows detection of dopamine (DA) through an emission enhancement effect. Its luminescence, peaking at 545 nm, has been improved by a factor of 25 in the presence of DA (detection limit = 80 nM). In addition, this covalently bonded terbium complex functionalized reduced graphene oxide (RGO-DTPA-Tb) can be successfully assembled on a glassy carbon electrode. The assay performed through differential pulse voltammetry (DPV) yielded obvious peak separation between DA and excessive amounts of the interfering ascorbic acid (AA).

In situ generated AgBr-enhanced ZnO nanorod-based photoelectrochemical aptasensing via layer-by-layer assembly

A robust aptasensor for Ag(+) was proposed for the first time using an enhanced ZnO nanorod-based photoelectrochemistry by in situ generated AgBr via layer-by-layer assembly. This work opens up new avenues for application of one-dimensional ZnO nanorod arrays in photoelectrochemical sensing. Additionally, the strategy of employing in situ generated narrow-bandgap semiconductors paves a new way for photoelectrochemical sensing.

Ultrathin g-C3N4/TiO2composites as photoelectrochemical elements for the real-time evaluation of global antioxidant capacity

Using utg-C₃N₄/TiO₂, a photoelectrochemical platform was designed for the sensing of global antioxidant capacity, which presented a rapid response, and anti-fouling and colour-interference-proof properties.