An Inverse Electron-Demand Diels–Alder Approach to Selective Activity-Based Sensing of Acetaldehyde in Living Cells

Acetaldehyde (AA) is a reactive aldehyde primarily produced in cells as a metabolic intermediate during ethanol oxidation. Excess AA, often resulting from impaired AA detoxification, leads to aberrant DNA, protein, and/or lipid damage and increases risk of diseases such as cancer, hepatitis, and cirrhosis. Traditional methods for detecting biological AA often require sample destruction or extensive processing, which compromise spatiotemporal resolution, or do not exhibit sufficient selectivity for this two-carbon metabolite over other competing aldehydes and reactive carbon species in living systems. To overcome these limitations, we now report the design, synthesis, and biological applications of a fluorescent probe platform for acetaldehyde-specific activity-based sensing. The first-generation reagent Acetaldehyde Probe-1 (AAP-1) utilizes an AA-triggered inverse electron-demand Diels-Alder (IEDDA) reaction to enable selective detection of physiologically relevant levels of this two-carbon aldehyde in aqueous solution and in live cells, with minimal interference from competing biological analytes, including highly similar aldehydes like formaldehyde (FA) and methylglyoxal (MGO). Furthermore, AAP-1 enables visualization of endogenous AA pools generated during ethanol metabolism in a human liver cancer cell line, highlighting the potential of this chemical activity-based sensing strategy for studying two-carbon biology in living systems.