Preparation of a novel molecularly imprinted polymer by the sol–gel process for sensing creatinine

A novel molecularly imprinted polymer (MIP) was prepared and used as an artificial receptor for creatinine (Cre). A sol–gel process was used to prepare the MIP. Tetraethoxysilane (TEOS) was employed as the crosslinker for the formation of a silica matrix for the MIP. Aluminum ion (Al³⁺) was chosen as the dopant to generate Lewis acid sites in the silica matrix for interactions with Cre. Through the sol–gel process, a polymeric matrix with memory sites for Cre was obtained, and this is mentioned here as the molecularly imprinted polymer for creatinine (MIP_Cre). The imprinting efficiency of MIP_Cre was evaluated by contrasting the adsorbed amount of Cre by MIP_Cre with that by the corresponding non-imprinted polymer (NIP). Creatine (Cn), N-hydroxysuccinimide (NHS), and l-tyrosine (l-tyr) were selected as interferences to study the selectivity of the MIP_Cre. The interference studies were also conducted using binary mixtures, such as Cre/Cn, Cre/NHS, and Cre/l-tyr. All these studies reveal that the MIP_Cre possess a remarkable affinity for Cre. The crucial role of Al³⁺ in this system is discussed in detail. Furthermore, the effects of concentrations of Al³⁺ and TEOS on the adsorbed amount of Cre by MIP_Cre were also investigated.     

Screening of a molecularly imprinted sol–gel library for nafcillin recognition

Properties of tailored imprinted sol–gels are extremely dependent on the synthesis conditions and on the nature of the reagents used due to the diversity of combinatory interactions among the sol–gel components and the large number of chemical requirements for the sol–gel process. In this paper, methyltrimethyl orthosilicate was used as precursor to create molecularly imprinted polymers against the β-lactamic antibiotic nafcillin under different experimental conditions. A 22 member–library of imprinted sol–gels against nafcillin, and the respective control materials, was produced. Screening of the library members was performed by room temperature phosphorescence (RTP) flow-injection analysis and by batch RTP re-binding assays. A 2² factorial experimental design was also performed in selected sub-libraries of imprinted sol–gels as a function of the template and the additive concentrations, both using acid and basic catalysis.     

Molecularly imprinted sol–gel nanoparticles for mass-sensitive engine oil degradation sensing

Titanate sol–gel layers imprinted with midchain carbonic acids have proven highly useful for detecting engine oil degradation processes owing to selective incorporation of oxidised base oil components. Synthesising the material from TiCl₄ in CCl₄ and precipitating with water leads to imprinted TiO₂ nanoparticles with a diameter of 200–300 nm. Replacing the water by a 1 M ammonium hydroxide solution reduces the average particle size to 50–100 nm with retention of the interaction capabilities. Experiments with the latter solution revealed that the 100-nm particles take up substantially more analyte, indicating a size-dependent phenomenon. As the number of interaction sites within each material is the same, this cannot be a consequence of thermodynamics but must be one of accessibility. The sensor characteristic of water-precipitated particles towards engine oil degradation products shows substantially increased sensitivity and dynamic range compared with the corresponding thin films. Coating quartz crystal microbalances with such nanoparticle materials leads to engine oil degradation sensors owing to incorporation of acidic base oil oxidation products. Interaction studies over a large range of layer thicknesses revealed that both the absolute signal and the steepness of the correlation between the sensor signal and the layer height is 2 times higher for the particles. Figure Generation of molecularly imprinted sol–gel nanoparticles     

Matrix molecularly imprinted mesoporous sol–gel sorbent for efficient solid-phase extraction of chloramphenicol from milk

Highly selective and efficient chloramphenicol imprinted sol–gel silica based inorganic polymeric sorbent (sol–gel MIP) was synthesized via matrix imprinting approach for the extraction of chloramphenicol in milk. Chloramphenicol was used as the template molecule, 3-aminopropyltriethoxysilane (3-APTES) and triethoxyphenylsilane (TEPS) as the functional precursors, tetramethyl orthosilicate (TMOS) as the cross-linker, isopropanol as the solvent/porogen, and HCl as the sol–gel catalyst. Non-imprinted sol–gel polymer (sol–gel NIP) was synthesized under identical conditions in absence of template molecules for comparison purpose. Both synthesized materials were characterized by Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FT-IR) and nitrogen adsorption porosimetry, which unambiguously confirmed their significant structural and morphological differences.     

Preparation and characterization of protein molecularly imprinted polysiloxane using mesoporous calcium silicate as matrix by sol–gel technology

Calcium silicate particles containing mesoporous SiO₂ on the surface (CaSiO₃@SiO₂) were prepared by acid modification of calcium silicate with diluted hydrochloric acid. Bovine serum albumin (BSA) molecularly imprinted polysiloxane (MIP) was synthesized using silane as the functional monomer, BSA as the template and CaSiO₃@SiO₂ particles as the matrix in an aqueous phase. SEM, granulometry, FT-IR and BET analysis were used to characterize the protein MIP. Influence factors on the rebinding capacity of the MIP were investigated, such as the pH in treating CaSiO₃, eluent type and silane proportion. The mass of BSA loading and rebinding on CaSiO₃@SiO₂ and MIP was investigated. The adsorption and recognition properties of the MIP were evaluated and the results showed that the MIP exhibited an obvious improvement in terms of rebinding capacity for BSA as compared with non-imprinted polysiloxane (NIP). BSA imprinted polysiloxane could recognize the template protein by using Lys, Ova, Hb, and Glo as control proteins, and the selectivity factor (β) was above 2.3. The rebinding capacity of BSA imprinted polysiloxane for BSA reached 81.31 mg/g, which was 2.25 times of NIP.     

Preparation and characterization of molecularly imprinted organic–inorganic hybrid materials by sol–gel processing for selective recognition of ibuprofen

This work adopted semi-covalent imprinting to prepare molecularly imprinted polymers (MIP) with ibuprofen, a non-steroidal anti-inflammatory drug, as template by sol–gel processing, which is characterized by both the high affinity of covalent binding and the mild operation conditions of non-covalent rebinding. A functional monomer, which was used to synthesize the monomer-imprinted molecule complex, was prepared by multi-step synthesis for the first time. MIP was characterized by Fourier transform IR spectrum and nitrogen adsorption. Thin-layer chromatography separation was used to evaluate the specific molecular recognition ability of MIP. In addition, dynamic and thermodynamic studies on MIP imprinting ibuprofen were undertaken. The results of equilibrium rebinding experiments showed that MIP exhibited good adsorption capacity for ibuprofen. Scatchard analysis illustrated that the template-polymer system shows only one-site binding behavior with a dissociation constant of 1.84 mmol L^?1. Dynamic adsorption exhibited pseudo-second-order kinetics. The positive value of ΔH^θ and the negative values of ΔG^θ demonstrated that the binding system for MIP is endothermic and spontaneous.     

Fluorescent organic nanocrystal confined in sol–gel matrix for bio-imaging

The sol–gel chemistry combined to a spray-drying process allowed us to control the formation of original hybrid core–shell nanoparticles constituted by molecular nanocrystals of rubrene embedded in biocompatible silicate spheres. With a good management of all the physical (gas flows, temperatures) and chemical (dye, solvent and alkoxide natures, concentrations, and hydrolysis and condensation conditions) parameters, we optimized a one-step and self-assembly process allowing to obtain nanoparticles exhibiting promising optical properties such as highly fluorescent labels (two-photon excitation) for medical imaging. Moreover, the presence of Si–OH functions on the silicate shell surface make easy to functionalize these fluorescent nanoparticles by grafting biomolecules for targeting properties. The confined nucleation and growth of rubrene nanocrystals in sol–gel silicate spheres during their drying in the air laminar flows, prevents any phase segregation or particle coalescence and stabilizes mechanically and chemically the organic cores. The first particle sizes obtained in these first experiments are ranging between 80 and 600 nm, but lower diameters will be easily prepared by increasing the solvent amount. Transmission electron microscopy was used to characterize the rubrene organic cores. The electron diffraction patterns performed at 100 K, under low-dose illumination to avoid amorphization of the samples during electron irradiation, have shown the good crystallinity of the NP rubrene cores that seem to be constituted by single rubrene nanocrystals. Finally, optical confocal microscopy, used in reflection and fluorescence modes, showed that all the core–shell particles are strongly fluorescent. This high fluorescence intensity arises from the high molecule numbers of rubrene nanocrystals, which enhance the absorption and emission cross sections.     

Electrochemical oxidation of aniline in a silica sol–gel matrix

Electrochemical oxidation of aniline encapsulated in a silica solid electrolyte prepared by a sol–gel process yielded products that were dependent on the pore size. An acid-catalyzed process that used tetramethyl orthosilicate as the precursor and aniline as a dopant yielded the silica. When the aging time was limited to one day so that a mesoporous solid was obtained, the potentiodynamic oxidation of aniline at a carbon fiber electrode resulted in the formation of polyaniline. With aging times of 3–5 days, microporous silica was obtained. In this electrolyte, the formation of dimers and other oligomers was observed by cyclic voltammetry. Evidence for these products was the presence of a quasi-reversible redox couple at 0.2 V vs Ag/AgCl that was previously related to oligomeric aniline by Raman spectroscopy. The results supported the hypothesis that the pore structure of sol–gel electrolytes can influence the pathways of electrode reactions therein.     

Surfactants for CNTs dispersion in zirconia-based ceramic matrix by sol–gel method

Zirconium oxide is a ceramic material widely studied due to its mechanical and electrical properties that can be improved with the use of carbon nanotubes (CNTs) as reinforcement. The synthesis of CNT/zirconia composites by sol–gel method is still very scarce, due to the hydrophobic nature of the CNTs, being their dispersion in aqueous medium an intrinsic difficulty to the synthesis. In this work, we present a sol–gel synthesis for MWCNTs/zirconia composites, where two kinds of surfactants, sodium and ammonium stearates dissolved in water (1 g/100 mL), were used as dispersant agents for multiwall carbon nanotubes (MWCNTs). They are cheap and easy to prepare, and were very effective in dispersing the MWCNTs. Different quantities of MWCNTs (up to 5 wt%) were added in the solution of stearate/water and this solution with the highly dispersed MWCNTs was added to the zirconia sol–gel, producing composites of MWCNTs/zirconia with different concentrations of MWCNTs. All the powders were heat treated at 300 and 500 °C and the powder characterization was performed by transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and infrared spectroscopy (FTIR). The composite MWCNTs/zirconia remained amorphous at 300 °C and presented a tetragonal phase at 500 °C with an average grain size of about 20 ± 3 nm, determined by the Scherrer equation from the XRD patterns. For these crystalline samples, TEM images suggest a more effective interaction between MWCNTs with ZrO₂ matrix, where it can be observed that the carbon nanotubes are fully coated by the matrix.     

Bioactive sol–gel scaffolds with dual porosity for tissue engineering

Scaffolds containing dual porosity at the nano and macroscale appear to exhibit improved performance in terms of crystallization of hydroxycarbonate apatite plus cell adhesion and proliferation, as well as vascularization. The aim of the present work is to develop a novel, simple sol–gel process for the preparation of silica-based bioactive porous bone tissue scaffold, with a pore structure consisting of interconnected pores of both 100’s of micrometers and 10’s of nanometers in size, optimized for enhanced bone regeneration performance. SiO₂–CaO and SiO₂–CaO–P₂O₅ porous glass monoliths have been prepared with a dual pore structure including pores of both ~50–200 micrometers and a few to 10’s of nanometers in size, based on polymerization-induced phase separation together with the sol-gel transition, by adding a water soluble polymer to the precursor sol. The nanopore (~5–40 nm) structure of such macroporous gel skeletons was tailored by solvent exchange, followed by heat treatment at 600–700 °C. The overall pore structure has been studied by Scanning Electron Microscopy (SEM), N₂-adsorption (BET), Mercury intrusion porosimetry and Infrared spectroscopy. The scaffold bioactivity, tested in simulated body fluid, has been demonstrated by means of DRIFTS, SEM and X-ray diffraction measurements.     

Hybrid organic–inorganic sol–gel coatings with interpenetrating network for corrosion protection of tinplate

Novel hybrid organic–inorganic coatings with interpenetrating network were synthesized by the acid-catalyzed hydrolytic co-polycondensation of tetraethoxysilane and 3-metacryloxypropyltrimethoxysilane, followed by radical polymerization with methyl methacrylate and triallyl isocyanurate (TAIC). The hybrid coatings were characterized by Fourier transformed infrared spectroscopy, thermogravimetric analysis and scanning electron microscope, and their anti-corrosion behaviors were evaluated by potentiodynamic polarization, electrochemical impedance spectroscopy and salt spray test. The results indicated that the hybrid coatings exhibited excellent anti-corrosion ability by forming a physical barrier between metal and its external environment. Thermal stability of the hybrid coatings was increased after the addition of TAIC. Furthermore, hydrophobic properties of the hybrid coatings were examined by measuring the contact angles, and the change in wetting characteristics of the hybrid coatings was not obvious.     

Preparation and evaluation of an ion imprinted sol–gel material for selective solid-phase extraction of Ni(II)

An ion imprinted silica sorbent was prepared using a sol–gel process for selective extraction of Ni(II) ions from water samples. Bis(dibenzoylmethanto)nickel(II) complex was used as template; phenyltrimethoxysilane and 3-aminopropyltriethoxysilane as functional monomers and tetraethylorthosilicate as reticulating agent. The material was packed in solid-phase extraction (SPE) column. The effect of sampling volume, elution conditions, sample pH and sample flow rate on the extraction of Ni ions from water samples were studied. The relative selectivity coefficients of imprinted sorbent for Ni(II)/Co(II), Ni(II)/Cu(II) and Ni(II)/Cd(II) were 23.7, 30.3 and 24.4, times greater than non-imprinted sorbent, respectively. The relative standard deviation of the eight replicate determinations of Ni(II) was 4.2%. The detection limit was 0.9 µg L^?1 using flame atomic absorption spectrometry. The developed method was successfully applied to the determination of trace nickel in water samples.     

Selective sensing of Hg2+ via sol–gel transformation of a cholesterol-based compound

A cholesterol-based dithioacetal functionalised compound 1 has been designed, synthesised and successfully applied for the selective detection of Hg²⁺ ion. The specific Hg²⁺-induced deprotection of the thioacetal functionality of 1 resulted in sol-to-gel transition in DMF-H₂O (1:1, v/v) via the formation of precursor aldehyde 3. This Hg²⁺-prompted rapid sol to gel conversion is insensitive to the nature of Hg²⁺-salt. In the study, other metal ions did not show any change. To the best of our knowledge, this is a first time report of a chemodosimeter that functions as a selective ‘naked-eye’ Hg²⁺-detector by showing in situ sol-to-gel conversion.     

Utilization of sol–gel ceramics for the immobilization of living microorganisms

Two possible methods are described for using sol–gel technology to immobilize living microorganisms, either embedding the cells within thin silica layers, or using the technique of freeze-gelation to immobilize microorganisms within molded ceramic parts. The preparation and structure of both biocer variants are outlined, and examples are given for the activity and storage stability of embedded microorganisms. Silica layers were used to immobilize various bacteria and algae. Survival rates after storage are given for Pseudomonas fluorescence bacteria and for green algae such as H. pluvialis, C. vulgaris, B. braunii and N. limnetica embedded within thin transparent silica layers. The bioactivity of bacteria immobilized in freeze-gelation ceramics was investigated by monitoring glucose consumption for P. fluorescens NCIMB 11764, and phenol degradation for Rhodococcus ruber.     

Immobilization of Candida antarctica lipase B on the surface of modified sol–gel matrix

The use of modified sol–gel matrix to immobilize the enzyme Candida antartica lipase B (CALB) was investigated. Free hydroxyl groups on the matrix surface were exploited to covalently immobilize the enzyme. Based from the results, incorporating hydrophobic sol–gel precursor (ethyltrimethoxysilane) enhanced enzyme activity. An enzyme activity of 192.02 U/g beads with 80.88 % attachment was obtained. At alkaline pH, immobilization yield of enzyme increased. The attachment of enzyme on the surface of the matrix was confirmed by scanning electron microscope images. Covalently immobilized CALB on sol–gel supports has higher thermal stability with 2.7 times higher half-life compared to soluble enzymes at 60 °C. This enzyme immobilization system retains the enzyme residual activity even for repetitive use. Hence, the immobilization approach developed recommends its further application.     

Optical spectroscopy methods for the characterization of sol–gel materials

Journal of Sol-Gel Science and Technology - In this paper, structural, optical, and electrical features of undoped and copper-incorporated nickel oxide (Cu/NiO) films with different mole ratios...