Light harvesting enhancement through band structure engineering in graphite carbon nitride / polydopamine nanocomposite photocatalyst: Addressing persistent organophosphorus pesticide pollution in water systems

Organophosphorus pesticides, particularly profenofos (PF), pose a significant threat to the food supply and human health due to their persistence, toxicity, and resistance to natural breakdown processes. An urgent need exists for an environmentally friendly solution, and photocatalysis emerges as a practical, cost-effective option. However, challenges like poor light responsiveness and difficulties in material separation and reusability persist. To address these issues, we developed a nanocomposite consisting of graphite carbon nitride (g-C3N4) doped with polydopamine (pDA) through a hydrothermal synthesis method. This innovative nanocomposite was employed as a photocatalyst to degrade PF. Various analytical techniques, including UV-DRS, FT-IR, XRD, HR-TEM, and EDAX, were utilized to characterize the synthesized nanocomposite. The strategically modulated band gaps of the nanocomposite enable efficient absorption of UV light, facilitating the robust photocatalytic degradation of PF (96.4%). Our study explored photodegradation using different g-C3N4/pDA catalyst dosages, varied PF concentrations, and pH levels (3, 5, 9, and 11) under UV light. Our findings promise applications in wastewater management, offering an efficient catalyst for PF degradation. This marks a significant stride in addressing challenges related to pesticide pollution in the environment.

Aptamer-binding zirconium-based metal-organic framework composites prepared by two conjunction approaches with enhanced bio-sensing for detecting isocarbophos

A novel label-free and enzyme-free detection strategy has been developed for the electrochemical biosensor detection of isocarbophos (ICP) using UiO-66-NH₂ and aptamer as the signal transducers. In this work, the ICP aptamers were attached to UiO-66-NH₂ through physical mixing and chemical combination methods. In the presence of ICP, the aptamers could undergo conformational change and bind to them, which prevent the electron transfer to the surface of electrode. By comparing the two conjunction approaches of aptasensors, these proposed strategies could selectively and sensitively detect ICP with a detection limit of 6 ng mL^-1 (20.74 nM) and 0.9 ng mL^-1 (3.11 nM). Furthermore, we have also demonstrated the capability of this strategy in the detection of ICP in real samples from vegetable and fruit extract, indicating the potential application of this strategy in food safety issues.

Development of a MIP-Based QCM Sensor for Selective Detection of Penicillins in Aqueous Media

Pharmaceuticals wastes have been recognized as emerging pollutants to the environment. Among those, antibiotics in the aquatic environment are one of the major sources of concern, as chronic, low-dose exposure can lead to antibiotic resistance. Herein, we report on molecularly imprinted polymers (MIP) to recognize penicillin V potassium salt (PenV-K), penicillin G potassium salt (PenG-K), and amoxicillin sodium salt (Amo-Na), which belong to the most widespread group of antibiotics worldwide. Characterization and optimization led to two MIPs comprising methacrylic acid as the monomer and roughly 55% ethylene glycol dimethacrylate as the crosslinker. The obtained layers led to sensitive, selective, repeatable, and reusable sensor responses on quartz crystal microbalances (QCM). The LoD for PenV-K, PenG-K, and Amo-Na sensors are 0.25 mM, 0.30 mM, and 0.28 mM, respectively; imprinting factors reach at least around three. Furthermore, the sensors displayed relative selectivity factors of up to 50% among the three penicillins, which is appreciable given their structural similarity.

The Selectivity of Molecularly Imprinted Polymers

The general claim about novel molecularly imprinted polymers is that they are selective for their template or for another target compound. This claim is usually proved by some kind of experiment, in which a performance parameter of the imprinted polymer is shown to be better towards its template than towards interferents. A closer look at such experiments shows, however, that different experiments may differ substantially in what they tell about the same imprinted polymer's selectivity. Following a short general discussion of selectivity concepts, the selectivity of imprinted polymers is analyzed in batch adsorption, binding assays, chromatography, solid phase extraction, sensors, membranes, and catalysts. A number of examples show the problems arising with each type of application. Suggestions for practical method design are provided.

A Perspective on Recent Advances in Piezoelectric Chemical Sensors for Environmental Monitoring and Foodstuffs Analysis

This paper provides a selection of the last two decades publications on the development and application of chemical sensors based on piezoelectric quartz resonators for a wide range of analytical tasks. Most of the attention is devoted to an analysis of gas and liquid media and to industrial processes controls utilizing single quartz crystal microbalance (QCM) sensors, bulk acoustic wave (BAW) sensors, and their arrays in e-nose systems. The unique opportunity to estimate several heavy metals in natural and wastewater samples from the output of a QCM sensor array highly sensitive to changes in metal ion activity in water vapor is shown. The high potential of QCM multisensor systems for fast and cost-effective water contamination assessments “in situ” without sample pretreatment is demonstrated.

Novel three-Dimensional molecularly imprinted polymer-coated carbon nanotubes (3D-CNTs@MIP) for selective detection of profenofos in food

A new and facile method for selective measurement of profenofos (PFF) using a simple flow-injection system with a molecularly-imprinted-polymer-coated carbon nanotube (3D-CNTs@MIP) amperometric sensor is proposed. The 3D-CNTs@MIP was synthesized by successively coating the surface of carboxylated CNTs with SiO₂ and vinyl end groups, then terminating with molecularly imprinted polymer (MIP) shells. MIP was grafted to the CNT cores using methacrylic acid (MAA) monomer, ethylene glycol dimethacrylate (EGDMA) as cross linker, and 2,2'-azobisisobutyronitrile (AIBN) as initiator. We constructed the PFF sensor by coating the surface of a glassy carbon electrode (GCE) with 3D-CNTs@MIP and removed the imprinting template by solvent extraction. Morphological and structural characterization reveal that blending of the MIP on the CNT surface significantly increases the selective surface area, leading to greater numbers of imprinting sites for improved sensitivity and electron transfer. The 3D-CNTs@MIP sensor exhibits a fast response with good recognition when applied to PFF detection by cyclic voltammetry and amperometry. The PFF oxidation current signal appears at +0.7 V vs Ag/AgCl using 0.1 M phosphate buffer (pH 7.0) as the carrier solution. The designed 3D-imprinted sensor provides a linear response over the range 0.01-200 μM (r² = 0.995) with a low detection limit of 0.002 μM (3σ). The sensor was successfully applied to detection of PFF in vegetable samples.

Electrochemical sensor based on molecularly imprinted polymer for sensitive triclosan detection in wastewater and mineral water

Triclosan (TCS) is a topical antiseptic widely used in different cosmetic products. It is also a common additive in many antimicrobial household consumables. Over a certain concentration, it becomes risky for human and environmental health. This work describes the development of an electrochemical sensor based on molecularly imprinted polymer (MIP), assembled on screen-printed gold electrode (Au-SPE), dedicated to the TCS detection in environmental water sources. To achieve this goal, an acrylamide/bisacrylamide solution was polymerized after linking TCS with the carboxylic polyvinyl chloride (PVC-COOH) layer onto the Au-SPE. The sensor device fabrication and its retention capabilities were characterized through cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy. As control experiment, negligible responses were obtained during the non-imprinted polymer (NIP) test. The sensor could effectively detect TCS avoiding interferences of structural similar substances like 2,4,6-trichlorophenol and catechol. Under optimal conditions, the sensor responses were found logarithmic in the concentration range from 0.1 to 1000 pg mL^-1. Indeed, compared with reported works, this sensor exhibits lower detection limit (LOD) and quantification limit (LOQ) of 0.23 and 0.78 pg mL^-1, respectively. The developed sensor was effectively applied to wastewater samples for TCS detection and displayed satisfactory performances. Moreover, the different wastewater samples, regarding their TCS contents, were correctly classified by using principal component analysis (PCA) technique. Correspondingly, this work has demonstrated a cheap, simple and effective sensing platform for TCS detection thus making it a promising tool for future evolution of accurate and reliable environmental analysis.

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.

Molecularly Imprinted Polymer as an Antibody Substitution in Pseudo-immunoassays for Chemical Contaminants in Food and Environmental Samples

The chemical contaminants in food and the environment are quite harmful to food safety and human health. Rapid, accurate, and cheap detection can effectively control the potential risks derived from these chemical contaminants. Among all detection methods, the immunoassay based on the specific interaction of antibody-analyte is one of the most widely used techniques in the field. However, biological antibodies employed in the immunoassay usually cannot tolerate extreme conditions, resulting in an unstable state in both physical and chemical profiles. Molecularly imprinted polymers (MIPs) are a class of polymers with specific molecular recognition abilities, which are highly robust, showing excellent operational stability under a wide variety of conditions. Recently, MIPs have been used in biomimetic immunoassays for chemical contaminants as an antibody substitute in food and the environment. Here, we reviewed these applications of MIPs incorporated in different analytical platforms, such as enzyme-linked immunosorbent assay, fluorescent immunoassay, chemiluminescent immunoassay, electrochemical immunoassay, microfluidic paper-based immunoassay, and homogeneous immunoassay, and discussed current challenges and future trends in the use of MIPs in biomimetic immunoassays.

An electrodeposited molecularly imprinted quartz crystal microbalance sensor sensitized with AuNPs and rGO material for highly selective and sensitive detection of amantadine

In the present work, a new amantadine (AM) imprinted quartz crystal microbalance (QCM) sensor sensitized by Au nanoparticles (AuNPs) and reduced graphene oxide (rGO) material was fabricated by electrodeposition in the presence of o-aminothiophenol (o-AT) by cyclic voltammetry scanning. AuNPs and graphene, with the advantages of great chemical stability, electrical conductivity, and large surface area, show exceptionally high sensitivity. The results of different modifications of the QCM sensor fabrication process were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman spectroscopy. Under the optimal experimental conditions, the frequency shift of the MIP-QCM sensor showed a linear relationship with the concentration of the AM template in the range of 1.0 × 10⁻⁵ to 1.0 × 10⁻³ mmol L⁻¹ with a limit of detection (LOD) of 5.40 × 10⁻⁶ mmol L⁻¹. The imprinting factor for AM reached 7.1, the selectivity coefficient for the analogues rimantadine (RT), adamantine (AMT) and 1-chloroadamantane (CMT) were 7.3, 5.6, and 6.1, respectively. Here, a highly sensitive, selective and stable QCM sensor prepared via the imprinting approach is reported for the first time for detection of AM from animal-derived food samples.

In the present work, a new amantadine imprinted quartz crystal microbalance sensor sensitized by Au nanoparticles and reduced graphene oxide material was fabricated by electrodeposition of o-aminothiophenol by cyclic voltammetry scanning.

Molecular Imprinting Technology in Quartz Crystal Microbalance (QCM) Sensors

Molecularly imprinted polymers (MIPs) as artificial antibodies have received considerable scientific attention in the past years in the field of (bio)sensors since they have unique features that distinguish them from natural antibodies such as robustness, multiple binding sites, low cost, facile preparation and high stability under extreme operation conditions (higher pH and temperature values, etc.). On the other hand, the Quartz Crystal Microbalance (QCM) is an analytical tool based on the measurement of small mass changes on the sensor surface. QCM sensors are practical and convenient monitoring tools because of their specificity, sensitivity, high accuracy, stability and reproducibility. QCM devices are highly suitable for converting the recognition process achieved using MIP-based memories into a sensor signal. Therefore, the combination of a QCM and MIPs as synthetic receptors enhances the sensitivity through MIP process-based multiplexed binding sites using size, 3D-shape and chemical function having molecular memories of the prepared sensor system toward the target compound to be detected. This review aims to highlight and summarize the recent progress and studies in the field of (bio)sensor systems based on QCMs combined with molecular imprinting technology.

A novel quartz crystal microbalance sensor array based on molecular imprinted polymers for simultaneous detection of clenbuterol and its metabolites

For the rapid and robust detection of both parent clenbuterol (CLB) and its metabolites in swine urine samples, a novel quartz crystal microbalance (QCM) sensor array for CLB detection based on molecularly imprinted polymers (MIPs) was developed in this investigation. At first, clenbuterol and the structural analogs of its metabolites, 4-Aminohippuric acid (AHA) and 4-hydroxymandelic acid (HMA), were chosen as molecular templates. Through computational molecular modeling, the optimum ratio between the functional monomer and molecular template was selected. The surface imprinting method was applied to modify QCM electrode surface to graft a thin MIP film. The grafting polymer was characterized by Fourier-transformed infrared spectrometry (FTIR) and atomic force microscopy (AFM), respectively. After then, an array system composed of three sensors was employed to test the responses with different solutions and the principal component analysis (PCA) was adopted to analyze the corresponding data. As a result, for the designed sensor to clenbuterol, a linear equation y=100.07x-722.96 (R²=0.9928) was found between the sensor frequency shift ΔF and negative logarithm of clenbuterol concentration (-lgC). The limitation of detection (LOD) was 3.0ng/mL, which is lower than the Codex Alimentarius Commission regulations residue limit 10μg/L. The corresponding data of the three template solutions were analyzed by PCA, obtaining 100% recognition. The result demonstrated the feasibility that the developed method could be applied to detect whether the livestock was feed with CLB nutrient redistribution agent by checking the urine samples.

Fiber optic profenofos sensor based on surface plasmon resonance technique and molecular imprinting

A successful approach for the fabrication and characterization of an optical fiber sensor for the detection of profenofos based on surface plasmon resonance (SPR) and molecular imprinting is introduced. Molecular imprinting technology is used for the creation of three dimensional binding sites having complementary shape and size of the specific template molecule over a polymer for the recognition of the same. Binding of template molecule with molecularly imprinted polymer (MIP) layer results in the change in the dielectric nature of the sensing surface (polymer) and is identified by SPR technique. Spectral interrogation method is used for the characterization of the sensing probe. The operating profenofos concentration range of the sensor is from 10(-4) to 10(-1)µg/L. A red shift of 18.7 nm in resonance wavelength is recorded for this profenofos concentration range. The maximum sensitivity of the sensor is 12.7 nm/log (µg/L) at 10(-4)µg/L profenofos concentration. Limit of detection (LOD) of the sensor is found to be 2.5×10(-6)µg/L. Selectivity measurements predict the probe highly selective for the profenofos molecule. Besides high sensitivity due to SPR technique and selectivity due to molecular imprinting, proposed sensor has numerous other advantages like immunity to electromagnetic interference, fast response, low cost and capability of online monitoring and remote sensing of analyte due to the fabrication of the probe on optical fiber.

Quartz-Crystal Microbalance (QCM) for Public Health: An Overview of Its Applications

Nanobiotechnologies, from the convergence of nanotechnology and molecular biology and postgenomics medicine, play a major role in the field of public health. This overview summarizes the potentiality of piezoelectric sensors, and in particular, of quartz-crystal microbalance (QCM), a physical nanogram-sensitive device. QCM enables the rapid, real time, on-site detection of pathogens with an enormous burden in public health, such as influenza and other respiratory viruses, hepatitis B virus (HBV), and drug-resistant bacteria, among others. Further, it allows to detect food allergens, food-borne pathogens, such as Escherichia coli and Salmonella typhimurium, and food chemical contaminants, as well as water-borne microorganisms and environmental contaminants. Moreover, QCM holds promises in early cancer detection and screening of new antiblastic drugs. Applications for monitoring biohazards, for assuring homeland security, and preventing bioterrorism are also discussed.

Quantum dot-DNA aptamer conjugates coupled with capillary electrophoresis: A universal strategy for ratiometric detection of organophosphorus pesticides

Based on the highly sensitivity and stable-fluorescence of water-soluble CdTe/CdS core-shell quantum dots (QDs) with broad-specificity DNA aptamers, a novel ratiometric detection strategy was proposed for the sensitive detection of organophosphorus pesticides by capillary electrophoresis with laser-induced fluorescence (CE-LIF). The as-prepared QDs were first conjugated with the amino-modified oligonucleotide (AMO) by amidation reaction, which is partial complementary to the DNA aptamer of organophosphorus pesticides. Then QD-labeled AMO (QD-AMO) was incubated with the DNA aptamer to form QD-AMO-aptamer duplex. When the target organophosphorus pesticides were added, they could specifically bind the DNA aptamer, leading to the cleavage of QD-AMO-aptamer duplex, accompany with the release of QD-AMO. As a result, the ratio of peak height between QD-AMO and QD-AMO-aptamer duplex changed in the detection process of CE-LIF. This strategy was subsequently applied for the detection of phorate, profenofos, isocarbophos, and omethoate with the detection limits of 0.20, 0.10, 0.17, and 0.23μM, respectively. This is the first report about using QDs as the signal indicators for organophosphorus pesticides detection based on broad-specificity DNA aptamers by CE-LIF, thus contributing to extend the scope of application of QDs in different fields. The proposed method has great potential to be a universal strategy for rapid detection of aptamer-specific small molecule targets by simply changing the types of aptamer sequences.

Surface plasmon resonance sensor for femtomolar detection of testosterone with water-compatible macroporous molecularly imprinted film

A novel water-compatible macroporous molecularly imprinted film (MIF) has been developed for rapid, sensitive, and label-free detection of small molecule testosterone in urine. The MIF was synthesized by photo copolymerization of monomers (methacrylic acid [MAA] and 2-hydroxyethyl methacrylate [HEMA]), cross-linker (ethylene glycol dimethacrylate, EGDMA), and polystyrene nanoparticles (PS NPs) in combination with template testosterone molecules. The PS NPs and template molecules were subsequently removed to form an MIF with macroporous structures and the specific recognition sites of testosterone. Incubation of artificial urine and human urine on the MIF and the non-imprinted film (NIF), respectively, indicated undetectable nonspecific adsorption. Accordingly, the MIF was applied on a surface plasmon resonance (SPR) sensor for the detection of testosterone in phosphate-buffered saline (PBS) and artificial urine with a limit of detection (LOD) down to 10(-15)g/ml. To the best of our knowledge, the LOD is considered as one of the lowest among the SPR sensors for the detection of small molecules. The control experiments performed with analogue molecules such as progesterone and estradiol demonstrated the good selectivity of this MIF for sensing testosterone. Furthermore, this MIF-based SPR sensor shows high stability and reproducibility over 8months of storage at room temperature, which is more robust than protein-based biosensors.

Zinc phthalocyanines with fluorinated substituents for direct sensing of carbamate and organophosphate pesticides in water

Water pollution by pesticides as the result of intensive agriculture and horticulture has brought many negative consequences to humans and ecosystems. Among others, chemical sensor systems are under intense development for direct pesticide analysis in aqueous samples as a cost effective and simple alternative analytical method. In this work, a set of zinc phthalocyanines is studied in its liquid sensing properties using quartz crystal microbalances. Four different species selected from the two most common organophosphorus and carbamate classes of pesticides are used as test analytes. The phthalocyanines are chemically modified with different fluorinated substituents to increase sensor sensitivity and govern pesticide selectivity in order to create sensors with widely diverging analyte responses. By this means, sensors with a general high sensitivity and selectivity for the two pesticide classes were obtained and detection limits down to 0.03 mg.L-1 could be achieved. The response data of the sensors are analyzed in detail using exploratory multivariate data evaluation methods. The results show that phthalocyanine based sensors are a truly capable platform for chemical analysis systems of aqueous samples.