WO2016050226A1

WO2016050226A1 - Potentiostat

Info

Publication number: WO2016050226A1
Application number: PCT/CZ2015/000104
Authority: WO
Inventors: Jiri HAZE; Marek BOHRN; Lukas FUJCIK; Vilém KLEDROWETZ; Michal PAVLIK; Roman PROKOP
Original assignee: Vysoke Uceni Technicke V Brne
Priority date: 2014-09-30
Filing date: 2015-09-10
Publication date: 2016-04-07
Also published as: CZ305358B6; CZ2014672A3

Abstract

The invention relates to a potentiostat (1) containing a control logic (41) and an electronic circuit, whereby the electronic circuit of the potentiostat contains an analog block (2), a converter block (3) consisting of analog-numeric and numeric-analog converters, and a supply block (5). The analog block (2) contains a connecting means (21) having a contact (211) for connecting a working electrode of a sensor, a contact (212) for connecting a reference electrode of the sensor and a contact (213) for connecting an auxiliary (common) electrode of the sensor, whereby the contact (212) for connecting the reference electrode of the sensor is connected to the non-inverting input of the operational amplifier (222) and the contact (213) for connecting the auxiliary (common) electrode of the sensor is connected to the output of the operational amplifier (221), whereby the output of the operational amplifier (222) is connected to the inverting input of this operational amplifier (222) and, at the same time, to the inverting input of the operational amplifier (221), and the contact (211) for connecting the working electrode of the sensor is connected to the inverting input of the operational amplifier (23) and at the same time through a switchable resistor network (231) to its output, whereby the non-inverting input of this operational amplifier (23) is connected to a source (232) or precise voltage, and its output to the non-inverting input of a differential operational amplifier (24) as well as to the input of a low-pass filter (25) of first or higher order.

Description

Potentiostat

Technical field

The invention relates to a potentiostat - i.e. an electroanalytical device for determination of the presence and/or quantity ofa biologically and/or toxicologically significant substance/substances in a liquid sample.

Background art

The potentiostat is an electroanalytical device which is used, for example, to determine the presence and/or quantity of a biologically significant substance/substances (e.g. proteins, lactic acid, DNA, hydrogen peroxide, etc.) and/or a toxicologically significant substance/substances (e.g. heavy metals, etc.) generally in any liquid sample, including e.g. a sample of human or animal body fluids (blood, urine, sweat, etc.), surface water or ground water, etc., or in a liquid sample made by dissolving or washing a solid material, e.g. soil, etc.

The principle of this device is based on monitoring electrochemical parameters of liquid samples and their evaluation by appropriate methods of analysis.

Presently known potentiostats consist of three main parts - the first is composed of a sensor containing two or three electrodes, the second is an electronic circuit, which conducts and, if necessary, modifies and/or amplifies the signals of the sensor and transmits them to the third component - a control logic. The control logic then controls the correct operation of the electronic circuit and of the sensor, transmits the sensor signals into an assigned evaluation unit located outside the potentionstat, formed e.g. by a PC or another similar device. Preferably, the electronic circuit and/or control logic may be equipped with their own memory, e.g. for storing different settings (calibration) of the sensor, etc.

However, existing types of construction of potentiostats suffer from a number of drawbacks which negatively influence and limit their utilization. One of the essential problems is interference within the cables interconnecting the sensor and the electronic circuit, which can result in distortion of the signal of the sensor and thereby also distortion of the analysis result. Still more important, however, is another disadvantage - low speed of signal propagation between the main components of the potentiostat - especially of the excitation signal passing from the control logic to the sensor, which leads to low speed of the response of the potentiostat to possible step changes of the sample parameters, e.g. after adding an auxiliary substance, etc. Given that the overall delay is of the order of up to several tens of milliseconds, in many cases some short-term transient events occurring in the sample are not monitored at all.

A further disadvantage of existing potentiostats relates to their relatively large dimensions, high demands on the power supply, high investment and running costs and, furthermore, their uncompactness when in order to use different methods of analysis, it is necessary to complement them by special and often high-priced external modules. The goal of the invention is therefore to eliminate the disadvantages of the background art by providing a potentiostat which would solve the interference problem within the service cables, accelerate the response of the potentiostat to step changes of the parameters of the sample solution, enabling to reduce investment and running costs, and, moreover, reduce the dimensions of the final device.

Principle of the invention

The aim of the invention is achieved by a potentiostat according to the invention which contains acontroi logic and an electronic circuit, whose principle consists in that its electronic circuit contains an analog block, a converter block and a supply block. The analog block contains a connecting means having a contact for connecting a working electrode of the sensor, a contact for connecting a reference electrode of the sensor and a contact for connecting an auxiliary (common) electrode of the sensor, whereby the contact for connecting the reference electrode of the sensor is connected to the non-inverting input of a second operational amplifier and the contact for connecting the auxiliary (common) electrode of the sensor is connected to the output of a first operational amplifier. At the same time, the output of the second operational amplifier is connected in feedback to an inverting input of this operational amplifier and also to an inverting input of the first operational amplifier. The contact for connecting the working electrode of the sensor is further connected to an inverting input of another operational amplifier and, at the same time, through a switchable resistor network to the output of this operational amplifier, whereby the non-inverting input of this operational amplifier is connected to a source of precise voltage, the output of this operational amplifier being connected to the non-inverting input of a differential operational amplifier and also to the input of a low-pass filter of the first or higher order.

The converter block contains two numeric-analog converters and three analog-numeric converters, whereby the output of the first numeric-analog converter is connected to the non-inverting input of the first operational amplifier of the analog block, the output of the second numeric-analog converter being connected to the inverting input of the differential amplifier of the analog block. The input of the first analog-numeric converter is further connected to the output of the differential operational amplifier of the analog block, the input of the second analog-numeric converter being connected to the output of the low-pass filter of the first or higher order of the analog block.

In addition, the converter block of the potentiostat according to the invention preferably contains another analog-numeric converter, whose output is connected to the control logic of the numeric block and whose input is connected to the output of the second operational amplifier of the analog block. This analog-numeric converter measures the actual intensity of the electric field in the sample.

The numeric block of the potentiostat further contains the control logic itself, whereby the outputs of the analog-numeric converters of the converter block are connected to the respective inputs of the control logic, the control logic being connected to the inputs of the numeric-analog converters of the converter block.

The electronic circuit constructed in this manner ensures high speed of signal transmission between the control logic of the potentiostat and its other components, so, consequently, the signals are not attenuated and the communication of the control logic with the sensor takes place at a speed that allows monitoring transient events, especially step changes occurring in the sample, e.g. after adding an auxiliary substance.

In a preferred embodiment, the supply block contains a source of power supply connected to the primary winding of the high-frequency transformer, to which it is also connected, a transistor switch circuit, whereby the secondary winding of the high-frequency transformer is connected to a voltage rectifier, the voltage rectifier being connected to an output filter, and the output filter is connected to a linear compensator, whereby the linear compensator is further connected to all components of the other blocks and ensures their power supply. The source of power supply is connected to the control logic of the numeric block through the third analog-numeric converter of the converter block. Also the transistor switch circuit is connected to the control logic of the numeric block.

Thus, small dimensions of the potentiostat according to the invention, combined with the source of power supply consisting of or containing a battery/batteries, make it possible to carry this potentiostat and use it in field conditions.

Description of the drawing

In the enclosed drawing Fig. 1 represents schematica! flow chart of two variants of a potentiostat according to the invention.

Example of embodiment of the invention

The potentiostat according to the invention will be further described using two variants of its embodiment shown in Fig. 1. This potentiostat 1 contains four mutually interconnected and collaborating blocks - an analog block 2, a converter block 3, containing analog-numeric and numeric-analog converters, a numeric block 4 and a supply block 5.

The analog block 2 contains a connecting means 21. for connecting an unillustrated sensor of the potentiostat . Depending on the sensor type in question this connecting means 21, contains a contact 211 for connecting the working electrode of the sensor and a contact 212 for connecting the reference electrode of the sensor (if the sensor has only two electrodes - that means it has a two electrode arrangement) and possibly also a contact 213 for connecting an auxiliary (common) electrode (if the sensor has three electrodes - i.e. it has a three electrode arrangement, or if two conductors are led from the electrode of the sensor formed by connecting the auxiliary (common) electrode and the reference electrode - i.e. the sensor has a two electrode arrangement). Nevertheless, all the other components of the potentiostat 1., their mutual interconnection and their functions are in both variants identical.

The contact 213 for connecting the auxiliary electrode of the sensor is connected to the output of the operational amplifier 221 and the contact 212 for connecting the reference electrode of the sensor is connected to the non- inverting input of the second operational amplifier 222, whose output is connected to the inverting input of the operational amplifier 221 and in feedback to the inverting input of the same operational amplifier 222. Thus the operational amplifiers 221 and 222 together constitute an output buffer 22. This type of circuit of the operational amplifiers makes it possible to achieve a bandwidth of up to 200 kHz at a loading capacity of up to 1 pF.

The connector 211 for connecting the working electrode of the sensor is further connected to the inverting input of the operational amplifier 23 and via the switchable resistor network 231 also to its output. Parallel connection of the operational amplifier 23 and the switchable resistor network 231 constitute a converter of the current/voltage. A source 232 of precise voltage, which constitutes virtual analog ground, or, in other words, voltage reference, is further connected to the non-inverting input of the operational amplifier 23.

The output of the operational amplifier 23 is connected to the non- inverting input of the differential operational amplifier 24 and also to the input of the low-pass filter 25 of first or, in case of need, of a higher order.

The converter block 3 contains numeric-analog converters 31 and 32 and analog-to-digital converters 33, 34 and 35. The first numeric-analog converter 3 is by its output connected to the non-inverting input of the operational amplifier 221 and the second numeric-analog converter 32 to the inverting input of the differential operational amplifier 24 of the analog block 2. Their inputs are further connected to the outputs of the control logic 41. of the potentiostat i on the numeric block 4. The input of the first analog-numeric converter 33 is further connected to the output of the differential operational amplifier 24, the input of the second analog-numeric converter 34 being connected to the output of the low-pass filter 25 of the analog block 2 and the input of the third analog-numeric converter 35 to the source 51 of power supply of the supply block 5. The outputs of all analog-to-digital converters 33 to 35 are further connected to the inputs of the control logic 41 of the potentiostat1 on the numeric block 4.

Optionally, the converter block 3 can also contain an analog-to-digital converter (in Fig. 1 indicated by a dashed line), which is by its input connected to the output of the second operational amplifier 222 of the output buffer 22 of the analog block 2, and by its output to the input of the control logic 41.

The numeric block 4 further contains a control logic 41 of the potentiostat 1 , which is preferably formed by a field programmable gate array (FPGA). This control logic 41 , apart from the above-described connections to numeric-analog converters 31, 32, and analog-to-digital converters 33, 34 and 35 and optionally also to 36, is also connected to the circuit 52 of transistor switches of the supply block 5. Moreover, it is provided with means for connecting (via cable or wirelessly) to an unillustrated evaluation device (e.g. a PC or a similar device), in which the data obtained or the results of the analysis is evaluated or, as the case may be, displayed. If the control logic 41 is appropriately programmed, evaluation can take place directly in it, and interconnection to an external evaluation unit is therefore not necessary. Nevertheless, for this reason it is preferred if the control logic 41 is provided with an unillustrated user interface.

In order to provide power supply to the potentiostat 1_ according to the invention, it is possible to use substantially any known supply block 5. in a preferred embodiment shown in Fig. 1, the supply block 5 contains a source of power supply 51 composed of a battery/batteries and/or by connecting to an unillustrated external source of energy, e.g. via a corresponding supply adapter to the electricity grid, and a voltage compensation device composed of a circuit 52 of transistor switches, which is connected to the primary winding of a high- frequency transformer 53, whose secondary winding is via a voltage rectifier 54 and an output filter 55 connected to a linear stabilizer 56. The linear stabilizer 56 is further connected to the other components of the potentiostat1, including the control logic 41 , thus ensuring their power supply.

For the purpose of analysis, or, more specifically, for determination of the presence and/or quantity of a biologically significant substance/substances in the sample, the potentiostat 1 according to the invention is connected to a suitable sensor via a connecting means 21. A suitable sensor is any known sensor used in existing potentiostats, preferably e.g. a printed sensor with microelectrodes located on the sensor module, made, e.g., of corundum (AI₂O₃) ceramics, prepared by technology TFT (thick film technology). In that case the reference electrode of the sensor is made, e.g., of silver and its working electrode and the auxiliary (common) electrode are made of gold. The user sets the size and course of the excitation signal by means of a user interface of an unillustrated assigned evaluation device or by means of an unillustrated user interface of the control logic 41. This signal is generated by the control logic 41 and is created by the numeric-analog converter 31 and then it is transmitted in the form of electric voltage, which contains a DC component and at the same time also an AC component (whereby depending on the selected analytic method one of these components may be equal to zero), to the output buffer 22, or its operational amplifier 221 respectively, from where the signal is further conducted via the contact for connecting 213 the auxiliary (common) electrode to this electrode of the sensor, and through this electrode to the sample.

Due to supplying voltage to the auxiliary (common) electrode of the sensor an electric field is formed between this electrode of the sensor and the working electrode, which are immersed in the sample or they are in contact with it and electric current starts to flow between them. The electric current is conducted from the sample by means of the working electrode of the sensor, and via the contact 211 for connecting the working electrode of the sensor is conducted to the converter current/voltage, or, more specifically, to the inverting input of its operational amplifier 23 and via a parallel-connected switchable resistor network 231 also to its output. At the same time, from the source of precise voltage 232 precise voltage of a specific, pre-determined size (the so- called analog ground) is supplied to the non-inverting input of the operational amplifier 23. The operational amplifier 23 responds to the power supply to its output by generating a voltage, maintaining the same voltage at both its inputs. The resulting electric voltage corresponds to the electric current led by the working electrode of the sensor away from the sample, the electric voltage being complemented by a specific non-zero value of the electric voltage from the source 232 of precise voltage (the so-called analog ground), by which means all its components are converted into a measurable (i.e. plus) region. This electric voltage is then conducted in parallel to the non-inverting input of the differential operational amplifier 24 and to the input of the low-pass filter 25.

The low-pass filter 25 (of the first or higher order) lets through only the DC component of this voltage to the analog-numeric converter 34, whereby the DC component of this voltage is converted by this analog-numeric converter 34 into numeric data which is sent to the control logic 4J. of the potentiostat . After that the control logic 41 sends the numeric data to the numeric-analog converter 32, which converts the data into analog form, i.e. into the form of the voltage, and sends it to the inverting input of the differential operational amplifier 24. The operational amplifier 24 then subtracts this voltage representing the DC component from the original voltage, which contains both AC and DC components and generates a differential voltage which has an AC component and which carries the information about of the influence on the voltage supplied to the (auxiliary) common electrode of the sensor of the potentiostat through the analyzed sample.

As a result, the control logic 41 has both AC and DC components of the voltage at its disposal, whereby it uses at least the AC component or sends it according to a selected analytical method to an assigned unillustrated evaluation device (e.g. a PC or another similar device) for evaluation using a pre-selected analytical method, such as cyclic voltammetry, or by measuring the dependence of the capacity of the solution on time (C/t analysis), etc., or it evaluates it/them by itself. This results in determining the presence and/or quantity of a substance of interest in the analyzed sample.

The reference electrode of the sensor, in cooperation with the output buffer 22, to which it is connected through the contact 212, senses the intensity of the electric field in the sample, and throughout the whole process of analysis modifies the voltage fed to the common electrode of the sensor in feedback via the output buffer 22, or its operational amplifiers 222 and 221 , so that the value and course of the voltage will correspond to the excitation signal generated by the control logic.

The power supply of the potentiostat A is then ensured by the source 51 of power supply located on the supply block 5. The control logic 41 obtains information about the current voltage of the source 51 of power supply via a numeric-analog converter, whereby if this voltage drops, a signal of pulse-width modulation (PWM signal) is generated, which continuously switches the transistor switches 52, which ensures the passage of the current from the source 51 of power supply by the primary winding of a high-frequency transformer 53. As a result of this, voltage is generated on the secondary winding of the transformer 53, the voltage being determined by the ratio of the threads of both windings. Consequently, current starts to flow through the voltage rectifier 54, the output filter 55 and the linear stabilizer 56 and at the output of the linear stabilizer 56 there is voltage of the required size for supplying power to the other components of the potentiostat

The advantage of both the above-described variants of the potentiostat 1 according to the invention is low price, low requirements for power supply (e.g. +/-5 V) and, above all, small dimensions, which make this potentiostat 1 extremely mobile, and also increase the speed of signal propagation in it. Due to this, the sensor and the potentiostat can be directly interconnected through the connecting means 21, reducing considerably the pathway of individual signals and their interference.

When using precise (having a bandwidth of at least 100 kHz) and low- noise operational amplifiers 221 and 222, 23 and 24, a high speed of signal propagation is achieved and the signals are not attenuated. In particular, the communication of the control logic 4 with the sensor in that case takes place at a very high speed, which enables to monitor transient events, especially step changes, taking place in the sample, e.g. after adding an auxiliary substance. All this is achieved while maintaining a low supply voltage (typically e.g. +/-5 V). List of references

1 potentiostat

2 analog block

21 connecting means for connecting the sensor

211 contact for connecting the working electrode of the sensor

212 contact for connecting the reference electrode of the sensor

213 contact for connecting the auxiliary (common) electrode of the sensor

22 output buffer

221 operational amplifier

222 operational amplifier

23 operational amplifier

231 switchable resistor network

232 source of precise voltage

24 differential operational amplifier

25 low-pass filter of first or higher order

3 converter block

31 numeric-analog converter

32 numeric-analog converter

33 analog-numeric converter

34 analog-numeric converter

35 analog-numeric converter

36 analog-numeric converter

4 numeric block

41 control logic

5 the supply block

51 source of power supply

52 circuit of transistor switches

54 voltage rectifier

55 output filter

56 linear stabilizer

Claims

PATENT CLAIMS

1. A potentiostat (1) containing a control logic (41) and an electronic circuit, characterized in that its electronic circuit contains an analog block (2), a converter block (3) containing analog-numeric and numeric-analog converters, and a supply block (5), whereby:

the analog block (2) contains a connecting means (21) with a contact

(211) for connecting a working electrode of a sensor, a contact (212) for connecting a reference electrode of the sensor and a contact (213) for connecting an auxiliary (common) electrode of the sensor, whereby the contact

(212) for connecting the reference electrode of the sensor is connected to the non-inverting input of the operational amplifier (222) and the contact (213) for connecting the auxiliary (common) electrode of the sensor is connected to the output of the operational amplifier (221), whereby the output of the operational amplifier (222) is connected to the inverting input of this operational amplifier (222) as well as to the inverting input of the operational amplifier (221), and the contact (211) for connecting the working electrode of the sensor is connected to the inverting input of the operational amplifier (23) and at the same time through a switchable resistor network (231) to its output, whereby the non-inverting input of this operational amplifier (23) is connected to a source (232) of precise voltage, its output being connected to the non-inverting input of the differential operational amplifier (24) and also to the input of the low-pass filter (25) of first or higher order,

the converter block (3) contains analog-numeric converters (33), (34) and

(35) and numeric-analog converters (31) and (32), whereby the output of the numeric-analog converter (31) is connected to the non-inverting input of the operational amplifier (221) of the analog block (2), the output of the numeric- analog converter (32) is connected to the inverting input of the differential amplifier (24) of the analog block (2), the input of the analog-numeric converter (33) is connected to the output of the operational amplifier (24) of the analog block (2), the input of the analog-numeric converter (34) being connected to the output of the low-pass filter (25) of first or higher order of the analog block (2), the numeric block (4) contains a control logic (41), whereby the outputs of the analog-numeric converters (33), (34) and (35) of the converter block (3) are connected to the inputs of the control logic (41), whereby the control logic (41) is connected to the inputs of the numeric-analog converters (31) and (32) of the converter block (3), whereby the control logic (41) of the potentiostat and the other powered components are connected to the supply block (5).

2. The potentiostat according to Claim 1 , characterized in that the supply block (5) contains a source of power supply (51) interconnected to the primary winding of a high-frequency transformer (53), to which is also connected a circuit of transistor switches (52), whereby the secondary winding of the high-frequency transformer (53) is connected to a voltage rectifier (54), which is connected to an output filter (55), which is connected to a linear compensator (56), whereby the linear compensator (56) is also connected to the control logic (41) of the numeric block (4) of the potentiostat (1) as well as to the other powered components of the potentiostat (1), and the source of power supply (51) of the supply block (5) and the control logic (41) of the numeric block (4) are interconnected by means of the analog-numeric converter (35) of the converter block (3) connected to the control logic (41) of the numeric block (4), the circuit of transistor switches (52) being connected to the control logic (41) of the numeric block (4).

3. The potentiostat (1) according to Claim 1, characterized in that the converter block (3) contains an analog-numeric converter (36), whose output is connected to the control logic (41) of the numeric block (4) and whose input is connected to the output of the operational amplifier (222) of the analog block (2).

4. The potentiostat (1) according to Claim 2, characterized in that the source of power supply (51) of the supply block (5) contains a battery/batteries.