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Norfloxacin (NOX), a broad spectrum fluoroquinolone (FQ) antibiotic, is commonly detected in environmental residues, potentially contributing to biological drug resistance. In this paper, an aptamer recognition probe has been used to develop a label-free liquid crystal-based biosensor for simple and robust optical detection of NOX in aqueous solutions. Stimuli-receptive liquid crystals (LCs) have been employed to report aptamer–target binding events at the LC–aqueous interface. The homeotropic alignment of LCs at the aqueous–LC interface is due to the self-assembly of the cationic surfactant cetyltrimethylammonium bromide (CTAB). In the presence of the negatively charged NOX aptamer, the ordering changes to planar/tilted. On addition of NOX, the aptamer–NOX binding causes redistribution of CTAB at the LC–aqueous interface and the homeotropic orientation is restored. This results in a bright-to-dark optical transition under a polarized optical microscope (POM). This optical transition serves as a visual indicator to mark the presence of NOX. The devised aptasensor demonstrates high specificity with a minimum detection limit of 5 nM (1.596 ppb). Moreover, the application of the developed aptasensor for the detection of NOX in freshwater and soil samples underscores its practical utility in environmental monitoring. This proposed LC-based method offers several advantages over conventional detection techniques for a rapid, feasible and convenient way to detect norfloxacin. [ABSTRACT FROM AUTHOR]

The advancement of liquid crystal (LC)-based biosensing platform for understanding the interactions of adsorbed proteins with lipid-designed LC-aqueous interface has significant scientific interest due to its point-of-care diagnostic applications and fundamental biological research. The ordering transition of LCs at 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) decorated LC-aqueous interface was examined to observe the biosensing of a physiologically important Ca2+ signalling protein recombinant human calmodulin (CaM). Self-assembled POPC molecules promote homeotropic anchoring of LC at the LC-aqueous interface with dark optical appearance under crossed polarizers. Interestingly, the optical state of LC changed to planar (bright optical appearance) when CaM was in the proximity of lipid adsorbed LC-aqueous interface, indicating label-free detection of CaM at those interfaces. It was further observed that the POPC decorated LC-aqueous interface is specific for the detection of CaM protein among other amphiphiles (LPA, DLPC, CTAB and SDS) decorated LC-aqueous interfaces tested. The sensitivity of the POPC decorated LC-aqueous interface towards the detection of CaM was observed in the nanomolar regime (~150 nM). CaM is a Ca2+ binding protein; hence, the CaM-POPC decorated LC-aqueous interface was further utilized for the detection of Ca2+. Interaction of CaM with Ca2+ increases the α-helical content of CaM, which results in the reorganization of POPC molecules at the LC-aqueous interface and leads to the homeotropic orientation of LC with a dark appearance under crossed polarizer. Compared to other spectroscopic/biological techniques, the LC-based system is easy to handle due to its simple label-free optical data, high sensitivity, cost-effectivity and low sample requirement. [ABSTRACT FROM AUTHOR]

We design amphiphilic di-block copolymers (P-b-F and P-b-C) tethered with stimuli-responsive ferrocene and coumarin hydrophobic pendants that exhibit chain collapse behaviour in response to light, redox and chemical cues, with subsequent transformation of the vesicles into micelles. Interestingly, the co-assembled vesicles of the polymer blend under orthogonal stimuli furnish self-sorted micelles and vesicles. [ABSTRACT FROM AUTHOR]

The precise sequence of a protein's primary structure is essential in determining its folding pathways. To emulate the complexity of these biomolecules, functional block copolymers consisting of segmented triblocks with distinct functionalities positioned in a sequence-specific manner are designed to control the polymer chain compaction. Triblock polymers P- b -C- b -F and P- b -F- b -C and random diblock copolymer P- b -C- r -F consist of a hydrophilic poly(ethylene oxide) (PEO) block and a hydrophobic block with coumarin ( C ) and ferrocene ( F ) moieties that are grafted in a sequence-specific or random manner onto the hydrophilic block. External stimuli such as UV B light, redox, and chemical cues influence the functional hydrophobic block to alter the packing parameters that are monitored with spectroscopic and scattering techniques. Interestingly, the positioning of the stimuli-responsive moiety within the hydrophobic block of P- b -C- b -F , P- b -F- b -C , and P- b -C- r -F affects the extent of the hydrophobic-hydrophilic balance in block copolymers that renders orthogonal control in stimuli-responsive transformation of self-assembled vesicles to micelles., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)