A Rationally Designed Upconversion Nanoprobe for <i>in Vivo</i> Detection of Hydroxyl Radical

The detection of •OH in live organisms is crucial to the understanding of its physiological and pathological roles; while this is too challenging because of the extremely low concentration and high reactivity of the species in the body. Herein, we report the rational design and fabrication of an NIR-light excited luminescence resonance energy transfer-based nanoprobe, which for the first time realizes the <i>in vivo</i> detection of •OH. The nanoprobe is composed of two moieties: upconversion nanoparticles with sandwich structure and bared surface as the energy donor; and mOG, a modified azo dye with tunable light absorption, as both the energy acceptor and the •OH recognizing ligand. The as-constructed nanoprobe exhibited ultrahigh sensitivity (with the quantification limit down to 1.2 femtomolar, several orders of magnitude lower than that of most previous •OH probes), good biocompatibility, and specificity. It was successfully used for monitoring [•OH] levels in live cells and tissues

Modulating the Luminescence of Upconversion Nanoparticles with Heavy Metal Ions: A New Strategy for Probe Design

Upconversion nanoparticles (UCNPs) are attracting increasing attention in biosensing and imaging. The design of UCNP-based probes currently relies exclusively on the luminescence resonance energy transfer (LRET) principle. The prerequisite spectral overlap in LRET leads to limited flexibility in probe design, thus hindering the construction and application of upconversion (UC) probes. To change this situation, we herein present a new approach to construct UC probes by use of heavy metal ion-induced quenching. We reveal that heavy metal ions can quench the upconversion luminescence (UCL) to >95% without the occurrence of spectral overlap. A proof-of-concept UC probe for biothiols by manipulating Cu²⁺ as the switch of luminescence exhibits satisfying performance both in vitro and in bioimaging. This is the first report of a UC probe utilizing heavy metal ions to govern the read-out signal. The strategy is much simpler than the LRET principle and highly efficient, which provides a new way to design and apply UCNP-based probes

Demonstration of In Vitro Resurrection of Aged Acetylcholinesterase after Exposure to Organophosphorus Chemical Nerve Agents

After the inhibition of acetylcholinesterase (AChE) by organophosphorus (OP) nerve agents, a dealkylation reaction of the phosphylated serine, referred to as aging, can occur. When aged, known reactivators of OP-inhibited AChE are no longer effective. Realkylation of aged AChE may provide a route to reversing aging. We designed and synthesized a library of quinone methide precursors (QMPs) as proposed realkylators of aged AChE. Our lead compound (<b>C8</b>) from an in vitro screen successfully resurrected 32.7 and 20.4% of the activity of methylphosphonate-aged and isopropyl phosphate-aged electric-eel AChE, respectively, after 4 days. <b>C8</b> displays properties of both resurrection (recovery from the aged to the native state) and reactivation (recovery from the inhibited to the native state). Resurrection of methylphosphonate-aged AChE by <b>C8</b> was significantly pH-dependent, recovering 21% of activity at 4 mM and pH 9 after only 1 day. <b>C8</b> is also effective against isopropyl phosphate-aged human AChE

Demonstration of In Vitro Resurrection of Aged Acetylcholinesterase after Exposure to Organophosphorus Chemical Nerve Agents

After the inhibition of acetylcholinesterase (AChE) by organophosphorus (OP) nerve agents, a dealkylation reaction of the phosphylated serine, referred to as aging, can occur. When aged, known reactivators of OP-inhibited AChE are no longer effective. Realkylation of aged AChE may provide a route to reversing aging. We designed and synthesized a library of quinone methide precursors (QMPs) as proposed realkylators of aged AChE. Our lead compound (<b>C8</b>) from an in vitro screen successfully resurrected 32.7 and 20.4% of the activity of methylphosphonate-aged and isopropyl phosphate-aged electric-eel AChE, respectively, after 4 days. <b>C8</b> displays properties of both resurrection (recovery from the aged to the native state) and reactivation (recovery from the inhibited to the native state). Resurrection of methylphosphonate-aged AChE by <b>C8</b> was significantly pH-dependent, recovering 21% of activity at 4 mM and pH 9 after only 1 day. <b>C8</b> is also effective against isopropyl phosphate-aged human AChE