An integrated relay/nitrate reductase field-effect transistor for the sensing of nitrate (NO3−)

Abstract

An integrated enzyme-functionalized field-effect transistor (ENFET) device for the sensing of nitrate ions is described. An aminosiloxane-functionalized gate interface is modified with N-methyl-N'-(carboxyalkyl)-4,4'-bipyridinium relay units. The complex formed between nitrate reductase and the bipyridinium units on the gate surface is crosslinked with glutaric dialdehyde to yield a stable relay-enzyme layer on the gate interface. In the presence of sodium dithionite as electron donor, the biocatalyzed reduction of nitrate to nitrite ion is stimulated. The ratio between the oxidized and reduced states of the bipyridinium sites regulates the gate potential, and is controlled by the concentration of NO3- ions in the system. The effect of the chain length tethering the N-methyl-N'-(carboxyalkyl)-4,4'-bipyridinium units to the gate surface on the biocatalyzed reduction of NO3- ions, and on the NO3- FET sensor performance is discussed. The devices that include the bipyridinium units tethered to the gate interface with methylene chain length, -(CH2)n, where n > or = 7, reveal a detection limit of 7 x 10(-5) M for nitrate and a sensitivity of 52 +/- 2 mV dec-1. The response time of the device is as low as 50 s, and the operational time of the system is ca. 85 s. We estimate the surface coverage of nitrate reductase on the gate surface to be ca. 1.2 x 10(-12) mol cm-2.

Electroimmobilization of nitrate reductase and nicotinamide adenine dinucleotide into polypyrrole films for potentiometric detection of nitrate

“…The range of materials that have been used for the immobilization of NaR for construction of nitrate biosensor include acrylamide copolymer, polythiophene-bipyridinium [24], polyvinyl alcohol [27], polystyrene-polybutadiene [30], viologen-acrylamide [31], sol-gel matrix [15], decanethiol [32], alkylpyrroleviologen [29,33], and polyviologen [26]. The detection of nitrate with the immobilized NaR is often achieved in the presence of NAD(P)H or other suitable co-factor by amperometry [19,22,25,27,34,35], cyclic voltammetry [19,29], luminescence [16,36,37], optical [15,38] and field effect transistor [39] detection. Most of these biosensors have a narrow linear concentration range and the upper concentration limit is often less than 1 mM.…”

Printed Organic Transistor‐Based Enzyme Sensor for Continuous Glucose Monitoring in Wearable Healthcare Applications

“…Willner et al induced redox cycling of the mediators immobilized on the gate electrode using dissolved oxygen as the oxidant of the reduced mediator with external addition of Ca 2 + ion as a catalyst for the redox cycling reaction, or external addition of a reducing agent. [25,26] Another type of transistorbased enzyme sensor employs a reversibly responsive ISFETbased pH sensor, where the enzyme is immobilized on the pHsensitive gate electrode to detect the pH change induced by the enzymatic reaction. [27,28] However, there are few reports on transistor-based enzyme sensors that can monitor the change in analyte concentration in a physiologically buffered solution without any addition of chemical reagents.…”

A Dip‐and‐Read Test Strip for the Determination of Nitrite in Food Samples for the Field Screening

“…At the same time, many sepectrophotometric (Chen et al 1999;Abbas and Mostafa 2000;Ensafi and Kazemzadeh 1999), FIA (Fang et al 2001;Kazemzadeh and Ensafi 2001), chemiluminescence (Mikuška and Vecera 2003;Lu et al 2004), biosensor (Larsen et al 2000;Zayats et al 2001), and chromatographic (Connolly and Paull 2001;Barciela Alonso 2000) methods have been established for the determination of nitrite. These methods are sensitive and accurate, but most of them require a tedious sample pretreatment, sophisticated performance and expensive equipment, neither one of which can be used for the field screening, especially for in situ monitoring of nitrite in the poisoning food samples.…”