Triethanolamine Borate with a Rigid, Nonplanar Configuration as an Unexpectedly Highly Efficient Coreactant for Tris(2,2′-bipyridine)ruthenium(II) Electrochemiluminescence

Over 2 billion microbead-based bioassays by tris(2,2′-bipyridine) ruthenium(II)/tri-n-propylamine (TPrA) electrochemiluminescence (ECL) at a platinum working electrode have been conducted annually. However, TPrA is limited by toxicity, alkaline nature, unpleasant odor, poor solubility, and strong dependence on the electrode material. To the best of our knowledge, amines with rigid, nonplanar configurations reported to date exhibit weak ECL. Triethanolamine borate (TEAB) is an amine with a rigid, nonplanar configuration. It is neutral, odorless, biocompatible, highly soluble, and cost-effective. Here, we report for the first time the ECL of TEAB. Despite its rigid, nonplanar configuration, it unexpectedly produces a 7-fold increase in ECL intensity on platinum electrodes compared with classical TPrA, owing to its favorable electrochemical oxidation kinetics. The use of TEAB as a coreactant enables the highly sensitive detection of Ru(bpy)32+ in solution with a wide linear dynamic range from 1 pM to 1 μM. Furthermore, we imaged the ECL at the surface of single Ru(bpy)32+-labeled microbeads by employing ECL microscopy. Under chronoamperometric conditions, TEAB unprecedentedly exhibits 74- and 60-fold higher ECL than TPrA at 0.925 V as well as 11- and 25-fold higher ECL than TPrA at 1.3 V on Au and Pt electrodes, respectively. These results highlight TEAB as a user-friendly and highly promising alternative to TPrA, with significant potential to advance analytical and diagnostic applications.