Abstract
Biosensors based on Organic Electrochemical Transistors (OECTs) are developed for the selective detection of glucose and lactate. The transistor architecture provides signal amplification (gain) with respect to the simple amperometric response. The biosensors are based on a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) channel and the gate electrode is functionalised with glucose oxidase (GOx) or lactate oxidase (LOx) enzymes, which are immobilised within a Ni/Al Layered Double Hydroxide (LDH) through a one-step electrodeposition procedure. The here-designed OECT architecture allows minimising the required amount of enzyme during electrodeposition. The output signal of the biosensor is the drain current (Id), which decreases as the analyte concentration increases. In the optimised conditions, the biosensor responds to glucose in the range of 0.1–8.0 mM with a limit of detection (LOD) of 0.02 mM. Two regimes of proportionality are observed. For concentrations lower than 1.0 mM, a linear response is obtained with a mean gain of 360, whereas for concentrations higher than 1.0 mM, Id is proportional to the logarithm of glucose concentration, with a gain of 220. For lactate detection, the biosensor response is linear in the whole concentration range (0.05–8.0 mM). A LOD of 0.04 mM is reached, with a net gain equal to 400.
Highlights
In the last 40 years, amperometric biosensors have attracted a great deal of attention due to very appealing features such as fast response, low cost, miniaturisation, and robustness [1,2,3]
The Organic Electrochemical Transistors (OECTs) based on glucose oxidase (GOx) was first developed to optimise the architecture of the device and to find out the best experimental conditions to carry out the detection of the analyte
The OECT configuration of choice (Figure 1a) allows keeping only the gate terminal dipped into the electrolytic solution employed for the enzyme/Layered Double Hydroxide (LDH) immobilisation (Figure 1b), avoiding the use of a large amount of solution and reducing the device preparation costs
Summary
In the last 40 years, amperometric biosensors have attracted a great deal of attention due to very appealing features such as fast response, low cost, miniaturisation, and robustness [1,2,3]. A wide range of biologically relevant analytes has been determined through amperometric detection. The literature offers many examples of amperometric biosensors for glucose and lactate detection, most of them based on the functionalisation with glucose oxidase (GOx) [11] or lactate oxidase (LOx) [12] enzymes. The real-time analysis of glucose is generally carried out invasively by subcutaneous electrodes, limiting the determination to the most relevant medical cases, such as diabetic patients. Lactate determination is usually performed in blood, and real-time data acquisition systems are commercially unavailable, even if some sweat sensors are under development to meet the market demand (http://www.epicorebiosystems.com/). Other biological fluids such as sweat, saliva, and tears are more readily accessible and are attractive
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