Hailong Peng

Label-free colorimetric detection of trace cholesterol based on molecularly imprinted photonic hydrogels

A novel colorimetric sensor for cholesterol assay was constructed by combining a molecular imprinting technique with photonic crystals. The molecularly imprinted photonic hydrogel (MIPH) film was prepared by a non-covalent, self-assembly approach using cholesterol as a template molecule, and exhibited a highly ordered three-dimensional macroporous structure characterized by scanning electron microscopy under the optimized imprinting conditions. Various factors affecting rebinding of cholesterol are discussed along with recognition specificity studies on its analogues of stigmasterol and ergosterol through estimation of UV-Vis and electrochemical impedance spectroscopy. The MIPH film generated a significantly readable optical signal directly self-reporting within less than 2 min upon binding cholesterol. The colorimetric measurement of cholesterol concentration strongly relies on the fact that the blue shift effect of the Bragg diffraction peak of the MIPH is gradually enlarged with the increase of cholesterol amounts. The detection level approached 10−13 g mL−1, which is comparable to that of fluorescence measurements. The simultaneous possession of high selectivity, high sensitivity, high stability, easy operation and being label-free enables this sensor to be potentially applicable for rapid on-site detection of trace cholesterol.

Selective solid-phase extraction of Sudan I in chilli sauce by single-hole hollow molecularly imprinted polymers.

A new single-hole hollow molecularly imprinted polymer (SHH-MIP) was prepared by multistep seed swelling polymerization using Sudan I as template molecule and successfully applied to selective solid-phase extraction (SPE) of Sudan dyes in chilli sauce samples. The polymers possessed high specific surface area obtained by nitrogen adsorption and good thermal stability without decomposition lower than 380 °C by thermogravimetry analysis. Much higher binding capacity was exhibited than with irregular solid MIP prepared by bulk polymerization, because most of the binding sites were located in the surface of the polymers, facilitating template removal and mass transfer. Accordingly, the SHH-MIP was employed as SPE adsorbent for chilli sauce analysis and offered high recoveries for Sudan I in the range of 87.5-103.4% with the precision of 1.94-5.33% at three spiked levels. The SHH-MIP with high selectivity and high stability was demonstrated to be potentially applicable for high selective preconcentration and determination of trace Sudan dyes in complicated samples.

A pH-responsive nano-carrier with mesoporous silica nanoparticles cores and poly(acrylic acid) shell-layers: Fabrication, characterization and properties for controlled release of salidroside

A novel pH-responsive nano-carrier MSNs-PAA, possessing mesoporous silica nanoparticles (MSNs) cores and poly(acrylic acid) (PAA) shell-layers, was developed for controlled release of salidroside. The vinyl double bonds modified MSNs were synthesized by using cetyltrimethylammonium bromide (CTAB) as templates, tetraethyl orthosilicate (TEOS) as silicon source, and 3-(trimethoxylsilyl) propyl methacrylate (MPS) as surface modification functionalities. The pH-responsive layers of PAA were grafted onto the vinyl double bonds of the MSNs via precipitation polymerization, producing the MSNs-PAA with a hollow cubic core and mesoporous shell with penetrating pore channels. The characteristic results also showed that PAA was successfully grafted onto the surface of the MSNs. The MSNs-PAA was investigated as carriers for loading and regulating the release of salidroside in different pH solutions for the first time. The results demonstrated that the PAA layers on the surface of MSNs-PAA exhibited opened and closed states at different pH values, and thus could regulate the uptake and release of salidroside. The application of such pH-responsive nano-carrier might offer a potential platform for controlled delivery and increasing the bioavailability of drugs.

Molecularly imprinted polymer on magnetic graphene oxide for fast and selective extraction of 17β-estradiol.

A novel nanosized substrate imprinted polymer (MIPs-GO-Fe3O4) was developed on a magnetic graphene oxide (GO-Fe3O4) surface for selective recognition and fast removal of 17β-estradiol (17β-E2). The characteristics of MIPs-GO-Fe3O4 were evaluated by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy. and vibrating sample magnetometer (VSM). Results suggested that GO had a thin single-layer structure anchoring Fe3O4 nanoparticles and that the imprinted film was coated on the GO-Fe3O4 surface. MIPs-GO-Fe3O4 was sensitive to the magnetic field and could be easily separated using an external magnet. The adsorption results indicated that the kinetic value and binding capacity of MIPs-GO-Fe3O4 were 0.0062 g (mg·min)(-1) and 4.378 μmol g(-1), respectively. The Langmuir-Freundlich isotherm and pseudo-second-order kinetic models were the main adsorption mechanisms for MIPs-GO-Fe3O4. MIPs-GO-Fe3O4 showed excellent recognition selectivity, as well as enrichment and separation abilities for 17β-E2 in complex matrices. MIPs-GO-Fe3O4 was also used to analyze 17β-E2 in real food samples, and satisfactory recoveries such as 84.20% with relative standard deviation (RSD) of 4.67% at a spike of 0.5 μmol L(-1) were obtained. Thus, the MIPs-GO-Fe3O4-based method provided a convenient and practical platform for the separation, enrichment, and removal of 17β-E2 in food samples.

Molecularly Imprinted Photonic Hydrogels as Colorimetric Sensors for Rapid and Label-free Detection of Vanillin

A novel colorimetric sensor for the rapid and label-free detection of vanillin, based on the combination of photonic crystal and molecular imprinting technique, was developed. The sensing platform of molecularly imprinted photonic hydrogel (MIPH) was prepared by a noncovalent and self-assembly approach using vanillin as a template molecule. Morphology characterization by scanning electron microscope (SEM) showed that the MIPH possessed a highly ordered three-dimensional (3D) macroporous structure with nanocavities. The vanillin recognition events of the created nonocavities could be directly transferred into readable optical signals through a change in Bragg diffraction of the ordered macropores array of MIPH. The Bragg diffraction peak shifted from 451 to 486 nm when the concentration of the vanillin was increased from 10⁻¹² to 10⁻³ mol L⁻¹ within 60 s, whereas there were no obvious peak shifts for methyl and ethyl vanillin, indicating that the MIPH had high selectivity and rapid response for vanillin. The adsorption results showed that the hierarchical porous structure and homogeneous layers were formed in the MIPH with higher adsorption capacity. The application of such a label-free sensor with high selectivity, high sensitivity, high stability, and easy operation might offer a potential method for rapid real-time detection of trace vanillin.

Amphiphilic chitosan derivative-based core–shell micelles: Synthesis, characterisation and properties for sustained release of Vitamin D3

Novel amphiphilic chitosan derivative of N,N-dimethylhexadecyl carboxymethyl chitosan (DCMCs) was synthesised. The physical properties of DCMCs were characterised by Fourier transform-infrared spectroscopy, nuclear magnetic resonance spectroscopy, X-ray diffraction and differential scanning calorimetry. DCMCs can form core-shell micelles with low critical micelle concentration (31 mg L(-1)). The core-shell micelles exhibited spherical shape with positive charge (+50.7 mV) and narrow size distribution (polydispersity index <0.5). Vitamin D3 (VD3) was initially used to load into the core-shell micelles, and the solubility of VD3 was improved with higher encapsulation efficiency (53.2%). The in vitro release processes of VD3 from the core-shell micelles were initially rapid and then followed by a sustained release. The Higuchi model was the most suitable for describing the entire release procedure. DCMCs core-shell micelles are promising carriers for VD3 and other hydrophobic bioactive food factors.

Thermosensitive molecularly imprinted polymers on porous carriers: Preparation, characterization and properties as novel adsorbents for bisphenol A

Thermosensitive molecularly imprinted polymers (T-MIPs) on porous carriers were prepared via the synergy of dual functional monomers of 4-vinylpyridine (VP) and N-isopropylacrylamide (NIPAM), for selective recognition and controlled adsorption and release of bisphenol A (BPA) by the temperature regulation. The porous polymer supporter was synthesized by multistep swelling of polystyrene and then both the NIPAM with temperature responsiveness and the basic monomers of VP were grafted on them in a simple way. The resultant T-MIPs showed high binding capacity, fast kinetics, and the adsorption processes were found to follow Langmuir-Freundlich isotherm and pseudo-second-order kinetic models. The adsorption capacity increased slightly along with the rise of temperature (such as 20°C) under lower critical solution temperature (LCST, 33°C) and decreased fast above LCST (such as 50°C). Subsequently, the T-MIPs were employed as novel adsorbents for selective solid-phase extraction (SPE) of BPA from seawater and yogurt samples. Satisfying recoveries in the range of 94.83-98.47% were obtained with the precision of 3.21% at ambient temperature (20°C). Through 6 adsorption-desorption cycles, the reusable T-MIPs exhibited a good recoverability with the relative standard error within 9.8%. The smart T-MIPs provided great potentials for selective identification, adsorption/release and removal of BPA by simple stimuli responsive regulation.

Dummy-surface molecularly imprinted polymers on magnetic graphene oxide for rapid and selective quantification of acrylamide in heat-processed (including fried) foods

Novel nano-sized dummy-surface molecularly imprinted polymers (DSMIPs) on a magnetic graphene oxide (GO-Fe3O4) surface were developed as substrates, using propionamide as a dummy template molecule for the selective recognition and rapid pre-concentration and removal of acrylamide (AM) from food samples. These products showed rapid kinetics, high binding capacity (adsorption at 3.68mg·g-1), and selectivity (imprinting factor α 2.83); the adsorption processes followed the Langmuir-Freundlich isotherm and pseudo-second-order kinetic models. Excellent recognition selectivity toward acrylamide was achieved compared to structural analogs, such as propionic and acrylic acids (selectivity factor β 2.33, and 2.20, respectively). Moreover, DSMIPs-GO-Fe3O4 was used to quantify acrylamide in food samples, yielding satisfactory recovery (86.7-94.3%) and low relative standard deviation (<4.85%). Thus, our DSMIPs-GO-Fe3O4-based procedure was demonstrated to be a convenient and practical method for the separation, enrichment, and removal of acrylamide from food samples.

Preparation and Characterization of Superparamagnetic Molecularly Imprinted Polymers for Selective Adsorption and Separation of Vanillin in Food Samples

Novel water-compatible superparamagnetic molecularly imprinted polymers (M-MIPs) were prepared by coating superparamagnetic Fe3O4 nanoparticles with MIPs in a methanol-water reaction system. The M-MIPs were used for the selective adsorption and separation of vanillin from aqueous solution. The M-MIPs were characterized by X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), vibrating sample magnetometry (VSM), and scanning electron microscopy (SEM). Results indicated that a core-shell structure of M-MIPs was obtained by coating a layer of silica and MIPs on the surface of the Fe3O4 nanoparticles. The obtained M-MIPs possess a loose and porous structure and can be rapidly separated from the solution using a magnet. The adsorption experiments showed that the binding capacity of the M-MIPs was significantly higher than that of the superparamagnetic non-molecularly imprinted polymers (M-NIPs). Meanwhile, the adsorption of M-MIPs reached equilibrium within 100 min, and the apparent maximum adsorption quantity (Qmax) and dissociation constant (Kd) were 64.12 μmol g(-1) and 58.82 μmol L(-1), respectively. The Scatchard analysis showed that homogeneous binding sites were formed on the M-MIP surface. The recoveries of 83.39-95.58% were achieved when M-MIPs were used for the pre-concentration and selective separation of vanillin in spiked food samples. These results provided the possibility for the separation and enrichment of vanillin from complicated food matrices by M-MIPs.

Preparation of photonic-magnetic responsive molecularly imprinted microspheres and their application to fast and selective extraction of 17β-estradiol

Photonic-magnetic responsive molecularly imprinted microspheres (PM-MIMs) were prepared by seed polymerization, through suitable functionalization of magnetic nanoparticles for further coating with photoresponsive functional monomer and imprinted layers, and then were successfully applied to the fast and selective extraction of 17β-estradiol (17β-E2) from real samples. The PM-MIMs possessed a sandwich micro-spherical structure containing Fe3O4 core, SiO2 middle layer, and MIPs shell with thickness of 25 nm. The PM-MIMs displayed excellent photoresponsive properties and could be rapidly separated from solutions under an external magnet. The PM-MIMs had specific affinity towards 17β-E2 with high adsorption capacity (Qmax=0.84 mg g(-1)) and fast binding kinetics (Kd=26.08 mg L(-1)). The PM-MIMs proved to be an ideal photoswitch with the ability of reversible uptake and release of 17β-E2 upon alternate 365 and 440 nm irradiation: 45.0% of 17β-E2 released from the PM-MIMs upon 365 nm irradiation, and 94.0% of the released 17β-E2 was rebound to the PM-MIMs at 440 nm. Accordingly, the PM-MIMs were applied for fast separation and extraction of 17β-E2 followed by HPLC-UV determination, presenting the low limit of detection (LOD, S/N=3) and quantification (LOQ, S/N=10) of 0.18 and 0.62 μmol L(-1), respectively. The high recoveries for spiked milk powder and drinking water samples were in the range of 97.5-113.0% with relative standard deviations less than 4.4%. This study reasonably combined photonic response, magnetic separation and surface imprinting, which endowed the PM-MIMs with significant advantages of high adsorption capacity and fast binding kinetics, convenient separation and recycled use, and simple rapid eco-benign adsorption/elution processes for template molecules. Thus, the PM-MIMs based method may be a simple, rapid, convenient, cost-effective and environmentally-friendly way for simultaneous separation, enrichment and detection of trace 17β-E2 in complicated matrices.