Highly Sensitive Off/On EPR Probes to Monitor Enzymatic Activity

The assessment of unregulated level of enzyme activity is a crucial parameter for early diagnoses in a wide range of pathologies. In this study, we propose the use of electron paramagnetic resonance (EPR) as an easy method to probe carboxylesterase (CE) enzymatic activity in vitro. For this application, were synthesized two amphiphilic, nitroxide containing esters, namely Tempo-C12 (T-C12) and Tempo-2C12 (T-2-C12). They exhibit low solubility in water and form stable micelles in which the radicals are EPR almost silent, but the hydrolysis of the ester bond yields narrows and intense EPR signals. The intensity of the EPR signals is proportional to the enzymatic activity. CEs1, CEs2 and esterase from porcine liver (PLE) were investigated. The obtained results show that T-C12 and T-2-C12-containing systems display a much higher selectivity toward the CEs2, with a Limit of Detection of the same order of those ones obtained with optical methods.

Automated summary

The assessment of enzyme activity is crucial for early diagnoses in various diseases. This study proposes the use of electron paramagnetic resonance (EPR) as an easy method to quantify carboxylesterase (CE) activity. By synthesizing two amphiphilic compounds with ester groups and observing the EPR signals produced by their hydrolysis, enzyme activity can be measured quantitatively. The results show that this method has high selectivity towards CE2 and comparable detection limits to optical methods.