Highly sensitive and catalytic electrochemical aptamer-based biosensor for β-lactoglobulin via coupling redox recycling background minimization with DNAzyme amplification.

Background: β-lactoglobulin (β-Lg), a major allergen in dairy products, can trigger severe allergic reactions and even fatal outcomes in infants. In this work, we develop a new low background current redox recycling strategy by conjugating the electrochemical mediator to trimetallic hybrid nanoparticles (NPs)-dispersed graphene as the signal tag, which is coupled with DNAzyme amplifications to construct highly catalytic and ultrasensitive β-Lg aptasensor.

Results: Target β-Lg molecules bind aptamers in DNAzyme/aptamer duplexes to release active DNAzymes to initiate cyclic cleavage of hairpin substrates. This subsequently leads to confinement of many probes for signal generation on electrode. Assisted by K [Fe(CN)] in detection buffer, catalytic redox recycling of mediators induced by trimetallic hybrid NPs thus yield considerably magnified currents for detecting β-Lg with detection limit of 5.4 pg/mL. Our results show that attachment of redox mediator to NP-dispersed graphene can effectively and significantly lower the background current compared with its presence in buffer. At the meantime, the coupling of the DNAzyme amplification with catalytic hybrid NPs can enhance the current signal, leading to high signal-to-noise ratio and sensitivity. Such aptasensor also exhibits high selectivity and can achieve detection of low levels of β-Lg in infant rice cereal.

Significance: The simultaneous background current reduction and dual catalytic signal amplification of our biosensor strategy leads to highly improved signal-to-noise ratio and sensitivity, which suggesting its promising potential for the monitoring of different trace molecular biomarkers for diverse applications.