Ultrasensitive Nanosensor for Detection of Malic Acid in Tomato as Fruit Ripening Indicator

Malic acid is an important fruit ripening indicator. Fruit industry losses every year due to non-availability of rapid technology for early detection of ripening of fruits. Therefore, nanosensor was developed for detection of malic acid concentrations in tomato at early stage of ripening before transport to the market. The enzyme NADP-malate dehydrogenase (Malic enzyme) was covalently immobilized on to screen printed carboxylated-multiwall carbon nanotubes working electrode using EDC-NHS chemistry. The enzyme electrode was characterized using scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The immobilized enzyme/c-MWCNT electrode was used for amperometric determination of different concentrations of malic acid in tomato using differential pulse voltammogram (DPV) at scan rate of 100 mv/s. The limit of detection of malic acid was 0.01 mM. The nanosensor showed low K-m (0.12 mM), less response time (2 min), high sensitivity (0.01 mM) and better storage stability 180 days at 4 A degrees C compared to earlier reported malate biosensor. The nanosensor was also validated at different stages of ripening of tomato using enzymatic method.