Happy Holidays Again!

This is another short week for Sterlitech as we get ready to celebrate the New Year. We will be closed Thursday and Friday, and we look forward to working with you all again in 2011!

Happy Holidays Everyone!

Just a reminder, but the Sterlitech office will be closed for the holiday tomorrow and Friday and we will reopen on Monday, December 27th. Have a happy and safe holiday weekend!

See How Nano-Water Filters are Made

We've previously discussed how the combination of silver and carbon nanotubes can be used to create more efficient water purification filters, now you can see a little bit about how this filter is made thanks to Technology Review and Stanford University. You can read more about the process here.

FAQ: Black Polycarbonate Membranes

When counting bacteria as part of epifluorescent microscopy we generally recommend using the black polycarbonate membranes instead of cellulose membranes. This is because the black polycarbonate materials have a uniform pore size and flat surface that will retain all of the bacteria without trapping any inside of the filter. Though cellulose membranes will retain bacteria, it often will become trapped inside of the filter, where it cannot be counted.

Say it ain't so Periodic Table!

Is nothing sacred? In the news today came word that the period table is changing the atomic weights of 10 elements. Instead of being listed as one static value, the atomic weight for these elements will now be displayed as a a range that will more accurately reflect how the elements actually appear in nature.

The change is being made after decades of study and this is the first time in the history of the periodic table that any atomic weights will be altered. Measuring the variance of atomic weights is being used in real world applications for everything from analyzing food purity, to determining which athletes are using performance enhancing drugs!

The elements being changed are: Boron, carbon, chlorine, hydrogen, lithium, nitrogen, oxygen, silicon, sulfur, and thallium.

I hope this doesn't mean we'll have to memorize the table all over again...

You can read more about the change here or here.

Laboratory Equipment in Motion

We created a handful of brief product videos last week to show you all some of our equipment in operation. First up is the Mini Centrifuge.



...then we have the Magnetic Stirrer. Seen here making some delicious blue water...



...next up is the Benchmark Digital Dry Bath so you can get an idea of how clear the display looks...



...and finally we have the Bactizapper Infrared Micro Sterilizer. It may look small, but don't be fooled, this model can produce temperatures up to 815 C!

Polycarbonate Filters in Legionella Detection

Recently one of our customers was interested in testing Legionella bacteria and asked us how our polycarbonate membranes fit into the process mentioned on our website. If you are unfamiliar with Legionella, it is a waterborne pathogen commonly found in aerosolized waters such as cooling towers, showers, and humidifiers, and it is best known as the cause of Legionnaire’s Disease as well as Pontiac Fever. Its name originated from an outbreak that occurred at the 1976 convention of the American Legion in Philadelphia.

There are actually two areas in which membranes are used in regards to Legionella: Sample preparation and point-of-use filtration. For sample preparation the CDC (Centers for Disease Control) recommends using a 0.2 micron, 47mm polycarbonate filter to extract Legionella bacterium from potable water. Non potable water utilizes a direct plating procedure.

Point of use filtration frequently involves a device that attaches to a faucet or showerhead to eliminate Legionella. Such devices have filters built into them, usually made of Nylon or PFT. A few years ago the American Journal of Infection Control conducted a study of these devices and found them to be extremely effective at preventing the spread of waterborne pathogens.

For more information on Legionella testing and guidelines, you can visit:

http://www.cdc.gov/legionella/files/legionellaprocedures-508.pdf
http://www.specialpathogenslab.com/SPL-Advantage/AJICFilterpaper05.pdf

ASTM Standards for SDI Testing

The good people at ASTM (American Society for Testing and Materials) have released their standard for determining the Silt Density Index of water. If you're interested in learning more about it, you can preview the document here. You can also look at our very own SDI test kits here.

November in Seattle: Turkey and Bus Crashes

We just got blasted with our first winter storm of the year and it was a mean one for Seattle.  Take a look at the video and you can tell that while there are many things we do well here (computer programming, watching soccer), driving around in the snow clearly isn't one of them.  Even our own metro buses can't quite get the hang of it!

Just a reminder, but Sterlitech will be closed this Thursday and Friday for the Thanksgiving holiday (November 25th and 26th. We will open again on Monday the 29th. We wish you all a safe and happy Thanksgiving!

Beta Ratios and Filter Efficency

Here is an article that does a great job of explaining what efficiency ratings mean on a filter and how they are calculated, courtesy of the American Filtration & Separation Society.  This is very useful information for filter users and purchasing agents on the practical effects the filter efficiency will have in a real world setting. 

You can read the whole thing here.

Putting on a Shiny Suit: Polycarbonate Membranes get Sputtered!

Polycarbonate (PCTE) track-etch membranes, created decades ago, are finding some new uses in the development of nanotechnology applications.  They owe this new application to their precise pore geometry and organization.  PCTE membranes were previously utilized in the manufacture of single-walled nanotubes (SWNT) due to the relative ease of depositing metal ions on the inside of their pores, then selectively dissolving the PCTE; leaving behind nanotubes for use as super-conducting wires, micro-diode arrays, or magnetic-data storage devices.  

PCTE membranes are traditionally sputter coated with gold for use in scanning electron microscopy (SEM) imaging because it is easier to capture samples on their smooth membrane surface.  Now scientists are developing new ways to utilize PCTE membranes by sputter-coating metal ions on the membrane.  One new use is to construct a biocompatible glucose sensor¹ that can be implanted inside a diabetic’s body.  The membrane is sputter coated with platinum and the pores filled with an enzyme chemically anchored inside the pore.  When excess glucose enters the pores, an electrochemical reaction is started, traveling down the pore to the thin sputtered metal layer, where the signal is picked up and sent to a microprocessor inside the sensor.  The amount of glucose triggering inside each pore determines the strength of the electrical response.  The size of the entire sensor area might be as small as 0.15cm²!  There’s even work filling PCTE pores with photosensitive materials to turn the membrane into flexible solar cells.   

Sputtered membranes are also finding niches in synthesizing catalysts to help make ethanol from syngas (CO and H₂) as this ethanol can be used as an inexpensive and environmentally friendly fuel and fuel additive².  PCTE sheets can be sputter coated with gold and sandwiched onto a Zn sheet to make the necessary anode and cathode for electrodepositing Mn-Cu-ZnO nanowires/tubes.  These nanotubes can then be successfully used as catalysts in CO hydrogenation reaction to produce alcohols.  With so many industrial nations moving towards ethanol as an alternative to petroleum fuels, the need for synthesizing ethanol from available materials may have a new ally in track-etch membranes.

1: A. Kros, M. Gerritsen, V.S.I. Sprakel, N.A.J.M. Sommerdijk, J. Jansen, R.J.M. Nolte, Silica-based hybrid materials as biocompatible coatings for glucose sensors. Sensors and Actuators B, (2001) 68-75.

2: M.Gupta1, V. Kalpathi and J. J. Spivey, Electrodeposition of Cu-ZnO and Mn-Cu-ZnO Nanowires/tubes for Synthesis of Ethanol [abstract] In: Proceedings of the Electrochemical Society, 214^th Meeting Honolulu, Hawaii. October 12-17, 2008.  Abstract no. 0281

Silver Nanoparticles to Reduce Membrane Biofouling

Scientists at Michigan State University and the PERMEANT Group describes how they are infusing membranes with nanotechnology in order to improve membrane performance, particularly in the field of water purification.  While the use of nanotechnology to expand membrane permeability, selectivity, and resistance has grown more frequent over the last 20 or so years, the new research by these groups is taking this approach in interesting directions.  For instance, on one project they have demonstrated that by adding silver nanoparticles into the polymer matrix of the membrane that the mixture is effective at reducing intrapore biofouling.  Experimentation also shows that this method could also be used to inhibit the biofilm growth on downstream membrane surfaces.  

Hopefully with every little improvement that these teams make will lead them a step closer to their goal of making the world’s supply of drinking water safer for all of us.  

   

You can read more about this research here.

FAQ: Clarification of Fruit (Apple) Juice

Over the years we have seen an increased use of filtration equipment in juice processing, particularly regarding ultrafiltration (UF) or microfiltration (MF) for the clarification of apple juice.  Since it has been demonstrated that membrane filtration can produce yields of 95%-99% - compared to only 80-94% through conventional processes – it is no wonder that filtration methods are growing in prevalence.  The greater yield combined with the reduced time and labor costs have translated to hundreds of thousands of dollars saved for juice processing plants!

If you are considering juice filtration, here a couple of tips to keep in mind:

• The juice must be clear.  Of the four common types of apple juice produced – natural, crushed, clarified, and clear – only clear juice is suitable for membrane processing.    
• Consider ceramic membranes.  More and more fruit juice installations are installing ceramic membranes.  While these do have  a higher cost than other materials, they do offer a higher flux, much longer life, and better resistance to aggressive processing and cleaning conditions. 
• Know your operation.  Since fruit juices have a very low level of retained solids, the optimum mode of operation is the modified batch operation with a partial recycle of retentate.
• Not just for apples.  Other fruit and vegetables that have benefited from membrane filtration include: apricot, carrot, cherry, cranberry, grape, lemon, lime, orange, peach, passion fruit, and tomato.

References:
Ultrafiltration and Microfiltration Handbook.  Cheryan, Munir.  Technomic Publishing Company, 1998.
Microfiltration and Ultrafiltration: Principles and Applications.  Zemon, Leos & Zydney, Andrew.  Marcel Dekker, 1996.

Water Sterilization & Silver

From this recent article in NanoLetters, the American Chemical Society Journal, comes information about a new form of water sterilization out of Stanford University that takes advantages of the unique bacteria-killing properties of silver (the vampire and werewolf killing properties of silver have yet to be proven).  Basically, the proposed multiscale device would perform high speed electrical sterilization of water using a combination of silver nanowires, carbon nanotubes, and cotton.  The end result is that when operating at 100,000 L/(h m²) this device can inactivate greater than 98% of bacteria with only several seconds of total incubation time.

The author’s of this paper mention two interesting reasons for why silver is used in the device.  The first:        

Taking advantage of silver nanowires’ (AgNWs) and CNTs’ [Carbon Nanotube] unique ability to form complex multiscale coatings on cotton to produce an electrically conducting and high surface area device for the active, high-throughput inactivation of bacteria in water.

The other reason described for using silver in water sterilization:

Silver is chosen since it is a very well-known bactericidal agent, and recently a large amount of interest has been spurred by the discovery that silver nanoparticles work extremely well at killing bacteria and can be attached to various surfaces with chemical techniques.    

The outcome of the silver treatment in the author’s experiment provides further evidence of these properties:

The results clearly show that filters not treated with silver, including CNT-only cotton, showed a robust growth of bacteria, while the bacteria concentration in the solutions incubated with AgNW-treated material was reduced to the detection limit of the absorbance system used, at least a 2 to 3 order of magnitude reduction.

All in all, the findings in this paper are encouraging that implementation of this approach can kill microorganisms which cause biofouling in downstream filters.  The authors of the paper state, “Such technology could dramatically lower the cost of a wide array of filtration technologies for water as well as food, air, and pharmaceuticals, where the need to frequently replace filters is a large cost and difficult challenge.”

Their next step is to expand their experimentation to other microorganisms beyond the E. coli that was used for this study.  In their conclusion the authors note that, “Silver is known to be an extremely general agent so it can be expected that this device will also work over a wide array of organisms.” 

We’ll continue to monitor their progress and hope for the best!

New Technique to Improve Crossflow Filtration

One of the biggest issues for crossflow filtration is figuring out how to control the loss of permeate flux in the process. Whether using reverse osmosis (RO), ultrafiltration (UF), or microfiltration (MF), the loss due to polarization and membrane fouling prevents many potential users in the biological or chemical processing fields from adopting this method.

If you are using crossflow filtration, or considering using it, and fear the effects of permeate loss, then you may want to consider this technique courtesy of North Carolina A&T University and the U.S. National Energy Technology Laboratory. Their study (see here) produced drastically improved results by implementing flow reversal to enhance the membrane flux.

They found that by periodically reversing the flow direction of the feed stream at the membrane surface results in prevention and mitigation of membrane fouling. This particular study conducted experiments with bovine serum albumin, Detran T-70, and apple juice. We’d love to hear from any of you in the field that may have tried this technique to see how it worked out!

Silver Membranes: Your last line of defense?

We ran across an interesting patent that involves silver membranes – As part of a system designed to detect and identify chemical and biological contaminants in the air!  In the proposed sampling method and system, the silver membrane is used to capture liquid, solid, and gas constituents that would then be analyzed by means of spectroscopy for contaminants. 

For more versatility, the surface of the membrane can be modified physically or chemically in order to increase the surface area and/or provide specific affinity towards analytes of interest.   For instance, a pure length of silver membrane would trap solid particulate materials while a silver membrane treated with a metal oxide such as magnesium oxide would adsorb volatile organic compounds from a gas or liquid state.   The suitable thickness for the silver membranes is between 10 - 50 microns, with 30 microns being the preferred thickness.  The standard thickness for Sterlitech silver membranes is between 30 - 50 microns.   
         
The implications for this patent are intriguing to say the least.  It’s nice to know that there’s a possibility of our silver membranes being used to save lives…

You can look at the full patent here.

Liquid State of Mind

Had your fill of liquids?  You're probably not alone.  According to a new survey by Laboratory Equipment magazine, over 90% of lab researchers use liquid handling equipment, and about 60% are using their equipment either continuously or several times daily.  As for filtration equipment, 52% of respondents are using it - now we just need to get the other 48% on board!!!    

You can check out the full results over at the Laboratory Equipment site: Liquid Handling Dominates Lab Activities

Hydrophilic and Hydrophobic

One of the important characteristics in membrane selection is whether you want a membrane that is Hydrophobic or Hydrophilic. Here we'll define these terms, as well as provide some examples of membrane materials and applications for both types. 

Hydrophilic literally means “water loving.” Hydrophilic membranes will attract water, and in the process push away other molecules in order to allow water access to the membrane. This keeps contaminants away from the membrane allowing it stay clean and functioning for a longer period of time. Because of this trait hydrophilic membranes are especially well suited for medical applications and biological assays.

Hydrophobic on the other hand, literally means “afraid of water.” These membranes will block the passage of water and are commonly used for applications involving separation of water from other materials, such as venting gases.

Here is a helpful table that compares membrane materials and common uses for hydrophilic and hydrophobic properties:

	Hydrophilic	Hydrophobic
Materials	Silver Metal Polyethersulfone (PES) Glass Fiber Polycarbonate Track Etch (PCTE) (*When coated with PVP) Polyester (PETE) Mixed Cellulose Esters (MCE) Nylon Cellulose Acetate	Polypropylene Teflon (PTFE) - Laminated or unlaminated Polycarbonate Track Etch (*When not coated with PVP)
Applications	Sterilization or clarification of aqueous and organic solvent solutions Medical assays Bacterial removal Protein arrays Drug filtration IV filters HPLC sample preparation	Venting applications Protecting gas sensors from moisture or heavy particulates CO2 monitors Sterile process gases Filtration of strong acids and aggressive solutions Phase separations HPLC sample preparation requiring low detection levels

FAQ: Do Silver Membranes have a coating on them?

From time to time we hear from customers that they have "scratched" their silver membranes.  This occasionally leads them to ask: Is there some sort of coating on the membrane that is being rubbed off?

Answer: Our silver membranes are made of 99.97% pure silver and do not have any coating on them.  What may appear to be scratching is actually a polishing of the silver surface, which makes the silver reflective.  This can be done when the membrane is rubbed with a metal object, such as tweezers.  We also posted a brief video demonstrating the effect.  You can watch it here.

CF042 Cell In Use

We had an interesting discovery recently.  One of our customers had put a good example of a low flow CF042 setup on a blog site.  The images are an excellent example of how to use the CF042 in a low flow application.  Check it out and let us know what you think of his example.
http://www.insiderweblog.com/