The accurate detection of biological materials has remained at the forefront of scientific research for decades. This includes the detection of molecules, proteins, and bacteria. Biomimetic sensors look to replicate the sensitive and selective mechanisms that are found in biological systems and incorporate these properties into functional sensing platforms. Molecularly imprinted polymers (MIPs) are synthetic receptors that can form high affinity binding sites complementary to the specific analyte of interest. They utilise the shape, size, and functionality to produce sensitive and selective recognition of target analytes. One route of synthesizing MIPs is through electropolymerization, utilising predominantly constant potential methods or cyclic voltammetry. This methodology allows for the formation of a polymer directly onto the surface of a transducer. The thickness, morphology, and topography of the films can be manipulated specifically for each template. Recently, numerous reviews have been published in the production and sensing applications of MIPs; however, there are few reports on the use of electrosynthesized MIPs (eMIPs). The number of publications and citations utilising eMIPs is increasing each year, with a review produced on the topic in 2012. This review will primarily focus on advancements from 2012 in the use of eMIPs in sensing platforms for the detection of biologically relevant materials, including the development of increased polymer layer dimensions for whole bacteria detection and the use of mixed monomer compositions to increase selectivity toward analytes.

https://www.mdpi.com/1424-8220/19/5/1204/pdf

Recent Advances in Electrosynthesized Molecularly Imprinted Polymer Sensing Platforms for Bioanalyte Detection

In this work, a highly selective and sensitive electrochemical sensor based on hierarchical porous MXene/amino carbon nanotubes (MXene/NH2-CNTs) composite and molecularly imprinted polymer (MIP) was developed for fisetin detection. The porous MXene/NH2-CNTs films were fabricated by self-assembly of negatively charged Ti3C2Tx MXene flakes and positively charged NH2-CNTs. The utilization of conductive NH2-CNTs as interlayer spacers efficiently inhibited the aggregation of MXene flakes and formed a well-defined porous structure, as a result of increasing the effective surface area, an enhancement of the electrical conductivity and electrocatalytic activity was observed. This sensor takes advantages of molecularly imprinted technique and MXene/NH2-CNTs nanomaterials to achieve high selectivity and high sensitivity for the determination of fisetin. The factors that affect sensor response were studied and optimized. The as-prepared molecular imprinting sensor, under the optimized conditions, presented a good linear relationship with the fisetin concentration ranging from 0.003 μmol L−1 to 20.0 μmol L−1 with a limit of detection (LOD) of 1.0 nmol L−1. Besides, with favorable stability and selectivity, this newly developed sensor was utilized for the detection of fisetin in actual samples with satisfactory results.

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Hierarchical porous MXene/amino carbon nanotubes-based molecular imprinting sensor for highly sensitive and selective sensing of fisetin

In biosensors and biofuel cells, it is often desirable to accelerate the electron transfer rate between the enzyme and electrode surface to improve the performance of the devices (sensitivity or power output). To this end, in this review, we focus on three important strategies available to improve the performance of enzyme-modified electrodes: the use of protein engineering, designer polymers, and the introduction of nanomaterials. Engineering the protein or proteins that constitute the biocatalytic elements allow tuning their stability, activity, and specificity. It can also allow changing the enzyme immobilization efficiency (adsorption vs. covalent immobilization, for example). If direct electron transfer is not favorable, it may be possible to introduce polymers in the system that mediate the electron transfer to or from the electrode surface. Significant advances have recently been made on the design of polymers to modify electrodes, including molecularly imprinted polymers and responsive polymers. A third element that can be incorporated into electrodes is nanoparticles. These nanomaterials can act as scaffolds to immobilize the biocatalytic elements through adsorption or chemical reaction with functional groups, increasing the surface area and the robustness of the electrode. A wealth of nanomaterials is being tested as part of novel enzyme-modified electrode designs, including graphene, carbon nanotubes, metallic nanoparticles, silicas, and metal–organic frameworks. Some of these can also be designed as nanowires to enable or shorten the direct electron transfer from distal active sites in the enzymes. In addition to these strategies, we also highlight selected applications of enzyme-modified electrodes, including glucose biosensing, self-powered biosensors, and self-charging biosupercapacitors. We conclude the review with a reflection on novel approaches, applications, and challenges that we foresee can impact how to design the enzyme-modified electrodes of tomorrow.

Enzyme-modified electrodes for biosensors and biofuel cells

Highly sensitive paper-based electrochemical sensor for reagent free detection of bisphenol A.

Molecularly imprinted polymers (MIPs) are artificially synthesized materials to mimic the molecular recognition process of biological macromolecules such as substrate-enzyme or antigen-antibody. The combination of these biomimetic materials with electrochemical techniques has allowed the development of advanced sensing devices, which significantly improve the performance of bare or catalyst-modified sensors, being able to unleash new applications. However, despite the high selectivity that MIPs exhibit, those can still show some cross-response towards other compounds, especially with chemically analogous (bio)molecules. Thus, the combination of MIPs with chemometric methods opens the room for the development of what could be considered a new type of electronic tongues, i.e. sensor array systems,  based on its usage. In this direction, this review provides an overview of the more common synthetic approaches, as well as the strategies that can be used to achieve the integration of MIPs and electrochemical sensors, followed by some recent examples over different areas in order to illustrate the potential of such combination in very diverse applications.

/pdf/molecularly-imprinted-polymers-towards-electrochemical-314imn3762.pdf

Molecularly imprinted polymers - towards electrochemical sensors and electronic tongues

Detection of Bisphenol A in aqueous medium by screen printed carbon electrodes incorporating electrochemical molecularly imprinted polymers.

Irvingia gabonensis is a non-timber forest product, whose fruit contains an edible fat-rich kernel. This fat can be used not only in human food but also as a source of raw materials in the cosmetic, pharmaceutical and nutraceutical industries. This work aimed to provide a physicochemical description of components present in the almonds and butter of I. gabonensis. Oil was extracted by soxhlet and hot-pressing from almonds. Cryo-MEB analyses allowed the observation of oleosomes in which the triglycerides of almonds are located. The triglyceride profile and the fatty acids profile of the butter were determined by gas chromatography, and a statistical analysis was performed. The thermal properties of oil were analyzed by thermogravimetric analysis. The results revealed that oil bodies have sizes ranging from 30 to 60 µm. With a 63.8 ± 0.2% fat content, I. gabonensis is composed of 98.4% triglycerides. The hot-pressing yield is 47.9%. The main triglycerides are essentially made up of lauric (38.5 ± 0.1%) and myristic (51.9 ± 0.2%) acids. Thermogravimetric analysis showed that the butter melted at 43.4 °C and decomposed at 415.2 °C. These results show that I. gabonensis butter may be proposed as a good source of lauric acid for food and nutrition.

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Raphaël Bikanga

Papers

Detection of Bisphenol A in aqueous medium by screen printed carbon electrodes incorporating electrochemical molecularly imprinted polymers.

Extraction and Physicochemical Composition of Irvingiagabonensis Almond Oil: A Potential Healthy Source of Lauric-Myristic Oil

Dynamic Covalent Bond: Modes of Activation of the C—ON Bond in Alkoxyamines