A sensitive fluorescent sensor for the detection of trace water in organic solvents based on carbon quantum dots with yellow fluorescence

Rapid and ultra-sensitive trace water determination in organic solvents utilizing nitrobenzoxadiazole (NBD)-based fluorescent sensing system

The presence of minute quantities of water in organic solvents can affect the progress of many reactions and cause unnecessary losses and even safety accidents in the chemical industry, especially in the productions process of organic fine chemicals. Therefore, it is necessary to carry out high-performance strategies for trace water detections in commonly used organic solvents. In this work, a fluorescent sensing system based on competitive binding of protons has been developed, demonstrating remarkable responses by UV-vis absorption and fluorescence two-modes toward a trace amount of water in organic solvents including 1,4-dioxane (Diox), tetrahydrofuran (THF), acetonitrile (MeCN), acetone (ACE), dimethylsulfoxide (DMSO) and mixed organic solvents (THF: MeCN=1: 1). The key component of the sensing system is a newly designed fluorophore NBD-PMA, which can be deprotonated to form a dynamic non-luminescent adduct, namely NBD-PMA-F, by an organic fluoride salt tetrabutylammonium fluoride (TBAF). NBD-PMA-F can be reprotonated via using trace water, exhibiting fluorescence turn on of the system. The as-prepared sensing system shows superior sensitivity, low detection limits (v/v, 0.0007 %), quick response speed (≤1.2 s) and good reversibility. Moreover, naked-eye visual rapid detection has also been successfully realized at ambient temperature, which demonstrated their practical applications value for trace water determinations.

Biomass-derived multiatom-doped carbon dots for water sensing based on excited state intraparticle proton transfer in organic solvents

The presence of trace water impurities in organic solvents can significantly influence chemical reactions and product quality; thus, the accurate detection of water content in these solvents is a critical requirement for industrial applications. Accordingly, an eco-friendly, effective, and economical sensor for detecting trace quantities of miscible water in organic solvents is required for industrial applications. In this study, we synthesized biomass-derived multi-atom-doped carbon dots (MACDs) as fluorescent probes and employed them for the detection of trace amounts of water impurities in several water-miscible organic solvents. The MACDs exhibited stable dual-color fluorescence emission under ultraviolet light irradiation and red and blue emissions in organic solvents and water. The fluorescence quantum yield was approximately 11 %, which indicates an excited intraparticle proton transfer response due to an increase in the water content within a wide response range from 0 % to 100 % (v/v) in organic solvents. The intensity of the red emission signal at 670 nm gradually decreased with an increase in the water content in the organic solvent. The MACDs could detect water with an instant response time of 55 s, a high sensitivity, and low limits of detection of 0.08 %, 1.36 %, 0.03 %, 0.04 %, 0.12 %, and 0.05 % (v/v) in ethanol, acetonitrile, dimethylformamide, methanol, isopropanol, and tetrahydrofuran, respectively. Hence, biomass-derived MACDs can serve as efficient and eco-friendly water sensors in organic solvents.

Propeller shaped triarylamine acid: An ultra-sensitive fluorescence probe for distinguishing propanol isomers and water sensing in organic solvents

The photophysical properties of conformationally flexible (TPA-C) and partially rigidified (Cz-C) triarylamine acids were explored in solid as well as solution state and correlated with the structure. TPA-C and Cz-C exhibited moderate solid-state fluorescence (Φf = 6.2 % (TPA-C) and 5.6 % (Cz-C)) and self-reversible mechanofluorochromism. TPA-C produced fluorescent polymorphs (TPA-C-1 and TPA-C-2) with tunable fluorescence. TPA-C-1 showed unusual carboxylic acid intermolecular interactions whereas TPA-C-2 and Cz-C showed usual carboxylic acid dimer. TPA-C exhibited strong solvent polarity dependent tunable fluorescence (Φf = 0.01 to 0.11 compared to quinine sulphate standard) but Cz-C was non-emissive in the solution state. The dual emissive TPA-C showed highly sensitive fluorescence changes in organic solvents (CH3CN, THF, DMF, EtOH) when trace amount of water was added. In CH3CN, TPA-C showed weak fluorescence at 474 nm and addition of water (1 %) exhibited significant blue shift (λmax = 416 nm). The fluorescence intensity was gradually decreased with blue shifting in DMF, THF and EtOH with water addition. Importantly, TPA-C showed drastically different fluorescence in n-propanol (n-PA) and iso-propanol (IPA). TPA-C in n-PA showed fluorescence at 408 nm that was clearly red shifted to 438 nm with 0.1 % addition of IPA. The limit of detection (LOD) of water in CH3CN, DMF, THF and EtOH by TPA-C revealed 0.02, 0.7, 0.08 and 0.77 %, respectively. The LOD of IPA sensing in n-PA is 0.05 % and indicated the very efficient sensing and distinguishing propanol isomers. Thus, simple triphenylamine acid showed excellent water sensing and propanol isomers discrimination that could be attributed to the twisted intramolecular charge transfer (TICT) formation.

Advances on fluorescence chemosensors for selective detection of water

Water, although an important part of everyday life, is acts as one of the most significant contaminants in various applications such as biomedical monitoring, chemical production, petroleum-based fuel and food processing. In fact, the presence of water in other solvents is a huge concern. For the quantification of trace water content, different methods such as Karl-Fischer, electrochemical, nuclear magnetic resonance, chromatography, and thermogravimetric analysis have been used. Although every technique has its own benefit, each one suffers from several drawbacks that include high detection costs, lengthy procedures and specialized operations. Nowadays, the development of fluorescence-based chemical probes has become an exciting area of research for the quick and accurate estimation of water content in organic solvents. A variety of chemical processes such as hydrolysis reaction, metal ions promoted oxidation reaction, suppression of the -C═N isomerization, protonation and deprotonation reactions, and molecular aggregation have been well researched in the last few years for the fluorescent detection of trace water. These chemical processes eventually lead to different photophysical events such as aggregation-induced emission (AIE), aggregation-induced emission enhancement (AIEE), aggregation-caused quenching (ACQ), fluorescent resonance energy transfer (FRET), charge transfer, photo-induced electron transfer (PET), excited state intramolecular proton transfer (ESIPT) that are responsible for the detection. This review presents a summary of the fluorescence-based chemosensors reported in recent years. The design of water sensors, sensing mechanisms and their potential applications are reviewed and discussed.

Water bridges as the trigger in an amino functionalized Zn-MOF for highly selective and sensitive fluorescent sensing of water

Water is a fundamental element for life. The highly selective and sensitive sensing of water is always attractive for mankind in activities such as physiological processes study and extraterrestrial life exploration. Fluorescent MOFs with precise channels and functional groups might specifically recognize water molecules with hydrogen-bond interaction or coordination effects and work as water sensors. As a proof of concept, herein, an amino functionalized Zn-MOF (named as complex 1) with pores that just right for water molecules to form hydrogen bond bridges is revealed for highly selective and sensitive fluorescent sensing of water. The single-crystal X-ray diffraction analysis indicates that the 3D framework of complex 1 is functionalized with free amino groups in the channels. Hydrogen bonds formed in the channel along b-axis as water bridges to connect two adjacent NH2bdc ligands and result in the restriction of intramolecular motions (RIM) which could responsible for the selective turn-on fluorescence response to water. Complex 1 exhibits high sensitive to trace amount of water in organic solvents and could be used for water detection in a wide range water contents. Take advantages of complex 1, portable sensors (complex 1@PMMA) were prepared and used in the highly sensitive water sensing.

p-Phenylenediamine-derived carbon nanodots for probing solvent interactions

Carbon nanodots, the luminescent nanoparticles of carbon with size restriction below 10 nm, have attracted inordinate attention in materials science due to their widespread applications in optoelectronic and biological fields. Low toxicity and facile synthesis pathways render them favourites in the above-mentioned areas in the context of green chemistry. This work presents fine applications of p-phenylenediamine-derived carbon nanodots (PD-CNDs) achieved via a facile one-pot hydrothermal method. Adequate characterization using X-ray diffraction and spectroscopic and microscopic studies confirmed spherical particles with an average particle size of 2.8 nm, functionalised with amino, carboxyl, and hydroxyl groups. The carbon framework was functionalised with pyridinic and pyrrolic nitrogens. Upon 365 nm UV light illumination, an aqueous dispersion of PD-CNDs showed red-orange fluorescence. Detailed spectral analysis using UV-visible absorption and fluorescence spectroscopy identified edge states and surface groups as luminescent centres, with a significant contribution arising from the latter. The investigation conducted using a collection of solvents, categorized into polar and nonpolar, indicated the potential of the system for applications based on its solvatochromic nature. The feature enabled the determination of different polarity parameters of the solvents, as well as dielectric constants of solvents and solvent mixtures, with considerable accuracy. The system was potent for predicting the composition of a given pair of solvents. The service of the system is also extended for moisture sensing in organic solvents within an error percentage < 1. High quantum yield values (0.61) combined with solvent composition-dependent optical features ensure broader applications of the system to probe solvent interactions.

Fluorescence-Based Portable Assays for Detection of Biological and Chemical Analytes

Fluorescence-based detection techniques are part of an ever-expanding field and are widely used in biomedical and environmental research as a biosensing tool. These techniques have high sensitivity, selectivity, and a short response time, making them a valuable tool for developing bio-chemical assays. The endpoint of these assays is defined by changes in fluorescence signal, in terms of its intensity, lifetime, and/or shift in spectrum, which is monitored using readout devices such as microscopes, fluorometers, and cytometers. However, these devices are often bulky, expensive, and require supervision to operate, which makes them inaccessible in resource-limited settings. To address these issues, significant effort has been directed towards integrating fluorescence-based assays into miniature platforms based on papers, hydrogels, and microfluidic devices, and to couple these assays with portable readout devices like smartphones and wearable optical sensors, thereby enabling point-of-care detection of bio-chemical analytes. This review highlights some of the recently developed portable fluorescence-based assays by discussing the design of fluorescent sensor molecules, their sensing strategy, and the fabrication of point-of-care devices.

Fluorescence Sensor for Water in Organic Solvent Using Graphene Oxide- Rhodamine B and Cucurbit[7]uril

Detection of water in organic solvents gained much importance as these solvents have been used as a medium for conducting organic reactions and water was considered as an inhibitor, when it is present in the reaction medium. There are number of methods available to measure the water content in organic solvents, however, such methods are time consuming and expensive. Here, we developed a facile method for detecting water in organic solvents using an inexpensive fluorescent probe - Rhodamine B decorated Graphene oxide (RBGO). The fluorescent probe, RBGO can be conveniently prepared by mixing the rhodamine B (RB) with graphene oxide (GO) in water. However, the probe will function as a sensor for water in the organic solvents through the release of dye upon interaction with the water present in organic solvents. Surprisingly, combination of cucurbit[7]uril (CB[7]) and RBGO increased the sensitivity of this sensor dramatically for the detection of water. This is the first example of water sensor with best detection limit by the involvement of host molecules such as CB[7]. This sensor displayed the low limit of detection (LOD) for organic solvents (LOD: 0.0015% for DMSO, 0.0025% for DMF), through the two-way process such as decomplexation and encapsulation. We presume that the role of CB [7] can be implemented in other similar sensors to enhance the sensitivity.

Preparation of Carbon Dots with Ultrahigh Fluorescence Quantum Yield Based on PET Waste

Environmentally friendly polyethylene terephthalate-based carbon dots (PET-CDs) with ultrahigh fluorescence quantum yield were prepared with waste PET textiles as raw materials. First, oligomers were prepared from the reaction of waste PET textile and ethylene glycol by the microwave method. Then, the mixture without isolation and purification as well as pyromellitic acid and urea were adopted as precursors for the preparation of PET-CDs by the hydrothermal method. It was found that the as-prepared PET-CDs had a spherical structure with an average particle size of 2.8 nm. The carbon core of PET-CDs was a graphene-like structure doped with nitrogen atoms in the form of pyrrole nitrogen and the surface contained -NH₂, which is convenient for modification and functionalization with various materials in the form of chemical bonds. The as-prepared PET-CDs exhibit excitation-independent emission properties in the range from 340 to 440 nm, and the best excitation and emission wavelengths of PET-CDs are 406 and 485 nm, respectively, while the fluorescence quantum yield is 97.3%. In terms of the application, the as-prepared PET-CDs could be adopted as a fluorescence probe for the detection of Fe³⁺, and the limit of detection is as low as 0.2 μmol/L. The mechanism of PET-CDs by Fe³⁺ was found to be the static quenching mechanism. In addition, PET-CDs can be used in LEDs and fluorescent anticounterfeiting.

Metal-Organic Frameworks Encapsulating Carbon Dots Enable Fast Speciation of Mono- and Divalent Copper

Copper is an essential element to play significant roles in human health associated to the strong redox properties of Cu(I) and Cu(II). The concurrent monitoring of copper species in biological matrixes is highly desired. Herein, a dual-channel fluorescence nanoprobe was designed for the speciation of mono- and divalent copper by conjugating carbon dots (CDs) with Eu-based metal-organic frameworks (Eu-MOFs). The obtained Eu-MOFs@CD nanoprobe exhibits fluorescence at λ_ex/λ_em = 380/454 nm from CDs and λ_ex/λ_em = 275/615 nm from Eu-MOFs. Bathocuproine disulfonate (BCS) specifically chelates Cu⁺ to produce a BCS-Cu⁺ adduct with absorption at 480 nm, which quenches the fluorescence of CDs at 454 nm due to the inner filter effect. On the other hand, Cu²⁺ quenches the fluorescence of Eu-MOFs due to the replacement of Eu³⁺ by Cu²⁺. Thus, Eu-MOFs@CDs enable extremely fast detection of Cu⁺ and Cu²⁺ within 1 min. Furthermore, the nanoprobe is demonstrated by monitoring the variation of Cu⁺ and Cu²⁺ in the degradation process of copper nanoparticles and Cu-based MOFs.

Pyrene – N-phenylparaphenylene diamine-Based Imine Conjugate for the Detection of Trace Amounts of Water in Organic Solvents: Real-Time Application in Honey Samples

A one-step condensation procedure in the presence of green solvent EtOH was used to make a pyrene-based fluorescent sensor (PNPD). It could be used as a rapid, low-cost, selective, and...

Cutting COF-like C4N into Colloidal Quantum Dots toward Optical Encryption and Bidirectional Sulfur Chemistry via Functional Group and Edge Effects

As a newly-emerged two-dimensional (2D) layered polymer, C 4 N has aroused increasing interest. Yet, the inferior solubility of bulk C 4 N constrains its application scope. Nanostructing bulk C 4 N into quantum dots (QDs) can enable enhanced or entirely-new properties, but the C 4 NQDs study remains unavailable. Here, starting from predesigned COF-like C 4 N, we report the first synthesis of colloidal C 4 NQDs and their functional composites, and explore their optical activities for dual-mode information encryption and edge-selective adsorption-catalytic ability toward boosted sulfur chemistry in Li-S cells. Colloidal C 4 NQDs with ultrasmall size of ~2.2 nm bear rich carbonyl groups and edges, allowing good solution processability and facile assembly with other moieties for creating intriguing functionalities by exploiting functional group and edge effects of QDs. While C 4 NQDs show normal fluorescence (FL), the QD/poly (vinyl alcohol) (PVA) composites attain color-tunable afterglow and FL/room-temperature - phosphorescence (RTP) dual-mode emission, enabling the corresponding solution as a new encryption ink. The QDs anchored onto carbon nanotubes can be used as a robust barrier layer to decorate commercial separators and afford superior polysulfide adsorption-catalysis ability, endowing a Li-S cell with excellent cycling stability, high rate capability and large areal capacity of 5.8 mAh cm -2 at high sulfur loading of 7.2 mg cm -2 . Computation and experiment studies unveil that edge sites in C 4 N favor polysulfide adsorption and catalysis relative to in-plane sites and the synergy of enriched edges and carbonyl groups in QDs expedites bidirectional catalytic conversion of sulfur species.

PVDF-triggered multicolor fluorine-doped graphene quantum dots for water detection and anti-counterfeiting

Fluorescent fluorine-doped graphene quantum dots (F-GQDs) have been synthesized via the hydrothermal method using long-chain polymer polyvinylidene fluoride (PVDF) as the precursor. Due to the unique molecular structure of PVDF, a possible synthesis process of F-GQDs has been put forward. F-GQDs have adjustable emission wavelength by simply adjusting the concentration of the solution. As the concentration increases, the emission wavelength of F-GQDs gradually red shifts from 455 nm (blue) to 551 nm (yellow-green). In addition, F-GQDs also exhibit a sensitive fluorescence response to water content in organic solvents, and the ultralow detections limit are 0.056% in ethanol and 0.124% in DMF. Besides, due to strong UV absorption capacity, a photothermal film is fabricated by embedding F-GQDs in PDMS. The temperature of F-GQDs/PDMS polymer film can reach 33.4 ^oC under simulated sunlight, while the maximum temperature of blank PDMS film only reach 29.4 ^oC. Based on this phenomenon, a new type of anti-counterfeiting device is designed by combining F-GQDs/PDMS film with temperature change ink.

Excited-State Dynamics of a meta-Dimethylamino Locked GFP Chromophore as a Fluorescence Turn-on Water Sensor†

Strategic incorporation of a meta-dimethylamino (-NMe₂ ) group on the conformationally locked green fluorescent protein (GFP) model chromophore (m-NMe₂ -LpHBDI) has drastically altered molecular electronic properties, counterintuitively enhancing fluorescence of only the neutral and cationic chromophores in aqueous solution. A ˜200-fold decrease in fluorescence quantum yield of m-NMe₂ -LpHBDI in alcohols (e.g., MeOH, EtOH and 2-PrOH) supports this GFP-derived compound as a fluorescence turn-on water sensor, with large fluorescence intensity differences between H₂ O and ROH emissions in various H₂ O/ROH binary mixtures. A combination of steady-state electronic spectroscopy, femtosecond transient absorption, ground-state femtosecond stimulated Raman spectroscopy (FSRS) and quantum calculations elucidates an intermolecular hydrogen-bonding chain between a solvent -OH group and the chromophore phenolic ring -NMe₂ and -OH functional groups, wherein fluorescence differences arise from an extended hydrogen-bonding network beyond the first solvation shell, as opposed to fluorescence quenching via a dark twisted intramolecular charge-transfer state. The absence of a meta-NMe₂ group twisting coordinate upon electronic excitation was corroborated by experiments on control samples without the meta-NMe₂ group or with both meta-NMe₂ and para-OH groups locked in a six-membered ring. These deep mechanistic insights stemming from GFP chromophore scaffold will enable rational design of organic, compact and environmentally friendly water sensors.

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.

Red-Emitting Fluorophores as Local Water-Sensing Probes

Fluorescent probes are known for their ability to sense changes in their direct environment. We introduce here the idea that common red-emitting fluorophores recommended for biological labeling and typically used for simple visualization of biomolecules can also act as reporters of the water content in their first solvent sphere by a simple measurement of their fluorescence lifetime. Using fluorescence spectroscopy, we investigated the excited-state dynamics of seven commercially available fluorophores emitting between 650 and 800 nm that are efficiently quenched by H₂O. The amount of H₂O in their direct surrounding was modulated in homogeneous H₂O-D₂O mixtures or, in heterogeneous systems, by confining them into reverse micelles, by encapsulating them into host-guest complexes with cyclodextrins, or by attaching them to peptides and proteins. We found that their fluorescence properties can be rationalized in terms of the amount of H₂O in their direct surroundings, which provides a general mechanism for protein-induced fluorescence enhancements of red-emitting dyes and opens perspectives for directly counting water molecules in key biological environments or in polymers.

Colorimetric detection of water content in organic solvents via a smartphone with fluorescent Ag nanoclusters

We detected the water content in ethanol and dimethyl sulfoxide (DMSO) solvents via a smartphone with the help of fluorescent Ag nanoclusters (Ag NCs). The Ag NCs intrinsically have two emission peaks, among which the long-wavelength emission intensified with decreasing water content due to the aggregation induced emission enhancement (AIEE) effect, but in contrast the short-wavelength emission was relatively insensitive to water content. This fact makes the Ag NCs an ideal colorimetric indicator of water content in organic solvents. A smartphone was applied to take pictures of Ag NC samples and read the R, G, and B values from the images. When the water content increased from 20% to 55% in ethanol, the G/B values displayed a good linear relationship with the water content, and a limit of detection (LOD) of 4.48% was achieved. Moreover, good consistency was observed when the colorimetric fluorescent Ag NCs were applied to detect water content in real samples such as white wine and medical alcohol. These studies demonstrated a convenient and practical method for the detection of water content via a smartphone.

Ratiometric dual-emission of Rhodamine-B grafted carbon dots for full-range solvent components detection

Quick and visual detection of component contents, such as water, in a mixed solvent is important for many practical applications, and a full range detection is especially preferred. In this work, a carbon dots based ratiometric fluorescent sensor was synthesized by grafting fluorescent group (Rhodamine B, RhB) on carbon dots, and the dual emission peaks exhibited a linear ratiometric response with the change of polarity and hydrogen bond of Solvent Hansen solubility parameters. This responsive behavior is attributed to surface state photoluminescence mechanisms, and has been used for the quantitative detection of water content in ethanol with an excellent linear relationship (R² = 0.996), a low detection limit (0.2%), and a full detection range (0-100%). Furthermore, a paper-based ratiometric fluorescence sensing strip is also demonstrated, which exhibits good storage stability and sensitivity. This study suggests that RhB grafted carbon dots could be feasibly and effectively used as ratiometric fluorescent sensors for solvent content detection.

Development of optical sensor for water in acetonitrile based on propeller-structured BODIPY-type pyridine-boron trifluoride complex

A propeller-structured 3,5,8-trithienyl-BODIPY-type pyridine–boron trifluoride complex, ST-3-BF₃, which has three units of 2-(pyridin-4-yl)-3-(thiophen-2-yl)acrylonitrile at the 3-, 5-, and 8-positions on the BODIPY skeleton, was designed and developed as an intramolecular charge transfer (ICT)-type optical sensor for the detection of a trace amount of water in acetonitrile. The characterization of ST-3-BF₃ was successfully determined by FTIR, ¹H and ¹¹B NMR measurements, high-resolution mass spectrometry (HRMS) analysis, thermogravimetry-differential thermal analysis (TG-DTA), photoabsorption and fluorescence spectral measurements, and density functional theory (DFT) calculations. ST-3-BF₃ showed a broad photoabsorption band in the range of 600 to 800 nm, which is assigned to the S₀ → S₁ transition of the BODIPY skeleton with the expanded π-conjugated system over the 2-(pyridin-4-yl)-3-(thiophen-2-yl)acrylonitrile units at the 3-, 5-, and 8-positions onto the BODIPY core. In addition, a photoabsorption band was also observed in the range of 300 to 550 nm, which can be assigned to the ICT band between the 2-(pyridin-4-yl)-3-(thiophen-2-yl)acrylonitrile units at 3-, 5-, and 8-positions and the BODIPY core. ST-3-BF₃ exhibited a characteristic fluorescence band originating from the BODIPY skeleton at around 730 nm. It was found that by addition of a trace amount of water to the acetonitrile solution of ST-3-BF₃, the photoabsorption band at around 415 nm and the fluorescence band at around 730 nm increased linearly as a function of the water content below only 0.2 wt%, which could be ascribed to the change in the ICT characteristics due to the dissociation of ST-3-BF₃ into ST-3 by water molecules. Thus, this work demonstrated that the 3,5,8-trithienyl-BODIPY-type pyridine–boron trifluoride complex can act as a highly-sensitive optical sensor for the detection of a trace amount of water in acetonitrile.

Propeller-structured 3,5,8-trithienyl-BODIPY-type pyridine–boron trifluoride complex, ST-3-BF₃, has been developed as an intramolecular charge transfer (ICT)-type optical sensor for the detection of a trace amount of water in acetonitrile.

N-doped oxidized carbon dots for methanol sensing in alcoholic beverages

Methanol (MeOH) adulteration in alcoholic beverages resulting in irreparable health damage demands highly sensitive and cost-effective sensors for its quantification. As carbon dots are emerging as new biocompatible and sustainable light-emitting detectors, this work demonstrates the hydrothermally prepared nitrogen-doped oxidized carbon dots (NOCDs) as on-off fluorescent nanoprobes to detect MeOH traces in water and alcoholic beverages. The presence of 1% of MeOH in distilled water is found to decrease the NOCD fluorescent emission intensity by more than 90% whereas up to 70% ethanol (EtOH) content changes the signal to within 20% of its initial value. HR-TEM analysis reveals the agglomeration of the nanoprobes suspended in MeOH. Due to their selectivity towards MeOH, the fluorescent nanoprobes were successfully tested using a few MeOH spiked branded and unbranded Mexican alcoholic beverages. Varying degrees of signal quenching is observed from the fluorescent nanoprobes dispersed in different pristine beverages with a detection limit of less than 0.11 v%. Herein, we establish a new perspective towards economically viable non-toxic fluorescent probes as a potential alternative for the detection of MeOH in alcoholic beverages.

Herein, we establish a new perspective towards economically viable non-toxic fluorescent probes as a potential substitute of expensive alternative for the detection of MeOH in alcoholic beverages.

Smilax China-derived yellow-fluorescent carbon dots for temperature sensing, Cu2+ detection and cell imaging

Here, we report an environmentally friendly fabrication strategy of bright yellow fluorescent carbon dots (y-CDs) and construct a rapid and accurate multifunctional sensing platform for the effective detection of temperature and Cu²⁺.

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

Smart, stimuli-responsive, photoluminescent materials that undergo a visually perceptible emission color change in the presence of an external stimulus have long been attractive for use in sensor platforms. When the stimulus is the presence of water, the materials that undergo changes in their light emission properties are called hydrochromic and they can be used for the development of sensors to detect and quantify the water content in organic solvents, which is fundamental for laboratory safety and numerous industrial applications. Herein, we demonstrate the preparation of structurally different carbon dots with tunable emission wavelengths via a simple carbonization approach under controlled temperature and time, involving commercial brown sugar as a starting material. The detailed experimental analysis reveals the "structure-hydrochromic property" relationship of the carbon dots and assesses their capability as effective water sensors. The carbon dots that were proved most efficient for the specific application were then used to identify the presence of water in various aprotic and protic organic solvents via a sensing mechanism based either on the fluorescence wavelength shift or on the fluorescence intensity enhancement, respectively, attributed to the formation of intermolecular hydrogen bonds between carbon dots and water molecules. This is the first demonstration of structurally defined carbon dots in a specific application. The developed carbon dots, apart from being environmentally friendly, were proved to also be biocompatible, enabling this presented process to be a path to "green" sensors.

Dyeing and Functionalization of Wearable Silk Fibroin/Cellulose Composite by Nanocolloidal Array

A wearable silk fibroin/cellulose composite is reported. It is structurally dyed and functionalized by embedding three-dimensional (3D) or two-dimensional poly(methyl methacrylate) and polystyrene nanocolloidal arrays to form opal and inverse opal silk methylcellulose photonic crystal films (SMPCF). The brilliant color of SMPCF is utilized for naked-eye detection of humidity and a trace amount (0.02%) of H₂O content in organic solvents. Volatile organic compounds gases of 5 types were detected. By alternately exposed to organic solvents of methanol, acetonitrile, acetone, ethanol, isopropanol, n-butanol, carbon tetrachloride, and toluene, 3D inverse opal SMPCF displayed an excellent sensing performance with instantaneously color changes from green to red. The organic solvent sensitive SMPCF are wearable by integrated into a rubber glove. This composite has the potential to be used in wearable real-time sensing materials.

Colorimetric and ratiometric fluorescence sensing of water based on 9-methyl pyrido[3,4-b]indole-boron trifluoride complex

In this work, 9-methyl pyrido[3,4-b]indole-boron trifluoride complex, 9-MP-BF3, was designed and developed as a colorimetric and ratiometric fluorescent sensor for the detection of water in the low- and high-water-content regions in solvents. In the low-water-content region, a new photoabsorption band at around 360 nm and a fluorescence band at around 370 nm gradually appeared due to the dissociation of 9-MP-BF3 into 9-methyl pyrido[3,4-b]indole (9-MP) by water molecules with a simultaneous decrease in the photoabsorption band at around 390 nm and the fluorescence band at around 460 nm originating from 9-MP-BF3. In the moderate-water-content region, the photoabsorption band at around 360 nm and the fluorescence band at around 370 nm gradually shifted to a longer wavelength region with an increase in the fluorescence intensity, which could be ascribed to the formation of a hydrogen-bonded complex (9-MP-H2O) with water molecules. Furthermore, in the high-water-content region, two photoabsorption bands at around 305 nm and 390 nm and one fluorescence band at around 460 nm gradually reappeared with simultaneous decrease in the photoabsorption band at around 290 nm and the fluorescence band at around 370 nm, which was attributed to the formation of a hydrogen-bonded proton transfer complex (9-MP-H+) with water molecules. Thus, this work revealed the mechanism of a colorimetric and ratiometric fluorescent sensor based on pyrido[3,4-b]indole-boron trifluoride complex for the detection of water over a wide range from low water content to high water content in solvents.

Highly photoluminescent and temperature-sensitive P, N, B-co-doped carbon quantum dots and their highly sensitive recognition for curcumin

Temperature-sensitive P, N, B-co-doped carbon quantum dots (PNBCDs) synthesized using one-pot method exhibit many excellent features, such as strong fluorescence, good stability and sensitive detection for curcumin.