Rapid synthesis of microwave-assisted zinc oxide nanorods on a paper-based analytical device for fluorometric detection of l-dopa.

l-dopa is a catecholamine neurotransmitter used to treat Parkinson's disease. This paper presents a low-cost paper-based biosensor aimed at enhancing the convenience of monitoring l-dopa concentrations. ZnO nanorods (ZnO-NRs) were synthesized on papers in less than 90 min using a microwave-assisted hydrothermal method. The ZnO-NRs amplify green fluorescence signals to enhance the detection sensitivity of l-dopa, best measured at excitation/emission wavelengths of 475/537 nm. We systematically characterized the effect of reaction conditions on the corresponding fluorescence enhancements. The proposed ZnO NRs-paper biosensor presented a ∼3-fold increase in green fluorescence compared to unmodified papers. The linear range of detection for l-dopa was 25-2000 nM, with a limit of detection of 24 nM, which meets the clinical requirements for the monitoring of l-dopa in Parkinson's patients.