Sensitive detection of dopamine and quinone drugs based on the quenching of the fluorescence of carbon dots

Dual-mode fluorimetric and colorimetric sensors based on iron and nitrogen co-doped carbon dots for the detection of dopamine

Determination of dopamine (DA) is crucial for its intimate relationship with clinical trials and biological environment. Herein, Fe, N co-doped carbon dots (AFC-CDs) were fabricated by optimizing precursors and reaction conditions for fluorimetric/colorimetric dual-mode sensing of DA. With synergistic influence of Förster resonance energy transfer and static quenching effect, DA significantly quenched the blue luminescence of AFC-CDs at 442 nm, the production of recognizable tan-brown complex caused evident colorimetric response, achieved the dual-mode fluorimetric/colorimetric sensing for DA. The excellent selectivity and satisfied sensitivity can be confirmed with the limit of detection at 0.29 μM and 2.31 μM via fluorimetric/colorimetric mode respectively. The reliability and practicability were proved by recovery of 94.81-101.61% in real samples. Notably, the proposed electron transfer way between AFC-CDs and DA was hypothesized logically, indicated dual-mode probe provided a promising platform for the sensing of trace DA, and could be expanded in environment and food safety.

Hierarchical Scaffold with Directional Microchannels Promotes Cell Ingrowth for Bone Regeneration

Bone regenerative scaffolds with a bionic natural bone hierarchical porous structure provide a suitable microenvironment for cell migration and proliferation. Here, a bionic scaffold (DP-PLGA/HAp) with directional microchannels is prepared by combining 3D printing and directional freezing technology. The 3D printed framework provides structural support for new bone tissue growth, while the directional pore embedded in the scaffolds provides an express lane for cell migration and nutrition transport, facilitating cell growth and differentiation. The hierarchical porous scaffolds achieve rapid infiltration and adhesion of bone marrow mesenchymal stem cells (BMSCs) and improve the expression of osteogenesis-related genes. The rabbit cranial defect experiment presents significant new bone formation, demonstrating that DP-PLGA/HAp offers an effective means to guide cranial bone regeneration. The combination of 3D printing and directional freezing technology might be a promising strategy for developing bone regenerative biomaterials.

Tailoring Efficient Fluorogenic Tactic for Ultrasensitive Detection of Dopamine in Urine and Rat Brain through Real-Time and In Situ Formation of High-Performance Fluorophore

Owing to the predominance of dopamine (DA) in controlling mental health, planning an innovative method for DA detection with simplicity and high efficacy is conducive to the assessment of neurological disorders. Herein, an efficient fluorogenic tactic has been elaborated for ultrasensitive detection of DA with remarkably enhanced turn-on response. Utilizing a twisted intramolecular charge-transfer (TICT)-suppressing strategy, a highly emissive azocine derivative 11-hydroxy-2,3,6,7,11,12,13,14-octahydro-1H,5H,10H-11,14a-methanoazocino[5',4':4,5]furo[2,3-f]pyrido[3,2,1-ij]quinolin-10-one (J-Aza) is generated via a one-step reaction between DA and 8-hydroxyjulolidine. It is marvelous that J-Aza not only possesses ideal fluorescence quantum yield (ΦF) as high as 0.956 but also exhibits bathochromic shifted fluorescence (green emissive) and stronger anti-photobleaching capacity superior to traditional azocine-derived 1,2,3,4-tetrahydro-5H-4,11a-methanobenzofuro[2,3-d]azocin-5-one (Aza) with moderate ΦF, blue fluorescence, and poor photostability. By confining the TICT process, the detection limit to DA can be reduced to 80 pM, which is competitive in contrast to previously reported fluorescence methods. Encouraged by the instant response (within 90 s), wide linear range (0.1-500 nM), great selectivity, and excellent sensitivity, this fluorogenic method has been used for the real-time measurement of DA contents in practical urine samples with satisfactory results. Furthermore, the cerebral DA level in the reserpine-induced depression rat model has also been evaluated by our designed method, demonstrating its potent analytical applicability in the biosensing field.

Facilely Prepared Thirsty Granules Arouse Tough Wet Adhesion on Overmoist Wounds for Hemostasis and Tissue Repair

Bioadhesives have been widely used in hemostasis and tissue repair, but the overmoist and wet nature of wound surface (due to the presence of blood and/or wound exudate) has led to poor wet adhesion of bioadhesives, which interrupts the continuous care of wounds. Here, a thirsty polyphenolic silk granule (Tan@SF-pwd-hydro), which absorbs blood and exudate to self-convert to robust bioadhesives (Tan@SF-gel-hydro) in situ, was facilely developed in this study for enhanced wet adhesion toward hemostasis and tissue repair. Tan@SF-pwd-hydro could shield wounds' wetness and immediately convert itself to Tan@SF-gel-hydro to seal wounds for hemorrhage control and wound healing. The maximum adhesiveness of Tan@SF-gel-hydro over wet pigskin was as high as 59.8 ± 2.1 kPa. Tan@SF-pwd-hydro is a promising transformative dressing for hemostasis and tissue repair since its hemostatic time was approximately half of that of the commercial hemostatic product, CeloxTM, and its healing period was much shorter than that of the commercial bioadhesive product, TegadermTM. This pioneering study utilized adverse wetness over wounds to arouse robust adhesiveness by converting thirsty granules to bioadhesives in situ, creatively turning adversity into opportunities. The facile fabrication approach also offers new perspectives for manufacturing sustainability of biomaterials.

Carbonized human hair derived carbon dots for detection of clozapine

Clozapine (CLZ) is known as the most effective antipsychotic medication for schizophrenia. However, low dosage or over dosage of CLZ is adverse to the treatment of Schizophrenia. Thus, it is necessary to develop effective detection method for CLZ. Recently, due to the advantages such as excellent optical properties, good photobleachability and sensitivity, carbon dots (CDs)-based fluorescent sensors for the detection of target analytes have drawn a great deal of attention. In this work, blue fluorescent CDs (Named as B-CDs) with quantum yield (QY) as high as 38% were obtained by using carbonized human hair as source material through one-step dialysis method for the first time. B-CDs showed obvious graphite-like structure with an average of 1.76 nm, containing abundant functional groups such as -C=O, amino N and C-N on the surface of carbon cores. Optical analysis showed that the B-CDs exhibited excitation-dependent emission property with maximum emission wavelength of 450 nm. Moreover, B-CDs were further applied as a fluorescence sensor to the detection of CLZ. The B-CDs based sensor exhibited a good quenching response by CLZ through the inner filter effect and static quenching mechanism with a limit of detection of 67 ng/mL, which was much lower than the minimal effective concentration in blood (0.35 μg/mL). Finally, to test the practical application value of the developed fluorescence method, the determination of the content of CLZ in tablets and the concentration in blood was carried out. Compared with the results of high-performance liquid chromatography (HPLC) method, it can be found that the constructed fluorescence detection method showed high accuracy and had great application potential in the detection of CLZ. Additionally, the results of cytotoxicity experiment showed that B-CDs had low cytotoxicity, which laid the foundation for the subsequent application of B-CDs in biological systems.

A comprehensive review on multi-colored emissive carbon dots as fluorescent probes for the detection of pharmaceutical drugs in water

Exposure to constituent hazardous chemicals in medical products has become a threat to environmental health across the globe. Excessive medication and the mishandling of pharmaceutical drugs can lead to the increased presence of chemicals in the aquatic environment, causing water pollution. Only a few nanomaterials exist for the detection of these chemicals and they are limited in use due to their adverse toxicity, instability, cost, and low aqueous solubility. In contrast, carbon dots (C-dots), a member of the family of carbon-based nanomaterials, have various beneficial properties including excellent biocompatibility, strong photoluminescence, low photobleaching, tunable fluorescence, and easy surface modification. Herein, we summarize recent advancements in various synthetic strategies for high-quality tunable fluorescent C-dots. The root of fluorescence has been briefly explained via the quantum confinement effect, surface defects, and molecular fluorescence. The surface functional moieties of C-dots have been investigated in depth to recognize the various types of pharmaceutical drugs that are used for the treatment of patients. The modulation of C-dot fluorescence in the course of their interactions with these drugs has been carefully explained. Different types of interaction mechanisms behind the C-dot fluorescence alteration have been discussed. Finally, the challenges and future perspectives of C-dots have been proposed for the vibrant field development of C-dot-based drug sensors.

Dual-emission carbon dots for sensitive fluorescence detection of metal ions and ethanol in water

Carbon dots (CDs) have been widely used in biomedical fields because of their superior optical properties, high sensitivity and high selectivity to specific substances. However, there are few studies on trace detection of the ethanol content in aqueous solution using CDs. Herein, novel red fluorescent CDs with dual emission are synthesized and show good dispersibility in various solvents and excitation independence of photoluminescence (PL). After investigating the structure and properties of the red CDs, a multifunctional fluorescent nanoprobe based on the red CDs with high-sensitivity detection for dual-ion trace detection of Fe³⁺ and Cu²⁺ can be successfully constructed. The limit of detection of Fe³⁺ and Cu²⁺ can be up to 0.024 μM and 0.036 μM, respectively, which is superior to that in previous reports. Meanwhile, in view of the specific solvent effect on their PL, the red CDs are able to be applied for trace detection of the ethanol content in aqueous solution. The methods of colorimetry and fluorescence spectrometry are utilized to perform the threshold test and high-sensitivity quantitative analysis of the ethanol content in aqueous solution. Based on this, a multifunctional fluorescent nanoprobe based on the dual-emission red CDs can be obtained, which provides a promising way for their applications in detection and sensing fields.

Recent developments on carbon dots-based green analytical methods: New opportunities in fluorescence assay of pesticides, drugs and biomolecules

Fluorescent carbon dots (CDs) grabs huge attention in analytical and bioanalytical applications due to their high selectivity towards target analyte, specificity, photostability, and quantum yield. Cost-effective and biocompatible properties of...

Quantitatively Switchable pH-Sensitive Photoluminescence of Carbon Nanodots

pH sensing plays a key role in the life sciences as well as the environmental, industrial, and agricultural fields. Carbon nanodots (C-dots) with small size, low toxicity, and excellent stability hold great potential in pH sensing as nanoprobes due to their intrinsic pH-sensitive photoluminescence (PL). Nonetheless, the undesirable sensitivity and response range of C-dot PL toward pH cannot meet the requirements of practical applications, and the unclear pH-sensitive PL mechanism makes it difficult to control their pH sensitivity. Herein, the quantitative correlation of pH-sensitive PL with specific surface structures of C-dots is uncovered for the first time, to our best knowledge. The association of carboxylate and H⁺ increases the ratio of nonradiation to radiation decay of C-dots through excited-state proton transfer, resulting in the decrease of PL intensity. Meanwhile, the dissociation of α-H in β-dicarbonyl forming enolate increases the extent of delocalization of the C-dots conjugated system, which induces the PL broadening to the red region and a decreasing intensity. Based on the understanding of the pH-sensitive PL mechanism, the pH-sensitive PL of C-dots can be switched by quantitative modulation of carboxyl and β-dicarbonyl groups to achieve a desirable pH response range with high sensitivity. This work contributes to a better understanding of the pH-sensitive PL of C-dots and therefore presents an effective strategy for controllably tuning their pH sensitivity, facilitating the rational design of C-dot-based pH sensors.

Absolutely "off-on" fluorescent CD-based nanotheranostics for tumor intracellular real-time imaging and pH-triggered DOX delivery

Carbon dots (CDs) have attracted intense attention in tumor nanotheranostics recently; however, those nanotheranostics exhibited similar fluorescence in both normal and tumor tissues, limiting their practical application. In the present work, absolutely "off-on" fluorescent CD-based nanotheranostics was designed for tumor intracellular real-time imaging and pH-triggered DOX delivery via both static quenching by the crosslinking of benzaldehyde-containing diblock copolymers and dynamic quenching because of the surrounding conjugated DOX molecules. The proposed PPEGMA₄₂-b-PFPMA₁₂₂-(CDs)-DOX nanotheranostics did not exhibit fluorescence in a normal physiological medium, while strong fluorescence recovery occurred in the tumor intracellular microenvironment due to pH-triggered disintegration, releasing the CDs and DOX. The pH-triggered DOX release and absolute "off-on" fluorescence make the proposed nanotheranostics promising for tumor-specific pH-triggered DOX delivery and imaging.

Growing Poly(norepinephrine) Layer over Individual Nanoparticles To Boost Hybrid Perovskite Photocatalysts

To address the poor stability of lead halide perovskite nanoparticles (NPs), monodisperse methylammonium lead bromide (MAPbBr₃, M-PE) NPs were successfully encapsulated with a thin layer (10 nm) of poly(norepinephrine) (PNE) by in situ polymerization. The PNE layer endowed M-PE NPs with high structural stability against severe environmental conditions. Furthermore, the chemical interaction between M-PE and PNE facilitates the construction of the core@shell composite, as well as contributes to the enhanced light-harvesting capacity and improved photoelectronic conversion efficiency in photocatalytic activity. The encapsulated NP M-PE@PNE with a band gap of 2.04 eV degraded the organic pollutant of malachite green by 81% in less than 2 h under visible light, which was 4.5 times higher than pristine M-PE NPs. This work provides a practical approach to stabilize and boost the MAPbX₃ photocatalyst and carries enormous potential in wide engineering applications.

A novel immobilization fluorescence capillary analysis method and its applications

Fluorescence capillary analysis (FCA) realizes trace-level analysis of micro-volume samples; it is easy to operate, extremely low in analytical cost and can significantly lessen environmental pollution from analytical chemistry waste. FCA has the characteristics of green analytical chemistry and has been applied in clinical, biochemical, pharmaceutical, food safety and other fields. FCA basically involves a micro-volume glass capillary, a capillary holder and an ordinary fluorescence detector. The capillary is not only a container for chemical reaction and detection but also functions as a carrier to immobilize enzymes, gene probes or reagents; it can be used repeatedly or can be disposable. In analysis, the capillary which is modified with functional reagents sucks in a measured liquid for the reaction and is then inserted into the holder within the fluorescent detector for measurement. The immobilized FCA method has been successfully used in the determination of reduced coenzyme I, ethanol in liqueur, lactic acid in dairy products, pyruvic acid and glucose in serum, trace-level sulfated bile acid in urine, the ratio of pyruvic/lactic acid in serum, and pyruvic acid in cells as well as in DNA end-labeling and dyeing methods. Further, FCA can also be extended to capillary arrays to complete multipurpose simultaneous determinations and can be combined with mobile phones as fluorescence detectors for use in mobile health analytical technology. FCA will produce considerable social benefits in medicine, pharmacy, fermentation of food, environmental protection and other fields. Therefore, the relevant contents are presented in this tutorial review.

A new fluorescent hemicryptophane for acetylcholine recognition with an unusual recognition mode

The ammonium of the target interacts with the south part of the hemicryptophane probably because the cyclotriveratrylene's electronic density is altered by the extension of conjugation.

CdTe0.5S0.5/ZnS Quantum Dots Embedded in a Molecularly Imprinted Polymer for the Selective Optosensing of Dopamine

This work describes the preparation of molecularly imprinted polymer (MIP)-modified core/shell CdTe_0.5S_0.5/ZnS quantum dots (QDs). The QDs@MIP particles were used for the selective and sensitive detection of dopamine (DA). Acrylamide, which is able to form hydrogen bonds with DA, and ethylene glycol dimethylacrylate (EGDMA) as cross-linker were used for the preparation of the MIP. Highly cross-linked polymer particles with sizes up to 1 µm containing the dots were obtained after the polymerization. After the removal of the DA template, MIP-modified QDs (QDs@MIP) exhibit a high photoluminescence (PL) with an intensity similar to that of QDs embedded in the nonimprinted polymer (NIP). A linear PL decrease was observed upon addition of DA to QDs@MIP and the PL response was in the linear ranges from 2.63 µM to 26.30 µM with a limit of detection of 6.6 nM. The PL intensity of QDs@MIP was quenched selectively by DA. The QDs@MIP particles developed in this work are easily prepared and of low cost and are therefore of high interest for the sensitive and selective detection of DA in biological samples.

A Simple, Rapid, Fluorometric Assay for Dopamine by In Situ Reaction of Boronic Acids and cis-Diol

An efficient, sensitive, and low-cost method has been developed for turn-on fluorescence sensing of dopamine (DA). The method relies on the rapid reaction of DA and 3-Hydroxyphenylboronic acid (3-HPBA) via specific recognition between boronic acids and cis-diol of DA in alkaline solution. The reaction product shows an excitation wavelength of 417 nm and the maximum emission peak at 470 nm. The proposed method allows the determination of DA in the range of 50 nM-25 μM, and the whole detection can be completed within 5 minutes. Furthermore, the presented approach has good selectivity and has been successfully applied to DA sensing in human serum samples, showing great potential in clinical diagnosis.

A facile synthesis of CuFe2O4/Cu9S8/PPy ternary nanotubes as peroxidase mimics for the sensitive colorimetric detection of H2O2 and dopamine

Synergistic effects play an important role in improving the catalytic activity for enzyme-like reactions. Compared to individual nanomaterials, a system consisting of multiple components usually exhibits enhanced catalytic activity as an enzyme mimic. Herein we describe the synthesis of CuFe₂O₄/Cu₉S₈/polypyrrole (PPy) ternary nanotubes as an efficient peroxidase mimic via a three-step approach involving an electrospinning process, annealing treatment and hydrothermal reaction. The remarkably enhanced catalytic activity of CuFe₂O₄/Cu₉S₈/PPy ternary nanotubes as peroxidase mimics over individual CuFe₂O₄ nanofibers, CuFe₂O₄/CuO composite nanofibers, CuFe₂O₄/CuS composite nanofibers, and PPy materials has been achieved, demonstrating the presence of a synergistic effect among the components. The steady-state kinetic experiment suggests a good catalytic efficiency of the CuFe₂O₄/Cu₉S₈/PPy ternary nanotubes. On the basis of high catalytic activity, a colorimetric platform for the sensitive detection of H₂O₂ and dopamine has been developed. This work not only offers a simple approach for the fabrication of a high performance peroxidase-like nanocatalyst, but also provides its promising potential applications in biosensors, medical diagnosis, and environmental monitoring.

Synergistic electron transfer effect-based signal amplification strategy for the ultrasensitive detection of dopamine

The selective and sensitive detection of dopamine (DA) is of great significance for the identification of schizophrenia, Huntington's disease, and Parkinson's disease from the perspective of molecular diagnostics. So far, most of DA fluorescence sensors are based on the electron transfer from the fluorescence nanomaterials to DA-quinone. However, the limited electron transfer ability of the DA-quinone affects the level of detection sensitivity of these sensors. In this work, based on the DA can reduce Ag⁺ into AgNPs followed by oxidized to DA-quinone, we developed a novel silicon nanoparticles-based electron transfer fluorescent sensor for the detection of DA. As electron transfer acceptor, the AgNPs and DA-quinone can quench the fluorescence of silicon nanoparticles effectively through the synergistic electron transfer effect. Compared with traditional fluorescence DA sensors, the proposed synergistic electron transfer-based sensor improves the detection sensitivity to a great extent (at least 10-fold improvement). The proposed sensor shows a low detection limit of DA, which is as low as 0.1 nM under the optimal conditions. This sensor has potential applicability for the detection of DA in practical sample. This work has been demonstrated to contribute to a substantial improvement in the sensitivity of the sensors. It also gives new insight into design electron transfer-based sensors.

Hydrothermal Synthesis of Nitrogen-Doped Carbon Quantum Dots as Fluorescent Probes for the Detection of Dopamine

Nitrogen-doped carbon quantum dots (N-CQDs) were synthesized though a facile, economical and straightforward hydrothermal method by using polyacrylamide as both carbon and nitrogen sources. The as-prepared N-CQDs offered high quantum yield of 23.1%, exhibited good water solubility and fluorescence properties. Moreover, the N-CQDs can be used as effective probes for sensitive and selective detection of dopamine. Fluorescence of N-CQDs was effectively quenched after the addition of dopamine owing to dopamine would be transformed into dopamine-quinone under alkaline conditions. A good linear relationship between fluorescence quenching and the concentration of dopamine in the range 0.1-200 μM was obtained with a low detection limit of 0.05 μM. The proposed method showed high selectivity for dopamine in the presence of potential interfering species. Moreover, this method was successfully applied to the determination of DA in urine sample with satisfactory recoveries.

Facile and large-scale synthesis of green-emitting carbon nanodots from aspartame and the applications for ferric ions sensing and cell imaging

A facile, economical and green strategy to prepare green-fluorescent nitrogen-doped carbon nanodots (N-CDs) with a quantum yield (QY) of approximately 31.91% has been built up, while aspartame was employed as the carbon-nitrogen source for the first time. The prepared N-CDs exhibited ultrahigh brightness, favorable strong photostability and negligible cytotoxicity. The outstanding optical properties are mainly derived from the their robost composition and steric distribution of the doped nitrogen atoms, which have been characterized detailedly. The obtained N-CDs showed highly selective and sensitive response toward ferric ions (Fe³⁺) through a fluorescence static quenching process in a wide linear range of 0.005-60µmol/L. The detection limit was as low as 1.43nmol/L, allowing the analysis of Fe³⁺ in a very simple method. The excitation-dependent luminescent behavior of the obtained N-CDs guaranteed the multicolor emissive property when they were used in cell imaging. And the application for intracellular Fe³⁺ sensing further verified this novel N-CDs may open more opportunities in biosensor, bioimaging and biological assay.

Mussel Inspired Polynorepinephrine Functionalized Electrospun Polycaprolactone Microfibers for Muscle Regeneration

Electrospun scaffolds with excellent mechanical properties, high specific surface area and a commendable porous network are widely used in tissue engineering. Improving the hydrophilicity and cell adhesion of hydrophobic substrates is the key point to enhance the effectiveness of electrospun scaffolds. In this study, polycaprolactone (PCL) fibrous membranes with appropriate diameter were selected and coated by mussel-inspired poly norepinephrine (pNE). And norepinephrine is a catecholamine functioning as a hormone and neurotransmitter in the human brain. The membrane with smaller diameter fibers, a relative larger specific surface area and the suitable pNE functionalization provided more suitable microenvironment for cell adhesion and proliferation both in vitro and in vivo. The regenerated muscle layer can be integrated well with fibrous membranes and surrounding tissues at the impaired site and thus the mechanical strength reached the value of native tissue. The underlying molecular mechanism is mediated via inhibiting myostatin expression by PI3K/AKT/mTOR hypertrophy pathway. The properly functionalized fibrous membranes hold the potential for repairing muscle injuries. Our current work also provides an insight for rational design and development of better tissue engineering materials for skeletal muscle regeneration.