Table 1.
Comparison of different potentiostats.
Fig 1.
Circuit to control the reference and counter electrodes.
One of two DACs can be used to control the voltage, based on if the external capacitor is installed. An Opamp buffers the DAC voltage and an analog multiplexer is used to select if 2 or 3 electrode experiments should be performed.
Fig 2.
A transimpedance amplifier (TIA) and a DAC are used to set the voltage and measure the current passing through the working electrode. The TIA output voltage is passed into a delta sigma ADC, which converts the analog signal into a digital signal. A current DAC is used to calibrate the TIA / ADC signal chain. If an increase in the maximum current is needed, pins are made available that external resistors can be connected to.
Fig 3.
To set the timing of when to change the DAC controlling the electrode voltage and when to measure the current, a PWM is used to trigger a set of interrupt service routines (isr). Communication to and from the device is done through a USB component, and an EEPROM is used to save what DAC the user wants to use.
Fig 4.
Screenshot of GUI to control the potentiostat.
Different electrochemical techniques use different tabs in the main GUI. Important information for each experiment type is displayed to the user and a pop-up interface allows the user to change each parameter. The voltage source and electrode configuration settings are displayed to the user.
Fig 5.
Potentiostat parts and completed device.
A) Photo of all the components needed to develop a single chip potentiostat and perform the experiments in this paper. From the top: EZ-Hook electrical connectors used to connect the device to glucose strips; CY8CKIT-059 that has the PSoC 5LP that contains all the electrical components needed for a potentiostat; headers that can be connected to the board, with either solder or conductive glue (Conductive glue is not as strong over time but requires less equipment and skill to use); The DVDAC capacitor is optional but will increase the resolution of the potentiostat; 3 alligator clips with female jumper cables ends to attach electrodes to the device; a pencil lead electrode attached to a jumper wire with electrical glue. B) Photo of the assembled device with a case. C) Device assembled in its case. D) Close up of the CY8CKIT-059 with labels for where the electrodes, capacitor and USB connections should be attached.
Fig 6.
Comparison to a commercial potentiostat using standard electrodes.
A) Raw current traces of cyclic voltammetry experiments in 5 mM ferricyanide using an EmStat (black) and PSoC-Stat (blue) with the voltage in reference to a Ag /AgCl reference electrode. B) Currents from A with the noise removed using a 10 point rolling sample.
Fig 7.
Cyclic voltammetry experiments.
A) Raw current traces of cyclic voltammetry experiments in orange juice with different levels of added ascorbate. Voltage is in reference to a Ag /AgCl reference electrode. B) Standard addition results of the cyclic voltammetry experiments. The current value at +550 mV was used and a fitted line to the data was used to calculate the amount of ascorbate in the orange juice.
Fig 8.
A) Current traces measure at +500 mV using Accu-Check Performa glucose strips. 3 strips were used for each glucose sample. B) Average current between 4.8 and 5 seconds of the amperometric currents is plotted versus the glucose in the samples. Our device measured a linear relationship (R2 = 0.98) over the physiological range of glucose within the range of the FDA’s guidelines.
Fig 9.
Anodic Stripping Electrode experiments.
A) Raw current traces of the stripping step with added Pb2+. Voltage is in reference to a Ag /AgCl reference. electrode. B) Raw traces normalized to the -350 mV current level. C) Current with the average baseline subtracted from all traces. D) Relationship of the current at -175 mV of the baseline subtracted traces versus the Pb2+ concentration.