Anionic Polyelectrolyte-Induced Aggregation of Basic Orange 21: A Clue toward Metachromasia

New insights into the photophysical properties and interaction mechanisms of Janus green blue dye with polyanions and its applications in colorimetric visualization of loop-mediated isothermal amplification and polymerase chain reaction

In this investigation, the photophysical properties and interaction mechanisms of Janus green blue (JGB) dye with polyanions were systematically studied using spectroscopic techniques. The absorption spectral analysis revealed that JGB binds cooperatively to sodium alginate, leading to dye stacking along the polymer chain. The interaction of JGB dye with DNA was characterized by the emergence of a metachromatic peak at 564 nm, indicating the formation of dye aggregates. The analysis of absorption data reveals that JGB dye interacts with DNA at multiple binding sites, including at least one high-affinity site. The AutoDock Vina based blind docking approach was used to analyze the most probable binding location of JGB dye in DNA. By making use of the DNA-induced metachromasia, a colorimetric approach was developed for the visualization of loop-mediated isothermal amplification (LAMP) and polymerase chain reaction (PCR). The LAMP-colorimetric assay, targeting the Streptococcus pneumoniae gene, demonstrated a noticeable colour change with a detection limit of 1 pg μL-1. The practical applicability was validated by detecting S. pneumoniae in artificial urine. In addition to LAMP, we tested the JGB dye based colorimetric assay for applicability in PCR reactions. The colorimetric PCR assay using the metal-responsive transcription factor (MTF-1) gene achieved a detection limit as low as 0.1 pg μL-1. The study highlights the potential of DNA binding metachromic dye to significantly enhance colorimetric assays, offering a robust and sensitive tool for molecular diagnostics.

Ratiometric detection of polymyxin B based on the disaggregation of pyrenyl nanoassemblies in 100% aqueous media

Polymyxin B (PMB) was an antibiotic with highly effective antibacterial effect but narrow safety interval, and its residues in food had attracted widespread attention. It was important to develop an accurate method for the rapid detection of PMB in animal foods. In this work, we had established a ratiometric sensing system based on the formation of supramolecular assemblies of pyrenyl probes, which were driven by the synergy of noncovalent forces such as multiple-electrostatic and π-π stacking interactions. Compared with the traditional fluorescence detection based on the single wavelength change, the present approach showing two-wavelength fluorescence response could reduce the interference of other factors making the experimental results more accurate. The sensor exhibited high sensitivity and selectivity with a low detection limit (28.3 nM). This method could be used to realize visual detection and had a visual detection limit of 1 μM. As we had learned yet, this was the first ratiometric sensor for PMB detection in aqueous solution. We believed all our preliminary would not only provide a complementary strategy for the detection of PMB, but also develop some new ideas for the construction of sensors for rapid antibiotic detection.