Self-Assembly Controls Reactivity with Nitric Oxide: Implications for Fluorescence Sensing

Detection of subcellular nitric oxide in mitochondria using a pyrylium probe: assays in cell cultures and peripheral blood

Fluorescent probes for the detection of intracellular nitric oxide (NO) are abundant, but those targeted to the mitochondria are scarce. Among those molecules targeting mitochondrial NO (mNO), the majority use a triphenylphosphonium (TPP) cation as a vector to reach such organelles. Here we describe a simple molecule (mtNOpy) based on the pyrylium structure, made in a few synthetic steps, capable of detecting selectively NO (aerated medium) over other reactive species. The calculated detection limit for mtNOpy is 88 nM. The main novelty of this probe is that it has a simple molecular architecture and can act both as a fluorogenic and as a mitochondriotropic agent, without using TPP. mtNOpy has been tested in two different scenarios: (a) in a controlled environment of cell line cultures (human colon carcinoma HT-29 cells and mouse macrophage RAW 264.7 cells), using confocal laser scanning microscopy, and (b) on a much more complex sample of peripheral blood, using flow cytometry. In the first context, mtNOpy has been found to be responsive (turn-on fluorescence) to exogenous and endogenous NO stimuli (via SNAP donor and LPS stimulation, respectively). In the second area, mtNOpy has been able to discriminate between NO-generating phagocytes (neutrophils and monocytes) from other leukocytes (NK, B and T cells).

Lipase sensing by naphthalene diimide based fluorescent organic nanoparticles: a solvent induced manifestation of self-assembly

The precise control of supramolecular self-assembly is gaining utmost interest for the demanding applications of manifested nano-architecture across the scientific domain. This study delineates the morphological transformation of naphthalene diimide (NDI) derived amphiphiles with varying water content in dimethyl sulfoxide (DMSO) and the selective sensing of lipase using its aggregation-induced emission (AIE) properties. To this end, NDI-based, benzyl alcohol protected alkyl chain (C1, C5, and C10) linked amphiphilic molecules (NDI-1,2,3) were synthesized. Among the synthesized amphiphiles, benzyl ester linked C5 tailored naphthalene diimide (NDI-2) exhibited AIE with an emission maximum at 490 nm in a DMSO-water binary solvent system from fw = 30% and above water content. The fibrous morphology of NDI-2 at fw = 30% got gradually transformed to spherical aggregated particles along with steady increment in the emission intensity upon increasing the amount of water in DMSO. At fw = 99% water in DMSO, complete transformation to fluorescent organic nanoparticles (FONPs) was observed. Microscopic and spectroscopic techniques demonstrated the solvent driven morphological transformation and the AIE property of NDI-2. Moreover, this AIE of NDI-2 FONPs was employed in the selective turn-off sensing of lipase against many other enzymes including esterase, through hydrolysis of a benzyl ester linkage with a limit of detection 10.0 ± 0.8 μg L-1. The NDI-2 FONP also exhibited its lipase sensing efficiency in vitro using a human serum sample.