Preparation of molecularly imprinted polymers on hemin-graphene surface for recognition of high molecular weight protein

Introducing molecular imprinting onto nanozymes: toward selective catalytic analysis

The discovery of enzyme-like catalytic characteristics in nanomaterials triggers the generation of nanozymes and their multifarious applications. As a class of artificial mimetic enzymes, nanozymes are widely recognized to have better stability and lower cost than natural bio-enzymes, but the lack of catalytic specificity hinders their wider use. To solve the problem, several potential strategies are explored, among which molecular imprinting attracts much attention because of its powerful capacity for creating specific binding cavities as biomimetic receptors. Attractively, introducing molecularly imprinted polymers (MIPs) onto nanozyme surfaces can make an impact on the latter's catalytic activity. As a result, in recent years, MIPs featuring universal fabrication, low cost, and good stability have been intensively integrated with nanozymes for biochemical detection. In this critical review, we first summarize the general fabrication of nanozyme@MIPs, followed by clarifying the potential effects of molecular imprinting on the catalytic performance of nanozymes in terms of selectivity and activity. Typical examples are emphatically discussed to highlight the latest progress of nanozyme@MIPs applied in catalytic analysis. In the end, personal viewpoints on the future directions of nanozyme@MIPs are presented, to provide a reference for studying the interactions between MIPs and nanozymes and attract more efforts to advance this promising area.

Colorimetric Sensors for Chemical and Biological Sensing Applications

Colorimetric sensors have been widely used to detect numerous analytes due to their cost-effectiveness, high sensitivity and specificity, and clear visibility, even with the naked eye. In recent years, the emergence of advanced nanomaterials has greatly improved the development of colorimetric sensors. This review focuses on the recent (from the years 2015 to 2022) advances in the design, fabrication, and applications of colorimetric sensors. First, the classification and sensing mechanisms of colorimetric sensors are briefly described, and the design of colorimetric sensors based on several typical nanomaterials, including graphene and its derivatives, metal and metal oxide nanoparticles, DNA nanomaterials, quantum dots, and some other materials are discussed. Then the applications, especially for the detection of metallic and non-metallic ions, proteins, small molecules, gas, virus and bacteria, and DNA/RNA are summarized. Finally, the remaining challenges and future trends in the development of colorimetric sensors are also discussed.

State-of-the-art molecular imprinted colorimetric sensors and their on-site inspecting applications

Molecular imprinted colorimetric sensors can realize visual semi-quantitative analysis without the use of any equipment. With the advantages of low cost, fast response, ease of handling, and excellent recognition ability, the molecular imprinted colorimetric sensor shows great application potential in the field of sample rapid assay. Molecular imprinted colorimetric sensors can be prepared in various forms to meet the needs of different sample determination, such as film, hydrogel, strip, and adsorption coating. In this review, the preparation methods for various types of molecularly imprinted colorimetric sensors are systematically introduced. Their applications in the field of on-site biological sample detection, drug detection, disease treatment, chiral substance detection and separation, environmental analysis, and food safety detection are introduced. The limitations encountered in the practical application are presented, and the future development directions prospect.

Bio-Inspired Imprinting Materials for Biomedical Applications

Inspired by the recognition mechanism of biological molecules, molecular imprinting techniques (MITs) are imparted with numerous merits like excellent stability, recognition specificity, adsorption properties, and easy synthesis processes, and thus broaden the avenues for convenient fabrication protocol of bio-inspired molecularly imprinted polymers (MIPs) with desirable functions to satisfy the extensive demands of biomedical applications. Herein, the recent research progress made with respect to bio-inspired imprinting materials is discussed in this review. First, the underlying mechanism and basic components of a typical molecular imprinting procedure are briefly explored. Then, emphasis is put on the introduction of diverse MITs and novel bio-inspired imprinting materials. Following these two sections, practical applications of MIPs in the field of biomedical science are focused on. Last but not least, perspectives on the remaining challenges and future development of bio-inspired imprinting materials are presented.

A novel surface imprinted resin for the selective removal of metal-complexed dyes from aqueous solution in batch experiments: ACB GGN as a representative contaminant

Metal-complexed dyes are harmful to the environment and human health because they contain heavy metals and complex organic ligands. It is difficult to separate and recover these dyes from wastewater owing to their complex components and poor selectivity of common adsorbents. In this study, a novel surface molecularly imprinted polymer (SMIP) was prepared using 4-vinyl pyridine as the functional monomer and polystyrene resin as the carrier. SMIP showed better adsorption performance than non-imprinted polymer (SNIP) in the whole pH range with the best adsorption capacity at pH 1.5. The correlation coefficients (R²) fitted by Langmuir and Temkin models were greater than 0.97, and the adsorption was a spontaneous exothermic process. The pseudo-second-order and Elovich models fitted the adsorption kinetic curves well. The adsorption capacity of SMIP was approximately 20% higher than that of SNIP in the salt concentration ranging from 2 to 80 mg/L. In selective adsorption experiments, the relative selectivity coefficients (I) of SMIP for competitors were all greater than 2.41, and the Cr (Ⅲ) components of ACB GGN played a more important role in the recognition performance of SMIP than the sulfonic groups. Adsorption mechanism tests revealed that although the adsorption of ACB GGN by SMIP mainly relied on electrostatic attraction, hydrophobic interactions, π-π conjugation, and Cr (Ⅲ) coordination were also involved. These results show that SMIP has excellent selective adsorption properties for ACB GGN and a promising application potential in the treatment of metal-complexed dye wastewater.

Fluorescent turn-on assay of C-type natriuretic peptide using a molecularly imprinted ratiometric fluorescent probe with high selectivity and sensitivity

A novel molecularly imprinted ratiometric fluorescent probe was fabricated by simple sol-gel polymerization for selective and sensitive assay of C-type natriuretic peptide (CNP) in biosamples. Both the nitrobenzoxadiazole (NBD) and carbon dots (CDs) were located on the surface of silica, used as the detection signal and reference signal, respectively. For the turn-on-based probe, the fluorescence intensity of NBD could be quantitatively enhanced by CNP based on the strategy of photo-induced electron transfer (PET), while the fluorescence of CDs remained unchanged. The obtained probe exhibited excellent recognition selectivity and fast kinetics to CNP templates, and also showed good stability. The linear range of CNP determination was 5-80 pg mL^-1 with a low detection limit of 2.87 pg mL^-1. Finally, the probe was successfully applied to determine CNP in human serum samples and attained high recoveries between 97.3 and 104% with precisions below 4.7%. The result indicates that the proposed method has promising potential for the assay of trace peptides in complex matrices. Schematic illustration for the formation and determination mechanism of the probe.

Glypican-3 electrochemical aptamer nanobiosensor based on hemin/graphene nanohybrids peroxidase-like catalytic silver deposition

A Glypican-3 (GPC3) electrochemical aptamer nanobiosensor based on hemin/graphene nanohybrids (HGNs) peroxidase-like catalytic silver deposition and GPC3 aptamer has been constructed for the determination of GPC3. The HGNs were prepared by an one-step reduction method. Fourier transform infrared spectroscopy (FT-IR), ultraviolet spectroscopy (UV-vis), and transmission electron microscopy (TEM) were used to study the structure and morphological characteristics of the HGNs. The GPC3 electrochemical aptamer nanobiosensor was constructed using HGNs-aptamer (HGNs-Apt) as the signal probe and GPC3 aptamer as the capture probe. With the help of the catalytic action of peroxidase-like properties of HGNs, H₂O₂ reduces the silver (Ag) ions in solution to metallic Ag, which deposit on the surface of the electrode. The amount of deposited Ag, which was derived from the amount of GPC3, was quantified by differential pulse voltammetry (DPV). Under optimal conditions, the current response of Ag had a good positive correlation with the GPC3 concentration in the range 10.0-100.0 μg mL^-1 with a correlation coefficient of 0.9958. The detection limit was 3.16 μg mL^-1 at a signal-to-noise ratio of 3, and the sensitivity was calculated to be 0.807 μA μM^-1 cm^-2. The method is validated by analyzing spiked human serum samples with good recovery ranging from 101 to 122%. In addition, the GPC3 electrochemical aptamer nanobiosensor has acceptable selectivity, stability, and reproducibility. Graphical abstract A Glypican-3 electrochemical aptamer nanobiosensor based on hemin/graphene nanohybrids (HGNs) peroxidase-like catalytic silver deposition and GPC3 aptamer has been constructed for the determination of GPC3. The electrochemical aptamer nanobiosensor exhibits high selectivity, acceptance reproducibility, and good recovery performances.