We present dye-doped polymer nanoparticles that are able to detect mercury in aqueous solution at parts per billion levels via fluorescence resonance energy transfer (FRET). The nanoparticles are prepared by reprecipitation of highly fluorescent conjugated polymers in water and are stable in aqueous suspension. They are doped with rhodamine spirolactam dyes that are nonfluorescent until they encounter mercury ions, which promote an irreversible reaction that converts the dyes to fluorescent rhodamines. The rhodamine dyes act as FRET acceptors for the fluorescent nanoparticles, and the ratio of nanoparticle-to-rhodamine fluorescence intensities functions as a ratiometric fluorescence chemodosimeter for mercury. The light harvesting capability of the conjugated polymer nanoparticles enhances the fluorescence intensity of the rhodamine dyes by a factor of 10, enabling sensitive detection of mercury ions in water at levels as low as 0.7 parts per billion.

Small molecule mitochondrial uncouplers transport protons from the mitochondrial inner membrane space into the mitochondrial matrix independent of ATP synthase, uncoupling nutrient metabolism from ATP generation. The therapeutic potential of mitochondrial uncouplers has been investigated for the treatment of metabolic diseases such as obesity and type 2 diabetes (T2D), ischemia-reperfusion injury, and neurodegenerative diseases. This communication will review the small molecule mitochondrial uncouplers reported to date and explore their potential as therapeutics.

Fluorescent systems that can undergo intensity photomodulation in aqueous environments are finding increasing applications, particularly in high-resolution imaging of biological samples. We seek to develop conjugated polymer nanoparticles (CPNs) with bright fluorescence that can be modulated with a light signal. Here, we present CPNs, doped with a photochromic diarylethene dye, that exhibit efficient fluorescence photomodulation that is thermally irreversible. In their UVabsorbing open form, the diarylethenes have no effect on the fluorescence properties of the bright CPNs. A brief period of UV irradiation converts the dyes to their visible-absorbing closed form, which is an efficient fluorescence quencher for the CPNs, likely via a fluorescence resonance energy transfer mechanism. Aqueous suspensions of dye-doped CPNs prepared from the homopolymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) or a polyfluorene-phenylenevinylene copolymer (PFPV) exhibit thermally stable bright and dark levels. The dye-doped MEH-PPV CPNs also exhibit photomodulation in single-nanoparticle imaging experiments, which reveal that nearly all CPNs retain a small amount of residual emission in the dark state. Their PFPV counterparts undergo irreversible fluorescence photobleaching rather than photomodulation in singlenanoparticle studies. The photostability of the CPNs under the UV irradiation conditions required for photochromic conversion is investigated on the single-particle level, and PFPV CPNs are found to be particularly susceptible to photobleaching upon 254 nm irradiation. These results will guide the selection of polymers and photochromes for CPNs intended for single-particle photomodulation.