The sensor selectivity and affinity towards the target analyte depends solely on the sensing surface because the analyte interacts only at the sensing surface as illustrated in Fig. The sensor performance characteristics depend on both the components. The sensing surface interacts with the target analyte and the transducer converts this interaction into a readable electronic signal. 1: the sensing surface (or receptor) and the transducer. The objective is to evaluate the impact of the transducer type on the performance metrics of an electrochemical sensor.Īn electrochemical sensor has two basic components as shown in Fig. In this study, we compare a FET transducer with the recently proposed BJT transducer. Recently, bipolar junction transistor (BJT) device 16, 17, 18 was proposed as a transducer in an electrochemical sensor. Over the years, these electrochemical sensors have been demonstrated to detect both ions and biomolecules 2, 3, 4, 5, 6, 7, 8, 9, and have several sensing applications, including DNA sequencing 12, 13 and mobile diagnostics 14, 15. Since then, field effect transistor (FET) based electrochemical sensors 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 have been extensively investigated due to their enhanced sensitivity, resolution, low power, portability and fabrication compatibility with silicon processing technology. The application of field effect transistors (FET) as transducers in electrochemical sensors was first described in 1970 by Bergveld 1. In summary, the BJT device is demonstrated to be a superior transducer in comparison to a FET in an electrochemical sensor. As a demonstration for mobile applications, these BJT sensors are further investigated by measuring chloride levels in artificial human sweat for potential cystic fibrosis diagnostic use. Hence, a BJT sensor can make quantitative sensing measurements with minimal calibration requirements, an important characteristic for mobile sensing applications. Unlike a FET sensor, the calibration curve of the BJT sensor is independent of applied voltages. Also, sensor calibration curves are impacted by the transducer choice. Sensitivity is also enhanced: BJT sensing signal changes by 10 times per pCl, whereas the FET signal changes by 8 or less times. Signal to noise ratio is 20 to 2 times greater for the BJT sensor. Comparative measurements show that the transducer choice significantly impacts the electrochemical sensor characteristics. Measurements are performed on two chloride electrochemical sensors that are identical in all details except for the transducer device type. In this report, a FET transducer is compared with the recently proposed bipolar junction transistor (BJT) transducer. Field effect transistors (FET) have been widely used as transducers in electrochemical sensors for over 40 years.
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