Currently, the technologies accompanying the usage of waste materials for the fabrication of innovative useful materials have been significantly advanced. For the same purpose, a possible sustainable approach was demonstrated for the utilization of jute caddies, known as jute industry waste. From the industrial waste, carbon dots (CDs) were sonochemically prepared, followed by their surface modification with benzalkonium chloride (BZC) to yield waste jute-derived fluorescent surface-quaternized CDs (JB-CDs), which exhibit excellent water solubility, excitation-dependent emission, and good photostability, and were utilized as a fluorescent nanoswitch to detect inorganic pollutants, such as chromium (VI) [Cr­(VI)] ions, in aqueous solutions. JB-CDs can detect Cr­(VI) concentrations as low as 0.03 μM through luminescence quenching (“turn-off”) and further recover their fluorescence (“turn-on”) selectively for sensing ascorbic acid (AA), compared with other metal ions and biomolecules tested. The present technique has the advantages of fast response time and high selectivity and sensitivity in practical applications. JB-CDs were tested against a Gram-negative bacterium, Escherichia coli, and a Gram-positive bacterium, Staphylococcus aureus, to confirm their bactericidal activity. The results indicated that JB-CDs substantially inhibited the growth of the tested bacteria. Besides this, JB-CDs played the role of a nanovehicle to exemplify the release study of a model drug ciprofloxacin. It was observed that the surface-quaternized JB-CDs showed a pH-responsive release behavior, where the release behavior was found to be better controlled at pH 7.4 than at pH 5.2 and 6.8. The synthesis of such a fluorescent nanobutton, stimuli-responsive drug release, and antibacterial nanomaterial using a sustainable material such as jute industrial waste can pave the path for a smart multifunctional material.

Fluorescent carbon dots (CDs) play a versatile role in materials science. Herein, we have developed alginate-derived nitrogen-doped CDs as a drug carrier and a toughening agent for hydrogels by a microwave-assisted method. In the first phase of work, we carried out covalent conjugation of the drug onto the CD surface for controlled delivery of drug molecules, and in the second phase of work, we demonstrated how CDs could act as a toughening agent as well as a viscosity modifier for poly­(acrylic acid-co-methacrylamide) copolymer hydrogels. The hydrogels were evaluated by Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy, and solid-state nuclear magnetic resonance. The hybrid hydrogels have been tested to be mechanically robust with extraordinary stretchability (∼1200% elongation at break), recoverable to the original position (low permanent set), tunable water uptake, and thixotropic character in dynamic stress. The crosslinked structure has been evaluated through void calculation revealing gradual densification of the network with increasing CD content. Exceptional gel strength (ratio of elastic modulus to loss modulus; G′/G″) has been achieved from analogous crosslinking made by CDs. The delayed network rupturing and superstretchability could make this material a good choice for soft biomaterials and soft robotics.

No abstract

The synthesis of nitrogen-doped carbon dots (N@CDs) was accomplished by a hydrothermal process using meta-phenylenediamine as a source of carbon and nitrogen. As prepared N@CDs exhibited bright blue color fluorescence emission (λ ex = 340 nm and λ em = 420 nm) with a quantum yield of 12%. Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus were eradicated by N@CDs with a minimum inhibition concentration (MIC) of 1 and 0.75 mg/mL, respectively. The N@CDs were also proven as nanovesicles for drug molecules where the drug release displayed a sustained time-dependent profile at the physiological condition. The release of ciprofloxacin as a model drug was governed by the Korsmeyer-Peppas model, indicating ∼60% of its release from the N@CD conjugated drug system at the physiological pH. Selective analysis of trinitrophenol (TNP), a popular explosive, was achieved by fluorescence quenching of N@CDs, compared favorably with other nitrophenols. An estimated detection limit of TNP was 2.45 μM with a linear response spanning from 1 to 75 μM.

Carbon dots (CDs) were obtained from medicinal turmeric leaves (Curcuma longa) by a facile one-step hydrothermal method and evaluated for their bactericidal activities against two gram-negative; Escherichia coli, Klebsiella pneumoniae, and two gram-positive counterparts; Staphylococcus aureus, S. epidermidis. The CDs exhibited spherical shapes with a mean size of 2.6 nm. The fluorescence spectra of CDs revealed intense fluorescence at λex/em = 362/429 nm with a bright blue color in an aqueous solution. The CDs showed strong photostability under various environmental conditions (pH, salt, and UV-radiation). The complete bactericidal potency of CDs was 0.25 mg/mL for E.coli and S. aureus after 8 h of exposure, while for K. pneumoniae, and S. epidermidis, the CDs at 0.5 mg/mL good antibacterial effect within 8 h and complete eradication after 24 h of exposure is observed. The release of reactive oxygen species played a crucial role in the death of the bacterial cell. The present study provides a strategy for the preparation of CDs from a medicinal plant and their potential antibacterial activities against four common contagious pathogens.