Development of quantum dots-based biosensor towards on-farm detection of subclinical ketosis

• A NAD+ sensitive quantum dots (QDs) nanoprobe is prepared for monitoring subclinical ketosis in dairy cow.
• An integrated microfluidic platform and quantum dots based resonance energy transfer nanosensor was successfully developed.
• The microfluidic based QD biosensor is able to detect β-hydroxybutyrate from serum and milk samples at submicromolar level in less than 3 min.

Early detection of dairy animal health issues allows the producer or veterinarian to intervene before the animals' production levels, or even survival, is threatened. An increased concentration of β-hydroxybutyrate (βHBA) is a key biomarker for diagnosis of subclinical ketosis (SCK), and provides information on the health stress in cows well before any external symptoms are observable. In this study, quantum dots (QDs) modified with cofactor nicotinamide adenine dinucleotide (NAD+) were prepared for the sensing event, by which the βHBA concentration in the cow's blood and milk samples was determined via fluorescence analysis of the functionalized QDs. The detection was performed on a custom designed microfluidic platform combining with a low cost and miniaturized optical sensor. The sensing mechanism was first validated by a microplate reader method and then applied to the microfluidic platform. Standard βHBA solution, βHBA in blood and milk samples from cows were successfully measured by this novel technology with a detection limit at a level of 35 µM. Side by side comparison of the developed microfluidic biosensor with a commercial kit presented its good performance.