Ferric ion detection mechanism of a dicarboxylic cellulose nanocrystal and a 7-amino-4-methylcoumarin based fluorescent chemosensor

A flavonol-labelled cellulose fluorescent probe combined with composite fluorescent film imaging and smartphone technology for the detection of Fe3

Fe3+ is one of the most widely distributed and abundant elements on earth. Realizing efficient and real-time monitoring of Fe3+ is of great significance for the natural environment and the health of living organisms. In this paper, a flavonol-labelled cellulose-based fluorescent probe (ACHM) was synthesized by using dialdehyde cellulose (DAC) as the backbone and combining with flavonol derivatives (AHM - 1). The mechanism of recognizing Fe3+ was verified by characterizing the structure of ACHM by NMR, HRMS (High Resolution Mass Spectrometry), FTIR (Fourier Transform Infrared Spectroscopy), XRD (X-ray Diffraction), TG (Thermogravimetry) and SEM (Scanning Electron Microscopy). The H2O solution of the probe ACHM showed good fluorescence properties. It has quenching fluorescence properties for Fe3+, with a low limit of detection (LOD) of 0.10 μM and a fast response time of only 20 s. In addition, in order to expand the application range of the probe, ACHM was prepared as a fluorescent composite film with an average tensile strength of 32.9 MPa and an average elongation at break of 3.39 %. It shows its superiority in mechanical properties. The probe also demonstrated its practical application value for detecting Fe3+ in smartphone imaging applications.

Light and pH dual-responsive spiropyran-based cellulose nanocrystals

Reversibly light and pH dual-responsive spiropyran-based cellulose nanocrystals (SP-CNCs) is synthesized by the attachment of carboxyl-containing spiropyran (SP-COOH) onto cellulose nanocrystals (CNCs). The resulting structure and properties of SP-CNCs are examined by Fourier transform infrared spectroscopy (FT-IR), elemental analysis, transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic laser light scattering (DSL), ζ-potential measurements and ultraviolet-visible (UV-Vis) light absorption spectroscopy. SP-CNCs exhibit excellent photochromic and photoswitching properties. Spiropyran moieties on SP-CNCs can be switched between open-ring merocyanine (MC) and closed ring spiropyran (SP) forms under UV/Vis irradiation, leading to color changes. Moreover, SP-CNCs display improved photoresponsiveness, photoreversibility, fatigue resistance, and stability in DMSO than in H₂O. We further investigate the pH-responsive behavior of SP-CNCs in H₂O. SP-CNCs aqueous solution display different colors at different pH values, which can be directly observed by naked eye, indicating that SP-CNCs can function as a visual pH sensor. These results suggest that light and pH dual-responsive SP-CNCs possess great potential for applications in reversible data storage, sensing, optical switching and light-controlled nanomaterials.

Isolation and characterization of cellulose nanocrystals from Chinese medicine residues

Nanocellulose has become a vital material with excellent and crucial properties in the field of nanotechnology and advanced materials science. Plant-based traditional Chinese medicines are mostly plant rhizomes, which contain a large amount of cellulose, hemicellulose, and lignin. In this study, carboxylated cellulose nanocrystals (CNCs) were prepared from traditional Chinese medicine residues (CMR) by sequential periodate-chlorite oxidation without mechanical treatment. The obtained nanocelluloses were analyzed by transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and X-ray diffractometry (XRD); the carboxyl content and specific surface area were also measured, simultaneously. XRD results revealed that the crystallinity index decreased after sequential oxidation; however, the cellulose I structure was maintained. From the morphology analysis, the average length and width of CNCs were 139.3 and 10 nm, respectively. From the FTIR analysis, with the particle size decreasing, hydrogen bonds were broken and recombined. TGA results showed that the thermal property was decreased with a reduction of nanocellulose particle size and crystallinity index. This study is the first to refine utilization of traditional Chinese medicine residues as a potential source of cellulose, that is, to prepare nanocellulose efficiently with high carboxyl content which finds its application in nanomaterials.

Research on a Fiber Optic Oxygen Sensor Based on All-Phase Fast Fourier Transform (apFFT) Phase Detection

Fiber optic oxygen sensors based on fluorescence quenching play an important role in oxygen sensors. They have several advantages over other methods of oxygen sensing-they do not consume oxygen, have a short response time and are of high sensitivity. They are often used in special environments, such as hazardous environments and in vivo. In this paper, a new fiber optic oxygen sensor is introduced, which uses the all-phase fast Fourier transform (apFFT) algorithm, instead of the previous lock-in amplifier, for the phase detection of excitation light and fluorescence. The excitation and fluorescence frequency was 4 KHz, which was conducted between the oxygen-sensitive membrane and the photoelectric conversion module by the optical fiber and specially-designed optical path. The phase difference of the corresponding oxygen concentration was obtained by processing the corresponding electric signals of the excitation light and the fluorescence. At 0%, 5%, 15%, 21% and 50% oxygen concentrations, the experimental results showed that the apFFT had good linearity, precision and resolution-0.999°, 0.05° and 0.0001°, respectively-and the fiber optic oxygen sensor with apFFT had high stability. When the oxygen concentrations were 0%, 5%, 15%, 21% and 50%, the detection errors of the fiber optic oxygen sensor were 0.0447%, 0.1271%, 0.3801%, 1.3426% and 12.6316%, respectively. Therefore, the sensor that we designed has greater accuracy when measuring low oxygen concentrations, compared with high oxygen concentrations.

Application of Plackett–Burman Design for Spectrochemical Determination of the Last-Resort Antibiotic, Tigecycline, in Pure Form and in Pharmaceuticals: Investigation of Thermodynamics and Kinetics

Tigecycline (TIGC) reacts with 7,7,8,8-tetracyanoquinodimethane (TCNQ) to form a bright green charge transfer complex (CTC). The spectrum of the CTC showed multiple charge transfer bands with a major peak at 843 nm. The Plackett–Burman design (PBD) was used to investigate the process variables with the objective being set to obtaining the maximum absorbance and thus sensitivity. Four variables, three of which were numerical (temperature—Temp; reagent volume—RV; reaction time—RT) and one non-numerical (diluting solvent—DS), were studied. The maximum absorbance was achieved using a factorial blend of Temp: 25 °C, RV: 0.50 mL, RT: 60 min, and acetonitrile (ACN) as a DS. The molecular composition that was investigated using Job’s method showed a 1:1 CTC. The method’s validation was performed following the International Conference of Harmonization (ICH) guidelines. The linearity was achieved over a range of 0.5–10 µg mL−1 with the limits of detection (LOD) and quantification (LOQ) of 166 and 504 ng mL−1, respectively. The method was applicable to TIGC per se and in formulations without interferences from common additives. The application of the Benesi–Hildebrand equation revealed the formation of a stable complex with a standard Gibbs free energy change (∆G°) value of −26.42 to −27.95 kJ/mol. A study of the reaction kinetics revealed that the CTC formation could be best described using a pseudo-first-order reaction.