Imprinted Oxide and MIP/Oxide Hybrid Nanomaterials for Chemical Sensors †

Microwave-assisted preparation of yellow fluorescent graphitic carbon nitride quantum dots for trace tetracycline-specific detection

Tetracycline (TC) is extensively utilized in livestock breeding, aquaculture, and medical industry. TC residues seriously harm food security, the environment, and human health. There is an urgent need to exploit a highly efficient and sensitive testing method to monitor TC residue levels in aquatic environments. In this study, graphitic carbon nitride quantum dots (g-CNQDs) were successfully synthesized by a one-step microwave-assisted method using citric acid and urea as precursors. The as-prepared g-CNQDs with size of 1.25-3.75 nm exhibited bright yellow fluorescence at 523 nm when excited at 397 nm. Interestingly, this characteristic fluorescence emission of g-CNQDs could be selectively and efficiently quenched by TC. Based on this phenomenon, for TC detection was successfully explored and applied in real water samples. Wide linear scope of 7-100 μM, low detection limit (LOD) of 0.48 μM, satisfactory recovery of 97.77%-103.4%, and good relative standard deviation (RSD) of 1.05-5.87% were obtained. Mechanism investigations revealed that the static quenching and the inner filter effect (IFE) were responsible for this fluorescence quenching between g-CNQDs and TC. This work not only provided a facile approach for g-CNQDs synthesis but also constructed a g-CNQDs-based fluorescent sensor platform for the highly sensitive and selective detection of TC in aquatic environments.

Hydrothermally Synthesized Z-Scheme Nanocomposite of ZIF-9 Modified MXene for Photocatalytic Degradation of 4-Chlorophenol

4-Chlorophenol (4CP) is a well-known environmental contaminant often detected in wastewater, generally arising from industrial processes such as chemical manufacture, pharmaceutical production, and pesticide formulation. 4CP is a matter of great concern since it is persistent and has the potential to have harmful impacts on both aquatic ecosystems and human health, owing to its hazardous and mutagenic properties. Hence, degradation of 4CP is of utmost significance. This research investigates the photocatalytic degradation of 4CP using a novel Z-scheme heterojunction nanocomposite composed of MXene and ZIF-9. The nanocomposite is synthesized through a two-step hydrothermal method and thoroughly characterized by using XRD, SEM, UV-visible spectroscopy, zeta potential, and electrochemical impedance spectroscopy studies, confirming successful fabrication with improved surface properties. The comparative photocatalytic degradation studies between pristine materials and the nanocomposite were performed, and significant enhancement in performance was observed. The effect of pH on the degradation efficiency is also explored and correlated with the surface charge. The Z-scheme photocatalysis mechanism is proposed, which is supported by time-resolved photoluminescence studies and scavenger experiments. The reusability of the nanocomposite is also evaluated. The study contributes to the development of efficient and sustainable photocatalysts for wastewater treatment.

Sonochemical Synthesized Manganese Oxide Nanoparticles as Fluorescent Sensor for Selenium (IV) Quantification. Application to Food and Drink Samples

Manganese oxide nanoparticles (MnO Nps), sonochemical synthesized and characterized in our laboratory, are proposed as fluorescent sensor for selenium (Se) determination. The new methodology has been developed based on the enhancing effect of the Se(IV) on fluorescent emission of MnO Nps. Experimental variables that influence on fluorimetric sensitivity were optimized. The calibration graph using zeroth order regression was linear from 0.189 ng L-1 to 8.00 × 103 µg L-1, with correlation coefficient better than 0.99. Under the optimal conditions, the limits of detection and quantification were of 0.062 ng L-1 and 0.189 ng L-1, respectively. The trueness of the methodology was assessed through standard addition method obtaining recovery near to 100%. This method showed good tolerance to foreign ions, particularly to Se(VI), and was applied to determination of Se(IV) trace in food and drink samples with satisfactory results. With the intention of preserving the environment from harmful effects, a degradation study of the used nanomaterials has been included for their subsequent disposal.

Highly selective molecularly imprinted polymer nanoparticles (MIP NPs)-based microfluidic gas sensor for tetrahydrocannabinol (THC) detection

A highly selective microfluidic integrated metal oxide gas sensor for THC detection is reported based on MIP nanoparticles (MIP NPs). We synthesized MIP NPs with THC recognition sites and coated them on a 3D-printed microfluidic channel surface. The sensitivity and selectivity of coated microfluidic integrated gas sensors were evaluated by exposure to THC, cannabidiol (CBD), methanol, and ethanol analytes in 300-700 ppm at 300 °C. For comparison, reference signals were obtained from a microfluidic channel coated with nonimprinted polymers (NIP NPs). The MIP and NIP NPs were characterized using scanning electron microscopy (SEM) and Raman spectroscopy. MIP and NIP NPs channels response data were combined and classified with 96.3% accuracy using the Fine KNN classification model in MATLAB R2021b Classification Learner App. Compared to the MIP NPs coated channel, the NIP NPs channel had poor selectivity towards THC, demonstrating that the THC recognition sites in the MIP structure enabled selective detection of THC. The findings demonstrated that the recognition sites of MIP NPs properly captured THC molecules, enabling the selective detection of THC compared to CBD, methanol, and ethanol.

Use of molecular imprinted polymers as sensitive/selective luminescent sensing probes for pesticides/herbicides in water and food samples

As non-biological molecules, molecular imprinted polymers (MIPs) can be made as antibody mimics for the development of luminescence sensors for various targets. The combination of MIPs with nanomaterials is further recognized as a useful option to improve the sensitivity of luminescence sensors. In this work, the recent progresses made in the fabrication of fluorescence, phosphorescence, chemiluminescence, and electrochemiluminescence sensors based on such combination have been reviewed with emphasis on the detection of pesticides/herbicides. Accordingly, the materials that are most feasible for the detection of such targets are recommended based on the MIP technologies.

Kinetic Resolution of Racemic Mixtures via Enantioselective Photocatalysis

Despite the increasing demand for enantiopure drugs in the pharmaceutical industry, currently available chiral separation technologies are still lagging behind, whether due to throughput or to operability considerations. This paper presents a new kinetic resolution method, based on the specific adsorption of a target enantiomer onto a molecularly imprinted surface of a photocatalyst and its subsequent degradation through a photocatalytic mechanism. The current model system is composed of an active TiO₂ layer, on which the target enantiomer is adsorbed. A photocatalytic suppression layer of Al₂O₃ is then grown around the adsorbed target molecules by atomic layer deposition. Following the removal of the templating molecules, molecularly imprinted cavities that correspond to the adsorbed species are formed. The stereospecific nature of these pores encourages enantioselective degradation of the undesired species through its enhanced adsorption on the photocatalyst surface, while dampening nonselective photocatalytic activity around the imprinted sites. The method, demonstrated with the dipeptide leucylglycine as a model system, revealed a selectivity factor of up to 7 and an enrichment of a single enantiomer to 85% from an initially racemic mixture. The wide range of parameters that can be optimized (photocatalyst, concentration of imprinted sites, type of passivating layer, etc.) points to the great potential of this method for obtaining enantiomerically pure compounds, beginning from racemic mixtures.

A molecularly imprinted polymer on chromium (ΙΙΙ) oxide nanoparticles for spectrofluorometric detection of bisphenol A

A unique fluorescent probe for the detection of bisphenol A (BPA) was established by creating a molecularly imprinted polymer (MIP) shell on chromium (ΙΙΙ) oxide nanoparticles (Cr₂O₃ NPs). The advantages of high selectivity of MIPs and the strong fluorescence property of Cr₂O₃ NPs were combined for the preparation of the probe. MIPs-coated Cr₂O₃ NPs were composed by anchoring MIP layer on the surface of Cr₂O₃ NPs using one-pot precipitation polymerization. Acrylic-based monomer and cross-linker were used to prepared MIP. The MIP-coated Cr₂O₃ NPs were characterized by spectrofluorometery, Fourier transform infrared spectroscopy, transmission electron microscopy, field transmission electron microscopy, dynamic light scattering, EDX and elemental mapping. The prepared NPs showed strong fluorescence emission at 360 nm excited at 300 nm which quenched in the presence of BPA. The dynamic range of the optical sensor was in the range of 0.04-4.4 μmol L^-1 and the detection limit was 0.015 μmol L^-1. The relative standard deviation was 2.2 and 1.3% for the concentration levels of 0.14 and 3.1 μmol L^-1, respectively. The probe had a great selectivity in the determination of BPA with an imprinting factor of 6.3. The sensor was applied for the quantification of bisphenol A in water samples.

Recent Applications of Molecularly Imprinted Sol-Gel Methodology in Sample Preparation

Due to their selectivity and chemical stability, molecularly imprinted polymers have attracted great interest in sample preparation. Imprinted polymers have been applied for the extraction and the enrichment of different sorts of trace analytes in biological and environmental samples before their analysis. Additionally, MIPs are utilized in various sample preparation techniques such as SPE, SPME, SBSE and MEPS. Nevertheless, molecularly imprinted polymers suffer from thermal (stable only up to 150 °C) and mechanical stability issues, improper porosity and poor capacity. The sol-gel methodology as a promising alternative to address these limitations allowing the production of sorbents with controlled porosity and higher surface area. Thus the combination of molecularly imprinted technology and sol-gel technology can create influential materials with high selectivity, high capacity and high thermal stability. This work aims to present an overview of molecularly imprinted sol-gel polymerization methods and their applications in analytical and bioanalytical fields.

Recent Progress of Imprinted Nanomaterials in Analytical Chemistry

Molecularly imprinted polymers (MIPs) are a type of tailor-made materials that have ability to selectively recognize the target compound/s. MIPs have gained significant research interest in solid-phase extraction, catalysis, and sensor applications due to their unique properties such as low cost, robustness, and high selectivity. In addition, MIPs can be prepared as composite nanomaterials using nanoparticles, multiwalled carbon nanotubes (MWCNTs), nanorods, quantum dots (QDs), graphene, and clays. This review paper aims to demonstrate and highlight the recent progress of the applications of imprinted nanocomposite materials in analytical chemistry.