Greenificated Molecularly Imprinted Materials for Advanced Applications

Fluorescence determination of tannic acid imprinted in conjugated hypercrosslinked polymers by Friedel-Crafts acylation

A molecularly imprinted hypercrosslinked polymer (HCP) was synthesized from the polymerization of mesitylene monomer, terephthaloyl chloride crosslinker, and tannic acid (TA) template through FeCl₃-catalyzed Friedel-Crafts acylation. The TA-imprinted HCP (TAHCP) was capable of IUPAC Type I mesoporosity, with specific surface area of 1258 m² g^-1, monolayer adsorption capacity of 289 cm² g^-1, pore sizes ranging from 4.4 to 12.6 Å, amorphous morphology, and characteristic absorption and emission bands. The extended π-conjugation framework of TAHCP was endowed with 385-nm fluorescent emission at 310-nm excitation. The fluorescence intensity of TAHCP could be dynamically quenched by TA and was linearly correlated with 20-1000 nM TA concentrations on the Stern-Volmer plot in the optimized conditions of pH 5.5 buffer, 100 μg mL^-1 TAHCP, and 3.5 min equilibrium. The relative standard deviation (RSD) for 50 nM TA was 3.4% (n = 5), and the limit of detection was 6.2 nM based on the 3σ of the TA blanks). For 50nM TA, the imprinted factor was calculated to be 7.8, and the selectivity for 250 nM interferents, including ions, organic acids, saccharides, amino acids, and caffeine, which are commonly found in beverages, was 7.5-9.5, except for gallic acid (1.2). The recoveries of TA spiked in tea and juice beverages at three levels (10-150 nM) were 93.6-101.9% (RSD = 3.6-4.3%).

Multi-well plate as headspaces for paper-based colorimetric detection of sulfur dioxide gas: An alternative method of sulfite titration for determination of formaldehyde

This work describes the analysis of formaldehyde using a 96-well microplate as multiple headspaces for the separation of sulfur dioxide gas generated from the sulfite remaining after its reaction with the formaldehyde in the sample. The quantitation of the gas is by colorimetric detection of an indicator paper placed over the microplate. The samples are aqueous extracts of various foods that are possibly adulterated with formaldehyde. A known excess amount of sulfite is added to the extract solution aliquoted in the well. The remaining sulfite is acidified with hydrochloric acid to generate sulfur dioxide gas which diffuses through the headspace above the solution to be absorbed at the moist strip of the indicator paper placed over the mouth of the wells. Anthocyanins extracted from the butterfly pea flower is used as the pH indicator giving a color change from the increase of hydrogen ions by hydrolysis of the absorbed sulfur dioxide gas. The exposed paper strip is scanned, and the digital images of the colored region analyzed using ImageJ software. The optimized method has a linear range of 200-1000 mg L^-1 formaldehyde with limit of detection ((2.57*SD of intercept)/(slope of calibration line)) of the aqueous extract of 40 mg L^-1 and coefficient of determination (r²) > 0.9979. Samples of fresh produce, such as seafood, meat, and vegetables, and various processed food were analyzed for their possible formaldehyde content. The results obtained from the headspace paper-based colorimetric detection are not statistically different from the values obtained from the titration method by paired t-tests.

Smart green CQD@SiO2 hybrid coated optical fiber manifesting dual versatile absorptive and MIP features towards epinephrine detection

For the first time, in this study, a novel optical fiber biosensor is proposed and developed via coating only one smart functional layer of silica-supported carbon dots realizing the concepts of both lossy mode resonance (LMR) and molecularly imprinted polymer (MIP) for epinephrine detection. The carbon quantum dots (CQDs) are prepared using a green synthesis method and then treated with a molecularly imprinted polymer (MIP) strategy. Under ultrasonic irradiation, a SiO2 shell was stabilized on the surface of the CQDs to graft and to provide the LMR/MIP functional layer onto the curved optical fiber surface. Accurate structural and morphological characterization confirmed the carbon quantum dot agents and also the SiO2 supporting shells on the optical fiber, while spectroscopic analysis confirms the formation of the imprinted polymer and desirable absorbance characteristics. The experimental and numerical sensing studies revealed that the proposed sensing probe allows the rapid adsorption/desorption of epinephrine to the sensing films and highly permeable coating for studying the influence of effective parameters. Under the optimal experimental conditions, the sensitivity of the proposed LMR-based optical fiber sensor is reported to be 0.37 nm μM-1 with a correlation coefficient of 0.99. So, sensitive detection of epinephrine at a low concentration can be guaranteed with a 0.72 mM LOD.

Colorimetric and photothermal dual-mode immunoassay of aflatoxin B1 based on peroxidase-like activity of Pt supported on nitrogen-doped carbon

In this work, a split-type dual-mode (colorimetric/photothermal) immunoassay method was designed for point-of-care testing (POCT) detection of mycotoxins (aflatoxin B₁, AFB₁ as the model analyte) in foodstuffs based on Pt supported on nitrogen-doped carbon amorphous (Pt-CN). The as-synthesized Pt-CN exhibits excellent peroxidase-mimicking activity, which can catalyze the oxidization of 3,3',5,5'-tetramethylbenzidine (TMB) into TMB_ox with sensitive colorimetric readout in the presence of hydrogen peroxide (H₂O₂). Moreover, the TMB_ox also serves as a near-infrared (NIR) photothermal agent to convert the colorimetric readout into heat under the irradiation of an 808 nm laser. A competitive-type immunoreaction is carried out between AFB₁ and glucose oxidase (GOx)-labeled AFB₁-bovine serum albumin (AFB₁-BSA-GOx) conjugates. With the formation of immune complexes, the entrained GOx catalyzes the hydrolysis of glucose to generate H₂O_2, which further involves the Pt-CN catalyzed production of TMB_ox to increase colorimetric/photothermal readouts. Depending on the degree of TMB oxidation, the dual-mode immunoassay provides a linear range of 1.0 pg/mL to 10 ng/mL, with a limit of detection (LOD) of 0.22 pg/mL for the colorimetric assay and 0.76 pg/mL for the photothermal assay. Moreover, the developed method is successfully used to detect AFB₁ in peanuts with acceptable accuracy compared with commercially enzyme-linked immunosorbent assay (ELISA) kits. Significantly, the photothermal readout in this method is recorded on a mobile phone device without any expensive instruments, providing an affordable and convenient tool for food safety testing.

Recent Advances in Molecularly Imprinted Polymers for Antibiotic Analysis

The abuse and residues of antibiotics have a great impact on the environment and organisms, and their determination has become very important. Due to their low contents, varieties and complex matrices, effective recognition, separation and enrichment are usually required prior to determination. Molecularly imprinted polymers (MIPs), a kind of highly selective polymer prepared via molecular imprinting technology (MIT), are used widely in the analytical detection of antibiotics, as adsorbents of solid-phase extraction (SPE) and as recognition elements of sensors. Herein, recent advances in MIPs for antibiotic residue analysis are reviewed. Firstly, several new preparation techniques of MIPs for detecting antibiotics are briefly introduced, including surface imprinting, nanoimprinting, living/controlled radical polymerization, and multi-template imprinting, multi-functional monomer imprinting and dummy template imprinting. Secondly, several SPE modes based on MIPs are summarized, namely packed SPE, magnetic SPE, dispersive SPE, matrix solid-phase dispersive extraction, solid-phase microextraction, stir-bar sorptive extraction and pipette-tip SPE. Thirdly, the basic principles of MIP-based sensors and three sensing modes, including electrochemical sensing, optical sensing and mass sensing, are also outlined. Fourthly, the research progress on molecularly imprinted SPEs (MISPEs) and MIP-based electrochemical/optical/mass sensors for the detection of various antibiotic residues in environmental and food samples since 2018 are comprehensively reviewed, including sulfonamides, quinolones, β-lactams and so on. Finally, the preparation and application prospects of MIPs for detecting antibiotics are outlined.

Applications of Molecular Imprinting Technology in the Study of Traditional Chinese Medicine

Traditional Chinese medicine (TCM) is one of the most internationally competitive industries. In the context of TCM modernization and internationalization, TCM-related research studies have entered a fast track of development. At the same time, research of TCM is also faced with challenges, such as matrix complexity, component diversity and low level of active components. As an interdisciplinary technology, molecular imprinting technology (MIT) has gained popularity in TCM study, owing to the produced molecularly imprinted polymers (MIPs) possessing the unique features of structure predictability, recognition specificity and application universality, as well as physical robustness, thermal stability, low cost and easy preparation. Herein, we comprehensively review the recent advances of MIT for TCM studies since 2017, focusing on two main aspects including extraction/separation and purification and detection of active components, and identification analysis of hazardous components. The fundamentals of MIT are briefly outlined and emerging preparation techniques for MIPs applied in TCM are highlighted, such as surface imprinting, nanoimprinting and multitemplate and multifunctional monomer imprinting. Then, applications of MIPs in common active components research including flavonoids, alkaloids, terpenoids, glycosides and polyphenols, etc. are respectively summarized, followed by screening and enantioseparation. Related identification detection of hazardous components from TCM itself, illegal addition, or pollution residues (e.g., heavy metals, pesticides) are discussed. Moreover, the applications of MIT in new formulation of TCM, chiral drug resolution and detection of growing environment are summarized. Finally, we propose some issues still to be solved and future research directions to be expected of MIT for TCM studies.

Photoelectrochemical determination of cardiac troponin I based on rod-like g-C3N5@MnO2 heterostructure

Rod-like graphite carbon nitride@MnO₂ (R-g-C₃N₅@MnO₂) heterostructure was prepared by in situ self-anchored growth of MnO₂ nanosheet on the surface of R-g-C₃N₅. The synthesized R-g-C₃N₅@MnO₂ heterostructure as photoactive material exhibited excellent photoelectrochemical (PEC) performance, and the prepared heterostructure-aptamer probe displayed sensitive PEC response to cTnI. Therefore, the PEC method was developed to detect cTnI based on the R-g-C₃N₅@MnO₂ heterostructure. It was found that the linear response to cTnI was in the range 0.001-30 ng/mL under optimized conditions, and the detection limit of the proposed sensor was 0.3 pg/mL. The PEC method displays stable photocurrent response up to 8 cycles and exhibited outstanding selectivity and sensitivity. The PEC method was successfully applied to detect cTnI in serum samples. The recoveries of cTnI detection in serums reach 95.5-104%, and the relative standard deviations range from 3.20 to 4.45%.

Research Trends in Carbon Chain Polymers and Their Derivatives: Highlighting the Decade-Long Research

Polyolefins include low-density polyethylene (LDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), polypropylene (PP), and polybutylene (PB). Polyolefins offer unique characteristics such as chemical resistance, smooth surface, re-shapability, and are lighter than glass and metal-based materials. The global plastics industry produces polyolefin as their major product and these polyolefins are mostly used as commercial commodity plastics. Moreover, the characteristics of polyolefin can be further improved by forming their blends and/or composites and incorporating fillers. This review highlights the role of various fillers such as titanium dioixde-based, nitride-based, and carbon-based nanomaterials, in influencing polyolefin composites. Moreover, the contribution of layered double hydroxide in olefin polymerization, and the impact of filler properties such as filler content, filler type, filler phase stability, and synergistic effect between the fillers and polymers on nanocomposites are discussed.

Colorimetric detection of H2O2 with Fe3O4@Chi nanozyme modified µPADs using artificial intelligence

Peroxidase mimicking Fe₃O₄@Chitosan (Fe₃O₄@Chi) nanozyme was synthesized and used for high-sensitive enzyme-free colorimetric detection of H₂O₂. The nanozyme was characterized in comparison with  Fe₃O₄ nanoparticles (NPs) using X-ray diffraction, Fourier-transform infrared spectroscopy, dynamic light scattering, and thermogravimetric analysis. The catalytic performance of Fe₃O₄@Chi nanozyme was first evaluated by UV-Vis spectroscopy using 3,3',5,5'-tetramethylbenzidine. Unlike Fe₃O₄NPs, Fe₃O₄@Chi nanozyme exhibited an intrinsic peroxidase activity with a detection limit of 69 nM. Next, the nanozyme was applied to a microfluidic paper-based analytical device (µPAD) and colorimetric analysis was performed at varying concentrations of H₂O₂ using a machine learning-based smartphone app called "Hi-perox Sens++ ." The app with machine learning classifiers made the system user-friendly as well as more robust and adaptive against variation in illumination and camera optics. In order to train various machine learning classifiers, the images of the µPADs were taken at 30 s and 10 min by four smartphone brands under seven different illuminations. According to the results, linear discriminant analysis exhibited the highest classification accuracy (98.7%) with phone-independent repeatability at t = 30 s and the accuracy was preserved for 10 min. The proposed system also showed excellent selectivity in the presence of various interfering molecules and good detection performance in tap water.