Fluorometric determination of dopamine by using molybdenum disulfide quantum dots

Differential pulse voltametric detection of dopamine using polyaniline-functionalized graphene oxide/silica nanocomposite for point-of-care diagnostics

In this study, a novel composite material, GO/SiO2@PANI, was synthesized and employed as an electrochemical sensor for the detection of dopamine in urine using differential pulse voltammetry (DPV). This work introduced a first-time combination of graphene oxide (GO) with silicon dioxide (SiO2) and the conducting polymer polyaniline (PANI) to improve dopamine detection. The composite material was synthesized using an in situ polymerization process, ensuring uniform integration of GO/SiO2 with PANI. The GO/SiO2@PANI-modified glassy carbon electrode (GCE) demonstrated a notable electrocatalytic activity for dopamine detection using DPV and CV. The performance of the sensor was evaluated across a range of dopamine concentrations, showing a linear detection range between 2 and 12 μM with a detection limit of 1.7 μM and relative standard deviation of 2.5%. The material's performance was attributed to the combined effects of graphene's surface area, PANI's conducting properties, and the structural integrity provided by SiO2 nanoparticles (NPs). Additionally, the sensor's robustness and high selectivity were confirmed through tests with synthetic urine samples, where dopamine concentrations were detected with high accuracy. This work provides a promising avenue for the development of low-cost and efficient dopamine sensors for clinical applications.

Developing multifunctional cellulose derivatives for environmental and biomedical applications: Insights into modification processes and advanced material properties

The growing bioeconomic demand for lightweight, eco-friendly materials with functional versatility and competitive mechanical properties drives the resurgence of cellulose as a sustainable scaffold for various applications. This review comprehensively scrutinizes current progressions in cellulose functional materials (CFMs), concentrating on their structure-property connections. Significant modification methods, including cross-linking, grafting, and oxidation, are discussed together with preparation techniques categorized by cellulose sources. This review article highlights the extensive usage of modified cellulose in various industries, particularly its potential in optical and toughening applications, membrane production, and intelligent bio-based systems. Prominence is located on low-cost procedures for developing biodegradable polymers and the physical-chemical characteristics essential for biomedical applications. Furthermore, the review explores the role of cellulose derivatives in smart packaging films for food quality monitoring and deep probes into cellulose's mechanical, thermal, and structural characteristics. The multifunctional features of cellulose derivatives highlight their worth in evolving environmental and biomedical engineering applications.

MoS2 quantum dots-based optical sensing platform for the analysis of synthetic colorants. Application to quinoline yellow determination

In this work, a novel fluorescence sensor has been designed to solve the actual need of new fast and inexpensive sensing platforms for the analysis of synthetic colorants. It is based on MoS2 quantum dots obtained by a hydrothermal method and incorporated as fluorophore into the matrix of PVC membranes, which are deposited on quartz substrates by spin-coating. It was proven, as in these conditions, MoS2 quantum dots maintain the fluorescent properties that they present in solution. Experiments carried out in solution displayed a maximum emission when they were excited under 310 nm. This initial fluorescence decreases linearly in presence of increasing concentrations of various synthetic colorants namely quinoline yellow, tartrazine, sunset yellow, allura red, ponceau 4R and carmoisine. The two possible mechanisms that can explain this quenching effect, colorants absorbing photons emitted by quantum dots and/or competing with the nanomaterial for photons coming from the excitation source, were evaluated. The most pronounced effect was observed with quinoline yellow, as a result of a mixed mechanism. The optimized methodology developed for the determination of quinoline yellow showed a linear concentration range between 5.4 and 55.0 µg with a limit of detection of 1.6 µg. The sensor was applied to the determination of quinoline yellow in a food colour paste obtaining results in good agreement with those obtained by HPLC-UV-vis measurements.

Rapid and ratiometric fluorescent detection of hypochlorite by glutathione functionalized molybdenum disulfide quantum dots

We proposed a rapid and ratiometric fluorescent detection method for hypochlorite by glutathione functionalized molybdenum disulfide quantum dots (G-MoS₂ QDs). The G-MoS₂ QDs were obtained through a hydrothermal method and the maximum fluorescence intensity was obtained at 430 nm under excitation of 360 nm. The fluorescence of G-MoS₂ QDs at 430 nm can be weakened by curcumin through the inner filter effect, meanwhile the fluorescence of curcumin at 540 nm appeared. Hypochlorite can fast oxidize curcumin and weaken the inner filter effect, thus the fluorescence of curcumin at 540 nm decreased and the fluorescence of G-MoS₂ QDs at 430 nm increased. This process takes only 30 s at room temperature. This is the rationale behind our rapid ratiometric fluorescent detection model for hypochlorite. Two linear detection ranges for hypochlorite are obtained with concentration from 1 to 20 μM and 20 to 30 μM, the limit of detection (LOD) was 11.5 nM. The standard spike recovery tests on milk and tap water samples showed satisfactory results, which extended the application of G-MoS₂ QDs in the field of ratiometric fluorescence detection assays.

Ultrasensitive and Simple Dopamine Electrochemical Sensor Based on the Synergistic Effect of Cu-TCPP Frameworks and Graphene Nanosheets

Dopamine (DA) is an important neurotransmitter. Abnormal concentration of DA can result in many neurological diseases. Developing reliable determination methods for DA is of great significance for the diagnosis and monitoring of neurological diseases. Here, a novel and simple electrochemical sensing platform for quantitative analysis of DA was constructed based on the Cu-TCPP/graphene composite (TCPP: Tetrakis(4-carboxyphenyl)porphyrin). Cu-TCPP frameworks were selected in consideration of their good electrochemical sensing potential. The graphene nanosheets with excellent conductivity were then added to further improve the sensing efficiency and stability of Cu-TCPP frameworks. The electrochemical properties of the Cu-TCPP/graphene composite were characterized, showing its large electrode active area, fast electron transfer, and good sensing performance toward DA. The signal enhancement mechanism of DA was explored. Strong accumulation ability and high electrocatalytic rate were observed on the surface of Cu-TCPP/graphene-modified glassy carbon electrode (Cu-TCPP/graphene/GCE). Based on the synergistic sensitization effect, an ultrasensitive and simple DA electrochemical sensor was developed. The linear range is 0.02–100 and 100–1000 µM, and the detection limit is 3.6 nM for the first linear range. It was also successfully used in detecting DA in serum samples, and a satisfactory recovery was obtained.

A Review on the Modification of Cellulose and Its Applications

The latest advancements in cellulose and its derivatives are the subject of this study. We summarize the characteristics, modifications, applications, and properties of cellulose. Here, we discuss new breakthroughs in modified cellulose that allow for enhanced control. In addition to standard approaches, improvements in different techniques employed for cellulose and its derivatives are the subject of this review. The various strategies for synthetic polymers are also discussed. The recent advancements in polymer production allow for more precise control, and make it possible to make functional celluloses with better physical qualities. For sustainability and environmental preservation, the development of cellulose green processing is the most abundant renewable substance in nature. The discovery of cellulose disintegration opens up new possibilities for sustainable techniques. Based on the review of recent scientific literature, we believe that additional chemical units of cellulose solubility should be used. This evaluation will evaluate the sustainability of biomass and processing the greenness for the long term. It appears not only crucial to dissolution, but also to the greenness of any process.

Microenvironment-tailored nanoassemblies for the diagnosis and therapy of neurodegenerative diseases

Neurodegenerative disorder is an illness involving neural dysfunction/death attributed to complex pathological processes, which eventually lead to the mortality of the host. It is generally recognized through features such as mitochondrial dysfunction, protein aggregation, oxidative stress, metal ions dyshomeostasis, membrane potential change, neuroinflammation and neurotransmitter impairment. The aforementioned neuronal dysregulations result in the formation of a complex neurodegenerative microenvironment (NME), and may interact with each other, hindering the performance of therapeutics for neurodegenerative disease (ND). Recently, smart nanoassemblies prepared from functional nanoparticles, which possess the ability to interfere with different NME factors, have shown great promise to enhance the diagnostic and therapeutic efficacy of NDs. Herein, this review highlights the recent advances of stimuli-responsive nanoassemblies that can effectively combat the NME for the management of ND. The first section outlined the NME properties and their interrelations that are exploitable for nanoscale targeting. The discussion is then extended to the controlled assembly of functional nanoparticles for the construction of stimuli-responsive nanoassemblies. Further, the applications of stimuli-responsive nanoassemblies for the enhanced diagnosis and therapy of ND are introduced. Finally, perspectives on the future development of NME-tailored nanomedicines are given.

Selective dopamine detection by SPR sensor signal amplification using gold nanoparticles

In this study, selective and sensitive detection of neurotransmitter dopamine from both aqueous solution and biological samples was performed by surface plasmon resonance sensor based on molecular imprinting technique.

MoS2 quantum dots for on-line fluorescence determination of the food additive allura red

This work presents an on-line fluorescence method for the allura red (AR) determination. The method is based on the fluorescence quenching of dots of MoS₂ because of their interaction with the non-fluorescence dye. MoS₂-dots were synthetized and characterized by spectroscopic techniques and High Resolution Transmission Electronic Microscopy (HR-TEM). The simultaneous injection of the nanomaterial and the dye in a flow injection analysis system allows the determination of allura red at 1.7 × 10^-6 M concentration level with a very good accuracy and precision (Er minor than 10% and RSD lower than 8%) and a sampling frequency of 180 samples per hour. Moreover, the interaction fluorophore-quencher results a dynamic inhibition mechanism. The proposed methodology was applied to the AR analysis in soft beverages and powders for gelatine preparation. Colourant concentrations of 63 ± 2 mg/L (n = 3) and 0.30 ± 0.01 mg/g (n = 3) were found, respectively. These results were validated by high performance liquid chromatography technique.

3-Aminobenzeneboronic Acid Functionalized MoS2 Quantum Dot as Fluorescent Nanoprobe for the Determination of o-Dihydroxybenzene

In this work, by functionalizing MoS₂ quantum dot with 3-aminobenzeneboronic acid, a novel multifunctional quantum dot (denoted as B-MoS₂ QD) was obtained and used successfully for a fluorescence nanoprobe for detecting o-dihydroxybenzene (o-DHB). Transmission electron microscopy, fluorescence spectrum, UV-vis spectrum and fluorescence lifetime were used to investigate the prepared nanoprobe. The results show that the B-MoS₂ QD nanoprobe can exhibit strong fluorescence and excellent light fastness owing to the coupled effect from the MoS₂ QDs and boronic acid; interestingly, the vicinal diols structure from its surface can bridge covalently with o-DHB, resulting in the fluorescence quenching of B-MoS₂ QDs and selective recognition toward o-DHB. With the increasing of o-DHB concentration, the nanoprobe fluorescence would gradually decrease. By measuring the fluorescence intensity of B-MoS₂ QDs, a wide linear range from 0.1 to 200.0 μM with a low detection limit of 0.025 μM was obtained for o-DHB analysis; meanwhile, this fluorescence nanoprobe possesses excellent selectivity for the selective detection of o-DHB from its analogues.

Fluorometric detection of dopamine based on 3-aminophenylboronic acid-functionalized AgInZnS QDs and cells imaging

Herein, cysteine capped AgInZnS QDs (Cys-AIZS QDs) with a large stoke shift and excellent biocompatibility were synthesized by a one-step aqueous method, followed by modified with 3-aminophenylboronic acid (APBA). Dopamine (DA) as an important neurotransmitter in brain can lead to significantly decrease in the fluorescence intensity of 3-aminophenylboronic acid-functionalized Cys-AIZS QDs (APBA-AIZS QDs) in a large concentration range of 1.5-900 μM. Good linearity can be obtained in the range of 15-120 μM, with a limit of detection (LOD) of 0.65 μM. Moreover, Cys-AIZS QDs and APBA-AIZS QDs were applied to living cells imaging, and Cys-AIZS QDs were applied to the co-localization with lysosomes, indicative of the feasibility of intracellular detection.

UV-emitting polyelectrolyte-modified MoS2 quantum dots for selective determination of nitrophenol in water samples based on inner filter effect

In this work, poly(sodium 4-styrenesulfonate) (PSS) modified molybdenum disulfide quantum dots (MoS2-PSS QDs) were synthesized via a simple hydrothermal method using l-cysteine and anhydrous sodium molybdate as precursors and PSS as a modification reagent, and a selective and sensitive fluorescent sensing method for the determination of p-nitrophenol (p-NP) based on their UV emission was developed. The obtained MoS2-PSS QDs have an obvious UV emission peak (390 nm) with quantum yield of 5.13%. The strong absorption peak of p-NP at 400 nm has large spectral overlap with the UV emission peak (390 nm) of MoS2-PSS QDs. Because of this p-NP absorption, the fluorescence of MoS2-PSS QDs at 390 nm is quenched with the introduction of p-NP via the inner filter effect (IFE) and the decreased fluorescence intensity was linearly proportional to the p-NP concentration in the range of 1–20 μmol/L, leading to a detection limit of 0.13 μmol/L for p-NP. The MoS2 QDs-based fluorescent probe for p-NP is sensitive and selective and was successfully applied in the determination of p-NP in the pond water samples with satisfactory results.

Simple hydrothermal approach for synthesis of fluorescent molybdenum disulfide quantum dots: Sensing of Cr3+ ion and cellular imaging

Nowadays, fluorescent molybdenum disulfide quantum dots (MoS₂ QDs) have proven to be potential candidates in the sensing and bioimaging areas owing to their exceptional intrinsic characteristics. Here, a simple hydrothermal strategy was explored for the preparation of MoS₂ QDs using ammonium heptamolybdate and 6-mercaptopurine (6-MP) as precursors. The emission peak of MoS₂ QDs was significantly quenched in the presence Cr³⁺ ion due to the selective surface chemistry on the surfaces of MoS₂ QDs. The designed fluorescent MoS₂ QDs showed a linear fluorescence quenching response with increasing concentration of Cr³⁺ ion (0.1-10 μM), allowing to detect Cr³⁺ ion even at 0.08 μM. This fluorescent MoS₂ QDs were utilized for the quantification of Cr³⁺ ion in real samples (water and biological samples). Interestingly, the synthesized MoS₂ QDs exhibited negligible cytotoxicity on NRK cells and acted as good candidates for imaging of Trichoderma viride fungal cells.

Bi-functional Ag-CuxO/g-C3N4 hybrid catalysts for the reduction of 4-nitrophenol and the electrochemical detection of dopamine

The immense need to build highly efficient catalysts has always been at the forefront of environmental remediation research. Herein, we have synthesized dual-phase copper oxide containing Cu2O and CuO originating from the same reaction using hexamethyltetramine (HMT). Simultaneously, we coupled it with g-C3N4 (g-CN), constructing a triple synergetic heterojunction, which is reported significantly less often in the literature. Hydrothermal reactions led to the formation of various catalysts, namely, Ag-Cu2O-CuO-gCN (ACCG), Ag-CuO-gCN (ACG), Ag-Cu2O-CuO (ACC) and Ag-CuO (AC), which were thoroughly characterized via XRD and FESEM to gain structural, crystallographic and morphological insights. We clearly observed the pure phase formation of the catalysts and the development of sheet-like CuO and truncated octahedrons of Cu2O fused together within the g-CN framework. Also, XPS studies revealed the presence of copper in two different oxidation states, namely, Cu2+ and Cu+. BET analysis was performed to analyze the surface area and pore volume of the catalysts, which play very significant roles in catalytic reduction. The catalytic efficiencies of the catalysts were evaluated via the reduction of 100 ppm 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) without using any light irradiation. The most efficient catalyst was ACCG, revealing the reduction of 4-NP in 4 minutes. Both Cu2O and g-CN played significant roles in reduction, following zero-order kinetics, unlike that which is often reported in the literature. We also evaluated the catalytic reduction with different concentrations of 4-NP and tuning the catalyst amount as well. A mechanism was postulated based on the XRD results of the post-catalytic reduction catalyst. The ACCG catalyst was also successfully tested as an effective dopamine sensor. The GC/ACCG electrode exhibited oxidation peak current density of 0.28 mA cm-2, which was much higher than those of the other catalysts. This unique combination of pure phase materials to form a composite as an effective catalyst as well as a sensor is an exclusive effort towards environmental remediation.

The design and growth of peanut-like CuS/BiVO4 composites for photoelectrochemical sensing

In this study, the CuS/BiVO₄-X (where X represents the mass percentage of CuS associated with CuS/BiVO₄; X = 2%, 5% and 7%) p–n heterostructures were fabricated using a two-step hydrothermal method.

Fluorescence enhancement of fungicide thiabendazole by van der Waals interaction with transition metal dichalcogenide nanosheets for highly specific sensors

Many molecules quench their fluorescence upon adsorption on surfaces. Herein we show that the interaction of thiabendazole, a widespread used fungicide of the benzimidazole family, with nanosheets of transition metal dichalcogenides, particularly of WS2, leads to a significant increase, more than a factor of 5, of the fluorescence yield. This surprising effect is rationalized by DFT calculations and found to be related to the inhibition of the intramolecular rotation between the benzimidazole and thiazole groups due to a bonding rigidization upon interaction with the MoS2 surface. This non-covalent adsorption leads to a redistribution of the molecular LUMO that blocks the non-radiative energy dissipation channel. This unusual behaviour does not operate either for other molecules of the same benzimidazole family or for other 2D materials (graphene or graphene oxide). Moreover, we found that a linear dependence of the emission with the concentration of thiabendazole in solution, which combined with the specificity of the process, allows the development of a highly sensitive and selective method towards thiabendazole determination that can be applied to real river water samples. An excellent detection limit of 2.7 nM, comparable to the best performing reported methods, is obtained with very good accuracy (Er ≤ 6.1%) and reproducibility (RSD ≤ 4.1%) in the concentration range assayed.

Cysteamine-capped gold-copper nanoclusters for fluorometric determination and imaging of chromium(VI) and dopamine

Highly emissive cysteamine-capped gold-copper bimetallic nanoclusters (CA-AuCu NCs) with a quantum yield of 18% were synthesized via one-pot anti-galvanic reduction. The CA-AuCu NCs were characterized by HR-TEM, XPS, FTIR, MALDI-TOF mass spectrometry, DLS, and zeta potential analyses. The NCs are shown to be viable fluorescent probes for Cr(VI) ions and dopamine (DA) via quenching of the blue fluorescence, typically measured at excitation/emission wavelengths of 350/436 nm. During DA recognition, a dark brown color appears, which is distinguishable from that of Cr(VI) detection. The aggregation induced quenching due to electron transfer was demonstrated by photoluminescence, HR-TEM, FTIR, DLS, and zeta potential interrogations. In buffer of pH 7, response is linear in the 0.2 ~ 100 μM for Cr(VI) and from 0.4 ~ 250 μM for DA. The respective detection limits are 80 and 135 nM. The method was applied to the determination of both Cr(VI) and DA in (spiked) tap, lake and sea water, and in human urine samples. The low toxicity of CA-AuCu NCs was validated by the MTT assay, and their responses to Cr(VI) ions and DA was also proven by Raw 264.7 cell imaging. Graphical abstractCysteamine capped Au-Cu nanoclusters (CA-AuCu NCs) were synthesized via one-pot anti-galvanic reduction and utilized in sensing of Cr(VI) ions and dopamine (DA) with demonstrated real/urine and cell imaging applications.

Boronic acid-functionalized molybdenum disulfide quantum dots for the ultrasensitive analysis of dopamine based on synergistic quenching effects from IFE and aggregation

Herein, a novel fluorescent material, boronic acid-functionalized molybdenum disulfide quantum dots (B-MoS₂ QDs) produced by an amidation reaction between 3-aminobenzeneboronic acid and previously prepared molybdenum disulfide quantum dots (MoS₂ QDs), was prepared to fabricate a rapid and sensitive platform for the quantitative analysis of dopamine. This material exhibits strong fluorescence, excellent salt tolerance and light fastness. In particular, the quantum yield of this material is about 21.1 times that of its fundamental material, MoS₂ QDs. Notably, owing to an interesting synergistic effect between the inner filter effect and the aggregation quenching effect, this material was successfully applied for the determination of dopamine in the linear range 0.25-35 μmol L^-1 with the detection limit of 0.087 μmol L^-1; moreover, B-MoS₂ QDs manifested better selectivity in the presence of multiple interferences due to their inert surface. As expected, this proposed material shows satisfactory performance in human serum; thus, the present study exploits a new avenue for the application of functionalized MoS₂ QDs in fluorescence sensing.

Biosensors for Epilepsy Management: State-of-Art and Future Aspects

Epilepsy is a serious neurological disorder which affects every aspect of patients’ life, including added socio-economic burden. Unfortunately, only a few suppressive medicines are available, and a complete cure for the disease has not been found yet. Excluding the effectiveness of available therapies, the timely detection and monitoring of epilepsy are of utmost priority for early remediation and prevention. Inability to detect underlying epileptic signatures at early stage causes serious damage to the central nervous system (CNS) and irreversible detrimental variations in the organ system. Therefore, development of a multi-task solving novel smart biosensing systems is urgently required. The present review highlights advancements in state-of-art biosensing technology investigated for epilepsy diseases diagnostics and progression monitoring or both together. State of art epilepsy biosensors are composed of nano-enabled smart sensing platform integrated with micro/electronics and display. These diagnostics systems provide bio-information needed to understand disease progression and therapy optimization timely. The associated challenges related to the development of an efficient epilepsy biosensor and vision considering future prospects are also discussed in this report. This review will serve as a guide platform to scholars for understanding and planning of future research aiming to develop a smart bio-sensing system to detect and monitor epilepsy for point-of-care (PoC) applications.

Water-soluble MoS2 quantum dots for facile and sensitive fluorescence sensing of alkaline phosphatase activity in serum and live cells based on the inner filter effect

We report a facile and sensitive method for the detection of alkaline phosphatase (ALP) activity in serum and live cells using molybdenum disulfide quantum dots (MoS₂ QDs) based on the Inner Filter Effect (IFE). In the present work, water soluble MoS₂ QDs with bright green fluorescence were synthesized through direct ultrasonic exfoliation of MoS₂ powder in 85 vol% aqueous ethanol solution. p-Nitrophenylphosphate (PNPP) was employed to act as an ALP substrate, and its enzyme catalytic product (p-nitrophenol (PNP)) functioned as a powerful absorber in the IFE to influence the excitation of MoS₂ QDs. PNPP was transformed into PNP in the presence of ALP, leading to the transition of the absorption peak from 310 nm to 405 nm and therefore resulted in a complementary overlap between the absorption of PNP and the excitation of MoS₂ QDs. The fluorescence of MoS₂ QDs was quenched due to the significant weakening of the excitation of MoS₂ QDs by competitive absorption between QDs and PNP. A good linear relationship was obtained from 0 to 5 U L^-1 (R² = 0.9919) using the present IFE based sensing strategy with the lowest detection activity of 0.1 U L^-1. The proposed sensing approach was successfully applied to ALP sensing in serum samples and ALP inhibitor investigation, as well as in ALP cell imaging.

A photoelectrochemical sensing strategy based on single-layer MoS2 modified electrode for methionine detection

MoS₂, a typical transition metal disulfide, is widely used in the photoelectrochemical (PEC) sensor construction. In general, MoS₂ based PEC sensor are "signal-on" strategies. Surprisingly, we discovered that the PEC response of MoS₂ was quenched by methionine greatly. Based on this discovery, a reduction PEC sensing strategy utilized MoS₂ modified electrode for methionine detection was fabricated for the first time. Experimental factors, such as, bias potential, volume of MoS₂ and pH were studied. Under optimized conditions, the decreased intensity of the photocurrent signal was proportional to the logarithmic value of methionine concentrations from 0.1 nM to 1 μM with the detection limit of 0.03 nM. Moreover, this method exhibited good performance of excellent selectivity. And it showed potential applications in the practical determination of methionine in real-life sample. This strategy not only expands the PEC detection method but also provides a simple, rapid response, good selectivity and high sensitivity way to detect methionine.

Simple construction of ratiometric fluorescent probe for the detection of dopamine and tyrosinase by the naked eye

A simple and effective method for constructing a ratiometric fluorescent probe for the detection of dopamine and tyrosinase was developed.