Jie Yi

Carbon Nanodots-Based Fluorescent Turn-On Sensor Array for Biothiols

Biothiols play important roles in biological processes. In this study, a novel sensor array-based method was proposed to detect and differentiate biothiols. The sensor array was constructed using three kinds of Ag+-sensitive carbon nanodots (CDs). The CDs were synthesized with amino acids and urea as carbon sources via a simple microwave method. Results revealed that Ag+ can bind with CDs and depress the fluorescence of CDs, while the subsequently joined biothiols can take Ag+ away from CDs and recover the fluorescence of CDs. Due to the different binding ability between Ag+ and various CDs, as well as Ag+ and various biothiols, the CD-Ag+ array exhibits a unique pattern of fluorescence variations when interacting with six biothiol samples (cysteamine, dithiothreitol, mercaptosuccinic acid, glutathione, mercaptoacetic acid, and mercaptoethanol). Principal component analysis (PCA) was applied to analyze the pattern and generate a clustering map for a clearer identification of these biothiols. PCA can also be employed to simplify the established three-sensor array into a two-sensor array. Both the three- and two-sensor arrays can identify these biothiols in a wide biothiol concentration range (>10 μM).

Synthesis and self-assembly of new amphiphilic thermosensitive poly(N-vinylcaprolactam)/poly(ε-caprolactone) block copolymers via the combination of ring-opening polymerization and click chemistry

New amphiphilic thermosensitive poly(N-vinylcaprolactam)/poly(ε-caprolactone) (PNVCL-b-PCL) block copolymers were synthesized by click reaction with alkynyl-terminated poly(N-vinylcaprolactam) (PNVCL-C ≡ CH) and azido-terminated poly(ε-caprolactone) (N3-PCL). The structures of the polymers were determined by proton nuclear magnetic resonance spectroscopy (1H NMR) and gel permeation chromatography (GPC) measurements. The fluorescence technique was used to determine the critical micelle concentrations (CMC) of copolymer solutions. The factors affecting the lower critical solution temperature (LCST) of the copolymers were studied by UV-visible analysis. The diameters and distribution of the micelles were characterized by dynamic light scattering (DLS), and their shapes were observed by transmission electron microscopy (TEM). The results showed that these copolymers could self-assemble into nano-micelles in water. The CMC values of the copolymer solutions and the sizes of micelles reduced with increasing proportion of hydrophobic parts. TEM images demonstrated that the micelles are all spherical. On the other hand, the UV–visible measurements showed that these block copolymers exhibit a reproducible temperature-responsive behavior with a LCST that is tunable by block composition.

Microwave synthesis of carbon dots with multi-response using denatured proteins as carbon source

A new synthetic strategy has been developed for facile and green fabrication of highly photoluminescent carbon dots (CDs) via a one-step microwave treatment of the denatured proteins in aqueous solution. The as-prepared CDs, possessing excellent up-conversion fluorescent properties, can serve as a multifunctional fluorescent nanosensor for pH and temperature. CDs prepared from various protein carbon source can be sensitive to a specific metal ion.

Thermo/pH Dual Responsive Mixed-Shell Polymeric Micelles Based on the Complementary Multiple Hydrogen Bonds for Drug Delivery

Thermo/pH dual responsive mixed-shell polymeric micelles based on multiple hydrogen bonding were prepared by self-assembly of diaminotriazine-terminated poly(ɛ-caprolactone) (DAT-PCL), uracil-terminated methoxy poly(ethylene glycol) (MPEG-U), and uracil-terminated poly(N-vinylcaprolactam) (PNVCL-U) at room temperature. PCL acted as the core and MPEG/PNVCL as the mixed shell. Increasing the temperature, PNVCL collapsed and enclosed the PCL core, while MPEG penetrated through the PNVCL shell, thereby leading to the formation of MPEG channels on the micelles surface. The low cytotoxicity of the mixed micelles was confirmed by an MTT assay against BGC-823 cells. Studies on the in vitro drug release showed that a much faster release rate was observed at pH 5.0 compared to physiological pH, owing to the dissociation of hydrogen bonds. Therefore, the mixed-shell polymeric micelles would be very promising candidates in drug delivery systems.

Multicompartment micelles based on hierarchical co-assembly of PCL-b-PEG and PCL-b-P4VP diblock copolymers

Multicompartment micelles are prepared via the hierarchical co-assembly of two diblock copolymers, poly(e-caprolactone)-b-poly(ethylene glycol) (PCL-b-PEG) and poly(e-caprolactone)-b-poly(4-vinylpyridine) (PCL-b-P4VP) in aqueous solution. These two polymers first assemble into mixed shell micelles through hydrophobic interaction among PCL chains. PCL chains form the micellar core, while PEG and P4VP chains form the micellar shell. Regulating the pH value above the pKa of P4VP can induce hydrophobic phase-segregated P4VP patches forming on the surface of mixed shell micelles. When hydrophilic PEG chains cannot stabilize theses micelles with hydrophobic patches, they will furthermore assemble as the subunits into MMs with different morphologies. These MMs can be revealed by transmission electron microscopy through P4VP chains positive staining.

Nucleobase chemosensor based on carbon nanodots

A facile and sensitive fluorescence protocol for nucleobase detection was developed based on carbon nanodot (CD) chemosensors. The novel fluorescent CDs were prepared using four kinds of nucleobases (including adenine, guanine, thymine and cytosine) as separate carbon sources via simple hydrothermal strategy. The quantum yield of adenine CDs (A-CDs), guanine CDs (G-CDs), thymine CDs (T-CDs) and cytosine CDs (C-CDs) was checked as 15.1%, 28.3%, 10.6% and 11.7%, respectively. Four CDs can recognize their complementary nucleobases based on the principle of complementary base pairing. Their fluorescence was linearly quenched with the increase of nucleobase concentrations under optimal conditions. Combining the calibration curve, quantitative assay of nucleobase in solution can be realized. For example, A-CDs could determine thymine in the concentration range of 2-20mM with a detection limit of ca. 0.053mM, and the linear equation is fitting as (I0-I) / I = 0.01961 × CT(mM) + 0.01756 (R2 = 0.994). Thymine can induce the fluorescence lifetime of A-CDs decreasing from 5.58 to 3.34ns, indicating a dynamic quenching mechanism. The novel nucleobase sensors were also evaluated in specific solution environment. A-CDs showed a relatively minor relative standard deviation (< 4.0%) in fetal calf serum solution, indicating a high accuracy and credibility of the sensing system. In view of the excellent sensitivity, preferable biocompatibility as well as simple constructing method, the sensing platform derived from the nucleobase-based CDs present great potential in biological sensing applications.

Synthesis and self-assembly of new amphiphilic thermosensitive poly(N-vinylcaprolactam)/poly(d,l-lactide) block copolymers via the combination of ring-opening polymerization and click chemistry

New amphiphilic thermosensitive poly(N-vinylcaprolactam)/poly(d,l-lactide) (PNVCL-b-PLA) block copolymers were synthesized by combining ring-opening polymerization of d,l-lactide (LA), free radical polymerization of N-vinylcaprolactam, and subsequent click chemistry. Their structures were characterized by IR, 1H NMR, 13C NMR, and GPC measurements. The fluorescence technique showed that these copolymers could self-assemble into nano-micelles in water and the CMC values of the copolymer solutions reduced with the increasing of the proportion of hydrophobic segments. Dynamic light scattering demonstrated that the sizes of micelles reduced with the increasing of the proportion of hydrophobic segments. Transmission electron microscopy images demonstrated that all micelles were spherical. On the other hand, the UV–vis measurement showed that these block copolymers exhibited a reproducible temperature-responsive behavior with a lower critical solution temperature that was tunable by the block composition and the concentration of the copolymers.

Bioinspired fabrication of macroporous calcium carbonate crystals mediated by thermoresponsive copolymers

A new thermoresponsive copolymer, poly(N-vinylcaprolactam)-β-cyclodextrin (PNVCL–β-CD), was synthesized by click chemistry and applied in regulating the crystallization of CaCO3. At low temperature (25 °C), the copolymers self-assembled into micelles with β-CD as the core and PNVCL as the shell. The micelles with different PNVCL chain lengths induced the formation of crystals with elongated, typical rhombohedral and surface concaved morphologies. At high temperature (50 °C), the micelles assembled into compact and regular aggregates with sizes of about 1 μm. The copolymer aggregates were encapsulated in the crystals and removed after cooling and rinsing. Porous, cheese-like crystals were obtained. This study could enrich our knowledge of biomineralization and offer a convenient scheme for synthesis of porous inorganic materials.