Hydrochromic carbon dots as smart sensors for water sensing in organic solvents

Carbon dots for efficient detection of water content in organic solvents

The trace amount of water in organic solvents can affect the progress of chemical reactions, which will adversely affect chemical production in many industries, resulting in a doubling of costs. In this work, carbon dots (CDs) with abundant polar groups were synthesized by a simple one-step hydrothermal method. The prepared CDs showed superior dispersibility and fluorescence performance compared to the CDs that have been reported for the detection of water content in organic solvents. It can realize the fluorescence detection of trace water in several water-soluble organic solvents such as N,N-dimethylformamide, ethanol and methanol with wide linear range (0 %-100 %) and high sensitivity. This will provide a powerful tool for the rapid detection of water content in organic solvents in chemical production.

A highly water-soluble hydrogen-bond-induced emission carbon dots for ratiometric fluorescent detection of water content in organic solvents

Water in organic solvents is a prevalent impurity that significantly influences chemical reactions and industrial processes. Carbon dots (CDs) gained attention as promising tools for chemosensing due to their advantageous characteristics, including easy synthesis, cost-effectiveness, and excellent adjustability and stability. However, limited solubility in water and turn off fluorescence response mode hinder the practical utilization of CDs for water sensing. To tackle such dilemma, a highly water-soluble CDs with distinctive hydrogen-bond-induced emission (HBIE) was rationally designed through introducing sulfone group into the widely employed p-phenylenediamine precursor. The inclusion of sulfone group imparts the CDs with notable water solubility, as well as distinctive ratiometric fluorescent response towards water content, exhibiting high sensitivity and selectivity. Upon exposure to water, the emission color of CDs undergoes a real-time transition from blue to yellow-green, which can be readily discerned by naked eyes. The CDs have been successfully applied in detecting water in commercially available alcohol. This study presents a straightforward yet efficacious approach for rationally design of CDs with unique HBIE characteristics and ratiometric fluorescent response, offering great potential for practical chemosensing applications.

Searching for the true origin of the red fluorescence of leaf-derived carbon dots

We report for the first time that the red fluorescence of leaf-derived carbon dots is derived from chlorophyll, and a possible formation structure is proposed. By controlling the solvothermal reaction temperature, the new luminescence center of CDs can be adjusted. This work provides unprecedented insights into the luminescence mechanism of biomass-derived CDs.

The Emerging Development of Multicolor Carbon Dots

As a relatively new type of fluorescent carbon-based nanomaterials, multicolor carbon dots (MCDs) have attracted much attention because of their excellent biocompatibility, tunable photoluminescence (PL), high quantum yield, and unique electronic and physicochemical properties. The multicolor emission characteristics of carbon dots (CDs) obviously depend on the carbon source precursor, reaction conditions, and reaction environment, which directly or indirectly determines the multicolor emission characteristics of CDs. Therefore, this review is the first systematic classification and summary of multiple regulation methods of synthetic MCDs and reviews the recent research progress in the synthesis of MCDs from a variety of precursor materials such as aromatic molecules, small organic molecules, and natural biomass, focusing on how different regulation methods produce corresponding MCDs. This review also introduces the innovative applications of MCDs in the fields of biological imaging, light-emitting diodes (LEDs), sensing, and anti-counterfeiting due to their excellent PL properties. It is hoped that by selecting appropriate adjustment methods, this review can inspire and guide the future research on the design of tailored MCDs, and provide corresponding help for the development of multifunctional MCDs.

A Hydrothermal Method to Generate Carbon Quantum Dots from Waste Bones and Their Detection of Laundry Powder

Surfactants are one of the major pollutants in laundry powder, which have an impact on the environment and human health. Carbon quantum dots (CQDs) are spherical zero-dimensional fluorescent nanoparticles with great potential for fluorescent probing, electrochemical biosensing and ion sensing. Herein, a bottom-up approach was developed for the synthesis of CQDs from biomass to detect laundry detergent and laundry powder. Waste chicken bones were used as carbon precursors after being dried, crushed and reacted with pure water at 180 °C for 4 h to generate CQDs, which exhibited a monodisperse quasi-spherical structure with an average particle size of 3.2 ± 0.2 nm. Functional groups, including -OH, C=O, C=C and C-O, were identified on the surface of the prepared CQDs. The optimal fluorescence excitation wavelength of the yellow-brown CQDs was 380 nm, with a corresponding emission peak at 465 nm. CQDs did not significantly increase cell death in multiple cell lines at concentrations of 200 µg·mL⁻¹. Fluorescence enhancement of CQDs was observed after addition of sodium dodecyl benzene sulphonate, a major anionic surfactant in laundry powder. A linear relationship between fluorescence enhancement CQDs and the concentration of laundry powder was established. Thus, a hydrothermal method was developed to generate CQDs from waste biomass that may be used as a fluorescent probe to detect laundry powder.

Mechanisms behind multicolor tunable Near-Infrared triple emission in graphene quantum dots and ratio fluorescent probe for water detection

Developing environmental-friendly and low-cost strategies of synthesizing red-emission graphene quantum dots (R-GQDs) is a considerable challenge. Herein, we present the green and facile preparation of R-GQDs by using o-phenylenediamine (o-PD) and catechol as precursors via oxidation/polymerization and Schiff base reaction at low temperature (80 °C) for 3 hrs. Results show that the prepared R-GQDs exhibit triple fluorescence emissions, which is enabled by the introduce of different nitrogen (pyrrolic N, pyridinic N, and amino N) species on the surface of R-GQDs. Moreover, the R-GQDs are implemented to detect the moisture in different organic solvent. A highly sensitive ratiometric sensing of water in organic solvents is achieved, and the relationship between the change of fluorescence signal caused by moisture and the corresponding internal emission site is also determined. In the end, the multicolor light emissions of R-GQDs are realized by simply adjusting the polarity of surrounding solvents. And based on the solvatochromism of R-GQDs, the multicolor solid fluorescent powder and ink are prepared for illumination application. All in all, the above research work presents a novel R-GQDs for wide application in detecting and illumination.

Preparation, characterization and cell labelling of strong pH-controlled bicolor fluorescence carbonized polymer dots

As a class of important carbon nanomaterial, carbonized polymer dots (CPDs), also called carbon dots (CDs), have aroused wide interest owing to their unique water solubility, fluorescence properties, and rich surface functional groups. However, the directional tuning of the fluorescence properties of CPDs remains incomplete because of the influence of many factors like diameter, solvent and surface groups. Particularly, most carbonized polymer dots are synthesized in a neutral pH environment. Herein, by modulating the pH (strongly acidic or alkaline) of dextrin water solution, bicolor fluorescence emission (blue and yellow) CPDs were prepared by a hydrothermal reaction. Through systematic characterization, it was found that the different fluorescence properties are regulated by the diameters and surface groups of the carbon cores. Simultaneously, the pH value affected the nucleation process. Based on the excellent fluorescence properties, cell fluorescence imaging and cytotoxicity were tested. The bicolor fluorescence CPDs obtained by tuning the pH provide an important theoretical basis for the design of broadband CPDs.

Imidazole-based AIEgens for highly sensitive and selective detection of picric acid

A new family of imidazole-based AIEgens has been synthesized as fluorescent probes for specific recognition of picric acids over a variety of nitroaromatic compounds in aqueous media with high sensitivity.

In Situ Femtosecond-Laser-Induced Fluorophores on Surface of Polyvinyl Alcohol for H2O/Co2+ Sensing and Data Security

In situ fluorophores were induced on polyvinyl alcohol (PVA) bulk materials by direct femtosecond laser writing. The generation of fluorophores was ascribed to localized laser-assisted carbonization. The carbonization of PVA polymers was confirmed through X-ray photoelectron spectroscopy analysis. The distinct fluorescence responses of fluorophores in various solutions were harnessed for implementing in situ reagent sensors, metal ion sensors, data encryption, and data security applications. The demonstrated water detection sensor in acetone exhibited a sensitivity of 3%. Meanwhile, a data encryption scheme and a "burn after reading" technique were demonstrated by taking advantage of the respective reversible and irreversible switching properties of the in situ laser-induced fluorophores. Taking a step further, a quantitative cobalt ion measurement was demonstrated based on the concentration-dependent fluorescence recovery. Combined with a laser-induced hydrophilic modification, our scheme could enable "lab-on-a-chip" microfluidics sensors with arbitrary shape, varied flow delay, designed reaction zones, and targeted functionalities in the future.

NaCl nanocrystal-encapsulated carbon dots as a solution-based sensor for phosphorescent sensing of trace amounts of water in organic solvents

The phosphorescence of solid-state carbon dots (CDs) has been demonstrated to be susceptible to water molecules. However, solution-based CDs have been rarely exploited for phosphorescence detection of trace amounts of water in organic solvents. Here, we present a straightforward method to embed the CDs into NaCl nanocrystals and show their application for phosphorescence detection of the water content in organic solvents. The phosphorescent CDs inside NaCl nanocrystals were fabricated by hydrothermal treatment of poly(diallyldimethylammonium) (PDDA) polymers and their counter chloride ions (Cl^-) in the presence of NaOH. Because of the interaction with quaternary ammonium surface groups of PDDA-based CDs (PDDA-CDs), the Cl^- ions serve as a nucleation site to trigger NaCl nanocrystal formation. Electron microscopy and spectroscopy techniques demonstrate the embedment of PDDA-CDs into NaCl nanocrystals (PDDA-CDs@NaCl). The PDDA-CDs@NaCl exhibited excitation-independent phosphorescence and excitation-dependent fluorescence in ethanol, methanol, dimethyl sulfoxide, and dimethylformamide. In four different organic solvents, the phosphorescence QYs and lasting times of PDDA-CDs@NaCl range from 23 to 35% and 1.2 to 1.5 s, respectively. Once trace amounts of water are present in an organic solvent, the water-induced dissolution of NaCl nanocrystals switches off the phosphorescence of PDDA-CDs@NaCl. It was found that PDDA-CDs@NaCl was capable of detecting as low as 0.25% v/v water in ethanol and 0.125% v/v water in methanol. The above-discussed results provide fundamental insights regarding the embedment of phosphorescent CDs into a solid matrix as a solution-based sensor.

N, Cl-doped carbon dots for fluorescence and colorimetric dual-mode detection of water in tetrahydrofuran and development of a paper-based sensor

N, Cl-doped carbon dots (N, Cl-CDs) were prepared by hydrothermal method from rhodamine B (RhB) and ethylenediamine (EDA). The resulting N, Cl-CDs exhibited fascinating solvent dependence and strict excitation independence. As the polarity of the solvent increased (from tetrahydrofuran (THF) to water), the emission spectrum of N, Cl-CDs was redshifted and the fluorescence efficiency decreased, which were attributed to hydrogen bond-induced aggregation. Taking advantage of these attributes, the N, Cl-CDs were used as suitable probes for fluorescence and colorimetric dual-mode detection of water in THF. The linear relationship was 0.5-100% water with the detection limit down to 0.093%. Moreover, the sensing platform was converted into a paper-based sensor for handy, real-time, and visible humidity sensing. N, Cl-CDs/PVA films were fabricated and realized continuously tunable solid-state fluorescence, further expanding their practical application.

Onge PBJ, Rondeau-Gagné S, Mirhassani M. Computational Design of an Integrated CMOS Readout Circuit for Sensing With Organic Field-Effect Transistors

Organic field-effect transistors (OFETs) are at the forefront of next generation electronics. This class of devices is particularly promising due to the possibility of fabrication on mechanically compliant and conformable substrates, and potential manufacturing at large scale through solution deposition techniques. However, their integration in circuits, especially using stretchable materials, is still challenging. In this work, the design and implementation of a novel structure for an integrated CMOS readout circuitry is presented and its fundamentals of operation are provided. Critical for sensing applications, the readout circuitry described is highly linear. Moreover, as several sources of mismatch and error are present in CMOS and OFET devices, a calibration technique is used to cancel out all the mismatches, thus delivering a reliable output. The readout circuit is verified in TSMC 0.18 μm CMOS technology. The maximum total power consumption in the proposed readout circuit is less than 571 μW, while fully loaded calibration circuit consumes a power less than 153 μW, making it suitable for sensors applications. Based on previously reported high mobility and stretchable semiconducting polymers, this new design and readout circuitry is an important step toward a broader utilization of OFETs and the design of stretchable sensors.

Unexpected three-state hydrochromism of a donor-acceptor self-complex with fluctuations in relative humidity

Water in our environment is ever present, particularly in our atmosphere, from which it may be adsorbed by materials hygroscopically. At the molecular level, the binding of water molecules to various materials is driven by weak interactions but can have profound effects on physical properties, including the donor-acceptor interactions in charge transfer (CT) salts. Herein we present the unexpected three-state hydrochromatic switching of a bipyridinium-based donor-acceptor self-complex with changes in relative humidity (RH) and subsequent stable hydrate formation. RH is typically an overlooked variable that can vary greatly. These findings suggest that care should be taken to consider fluctuations in RH when characterizing the solid state optical band gap and CT absorption bands for organic donor-acceptor CT salt complexes.

The Unusual Photochromic and Hydrochromic Switching Behavior of Cellulose-Embedded 1,8-Naphthalimide-Viologen Derivatives in the Solid-State

Stimuli-responsive chromic materials such as photochromics, hydrochromics, thermochromics, and electrochromics have a long history of capturing the attention of scientists due to their potential industrial applications and novelty in popular culture. However, hybrid chromic materials that combine two or more stimuli-triggered color changing properties are not so well known. Herein, we report a design strategy that has led to a series of emissive 1,8-naphthalimide-viologen dyads which exhibit unusual dual photochromic and hydrochromic switching behavior in the solid-state when embedded in a cellulose matrix. This behavior manifests as reversible solid state fluorescence hydrochromism upon changes in atmospheric relative humidity (RH), and reversible solid state photochromism upon generation of a cellulose-stabilized viologen radical cation. In this design strategy, the bipyridinium unit serves as both a water-sensitive receptor for the hydrochromic fluorophore-receptor system, and a photochromic group, capable of eliciting its own visible colorimetric response, generating a fluorescence quenching radical cation with prolonged exposure to ultraviolet (UV) light. These dyes can be inkjet-printed onto cellulose paper or drop-cast as cellulose powder-based films and can be unidirectionally cycled between three different states which can be characteristically visualized under UV light or visible light. The material's photochromism, hydrochromism, and underlying mechanism of action was investigated using computational analysis, dynamic vapor sorption/desorption isotherms, electron paramagnetic resonance spectroscopy, and variable humidity UV-Vis adsorption and fluorescence spectroscopies.

Carbon Dots: An Emerging Smart Material for Analytical Applications

Carbon dots (CDs) are optically active carbon-based nanomaterials. These nanomaterials can change their light emission properties in response to various external stimuli such as pH, temperature, pressure, and light. The CD's remarkable stimuli-responsive smart material properties have recently stimulated massive research interest for their exploitation to develop various sensor platforms. Herein, an effort has been made to review the major advances made on CDs, focusing mainly on its smart material attributes and linked applications. Since the CD's material properties are largely linked to their synthesis approaches, various synthesis methods, including surface passivation and functionalization of CDs and the mechanisms reported so far in their photophysical properties, are also delineated in this review. Finally, the challenges of using CDs and the scope for their further improvement as an optical signal transducer to expand their application horizon for developing analytical platforms have been discussed.

Cucurbituril-assisted formation of tunable carbon dots from single organic precursors in water

A facile method by utilizing the host–guest interaction of Q[n]s for the catalytic fabrication of CDs with high emitting qualities and a tunable particle size from a single organic precursor in water with high output has been demonstrated.

Progress in the design and development of "fast-dissolving" electrospun nanofibers based drug delivery systems - A systematic review

Electrospinning has emerged as most viable approach for the fabrication of nanofibers with several beneficial features that are essential to various applications ranging from environment to biomedicine. The electrospun nanofiber based drug delivery systems have shown tremendous advancements over the controlled and sustained release complemented from their high surface area, tunable porosity, mechanical endurance, offer compatible environment for drug encapsulation, biocompatibility, high drug loading and tailorable release characteristics. The dosage formulation of poorly water-soluble drugs often faces several challenges including complete dissolution with maximum therapeutic efficiency over a short period of time especially through oral administration. In this context, challenges associated with the dosage formulation of poorly-water soluble drugs can be addressed through combining the beneficial features of electrospun nanofibers. This review describes major developments progressed in the preparation of electrospun nanofibers based "fast dissolving" drug delivery systems by employing variety of polymers, drug molecules and encapsulation approaches with primary focus on oral delivery. Furthermore, the review also highlights current scientific challenges and provide an outlook with regard to future prospectus.

Effect of Solvent-Derived Highly Luminescent Multicolor Carbon Dots for White-Light-Emitting Diodes and Water Detection

Recently, the multicolor fluorescent carbon dots (CDs) have drawn much attention due to their various applications. Herein, we report multicolor emissive CDs by solvent-controlled and solvent-responded approaches. The blue to red color emissive CDs are obtained by the solvothermal method by varying the solvent during the reaction. The red color emissive CDs (R-CDs) with good quantum yield is obtained in a water medium. The detailed characterization revealed that the solvent controls the particle size, band gap, and nitrogen doping concentration. Specifically, in the protic solvent, the high N content and presence of imine nitrogen are the reason for red emission. However, in an aprotic solvent, the least N doping and a lack of C-O groups are responsible for a blueshift. Interestingly, it was observed that the R-CDs provide a full range of visible color by dispersing in different immiscible solvents. The fluorescence emission in immiscible solvents is redshifted by enhancing the polarity. Moreover, the developed CDs detected the low water concentrations (≤0.2%, v/v) visually and fluorometrically in various organic solvents. Simultaneously, we have employed synthesized CDs in white-light-emitting diodes and fluorescent ink.