Chloramphenicol-imprinted polychitosan bounded with carbon dots as fluorescent sensor, dispersive sorbent, and drug carrier.

Chitosan, an abundant natural polysaccharide, was conjugated with carbon dots (CDs) and self-polymerized with chloramphenicol (CAP) templates to synthesize CD-incorporated and molecularly CAP-imprinted polychitosan (CD-MIC). The CD-MIC was used for fluorescent sensing, dispersive sorption, and dosage release of CAP at different pH levels. The sphere of action mechanism, approved by emission and excitation fluorescence, UV-Vis absorption, and fluorescence lifetime measurements, regulated the fluorescence static quenching. By the Perrin model, the quenching extent was linearly correlated to CAP within 0.17 - 33.2 µM (LOD = 37 nM) at pH 7.0. With an imprinting factor of 3.1, the CD-MIC was more selective for CAP than CD, although it was less sensitive to CAP. The recoveries of 5.0 µM CAP from milk matrix were 95% (RSD = 2.3%) for CD-MIC probes and 62% (RSD = 4.5%) for CD. The Langmuir and pseudo-second-order models preferably described the isothermal and kinetic sorptions of CAP into the imprinted cavities in CD-MICs, respectively. The Weber - Morris kinetic model showed three stages involved in intraparticle diffusion, which was pH-dependent and gradually arduous at the later stage, and showed external diffusion partly engaged in the diffusion mechanism. The 20 - 70% of CAP formulated in CAP-embedded CD-MICs were released in 8 - 48 h. The release percentage was lower at pH 7.0 than at pH 5.0 and 9.0, but the equilibrium time was shorter. At pH 7.0, the release percentage reached 45% at 10 min and slowly increased to 51% at 24 h.

Fluorescence determination of tannic acid imprinted in conjugated hypercrosslinked polymers by Friedel-Crafts acylation.

A molecularly imprinted hypercrosslinked polymer (HCP) was synthesized from the polymerization of mesitylene monomer, terephthaloyl chloride crosslinker, and tannic acid (TA) template through FeCl3-catalyzed Friedel-Crafts acylation. The TA-imprinted HCP (TAHCP) was capable of IUPAC Type I mesoporosity, with specific surface area of 1258 m2 g-1, monolayer adsorption capacity of 289 cm2 g-1, pore sizes ranging from 4.4 to 12.6 Å, amorphous morphology, and characteristic absorption and emission bands. The extended π-conjugation framework of TAHCP was endowed with 385-nm fluorescent emission at 310-nm excitation. The fluorescence intensity of TAHCP could be dynamically quenched by TA and was linearly correlated with 20-1000 nM TA concentrations on the Stern-Volmer plot in the optimized conditions of pH 5.5 buffer, 100 µg mL-1 TAHCP, and 3.5 min equilibrium. The relative standard deviation (RSD) for 50 nM TA was 3.4% (n = 5), and the limit of detection was 6.2 nM based on the 3σ of the TA blanks). For 50nM TA, the imprinted factor was calculated to be 7.8, and the selectivity for 250 nM interferents, including ions, organic acids, saccharides, amino acids, and caffeine, which are commonly found in beverages, was 7.5-9.5, except for gallic acid (1.2). The recoveries of TA spiked in tea and juice beverages at three levels (10-150 nM) were 93.6-101.9% (RSD = 3.6-4.3%).

Diltiazem-imprinted porphyrinic covalent organic frameworks as solid-phase extractants and fluorescent sensors.

Diltiazem, which is a calcium channel blocker, is involved in the formation of covalent organic frameworks (COFs) through the Schiff base reaction of tetrakis (4-aminophenyl)-porphine (TAPP) and dihydroxynaphthalene-dicarbaldehyde (DHNDC) and the next enol-to-keto tautomerization. The diltiazem-imprinted COFs (DICOFs) were optimally formed using Sc(OTf)3 as the catalyst, TAPP/DHNDC/diltiazem in a molar ratio of 2/3/4, N-methylpyrrolidone/mesitylene (v/v = 3/5) as the porogen, and a 1-h reaction with a high imprinting factor of 10.5 compared to the nonimprinted counterparts (NICOFs). The optimized DICOF exhibited a more amorphous XRD pattern, a larger surface area (1650 vs. 930 m2/g), a larger pore volume (1.33 vs. 0.75 cm3/g), and a finer porous SEM feature than NICOF. The selectivity of NICOF toward diltiazem and diazepam at 250 nM (α = 1.03, RSD = 1.3%) was smaller than the selectivity of DICOF (α = 2.94, RSD = 1.6%). The diltiazem samples (5.0-300 ng mL-1) dynamically quenched the fluorescence of 15 µg/mL DICOF in 50 mM phosphate buffer at pH 6.5 at 8.0 min equilibrium; thus, Stern-Volmer plots were linearly constructed for sensing diltiazem with an LOD of 3.4 ng mL-1 and an LOQ of 10.2 ng mL-1. According to the plots, 30 ng mL-1 diltiazem solutions that were diluted from 30 mg-specified tablets had an average measured concentration of 29.5 ng mL-1 (σ = 1.3% and n = 5). In addition to application as fluorescent sensors, DICOFs (30 mg) could be used as dispersive extractants to recover 95.2% of 0.6 ng mL-1 diltiazem from 25 mL phosphate buffer with quadruplicate uses of 0.5 mL methanol/acetic acid (v/v = 9/1) as the eluent. Langmuir and pseudo-second-order models were fitted to the isothermal and kinetic sorption mechanisms, respectively. The maximum sorption capacity of DICOF was ten times larger than that of NICOF (156 vs. 15.2 mg/g). The interday recoveries of 0.6 ng mL-1 spiked in 20-fold diluted human urine, and 60-fold diluted human serum were 93.2% and 90.6%, respectively.

Imprinted ß-ketoenamine-linked covalent organic frameworks as dispersive sorbents for the fluorometric determination of timolol.

Timolol accompanied the formation of fluorescent ß-ketoenamine-linked covalent organic frameworks (COFs) via the Sc(Tof)3-catalyzed condensation of derivated carbaldehyde and hydrazide in a 1,4-dioxane/mesitylene porogen to construct timolol-imprinted COFs (TICOFs). With high imprinting factors, the synthesis-optimized TICOFs were characterized by fluorescence, UV-Vis spectrometry, X-ray diffraction, N2 adsorption/desorption analyses, scanning electron microscopy, and FTIR spectrometry. The TICOF fluorescence measured at 390 nm/510 nm is dynamically quenched by timolol and was thus utilized to quantify timolol in a linear range of 25-500 nM with a LOD of 8 nM. The TICOF recovered 99.4% of 0.5% timolol maleate in a commercial eye drop (RSD = 1.1%, n = 5). In addition, TICOF was used as a dispersive sorbent to recover 95% of 2.0 nM timolol from 20 mg of TICOF in 25 mL phosphate buffer. Dilution factors of 25 and 75 were the maximum tolerated proportions of the urine and serum matrix spiked with 2.0 nM timolol to reach recoveries of 92.4% and 90.3%, respectively.

Effective and Efficient Pretreatment of Polyimide Substrates by Capacitively Coupled Plasma for Coating the Composites of Tetracycline-Imprinted Polymers and Quantum Dots: Comparison with Chemical Pretreatment.

Composites of tetracycline (Tc)-imprinted polymethacrylates and quantum dots have been coated on chemically pretreated polyimide substrates (PIs) as fluorescent sensors. In this study, PIs were pretreated by capacitively coupled plasma (CCP) before coating the same composites on them. For the first time, to fabricate sensors by plasma modification of PIs, the CCP conditions, including plasma gas, flow rate, radio frequency generation power, and duration time, the fabrication details, including coating, baking, and stripping steps, and the sample loading process were optimized to perform a linear decrease in fluorescent intensity with Tc concentrations in the range of 5.0-3000 µM (R2 = 0.9995) with a limit of detection of 0.2 µM (S/N = 3, relative standard deviation (RSD) = 2.2%). The selectivity of the stripped PIs was evaluated by the imprinting factors (IFs) for Tc (IF = 7.2), other Tc analogues (IF = 3.4-5.3), and steroids (IF ≈ 1) and by the recoveries of 5.0 µM Tc from bovine serum albumin at 300 µg∙mL-1 (98%, RSD = 3.2%), fetal bovine serum at 1.5 ppt (98%, RSD = 2.8%), and liquid milk (94.5%, RSD = 5.3%). The superiority of the present plasma-treated-based sensor over the previous chemically-treated one in fabrication efficiency and detection effectiveness was clear.

Fluorometric determination of amifostine and alkaline phosphatase on amphiprotic molecularly imprinted silica crosslinked with binary functional silanes and carbon dots.

A silica-based molecularly imprinted polymer (MIP) formed by functional silanes (basic 3-aminopropyltriethoxysilane (APTES) and acidic 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (CSPTMS)) was crosslinked with carbon dots (CDs) to develop a fluorescent sensor toward an amphiprotic template, amifostine (AMF). The CDs were synthesized by hydrothermal carbonization of succinic acid and an ionic liquid and possessed hydroxyl and pyrrolic functional groups, which enabled the CDs to be derivatized with silanes for subsequent sol-gel polymerization. Except for the CDs derivatized with tetraethoxysilane, CD-APTES, CD-CSPTMS, and CD-APTES/CSPTMS (molar ratio = 1/1) all presented distinct fluorescence dynamic quenching when interacted with AMF. However, APTES/CSPTMS was selected as the sol-gel monomer for the formation of MIP because its quenching ratio and imprinted factor were the highest among the CD-silane-MIPs. Moreover, 0.5 mg/mL of CD-APTES/CSPTMS -MIP in pH 7.5 buffer was used to quantify AMF (0.5-200 nM, LOD = 0.15 nM) and alkaline phosphatase (ALP) (2-150 µU/mL, LOD = 0.5 µU/mL), which activates the metabolism of AMF, and the calibration curves of AMF and ALP were determined via fluorescence quenching and restoration, respectively. The recoveries of 1, 10, and 60 nM AMF from 360-fold-diluted human serum solutions were 95, 104, and 103%, respectively, with RSD values that were lower than 4.2%. The average ALP activity of the original human serum was determined to be 32.1 U/L (RSD = 5.41%).

Excitation-independent dual emissions of carbon dots synthesized by plasma irradiation of ionic liquids: Ratiometric fluorometric determination of norfloxacin and mercury(II).

The capacitively coupled plasma (CCP) discharge of an ionic liquid solution of citric acid produces carbon dots (CDs) with excitation-independent fluorescent dual-emissions peaking at 410 nm and 480 nm. The intensity of the purple photoluminescence at 410 nm increases with (a) the flow rate of O2 plasma gas supply from 2.0 to 30 standard cubic centimeters per minute (sccm), (b) the 2-h exposure of the CDs to 254 nm light, and (c) the 8-h immersion of the CDs in a solution of NaBH4. The UV exposure and the hydride immersion reduce the fluorescence intensity peaking at 480 nm, which is highest at 5.0 and 10 sccm. The two emissive states were revealed by UV-vis absorption, XPS spectra, and time-resolved fluorescence. Control of the O2 flow rate can simply tune the ratiometric fluorescence of the CCP-CDs. The CDs obtained from 5 and 30 sccm O2 supplies present a high-intensity ratio (I480 nm/I410 nm ≈ 3.35) and a low one (≈ 0.48), respectively. The 480 nm fluorescence of the former CDs is quenched by mercury(II) ions in the 0.2 to 50 µM concentration range. The 410 nm fluorescence of the latter CDs is enhanced by norfloxacin in the 25 nM to 1.0 µM concentration range. The detection limits are 75 nM for Hg(II) and 7.3 nM for norfloxacin. Graphical abstract Schematic presentation of the effect of the oxygen flow rate in capacitively coupled radio frequency (RF) plasma on the formed CDs. The emission can be quenched by Hg2+ or enhanced by norfloxacin.

Capacitively Coupled Plasma Discharge of Ionic Liquid Solutions to Synthesize Carbon Dots as Fluorescent Sensors.

Oxygen and nitrogen capacitively coupled plasma (CCP) was used to irradiate mixtures of aliphatic acids in high boiling point solvents to synthesize fluorescent carbon dots (C-dots). With a high fluorescence intensity, the C-dots obtained from the O2/CCP radiation of a 1-ethyl-3-methylimidazolium dicyanamide ionic liquid solution of citric acid were characterized with an average diameter of 8.6 nm (σ = 1.1 nm), nitrogen and oxygen bonding functionalities, excitation-independent emissions, and upconversion fluorescence. Through dialysis of the CCP-treated C-dots, two emissive surface states corresponding to their respective functionalities and emissions were identified. The fluorescence spectrum of the CCP-treated C-dots was different from that of the microwave irradiation and possessed higher intensity than that of hydrothermal pyrolysis. By evaluation of the fluorescence quenching effect on flavonoids and metal ions, the CCP-treated C-dots showed a high selectivity for quercetin and sensitivity to Hg2+. Based on the Perrin model, a calibration curve (R² = 0.9992) was established for quercetin ranging from 2.4 µM to 119 µM with an LOD (limit of detection) = 0.5 µM. The quercetin in the ethanol extract of the sun-dried peel of Citrus reticulata cv. Chachiensis was determined by a standard addition method to be 4.20 ± 0.15 mg/g with a matrix effect of 8.16%.