Imidazolium-tethered red-emissive iridium AIEgen for sensitive detection of NAD(P)H in aqueous and cellular media

Abstract

NADH and NADPH are essential coenzymes involved in diverse biochemical processes and their deregulated levels are closely linked to various pathological conditions in eukaryotic systems. Accurate determination of NAD(P)H levels under physiological conditions is therefore critical for elucidating their biological functions and roles in disease. In this study, we present an NIR-emissive, cationic iridium-based aggregation-induced emission (AIE) probe (Ir2), functionalized with an imidazolium moiety, for the sensitive and selective detection of NAD(P)H. Ir2 exhibited excellent sensitivity, with limits of detection of 3.6 nM for NADPH and 6.2 nM for NADH in aqueous media. The probe's positive charge facilitates strong electrostatic interactions with the negatively charged NAD(P)H, while the imidazolium group promotes the formation of Ir2–NAD(P)H aggregates, resulting in aggregation-induced luminescence enhancement. Ir2 also showed high selectivity for NAD(P)H over other biologically relevant species and retained functionality across physiological pH ranges (7–10), supporting its potential for intracellular imaging. Moreover, Ir2 selectively accumulates in mitochondria and effectively monitors NADH levels in living cells. These findings highlight the promise of Ir2 as a valuable tool for detecting NAD(P)H in both aqueous and biological environments.