Magnetic halloysite‐ based molecularly imprinted polymer for specific recognition of sunset yellow in dyes mixture

Enhanced Molecularly Imprinted Fluorescent Test Strip for Rapid and Visual Detection of Norfloxacin via a Smartphone

Paper-based test strips with on-site visual detection have become a hot spot in the field of target detection. Yet, low specific surface area and uneven deposition limit the further application of test strips. Herein, a novel "turn-on" ratio of molecularly imprinted membranes (Eu@CDs-MIMs) was successfully prepared based on a Eu complex-doped polyvinylidene fluoride membrane for the selective, rapid and on-site visual detection of norfloxacin (NOR). The formation of surface-imprinted polymer-containing carbon dots (CDs) improves the roughness and hydrophilicity of Eu@CDs-MIMs. Fluorescence lifetimes and UV absorption spectra verified that the fluorescence enhancement of CDs is based on the synergistic effect of charge transfer and hydrogen bonding between CDs and NOR. The fluorescent test strip showed a linear fluorescent response within the concentration range of 5-50 nM with a limit of detection of 1.35 nM and a short response time of 1 min. In comparison with filter paper-based test strips, Eu@CDs-MIMs exhibit a brighter and more uniform fluorescent color change from red to blue that is visible to the naked eye. Additionally, the applied ratio fluorescent test strip was combined with a smartphone to translate RGB values into concentrations for the visual and quantitative detection of NOR and verified the detection results using high-performance liquid chromatography. The portable fluorescent test strip provides a reliable approach for the rapid, visual, and on-site detection of NOR and quinolones.

Adsorption kinetics of methylene blue from wastewater using pH-sensitive starch-based hydrogels

In this work, starch/poly(acylic acid) hydrogels were synthesized through a free radical polymerization technique. The molar ratios of acrylic acid to N,N'-methylenebisacrylamide were 95:5, 94:6, and 93:7. The samples exhibited an amorphous porous structure, indicating that the size of the pores was contingent upon the amount of cross-linking agent. The quantity of acrylic acid in structure rose with a little increase in the amount of the cross-linking agent, which improved the hydrogels' heat stability. The swelling characteristics of the hydrogels were influenced by both the pH level and the amount of cross-linking agent. The hydrogel with a ratio of 94:6 exhibited the highest degree of swelling (201.90%) at a pH of 7.4. The dominance of the Fickian effect in regulating water absorption in the synthesized hydrogels was demonstrated, and the kinetics of swelling exhibited agreement with Schott's pseudo-second order model. The absorption of methylene blue by the hydrogels that were developed was found to be influenced by various factors, including the concentration of the dye, the quantity of the cross-linking agent, the pH level, and the duration of exposure. The hydrogel 95:5 exhibited the highest adsorption effectiveness (66.7%) for the dye solution with a concentration of 20 mg/L at pH 10.0. The examination of the kinetics and isotherms of adsorption has provided evidence that the process of physisorption takes place on heterogeneous adsorbent surfaces and can be explained by an exothermic nature.

Core-shell magnetic molecularly imprinted polymer for selective recognition and detection of sunset yellow in aqueous environment and real samples

Magnetic Molecularly imprinted polymers (MMIPs) have been recently recognized as an exceptional tool for monitoring and decontamination of environmental and biological samples of diverse nature. Based on the potential applications as sorbents and biomimetic sensors, herein, a core-shell magnetic-molecularly imprinted polymer (MMIP) was developed as a selective material for separation and sensing of sunset yellow (SY) dye in an aqueous environment and real samples. The MMIP was synthesized via precipitation polymerization using SY as a template, MAA as a functional monomer (chosen based on simulation studies), EGDMA as a cross-linking agent, and AIBN as an initiator. To elaborate the specificity of MMIP, a comparative agent, magnetic non-imprinted polymer (MNIP) was also synthesized. The XRD results showed that the MMIP showed both crystalline and amorphous structure attributed to the presence and polymeric and non-polymeric groups. The FTIR spectra confirmed synthesis of intermediate and final MMIP product. The SEM results showed spherical morphology and porous structure of the MMIP with an average particle size of 0.636 μm in diameter. The MMIP was first employed as a sorbent for the removal of SY from the aqueous environment. The binding experiments performed at optimized operating conditions (pH 2; time 30 min; sorbent dosage 3 mg; sorbate concentration 80 ppm) showed more selectivity when compared with MNIP. The data fitted best to Langmuir's sorption isotherm (Q_o 359.8 mg/g) and followed the pseudo-second-order kinetic model. The synthesized MMIP was also used as an electrochemical sensor for detection of SY dye in the aqueous environment, which exhibited a linear range of detection as (1.51 × 10^-6 - 1.5 × 10^-3 M). The limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.00413 M and 0.0137 M, respectively. While the R² value was found to be 0.997 at optimized analytical conditions. These results suggested that the synthesized MMIP can be applied for the selective separation and quantification of SY dye in sample of diverse nature.

Molecularly imprinted polymers via reversible addition-fragmentation chain-transfer synthesis in sensing and environmental applications

Molecularly imprinted polymers (MIP) have shown their potential as artificial and selective receptors for environmental monitoring. These materials can be tailor-made to achieve a specific binding event with a template through a chosen mechanism. They are capable of emulating the recognition capacity of biological receptors with superior stability and versatility of integration in sensing platforms. Commonly, these polymers are produced by traditional free radical bulk polymerization (FRP) which may not be the most suitable for enhancing the intended properties due to the poor imprinting performance. To improve the imprinting technique and the polymer capabilities, controlled/living radical polymerization (CRP) has been used to overcome the main drawbacks of FRP. Combining CRP techniques such as RAFT (reversible addition-fragmentation chain transfer) with MIP has achieved higher selectivity, sensitivity, and sorption capacity of these polymers when implemented as the transductor element in sensors. The present work focuses on RAFT-MIP design and synthesis strategies to enhance the binding affinities and their implementation in environmental contaminant sensing applications.

Fluorescent polydopamine based molecularly imprinted sensor for ultrafast and selective detection of p-nitrophenol in drinking water

A highly effective fluorescent molecularly imprinted sensor (F-PDA-MIS) based on fluorescent polydopamine (F-PDA) was successfully synthesized for selective and ultrafast detection of p-nitrophenol (P-NP) in drinking water. F-PDA with abundant surface functional groups has been artfully modified to firstly serve as both fluorescent monomer and functional monomer in the synthesis of a uniform luminous F-PDA-MIS, which can greatly improve the detection efficiency. As expected, F-PDA-MIS had an obvious emission wavelength of 535 nm with the optimal excitation wavelength at 400 nm. Specially, F-PDA-MIS could detect P-NP in the range 100 to 1100 nM with much lower detection limit of 24.2 nM within 120 s compared with other conventional imprinted fluorescent sensors based on pure quantum dots (QDs) or dyes. This excellent test phenomenon is mainly ascribed to the rapid electron transfer between F-PDA and P-NP. Satisfactory recovery of 98.0-104% for mineral water and 98.6-106% for boiling water were obtained with relative standard deviations (RSDs) of 2.7-3.4% and 2.6-3.5% respectively. The detection reliability of F-PDA-MIS was verified by the comparison with high-performance liquid chromatography (HPLC-UV). Consequently, F-PDA as a fluorescence functional monomer has been shown to be a possible strategy to effectively improve the detection limit and shorten response time of the target determination in water..

Magnetic molecularly imprinted polymers for extraction of S-phenylmercapturic acid from urine samples followed by high-performance liquid chromatography

In this study, magnetic molecularly imprinted polymers (MMIPs) were prepared and used as sorbents for extraction of S-phenylmercapturic acid (S-PMA) from urine samples, followed by high-performance liquid chromatography ultraviolet-visible (HPLC-UV/Vis) analysis. The MMIPs were synthesized by the copolymerization reaction of (phenylthio) acetic acid (template molecule), methacrylic acid (functional monomers) and ethylene glycol dimethacrylate (cross-linkers). The morphology, structure property and surface groups of the prepared MMIPs were characterized by scan electron microscopy, transmission electron microscopy, infrared spectroscopy, X-ray diffraction pattern, thermogravimetric analyses, Brunauer-Emmett-Teller and vibrating sample magnetometer. The selectivity of the MMIPs was investigated in the presence of interferents. Various parameters affecting the S-PMA extraction efficiency were investigated, including MMIPs amount, pH, sample volume, desorption solvent, as well as extraction and desorption time. The obtained optimal parameters were as follows: MMIPs amount (20 mg), pH (3.0), sample volume (5 mL), desorption solvent (methanol/acetic acid [9/1, v/v]), extraction time (30 minutes) and desorption time (2 minutes). The method was validated according to the Food and Drug Administration Guidance for Industry on Bioanalytical Method Validation. The calibration curve for the analyte was linear in the concentration range of 0.030-1.0 mg/L (r = 0.9995). The LOD and LOQ of the method were 0.0080 and 0.0267 mg/L, respectively. The enrichment factor of the MMIPs was 5. The relative standard deviations of intra- and inter-day tests were in the range of 3.8-5.1% and 3.9-6.3%, respectively. The recoveries at three different concentrations of 0.10, 0.50 and 0.80 mg/L ranged between 95.2% and 98.6%. In addition, the MMIPs could be reused for at least eight times. The proposed method was successfully applied to the determination of S-PMA in urine samples. In addition, this developed method could be used as a tool in the early screening and clinical diagnosis of benzene intoxication.