Self-quenching-resistant solid-state carbon dots for mechanism and applications

Application of polyamide 56 nanofiber membrane loaded with coffee grounds carbon dots in Fe3+ detection

One novel nanofiber membrane was fabricated which could detect Fe3+ with the help of either fluorescence spectrometer or smartphone. Coffee grounds carbon dots (CCDs) were prepared by the solvent-thermal method, followed by the fabrication of CCDs/polyamide 56 (PA56) composite nanofiber membrane through electrospinning process. The 4 % CCDs/PA56 composite nanofiber membrane (FNM4) maintained good fluorescence performance (λem = 554 nm, λex = 470 nm) even after 5-runs quenching-recovery cycles. Its fluorescence could be quenched by Fe3+ with the limit of detection (LOD) of 0.74 μM when the fluorescence spectrometer was used. In addition, FNM4 could also detect Fe3+ by reading its RGB values using one smartphone and the lowest LOD was 4.31 μM when one Apple smartphone was used. The second method is portable to operate and eliminates the constraints of bulky laboratory equipment.

A novel bio-based fluorescent N, P-CDs@CMC/PEI composite hydrogel for sensitive detection and efficient capture of toxic heavy metal ions

To address the serious environmental pollution problems of toxic heavy metal ions in water bodies, a novel fluorescent composite hydrogel N, P-CDs@CMC/PEI with a bio-based polymer matrix of carboxylmethyl cellulose (CMC), polyethylenimine (PEI) as a second interpenetrating network and N, P-doped carbon dots (N, P-CDs) as a fluorescent probe was prepared for simultaneous detection and capture of HMIs by a facile and simple one-step approach. The morphology, chemical structure, swelling ratio, mechanical strength and fluorescence property of these composite hydrogels were studied through varied characterization methods. The composite hydrogel showed sensitive and selective fluorescence response with Hg(II) and Fe(III) and the according LOD values were 0.48 and 0.27 mg L-1, respectively. The relationship between the types of the adsorbent, pH value, HMIs concentration and temperature on the adsorption capacity of these composite hydrogels were studied. The pseudo-second-order model and Langmuir model were applicable to explain the adsorption process of CPH2 for Hg(II) and Cr(VI). The maximum calculated adsorption capacities for the above targeted HMIs by Langmuir model were 846.7 and 289.5 mg g-1, respectively. Coexisting inorganic salts and organic acids in low concentration had little effects on Hg(II) and Cr(VI) removal and the composite hydrogel showed good recyclability and stability for Hg(II) and Cr(VI) removal after four cycles. The electrostatic attraction and coordination covalent bonds were responsible for the adsorption process.

A ratiometric fluorescence amine sensor based on carbon quantum dot-loaded electrospun polyvinylidene fluoride film for visual monitoring of food freshness

A ratiometric fluorescence sensor based on dual-emission carbon quantum dots (CQD) was developed to real time monitor food spoilage. Two hydrophobic electrospun fluorescent films were developed using polyvinylidene fluoride (PVDF) as the film-forming polymer in combination with CQD as the fluorescent probe. The CQD/PVDF film and CQD@PVDF film enabled the analysis of TMA with limits of detection (LODs) of 1.04 μM and 2.1 μM, respectively, and they exhibited excellent stability at 4 °C. By these virtues, the CQD@PVDF film exhibited visible fluorescence color changes from yellow green to blue by real time and nondestructively sensing volatile amines generated from beef, pork and shrimp in a packaging system with high humidity. This strategy provided a simple but useful, non-destructive, robust, and platform to real time monitor food spoilage for intelligent food packaging.

Enhanced Molecularly Imprinted Fluorescent Test Strip for Rapid and Visual Detection of Norfloxacin via a Smartphone

Paper-based test strips with on-site visual detection have become a hot spot in the field of target detection. Yet, low specific surface area and uneven deposition limit the further application of test strips. Herein, a novel "turn-on" ratio of molecularly imprinted membranes (Eu@CDs-MIMs) was successfully prepared based on a Eu complex-doped polyvinylidene fluoride membrane for the selective, rapid and on-site visual detection of norfloxacin (NOR). The formation of surface-imprinted polymer-containing carbon dots (CDs) improves the roughness and hydrophilicity of Eu@CDs-MIMs. Fluorescence lifetimes and UV absorption spectra verified that the fluorescence enhancement of CDs is based on the synergistic effect of charge transfer and hydrogen bonding between CDs and NOR. The fluorescent test strip showed a linear fluorescent response within the concentration range of 5-50 nM with a limit of detection of 1.35 nM and a short response time of 1 min. In comparison with filter paper-based test strips, Eu@CDs-MIMs exhibit a brighter and more uniform fluorescent color change from red to blue that is visible to the naked eye. Additionally, the applied ratio fluorescent test strip was combined with a smartphone to translate RGB values into concentrations for the visual and quantitative detection of NOR and verified the detection results using high-performance liquid chromatography. The portable fluorescent test strip provides a reliable approach for the rapid, visual, and on-site detection of NOR and quinolones.

The emergence and prospects of carbon dots with solid-state photoluminescence for light-emitting diodes

The significant features of carbon dots (CDs), such as bright and tunable photoluminescence, high thermal stability, and low toxicity, endow them with tremendous potential for application in next generation optoelectronics. Despite great progress achieved in the design of high-performance CDs so far, the practical applications in solid-state lighting and displays have been retarded by the aggregation-caused quenching (ACQ) effect ascribed to direct π-π interactions. This review provides a comprehensive overview of the recent progress made in solid-state CD emitters, including their synthesis, optical properties and applications in light-emitting diodes (LEDs). Their triplet-excited-state-involved properties, as well as their recent advances in phosphor-converted LEDs and electroluminescent LEDs, are mainly reviewed here. Finally, the prospects and challenges of solid-state CD-based LEDs are discussed with an eye on future development. We hope that this review will provide critical insights to inspire new exciting discoveries on solid-state CDs from both fundamental and practical standpoints so that the realization of their potential in optoelectronic areas can be facilitated.

Organosilicon-Based Carbon Dots and Their Versatile Applications

Carbon dots (CDs) are a newly discovered type of fluorescent material that has gained significant attention due to their exceptional optical properties, biocompatibility, and other remarkable characteristics. However, single CDs have some drawbacks such as self-quenching, low quantum yield (QY), and poor stability. To address these issues, researchers have turned to organosilicon, which is known for its green, economical, and abundant properties. Organosilicon is widely used in various fields including optics, electronics, and biology. By utilizing organosilicon as a synthetic precursor, the biocompatibility, QY, and resistance to self-quenching of CDs can be improved. Meanwhile, the combination of organosilicon with CDs enables the functionalization of CDs, which significantly expands their original application scenarios. This paper comprehensively analyzes organosilicon in two main categories: precursors for CD synthesis and matrix materials for compounding with CDs. The role of organosilicon in these categories is thoroughly reviewed. In addition, the paper presents various applications of organosilicon compounded CDs, including detection and sensing, anti-counterfeiting, optoelectronic applications, and biological applications. Finally, the paper briefly discusses current development challenges and future directions in the field.

A Smartphone-Integrated Molecularly Imprinted Fluorescence Sensor for Visual Detection of Chlortetracycline Based on N,P-Codoped Carbon Dots Decorated Iron-Based Metal-Organic Frameworks

The residue of chlortetracycline is potentially hazardous to human health; it is meaningful to exploit a portable, rapid, sensitive, and selective method for detection of chlortetracycline (CTC). In this study, a novel fluorescence bionic sensing probe (NH2-MIL-53&N,P-CDs@MIP) was successfully prepared based on the nitrogen and phosphorus codoped carbon dots decorated iron-based metal-organic frameworks combining with molecular imprinted polymer for the detection of CTC. A fluorescence intensity-responsive "on-off" detection of CTC on account of the inner-filter effect (IFE) was achieved by NH2-MIL-53&N,P-CDs@MIP. Under the optimal conditions, the fluorescence quenching degree of NH2-MIL-53&N,P-CDs@MIP presented a good linear relationship with the CTC concentration in the range 0.06-30 μg mL-1 and the limit of detection (LOD) was 0.019 μg mL-1. The fluorescent probe was applied to detect CTC in milk samples, and experimental results showed a good recovery rate (88.73%-96.28%). Additionally, a smartphone-integrated fluorescence sensing device based on NH2-MIL-53&N,P-CDs@MIP was exploited to replace the expensive and bulky fluorescence spectrophotometer for quantitative determination of CTC with the LOD of 0.033 μg mL-1. The sensing system showed high selectivity, strong stability, high specificity, and portability, which provide a great strategy for the quantitative detection of antibiotic residue.

Multiple Stimuli-Response Polychromatic Carbon Dots for Advanced Information Encryption and Safety

Optical information encryption and safety have aroused great attention since they are closely correlated to data protection and information safety. The development of multiple stimuli-response optical materials for constructing large-capacity information encryption and safety is very important for practical applications. Carbon dots (CDs) have many gratifying merits, such as polychromatic emission, diverse luminous categories, and stable physicochemical properties, and are considered as one of the most ideal candidates for information protection. Herein, carbon core, functional groups, solvents, and other crucial factors are reviewed for outputting polychromatic emission of multiple luminous categories. In particular, substrate engineering strategies have been emphasized for their critical role in yielding excellent optical features of multiple luminous categories. High-capacity information encryption and safety strategies are reviewed by relying on the rich optical properties of CDs, such as polychromatic emission, multiple luminous categories of fluorescence, afterglow, and upconversion, as well as external-stimuli-assisted optical changes. Some perspectives for preparing excellent CDs and further developing information security strategies are proposed. This review provides a good reference for the manipulation of polychromatic CDs and the development of next-generation information encryption and safety.