Polydiacetylenes (PDAs) comprise a class of chromatic polymers which have attracted significant interest over the past 40 years as a promising platform for chemo-and bio-sensing. Specifically, the unique colorimetric and fluorescent transformations of PDA, induced by varied external stimuli, are a core property of these polymers, and have been widely exploited for diverse applications. In this review, we focus on recent developments in PDA chemistry, materials, and practical applications. We summarize the progress in development of new synthetic routes and assembly methods resulting in enhanced chromatic properties and interesting molecular configurations. We further outline the challenges that still exist for practical utilization of PDA technology, and possible future directions.

New bacterial detection and imaging methods are desirable for diagnostics and healthcare applications, as well as in basic scientific research. We present a simple analytical platform for bacterial detection and imaging based upon attachment of amphiphilic carbon dots (CDs) to bacterial cells. We show that CDs functionalized with hydrocarbon chains readily bind to bacterial cells following short incubation and enable detection of bacteria through both fluorescence spectroscopy and microscopy. Importantly, we demonstrate that the intensity and spectral position of the carbon dots' fluorescence depend upon bacterial species, providing a tool for distinguishing among bacteria even in cases of mixed bacterial populations. Moreover, bacterial labelling with the amphiphilic CDs enables visualization of physiological processes such as cell division.

Biofilm formation is a critical facet of pathogenesis and resilience of human, animal, and plant bacteria. Extracellular polymeric substances (EPS) constitute the physical scaffolding for bacterial biofilms and thus play central roles in their development and virulence. We show that newly synthesized amphiphilic fluorescent carbon dots (C-dots) readily bind to the EPS scaffold of Pseudomonas aeruginosa, a major biofilm-forming pathogen, resulting in unprecedented microscopic visualization of the EPS structural features. Fluorescence microscopy analysis utilizing the C-dots reveals that the P. aeruginosa EPS matrix exhibits a remarkable dendritic morphology. The experiments further illuminate the growth kinetics of the EPS and the effect of external factors such as temperature. We also show that the amphiphilic C-dot platform enabled screening of substances disrupting biofilm development, specifically quorum sensing inhibitors.

Polydiacetylenes (PDAs) constitute a family of conjugated polymers exhibiting unique colorimetric and fluorescence transitions, and have attracted significant interest as chemo- and biosensing materials. We spin-coated PDA films upon poly(methyl methacrylate) (PMMA), and investigated the photophysical properties and sensing applications of the new PDA configuration. Specifically, the as-polymerized blue PDA layer underwent distinct transformations to purple, red, and yellow phases, which could be quantified through conventional color scanning combined with application of image analysis algorithms. Furthermore, we recorded a reversible red-purple PDA transition that was induced by ultraviolet irradiation, a phenomenon that had not been reported previously in PDA film systems. We show that distinct color and fluorescence transitions were induced in the PMMA-supported PDA films by amphiphilic substances-surfactants and ionic liquids-and that the chromatic transformations were correlated to the analyte structures and properties. Overall, this study presents a new chromatic PDA film system in which noncovalent interactions between the PMMA substrate and spin-coated PDA give rise to distinct chromatic properties and molecular sensing capabilities.