Template Imprinting Versus Porogen Imprinting of Small Molecules: A Review of Molecularly Imprinted Polymers in Gas Sensing

A new multi-template molecularly imprinted polymer for separation and purification of dioscin, protodioscin, and diosgenin from purple yam

Saponin is an essential natural compound in purple yams with high nutritional and medicinal value. In this work, a multitemplate molecule-imprinted polymer (MMIP) was synthesized with dioscin, protodioscin, and diosgenin templates. The MMIPs were characterized with scanning electron microscopy, thermogravimetric analysis, Brunauer-Emmett-Teller (BET) adsorption, and Fourier transform infrared spectroscopy. The efficacy of the MMIPs was assessed with static, dynamic, selective adsorption, desorption, and reusability experiments. The three saponins were selectively extracted and determined by MMIP-high-performance liquid chromatography. The polymer morphology was regular and spherical. The amount of the MMIP adsorbed was 74.825 mg/g, and the imprinting factor was 2.1. The MMIP adsorbed the three saponins from purple yam extract, with recovery rates of 95.5-103.43 % and desorption rates of 85 %-98 %. In addition, the MMIPs were reused at least six times. These results demonstrated that the MMIPs efficiently and selectively extracted dioscin, protodioscin, and diosgenin from food matrices at high rates.

Molecularly imprinted polymer nanoparticle-carbon nanotube composite electrochemical gas sensor for highly selective and sensitive detection of methanol vapour

An electrochemical gas sensor has been fabricated using molecularly imprinted polymer nanoparticles (nanoMIPs) and multiwalled carbon nanotubes on screen-printed electrodes. Methanol vapour was chosen as the target due to its toxicity as its suitability as a model for more harmful pollutant gases. The sensor functions under ambient conditions and in the required concentration range, in contrast to all previous MIP-based gas sensors for methanol. The sensitivity of the sensor was greatly improved by the addition of multiwall carbon nanotubes, resulting in a limit of detection of approximately 10 ppm. The nanoMIPs provide an inherent selectivity for the target inherent in its design. Selectivity studies were performed with structurally analogous alcohols at various concentrations, demonstrating selectivity for methanol 12.1 times that for ethanol at 2 mmol dm-3 and 4.2 times that for ethanol at 1 mmol dm-3. Interactions with isopropanol and n-propanol were found to be non-specific, and the response to water was negligible. This demonstrates an improvement over previous methanol gas sensors based on molecularly imprinted polymers. No response was observed with carbon nanotubes alone, and no selectivity was observed with non-imprinted equivalents of the nanoMIP sensor. The resulting device is by far the most practical MIP-based instrument for methanol gas sensing thus far described in the literature, being the only example capable of functioning at the necessary methanol vapour concentrations and at the required temperature and humidity. With the selectivity and sensitivity described and the simple design, the developed device provides a substantial advance in the field of molecularly imprinted gas sensors.

A smart chitosan-graphite molecular imprinted composite for the effective trapping and sensing of dimethyl methylphosphonate based on changes in resistance

A molecular imprinted polymer (MIP) fabricated from a chitosan doped with graphite to create a conductive composite (CG-MIC) with the ability to trap and detect dimethyl methylphosphonate (DMMP) through a change in resistance of the material has been successfully manufactured. The GC-MIC presented a maximum trapping capacity of 96 ppm (0.096 mg g-1) of DMMP. A similar non-imprinted composite made of chitosan-graphite (CG-NIC) had a surface adsorption of 48 ppm (0.048 mg g-1) of DMMP. The manufacturing process was tested for consistency and there were no significant differences in resistance between batches of CG-MIC before (around 450 Ω) and after (around 70 Ω) DMMP extraction, representing a homogeneous manufacturing process. Although Atomic Force Microscopy studies revealed that the graphite was not homogenously distributed throughout the chitosan matrix, the response was consistent. The changes in the concentration of DMMP within the self-sensing material, being proportional to those in gas concentration, could be followed by the changes in resistance. The inclusion of common interferents: Acetic acid, acetone, ethanol, ammonium hydroxide and 2-propanol, equivalent in concentration to the DMMP, caused a change in the resistance of the material but did not substantially affect the specific resistance response of the composite material. Based on this data, the CG-MIC could be used as a smart material with sensing capabilities to monitor trapping levels of DMMP.

A Turn-Off Fluorescent Biomimetic Sensor Based on a Molecularly Imprinted Polymer-Coated Amino-Functionalized Zirconium (IV) Metal-Organic Framework for the Ultrasensitive and Selective Detection of Trace Oxytetracycline in Milk

Developing sensitive and effective methods to monitor oxytetracycline residues in food is of great significance for maintaining public health. Herein, a fluorescent sensor (NH₂-UIO-66 (Zr)@MIP) based on a molecularly imprinted polymer-coated amino-functionalized zirconium (IV) metal-organic framework was successfully constructed and first used for the ultrasensitive determination of oxytetracycline. NH₂-UIO-66 (Zr), with a maximum emission wavelength of 455 nm under 350 nm excitation, was prepared using a microwave-assisted heating method. The NH₂-UIO-66 (Zr)@MIP sensor with specific recognition sites for oxytetracycline was then acquired by modifying a molecularly imprinted polymer on the surface of NH₂-UIO-66 (Zr). The introduction of NH₂-UIO-66 (Zr) as both a signal tag and supporter can strengthen the sensitivity of the fluorescence sensor. Thanks to the combination of the unique characteristics of the molecularly imprinted polymer and NH₂-UIO-66 (Zr), the prepared sensor not only exhibited a sensitive fluorescence response, specific identification capabilities and a high selectivity for oxytetracycline, but also showed good fluorescence stability, satisfactory precision and reproducibility. The fabricated sensor displayed a fluorescent linear quenching in the OTC concentration range of 0.05-40 μg mL^-1, with a detection limit of 0.012 μg mL^-1. More importantly, the fluorescence sensor was finally applied for the detection of oxytetracycline in milk, and the results were comparable to those obtained using the HPLC approach. Hence, the NH₂-UIO-66 (Zr)@MIP sensor possesses great application potential for the accurate evaluation of trace oxytetracycline in dairy products.

Artificial Olfactory Biohybrid System: An Evolving Sense of Smell

The olfactory system can detect and recognize tens of thousands of volatile organic compounds (VOCs) at low concentrations in complex environments. Bioelectronic nose (B-EN), which mimics olfactory systems, is becoming an emerging sensing technology for identifying VOCs with sensitivity and specificity. B-ENs integrate electronic sensors with bioreceptors and pattern recognition technologies to enable medical diagnosis, public security, environmental monitoring, and food safety. However, there is currently no commercially available B-EN on the market. Apart from the high selectivity and sensitivity necessary for volatile organic compound analysis, commercial B-ENs must overcome issues impacting sensor operation and other problems associated with odor localization. The emergence of nanotechnology has provided a novel research concept for addressing these problems. In this work, the structure and operational mechanisms of biomimetic olfactory systems are discussed, with an emphasis on the development and immobilization of materials. Various biosensor applications and current developments are reviewed. Challenges and opportunities for fulfilling the potential of artificial olfactory biohybrid systems in fundamental and practical research are investigated in greater depth.