A sandwich-type analytical sensor device for the determination of fluoride in aqueous samples was developed. The device is based on a versatile sandwich design, consisting of a molecularly imprinted polymer layer confined between two material layers. One layer is transparent to UV radiation while the other allows the passage of the analyte. The imprinted polymer, previously reported by our team, presents an increase on its fluorescence that correlates with the concentration of fluoride.

Analytical parameters such as limit of detection (LOD), limit of quantification (LOQ), linear range, repeatability, and accuracy were quantified to evaluate the device's performance. Furthermore, the sensor's response to interfering substances, such as phosphate and chloride, was assessed. With promising performance characteristics, this sandwich-type sensor demonstrates potential for application in diverse sample matrices, including industrial, environmental, and other relevant aqueous samples for fluoride analysis.

There is a growing need for portable, highly sensitive measuring equipment to analyze samples in-situ and in real time. For these reasons, it is becoming increasingly important to research for new experimental equipment to carry out this work with advanced, robust and low-cost devices. In this framework, a flexible, portable and low-cost fluorimeter (under 500€) based on a C12880MA MEMS micro-spectrometer with an Arduino compatible breakout board has been developed for trace analysis of biological substances. The proposed system can employ two selectable excitation sources for flexibility, one in the visible region at 405 nm (incorporated in the board) and an external LED at 365 nm in the UV region. This additional excitation source can be easily interchanged varying the LED type for other wavelengths of interest. The measurement process is micro-controlled, which allows a precise control of the spectrometer sensitivity by adjusting the integration time of each experiment separately. Data acquisition is easy, reliable and interfaced with a spreadsheet for fast spectra visualization and calculations. For testing the performance of the new device in fluorescence measurements, different fluorophore molecules which can be commonly found in biological samples, such as Fluorescein, Riboflavin, Quinine, Rhodamine b and Ru(II)-bipyridyl have been employed showing a high sensitivity in all cases and low quantitation limits (in the ppb range). It is also suitable for the study of other interesting phenomena, such as fluorescence quenching induced by chemical agents (such as halide anions or even auto-quenching). In this sense, an application for the chloride anions quantification in aqueous solutions, has been performed obtaining a LOD value of 18 ppm. Obtained results for all chemicals investigated with the proposed fluorimeter are always very similar in quantification figures or even better than literature data reported with commercial laboratory equipment

Quaternary Ammoniums Compounds (QACs) are biocide disinfectants used in the food industry to decontaminate and prevent the spread of infection. For example, milk tanks can be decontaminated with benzalkonium chloride (BAC) and/or dimethyldidecylammonium chloride (DDAC). The presence of QAC residues in rinsing water after cleaning and disinfection procedures and in milk products is monitored in industry with commercial tests, which are not sensitive enough.

An enzymatic sensor for the detection of QACs was obtained for the first time. We have developed a simple electrochemical method for the immobilization of acetylcholinesterase (AChE). It was based on the covalent bonding of AChE to a multiwall carbon nanotube (c-MWNT)-cross-linked chitosan (Chi) modified glassy carbon screen-printed electrode (SPE) [1]. The AChE activity was inhibited in the presence of QACs, which induced a change in the measured current.

The native structure of the immobilized enzyme AChE was preserved on this composite film, because of the excellent biocompatibility and non-toxicity of chitosan. This film was elaborated by one-step electrodeposition on a glassy carbon screen-printed electrode (GC).

Incorporation of functionalized multiwalled carbon nanotubes (c-MWCNT) into a chitosan film promoted electron transfer reaction and enhanced the electrochemical response.

Glutaraldehyde (GA) was used as cross-linker to covalently bind the AChE, and efficiently prevented leakage of the enzyme from the film.

A sensitive voltammetric sensor was optimized for the rapid detection of QACs (eg. DDAC) in milk [2]. This biosensor is a promising new tool for QACs analysis.

1. Du, D., et al., Amperometric detection of triazophos pesticide using acetylcholinesterase biosensor based on multiwall carbon nanotube–chitosan matrix. Sensors and Actuators B: Chemical, 2007. 127(2): p. 531-535.
2. Zhai, C., et al., Acetylcholinesterase biosensor based on chitosan/prussian blue/multiwall carbon nanotubes/hollow gold nanospheres nanocomposite film by one-stepelectrodeposition. Biosensors and Bioelectronics, 2013. 42: p. 124-130.

Colorimetric and fluorimetric fingerprinting techniques have gained popularity in solving various practical tasks associated with recognition and discrimination of samples. An underdeveloped aspect of optical fingerprinting methods is the use of kinetic factor that can serve as an additional variable. For the recognition of each type of sample we propose to select an indicator reaction whose rate is sensitive to the small variations in the composition of the sample. The samples and reactants are mixed in the 96-well fluorimetric plates, after which absorbance and fluorescence of the wells is registered photographically every several minutes. After digitization, the results are subjected to chemometric processing.

For the recognition of 8 model proteins or 10 samples of rennet enzymes, pre-oxidation of the sample with hypochlorite was suggested, and then a carbocyanine dye was added as reductant. For the recognition of motor oils, a set of reactions occurring in ethanol was proposed, and the reaction of oxidation of a commercial carbocyanine dye with nitric acid permitted to completely discriminate 6 oils. For the estimation of the doses absorbed by irradiated food (potatoes, ground beef), oxidation reactions of several carbocyanine dyes with hydrogen peroxide were used, which allowed for confident recognition of the dose to an order of magnitude (0, 100, 1000, 10,000 Gy). The proposed reaction-based approach turned out to be a powerful technique for solving various recognition tasks.

Gas sensors, such as chemoresistors and functionalized quartz microbalances and other types, often exhibit limited selectivity, necessitating their integration into sensor arrays. Through the utilization of statistical analysis techniques, these arrays can collectively provide enhanced selectivity. However, it is important to note that the selectivity achieved by electronic noses is artificial in nature. Consequently, despite their ability to discriminate between different samples, electronic noses do not provide insights into the specific gases or volatile organic compounds (VOCs) being detected. This inherent limitation poses challenges in understanding the precise analytes detected by electronic noses, further emphasizing the need for complementary analytical techniques to identify and characterize specific gas or VOC targets.

Proton transfer reaction mass spectrometry (PTR-MS) is a powerful and fast analytical technique that can be used simultaneously with sensors to help understand which molecules they are detecting. In addition to this reference technique role, PTR-MS can also be used to better understand the sampling process and thus optimize it.

Spiropyran-based sensors have garnered significant attention in recent years due to their unique photochromic properties and their potential applications in various fields. This collaborative study focuses on the molecular and photophysical properties of an amphiphilic molecule that contains spiropyran. The research specifically investigating these properties in both organic and aqueous solutions. In organic solvents, the spiropyran-containing system exhibits positive photochromism, meaning that upon exposure to UV light, the initially colorless spiropyran form undergoes a transformation into a colorful merocyanine isomer. However, when the amphiphile is dissolved in an aqueous solution, it displays negative photochromism. In water, the orange-red merocyanine form becomes thermodynamically more stable, and both UV and visible light stimuli cause partial or complete photobleaching of the solution.

The explanation for this phenomenon is elucidated through the use of density functional theory calculations and classical modeling, which includes thermodynamic integration. The simulations uncover that the stabilization of the merocyanine form in water occurs with an energy of approximately 70 kJ mol⁻¹. Furthermore, the Helmholtz free energy of hydration for the merocyanine form is 100 kJ mol⁻¹ lower than that of the spiropyran isomer in water. This disparity arises from the molecular properties of merocyanine: after undergoing a ring-opening reaction, the molecule transforms into a zwitterionic form, as confirmed by the electrostatic potential plotted around the opened structure. The presence of three charged groups on the periphery of the planar conjugated backbone facilitates the self-assembly of merocyanine molecules in water. This self-assembly leads to the formation of elongated associates with stack-like building blocks, as observed in molecular dynamics simulations of the aqueous solution at concentrations surpassing the critical micelle concentration.

By quantitatively evaluating the hydrophilicity switching in surfactants containing spiropyran/merocyanine, this study provides insights that could drive the exploration of new sersoric systems, including colloidal and polymeric ones. The aim is to enable the remote tuning of their morphology, thereby generating promising shapes and patterns relevant to the demands of modern nanotechnology.

Additive manufacturing (most commonly known as 3D printing) is emerging as an alternative approach for the fabrication of customized electrochemical sensors, owing to their many unique advantages such as its low-cost (both of the material and equipment), tunability and easy prototyping. Concretely, electrodes are fabricated by fused deposition modelling (FDM) from thermoplastics such as poly-lactic acid (PLA) or acrylonitrile-butadiene-styrene (ABS), commonly doped with different carbon-based materials such as carbon black, carbon nanotubes (CNTs) or graphene to overcome the insulating nature of PLA and ABS. Furthermore, the ease of fabrication of composite materials (through the incorporation of redox mediators/electrocatalysts during the extrusion of customized filaments) combined with the automatized fabrication and miniaturization makes 3D printing even more appealing.

In this direction, the development of a simple protocol for the preparation of bulk-modified conductive filaments for the printing of voltammetric sensors is explored herein. Firstly, optimum proportions of the composite material were found by percolation theory. Next, the process for the printing and activation of the filament were also optimized to ensure the highest reproducibility, sensitivity, stability and fast response. To this aim, devices were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and their performance was benchmarked against commercial electrodes. Additionally, morphological characterization of the electrodes was conducted by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX). Finally, the potential of the approach is demonstrated through the amperometric detection of melatonin in over the counter (OTC) pharmaceuticals.

Food contact materials are materials and utensils with direct contact with food products. Different plastic polymers, glass, paper, and board are examples of compounds used to produce these packages. Moreover, these compounds are usually fortified with different additives, such as antioxidants and plasticizers, improving the food contact materials’ technological properties. There is a concern regarding the diffusion of these chemicals from materials to food since these molecules do not have an inert behavior in the package. Furthermore, additives incorporated into food contact materials have been related to toxicological effects, leading to interferences in the reproductive system or affecting the gut microbiota. In this way, to carry out assessments in which migration is evaluated must be performed using the gas chromatography-mass spectrometry (GC-MS) technique as the most for both target and non-target analysis of compounds present in plastic packaging materials due to its high sensitivity and accessibility in the routine control analysis. Moreover, in silico tools have been suggested as cost-effective and throughout identification predictors, which can provide a screening of compounds, complementing in vivo and in vitro test results. In this work, the identification techniques of non-intentional and intentional added compounds present in food contact materials are studied to determine the status in this field.

Food spoilage concerns from ethical, social, economic, and environmental points of view because of its direct link to food insecurity. At every stage of the value chain, food products are subject to spoilage due to the loss of freshness resulting from contamination caused by flaws in the traceability or adulteration events. The existing quality controls and detection methods are time-consuming, and need a significant amount of sample concentration, expertise, and expense. Nanotechnology, particularly nanosensors, could be a game-changer in identifying food contaminants such as pathogens, allergens, or pesticides. Nanosensors are a promising tool for food quality assessment, as they are selective, sensitive, and reliable devices capable of real-time monitoring. Nevertheless, we must consider the uncertainties surrounding nanotechnology, including the unawareness of nanomaterials and their toxicity. Also, consumers' perspectives, the feasibility of implementation, and cost-effectiveness must be considered for the future applications of these devices. Yet, intensive evaluation and validation by regulatory organizations responsible for food safety control and monitoring are crucial for their continuous development and implementation. It is essential to continue researching to ensure the growth of nanotechnology. This communication focuses on the most current research on the potential advantages of this cutting-edge technology of applying nanosensors to detect biological and chemical contaminants in food samples.

Hydrogen peroxide, a vital component in oxidative reactions during biosynthesis, serves as a crucial defense against bacteria, particularly in urine. Nevertheless, its presence can also indicate severe diseases and disorders, such as asthma or lung cancer. Consequently, the demand for more precise and sensitive materials and techniques to detect hydrogen peroxide is rapidly growing. This study aim to explore the electrochemical sensing capabilities of newly developed copper selenide nanobelts.

Copper selenide was choose an electrocatalyst for the detection of hydrogen peroxide, based on copper study for H₂O₂ detection even in its gaseous form. To synthesize the copper selenide nanobelts, a straightforward solvothermal method was employed, utilizing DETA (Diethylenetriamine) as both a reaction medium and a morphology-directing agent. The reaction was conducted at 180°C for 16 hours to obtain the final product.

Characterization techniques including SEM, TEM, and XRD were employed to confirm the nanobelts' morphology, crystallinity, and purity. Encouragingly, the copper selenide nanobelts exhibited excellent sensitivity in detecting hydrogen peroxide in an electrolyte solution consisting of 0.1M KOH and 0.25% PAA. The sensing application of copper selenide was studied across a range of hydrogen peroxide concentrations, from 0.03 to 1 mmol, demonstrating a highly linear response with impressively low limits of detection (LOD) and quantification (LOQ) values.

This research sheds light on the significant role of copper selenide nanobelts for precise and sensitive detection, paving the way for advancements in diagnosing and monitoring various diseases and disorders associated with hydrogen peroxide levels.