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Fabrication of a Configurable Multi-Potentiostat for LOC Applications
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 5 (2018) 16732–16739
www.materialstoday.com/proceedings
SCICON 2016
Fabrication of a Configurable Multi-Potentiostat for LOC Applications Vineeth Raj Sab, John Stanleyc, T. G. SatheeshBabuc* a
b
Amrita School of Biotechnology, Kollam, Amrita Vishwa Vidyapeetham, Amrita University, India.
Department of Electronics and Communication Engineering, Amrita School of Engineering, Coimbatore, Amrita Vishwa Vidyapeetham, Amrita University, India. c
Department of Sciences, Amrita School of Engineering, Coimbatore, Amrita Vishwa Vidyapeetham, Amrita University, India.
Abstract This paper describes the development of a portable, cost effective reconfigurable multi-analyte detection electronics meter module for Lab-on-a-chip applications. A low costpotentiostat(LMP91000) was used as the analog front end (AFE) in this work. The advanced core microcontroller from Microchip (PIC16LF1783) was used for controlling the different operation of the meter. The current obtained by amperometrictechniques was calibrated and displayed on a graphical LCD and alsodisplayed on a smart phone using Bluetooth technology. © 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Advanced Materials(SCICON ‘16). Keywords:Multi-Potentiostat; Lab-on-a-chip; Wireless communication
1. Introduction Early and accurate diagnosis of diseases is vital as it helps in prompt and proper treatment, prevents the spread of disease in the population, and minimizes the waste of resources on ineffective treatments [1]. In-vitro diagnostic devices have played a vital role in creating a world with improved healthcare environment through advanced manufacturing process and a spur in globalization. However, time constraints, difficulties associated with frequent
* Corresponding author. Tel.: +919442368632 E-mail address:[email protected] 2214-7853© 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Advanced Materials(SCICON ‘16).
Vineeth Raj et al. / Materials Today: Proceedings 5 (2018) 16732–16739
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visits to clinical laboratories and lack of access to laboratory facilities in developing countries led to a new era in diagnostics known as Point of Care Testing (POCT). POCT devices are increasingly used in hospital wards, general practitioner (GP) offices, nursing homes, pharmaceutical trials and most commonly for self-measurements. These devices have numerous advantages including the elimination of the requirement for skilled personnel, use of unprocessed sample and instantaneous diagnostic results with reduced sample volumes [2-5]. With increasing technological and analytical possibilities, a large number of analyses can be carried out on POC instruments. Currently, Point of Care Testing (POCT) is the most rapidly growing field in laboratory medicine. Lab-on-a-Chip systems are a class of miniaturized POCT devices that integrate fluidics, electronics and various sensors. They are capable of analyzing biochemical liquid samples, like solutions of metabolites, macromolecules, proteins, nucleic acids, or cells and viruses. These devices are usually in the order of micrometers to a few millimeters in size and are capable of analyzing biochemical liquid samples, like solutions of metabolites, macromolecules, proteins, nucleic acids, or cells and viruses [6]. Also, these devices facilitate fluidic transportation, sorting, mixing and separation of liquid samples [7]. These devices with their unique capabilities help counter the challenge of providing accurate diagnosis in remote and underdeveloped parts of the world. They have many advantages including compactness, portability, modularity, re-configurability, embedded computing, automated sample handling, low electronic noise, limited power consumption and straightforward integration of components [8,9]. A number of researchers have tried to develop compact and portable meter module that can perform a variety of electrochemical techniques for the detection of biomolecules. Hu et al. had developed a multi parameter monitoring system for the detection of multiple analytes using LABVIEW software [10]. This was achieved by using a multi potentiostat circuit and the output of each potentiostat was fed to individual channels of the ADC module and the outputs was displayed on a computer. A low cost, miniaturized potentiostat for voltammetric measurements of biomarkers was developed by Cruz et al. [11]. This potentiostat was interfaced with the micrcontroller using the I2C communication protocol. A multi-parametric analyzer developed using customized transducers, micro fabricated inter-digitated electrodes (IDEs), and based on polymeric substance for four parameter analysis was developed by Punter et al. [12]. Custom low-power, low-cost instrumentation electronics for both voltammetry and impedance analysis techniques were used. This unit had a disposable thin film flexible electrochemical battery as the power source. An embedded system for a portable potentiostat was developed by Kwakye et al. [13]. A detailed study of controller selection and power optimization techniques were studied. MSP430 based control circuit was used. A pulse width modulated signal was used as the source for biasing the circuit and Ultralow power MSP430 controller was used to process the data and display the result on an LCD.A portable glucometer that responds to the test strips of different manufacturers was developed by Anoop et al. [14]. A major drawback of the present day glucometer is that the instrument and test strips of one manufacturer are incompatible with those of another. Hence, they had designed and simulated a circuit which will overcome this limitation, using the appropriate biasing potential for different test strips, by means of a variable potentiostat. In this work, a multipotentiostat for the simultaneous detection of three analytes was successfully developed. The programmable potentiostat LMP91000 was used as the analog front end and PIC16LF1783 was used as the microcontroller. With the help of the software, the obtained data was successfully converted to resultant analyte concentration and the result was displayed on a graphical LCD.
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2. Materials and Methods 2.1. Chemical, electronic components and instruments Glucose (Glu, ACS reagent), was purchased from Sigma Aldrich. Conducting inks of carbon, silver and Ag/AgCl and their respective reducers were purchased from Dupont Pvt. Ltd. Singapore All other chemicals were of analytical grade and purchased from FINAR chemicals, India and used without further purification. All stock solutions except were prepared in Millipore deionized water (15.2 MΩ cm, Millipore, Germany) and stored at 4 °C when not in use. Polyethylene terephthalate (PET) sheets of 0.6 mm thickness were purchased from Polymer Inc, Bengaluru, India. The following electronic components were used to build the meter module Microcontroller PIC16LF1783 from Microchip, Analog Front End LMP91000 from Texas Instruments, Real Time Clock DS1338Z from Maxim Integrated, Low dropout Regulator LM4132AMF3.3,Li-ion rechargeable battery 3.7 V-1020 mAh from SGM, and SMD capacitors, Resistors , Quartz crystal oscillator and switches were brought from Mouser Electronics (http://mouser.in). 84*48 Graphical Serial LCD was purchased from Spark fun(https://www.sparkfun.com). FR4 1/16”(1.60 mm) double sided copper clad from MG chemicals (http://www.mgchemicals.com) was purchased for the PCB fabrication. For wireless connection, HC05 Bluetooth module was purchased from Rhydolabz (http://www.rhydolabz.com). Semi-automated screen printer TP-450L (Hanky, Taiwan) was used for the fabrication of disposable sensor strips. For the electrochemical characterization of the sensor strips, CHI 660C (CH instruments, Texas USA) was used. Weller SMD soldering station was used for soldering. For the simulation of electronic circuits, Proteus v.8.0 was used. PCB design was done using DipTrace software. MPLab IDE was used for programming the microcontroller programming using HiTech PICC compiler. The final code is compiled and burnt into the controller using PICKIT3 in circuit serial programmer. 2.2. Fabrication of screen printed electrode Disposable electrodes were fabricated by screen printing as described by Keerthy et al. [15]. Briefly, the PET sheet was cleaned with acetone and was pre-heated at 90 oC for 12 hours prior to screen printing. The first layer to be screen printed on the PET substrate is the silver conducting layer. Ag/AgCl is then applied to the tip of the reference electrode. The silver layer is then coated with conductive carbon ink to prevent it from oxidization. Thermal curing at 65 oC for 15 min was carried out after printing of each layer. CuO nanoparticles were synthesized as reported [16]. Briefly, 26 ml of ammonia was added drop wise to 700 ml 0.05 molL-1 CuSO4 under constant stirring till the solution turns to dark blue. 150 ml of 1 molL-1 NaOH solution was added drop wise which resulted in the formation of a light blue colored precipitate of [Cu(OH)4]2- as the pH reaches 14. This precipitate was filtered and washed with distilled water several times and calcined at 400 oC for 3 hours. The synthesized nano material was mixed with the Dupont Carbon ink to obtain a nano slurry and this slurry is screen printed on the working area. An insulation layer is provided for easily handling of the sensor strips. 2.3. Design and fabrication of portable meter For the electrochemical analysis using amperometry and voltammetry a constant controlled potential is required between the working and reference electrodes. This can be achieved with the help of a potentiostat circuit. The block diagram of the developed amperometric meter module is shown in Fig. 2.
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Fig. 1. Screen printing process
Fig. 2. Block Diagram of the developed meter
An enhanced midrange microcontroller PIC16LF1783 was used as the brain of the system. The controller controls AFEs, RTC, LCD and BLUETOOTH module. PIC16LF1783 has an ADC resolution of 12 bits. Since the controller is XLP (extreme low power) enabled technology, it is well suited for battery powered portable device applications. DS1338Z was used as the Real Time Clock (RTC). It helps maintain the date and time required for data logging. I2C communication is used for communication between theRTC and microcontroller. LMP91000 acts as the potentiostat for electrochemical reaction. The internal block diagram of LMP91000 is shown in Fig. 3. The advantage of this IC is that it is programmable. The cell bias and transimpedance amplifier gain can be easily programmed through the I2C interface, helping maintain the required potential for the different sensors accurately as well as obtain current readings that are easily measurable.
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Vineeth Raj et al. / Materials Today: Proceedings 5 (2018) 16732–16739
Three miniaturized potentiostats (LMP91000) were used and they were connected to the controller using a common I2C channel. The current response obtained for various biomolecules obtained by amperometric and was calibrated and displayed on a graphical LCD. The microcontroller was connected to the analog front end and the output voltage from each AFE was fed to three separate ADC channels of the microcontroller. With the help of the programme, the microcontroller converts the obtained voltage into the corresponding analyte concentrations. Since I2C is an address based communication, the controller can communicate to each one separately by calling its address. But all the three AFEs are using the same address so when the controller try to communicate to one AFE all will respond. In order to avoid this situation a MENB pin is provided to activate each AFEs separately. Once the MENB is activated, then that particular AFE will respond to I2C bus communication.
Fig. 3. LMP91000 Analog Front End (AFE) internal block diagram
2.4. Fabrication of Printed Circuit Board
Fig. 4. Top and Bottom layer of the designed PCB
A double sided PCB with surface mount package of all components was designed in order to reduce the board space. The error checking option available in DipTrace software helps to avoid errors that occur due to manual routing. Both the layers of the circuit were transferred to a double side copper clad using carbon ink. The copper clad was dried at 50°C for 30 minutes in hot air oven. Etching of unwanted copper portion is done by Ferric chloride etching solution (Ferric Chloride: HCL: H2O=1: 4: 6). Air bubbles were passed through the solution to increase the etching rate. The obtained copper sheet has copper pads only at the places where carbon ink got transferred. The
Vineeth Raj et al. / Materials Today: Proceedings 5 (2018) 16732–16739
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carbon ink on the copper lines was removed using carbon ink thinner solvent. Holes were drilled and through-hole connections were made to connect between the top and bottom layers. The PCB was placed in Tin-Lead bath for tinning the copper traces. Using Weller soldering station, all components were fixed to the PCB. The PCB was thoroughly cleaned using IPA solution. The obtained final PCB was tested using Digital Multimeter. 3. Results and Discussion
Fig.5.Chronoamperometric experiments carried out at 3.3 V with different concentrations of glucose in 0.1 M NaOH
Fig. 6. Calibration plot
The fabricated glucose sensor strips were characterized electrochemically using chronoamperometry. Fig 5 represents the chronoamperometry obtained towards different concentrations of glucose at 3.3 V in 0.1 M NaOH. It is observed that the current response towards glucose increases linearly with increase in glucose concentration from 3 mM to 27 mM. From the graph it is observed that that the current from glucose oxidation stabilizes after 5 seconds. This was taken into consideration while developing the meter module. Since the ADC module have 12 bit resolution, and the circuit is designed for 3.3V operation so the ADC is able to measure the voltage with a resolution of 0.8mV. The meter was calibrated (Fig .6) such that the current obtained from oxidation of glucose was measured after 5 seconds of sample injection. First the meter was tested with different concentration of analyte for
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Vineeth Raj et al. / Materials Today: Proceedings 5 (2018) 16732–16739
understanding the voltage for different concentrations of sample. From the values obtained, a voltage (V) vs Concentration (mg/dl) is plotted and linear fit is derived using the equation y= mx +C. With the help of slope (m) and constant, entered in the program, the microcontroller converts the obtained voltage into corresponding glucose concentrations. The output from the current-voltage converter has usually a base value depending upon the value set for internal zero. The base value will be subtracted from the voltage measured after the time interval. The resulting voltage corresponds to the oxidation/reduction current. The results obtained from the meter were compared with those obtained from the electrochemical workstation as shown in Fig 7. From the graph it is observed that the results obtained from the meter module are highly consistent with those obtained from the electrochemical work station. The developed meter module is shown in Fig .8.
Fig. 7. Oxidation current obtained for different concentrations of glucose at a constant potential of 0.52 V with electrochemical work station and developed meter
Fig. 8.Developed Lab-on-a-chip meter module
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4. Conclusion A meter module was successfully developed for the simultaneous detection of multiple analytes such as glucose, ascorbic acid and dopamine from a single drop of sample. The developed electronic module was able to simultaneously receive signals from the three different sensors with the help of the analog front end. These signals were further successfully processed and converted into analyte concentrations with the help of the calibration plot. The obtained results were successfully displayed on an LCD screen. To make the device telemedicine friendly, the obtained analyte concentrations were successfully transmitted to a mobile device using bluetooth communication References [1] Chin CD, Linder V, Sia SK: Lab-on-a-Chip devices for global health: Past studies and future opportunities. Lab on a Chip 2007, 7(1):41-57. [2] Kost GJ: Guidelines for point-of-care testing. Improving patient outcomes. American journal of clinical pathology 1995, 104(4 Suppl 1):S111-127. [3]Kilgore ML, Steindel SJ, Smith JA: Evaluating stat testing options in an academic health center: therapeutic turnaround time and staff satisfaction. Clinical Chemistry 1998, 44(8):1597-1603. [4] Louie RF, Tang Z, Shelby DG, Kost GJ: Point-of-care testing: millennium technology for critical care. Laboratory Medicine 2000, 31(7):402408. [5] Chernow B, Salem M, Stacey J: Blood conservation: a critical care imperative. Critical care medicine 1991, 19(3):313-314. [6]A. Ng and A. Wheeler, "Next-Generation Microfluidic Point-of-Care Diagnostics", Clinical Chemistry, vol. 61, no. 10, pp. 1233-1234, 2015. [7] A. Pradeep, J. Raveendran, R. T., B. Nair and S. T.G., "Computational simulation and fabrication of smooth edged passive micromixers with alternately varying diameter for efficient mixing", Microelectronic Engineering, vol. 165, pp. 32-40, 2016. [8]W. Jung, J. Han, J. Choi and C. Ahn, "Point-of-care testing (POCT) diagnostic systems using microfluidic lab-on-a-chip technologies", Microelectronic Engineering, vol. 132, pp. 46-57, 2015. [9] T. Ackermann, P. Giménez-Gómez, X. Muñoz-Berbel and A. Llobera, "Plug and measure – a chip-to-world interface for photonic lab-on-achip applications", Lab Chip, vol. 16, no. 17, pp. 3220-3226, 2016. [10] B. Hu and X. Liu, "Design and Research of Multi-Channel Temperature Calibration System Based on the LabVIEW", AMR, vol. 304, pp. 241-246, 2011. [11] A. Cruz, N. Norena, A. Kaushik and S. Bhansali, "A low-cost miniaturized potentiostat for point-of-care diagnosis", Biosensors and Bioelectronics, vol.62, pp. 249-254, 2014. [12] V. Jaime Punter, A. Cristina Paez, F. Jordi Colomer, S. Jaime Lopez, F.EsteveJuanola and C. Pere Miribel, "A Portable Point-of-Care Device for Multi-Parametric Diabetes Mellitus Analysis", in IECON2015, Yokohama, 2015, pp. 1252-1257. [13] S. Kwakye and A. Baeumner, "An embedded system for portable electrochemical detection", Sensors and Actuators B: Chemical, vol. 123, no.1, pp. 336-343, 2007. [14] Anoop, A.E., Madhu Mohan, N, and Guruvayurappan, K,“Simulation of a multi-strip blood glucometer”. In: TENCON 2014, 2014. [online] IEEE Proceedings. Available at: http://ieeexplore.ieee.org/document/7022473/]. [15] Dhara, K., Stanley, J., Ramachandran, T., Nair, B. and Babu, T.,“ Cupric Oxide Modified Screen Printed Electrode for the Nonenzymatic Glucose Sensing”, Journal of Nanoscience and Nanotechnology, 16(8), pp.8772-8778, 2016. [16] Yanga M., Hea J., Hua X., Yana C., Chenga Z., Zhaoa Y. and Zuo G., “Copper oxide nanoparticle sensors for hydrogen cyanide detection: Unprecedented selectivity and sensitivity”, Sensors and Actuators B, vol.155, pp. 692–698, 2011.
ScienceDirect Materials Today: Proceedings 5 (2018) 16732–16739
www.materialstoday.com/proceedings
SCICON 2016
Fabrication of a Configurable Multi-Potentiostat for LOC Applications Vineeth Raj Sab, John Stanleyc, T. G. SatheeshBabuc* a
b
Amrita School of Biotechnology, Kollam, Amrita Vishwa Vidyapeetham, Amrita University, India.
Department of Electronics and Communication Engineering, Amrita School of Engineering, Coimbatore, Amrita Vishwa Vidyapeetham, Amrita University, India. c
Department of Sciences, Amrita School of Engineering, Coimbatore, Amrita Vishwa Vidyapeetham, Amrita University, India.
Abstract This paper describes the development of a portable, cost effective reconfigurable multi-analyte detection electronics meter module for Lab-on-a-chip applications. A low costpotentiostat(LMP91000) was used as the analog front end (AFE) in this work. The advanced core microcontroller from Microchip (PIC16LF1783) was used for controlling the different operation of the meter. The current obtained by amperometrictechniques was calibrated and displayed on a graphical LCD and alsodisplayed on a smart phone using Bluetooth technology. © 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Advanced Materials(SCICON ‘16). Keywords:Multi-Potentiostat; Lab-on-a-chip; Wireless communication
1. Introduction Early and accurate diagnosis of diseases is vital as it helps in prompt and proper treatment, prevents the spread of disease in the population, and minimizes the waste of resources on ineffective treatments [1]. In-vitro diagnostic devices have played a vital role in creating a world with improved healthcare environment through advanced manufacturing process and a spur in globalization. However, time constraints, difficulties associated with frequent
* Corresponding author. Tel.: +919442368632 E-mail address:[email protected] 2214-7853© 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Advanced Materials(SCICON ‘16).
Vineeth Raj et al. / Materials Today: Proceedings 5 (2018) 16732–16739
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visits to clinical laboratories and lack of access to laboratory facilities in developing countries led to a new era in diagnostics known as Point of Care Testing (POCT). POCT devices are increasingly used in hospital wards, general practitioner (GP) offices, nursing homes, pharmaceutical trials and most commonly for self-measurements. These devices have numerous advantages including the elimination of the requirement for skilled personnel, use of unprocessed sample and instantaneous diagnostic results with reduced sample volumes [2-5]. With increasing technological and analytical possibilities, a large number of analyses can be carried out on POC instruments. Currently, Point of Care Testing (POCT) is the most rapidly growing field in laboratory medicine. Lab-on-a-Chip systems are a class of miniaturized POCT devices that integrate fluidics, electronics and various sensors. They are capable of analyzing biochemical liquid samples, like solutions of metabolites, macromolecules, proteins, nucleic acids, or cells and viruses. These devices are usually in the order of micrometers to a few millimeters in size and are capable of analyzing biochemical liquid samples, like solutions of metabolites, macromolecules, proteins, nucleic acids, or cells and viruses [6]. Also, these devices facilitate fluidic transportation, sorting, mixing and separation of liquid samples [7]. These devices with their unique capabilities help counter the challenge of providing accurate diagnosis in remote and underdeveloped parts of the world. They have many advantages including compactness, portability, modularity, re-configurability, embedded computing, automated sample handling, low electronic noise, limited power consumption and straightforward integration of components [8,9]. A number of researchers have tried to develop compact and portable meter module that can perform a variety of electrochemical techniques for the detection of biomolecules. Hu et al. had developed a multi parameter monitoring system for the detection of multiple analytes using LABVIEW software [10]. This was achieved by using a multi potentiostat circuit and the output of each potentiostat was fed to individual channels of the ADC module and the outputs was displayed on a computer. A low cost, miniaturized potentiostat for voltammetric measurements of biomarkers was developed by Cruz et al. [11]. This potentiostat was interfaced with the micrcontroller using the I2C communication protocol. A multi-parametric analyzer developed using customized transducers, micro fabricated inter-digitated electrodes (IDEs), and based on polymeric substance for four parameter analysis was developed by Punter et al. [12]. Custom low-power, low-cost instrumentation electronics for both voltammetry and impedance analysis techniques were used. This unit had a disposable thin film flexible electrochemical battery as the power source. An embedded system for a portable potentiostat was developed by Kwakye et al. [13]. A detailed study of controller selection and power optimization techniques were studied. MSP430 based control circuit was used. A pulse width modulated signal was used as the source for biasing the circuit and Ultralow power MSP430 controller was used to process the data and display the result on an LCD.A portable glucometer that responds to the test strips of different manufacturers was developed by Anoop et al. [14]. A major drawback of the present day glucometer is that the instrument and test strips of one manufacturer are incompatible with those of another. Hence, they had designed and simulated a circuit which will overcome this limitation, using the appropriate biasing potential for different test strips, by means of a variable potentiostat. In this work, a multipotentiostat for the simultaneous detection of three analytes was successfully developed. The programmable potentiostat LMP91000 was used as the analog front end and PIC16LF1783 was used as the microcontroller. With the help of the software, the obtained data was successfully converted to resultant analyte concentration and the result was displayed on a graphical LCD.
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2. Materials and Methods 2.1. Chemical, electronic components and instruments Glucose (Glu, ACS reagent), was purchased from Sigma Aldrich. Conducting inks of carbon, silver and Ag/AgCl and their respective reducers were purchased from Dupont Pvt. Ltd. Singapore All other chemicals were of analytical grade and purchased from FINAR chemicals, India and used without further purification. All stock solutions except were prepared in Millipore deionized water (15.2 MΩ cm, Millipore, Germany) and stored at 4 °C when not in use. Polyethylene terephthalate (PET) sheets of 0.6 mm thickness were purchased from Polymer Inc, Bengaluru, India. The following electronic components were used to build the meter module Microcontroller PIC16LF1783 from Microchip, Analog Front End LMP91000 from Texas Instruments, Real Time Clock DS1338Z from Maxim Integrated, Low dropout Regulator LM4132AMF3.3,Li-ion rechargeable battery 3.7 V-1020 mAh from SGM, and SMD capacitors, Resistors , Quartz crystal oscillator and switches were brought from Mouser Electronics (http://mouser.in). 84*48 Graphical Serial LCD was purchased from Spark fun(https://www.sparkfun.com). FR4 1/16”(1.60 mm) double sided copper clad from MG chemicals (http://www.mgchemicals.com) was purchased for the PCB fabrication. For wireless connection, HC05 Bluetooth module was purchased from Rhydolabz (http://www.rhydolabz.com). Semi-automated screen printer TP-450L (Hanky, Taiwan) was used for the fabrication of disposable sensor strips. For the electrochemical characterization of the sensor strips, CHI 660C (CH instruments, Texas USA) was used. Weller SMD soldering station was used for soldering. For the simulation of electronic circuits, Proteus v.8.0 was used. PCB design was done using DipTrace software. MPLab IDE was used for programming the microcontroller programming using HiTech PICC compiler. The final code is compiled and burnt into the controller using PICKIT3 in circuit serial programmer. 2.2. Fabrication of screen printed electrode Disposable electrodes were fabricated by screen printing as described by Keerthy et al. [15]. Briefly, the PET sheet was cleaned with acetone and was pre-heated at 90 oC for 12 hours prior to screen printing. The first layer to be screen printed on the PET substrate is the silver conducting layer. Ag/AgCl is then applied to the tip of the reference electrode. The silver layer is then coated with conductive carbon ink to prevent it from oxidization. Thermal curing at 65 oC for 15 min was carried out after printing of each layer. CuO nanoparticles were synthesized as reported [16]. Briefly, 26 ml of ammonia was added drop wise to 700 ml 0.05 molL-1 CuSO4 under constant stirring till the solution turns to dark blue. 150 ml of 1 molL-1 NaOH solution was added drop wise which resulted in the formation of a light blue colored precipitate of [Cu(OH)4]2- as the pH reaches 14. This precipitate was filtered and washed with distilled water several times and calcined at 400 oC for 3 hours. The synthesized nano material was mixed with the Dupont Carbon ink to obtain a nano slurry and this slurry is screen printed on the working area. An insulation layer is provided for easily handling of the sensor strips. 2.3. Design and fabrication of portable meter For the electrochemical analysis using amperometry and voltammetry a constant controlled potential is required between the working and reference electrodes. This can be achieved with the help of a potentiostat circuit. The block diagram of the developed amperometric meter module is shown in Fig. 2.
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Fig. 1. Screen printing process
Fig. 2. Block Diagram of the developed meter
An enhanced midrange microcontroller PIC16LF1783 was used as the brain of the system. The controller controls AFEs, RTC, LCD and BLUETOOTH module. PIC16LF1783 has an ADC resolution of 12 bits. Since the controller is XLP (extreme low power) enabled technology, it is well suited for battery powered portable device applications. DS1338Z was used as the Real Time Clock (RTC). It helps maintain the date and time required for data logging. I2C communication is used for communication between theRTC and microcontroller. LMP91000 acts as the potentiostat for electrochemical reaction. The internal block diagram of LMP91000 is shown in Fig. 3. The advantage of this IC is that it is programmable. The cell bias and transimpedance amplifier gain can be easily programmed through the I2C interface, helping maintain the required potential for the different sensors accurately as well as obtain current readings that are easily measurable.
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Vineeth Raj et al. / Materials Today: Proceedings 5 (2018) 16732–16739
Three miniaturized potentiostats (LMP91000) were used and they were connected to the controller using a common I2C channel. The current response obtained for various biomolecules obtained by amperometric and was calibrated and displayed on a graphical LCD. The microcontroller was connected to the analog front end and the output voltage from each AFE was fed to three separate ADC channels of the microcontroller. With the help of the programme, the microcontroller converts the obtained voltage into the corresponding analyte concentrations. Since I2C is an address based communication, the controller can communicate to each one separately by calling its address. But all the three AFEs are using the same address so when the controller try to communicate to one AFE all will respond. In order to avoid this situation a MENB pin is provided to activate each AFEs separately. Once the MENB is activated, then that particular AFE will respond to I2C bus communication.
Fig. 3. LMP91000 Analog Front End (AFE) internal block diagram
2.4. Fabrication of Printed Circuit Board
Fig. 4. Top and Bottom layer of the designed PCB
A double sided PCB with surface mount package of all components was designed in order to reduce the board space. The error checking option available in DipTrace software helps to avoid errors that occur due to manual routing. Both the layers of the circuit were transferred to a double side copper clad using carbon ink. The copper clad was dried at 50°C for 30 minutes in hot air oven. Etching of unwanted copper portion is done by Ferric chloride etching solution (Ferric Chloride: HCL: H2O=1: 4: 6). Air bubbles were passed through the solution to increase the etching rate. The obtained copper sheet has copper pads only at the places where carbon ink got transferred. The
Vineeth Raj et al. / Materials Today: Proceedings 5 (2018) 16732–16739
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carbon ink on the copper lines was removed using carbon ink thinner solvent. Holes were drilled and through-hole connections were made to connect between the top and bottom layers. The PCB was placed in Tin-Lead bath for tinning the copper traces. Using Weller soldering station, all components were fixed to the PCB. The PCB was thoroughly cleaned using IPA solution. The obtained final PCB was tested using Digital Multimeter. 3. Results and Discussion
Fig.5.Chronoamperometric experiments carried out at 3.3 V with different concentrations of glucose in 0.1 M NaOH
Fig. 6. Calibration plot
The fabricated glucose sensor strips were characterized electrochemically using chronoamperometry. Fig 5 represents the chronoamperometry obtained towards different concentrations of glucose at 3.3 V in 0.1 M NaOH. It is observed that the current response towards glucose increases linearly with increase in glucose concentration from 3 mM to 27 mM. From the graph it is observed that that the current from glucose oxidation stabilizes after 5 seconds. This was taken into consideration while developing the meter module. Since the ADC module have 12 bit resolution, and the circuit is designed for 3.3V operation so the ADC is able to measure the voltage with a resolution of 0.8mV. The meter was calibrated (Fig .6) such that the current obtained from oxidation of glucose was measured after 5 seconds of sample injection. First the meter was tested with different concentration of analyte for
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Vineeth Raj et al. / Materials Today: Proceedings 5 (2018) 16732–16739
understanding the voltage for different concentrations of sample. From the values obtained, a voltage (V) vs Concentration (mg/dl) is plotted and linear fit is derived using the equation y= mx +C. With the help of slope (m) and constant, entered in the program, the microcontroller converts the obtained voltage into corresponding glucose concentrations. The output from the current-voltage converter has usually a base value depending upon the value set for internal zero. The base value will be subtracted from the voltage measured after the time interval. The resulting voltage corresponds to the oxidation/reduction current. The results obtained from the meter were compared with those obtained from the electrochemical workstation as shown in Fig 7. From the graph it is observed that the results obtained from the meter module are highly consistent with those obtained from the electrochemical work station. The developed meter module is shown in Fig .8.
Fig. 7. Oxidation current obtained for different concentrations of glucose at a constant potential of 0.52 V with electrochemical work station and developed meter
Fig. 8.Developed Lab-on-a-chip meter module
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4. Conclusion A meter module was successfully developed for the simultaneous detection of multiple analytes such as glucose, ascorbic acid and dopamine from a single drop of sample. The developed electronic module was able to simultaneously receive signals from the three different sensors with the help of the analog front end. These signals were further successfully processed and converted into analyte concentrations with the help of the calibration plot. The obtained results were successfully displayed on an LCD screen. To make the device telemedicine friendly, the obtained analyte concentrations were successfully transmitted to a mobile device using bluetooth communication References [1] Chin CD, Linder V, Sia SK: Lab-on-a-Chip devices for global health: Past studies and future opportunities. Lab on a Chip 2007, 7(1):41-57. [2] Kost GJ: Guidelines for point-of-care testing. Improving patient outcomes. American journal of clinical pathology 1995, 104(4 Suppl 1):S111-127. [3]Kilgore ML, Steindel SJ, Smith JA: Evaluating stat testing options in an academic health center: therapeutic turnaround time and staff satisfaction. Clinical Chemistry 1998, 44(8):1597-1603. [4] Louie RF, Tang Z, Shelby DG, Kost GJ: Point-of-care testing: millennium technology for critical care. Laboratory Medicine 2000, 31(7):402408. [5] Chernow B, Salem M, Stacey J: Blood conservation: a critical care imperative. Critical care medicine 1991, 19(3):313-314. [6]A. Ng and A. Wheeler, "Next-Generation Microfluidic Point-of-Care Diagnostics", Clinical Chemistry, vol. 61, no. 10, pp. 1233-1234, 2015. [7] A. Pradeep, J. Raveendran, R. T., B. Nair and S. T.G., "Computational simulation and fabrication of smooth edged passive micromixers with alternately varying diameter for efficient mixing", Microelectronic Engineering, vol. 165, pp. 32-40, 2016. [8]W. Jung, J. Han, J. Choi and C. Ahn, "Point-of-care testing (POCT) diagnostic systems using microfluidic lab-on-a-chip technologies", Microelectronic Engineering, vol. 132, pp. 46-57, 2015. [9] T. Ackermann, P. Giménez-Gómez, X. Muñoz-Berbel and A. Llobera, "Plug and measure – a chip-to-world interface for photonic lab-on-achip applications", Lab Chip, vol. 16, no. 17, pp. 3220-3226, 2016. [10] B. Hu and X. Liu, "Design and Research of Multi-Channel Temperature Calibration System Based on the LabVIEW", AMR, vol. 304, pp. 241-246, 2011. [11] A. Cruz, N. Norena, A. Kaushik and S. Bhansali, "A low-cost miniaturized potentiostat for point-of-care diagnosis", Biosensors and Bioelectronics, vol.62, pp. 249-254, 2014. [12] V. Jaime Punter, A. Cristina Paez, F. Jordi Colomer, S. Jaime Lopez, F.EsteveJuanola and C. Pere Miribel, "A Portable Point-of-Care Device for Multi-Parametric Diabetes Mellitus Analysis", in IECON2015, Yokohama, 2015, pp. 1252-1257. [13] S. Kwakye and A. Baeumner, "An embedded system for portable electrochemical detection", Sensors and Actuators B: Chemical, vol. 123, no.1, pp. 336-343, 2007. [14] Anoop, A.E., Madhu Mohan, N, and Guruvayurappan, K,“Simulation of a multi-strip blood glucometer”. In: TENCON 2014, 2014. [online] IEEE Proceedings. Available at: http://ieeexplore.ieee.org/document/7022473/]. [15] Dhara, K., Stanley, J., Ramachandran, T., Nair, B. and Babu, T.,“ Cupric Oxide Modified Screen Printed Electrode for the Nonenzymatic Glucose Sensing”, Journal of Nanoscience and Nanotechnology, 16(8), pp.8772-8778, 2016. [16] Yanga M., Hea J., Hua X., Yana C., Chenga Z., Zhaoa Y. and Zuo G., “Copper oxide nanoparticle sensors for hydrogen cyanide detection: Unprecedented selectivity and sensitivity”, Sensors and Actuators B, vol.155, pp. 692–698, 2011.