In situ interface reaction-enabled electrochemiluminescence imaging for single-cell formaldehyde release analysis

Monitoring metabolites in situ at the single-cell scale is important for revealing cellular heterogeneity and dynamic changes of cell status, which provides new possibilities for disease research. Benefiting from the advantages of both electrochemical and optical methods, electrochemiluminescence (ECL) has great potential in this field. However, developing real-time in situ imaging methods is full of challenges. In this study, an ECL imaging method for formaldehyde (FA), a kind of cellular metabolite, was developed based on the in situ generation of co-reactants at the electrode interface and was successfully applied to the monitoring of single-cell FA release. Amino groups can undergo a rapid nucleophilic addition reaction with FA to form amino alcohol intermediates, which can be used as co-reactants for tris(2,2 '-bipyridyl)ruthenium(II) [Ru(bpy)(3)(2+)] to significantly enhance the strength of ECL. Poly(amidoamine) (PAMAM), with a large number of amino groups, and reduced graphene oxide (rGO), with excellent electrical conductivity and electrocatalytic properties, were introduced as the modification layer on the electrode surface to realize the "turn on" detection of FA. This sensing method also eliminated the use of the classic toxic co-reactant tripropylamine (TPrA) and was further applied to in situ imaging of single-cell FA release. It successfully obtained ECL images at different time points after the stimulation of HeLa cells with thapsigargin (TG), revealing the change pattern in drug efficacy over time. This work proposes a new ECL imaging approach for real-time in situ monitoring of FA release from single cells, further broadening the application of ECL imaging in single-cell analysis.