Hydrogen peroxide is a compound of great importance both chemically and biologically. It plays a key role in oxidative reactions during biosynthesis and aids in the body's defense against bacteria, particularly in urine. However, its presence can also indicate serious diseases and disorders. An elevated concentration of hydrogen peroxide in breath may suggest conditions such as asthma or lung cancer. Therefore, there is a growing need for more accurate and sensitive methods to determine this substance. This study aims to compare the potential of different polymers as supporting electrolytes for the electrochemical determination of hydrogen peroxide, utilizing copper (II) ions as a catalyst for its reduction.

Polyacrylic acid has long been recognized for its excellent absorption properties, and its use in hydrogen peroxide determination has been partially acknowledged [Sensors and Actuators Reports, 2023, 5, 100144; Journal of Physical Chemistry C, 2022, 126(43), 18313–18322]. It is hypothesized that poly(2-acrylamido-2-methyl-1-propanesulfonic acid) exhibits similar or improved properties compared to polyacrylic acid, especially when considering its conductive properties. This research introduces a method for the determination of hydrogen peroxide in the presence of copper (II) ions as a redox mediator, utilizing poly(2-acrylamido-2-methyl-1-propanesulfonic acid) as the supporting electrolyte. Additionally, a comparison is made between this method and the previously known method using polyacrylic acid as the supporting electrolyte.

Electrochemical sensors and biosensors have great interest in food quality control due to their fast analysis and low prices. However, there are several problems related to the fouling of the electrodes and the preservation conditions that restrict their use in real sample analysis. An alternate method for analyzing complex liquids, such as milk, relies on a multivariate description of the chemical composition of samples based on non-specific fingerprints provided by an array of sensors and the quimiometric analysis of their responses [1-2]. The purpose of this work was to develop an array of biosensors for its application in milk analysis using differential pulse voltammetry (DPV) as the transduction mechanism. In order to develop sensors with enhanced sensitivities and selectivity towards certain molecules, such as galactose and glucose, enzymes were immobilized on the sensors surface resulting in an array of five sensors. Higher sensitivities were achieved in the responses of the biosensors developed showing evident increases on the intensities in presence of the target molecules on standard solutions confirming the correct immobilization of the biomaterial. Furthermore, a first approach on the analysis of raw milk samples was also made by analyzing milks from individual cows to determine differences in their nutritional composition.

[1]Wasilewski T., Kamysz W., Gębicki J. "Bioelectronic tongue: Current status and perspectives" Biosensors and Bioelectronics 150, 2020, 111923. https://doi.org/10.1016/j.bios.2019.111923.

[2] Skládal P. "Smart bioelectronic tongues for food and drinks control" TrAC Trends in Analytical Chemistry 127, 2020, 115887. https://doi.org/10.1016/j.trac.2020.115887.

Diphenylamine (DPA) is mainly utilized as a scald inhibitor in fruits, and its residues are found in different fruit and environmental samples. Those residues, even in the smallest concentrations pose a hazard to human health since DPA is classified as a probable human carcinogen. Thus, in this study, a novel molecularly imprinted polymer (MIP) sensor was developed for the detection of diphenylamine. The surface of a boron-doped diamond electrode was modified by chitosan electrodeposition using DPA as template. Electrodeposition was carried out using chronoamperometry. The molecularly non-imprinted polymer (NIP) was prepared similarly to the MIP in the absence of DPA. Different parameters including deposition time, concentration of template and incubation time were optimized. The performances of the MIP and NIP-modified electrodes were compared using differential pulse voltammetry. Electrochemical signal was registered using DPA response. Under optimum conditions, a linear concentration range towards DPA was obtained by the MIP-modified electrode between 25 and 200 µM with a good sensitivity. The possibility of reusing the electrodes was also tested and a recovery range of more than 80% was obtained in PBS buffer.

The European Food Safety Authority (EFSA) has recently updated the tolerable daily intake (TDI) of Bisphenol A (BPA), from 4 µg/kg bw per day to 0.2 ng/kg bw per day, reducing TDI by 20,000 times more than before. This change came as a result of the potent health effects of BPA as it can induce cancer and mutagenesis, and plays a vital role in hormonal disruption, immunosuppression, and infertility. Accordingly, the aim of this study is to prepare a novel sensor for the detection and possible removal of BPA from aqueous media. Molecularly Imprinted Polymers (MIP) was first prepared using iron oxide nanoparticles (Fe₃O₄ NPs) coated with (3-aminopropyl)triethyoxysilane (APTES) as the functional monomer, tetraethoxysilane (TEOS) as crosslinker and BPA as a template. The successful synthesis of the MIP was confirmed using Fourier transform infrared spectroscopy (FTIR). Boron-doped diamond electrodes were modified with the functionalized MIP/Fe₃O₄ NP_S and the template was removed by washing with a methanol/acetic acid solution. Electrochemical signal was recorded following the BPA response. The electrochemical performance of the proposed MIP based sensor was assessed by differential pulse voltammetry (DPV). Under optimum conditions, experimental results showed a linear response towards the BPA concentrations in the range from 1.5 to 120 µM, with a good sensitivity. The sensor also possesses a good stability, selectivity and high recovery range of more than 85% towards BPA in PBS buffer.

Milk is an important and necessary food product for reducing morbidity in the human body. There are numerous falsifications of milk and dairy products in this regard. At the same time, one of the most time-consuming indicators of raw milk is microbiological parameters. The purpose of this research is to study the gas phase over raw milk samples using piezoelectric sensors with polycomposite coatings to assess its physicochemical and microbiological parameters. The sorption of volatile compounds onto the coatings based on chitosan, micellar casein concentrate, and amorphous silicon oxide in impact with polymeric sorbents was studied. This array was employed to analyse the gas phase over raw milk samples. It has been evaluated physicochemical indicators of milk (content of fat, protein, solid substances; acidity) and microbiological indicators (total microbial count; the presence of mould, yeasts, pathogenic microorganisms). The influence of several factors on the composition of volatile compounds in milk was evaluated using the output data of sensors. There are injector and frontal mode of input gas phase into the detection cell, the processing of milk samples by ultrasound and microwave radiation, the introduction of glucose and peroxide additives into samples. It has been established statistically significant correlations between the sensor output data and the physicochemical or microbiological parameters of raw milk samples. The regression models were constructed employing chemometrics techniques to predict the quality indicators of milk based on the output data of piezoelectric sensors with composite coatings, with an error comparable to that of standard methods.

In this work, we describe the fabrication of paper-based aptasensing devices for ampicillin determination that rely on the salt-induced aggregation of gold nanoparticles (AuNPs) in the presence of the target. Circular paper-based devices were created on paper by pen-plotting (using water-repellent ink to create hydrophobic barriers) and were modified with NaCl. The sample was incubated with an ampicillin aptamer and AuNPs and was added to the assay zones of the paper-based devices. In the absence of ampicillin, the aptamer prevented aggregation of the AuNPs and the assay zones remained red. When ampicillin was present, it selectively bound with the aptamer and the AuNPs aggregate producing a purple color. The color of the assay zones was monitored via a smartphone and the color graduation was related to the ampicillin concentration in the sample. Different experimental parameters (type of paper, concentration of reagents, incubation times) were investigated and the analytical features of the method for the determination of ampicillin were established.

Compared with other gas-phase analytes, the coexistence and competing effect of moisture component has long faced great difficulty and technical challenge for the reliable detection of chemically oxidizing active H₂O₂ vapor (HPV). Recently, our group designed and prepared a chemiresistive sensor based on conductive films of poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and PEDOT:PSS/PEDOT to achieve direct detection of HPV at ppm level. Specially, the hydrophobic PEDOT layer was polymerized on the surface of the PEDOT:PSS film by electrochemical method to attenuate the adverse effect of moisture within HPV on the stability and detection performance of the sensing film of PEDOT:PSS/PEDOT.

Through the selection of N-type organic semiconductor molecules and the method of supramolecular self-assembly at the solvent phase interface, the perylene tetracarboxylic diimide (PTCDIs) nanofiber film with loose and porous morphology was constructed by in-situ deposition on the surface of ITO conductive glass. Then the P-type organic semiconducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) was grown in the fiber interweaving network of this film via quantitative electrochemical polymerization, thus preparing PTCDIs@PEDOT composite film with N-P heterojunction architecture. PTCDIs@PEDOT film has good moisture resistance and improved sensitivity and signal response for gas phase H₂O₂ detection.

Iron is the most common element in nature, and is included among the physiological and active, irreplaceable macroelements. Today, photometric methods are widely used for the determination of toxic and highly toxic heavy metals. This method is of great importance due to its sensitivity, simplicity, and less time spent on analysis. In this article, the optimal conditions for the formation of a complex of Fe(III) with 2-napthylcarboxymethylnitrate reagent were studied and the method of photometric determination of Fe(III) was developed. In the process of photometric determination of Fe (III) with 2-napthylcarboxymethylcitrate, the following was performed: choice of light filter, dependence of complex formation on the acidity of the environment, dependence on the composition of the buffer solution, dependence on the composition of the reagent, field of obedience to Ber's law , spectral characteristics, sensitivity according to Sendal, lower detection limit of Fe(III), molar extinction coefficient, determination of the ratio of component moles of the complex and method of photometric determination of Fe(III).

This overview concerns recent patents and patented technologies in relation to the development of hydrogel-based biosensors, published until 2022. As a result, 257 patent documents and 145 simple patent families have been searched through different specialized patent databases. Furthermore, the patent classification confirmed that the most claimed inventions concern chemical analysis of biological material and biospecific binding assay materials with an insoluble carrier for immobilizing immunochemicals. Overall, research, development, and innovation concerning hydrogel-based biosensors are based on improvements in the synthesis of hydrogels, biomolecule immobilization and detection, as well as microelectronic device integration and microfabrication techniques. A collection of recent patented technologies is proposed at the end. In this respect, it aimed to demonstrate potential trends and challenges in relation to the development of hydrogel-based biosensors.