We report the synthesis and characterisation of photosensitive cationic surfactants with various hydrophobic tail lengths. These molecules, called AzoCx, are used as photosensitive nucleic acid binders (pNABs) and are applied to the photocontrol of DNA conformation. All these molecules induce DNA compaction in a photodependent way, originating in the photodependent polarity of their hydrophobic tails. We show that increasing hydrophobicity strongly enhances the compaction efficiencies of these molecules, but reduces the possibility of reversible photocontrol of a DNA conformation. Optimal performance was achieved with AzoC5, which allowed reversible control of DNA conformation with light at a concentration seven times smaller than previously reported.

We present a rapid (<10 s), cost-effective, unique single-step method for fabricating paper-based devices without necessitating any expensive instrumentation, simply by deploying correction pens that are otherwise commonly used for masking typos in printed or written matters. The marked regions formed by deposits from the correction pen demonstrate ubiquitous flow resistances to typical aqueous solutions and organic solvents in the transverse direction, resulting in a preferential bulk flow along the axial direction of the paper channels ‘fabricated’ in the process. Considering the simplicity and cost-effectiveness of this platform, it is deemed to be ideal for (bio) chemical sensing and point-of-care diagnostics in resource-limited settings.

We present a high resolution, ultra-frugal printing of paper microfluidic devices using in-house paraffin formulation on a simple filter paper. The patterns printed using an office inkjet printer formed a selective hydrophobic barrier of 4 ± 1 µm thickness with a hydrophilic channel width of 275 µm. These printed patterns effectively confine common aqueous solutions and solvents, which was verified by solvent compatibility studies. SEM analysis reveals that the solvent confinement is due to pore blockage in the filter paper. The fabricated paper-based device was validated for qualitative assessment of Candida albicans (pathogenic fungi) by using a combination of L-proline β-naphthylamide as the substrate and cinnamaldehyde as an indicator. Our studies reveal that the pathogenic fungi can be detected within 10 min with the limit of detection (LOD) of 0.86 × 106 cfu/mL. Owing to its simplicity, this facile method shows high potential and can be scaled up for developing robust paper-based devices for biomarker detection in resource-limited settings. Graphic abstract

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