Hello all,

I have a project in mind, but I am fairly new to project design.

The goal is to produce a device similar to a modified TENs device. The idea would be to have controllable parameters such as voltage, current, and wave forms.

The research I have on eradicating bacteria/biofilms all range from either saying pulsed high voltage works well, to direct current varying from 20 uA to 2,000 uA works well, to a combination of both with varying application time.

I am not interested in which works the best as I will perform my own experiments. I just need help in understanding what could be develop for an electrical stimulation output device with controllable/adjustable parameters.

Also, I am compiling together an excel spreadsheet of all the various in vitro experiments that have already been done using electrical stimulation and I am coming across a wide range of used parameters, which is fine like I said, but I have a basic electrical engineering question I am wondering about with using one of these programmable power supplies.

If one researcher states that direct currents of anywhere between 500 uA to 5 mA successfully kills bacteria, and another states that high pulsed voltages around 250 - 300 Volts at 40 - 128 pulses per second successfully kill bacteria. Can I combine these values and stimulate bacteria with a pulsed 250 - 300 Volts AND have a current flowing in the range of 500 uA - 5mA?

In my head I almost imagine these pulses acting like a switch, and when they are switched 'on' current is also being the circuit element (bacteria).

Thanks again for all your help.


I have also attached some interesting articles on the matter for reading.

 

Electrical current destroys bacteria in less than a second, depending on the current passed, the conductivity of the media bacteria are in, and conductivity of the bacteria itself.
Current can be provided by a direct current power supply, a pulsing power supply, alternating, triangle wave, sine wave and any others you can try. The current density trough the bacterial media is mandated by electrodes area, their proximity, their voltage, the 'vessel' volume...

Continue evaluating your experiments with all the variables and waveforms you may like, they should all produce results departing from any adjustable frequency/amplitude signal generator/AC/DC power supply capable of around 2 Amperes.

 

Ohms law- you cannot have an arbitrary voltage AND current.

You can have a controlled voltage, or a controlled current, but not at the same time.

The impedance (resistance) of your bacteria is the tricky part.
To get a specific flow of current to flow, you may need a dangerously high voltage if the impedance (resistance) is high.

 

Ohms law- you cannot have an arbitrary voltage AND current.

You can have a controlled voltage, or a controlled current, but not at the same time.

The impedance (resistance) of your bacteria is the tricky part.
To get a specific flow of current to flow, you may need a dangerously high voltage if the impedance (resistance) is high.

I have read a multitude of articles on this subject, and some researchers claim high voltage pulsed current works the best at killing bacteria, and some will say low intensity current (micro current - 30 mA) will work the best. In my opinion going back to what you said about you either control voltage, or current makes me think they are essentially saying the same thing. Correct me if I am wrong, but if you have high voltage you will also have low current, and vice versa?

Like the properties of a transformer, if you step up voltage, you are also stepping down current. I have discussed with a couple of microbiologist, and have concluded, or assumed that the resistance of the bacteria/biofilms will be so small it will basically be negligible. The medium, or salty solution will have the most resistance, which will still be relatively conductive.

Side note: I understand impedance is equivalent to resistance when we are using an AC signal, but if I am using a square wave signal are my 'resistances' defined as an impedance or resistance?

Correct me if my understanding in any of this is wrong, or you see a potentially better way of doing something, please. Thank you for your reply.

Now, to address:

Electrical current destroys bacteria in less than a second, depending on the current passed, the conductivity of the media bacteria are in, and conductivity of the bacteria itself.
Current can be provided by a direct current power supply, a pulsing power supply, alternating, triangle wave, sine wave and any others you can try. The current density trough the bacterial media is mandated by electrodes area, their proximity, their voltage, the 'vessel' volume...

Continue evaluating your experiments with all the variables and waveforms you may like, they should all produce results departing from any adjustable frequency/amplitude signal generator/AC/DC power supply capable of around 2 Amperes.

I really appreciate your reply, but I am a bit confused or lacking an understanding in current density (in general). Could you elaborate on current density and how it applies here, or point me in the right direction to complete my understanding of current density? Specifically how it will relate to the electrode area size, and voltage.

Maybe, my understanding of voltage is a little askew. I sort of understand it as a force applied to the electrons. Something like a dam holding back water. You may have a big dam (high voltage), and a tiny hole in the dam for water to pass (low current) something to that illustration.

I also am unsure of what you mean by the 'vessel' volume?

Also when you mention my results will depart from any adjustable frequency/amplitude do you mean my results are not dependent on these parameters?

Thanks again guys for your input and help. Look forward to hearing back from you.

 

Would it be easier to use an anti bacterial ultra violet lamp? What is the bacteria you are try to kill on or in?

 

Correct me if I am wrong, but if you have high voltage you will also have low current, and vice versa?

Higher voltage yields higher current.

Like the properties of a transformer, if you step up voltage, you are also stepping down current.

Does not work that way. Ignore such analogy which is more like conservation of power.

if I am using a square wave signal are my 'resistances' defined as an impedance or resistance?

If the square wave goes into positive and negative excursions, it should be referred as impedance. For square pulsing wave, you may refer as resistance. But should not affect much other than proper terminology. Pulsing square DC will encounter an average value as resistance.

to complete my understanding of current density? Specifically how it will relate to the electrode area size, and voltage.

Current flowing in a confined conductive path will be denser than in an open wide path. Can be referred as amperes per m2, or submultiple of mm2.
The current path between -say 1cm2 electrodes- will be denser in narrow passages. Like passing 0.1A in a hair thin wire conduction path wire or in a AWG4 wire comparison. Take it as 1 car every second on a 1 lane way to a one car every second on a 6 lane way.
The path in your experiments can be tiny 1mm2, as between probes or in a 10 litre container (vessel) with a soup of bacteria. I do not know that.

I sort of understand it as a force applied to the electrons. Something like a dam holding back water. You may have a big dam (high voltage), and a tiny hole in the dam for water to pass (low current) something to that illustration.

Nope, take as voltage as the force electrons are pushed to flow. The dam hole being the resistance if their flow path.

I unclearly meant that for a given supply chosen, the observed results will be proportional to the settings of voltage, electrode area, current density, resistance (or impedance) of the bacteria laden media. I cannot visualize a biofilm.

 

Would it be easier to use an anti bacterial ultra violet lamp? What is the bacteria you are try to kill on or in?

I am not sure if it will be easier using an ultra violet lamp. What do you think the advantages are for doing so, versus directing stimulating the bacteria with current? The bacteria are on a tiny circular disk called a coupon.

Higher voltage yields higher current.

Does not work that way. Ignore such analogy which is more like conservation of power.


If the square wave goes into positive and negative excursions, it should be referred as impedance. For square pulsing wave, you may refer as resistance. But should not affect much other than proper terminology. Pulsing square DC will encounter an average value as resistance.


Current flowing in a confined conductive path will be denser than in an open wide path. Can be referred as amperes per m2, or submultiple of mm2.
The current path between -say 1cm2 electrodes- will be denser in narrow passages. Like passing 0.1A in a hair thin wire conduction path wire or in a AWG4 wire comparison. Take it as 1 car every second on a 1 lane way to a one car every second on a 6 lane way.
The path in your experiments can be tiny 1mm2, as between probes or in a 10 litre container (vessel) with a soup of bacteria. I do not know that.


Nope, take as voltage as the force electrons are pushed to flow. The dam hole being the resistance if their flow path.

I unclearly meant that for a given supply chosen, the observed results will be proportional to the settings of voltage, electrode area, current density, resistance (or impedance) of the bacteria laden media. I cannot visualize a biofilm.

A couple of questions:

1) The greater the size of conductive material for current to flow through the smaller its current density is? As in if I have a larger current density I am passing more electrons between a tighter space?

2) How do some of these researchers then apply either high voltage pulsed current to a sample versus direct current micro current?
How would you achieve high voltages at low current values? When they run their experiments involving high voltages, which I am assuming now involves high current, do you think they have a high current density in their probes?

3) What is the difference between a 'normal' square wave, and a 'pulsating' square wave?

A biofilm is a group of bacteria that have attached themselves together and formed a very protective coating against antimicrobial agents. Essentially imagine a shield around a group of bacteria which makes them are to kill.

 

The advantage I see of using a U.V lamp is the simplicity, Make A light proof box, fit the lamp inside, put your "coupon" in and expose the little devils to the light and it will soon polish them off.
Uv light is used in sewage treatment to kill the bugs off before the waste is dumped in the sea, also small ones are used in aquarium filters to keep the water bacteria down.

 

Anti bacterial lamp. Cost under £30.00 from Amazon,UV-C light is germicidal – i.e., it deactivates the DNA of bacteria, viruses and other pathogens and thus destroys their ability to multiply and cause disease. Specifically, UV-C light causes damage to the nucleic acid of microorganisms by forming covalent bonds between certain adjacent bases in the DNA. The formation of such bonds prevent the DNA from being unzipped for replication, and the organism is unable to reproduce. In fact, when the organism tries to replicate, it dies.

 

1) Yes
2)

How would you achieve high voltages at low current values?

In electronics, can be done with a resistor in series to the high voltage supply. For killing bacteria, do not see the need to use high voltage.
3) an alternating square wave ----> https://cdn.sparkfun.com/assets/0/2/0/3/d/521e6ed1757b7fa1778b4567.png
A pulsing square wave ----> http://goldwingdocs.com/forum/download/file.php?id=21444

Look where the zero voltage levels are drawn.

If the biofilm is -say 1mm thin-, floating in saline water; in a 100mm petri dish - A 100mm metal disk placed on the bottom is electrode1.
A second 100mm metal disc placed on top of the film is electrode2. Applying a voltage to the electrodes will fry the bacteria in a certain time with a low density current that can be high or low voltage source.

The same film, with a couple of electrodes at diametral opposites in the petri dish - Applying a voltage will fry the bacteria nearest the electrodes faster than in the middle of the film. There is areas of high current density, and lower current density by the center.
If the bacteria film is inside a narrow tube and its ends have electrodes, applying voltage will fry the bacteria with high density current.

Keep in mind that very conductive media can be less lethal as the bacteria may be less conductive and the current bypasses them for an 'easier' (less resistive) path to flow.

 

2)
In electronics, can be done with a resistor in series to the high voltage supply. For killing bacteria, do not see the need to use high voltage.

So, this is called a 'Current limiting resistor', correct?
Thank you for clarifying the pulsating square wave versus alternating square wave.
If I have a pulsating square wave with an amplitude of roughly 250 volts at about 100 pulses per second with an intraphase of 70 micro S running across a bacteria. What would be the natural current (without limiting resistors) across the bacteria. Is this current safe? How do you define 'safe current', because I have read that current at 30 mA can kill you with high voltages, and current at .5 A at whatever voltage can kill you. I am a bit unsure of that relationship.

Also these are exact parameters pulled off a research paper about killing bacteria using a pulsating square wave at 250 volts.

If the biofilm is -say 1mm thin-, floating in saline water; in a 100mm petri dish - A 100mm metal disk placed on the bottom is electrode1.
A second 100mm metal disc placed on top of the film is electrode2. Applying a voltage to the electrodes will fry the bacteria in a certain time with a low density current that can be high or low voltage source.

The same film, with a couple of electrodes at diametral opposites in the petri dish - Applying a voltage will fry the bacteria nearest the electrodes faster than in the middle of the film. There is areas of high current density, and lower current density by the center.
If the bacteria film is inside a narrow tube and its ends have electrodes, applying voltage will fry the bacteria with high density current.

Keep in mind that very conductive media can be less lethal as the bacteria may be less conductive and the current bypasses them for an 'easier' (less resistive) path to flow.

I understand current wants to take the path of less resistance, and because of this if the medium in which my bacteria are part of is more conductive then the current will just redirect around them, correct?

I think I am beginning to understand density a bit more, and that if I stick a probe in a solution and measure 'how many electrons are present in the entire solution I will see a gradually change from the local point versus the outer reaches of the solution, because density of electrons decreases as you stray away from the source", correct?

So if I have a probe on top of a small group of bacteria, which covers the entire size of the bacteria population I am probably going to kill all the bacteria under the probe, versus if I have a larger group of bacteria under a smaller probe I am most likely going to see the population size is greater the further away from the probe I get?

I have tried an experiment using a TENs 7000 unit to kill bacteria at a mid range setting (around 50 Volts, pulsating square wave, 5 Hz, 100 micro S pulse width). What I found though was that when I used the gel electrode pads I killed all bacteria under the surface of the pad. I believe this is because the electrode by itself is antimicrobial, because I ran a second similar experiment without the TENs device on and in both cases bacteria under the pads were killed.

I adjusted the experiment by eliminating the electrode pads, and used the bare wires from the device before you attach the electrode pads on the ends, and the results were very inconclusive. No noticeable changes from either experiment or control where made. Which is why I am wondering if I am even making a connection between one probe and the other with the bacteria sitting in the middle.

 

if the medium in which my bacteria are part of is more conductive then the current will just redirect around them, correct?

Yes. The bacteria in the medium is like 2 resistors in parallel. Current will take both paths (medium alone/bacteria alone), more current at the lowest resistance.

bare wires from the device before you attach the electrode pads on the ends, and the results were very inconclusive.

The area surface that wires present to current flow into the medium is much smaller than the electrode pads do. They insert resistance to current flow.

Great if you are into learning with the experiment, but cannot discern what is the goal. To find the minimum current needed for the kill with minimal electrodes ?
For the goal of just killing, if you just blast the bacteria with cheap brute force - extra enough power (from the wall outlet) they will explode their guts out sooner than 0.1 second and surely.

"a pulsating square wave with an amplitude of roughly 250 volts at about 100 pulses per second with an intraphase of 70 micro S running across a bacteria. What would be the natural current (without limiting resistors) across the bacteria. Is this current safe?"
Absolutely lethal for the bacteria, unsafe for clumsy/inexpert experimenters. Seek assistance if unsure. 250V/100pps is near wall outlet power.

Do it safely :
120VAC-------------pushswitch---------100Wbulb-------------electrode1------->medium<------electrode2---------neutral.

Enjoy ! ----> https://www.ncbi.nlm.nih.gov/pmc/articles/PMC154785/

 

This reminds me of when NASA spent a million dollars to make a pen that would work in space and the Russians used pencils!
Lets find the most complicated way to solve a problem ha ha

 

Great if you are into learning with the experiment, but cannot discern what is the goal. To find the minimum current needed for the kill with minimal electrodes ?

Yes, I am trying to determine the most optimal setting for killing bacteria, but as of right now I am struggling in the electrical parameter design. Designing a repeatable testing condition with an electrical system I can adjust measurable values. I have limited the test conditions based around the various papers I have read to be either a pulsating square wave at high voltages for a very brief duration, or direct current in the micro amp ranges.

I plan on running some current/resistance tests with my medium, because what you said about the bacteria and the medium running in parallel with each other will allow me to calculate the bacteria's resistance, and current level by KCL, correct? If I can figure out what current is passing through my medium, and calculate the resistance based on Ohms law, when I run an experiment with the bacteria any missing current from my original pretest will be what is running into the bacteria, yes?

Do it safely :
120VAC-------------pushswitch---------100Wbulb-------------electrode1------->medium<------electrode2---------neutral.

The push switch will allow me to control the flow of current? What if I wanted to using an Arduino to act as switch on a timer, but pulsate very quickly? Would I need an low pass filter for this?

 

The push switch or Arduino driven relay (instead) will energize the bacteria soup for an imprecise fingerpush duration or programmed precise time, but no control on current; just brute force zap current with such "optimal" $0 power supply.
All samples under zap tests would have to be very identical to obtain meaningful results. A voltage-adjustable laboratory power supply/function generator and your Arduino for zap-time controlling would suit you better to fill your spreadsheet.

 

The push switch or Arduino driven relay (instead) will energize the bacteria soup for an imprecise fingerpush duration or programmed precise time, but no control on current; just brute force zap current with such "optimal" $0 power supply.
All samples under zap tests would have to be very identical to obtain meaningful results. A voltage-adjustable laboratory power supply/function generator and your Arduino for zap-time controlling would suit you better to fill your spreadsheet.

This is what I originally was trying to accomplish. Here is a link to this discussion https://forum.arduino.cc/index.php?topic=488615.0 if you are interested, but in short I asked if it was possible if I had a controllable power supply, ranging between 0-50 Volts connected with an Arduino for precise Voltage control. They insisted I needed to have a power supply that would accept 5V logic, as well as a low pass filter on the output of my signal.

I am not sure exactly how to accomplish this, or even if I want to. I am simple looking for the most optimal path at killing bugs using electrical stimulation, right?

So, I want to make sure whatever my means are of killing bacteria with electrical stimulation I can repeat the experiment several times without any variances, and have accurate/measurable results on the output side.

Would I be successful in assuming that if I test a medium as an element in an electric circuit to make sure 1) I can achieve current flow through the medium to ground, and measure that current accurately. 2) When I add a layer of bacteria, because I can't directly measure the bacteria for resistance or current without changing/disrupting the experiment I can use ohms law and treat the two as two parallel resistors assuming I have loss of current?

 

One thing that I didn't see (maybe missed it) is the specified physical containment of the experimental bacteria/biofilm. That would be the biggest factor in voltage/current/current/electrode measurements and how this would be extrapolated to other environments.

Ken

• Mark Forums Read

 

One thing that I didn't see (maybe missed it) is the specified physical containment of the experimental bacteria/biofilm. That would be the biggest factor in voltage/current/current/electrode measurements and how this would be extrapolated to other environments.

Ken

• Mark Forums Read

I ran an experiment with a simple programmed Arduino to output between 0 - 5 V using a keypad. For this particular experiment I only used an output of 5 V though, the idea was this:

Vin (5V) ---- 1k Ohm resistor ----- 1.3 V drop Blue LED ------- Tryptic Soy Broth Medium ----- Multimeter to measure current ---- GND

I measured out a small amount of Tryptic Soy Broth (TSB ) into a petri dish, and measured the diameter of the petri dish (8.7 cm), and marked .5 cm across the length of the petri dish where I would move my probe to measure current at various marked distances .5 cm's away from one another. I made a make shift Aluminum foil probe measuring 1.2 cm across which was stationary at the 0 cm mark, and the other probe was a stainless steel probe from the multimeter. I essentially used a method called 'spot sampling' across the length of petri dish and noted down the current at 5 V at different distances 0 - 8.7 cm.

I then removed the resistor and LED and ran straight 5 V into my TSB, and did the same exact experiment. What I found though was that galvanic corrosion had been taken place on the Aluminum foil and in relatively short time I had eroded the stationary probe away. Looking under a microscope I could see this happening (in both cases, it just became more prominent over time- like a bike lock rusting away on a chain link fence).

Today I will experiment with different probe materials. The first one will be a carbon fiber thread. I will take apart the an adhesive electrode I used in previous experiments and strip it down to the carbon thread material lining the inside of the square pad, and see if I experience any galvanic corrosion with this in such short time.

I do think I have been successful in achieving a steady draw of current in this experiment. When I get my hands on some more bacteria I think will be able to kill bacteria using only 5 V, as the most current I had drawn across the medium was only 33 mA when the probes were .2 cm away from each other. Other researchers had observed bacteria kill at 500 micro A. I can then limit current even further by adding more resistors in series with this experiment.