Application of aptamers as the sensing layers in biosensors offers several advantages for the detection of various analytes. Herein, an electrochemical label - free biosensor for dopamine (DA) was developed with the use of 57-mer DNA aptamer. The proposed aptasensor operates via specific interaction between dopamine and aptamer sequence tethered to the gold disk electrode via thiol group. DA concentration was determined without use of any external redox indicator and the dopamine oxidation current serves as the analytical signal. Electrodes modified with DNA aptamer show selectivity toward dopamine within micromolar range with the lower detection limit of 26.8 μmol·L⁻¹. The developed assay exhibits minor response in the presence of various interferents and its utility was tested in sample of diluted serum. Furthermore, the performance of proposed sensor was improved with LOD of 3.36 μmol·L⁻¹ and the range of linear response from 5 to 75 μmol·L⁻¹ by utilization of DNA aptamer/AuNP/reduced graphene oxide - modified glassy carbon electrode.

Most point-of-care tests (POCT) use swabs for sampling and/or for applying a sample on the test. A variety of swabs differing in tip materials is commercially available. Different tip materials have different chemical and physical characteristics which might influence the specimen collection and release. We investigated properties of various types of swabs used in clinical diagnostics with focusing on two kinds of analytes, DNA and proteins, which are most often used targets in POCT. As the model samples we used diphtheria toxoid NIBSC 69/017 for investigating recovery of protein analytes such as antigens and bacterial strains of Escherichia coli ATCC 25922, diphtheria toxin-producing Corynebacterium diphtheriae NCTC 10648, and the clinical isolate nontoxigenic C. diphtheriae 5820/15 for investigating the recovery of nucleic acids. We investigated four types of swabs most commonly used in clinical diagnostics in terms of absorption capacity and efficiency of release of nucleic acids and proteins. Volume uptake was measured in milligrams. For DNA release various washing out buffers were used and the amount of released DNA was measured spectrophotometrically. The amount of protein released from the swabs were examined using the Lowry assay. We observed statistically significant differences (p < 0.05) in the mean weights of absorbed liquid, in the DNA recovery and protein recovery by the four variety of swab examined. However, the efficiency of DNA and protein release was not correlated to the absorbed volume of a sample, but rather to the properties of swabs. The swab composition and structure can have a significant impact on the collection and release efficiency of a sample. Therefore, validation of POCT in relation to the used swabs for sampling is really important. The use of inappropriate swabs could lead to false negative or misleading analysis results.

Nucleic acid extraction and purification are crucial steps in sample preparation for multiple diagnostic procedures. Routine methodologies of DNA isolation require benchtop equipment (e.g., centrifuges) and labor-intensive steps. Magnetic nanoparticles (MNPs) as solid-phase sorbents could simplify this procedure. A wide range of surface coatings employs various molecular interactions between dsDNA and magnetic nano-sorbents. However, a reliable, comparative evaluation of their performance is complex. In this work, selected Fe₃O₄ modifications, i.e., polyethyleneimine, gold, silica, and graphene derivatives, were comprehensively evaluated for applications in dsDNA extraction. A family of single batch nanoparticles was compared in terms of morphology (STEM), composition (ICP-MS/MS and elemental analysis), surface coating (UV-Vis, TGA, FTIR), and MNP charge (ζ-potential). ICP-MS/MS was also used to unify MNPs concentration allowing a reliable assessment of individual coatings on DNA extraction. Moreover, studies on adsorption medium (monovalent vs. divalent ions) and extraction buffer composition were carried out. As a result, essential relationships between nanoparticle coatings and DNA adsorption efficiencies have been noticed. Fe₃O₄@PEI MNPs turned out to be the most efficient nano sorbents. The optimized composition of the extraction buffer (medium containing 0.1 mM EDTA) helped avoid problems with Fe³⁺ stripping, which improved the validity of the spectroscopic determination of DNA recovery.