Biosensing
and molecular diagnostics

Drop-coating deposition Raman (DCDR) spectroscopy is a promising approach for enhancing Raman signal sensitivity for dilute biological samples. However, its reliability for the quantitative analysis of multicomponent mixtures remains insufficiently explored due to potential solute fractionation effects during droplet drying. In this work, we investigate the limits of applicability of the DCDR method for quantifying binary mixtures of proteinogenic amino acids. Raman spectra of dried droplets containing individual amino acids and their mixtures were measured and analyzed using a linear combination approach combined with least-squares fitting. As a model system, the L-alanine/l-glutamine mixture was first examined to determine optimal spectral processing parameters and sampling region within the "coffee-ring" structure. The approach was subsequently extended to binary mixtures of L-alanine with the remaining 19 proteinogenic amino acids. The results reveal that estimated amino acid relative concentrations strongly depend on the physicochemical properties of the mixture components, including solubility and molecular mobility, which affect their spatial fractionation during droplet drying. These results provide important insights into the applicability of DCDR spectroscopy for complex biological samples paving the way for future analyses of multicomponent systems under physiologically relevant conditions.

The development of rapid, sensitive, and specific methods for nucleic acid detection is critical for molecular diagnostics and biosafety. Here, we report the design and validation of a peroxidase-like DNA nanomachine (PxDm) that integrates target-templated assembly of a split G-quadruplex (G4) DNAzyme with chemiluminescent (CL) detection via photon counting in a compact, closed-cuvette device for the accurate detection of S. aureus. Following systematic optimization of the CL reaction, the PxDm platform demonstrated robust analytical performance at room temperature, reaching a nanomolar limit of detection (LOD) for single-stranded DNA (ssDNA) approximately 30 min after the start of the analysis. The assay was shown to be able of discriminating target sequences from those bearing single-nucleotide substitutions (SNS) with up to 98 % signal reduction. This CL approach proved to be more sensitive than colorimetric and fluorescent detection modalities for the same PxDm, with a 19.6-fold and 4.3-fold lower LOD, respectively. The platform's versatility was demonstrated through successful adaptation for double-stranded DNA (dsDNA) detection and integration with dual-priming isothermal amplification (DAMP). The integrated DAMP-PxDm assay achieved clinically relevant sensitivity, with a detection limit of 227 genomic equivalents, while maintaining high selectivity, as indicated by reduction factor (RF) values of 62.1 % for non-target DNA amplicons and 63.9 % for simulated target amplicons containing an SNS. The system demonstrated robustness in complex matrices, accurately detecting S. aureus amplicons from bacteria recovered from lettuce and spinach leaves, even in the presence of non-target organisms. The PxDm platform offers a powerful combination of low-nanomolar sensitivity, single-nucleotide specificity, and sufficient operational time, establishing it as a promising tool for on-site pathogen detection and environmental monitoring applications.

Here we propose a fast and scalable (up to 3 min for 6 × 1 cm size substrate) innovative approach to fabricate coral-shaped TiO2 nanostructured substrates based on thermal oxidation of titanium foil followed by deposition of Ag nanoparticles for bifunctional sensing and photocatalysis. Comprehensive studies on the morphology, crystal structure, stoichiometry, optical, and electronic properties of these nanostructures reveal the formation of a Schottky barrier at the Ag/TiO2 interface. This interface alters the electronic structure of the Ag/TiO2 nanosystem, retaining the plasmonic properties of Ag nanoparticles while enhancing their catalytic activity. The SERS performance and photocatalytic activity of Ag/TiO2 nanostructures are demonstrated by the test analyte Rhodamine 6G detection down to concentrations of 10-12 M and acceleration of its degradation under simulated sunlight by 5.8 times. Tests with tetracycline water solutions indicate a nanomolar detection limit and 4.4-fold increase in degradation rate. The proposed Ag/TiO2 nanostructures are prospective for creation of low-cost bifunctional platforms for the sensitive detection of organic residues in water as well as their fast neutralization under solar light.

The development of systems capable of efficiently eliminating organic dyes from wastewater is crucial for the environment. In this context, TiO2 -based photocatalytic systems are of particular interest. However, the development of eco-friendly and single-step methods for the fabrication of such systems remains a challenge to their practical use. Here, we demonstrate a fabrication approach for a catalytic system composed of TiO2 nanocoating created on the surface of a bulk titanium plate by exposure to a nanosecond laser. The exposure conditions affect the relief and phase composition of the nanocoating, as revealed by a combination of scanning electron microscopy (SEM), contact profilometry, Raman, High-resolution X-ray photoelectron spectroscopy (HR XPS), and grazing incidence X-ray diffraction (GIXRD) methods. Using the GIXRD method, we establish that nanocoatings consist of a mixture of anatase and rutile grains with sizes of 22.7–24.4 and 29.8–32.2 nm, respectively. HR XPS analysis demonstrates that changes in the number of pulses per spot modify the anatase surface content from 40.6 to 70.4%. The samples with a higher anatase content exhibit up to 6.3 times higher catalytic activity, which is confirmed by methylene blue degradation when exposed to UV light and can be related to the synergistic effect of the anatase–rutile heterojunction. The reusability of the samples is supported by repeated degradation experiments. The photocatalytic activity of the obtained TiO2 nanocoatings is improved by Au nanoparticles deposited on their surface by magnetron sputtering. The proposed approach lays the foundation for the application of nanosecond laser-assisted technologies in the eco-friendly fabrication of catalytic systems.