Ultrasensitive Nanosensor for Detection of Malic Acid in Tomato as Fruit Ripening Indicator
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Ultrasensitive Nanosensor for Detection of Malic Acid in Tomato as Fruit Ripening Indicator Anita Dalal 1,2 & J. S. Rana 2 & Ashok Kumar 1
Received: 16 November 2016 / Accepted: 24 April 2017 # Springer Science+Business Media New York 2017
Abstract 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 Km (0.12 mM), less response time (2 min), high sensitivity (0.01 mM) and better storage stability 180 days at 4 °C compared to earlier reported malate biosensor. The nanosensor was also validated at different stages of ripening of tomato using enzymatic method.
Keywords Fruit ripening . Malate dehydrogenase . Malate sensor . Malic enzyme . Nanosensor
* Ashok Kumar [email protected] 1
CSIR-Institute of Genomics and Integrative Biology, Mall Road, Delhi 110007, India
2
Deenbandhu Chhotu Ram University of Science and Technology, Murthal, Sonepat, Haryana 131039, India
Introduction The emergence of nanotechnology offers great opportunities to improve the sensitivity, stability and anti-interference ability of the biosensing systems. In recent years, a number of novel nanomaterials have been used for fabrication of different biosensors. Performance of direct electron transfer between the enzyme and electrode is enhanced by carbon nanotubes (CNT) and metal nanoparticles (Sharma et al. 2009). Direct electrochemistry of enzyme has an important role in development of biosensors, biofuel cells and biomedical devices (Zhang et al. 2004; Prakash et al. 2009). CNT acts as an excellent transducer and is used in different electrochemical biosensor which promotes the electron transfer between immobilized enzyme electrode and substrate due to its extraordinary electron transport property (Iijima 1991; Nugent et al. 2001; Harris 2004; Arvinte et al. 2008). CNT improves the sensor performance because it posses high surface to volume ratio which help in higher enzyme loading and make an effective contact between deeply buried active sites of enzymes and the electrode (Tu et al. 2005; Doubnerova and Ryslava 2011; Hegde et al. 2011).Various biosensors have been reported for detection of water contamination, malic acid and glucose (Lin et al. 2004; Gautam et al. 2012). Malic acid i
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