Preparation, characterization, and application of soluble liquid crystalline molecularly imprinted polymer in electrochemical sensor

A facile and selective resonance Rayleigh scattering method for trace nitrite using gold nanocluster surface molecularly imprinted polyisopropylacrylamide probe

A novel gold nanocluster surface molecularly imprinted polyisopropylacrylamide probe (AuNC@MIP) was synthesized for the specific detection of NO2-, using N-isopropylacrylamide (NIPAM) as the functional monomer, gold nanoclusters (AuNC) as the substrate, ethylene glycol dimethacrylate (EGDMA) as the cross-linking agent, and nitrosophenol (NPN) produced from sodium nitrite (NaNO2) and phenol (PN) as the template molecule, N,N-dimethylformamide (DMF) as the solvent, and azobisisobutyronitrile (AIBN) as the initiator. The nanoprobe was characterized using molecular spectroscopy, XPS, TEM, TGA, and zeta potential analysis. The probes revealed a prominent resonance Rayleigh scattering (RRS) peak at 370 nm. Upon addition of NO2-, the RRS intensity at 370 nm decreased due to the RRS energy transfer enhancing. The linear determination range is 0.125-1.50 nmol/L NO2-, with a limit of detection (LOD) of 0.085 nmol/L. The new RRS method was applied to determine NO2- in meat, dairy products, and water samples, with recovery of 96-107% also relative standard deviations (RSDs) of 1.1-8.0%.

Surface-Enhanced Raman Spectroscopy Substrate Time Stability Improvement Using an External Oxygen Barrier Method

The poor time stability of surface-enhanced Raman scattering (SERS) substrates greatly limits their application potential. Although core-shell structures are commonly used to enhance stability, their complex preparation processes, high costs, and susceptibility under acidic or alkaline conditions result in serious disadvantages for practical applications. Here, we propose a new method of external oxygen barrier to improve spectral stability, in which SERS substrates are stored in an oxygen-free environment. Controlled experiments are carried out under air and vacuum. Raman spectrum intensity is measured 11 times within six months for each group. Using the attenuation formula, the Raman spectrum intensity decay results of each SERS substrate over time are obtained. The effectiveness of the external oxygen barrier method is demonstrated through curve fitting using the corresponding function. The substrate spectral attenuation rates of the vacuum group and the argon group within six months are <20%, proving the effectiveness of the external oxygen barrier method.

Facile synthesis of core–shell structured magnetic Fe3O4@SiO2@Au molecularly imprinted polymers for high effective extraction and determination of 4-methylmethcathinone in human urine samples

In this study, a novel material of core–shell structured magnetic molecularly imprinted polymers (Fe3O4@SiO2@Au (FSA)-MIPs) was successfully prepared for the rapid and selective determination of 4-methylmethcathinone (mephedrone, 4-MMC). The adsorption capacity of FSA-MIPs is 34.7 mg·g−1 at 308 K, which is significantly higher than magnetic non-imprinted polymers profiting from the imprinting effect. The FSA-MIPs have a short equilibrium (20 min) and could be reused more than six times. Moreover, the selectivity coefficients of FSA-MIPs for 4-MMC, 3,4-dimethylmethcathinone, butylone, 4-ethylmethcathinone, acetylfentanyl, and methylene blue are 4.01, 5.65, 7.62, 12.30, and 20.87 respectively, further indicating the markedly enhanced binding selectivity of FSA-MIPs. As an adsorbent, the FSA-MIPs were successfully applied for effective extraction of 4-MMC in three human urine samples with the recovery rates ranging from 85.5–92.6%. The results confirmed that the FSA-MIPs have good prospects in the extraction and separation of synthetic cathinones, which is suitable for further application in the criminal sciences field.

[Preparation of liquid crystal-based molecularly imprinted monolith and its molecular recognition thermodynamics]

Molecularly imprinted polymers (MIPs) incorporated with liquid crystalline monomers can imprint and recognize templates at a very low level of crosslinking, thus addressing challenges associated with conventional MIPs, such as the embedding of the imprinted sites, low binding capacity, and slow mass transfer due to the high degree of crosslinking. Compared with traditional MIPs, the prepared MIPs have a greater number of easily binding sites, which can effectively overcome the embedding and low utilization of imprinting sites. Simultaneously, with a decrease in the level of chemical crosslinking, the mass transfer of template molecules can be significantly improved. However, the imprinting effect of liquid crystalline MIPs is generally weaker than that of traditional MIPs due to the low degree of crosslinking. Therefore, to obtain liquid crystalline MIPs with a good imprinting effect, a series of low-crosslinked liquid crystalline molecularly imprinted monoliths were prepared by graft polymerization and evaluated by high performance liquid chromatography (HPLC) to systematically determine the relation between the polymerization parameters and the affinity of the resulting liquid crystalline MIPs. In this experiment, trimethylolpropane trimethacrylate (TRIM) was used to synthesize a monolithic column skeleton with toluene and dodecyl alcohol as porogens. (S)-Naproxen was used as a template and liquid crystalline monomer 4-(4-cyanophenyl)-cyclohexyl ethylene (CPCE) was added for grafting to synthesize the liquid crystalline MIP monolith. The influence of the acetonitrile content and pH in the mobile phase on the chromatographic retention of the template molecule was investigated. The results showed that the main force of MIP recognizing naproxen changed from hydrogen bonding to hydrophobic interaction by the addition of the liquid crystalline monomer. Frontal analysis and adsorption isotherm fitting, including Langmuir, Freundlich, and Scatchard fitting, showed that when the crosslinking degree was 15%, the liquid crystalline MIPs exhibited the highest imprinting factor and heterogeneity, and the specific adsorption was stronger than non-specific adsorption. By analyzing the stoichiometric displacement model, the total affinity of the MIP monoliths for the template molecules (ln A) was determined to be 0.645, significantly higher than that of its analogues, indicating that the liquid crystalline imprinted monolith had a higher total affinity for the template molecule. The spatial matching degree (nβ) of the template molecule to the cavity structures of MIPs was also very high, and only inferior to that of ketoprofen. Nevertheless, the ln A value of ketoprofen was only 0.242, which indicated that the spatial effect was not the key factor in determining the recognition ability of liquid crystalline imprinting systems. An analysis of the separation thermodynamics revealed that the separation of the liquid crystalline MIPs was an entropy-controlled process, while that of conventional liquid crystalline-free MIPs was an enthalpy-controlled process. Based on the above results, the addition of a liquid crystalline monomer may alter the recognition mechanism of MIPs, and an appropriately low crosslinking degree can significantly improve the recognition performance of liquid crystalline MIPs, paving the way for a new generation of MIPs.