Smartphone-based Electrochemical Sensor Systems And Their Applications In Biomedical Detections

Electrochemical methods are one of the most common qualitative and quantitative detection techniques. They have been widely used in environmental monitoring, healthcare diagnostics, and food quality control, because they are often stable, sensitive and easily designed into portability. Although used in a variety of detections, these electrochemical methods, for now, are generally performed by scientific analytic instruments and operated by experienced staffs in well-resourced laboratories. It limits applications of electrochemical detections in point-of-care test (POCT), which was often designed for primary-level clinics and personal users. Thus, development of miniaturized, portable, and low-cost electrochemical devices can satisfy requirement of POCT for fast-field analysis, which has important practical significances and broad application prospects.In this study, we developed several smartphone-based electrochemical detectors to perform alternating-current (AC) impedance measurement, electrochemical impedance spectroscopy (EIS) measurement, and cyclic voltammetry measurement, respectively. The smartphones were used as mobile platforms to input command, control measurement, and analyze data, which simplified electronic circuits and lowered costing of electrochemical devices. Then, those smartphone-based electrochemical devices were further applied to detect environmental odorants, analyze protein interactions, and investigate electrochemical-coupled localized surface plasmon resonance (LSPR) biosensors, to show application demonstrations of those smartphone-based devices in biomedical detections. The main contents and contributions of this thesis are given as following:1. Development of smartphone-based impedance monitoring devices.AC impedance monitoring is one of the most important electrochemical conductive techniques, which has been widely used in biomedical detections. In this thesis, two kinds of smartphone-based impedance monitoring devices were developed to perform time-impedance and frequency-impedance measurements, respectively. Electronic circuits were designed and software programs were written to meet biomedical sensing requirements. Then, performances of the devices, such as accuracy, stability, and EIS, were tested when electrochemical workstation was employed as the control. These all suggested feasibility of the smartphone-based device for biomedical detections.2. Development of smartphone-based cyclic voltammetry devices.Cyclic voltammetry is one of the most common electrochemical amperometric techniques utilizing redox reactions on sensor surfaces. In this thesis, a smartphone-based device was developed to perform cyclic voltammetry by monitoring currents modulated by linear potentials. Electronic circuits were designed, while programs were written on microcontroller chip and smartphone, respectively. Using electrochemical workstation as the control, relative error and measuring accuracy of the device were tested to suggest feasibility of the smartphone-based device for biomedical detections.3. Usage of the smartphone-based monitoring system for typical environmental odorant detections.Environmental odorant detection is an analytic technique utilizing sensor devices to trace environmental odor molecules. In this thesis, we proposed to use the smartphone-based impedance monitoring system for detections of environmental odorants, including explosive compound of 2,4,6-trinitrotoluene (TNT) and volatile organic compound of acetone. Using printed electrodes modified with TNT-specific peptides, the smartphone-based device can rapidly detect TNT at concentration as low as 7.09×10-7 M. Meanwhile, using interdigital electrodes modified graphene and ZnO, the device can detect acetone with detection limit of 1.56 ppm. The acetone in breath gas can also be detected by the device to monitor personal exercise and metabolism.4. Usage of the smartphone-based monitoring system for protein detections.Proteins are closely related to life activities and thus are often used as biomarkers in medical diagnostics. In this thesis, we proposed to use the smartphone-based EIS system for detections of proteins, such as bull serum albumin (BSA) and thrombin. Using printed electrodes modified with anti-BSA and interdigital microelectrodes self-assembled by of polyethylene glycol-peptide-BSA, the device can detect BSA and thrombin rapidly. Their detection limits were at level of μg/mL and ng/mL, respectively, satisfying requirements of biomedical detections.5. Usage of the smartphone-based cyclic voltammetry system for electrochemical coupled LSPR biosensor investigation.LSPR is a widely used optical technique for real-time detections of analytes. In this thesis, a synchronous measurement of optical and electrochemical measurement was designed by electrochemical workstation and spectrograph, and then used to monitor electrochemical coupled LSPR on nanocup device. The electrochemical coupled detection can be used to detect BSA with improvement in detection limit. The smartphone-based cyclic voltammetry system was also used to take place of the electrochemical workstation in the synchronous measurements for BSA/anti-BSA reaction. The results suggested the possibility of application of the smartphone-based cyclic voltammetry system for electrochemical coupled LSPR biosensors.