Beta-lactamase substrate compounds and electrochemical detection methods using them

A beta-lactamase substrate compound for electrochemical detection of beta-lactamases, wherein the beta-lactamase substrate compound is according to formula (I)

• wherein
• β is hydrogen, C1-C16 alkyl, C1-C16 fluoroalkyl or is according to formula (II):
• wherein
• X is S or O, and
• R1 is C1-C16 alkyl, optionally comprising one or more carbonyl, hydroxyl, ether, ester or carboxyl functional groups;
• and
• R is selected from the group consisting of 4-cyanophenyl, 4-nitrophenyl, 4-sulfonephenyl, 2,4-dicyanophenyl, 2-nitro-4-cyanophenyl, 3,4-dinitrophenyl and 3,5-dinitrophenyl;
• wherein the beta-lactamase substrate compound is hydrolysable by a beta-lactamase;
• and
• wherein the beta-lactamase substrate compound has a degradation at 4° C. equal to or lower than 50% after 4 weeks and equal to or lower than 70% after 18 weeks, and/or a degradation at 20° C. equal to or lower than 80% after 4 weeks and equal to or lower than 85% after 18 weeks, wherein the degradation is determined from a difference of an integration of nuclear magnetic resonance (NMR) measurement signals of the beta-lactamase substrate compound and of dimethylformamide.